Orexins Facilitates Osteogenic Differentiation of MC3T3‐E1 Cells

Abstract Dysfunction of osteoblastic bone formation and matrix mineralization plays a key role in the pathological development of osteoporosis. The orexin peptide orexin‐A, a highly excitatory neuropeptide hormone, possesses various biological functions by activating its specific G protein‐coupled receptors, orexin‐1 receptor (OX1R) and orexin‐2 receptor (OX2R). Here, we report that OX1R but not OX2R was expressed in MC3T3‐E1 cells. Importantly, we found that orexin‐A accelerated osteoblast differentiation and matrix mineralization in MC3T3‐E1 cells, as manifested by elevation of physiological markers of osteoblastic differentiation [alkaline phosphatase (ALP) and osteogenic genes] and Alizarin Red staining, respectively. Importantly, our findings indicated that orexin‐A significantly increased the expression of runt‐related transcription factor 2 (Runx‐2), which is the central transcriptional factor. Orexin‐A treatment phosphorylated the kinase p38 mitogen‐activated protein kinase (MAPK) in a dose‐ and time‐dependent manner. Also, orexin‐induced increase in gene expression (Runx‐2, ALP, osteocalcin, and osterix) and matrix mineralization were prevented by the p38 MAPK specific inhibitor SB203580. Additionally, we also revealed that protein kinase D (PKD) is involved in the effects of Orexin‐A on p38 MAPK activation and Runx‐2 expression. Finally, we found that Orexin‐A‐induced osteoblastic formation and matrix mineralization and the activation of the PKD/p38 MAPK pathway are mediated by OX1R. Based on these findings, we concluded that activation of OX1R by orexin‐A might possess a therapeutic strategy for bone disease. © 2018 IUBMB Life, 70(7):633–641, 2018