The Alzheimer’s disease associated bacterial protease RgpB from P. gingivalis activates the alternative β-secretase meprin β thereby increasing Aβ generation

Alzheimer’s disease (AD) is the most common type of dementia and characterized by tau hyperphosphorylation, oxidative stress, reactive microglia and amyloid-β (Aβ) deposits. A recent study revealed that Porphyromonas gingivalis infection is associated with amyloid β generation in Alzheimer’s disease. Increased Aβ levels, tau degradation and neuronal toxicity were observed as a consequence of ginigipain R (RgpB) activity, a cysteine protease constitutively secreted by P. gingivalis . Of note, we previously identified RgpB as a potent activator of the metalloproteinase meprin β. Interestingly, meprin β is an alternative β-secretase of the amyloid precursor protein (APP), which together with the γ-secretase leads to the generation of aggregation-prone N-terminally truncated Aβ2-x peptides. Importantly, identification of a risk gene variant of meprin β (rs173032) for Alzheimer’s disease using whole-exome sequencing of the BDR cohort further supports the impact of this alternative β-secretase. Thus, we wondered if increased Aβ levels as a consequence of P. gingivalis colonization into the brain might be due to meprin β activation by RgpB. Here, we demonstrate that i) upon incubation with RgpB the proteolytic activity of meprin β at the cell surface of transfected HEK cells or of endogenously expressed enzyme in SH-SY5Y neuroblastoma cells was significantly increased, and that ii) RgpB-mediated increase in meprin β activity leads to massive generation of Aβ-peptides. In conclusion, our findings would further explain the pathogenesis of P. gingivalis in AD brain.