BACKGROUND: Recent studies have indicated an association between periodontitis and atrial fibrillation (AF), although the underlying mechanisms remain unclear. Porphyromonas gingivalis (P ginigivalis ) is a causative agent of periodontal disease and is highly pathogenic. This study focused on P gingivalis and aimed to investigate the relationship among periodontitis, atrial translocation of P gingivalis , and atrial fibrosis and AF. METHODS: An experiment was conducted using P gingivalis –infected C57BL/6J mice, in which P gingivalis was inoculated into the pulp of the molars. Immunohistochemistry was used to visualize the localization of P gingivalis , and loop-mediated isothermal amplification was employed to detect P gingivalis DNA in the left atrium. AF inducibility was examined by intracardiac stimulation. Moreover, left atrial appendage specimens were obtained from 68 patients with AF. A periodontal examination was conducted before the surgery, and the periodontal epithelial surface area and periodontal inflamed surface area, which are quantitative indices used to determine the clinical severity of periodontitis, were measured. The bacterial number of P gingivalis in human atrial tissue was analyzed via quantitative polymerase chain reaction. Atrial fibrosis was assessed using Azan-Mallory staining. RESULTS: The translocation path of P gingivalis from the dental granuloma to the left atrium via the circulatory system was demonstrated by immunohistochemistry and loop-mediated isothermal amplification in P gingivalis –infected mice, which showed a higher degree of atrial fibrosis (21.9% versus 16.3%; P =0.0003) and a higher AF inducibility (30.0% versus 5.0%; P =0.04) than the control mice. Upregulation of galectin-3 and transforming growth factor-beta 1 in the left atrium was observed in P gingivalis –infected mice. Moreover, immunohistochemistry revealed that P gingivalis was also present in human atrial tissue. The number of P gingivalis in the human atrial tissue was positively correlated with periodontal epithelial surface area (ρ=0.35; P =0.004), periodontal inflamed surface area (ρ=0.52, P <0.0001), and the degree of atrial fibrosis (ρ=0.38; P =0.002). CONCLUSIONS: P gingivalis translocation to the left atrium correlates with the clinical severity of periodontitis, which may exacerbate atrial fibrosis and AF. Atrial translocation of P gingivalis is a potential pathway explaining the causal relationship between periodontitis and AF.

Unexplained cardiac arrest (UCA) with documented ventricular fibrillation (VF) is a major cause of sudden cardiac death. Abnormal sympathetic innervations have been shown to be a trigger of ventricular fibrillation. Further, adequate expression of SEMA3A was reported to be critical for normal patterning of cardiac sympathetic innervation. We investigated the relevance of the semaphorin 3A (SEMA3A) gene located at chromosome 5 in the etiology of UCA. Eighty-three Japanese patients diagnosed with UCA and 2,958 healthy controls from two different geographic regions in Japan were enrolled. A nonsynonymous polymorphism (I334V, rs138694505A>G) in exon 10 of the SEMA3A gene identified through resequencing was significantly associated with UCA (combined P = 0.0004, OR 3.08, 95%CI 1.67–5.7). Overall, 15.7% of UCA patients carried the risk genotype G, whereas only 5.6% did in controls. In patients with SEMA3A^I334V, VF predominantly occurred at rest during the night. They showed sinus bradycardia, and their RR intervals on the 12-lead electrocardiography tended to be longer than those in patients without SEMA3A^I334V (1031±111 ms versus 932±182 ms, P = 0.039). Immunofluorescence staining of cardiac biopsy specimens revealed that sympathetic nerves, which are absent in the subendocardial layer in normal hearts, extended to the subendocardial layer only in patients with SEMA3A^I334V. Functional analyses revealed that the axon-repelling and axon-collapsing activities of mutant SEMA3A^I334V genes were significantly weaker than those of wild-type SEMA3A genes. A high incidence of SEMA3A^I334V in UCA patients and inappropriate innervation patterning in their hearts implicate involvement of the SEMA3A gene in the pathogenesis of UCA. Unexplained cardiac arrest with documented ventricular fibrillation (UCA) is defined as spontaneous ventricular fibrillation (VF) that is not associated with known structural or electrical heart diseases and is one of the major causes of sudden cardiac death. Identification of the genes responsible for UCA may further increase our understanding of mechanisms of UCA and facilitate more accurate diagnosis and preventive treatment, especially in asymptomatic disease-carrying relatives of the patient. However, molecular mechanisms of UCA have not been fully clarified due to the high mortality rate and difficulty of diagnosis. In this study, UCA patients are shown to have a high incidence of a polymorphism in the Semaphorin 3A gene (rs138694505, SEMA3A^I334V). The result confirms previous reports that the abnormal sympathetic innervation is a trigger of UCA because SEMA3A is crucial for the establishment of normal innervation patterns in the heart. Furthermore, experimental data presented here indicate that SEMA3A^I334V disrupts the SEMA3A function and impairs appropriate innervation patterning. Finally, the study suggests that SEMA3A^I334V is a risk factor for human UCA and contributes to the etiology of UCA.