Supersulfides support bone growth by promoting chondrocyte proliferation in the growth plates

Objectives

While chondrocytes have mitochondria, they receive little O₂ from the bloodstream. Sulfur respiration, an essential energy production system in mitochondria, uses supersulfides instead of O₂. Supersulfides are inorganic and organic sulfides with catenated sulfur atoms and are primarily produced by cysteinyl tRNA synthetase-2 (CARS2). Here, we investigated the role of supersulfides in chondrocyte proliferation and bone growth driven by growth plate chondrocyte proliferation.

Methods

We examined the effects of NaHS, an HS⁻/H₂S donor, and cystine, the cellular source of cysteine, on the proliferation of mouse primary chondrocytes and growth of embryonic mouse tibia in vitro. We also examined the effect of RNA interference acting on the Cars2 gene on chondrocyte proliferation in the presence of cystine.

Results

NaHS (30 μmol/L) enhanced tibia longitudinal growth in vitro with expansion of the proliferating zone of their growth plates. While NaHS (30 μmol/L) also promoted chondrocyte proliferation only under normoxic conditions (20 % O₂), cystine (0.5 mmol/L) promoted it under both normoxic and hypoxic (2 % O₂) conditions. Cars2 gene knockdown abrogated the ability of cystine (0.5 mmol/L) to promote chondrocyte proliferation under normoxic conditions, indicating that supersulfides produced by CARS2 were responsible for the cystine-dependent promotion of bone growth.

Conclusions

The presented results indicate that supersulfides play a vital role in bone growth achieved by chondrocyte proliferation in the growth plates driven by sulfur respiration.