IL-17A modulates osteoclast precursors' apoptosis through autophagy-TRAF3 signaling during osteoclastogenesis

Abstract

Osteoclasts play an important role in bone remodeling. The inflammatory cytokine IL-17A could modulate the RANKL-induced osteoclastogenesis by regulating the autophagic activity. It is well accepted that protective autophagy has an anti-apoptotic effect. It is necessary to elucidate whether IL-17A can influence the apoptosis of osteoclast precursors (OCPs) through autophagy responses during osteoclastogenesis. The results showed that apoptosis of RAW264.7-derived OCPs was promoted by high levels of IL-17A, but the opposite anti-apoptotic function was shown by low levels of IL-17A. Furthermore, the enhanced apoptosis by high levels of IL-17A was reversed by overexpression of autophagy protein Beclin1; conversely, the inhibited apoptosis by low levels of IL-17A was restored by knockdown of Beclin1. It was also found that Beclin1 suppression with Beclin1 inhibitor (spautin1) could block the reduced apoptosis by low levels of IL-17A, which was recovered by TRAF3 knockdown. Moreover, the enhanced apoptosis by high levels of IL-17A decreased following the downregulation of TRAF3. Importantly, overexpression of caspase3 further attenuated osteoclastogenesis treated by high levels of IL-17A, without significantly affecting osteoclastogenesis stimulated by low levels of IL-17A. In conclusion, IL-17A modulates apoptosis of OCPs through Beclin1-autophagy-TRAF3 signaling pathway, thereby influencing osteoclastogenesis. Therefore, our study sheds lights on the improvement of clinical strategies of dental implantation or orthodontic treatment by revealing the novel targets in the bone remodeling.