Role of Gut Microbiota and Immunity in the Dietary Modulation of Dahl Salt‐Sensitive Hypertension

Studies from our laboratory have demonstrated that immune cells infiltrate the kidneys and amplify the hypertension and renal damage observed in Dahl Salt-Sensitive (SS) rats when fed 4.0% high salt (HS). These rats are bred at the Medical College of Wisconsin (SS/MCW) and are maintained on a highly purified, casein-based diet. Interestingly, SS rats fed a whole grain diet (SS/CRL) or modified wheat gluten diet (SS/WG) have drastically reduced salt-induced hypertension, albuminuria, and renal inflammation compared to the casein-fed SS/MCW. With the linkage of the gut microbial composition to many of the risk factors associated with hypertension, the current study sought to define the Dahl SS gut microbiome in the presence of these dietary modulations and to test the hypothesis that gut bacteria directly contribute to the development of hypertension and renal disease. Fecal 16S rRNA sequencing revealed distinct microbiome profiles between SS/MCW, SS/CRL, and SS/WG, with significant shifts in gut microbiome composition due to age, salt, and sex (n=4–6). Furthermore, there were families of salt responsive bacteria that, depending on the diet of the group, became specifically enriched (Ruminococcaceae, Clostridiaceae, Prevotellaceae) or depleted (Lachnospiraceae) after 3 weeks of HS. To assess the direct contribution of gut bacteria to the development of SS hypertension, we treated SS/MCW rats with a broad-spectrum antibiotic cocktail of bacitracin and streptomycin (Bac/Strep, 2 g/L in drinking water). Bac/Strep treatment resulted in a significant reduction in mean arterial pressure (167.3±5.0 vs 148.9±3.0 mmHg, Vehicle vs Bac/Strep, n=6–8, p<0.001) and albuminuria (221.5±34.3 vs 130.2±16.2 mg/day, p<0.05) compared to vehicletreated rats, suggesting that Bac/Strep treatment eliminated certain gut bacteria responsible for driving the phenotype in Dahl SS rats. As further proof of principle, SS/CRL recipient rats were administered daily fecal microbiota transfer (FMT, 0.1g stool/day) from SS/MCW donor rats starting at 6 weeks of age and throughout the HS period starting at 9 weeks of age. These transfer experiments of the SS/MCW microbiota into SS/CRL rats worsened renal disease progression by increasing both proteinuria (148.0±15.0 vs 209.4±39.8 mg/day, Vehicle vs SS/MCW FMT, n=5, p<0.05) and albuminuria (67.3±6.9 vs 113.7±25.0 mg/day, p<0.01), which also coincided with an increase in systolic arterial pressure (158.6±5.8 vs 177.8±8.9 mmHg, p=0.09). Upon analysis of the immune cells in the kidneys of the SS/MCW FMT, there was a specific increase in the number of CD4+ T helper cells (1.7-fold, p<0.05) and CD8+ cytotoxic T cells (2.0-fold, p<0.05), with no differences observed in the number of CD11b/c+ monocytes/macrophages or CD45R+ B cells. While the specific mechanisms linking gut dysbiosis to the SS hypertensive, renal injury, and renal inflammatory phenotype are still under current investigation, our present data excitingly demonstrate that the dietary modulation of gut bacteria are directly contributing to the development and progression of the Dahl SS phenotype. Support or Funding Information HL116264, HL137748, 15SFRN2391002 This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.