Endoplasmic reticulum protein of 57 kDa sulfhydration promotes intestinal calcium absorption to attenuate primary osteoporosis

Abstract

Endogenous hydrogen sulfide (H₂S) plays an important role in bone metabolism. However, the exact role of H₂S in intestinal calcium and phosphorus absorption and its potential in preventing and treating primary osteoporosis remains unknown. Therefore, this study aimed to investigate the potential of H₂S in promoting intestinal calcium and phosphorus absorption and alleviating primary osteoporosis. We measured the apparent absorptivity of calcium, femoral bone density, expression and sulfhydration of the duodenal endoplasmic reticulum protein of 57 kDa (ERp57), duodenal cystathionine γ-lyase (CSE) expression, and serum H₂S content in adult and old CSE-knockout and wild-type mice. We also assessed intracellular reactive oxygen species (ROS) and Ca²⁺ content in CSE-overexpressing or knockout intestinal epithelial cell (IEC)-6 cells. In senile mice, CSE knockout decreased endogenous H₂S, ERp57 sulfhydration, and intestinal calcium absorption and worsened osteoporosis, which were partially reversed by GYY4137, an H₂S donor. CSE overexpression in IEC-6 cells increased ERp57 sulfhydration, protein kinase A and C activity, and intracellular Ca²⁺, whereas CSE knockout exerted the opposite effects. Furthermore, hydrogen peroxide (H₂O₂) stimulation had similar effects as in CSE knockout, which were reversed by pretreatment with sodium hydrosulfide before H₂O₂ stimulation and restored by DL-dithiothreitol. These findings suggest that H₂S attenuates primary osteoporosis by preventing ROS-induced ERp57 damage in intestinal epithelial cells by enhancing ERp57 activity and promoting intestinal calcium absorption, thereby aiding in developing therapeutic interventions to prevent osteoporosis.