Hypoxia inhibits RANKL-induced ferritinophagy and protects osteoclasts from ferroptosis

• Published in: Free radical biology & medicine 2021-06, Vol.169, p.271-282
• Main Authors: Ni, Shuo, Yuan, Yin, Qian, Zhi, Zhong, Zeyuan, Lv, Tao, Kuang, Yanbin, Yu, Baoqing
• Format: Article
• Language: English
• Subjects: Ferritinophagy; Ferritins; Ferroptosis; HIF-1α; Humans; Hypoxia; Iron; Iron - metabolism; Osteoclast; Osteoclasts - metabolism; RANK Ligand - pharmacology
• ISSN: 0891-5849; 1873-4596
• DOI: 10.1016/j.freeradbiomed.2021.04.027

Ferroptosis is a new form of regulated cell death. Several studies have demonstrated that ferroptosis was involved in multiple diseases. However, the precise role of ferroptosis in osteoporosis remains unclear. Here, we demonstrated that ferroptosis was involved in osteoclasts over the course of RANKL-induced differentiation, and it was induced by iron-starvation response and ferrintinophagy. Mechanistically, under normoxia but not hypoxia, ferroptosis could be induced due to iron-starvation response (increased transferrin receptor 1, decreased ferritin) followed by RANKL stimulation, and this was attributed to the down-regulation of aconitase activity. We further investigated intracellular iron homeostasis and found that ferritinophagy, a process initiated by FTH-NCOA4 complex autophagosome degradation, was activated followed by RANKL stimulation under normoxia. Interestingly, these processes could not be observed under hypoxia. Moreover, we demonstrated that HIF-1α contributed to the decrease of ferritinophagy and autophagy flux under hypoxia. Additionally, HIF-1α impair autophagy flux via inhibition of autophagosome formation under hypoxia in BMDMs. In vivo study, we indicated that HIF-1α specific inhibitor 2ME2 prevent OVX bone loss. In conclusion, our study comprehensively investigated the role of ferroptosis in osteoclasts in vitro and in vivo, and innovatively suggested that targeting HIF-1α and ferritin thus inducing ferroptosis in osteoclasts could be an alternative in treatment of osteoporosis. Hypoxia inhibits RANKL-induced ferritinophagy and protects osteoclasts from ferroptosis. HIF-1α inhibits ferritinophagy and thus reducing free iron pool and reactive oxygen species under hypoxia. Ferroptosis could be induced due to ferritinophagy and iron-starvation response (increased transferrin receptor 1, decreased ferritin) followed by RANKL stimulation under normoxia. [Display omitted] •Ferroptosis is involved in RANKL-induced osteoclasts differentiation.•Iron-starvation response and ferritinophagy contributed to RANKL-induced ferroptosis in osteoclasts.•HIF-1α impair autophagy flux via inhibition of autophagosome formation in BMDMs under hypoxia.•HIF-1α specific inhibitor prevents OVX mice bone loss in vivo.