High glucose induces podocyte epithelial-to-mesenchymal transition by demethylation-mediated enhancement of MMP9 expression

Abnormal expression of matrix metalloproteinase 9 (MMP9) is correlated with podocyte epithelial-to-mesenchymal transition (EMT) in diabetic nephropathy (DN). However, the mechanisms underlying this process are not well defined. Site-specific demethylation may sustain high expression levels of target genes. In the present study, in order to investigate the association between DNA demethylation of MMP9 promoter and podocyte EMT in DN, human podocytes were cultured in high-glucose (HG) medium and a rat model of DN was established by intraperitoneal injection of streptozotocin (STZ) to determine whether site-specific demethylation of the MMP9 promoter was involved in regulating podocyte EMT in DN. The MTT assay was used to assess the effects of HG culture on the growth of podocytes, and the demethylation status of the MMP9 promoter was assessed by bisulfite sequencing polymerase chain reaction. mRNA and protein expression levels of MMP9, α-smooth muscle actin (α-SMA), podocalyxin and fibronectin-1 in podocytes were assessed by reverse transcription-quantitative PCR (RT-qPCR) and western blot analyses. The results demonstrated that HG treatment up regulated the expression of MMP9, α-SMA and fibronectin-1, but down regulated the expression of podocalyxin in podocytes. The MMP9 promoter region was revealed to contain a variety of demethylated CpG sites, and HG treatment reduced the rate of MMP9 promotermethylation, which, in turn, enhanced its promoter activity. In summary, these data suggested that demethylation of the MMP9 promoter may serve an important role in podocyte EMT in DN. The demethylation status of the MMP9 promoter maybe used as an important prognostic marker of DN in clinic.