Lack of Toll‐like receptor 4 decreases lipopolysaccharide‐induced bone resorption in C3H/HeJ mice in vivo

Introduction: Few in vivo studies have demonstrated whether Toll‐like receptor 4 (TLR4) is indispensable for lipopolysaccharide (LPS)‐induced bone resorption and little is known about the receptor activator of nuclear factor‐κB ligand (RANKL) and osteoprotegerin (OPG) expression induced by LPS under conditions of lack of TLR4. Methods: We compared bone resorption histomorphometrically in C3H/HeN and C3H/HeJ mice that were repeatedly injected with Actinobacillus actionmycetemcomitans LPS into their gingiva every 48 h. RANKL‐, interleukin‐1β‐ and OPG‐positive cells in the connective tissue were also compared immunohistochemically. Results: Bone resorption in C3H/HeJ mice in the fourth, seventh, and tenth injection groups was significantly less than that C3H/HeN mice (P < 0.05). The number of RANKL‐positive cells in C3H/HeJ mice in the 10th injection group was significantly smaller than that in C3H/HeN mice (P < 0.05). The numbers of interleukin‐1β‐positive cells in C3H/HeJ mice in the seventh and tenth injection groups were significantly decreased compared with those in C3H/HeN mice (P < 0.05). The numbers of OPG‐positive cells in C3H/HeN and C3H/HeJ mice gradually increased, but there was no significant difference between the two strains of mice. Conclusion: TLR4 is indispensable for LPS‐induced bone resorption in vivo.