title: Autophagy regulates hypoxia-induced osteoclastogenesis through the HIF-1α/BNIP3 signaling pathway.
abstract: Previous studies have implicated that hypoxic stress could enhance osteoclast differentiation; however, the underlying mechanism remains poorly understood. Autophagy is a dynamic lysosomal degradation process that has emerged as an important regulator under hypoxic environment. In the present study, we demonstrate for the first time that autophagy regulates hypoxia-induced osteoclastogenesis in vitro. We found that exposure of RAW264.7 cells to hypoxia (0.2% oxygen) resulted in enhanced osteoclast differentiation, accompanied by the observation of several specific features of autophagy, including appearance of membranous vacuoles, formation of acidic vesicular organelles, cleavage and recruitment of microtubule-associated protein 1 light chain 3 (LC3) to autophagosomes, increase in autophagic flux, as well as up-regulation of autophagy-related gene (Atg) expression. Moreover, suppression of autophagy with DN-Atg5(K130R) or 3-methyladenine (3-MA) significantly attenuated the osteoclast differentiation under hypoxic conditions, indicating the functional significance of autophagy in hypoxia-induced osteoclastogenesis. The data also showed that the activation of autophagy under hypoxic conditions was caused by up-regulated expression of hypoxia-inducible factor-1α (HIF-1α)-dependent Bcl-2 adenovirus E1a 19  kDa interacting protein 3 (BNIP3). Importantly, knockdown of HIF-1α or BNIP3 obviously abrogated hypoxia-induced autophagy activation and osteoclastogenesis enhancement. Collectively, our results highlight the fact that autophagy is a pivotal regulator for hypoxia-induced osteoclast differentiation, which may provide new insight into the pathological processes of osteoclastogenesis under hypoxic stress and help develop new therapeutic strategies for abnormal osteoclastogenesis.
authors.affiliation: The State Key Laboratory Breeding Base of Basic Science of Stomatology, School & Hospital of Stomatology, Wuhan University, Wuhan, China.
authors.forename: Yi
authors.initials: Y
authors.lastname: Zhao
authors.forename: Gang
authors.initials: G
authors.lastname: Chen
authors.forename: Wei
authors.initials: W
authors.lastname: Zhang
authors.forename: Ning
authors.initials: N
authors.lastname: Xu
authors.forename: Jun-Yi
authors.initials: JY
authors.lastname: Zhu
authors.forename: Jun
authors.initials: J
authors.lastname: Jia
authors.forename: Zhi-Jun
authors.initials: ZJ
authors.lastname: Sun
authors.forename: Yi-Ning
authors.initials: YN
authors.lastname: Wang
authors.forename: Yi-Fang
authors.initials: YF
authors.lastname: Zhao
mesh_terms: D000818:Animals; D001343:Autophagy / Q000502:physiology*; D002454:Cell Differentiation; D000860:Hypoxia; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000235:genetics / Q000378:metabolism*; D008264:Macrophages / Q000378:metabolism*; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D024101:Mitochondrial Proteins / Q000235:genetics / Q000378:metabolism*; D010010:Osteoclasts / Q000166:cytology* / Q000502:physiology; D015398:Signal Transduction / Q000502:physiology; D013312:Stress, Physiological
chemical_list: C508686:BNip3 protein, mouse; C497443:Hif1a protein, mouse; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D008565:Membrane Proteins; D024101:Mitochondrial Proteins