Drug Design, Development and Therapy (Jul 2022)
Orexin-A Reverse Bone Mass Loss Induced by Chronic Intermittent Hypoxia Through OX1R-Nrf2/HIF-1α Pathway
Abstract
Hong Gu,1,* Yiwen Ru,1,* Wei Wang,1,2 Guanhui Cai,1 Lanxin Gu,1 Junjie Ye,1 Wei-Bing Zhang,3,4 Lin Wang1,2 1Jiangsu Key Laboratory of Oral Diseases, Nanjing Medical University, Nanjing, People′s Republic of China; 2Department of Orthodontics, Affiliated Hospital of Stomatology, Nanjing Medical University, Nanjing, People′s Republic of China; 3Department of Stomatology, Dushu Lake Hospital Affiliated to Soochow University, Suzhou, People′s Republic of China; 4Department of Stomatology, Medical Center of Soochow University, Suzhou, People′s Republic of China*These authors contributed equally to this workCorrespondence: Wei-Bing Zhang, Department of Stomatology, Dushu Lake Hospital Affiliated to Soochow University, 9 Chongwen Road, Suzhou, 215000, People′s Republic of China, Tel +86-512-67505200, Email [email protected] Lin Wang, Department of Orthodontics, Affiliated Hospital of Stomatology, Nanjing Medical University, 136 Hanzhong Road, Nanjing, 210029, People′s Republic of China, Tel +86-025-69593060, Email [email protected]: Recent studies suggest that there is a potential connection between obstructive sleep apnea (OSA) and osteoporosis through dysregulation of bone metabolism. Orexin-A, a neuroprotective peptide secreted by the hypothalamus, is at a lower level in the plasma of OSA patients, which regulates appetite, energy expenditure and sleep-wake states. However, the protective effect of orexin-A on bone metabolism in OSA is unclear.Purpose: To investigate whether the activation of OX1R by orexin-A can reverse bone mass loss induced by chronic intermittent hypoxia (CIH).Methods: Mice were randomly divided into the normoxia group and CIH group. Within the CIH or normoxia groups, treatment groups were given a subcutaneous injection of either orexin-A or saline vehicle once every day for 4 weeks and then femurs were removed for micro-CT scans. Histology and immunohistochemical staining were performed to observe and calculate the changes in femurs as a result of hypoxia. Cell immunofluorescence and immunohistochemical staining were used to detect the expression of orexin receptors in MC3T3-E1 cells or in bones. CCK-8 assay, ALP assay kit and alizarin red staining were used to detect the viability, alkaline phosphatase (ALP) activity, and capacity of mineralization, respectively. The effect of orexin-A on osteogenic differentiation of MC3T3-E1 cells was evaluated using qRT-PCR, Western blot and cell staining.Results: CIH led to a decrease in the amount and density of trabecular bone, downregulated OCN expression while increasing osteoclast numbers in femurs and inhibited the expression of RUNX2, OSX, OPN and Nrf2 in MC3T3-E1 cells. Orexin-A treatment alleviated these CIH-induced effects by combining to OX1R. The level of HIF-1α was elevated both in CIH and orexin-A treatment groups.Conclusion: CIH environment inhibits osteogenesis and orexin-A can reverse bone mass loss induced by CIH through OX1R-Nrf2/HIF-1α pathway.Keywords: obstructive sleep apnea, dysregulation, bone metabolism, osteogenesis
