ABSTRACT
Alzheimer's disease (AD) is a neurodegenerative disorder histologically characterized by amyloid-ß (Aß) protein accumulation and activation of associated microglia. Although these features are well described in the central nervous system, the process and consequences of Aß accumulation in the enteric nervous system have not been extensively studied. We hypothesized that Aß also may accumulate in the enteric nervous system and lead to immune cell activation and neuronal dysfunction in the digestive tract not unlike that observed in diseased brain. To test this hypothesis, ileums of the small intestine of thirteen month old AßPP/PS1 and C57BL/6 (wild type) mice were collected and analyzed using immunohistochemistry, western blot analysis, cytokine arrays, and ELISA. AßPP/PS1 mice demonstrated no differences in intestinal motility or water absorption but elevated luminal IgA levels compared to wild type mice. They also had increased protein levels of AßPP and the proteolytic enzyme, BACE, corresponding to an increase in Aß1-40 in the intestinal lysate as well as an increase in both Aß1-40 and Aß1-42 in the stool. This correlated with increased protein markers of proinflammatory and immune cell activation. Histologic analysis localized AßPP within enteric neurons but also intestinal epithelial cells with elevated Aß immunoreactivity in the AßPP/PS1 mice. The presence of AßPP, Aß, and CD68 immunoreactivity in the intestines of some patients with neuropathologically-confirmed AD are consistent with the findings in this mouse model. These data support the hypothesis that in AD the intestine, much like the brain, may develop proinflammatory and immune changes related to AßPP and Aß.
