EZH2 deletion in early mesenchyme compromises postnatal bone microarchitecture & structural integrity and accelerates remodeling

In this study, we examined the functional importance of EZH2 during skeletal development and homeostasis using the conditional deletion of Ezh2 (Ezh2fl/fl) in early mesenchyme with the use of a Prrx-1-cre driver mouse (Ezh2⁺⁄⁺). Heterozygous (Ezh2⁺⁄⁻) newborn and 4-wk-old mice exhibited increased skeletal size, growth plate size, and weight when compared to the wild-type control (Ezh2⁺⁄⁺), whereas homozygous deletion of Ezh2 (Ezh2−/−) resulted in skeletal deformities and reduced skeletal size, growth plate size, and weight in newborn and 4-wk-old mice. Ezh2⁻⁄⁻ mice exhibited enhanced trabecular patterning. Osteogenic cortical and trabecular bone formation was enhanced in Ezh2⁺⁄⁻ and Ezh2⁻⁄⁻ animals. Ezh2⁺⁄⁻ and Ezh2⁻⁄⁻ mice displayed thinner cortical bone and decreased mechanical strength compared to the wild-type control. Differences in cortical bone thickness were attributed to an increased number of osteoclasts, corresponding with elevated levels of the bone turnover markers cross-linked C-telopeptide-1 and tartrate-resistant acid phosphatase, detected within serum. Moreover, Ezh2⁺⁄⁻ mice displayed increased osteoclastogenic potential coinciding with an upregulation of Rankl and M-csf expression by mesenchymal stem cells (MSCs). MSCs isolated from Ezh2⁺⁄⁻ mice also exhibited increased trilineage potential compared with wild-type bone marrow stromal/stem cells (BMSCs). Gene expression studies confirmed the upregulation of known Ezh2 target genes in Ezh2⁻⁄⁻ bone tissue, many of which are involved in Wnt/BMP signaling as promoters of osteogenesis and inhibitors of adipogenesis. In summary, EZH2 appears to be an important orchestrator of skeletal development, postnatal bone remodelling and BMSC fate determination in vitro and in vivo.—Hemming, S., Cakouros, D., Codrington, J., Vandyke, K., Arthur, A., Zannettino, A., Gronthos, S. EZH2 deletion in early mesenchyme compromises postnatal bone microarchitecture and structural integrity and accelerates remodeling.Sarah Hemming, Dimitrios Cakouros, John Codrington, Kate Vandyke, Agneiszka Arthur, Andrew Zannettino and Stan Grontho