Rationale: The elderly experience profound systemic responses after stroke, which contribute to higher mortality and more severe long-term disability. Recent studies have revealed that stroke outcomes can be influenced by the composition of gut microbiome. However, the potential benefits of manipulating the gut microbiome after injury is unknown. Objective: To determine if restoring youthful gut microbiota after stroke aids in recovery in aged subjects, we altered the gut microbiome through young fecal transplant gavage (young FTG) in aged mice after experimental stroke. Further, the effect of direct enrichment of selective bacteria producing short-chain fatty acids (SCFAs) was tested as a more targeted and refined microbiome therapy. Methods and Results: Aged male mice (18-20 months) were subjected to ischemic stroke by middle cerebral artery occlusion (MCAO). We performed FTG three days after MCAO using young donor biome (2-3 months) or aged biome (18-20 months). At day 14 after stroke, aged stroke mice receiving young FTG had less behavioral impairment, and reduced brain and gut inflammation. Based on data from microbial sequencing and metabolomics analysis demonstrating that young fecal transplants contained much higher SCFA levels and related bacterial strains, we selected four SCFA-producers (Bifidobacterium longum, Clostridium symbiosum, Faecalibacterium prausnitzii and Lactobacillus fermentum) for transplantation. These SCFA-producers alleviated post-stroke neurological deficits and inflammation, and elevated gut, brain and plasma SCFA concentrations in aged stroke mice. Conclusions: This is the first study suggesting that the poor stroke recovery in aged mice can be reversed via "post-stroke bacteriotherapy" following the replenishment of youthful gut microbiome via modulation of immunologic, microbial and metabolomic profiles in the host.

Background The ability to distinguish resident microglia from infiltrating myeloid cells by flow cytometry-based surface phenotyping is an important technique for examining age-related neuroinflammation. The most commonly used surface markers for the identification of microglia include CD45 (low-intermediate expression), CD11b, Tmem119, and P2RY12. Methods In this study, we examined changes in expression levels of these putative microglia markers in in vivo animal models of stroke, cerebral amyloid angiopathy (CAA), and aging as well as in an ex vivo LPS-induced inflammation model. Results We demonstrate that Tmem119 and P2RY12 expression is evident within both CD45int and CD45high myeloid populations in models of stroke, CAA, and aging. Interestingly, LPS stimulation of FACS-sorted adult microglia suggested that these brain-resident myeloid cells can upregulate CD45 and downregulate Tmem119 and P2RY12, making them indistinguishable from peripherally derived myeloid populations. Importantly, our findings show that these changes in the molecular signatures of microglia can occur without a contribution from the other brain-resident or peripherally sourced immune cells. Conclusion We recommend future studies approach microglia identification by flow cytometry with caution, particularly in the absence of the use of a combination of markers validated for the specific neuroinflammation model of interest. The subpopulation of resident microglia residing within the “infiltrating myeloid” population, albeit small, may be functionally important in maintaining immune vigilance in the brain thus should not be overlooked in neuroimmunological studies.

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Aging and stroke alter the composition of the basement membrane and reduce the perivascular distribution of cerebrospinal fluid and solutes, which may contribute to poor functional recovery in elderly patients. Following stroke, TGF-β induces astrocyte activation and subsequent glial scar development. This is dysregulated with aging and could lead to chronic, detrimental changes within the basement membrane. We hypothesized that TGF-β induces basement membrane fibrosis after stroke, leading to impaired perivascular CSF distribution and poor functional recovery in aged animals. We found that CSF entered the aged brain along perivascular tracts; this process was reduced by experimental stroke and was rescued by TGF-β receptor inhibition. Brain fibronectin levels increased with experimental stroke, which was reversed with inhibitor treatment. Exogenous TGF-β stimulation increased fibronectin expression, both in vivo and in primary cultured astrocytes. Oxygen-glucose deprivation of cultured astrocytes induced multiple changes in genes related to astrocyte activation and extracellular matrix