Year of Publication

2013

Degree Name

Doctor of Philosophy (PhD)

Document Type

Doctoral Dissertation

College

Medicine

Department

Physiology

First Advisor

Dr. Charlotte A. Peterson

Second Advisor

Dr. Michael B. Reid

Abstract

Muscle biopsies were taken at baseline, post eccentric exercise, post aerobic training, and after training followed by eccentric exercise from adults with different health status. In Cell Western analysis of pAkt/Akt ratio suggests that muscle cells isolated from baseline biopsies respond to insulin in a dose dependent manner that tracks with sensitivity to insulin of the host; however, this is uncoupled from glucose disposal in vitro. Nitrotyrosine (NY), a marker of free radical damage, was employed to assess the efficacy of the exercise paradigm. NY immunohistochemistry on muscle cross-sections revealed that eccentric exercise significantly increased damage in older (>55 years of age), but not middle aged (age) subjects, and that training reversed the post eccentric damage significantly in the younger, but not the older group, suggesting distinct adaptation to eccentric exercise. Assessment of total macrophage content by CD68 immunohistochemistry showed that macrophage abundance increased in response to training in the >55 years age group, but not in the training, macrophages increased in response to eccentric exercise in middle aged and decreased in older subjects, showing a disconnect from NY damage. Macrophage phenotypes were assessed in these groups via the M1 marker CD11b, and the M2 marker, CD206. Two dominant populations of macrophages were identified, one of which co-expressed CD11b and CD206, and another which only expressed CD11b. These two populations of macrophages showed the same trends in expression in response to exercise observed with CD68, but did not achieve statistical significance. Bivariate analysis revealed that CD11b/CD206 macrophage densities were correlated with gene activities associated with fibrosis and angiogenesis, whereas CD11b macrophages correlated with gene activities associated with proteostasis and cellular turnover. Lastly, an in vitro model of skeletal muscle cell and macrophage integration was developed to study how macrophage phenotype influences insulin responsiveness. Data suggest that M1 macrophages inhibit insulin stimulated glucose disposal, whereas M2 macrophages enhance this response. Taken together these results suggest a functional distinction between inflammatory (M1) and alternative macrophages (M2) in exercise and insulin resistance that is altered with age.

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