MicroRNA-9 controls the expression of Granuphilin/Slp4 and the secretory response of insulin-producing cells

A decrease in hepatic microRNA-9 expression impairs gluconeogenesis by targeting FOXO1 in obese mice

AIM/HYPOTHESIS

MicroRNA-9 (miR-9) is involved in the regulation of pancreatic beta cell function. However, its role in gluconeogenesis is still unclear. Our objective was to investigate the role of miR-9 in hepatic glucose production (HGP).

METHODS

MiR-9 expression was measured in livers of high-fat diet (HFD) mice and ob/ob mice. The methylation status of the miR-9-3 promoter regions in hepatocytes was determined by the methylation-specific PCR procedure. The binding activity of DNA methyltransferase (DNMT)1, DNMT3a and DNMT3b on the miR-9-3 promoter was detected by chromatin immunoprecipitation (ChIP) and quantitative real-time PCR assays. HGP was evaluated in vitro and in vivo. Glucose tolerance, insulin tolerance and pyruvate tolerance tests were also performed.

RESULTS

Reduced miR-9 expression and hypermethylation of the miR-9-3 promoter were observed in the livers of obese mice. Further study showed that the binding of DNMT1, but not of DNMT3a and DNMT3b, to the miR-9-3 promoter was increased in hepatocytes from ob/ob mice. Knockdown of DNMT1 alleviated the decrease in hepatic miR-9 expression in vivo and in vitro. Overexpression of hepatic miR-9 improved insulin sensitivity in obese mice and inhibited HGP. In addition, deletion of hepatic miR-9 led to an increase in random and fasting blood glucose levels in lean mice. Importantly, silenced forkhead box O1 (FOXO1) expression reversed the gluconeogenesis and glucose production in hepatocytes induced by miR-9 deletion.

CONCLUSIONS/INTERPRETATION

Our observations suggest that the decrease in miR-9 expression contributes to an inappropriately activated gluconeogenesis in obese mice.

The Role of microRNAs in Animal Cell Reprogramming

Our concept of cell reprogramming and cell plasticity has evolved since John Gurdon transferred the nucleus of a completely differentiated cell into an enucleated Xenopus laevis egg, thereby generating embryos that developed into tadpoles. More recently, induced expression of transcription factors, oct4, sox2, klf4, and c-myc has evidenced the plasticity of the genome to change the expression program and cell phenotype by driving differentiated cells to the pluripotent state. Beyond these milestone achievements, research in artificial cell reprogramming has been focused on other molecules that are different than transcription factors. Among the candidate molecules, microRNAs (miRNAs) stand out due to their potential to control the levels of proteins that are involved in cellular processes such as self-renewal, proliferation, and differentiation. Here, we review the role of miRNAs in the maintenance and differentiation of mesenchymal stem cells, epimorphic regeneration, and somatic cell reprogramming to induced pluripotent stem cells.

Circulating miRNAs as intercellular messengers, potential biomarkers and therapeutic targets for Type 2 diabetes

miRNAs have emerged as key epigenetic regulators of metabolism. Their deregulation contributes to metabolic abnormalities, proposing their potential role as therapeutic targets for Type 2 diabetes. The exciting finding that miRNAs exist in the bloodstream suggests that circulating miRNAs may act in a hormone-like fashion. Despite the fact that significant progress has been made in understanding circulating miRNAs, this topic is full of complexities and many questions remain unanswered. The goal of this review is to bring together up-to-date knowledge about circulating miRNAs and their role as intercellular communicators as well as potential biomarkers and therapeutic targets in metabolic diseases, providing examples of possible clinical applications for circulating miRNAs in diabetes and cardiovascular complications.

MicroRNAs as regulators of beta-cell function and dysfunction

In the last decade, there has been an explosion in both the number of and knowledge about miRNAs associated with both type 1 and type 2 diabetes. Even though we are presently in the initial stages of understanding how this novel class of posttranscriptional regulators are involved in diabetes, recent studies have demonstrated that miRNAs are important regulators of the islet transcriptome, controlling apoptosis, differentiation and proliferation, as well as regulating unique islet and beta-cell functions and pathways such as insulin expression, processing and secretion. Furthermore, a large number of miRNAs have been linked to diabetogenic processes induced by elevated levels of glucose, free fatty acids and inflammatory cytokines. Thus, miRNAs are novel therapeutic targets with the potential of protecting the beta-cell, and there is proof of principle that miRNA antagonists, so-called antagomirs, are effective in vivo for other disorders. miRNAs are exported out of cells in exosomes, raising the intriguing possibility of cell-to-cell communication between distant tissues via miRNAs and that miRNAs can be used as biomarkers of beta-cell function, mass and survival. The purpose of this review is to provide a status on how miRNAs control beta-cell function and viability in health and disease.

MicroRNA 152 regulates hepatic glycogenesis by targeting PTEN

Hepatic insulin resistance, defined as a diminished ability of hepatocytes to respond to the action of insulin, plays an important role in the development of type 2 diabetes and metabolic syndrome. Aberrant expression of mmu-miR-152-3p (miR-152) is related to the pathogenesis of tumors such as hepatitis B virus related hepatocellular carcinoma. However, the role of miR-152 in hepatic insulin resistance remains unknown. In the present study, we identified the potential role of miR-152 in regulating hepatic glycogenesis. The expression of miR-152 and the level of glycogen were significantly downregulated in the liver of db/db mice and mice fed a high fat diet. In vivo and in vitro results suggest that inhibition of miR-152 expression induced impaired glycogenesis in hepatocytes. Interestingly, miR-152 expression, glycogen synthesis and protein kinase B/glycogen synthase kinase (AKT/GSK) pathway activation were significantly decreased in the liver of mice injected with 16 μg·mL(-1) interleukin 6 (IL-6) by pumps for 7 days and in NCTC 1469 cells treated with 10 ng·mL(-1) IL-6 for 24 h. Moreover, hepatic overexpression of miR-152 rescued IL-6-induced impaired glycogenesis. Finally, phosphatase and tensin homolog (PTEN) was identified as a direct target of miR-152 to mediate hepatic glycogen synthesis. Our findings provide mechanistic insight into the effects of miR-152 on the regulation of the AKT/GSK pathway and the synthesis of glycogen in hepatocytes. Downregulated miR-152 induced impaired hepatic glycogenesis by targeting PTEN. PTEN participated in miR-152-mediated glycogenesis in hepatocytes via regulation of the AKT/GSK pathway.

