This study aimed to reveal the overall composition of gut microbiota in women with POI. As 15–30% of POI occurrences are considered to be familial (Fenton, 2015). To rule out genetic influences, all subjects recruited in this study were without blood relationship. The results showed all recruited subjects composed primarily of phyla Actinobacteria, Bacteriodetes, Firmicutes and Proteobacteria. The sum relative abundance of Bacteriodetes and Firmicutes accounted for more than 90%, which was consistent with previous studies (Turnbaugh et al., 2006)(Baker et al., 2017). A balance between Bacteriodetes and Firmicutes is important to maintain intestinal homeostasis (Baker et al., 2017), while a significant higher Bacteriodetes/Firmicutes ratio was observed in POI subjects compared to control subjects in this study. Furthermore, the abundant genera were Bacteroides, Bifidobacterium, Blautia, Clostridium, Coprococcus, Faecalibacterium, Megamonas, Prevotella, Roseburia and Ruminococcus in this study. Most of them play important roles in the maintenance of host gastrointestinal homeostasis and health (Sarkar and Pitchumoni, 2017)(Lopetuso et al., 2013). Notably, genera Bifidobacterium, Blautia, Clostridium, Faecalibacterium, Roseburia and Ruminococcus can produce short chain fatty acids (SCFAs) in human gut, such as acetate, butyrate and succinate and so on (Parada Venegas et al., 2019)(Ríos-Covián et al., 2016). SCFAs not only have anti-inflammatory and immunomodulatory properties, but also can influence psychological function and cognitive processes (Ríos-Covián et al., 2016)(Dalile et al., 2019). While the relative abundances of Blautia, Clostridium, Faecalibacterium, Roseburia and Ruminococcus presented decrease trends, especially Faecalibacterium decreased significantly in POI women in this study. Their reduction may impact the cognitive function and inflammation in POI subjects.
There were significant decrease of Firmicutes, and significant increase of Bacteroidetes and Bacteroidetes/Firmicutes ratio in POI women. It is consistent with the microbial community structure of type 1 diabetes and systemic lupus erythematosus patients, with a low proportion of Firmicutes, high proportion of Bacteroidetes and Bacteroidetes/Firmicutes ratio (Demirci et al., 2020)(He et al., 2016). These changes of gut microbiome also play key roles in the pathogenesis of autoimmune disease (De Luca and Shoenfeld, 2019). Moreover, genera Dorea and Sutterella were more abundant in POI group. Increase proportion of Dorea is related to multiple multiple sclerosis, an autoimmune condition (Chen et al., 2016). Sutterella is a mildly pro-inflammatory genus, and its elevated level is associated with cognitive function (Wang et al., 2013)(Ticinesi et al., 2018). As SCFAs producing members with anti-inflammatory properties, Faecalibacterium decreased significantly in POI group in this study, its low proportion is also related to multiple sclerosis (Cantarel et al., 2015). Butyrate producer Butyricimonas (de Oliveira et al., 2017) increased significantly in POI group in this study. On the contrary, a low abundance of Butyricimonas was observed in multiple sclerosis fecal samples (Forbes et al., 2016), that maybe due to different species under Butyricimonas. Type 1 diabetes, systemic lupus erythematousus and multiple sclerosis, and cognitive dysfunction are all closely related to POI. Thus, the alterations of gut microbiome observed in this study may contribute to the development of POI.
Considering hormones, significant lower level of E2 was observed in POI subjects, and it was significantly correlated with the proportion of Bacteroidetes, Firmicutes and Faecalibacterium by adjusting for BMI. Moreover, the FSH, LH and AMH levels were also affected by gut microbiome observed in this study. Accumulating researches indicates that estrogens regulate glucose and lipid metabolism, bone formation and inflammatory response, its reduction can impair estrogen-dependent processes, triggering cardiovascular disease, osteoporosis and so on (Baker et al., 2003)(Li et al., 2016). The gut microbiome has been shown to play a important part in impacting estrogen level through the secretion of β-glucuronidase, which could deconjugate estrogen and affect related physiological process (Plottel and Blaser, 2011)(Baker et al., 2017). It indicates that the altered gut microbiota of POI is associated with the sex hormones. Yet the mechanism under the relations between gut microbiome and sex hormones is not clear due to limited data in this study.
POI leads to several complications, including decrease in bone mineral density, autoimmune, thyroid disease risk and cognitive dysfunction. This study revealed the association between gut microbiota and these complications. These indicate that the dysbiosis of gut microbiota may contribute to the development of POI discussed above. However, limited sample size, participants from the same hospital and the observation of association but not causality, large sample size and multi-center are needed in the further studies. Moreover, metagenome sequencing, measurements of metabolites produced by gut microbiota, animal experiments should also be considered to explore the potential causal mechanism.
In summary, this study demonstrated an altered gut microbial pattern in women with POI against healthy controls. These changes of microbes were closely related to serum hormones. It lays a foundation for revealing the interaction between gut microbiota and POI certainly.