The transcriptional coactivator peroxisome proliferator-activated receptor (PPAR)gamma coactivator-1 alpha and the nuclear receptor PPAR alpha control the expression of glycerol kinase and metabolism genes independently of PPAR gamma activation in human white adipocytes
Abstract
OBJECTIVE-The purpose of this work was to determine the pattern of genes regulated by peroxisome proliferator-activated receptor (PPAR) gamma coactivator lot (PGC-1 alpha) in human adipocytes and the involvement of PPAR alpha and PPAR gamma in PGC-1 alpha transcriptional action. RESEARCH DESIGN AND METHODS-Primary cultures of human adipocytes were transduced with a PGC-1 alpha adenovirus and treated with PPAR gamma and PPAR alpha agonists.
Variation in gene expression was assessed using pangenomic microarrays and quantitative RT-PCR. To investigate glycerol kinase (GyK), a target of PGC-1 alpha we measured enzymatic activity and glycerol incorporation into triglycerides.
In vivo studies were performed on wild-type and PPAR alpha(-/-) mice. The GyK promoter was studied using chromatin immunoprecipitation and promoter reporter gene assays.
RESULTS-Among the large number of genes regulated by PGC-1 alpha independently of PPAR gamma, new targets involved in metabolism included the gene encoding GyK The induction of GyK by PGC-1 alpha was observed at the levels of mRNA, enzymatic activity, and glycerol incorporation into triglycerides. PPAR alpha was also upregulated by PGC-1 alpha.
Its activation led to an increase in GyK expression and activity. PPARot was shown to bind and activate the GyK promoter.
Experiments in mice confirmed the role of PGC-1 alpha. and PPAR(x in the regulation of GyK in vivo. CONCLUSIONS-This work uncovers novel pathways regulated by PGC-1 alpha and reveals that PPARot controls gene expression in human white adipocytes.
The induction of GyK by PGC-1 alpha and PPARa may promote a futile cycle of triglyceride hydrolysis and fatty acid reesterification.