Loss of miR-182 affects B-cell extrafollicular antibody response

MicroRNAs have been shown to play a role in B-cell differentiation and activation. Here, we found miR-182 to be highly induced in activated B cells. However, mice lacking miR-182 have normal B-cell and T-cell development. Interestingly, mutant mice exhibited a defective antibody response at early time-points in the immunization regimen when challenged with a T-cell-dependent antigen. Germinal centres were formed but the generation of extrafollicular plasma cells was defective in the spleens of immunized miR-182-deficient mice. Mutant mice were also not able to respond to a T-cell-independent type 2 antigen, which typically elicited an extrafollicular B-cell response. Taken together, the data indicated that miR-182 plays a critical role in driving extrafollicular B-cell antibody responses.

Regenerative Therapy of Type 1 Diabetes Mellitus: From Pancreatic Islet Transplantation to Mesenchymal Stem Cells

Type 1 diabetes is an autoimmune disease resulting in the permanent destruction of pancreatic islets. Islet transplantation to portal vein provides an approach to compensate for loss of insulin producing cells. Clinical trials demonstrated that even partial islet graft function reduces severe hypoglycemic events in patients. However, therapeutic impact is restrained due to shortage of pancreas organ donors and instant inflammation occurring in the hepatic environment of the graft. We summarize on what is known about regenerative therapy in type 1 diabetes focusing on pancreatic islet transplantation and new avenues of cell substitution. Metabolic pathways and energy production of transplanted cells are required to be balanced and protection from inflammation in their intravascular bed is desired. Mesenchymal stem cells (MSCs) have anti-inflammatory features, and so they are interesting as a therapy for type 1 diabetes. Recently, they were reported to reduce hyperglycemia in diabetic rodents, and they were even discussed as being turned into endodermal or pancreatic progenitor cells. MSCs are recognized to meet the demand of an individual therapy not raising the concerns of embryonic or induced pluripotent stem cells for therapy.

microRNAs with different functions and roles in disease development and as potential biomarkers of diabetes: progress and challenges

Biomarkers provide information on early detection of diseases, in determining individuals at risk of developing complications or subtyping individuals for disease phenotypes. In addition, biomarkers may lead to better treatment strategies, personalized therapy, and improved outcome. A major gap in the field of biomarker development is that we have not identified appropriate (minimally invasive, life-style independent and informative) biomarkers for the underlying disease process(es) that can be measured in readily accessible samples (e.g. serum, plasma, blood, urine). miRNAs function as regulators in wide ranging cellular and physiological functions and also participate in many physiopathological processes and thus have been linked to many diseases including diabetes, metabolic and cardiovascular diseases, cancer, neurodegenerative diseases, and autoimmunity. Many miRNAs have been shown to have predictive value as potential biomarkers in a variety of diseases including diabetes, which are detectable in some instances many years before the manifestation of disease. Although some technical challenges still remain, due to their availability in the circulation, relative stability, and ease of detection; miRNAs have emerged as a promising new class of biomarkers to provide information on early detection of disease, monitoring disease progression, in determining individual's risk of developing complications or subtyping individuals for disease phenotypes, and to monitor response to therapeutic interventions. As a final note, most of the miRNAs reported in the literature have not yet been validated in sufficiently powered and longitudinal studies for specificity for that particular disease.

Differential DNA methylation of microRNAs within promoters, intergenic and intragenic regions of type 2 diabetic, pre-diabetic and non-diabetic individuals

OBJECTIVE

Accumulating evidence supports the role of epigenetic modifications, and in particular DNA methylation and non-coding RNAs in the pathophysiology of type 2 diabetes. Alterations in methylation patterns within promoter regions are linked with aberrant transcription and pathological gene expression; however the role of methylation within non-promoter regions is not yet fully elucidated.

DESIGN AND METHODS

We performed whole genome methylated DNA immunoprecipitation sequencing (MeDIP-Seq) in peripheral-blood-derived DNA from age-gender-body mass index (BMI)-ethnicity matched type 2 diabetic, pre-diabetic and non-diabetic individuals.

RESULTS

The density of methylation normalized to the average length of the promoter, intergenic and intragenic regions and to CpG count was 3.17, 9.80 and 0.09 for the promoter, intergenic and intragenic regions, respectively. Methylation within these regions varied according to glucose tolerance status and was associated with hypermethylation rather than hypomethylation. MicroRNA-DNA methylation peaks accounted for 4.8% of the total number of peaks detected. Differential DNA methylation of these microRNA peaks was observed during dysglycemia, with the promoter, intergenic and intragenic regions accounting for 2%, 95% and 3% respectively, of the differentially methylated microRNA peaks.

CONCLUSION

Genome-wide DNA methylation varied according to glucose tolerance. Methylation within non-promoter regions accounted for the majority of differentially methylated peaks identified, thus highlighting the importance of DNA methylation within these non-promoter regions in the pathogenesis of type 2 diabetes. This study suggests that DNA methylation within intergenic regions is a mechanism regulating microRNAs, another increasingly important epigenetic factor, during type 2 diabetes.

miR-101a and miR-30b contribute to inflammatory cytokine-mediated β-cell dysfunction

Inflammatory cytokines have a critical role in the progressive deterioration of pancreatic β-cell function and development of type 1 diabetes. Prolonged exposure of β-cells to inflammatory cytokines results in gene expression modifications, leading to loss of β-cell function. MicroRNAs (miRNAs) are small non-coding RNAs acting as key regulators of gene expression. Here, we demonstrate that miR-101a and miR-30b are key players in cytokine-mediated β-cell dysfunction. We found that IL-1β induces an increase in miR-101a and miR-30b in MIN6 cells, and that the two miRNAs participate in β-cell dysfunction, including decreased insulin content, gene expression, and increased β-cell death. miR-101a and miR-30b reduce proinsulin expression and insulin content by directly targeting the transcriptional factor Neurod1. In addition, β-cell apoptosis mediated by miR-101a and miR-30b is associated with diminished expression level of the antiapoptotic protein Bcl2. Moreover, we show that miR-101a causes an impairment in glucose-induced insulin secretion by decreasing the expression of the transcription factor Onecut2. Taken together, our findings suggest that changes in the levels of miR-101a and miR-30b contribute to cytokine-mediated β-cell dysfunction occurring during the development and progression of type 1 diabetes.

