LAUSR

Introduction: Bile acids are a class of metabolites in the gut-liver axis. Primary bile acids synthesized in the liver are converted into secondary bile acids via gut microbiota. We and others have previously reported that compositions of both bile acids and microbiota regulate blood pressure (BP), but the mechanisms remain largely unknown. Here, we focused on Takeda G-protein coupled receptor 5 (TGR5), which is a major receptor for secondary bile acids, and asked whether the loss-of-function of this receptor reshapes the microbiome to regulate BP. We, therefore, hypothesized that deletion of TGR5 decreases BP by reshaping the gut microbiome to generate beneficial metabolites. Methods: Dahl Salt-Sensitive rats (S) were genetically engineered using CRISPR/Cas9 to create TGR5 knock out rats ( Tgr5 KO). BP was measured weekly for 4 weeks by radiotelemetry in 8-week-old female Tgr5 KO rats and control S rats (n=7/group). The gut microbiome was profiled using the Illumina 16S rRNA gene sequencing and Oxford Nanopore whole genome sequencing. Ultra-Performance Liquid Chromatography-Mass Spectrometry was used to quantify targeted bile acids and Gas Chromatography-Flame Ionization Detector was used to quantify short-chain fatty acids (SCFAs). Cardiac function was measured by echocardiography and vascular function was examined ex vivo by wire myography. Kidney function was measured by urinary sodium and total protein excretion levels and liver function was examined by measuring levels of serum alkaline phosphatase, alanine aminotransferase, and aspartate aminotransferase. Sympathetic activity and neurotransmission were analyzed by measuring serum levels of norepinephrine and serotonin, respectively, via ELISA. Results: Tgr5 KO rats had significantly lower 24-hour systolic BP (151.8mmHg vs. 156.9mmHg, p<0.0001), diastolic BP (107.9mmHg vs. 115.5mmHg, p<0.0001), and mean arterial BP (128.8mmHg vs. 134.9mmHg, p<0.0001) compared to controls. This lowering of BP was exclusively accompanied by a 3-4-fold increase in the levels of the secondary bile acid, glycodeoxycholic acid (0.04µM vs. 0.01µM, p<0.05), which did not show any effects on cardiac, renal, vascular, neural or hepatic functions. Since secondary bile acids have significant antimicrobial properties, we examined the gut microbiome. The α-diversity (Observed features; p<0.05) was significantly reduced in Tgr5 KO rats compared to controls, and a significant shift in β-diversity (Jaccard index; p<0.01) was observed between Tgr5 KO and control rats. Specifically, Ligilactobacillus ruminis and Agathobacter rectalis were less abundant in Tgr5 KO rats compared to the controls. Importantly, the abundances of each of these bacteria were negatively correlated with the levels of the secondary bile acid, glycodeoxycholic acid (r=-0.52, p<0.05 and r=-0.63, p<0.05 respectively). Given that these bacteria are known producers of SCFAs, we quantified fecal SCFA levels and found a significant reduction in total SCFAs in Tgr5 KO rats compared to controls (12.45μM/g vs. 23.44 μM/g; p<0.01). This lowering of SCFAs positively correlated with the lower abundances of both bacteria, Ligilactobacillus ruminis (r=0.73, p<0.01) and Agathobacter rectalis (r=0.70, p<0.01) and diastolic BP (r=0.67, p<0.01). Conclusions: This is the first loss-of-function study to demonstrate that the deletion of the secondary bile acid receptor, TGR5, promotes the abundance of an antimicrobial secondary bile acid, remodels the gut microbiome, and lowers BP in S rats. Although further mechanistic studies are warranted, the current results clearly demonstrate that targeting the gut-liver axis via TGR5 could serve as a novel therapeutic strategy for hypertension. Bina Joe gratefully acknowledges funding support from the National Institutes of Health (R01HL171401-01). This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.