Effect Of Notch, Exercise, And Obesity On Markers Of Myogenesis And Atrophy

Notch has a pleiotropic role during skeletal muscle repair. It promotes cellular proliferation, inhibits muscle differentiation, and influences cellular quiescence. Notch is also suggested to affect muscle atrophy, but there is little published work describing that interaction. In addition, the effect of different disease states on Notch’s influence on repair and atrophy processes is unknown. Obesity delays muscle repair, but the influence of Notch on the impaired repair is unknown. PURPOSE: To measure markers of muscle repair and atrophy in young obese mice with inhibited Notch signaling and were exposed to injurious exercise. METHODS: Two mouse trial studies were performed. In Study #1, Young (2-4 months) male C57BL/6 mice were injected with 100,000 TUs of shRNA Notch1 inhibitor into the left gastrocnemius (Control vector in right) for five consecutive days. Mice were exposed to an injurious bout of downhill running and were euthanized at 1D, 2D, 3D, and 4D post-exercise. In Study #2, Young (2-4 months) male and female C57BL/6 mice were fed either standard chow or a high-fat diet for 12 weeks and were injected with shRNA Notch1 inhibitor into the left gastrocnemius for five consecutive days. Mice were exposed to an injurious bout of downhill running and were euthanized at 3D, and 5D post-exercise. The rodent treatments were approved by UNC Charlotte’s Institutional Animal Care and Use Committee. Markers of muscle repair and atrophy were measured in the gastrocnemius via western blot analysis. Depending on groups, either one way or two-way analysis of variance (ANOVA) tests were performed to determine differences between experimental groups and post-hoc comparisons were accomplished via a Tukey’s test, with statistical significance set a priori at p < 0.05. RESULTS: There was a main effect of muscle repair markers, MyoD, Myogenin, and embryonic Myosin Heavy Chain (eMHC) with significant elevation of these myogenic markers in Notch inhibited mice relative to control (p < 0.05). CONCLUSION: Downregulation of Notch accelerates the expression of later-stage muscle repair markers and inhibits muscle atrophy. The role of Notch signaling may be better described as a moderator of muscle size rather than a requirement for muscle repair. UNC Charlotte's Faculty Research Grant