Differential Acute Adipogenic Signaling Changes Following Neuromusculoskeletal Injuries
Authors: Crum Braydon , Bruzina Angela , Raymond-Pope Christiana , Lillquist Thomas , Hoffman Daniel , Call Jarrod , Greising Sarah 
Published: May 2024

Following traumatic injury, neuromusculoskeletal tissue undergoes extensive plastic modification. Changes can be observed at the local and systemic levels and can involve tissue function, signaling, and local composition. Currently there is limited understanding of early adipogenic changes following some traumatic injuries, which is needed to understand the long-term lack of functional muscle recovery. The objective of this project was to examine plasticity after injury, namely systemic and local adipogenic signaling and fat droplet deposition following volumetric muscle loss (VML) and denervation injuries. We hypothesized there would be differential changes in local and systemic adipogenic signaling, specifically changes in fat droplet accumulation following neuromusculoskeletal injuries. Adult C57B1/6J mice (n=36; 6 male, 6 female/group): posterior compartment VML, tibial nerve denervation, and naïve control. Both injury models target plantarflexor muscles. Mice were euthanized 72-hrs post-injury. In vivo muscle function was assessed, and gastrocnemius, liver, and serum were saved for analysis. Whole gastrocnemius muscles from a subset (n=4/group) were saved for histology, and five standardized sections were systematically obtained 1.5mm apart; muscle sections were stained with H&E and Oil-Red-O to evaluate total fiber number and fat droplet accumulation, respectively. Data were analyzed by two- and three-way ANOVA with Tukey’s HSD post hoc. Maximal torque declined ~81 and 98% following VML and denervation injury, respectively (main effect p<0.001), and VML-injured muscle was more fatigable than injury naïve (main effect p=0.001). Following denervation, liver insulin-like growth factor 1 (IGF-1) was increased ~52% compared to other groups, and was most pronounced in males (main effect injury p<0.001; sex p=0.021). VML injury resulted in a 4-fold higher muscle IGF-1 regardless of sex (interaction p=0.021), and greater muscle interleukin-6 (IL-6), which was more pronounced in females (main effect injury p=0.001; sex p=0.049). Platelet-derived factor growth receptor (PDFGRα) expression was diminished following VML injury in both sexes (interaction p=0.016); suggesting a decrease in fibro-adipogenic progenitors (FAPs) and an alternative origin responsible for increases in IGF-1 and IL-6 rather than FAPs. Serum leptin concentrations were blunted following both VML- and denervation-injury (main effect p=0.002), which may illicit alterations in the regenerative process, specifically the maintenance of muscle quality. Serum IGF-1 and IL-6 concentrations were not affected by injury (p≥0.164). Histological analysis revealed a significant decrease in total fiber number across the middle three sections of the VML-injured muscle (i.e., the section initially injured) compared to other groups (p≤0.034). Findings provide a foundation for characterizing adipocyte development in the muscle remaining after injury and identify therapeutic targets for rehabilitative and nutritional approaches to address contractile and metabolic impairments following injury. Future work should elucidate the time course of adipogenic signaling following these injuries, with particular interest in their relationship to changes in metabolic and contractile impairments. R01-AR078903 (JAC & SMG); University of Minnesota UROP (BAC). 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.