IL-15 deficiency alleviates steroid-induced osteonecrosis of the femoral head by impact osteoclasts via RANKL-RANK-OPG system

BACKGROUND: Whether IL-15 is involved in the development of steroid-induced osteonecrosis of the femoral head (ONFH) is investigated. METHODS: C57BL/6 J and l15(−/−)mice were injected with methylprednisolone to induce wide type osteonecrosis (WT ON) and IL-15 deficiency osteonecrosis (IL-15(−/−) ON). Hematoxylin-Eosin (H&E) staining and micro-computed tomography (micro-CT) scanning was used to detect the microstructure. The differentiation and formation of osteoclasts were determined with colony-forming unit-granulocyte macrophages (CFU-GM), colony-forming unit-macrophage/mononuclear (CFU-M) per tibia, and tartrate-resistant acid phosphatase (TRACP or TRAP) positive cells. Serum interleukin (IL)-15, osteocalcin, bone alkaline phosphatase (BAP), bone Gla protein (BGP), and TRACP were assayed with enzyme-linked immunosorbent assay (ELISA). The receptor activator of nuclear factor-κB (RANK), RANK ligand (RANKL), and osteoprotegerin (OPG) in the femoral heads were detected by Western blot. CD34 staining was performed to detect microvascular density. RESULTS: IL-15 secretion was increased in the femoral heads and the serum of steroid-induced ONFH mice. IL-15 deficiency may lead to up-regulated vessel remodeling, improved microstructure, and up-regulated serum osteocalcin, BAP, and BGP secretion. Both the expression of RANKL/RANK/OPG and osteoclast differentiation and formation can be down-regulated by IL-15 deficiency. CONCLUSION: IL-15 deficiency alleviates steroid-induced ONFH by impact osteoclasts via RANKL-RANK-OPG system.