The importance of a healthy gut microbiota on host physiology is becoming increasingly evident. Recent studies suggest that alterations to the microbiota can have adverse effects beyond the GI tract, and has been linked to hypertension and stroke. Thus we hypothesized that gut dysbiosis could contribute to the development of cerebral small vessel disease (CSVD). Giving merit to this hypothesis, we found that the microbiota of the spontaneously hypertensive stroke prone rat (SHRSP) is significantly different than that of WKY controls. Using 16s rRNA sequencing of bacterial DNA we found that SHRSP animals had decreases in measures of bacterial richness (p=.005) and diversity (p=.028), indicative of gut dysbiosis. Phenotypically, CSVD includes vessel remodeling, BBB breakdown and neuroinflammation. Gut dysbiosis is often associated with a leaky gut barrier that allows bacteria to enter the systemic circulation. We observed significantly greater permeability of the SHRSP colon barrier when compared to WKY (p=.026). We next sought to determine if impaired colon barrier function in SHRSP could lead to increased bacterial translocation to the periphery and ultimately to the brain. Brains were harvested from 24 week old SHRSP and WKY animals and qRT-PCR of the 16s rRNA gene was performed to detect the presence of bacteria in the brain. We discovered that SHRSP animals displayed a 50% increase in bacterial 16S rRNA load in the brain compared to WKY animals (p=.0063) confirming that bacteria are not only present in CSVD rats, but also in greater abundance than WKYs. Similarly, we found that SHRSP animals displayed a near 2-fold increase of the bacterial endotoxin LPS in the brain, as compared to WKY brain LPS levels (p=.01). Finally, to further confirm the presence of bacterial components in the brain we used immunofluorescence imaging to visualize peptidoglycan (PG), a molecule found solely in bacterial cell walls. We discovered that we could visualize the presence of PG in the brains of SHRSP animals, and note that PG was commonly observed inside microglia. We conclude from this study that SHRSP rats exhibit gut dysbiosis, gut barrier breakdown, and bacterial products in the brain. Further studies will examine how this bacterial presence contributes to the CSVD phenotypes.
Gut dysbiosis in the development of cerebral small vessel disease