Osteocytes directly regulate osteolysis via MYD88 signaling in bacterial bone infection

Abstract

The impact of bone cell activation on bacterially-induced osteolysis remains elusive. Here, we show that matrix-embedded osteocytes stimulated with bacterial pathogen-associated molecular patterns (PAMPs) directly drive bone resorption through an MYD88-regulated signaling pathway. Mice lacking MYD88, primarily in osteocytes, protect against osteolysis caused by calvarial injections of bacterial PAMPs and resist alveolar bone resorption induced by oral Porphyromonas gingivalis (Pg) infection. In contrast, mice with targeted MYD88 restoration in osteocytes exhibit osteolysis with inflammatory cell infiltration. In vitro, bacterial PAMPs induce significantly higher expression of the cytokine RANKL in osteocytes than osteoblasts. Mechanistically, activation of the osteocyte MYD88 pathway up-regulates RANKL by increasing binding of the transcription factors CREB and STAT3 to Rankl enhancers and by suppressing K48-ubiquitination of CREB/CREB binding protein and STAT3. Systemic administration of an MYD88 inhibitor prevents jawbone loss in Pg-driven periodontitis. These findings reveal that osteocytes directly regulate inflammatory osteolysis in bone infection, suggesting that MYD88 and downstream RANKL regulators in osteocytes are therapeutic targets for osteolysis in periodontitis and osteomyelitis.

Osteocyte RANKL Drives Bone Resorption in Mouse Ligature-Induced Periodontitis

“…S12D, E for female data). Considering our recent finding that Dmp1-Cre deletes RANKL predominantly in osteocytes rather than in osteoblasts, and the fact that osteocytes are the most abundant cell type in bone, (28,48) these data suggest that osteocytes, rather than osteoblasts and PDL cells, are a major source of RANKL in LIP to regulate bone resorption.…”

“…The MLO-Y4, IDG-SW3, and osteoblast lineage cells from mouse calvaria were used. (28,36,37) MLO-Y4 cells were cultured on plates coated with rat tail type I collagen using α-MEM supplemented with 2.5% fetal bovine serum (FBS), 2.5% calf serum, and 1% penicillin/streptomycin. IDG-SW3 cells were cultured on plates coated with rat tail type I collagen using α-MEM supplemented with 10% FBS, 50 U/mL interferon-gamma, and 1% penicillin/ streptomycin at 33 C until they become confluent completely.…”

“…(48) They are the most abundant cells in the bone and are known to be a major source of RANKL in physiological bone remodeling as well as in Pg-induced periodontitis in mice. (20,23,24,28,49) However, despite these facts, it remains unknown whether osteocytes provide RANKL for osteoclast formation in LIP. To study the effect of osteocyte RANKL in LIP, Dmp1-Cre;Rankl fl/fl mice lacking RANKL in osteocytes and mature osteoblasts, but predominantly in osteocytes, were generated.…”

“…(12,18,19) In particular, osteocyte RANKL has been shown to play a critical role in bone resorption under physiological and pathological conditions. (20)(21)(22)(23)(24)(25)(26)(27)(28) However, the impact of osteocyte RANKL on bone resorption in LIP remains unknown. Furthermore, although a variety of bacterial pathogen-associated molecular patterns (PAMPs) have been shown to induce RANKL expression in osteocytic cells, (28,29) the impact of nucleotidebinding oligomerization domain containing 1 (NOD1)-mediated signaling pathways, which is known to regulate LIP-induced alveolar bone osteolysis, (30) on osteocyte RANKL expression remains uninvestigated.…”

Posttraumatic Osteomyelitis Risks Associated with NLRP3 Gene Polymorphisms in the Chinese Population

“…NLRP3 rs35829419 and rs4612666 were not statistically different from PTOM in genotype distribution, mutant allele frequency, the homozygous/heterozygous model, or IL-6 and TNF-α levels, indicating that rs35829419 and rs4612666 may not be associated with the occurrence and development of PTOM. In the remaining seven genes, some studies have found that STAT3 (rs4796793, rs744166, rs1026916, rs2293152, rs1053004) is involved in the regulation of inflammatory osteolysis in bone infection [ 27 ], and the level of CASP-1 (rs501192, rs580253, rs556205, rs530537) in peripheral blood mononuclear cells of freshly isolated multifocal osteomyelitis patients in active and remission stages is significantly higher than that of healthy controls [ 28 ], suggesting that STAT3 and CASP-1 may be the risk genes for PTOM. In our research, we did not find that ELP2 (rs1785929, rs178989547, rs1785928, rs12185396, rs681757, rs8299, rs2032206, rs559289), NFKBIA (rs696), NFKB1 (rs4648068), CARD8 (rs204321), or CD14 (rs2569190) were associated with the risk of PTOM in Chinese populations.…”