Ovariectomy-induced bone loss in TNFα and IL6 gene knockout mice is regulated by different mechanisms.

We examined the effects of tumor necrosis factor-α (TNFα) and interleukin-6 (IL6) gene knockout in preserving the bone loss induced by ovariectomy (OVX) and the mechanisms involved in bone metabolism. Twenty female wild-type (WT), TNFα -knockout (TNFα ^-/- ) or IL6- knockout (IL6 ^-/- ) mice aged 12 weeks were sham-operated (SHAM) or subjected to OVX and killed after 4 weeks. Bone mass and skeletal microarchitecture were determined using micro-CT. Bone marrow stromal cells (BMSCs) from all three groups (WT, TNFα ^-/- and IL6 ^-/- ) were induced to differentiate into osteoblasts or osteoclasts and treated with 17-β-estradiol. Bone metabolism was assessed by histological analysis, serum analyses and qRT-PCR. OVX successfully induced a high turnover in all mice, but a repair effect was observed in TNFα ^-/- and IL6 ^-/- mice. The ratio of femoral trabecular bone volume to tissue volume, trabecular number and trabecular thickness were significantly decreased in WT mice subjected to OVX, but increased in TNFα ^-/- mice (1.62, 1.34, 0.27-fold respectively; P  < 0.01) and IL6 ^-/- mice (1.34, 0.80, 0.22-fold respectively; P  < 0.01). Furthermore, we observed a 29.6% increase in the trabecular number in TNFα ^-/- mice when compared to the IL6 ^-/- mice. Both, TNFα ^-/- and IL6 ^-/- BMSCs exhibited decreased numbers of TRAP-positive cells and an increase in ALP-positive cells, with or without E2 treatment ( P  < 0.05). While the knockout of TNFα or IL6 significantly upregulated mRNA expressions of osteoblast-related genes ( Runx2 and Col1a1 ) and downregulated osteoclast-related mRNA for TRAP , MMP9 and CTSK in vivo and in vitro , TNFα knockout appeared to have roles beyond IL6 knockout in upregulating Col1a1 mRNA expression and downregulating mRNA expressions of WNT-related genes ( DKK1 and Sost ) and TNF-related activation-induced genes ( TRAF6 ). TNFα seemed to be more potentially invasive in inhibiting bone formation and enhancing TRAF6-mediated osteoclastogenesis than IL6, implying that the regulatory mechanisms of TNFα and IL6 in bone metabolism may be different.
(© 2018 Society for Endocrinology.)