ProBDNF-p75NTR signaling in sterile inflammation

Abstract

Trauma, injury, and surgical procedures cause tissue damage, sterile inflammatory responses, and significant immune system stress leading to immune dysregulation and increased susceptibility to secondary infections. The spleen is a reservoir of myeloid immune cells that are involved in inflammation following various tissue injuries. One potential signaling pathway that may be involved in this process is proBDNF-p75NTR signaling in myeloid cells. Brain derived neurotrophic factor (BDNF) is a previously reported myokine, however there is little known about its role in skeletal muscle injury. We recently found that p75NTR, the receptor for proBDNF, was significantly upregulated (p=0.004) in myeloid cells isolated from the spleen of animals with hindlimb IR injury compared to sham controls, potentially in a sexually dimorphic manner. Our previous studies have shown that proBDNF, the precursor protein to BDNF, is the predominant form of BDNF expressed in skeletal muscle tissue and is significantly upregulated following tourniquet induced hind limb IR injury in mice (p=0.013). We hypothesize that proBDNF released from injured skeletal muscle could act through p75NTR in myeloid cells to regulate inflammatory responses following IR injury. The hind limb IR injury was induced using a tourniquet model in which an orthodontic rubber band placed on the hind limb at the level of the hip and left in place for 1.5 hours followed by tourniquet removal and reperfusion. A series of in vitro experiments were conducted on myeloid cells isolated from the spleen of sham mice, or mice with skeletal muscle IR injury. As a model of secondary infection, myeloid cells were stimulated with lipopolysaccharide (LPS) and cytokine release into culture media was measured using ELISA assays. We found that in myeloid cells isolated from IR injured animals, LPS stimulated cytokine release was increased. Further, treating isolated myeloid cells from IR injured animals with recombinant cleavage resistant proBDNF increased cytokine release compared to controls. To confirm that p75NTR on myeloid cells was at least partially responsible for the induction of cytokine expression following LPS or proBDNF stimulation, myeloid cells were treated with LM11A-31, a modulator of p75NTR in combination with LPS or proBDNF. Treatment with C31 (100ng) blunted cytokine release following LPS and proBDNF stimulation. These results suggest that the p75NTR pathway is involved in the innate immune function of splenic myeloid cells in injury induced inflammation and therefore is potentially a novel therapeutic target. This work was funded by NIH grant R01HL147105, NIH Training Grant T32-GM136503, and NIH F31 Fellowship F31HL167480. This is the full abstract presented at the American Physiology Summit 2024 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.