Porphyromonas gingivalis Conditioned Medium Induces Amyloidogenic Processing of the Amyloid- Protein Precursor upon in vitro Infection of SH-SY5Y Cells.
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BACKGROUND: Cleavage of the amyloid- protein precursor (APP) mediated by host secretase enzymes, releases several fragments including amyloid- (A40 and A42). OBJECTIVE: To determine if Porphyromonas gingivalis conditioned medium cleaved APP to release A40 and A42. METHODS: The SH-SY5Y cell line was challenged, in vitro, with P. gingivalis (Pg381) conditioned medium in the presence/absence of cytokines. The cells and their supernatants were assessed for APP cleavage fragments by immunoblotting and transmission electron microscopy. RESULTS: Western blotting of the cell lysates with the anti-APP C-terminal antibody demonstrated variable molecular weight bands corresponding to full length and fragmented APP in lanes treated with the following factors: Tryptic soy broth (TSB), Pg381, IL-6, Pg381+IL-1, and Pg381+TNF-. The low molecular weight bands corresponding to the C99 dimerized fragment were observed in the Pg381 and interlukin-6 (IL-6) treated groups and were significantly more intense in the presence of Pg381 with either IL-6 or TNF-. Bands corresponding to the dimerized C83 fragment were observed with cells treated with TNF- alone and with Pg381 combined with IL-1 or IL-6 or TNF-. The anti-A antibody detected statistically significant A40 and A42, levels when these two A species were pooled across test samples and compared to the untreated group. Electron microscopic examination of the supernatants demonstrated insoluble A40 and A42. CONCLUSION: These observations strongly imply that APP is an infection responsive protein cleaved via the amyloidogenic pathway on exposure to conditioned medium and in the presence of pro-inflammatory mediators.
