Skeletal muscle derived pro-brain derived neurotropic factor promotes ischemia-reperfusion induced inflammation

Skeletal muscle ischemia-reperfusion (IR) injury is prevalent in trauma, peripheral vascular diseases, and following surgical procedures, however, effective prevention and treatment for skeletal muscle IR injury are lacking. Brain-derived neurotrophic factor (BDNF), originally discovered in the brain, is expressed and released from skeletal muscle as a myokine. However, the transcription splice variants, posttranslational modifications, and functions of BDNF in skeletal muscle are poorly defined. In this study, we first showed that skeletal muscle expressed unique splice variants of BDNF compared to the brain. At the protein level, Western blot comparing BDNF in brain and skeletal muscle revealed that skeletal muscle expresses significantly more proBDNF than mature BDNF under basal conditions, opposite to brain tissue. Consistent with this, the levels of the major protein convertases in skeletal muscle were significantly lower compared to the brain, suggesting that the high level of proBDNF is at least partially due to the low cleavage activity in skeletal muscle. The potential function of the proBDNF in disease conditions was then examined in mice with skeletal muscle IR injury. IR injury was induced in 3-month-old male and female C57BL/6 mice by placing a tourniquet on one hind limb for 1 hour, then removing it, allowing reperfusion for 1-14 days, with the contralateral hind limb serving as a control. We hypothesize that proBDNF may be necessary for facilitating the inflammatory response, while mature BDNF may be necessary for promoting inflammation resolution and myogenesis following IR injury. Remarkably, the level of proBDNF, but not mature BDNF, was increased significantly in IR muscle compared to the contralateral control (p=0.013). This was accompanied by increased proinflammatory cytokines and macrophage infiltration in the injured muscle. Mice with skeletal muscle-specific knockout of BDNF showed a significant reduction in proinflammatory cytokine production and macrophage infiltration following IR injury compared to wild-type animals. To confirm the role of proBDNF in this finding, the receptor for proBDNF, p75NTR, was blocked using the small molecule LM11A-31. In IR injured muscle, LM11A-31 treatment significantly reduced the proinflammatory response and macrophage infiltration compared to control animals, similar to what is seen in BDNF knockout animals. Collectively, these results indicate that myokine proBDNF promotes inflammation and macrophage recruitment in the IR-injured muscle, and therefore is a potential target for the treatment of skeletal muscle injury. This work was funded by NIH grant R01HL147105 and NIH Training Grant T32-GM136503. This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.