ASH1L Suppresses Matrix Metalloproteinase through Mitogen-activated Protein Kinase Signaling Pathway in Pulpitis

Abstract

Introduction: Pulpitis is an inflammation of dental pulp produced by a response to external stimuli. The response entails substantial cellular and molecular activities. Both genetic and epigenetic regulators contribute to the occurrence of pulpitis. However, the epigenetic mechanisms are still poorly understood. In this research, we studied the role of the absent, small, or homeotic-like (ASH1L) gene in the process of pulpitis.

Methods: Human dental pulp cells (HDPCs) were stimulated with proinflammatory cytokine tumor necrosis factor alpha (TNF-α). Gene expression profiling was performed to assess the occurrence of epigenetic regulators. Pulp tissue from rat experimental pulpitis was subjected to immunofluorescence to detect the occurrence of ASH1L and trimethylation of lysine 4 histone 3 (H3K4me3). The presence of ASH1L in HDPCs that had been generated by TNF-α stimulation was analyzed by Western blot procedures and cellular immunofluorescence. Once detected, ASH1L was silenced through the use of specific small interfering RNA. The effects of ASH1L on the occurrence and operation of matrix metalloproteinases (MMPs) were then tested by analysis of quantitative polymerase chain reactions, Western blotting, and zymography. Chromatin immunoprecipitation was performed to detect whether ASH1L and H3K4me3 were present in the promoter regions of MMPs. We then used Western blot procedures to examine the nuclear factor kappa B and the mitogen-activated protein kinase (MAPK) responses to the silencing of ASH1L. We also examined the specific pathway involved in ASH1L regulation of the MMPs.

Results: After stimulating HDPCs with TNF-α, ASH1L emerged as 1 of the most strongly induced epigenetic mediators. We found that TNF-α treatment induced the expression of ASH1L through the nuclear factor kappa B and MAPK signal pathways. ASH1L was found in both the nucleus and the cytoplasm. TNF-α treatment was particularly active in inducing the accumulation of ASH1L in cellular cytoplasm. As is also consistent with in vitro results, ASH1L was found in increased quantities in experimental dental pulpitis tissue. ASH1L knockdown markedly up-regulated the occurrence of MMP-1, MMP-2, and MMP-13. It also exercised an impact on the enzymatic activity of MMP-2 in HDPCs that had been stimulated with TNF-α. ASH1L knockdown activated the MAPK signal pathway in TNF-α-triggered HDPCs, the inhibition of which reversed the induction of MMPs.

Conclusions: Our research identifies a mechanism by which ASH1L suppresses the occurrence and operation of MMPs during pulpitis. It does this through the MAPK pathway.

Keywords: ASH1L; epigenetic; matrix metalloproteinase; pulpitis.