Graduation Date

Summer 8-14-2026

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Programs

Medical Sciences Interdepartmental Area

First Advisor

Lie Gao

Second Advisor

Irving H. Zucker

Abstract

It is well established that exercise is cardioprotective however, the underlying mechanisms that induce cardioprotection, especially those which involve skeletal muscle (SkM), remain to be elucidated. First, this dissertation focused on the activation of the Nrf2 pathway during SkM contraction. It was discovered that electrical pulse stimulation (EPS) of differentiated C2C12 myotubes significantly upregulates the Nrf2/antioxidant pathway. This antioxidant adaptation provides C2C12 myotubes with protection against oxidative-stress induced cytotoxicity. Second, we hypothesized that the upregulated antioxidant enzymes, observed in EPS-C2C12 myotubes in the first study, are secreted into the conditioned media (CdM) via extracellular vesicles (EVs) and non-vesicular extracellular nanoparticles (nvEPs). Additionally, we hypothesized that these antioxidant-enriched EV/nvEPs could protect H9c2 cardiomyocytes from H2O2-induced oxidative stress. To test this, EVs and nvEPs were isolated from the CdM of non-stimulated (NS)-control and EPS-C2C12 myotubes using differential ultracentrifugation. This study illustrated that EV/nvEPs isolated from the CdM of EPS-C2C12 myotubes contain increased levels of NQO1 and GSTA2, two enzymes downstream of the Nrf2-antioxidant pathway. Functionally, select nvEPs protect H9c2 cardiomyocytes against H2O2-induced oxidative injury, demonstrating a potential molecular mechanism by which contracting SkM could protect cardiomyocytes via transfer of antioxidant enriched (AOE)-EV/nvEPs. The final study of this dissertation studied SkM-to-heart interorgan crosstalk in a transgenic mouse model (iMS-Keap1flox/flox). This transgenic model selectively activates SkM-Nrf2; it was used so that the protective effects of SkM-Nrf2 activation against cardiac ischemia-reperfusion (I/R) injury could be tested. Overexpression of SkM-Nrf2 was found to significantly reduce myocardial infarct size and improve LV function during reperfusion. Mechanistically, SkM-Keap1 KO mice showed pronounced upregulation of antioxidant enzymes NQO1 and SOD2 across SkM, plasma EV/nvEPs, and myocardium. As Nrf2 upregulation was observed only in SkM tissue, this upregulation in antioxidants in SkM, plasma EV/nvEPs, and myocardium supports a potential SkM-to-heart antioxidant transfer, which may be mediated by circulating EV/nvEPs. This dissertation reframes exercise-induced antioxidant protection as an interorgan communication mechanism providing new insights into potential exercise mimetics that could protect the heart against oxidative-stress-induced damage, such as that observed in I/R injury.

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