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 .