Obstructive Sleep Apnea Induced Gut Dysbiosis Stimulates a Proinflammatory Response that Promotes Neuroinflammation and Hypertension Sriram Ayyaswamy, Bojun Zhang, Huanan Shi, Sharon Phillips, Robert Bryan and David Durgan Baylor College of Medicine, Department of Anesthesiology, Houston, Texas, United States

Abstract

Background and HypothesisObstructive sleep apnea (OSA) is an independent risk factor for the development of hypertension (HT). We have previously demonstrated that OSA induces gut dysbiosis, and a dysbiotic microbiota is causal in the development of HT. However, the mechanisms linking gut dysbiosis to blood pressure (BP) regulation are unclear. Recent studies have demonstrated that gut dysbiosis can induce a pro‐inflammatory response of the host resulting in peripheral‐ and neuro‐inflammation, key factors in the development of HT. We therefore hypothesized that OSA induced gut dysbiosis elicits a pro‐inflammatory response that promotes neuroinflammation and hypertension.MethodsOSA was induced in 8‐week‐old male rats (60 apneas/hour for 8 hours during the sleep phase) by repeatedly inflating a surgically implanted tracheal balloon. Sham rats underwent balloon implantation without inflations. After two weeks of apneas, lymphocytes were isolated from aorta, brain, cecum, ileum, mesenteric lymph node, and spleen for assessment by flow cytometry. In studies examining the role of IL‐17, a monoclonal antibody to IL‐17 was injected every 48 hours during the 2 weeks of apneas to neutralize circulating IL‐17. To track the distribution of lymphocytes originating from the gut, cells in the Peyer’s patches of the small intestine were labelled by microinjection of carboxyfluorescein succinimidyl ester (CFSE) dye.Summary of resultsFollowing 2 weeks of OSA we found a significant decrease in anti‐inflammatory regulatory T (Treg) cells along with an increase in TH17 (IL‐17+) in the brain, cecum, and ileum and TH1 (IFN‐γ+) in cecum and ileum (n=7, p<0.05 for each). A significant increase in the Th17/Treg ratio, a sign of inflammation associated with hypertension, was observed in brain, cecum and ileum of OSA, versus sham, rats (n=7, p<0.05 for each). To examine the role of TH17 cells, we injected an IL‐17 neutralizing antibody or control IgG antibody during the 2 weeks of OSA. Compared to OSA rats receiving IgG control, neutralization of IL‐17 significantly reduced BP of OSA rats after 1 and 2 weeks (n=6, p<0.05 for each). Additionally, neutralization of IL‐17 resulted in a significant increase of Tregs and decreased Th1 cells and TNFα expressing cells in brain, cecum and ileum of OSA rats (n=6, p<0.01 for each). To examine the distribution of lymphocytes originating from the gut, cells in the Peyer’s patches of sham and OSA rats were labelled with CFSE. We observed significant increases in CFSE+ Th1, Th2, and Th17 cells in the brain, MLN and spleen of OSA as compared to sham rats (n=6, p<0.05).ConclusionOverall, we found that OSA induced gut dysbiosis is associated with a pro‐inflammatory response in the gut and brain that involves IL‐17 signaling. Our findings suggest that gut dysbiosis may serve as the trigger for widespread inflammation, and treatment strategies to prevent or reverse gut dysbiosis may prove useful in reducing neuroinflammation and HT.