New emerging tasks for microRNAs in the control of β-cell activities

Unraveling the role of microRNAs: potential biomarkers for gestational diabetes mellitus revealed through RNA sequencing analysis

BACKGROUND

Gestational diabetes mellitus (GDM) poses significant health risks for both mothers and children, contributing to long-term complications such as type 2 diabetes and cardiovascular disease. This study explores the potential of microRNAs (miRNAs) as biomarkers for GDM by analyzing peripheral blood samples from GDM patients.

METHOD

Ten samples, including peripheral blood from 5 GDM patients and 5 controls, were collected to perform the RNA sequencing analysis. Differentially expressed miRNAs were further validated by quantitative real-time polymerase chain reaction.

RESULTS

A total of 2287 miRNAs were identified, 229 of which showed differential expression. Validation by qRT-PCR confirmed significant up-regulation of miR-5193, miR-5003-3p, miR-3127-5p, novel-miR-96, miR-6734-5p, and miR-122-5p, while miR-10395-3p was down-regulated. Bioinformatics analyses revealed the involvement of these miRNAs in pathways associated with herpes simplex virus 1 infection.

CONCLUSION

This study provides insights into the differential expression of miRNAs in GDM patients and their potential roles in disease pathogenesis. It suggests that the differentially expressed miRNAs could serve as potential biomarkers for GDM, shedding light on the complex molecular mechanisms involved.

MicroRNA-125b regulates vitamin D resistance by targeting CYP24A1 in the progression of gestational diabetes mellitus

Vitamin D deficiency is prevalent in pregnancy and has been associated with increased occurrences of preeclampsia, cesarean delivery, neonatal bacterial vaginosis, and gestational diabetes. CYP24A1, recognized as a key factor in vitamin D metabolism homeostasis, encodes 24-hydroxylase responsible for converting 25(OH)D3 and 1,25(OH)2D3 into inactive metabolites. Recently, we have reported CYP24A1 overexpression in patients with gestational diabetes mellitus (GDM) and trophoblast cells exposed to hyperglycemia. In this study, we explored miRNA-mediated regulation of CYP24A1 in GDM progression, validating our findings through silencing experiments in a trophoblast cell line. In silico tools identified miR-125b-5p as a putative target of CYP24A1. Expression analysis revealed downregulation of miR-125b-5p in blood samples from early GDM and GDM compared to healthy pregnant women, positively correlating with vitamin D levels. Hyperglycemic exposure in human trophoblastic cell lines (BeWo) decreased miR-125b-5p expression, concomitant with an increase in CYP24A1. To confirm the regulatory role of miR-125b on CYP24A1, we transfected BeWo cells with antimiR-125b or miR-125b mimic. AntimiR-125b transfection heightened CYP24A1 levels, while miR-125b mimic overexpression resulted in decreased CYP24A1 expression. These findings establish miR-125b as a regulator of CYP24A1. To explore the influence of miR-125b on vitamin D metabolism, trophoblast cells overexpressing miR-125b were treated with 0.1 and 1 µM calcitriol. Hyperglycemic conditions exhibited a reduction in CYP24A1 levels. Collectively, our results indicate that miR-125b may regulate vitamin D metabolism by targeting CYP24A1, contributing to GDM progression. These findings may pave the way for understanding vitamin D resistance in concurrent GDM development and identifying novel miRNAs targeting CYP24A1.

Glimepiride Compared to Liraglutide Increases Plasma Levels of miR-206, miR-182-5p, and miR-766-3p in Type 2 Diabetes Mellitus: A Randomized Controlled Trial

BACKGRUOUND

Diabetes is a chronic disease with several long-term complications. Several glucose-lowering drugs are used to treat type 2 diabetes mellitus (T2DM), e.g., glimepiride and liraglutide, in which both having different modes of action. Circulating microRNAs (miRNAs) are suggested as potential biomarkers that are associated with the disease development and the effects of the treatment. In the current study we evaluated the effect of glimepiride, liraglutide on the expression of the circulating miRNAs.

METHODS

The present study is a post hoc trial from a previously randomized control trial comparing liraglutide versus glimepiride both in combination with metformin in subjects with T2DM, and subclinical heart failure. miRNAs were determined in the subjects' serum samples with next generation sequencing. Expression patterns of the circulating miRNAs were analyzed using bioinformatic univariate and multivariate analyses (clinical trial registration: NCT01425580).

RESULTS

Univariate analyses show that treatment with glimepiride altered expression of three miRNAs in patient serum, miR-206, miR-182-5p, and miR-766-3p. Both miR-182-5p and miR-766-3p were also picked up among the top contributing miRNAs with penalized regularised logistic regressions (Lasso). The highest-ranked miRNAs with respect to Lasso coefficients were miR-3960, miR-31-5p, miR-3613-3p, and miR-378a-3p. Liraglutide treatment did not significantly influence levels of circulating miRNAs.

CONCLUSION

Present study indicates that glucose-lowering drugs differently affect the expression of circulating miRNAs in serum in individuals with T2DM. More studies are required to investigate possible mechanisms by which glimepiride is affecting the expression of circulating miRNAs.

