Histone Demethylation: Key Chromatin Modification in the Regulation of Osteogenesis

Objectives: Epigenetic regulation by histone modifications is tightly regulated at every stage of bone development and post natal bone formation. Recently, we found that histone H3K27 demethylation activity is highest at Day 7 during induction of in vitro osteogenesis. Based on these preliminary findings our objective is to understand the histone demethylation switch from a repressive to an active chromatin state for bone essential genes that support bone formation.
Methods: We study the differential expression of two main histone demethylase families: JMJC (Jumanji Domain Containing) and LSD (Lysine Demethylases) using monoclonal murine calvarial pre-osteoblast cell lines (MC3T3-E1).
Results: Gene expression analysis of histone demethylase by real-time PCRhas been performed in order to understand the inductive role of histone demethylases in chromatin modification during osteoblastogenesis. Quantitative RT-PCR analysis revealed significantly higher expression of LSD and JMJC demethylases including UTX, JMJD3, LSD1, and SetD1B at the induction of osteogenesis (day 7). Gain of function (over expression) and loss of function (knockdown) studiesfor key demethylases demonstrated a switch in chromatin demethylation-methylation modification that support activation and repression of bone specific chromatin and their gene expression. BMP-2 induced however TGF-β decreases demethylase activity. Inactivation of histone methyl transferase complex (Ezh2/PRC2) increases the activation of chromatin.Taken together, our findings of chromatin modifications by histone demethylases will help to understand the epigenetic basis of bone development and maintenance.
Conclusions: Our studies have identified histone demethylases and their correlation with chromatin activating mechanism in bone development and osteogenesis.