Experimental arthritis and Porphyromonas gingivalis administration synergistically decrease bone regeneration in femoral cortical defects

Imbalanced EphB4/EphrinB2 Signaling Modulates Bone Resorption in Periodontitis Induced by Porphyromonas gingivalis

Periodontitis, a chronic infectious disease in periodontal tissues, is characterized by an imbalance of alveolar bone resorption and remodeling, which eventually results in tooth loosening and even tooth loss. The etiology of periodontitis is polymicrobial synergy and dysbiosis, in which Porphyromonas gingivalis (P. gingivalis) is one of the primary pathogens responsible for periodontitis progression. The interplay of EphrinB2/EphB4 is crucial for osteoblast-osteoclast communication during bone remodeling and healing. This study investigates the mechanism of EphB4/EphrinB2 transduction modulating osteogenesis inhibition and bone resorption in periodontitis induced by P. gingivalis. An in vivo model of chronic periodontitis provoked by P. gingivalis was constructed, the inflammation and bone resorption were evaluated. The expression of EphB4 and EphrinB2 proteins in periodontal tissues was detected, which was also evaluated, respectively, in osteoblasts and osteoclasts infected with P. gingivalis in vitro. Then, a simulated coculture model of osteoblasts and osteoclasts was established to activate the forward and reverse pathways of EphB4/EphrinB2 with P. gingivalis infection. This study showed that P. gingivalis infection promoted alveolar bone resorption in rats and enhanced EphB4 and EphrinB2 expression in periodontal tissues. EphB4 and molecules associated with osteogenesis in osteoblasts infected with P. gingivalis were inhibited, while EphrinB2 and osteoclast differentiation-related markers in osteoclasts were activated. In conclusion, this study suggested that EphB4/EphrinB2 proteins were involved in alveolar bone remodeling in the process of periodontitis induced by P. gingivalis infection. Moreover, attenuated EphB4/EphrinB2 with P. gingivalis infection weakened osteoblast activity and enhanced osteoclast activity.

DNA methylation-mediated Rbpjk suppression protects against fracture nonunion caused by systemic inflammation

Challenging skeletal repairs are frequently seen in patients experiencing systemic inflammation. To tackle the complexity and heterogeneity of the skeletal repair process, we performed single-cell RNA sequencing and revealed that progenitor cells were one of the major lineages responsive to elevated inflammation and this response adversely affected progenitor differentiation by upregulation of Rbpjk in fracture nonunion. We then validated the interplay between inflammation (via constitutive activation of Ikk2, Ikk2ca) and Rbpjk specifically in progenitors by using genetic animal models. Focusing on epigenetic regulation, we identified Rbpjk as a direct target of Dnmt3b. Mechanistically, inflammation decreased Dnmt3b expression in progenitor cells, consequently leading to Rbpjk upregulation via hypomethylation within its promoter region. We also showed that Dnmt3b loss-of-function mice phenotypically recapitulated the fracture repair defects observed in Ikk2ca-transgenic mice, whereas Dnmt3b-transgenic mice alleviated fracture repair defects induced by Ikk2ca. Moreover, Rbpjk ablation restored fracture repair in both Ikk2ca mice and Dnmt3b loss-of-function mice. Altogether, this work elucidates a common mechanism involving a NF-κB/Dnmt3b/Rbpjk axis within the context of inflamed bone regeneration. Building on this mechanistic insight, we applied local treatment with epigenetically modified progenitor cells in a previously established mouse model of inflammation-mediated fracture nonunion and showed a functional restoration of bone regeneration under inflammatory conditions through an increase in progenitor differentiation potential.

