Suppression of AMP-activated protein kinase reverses osteoprotegerin-induced inhibition of osteoclast differentiation by reducing autophagy.
Tong Xishuai,Zhang Chuang,Wang Dong,Song Ruilong,Ma Yonggang,Cao Ying,Zhao Hongyan,Bian Jianchun,Gu Jianhong,Liu Zongping
OBJECTIVES:Osteoclasts (OC) are unique terminally differentiated cells whose primary function is bone resorption. We previously showed that osteoprotegerin (OPG) inhibits OC differentiation in vitro by enhancing autophagy via the adenosine monophosphate-activated protein kinase (AMPK)/mTOR/p70S6K signalling pathway in vitro. Here, we aimed to elucidate the mechanism of AMPK mediated autophagy to regulate OPG-mediated inhibition of OC differentiation and identify potential therapeutic targets associated with bone loss. MATERIALS AND METHODS:We used the AMPK activator AICAR to determine the relationship between AMPK activation and OC differentiation, and studied the role of AMPK-mediated autophagy in OPG-mediated inhibition of OC differentiation by using autophagy inhibitors or AMPK knockdown. RESULTS:AMP-activated protein kinase activation caused LC3II accumulation and weakened OC differentiation activity. In contrast, inactivation of autophagy by 3-methyladenine or Bafilomycin A1 could attenuate OPG-mediated inhibition of OC differentiation via the AMPK/mTOR/p70S6K signalling pathway. Furthermore, the AMPK inhibitor compound C and knockdown of AMPK impaired OPG-mediated inhibition of OC differentiation by inducing autophagy. CONCLUSIONS:These results demonstrated that the AMPK signalling pathway functions as a critical regulator in the OPG-mediated inhibition of OC differentiation, by inducing autophagy. Our results provide a basis for future bone-related studies on the AMPK signalling pathway.
Mechanisms of mitophagy in cellular homeostasis, physiology and pathology.
Palikaras Konstantinos,Lionaki Eirini,Tavernarakis Nektarios
Nature cell biology
Mitophagy is an evolutionarily conserved cellular process to remove dysfunctional or superfluous mitochondria, thus fine-tuning mitochondrial number and preserving energy metabolism. In this Review, we survey recent advances towards elucidating the molecular mechanisms that mediate mitochondrial elimination and the signalling pathways that govern mitophagy. We consider the contributions of mitophagy in physiological and pathological contexts and discuss emerging findings, highlighting the potential value of mitophagy modulation in therapeutic intervention.