Abstract 365: Inhibiting Hmg Coa Reductase Reduces Palmitate-Induced Inflammation in Adipocytes

Abstract

Adipose tissue inflammation associates with insulin resistance and increased cardiovascular disease risk. We previously observed that 3T3-L1 adipocytes exposed to palmitate become inflamed and demonstrate increased plasma membrane cholesterol and lipid raft content. It is known that palmitate induces translocation of NAPH oxidase and toll-like receptor 4 into lipid rafts, increasing adipocyte inflammation. However, it is unclear (1) how palmitate alters plasma membrane cholesterol content; and (2) whether increased cholesterol content in the plasma membrane is related to adipocyte inflammation induced by palmitate exposure. We hypothesize that mechanisms involved in increasing plasma membrane cholesterol content after palmitate treatment could be related to cholesterol synthesis and/or ER stress, and that increased cholesterol in lipid rafts is essential for induction of inflammation in adipocytes. To test these hypotheses, differentiated murine 3T3-L1 adipocytes were exposed to palmitate for 24 hours, with and without pre-treatment with HMG-CoA reductase inhibitors (statins) or HDL. RT-PCR was used to evaluate gene expression of inflammation ( Saa3 , Ccl2 ), ER stress ( Bip , Chop ), and HMG-CoA reductase ( Hmgcr ). Cholera toxin subunit β staining and flow cytometry were used to evaluate plasma membrane lipid raft content. In differentiated adipocytes, palmitate-induced inflammation neither increased expression of ER stress genes nor HMG-CoA reductase gene expression. However, treatment with 3 different statins (simvastatin, lovastatin, atorvastatin) significantly reduced palmitate-induced adipocyte inflammation as indicated by decreased gene expression of Saa3 and Ccl2 ( P <0.05). A similar effect was seen with pre-treatment with HDL. Lipid raft content induced by palmitate was decreased by HMG-CoA reductase inhibitors (difference in mean fluorescence intensity P <0.05) and also by pre-treatment with HDL. These findings indicate that ER stress was not involved in increased plasma membrane cholesterol after palmitate-induced inflammation in adipocytes. However, regulating cholesterol content in lipid rafts plays an important role in adipocyte inflammation induced by palmitate.