β-Cell MicroRNAs: Small but Powerful

Noncoding RNA and especially microRNAs (miRs) have emerged as important regulators of key processes in cell biology, including development, differentiation, and survival. Currently, over 2,500 mature miRs have been reported in humans, and considering that each miR has multiple targets, the number of genes and pathways potentially affected is huge. Not surprisingly, many miRs have also been implicated in diabetes, and more recently, some have been discovered to play important roles in the pancreatic islet, including β-cell function, proliferation, and survival. The goal of this Perspective is to offer an overview of this rapidly evolving field and the miRs involved, reveal novel networks of β-cell miR signaling, and provide an outlook of the opportunities and challenges ahead.

Inhibition of microRNA-9-3p reduces lipid accumulation in HepG2 cells by targeting the expression of sirtuin type 1

Type 2 diabetes mellitus (T2DM) is a complex metabolic disorder caused by the interaction of environmental factors and multiple genes. The genetic background of T2DM is complex and remains to be fully elucidated. MicroRNAs (miRNAs) are negative regulators of gene expression and several miRNAs are associated with the development of T2DM. However, the expression and biological function of miRNA‑9‑3p in lipid metabolism of patients with T2DM remain to be fully elucidated. The predominant aim of the present study was to examine the effect of miRNA‑9‑3p on lipid accumulation in HepG2 cells. To investigate this, an MTT assay was used to determine cell proliferation, and the effects of miRNA‑9‑3p on triglycerides (TG) and total cholesterol (TC) in the HepG2 cells were also examined. Reverse transcription‑quantitative polymerase chain reaction and western blot analyses were used to measure the expression levels of SIRT1 at the gene and protein levels, respectively. The date revealed that downregulation of miRNA‑9‑3p inhibited the proliferation of HepG2 cells, and significantly reduced the accumulation of lipids, and decreased TG and TC content. In addition, the present study demonstrated that inhibition of miRNA‑9‑3p increased the protein expression of sirtuin type 1 (SIRT1), but had no effects on the gene expression of SIRT1. Therefore, these findings demonstrated that the inhibition of miRNA‑9‑3p reduced the proliferation of HepG2 cells and lipid accumulation by upregulating the expression of SIRT1, indicating its potential as a therapeutic target.

Minireview: microRNA function in pancreatic β cells

MicroRNAs are small noncoding ribonucleotides that regulate mRNA translation or degradation and have major roles in cellular function. MicroRNA (miRNA) levels are deregulated or altered in many diseases. There is overwhelming evidence that miRNAs also play an important role in the regulation of glucose homeostasis and thereby may contribute to the establishment of diabetes. MiRNAs have been shown to affect insulin levels by regulating insulin production, insulin exocytosis, and endocrine pancreas development. Although a large number of miRNAs have been identified from pancreatic β-cells using various screens, functional studies that link most of the identified miRNAs to regulation of pancreatic β-cell function are lacking. This review focuses on miRNAs with important roles in regulation of insulin production, insulin secretion, and β-cell development, and will discuss only miRNAs with established roles in β-cell function.

Gender and Obesity Specific MicroRNA Expression in Adipose Tissue from Lean and Obese Pigs

Obesity is a complex condition that increases the risk of life threatening diseases such as cardiovascular disease and diabetes. Studying the gene regulation of obesity is important for understanding the molecular mechanisms behind the obesity derived diseases and may lead to better intervention and treatment plans. MicroRNAs (miRNAs) are short non-coding RNAs regulating target mRNA by binding to their 3'UTR. They are involved in numerous biological processes and diseases, including obesity. In this study we use a mixed breed pig model designed for obesity studies to investigate differentially expressed miRNAs in subcutaneous adipose tissue by RNA sequencing (RNAseq). Both male and female pigs are included to explore gender differences. The RNAseq study shows that the most highly expressed miRNAs are in accordance with comparable studies in pigs and humans. A total of six miRNAs are differentially expressed in subcutaneous adipose tissue between the lean and obese group of pigs, and in addition gender specific significant differential expression is observed for a number of miRNAs. The differentially expressed miRNAs have been verified using qPCR. The results of these studies in general confirm the trends found by RNAseq. Mir-9 and mir-124a are significantly differentially expressed with large fold changes in subcutaneous adipose tissue between lean and obese pigs. Mir-9 is more highly expressed in the obese pigs with a fold change of 10 and a p-value < 0.001. Mir-124a is more highly expressed in the obese pigs with a fold change of 114 and a p-value < 0.001. In addition, mir-124a is significantly higher expressed in abdominal adipose tissue in male pigs with a fold change of 119 and a p-value < 0.05. Both miRNAs are also significantly higher expressed in the liver of obese male pigs where mir-124a has a fold change of 12 and mir-9 has a fold change of 1.6, both with p-values < 0.05.

Induction of miR-132 and miR-212 Expression by Glucagon-Like Peptide 1 (GLP-1) in Rodent and Human Pancreatic β-Cells

Better understanding how glucagon-like peptide 1 (GLP-1) promotes pancreatic β-cell function and/or mass may uncover new treatment for type 2 diabetes. In this study, we investigated the potential involvement of microRNAs (miRNAs) in the effect of GLP-1 on glucose-stimulated insulin secretion. miRNA levels in INS-1 cells and isolated rodent and human islets treated with GLP-1 in vitro and in vivo (with osmotic pumps) were measured by real-time quantitative PCR. The role of miRNAs on insulin secretion was studied by transfecting INS-1 cells with either precursors or antisense inhibitors of miRNAs. Among the 250 miRNAs surveyed, miR-132 and miR-212 were significantly up-regulated by GLP-1 by greater than 2-fold in INS-1 832/3 cells, which were subsequently reproduced in freshly isolated rat, mouse, and human islets, as well as the islets from GLP-1 infusion in vivo in mice. The inductions of miR-132 and miR-212 by GLP-1 were correlated with cAMP production and were blocked by the protein kinase A inhibitor H-89 but not affected by the exchange protein activated by cAMP activator 8-pCPT-2'-O-Me-cAMP-AM. GLP-1 failed to increase miR-132 or miR-212 expression levels in the 832/13 line of INS-1 cells, which lacks robust cAMP and insulin responses to GLP-1 treatment. Overexpression of miR-132 or miR-212 significantly enhanced glucose-stimulated insulin secretion in both 832/3 and 832/13 cells, and restored insulin responses to GLP-1 in INS-1 832/13 cells. GLP-1 increases the expression of miRNAs 132 and 212 via a cAMP/protein kinase A-dependent pathway in pancreatic β-cells. Overexpression of miR-132 or miR-212 enhances glucose and GLP-1-stimulated insulin secretion.

