Periodontitis induced by bacterial infection exacerbates features of Alzheimer's disease in transgenic mice

Periodontitis is a localized infectious disease caused by periodontopathic bacteria, such as Porphyromonas gingivalis. Recently, it has been suggested that bacterial infections may contribute to the onset and the progression of Alzheimer's disease (AD). However, we do not have any evidence about a causative relationship between periodontitis and AD. In this study, we investigated by using a transgenic mouse model of AD whether periodontitis evoked by P. gingivalis modulates the pathological features of AD. Cognitive function was significantly impaired in periodontitis-induced APP-Tg mice, compared to that in control APP-Tg mice. Levels of Amiloid beta(A beta) deposition, A beta 40, and A beta 42 in both the hippocampus and cortex were higher in inoculated APP-Tg mice than in control APP-Tg mice. Furthermore, levels of IL-1 beta and TNF-alpha in the brain were higher in inoculated mice than in control mice. The levels of LPS were increased in the serum and brain of P. gingivalis-inoculated mice. P. gingivalis LPS-induced production of A beta 40 and A beta 42 in neural cell cultures and strongly enhanced TNF-alpha and IL-1 beta production in a culture of microglial cells primed with A beta. Periodontitis evoked by P. gingivalis may exacerbate brain A beta deposition, leading to enhanced cognitive impairments, by a mechanism that involves triggering brain inflammation.