The Lipid-Oxidative Stress Axis: Novel Therapeutic Targets for Podocytopathy

Introduction

As a highly differentiated cell, podocytes are fundamental to maintaining the integrity of the glomerular filtration barrier and have a key intervention target in chronic kidney disease (CKD).¹ Podocytes play a crucial role in maintaining homeostasis in response to diverse physiological and pathological stimuli. However, excessive stress can lead to podocyte maladaptation, resulting in a cascade of complex biological alterations.² These pathological manifestations include foot process effacement (FPE), cellular vacuolization, microvillus formation, cellular hypertrophy, and ultimately podocyte detachment and loss. Concurrently, these changes trigger the activation and proliferation of parietal epithelial cells (PECs), induce structural modifications in the glomerular basement membrane (GBM) and stimulate excessive extracellular matrix (ECM) production.³ The limited regenerative capacity of podocytes exacerbates these pathological processes, resulting in a critical mismatch between podocyte coverage and the GBM surface area. This disparity leads to the emergence of uncovered GBM regions, ultimately compromising the integrity of the glomerular filtration barrier (GFB) and accelerating podocyte detachment and loss.^4,5 Clinically, these pathological changes manifest as proteinuria and its associated clinical manifestations, characteristic of all podocytopathies.⁶ Furthermore, the migration of activated parietal epithelial cells (PECs) to the glomerular tuft contributes to the formation of sclerotic lesions.⁷ This process is accompanied by excessive ECM deposition, which progressively disrupts normal renal architecture. The resultant glomerular dysfunction not only impairs kidney function but also promotes the development of glomerulosclerosis and renal fibrosis, thereby accelerating the progression of chronic kidney disease (CKD).⁸ Therefore, great importance is attached to understanding how the structure and function of podocytes are programmed in many settings and developing techniques for the beneficial therapeutic properties of podocytes.

In studies of CKD, the pathogenic mechanisms of dyslipidemia have been extensively studied.⁹ Cellular dysfunction caused by accumulation of lipids, ie lipotoxicity,¹⁰ is manifested by insulin resistance, actin cytoskeletal rearrangement, mitochondrial oxidative damage and inflammatory responses.^11,12 Recent evidence has confirmed that pathological lipid build-up is the result of intracellular disorders of genes or proteins that regulate lipid metabolism, which mainly affects cellular lipid metabolism in terms of lipid synthesis, uptake, storage, utilization and cell output.^13,14 Therefore, Lipid metabolism is a critical link between pathology, physiological research, and biochemical communication.

In this review, we will introduce how lipids affect the structure and function of podocytes in pathological environments. We first discuss the basic structure and injury mechanism of podocytes; Then, the significance of intracellular lipid metabolism on podocyte regulation in various immune backgrounds and disease microenvironments is described. Finally, we summarize the effects on lipid metabolism in reaction to oxidative stress. We also emphasized the interaction of intracellular oxidative stress and lipid metabolism at multiple levels, mediating podocyte injury.

Podocyte Structure and Damage

Podocytes are terminally differentiated epithelial cells of the renal glomeruli, characterized by large cell bodies and intricate cytoplasmic extensions. The cell body resides within Bowman’s space, while primary processes branch into finer secondary and tertiary processes, ultimately forming foot processes (FPs).¹⁵ These foot processes (FPs) line the outer surface of the glomerular basement membrane (GBM) and anchor tightly to it through adhesion receptors and proteoglycans such as integrins, dystroglycans and agrin.¹⁶ A highly organized actin cytoskeleton underpins the structural integrity of FPs. Dynamically regulated by Rho GTPases, this cytoskeletal network not only reinforces FP adhesion to the GBM but also facilitates interdigitation with neighboring podocytes, thereby ensheathing the glomerular capillary wall while maintaining filtration slit architecture.¹⁷ In recent years, the fourth critical structural component of podocytes - the Ridge-like Prominence (RLP) - has been identified as an essential element in glomerular filtration. These specialized basal membrane protrusions extend perpendicularly from the podocyte cell body, serving as primary adhesion devices that establish stable connections between the podocyte and glomerular basement membrane (GBM).¹⁸ These staggered FPs create filtration slits, which are bridged by an extracellular structure called the slit diaphragms (SDs).^19,20 These SDs represent sophisticated extracellular structures that function as ultimate barrier against macromolecular proteinuria.^21,22 These specialized podocyte structures cooperate synergistically with glomerular endothelial cells and the GBM to form the tripartite glomerular filtration barrier (GFB).²³ (Figure 1) The filtration process involves sequential passage of plasma constituents through Fenestrated endothelial cells (size-selective barrier), The GBM (charge-selective collagenous matrix) and SD-bridged filtration slits (final macromolecular barrier). This coordinated ultrastructural organization enables the production of primary ultrafiltrate while maintaining essential plasma proteins within the vascular compartment.^24,25

Figure 1 The normal kidney and glomeruli structure. The podocyte, glomerular basement membrane and capillary endothelium form the GFB and work together to filter blood.

The study of podocyte function is not a new field; these cells were first observed in the glomerular filtration barrier via electron microscopy in the 1950s.²⁶ In adult kidneys, there are approximately 500–600 podocytes in each glomerular capillary tuft.²⁶ In addition to their adhesive functions essential for maintaining filtration-barrier integrity, podocytes also directly contribute to the synthesis and remodeling of various GBM components.²⁷ Furthermore, it also actively secretes vascular endothelial growth factor (VEGF) as well as a variety of pro-inflammatory and anti-inflammatory cytokines,^28,29 wild synthesizing key complement cascade proteins. Through highly dynamic paracrine and autocrine signaling—mediated by endothelin-1 (ET-1), VEGF, TGF-β, BMP-7, latent TGF-β–binding protein-1 (LTBP1), and extracellular vesicles—podocytes modulate mesangial cell and local immune responses.^28,30,31 Emerging evidence indicates that podocytes not only perform innate immune roles³²—expressing pattern recognition receptors and secreting antimicrobial peptides—but also exhibit adaptive immune functions by presenting antigens and releasing pro-inflammatory or regulatory chemokines,^32,33 thus precisely regulating immune homeostasis within the glomerular microenvironment.

However, despite their functional sophistication, podocytes are intrinsically vulnerable to injury due to their unique cytoarchitecture. As terminally differentiated epithelial cells with limited proliferative capacity, they endure substantial hemodynamic forces from glomerular capillary blood flow, primarily comprising two mechanical components: circumferential stress and shear stress.³⁴ When exposed to excessive stress, podocytes undergo a series of complex pathological changes, including foot process effacement (FPE), hypertrophy, cell body attenuation, rapid dynamic changes of pseudocyst filling, emptying, and rupture, pseudocyst formation, and podocyte shedding.^5,35–37 In glomerular disease, the “Foot Process Effacement (FPE)” causes a decline in the filtration barrier and is recognized as a pathological indicator of podocyte injury.^38,39

In a clinical study of children with idiopathic nephrotic syndrome (INS), researchers found that at least 66% of patients exhibited serum autoantibodies targeting podocytes. Subsequent screening identified 14 specific podocyte autoantigens, with antibody titers showing significant positive correlation with 24-hour urinary protein excretion. Notably, following effective hormone or immunosuppressive therapy, the levels of these autoantibodies decreased markedly, and this decline was highly consistent with the time window for proteinuria resolution. These findings indicate that podocyte autoantibodies may serve as dual-purpose biomarkers for both disease severity assessment and real-time therapeutic monitoring, enabling personalized treatment evaluation.⁴⁰ Kotaro Haruhara et al demonstrated in a retrospective clinicopathological study that podocyte density outperforms absolute podocyte count in predicting renal outcomes in obesity-related glomerulopathy (ORG), as it more sensitively reflects the vulnerability of the filtration barrier caused by mismatched glomerular enlargement and podocyte spreading. The study results showed that patients with reduced podocyte density exhibited independently associated severe proteinuria, marked glomerulomegaly, and inferior renal survival, indicating that such patients experience rapid disease progression and warrants close clinical attention.⁴¹ Another study on INS revealed that loss of nuclear glucocorticoid receptor (GR) expression in podocyte was correlates with delayed therapeutic response to glucocorticoids. By analyzing of podocyte-specific markers in renal biopsies demonstrated potential for predicting glucocorticoid efficacy, supporting targeted investigation of podocyte GR protein in INS patients.⁴² Although this study shows promise of podocytes as diagnostic biomarkers for kidney diseases, an unequivocal molecular signature for identifying podocyte injury requires validation prior to clinical applications.

