Commensal microbiota are essential for vascular contractility mediated by actin polymerization

Abstract

IntroductionCommensal microbiota within a holobiont contribute to the overall health of the host via mutualistic symbiosis. Disturbances in such symbiosis are prominently correlated with a variety of diseases affecting humans, including cardiovascular diseases, which are the number one contributors to mortality. Given that a hallmark of all cardiovascular diseases is changes in vascular function, we hypothesized that depleting microbiota from a holobiont would induce vascular dysfunction.MethodsTo test this hypothesis we used male inbred Sprague Dawley (SD) rats that were either germ‐free (GF) or re‐conventionalized germ‐free (GFC) rat (7 weeks‐old). Re‐conventionalization of GF rats were performed by co‐housing GF rats with conventionally‐raised SD rats for 10 days (1:1 ratio); this allows GF rats to receive a natural, continuous exposure to gut microbiota via coprophagy. Mesenteric resistance arteries were used to evaluate vascular function using a wire myograph. Vascular smooth muscle cells (VSMC) were cultured from aorta to evaluate cell migration via scratch assay; proliferation via IncuCyte; and cofilin phosphorylation (inactive form) via Western blot. We quantified cardiac hypertrophy by dividing the left ventricle weight by 26.73 + tibia length3. (Statistics: t‐test: p<0.05: *vs. GF, n=5–6/group)ResultsGF rats had a lower LV mass compared to GFC (GF: 6.9±0.2; GFC: 7.5±0.2*). Intriguingly, GF rats presented a reduction in both KCl‐and phenylephrine‐induced contraction and GFC ameliorated these responses [KCl: Emax (mN): GF: 4.8±1.0 vs. GFC: 8.5±1.1* and phenylephrine: Emax (mN): GF: 6.9±1.3 vs. GFC: 11.7±0.7*]. Given that no differences were observed in acetylcholine‐induced relaxation, we hypothesized that the hyporesponsiveness of the GF arteries were due to cytoskeleton dynamics. Indeed, we observed that GF rats present a reduction in cofilin phosphorylation (phosphoCofilin/TotalCofilin; AU: GF: 0.3±0.03 vs. GFC: 0.6±0.11*). Decreased phospho‐cofilin leads to its active form and subsequently actin depolymerization in VSMCs.ConclusionThis study shows that commensal bacteria are essential for normal structure and function of the vascular system of the host.Support or Funding InformationNIH: R00GM118885