Histone deacetylase inhibitors epigenetically promote reparative events in primary dental pulp cells

Application of histone deacetylase inhibitors (HDACi) to cells epigenetically alters their chromatin structure and induces transcriptional and cellular reparative events. This study investigated the application of two HDACi, valproic acid (VPA) and trichostatin A (TSA) on the induction of repair-associated responses in primary dental pulp cell (DPC) cultures. Flow cytometry demonstrated that TSA (100nM, 400nM) significantly increased cell viability. Neither HDACi was cytotoxic, although cell growth analysis revealed significant anti-proliferative effects at higher concentrations for VPA (>0.5mM) and TSA (>50nM). While high-content-analysis demonstrated that HDACi did not significantly induce caspase-3 or p21 activity, p53-expression was increased by VPA (3mM, 5mM) at 48h. HDACi-exposure induced mineralization per cell dose-dependently to a plateau level (VPA-0.125mM and TSA-25nM) with accompanying increases in mineralization/dentinogenic-associated gene expression at 5 days (DMP-1, BMP-2/-4, Nestin) and 10 days (DSPP, BMP-2/-4). Both HDACis, at a range of concentrations, significantly stimulated osteopontin and BMP-2 protein expression at 10 and 14 days further supporting the ability of HDACi to promote differentiation. HDACi exert different effects on primary compared with transformed DPCs and promote mineralization and differentiation events without cytotoxic effects. These novel data now highlight the potential in restorative dentistry for applying low concentrations of HDACi in vital pulp treatment.