The possible role of visceral fat in early pregnancy as a predictor of gestational diabetes mellitus by regulating adipose-derived exosomes miRNA-148 family: protocol for a nested case-control study in a cohort study

Gestational diabetes mellitus (GDM) is a common complication of pregnancy, affecting 7–25% of pregnancies worldwide [1, 2], forming a severe public health concern. GDM contributes to the occurrence of preeclampsia [3], gestational hypertension [4], macrosomia [5] and preterm birth [6]. It is also associated with long-term adverse outcomes in postpartum women and offspring, including increased risk of developing obesity [7], cardiovascular disease [8] and type 2 diabetes [9]. Previous study reported that the incidence of GDM in Asia was as high as 20.9% [10]. A systematic review [11] suggested that the incidence of GDM in Chinese mainland was 14.8%, which indicated that China might have the largest number of GDM patients in the world. The city of Qingdao, the cite of our field work, had an incidence of GDM as 17.4% [12], which was higher than that reported as the average level in the mainland of China. In recent years, there is an increasing trend in the prevalence of GDM globally, including in China [13‐15]. In view of the adverse consequences and high prevalence of GDM, identifying the major risk factors for GDM in an early stage of the pregnant is essential.

Risk factors such as pre-pregnancy overweight and obesity [16], advanced maternal age [17], family history of diabetes [18] have been proposed to be related to the incidence of GDM, previously. However, different from those constant risk factors, overweight/obesity is a potentially modifiable factor of GDM. Accordingly, body mass index (BMI), waist circumference and other related anthroprometric parameters have been proposed to predict GDM. However, their predictive power for GDM was controversial. Visceral fat, better reflecting of the distribution of body fat [19], has been reported to play an important role in the prevalence of GDM [20, 21]. A cohort study [22] showed that visceral fat may be a powerful predictor of GDM. Additionally, another study concluded that the accuracy of visceral fat thickness in early pregnancy to predict GDM may be better than that of BMI [20]. However, the pathogenesis of GDM due to visceral fat remains largely unknown. In recent years, studies have shown that adipose-derived exosomes play a significant role in the occurrence and development of GDM. The research results published on journal of Cell [23] in 2017 showed that adipose tissue in obese mice secreted miRNA-containing exosomes, which induced glucose intolerance and insulin resistance when administered to lean mice. In the process, adipose-derived exosomes miRNA played an important role. Another research indicated that visceral adipose-derived exosomes participated in receptor-insulin signal transduction through down-regulation of miRNA-148-a and miRNA-148-b expression [24‐26]. Therefore, the abnormal expression of miRNA in adipose-derived exosomes caused by visceral fat accumulation may be an important mechanism in the pathogenesis of GDM.

We hypothesized that visceral fat thickness may predict GDM by regulating the adipose-derived exosomes miRNA-148 family, and verify this hypothesis in a cohort & nested case-control study.

Our study is a population-based study aimed to assess accuracy of visceral fat thickness in predicting GDM and the visceral fat how regulates the miRNA-148 family of adipose-derived exosomes to cause GDM. Currently, more and more scholars discuss the predictive efficiency of anthropometric parameters for GDM [29‐31]. However, there were few studies on the prediction of visceral fat thickness to GDM, moreover, the pathogenesis of visceral fat leading to GDM was unclear. At present, extensive efforts are being focused on the adipose-derived exosomes in relation to GDM. Previous study found that adipose-derived exosomes were the main source of circulating miRNA [32], these circulating miRNAs played an important role in regulating mRNA expression and translation. Adipose-derived exosomes miRNA were also associated with development of insulin resistance. The analysis of adipose-derived exosomes miRNA content pre- and post-gastric bypass showed upregulation of miR103-3p which was known to target the insulin receptor signaling pathway and was previously found to be downregulated in diabetes [33‐35]. These studies demonstrated that adipose-derived exosomes can mediate gene regulation and functioning in distant cells. Therefore, in obese pregnancies, adipose-derived exosomes may communicate with the placenta and induce changes in its function which may contribute to the development of GDM. Thus, it is possible that adipose-derived exosomes were factors in the pathogenesis of GDM. However, there were few studies about visceral fat regulating the miRNA-148 family of adipose-derived exosomes to cause GDM, so we designed this study.

Our research has some advantages. Firstly, our case control study will be nested within a prospective cohort and the measurement of visceral fat thickness and adipose-derived exosomes miRNA-148 family will prior to the diagnosis of GDM, which allow us to estimate the causal relationship of visceral fat thickness on the development of GDM, although there are more and more studies on the effect of adipose-derived exosomes on diseases, our study nested case-control study on the basis of prospective cohort study, which is more scientific and reliable. Secondly, nested case-control study will save time, effort, and money. Thirdly, the GDM cases will be confirmed by medical records following a clear definition based on IADPSG guidelines rather than self-reported and it will guarantee reliability of results. However, on the basis of cohort study, a limitation of this study is loss of follow-up, but we will keep in touch with pregnant women at any time through wechat, which will greatly reduce our loss rate.

In conclusion, to a certain extent, the study is helpful to verify the effect of visceral fat on the development of GDM, and it is helpful to further clarify the pathophysiological mechanism of gestational diabetes. It also provides technical support for effective screening of high-risk pregnant women with GDM.