Regulation of osteoblast activity by Pyk2-targeted approaches

Abstract

The hormonal and cellular mechanisms controlling bone formation are not completely understood. The proline-rich tyrosine kinase 2 (Pyk2) is important for osteoblast (OB) activity and bone formation. However, female mice lacking Pyk2 (Pyk2-KO) exhibit elevated bone volume/total volume. Previously, our laboratory found ovariectomized Pyk2-KO mice supplemented with 17β-estradiol (E2) exhibited a greater increase in bone volume than WT mice treated with E2. The overall hypotheses of our studies are that Pyk2 regulates OB activity by modulating the E2-signaling cascade and that a Pyk2-inhibitor will promote OB activity and be suitable for bone regeneration applications. In Aim1, we determined the mechanism of action of Pyk2 and E2 in OBs. Pyk2-KO OBs showed significantly higher proliferation, matrix formation, and mineralization than WT OBs. In the presence of E2 or raloxifene, a selective estrogen receptor (ER) modulator, both matrix formation and mineralization were further increased in Pyk2-KO OBs, but not WT OBs. Consistent with a role of Pyk2 in E2 signaling, Pyk2-depletion led to the proteasome-mediated degradation of ERα, but not ERβ. Finally, we found Pyk2-depletion and E2 have an additive effect on ERK phosphorylation, known to increase cell differentiation and survival. In Aim2, we developed a Pyk2-inhibitor loaded hydrogel and evaluated its viscosity, gelation time, swelling, degradation, and release behavior. We found that a hydrogel composed of PEGDA1000 plus 10% gelatin exhibited viscosity and shear-thinning behavior suitable for use as an injectable-carrier. Importantly, the Pyk2-inhibitor-hydrogel was cytocompatible, retained its inhibitory activity against Pyk2 leading to an increase in OB activity. In conclusion, therapeutic strategies targeting Pyk2 may improve systemic bone formation, while Pyk2-inhibitor loaded hydrogels may be suitable for targeted bone regeneration in craniofacial and/or the other skeletal defects.