Nephrin

As a transmembrane protein, Nephrin is in the SD of mature glomeruli and has eight extracellular immunoglobulin-like structural domains. It is a key protein among the molecules that assemble and strengthen the SD.⁴³ Nephrin is required to keep the glomerular filter in a healthy state, whose downregulated expression is considered an early indication of glomerular damage. Long-term studies have shown that reduced Nephrin levels are associated with increased proteinuria and severity of podocyte injury.^44–46

Podocin

Alongside Nephrin, Podocin constitutes another essential component in maintaining slit diaphragm (SD) integrity. This transmembrane protein, encoded by the NPHS2 gene, exhibits podocyte-specific expression during glomerular maturation. Podocin demonstrates a unique bipolar localization flanking the SD,⁴⁷ where it functions as a critical scaffolding molecule. It facilitates the structural integration of tight junction proteins (TJs) - key regulators of paracellular transport for ions, solutes, and macromolecules⁴⁸- with the underlying actin cytoskeleton.^47,49 Pathogenic mutations in Podocin induce significant cytoskeletal alterations, manifesting as abnormal cortical redistribution of actin filaments and characteristic cytoplasmic depletion.⁵⁰

Podoplanin

Podoplanin is a 43-kDa transmembrane podocyte glycoprotein that is associated with cell motility and modeling of the actin cytoskeleton. In an in vitro study, the formation of cell extensions increasing with ectopic expression of podoplanin in podocyte, which also enhances cell adhesion and migration, and induces morphological changes in these cells.^51,52

These proteins also require an interface molecule, CD2AP—a bridging protein on the cytoplasmic side of the plasma membrane—to bind cytoskeletal proteins. Podocin binds with CD2AP and Nephrin through its C-terminal domain and directly interacts with CD2AP in vivo.^53–55 Moreover, podocytes are firmly attached to the GBM, and their function is maintained through podocyte-associated molecules, including α-actinin-4, glomerular epithelial protein 1, Wilms tumor antigen 1, synaptopodin, and dystroglycan. These molecules exhibit a significant positive correlation with acquired proteinuric diseases.⁵⁶ Initial podocyte injury serves as the pivotal trigger for mesangial expansion and subsequent glomerular albuminuria.^57–59

In a genetically engineered rat model of podocyte depletion, 20% podocyte loss resulted in glomerular mesangial expansion and transient proteinuria; 40% depletion led to focal segmental glomerulosclerosis (FSGS) lesions and capsular adhesions, while depletion exceeding 40% caused severe mesangial expansion and global glomerulosclerosis.⁶⁰ Podocyte injury arises from multiple causes. In addition to genetic variants, environmental factors such as immunological, infectious, toxic, hemodynamic, and obesity-related stressors can damage podocytes.^59,61–65

Lipid Metabolism

Lipids are a widely existing class of compounds with multiple important biological functions, acting through the synergistic effects of multiple enzymes, binding proteins, and receptors.⁶⁶ Lipids display remarkable structural diversity, such as a wide variety of chemical structures of cellular lipids, numerous stereoisomers, and compositional variability. This characteristic demonstrates the multiple roles of lipids in physiology and pathology.^67–69 In the Integrated Lipid Classification System (Comprehensive Classification System for LIPID, https://www.lipidmaps. In org), the lipid classification system consists of eight lipid classes, each with its own subclassification hierarchy. Such as: Fatty Acyls (FA), Glycerolipids (GL), Glycerophospholipids (GP), Sphingolipids (SP), Sterol Lipids (ST), Prenol Lipids (PR), Saccharolipids (SL), Polyketides (PK).⁶⁶

Disorders in lipid metabolism are linked to diseases such as obesity, hyperlipidemia, lipid deposition disease, and metabolic syndrome. They alter gene and protein expression, resulting in cytokine and signaling pathway dysregulation.¹⁰ An excess of lipids that accumulate in non-adipose tissue causes cell dysfunction or cell death, an appearance known as Lipotoxic.^10,70 The molecular mechanisms of underlying lipotoxicity encompass ER stress, oxidative stress, mitochondrial dysfunction, impaired autophagy, and inflammatory.^71,72

Podocytes exhibit a uniquely high membrane cholesterol and sphingolipid content, which is essential for maintaining the structural integrity and dynamic flexibility of their intricate FPs.⁷³ Moreover, podocytes rely heavily on lipid rafts—cholesterol- and sphingolipid-enriched microdomains within the plasma membrane—that serve as critical platforms for organizing signaling molecules and receptors.^73,74 These lipid rafts facilitate efficient signal transduction, including insulin signaling and mechanosensitive pathways,⁷⁵ both of which are vital for podocyte function, survival, and adaptation to mechanical stress.

In addition to their reliance on lipid rafts, a defining aspect of podocyte lipid metabolism is the expression of specific regulatory enzymes, such as sphingomyelin phosphodiesterase acid-like 3b (SMPDL3b),⁷⁶ which plays a pivotal role in modulating ceramide homeostasis. It is suggested that SMPDL3b enhance podocyte resilience by regulating ceramide-S1P homeostasis⁷⁶ while also contributing to podocyte injury through the activation of STING.⁷⁷ This delicate balance underscores the critical need for precise regulation of lipid metabolism to safeguard podocyte integrity and function.

Podocyte Injury Caused by Lipid Metabolism Disorders

The intracellular lipid homeostasis is balanced by regulating the dynamic changes of lipid synthesis, catabolism, and storage (Figure 2). Numerous laboratory studies have shown that intracellular lipid overload in podocytes is an important factor causing proteinuria in chronic kidney disease (CKD), such as diabetic nephropathy (DN) and focal segmental glomerulosclerosis (FSGS).^78–81 The disorder of lipid metabolism is not only a consequence of kidney injury but also aggravates the progression of kidney injury.

Figure 2 Lipid metabolism in the podocyte. In this cartoon, we illustrate the intracellular lipid accumulation is governed by an imbalance between the syntheses, catabolism and storage of FAs and cholesterol. Our results provide insights into the expression of key molecules of lipid metabolism disorders in the podocyte injury.

Lipid Synthesis

The balance of intracellular lipids is attributed to dynamic lipid synthesis, decomposition and storage. As a part of the glomerular, the podocytes have a huge energy demand to maintain the physiological function of the glomerulus.⁸² ATP in podocytes is generated mainly through glycolysis and oxidative phosphorylation.^82–84 Podocytes exhibit unique cellular structures, such as the integrity of foot processes (FPs), which is critical for glomerular filtration and determine the different regionalization of ATP generation. Mitochondria must be properly localized and mobilized within podocytes to meet cellular energy needs. Usually, mitochondria are absent in the foot processes (FPs) of podocytes, which is likely because mitochondria are larger in volume than the FPs. Therefore, the energy metabolism in the portion of the FPs is provided by glycolysis.⁸² Studies demonstrate that podocyte energy metabolism relies on both glycolysis and mitochondrial respiration, with their contributions varying under different conditions. Reduced mitochondrial capacity or glycolytic disorder can aggravate abnormal podocyte function.^85,86 Beyond their role as essential energy sources, lipids are integral to the structural organization of mitochondrial membranes.^87,88 Disruption of mitochondrial oxidative metabolism and elevated ROS levels compromise lipid metabolism in mitochondria, resulting in the lipid excess. In turn, lipid overload can damage mitochondrial DNA, RNA, and respiratory chain proteins, ultimately leading to functional decline.^10,89 In an in vitro model of podocyte injury with knockdown PKM2, the expression of pyruvate kinase M2 (a key glycolytic enzyme) rapidly declines, accompanied by reduced glycolytic flux, glomerular and podocyte injury, loss of foot processes, and proteinuria. Inhibition of the glycolytic pathway leads to ATP insufficiency, resulting in cytoskeletal remodeling and podocyte apoptosis.⁹⁰ Furthermore, reduced expression of pyruvate kinase M2 in podocytes was also found in renal biopsies from patients with hypertensive nephropathy and diabetic kidney disease (DKD).⁸⁶ Abnormal mitochondrial energy metabolism in podocytes is closely related to lipid metabolism disorders. The roles of lipid in podocytes metabolic and signaling will be discussed below.

Fatty Acids (FAs)

FAs are important nutrients stored in adipose tissue as triglycerides, enabling humans to tolerate prolonged starvation, fasting, and metabolic diseases (such as febrile illnesses) and serve as the main substrates for podocyte mitochondria.^91,92 Podocyte injury upregulates de novo lipogenesis (DNL) programs, leading to increased production of FAs. Fatty acid synthesis (FAS) is coordinated by several key enzymes, including acetyl-CoA citrate lyase (ACLY), Acetyl-CoA carboxylase (ACC), fatty acid synthase (FASN), and Stearyl-CoA desaturase 1 (SCD 1). Podocyte-specific ACCβ overexpression brings about serious podocyte damage in animal models of diabetic nephropathy,⁹³ whereas inhibition of ACC reduces gene expression of fibrosis markers and apoptosis in podocytes.⁹⁴ In addition, ACLY serves as a key enzyme regulating FAS and fatty acid β-oxidation (FAO), which is located in the cytoplasm and nucleus and responsible for converting citric into acetyl-CoA in the cytoplasm.⁹⁵ Studies on renal reperfusion injury evidence that suppressing ACLY transcription reduces renal fibrosis, accompanied by enhanced fatty acid oxidation (FAO) and decreased lipid accumulation.⁹⁶ Overall, these studies highlight the significant role of FAs in the controlling podocyte injury and renal dysfunction.

