Ezh2 mediates epigenetic regulation of osteoclastogenesis and bone remodeling in mice

Abstract

Osteoclasts derived from hematopoietic stem cells control bone resorption. Identifying novel molecules that can epigenetically regulate osteoclastogenesis has been an important basic and clinical issue. The polycomb group (PcG) protein enhancer of zeste homologue 2 (Ezh2), a histone lysine methyltransferase is associated with epigenetic regulation of numerous cellular processes, it is not yet clear on its involvement in bone cell development and homeostasis. Here, we crossed LysM-Cre mice with Ezh2flox/flox mice to delete Ezh2 in myeloid cell lineage mature macrophages. Conditional deletion of Ezh2 in macrophages resulted in significant increases in postnatal bone growth in the first 6 months of life, but tibia length and body weight gains were not different in knockout mice compared with their wild type controls. Significantly decreased osteoclastogenesis but increased bone mass without osteopetrosis were found in Ezh2 conditional knockout (CKO) mice. In contrast to female mice, one floxed Ezh2 gene copy recombinant with LysM-Cre+ (Ezh2flox/+LysM-Cre+) produced increased bone mass in young adult male mice compared with control mice (Ezh2flox/flox, LysM-Cre+ and wild type). Inflammatory milieu in bone was significantly lower in both male and female CKO mice compared with their respective controls. Deletion of Ezh2 in macrophages triggered increased gene expression of osteoclast suppressors, IRF8, MafB and Arg1 due to decreased Ezh2-induced trimethylation of H3K27me3. Conversely, NFATc1 and Cathepsin k expression were decreased. These findings suggest that pre-osteoclastic cell differentiation is under epigenetic control of osteoclast suppressive gene expression via an Ezh2-dependent mechanisms.