PPARγ Transcription Deficiency Exacerbates High-Fat Diet-Induced Adipocyte Hypertrophy and Insulin Resistance in Mice

Background: The transcriptional factor peroxisome proliferator-activated receptor gamma (PPAR gamma) is an important therapeutic target for the treatment of type 2 diabetes. However, the role of the PPAR gamma transcriptional activity remains ambiguous in its metabolic regulation. Methods: Based on the crystal structure of PPAR gamma bound with the DNA target of PPAR gamma response element (PPRE), Arg134, Arg135, and Arg138, three crucial DNA binding sites for PPAR gamma, were mutated to alanine (3RA), respectively.In vitroAlphaScreen assay and cell-based reporter assay validated that PPAR gamma 3RA mutant cannot bind with PPRE and lost transcriptional activity, while can still bind ligand (rosiglitazone) and cofactors (SRC1, SRC2, and NCoR). By using CRISPR/Cas9, we created mice that were heterozygous for PPAR gamma-3RA (PPAR gamma(3RA/+)). The phenotypes of chow diet and high-fat diet fed PPAR gamma(3RA/+)mice were investigated, and the molecular mechanism were analyzed by assessing the PPAR gamma transcriptional activity. Results: Homozygous PPAR gamma-3RA mutant mice are embryonically lethal. The mRNA levels of PPAR gamma target genes were significantly decreased in PPAR gamma(3RA/+) mice. PPAR gamma(3RA/+) mice showed more severe adipocyte hypertrophy, insulin resistance, and hepatic steatosis than wild type mice when fed with high-fat diet. These phenotypes were ameliorated after the transcription activity of PPAR gamma was restored by rosiglitazone, a PPAR gamma agonist. Conclusion: The current report presents a novel mouse model for investigating the role of PPAR gamma transcription in physiological functions. The data demonstrate that the transcriptional activity plays an indispensable role for PPAR gamma in metabolic regulation.