GSBS Dissertations and Theses

Title

Analysis of Mitochondrial Remodeling in Adipocytes during Adipogenesis and Obesity Development: a Dissertation

Approval Date

April 2004

Document Type

Doctoral Dissertation

Department

Graduate School of Biomedical Sciences

Subjects

3T3-L1 Cells; Adipocytes; Adipose Tissue; Insulin Resistance; Mitochondrial Proteins; Obesity in Diabetes; Thiazolidinediones; Academic Dissertations

Abstract

The prevalence of type 2 diabetes mellitus is increasing worldwide and is considered one of the top health concerns globally. The occurrence of type 2 diabetes is linked to the rapidly increasing trend of obesity in both adults and children, which is proposed to be a contributing factor in the development of insulin resistance and type 2 diabetes. White adipose tissue, an insulin target tissue, is an important endocrine organ involved in the control of energy homeostasis through its direct influence on metabolism, insulin sensitivity and food intake. To better understand these functions, we studied adipocyte differentiation in 3T3-Ll cells, a white adipose tissue cell line. Many mitochondrial proteins exhibit an increase in expression levels during adipogenesis as identified by mass spectrometry. Moreover, increased mitochondrial mass and altered morphology was observed by light microscopy. Qualitative changes in mitochondrial gene expression were also observed during adipogenesis as revealed by Affymetrix GeneChip analysis. Additionally, striking changes in mitochondrial protein expression and morphology were identified following treatment with the insulin sensitizing agent, rosiglitazone. These results suggest that mitochondrial biogenesis and remodeling is inherent to white adipocyte differentiation. To investigate the physiological relevance of these findings, mRNA and protein expression profiles and mitochondrial morphology were studied during the development of insulin resistance and obesity and following treatment with rosiglitazone in ob/ob mice. These studies reveal a marked decrease in transcript levels for over 50% of mitochondrial genes with the onset of obesity in ob/ob mice. Rosiglitazone treatment stimulates enhanced expression in approximately half of these genes, as well as changes in mitochondrial mass and remodeling. Furthermore, these studies reveal that depressed oxygen consumption and fatty acid oxidation occur with obesity development and these alterations can be reversed with rosiglitazone treatment. This work identifies the previously underscored plasticity of mitochondria in white fat and suggests that mitochondrial biogenesis and remodeling in white adipose tissue may lead to systemic changes in insulin sensitivity and energy homeostasis. Lastly, these studies suggest that mitochondria may be an important therapeutic target for antidiabetic drugs.

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