CREB activation induced by mitochondrial dysfunction triggers triglyceride accumulation in 3T3-L1 preadipocytes.

Several mitochondrial pathologies are characterized by lipid redistribution and microvesicular cell phenotypes resulting from triglyceride accumulation in lipid-metabolizing tissues. However, the molecular mechanisms underlying abnormal fat distribution induced by mitochondrial dysfunction remain poorly understood. In this study, we show that inhibition of respiratory complex III by antimycin A as well as inhibition of mitochondrial protein synthesis trigger the accumulation of triglyceride vesicles in 3T3-L1 fibroblasts. We also show that treatment with antimycin A triggers CREB activation in these cells. To better delineate how mitochondrial dysfunction induces triglyceride accumulation in preadipocytes, we developed a low-density DNA microarray containing 89 probes, which allows gene expression analysis for major effectors and/or markers of adipogenesis. We thus determined gene expression profiles in 3T3-L1 cells incubated with antimycin A and compared the patterns obtained with differentially expressed genes during the course of in vitro adipogenesis induced by a standard pro-adipogenic cocktail. After an 8-day treatment, a set of 39 genes was found to be differentially expressed in cells treated with antimycin A, among them CCAAT/enhancer-binding protein alpha (C/EBPalpha), C/EBP homologous protein-10 (CHOP-10), mitochondrial glycerol-3-phosphate dehydrogenase (GPDmit), and stearoyl-CoA desaturase 1 (SCD1). We also demonstrate that overexpression of two dominant negative mutants of the cAMP-response element-binding protein CREB (K-CREB and M1-CREB) and siRNA transfection, which disrupt the factor activity and expression, respectively, inhibit antimycin-A-induced triglyceride accumulation. Furthermore, CREB knockdown with siRNA also downregulates the expression of several genes that contain cAMP-response element (CRE) sites in their promoter, among them one that is potentially involved in synthesis of triglycerides such as SCD1. These results highlight a new role for CREB in the control of triglyceride metabolism during the adaptative response of preadipocytes to mitochondrial dysfunction.