Genome-wide microRNA screening reveals that the evolutionary conserved miR-9a regulates body growth by targeting sNPFR1/NPYR

MicroRNAs (miRNAs) regulate many physiological processes including body growth. Insulin/IGF signalling is the primary regulator of animal body growth, but the extent to which miRNAs act in insulin-producing cells (IPCs) is unclear. Here we generate a UAS-miRNA library of Drosophila stocks and perform a genetic screen to identify miRNAs whose overexpression in the IPCs inhibits body growth in Drosophila. Through this screen, we identify miR-9a as an evolutionarily conserved regulator of insulin signalling and body growth. IPC-specific miR-9a overexpression reduces insulin signalling and body size. Of the predicted targets of miR-9a, we find that loss of miR-9a enhances the level of sNPFR1. We show via an in vitro binding assay that miR-9a binds to sNPFR1 mRNA in insect cells and to the mammalian orthologue NPY2R in rat insulinoma cells. These findings indicate that the conserved miR-9a regulates body growth by controlling sNPFR1/NPYR-mediated modulation of insulin signalling.

Insulin signaling governs many physiological processes but the molecular and neural mechanisms of its regulation are largely unknown. Here the authors describe a novel molecular pathway controlling sNPF regulation of insulin signalling in the fruit fly, which is mediated by the evolutionary conserved miR-9a.

The Generation of Insulin Producing Cells from Human Mesenchymal Stem Cells by MiR-375 and Anti-MiR-9

Background

MicroRNAs (miRNAs) are a group of endogenous small non-coding RNAs that regulate gene expression at the post-transcriptional level. A number of studies have led to the notion that some miRNAs have key roles in control of pancreatic islet development and insulin secretion. Based on some studies on miRNAs pattern, the researchers in this paper investigated the pancreatic differentiation of human bone marrow mesenchymal stem cells (hBM-MSCs) by up-regulation of miR-375 and down-regulation of miR-9 by lentiviruses containing miR-375 and anti-miR-9.

Methodology

After 21 days of induction, islet-like clusters containing insulin producing cells (IPCs) were confirmed by dithizone (DTZ) staining. The IPCs and β cell specific related genes and proteins were detected using qRT-PCR and immunofluorescence on days 7, 14 and 21 of differentiation. Glucose challenge test was performed at different concentrations of glucose so extracellular and intracellular insulin and C-peptide were assayed using ELISA kit. Although derived IPCs by miR-375 alone were capable to express insulin and other endocrine specific transcription factors, the cells lacked the machinery to respond to glucose.

Conclusion

It was found that over-expression of miR-375 led to a reduction in levels of Mtpn protein in derived IPCs, while treatment with anti-miR-9 following miR-375 over-expression had synergistic effects on MSCs differentiation and insulin secretion in a glucose-regulated manner. The researchers reported that silencing of miR-9 increased OC-2 protein in IPCs that may contribute to the observed glucose-regulated insulin secretion. Although the roles of miR-375 and miR-9 are well known in pancreatic development and insulin secretion, the use of these miRNAs in transdifferentiation was never demonstrated. These findings highlight miRNAs functions in stem cells differentiation and suggest that they could be used as therapeutic tools for gene-based therapy in diabetes mellitus.

DICER Inactivation Identifies Pancreatic β-Cell "Disallowed" Genes Targeted by MicroRNAs

Pancreatic β-cells are the body's sole source of circulating insulin and essential for the maintenance of blood glucose homeostasis. Levels of up to 66 “disallowed” genes, which are strongly expressed and play housekeeping roles in most other mammalian tissues, are unusually low in β-cells. The molecular mechanisms involved in repressing these genes are largely unknown. Here, we explore the role in gene disallowance of microRNAs (miRNAs), a type of small noncoding RNAs that silence gene expression at the posttranscriptional level and are essential for β-cell development and function. To selectively deplete miRNAs from adult β-cells, the miRNA-processing enzyme DICER was inactivated by deletion of the RNase III domain with a tamoxifen-inducible Pdx1CreER transgene. In this model, β-cell dysfunction was apparent 2 weeks after recombination and preceded a decrease in insulin content and loss of β-cell mass. Of the 14 disallowed genes studied, quantitative RT-quantitative real-time PCR revealed that 6 genes (Fcgrt, Igfbp4, Maf, Oat, Pdgfra, and Slc16a1) were up-regulated (1.4- to 2.1-fold, P < .05) at this early stage. Expression of luciferase constructs bearing the 3′-untranslated regions of the corresponding mRNAs in wild-type or DICER-null β-cells demonstrated that Fcgrt, Oat, and Pdgfra are miRNA direct targets. We thus reveal a role for miRNAs in the regulation of disallowed genes in β-cells and provide evidence for a novel means through which noncoding RNAs control the functional identity of these cells independently of actions on β-cell mass.

MicroRNAs 9 and 370 Association with Biochemical Markers in T2D and CAD Complication of T2D

BACKGROUND

MicroRNAs (miRNAs) are small non coding RNAs with essential roles, of which any alteration leads to several conditions. Their roles in diabetes (DM) and its vascular complications have not been completely assessed.

AIM

to study the association of two miRNAs; 9 and 370, with biochemical parameters of type 2 diabetic (T2D), dyslipidemia and coronary artery disease (CAD).

SUBJECTS AND METHODS

Blood samples were taken from 200 subjects of both genders, in the Outpatient clinic of Al Qasr El-Einy teaching hospitals, in which levels of both miRNAs (using real time PCR) and routine parameters were measured. Subjects were divided over four groups, 50 in each group as follows; patients with T2D, patients with CAD, patients with T2D and CAD, and healthy control subjects.

MAIN OUTCOME

miRNA 9 levels were expected to be over expressed in diabetic patients, while miRNA 370 levels were expected to be over expressed in those suffering from CAD and their association with CAD complication of T2D.

RESULTS

miRNA 9 levels were significantly higher in T2D patients and T2D patients with CAD, (1.18±0.07, and 1.31±0.08 respectively), while miRNA 370 levels were significantly higher in T2D patients, CAD patients, and T2D patients with CAD (0.59±0.05, 1.00±0.05, and 1.20±0.06 respectively), compared to control group at p = 0.000. In addition both miRNAs were still significantly associated with each other even after conducting multiple regression analysis.

