Date of Award

5-31-2022

Document Type

Campus Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Exercise and Health Science

First Advisor

Kai Zou

Second Advisor

Tongjian You

Third Advisor

Philimon Gona

Abstract

Insulin resistance is a hallmark of obesity and a precursor of type 2 diabetes. Excessive activity of dynamin-related protein 1 (Drp1), a key regulator of mitochondrial fission, is strongly associated with impaired insulin sensitivity in obesity. However, whether Drp1 directly regulates skeletal muscle and whole-body insulin sensitivity remains unclear. Therefore, the purpose of the study was to determine the role of Drp1-mediated mitochondrial fission in the regulation of skeletal muscle and whole-body insulin sensitivity under obesity-induced insulin-resistant conditions.

Eight-week-old male skeletal muscle-specific heterozygous tamoxifen-induced Drp1 partial knockout mice (mDrp1+/-) and wildtype (WT) mice were randomly assigned to either a high-fat diet or low-fat diet group. Four weeks after the transition to their respective diets, all mice received five intraperitoneal injections of tamoxifen and remained on their diet for another four weeks. The partial deletion of skeletal muscle Drp1 reduced Drp1 content (26%), rebalanced mitochondrial dynamics, and reduced mitochondrial H2O2 emission, which leads to enhanced skeletal muscle insulin signaling and whole-body glucose homeostasis in diet-induced insulin-resistant mice.

To further examine the role of Drp1 in regulating skeletal muscle insulin sensitivity in humans, human skeletal muscle cells from lean, insulin-sensitive (BMI = 23.1 ± 1.6 kg/m2, HOMA-IR = 1.44 ± 0.23), and severely obese insulin-resistant (BMI = 52.2 ± 2.3 kg/m2, HOMA-IR = 4.11 ± 0.43) subjects with or without short hairpin RNA-mediated silencing of Drp1 were used and differentiated into myotubes. We demonstrated that the loss of Drp1 restored the mitochondrial network structure, decreased cellular reactive oxygen species content, and enhanced insulin action at the cellular level in myotubes derived from severely obese and insulin-resistant humans. By performing RNA sequencing, we found that Drp1 knockdown upregulated the transcription of genes associated with fatty acid metabolism and downregulated genes associated with glycolysis in myotubes from severely obese and insulin-resistant humans.

These data demonstrated that reducing skeletal muscle Drp1 directly improves skeletal muscle and whole-body glucose homeostasis in obese insulin-resistant conditions, but not in lean, healthy conditions. Our study suggests that targeting skeletal muscle Drp1 may be a viable approach to treat obesity-induced insulin resistance and type 2 diabetes.

Comments

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