The Cx43/p38 MAPK/Runx2 signaling pathway as a potential regulatory axis in insufficient osteogenesis associated with osteoporosis

Abstract

Osteoporosis is characterized by severe osteogenic insufficiency, which severely impairs bone regeneration and repair. Connexin 43 (Cx43) participates in the modulation of osteoblast function, yet its regulatory mechanism linking osteoporosis and osteogenic deficiency through the p38 mitogen-activated protein kinase (p38 MAPK)-Runt-related transcription factor 2 (Runx2) signaling axis remains unclear. This study aimed to clarify the above regulatory relationship. We constructed an ovariectomized (OVX) mouse osteoporosis model and a Cx43-knockdown MC3T3-E1 osteoblast model. Alkaline phosphatase (ALP) and Alizarin Red S staining were performed to assess osteogenic differentiation capacity, and western blot (WB) was adopted to measure the protein expression of p38, phosphorylated p38 (p-p38) and Runx2. The p38 MAPK activator DIPQUO was utilized to explore the potential molecular mechanism. Hematoxylin-eosin (HE) staining combined with WB assays were further applied to verify the in vivo experimental outcomes. Cx43 expression was significantly decreased in the bone tissues of OVX mice, accompanied by suppressed p38 MAPK phosphorylation and downregulated Runx2 expression. Cx43 knockdown inhibited osteogenic activity, matrix mineralization as well as the activation of the p38 MAPK-Runx2 pathway in MC3T3-E1 cells. Activation of p38 MAPK by DIPQUO recovered Runx2 expression and partially rescued osteogenic defects induced by Cx43 deficiency under in vitro conditions. Consistent with cellular findings, OVX osteoporotic mice showed trabecular deterioration on histological examination, accompanied by reduced p-p38 and Runx2 protein levels in bone tissue. Collectively, Cx43 deficiency hinders osteoblast differentiation under osteoporotic status by suppressing the p38 MAPK-Runx2 signaling cascade. Pharmacological activation of p38 MAPK by DIPQUO may partially rescue osteogenic dysfunction induced by Cx43 downregulation under in vitro conditions. The potential relevance of the Cx43/p38 MAPK/Runx2 signaling axis to perioperative bone repair in patients with osteoporosis remains to be validated in appropriate in-vivo models.