Reduced miR-184-3p expression protects pancreatic β-cells from lipotoxic and proinflammatory apoptosis in type 2 diabetes via CRTC1 upregulation

The loss of functional β-cell mass in type 2 diabetes (T2D) is associated with molecular events that include β-cell apoptosis, dysfunction and/or dedifferentiation. MicroRNA miR-184-3p has been shown to be involved in several β-cell functions, including insulin secretion, proliferation and survival. However, the downstream targets and upstream regulators of miR-184-3p have not been fully elucidated. Here, we show reduced miR-184-3p levels in human T2D pancreatic islets, whereas its direct target CREB regulated transcription coactivator 1 (CRTC1) was increased and protects β-cells from lipotoxicity- and inflammation-induced apoptosis. Downregulation of miR-184-3p in β-cells leads to upregulation of CRTC1 at both the mRNA and protein levels. Remarkably, the protective effect of miR-184-3p is dependent on CRTC1, as its silencing in human β-cells abrogates the protective mechanism mediated by inhibition of miR-184-3p. Furthermore, in accordance with miR-184-3p downregulation, we also found that the β-cell-specific transcription factor NKX6.1, DNA-binding sites of which are predicted in the promoter sequence of human and mouse MIR184 gene, is reduced in human pancreatic T2D islets. Using chromatin immunoprecipitation analysis and mRNA silencing experiments, we demonstrated that NKX6.1 directly controls both human and murine miR-184 expression. In summary, we provide evidence that the decrease in NKX6.1 expression is accompanied by a significant reduction in miR-184-3p expression and that reduction of miR-184-3p protects β-cells from apoptosis through a CRTC1-dependent mechanism.

Exosomal miR-140-3p and miR-143-3p from TGF-β1-treated pancreatic stellate cells target BCL2 mRNA to increase β-cell apoptosis

BACKGROUND

People with chronic pancreatitis (CP) normally develop a fibrotic pancreas with reduced β-cell mass. Limited studies have focused on the development and pathogenesis of CP-related diabetes. MiRNAs packaged as exosomes are the key regulators of β-cell dysfunction. This study aimed to define the effect of exosomal miRNA from activated pancreatic stellate cells (PSCs) on β-cells.

METHODS

Exosomes in the supernatants of mouse PSCs lines were extracted via ultracentrifugation and then identified. The role of exosomes secreted by transforming growth factor-β1 (TGF-β1)-treated PSCs in β-cell function was assessed. MiRNAs were prepared from exosomes extracted from TGF-β1-treated and untreated PSCs (T-Exo or C-Exo), and the miRNA expression profiles were compared by microarray. Then, miR-140-3p and miR-143-3p were overexpressed or inhibited in MIN6 cells and islets to determine their molecular and functional effects.

RESULTS

Exosomes were the predominant extracellular vesicles secreted by PSCs into the culture medium. The MIN6 cells incubated with T-Exo had less insulin secretion and lower viability than the MIN6 cells incubated with PBS or C-Exo. MiR-140-3p and miR-143-3p were notably upregulated in T-Exo. Enhancing the expression of miR-140-3p and miR-143-3p in β-cells decreased the cell count and viability and increased the cleaved caspase-3 levels. Mechanistically, T-Exo mediated the intercellular transfer of miR-140-3p and miR-143-3p by targeting the B-cell lymphoma 2 gene in recipient β-cells to induce cell death.

CONCLUSIONS

Exosomal miRNA transfer as a communication mode between PSCs and β-cells, which may be explored for its therapeutic utility.

Maturation of beta cells: lessons from in vivo and in vitro models

The ability to maintain normoglycaemia, through glucose-sensitive insulin release, is a key aspect of postnatal beta cell function. However, terminally differentiated beta cell identity does not necessarily imply functional maturity. Beta cell maturation is therefore a continuation of beta cell development, albeit a process that occurs postnatally in mammals. Although many important features have been identified in the study of beta cell maturation, as of yet no unified mechanistic model of beta cell functional maturity exists. Here, we review recent findings about the underlying mechanisms of beta cell functional maturation. These findings include systemic hormonal and nutritional triggers that operate through energy-sensing machinery shifts within beta cells, resulting in primed metabolic states that allow for appropriate glucose trafficking and, ultimately, insulin release. We also draw attention to the expansive synergistic nature of these pathways and emphasise that beta cell maturation is dependent on overlapping regulatory and metabolic networks.

