The Loss Of PPARγ Transcriptional Function Worsen High-fat Diet Induced Adipocyte Hypertrophy And Insulin Resistance

The Peroxisome proliferatoractivated receptors(PPARs)belong to the nuclear receptor superfamily,that is a type of ligand-regulated transcription factors.As a vital member of PPARs,PPARγ is involved in a variety of crucial biological processes,which are further related to a series of metabolic diseases.Thiazolidinedione(TZDs)drugs are classical full agonists of PPARy that improve insulin sensitivity by targeting PPARy.However,lots of side effects have been reported for TZDs,such as weight gain.On one hand,enhancing the transcriptional activity of PPARy relieves metabolic disorders;on the other hand,excessive enhancement of PPARy trabscriptional activity may induce anharmonic side effects.Homozygous PPARy-deficient embryos died due to placental dysfunction,however,heterozygous PPARy-knockout mice were protected from insulin resistance due to adipocyte hypertrophy under a high-fat diet.In other word,the down-regulation of both PPARy transcriptional and non-transcriptional activities reduces metabolic disorders simulated by a high-fat diet.So far,it still remains ambiguous what distinct roles the transcriptonal and the non-transcriptional activities of PPARy play in vivo.Based on the crystallographic structure of the PPARy DNA binding domain(DBD)bound with the PPARy response element(PPRE),we found that Arg134,Arg135 and Arg138 residues of PPARy bind with the major groove of PPRE by forming six hydrogen bond interactions that play an irreplaceable role in the binding of PPARy on PPRE.Thus,we predict that PPARγ with the three Arg mutations(PPARy-3RA)might lose transcriptional activity while maintaining integral structure of PPARy without affecting its non-transcriptional activity,which is confirmed using cell-based reporter assay.We then prepared the PPARγ-3RA mutant mice.Homozygous PPARy-3RA mice embryos died.Compared with the littermate wild-type male mice,quite unexpectedly,heterozygous PPARy-3RA mice(PPARy3RA/+)possessed more serious insulin reesistance and hepatic steatosis under a high-fat diet(HFD).These phenotypes were partly abrogated by rosiglitazone administration.The white adipose tissue mass and adipocyte size of HFD-fed PPARγ3RA/+ mice were obviously larger than that of the HFD-fed WT mice.We found that the hepatic mRNA level of leptin in the PPARγ3RA/+mice was significantly lower than that in the WT mice,which provides a preliminary clue to explain the difference of these phenotypes.In conclusion,imparing the transcriptional activity of PPARy worsen the metabolic disorders stimulated by HFD.This research provides a useful mouse model to study the roles of transcriptional and non-transcriptional activities of PPARy.