Osteoclast precursor cell-derived Flot2 is a novel therapeutic target for bone loss diseases

Excessive osteoclastogenesis disrupts the bone homeostasis, leading to bone loss and other skeletal related events in osteolysis diseases including osteoporosis and breast cancer. Although successfully improving skeletal related events, the current osteoclast inhibitors all disturb physiological bone formation with certain unacceptable severe adverse effects. After the PCSK9-siRNA marketed in 2021, increasingly siRNA drugs have been enrolled into clinical studies. Here, we observed the mRNA expression of Flot2, a raft protein, was elevated in osteoporosis. Targeted ablation of Flot2 using CRISPR/Cas9 and specific siRNA inhibited osteoclastogenesis in vitro, and ovariectomy-induced osteoporosis without affecting physiological bone mass in vivo. Mechanistically, FLOT2 deficiency disrupted its interaction with PLCγ2 and subsequently reduced osteoclastogenesis. Furthermore, Flot2-siRNA-AAV also blocked breast cancer cells-induced osteolysis in vivo. In a translation research, homo-FLOT2-siRNA suppressed osteoclastogenesis in CD14⁺ osteoclast precursor cells obtained from osteolytic patients. Interestingly, the abnormal protein expression of FLOT2 in blood CD14⁺ cells distinguished early-stage malignant breast cancer patients from people with benign breast tumors. In summary, our findings reveal Flot2-siRNA as a potential inhibitor of pathological osteoclastogenesis to treat osteolytic diseases, and identify FLOT2 protein in peripheral osteoclast precursor cells as a novel marker to facilitate early diagnosis of breast cancer, especially in premenopausal women.