CONCLUSION

This study associates the possible role of miRNAs in the diagnosis/prognosis of CAD complication of T2D.

gga-miR-9* inhibits IFN production in antiviral innate immunity by targeting interferon regulatory factor 2 to promote IBDV replication

MicroRNAs (miRNAs) are small non-coding RNAs that contribute to the repertoire of host-pathogen interactions during viral infections. In the current study, miRNA analysis showed that a panel of microRNAs, including gga-miR-9*, were markedly upregulated in specific-pathogen-free (SPF) chickens upon infection with infectious bursal disease virus (IBDV); however, the biological function of gga-miR-9* during viral infection remains unknown. Using a TCID50 assay, it was found that ectopic expression of gga-miR-9* significantly promoted IBDV replication. In turn, gga-miR-9* negatively regulated IBDV-triggered type I IFN production, thus promoting IBDV replication in DF-1 cells. Bioinformatics analysis indicates that the 3' untranslated region (UTR) of interferon regulatory factor 2 (IRF2) has two putative binding sites for gga-miR-9*. Targeting of IRF2 3'UTR by gga-miR-9* was determined by luciferase assay. Functional overexpression of gga-miR-9*, using gga-miR-9* mimics, inhibited IRF2 mRNA and protein expression. Transfection of the gga-miR-9* inhibitor abolished the suppression of IRF2 protein expression. Furthermore, IRF2 knockdown mediated the enhancing effect of gga-miR-9* on the type I IFN-mediated antiviral response. These findings indicate that inducible gga-miR-9* feedback negatively regulates the host antiviral innate immune response by suppressing type I IFN production via targeting IRF2.

miR-9 enhances the transactivation of nuclear factor of activated T cells by targeting KPNB1 and DYRK1B

The fast response to stimuli and subsequent activation of the nuclear factor of activated T cells (NFAT) signaling pathway play an essential role in human T cell functions. MicroRNAs (miRNAs) are increasingly implicated in regulation of numerous biological and pathological processes. In this study we demonstrate a novel function of miRNA-9 (miR-9) in regulation of the NFAT signaling pathway. Upon PMA-ionomycin stimulation, miR-9 was markedly increased, consistent with NFAT activation. Overexpression of miR-9 significantly enhanced NFAT activity and accelerated NFAT dephosphorylation and its nuclear translocation in response to PMA-ionomycin. Karyopherin-β1 (KPNB1, a nucleocytoplasmic transporter) and dual-specificity tyrosine phosphorylation-regulated kinase 1B (DYRK1B) were identified as direct targets of miR-9. Functionally, miR-9 promoted IL-2 production in stimulated human lymphocyte Jurkat T cells. Collectively, our data reveal a novel role for miR-9 in regulation of the NFAT pathway by targeting KPNB1 and DYRK1B.

Therapeutic potential of miRNAs in diabetes mellitus

miRNAs are major regulators of gene expression that are emerging as central players in the development of many human diseases, including diabetes mellitus. In fact, the manifestation of diabetes is associated with alterations in the miRNA profile in insulin-secreting cells, insulin target tissues and, in case of long-term diabetes complications, in many additional organs. Diabetes also results in changes in the profile of miRNAs detectable in blood and other body fluids. This has boosted an ever increasing interest in the use of circulating miRNAs as potential biomarkers to predict the development of diabetes and its devastating complications. Moreover, promising approaches to correct the level of selected miRNAs are emerging, permitting to envisage new therapeutic strategies to treat diabetes and its complications.

Noncoding RNAs in β cell biology

PURPOSE OF REVIEW

The identification and characterization of essential islet transcription factors have improved our understanding of β cell development, provided insights into many of the cellular dysfunctions related to diabetes, and facilitated the successful generation of β cells from alternative cell sources. Recently, noncoding RNAs have emerged as a novel set of molecules that may represent missing components of the known islet regulatory pathways. The purpose of this article is to highlight studies that have implicated noncoding RNAs as important regulators of pancreas cell development and β cell function.

RECENT FINDINGS

Disruption of essential components of the microRNA processing machinery, in addition to misregulation of individual microRNAs, has revealed the importance of microRNAs in pancreas development and β cell function. Furthermore, over 1000 islet-specific long noncoding RNAs have been identified in mouse and human islets, suggesting that this class of noncoding molecules will also play important functional roles in the β cell.

SUMMARY

The analysis of noncoding RNAs in the pancreas will provide important new insights into pancreatic regulatory processes that will improve our ability to understand and treat diabetes, and may facilitate the generation of replacement β cells from alternative cell sources.

Changing trends in management of gestational diabetes mellitus

Gestational diabetes mellitus (GDM) is on the rise globally. In view of the increasing prevalence of GDM and fetal and neonatal complications associated with it, there is a splurge of research in this field and management of GDM is undergoing a sea change. Trends are changing in prevention, screening, diagnosis, treatment and future follow up. There is emerging evidence regarding use of moderate exercise, probiotics and vitamin D in the prevention of GDM. Regarding treatment, newer insulin analogs like aspart, lispro and detemir are associated with better glycemic control than older insulins. Continuous glucose monitoring systems and continuous subcutaneous insulin systems may play a role in those who require higher doses of insulin for sugar control. Evidence exists that favors metformin as a safer alternative to insulin in view of good glycemic control and better perinatal outcomes. As the risk of developing GDM in subsequent pregnancies and also the risk of overt diabetes in later life is high, regular assessment of these women is required in future. Lifestyle interventions or metformin should be offered to women with a history of GDM who develop pre-diabetes. Further studies are required in the field of prevention of GDM for optimizing obstetric outcome.

MicroRNA-9 regulates steroid-resistant airway hyperresponsiveness by reducing protein phosphatase 2A activity

BACKGROUND

Steroid-resistant asthma is a major clinical problem that is linked to activation of innate immune cells. Levels of IFN-γ and LPS are often increased in these patients. Cooperative signaling between IFN-γ/LPS induces macrophage-dependent steroid-resistant airway hyperresponsiveness (AHR) in mouse models. MicroRNAs (miRs) are small noncoding RNAs that regulate the function of innate immune cells by controlling mRNA stability and translation. Their role in regulating glucocorticoid responsiveness and AHR remains unexplored.

OBJECTIVE

IFN-γ and LPS synergistically increase the expression of miR-9 in macrophages and lung tissue, suggesting a role in the mechanisms of steroid resistance. Here we demonstrate the role of miR-9 in IFN-γ/LPS-induced inhibition of dexamethasone (DEX) signaling in macrophages and in induction of steroid-resistant AHR.

METHODS

MiRNA-9 expression was assessed by means of quantitative RT-PCR. Putative miR-9 targets were determined in silico and confirmed in luciferase reporter assays. miR-9 function was inhibited with sequence-specific antagomirs. The efficacy of DEX was assessed by quantifying glucocorticoid receptor (GR) cellular localization, protein phosphatase 2A (PP2A) activity, and AHR.

