Peroxisome Proliferator-activated Receptor γ Agonist Rosiglitazone Increases Expression of Very Low Density Lipoprotein Receptor Gene in Adipocytes

Abstract

Apolipoprotein E (apoE) and its receptor, very low density lipoprotein receptor (VLDLR), are involved in fat accumulation in adipocytes. Here, we investigated the effect of a peroxisome proliferator-activated receptor (PPAR) gamma agonist, rosiglitazone, on regulation of VLDLR expression both in white adipose tissue (WAT) of obese mice and in cultured adipocytes. Furthermore, to determine whether rosiglitazone directly regulates transcription of the VLDLR gene, we carried out luciferase assay with a reporter gene containing mouse VLDLR promoter region, electrophoretic mobility shift assay, and chromatin immunoprecipitation assay. Four-day treatment with rosiglitazone increased the expression of VLDLR in WAT of ob/ob mice. Moreover, rosiglitazone increased the expression of VLDLR in cultured adipocytes. The PPAR-responsive element (PPRE)-directed mutagenesis analyses revealed that the PPRE motif in the VLDLR promoter region plays a significant role in transcriptional activation of the VLDLR gene in adipocytes. In addition, electrophoretic mobility shift assay and chromatin immunoprecipitation assay demonstrated that endogenous PPARgamma directly binds to this functional PPRE motif in the VLDLR promoter region. We also investigated the effects of rosiglitazone on insulin sensitivity and lipid accumulation in both ob/ob mice and apoE-deficient ob/ob mice. Rosiglitazone ameliorated insulin sensitivity in both ob/ob mice and apoE-deficient ob/ob mice, possibly through decreasing the expression of monocyte chemoattractant protein-1 (MCP-1), increasing the expression of superoxide dismutase 1 (SOD1) in WAT, and increasing plasma adiponectin concentration. In ob/ob mice, body weight and WAT weight were significantly higher in the mice treated with rosiglitazone than those treated with vehicle. However, in apoE-deficient ob/ob mice, no significant difference in body weight or WAT weight was observed between the vehicle-treated group and the rosiglitazone-treated group. Moreover, rosiglitazone did not increase body weight and WAT weight in VLDLR-deficient mice. These findings indicate that rosiglitazone directly increases VLDLR expression, thereby enhancing apoE-VLDLR-dependent lipid accumulation in adipocytes.