Associations of Human Vaginal and Oral Microbiota with Metabolic Syndrome

Abstract

Human microbiome is the catalog of microbial taxa associated with humans and their genes. Scientific and clinical investigations of microbes were significantly advanced in appreciation of high-throughput sequencing techniques, which enabled discoveries of new taxa and their dynamics on the human body. The first phase of the human microbiome project (HMP), a systematic analysis to investigate the microbiome on major body sites, revealed vast microbial diversity on the mouth, gut, vagina, and skin. Recognizing the varied composition in individuals, an enormous research effort has been undertaken to connect the microbiome with human health and disease. First of all, host genetic variation is one vital factor that differentiates each individual and contributes to disease susceptibility. Recently, it was reported that host genetics interact with the gut microbiome and determine the host BMI proving its role in shaping the host phenotype. In the context, heritability estimates can be used to quantify the genetic influences on the microbial community using monozygotic (MZ) and dizygotic (DZ) twin pairs. Knowing the microbiome heritability, it is expected to understand the host control of and susceptibility to the microbiome. Obesity is an additional factor clearly associated with microbial ecology. It is now commonly accepted that large-scale alterations of the gut microbiota are associated with obesity, which in turn cause inflammation and insulin resistance. Metabolic syndrome (MetS) is closely linked medical conditions to obesity where the conditions include abdominal obesity, elevated blood pressure, hyperglyacemia, hypertension, and dyslipidemia. It is reported that the metabolic disorder increases the risk of cardiovascular disease and diabetes. Hence, association of periodontitis with pathogenic oral bacteria and cardiovascular disease suggests potential link between the obesity and the microbiome from other body sites. An increased ratio of Lactobacillus iners to L. crispatus in obese women adds supports to the notion. In this thesis, the effects of host health and obesity on the non-gut human microbiome from the vagina and the mouth were investigated. First, the vaginal microbiome from 542 female subjects including 222 monozygotic and 56 dizygotic twins aged 29-58 years were analyzed to investigate the host health and genetic contributions on the microbiome. As expected, vaginal microbiota significantly varied by the presence of menopause and bacterial vaginosis (BV) where Lactobacillus and Prevotella were dominant among the vaginal microbiota in terms of levels of microbial abundance and association with the two health conditions. Both UniFrac distance and intraclass correlation coefficients strongly suggested the genetic effects on the vaginal microbiota. With adjustment of key factors affecting the vaginal microbiota, heritability analysis indicated that the abundance of Prevotella in vaginal microbiota is strongly influenced by the host genetics. Subsequent candidate gene analysis showed that SNPs of interleukin 5 (IL-5) in human is strongly associated with both the abundance of Prevotella sp. Further investigation on microbial interactions showed the strongest anticorrelated relationship of Prevotella with Lactobacillus regardless of menopause status. The results provide insights into the interaction between the host genetics and health-associated vaginal bacteria and guides to personalized therapeutic targets to promote female health. Second, the effects of host obesity on the vaginal microbiome were analyzed. An epidemiological observation on a Korean twin cohort revealed a significant increase of microbial diversity in obese subjects regardless of their menopausal state. Subsequent correlation analysis of obese parameters with vaginal bacteria showed that underappreciated and pathogenic vaginal bacteria such as Prevotella, Actinomyces, and Enhydrobacter were positively correlated with waist-hip ratio in pre-menopausal women and systolic blood pressure (SBP) in post-menopausal women. To assess the direct interactions between the vaginal microbiome and obesity, mice were fed a control diet (CTD) or a high fat diet (HFD). Akin to the human, high-fat diet-induced obesity was associated with a significant increase in the level of diversity as well as pathogenic bacteria in female mice. Transplants of the vaginal microbiota across the diet significantly increased metabolic endotoxemia in CTD/HFD groups implying contribution of vaginal microbiota on systemic inflammation. Third, an association of the oral microbiome with metabolic syndrome (MetS) was analyzed using 228 subgingival plaque and fecal samples. Significant alterations of microbial diversity were observed in both oral and gut microbiome between individuals with MetS and healthy controls. Network analysis showed clear clusters of microbiome depending on the host health status, and further comprehensive analysis on the oral microbiome identified Granulicatella and Neisseria as enriched bacteria in individuals with MetS and Peptococcus as enriched bacteria in healthy controls. Subsequent validation of the oral bacteria by real-time quantitative PCR (qPCR) showed the healthy controls possessed significantly lower levels of Granulicatella (p = 0.023) and greater ratio of Peptococcus and Granulicatella (p < 0.05). In conclusion, this thesis revealed an intimate association of the non-gut human microbiome and systemic disorders such as obesity and metabolic syndrome. The results suggest that metabolic dysfunction can exert significant effects on the vaginal and the oral microbiome. Targeting specific vaginal or oral bacteria could alleviate the risks of the systemic disorder and improve the quality of public health.