RESULTS

Exposure of pulmonary macrophages to IFN-γ/LPS synergistically induced miR-9 expression; reduced levels of its target transcript, protein phosphatase 2 regulatory subunit B (B56) δ isoform; attenuated PP2A activity; and inhibited DEX-induced GR nuclear translocation. Inhibition of miR-9 increased both PP2A activity and GR nuclear translocation in macrophages and restored steroid sensitivity in multiple models of steroid-resistant AHR. Pharmacologic activation of PP2A restored DEX efficacy and inhibited AHR. MiR-9 expression was increased in sputum of patients with neutrophilic but not those with eosinophilic asthma.

CONCLUSION

MiR-9 regulates GR signaling and steroid-resistant AHR. Targeting miR-9 function might be a novel approach for the treatment of steroid-resistant asthma.

MicroRNA-185 targets SOCS3 to inhibit beta-cell dysfunction in diabetes

Diabetes is the most common and complex metabolic disorder, and one of the most important health threats now. MicroRNAs (miRNAs) are a group of small non-coding RNAs that have been suggested to play a vital role in a variety of physiological processes, including glucose homeostasis. In this study, we investigated the role of miR-185 in diabetes. MiR-185 was significantly downregulated in diabetic patients and mice, and the low level was correlated to blood glucose concentration. Overexpression of miR-185 enhanced insulin secretion of pancreatic β-cells, promoted cell proliferation and protected cells from apoptosis. Further experiments using in silico prediction, luciferase reporter assay and western blot assay demonstrated that miR-185 directly targeted SOCS3 by binding to its 3'-UTR. On the contrary to miR-185's protective effects, SOCS3 significantly suppressed functions of β-cell and inactivated Stat3 pathway. When treating cells with miR-185 mimics in combination with SOCS3 overexpression plasmid, the inhibitory effects of SOCS3 were reversed. While combined treatment of miR-185 mimics and SOCS3 siRNA induced synergistically promotive effects compared to either miR-185 mimics or SOCS3 siRNA treatment alone. Moreover, we observed that miR-185 level was inversely correlated with SOCS3 expression in diabetes patients. In conclusion, this study revealed a functional and mechanistic link between miR-185 and SOCS3 in the pathogenesis of diabetes. MiR-185 plays an important role in the regulation of insulin secretion and β-cell growth in diabetes. Restoration of miR-185 expression may serve a potentially promising and efficient therapeutic approach for diabetes.

microRNAs in Pancreatic β-Cell Physiology

The β-cells within the pancreas are responsible for production and secretion of insulin. Insulin is released from pancreatic β-cells in response to increasing blood glucose levels and acts on insulin-sensitive tissues such as skeletal muscle and liver in order to maintain normal glucose homeostasis. Therefore, defects in pancreatic β-cell function lead to hyperglycemia and diabetes mellitus. A new class of molecules called microRNAs has been recently demonstrated to play a crucial role in regulation of pancreatic β-cell function under normal and pathophysiological conditions. miRNAs have been shown to regulate endocrine pancreas development, insulin biosynthesis, insulin exocytosis, and β-cell expansion. Many of the β-cell enriched miRNAs have multiple functions and regulate pancreas development as well as insulin biosynthesis and exocytosis. Furthermore, several of the β-cell specific miRNAs have been shown to accumulate in the circulation before the onset of diabetes and may serve as potential biomarkers for prediabetes. This chapter will focus on miRNAs that are enriched in pancreatic β-cells and play a critical role in modulation of β-cell physiology and may have clinical significance in the treatment of diabetes.

MicroRNA-206 regulates surfactant secretion by targeting VAMP-2

Lung surfactant secretion is a highly regulated process. Our previous studies have shown that VAMP-2 is essential for surfactant secretion. In the present study we investigated the role of miR-206 in surfactant secretion through VAMP-2. VAMP-2 was confirmed to be a target of miR-206 by 3'-untranslational region (3'-UTR) luciferase assay. Mutations in the predicated miR-206 binding sites reduced the binding of miR-206 to the 3'-UTR of VAMP-2. miR-206 decreased the expression of VAMP-2 protein and decreased the lung surfactant secretion in alveolar type II cells. In conclusion, miR-206 regulates lung surfactant secretion by limiting the availability of VAMP-2 protein.

Leucine alters hepatic glucose/lipid homeostasis via the myostatin-AMP-activated protein kinase pathway - potential implications for nonalcoholic fatty liver disease

Background

Elevated plasma levels of the branched-chain amino acid (BCAA) leucine are associated with obesity and insulin resistance (IR), and thus the propensity for type 2 diabetes mellitus development. However, other clinical studies suggest the contradictory view that leucine may in fact offer a degree of protection against metabolic syndrome. Aiming to resolve this apparent paradox, we assessed the effect of leucine supplementation on the metabolism of human hepatic HepG2 cells.

Results

We demonstrate that pathophysiological leucine appears to be antagonistic to insulin, promotes glucose uptake (and not glycogen synthesis), but results in hepatic cell triglyceride (TG) accumulation. Further, we provide evidence that myostatin (MSTN) regulation of AMP-activated protein kinase (AMPK) is a key pathway in the metabolic effects elicited by excess leucine. Finally, we report associated changes in miRNA expression (some species previously linked to metabolic disease etiology), suggesting that epigenetic processes may contribute to these effects.

Conclusions

Collectively, our observations suggest leucine may be both ‘friend’ and ‘foe’ in the context of metabolic syndrome, promoting glucose sequestration and driving lipid accumulation in liver cells. These observations provide insight into the clinical consequences of excess plasma leucine, particularly for hyperglycemia, IR and nonalcoholic fatty liver disease (NAFLD).

Regulation of Pancreatic Beta Cell Stimulus-Secretion Coupling by microRNAs

Increased blood glucose after a meal is countered by the subsequent increased release of the hypoglycemic hormone insulin from the pancreatic beta cells. The cascade of molecular events encompassing the initial sensing and transport of glucose into the beta cell, culminating with the exocytosis of the insulin large dense core granules (LDCVs) is termed "stimulus-secretion coupling." Impairment in any of the relevant processes leads to insufficient insulin release, which contributes to the development of type 2 diabetes (T2D). The fate of the beta cell, when exposed to environmental triggers of the disease, is determined by the possibility to adapt to the new situation by regulation of gene expression. As established factors of post-transcriptional regulation, microRNAs (miRNAs) are well-recognized mediators of beta cell plasticity and adaptation. Here, we put focus on the importance of comprehending the transcriptional regulation of miRNAs, and how miRNAs are implicated in stimulus-secretion coupling, specifically those influencing the late stages of insulin secretion. We suggest that efficient beta cell adaptation requires an optimal balance between transcriptional regulation of miRNAs themselves, and miRNA-dependent gene regulation. The increased knowledge of the beta cell transcriptional network inclusive of non-coding RNAs such as miRNAs is essential in identifying novel targets for the treatment of T2D.

