The role of proBDNF-p75NTR signaling in hind limb ischemia.

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The role of proBDNF-p75NTR signaling in hind limb ischemia Brain-derived neurotrophic factor (BDNF) and its precursor proBDNF have been well characterized in their contrasting roles in neuroprotection and neuroinflammation in the central nervous system respectively. Recently, BDNF and proBDNF have been shown to exist in tissues outside of the central nervous system, but their role in these tissues is still unclear. In my study it was shown that whole muscle lysate contains high levels of proBDNF and relatively low levels of mature BDNF compared to whole brain lysate. This project aims to investigate the functional role of skeletal muscle-derived proBDNF in hind limb ischemia-reperfusion (IR) injury. In this model, in which C57BL/6 mice are subjected to ligation of the right hind limb, proBDNF and its receptor p75NTR were both upregulated, and p75NTR downstream signaling pathways were activated in the ischemic muscle compared to the contralateral control limb muscles. The data further showed that treatment with LM11A-31, a p75NTR moderator, following IR injury improved perfusion of the ischemic limb compared to untreated IR controls, indicating improved endothelial function. Moreover, skeletal muscle-specific knockout of BDNF significantly improved the blood perfusion in the ischemic limb compared to wild-type mice. Previous studies have suggested that endothelial p75NTR may mediate vascular injury. Based on these results, we hypothesize that the upregulated proBDNF in skeletal muscle following IR injury may stimulate endothelial p75NTR, promoting cleavage of the intercellular domain (ICD) and subsequent inhibition of PKA-induced phosphorylation of eNOS and nitric oxide production leading to vascular dysfunction and inflammation. To test this hypothesis, mice with skeletal muscle-specific knockout of BDNF will be used to determine the role of muscle-derived proBDNF in IR injury. Then mice with endothelial-specific knockout of p75NTR will be used to examine whether endothelial p75NTR mediates IR injury. Finally, in vitro and in vivo experiments will be used to define the inhibition of PKA by the ICD of p75NTR and subsequent eNOS function being responsible for the IR injury. The results of this project will reveal a novel mechanism underlying IR injury and suggest new targets for the prevention and treatment of IR injury in patients. While under the superior intellectual guidance and support of a mentor with over 20 years of experience in the field, functional knowledge of experimental design, data analysis and interpretation, and scientific communication will be developed, leading to Ph.D. and enabling a successful and productive career in biomedical research. Experiments will be carried out using top-of-the-line research equipment in premier facilities with ample opportunities for learning, growth, and support.