GSBS Dissertations and Theses

ORCID ID

0000-0002-0740-3481

Approval Date

12-30-2016

Document Type

Doctoral Dissertation

Academic Program

Interdisciplinary Graduate Program

Department

Molecular Medicine

First Thesis Advisor

Jason K. Kim

Keywords

Muscle, Inflammation, Type 2 diabetes, Insulin Resistance, Interleukin 10

Abstract

Skeletal muscle insulin resistance is a major characteristic of obesity and type 2 diabetes. Although obesity-mediated inflammation is causally associated with insulin resistance, the underlying mechanism is unclear. Our lab and others have shown that a chronic low-grade inflammation takes place in skeletal muscles during diet-induced obesity, as evidenced by increased macrophage markers and pro-inflammatory cytokine levels. Interleukin (IL)-10 is a Th2-type cytokine that inhibits the synthesis and activity of pro-inflammatory cytokines and counteracts the Toll-like receptor-mediated inflammation. Our lab has previously demonstrated the preventive role of IL-10 against insulin resistance. Here, I have analyzed the effects of IL-10 on the skeletal muscle glucose metabolism and myogenesis in three different insulin resistant states (high fat diet-induced, leptin-deficiency-induced and aging-induced). The first model involved long-term (16 weeks) high-fat diet (HFD) feeding that resulted in markedly obese and hyperglycemic mice, representative of obese type 2 diabetic subjects. In mice overexpressing IL-10 specifically in the skeletal muscle (MIL10), we observed improved whole-body and skeletal muscle insulin sensitivity as compared to wild-types after long-term high fat diet feeding. The improved insulin sensitivity in the skeletal muscle was due to increased Akt signaling and decreased muscle inflammation. Leptin is an important adipocyte-derived hormone that is elevated in obesity, and it regulates numerous physiological functions including the energy balance and inflammation. Thus, my second model examined the effects of muscle-specific overexpression of IL-10 on glucose metabolism in the hyperphagic, leptin-deficient ob/ob mice. We detected improved whole-body insulin sensitivity compared to the control mice. My third model examined the effects of increased IL-10 expression using MIL10 mice during aging-induced insulin resistance. In 18-month old MIL10 mice, we found enhanced whole-body and skeletal muscle insulin sensitivity due to improved insulin signaling and decreased muscle inflammation as compared to wild-type mice. Last, to test whether direct signaling of IL-10 on skeletal muscle is responsible for the beneficial effects of IL-10 on muscle glucose metabolism, I generated mice lacking IL-10 receptor 1 type chain selectively in skeletal muscle (M-IL10R-/-). We observed more prominent muscle inflammation and whole-body insulin resistance in HFD-fed M-IL10R-/- mice as compared to wild-type mice. Interestingly, when studying insulin resistance in the IL-10 transgenic mouse models, we identified a consistent increased lean mass phenotype, and conversely decreased lean mass in the HFD-fed M-IL10R-/- mice. Quantitative RT-PCR on HFD-fed MIL10 group muscles to measure myogenesis-related gene expression identified a correlation between lean mass and both IL-10 and MyoD mRNA expression levels. In support of this, I showed that IL-10 caused an increase in in vitro cultured myoblast proliferation rates. Together, these results highlight the potential benefits of IL-10 expression not only in muscle glucose metabolism but also in maintaining muscle mass during insulin resistant states. Overall, these results demonstrate that selective expression of IL-10 in skeletal muscle suppresses inflammation, improves glucose metabolism and muscle growth in obese and aging mice, and further establishes that these effects are at least partially mediated by direct activation of IL-10 signaling in skeletal muscle.

DOI

10.13028/M2QP42

Rights and Permissions

Copyright is held by the author, with all rights reserved.

Available for download on Saturday, December 23, 2017

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