Porphyromonas gingivalis Induces Bisphosphonate-Related Osteonecrosis of the Femur in Mice

One of the most prominent characteristics of bisphosphonate-related osteonecrosis of the jaw(BRONJ) is its site-specificity. Osteonecrosis tends to occur specifically in maxillofacial bones, in spite of a systemic administration of the medicine. Previous studies suggested rich blood supply and fast bone turnover might be reasons for BRONJ. Yet, a sound scientific basis explaining its occurrence is still lacking. The present study aimed to explore the role of Porphyromonas gingivalis (P. gingivalis), an important oral pathogen, on the site-specificity of bisphosphonate-induced osteonecrosis and to elucidate its underlying mechanism. Mice were intraperitoneally injected with zoledronic acid (ZA) or saline for 3 weeks. In the third week, the right mandibular first molars were extracted and circular bone defects with a diameter of 1 mm were created in right femurs. After the operation, drug administration was continued, and P. gingivalis suspension was applied to the oral cavities and femur defects. The mice were killed after four or eight weeks postoperatively. The right mandibles and femurs were harvested for micro-CT and histological analyses. A poor healing of bone defects of both jaws and femurs was noted in mice injected with both ZA and P. gingivalis. Micro-CT analysis showed a decreased bone volume, and histological staining showed an increased number of empty osteocyte lacunae, a decreased collagen regeneration, an increased inflammatory infiltration and a decreased number of osteoclasts. In addition, the left femurs were collected for isolation of osteoclast precursors (OCPs). The osteoclastogenesis potential of OCPs was analyzed in vitro. OCPs extracted from mice of ZA-treated groups were shown to have a lower osteoclast differentiation potential and the expression level of related genes and proteins was declined. In conclusion, we established a mouse model of bisphosphonate-related osteonecrosis of both the jaw and femur. P. gingivalis could inhibit the healing of femur defects under the administration of ZA. These findings suggest that P. gingivalis in the oral cavity might be one of the steering compounds for BRONJ to occur.

Dysbiotic relationship between arthritis and the oral-gut microbiome. A critical review

Arthritis and prosthetic joint infections (PJIs) overall are associated with reduced quality of life and limited work capacity. Multiple, overlapping factors contribute to these conditions. Some investigations have suggested a dysbiotic association between the oral-gut microbiome and pathogenesis of arthritis and PJIs. A better understanding of the role of the oral-gut microbiota in arthritis and PJI pathophysiology can shed light into how its disequilibrium can discharge a pro-inflammatory response, and impact the health of patients susceptible to arthritis or with established joint disease. A review of published in vivo and clinical data suggested that alterations in oral and gut microbiota can lead to a disturbance of immunoregulatory properties, and may be associated with joint infections and arthritis. This review brings new insights into the current status of the evidence on the potential molecules and inflammatory biomarkers disrupted by an oral-gut microbial dysbiosis. Normal commensals and pathogenic oral and gut microflora homeostasis are important not only to prevent infections per se but also its potential progression. Further experiments, especially controlled clinical trials, are needed to ascertain how microbiome manipulation and other microbiota-directed approaches can help control inflammation and effectively prevent and treat arthritic diseases. Additionally, studies on the effects of the long-term oral diseases, such as chronic periodontitis, on arthritis and PJIs need to be conducted.

Targeting angiogenesis for fracture nonunion treatment in inflammatory disease

Atrophic fracture nonunion poses a significant clinical problem with limited therapeutic interventions. In this study, we developed a unique nonunion model with high clinical relevance using serum transfer-induced rheumatoid arthritis (RA). Arthritic mice displayed fracture nonunion with the absence of fracture callus, diminished angiogenesis and fibrotic scar tissue formation leading to the failure of biomechanical properties, representing the major manifestations of atrophic nonunion in the clinic. Mechanistically, we demonstrated that the angiogenesis defect observed in RA mice was due to the downregulation of SPP1 and CXCL12 in chondrocytes, as evidenced by the restoration of angiogenesis upon SPP1 and CXCL12 treatment in vitro. In this regard, we developed a biodegradable scaffold loaded with SPP1 and CXCL12, which displayed a beneficial effect on angiogenesis and fracture repair in mice despite the presence of inflammation. Hence, these findings strongly suggest that the sustained release of SPP1 and CXCL12 represents an effective therapeutic approach to treat impaired angiogenesis and fracture nonunion under inflammatory conditions.

