O‐GlcNAc Modification of Runx2 Links Nutrient Metabolism with Osteogenesis

Abstract

The runt-related transcription factor 2 (Runx2) is the master switch controlling osteoblast differentiation and formation of the mineralized skeleton. The post-translational modification (PTM) of Runx2 by phosphorylation, ubiquitinylation, and acetylation modulates its activity, stability, and interactions with transcriptional co-regulators and chromatin remodeling proteins downstream of osteogenic signals. We have found that Runx2 is O-GlcNAc modified within the N-terminal activation domain and the proline/serine/threonine (PST)-rich domain, regions which are known to regulate Runx2 transcriptional activity. A chemoenzymatic labeling approach, employed to measure the stoichiometry of Runx2 O-GlcNAcylation in osteogenic bone marrow derived mesenchymal stem cells (BMMSCs), demonstrated approximately 40% of Runx2 was O-GlcNAc modified after pharmacological inhibition of O-GlcNAcase (OGA) with Thiamet G. In MC3T3-E1 preosteoblasts, Thiamet G treatment resulted in increased Runx2 transcriptional activity which was dependent on Mek1/2 activity. Furthermore, osteogenic differentiation in the presence of Thiamet G, enhanced basal and potentiated BMP2/7-induced activity of the early bone marker, alkaline phosphatase (ALP). These studies suggest that elevated O-GlcNAc modification in osteogenic stem cells and in osteoblasts potentiates Runx2 activity.