Fatty Acid Translocase CD36

The CD36 is a class B scavenger receptor and lipid sensor that is widely present in many immune and non-immune cells including macrophages,⁹⁷ microvascular endothelial cells⁹⁸ and podocytes.⁹⁹ It serves as a multifunctional receptor, mediating signaling in response to damage-associated molecular patterns (DAMPs) and pathogen-associated molecular patterns (PAMPs), as well as functioning as a transporter for long-chain free fatty acids.⁹⁷ The transport of FAs by CD36 involves a complex internalization process. During this process, FAs bind to CD36 on the cell membrane, activating its downstream kinase LYN. LYN phosphorylates and inactivates CD36’s palmitoyl transferase DHHC5 at the Tyr91 site, leading to the depalmitoylation of CD36 by acyl protein thioesterase 1 (APT1). This modification enables CD36 to recruit another tyrosine kinase, spleen tyrosine kinase (SYK), which phosphorylates c-Jun N-terminal kinase (JNK) and VAV proteins, initiating the endocytic uptake of FAs.¹⁰⁰ Disruption of CD36-dependent FA uptake can be achieved by interrupting CD36 internalization, which is mediated by blocking either LYN or SYK.^101,102 In podocytes, CD36 plays a dual role in lipid metabolism and inflammation. Beyond its function in FA transport, CD36 has been implicated in promoting podocyte injury through the activation of the NLRP3 inflammasome. Recent studies have shown that CD36-mediated NLRP3 inflammasome activation leads to the release of pro-inflammatory cytokines such as IL-1β and IL-18, exacerbating podocyte injury and contributing to glomerular damage.¹⁰³ Knockdown of CD36 in experimental models has been shown to significantly reduce inflammation, attenuate NLRP3 inflammasome activation, and alleviate podocyte injury, highlighting its potential as a therapeutic target in kidney diseases.¹⁰⁴ Moreover, CD36’s role in podocyte injury is further complicated by its interaction with oxidative stress and lipid peroxidation products. In conditions such as diabetic nephropathy, CD36 facilitates the uptake of oxidized low-density lipoprotein (oxLDL), leading to intracellular lipid accumulation, mitochondrial dysfunction, and podocyte apoptosis.¹⁰⁵ This process is exacerbated by the generation of reactive oxygen species (ROS), further amplifies CD36-dependent inflammatory signaling and podocyte damage.⁶¹

ATP Citrate Lyase (ACLY)

The ACLY is a key rate-limiting cytosolic enzyme involved in de novo fat synthesis by catalyzing the conversion of citrate to oxaloacetate (OAA) and Acetyl-CoA, while hydrolyzing ATP to ADP and phosphate.¹⁰⁶ The role of Acetyl-CoA in metabolism represents a key node as it facilitates crucial biochemical reactions, which includes the synthesis of FAs, cholesterol and acetylcholine, along with the acetylation of protein substrates including histones.^107,108 Under most physiological and nutritional conditions, Acetyl-CoA serves as the primary means through which carbon enters the tricarboxylic acid (TCA) cycle¹⁰⁹ - a series of chemical reactions that produce energy by oxidising carbohydrates, FAs and Acetyl-CoA. ACLY plays a role in acetyl-CoA production by cleaving citrate exported from the mitochondrial TCA cycle.¹¹⁰

In the renal tissue of overweight or obese patients (ORG) and ob/ob BTBR mice, ACLY is highly expressed the enzyme is linked with ELA increasing, glomerulosclerosis, and albuminuria.¹¹¹ Administration of the ACLY inhibitor BMS-303141 reduces serum lipids level and renal ELA, ameliorates renal injury, and tubulointerstitial fibrosis. Moreover, it decreases the levels of various lipogenic enzymes such as ACC, FAS and HMGCR in db/db mice.¹¹² In mouse embryonic fibroblasts, ACLY deletion resulted in Acetyl-CoA synthetase 2 (ACSS2) upregulation.¹¹³ ACSS2 regulates histone acetylation, produces acetyl-CoA in the promoter region of TFEB target genes, and enhances the transcriptional control of genes associated with lysosomal biogenesis and autophagy.¹¹⁴ For example, ACSS2 epigenetically induces raptor expression through histone H3K9 acetylation, thereby facilitating activation of raptor/mTORC1 pathway.

Fatty Acid-Binding Proteins (FABPs)

The FABPs were initially found to be intracellular proteins that are key mediators of local and systemic metabolic and inflammatory processes, and are therefore important therapeutic targets for immune and metabolic diseases.¹¹⁵ Functionally, FABPs regulate intracellular lipid homeostasis by modulating FA transport and metabolism between nuclear and extranuclear compartments.^116,117 There are many isoforms of FABPs. To date, scholars have identified 12 FABP genes. Tissue-specific deletion of FABP genes (eg, FABP4 in adipocytes) can impair lipid storage or mobilization, leading to altered adipose tissue homeostasis.¹¹⁸ In normal kidneys, FABP 4 is mainly expressed in glomerular mesangial cells, peritubular capillary endothelial cells, and cortical and medullary venous,¹¹⁹ which was found to be a potential vector in mediating the inflammatory response to renal interstitial fibrosis.¹²⁰ Induction of ectopic FABP4 expression occurs in glomerular injury and the level of ectopic FABP4 expression is relevantly linked with proteinuria and renal insufficiency.¹²¹ In recent reports, Heart-type fatty acid binding protein (H-FABP) exacerbates FA-induced metabolic disorders, inflammation, and oxidative stress markers in podocytes and aggravates FA-induced damage.¹²² The level of H-FABP was upregulated in both glomeruli of ORG and obese db/db mice, and the expression of H-FABP was more pronounced in the glomeruli of ORG patients. It was hypothesized that glomerular hypertrophy might be related to the abnormal expression level of H-FABP in glomeruli.¹²³ Although human liver-type fatty acid-binding protein (hL-FABP) is only expressed in the proximal renal tubules, it can serve as a predictor of renal injury by binding excess FFA in proteinuric renal disease.^124,125 Urinary hL-FABP is elevated in ischemic renal disease.¹²⁶ Increased level of L-FABP in tubular cells protects anti-GBM GN mice from worsening tubulointerstitial and glomerular injury.¹²⁷ Together, these studies established the significant role played by FABPs in regulating FA metabolism within podocytes.

Cholesterol

Synthesized by nearly all cell types, serves dual physiological roles as a critical component of cell membrane stability and the essential precursor for steroid hormone biosynthesis. These cholesterol-derived signaling molecules - including glucocorticoids, mineralocorticoids, sex hormones, and vitamin D- constitute a vital regulatory network governing systemic homeostasis through carbohydrate metabolism regulation, sodium balance maintenance, and modulation of reproductive and skeletal development.^128,129 The endoplasmic reticulum (ER) functions as a primary organelle for protein folding regulation, secretion, Ca2 + storage and release, as well as lipid synthesis in eukaryotic cells.¹³⁰ A multitude of studies have validated the pivotal function of the ER in cholesterol metabolism.¹³¹ Cholesterol has the capacity to interact with multitudes transmembrane proteins, continue contributing to the maintenance or alteration of their conformation. In addition to this, Cholesterol also engages with numerous sterol transport proteins to promote cholesterol transport and control its subcellular distribution.¹³² The biosynthesis of cholesterol is an energy-demanding process that requires substantial inputs of acetyl-CoA, ATP, oxygen, and the reducing agents NADPH and NADH. The synthesis process of this key substance involves five basic steps:^133–135 1) condensation of three Acetyl-CoA units to form HMG-CoA (3-hydroxy-3-methylglutaryl-CoA); 2) The reduction of HMG-CoA to mevalonate, catalyzed by HMG-CoA reductase (HMGCR), requires NADPH as a reducing agent; 3) The mevalonate is consecutively phosphorylated by three ATP-dependent phosphorylation reactions in the presence of three kinases. It is then decarboxylated to form the active isopentenyl unit, isopentenyl diphosphate; 4) Six Isoprenoid units to produce Squalene; 5) Then, The Squalene is converted to squalene 2,3-epoxide by squalene epoxidase in the ER. Squalene 2,3-epoxide is then cyclized by lanosterol cyclase to form lanosterol. Finally, the conversion of lanosterol to cholesterol occurs within the membranes of the ER.^{132,136–138} This process is regulated by three key factors: Sterol Regulatory Element Binding Protein 2 (SREBP2),¹³⁹ 3-Hydroxy-3-methylglutaryl-CoA reductase (HMGCR)¹⁴⁰ and Squalene monooxygenase (SM).¹⁴¹