MicroRNAs and Exosomal microRNAs May Be Possible Targets to Investigate in Gestational Diabetes Mellitus

Gestational diabetes mellitus (GDM) is defined as glucose intolerance that occurs during the second or third trimester of pregnancy. As the incidence of GDM rises, so does the risk of maternal and fetal complications with short- and long-term consequences. As a result, early diagnosis and treatment of this condition are important to avoiding adverse pregnancy outcomes. Exosomes are tiny vesicles secreted by living cells which contain a variety of bioactive substances. They are released by cells to facilitate cell-to-cell communication and regulate a variety of biological processes such as cellular immune response, inflammatory response, and apoptosis, among others. Many studies have recently confirmed that changes in the expression and secretion of exosomal miRNAs can be used as novel markers for the diagnosis, prognosis, and treatment of GDM. In this review, we summarized the various roles of exosomal miRNAs and circulating miRNAs in GDM. We found that the changes in the expression of certain miRNAs could be used to diagnosing GDM. Exosomal miRNAs target metabolic pathways, resulting in insulin resistance. We also highlighted the potential for miRNAs and exosomal miRNAs to be used as biomarkers for diagnosis or therapeutic agents.

Molecular Mechanisms of Nutrient-Mediated Regulation of MicroRNAs in Pancreatic β-cells

Pancreatic β-cells within the islets of Langerhans respond to rising blood glucose levels by secreting insulin that stimulates glucose uptake by peripheral tissues to maintain whole body energy homeostasis. To different extents, failure of β-cell function and/or β-cell loss contribute to the development of Type 1 and Type 2 diabetes. Chronically elevated glycaemia and high circulating free fatty acids, as often seen in obese diabetics, accelerate β-cell failure and the development of the disease. MiRNAs are essential for endocrine development and for mature pancreatic β-cell function and are dysregulated in diabetes. In this review, we summarize the different molecular mechanisms that control miRNA expression and function, including transcription, stability, posttranscriptional modifications, and interaction with RNA binding proteins and other non-coding RNAs. We also discuss which of these mechanisms are responsible for the nutrient-mediated regulation of the activity of β-cell miRNAs and identify some of the more important knowledge gaps in the field.

miR-124-3p Down-Regulation Influences Pancreatic-β-Cell Function by Targeting Secreted Frizzled-Related Protein 5 (SFRP5) in Diabetes Mellitus

Diabetes mellitus (DM) is a complex metabolic disease characterized by hyperglycemia, insulin resistance and pancreatic β-cell dysfunction. There are evidences showed that microRNAs (miRNAs) play important roles in DM. The purpose of our study was to determine the role of miR-124-3p in DM. Quantitative reverse transcription PCR (qRT-PCR) was applied to measure the level of miR- 124-3p in peripheral blood from healthy control patients and DM patients. Then we explored the effects of miR-124-3p inhibitor on the secretion of insulin of pancreatic β-cells. Moreover, we determined the effects of miR-124-3p inhibitor on the apoptosis and viability of pancreatic β-cells through flow cytometry and MTT assay. And we also used western blotting to detect the protein expression of cleaved-caspase3/pro-caspase3, and the activity of caspase3 was detected. In addition, we confirmed the direct target of miR-124-3p using Dual luciferase reporter assay. Our data showed that in the blood of DM patients, SFRP5 was significantly reduced, while miR-124-3p was increased significantly. Furthermore, we found that down-regulation of miR-124-3p increased total insulin content in INS-1 cells, enhanced insulin secretion in INS-1 cells. Furthermore, we revealed that miR-124-3p inhibitor enhanced INS-1 cell viability, decreased apoptosis of INS-1 cells, increased pro-caspase3 expression, decreased cleaved-caspase3 expression and caspase3 activity. In addition, we proved SFRP5 was a direct target of miR-124-3p in pancreatic β-cells. Moreover, SFRP5-siRNA reversed all the effects of miR-124-3p knockdown on pancreatic β-cells.

The Predominant microRNAs in β-cell Clusters for Insulin Regulation and Diabetic Control

micro (mi)-RNAs are vital regulators of multiple processes including insulin signaling pathways and glucose metabolism. Pancreatic β-cells function is dependent on some miRNAs and their target mRNA, which together form a complex regulative network. Several miRNAs are known to be directly involved in β-cells functions such as insulin expression and secretion. These small RNAs may also play significant roles in the fate of β-cells such as proliferation, differentiation, survival and apoptosis. Among the miRNAs, miR-7, miR-9, miR-375, miR-130 and miR-124 are of particular interest due to being highly expressed in these cells. Under diabetic conditions, although no specific miRNA profile has been noticed, the expression of some miRNAs and their target mRNAs are altered by posttranscriptional mechanisms, exerting diverse signs in the pathobiology of various diabetic complications. The aim of this review article is to discuss miRNAs involved in the process of stem cells differentiation into β-cells, resulting in enhanced β-cell functions with respect to diabetic disorders. This paper will also look into the impact of miRNA expression patterns on in vitro proliferation and differentiation of β-cells. The efficacy of the computational genomics and biochemical analysis to link the changes in miRNA expression profiles of stem cell-derived β-cells to therapeutically relevant outputs will be discussed as well.

