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-beta 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.