Sterol Regulatory Element Binding Proteins (SREBPs, Including SREBP1a, SREBP1c and SREBP2)

SREBPs are members of the bHLH-Zip family, function as key transcriptional regulators in cholesterol and fatty acid metabolism, with their activation and subsequent induction of cholesterol synthesis dependent on the assistance of SCAP (SREBPs cleavage activating protein).^142,143 Escorted by SCAP, SREBPs are transported from the ER to the Golgi for proteolytic cleavage, releasing their NH2-terminal domain. This domain then activates lipid synthesis genes, promoting cholesterol production.^144,145 SREBPs can regulate the transcription activation of HMG coenzyme A reductase, as well as the transcription of genes encoding other key enzymes in the cholesterol synthesis pathway, such as farnesyl diphosphate synthase (FPPS) and squalene synthase (SQS).^146,147 Studies have shown that the increased cholesterol in podocyte is accompanied by increased expression of LDL Receptor (LDLR), SREBPs (SREBP1 and SREBP2), and 3-hydroxy-3-methylglutaryl-CoA reductase (HMGCR).¹⁴⁸ This dysregulation leads to the intracellular accumulation of cholesterol and triglycerides (TGs), which disrupts podocyte function and contributes to glomerular injury. For example, SREBP2 activation in renal tissue mediates the accumulation of triglycerides and cholesterol, leading to podocyte damage and proteinuria.¹⁴⁹ Podocyte-specific lipid rafts, characterized as dynamic microdomains enriched in cholesterol and sphingolipids, are essential for preserving the structural stability of the SD. These specialized membrane domains are involved in nephron phosphorylation and organization of the Glomerular SD. They serve as dynamic platforms that recruit a diverse array of molecules, including receptors and signaling proteins, essential for cellular recognition and signal transduction processes.^150–152 This activation is associated with the upregulation of glomerulosclerosis-associated factors, including VEGF, PAI-1, collagen type IV, and fibronectin.¹⁵³ For instance, studies in db/db mice, a model of type 2 diabetes, have demonstrated that podocyte injury is accompanied by elevated SREBP1 and SREBP2 levels, along with increased cholesterol and TG deposition in glomeruli.¹⁵⁴ This lipid overload exacerbates podocyte injury by inducing oxidative stress, mitochondrial dysfunction, and apoptosis.¹⁵⁵ Furthermore, Pharmacological inhibitors of SREBP activation, such as fatostatin and betulin, have shown efficacy in reducing lipid accumulation and preserving glomerular function in preclinical models.^156–158 Therefore, podocyte-specific insights into SREBP pathways, including their effects on lipid rafts, autophagy, and oxidative stress, provide a deeper understanding of the mechanisms underlying lipid-induced podocyte damage.

3-Hydroxy-3-Methylglutaryl Coenzyme A Reductase (HMGCR or HMG-CoA Reductase)

HMGCR is a key enzyme in the mevalonate pathway, catalyzing the rate-limiting step of converting HMG-CoA to mevalonate. Mevalonate serves as a critical intermediate for the synthesis of isoprenoids, such as cholesterol, bile acids, and steroid hormones,¹⁵⁹ and non-sterol isoprenoids.¹⁶⁰ As the rate-limiting enzyme in cholesterol biosynthesis, HMGCR is a primary target of statins, which are widely used to lower serum cholesterol levels.¹⁶¹ Beyond their lipid-lowering effects, statins exhibit renoprotective properties, including anti-inflammatory and immunomodulatory effects, which have been demonstrated in various kidney disease models. For instance, studies have demonstrated that fluvastatin significantly lowers mortality in experimental deoxycorticosterone-acetate (DOCA) salt-treated rats. This protective effect is achieved through multiple mechanisms, including reducing urinary protein excretion, glomerular hyperplasia, macrophage infiltration, and suppressing glomerulosclerosis. Studies have demonstrated that fluvastatin significantly lowers.¹⁶²

In podocytes, statins exert significant protective effects against oxidative stress and injury, primarily through the modulation of key signaling pathways and epigenetic mechanisms. Research has demonstrated that statins prevent oxidative LDL-induced glomerular podocyte injury by activating the phosphatidylinositol 3-kinase/AKT signaling pathway.¹⁶³ Additionally, Atorvastatin improves renal pathology by suppressing HDAC activity, enhancing H3 and H4 acetylation in glomerular mesangial cells,¹⁶⁴ and downregulating MALAT1 and miR-200c to protect MPC-5 cells from pyroptosis while reducing renal oxidative stress levels.¹⁶⁵

Hyperglycemia-induced podocyte injury is another critical area where statins demonstrate protective effects. High glucose levels disrupt F-actin cytoskeletal organization, reduce the expression of podocyte-specific markers such as synaptopodin and Wilms tumor-1 (WT-1), and decrease the production of bone morphogenetic protein-7 (BMP-7). Pitavastatin has been shown to mitigate these effects by inhibiting Rho kinase activation, thereby preserving podocyte structure and function under hyperglycemic conditions.¹⁶⁶ Clinical studies further support the renoprotective effects of statins, particularly in patients with chronic kidney disease (CKD). For example, a 6-month treatment with simvastatin in hypercholesterolemic patients with chronic glomerulonephritis, which resulted in significant reductions in total cholesterol, LDL cholesterol, triglycerides, urinary protein excretion, and urinary podocyte excretion.¹⁶⁷ Moreover, statin therapy has been associated with reduced risks of all-cause mortality, cancer mortality, and cardiac mortality in hyperlipidemic patients with CKD and end-stage renal disease (ESRD). Notably, hydrophilic statins appear to offer superior benefits compared to lipophilic statins, suggesting that statin selection may influence clinical outcomes.¹⁶⁸ In podocytes, the protective mechanisms of statins extend beyond cholesterol reduction. Statins modulate key signaling pathways, including RhoA/ROCK, PI3K/AKT, and Wnt/β-catenin. Fluvastatin exerts its protective effects by inhibiting the RhoA, thereby preventing its membrane localization and activation.¹⁶⁹ This inhibition suppresses downstream Rho-associated kinase (ROCK) activity. The suppression of the ROCK pathway plays a crucial role in maintaining the stability of the podocyte cytoskeleton, preventing the reorganization and disruption of actin filaments (F-actin). This mechanism is particularly significant in diabetic nephropathy, where hyperglycemia leads to the overactivation of the RhoA/ROCK pathway, resulting in podocyte injury and detachment.¹⁷⁰ By inhibiting this pathway, statins reduce podocyte apoptosis and the occurrence of proteinuria, thereby preserving glomerular function.

In summary, HMGCR and the mevalonate pathway are central to podocyte biology, with statins providing multifaceted protection against podocyte injury through lipid-lowering, anti-inflammatory, and cytoprotective effects. Targeting cholesterol metabolism and its downstream pathways offers a promising therapeutic strategy to preserve podocyte function and slow glomerular disease progression. Future research should focus on podocyte-specific mechanisms to optimize statin-based treatments for kidney diseases.

Lipid Storage

In mammals, there exist two primary types of adipose tissue: White adipose tissue (WAT) and Brown adipose tissue (BAT). Brown adipose tissue (BAT) functions as a thermogenic organ, producing heat via mitochondrial uncoupling protein 1 (UCP1). It relies on multiple metabolites, such as glucose, lipids, and amino acids, to fuel thermogenic processes, while triglycerides (TG) act as a stored energy source.¹⁷¹ White adipose tissue (WAT) is the main form of fat storage in mammals, storing lipids in the form of TG. In addition to this, WAT is also a major secretory and endocrine organ, such as leptin.¹⁷² WAT consists of adipocytes, adipocyte progenitors, leukocytes and endothelial cells. Although adipocytes constitute only 20–40% of the total cell population, they account for more than 90% of the tissue volume.^173,174 WAT takes up excess lipids and stores them as triglycerides (TG) to prevent ectopic lipid deposition¹⁷⁵ and adverse metabolic complications, while on the other hand, it acts as a source of energy, releasing lipids as non-esterified fatty acids (NEFA) when energy is required.¹⁷⁶

