The Role of Inflammation and Oxidative Stress in Adipocytes in the Development of Insulin Resistance

University of Minnesota Ph.D. dissertation. 2015. Major: Biochemistry, Molecular Bio, and Biophysics. Advisor: David Bernlohr. 1 computer file (PDF); 214 pages.Inflammation plays a critical role in the pathology of obesity-linked insulin resistance and is mechanistically linked to the effects of macrophage-derived cytokines on adipocyte energy metabolism, particularly that of the mitochondrial branched chain amino acid (BCAA) and tricarboxylic acid (TCA) pathways. To address the role of inflammation on energy metabolism in adipocytes we utilized high fat fed C57Bl/6J mice and lean controls and measured down regulation of genes linked to BCAA and TCA cycle metabolism selectively in visceral but not in subcutaneous adipose tissue, brown fat, liver or muscle. Using 3T3-L1 cells, TNFα and other pro-inflammatory cytokine treatments reduced the expression of genes linked to BCAA transport and oxidation. Consistent with this, [14C]-leucine uptake and conversion to triglycerides was markedly attenuated in TNFα-treated adipocytes whereas conversion to protein was relatively unaffected. Since inflammatory cytokines lead to induction of ER stress, we evaluated the effects of tunicamycin or thapsigargin treatment of 3T3-L1 cells and measured a similar down regulation in the BCAA/TCA cycle pathway. Moreover, transgenic mice overexpressing XBP1s in adipocytes similarly down regulated genes of BCAA and TCA metabolism in vivo. These results indicate that inflammation and ER stress attenuate lipogenesis in visceral adipose depots by down regulating the BCAA/TCA metabolism pathway and are consistent with a model whereby the accumulation of serum BCAA in the obese insulin-resistant state is linked to adipose inflammation