The bone tissue is a dynamic complex that constitutes of several interdependent systems and is continuously remodeled through the concerted actions of bone cells. Osteoblasts are mononucleated cells, derived from mesenchymal stem cells, responsible for bone formation. Osteoclasts are large multinucleated cells that differentiate from hematopoietic progenitors of the myeloid lineage and are responsible for bone resorption. The lineage-specific differentiation of bone cells requires an epigenetic regulation of gene expressions involving chromatin dynamics. The key step for understanding gene regulatory networks during bone cell development lies in characterizing the chromatin modifying enzymes responsible for reorganizing and potentiating particular chromatin structure. This review covers the histone-modifying enzymes involved in bone development, discusses the impact of enzymes on gene expression, and provides future directions and clinical significance in this area.

Bone tissue is continuously remodeled by the coordinated action of osteoclasts and osteoblasts. Nuclear factor-activated T cells c1 (NFATc1) is a well-known transcription factor for osteoclastogenesis and transcriptionally activated by the c-Fos and nuclear factor-kappa B (NF-κB) signaling pathways in response to receptor activation of NF-κB ligand (RANKL). Since excessive RANKL signaling causes an increase of osteoclast formation and bone resorption, inhibition of RANKL or its signaling pathway is an attractive therapeutic approach to the treatment of pathologic bone loss. In this study, we show that an ethyl acetate fraction (LEA) from the shiitake mushroom, Lentinula edodes, inhibited RANKL-induced osteoclast differentiation by blocking the NFATc1 signaling pathway. We found that the water extract and its subsequent ethyl acetate fraction of L. edodes significantly suppressed osteoclast formation. Comparative transcriptome analysis revealed that LEA specifically downregulated a set of RANKL target genes, including Nfatc1. Next, we found that LEA suppresses Nfatc1 expression mainly through the inhibition of the transactivity of p65 and NFATc1. Moreover, treatment of LEA rescued an osteoporotic phenotype in a zebrafish model of glucocorticoid-induced osteoporosis. Collectively, our findings define an undocumented role of the shiitake mushroom extract in regulating bone development.

Abeliophyllum distichum Nakai is known as a monotypic genus endemic to South Korea. Currently, several pharmacological studies have revealed that A. distichum extract exhibits diverse biological functions, including anti-cancer, anti-diabetic, anti-hypertensive, and anti-inflammatory activities. In this study, we present the anti-osteoporotic activity of A. distichum extract by inhibiting osteoclast formation. First, we show that the methanolic extract of the leaves of A. distichum, but not extracts of the branches or fruits, significantly inhibits receptor activator of the NF-κB ligand (RANKL)-induced osteoclast differentiation. Second, our transcriptome analysis revealed that the leaf extract (LE) blocks sets of RANKL-mediated osteoclast-related genes. Third, the LE attenuates the phosphorylation of extracellular signal-related kinase. Finally, treatment with the LE effectively prevents postmenopausal bone loss in ovariectomized mice and glucocorticoid-induced osteoporosis in zebrafish. Our findings show that the extract of A. distichum efficiently suppressed osteoclastogenesis by regulating osteoclast-related genes, thus offering a novel therapeutic strategy for osteoporosis.