Bone Abstracts

Post-translational modifications of histone N-terminal tail domains affect the local chromatin conformation and serve as a dynamic regulatory layer for controlling gene transcription during cell differentiation. However, the role of epigenetic modifications in the regulation of osteoblast differentiation is still not fully understood. Recently, we identified RCOR2 as a novel regulator of osteoblast differentiation in a genome-wide transcription profiling of mouse MC3T3-E1 cells and showed that shRNA-mediated silencing of RCOR2 impairs osteoblast differentiation. RCOR2 is a close homolog of RCOR1 (CoREST), which forms a complex with lysine-specific demethylase 1 (LSD1) and regulates its activity and function. LSD1 has been shown to regulate embryonic development and cellular differentiation. We previously confirmed that RCOR2 and LSD1 physically interacted, which led us to hypothesize that the osteoblastogenesis-promoting effect of RCOR2 could be mediated by LSD1. Inhibition of LSD1 activity with micromolar concentrations of small molecular inhibitors S2101 and RN-1 resulted in impaired differentiation of MC3T3-E1 cells and mouse calvarial osteoblasts, shown by decreased ALP staining and decreased expression of osteoblast-related genes including ALP, OSX and OCN. S2101 and RN-1 did not show toxicity for osteoblasts at used concentrations. We found that LSD1 inhibition in MC3T3-E1 cells resulted in altered expression of a set of genes that we had previously identified to be regulated by RCOR2, further supporting the hypothesis that RCOR2 and LSD1 function in the same pathway to regulate common targets in osteoblastic cells. In conclusion, our results indicate that LSD1 is involved in the regulation of osteoblast differentiation. As inhibition of LSD1 resembles closely the effect of RCOR2 downregulation, they act likely as components of the same control node in the epigenetic regulation of osteoblast differentiation. Studying the possible bone-related effects of LSD1 inhibition is highly clinically relevant due to the recent interest of LSD1 as a drug target in oncology.