Background: Periodontal disease (PD) is a risk factor for systemic diseases, including neurodegenerative diseases. The role of the local and systemic inflammation induced by PD in neuroinflammation currently remains unclear. The present study investigated the involvement of periodontal inflammation in neuroinflammation and blood–brain barrier (BBB) disruption. Methods: To induce PD in mice (c57/BL6), a ligature was placed around the second maxillary molar. Periodontal, systemic, and neuroinflammation were assessed based on the inflammatory cytokine mRNA or protein levels using qPCR and ELISA. The BBB permeability was evaluated by the mRNA levels and protein levels of tight junction-related proteins in the hippocampus using qPCR and immunofluorescence. Dextran tracing in the hippocampus was also conducted to examine the role of periodontal inflammation in BBB disruption. Results: The TNF-α, IL-1β, and IL-6 levels markedly increased in gingival tissue 1 week after ligation. The IL-6 serum levels were also increased by ligature-induced PD. In the hippocampus, the IL-1β mRNA expression levels were significantly increased by ligature-induced PD through serum IL-6. The ligature-induced PD decreased the claudin 5 expression levels in the hippocampus, and the neutralization of IL-6 restored its levels. The extravascular 3-kDa dextran levels were increased by ligature-induced PD. Conclusions: These results suggest that the periodontal inflammation-induced expression of IL-6 is related to neuroinflammation and BBB disruption in the hippocampus, ultimately leading to cognitive impairment. Periodontal therapy may protect against neurodegenerative diseases.

Three-dimensional cultured clumps of a mesenchymal stem cell (MSC)/extracellular matrix (ECM) complex (C-MSC) consists of cells and self-produced ECM. C-MSC can regulate the cellular function in vitro and induce successful bone regeneration using ECM as a cell scaffold. Potentiating the immunomodulatory capacity of C-MSCs, which can ameliorate the allo-specific immune response, may be helpful in developing beneficial “off-the-shelf” cell therapy for tissue regeneration. It is well reported that interferon (IFN)-γ stimulates the immunosuppressive properties of MSC via upregulation of the immunomodulatory enzyme IDO. Therefore, the aim of this study was to investigate the effect of IFN-γ on the immunomodulatory capacity of C-MSC in vitro and to test the bone regenerative activity of C-MSC or IFN-γ-pretreated C-MSC (C-MSCγ) xenografts in a mice calvarial defect model. Human bone marrow-derived MSCs were seeded at a density of 2.0 × 105 cells/well into 24-well plates and cultured with growth medium supplemented with 50 μg/mL L-ascorbic acid for 4 days. To obtain C-MSC, confluent cells that had formed on the cellular sheet were scratched using a micropipette tip and were then torn off. The cellular sheet was rolled to make a round clump of cells. C-MSC was stimulated with IFN-γ and IDO expression, immunosuppressive capacity, and immunophenotype were evaluated in vitro. Moreover, C-MSC or C-MSCγ was xenotransplanted into immunocompetent or immunodeficient mice calvarial defect models without artificial scaffold, respectively. IFN-γ stimulated IDO expression in C-MSC. C-MSCγ, but not C-MSC, attenuated CD3/CD28-induced T cell proliferation and its suppressive effect was reversed by an IDO inhibitor. C-MSCγ showed upregulation of HLA-DR expression, but its co-stimulatory molecule, CD86, was not detected. Xenotransplantation of C-MSCγ into immunocompetent mice calvarial defect induced bone regeneration, whereas C-MSC xenograft failed and induced T cell infiltration in the grafted area. On the other hand, both C-MSC and C-MSCγ xenotransplantation into immunodeficient mice caused bone regeneration. Xenotransplantation of C-MSCγ, which exerts immunomodulatory properties via the upregulation of IDO activity in vitro, may attenuate xenoreactive host immune response, and thereby induce bone regeneration in mice. Accordingly, C-MSCγ may constitute a promising novel allograft cell therapy for bone regeneration.

Epidemiological evidence to suggest that periodontal disease (PD) is involved in the progression of rheumatoid arthritis (RA) is increasing. The complement system plays a critical role in immune responses. C5a has been implicated in chronic inflammatory diseases, including PD and RA. Porphyromonas gingivalis is the major causative bacteria of PD and can produce C5a. Therefore, it is hypothesized that P. gingivalis infection is involved in the progression of RA by elevating C5a levels. In the present study, P. gingivalis–infected RA model mice were established to investigate the involvement of C5a. SKG mice orally infected with P. gingivalis were immunized with intraperitoneal injection of laminarin (LA) to induce arthritis. Arthritis development was assessed by arthritis score (AS), bone destruction on the talus, histology, and serum markers of RA. In order to investigate the effects of serum C5a on bone destruction, osteoclast differentiation of bone marrow mononuclear cells was examined by using serum samples from each group of mice. The relationship between C5a levels and antibody titers to periodontal pathogens in patients with RA was investigated by enzyme-linked immunosorbent assay. P. gingivalis oral infection increased AS, infiltration of inflammatory cells, bone destruction on the talus, and serum markers of RA in mice immunized with LA. The addition of serum from LA-injected mice with the P. gingivalis oral infection promoted osteoclast differentiation, and the addition of a neutralization antibody against C5a suppressed osteoclast differentiation. C5a levels of serum in RA patients with positive P. gingivalis antibody were elevated compared with those in RA patients with negative P. gingivalis antibody. These results suggest that P. gingivalis infection enhances the progression of RA via C5a.

Background: Transplantation of bone marrow mesenchymal stem cells (MSCs) is believed to be a new modality for periodontal tissue regeneration. However, little is known about the factors that influence the functions of the transplanted MSCs. Periodontal ligament cells may be implicated in regulating MSC functions.Methods: To examine the effect of humoral factors (HFs) produced by human periodontal ligament (HPL) cells on human MSC (hMSC) gene expression, hMSCs were cocultured separately with HPL cells. The gene expression of the hMSCs was analyzed by microarray. Moreover, the effect of conditioned medium (CM) from cultures of HPL cells (CM‐HPL cells) on the proliferation and mineralizing capacity of hMSCs was examined.Results: Thirty‐five genes whose expressions were upregulated more than two‐fold and 32 genes whose expressions were downregulated more than two‐fold were identified in hMSCs cocultured separately with HPL cells. CM‐HPL cells prevented calcification in hMSCs cultured with bone morphogenetic protein‐2 but not dexamethasone. CM‐HPL cells stimulated cell proliferation in hMSCs, whereas CM from culture of human osteoblasts did not influence the proliferation.Conclusions: To the best of our knowledge, this is the first study on the global gene expression of MSCs cocultured with periodontal ligament cells. A particular humoral factor released from periodontal ligament cells is suggested to affect differentiation and proliferation in MSCs.