Lipid Droplets (LDs) are the main storage forms of neutral lipids in cells, which act as central agents, coordinating the pathway of intracellular lipid uptake, distribution, storage and use, and release FAs to replenish energy during energy shortage.¹⁷⁷ The biogenesis and breakdown of LDs are closely linked to cellular metabolism, which is essential for buffering the content of toxic lipid species. Thus, LDs promote coordination and communication between different organelles, which are an important hub for cellular metabolism.¹⁷⁸ As a highly dynamic organelles, changes in LDs closely reflect the cellular metabolism and nutrient availability cycles: When nutrients are sufficient, lipids are stored and later mobilized to provide energy during starvation or to synthesis phospholipid when membrane production is required. Lipid droplets also sequester potentially toxic lipids, thereby playing a crucial role in preventing lipotoxicity and oxidative stress.^179,180 It is currently accepted that lipid droplet biosynthesis occurs mainly in the ER: 1) Neutral lipid synthesis and lens formation. Riacylglycerol (TAG) synthesis and the activity of cholesteryl ester synthase deposit neutral lipids between the lobules of ER bilayers.^181,182 After exceeding a specific concentration threshold, neutral lipids delaminate and aggregate to form a lens.^183,184 However, it remains unclear whether neutral lipid crystals form randomly throughout the endoplasmic reticulum or if their formation is localized to specific sites. 2) The crystalline structure promotes the growth of nascent LD in response to a variety of LD biogenesis factors.¹⁷⁶ 3) Swelling of the neutral lipid lattice leads to the emergence of LD derived from the ER membrane.¹⁸⁵ After budding, LD swell and grow by fusion or localized lipid synthesis.¹⁸⁶

LD formation is mediated by diacylglycerol-acyltransferase 1 (DGAT1). DGAT1 upregulation promotes fatty acid (FA) storage as triglycerides and LD. Conversely, DGAT1 inhibition disrupts lipid homeostasis, leading to excessive FA oxidation in mitochondria. This process generates high levels of reactive oxygen species (ROS), triggers cytochrome c release, and induces apoptosis.¹⁸⁷ APOL1 usually locate in the ER and podocytes plasma membrane, of which overexpression can cause podocyte toxicity in the kidney.¹⁸⁸ However, specific APOL1 variants promote LD formation, reducing cytotoxicity, enhancing autophagic flux, and decreasing cell death.¹⁸⁹ These variants may protect cells by modulating lipid metabolism or interacting with LD-associated proteins.

Thus, the role of LDs in podocytes and the impact of aberrant LD metabolism on cellular function are key research focuses on CKD.

Lipid Catabolism

Lipid catabolism is defined as the metabolic process by which triacylglycerols, stored in lipid droplets (LDs) of cells, undergo sequential hydrolysis to produce FAs and glycerol.¹⁹⁰ FAs are not only efficient energy substrates but also essential components for the synthesis of membrane lipids and intracellular signaling molecules.¹⁹¹

Intracellular lipolysis generates energy through the release of FAs, which are then activated as Acyl-CoA into the mitochondria for β-oxidation cycle. The main process for FAs degradation is Mitochondrial Fatty Acid β-oxidation (FAO)⁹¹ as well as the primary source of ATP. After FAs enter the cells, Fatty Acyl-CoA synthase catalyze the thioesterification reaction of FAs with coenzyme A to synthesize Fatty acyl-CoA thioesters. Next, Fatty acyl-CoA esters enter the mitochondrial matrix via the carnitine transport cycle. The L-carnitine system enables long- and medium-chain fatty acyl carboxylic acids to pass through the mitochondrial membrane. Carnitine palmitoyltransferase-1 facilitates the transfer of acyl groups from coenzyme A to L-carnitine, creating acyl-carnitine esters at the outer mitochondrial membrane. Acyl-carnitine esters are converted back to Acyl-CoA esters by Carnitine palmitoyltransferase-2. Finally, Acyl-CoA esters undergo the β-oxidation pathway, generating acetyl-CoA and a Fatty acyl-CoA ester that is two carbons shorter.^192,193 Impairment of FAO leads to abnormal lipolysis, resulting in abnormal lipid concentration and lipotoxicity.¹⁷⁷

Peroxisome Proliferator-Activated Receptor α (PPARα)

The PPARα plays an indispensable role in podocytes FAO process.¹⁹⁴ PPARα is a transcription factor that forms a complex with the Retinoid X receptor α (RXRα) as a heterodimer and binds to the PPAR response elements (PPREs) sequence in the promoter region of target genes through the PPARα DNA-binding domain (DBD) and control of the transcription of many FAO-related which participate in lipid regulation.¹⁹⁵ Transcription initiation of PPARα requires several lipophilic molecules to activate it, include Natural Saturated FAs, Unsaturated FAs, Polyunsaturated FAs (PUFAs) and synthetic ligands, collectively known as PPARα activator.¹⁹⁶ After PPARβ/δ activation, the mRNA expression of transcription factors such as carnitine palmitoyl transferase-1b (CPT-1b), 2-CPT-1b, CPT-2, PGC-1α and nuclear respiratory factor 1 (NRF-1) also increases, which is associated with mitochondrial respiratory function,¹⁹⁷ thus participating in the FAO process. Besides, AMPK, Sirtuins, HIF-1 and TGF-α/SMAD3 signaling shown to play a key role in the regulation of FAO in kidney diseases and restoring FAO by regulating these molecules ameliorates the developing of such diseases. One of the major reasons increasing the genes expression of FAO was associated with increased AMP-activated protein kinase (AMPK) activity. AMPK is an important cellular energy sensor involved in insulin signaling and therefore controls glucose uptake and podocyte insulin sensitivity.^198,199 AMPK directly catalyzes the phosphorylation of specific serine (Ser) or threonine (Thr) residues (eg, Thr177 and Ser538) on the PGC-1α protein.²⁰⁰ This phosphorylation induces conformational changes in PGC-1α, enhancing its transcriptional coactivator activity, which subsequently activates the expression of genes involved in mitochondrial biogenesis, fatty acid oxidation, and antioxidant defense mechanisms.²⁰¹ Moreover, AMPK and Sirtuin 1 (SIRT1) reciprocally activate each other, synergistically suppressing PPARγ activity to attenuate lipid storage and enhance catabolic processes. Conversely, PPARγ activation exerts inhibitory effects on both AMPK and SIRT1 signaling pathways, thereby sustaining lipogenesis and adipocyte differentiation.²⁰²

Acetyl-CoA Carboxylase (ACC)

ACC is the enzyme that catalyzes the ATP-dependent carboxylation of Acetyl CoA to form Malonyl-CoA, serving as both an intermediate in fatty acid synthesis and a negative regulator of fatty acid oxidation, and it can regulate mitochondrial oxidation of long-chain fatty acids (LCFAs) by inhibiting carnitine palmitoyltransferases 1A and 1B (CPT1A, CPT1b).^203,204 Long-chain fatty acids (LCFAs) are transported into mitochondria through the carnitine shuttle. The carnitine shuttle system consists of carnitine palmitoyltransferase 1 (CPT1), carnitine-acylcarnitine translocase (CACT), and carnitine palmitoyltransferase 2 (CPT2), which allows LCFA-CoA to be converted into acylcarnitine for mitochondrial entry via an ester-exchange reaction, followed by FAO.²⁰⁵

In FA metabolism, ACC exists in two isoforms, ACC1 and ACC2. Among them, the ACCA gene encodes ACC1, while the ACCB gene encodes ACC2.²⁰⁶ ACC1 is a cytoplasmic protein that is the first rate-limiting enzyme in the de novo fatty acid synthesis pathway. ACC2, found in the outer mitochondrial membrane, generates malonyl coenzyme A to inhibit CPT1 activity and is primarily expressed in the liver, heart, and skeletal muscle.^207–209 The expression of ACC2 is associated with type 2 diabetes. Specifically, the inhibition of the ACC-encoding genes Acaca and Acacb can reduce fibrosis and programmed cell death, and even attenuate hyperglycaemia-induced upregulation of DNL in podocytes and renal tubular cells.⁹⁴ On the contrary, Overexpression of ACC2 gene (ACACB, rs2268388) will exacerbate podocyte injury. In a study of STZ-induced diabetic mice, those with podocyte-specific overexpression of the ACACB gene exhibited a significant increase in urinary albumin excretion, along with reduced synaptophysin expression and mislocalization of podocin in podocytes.⁹³

Targeted Lipid Metabolism in Primary and Secondary Diseases

These studies have definitively established lipid metabolism as a central driver of podocyte pathology. Consequently, researchers are expanding investigations of lipid metabolism–related targets in clinical studies of glomerular diseases, while also evaluating their potential relevance in primary and secondary glomerular diseases to advance translational research.