MiRNAs in Gestational Diabetes Mellitus: Potential Mechanisms and Clinical Applications

Gestational diabetes mellitus (GDM) is a common pregnancy complication which is normally diagnosed in the second trimester of gestation. With an increasing incidence, GDM poses a significant threat to maternal and offspring health. Therefore, we need a deeper understanding of GDM pathophysiology and novel investigation on the diagnosis and treatment for GDM. MicroRNAs (miRNAs), a class of endogenic small noncoding RNAs with a length of approximately 19-24 nucleotides, have been reported to exert their function in gene expression by binding to proteins or being enclosed in membranous vesicles, such as exosomes. Studies have investigated the roles of miRNAs in the pathophysiological mechanism of GDM and their potential as noninvasive biological candidates for the management of GDM, including diagnosis and treatment. This review is aimed at summarizing the pathophysiological significance of miRNAs in GDM development and their potential function in GDM clinical diagnosis and therapeutic approach. In this review, we summarized an integrated expressional profile and the pathophysiological significance of placental exosomes and associated miRNAs, as well as other plasma miRNAs such as exo-AT. Furthermore, we also discussed the practical application of exosomes in GDM postpartum outcomes and the potential function of several miRNAs as therapeutic target in the GDM pathological pathway, thus providing a novel clinical insight of these biological signatures into GDM therapeutic approach.

Association of miR-146a polymorphism rs2910164 and type 2 diabetes risk: a meta-analysis

OBJECTIVE

Circulating miR-146a is aberrantly expressed in patients with type 2 diabetes (T2D), probably resulting from gene polymorphisms. However, the role of polymorphism rs2910164 in T2D pathogenesis remains controversial. Thus, we designed a meta-analysis to investigate the association between rs2910164 and T2D.

METHODS

PubMed and Embase were searched for eligible papers in English published through September 2, 2019. Random or fixed effect models were used to determine risk estimates according to heterogeneities.

RESULTS

Four studies, involving 2,069 patients and 1,950 controls, were included. Odds ratios (ORs) and 95% confidence intervals (95% CIs) were used to pool the effect size. The pooled ORs and 95% CIs were 1.501 (0.887-2.541), 1.102 (0.931-1.304), 1.276 (0.900-1.811), 1.204 (0.878-1.652), 1.238 (0.880-1.740), and 1.350 (0.904-2.016) under the homozygote, heterozygote (CG vs. GG and CC vs. CG), dominant, allele, and recessive models, respectively. Heterogeneity was detected in most genetic models, with subgroup analyses performed by ethnicity, genotyping method, and disease duration. The co-dominant model was determined to be the most appropriate genetic model.

CONCLUSIONS

Our findings suggested that polymorphism rs2910164 is not correlated with T2D susceptibility. However, the results should be interpreted with caution because of confounding factors.

A surrogate of Roux-en-Y gastric bypass (the enterogastro anastomosis surgery) regulates multiple beta-cell pathways during resolution of diabetes in ob/ob mice

BACKGROUND

Bariatric surgery is an effective treatment for type 2 diabetes. Early post-surgical enhancement of insulin secretion is key for diabetes remission. The full complement of mechanisms responsible for improved pancreatic beta cell functionality after bariatric surgery is still unclear. Our aim was to identify pathways, evident in the islet transcriptome, that characterize the adaptive response to bariatric surgery independently of body weight changes.

METHODS

We performed entero-gastro-anastomosis (EGA) with pyloric ligature in leptin-deficient ob/ob mice as a surrogate of Roux-en-Y gastric bypass (RYGB) in humans. Multiple approaches such as determination of glucose tolerance, GLP-1 and insulin secretion, whole body insulin sensitivity, ex vivo glucose-stimulated insulin secretion (GSIS) and functional multicellular Ca2+-imaging, profiling of mRNA and of miRNA expression were utilized to identify significant biological processes involved in pancreatic islet recovery.

FINDINGS

EGA resolved diabetes, increased pancreatic insulin content and GSIS despite a persistent increase in fat mass, systemic and intra-islet inflammation, and lipotoxicity. Surgery differentially regulated 193 genes in the islet, most of which were involved in the regulation of glucose metabolism, insulin secretion, calcium signaling or beta cell viability, and these were normalized alongside changes in glucose metabolism, intracellular Ca2+ dynamics and the threshold for GSIS. Furthermore, 27 islet miRNAs were differentially regulated, four of them hubs in a miRNA-gene interaction network and four others part of a blood signature of diabetes resolution in ob/ob mice and in humans.

INTERPRETATION

Taken together, our data highlight novel miRNA-gene interactions in the pancreatic islet during the resolution of diabetes after bariatric surgery that form part of a blood signature of diabetes reversal.

FUNDING

European Union's Horizon 2020 research and innovation programme via the Innovative Medicines Initiative 2 Joint Undertaking (RHAPSODY), INSERM, Société Francophone du Diabète, Institut Benjamin Delessert, Wellcome Trust Investigator Award (212625/Z/18/Z), MRC Programme grants (MR/R022259/1, MR/J0003042/1, MR/L020149/1), Diabetes UK (BDA/11/0004210, BDA/15/0005275, BDA 16/0005485) project grants, National Science Foundation (310030-188447), Fondation de l'Avenir.

