Hypomethylation and activation of MMP-2: epigenetics and periodontal infection

Objective: To better understand oral microbe - host tissue interactions, we investigated expression and activation of MMP-2 in PDL cells following T. denticola challenge.

Methods: PDL cells isolated from extracted teeth of healthy patients were challenged with T. denticola (MOI=100:1). T. denticola internalization and survival was assayed by immunofluorescence microscopy and antibiotic protection assays, respectively. MMP-2 activation was detected by zymography. MMP-2, MT1/MMP-14, and TIMP-2 expression following T. denticola challenge was determined by qRT-PCR. Methylation status of these genes was screened using EpiTect Methyl qPCR (Qiagen) and hypomethylation of the MMP-2 promoter was confirmed by bisulfite DNA sequencing.

Results: T. denticola was internalized by PDL cells but did not survive intracellularly beyond 24 hours. Importantly, while dentilisin activity in PDL culture supernatants gradually decreased following T. denticola challenge, MMP-2 activation persisted for up to 5 days, suggesting involvement of other regulatory mechanisms. Transcription of MMP-2, MT1/MMP-14 and TIMP-2 increased in response to T. denticola challenge. However, consistent with previously reported constitutive pro-MMP-2 expression in PDL cells, the MMP-2 promoter was hypomethylated, independent of T. denticola challenge.

Conclusions: PDL cells’ constitutive pro-MMP-2 expression, which is likely due to hypomethylation of its promoter, coupled with T. denticola-mediated upregulation of the MMP-2 complex and chronic activation of pro-MMP-2, mimics key in vivo periodontal disease mechanisms. Adherence and/or internalization of T. denticola may contribute to these processes by one or more regulatory mechanisms, including contact-dependent signal transduction or epigenetic mechanisms such as histone modifications.