Early second-trimester serum microRNAs as potential biomarker for nondiabetic macrosomia

Background. Macrosomia has become a worldwide problem with the rapid economic growth in the past few years. However, the detailed mechanism of how the macrosomia happened remains unknown. Growing evidence indicates that miRNAs are involved in maintaining metabolic homeostasis. We hypothesized that serum miRNAs are potential biomarkers for macrosomia. Methods. We performed miRNAs profiling using TLDA chips in the discovery phase in two pooled samples from 30 cases and 30 controls, respectively. Individual qRT-PCR was conducted for the discovery phase samples. To confirm the results, we detected the miRNAs which were differentially expressed in the microarray assays and individual qRT-PCR in external validation phase with another 30 cases and 30 controls. Results. In the discovery stage, miR-194 and miR-376a expression levels were significantly different between macrosomia group and controls (P = 0.048 for miR-194 and P = 0.018 for miR-376a, resp.). Further evaluation of the two miRNAs on a total of 120 serum samples showed that the miR-376a remains significantly lower in macrosomia (P = 0.032). Receiver operating characteristic curve analyses showed that the area under curve for miR-376a was 67.8% (sensitivity = 96.7% and specificity = 40.0%). Conclusions. Serum miR-376a may serve as a potential noninvasive biomarker in detecting macrosomia.

PDYN, a gene implicated in brain/mental disorders, is targeted by REST in the adult human brain

The dynorphin κ-opioid receptor system is implicated in mental health and brain/mental disorders. However, despite accumulating evidence that PDYN and/or dynorphin peptide expression is altered in the brain of individuals with brain/mental disorders, little is known about transcriptional control of PDYN in humans. In the present study, we show that PDYN is targeted by the transcription factor REST in human neuroblastoma SH-SY5Y cells and that that interfering with REST activity increases PDYN expression in these cells. We also show that REST binding to PDYN is reduced in the adult human brain compared to SH-SY5Y cells, which coincides with higher PDYN expression. This may be related to MIR-9 mediated down-regulation of REST as suggested by a strong inverse correlation between REST and MIR-9 expression. Our results suggest that REST represses PDYN expression in SH-SY5Y cells and the adult human brain and may have implications for mental health and brain/mental disorders.

The ROS-sensitive microRNA-9/9* controls the expression of mitochondrial tRNA-modifying enzymes and is involved in the molecular mechanism of MELAS syndrome

Mitochondrial dysfunction activates mitochondria-to-nucleus signaling pathways whose components are mostly unknown. Identification of these components is important to understand the molecular mechanisms underlying mitochondrial diseases and to discover putative therapeutic targets. MELAS syndrome is a rare neurodegenerative disease caused by mutations in mitochondrial (mt) DNA affecting mt-tRNA(Leu(UUR)). Patient and cybrid cells exhibit elevated oxidative stress. Moreover, mutant mt-tRNAs(Leu(UUR)) lack the taurine-containing modification normally present at the wobble uridine (U34) of wild-type mt-tRNA(Leu(UUR)), which is considered an etiology of MELAS. However, the molecular mechanism is still unclear. We found that MELAS cybrids exhibit a significant decrease in the steady-state levels of several mt-tRNA-modification enzymes, which is not due to transcriptional regulation. We demonstrated that oxidative stress mediates an NFkB-dependent induction of microRNA-9/9*, which acts as a post-transcriptional negative regulator of the mt-tRNA-modification enzymes GTPBP3, MTO1 and TRMU. Down-regulation of these enzymes by microRNA-9/9* affects the U34 modification status of non-mutant tRNAs and contributes to the MELAS phenotype. Anti-microRNA-9 treatments of MELAS cybrids reverse the phenotype, whereas miR-9 transfection of wild-type cells mimics the effects of siRNA-mediated down-regulation of GTPBP3, MTO1 and TRMU. Our data represent the first evidence that an mt-DNA disease can directly affect microRNA expression. Moreover, we demonstrate that the modification status of mt-tRNAs is dynamic and that cells respond to stress by modulating the expression of mt-tRNA-modifying enzymes. microRNA-9/9* is a crucial player in mitochondria-to-nucleus signaling as it regulates expression of nuclear genes in response to changes in the functional state of mitochondria.

MicroRNA in teleost fish

MicroRNAs (miRNAs) are transcriptional and posttranscriptional regulators involved in nearly all known biological processes in distant eukaryotic clades. Their discovery and functional characterization have broadened our understanding of biological regulatory mechanisms in animals and plants. They show both evolutionary conserved and unique features across Metazoa. Here, we present the current status of the knowledge about the role of miRNA in development, growth, and physiology of teleost fishes, in comparison to other vertebrates. Infraclass Teleostei is the most abundant group among vertebrate lineage. Fish are an important component of aquatic ecosystems and human life, being the prolific source of animal proteins worldwide and a vertebrate model for biomedical research. We review miRNA biogenesis, regulation, modifications, and mechanisms of action. Specific sections are devoted to the role of miRNA in teleost development, organogenesis, tissue differentiation, growth, regeneration, reproduction, endocrine system, and responses to environmental stimuli. Each section discusses gaps in the current knowledge and pinpoints the future directions of research on miRNA in teleosts.

Relevance of microRNA in metabolic diseases

Metabolic syndrome is a complex metabolic condition caused by abnormal adipose deposition and function, dyslipidemia and hyperglycemia, which affects >47 million American adults and ∼1 million children. Individuals with the metabolic syndrome have essentially twice the risk for developing cardiovascular disease (CVD) and Type 2 diabetes mellitus (T2D), compared to those without the syndrome. In the search for improved and novel therapeutic strategies, microRNAs (miRNA) have been shown to be interesting targets due to their regulatory role on gene networks controlling different crucial aspects of metabolism, including lipid and glucose homeostasis. More recently, the discovery of circulating miRNAs suggest that miRNAs may be involved in facilitating metabolic crosstalk between organs as well as serving as novel biomarkers of diseases, including T2D and atherosclerosis. These findings highlight the importance of miRNAs for regulating pathways that underlie metabolic diseases, and their potential as therapeutic targets for the development of novel treatments.

miR-196b-mediated translation regulation of mouse insulin2 via the 5'UTR

The 5' and the 3' untranslated regions (UTR) of the insulin genes are very well conserved across species. Although microRNAs (miRNAs) are known to regulate insulin secretion process, direct regulation of insulin biosynthesis by miRNA has not been reported. Here, we show that mouse microRNA miR-196b can specifically target the 5'UTR of the long insulin2 splice isoform. Using reporter assays we show that miR-196b specifically increases the translation of the reporter protein luciferase. We further show that this translation activation is abolished when Argonaute 2 levels are knocked down after transfection with an Argonaute 2-directed siRNA. Binding of miR-196b to the target sequence in insulin 5'UTR causes the removal of HuD (a 5'UTR-associated translation inhibitor), suggesting that both miR-196b and HuD bind to the same RNA element. We present data suggesting that the RNA-binding protein HuD, which represses insulin translation, is displaced by miR-196b. Together, our findings identify a mechanism of post-transcriptional regulation of insulin biosynthesis.