Lymphocyte-Derived Exosomal MicroRNAs Promote Pancreatic β Cell Death and May Contribute to Type 1 Diabetes Development

Type 1 diabetes is an autoimmune disease initiated by the invasion of pancreatic islets by immune cells that selectively kill the β cells. We found that rodent and human T lymphocytes release exosomes containing the microRNAs (miRNAs) miR-142-3p, miR-142-5p, and miR-155, which can be transferred in active form to β cells favoring apoptosis. Inactivation of these miRNAs in recipient β cells prevents exosome-mediated apoptosis and protects non-obese diabetic (NOD) mice from diabetes development. Islets from protected NOD mice display higher insulin levels, lower insulitis scores, and reduced inflammation. Looking at the mechanisms underlying exosome action, we found that T lymphocyte exosomes trigger apoptosis and the expression of genes involved in chemokine signaling, including Ccl2, Ccl7, and Cxcl10, exclusively in β cells. The induction of these genes may promote the recruitment of immune cells and exacerbate β cell death during the autoimmune attack. Our data point to exosomal-miRNA transfer as a communication mode between immune and insulin-secreting cells.

MicroRNAs in islet hormone secretion

Pancreatic islet hormone secretion is central in the maintenance of blood glucose homeostasis. During development of hyperglycaemia, the β-cell is under pressure to release more insulin to compensate for increased insulin resistance. Failure of the β-cells to secrete enough insulin results in type 2 diabetes (T2D). MicroRNAs (miRNAs) are short non-coding RNA molecules suitable for rapid regulation of the changes in target gene expression needed in β-cell adaptations. Moreover, miRNAs are involved in the maintenance of α-cell and β-cell phenotypic identities via cell-specific, or cell-enriched expression. Although many of the abundant miRNAs are highly expressed in both cell types, recent research has focused on the role of miRNAs in β-cells. It has been shown that highly abundant miRNAs, such as miR-375, are involved in several cellular functions indispensable in maintaining β-cell phenotypic identity, almost acting as "housekeeping genes" in the context of hormone secretion. Despite the abundance and importance of miR-375, it has not been shown to be differentially expressed in T2D islets. On the contrary, the less abundant miRNAs such as miR-212/miR-132, miR-335, miR-130a/b and miR-152 are deregulated in T2D islets, wherein the latter three miRNAs were shown to play key roles in regulating β-cell metabolism. In this review, we focus on β-cell function and describe miRNAs involved in insulin biosynthesis and processing, glucose uptake and metabolism, electrical activity and Ca²⁺ -influx and exocytosis of the insulin granules. We present current status on miRNA regulation in α-cells, and finally we discuss the involvement of miRNAs in β-cell dysfunction underlying T2D pathogenesis.

MicroRNA Expression Analysis of In Vitro Dedifferentiated Human Pancreatic Islet Cells Reveals the Activation of the Pluripotency-Related MicroRNA Cluster miR-302s

β-cell dedifferentiation has been recently suggested as an additional mechanism contributing to type-1 and to type-2 diabetes pathogenesis. Moreover, several studies demonstrated that in vitro culture of native human pancreatic islets derived from non-diabetic donors resulted in the generation of an undifferentiated cell population. Additional evidence from in vitro human β-cell lineage tracing experiments, demonstrated that dedifferentiated cells derive from β-cells, thus representing a potential in vitro model of β-cell dedifferentiation. Here, we report the microRNA expression profiles analysis of in vitro dedifferentiated islet cells in comparison to mature human native pancreatic islets. We identified 13 microRNAs upregulated and 110 downregulated in islet cells upon in vitro dedifferentiation. Interestingly, among upregulated microRNAs, we observed the activation of microRNA miR-302s cluster, previously defined as pluripotency-associated. Bioinformatic analysis indicated that miR-302s are predicted to target several genes involved in the control of β-cell/epithelial phenotype maintenance; accordingly, such genes were downregulated upon human islet in vitro dedifferentiation. Moreover, we uncovered that cell–cell contacts are needed to maintain low/null expression levels of miR-302. In conclusion, we showed that miR-302 microRNA cluster genes are involved in in vitro dedifferentiation of human pancreatic islet cells and inhibits the expression of multiple genes involved in the maintenance of β-cell mature phenotype.

LncRNAs: Proverbial Genomic "Junk" or Key Epigenetic Regulators During Cardiac Fibrosis in Diabetes?

Long non-coding RNAs (lncRNAs) are critical regulators in a multitude of biological processes. Recent evidences demonstrate potential pathogenetic implications of lncRNAs in diabetic cardiomyopathy (DCM); however, the majority of lncRNAs have not been comprehensively characterized. While the precise molecular mechanisms underlying the functions of lncRNAs remain to be deciphered in DCM, emerging data in other pathophysiological conditions suggests that lncRNAs can have versatile features such as genomic imprinting, acting as guides for certain histone-modifying complexes, serving as scaffolds for specific molecules, or acting as molecular sponges. In an effort to better understand these features of lncRNAs in the context of DCM, our review will first summarize some of the key molecular alterations that occur during fibrosis in the diabetic heart (extracellular proteins and endothelial-to-mesenchymal transitioning), followed by a review of the current knowledge on the crosstalk between lncRNAs and major epigenetic mechanisms (histone methylation, histone acetylation, DNA methylation, and microRNAs) within this fibrotic process.

