Identification of key determinants in Porphyromonas gingivalis host-cell invasion assays

Alzheimer's Disease-Like Neurodegeneration in Porphyromonas gingivalis Infected Neurons with Persistent Expression of Active Gingipains

BACKGROUND

Porphyromonas gingivalis (P. gingivalis) and its gingipain virulence factors have been identified as pathogenic effectors in Alzheimer's disease (AD). In a recent study we demonstrated the presence of gingipains in over 90% of postmortem AD brains, with gingipains localizing to the cytoplasm of neurons. However, infection of neurons by P. gingivalis has not been previously reported.

OBJECTIVE

To demonstrate intraneuronal P. gingivalis and gingipain expression in vitro after infecting neurons derived from human inducible pluripotent stem cells (iPSC) with P. gingivalis for 24, 48, and 72 h.

METHODS

Infection was characterized by transmission electron microscopy, confocal microscopy, and bacterial colony forming unit assays. Gingipain expression was monitored by immunofluorescence and RT-qPCR, and protease activity monitored with activity-based probes. Neurodegenerative endpoints were assessed by immunofluorescence, western blot, and ELISA.

RESULTS

Neurons survived the initial infection and showed time dependent, infection induced cell death. P. gingivalis was found free in the cytoplasm or in lysosomes. Infected neurons displayed an accumulation of autophagic vacuoles and multivesicular bodies. Tau protein was strongly degraded, and phosphorylation increased at T231. Over time, the density of presynaptic boutons was decreased.

CONCLUSION

P. gingivalis can invade and persist in mature neurons. Infected neurons display signs of AD-like neuropathology including the accumulation of autophagic vacuoles and multivesicular bodies, cytoskeleton disruption, an increase in phospho-tau/tau ratio, and synapse loss. Infection of iPSC-derived mature neurons by P. gingivalis provides a novel model system to study the cellular mechanisms leading to AD and to investigate the potential of new therapeutic approaches.

Adhesion of anaerobic periodontal pathogens to extracellular matrix proteins

Extracellular matrix (ECM) proteins are highly abundant in the human body and can be found in various tissues, most prominently in connective tissue and basement membrane. For invasive bacterial pathogens, these structures function as physical barriers that block access to underlying tissues. The ability to bind and degrade these barriers is important for the establishment of infections and migration to other body sites. In the oral cavity, the ECM and the basement membrane (BM) are important components of the Junctional epithelium (JE) that closes the gap between the teeth surface and the mucosa. In periodontitis, the JE is breached by invading pathogenic bacteria, particularly strict anaerobic species. In periodontitis, invading microorganisms induce an unregulated and destructive host response through polymicrobial synergism and dysbiosis that attracts immune cells and contributes to the destruction of connective tissue and bone in the periodontal pocket. Colonization of the periodontal pocket is the first step to establish this infection, and binding to ECM is a major advantage in this site. Several species of strict anaerobic bacteria are implicated in acute and chronic periodontitis, and although binding to ECM proteins was studied in these species, few adhesins were identified so far, and the mechanisms involved in adhesion are largely unidentified. This review summarizes the data available on the interaction of strict anaerobic bacteria and components of the ECM.

Antimicrobial effect of photodynamic therapy using sinoporphyrin sodium and 390-400 nm light-emitting diode on Porphyromonas gingivalis in vitro

This study aims to investigate the effect of antimicrobial photodynamic therapy (a-PDT) using a novel combination of sinoporphyrin sodium (DVDMS) and light-emitting diode (LED) with a wavelength of 390-400 nm on Porphyromonas gingivalis in vitro. Absorption spectrum of DVDMS was determined by spectrometer for selecting suitable wavelength light source. The uptake of DVDMS by P. gingivalis was evaluated according to fluorescence intensity detected by a spectrometer. Then effects of DVDMS alone, 390-400 nm LED alone, and photodynamic therapy produced by 10, 20, 40, and 80 μg/mL DVDMS and 390-400 nm LED on the suspension of P. gingivalis were evaluated by counting the number of colony forming units (CFU) after incubation. In the experiment, the LED illumination time was 30, 60, 90, 120, 180, 240, and 360 s, respectively, and the corresponding energy density was 1, 2, 3, 4, 6, 8, and 12 J/cm², respectively. According to the absorption spectrum of DVDMS, the 390-400-nm light emitted by the LED was selected as the light source. The fluorescence intensity of DVDMS on P. gingivalis increased significantly at 5 min, and with the extension of time, it decreased at 30 min. DVDMS alone did not produce a significant toxicity on P. gingivalis compared with PBS (p = 0.979). While 390-400 nm LED alone had a certain bactericidal effect on P. gingivalis, the bactericidal effect was more obvious as the light dose increased (p < 0.001). The effect of a-PDT produced by 20, 40, and 80 μg/mL DVDMS and 390-400 nm LED were significantly better than that of 390-400 nm LED alone (p < 0.05). Both DVDMS concentration and light dose could enchance the bactericidal effect. The strongest photo-killing effect was generated by 80 μg/mL DVDMS with 360 s illumination (energy density is 12 J/cm²), and the log reduction of bacteria was 5.69 ± 1.70. a-PDT using the combination of DVDMS with 390-400 nm LED shows promise as a new treatment modality for pathogens elimination in periodontal therapy.