Increased levels of SV2A botulinum neurotoxin receptor in clinical sensory disorders and functional effects of botulinum toxins A and E in cultured human sensory neurons
Yiangos Yiangou1 Uma Anand1,2, William R. Otto2, Marco Sinisi3, Michael Fox3, Rolfe Birch3 Keith A. Foster4, Gaurav Mukerji1,5, Ayesha Akbar1,6, Sanjiv K. Agarwal5, Praveen Anand1
1Department of Clinical Neuroscience, Imperial College London, Hammersmith Hospital, London; 2Histopathology Laboratory, Cancer Research UK, London Research Institute, London; 3Peripheral Nerve Injury Unit, Royal National Orthopaedic Hospital, Stanmore; 4Syntaxin Ltd, Oxford; 5Department of Urology; 6Department of Gastroenterology, Imperial College London, Hammersmith Hospital, London, United Kingdom
Background: There is increasing evidence that botulinum neurotoxin A may affect sensory nociceptor fibers, but the expression of its receptors in clinical pain states, and its effects in human sensory neurons, are largely unknown.
Methods: We studied synaptic vesicle protein subtype SV2A, a receptor for botulinum neurotoxin A, by immunostaining in a range of clinical tissues, including human dorsal root ganglion sensory neurons, peripheral nerves, the urinary bladder, and the colon. We also determined the effects of botulinum neurotoxins A and E on localization of the capsaicin receptor, TRPV1, and functional sensitivity to capsaicin stimuli in cultured human dorsal root ganglion neurons.
Results: Image analysis showed that SV2A immunoreactive nerve fibers were increased in injured nerves proximal to the injury (P = 0.002), and in painful neuromas (P = 0.0027); the ratio of percentage area SV2A to neurofilaments (a structural marker) was increased proximal to injury (P = 0.0022) and in neuromas (P = 0.0001), indicating increased SV2A levels in injured nerve fibers. In the urinary bladder, SV2A nerve fibers were found in detrusor muscle and associated with blood vessels, with a significant increase in idiopathic detrusor overactivity (P = 0.002) and painful bladder syndrome (P = 0.0087). Colon biopsies showed numerous SV2A-positive nerve fibers, which were increased in quiescent inflammatory bowel disease with abdominal pain (P = 0.023), but not in inflammatory bowel disease without abdominal pain (P = 0.77) or in irritable bowel syndrome (P = 0.13). In vitro studies of botulinum neurotoxin A-treated and botulinum neurotoxin E-treated cultured human sensory neurons showed accumulation of cytoplasmic vesicles, neurite loss, and reduced immunofluorescence for the heat and capsaicin receptor, TRPV1. Functional effects included dose-related inhibition of capsaicin responses on calcium imaging after acute treatment with botulinum neurotoxins A and E.
Conclusion: Differential levels of SV2A protein expression in clinical disorders may identify potential new targets for botulinum neurotoxin therapy. In vitro studies indicate that treatment with botulinum neurotoxins A and E may affect receptor expression and nociceptor function in sensory neurons.
Keywords: SV2A, human, pain, botulinum neurotoxin, neurons
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