Insulin resistance in African-American and Caucasian women: differences in lipotoxicity, adipokines, and gene expression in adipose tissue and muscle.

ABSTRACT

OBJECTIVES: We tested whether African-American (AA) women are different from Caucasian women in regard to lipotoxicity, adipokines, and gene expression in adipose tissue and muscle. DESIGN: Insulin sensitivity (S(I)), plasma adipocytokine levels, intramyocellular lipid (IMCL), and the expression of candidate genes in adipose tissue and muscle were measured in AA and Caucasian women. SETTING: This study was performed in an ambulatory general clinical research center. SUBJECTS: Subjects were healthy, nondiabetic AA and Caucasian women. INTERVENTIONS: There were no interventions. MAIN OUTCOME MEASURES: Comparison of S(I), IMCL, plasma adiponectin, and the expression of candidate genes regulating adipogenesis, lipogenesis, and inflammation in adipose tissue and muscle. RESULTS: AA had lower plasma adiponectin and IMCL when compared with Caucasian women with similar S(I). In sc adipose tissue (SAT), the expression of genes involved in adipogenesis including peroxisomal proliferator-activated receptor-gamma (PPARgamma) and lipin-1beta were also reduced in SAT of AA subjects (19%, P = 0.06, and 25%, P = 0.05, respectively). Similarly, 1-acylglycerol-3-phosphate acyltransferase 2 (AGPAT 2), stearoyl-coenzyme A desaturase-1 (SCD1), and CD36 mRNA expression was significantly reduced in SAT by 19, 54, and 28% respectively (P < 0.01 for all) in AA compared with Caucasian women. Yet the expression of CD68 in SAT was similar in both ethnic groups. Gene expression studies in muscle revealed a 31% reduction in expression of AGPAT 2 and a 72% reduction in SCD1 genes in AA. CONCLUSION: AA women demonstrated lower expression of several PPARgamma-responsive genes in adipose tissue, lower plasma adiponectin, and decreased IMCL levels as compared with Caucasians, which suggests that African-Americans may be protected from lipotoxicity. Together these data suggest significant ethnic differences in the pathophysiology of insulin resistance.