MyD88 is essential for alveolar bone loss induced by Aggregatibacter actinomycetemcomitans lipopolysaccharide in mice

Abstract

Aggregatibacter actinomycetemcomitans is a Gram-negative bacteria highly associated with localized aggressive periodontitis. The recognition of microbial factors, such as lipopolysaccharide from A. actinomycetemcomitans ((Aa)LPS), in the oral environment is made mainly by surface receptors known as Toll-like receptors (TLR). TLR4 is the major LPS receptor. This interaction leads to the production of inflammatory cytokines by myeloid differentiation primary-response protein 88 (MyD88) -dependent and -independent pathways, which may involve the adaptor Toll/interleukin-1 receptor-domain-containing adaptor inducing interferon-β (TRIF). The aim of this study was to assess the involvement of MyD88 in alveolar bone loss induced by (Aa)LPS in mice. C57BL6/J wild-type (WT) mice, MyD88, TRIF or TRIF/MyD88 knockout mice received 10 injections of Aa LPS strain FDC Y4 (5 μg in 3 μl), in the palatal gingival tissue of the right first molar, every 48 h. Phosphate-buffered saline was injected in the opposite side and used as control. Animals were sacrificed 24 h after the 10th injection and the maxillae were removed for macroscopic and biochemical analyses. The injections of Aa LPS induced significant alveolar bone loss in WT mice. In the absence of MyD88 or TRIF/MyD88 no bone loss induced by (Aa)LPS was observed. In contrast, responses in TRIF(-/-) mice were similar to those in WT mice. Diminished bone loss in the absence of MyD88 was associated with fewer TRAP-positive cells and increased expression of osteoblast markers, RUNX2 and osteopontin. There was also reduced tumor necrosis factor-α production in MyD88(-/-) mice. There was less osteoclast differentiation of hematopoietic bone marrow cells from MyD88(-/-) mice after (Aa)LPS stimulation. Hence, the signaling through MyD88 is pivotal for (Aa)LPS-induced osteoclast formation and alveolar bone loss.

Apoptosis-associated uncoupling of bone formation and resorption in osteomyelitis

“…For example, the site of infection in animal models of S. aureus osteomyelitis contains high numbers of macrophages and osteoclasts (Wiggers et al, 2011), and S. aureus surface-associated proteins can stimulate osteoclast formation and activity (Meghji et al, 1998; Lau et al, 2006). Similarly, systemically administered lipopolysaccharide (LPS) or local application of LPS derived from Aggregatibacter actinomycetemcomitans can reduce bone volume (Ochi et al, 2010; Madeira et al, 2013) and macrophages and osteoclast-like cells respond to this Gram-negative bacterial product by releasing cytokines and nitric oxide (NO) (Wiggers et al, 2011). However, it is unclear whether such effects are due to a direct action on osteoclasts and/or their progenitors, or are secondary to the production of other mediators, such as inflammatory cytokines, which modulate osteoclast formation and activity (Meghji et al, 1998).…”

Enhanced Calvarial Bone Healing in CD11c-TLR4−/− and MyD88−/− Mice

“…20,21 Despite these identified interactions, the involvement of MyD88 signaling in a noncompromised fracture healing process has not been investigated. In this study, we observed the calvarial bone healing process in TLR2 −/− , TLR4 −/− , MyD88 −/− , and TRIF −/− mice.…”

Platelet-Activating Factor Receptor Blockade Ameliorates Aggregatibacter actinomycetemcomitans-Induced Periodontal Disease in Mice

“…One study indicates that the Toll-like receptor 4 (TLR4)/MyD88-dependent pathway is responsible for LPS-induced lyso-PAF-acetyltransferase activation (33). Accordingly, we have previously shown that the signaling due to A. actinomycetemcomitans LPS recognition is MyD88 dependent (29). Further, a marked reduction was detected in the severity of experimental alveolar bone loss induced by A. actinomycetemcomitans LPS injection or oral inoculation of A. actinomycetemcomitans in the absence of the PAF receptor, suggesting an important role of PAF and its receptor in the pathogenesis of experimental PD.…”

“…1A). It has already been reported that injection of A. actinomycetemcomitans LPS into periodontal tissues induces alveolar bone loss in mice (29); thus, this study assessed whether the absence of PAFR could influence alveolar bone loss after A. actinomycetemcomitans LPS injection. Injection of A. actinomycetemcomitans LPS resulted in significant alveolar bone loss in WT mice.…”