Notch, Numb and Numb-Like Responses to Exercise Induced Muscle Damage in Human Skeletal Muscle

Abstract

Introduction: Notch proteins are a single-pass type 1 transmembrane protein that regulates cellular proliferation and inhibits myogenic differentiation. Numb and Numb-Like are adaptor proteins. Among their functions is control of cell fate determination and progression of cell differentiation via inhibition of Notch. While no role for Numb-Like has been found in cells of the myogenic lineage, Numb promotes myogenic differentiation of satellite cells. The roles these proteins in human skeletal muscle in response to exercise-induced muscle damage have yet to be examined. Purpose: The purpose of this investigation is to examine changes in the expression of Notch, Numb and Numb-Like in human skeletal muscle after a bout of muscle damage via eccentric exercise. Methods: Seventeen, recreationally trained, male subjects signed an informed consent approved by The University of Kansas’s Institutional Review Board and were randomly assigned to one of two groups: a control group (n = 5) or a damage group (n = 12). Subjects completed a one repetition maximum (1RM) in leg extension followed by seven sets of ten repetitions of eccentric leg extension at %120 of 1RM with a two minutes of rest period between sets. Four muscle biopsies of the vastus lateralis were collected at baseline, 3-hours post- two days post-, and five days post-muscle damage and analyzed utilizing Western blot and quantitative reverse transcription polymerase chain reaction analyses. The results were analyzed using two separate analyses. The first being a 2X3 (Group X Time) Two-Way Repeated Measures ANOVA for the baseline measures, two days post- and five days post-muscle damage time points with the exclusion of the 3-hour post damage time point. The second being a One-Way Repeated Measures ANOVA with only the experimental group. Results: There were no significant main effects of time for the damage group with the inclusion of the three hour time point from baseline for Numb (p 0.05: 3-Hour p = 0.22, Day 2 p = 0.89, and Day 5 p = 0.17) and Numb-Like (3-Hour p = 0.63, Day 2 p = 0.30, and Day 5 p = 0.77). Additionally, no significant differences in mRNA expression were observed for Numb between groups two days post- and five days post-muscle damage for Numb (p = 0.13 and p = 0.74, respectively) and Numb-Like (p = 0.28 and p = 0.60, respectively). There was no significant main effect of time for Notch1 among the damage group with the inclusion of the three-hour time point from baseline (3-Hour p = 0.84, Day 2 p = 0.28, and Day 5 p = 0.20). Additionally, no significant differences in mRNA expression were observed for Notch1 between groups at two days post-muscle damage (p = 0.56). However, there was a significant increase in Notch1 at five days post-muscle damage between the exercise group (1.91 ± 1.29 fold change) and the control group (0.52 ± 0.38 fold change) from baseline measures (p = 0.04). Conclusion: Numb and Numb-Like expression was unaltered post-muscle damage, while Notch mRNA expression was increased after exercise-induced muscle damage. These results indicate that Notch and Numb-Like may have a greater role in muscle repair after strenuous exercise in humans than previously thought. Funding provided by NIA grant 5R01AG060341-02 to CPC and the CSACSM Doctoral Grant.