β-Hydroxybutyrate prevents bone loss partially via the histone β-hydroxybutyrylation pathway

Osteoporosis (OP) is a systemic metabolic bone disorder. The excessive activation of osteoclasts (OCs) leads to a decrease in bone mass and damage to the bone microstructure, which plays a crucial role in OP. β-Hydroxybutyrate (BHB), the main component of ketone bodies, not only serves as an ancillary fuel substituting for glucose but also induces anti-oxidative, anti-inflammatory, and cardioprotective features via binding to several target proteins, including histone β-hydroxybutyrylation (Kbhb). Recent research has found that BHB has a positive therapeutic effect on OP, but the underlying molecular mechanism remains unclear. In this study, we established OP animal models induced by estrogen deficiency and type 2 diabetes using ovariectomized (OVX) and db/db mice, respectively, and administered BHB to OP mice via free drinking in vivo. Our results indicated that BHB increased bone mineral density (BMD), improved bone microstructure, and inhibited OC formation. Additionally, BHB upregulated the levels of PanKbhb, H3K9bhb, and H3K27bhb modifications in the bone tissue of OP mice. In vitro, we found that BHB or β-hydroxybutyryl-CoA (BHB-CoA) could inhibit RANKL-induced OC differentiation and bone resorption, and upregulate histone Kbhb levels in a concentration-dependent manner. Furthermore, the effects of BHB or BHB-CoA-induced histone Kbhb were reversed by inhibiting the activity of acyl-CoA synthetase short-chain family member 2 (ACSS2) or histone acyltransferase P300. In summary, our data reveal that BHB may alleviate bone loss caused by estrogen deficiency and type 2 diabetes through ACSS2/P300-induced histone Kbhb.