The Role of Runx2 in Microtubule Dynamics and Its Effects on Osteoblast Migration.

The migration of osteoblasts (OBs) is crucial for bone formation, remodeling, and healing. This requires the coordinated activity of cytoskeletal components, including microtubules (MTs). MTs complement actin filaments by regulating focal adhesion turnover and facilitating the delivery of essential proteins and cargo. However, the roles and regulation of MTs during OB migration remain unclear. Previous studies show that Runt-related transcription factor-2 (Runx2), a master regulator of OB differentiation, promotes MT stability in pathological contexts, such as breast cancer metastasis. In this study, we investigated the effects of Runx2 deficiency on OB migration and MT dynamics using wild-type and Runx2-deficient calvarial OBs. To assess MT function more precisely, we treated cells with microtubule-targeting agents (MTAs) that differentially affect dynamic and stable MT populations. Measurements of K40 on α-tubulins were utilized to mark longer-lived and stable MTs. Our findings revealed distinct differences in the dynamics and regulation of MTs respective to Runx2 status. Runx2-deficient OBs demonstrated increased levels of acetyl-α-tub as measured by whole cell lysate. During nutrient stress, such as glucose starvation, Runx2-deficient OBs exhibit a more rapid increase in acetyl-α-tub. However, these cells are also more sensitive to losing this stable MT fraction, notably upon exposure to MTA vinblastine. Confocal microscopy of the enzymes regulating acetyl-α-tub, ATAT1 and HDAC6, reveals striking differences in subcellular localization and colocalization to α-tubulins. Interestingly, wound-healing assays suggest Runx2-deficient OBs possess enhanced migratory capacity under both basal conditions and following MT disruption. Altogether, these findings uncover a novel role for Runx2 in regulating MT dynamics and suggest that, in specific contexts, Runx2 may suppress OB migration.