Obstructive sleep apnea, the microbiome and cardiovascular disease

ABSTRACT Obstructive sleep apnea (OSA) is a common condition affecting >10% of the adult population and 2-3% of children in the USA. OSA is considered as an independent risk factor for the development of cardiovascular and lung disorders but the underlying mechanisms are still largely unknown. In particular, the role of intermittent hypoxia and hypercapnia (IHC, the integral components of OSA) in inducing or promoting cardiovascular conditions remains obscure. Recent advances in sequencing technology and microbial and metabolomic bioinformatics have shed light on an important relation between the gut microbiome and cardiovascular diseases. Since OSA is a critical risk factor for these disorders, and our preliminary studies have demonstrated that IHC alters the ecology of gut microbiome and have a strong impact on metabolism, we hypothesize that IHC induces specific alterations in the gut microbiome and microbial-derived metabolites, and these changes causally promote atherosclerosis. Indeed, we have obtained strong candidate microbial families and metabolites that can affect vascular integrity under IHC. For example, we have found that a) IHC accelerates the formation of atherosclerosis in ApoE-/- mice; b) IHC changes the gut microbiome ecology of families such as Verrucomicrobiaceae, Ruminococcaceae and Erysipelotrichaceae; and c) IHC alters microbial-derived metabolites (such as bile salts (BAs)). In the current application, we focus on these microbiota and metabolite candidates to investigate their role in atherosclerosis. First, we will isolate specific gut microbial strains that were altered by IHC treatment and determine the role of these specific microbial strain(s) in the development of cardiovascular disease in vivo using germ-free ApoE-/- mice that were currently created and established in our laboratory. Second, we will delineate the role of the major bile acid receptors (i.e., FXR and TGR5) in mediating the effect of candidate bile acids in IHC-induced cardiovascular disease in vivo using ApoE-/-/FXR-/- and ApoE-/-/TGR5-/- double knockout mice strains as well as the mice strains carrying cell specific conditional deletion of FXR and TGR5 on ApoE-/- background. And third, we will dissect the mechanisms underlying the role of specific IHC-altered bile acids (i.e., TβMCA and UDCA) in IHC-induced macrophage foam cell formation in vitro using primary cell cultures that are derived from mice with ApoE-/- /FXR-/- and ApoE-/-/TGR5-/- double deletion. This project will delineate novel mechanisms regulating OSA- induced cardiovascular disease and provide potential novel targets and strategies to improve treatment or prevent disease.