[Regulatory function and mechanism of autophagy on osteoclast]

Osteoclast (OC) is multinucleated, bone-resorbing cells originated from monocyte/macrophage lineage of cells, excessive production and abnormal activation of which could lead to many bone metabolic diseases, such as osteoporosis, osteoarthritis, etc. Autophagy, as a highly conserved catabolic process in eukaryotic cells, which plays an important role in maintaining cell homeostasis, stress damage repair, proliferation and differentiation. Recent studies have found that autophagy was also involved in the regulation of osteoclast generation and bone resorption. On the one hand, autophagy could be induced and activated by various factors in osteocalsts, such as nutrient deficiency, hypoxia, receptor activator of nuclear factor(NF)-κB ligand(RANKL), inflammatory factors, wear particles, microgravity environment, etc, different inducible factors, such as RANKL, inflammatory factors, wear particles, could interact with each other and work together. On the other hand, activated autophagy is involved in regulating various stages of osteoclast differentiation and maturation, autophagy could promote proliferation of osteoclasts, inhibiting apoptosis, and promoting differentiation, migration and bone resorption of osteoclast. The classical autophagy signaling pathway mediated by mammalian target of rapamycin complex 1(mTORC1) is currently a focus of research, and it could be regulated by upstream signalings such as phosphatidylinositol 3 kinase(PI-3K)/protein kinase B (PKB), AMP-activated protein kinase(AMPK). However, the paper found that mTORC1-mediated autophagy may play a bidirectional role in regulating differentiation and function of osteoclasts, and its underlying mechanism needs to be further ciarified. Integrin αvβ3 and Rab protein families are important targets for autophagy to play a role in osteoclast migration and bone resorption, respectively. In view of important role of osteoclast in the occurrence of various bone diseases, it is of great significance to elucidate the role of autophagy on osteoclast and its mechanism for the treatment of various bone diseases. The autophagy pathway could be used as a new therapeutic target for the treatment of clinical bone diseases such as osteoporosis.