An increase in obesity is positively correlated with metabolic diseases, such as type 2 diabetes mellitus, dyslipidemia, atherosclerosis, hypertension, and diabetes. Epidemiological survey shows that about 35% of adults and 20% of children in the United States and other countries have developed obesity in the past 30 years [8]. The risk factors of hypertension, coronary heart disease, diabetes, metabolic syndrome, and other complications caused by obesity are independent risk factors of coronary heart disease and ischemic stroke. Weight control is a key to the prevention and treatment of chronic diseases.
In recent years, considerable evidence on miRNA studies has shown that miRNA is an important factor in the epigenetic regulation of adipogenesis [9, 10] and obesity [11, 12]. A previous study [13] reported that miRNAs are highly important for fat development and the whole body. Therefore, elucidating the mechanisms of miRNAs is highly important. As a new endocrine factor, circulating microRNAs can be released from various tissues and act as endocrine and paracrine messengers to promote the interaction between donor cells and tissues and recipient cells or target tissues [14]. Increasing evidence suggests that circulating miRNAs are closely related to obese adults, young subjects, and children [15, 16]. A study of 2-6-year-old preschool obese children found that miR-190a and miR-95 in circulation can serve as molecular markers of insulin resistance in obese children [17]. In addition, a study of 70 children aged 5–10 years found that plasma miRNAs may be used as a potential screening tool for endothelial dysfunction in children with cardiovascular diseases [18]. Ortega [19] analyzed the response between different levels of circulating miRNA expression and obesity and weight loss in adults. Carlos found that obesity changes the miRNA profile of plasma exosomes in mice; in specific, it can increase the expression levels of miR-122, miR-192, miR-27a-3p, and miR-27b-3p. Treatment of lean mice with exosomes isolated from obese mice leads to glucose intolerance and insulin resistance [20]. In our study, the expression levels of miRNAs in circulating plasma of obese and lean children aged 8–12 years were significantly different. Among them, the expression levels of hsa-miR-126-3p, hsa-miR-15b-5p, hsa-miR-199a-3p, hsa-miR-20a-5p, hsa-miR-223-3p, hsa-miR-23a-3p, and hsa-miR-24-3p were upregulated and those of hsa-miR-21-5p, hsa-miR-27a-3p, and hsa-miR-130a-3p were downregulated in the obese group. The changes in miRNA expression may affect the growth and development of the body through apparent regulation, which plays an important role in obesity. Some studies found that circulating miR-15b-5p, miR-486-5p, and miR-122-5p are related to obesity and overweight, and analysis of four high-throughput sequencing articles revealed that these miRNAs are good candidates as obesity biomarkers [21]. In addition, miR-486, miR-146b, and miR-15b are significantly expressed in the circulation of obese children and adults with type 2 diabetes. Among them, miR-486 is involved in promoting pre-adipocyte proliferation and myotube glucose tolerance. Meanwhile, miR-146b and miR-15b are involved in the inhibition of pancreatic insulin secretion induced by high-concentration glucose and participate in the pathological process of obesity and T2D [22]. In a study, 16 of the 20 miRNAs tested in obese children are twice higher than those in the control group. Among them, miR199 and miR-122 are remarkably increased in obese children [23]. Adipogenesis is a pluripotent differentiation process in which mesenchymal stem cells can differentiate into adipocytes through adipocyte precursor cells [24]. The effects of miRNA on adipocyte differentiation are diverse. Some miRNAs promote adipocyte differentiation, and some miRNAs inhibit adipocyte differentiation [25]. MiR-143 is the first miRNA related to adipocyte differentiation. The expression of miR-143 gradually increases with the differentiation and maturation of human adipose precursor cells [26]. Price found that miR-33b overexpression can inhibit pre-adipocyte proliferation and reduce lipid droplets during adipocyte differentiation [27]. In the abdominal adipose tissue of human and obese mice, high expression of miR-146a can reduce the inflammatory response of adipocytes by inhibiting the JNK and p38 signaling pathways [28]. In conclusion, the mechanism by which miRNAs regulate adipocyte differentiation remains to be explored.
The expression levels of miRNAs in circulating plasma of obese and lean children aged 8–12 years were significantly different. Among them, the expression levels of hsa-miR-126-3p, hsa-miR-15b-5p, hsa-miR-199a-3p, hsa-miR-20a-5p, hsa-miR-223-3p, hsa-miR-23a-3p, and hsa-miR-24-3p were upregulated whereas those of hsa-miR-21-5p, hsa-miR-27a-3p, and hsa-miR-130a-3p were downregulated in the obese group. The changes in miRNA expression may affect the growth and development of the body through apparent regulation and play an important role in obesity. TaqMan probe were used to verify the accuracy expression of miRNA. Results showed that the expression levels of hsa-miR-126-3p, hsa-miR-15b-5p, hsa-miR-199a-3p, hsa-miR-20a-5p, and hsa-miR-24-3p were positively correlated with BMI and FMP but not with age, except for hsa-miR-23a-3p. This result indicates that the above six miRNAs are markers of obesity. Multiple linear regression analysis of the correlation between miRNA and obesity showed that the expression levels of hsa-miR-15b-5p and hsa-miR-223-3p were significantly different between the obese and lean groups regardless of age and gender. However, the specific mechanism needs further study.
A pathway analysis presented the reported and predicted target genes of significantly upregulated miRNAs. hsa-miR-15b-5p and hsa-miR-223-3p were involved in many obesity-related functions, such as the FoxO, insulin, Ras, and AMPK signaling pathways. In particular, hsa-miR-15b-5p-regulated genes are involved many functions. Collectively, changes in the expression of hsa-miR-15b-5p and hsa-miR-223-3p in obese individuals may influence the pathophysiology of obesity, insulin resistance, and diabetes.
The present study attempted to identify the key miRNAs regulating obesity through microarray and correlation analyses. Results suggest that hsa-miR-15b-5p and hsa-miR-223-3p are promising targets for early intervention of childhood obesity. However, the sample size needs to be further expanded for further study. In addition, the related mechanisms must be elaborated at the cellular and animal levels.