The Peroxisome Proliferator-activated Receptor-γ Regulates Murine Pyruvate Carboxylase Gene Expression in Vivo and in Vitro

Abstract

Pyruvate carboxylase (PC) plays a crucial role in various metabolic pathways, including gluconeogenesis, lipogenesis, and glucose-induced insulin secretion. Here we showed for the first time that the PC gene is transcriptionally regulated by peroxisome proliferator-activated receptor-␥ (PPAR␥) in vitro and in vivo in white and brown adipose tissue. PC mRNA and protein are markedly increased during differentiation of 3T3-L1 cells and HIB-1B, in parallel with the expression of the adipogenic transcription factors, CCAAT-enhancer binding protein ␣, PPAR␥1, and PPAR␥2. Tumor necrosis factor-␣, a cytokine that blocks differentiation of 3T3-L1 cells, suppressed PC expression. Co-transfection studies in 3T3-L1 preadipocytes or HEK293T cells with a 2.3-kb promoter fragment of mouse PC gene linked to a luciferase reporter construct and with plasmids overexpressing retinoid X receptor ␣/PPAR␥1 or retinoid X receptor ␣/PPAR␥2 showed a 6 -8-fold increase above the basal promoter activity. Furthermore, treatment of these transfected cells with the PPAR␥ agonist doubled the promoter activity. Mutation of the putative PPARresponse element-(؊386/؊374) of this 2.3-kb PC promoter fragment abolished the PPAR␥ response. Gel shift and chromatin immunoprecipitation assays demonstrated that endogenous PPAR␥ binds to this functional PPAR-response element of the PC promoter. Mice with targeted disruption of the PPAR␥2 gene displayed ϳ50 -60% reduction of PC mRNA and protein in white adipose tissue. Similarly, in brown adipose tissue of PPAR␥2-deficient mice subjected to cold exposure, PC mRNA was 40% lower than that of wild type mice. Impaired in vitro differentiation of white adipocytes of PPAR␥2 knock-out mice was also associated with a marked reduction of PC mRNA. Our findings identified PC as a PPAR␥-regulated gene and suggested a role for PPAR␥ regulating intermediary metabolism.

Prohibitin has an important role in adipocyte differentiation

“…26,34 It is not unexpected that PC is upregulated B20-fold during adipocyte differentiation. 50 In addition, PC has an important role in the TCA cycle by regeneration of oxaloacetate, a driving force not only for pyruvate and fatty acid oxidation but also for glyceroneogenesis. 26,50 Previously, we have reported that PHB interacts with PC and inhibits insulin-induced glucose and fatty acid oxidation in adipose tissues.…”

Amyotrophic Lateral Sclerosis: Role of the Canonical Wnt/Beta- Catenin Pathway and PPAR Gamma

“…Astrocytic GLT1/EAAT2 gene is a target of PPAR gamma, leading to neuroprotection by increasing the glutamate uptake [29]. PPAR gamma is a direct transcriptional modulator of the pyruvate carboxylase gene [30]. Given the fact that ALS patients suffer from massive weight loss, this provides a possible explanation for the potential protective effects of pioglitazone through increased lipogenesis.…”

Peroxisome Proliferator-activated Receptor γ (PPARγ) and Its Target Genes Are Downstream Effectors of FoxO1 Protein in Islet β-Cells

“…We have shown that PPAR␥ in ␤-cells regulates transcription of the prodifferentiation transcription factor Pdx1 (4,5) and the receptor for the incretin hormone glucose-dependent insulinotropic polypeptide (GIP) (6). Others have reported that PPAR␥ regulates expression of the anaplerotic enzyme pyruvate carboxylase in adipose tissue (7), but whether this occurs in ␤-cells is unknown. Collectively, these genes are key controllers of ␤-cell mass, mitochondrial fuel metabolism, and insulin secretion, suggesting the potential for a central role of PPAR␥ in ␤-cell compensation and/or failure.…”