Obesity is the most common and powerful force for creating insulin resistance and metabolic syndrome, however, the molecular basis of this association is not well understood. In this proposal, three independently funded researchers-Philip Kern, MD a clinical investigator, and Charlotte Peterson, PhD and Robert McGehee, PhD, with significant experience in muscle and adipocyte biology, respectively- will formalize a collaborative effort as a natural extension of previous work and shared interests in the fields of obesity, insulin resistance, and tissue lipid accumulation. Our overall hypothesis is that insulin resistance in humans stems largely from ectopic accumulation of intramyocellular lipid (IMCL) during the development of obesity. Further, we hypothesize that excess IMCL accumulation is dependent on secretary proteins derived from a complex interplay between adipocytes and macrophages in adipose tissue. To test these hypotheses, we will examine the interactions among adipocytes, macrophages, and muscle cells isolated and cultured from subjects that are moderately obese with insulin resistance and impaired glucose tolerance (IGT), but who do not yet have fasting hyperglycemia. This study population has elevated IMCL and is at high risk for obesity complications, but avoids the pathophysiologic complications of glucotoxicity. These subjects will be compared to moderately obese subjects with normal glucose tolerance (NOT).
Aim 1 will explore mechanisms that contribute to IMCL and elucidate its role in the development of IGT. Cultured muscle cells will be used to determine whether obese subjects with IGT versus NGT demonstrate intrinsic differences in muscle gene expression and metabolic activity under differing extracellular fatty acid concentrations. Lipid accumulation and oxidation, and insulin-mediated glycogen synthesis and signaling will be assessed.
Aim 2 will determine if the IMCL accumulation is dependent on adipose tissue secretary proteins. We will use co-cultures of adipocytes, myoblasts, and adipose stromal vascular cells to examine IMCL and the development of insulin resistance.
Aim 3 will determine whether the stromal fraction from IGT subjects promotes IMCL more effectively than that from NGT subjects in co-cultures with muscle cells. We will compare the stromal vascular fractions with regard to monocyte/macrophage accumulation and cytokine expression.
Aim 4 will determine if improved glucose tolerance in response to a 10- week treatment with pioglitazone results in decreased IMCL and identify cellular mechanisms involved. Co-culture studies will also be used with muscle and stromal cells, before and after pioglitazone treatment. These experiments will provide mechanistic insight into the link between obesity and muscle function leading to metabolic syndrome.

Agency
National Institute of Health (NIH)
Institute
National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Type
Research Project (R01)
Project #
5R01DK071277-04
Application #
7429763
Study Section
Special Emphasis Panel (ZDK1-GRB-N (J2))
Program Officer
Laughlin, Maren R
Project Start
2005-06-01
Project End
2010-05-31
Budget Start
2008-06-01
Budget End
2010-05-31
Support Year
4
Fiscal Year
2008
Total Cost
$204,521
Indirect Cost
Name
University of Arkansas for Medical Sciences
Department
Internal Medicine/Medicine
Type
Schools of Medicine
DUNS #
122452563
City
Little Rock
State
AR
Country
United States
Zip Code
72205
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Yao-Borengasser, Aiwei; Rassouli, Negah; Varma, Vijayalakshmi et al. (2008) Stearoyl-coenzyme A desaturase 1 gene expression increases after pioglitazone treatment and is associated with peroxisomal proliferator-activated receptor-gamma responsiveness. J Clin Endocrinol Metab 93:4431-9
Rasouli, Neda; Kern, Philip A (2008) Adipocytokines and the metabolic complications of obesity. J Clin Endocrinol Metab 93:S64-73
Varma, Vijayalakshmi; Yao-Borengasser, Aiwei; Rasouli, Neda et al. (2007) Human visfatin expression: relationship to insulin sensitivity, intramyocellular lipids, and inflammation. J Clin Endocrinol Metab 92:666-72
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