Numb And Numb-like Responses To Exercise Induced Muscle Damage In Human Skeletal Muscle

Abstract

Numb and Numb-Like (NumbL) are adaptor proteins. Among their functions is control of cell fate determination and progression of cell differentiation. While no role for NumbL 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 Numb and NumbL in human skeletal muscle after a bout of muscle damage via eccentric exercise. METHODS: Twelve 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 = 6) or an damage group (n = 6). 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. Three muscle biopsies of the vastus lateralis were collected at baseline, 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 a 2 X 3 (Group x Time) repeated-measures ANOVA. RESULTS: No significant differences in mRNA expression were observed for Numb between groups two days post- and five days post-damage (p = 0.37 and p = 0.29, respectively). There was no significant difference in NumbL for the exercise group (3.101 ± 1.763) in comparison to the control group (0.838 ± 0.234) two days post-exercise induced muscle damage (p = 0.27). However, there was a significant increase in NumbL at five days post-exercise between the exercise group (1.773 ± 0.358) and the control group (0.726 ± 0.087) from baseline measures (p = 0.04). No significant differences in Numb or NumbL proteins were observed at any time point or between the control group and exercise group (p > 0.05). CONCLUSION: Numb expression was unaltered post-muscle damage, while NumbL mRNA expression was increased after muscle damage. These results indicate that NumbL 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.