Interleukin-6 deletion stimulates revascularization and new bone formation following ischemic osteonecrosis in a murine model

• Published in: Bone (New York, N.Y.) N.Y.), 2018-11, Vol.116, p.221-231
• Main Authors: Kuroyanagi, Gen, Adapala, Naga Suresh, Yamaguchi, Ryosuke, Kamiya, Nobuhiro, Deng, Zhuo, Aruwajoye, Olumide, Kutschke, Michael, Chen, Elena, Jo, Chanhee, Ren, Yinshi, Kim, Harry K.W.
• Format: Article
• Language: English
• Subjects: Animals; Avascular necrosis; Bone formation; Cells, Cultured; Disease Models, Animal; Epiphyses - diagnostic imaging; Epiphyses - pathology; Femur Head - blood supply; Femur Head - pathology; Femur Head Necrosis - diagnostic imaging; Femur Head Necrosis - pathology; Femur Head Necrosis - physiopathology; Femur Head Necrosis - surgery; Gene Deletion; Hematopoiesis; IL-6 knockout mouse; Interleukin-6; Interleukin-6 - deficiency; Interleukin-6 - genetics; Ischemia - complications; Ischemia - pathology; Ischemic osteonecrosis; Legg-Calvé-Perthes disease; Male; Mice, Inbred C57BL; Mice, Knockout; Neovascularization, Physiologic; Osteoblasts - metabolism; Osteoblasts - pathology; Osteoclasts - metabolism; Osteoclasts - pathology; Osteogenesis; Phenotype; Reproducibility of Results; X-Ray Microtomography
• ISSN: 8756-3282; 1873-2763
• DOI: 10.1016/j.bone.2018.08.011

Legg-Calvé-Perthes disease (LCPD) is a childhood form of ischemic osteonecrosis of the femoral head which can produce a permanent femoral head deformity and early osteoarthritis. The femoral head deformity results from increased bone resorption and decreased bone formation during repair and remodeling of the necrotic femoral head. A recent study showed that a pro-inflammatory cytokine, interleukin-6 (IL-6), is significantly elevated in the synovial fluid of patients with LCPD. We hypothesized that IL-6 elevation decreases bone formation during the repair process following ischemic osteonecrosis and that IL-6 depletion will increase new bone formation. To test this hypothesis, we surgically induced ischemic osteonecrosis in the wild-type (n = 29) and IL-6 knockout (KO) mice (n = 25). The animals were assessed at 48 h, 2 weeks and 4 weeks following the induction of ischemic osteonecrosis using histologic, histomorphometric and micro-CT methods. IL-6 immunohistochemistry showed high expression of IL-6 in the osteonecrotic side of the wild-type mice at 48 h and 4 weeks following ischemic osteonecrosis, but not in the IL-6 KO mice. We also confirmed an undetectable level of IL-6 expression in the primary osteoblasts of the IL-6 KO mice compared to the readily detectable level in the wild-type mice. Furthermore, we confirmed that IL-6 deletion did not affect the extent of bone necrosis in the IL-6 KO mice compared to the wild-type mice by performing histologic and terminal deoxynucleotidyl transferase mediated dUTP nick-end labeling (TUNEL) assessments at 2 weeks following the induction of ischemia. Both groups had the same extent of ischemic osteonecrosis and absence of repair at 2 weeks. At 4 weeks, the necrotic epiphyses showed a significant increase in the extent of revascularization in the IL-6 KO mice compared to the wild-type mice (p = 0.001). In addition, a significantly greater recovery of the hematopoietic bone marrow was observed in the osteonecrotic side of the IL-6 KO mice compared to the wild-type mice (p