Estradiol mediates colonic epithelial protection in aged mice after stroke and is associated with shifts in the gut microbiome

The gut is a major source of bacteria and antigens that contribute to neuroinflammation after brain injury. Colonic epithelial cells (ECs) are responsible for secreting major cellular components of the innate defense system, including antimicrobial proteins (AMP) and mucins. These cells serve as a critical regulator of gut barrier function and maintain host-microbe homeostasis. In this study, we determined post-stroke host defense responses at the colonic epithelial surface in mice. We then tested if the enhancement of these epithelial protective mechanisms is beneficial in young and aged mice after stroke. AMPs were significantly increased in the colonic ECs of young males, but not in young females after experimental stroke. In contrast, mucin-related genes were enhanced in young females and contributed to mucus formation that maintains the distance between the host and gut bacteria. Bacterial community profiling was done using universal amplification of 16S rRNA gene sequences. The sex-specific colonic epithelial defense responses after stroke in young females were reversed with ovariectomy and led to a shift from a predominately mucin response to the enhanced AMP expression seen in males after stroke. Estradiol (E2) replacement prior to stroke in aged females increased mucin gene expression in the colonic ECs. Interestingly, we found that E2 treatment reduced stroke-associated neuronal hyperactivity in the insular cortex, a brain region that interacts with visceral organs such as the gut, in parallel to an increase in the composition of Lactobacillus and Bifidobacterium in the gut microbiota. This is the first study demonstrating sex differences in host defense mechanisms in the gut after brain injury.

Abstract WMP111: MicroRNAs As A Therapeutic Target To Reduce Microglial Activation After Post-stroke Social Isolation

Introduction: Social isolation (SI) and loneliness are linked to all-cause mortality, as well as mortality from stroke and other vascular diseases. However, the mechanisms mediating the effects of social factors on stroke recovery are unknown. We hypothesized that differential expression of miRNAs contributes to the deleterious effects of post-stroke SI.

Methods: Aged (18-20 months) C57BL/6 male mice were used to examine the detrimental effects of post-stroke SI on miRNA profiles in the brain. Mice were randomly assigned to either pair housing (PH), or single housing (SI) three days after a 60-minute transient right middle cerebral artery occlusion (MCAO). At this time point (post-stroke day 3), the infarct is complete, and was equivalent between groups, avoiding potential changes seen with differing infarct sizes. Temporal miRNA profiling of the ipsilateral hemisphere was assessed at two-time points (post-stroke SI D4 and D27). Brain cells were analyzed by flow cytometry.

Results: Post-stroke SI resulted in significant alterations of distinct miRNA profiles within the brain across both acute and chronic time points (n=4/grp, FDR adjusted * p <0.05). MiRNA-mRNA interactional analysis revealed miR-10a-5p and miR-10b-5p as pivotal nodes within the pool of miRNAs that interacted with the largest subset of miRNAs for post-stroke at SI D4 and D27, respectively. Downstream pathway analysis utilizing an independent repository, the KEGG pathway showed 4 days of isolation resulted in the enrichment of pathways related to microglial activation and 27 days of isolation lead to the activation of neuronal-specific pathways that regulate cognition and motivation (FDR adjusted * p <0.05). Independent validation cohorts demonstrated significant activation of microglia at post-stroke SI D4 as assessed by the median fluorescence intensity (MFI) of purinergic receptor P2Y12 (P2RY12), in CD45 int CD11b + P2RY12 + cells in the brain. MFI of P2RY12 was significantly downregulated in post-stroke SI mice at D4 (n=7-8/grp, * p <0.05) compared to PH mice.

Conclusions: These results support our hypothesis that post-stroke SI exacerbates microglia activation, and results in the differential expression of microglial pathway-related miRNAs.