The periodontal ligament is a soft connective tissue embedded between the alveolar bone and cementum, the surface hard tissue of teeth. Periodontal ligament fibroblasts (PDLF) actively express osteo/cementogenic genes, which contribute to periodontal tissue homeostasis. However, the key factors maintaining the osteo/cementogenic abilities of PDLF remain unclear. We herein demonstrated that PPARγ was expressed by in vivo periodontal ligament tissue and its distribution pattern correlated with alkaline phosphate enzyme activity. The knockdown of PPARγ markedly reduced the osteo/cementogenic abilities of PDLF in vitro, whereas PPARγ agonists exerted the opposite effects. PPARγ was required to maintain the acetylation status of H3K9 and H3K27, active chromatin markers, and the supplementation of acetyl-CoA, a donor of histone acetylation, restored PPARγ knockdown-induced decreases in the osteo/cementogenic abilities of PDLF. An RNA-seq/ChIP-seq combined analysis identified four osteogenic transcripts, RUNX2, SULF2, RCAN2, and RGMA, in the PPARγ-dependent active chromatin region marked by H3K27ac. Furthermore, RUNX2-binding sites were selectively enriched in the PPARγ-dependent active chromatin region. Collectively, these results identified PPARγ as the key transcriptional factor maintaining the osteo/cementogenic abilities of PDLF and revealed that global H3K27ac modifications play a role in the comprehensive osteo/cementogenic transcriptional alterations mediated by PPARγ.
Keywords: PPARγ; histone acetylation; osteogenic differentiation; periodontal ligament.