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.

Orexin-A Attenuates Inflammatory Responses in Lipopolysaccharide-Induced Neural Stem Cells by Regulating NF-KB and Phosphorylation of MAPK/P38/Erk Pathways

“…For example, Orexin-A-induced osteoblastic formation and matrix mineralization and the activation of the PKD/p38 MAPK pathway are mediated by OXR1. 32 Orexin-A could stimulate the expression of GLUT4 in a glucose-dependent manner in primary hepatocytes via Erk1/2, JNK, and p38 signaling. 33 In addition, Dandan’s studies have shown that Orexin-A exerted its neuroprotective effects in vivo and in vitro by suppressing over-activated autophagy by modulating the OXR1-mediated MAPK/Erk/mTOR pathway.…”

Dioscin improves postmenopausal osteoporosis through inducing bone formation and inhibiting apoptosis in ovariectomized rats

“…Bone metabolic balance depends on the interaction of bone formation and bone resorption, indicating the disorder is caused by an imbalance between osteoblasts and osteoclasts (15,16), which is also the key cause of PMO. Osteoblasts play a vital role in bone formation and are controlled by several signaling pathways, including PI3K/P38/AKT pathways (17)(18)(19). This study aimed to evaluate the osteoprotective effects of dioscin on PMO rats and explore dioscin's mechanism of action.…”

Orexin-A Reverse Bone Mass Loss Induced by Chronic Intermittent Hypoxia Through OX1R-Nrf2/HIF-1α Pathway

“…Orexin-A peptide and OX1R specific inhibitor SB334867 (MCE, China) were stored in α-MEM. 3T3 cells were stimulated with OM in the presence or absence of orexin-A (5µM) and SB334867 (10 nM) 13 for 14 days.…”

“…Upon orexin binding to OX1R or OX2R, orphan G protein-coupled receptors, it regulates sleep-wake states, feeding behaviors and energy homeostasis. 11 , 12 Furthermore, it is reported that orexin-A can accelerate osteoblast differentiation and matrix mineralization in the murine osteoblastic cell-line MC3T3-E1 cells in vitro 13 and orexin knockout mice display a lower-bone-mass phenotype. 14 Previous studies have suggested that orexin-A expression affects the occurrence of airway diseases, such as OSA, chronic obstructive pulmonary disease, and narcolepsy.…”

“…Some studies focused on the role of orexin-A in osteogenesis are consistent with our results on the positive effect of orexin-A on osteogenesis. 13,14 Figure 7 Simplified schematic diagram of mechanism on OXA promoting osteogenesis in CIH (drawn by Biorender software). Chronic intermittent hypoxia inhibits the expression of osteogenesis markers, while orexin-A promotes the expression through OX1R to exert its protective effect on bone metabolism imbalance.…”