Effect of ovariectomy induced osteoporosis on metaphysis and diaphysis repair process

The fracture repair process is known to be delayed in postmenopausal women, under estrogen-deficient status. Osteoporotic fracture mainly occurs in the metaphyseal region of the long bone; however, most studies on fracture healing have focused on the diaphyseal region. In this study, we compared the repair process between metaphysis and diaphysis of ovariectomized (OVX) and Sham mice, and analyzed the effects of short-term estrogen administration in OVX mice. Mice were divided into four experimental groups, including Sham, OVX, OVX + vehicle, and OVX + 17β-estradiol (E2). Bone apertures were formed in the tibial metaphysis and diaphysis. The samples were collected and examined by micro-computed tomography, and using histological, histochemical, and immunohistochemical analysis at different time points after the surgery. The cartilaginous callus was formed at the diaphysis site of both the groups, which was sequentially replaced by bone on the periosteum side. Medullary callus was formed in all the groups; however, the volume of the callus in OVX mice was significantly lesser (˜30%) than that in Sham mice. Furthermore, in the metaphysis, no differences were observed in the medullary callus and bone mineral density between the two groups from day 21 to 28. The diaphysis of OVX group was not completely repaired even by day 28. In both the sites of OVX mice, ALP activity and disappearance of Gr-1 positive cells were delayed compared to that of Sham. Estrogen administration improved medullary callus formation in the diaphysis, however not in the metaphysis. The effect of ovariectomy on the repair process in diaphysis was greater than that in metaphysis. Our findings clarify the differences between the metaphysis and diaphysis repair process using OVX mouse model and suggest that the estrogen sensitivities differ between the sites during the bone repair process.

Obesity-Related Gut Microbiota Aggravates Alveolar Bone Destruction in Experimental Periodontitis through Elevation of Uric Acid

Obesity is a risk factor for periodontal disease (PD). Initiation and progression of PD are modulated by complex interactions between oral dysbiosis and host responses. Although obesity is associated with increased susceptibility to bacterial infection, the detailed mechanisms that connect obesity and susceptibility to PD remain elusive. Using fecal microbiota transplantation and a ligature-induced PD model, we demonstrated that gut dysbiosis-associated metabolites from high-fat diet (HFD)-fed mice worsen alveolar bone destruction. Fecal metabolomics revealed elevated purine degradation pathway activity in HFD-fed mice, and recipient mice had elevated levels of serum uric acid upon PD induction. Furthermore, PD induction caused more severe bone destruction in hyperuricemic than normouricemic mice, and the worsened bone destruction was completely abrogated by allopurinol, a xanthine oxidase inhibitor. Thus, obesity increases the risk of PD by increasing production of uric acid mediated by gut dysbiosis.

Porphyromonas gingivalis, a Long-Range Pathogen: Systemic Impact and Therapeutic Implications

Periodontitis is an inflammatory disease associated with a dysbiosis of the oral flora characterized by a chronic sustained inflammation leading to destruction of tooth-supporting tissues. Over the last decade, an association between periodontitis and systemic disorders such as cardiovascular diseases, rheumatoid arthritis and obesity has been demonstrated. The role of periodontal pathogens, notably Porphyromonas gingivalis (P. gingivalis), in the onset or exacerbation of systemic diseases has been proposed. P. gingivalis expresses several virulence factors that promote its survival, spreading, and sustaining systemic inflammation. Recently, the impact of periodontitis on gut dysbiosis has also been suggested as a potential mechanism underlying the systemic influence of periodontitis. New therapeutic strategies for periodontitis and other dysbiotic conditions, including the use of beneficial microbes to restore healthy microbial flora, may pave the way to improved therapeutic outcomes and more thorough patient management.