Inhibition of ferroptosis rescues BMP osteogenic differentiation impaired by iron overload in the osteoporotic microenvironment.

Bone morphogenetic proteins (BMPs) are effective for treating various orthopedic conditions and are widely used clinically. However, their therapeutic efficacy is limited in osteoporosis patients. Iron overload represents a key risk factor for osteoporosis, inducing ferroptosis and suppressing the osteogenic differentiation of bone marrow stromal cells (BMSCs). This mechanism likely contributes to the suboptimal response to BMP therapy in these patients. Using ovariectomized (OVX) mouse models and sequencing analysis of human BMSCs, we confirmed ferroptosis occurs in BMSCs from both OVX mice and osteoporosis patients, correlating with reduced BMP sensitivity. To investigate this, we established a BMP osteogenic differentiation model using C2C12 and ST2 cell lines, along with mouse and human primary BMSCs. Treatment with FK506 (tacrolimus) effectively activated BMP signaling and promoted osteogenic differentiation in this model. We then induced iron-overload conditions using ammonium ferric citrate (FAC). FAC triggered ferroptosis in stem cells, subsequently reducing BMP signaling and inhibiting osteogenic differentiation. Sequencing analysis further linked osteoporosis to downregulated Wnt signaling. Consequently, we administered melatonin (Mel) - previously shown by our group to activate Wnt signaling - to stem cells under FAC-induced iron overload and to OVX mice. Mel reduced ferroptosis in stem cells by restoring BMP signaling, promoted osteogenic differentiation, and increased bone mass in the mice. Our findings suggest ferroptosis is a key factor limiting BMP treatment efficacy in osteoporosis. Melatonin holds promise as an effective adjunct therapy to overcome this limitation.