Do skeletal muscle-secreted factors influence the function of pancreatic β-cells?

Skeletal muscle is an endocrine organ that secretes a variety of compounds including proteins (myokines), metabolites, microRNAs (miRNAs), and exosomes, many of which are regulated by exercise and play important roles in endocrine signaling. Interorgan communication via muscle-secreted factors therefore provides a novel area for investigation and implicates the importance of skeletal muscle in the pathophysiology of metabolic diseases such as type 2 diabetes (T2D). Given that underlying molecular mechanisms of T2D are subject of ongoing research, in light of new evidence it is probable that interorgan cross-talk between skeletal muscle and pancreatic β-cells plays an important part. To date, the number of studies published in this field provide the basis of this review. Specifically, we discuss current experimental evidence in support for a role of skeletal muscle to β-cell cross-talk, paying particular attention to muscle-secreted factors including myokines, metabolites, miRNAs, and factors contained within exosomes that influence the function and/or the survival of β-cells in health and disease. In reviewing this evidence, we provide an update on the list of known muscle-secreted factors that have potential to influence the function and/or survival of β-cells under normal and diabetic conditions. We also report limitations of current cross-talk methods and discuss future directions in this growing field.

Circulating MicroRNAs in Elderly Type 2 Diabetic Patients

The circulating microRNAs (miRNAs) associated with type 2 diabetes (T2D) in elderly patients are still being defined. To identify novel miRNA biomarker candidates for monitoring responses to sitagliptin in such patients, we prospectively studied 40 T2D patients (age > 65) with HbA1c levels of 7.5-9.0% on metformin. After collection of baseline blood samples (t₀), the dipeptidyl peptidase-IV (DPP-IV) inhibitor (DPP-IVi) sitagliptin was added to the metformin regimen, and patients were followed for 15 months. Patients with HbA1c < 7.5% or HbA1c reduction > 0.5% after 3 and 15 months of therapy were classified as "responders" (group R, n = 34); all others were classified as "nonresponders" (group NR, n = 6). Circulating miRNA profiling was performed on plasma collected in each group before and after 15 months of therapy (t₀ and t₁₅). Intra- and intergroup comparison of miRNA profiles pinpointed three miRNAs that correlated with responses to sitagliptin: miR-378, which is a candidate biomarker of resistance to this DPP-IVi, and miR-126-3p and miR-223, which are associated with positive responses to the drug. The translational implications are as immediate as evident, with the possibility to develop noninvasive diagnostic tools to predict drug response and development of chronic complications.

Circulating MicroRNAs as Biomarkers of Gestational Diabetes Mellitus: Updates and Perspectives

Gestational diabetes mellitus (GDM) is defined as any degree of carbohydrate intolerance, with onset or first recognition during second or third trimester of gestation. It is estimated that approximately 7% of all pregnancies are complicated by GDM and that its prevalence is rising all over the world. Thus, the screening for abnormal glucose levels is generally recommended as a routine component of care for pregnant women. However, additional biomarkers are needed in order to predict the onset or accurately monitor the status of gestational diabetes. Recently, microRNAs, a class of small noncoding RNAs demonstrated to modulate gene expression, have been proven to be secreted by cells of origin and can be found in many biological fluids such as serum or plasma. Such feature renders microRNAs as optimal biomarkers and sensors of in situ tissue alterations. Furthermore, secretion of microRNAs via exosomes has been reported to contribute to tissue cross talk, thus potentially represents, if disrupted, a mechanistic cause of tissue/cell dysfunction in a specific disease. In this review, we summarized the recent findings on circulating microRNAs and gestational diabetes mellitus with particular focus on the potential use of microRNAs as putative biomarkers of disease as well as a potential cause of GDM complications and β cell dysfunction.

Prevention of diabetes in overweight/obese children through a family based intervention program including supervised exercise (PREDIKID project): study protocol for a randomized controlled trial

BACKGROUND

The global pandemic of obesity has led to an increased risk for prediabetes and type-2 diabetes (T2D). The aims of the current project are: (1) to evaluate the effect of a 22-week family based intervention program, including supervised exercise, on insulin resistance syndrome (IRS) risk in children with a high risk of developing T2D and (2) to identify the profile of microRNA in circulating exosomes and in peripheral blood mononuclear cells in children with a high risk of developing T2D and its response to a multidisciplinary intervention program including exercise.

METHODS

A total of 84 children, aged 8-12 years, with a high risk of T2D will be included and randomly assigned to control (N = 42) or intervention (N = 42) groups. The control group will receive a family based lifestyle education and psycho-educational program (2 days/month), while the intervention group will attend the same lifestyle education and psycho-educational program plus the exercise program (3 days/week, 90 min per session including warm-up, moderate to vigorous aerobic activities, and strength exercises). The following measurements will be evaluated at baseline prior to randomization and after the intervention: fasting insulin, glucose and hemoglobin A1c; body composition (dual-energy X-ray absorptiometry); ectopic fat (magnetic resonance imaging); microRNA expression in circulating exosomes and in peripheral blood mononuclear cells (MiSeq; Illumina); cardiorespiratory fitness (cardiopulmonary exercise testing); dietary habits and physical activity (accelerometry).

