BACKGROUND: Alzheimer’s disease (AD) is a progressive neurodegenerative condition affecting 39 million people worldwide. Although classically framed as a brain disorder, accumulating evidence also points to early disturbances in intestinal physiology. These gut changes may affect neural functions through the microbiota–gut–brain axis, where microbial and host signals engage immune, endocrine, and enteric pathways. OBJECTIVE: We hypothesize that 3xTg-AD mice exhibit early dysbiosis and disruption of intestinal barrier integrity. We tested whether intestinal microbiota composition and epithelial barrier integrity are altered in 3xTg-AD mice before and during symptomatic stages compared with age-matched controls. METHODS: Gross anatomy was assessed in 12-mo. 3xTg-AD mice and controls. Barrier integrity was evaluated by immunofluorescence for tight junction proteins (e.g. ZO-1, ZO-2) in ileum and colon. Intestinal permeability was measured by a permeability tracer assay (FITC-dextran), and serum endotoxin was quantified by chromogenic Limulus amebocyte lysate (LAL). Bacterial distribution was assessed on colonic sections by fluorescent in situ hybridization (FISH) using the universal EUB338 probe and an Akkermansia muciniphila–specific probe. Relative abundance of selected taxa was quantified by real-time PCR at 4 mo. (presymptomatic) and 12 mo. (symptomatic). RESULTS: At 12 mo., 3xTg females showed reduced body weight, increased lung weight, and shorter ileum compared to controls, whereas 3xTg males showed increased body weight and longer ileum compared to controls. Tight junction changes were region specific. In 3xTg mice, ZO-1 staining was discontinuous in both colon and ileum. ZO-2 expression was reduced at epithelial and endothelial colonic junctions in 3xTg mice, with more apical concentration in ileum compared to diffuse distribution in controls. Serum FITC-dextran did not differ significantly between groups, although 3xTg mice trended towards a higher mean. Serum endotoxin was significantly elevated in 3xTg mice compared with controls (p=0.0271). FISH with EUB 338 probe revealed predominantly luminal bacterial distribution in both groups, while A. muciniphila staining showed mucin-associated localization that appeared similar across groups. Across 4 and 12 mo., 3xTg-AD mice showed lower Firmicutes, Bacteroides spp. 2, and Lactobacillus versus controls. At 4 mo., 3xTg mice showed increased Butyrivibrio spp. 1, decreased Bacteroides spp. 1, and increased Bacteroides spp. 3, while 12 mo. 3xTg mice showed the inverse. Species-level shifts were observed for Adlercreutzia equolifaciens, A. muciniphila, and Blautia hansenii (decreased at 4 mo. and increased at 12 mo. in 3xTg-AD vs age-matched controls). CONCLUSIONS: Our studies have shown that presymptomatic species-level microbiota shifts at the species level are followed by symptomatic, region-specific barrier disruption with altered tight junctions and elevated serum endotoxin. These data suggest that dysbiosis and barrier dysfunction are potential contributors to AD and support the evaluation of intestinal and microbial changes as early biomarkers. FUNDING: NIDDK/National Institutes of Health grant R01 DK134343, R01DK114126, VA Merit Award VA 1 I01 BX004824-06, and VA Collaborative Merit Award 1 I01BX006878-01A1 to Jun Sun. This abstract was presented at the American Physiology Summit 2026 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.
Walton et al. (Fri,) studied this question.