Global and Regional DNA methylation silencing of PPARγ Associated with Glioblastoma Multiforme Pathogenesis

The relationship between peroxisome proliferator-activated receptor gamma (PPARγ) expression level and epigenetic modifications occurring in glioblastoma multiforme (GBM) pathogenesis is largely unknown. Herein, we examine the association of PPARγ expression with its promoter and genomic global DNA methylation status, as well as DNA methyltransferases (DNMTs) gene expression in GBM patients.

We examined the patterns of promoter methylation and PPARγ expression in 26 GBM tissues and 13 adjacent non-tumor tissues by methylation-specific PCR (MSP), real-time PCR, and ELISA, respectively. Also, we examined the genomic global 5-methyl cytosine levels and DNMTs gene expression using ELISA and real-time PCR methods, respectively.

We found that hypermethylation on a specific region of the PPARγ promoter is significantly associated with the downregulation of the PPARγ gene and protein level in GBM patients. Interestingly, the amount of 5-methyl cytosine level was significantly reduced in GBM patients and positively correlated with PPARγ protein expression. Furthermore, the expression level of DNMT1, DNMT3A, and 3B were upregulated in GBM patients and the average expression level of all three DNMTs was positively correlated with tumor area. Also, we found that tumors from cortical regions exhibited a higher global DNA hypomethylation and PPARγ hypermethylation was related to the increase in GBM risk.

Our study demonstrated that global DNA methylation and PPARγ epigenetic silencing is associated with the GBM risk. Our data provide a novel molecular mechanistic insight into epigenetic silencing of PPARγ in GBM patients that may be relevant as a key tumor marker for GBM pathogenesis.