DISCUSSION

Prevention and identification of children with a high risk of developing T2D could help to improve their cardiovascular health and to reduce the comorbidities associated with obesity.

TRIAL REGISTRATION

ClinicalTrials.gov, ID: NCT03027726 . Registered on 16 January 2017.

Gene-Diet Interactions in Type 2 Diabetes: The Chicken and Egg Debate

Consistent evidence from both experimental and human studies indicates that Type 2 diabetes mellitus (T2DM) is a complex disease resulting from the interaction of genetic, epigenetic, environmental, and lifestyle factors. Nutrients and dietary patterns are important environmental factors to consider in the prevention, development and treatment of this disease. Nutritional genomics focuses on the interaction between bioactive food components and the genome and includes studies of nutrigenetics, nutrigenomics and epigenetic modifications caused by nutrients. There is evidence supporting the existence of nutrient-gene and T2DM interactions coming from animal studies and family-based intervention studies. Moreover, many case-control, cohort, cross-sectional cohort studies and clinical trials have identified relationships between individual genetic load, diet and T2DM. Some of these studies were on a large scale. In addition, studies with animal models and human observational studies, in different countries over periods of time, support a causative relationship between adverse nutritional conditions during in utero development, persistent epigenetic changes and T2DM. This review provides comprehensive information on the current state of nutrient-gene interactions and their role in T2DM pathogenesis, the relationship between individual genetic load and diet, and the importance of epigenetic factors in influencing gene expression and defining the individual risk of T2DM.

Circulating microRNAs and diabetes mellitus: a novel tool for disease prediction, diagnosis, and staging?

Diabetes is a complex, multifactorial group of metabolic diseases characterized by chronic hyperglycaemia due to pancreatic beta-cell dysfunction and/or loss. It is characterized by an asymptomatic and highly variable prodromic phase, which renders diabetes mellitus difficult to be predicted with sufficient accuracy. Despite several efforts in the identification and standardization of newly trustable. Biomarkers able to predict and follow-up diabetes and to specifically subtype its different forms, few of them have proven of clinical utility. Recently, a new class of endogenous non-coding small RNAs, namely microRNAs, have been indicated as putative biomarkers, being released by cells and tissues and found in a cell-free circulating form in many biological fluids, including serum and/or plasma. MicroRNAs have been initially identified as promising biomarkers in cancer, and nowadays their application has been extended to other diseases, including diabetes. Although an increasing number of studies focused on the evaluation of circulating microRNAs in diabetes, few reproducibly identified microRNAs as biomarkers for disease prediction or follow-up. Technological problems as well as the need to obtain highly standardized operating procedures and methods are still an issue in such research field. In this review, we comprehensively resume the main and most recent findings on circulating microRNAs, and their possible use as biomarkers to predict and follow-up diabetes and its complications, as well as the methodological challenges to standardize accurate operating procedures for their analysis.

Role of MicroRNAs in Type 2 Diabetes and Associated Vascular Complications

Type 2 diabetes mellitus (T2DM) has become a major health threat worldwide. MicroRNAs (miRNAs) are a group of non-coding RNAs known to regulate various biological processes including the pathogenesis of T2DM. Recent studies have pointed out that specific miRNAs play a critical role in controlling β cell activities and the development of diabetic vascular complications. Their association with the disease pathogenesis and omnipresence in body fluids have made them important players for prognosis, diagnosis and management of T2DM. Owing to the limitations of classical biomarkers of diabetes such as fasting plasma glucose, glycosylated haemoglobin (HbA_1c) lack in predicting the risk of development of diabetes complications in a susceptible population. The miRNAs can act as ideal biomarkers for diabetes associated complications. Identification of specific miRNA signatures to detect diabetes and ideally to find out the risk of development of diabetes-associated complications in susceptible population is the essential requirement of the present clinical strategies for controlling diabetes worldwide. In this article, we summarize the potential miRNAs and miRNA signatures involved in the β cell activities and diabetes associated macrovascular and microvascular complications.

Exploring inter-organ crosstalk to uncover mechanisms that regulate β-cell function and mass

Impaired β-cell function and insufficient β-cell mass compensation are twin pathogenic features that underlie type 2 diabetes (T2D). Current therapeutic strategies continue to evolve to improve treatment outcomes in different ethnic populations and include approaches to counter insulin resistance and improve β-cell function. Although the effects of insulin secretion on metabolic organs such as liver, skeletal muscle and adipose is directly relevant for improving glucose uptake and reduce hyperglycemia, the ability of pancreatic β-cells to crosstalk with multiple non-metabolic tissues is providing novel insights into potential opportunities for improving β-cell function and/or mass that could have beneficial effects in patients with diabetes. For example, the role of the gastrointestinal system in the regulation of β-cell biology is well recognized and has been exploited clinically to develop incretin-related antidiabetic agents. The microbiome and the immune system are emerging as important players in regulating β-cell function and mass. The rich innervation of islet cells indicates it is a prime organ for regulation by the nervous system. In this review, we discuss the potential implications of signals from these organ systems as well as those from bone, placenta, kidney, thyroid, endothelial cells, reproductive organs and adrenal and pituitary glands that can directly impact β-cell biology. An added layer of complexity is the limited data regarding the relative relevance of one or more of these systems in different ethnic populations. It is evident that better understanding of this paradigm would provide clues to enhance β-cell function and/or mass in vivo in the long-term goal of treating or curing patients with diabetes.

