Transcriptional inhibition of adiponectin expression by adipose tissue hypoxia in obese mice

Abstract

Objective To investigate the effects of hypoxia on adiponectin mRNA transcription and protein expression in adipose tissue of obese mice. Methods The mRNA and protein of adiponectin and peroxisome proliferator activated receptor -γ(PPAR-γ) in epididymal fat tissues of genetic obese mice (ob/ob) and high fat diet-induced (HFD) obese mice were examined through quantitative real-time PCR (qRT-PCR) and western blotting. mRNA expression and promoter activity of adiponectin was measured with real-time qRT-PCR and luciferase reporter assay in 3T3-L1 adipocytes. Adiponectin mRNA stability was checked with real-time RT-PCR. mRNA and mRNA stability of PPAR-γ were examined with qRT-PCR in 3T3-L1 adipocytes after hypoxia treatment and then nuclear accumulation of PPAR-γ and peroxisome proliferator response element (PPRE) transcriptional activity were determined in mature adipocytes.Comparison of data between groups was applied by using t test. Results (1) Adiponectin expression was inhibited in white adipose tissue of obese mice at both mRNA and protein levels(P<0.01). In mature 3T3-L1 adipocytes, the qRT-PCR data showed that mRNA expression of adiponectin was reduced by hypoxia, compared with control group, especially after hypoxia for 8 and 24 hours, the level of adiponectin mRNA was reduced from 1.00±0.04 to 0.65±0.05 and 0.29±0.05 (t=11.548, 24.893, both P<0.01). Half life of mRNA was not reduced by hypoxia. A luciferase reporter driven by the adiponectin gene promoter was inhibited by hypoxia in 3T3-L1 adipocytes. (2)Protein and mRNA expression of PPAR-γ were decreased in white adipose tissue of obese mice and in 3T3-L1 adipocytes after hypoxia treatment. After hypoxia for 8 and 24 hours, compared with control group, level of PPAR-γ mRNA was significantly reduced from 1.00±0.09 to 0.72±0.09 and 0.54±0.07(t=5.134, 9.876, both P<0.01). PPAR-γ mRNA stability was reduced in 3T3-L1 adipocytes after hypoxia treatment. Nuclear translocation of PPAR-γ protein and transcriptional activity of PPAR-γ was also inhibited by hypoxia. Conclusion The adiponectin mRNA expression is reduced by hypoxia and the inhibition happened at the transcriptional level. It might be the result of suppression of PPAR-γ, an important transcription activator for adiponectin, at both mRNA expression level and its transcriptional activity. Key words: Obesity; Adiponectin; Peroxisome proliferator-activated receptor-γ; Hypoxia