Among various secondary glomerular diseases, a recent clinical and experimental study on diabetic nephropathy has revealed that Dock5 possesses previously unrecognized functions and mechanisms in two pathological states: podocyte lipotoxicity and proteinuria nephropathy. This molecule can regulate the uptake of fatty acids by modulating the LXRα/CD36 signaling pathway, thereby further participating in the regulation of podocyte uptake of FAs, suggesting that Dock5 regulation of lipid metabolism may serve as a promising therapeutic target for proteinuria nephropathy.²¹⁰ Meanwhile, in glomeruli isolated from DKD patient renal biopsy specimens, PCSK9 mRNA expression was markedly downregulated, and this downregulation was associated with mitochondrial dysfunction, apoptosis, and renal injury, and was accompanied by cellular lipid overload.²¹¹

In addition to DKD, significant effects of lipid metabolism have also been confirmed in studies of primary glomerular diseases such as FSGS. He Chao’s team conducted comparative transcriptomic analysis of glomeruli from patients with FSGS, minimal change disease (MCD), and healthy controls, identifying a set of differentially expressed lipid metabolism-related genes (DELMRGs). These genes are primarily involved in fatty acid synthesis and degradation and many exhibit oxidoreductase activity. Among these, ECHS1 was significantly upregulated in FSGS glomeruli and is considered a potential lipid metabolism biomarker for focal segmental glomerulosclerosis (FSGS) in children. This study not only elucidates the role of lipid metabolism disorders in the pathogenesis of FSGS but also provides new candidate molecules for the early diagnosis and targeted treatment of this disease.²¹² In Col4a3 knockout mouse models, the expression of SMPDL3b increased threefold in both glomeruli and tubules isolated from the kidneys, as well as in podocytes. Elevated SMPDL3b levels were closely associated with disrupted sphingolipid metabolism in the kidneys, primarily manifested as significant fluctuations in glomerular S1P levels. Further experiments demonstrated that specific knockout of Smpdl3b in podocytes effectively restored glomerular S1P levels, significantly reduced proteinuria, and improved podocyte loss, thereby highlighting the central role of lipid metabolism regulation in the progression of Alport syndrome.²¹³ Notably, recent studies have found that patients with podocyte injury-associated kidney disease (KD) exhibit significantly elevated concentrations of podocyte-derived vesicles in their urine, and these vesicles are rich in phospholipase A₂ receptor (PLA₂R) protein. Further analysis indicates that quantitative detection of urinary vesicles can accurately assess serum levels of anti-PLA₂R autoantibodies in patients with membranous nephropathy. These findings validate the potential of podocyte-derived vesicles in urine as a diagnostic biomarker for podocyte injury, not only reflecting the extent of podocyte damage but also providing a non-invasive diagnostic tool for clinical practice.²¹⁴

Shojiro Watanabe’s research found that compared with the non-proteinuria control group, patients with pediatric idiopathic nephrotic syndrome (INS), proteinuria-associated IgA nephropathy, and lupus nephritis all exhibited significantly reduced urinary SMPDL-3b excretion levels (most pronounced in the INS group), suggesting downregulation of SMPDL-3b expression on podocyte surfaces. Notably, serum SMPDL-3b concentrations and glomerular tissue immunostains in the same cohort showed no significant differences, further confirming that the expression changes exhibit podocyte-specific localization.²¹⁵ Not only that, Shojiro Watanabe also found that SMPDL-3b had the same effect in clinical sample tests for nephrotic syndrome (NS).²¹⁶

In patients with FSGS, serum levels of soluble urokinase-type plasminogen activator receptor (suPAR) are significantly elevated. suPAR binds to αvβ3 integrins on podocyte surfaces, inducing αvβ3-dependent cell migration and disrupting gap junction membrane homeostasis. Notably, FSGS renal biopsy tissues showed that the activation level of αvβ3 integrins was negatively correlated with reduced expression of SMPDL3b, suggesting that downregulation of SMPDL3b may enhance suPAR-αvβ3 signaling-mediated podocyte migration and injury. However, in DKD patients and human podocyte models treated with DKD serum, despite elevated suPAR levels, podocyte SMPDL3b expression was paradoxically increased. Its overexpression can antagonize suPAR-mediated activation of integrin αvβ3, inhibit excessive activation of the RhoA pathway, thereby maintaining cytoskeletal stability and reducing apoptosis. These differences reveal the bidirectional regulatory role of SMPDL3b in glomerular disease: its downregulation promotes pathological podocyte migration in FSGS, while its upregulation in DKD resists suPAR-mediated damage through a negative feedback mechanism.²¹⁷

In a Mendelian randomization analysis study of ACLY, it was found that ACLY is constitutively expressed in all cell types. A 34% reduction in ACLY expression score was associated with a reduced risk of CKD.²¹⁸

Bempedoic acid (BA), an innovative oral lipid-lowering drug and a prodrug of ACLY inhibitors, was approved by the FDA in 2020 for the treatment of hypercholesterolemia. It works by inhibiting cholesterol synthesis, with a mechanism of action similar to that of other statins.²¹⁹ In a study of angiotensin II–induced renal hypertension in rats, BA demonstrated significant activation of the cellular energy sensor AMPK, enhancing its downstream pathways to counteract Ang II–induced podocyte and endothelial stress; it also exhibited antioxidant effects, upregulating eNOS and alleviating ER stress. Furthermore, it mitigates glomerular and interstitial fibrosis by inhibiting the ERK/TGF-β signaling pathway, preserving renal microvascular structure, and preventing remodeling. Animal models demonstrate that these mechanisms translate into improved renal function and reduced proteinuria, highlighting its potential value in the prevention and treatment of kidney diseases.²²⁰ Although BA has gradually attracted significant attention in kidney disease, several research gaps remain in the regulation of podocyte lipid metabolism, such as the lack of long-term renal safety and adverse event monitoring data in patients with severe renal insufficiency and dialysis, insufficient studies on the synergistic or antagonistic effects of BA with commonly used medications such as SGLT2 inhibitors, statins, or PPAR agonists; and the optimization of multi-target combination therapy regimens and their validation in primary podocytes and animal models remain to be further explored.

Improve Podocyte Injury by Regulating Oxidative Stress

Oxidative stress (OS) refers to a state where the balance between prooxidants and antioxidants is disrupted under pathological conditions. Specifically, excessive prooxidant activity triggers overproduction of reactive oxygen species (ROS) and reactive nitrogen species (RNS) metabolites, while simultaneously impairing the antioxidant enzyme system. Consequently, this imbalance induces structural damage to cellular components, including membranes, lipids, proteins, DNA, and RNA.²²¹ Among organs affected by OS, the kidneys are particularly vulnerable due to their high mitochondrial density, which renders them susceptible to ROS-mediated injury. In this context, the NADPH oxidase (NOX) family emerges as the predominant source of renal ROS, with pathological oxidative stress primarily driven by excessive NOX activation.²²² Within the NOX family, NADPH oxidase 4 (Nox4) is uniquely prominent in renal tissues. Notably, Nox4 acts as a critical enzymatic driver in kidney pathologies such as diabetic kidney disease (DKD) and renal carcinoma.²²³ For instance, its overexpression exacerbates cisplatin-induced nephrotoxicity by amplifying programmed cell death and inflammatory responses. Conversely, targeted downregulation of Nox4 effectively suppresses pathological ROS elevation in podocytes.²²⁴

Beyond NOX-dependent mechanisms, ROS generation is tightly regulated by transcription factors Nrf1 and Nrf2. Intriguingly, aberrant Nrf2 upregulation enhances glycolysis to partially compensate for cellular energy demands yet paradoxically aggravates mitochondrial stress. In contrast, Nrf1 deficiency disrupts basal redox homeostasis, resulting in unchecked ROS accumulation and oxidative damage.²²⁵ Moreover, Nrf1 and Nrf 2 also differentially regulate ROS production through the UCP 2 pathway mediated by miR-195 and miR-497.²²⁵ Expanding on regulatory networks, multiple signaling pathways—including MAPK, HIF-1α, TRPML1 channels, NLRP3 inflammasomes, and TGF-β1—have been implicated in ROS modulation.^226–230 Expanding on regulatory networks, multiple signaling pathways—including MAPK, HIF-1α, TRPML1 channels, NLRP3 inflammasomes, and TGF-β1—have been implicated in ROS modulation (Figure 3).

Figure 3 Mechanism of lipid metabolism disorders and oxidative stress in podocyte.

