Ezh2 is a histone methyltransferase that suppresses osteoblast maturation and skeletal development. We evaluated the role of Ezh2 in chondrocyte lineage differentiation and endochondral ossification. Ezh2 was genetically inactivated in the mesenchymal, osteoblastic, and chondrocytic lineages in mice using the Prrx1-Cre, Osx1-Cre, and Col2a1-Cre drivers, respectively. WT and conditional knockout mice were phenotypically assessed by gross morphology, histology, and micro-CT imaging. Ezh2-de-ficient chondrocytes in micromass culture models were evaluated using RNA-Seq, histologic evaluation, and Western blotting. Aged mice with Ezh2 deficiency were also evaluated for premature development of osteoarthritis using radiographic analysis. Ezh2 deficiency in murine chondrocytes reduced bone density at 4 weeks of age but caused no other gross developmental effects. Knockdown of Ezh2 in chondrocyte micromass cultures resulted in a global reduction in trimethylation of histone 3 lysine 27 (H3K27me3) and altered differentiation in vitro. RNA-Seq analysis revealed enrichment of an osteogenic gene expression profile in Ezh2-deficient chondrocytes. Joint development proceeded normally in the absence of Ezh2 in chondrocytes without inducing excessive hypertrophy or premature osteoarthritis in vivo. In summary, loss of Ezh2 reduced H3K27me3 levels, increased the expression of osteogenic genes in chondrocytes, and resulted in a transient post-natal bone phenotype. Remarkably, Ezh2 activity is dispensable for normal chondrocyte maturation and endochondral ossification in vivo, even though it appears to have a critical role during early stages of mesenchymal lineage commitment.
Bibliographical noteFunding Information:
Acknowledgments—We thank Oksana Pichurin, David Razidlo, Bridget Stensgard, and Bashar Hassan for technical support and the members of our laboratories for stimulating discussions. We also acknowledge support from the Bioinformatics Core, Medical Genome Facility, and Robert and Arlene Kogod Center on Aging at the Mayo Clinic.
This work was supported by NIAMS, National Institutes of Health Grants R01 AR049069 (to A. J. v. W.), R03 AR066342 (to A. N. L.), F32 AR066508 (to A. D.), K01 AR065397 (to E. W. B.), and R01 AR068103 (to J. J. W.) as well as by intramural grants from the Center for Regenerative Medicine at the Mayo Clinic and Mayo Graduate School (Clinical and Translational Sciences Track) and the Center for Clinical and Translational Science (UL1 TR000135). We also appreciate generous philanthropic support from Wil-liam H. and Karen J. Eby and the charitable foundation in their name. A. J. K. is a paid consultant for Arthrex, Inc., and M. K. is a founder and chair holder of Hy2Care B.V. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.
© 2018 American Society for Biochemistry and Molecular Biology Inc. All Rights Reserved.
PubMed: MeSH publication types
- Journal Article
- Research Support, N.I.H., Extramural
- Research Support, N.I.H., Intramural
- Research Support, Non-U.S. Gov't