LAUSR

Aging is a non-modifiable risk factor for stroke. Aging is accompanied by chronic low-grade inflammation and gut dysbiosis (a pathological imbalance of microbial organisms in the gut). Age-related gut dysbiosis exacerbates stroke outcomes and can be reversed by manipulation of the gut microbiota (GM) via fecal microbiota transplants (FMTs) from young animals, or “rejuvenation.” But, the mechanisms that mediate these effects are poorly understood. Dendritic cells (DCs) are potent antigen presenting cells and uniquely equipped to mediate the effects of dysbiosis. DCs constantly sample their environment to regulate the inflammatory response to antigens and tissue injury. In this study we investigated the role of intestinal DCs in mediating the detrimental effects of dysbiosis on stroke outcomes. We hypothesize that age-related dysbiosis exacerbates stroke outcomes by inducing an inflammatory and migratory phenotype in intestinal DCs. We studied four cohorts of C57Bl6 mice consisting of (1) naïve young (4mo), (2) naïve aged (22-26mo), (3) middle-aged (14mo) with FMT from aged donors, and (4) naïve young with 60-min middle cerebral artery occlusion (MCAO). Phenotyping of DCs by flow cytometry was performed. Results: In our MCAO cohort, we found a significant increase in activated DCs in the gut (1.4% vs. 7.6%, p = 0.051) but a decrease in frequency of activated DCs in the brain (8.4% vs. 3.9%, p = 0.042). In our FMT cohort, frequency of intestinal DCs was altered in a subset-specific manner after FMT from aged donors. Specifically, our data showed that the MHC-II expression by DC subsets with a migratory phenotype (CD11b + DCs) and resident DCs (CD103 + DCs) were significantly increased when middle-aged mice received FMT from aged donors (p < 0.05). In our naïve cohorts, we found a significant decrease of MHC-II surface expression in brain DCs (p = 0.044) and a significant increase in splenic DCs (p = 0.049) with aging. Conclusion: Our findings show that frequency and maturity state of DCs significantly differ with aging in a tissue- specific manner and can be influenced by manipulation of the gut microbiota. Our data also support the notion that intestinal DCs are involved in mediating the detrimental effects of age-related gut dysbiosis on stroke outcomes.