Lipids are Metabolic Rheostats of Oxidative Stress in Podocytes

Free fatty acids (FFAs), particularly palmitic acid (PA), serve as a primary energy source for ATP synthesis through mitochondrial fatty acid oxidation (FAO). In experimental studies, exposure to high concentrations of palmitic acid induces lipotoxicity in podocytes, characterized by mitochondrial superoxide overproduction, oxidative stress, and impaired proteostasis. Prolonged PA exposure reduces immunoproteasome expression, thereby disrupting protein homeostasis (proteostasis)—a critical cellular process involving protein synthesis, folding, and degradation.²³¹ The primary function of the immunoproteasome involves selectively degrading misfolded, damaged, or oxidized proteins, which prevents toxic aggregate accumulation and maintains cellular integrity.²³² It is particularly important in immune cells and stressed cells, where it generates peptides for antigen presentation and enhances cellular responses to oxidative stress and inflammation. To ensure proteome stability and functionality, cells depend on three core processes: protein synthesis (translation), proper folding or assembly, and efficient clearance, which operate in a coordinated manner.^233–235 In response to protein damage, an intricate system comprising molecular chaperones and quality control pathways actively monitors and preserves proteome integrity. This system addresses damage either by facilitating the refolding of misfolded proteins or by targeting them for degradation, thus averting the accumulation of harmful cellular aggregates.^236–238 Within this framework, the immunoproteasome serves as a critical component, playing an essential role in the regulation of protein homeostasis.²³²

As the largest membrane-bound organelle in the cell, the ER is a central hub for the regulation of metabolic homeostasis. Dysregulation of ER structure and function impairs its capacity to process folded proteins, leading to the accumulation of misfolded proteins and disruption of calcium homeostasis. These changes trigger ER stress, which is characterized by the activation of the unfolded protein response (UPR).^239,240 The primary systems for protein degradation include the ubiquitin-proteasome system (UPS) and autophagy-lysosomal pathway (ALP). Several studies have found that ER stress and UPR can be strongly associated with lipotoxicity.²⁴¹

Studies using C57BL/6 mice revealed that dysregulated protein degradation during ER stress promotes lipid synthesis, leading to lipid deposits and impaired kidney function. Following tunicamycin treatment, metabolic changes in the mice were assessed at 8 and 24 hours. At the 8-hour mark, phosphorylation of renal UPR markers and upregulation of the adipogenic transcription factor SREBP1 were observed. By 24 hours, SREBP-1 levels further increased, accompanied by a significant rise in triglyceride (TG) content and a reduction in AMP-activated protein kinase (AMPK) expression.²⁴²

Furthermore, under conditions of ER stress, glomerular α5 collagen IV was observed to colocalize with RTN3L and autophagosomes, suggesting a potential interaction between ER stress and autophagy in podocytes. In murine models, the expression levels of Sec23B, RTN3L, and LC3-II were significantly upregulated in podocytes, indicating enhanced autophagic activity.²⁴³ Moreover, palmitic acid (PA) was shown to exacerbate ER stress and elevate reactive oxygen species (ROS) production, ultimately leading to podocyte apoptosis.²⁴⁴ In the renal cortex of type 2 diabetic mice, lipotoxicity aggravated podocyte injury and impaired expression of immune protectors.²³¹

Under conditions of energy stress, the AMP-activated protein kinase (AMPK) complex acts as a central sensor of intracellular ATP levels, orchestrating cellular responses to mitochondrial dysfunction and metabolic imbalance.²⁴⁵

The reduction in AMPKα activation leads to an increase in the activity of its downstream target, SREBP-1c. SREBP-1c is a transcription factor whose enhanced nuclear localization promotes the accumulation of FFA and Fatty acid-binding protein 4 (FABP4).²⁴⁶

Conversely, enhanced AMPK phosphorylation suppresses renal SREBP-1c upregulation, reducing acetyl-CoA carboxylase and fatty acid synthase activity, as well as adipose differentiation-related protein expression. This decreases renal triglyceride accumulation, potentially preserving renal function in diabetes.²⁴⁷ In addition to its role in lipid metabolism, AMPK is crucial for mitigating oxidative stress (OS) in podocytes. By inhibiting glycogen synthase kinase-3β (GSK3β), AMPK prevents GSK3β from suppressing Nrf2 activity through nuclear export and degradation. This Nrf2-mediated antioxidant response neutralizes reactive oxygen species (ROS) generated during oxidative stress, thereby enhancing cellular defenses against oxidative damage.²⁴⁸

AMPK and PPARα can inhibit FA uptake and lipogenesis, promote β-oxidation of FAs and reduce intracellular lipid accumulation. It also stimulates Nrf2 nuclear translocation and increases the expression of Nrf2-reactive enzymes HO-1 and Nqo-1, thus ameliorating OS.²⁴⁹ Moreover, AMPK collaborates with peroxisome proliferator-activated receptor alpha (PPARα) to regulate fatty acid metabolism and oxidative stress in podocytes. AMPK and PPARα synergistically inhibit fatty acid uptake and lipogenesis while promoting fatty acid β-oxidation, thereby reducing intracellular lipid accumulation. On the other hand, AMPK stimulates Nrf2 nuclear translocation and upregulates the expression of Nrf2-target genes, such as HO-1 and Nqo-1. These findings highlight the central role of AMPK in integrating lipid metabolism and oxidative stress responses, making it a promising therapeutic target for podocyte-related kidney diseases.

Oxidative Stress Leads to Cellular Lipotoxicity

While excessive oxidative stress and mitochondrial dysfunction have been proven to cause podocyte injury, the underlying mechanisms and the physiological energy metabolism of podocytes are still a matter of debate. Abe et al demonstrated that in mouse podocytes, energy metabolism is primarily driven by mitochondrial respiration, with restricted glycolytic activity, and that these cells can metabolize multiple substrates.²⁵⁰ Conversely, other studies have shown that ATP distribution in podocytes exhibits regional heterogeneity: glycolysis primarily maintains ATP supply in the cortical region, while mitochondrial oxidative phosphorylation (OXPHOS) is responsible for energy generation in the perinuclear cytosol. Glycolysis and mitochondrial OXPHOS regulate energy metabolism in distinct cellular regions, with glycolysis playing a dominant role in early differentiation and cell survival, while OXPHOS becomes the primary energy supply pathway after differentiation.⁸² Brinkkoetter et al pointed out that anaerobic glycolysis serves as the primary energy source for podocytes, while mitochondria may predominantly function in signaling rather than energy supply in these cells.¹¹⁸ In addition to glycolysis and OXPHOS, lactate has also been demonstrated to serve as an alternative substrate for maintaining podocyte energy homeostasis and glycolytic flux, indicating that podocytes possess an efficient lactate transport system.²⁵¹ Lactate stimulation can modulate mitochondrial dynamics and respiratory efficiency in primary rat podocytes, further supporting the role of lactate as a critical precursor for cellular energy metabolism.⁸⁴ Thus, elucidating the impact of specific energy metabolism pathways and mitochondrial function on podocyte biology could pave the way for innovative clinical interventions.

Mitochondrial structural disorder may be one of the mechanisms underlying podocyte damage. Specifically, ischemia-reperfusion injury induces mitochondrial fragmentation and impairs ATP synthesis, contributing to foot process effacement through the disruption of actin dynamics. Furthermore, pharmacological inhibition of DRP1, which prevents mitochondrial fission, has been shown to ameliorate podocyte injury.²⁵² In diabetic nephropathy, increased mitochondria-associated endoplasmic reticulum membranes (MAMs) promote excessive mitochondrial fission by regulating the phosphorylation and mitochondrial translocation of dynamin-related protein 1 (Drp1) via A-kinase anchoring protein 1 (AKAP1), ultimately leading to podocyte injury.²⁵³ However, how mitochondrial dysfunction affects the long-term viability of podocytes remains unclear. Additionally, whether the signaling function of podocyte mitochondria in communication with endothelial cells plays a role, as well as the specific signaling pathways involved, requires further investigation.

Oxidative stress also activates signaling pathways that exacerbate podocyte injury. For instance, Sirt6 significantly reduces oxidative stress in cellular, because its overexpression effectively reduces apoptosis, which is associated with AMPK phosphorylation.²⁵⁴ Upregulation of Sirt6 expression markedly reduces the level of mitochondrial superoxide and intracellular ROS production, also promotes increased AMPK phosphorylation. This suggests that Sirt 6 protects podocyte mitochondria and exerts anti-oxidative stress, anti-apoptotic effects by activating the AMPK pathway. AMPK regulates lipid synthesis, lipolysis and FAO by inhibits the ACC.²⁵⁵ ACC is an important regulatory site in the FA synthesis and oxidation pathways because it can catalyze the carboxylation of acetyl-CoA to malonyl-coenzyme during FA synthesis. ACC suppresses the lipogenic in terminating podocytes.⁹⁴

The final step of the glycolysis process also requires catalysis by a specific enzyme--Pyruvate kinase M2 (PKM2). Under oxidative stress, PKM2 translocates to the mitochondria, where it interacts with and phosphorylates Bcl2 at threonine 69. This phosphorylation prevents the integration of the Cul3-based E3 ligase with Bcl2, thereby inhibiting its following degradation and regulating oxidative stress-induced apoptosis.²⁵⁶ Activation of PKM2 can increase the metabolic flux caused by glycolysis, increased glycolytic flux in podocytes to induce mitochondrial dysfunction, upregulate glycolytic flux through the polyol pathway, and reinforce the accumulation of methylglyoxal and diacylglycerol (DAG) of synthetic.^257,258 DAG is a lipid second messenger that induces aberrant activation of protein kinase C (PKC).²⁵⁹ Activated PKC phosphorylates a variety of intracellular target proteins, which can mediate multiple pathways to ameliorate podocyte injury.^260,261 The following is a summary of the targets, mechanisms of action, and representative modulators (Table 1).