MiRNAs in β-Cell Development, Identity, and Disease

Pancreatic β-cells regulate glucose metabolism by secreting insulin, which in turn stimulates the utilization or storage of the sugar by peripheral tissues. Insulin insufficiency and a prolonged period of insulin resistance are usually the core components of type 2 diabetes (T2D). Although, decreased insulin levels in T2D have long been attributed to a decrease in β-cell function and/or mass, this model has recently been refined with the recognition that a loss of β-cell “identity” and dedifferentiation also contribute to the decline in insulin production. MicroRNAs (miRNAs) are key regulatory molecules that display tissue-specific expression patterns and maintain the differentiated state of somatic cells. During the past few years, great strides have been made in understanding how miRNA circuits impact β-cell identity. Here, we review current knowledge on the role of miRNAs in regulating the acquisition of the β-cell fate during development and in maintaining mature β-cell identity and function during stress situations such as obesity, pregnancy, aging, or diabetes. We also discuss how miRNA function could be harnessed to improve our ability to generate β-cells for replacement therapy for T2D.

Circulating microRNA (miRNA) Expression Profiling in Plasma of Patients with Gestational Diabetes Mellitus Reveals Upregulation of miRNA miR-330-3p

Gestational diabetes mellitus (GDM) is characterized by insulin resistance accompanied by low/absent beta-cell compensatory adaptation to the increased insulin demand. Although the molecular mechanisms and factors acting on beta-cell compensatory response during pregnancy have been partially elucidated and reported, those inducing an impaired beta-cell compensation and function, thus evolving in GDM, have yet to be fully addressed. MicroRNAs (miRNAs) are a class of small endogenous non-coding RNAs, which negatively modulate gene expression through their sequence-specific binding to 3'UTR of mRNA target. They have been described as potent modulators of cell survival and proliferation and, furthermore, as orchestrating molecules of beta-cell compensatory response and function in diabetes. Moreover, it has been reported that miRNAs can be actively secreted by cells and found in many biological fluids (e.g., serum/plasma), thus representing both optimal candidate disease biomarkers and mediators of tissues crosstalk(s). Here, we analyzed the expression profiles of circulating miRNAs in plasma samples obtained from n = 21 GDM patients and from n = 10 non-diabetic control pregnant women (24-33 weeks of gestation) using TaqMan array microfluidics cards followed by RT-real-time PCR single assay validation. The results highlighted the upregulation of miR-330-3p in plasma of GDM vs non-diabetics. Furthermore, the analysis of miR-330-3p expression levels revealed a bimodally distributed GDM patients group characterized by high or low circulating miR-330 expression and identified as GDM-miR-330^high and GDM-miR-330^low. Interestingly, GDM-miR-330^high subgroup retained lower levels of insulinemia, inversely correlated to miR-330-3p expression levels, and a significant higher rate of primary cesarean sections. Finally, miR-330-3p target genes analysis revealed major modulators of beta-cell proliferation and of insulin secretion, such as the experimentally validated genes E2F1 and CDC42 as well as AGT2R2, a gene involved in the differentiation of mature beta-cells. In conclusion, we demonstrated that plasma miR-330-3p could be of help in identifying GDM patients with potential worse gestational diabetes outcome; in GDM, miR-330-3p may directly be transferred from plasma to beta-cells thus modulating key target genes involved in proliferation, differentiation, and insulin secretion.

Biological roles of microRNAs in the control of insulin secretion and action

microRNAs (miRNAs) are intracellular and circulating molecular components contributing to genome expression control through binding mRNA targets, which generally results in downregulated mRNA expression. One miRNA can target several mRNAs, and one transcript can be targeted by several miRNAs, resulting in complex fine-tuning of regulation of gene networks and signaling pathways. miRNAs regulate metabolism, adipocyte differentiation, pancreatic development, β-cell mass, insulin biosynthesis, secretion, and signaling, and their role in diabetes and obesity is emerging. Their pathophysiological effects are essentially dependent on cellular coexpression with their mRNA targets, which can show tissue-specific transcriptional responses to disease conditions and environmental challenges. Current knowledge of miRNA biology and their impact on the pathogenesis of diabetes and obesity is based on experimental data documenting miRNA expression generally in single tissue types that can be correlated with expression of target mRNAs to integrate miRNA in functional pathways and gene networks. Here we present results from the most significant studies dealing with miRNA function in liver, fat, skeletal muscle, and endocrine pancreas and their implication in diabetes and obesity.