Gut microbiota dysbiosis exacerbates post-stroke depression via microglial NLRP3 inflammasome activation.

Background: Post-stroke depression (PSD) is a neuropsychiatric complication prevalent among stroke survivors. Emerging evidence suggests that dysregulation of the microbiota-gut-brain axis is implicated in the pathogenesis of PSD. However, the exact mechanism is not clear and further research is necessary.

Methods: Initially, Sprague-Dawley (SD) rats were randomly allocated into three experimental groups: Sham, Middle Cerebral Artery Occlusion (MCAO), and PSD. Behavioral tests were conducted to evaluate depressive-like behavior. Fecal samples from all groups underwent 16S rRNA sequencing for comprehensive gut microbiota analysis. Colonic tissues were collected from rats and subjected to immunohistochemical analysis for quantification of tight junction proteins (ZO-1, Occludin, and Claudin). Peripheral blood plasma was obtained for the determination of IL-1β, IL-6, TNF-α, and IL-18 levels using enzyme-linked immunosorbent assay (ELISA). Lastly, hippocampus tissues were harvested for molecular characterization of Nucleotide-binding oligomerization domain-like receptor protein 3 (NLRP3) inflammasome activation and inflammatory cytokines expression through tripartite methodology: Reverse Transcription quantitative PCR (RT-qPCR), Western blot, and immunofluorescence. Concurrently, hippocampal concentrations of 5-HT, BDNF, and PSD-95 were also measured by ELISA. Subsequently, Fecal Microbiota Transplantation (FMT) was performed by administering fecal suspensions from PSD and Sham donor rats to healthy SD recipients via oral gavage. Then, use the above methods to test the same indicator.

Result: Comparative analyses showed that microbial species richness and diversity indices were significantly reduced in PSD model rats, along with a compositional imbalance of the gut microbiota. Concurrently, reduced expression of the colonic tight junction proteins ZO-1, Occludin, and Claudin was observed, accompanied by elevated levels of peripheral inflammatory cytokines. In PSD rats, NLRP3 inflammasome activation was detected in the ischemic hippocampus, along with increased expression of the inflammatory cytokines IL-18 and IL-1β, and decreased levels of 5-HT, BDNF, and PSD-95. Subsequently, using FMT technology, PSD rat feces were innovatively prepared into a fecal suspension and administered to healthy SD rats. Analysis revealed that FMT-PSD rats exhibited a disrupted gut microbiota structure, impaired colonic barrier integrity, activation of the hippocampal NLRP3 inflammasome, elevated inflammatory cytokine levels, and reduced neurotransmitter expression.

Conclusion: In summary, these data demonstrate that dysbiosis of the intestinal microbiota compromises gut barrier integrity and elicits systemic inflammation, which may subsequently activate the NLRP3 inflammasome in hippocampal microglia. This activation promotes the release of pro-inflammatory cytokines IL-18 and IL-1β, and coincides with dysregulation of emotion-related neurotransmitters, collectively contributing to the pathogenesis of PSD.