Table 1 Multi-Signaling Pathway Targets in Podocyte Injury Amelioration

Mitochondria are a Double-Edged Sword

As mentioned earlier, podocytes, due to their highly specialized and complex foot process structure, have an extremely high demand for a continuous supply of local ATP. As a double-edged sword, mitochondria are both the primary generators of ROS and responsible for maintaining energy and clearing damaged mitochondria. Mitochondrial dynamics and mitochondrial autophagy are key processes in maintaining mitochondrial homeostasis to protect podocyte function.²⁷⁶ A recent study found that ROS-driven membrane lipid peroxidation increases ferroptosis, directly leading to damage and shedding of cystinosis podocytes, identifying lipid peroxidation as a new priority target for breaking the cycle of cystinosis podocyte damage and shedding.²⁷⁷

Yiqun Hao’s clinical research on hypertensive nephropathy (HN) also confirmed the role of mitochondrial function in podocyte lipid metabolism. In the glomeruli of HN patients, the levels of Sirt6 and mitochondrial outer membrane phospholipase PLD6 were significantly decreased. Similarly, in vivo and in vitro studies also demonstrated the same results. Further studies revealed that the Sirt6–PLD6 axis achieves its preventive effect against lipid nephrotoxicity by regulating the hydrolysis and remodeling of characteristic phospholipids—cardiolipin—on the mitochondrial inner membrane.²⁷⁸ In another study on lipid toxicity in podocytes with Alport syndrome, reduced contact between LDs and mitochondria was identified as one of the primary causes of inefficient fatty acid transfer in AS, exacerbating both mitochondrial dysfunction and podocyte damage in AS. Based on this, enhancing LD-mitochondrial contact formation is a promising direction for effectively preventing lipotoxicity.²⁷⁵ It is evident that mitochondrial homeostasis is a decisive factor in podocyte survival and functional maintenance.

Mitochondrial Dynamics

Mitochondrial dynamics maintain dynamic homeostasis by regulating mitochondrial mass and function. Restoring this balance reverses podocyte apoptosis in db/db mice, improves glucose metabolism disorders, reduces basement membrane thickening, alleviates mesangial expansion, and inhibits glomerular fibrosis.²⁷⁹ Further studies indicate that this process also reshapes the lipid profile within podocytes. In diabetic nephropathy patients and DKD mouse models, the expression of ABCA1, which is responsible for cholesterol and phospholipid efflux in podocytes, is significantly downregulated. In human podocytes lacking ABCA1, excessive accumulation of cardiolipin occurs, accompanied by mitochondrial respiratory chain complex dysfunction and structural reorganization.²⁸⁰ Additionally, in podocytes, ChREBP is a glucose-responsive transcription factor and a major regulator of lipid biogenesis, significantly increasing mitochondrial fission in podocytes of db/db mice. It also modulates the transcription of the Gnpat gene, thereby influencing the expression of its encoded protein, further inducing mitochondrial remodeling.²⁸¹ PGC-1α is a key regulator of mitochondrial biogenesis, and its reduced expression leads to mitochondrial and podocyte damage. In a study by Minmin Gong, pyruvate kinase M2 (PKM2) activates the PGC-1α/Opa1 pathway to reduce mitochondrial fragmentation and protect podocytes, which may represent a potential early strategy for DKD.²⁸²

Mitochondrial Autophagy

In addition to mitochondrial dynamics, mitochondrial autophagy is another critical component in maintaining mitochondrial homeostasis. A recent targeted lipidomics analysis and podocyte-specific measurement study identified cholesterol ester 20:4 as a key lipid metabolite accumulated in podocytes, which is associated with mitochondrial morphological changes, mitchondrial respiration, glycolysis, and reduced ATPase activity, accompanied by autophagy activation, indicating impaired mitochondrial function.²⁸³ As described earlier, PGC-1α not only maintains mitochondrial homeostasis by regulating mitochondrial fission and fusion, but in vitro experiments also confirm that it can activate mitochondrial autophagy in podocytes, thereby clearing damaged mitochondria and alleviating kidney damage in the DKD model.²⁸⁴ Xu-shun Jiang et al clearly demonstrated that PA increases the formation of autophagosomes and autophagolysosomes in podocytes, promoting podocyte autophagy. This suggests that the activation of autophagy serves as a self-protective mechanism for podocytes in response to PA-induced stress, attempting to clear damaged organelles and excess proteins through autophagy to maintain normal cellular function.²⁸⁵ Yiqun Hao also confirmed this finding.²⁶⁴ Existing studies have confirmed that mitochondrial-lipid metabolism axis dysfunction is a common pathological basis for podocyte injury, but its regulatory network exhibits significant disease-dependent contradictions: molecular functional heterogeneity: the same molecule (SMPDL3b) has opposite effects in different kidney diseases; pathway spatiotemporal specificity: the upstream and downstream effects of key nodes (the Sirt6-PLD6) exhibit upstream and downstream effects that dynamically change with the disease microenvironment. While targeted interventions targeting mitochondria have shown efficacy in animal models, the lack of a disease-specific precise regulatory framework hinders clinical translation. These bottlenecks urgently require breakthroughs.

Conclusion

Lipid metabolism and oxidative stress are intricately linked in the pathogenesis of podocyte injury. Dysregulated lipid metabolism leads to mitochondrial dysfunction, increased ROS production, and subsequent podocyte damage, contributing to proteinuria and glomerular disease progression. Therapeutic strategies targeting lipid metabolism, mitochondrial function, and oxidative stress pathways hold promise for mitigating podocyte injury and improving outcomes in chronic kidney disease. Future research should focus on elucidating the specific molecular mechanisms underlying these interactions and developing targeted therapies to restore podocyte homeostasis.

The current focus on the interplay between lipid metabolism disorders and oxidative stress offers a novel perspective. However, several critical issues and research directions warrant further exploration.

First, how does oxidative stress mediate podocyte injury and regulate lipid uptake, synthesis, breakdown, and storage both intracellularly and extracellularly? The complexity of metabolic pathways is evident, as lipid metabolism is not only directly linked to fat synthesis and degradation, but also intricately connected to glucose metabolism, amino acid metabolism, and protein synthesis. The interactions and feedback mechanisms among these pathways remain incompletely understood, particularly regarding how different fat types (white adipose tissue vs brown adipose tissue) interact. Additionally, individual variability—driven by factors such as age, gender, race, and genetic background—leads to diverse lipid metabolism patterns. Current research predominantly relies on laboratory models or specific populations, leaving a gap in comprehensive studies across broader human demographics.

Second, studies have demonstrated a strong link between oxidative stress and lipid metabolism, particularly in how oxidative stress exacerbates lipid metabolic disorders by impairing fatty acid oxidation and altering fat storage. However, the precise molecular mechanisms, such as the role of oxidative stress in regulating fatty acid transport and adipose tissue inflammation, remain unclear and require further investigation.

Third, there is a pressing need for effective and specific biomarkers to diagnose and predict these diseases. Many studies focus on general oxidative stress markers (MDA, 8-OHdG) and lipid metabolism-related indicators (fatty acids, triglycerides, cholesterol). However, these biomarkers often lack sufficient specificity and sensitivity for early diagnosis. The intertwined nature of oxidative stress and lipid metabolism disruption complicates biomarker detection, requiring consideration of multiple factors, such as oxidant types and metabolic product concentrations. Moreover, many oxidative stress biomarkers may not be detectable in the early stages of disease, posing challenges for timely diagnosis.

Lastly, it is crucial to delineate the specific signaling networks governing material metabolism in podocytes. This includes understanding how signal expression and transmission regulate lipid metabolic reorganization, as well as downstream responses controlled by lipids at transcriptional, epigenetic, and post-translational levels. Current therapeutic strategies for addressing lipid metabolism disruption and oxidative stress primarily involve pharmaceutical interventions (eg, antioxidants, lipid-lowering drugs) and lifestyle modifications (eg, diet, exercise). However, these approaches have limitations. For example, while some antioxidants (eg, vitamin C, vitamin E, selenium) have shown promise in clinical trials, many studies have failed to demonstrate significant improvements in disease outcomes. This may stem from antioxidants interfering with other physiological processes, potentially causing adverse effects. Furthermore, significant individual differences in lipid metabolism and oxidative stress highlight the need for personalized interventions, which current treatment protocols often fail to address. Developing tailored treatment strategies for specific patient groups will require extensive clinical data and research efforts.

In recent years, the combination of Gene-edited²⁸⁶ and induced pluripotent stem cell (iPSC)^287,288 technology has enabled researchers to simulate critical developmental stages in the process of human organ formation. By inducing iPSCs to undergo stepwise differentiation along embryological milestones, three-dimensional organoid models containing multiple cell types have been constructed, such as the cerebral cortex, intestine, and stomach. This strategy has also been successfully extended to the construction of kidney organoids, which partially recreate the tissue architecture and cellular composition of nephrons. This provides an unprecedented experimental model and research platform for studying the development, functional maintenance, and underlying mechanisms of human foot cells and related diseases.