Astrocyte HIF-2α supports learning in a passive avoidance paradigm under hypoxic stress
Received 11 May 2018
Accepted for publication 23 June 2018
Published 8 November 2018 Volume 2018:6 Pages 35—56
Checked for plagiarism Yes
Review by Single-blind
Peer reviewers approved by Dr Colin Mak
Peer reviewer comments 4
Editor who approved publication: Prof. Dr. Dörthe Katschinski
Cindy V Leiton,1,2 Elyssa Chen,2 Alissa Cutrone,3 Kristy Conn,2 Kennelia Mellanson,4 Dania M Malik,5 Michael Klingener,6 Ryan Lamm,7 Michael Cutrone,8 John Petrie IV,9 Joher Sheikh,10 Adriana DiBua,11 Betsy Cohen,12 Thomas F Floyd13–15
1Department of Pathology, Stony Brook University, Stony Brook, NY, USA; 2Department of Anesthesiology, Stony Brook University, Stony Brook, NY, USA; 3Department of Medicine, Vanderbilt University School of Medicine, Nashville, TN, USA; 4Department of Pharmacological Sciences, Stony Brook University, Stony Brook, NY, USA; 5Department of Systems Pharmacology and Translational Therapeutics, University of Pennsylvania, Philadelphia, PA, USA; 6Department of Genetics, Stony Brook University, Stony Brook, NY, USA; 7Department of General Surgery, Thomas Jefferson University Hospital, Philadelphia, PA, USA; 8Department of Anesthesiology, Duke University Medical Center, Durham, NC, USA; 9Department of Biochemistry & Molecular Biology, Bloomberg School of Public health, Johns Hopkins University, Baltimore, MD, USA; 10Department of Physiology and Biophysics, Georgetown University, Washington, DC, USA; 11Department of Chemistry, Hofstra University, Hempstead, NY, USA; 12Computer Science Department, Swarthmore College, Swarthmore, PA, USA; 13Department of Anesthesiology and Pain Management, University of Texas Southwestern, Dallas, TX, USA; 14Department of Cardiothoracic Surgery, University of Texas Southwestern, Dallas, TX, USA; 15Department of Radiology, University of Texas Southwestern, Dallas, TX, USA
Background: The brain is extensively vascularized, uses ~20% of the body’s oxygen, and is highly sensitive to changes in oxygen. While synaptic plasticity and memory are impaired in healthy individuals by exposure to mild hypoxia, aged individuals appear to be even more sensitive. Aging is associated with progressive failure in pulmonary and cardiovascular systems, exposing the aged to both chronic and superimposed acute hypoxia. The HIF proteins, the “master regulators” of the cellular response to hypoxia, are robustly expressed in neurons and astrocytes. Astrocytes support neurons and synaptic plasticity via complex metabolic and trophic mechanisms. The activity of HIF proteins in the brain is diminished with aging, and the increased exposure to chronic and acute hypoxia with aging combined with diminished HIF activity may impair synaptic plasticity.
Purpose: Herein, we test the hypothesis that astrocyte HIF supports synaptic plasticity and learning upon hypoxia.
Materials and Methods: An Astrocyte-specific HIF loss-of-function model was employed, where knock-out of HIF-1α or HIF-2α in GFAP expressing cells was accomplished by cre-mediated recombination. Animals were tested for behavioral (open field and rotarod), learning (passive avoidance paradigm), and electrophysiological (long term potentiation) responses to mild hypoxic challenge.
Results: In an astrocyte-specific HIF loss-of-function model followed by mild hypoxia, we identified that the depletion of HIF-2α resulted in an impaired passive avoidance learning performance. This was accompanied by an attenuated response to induction in long-term potentiation (LTP), suggesting that the hippocampal circuitry was perturbed upon hypoxic exposure following HIF-2α loss in astrocytes, and not due to hippocampal cell death. We investigated HIF-regulated trophic and metabolic target genes and found that they were not regulated by HIF-2α, suggesting that these specific targets may not be involved in mediating the phenotypes observed.
Conclusion: Together, these results point to a role for HIF-2α in the astrocyte’s regulatory role in synaptic plasticity and learning under hypoxia and suggest that even mild, acute hypoxic challenges can impair cognitive performance in the aged population who harbor impaired HIF function.
Keywords: astrocyte, hypoxia, HIF, learning, LTP, tripartite synapse, memory, glia, cognitive function
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