Bone Abstracts

Hydrogen sulfide (H₂S) is a gaseous molecule produced endogenously in mammalian cells. H₂S was recently found to play important roles in the regulation of inflammation, redox homeostasis and cell lifespan. Moreover, H₂S was shown to maintain mesenchymal stem cell (MSC) function and stimulate osteogenic differentiation of MSC. However, it is unclear whether H₂S plays any role in the bone loss induced by estrogen deficiency.

The objective of this study was to investigate the role of the endogenous pathway leading to H₂S generation in ovariectomy (ovx)-induced bone loss in mice.

We found that ovx induced a 29% decrease in femural BV/TV relative to sham mice (P<0.0001). Moreover, ovx decreased serum H₂S levels by 65% (P<0.001) and blunted the bone marrow (BM) mRNA expression of the two key H₂S-generating enzymes (P<0.001), cystathione β-synthase (CBS) and cystathione γ-lyase (CSE). To restore H₂S levels, mice were treated with a common H₂S-donor drug, GYY4137 (GYY) (1 mg/mouse, every other day) for 4 weeks and indexes of bone mass were measured by μCT and hystomorphometry. We found that treatment with GYY normalizes serum H₂S levels in ovx mice, and completely prevents the loss of femural BV/TV. Hystomorphometry revealed that GYY induced a significant increase in N.Ob-BS and Ob.S/BS (P<0.05). Furthermore, GYY-treated mice significantly increased serum levels of P1NP, a marker of bone formation, and increased CFU-ALP formation ex vivo by 28% relative to ovx mice (P<0.0001). Treatment with GYY resulted in increased WNT signaling in BMSCs and increased the expression of the WNT ligands Wnt16, Wnt2b, Wnt6 and Wnt10b in the BM. Experiments performed in human BM cells confirmed that H₂S stimulates osteogenic differentiation of MSC. In summary, we show that ovx is associated with impaired H₂S synthesis in mice, and that pharmacological replacement of H₂S stimulates bone formation preventing the bone loss induced by estrogen deficiency.