Sema4d regulates the bone metabolism in combination with leptin or melatonin

Abstract Purpose The present study aims to explore the regulatory function of Sema4D on bone metabolism in combination with leptin or melatonin, as well as the underlying mechanism. Methods The osteoporosis model was established in rats using the OVX method. The bilateral tibial specimens of rats were taken for Micro-CT scanning analysis and three-dimensional reconstruction. The pathological state of bone tissues was evaluated by the HE staining assay. The concentration of estradiol in the serum was detected by the ELISA assay. Six groups were divided in the present study: Control, OVX, OVX + NL, OVX + Sema4D, OVX + Sema4D + leptin, and OVX + Sema4D + MT groups. According to the above grouping, the Sema4D or leptin overexpressing vectors were injected into rats through the tail vein. 3D bone structure was detected by high-resolution micro-CT system. Serum bone-derived alkaline phosphatase (BALP) and tartrate-resistant acid phosphatase-5b (TRAP-5b) activities were measured by ELISA. TRAP staining was used to calculate the number of osteoclasts in the metaphysis of the upper tibia. The expressions of bone morphogenetic protein-2 (BMP-2) and leptin in bone tissue were detected by immunohistochemistry. Results Compared to OVX + NL, the level of V/TV, Tb.N, BMD, and BMC in the OVX + Sema4D + leptin and OVX + Sema4D + MT groups was extremely elevated, accompanied by a declined Tb.Sp level. Compared to the OVX group, in the OVX + Sema4D + leptin and OVX + Sema4D + MT groups, the structure of bone trabeculae was relatively complete and tended to be closely arranged. The number of bone trabeculae was greatly increased and the number of TRAP-positive osteoclasts decreased significantly, accompanied by an upregulation of BMP-2 and leptin, and a declined activity of BALP and TRAP-5b. Conclusion The function of Sema4d on the microstructure of trabecular bone, bone formation, and repairment on the trabecular bone damage in osteoporosis rats was improved by leptin or melatonin.