Department of Pharmacy, University of Pisa, 56126 Pisa, Italy.
Unit of Pharmacology and Pharmacovigilance, Department of Clinical and Experimental Medicine, University of Pisa, 56126 Pisa, Italy.
Int J Mol Sci. 2020 May 15;21(10):3523. doi: 10.3390/ijms21103523.
Increasing evidence suggests that intestinal dysfunctions may represent early events in Alzheimer's disease and contribute to brain pathology. This study examined the relationship between onset of cognitive impairment and colonic dysfunctions in a spontaneous AD model before the full development of brain pathology. SAMP8 mice underwent Morris water maze and assessment of faecal output at four, six and eight months of age. In vitro colonic motility was examined. Faecal and colonic Aβ, tau proteins, α-synuclein and IL-1β were assessed by ELISA. Colonic citrate synthase activity was assessed by spectrophotometry. Colonic NLRP3, caspase-1 and ASC expression were evaluated by Western blotting. Colonic eosinophil density and claudin-1 expression were evaluated by immunohistochemistry. The effect of Aβ on NLRP3 signalling and mitochondrial function was tested in cultured cells. Cognitive impairment and decreased faecal output occurred in SAMP8 mice from six months. When compared with SAMR1, SAMP8 animals displayed: (1) impaired in vitro colonic contractions; (2) increased enteric AD-related proteins, IL-1β, active-caspase-1 expression and eosinophil density; and (3) decreased citrate synthase activity and claudin-1 expression. In THP-1 cells, Aβ promoted IL-1β release, which was abrogated upon incubation with caspase-1 inhibitor or in ASC cells. Aβ decreased mitochondrial function in THP-1 cells. In SAMP8, enteric AD-related proteins deposition, inflammation and impaired colonic excitatory neurotransmission, occurring before the full brain pathology development, could contribute to bowel dysmotility and represent prodromal events in AD.
越来越多的证据表明，肠道功能障碍可能是阿尔茨海默病的早期事件，并导致大脑病理学变化。本研究在大脑病理学完全发展之前，在自发性 AD 模型中检查了认知障碍发作与结肠功能障碍之间的关系。SAMP8 小鼠接受 Morris 水迷宫和粪便排出量评估，分别在 4、6 和 8 个月时进行。通过 ELISA 检测粪便和结肠中的 Aβ、tau 蛋白、α-突触核蛋白和 IL-1β。通过分光光度法评估结肠柠檬酸合酶活性。通过 Western blot 评估结肠 NLRP3、caspase-1 和 ASC 的表达。通过免疫组织化学评估结肠嗜酸性粒细胞密度和 Claudin-1 的表达。通过培养细胞测试 Aβ 对 NLRP3 信号和线粒体功能的影响。认知障碍和粪便排出量减少发生在 SAMP8 小鼠 6 个月时。与 SAMR1 相比，SAMP8 动物表现出：（1）体外结肠收缩功能受损；（2）肠 AD 相关蛋白、IL-1β、活性 caspase-1 表达和嗜酸性粒细胞密度增加；（3）柠檬酸合酶活性和 Claudin-1 表达降低。在 THP-1 细胞中，Aβ 促进了 IL-1β 的释放，在用 caspase-1 抑制剂孵育或在 ASC 细胞中时，该释放被阻断。Aβ 降低了 THP-1 细胞中的线粒体功能。在 SAMP8 中，肠道 AD 相关蛋白沉积、炎症和结肠兴奋性神经传递受损，这些发生在大脑病理学完全发展之前，可能导致肠道运动障碍，并代表 AD 的前驱事件。
