Association between periodontal disease and inflammatory arthritis reveals modulatory functions by melanocortin receptor type 3.

Because there is clinical evidence for an association between periodontal disease and rheumatoid arthritis, it is important to develop suitable experimental models to explore pathogenic mechanisms and therapeutic opportunities. The K/BxN serum model of inflammatory arthritis was applied using distinct protocols, and modulation of joint disruption afforded by dexamethasone and calcitonin was established in comparison to the melanocortin (MC) receptor agonist DTrp(8)-γ-melanocyte stimulating hormone (MSH; DTrp). Wild-type and MC receptor type 3 (MC3)-null mice of different ages were also used. There was significant association between severity of joint disease, induced with distinct protocols and volumes of the arthritogenic K/BxN serum, and periodontal bone damage. Therapeutic treatment with 10 µg dexamethasone, 30 ng elcatonin, and 20 µg DTrp per mouse revealed unique and distinctive pharmacological properties, with only DTrp protecting both joint and periodontal tissue. Further analyses in nonarthritic animals revealed higher susceptibility to periodontal bone loss in Mc3r(-/-) compared with wild-type mice, with significant exacerbation at 14 weeks of age. These data reveal novel protective properties of endogenous MC3 on periodontal status in health and disease and indicate that MC3 activation could lead to the development of a new genus of anti-arthritic bone-sparing therapeutics.

Low-abundance biofilm species orchestrates inflammatory periodontal disease through the commensal microbiota and complement.

Porphyromonas gingivalis is a low-abundance oral anaerobic bacterium implicated in periodontitis, a polymicrobial inflammatory disease, and the associated systemic conditions. However, the mechanism by which P. gingivalis contributes to inflammation and disease has remained elusive. Here we show that P. gingivalis, at very low colonization levels, triggers changes to the amount and composition of the oral commensal microbiota leading to inflammatory periodontal bone loss. The commensal microbiota and complement were both required for P. gingivalis-induced bone loss, as germ-free mice or conventionally raised C3a and C5a receptor-deficient mice did not develop bone loss after inoculation with P. gingivalis. These findings demonstrate that a single, low-abundance species can disrupt host-microbial homeostasis to cause inflammatory disease. The identification and targeting of similar low-abundance pathogens with community-wide impact may be important for treating inflammatory diseases of polymicrobial etiology.

Nuclear targeting of Porphyromonas gingivalis W50 protease in epithelial cells.

Porphyromonas gingivalis is an important pathogen associated with destructive periodontal disease and is able to invade the epithelial cell barrier. Its cysteine proteases are recognized as major virulence factors, and in this study, we examined the interaction of the arginine-specific protease with epithelial cells in culture. Three cell lines (KB, HeLa, and SCC4) were incubated with strain W50 culture supernatant; stained with monoclonal antibody 1A1, which recognizes an epitope on the adhesin (beta) component of the cysteine protease-adhesin (alpha/beta) heterodimer; and viewed using immunofluorescence microscopy. Within 1 h, the protease traversed the plasma membrane and was localized around the nucleus before becoming concentrated in the cytoplasm after 24 to 48 h. In contrast, the purified arginine-specific heterodimeric protease (HRgpA) rapidly entered the nucleus within 15 to 30 min. This nuclear targeting (i) was seen with active and Nalpha-p-tosyl-L-lysine chloromethyl ketone (TLCK)-inactivated HRgpA, indicating it was independent of the proteolytic activity; (ii) occurred at both 4 and 37 degrees C; and (iii) failed to occur with the monomeric protease (RgpA(cat)), indicating the importance of the adhesin chain of the HRgpA protease to this process. Rapid cell entry was also observed with recombinant catalytic (alpha) and adhesin (beta) chains, with the latter again targeting the nuclear area. After 48 h of incubation with HRgpA, significant dose-dependent stimulation of metabolic activity was observed (measured by reduction of 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide), and a doubling of mitotic activity combined with the presence of apoptotic cells indicated that HRgpA may interfere with cell cycle control mechanisms. These effects were seen with both active and TLCK-inactivated protease, confirming that they were not dependent on proteolytic activity, and thus provide new insights into the functioning of this P. gingivalis protease.