Development of non-traumatic osteonecrosis of the femoral head requires toll-like receptor 7 and 9 stimulations and is boosted by repression on nuclear factor kappa B in rats

Okazaki, Shunichiro; Nagoya, Satoshi; Matsumoto, Hiroshi; Mizuo, Keisuke; Sasaki, Mikito; Watanabe, Satoshi; Yamashita, Toshihiko; Inoue, Hiromasa

and Imiquimod þ BAY11 þ MPSL (n ¼ 8, 5 mg/kg BAY11-7082) rats. BAY11-7082 administration did not alter the relative activity of NF-kB at 1 day. However, the activity of IRF7 was repressed significantly at 1 day in rats administered BAY11-7082 ( Figure 4 ; Imiquimod þ MPSL vs Imiquimod þ BAY11 þ MPSL, 100 ± 9.9 vs 58.9 ± 4.1; P ¼ 0.012). 25 conducted a nationwide epidemiologic survey in Japan and reported a high frequency of SLE, nephrotic syndrome, polymyositis/dermatomyositis, bronchial asthma, and thrombocytopenic purpura, as the underlying disease in patients with corticosteroid-induced ONFH. Recently, it was reported that innate immune signaling via TLR7 and TLR9 contributed to the pathogenesis of SLE, 9 TLR2, TLR3 and TLR4 signaling contributed to the pathogenesis of nephrotic syndrome, 10 TLR3, and TLR7 signaling contributed to the pathogenesis of polymyositis and dermatomyositis, 11 TLR4 signaling contributed to the pathogenesis of bronchial asthma, 12 and TLR4 and TLR7 signaling contributed to the pathogenesis of thrombocytopenic purpura. 13 These reports showed that innate immune signaling via TLRs contributes to the pathogenesis of underlying diseases in patients with corticosteroid-induced ONFH. We previously reported that TLR stimulation induces osteonecrosis S Okazaki et al corticosteroid treatment after a lipopolysaccharide (LPS), a TLR 4 ligand, injection induces ONFH in Wistar rats, and suggested that the TLR4 signaling pathway may have a role in the pathogenesis of ONFH in rats. [3] [4] [5] In the present study, we showed that the administration of TLR7 and TLR9 ligands in combination with MPSL treatment resulted in the development of ONFH in rats. In contrast, it was reported that mega-dose corticosteroid therapy, recommended under the national acute spinal cord injury protocol for spinal cord injury, resulting from trauma did not induce ONFH. 2 In the present study, ONFH was not observed in the Saline þ MPSL group, in which the rats did not receive the TLR ligands, indicating that corticosteroids alone failed to induce ONFH in healthy animals. There are several reports on osteonecrosis animal models using corticosteroid administration alone. Corticosteroid administration alone led to the development of ONFH in spontaneously hypertensive rats (SHRs). 26 However, this treatment in the SHRs model is different from corticosteroid administration in healthy animals because of a genetic abnormality in the background of the SHRs. 27 Further, it was reported that corticosteroids alone led to the development of ONFH in Leghorn chickens. 28 Histopathological examination of specimens in this model showed that the subchondral bone trabeculae in the femoral head had disappeared. 28 The diminution of the bone trabeculae was similar in appearance to micro-CT images of an osteoporosis animal model, 29 but it was not clear whether it resulted from osteonecrosis. In addition, Yamamoto et al 30 reported an osteonecrosis rabbit model in 1997. A characteristic of the rabbit model was that osteonecrosis developed in the metaphysis but not in the femoral head after the treatment of healthy rabbits with corticosteroids. On the other hand, Yamamoto et al 30 also reported that corticosteroid treatment after LPS administration led to the development of osteonecrosis in the femoral head and the metaphysis in rabbits in 1995. 22 These reports indicate that the administration of TLR ligands has a crucial role in the development of femoral head oste