Microbial short chain fatty acid metabolites lower blood pressure via endothelial G protein-coupled receptor 41

Abstract

Short chain fatty acid (SCFA) metabolites are byproducts of gut microbial metabolism that are known to affect host physiology via host G protein-coupled receptor (GPCRs). We previously showed that an acute SCFA bolus decreases blood pressure (BP) in anesthetized mice, an effect mediated primarily via Gpr41. In this study, our aims were to identify the cellular localization of Gpr41 and to determine its role in BP regulation. We localized Gpr41 to the vascular endothelium using RT-PCR: Gpr41 is detected in intact vessels (with endothelium) but is absent from denuded vessels (without endothelium). Furthermore, using pressure myography we confirmed that SCFAs dilate resistance vessels in an endothelium-dependent manner. Since we previously found that Gpr41 mediates a hypotensive response to acute SCFA administration, we hypothesized that Gpr41 knockout (KO) mice would be hypertensive. Here, we report that Gpr41 KO mice have isolated systolic hypertension compared with wild-type (WT) mice; diastolic BP was not different between WT and KO. Older Gpr41 KO mice also exhibited elevated pulse wave velocity, consistent with a phenotype of systolic hypertension; however, there was no increase in ex vivo aorta stiffness (measured by mechanical tensile testing). Plasma renin concentrations were also similar in KO and WT mice. The systolic hypertension in Gpr41 KO is not salt sensitive, as it is not significantly altered on either a high- or low-salt diet. In sum, these studies suggest that endothelial Gpr41 lowers baseline BP, likely by decreasing active vascular tone without altering passive characteristics of the blood vessels, and that Gpr41 KO mice have hypertension of a vascular origin.

Keywords: GPCR; acetate; endothelium; hypertension; microbiota; propionate.

Copyright © 2016 the American Physiological Society.

Figures

Fig. 1.

G protein-coupled receptor (Gpr)41 is expressed in the endothelium, and short chain fatty acid (SCFA)-mediated vasodilation is endothelium dependent. A: Gpr41 localizes to the vascular endothelium by RT-PCR. eNOS (endothelial nitric oxide synthase), an endothelial marker, is detected in intact vessels (+endo) but not in vessels lacking endothelium (−endo). β-Actin, as a control, is detected in both +endo and −endo vessels. Gpr41, like eNOS, is only detected in intact vessels. In isolated tail arteries, both propionate (B) and acetate (C) cause endothelium-dependent vasodilation. Vessels with endothelium (●) exhibit vasodilation, which is severely attenuated when the endothelium is denuded (○), n = 4. l-NAME, a pharmacological inhibitor of eNOS does not attenuate SCFA-mediated vasodilation. Closed circles (no l-NAME) and open circles (0.1 mM l-NAME) exhibit similar vasodilation upon addition of propionate (D) and acetate (E). n = 4, *P < 0.05, **P < 0.01, ***P < 0.001. B, baseline; PE, phenylephrine.

Fig. 2.

Gpr41 knockout (KO) mice exhibit isolated systolic hypertension at baseline. Gpr41 KO mice have significantly higher systolic pressure during the light cycle (A) and dark cycle (B), higher mean arterial pressure during the dark cycle (B), but similar diastolic pressure during both dark and light cycle. Pulse pressures of Gpr41 KO mice are significantly elevated both during light and dark cycles (C); however, heart rate (D) is not altered. n = 8 KO, 6 wild type (WT); *P < 0.05 between genotypes.

Fig. 3.

Vessel properties of Gpr41 KO mice. Three-month-old Gpr41 KO and WT mice have similar pulse wave velocities, whereas 6 mo old Gpr41 KO mice have increased pulse wave velocity; n = 6, ***P < 0.01 (A). However, the tensile properties of intact Gpr41 KO and Gpr41 WT aortas are similar; n = 4 (B). In fact, decellularized Gpr41 KO aortas have significantly greater compliance (C), P < 0.0001. D–F: representative images from histology of aortas from Gpr41 WT (left) and KO (right) mice. Hematoxylin and eosin staining of aortas from 6 mo old Gpr41 WT and Gpr41 KO mice (D) show no major histological differences, other than the thickening of aorta in Gpr41 KO mice. Verhoeff's van Gieson staining was used to quantify elastin (black) in 6 mo old Gpr41 WT aortas and Gpr41 WT aortas (E). Picrosirius red staining of aortas from 6 mo old male Gpr41 WT, Gpr41 KO (F) mice was used to quantify collagen. G: quantification of vascular properties of male Gpr41 mice; n = 4 (vessel thickness, diameter, collagen, elastin quantification); n = 6 (heart and kidney-to-body weight ratios).

Fig. 4.

Gpr41 KO mice do not exhibit salt-sensitive hypertension. A: day-wise trends of systolic pressure in Gpr41 KO and WT mice during the salt diet treatment period show the lack of effect of differing salt diets on systolic pressure. Baseline values shown are average systolic blood pressure (BP) values of the 5-day baseline recording period. n = 6 (WT), 5 (KO). Day-wise trends of diastolic pressure (B) and of heart rate (C) on normal, high-salt, and low-salt diets. *P < 0.05 between genotypes. #P < 0.05 baseline average vs. indicated day.