An Anti-inflammatory Proton Sensing-receptor Contributes To Cardiovascular Protection Of Gut Microbiota-derived Metabolites

High fibre (HF) diet protects against hypertension via the production of acidic metabolites, e.g. short-chain fatty acids, by the gut microbiota. While these metabolites have a direct role in blood pressure (BP) regulation, their acidic nature may activate proton-sensing receptors, which have anti-inflammatory functions. G-protein coupled receptor 65 (GPR65) is a proton-sensing receptor activated around pH 6.5 and is critical for gut homeostasis. We hypothesized that GPR65 is involved in the cardiovascular protection by dietary fibre. We first measured cecal pH of C57BL/6 (WT) mice after a 7-day dietary intervention with either HF or low fibre (LF) diets (n=6/group). HF diet lowered cecal pH to a level where GPR65 is highly activated, compared to the LF diet (6.5±0.1 vs 7.6±0.1, P<0.001). The impact of pH and GPR65 on T cell production of IFNγ, a pro-inflammatory cytokine, in vitro was measured by flow cytometry. Acidic pH inhibited the production of IFNγ by CD8+ T cells (pH 6.5 vs pH 7.5, P<0.001). Cells lacking GPR65 had higher IFNγ at both pH (P<0.001). To determine if GPR65 is involved in BP regulation by dietary fibre, WT and GPR65 knockout ( Gpr65 -/- ) mice were implanted with minipumps containing angiotensin II (Ang II, 0.5mg/kg/day, 28 days, n=8-9/group) and fed with HF diet. BP, cardiorenal function and immune cell infiltration were measured. Gpr65 -/- mice had higher BP compared to WT mice after 2 weeks (mean arterial pressure ± SEM; WT 79.8±2.4 vs Gpr65 -/- 95.8±1.6mmHg, P<0.001) and 4 weeks of Ang II infusion (WT 92.3±2.4 vs Gpr65 -/- 99.5±1.3, P=0.062). Gpr65 -/- mice developed cardiac (P=0.035) and renal (P=0.025) hypertrophy, and impaired renal natriuretic (P=0.054) and diuretic (P=0.056) function compared to WT mice. This was accompanied by higher macrophage (P=0.009) and γδ T cell (P=0.014) infiltration in the kidneys. In conclusion, our data suggest that pH-sensing by GPR65 contributes to the protection against hypertension by dietary fibre via inflammatory mechanisms. This is a novel mechanism that contributes to BP regulation via the gut microbiota.