α-Hemolysin suppresses osteogenesis by inducing lipid rafts accumulation in bone marrow stromal cells.

ABSTRACT

α-hemolysin (Hla) is considered an essential virulent factor for Staphylococcus aureus (S. aureus) toxicity, the mechanism by which Hla affect bone metabolism is poorly understood. In this study, 2-month-old C57BL/6 mice were treated with Hla (40 µg/kg, i.p.) or S. aureus (1 × 106 CFU/ml, 100 µl, i.v.) with the presence or absence of methyl-ß-cyclodextrin (MßCD) (300 mg/kg, i.p.). MicroCT analysis showed progressive bone loss from week 2 to week 4 after Hla treatment, accompanied by a decreased osteoblasts and increased osteoclasts in femoral metaphysis in mice. Further, Hla stimulated the expression of Caveolin-1 in vivo and in vitro, activated lipid rafts accumulation in cell membrane of bone marrow stromal cells (BMSCs), and suppressed osteogenesis of BMSCs. Destruction of lipid rafts with MßCD or inhibition of Caveolin-1 with Daidzein blocked the detrimental effect of Hla on osteogenesis of BMSCs. Importantly, treating mice with MßCD rescued the loss of osteoblasts and increased osteoclastogenesis induced by Hla as well as the bone loss induced by S. aureus infection. Together, we demonstrate that Hla induces bone destruction directly by suppressing osteogenesis and indirectly by stimulating osteoclastogenesis, and that lipid rafts may mediate the detrimental effect of Hla and S. aureus on osteogenesis and bone formation.