肠道菌群-胆汁酸代谢轴在慢性间歇低氧致动脉粥样硬化中的作用与机制研究

Cardiovascular disease (CVD) caused by atherosclerosis (AS) is the leading cause of human death. Recently, the mechanistic study of obstructive sleep apnea hypopnea syndrome (OSAHS)-related CVD has become a hotspot of the research field. However, specific mechanism of how chronic intermittent hypoxia (CIH) causes AS remains unclear. Previous studies showed that a higher abundance of Firmicutes and a smaller abundance of Bacteroidetes and Proteobacteria phyla were found in CIH-exposed mice, the diversity of faecal microbiota declined. Current study found that altered gut microbiota composition and diversity was an important factor for the occurrence of AS. Thus, we hypothesized that CIH-induced intestinal dysbiosis might be important for OSAHS-related AS occurred. Our metabolomic study found that metabolites were correlated to gut microbiome and bile acids fluctuated in patients with OSAHS. Considering gut microbiota and bile acids interact with each other, intestinal flora-bile acid metabolic axis might play a pivotal role in CIH-induced AS. This research will clarify the role of intestinal flora-bile acid metabolic axis in CIH related AS through assessing gut microbiome, bile acid profile, bile acid synthesis/metabolism and transport-related genes. This study will be meaningful to lucubrating the underlying mechanisms of OSAHS related CVD, and provide a reliable theoretical basis for exploring new medical treatments.

动脉粥样硬化（AS）所致心血管疾病（CVD）是引起人类死亡的首要病因，阻塞性睡眠呼吸暂停低通气综合征（OSAHS）致AS相关CVD发生的机制是目前的研究热点。但慢性间歇低氧（CIH）致AS发生的具体机制尚不明确。既往研究显示CIH可导致小鼠肠道厚壁菌、拟杆菌和变形菌属明显紊乱，多样性下降。而目前研究认为肠道菌群紊乱是AS发生的重要原因。因此我们推测CIH引起的肠道菌群紊乱可能是OSAHS相关AS发生的重要因素。我们既往通过代谢组学方法发现，OSAHS和肠道菌群相关代谢物及胆汁酸代谢紊乱均密切相关。肠道菌群和胆汁酸相互调节、相互影响，这提示肠道菌群-胆汁酸代谢轴或许是调控CIH致AS发生的关键环节。本研究拟通过观察CIH下肠道菌群、胆汁酸谱、胆汁酸合成/代谢和转运相关基因表达情况，明确肠道菌群-胆汁酸代谢轴在CIH致AS中的具体作用。本研究有望为探索OSAHS相关CVD治疗方法提供理论依据。

动脉粥样硬化（AS）所致心血管疾病（CVD）是引起人类死亡的首要病因，阻塞性睡眠呼吸暂停低通气综合征（OSAHS）致AS相关CVD发生的机制是目前的研究热点。但慢性间歇低氧（CIH）致AS发生的具体机制尚不明确。既往研究显示CIH可导致小鼠肠道厚壁菌、拟杆菌和变形菌属明显紊乱，多样性下降。而目前研究认为肠道菌群紊乱是AS发生的重要原因。因此我们推测CIH引起的肠道菌群紊乱可能是OSAHS相关AS发生的重要因素。本研究在成功建立CIH动物模型，高脂诱导+CIH等动物模型基础上，发现CIH干预后，小鼠睾丸脂肪、肾周脂肪及棕色脂肪的粒径也发生了明显改变，小鼠肝脏的重量出现了下降。相对于对照组结肠壁的平滑、致密、完整，CIH组小鼠的肠壁显得凹凸不平及疏松肠道通透性增加，肠上皮紧密连接蛋白（Claudin 1 和Occludin）表达存在明显差异。此外，CIH组的盲肠内容物肠道菌生物多样性下降，CIH+高脂组的肠道微生物多样性下降更明显，比较两组间门层次发现，正常组肠道菌群丰度较高的为Firmicutes，Bacteroidetes和Proteobacteria；而CIH干预后，Firmicutes丰度显著增加，而Proteobacteria和 Bacteroidetes丰度显著降低。代谢组学分析发现CIH组和对照组PLS-DA得分图存在明显差异，共发现了9种涉及9个通路的差异代谢物。相关性分析发现了部分差异菌和部分代谢物水平显著相关。给予小鼠 CIH 后，主动脉弓 HE 染色显示血管壁内皮欠连续，局灶内皮细胞局部聚集；局灶平滑肌纤维细胞排列紊乱及肥大，纤维玻璃样变；反映血管内皮细胞功能异常指标，如细胞间黏附分子-1（intercellular cell adhesion molecule-1，ICAM-1）及单核细胞趋化蛋白-2 （monocyte chemoattractant protein 2，MCP-2）高表达，且和Firmicutes/Bacteroidetes比例有显著的相关性。总之，本研究揭示了CIH对小鼠肠道菌及代谢的影响，寻找出了主要菌群和差异代谢物，并发现其丰度和血管内皮功能有一定的相关性，为以后OSAHS合并CVD的治疗提供重要靶点；为OSAHS合并CVD的个体化治疗提供新的思路和手段，最终会将相关成果转化并应用于临床，促进睡眠疾病转化医学研究的发展。