Hydrogen sulphide promotes osteoclastogenesis by inhibiting autophagy through the PI3K/AKT/mTOR pathway

Hydrogen sulphide (H₂S), a gasotransmitter, plays an important role in the regulation of bone homeostasis. However, the precise effect of H₂S on osteoclasts was still elusive. The goal of this study was to determine the potential role of H₂S in regulation of osteoclasts and the underlying mechanisms by which H₂S affected osteoclastogenesis. The present study applied western blot, quantitative real-time PCR, tartrate-resistant acid phosphatase staining, pit formation assay, immunofluorescence confocal microscopy, transmission electron microscopy and annexin V-fluorescein isothiocyanate/propidium iodide double-staining assay. The results showed that the expressions of cystathionine b-synthase (CBS) and cystathionine c-lyase (CSE) were obviously increased in osteoclast differentiation induced by the receptor activator of nuclear factor kappa-β ligand (RANKL). In addition, H₂S promoted RANKL-induced osteoclastogenesis and inhibited apoptosis of mature osteoclasts. Mechanistically, H₂S inhibited autophagy in Raw 264.7 cells. Autophagy activator (rapamycin) alleviated the induction of osteoclast differentiation by H₂S. Further studies showed that H₂S inhibited autophagy by activating the PI3K/AKT/mTOR signalling pathway. Taken together, our results implicated that exogenous H₂S could promote osteoclastogenesis by activating the PI3K/AKT/mTOR pathway to downregulate autophagy.