Application of microRNAs in diabetes mellitus

MicroRNAs (miRNAs) are small molecules negatively regulating gene expression by diminishing their target mRNAs. Emerging studies have shown that miRNAs play diverse roles in diabetes mellitus. Type 1 diabetes (T1D) and T2D are two major types of diabetes. T1D is characterized by a reduction in insulin release from the pancreatic β-cells, while T2D is caused by islet β-cell dysfunction in response to insulin resistance. This review describes the miRNAs that control insulin release and production by regulating cellular membrane electrical excitability (ATP:ADP ratio), insulin granule exocytosis, insulin synthesis in β-cells, and β-cell fate and islet mass formation. This review also examines miRNAs involved the insulin resistance of liver, fat, and skeletal muscle, which change insulin sensitivity pathways (insulin receptors, glucose transporter type 4, and protein kinase B pathways). This review discusses the potential application of miRNAs in diabetes, including the use of gene therapy and therapeutic compounds to recover miRNA function in diabetes, as well as the role of miRNAs as potential biomarkers for T1D and T2D.

DNA methylation of microRNA-375 in impaired glucose tolerance

In the present study, the expression levels and DNA methylation status of microRNA (miRNA)-375 in patients with impaired glucose tolerance (IGT) and type 2 diabetes mellitus (T2DM) were analyzed and the role of DNA methylation of miRNA-375 in the pathogenesis of T2DM was investigated. Compared with the miR-375 levels in patients with normal glucose tolerance (NGT; n=53), the samples from patients with IGT (n=44) exhibited downregulation of miR-375, while those from patients with T2DM (n=54) exhibited upregulation of miR-375 in the plasma. Additionally, the samples from patients with IGT were observed to be hypermethylated compared with those from patients with T2DM and NGT (P=0.042). Analysis of three CpG units (CpG1.2, CpG20 and CpG25.26.27) from 17 CpG sites (between −990 and −1,258 bp, relative to the transcription start site) revealed higher methylation levels in patients with IGT compared with those in patients with NGT (P<0.05). The methylation of two CpG units (CpG1.2 and CpG25.26.27) was higher in patients with IGT than in the patients with T2DM (P<0.05). Thus, the present study demonstrated that the miR-375 promoter was hypermethylated and the levels of miR-375 in the plasma were downregulated in the patients with IGT. DNA hypomethylation may have an important role in the regulation of miR-375 expression and may contribute to the pathogenesis of T2DM.

Influence of miRNA in insulin signaling pathway and insulin resistance: micro-molecules with a major role in type-2 diabetes

The prevalence of type-2 diabetes (T2D) is increasing significantly throughout the globe since the last decade. This heterogeneous and multifactorial disease, also known as insulin resistance, is caused by the disruption of the insulin signaling pathway. In this review, we discuss the existence of various miRNAs involved in regulating the main protein cascades in the insulin signaling pathway that affect insulin resistance. The influence of miRNAs (miR-7, miR-124a, miR-9, miR-96, miR-15a/b, miR-34a, miR-195, miR-376, miR-103, miR-107, and miR-146) in insulin secretion and beta (β) cell development has been well discussed. Here, we highlight the role of miRNAs in different significant protein cascades within the insulin signaling pathway such as miR-320, miR-383, miR-181b with IGF-1, and its receptor (IGF1R); miR-128a, miR-96, miR-126 with insulin receptor substrate (IRS) proteins; miR-29, miR-384-5p, miR-1 with phosphatidylinositol 3-kinase (PI3K); miR-143, miR-145, miR-29, miR-383, miR-33a/b miR-21 with AKT/protein kinase B (PKB) and miR-133a/b, miR-223, miR-143 with glucose transporter 4 (GLUT4). Insulin resistance, obesity, and hyperlipidemia (high lipid levels in the blood) have a strong connection with T2D and several miRNAs influence these clinical outcomes such as miR-143, miR-103, and miR-107, miR-29a, and miR-27b. We also corroborate from previous evidence how these interactions are related to insulin resistance and T2D. The insights highlighted in this review will provide a better understanding on the impact of miRNA in the insulin signaling pathway and insulin resistance-associated diagnostics and therapeutics for T2D.

Role of non-coding RNAs in pancreatic beta-cell development and physiology

The progression of diabetes is accompanied by increasing demand to the beta-cells to produce and secrete more insulin, requiring complex beta-cell adaptations. Functionally active and ubiquitous non-coding RNAs (ncRNAs) have the capacity to take part in such adaptations as they have been shown to be key regulatory molecules in various biological processes. In the pancreatic islets, the function of ncRNAs and their contribution to disease development is beginning to be understood. Here, we review the different classes of ncRNAs, such as long non-coding RNAs (lncRNAs) and microRNAs (miRNAs), and their potential contribution to insulin secretion. A special focus will be on miRNAs and their regulatory function in beta-cell physiology and insulin exocytosis. As important players in gene regulation, ncRNAs have huge potential in opening innovative therapeutic avenues against diabetes and associated complications.

MicroRNAs with Specific Roles in Diabetes and Psychiatric Diseases

Diabetes mellitus is one of the most cited non communicable diseases and the most common metabolic disorder. Epigenetics represents the field of study of heritable changes in gene expression which are not directly related to DNA. Epigenetics is concerned, alongside histone modifications, short interfering RNAs etc., with microRNAs (miRNAs) as well. These are small noncoding RNAs, 21 to 23 nucleotides in length, which either inhibit translation or affect mRNA stability and degradation. At present, there are dozens of miRNAs which have been proven to be involved in the animal and human pathology of diabetes (type 1 or 2). This review focuses on the miRNAs which have been identified as playing a role in both psychiatric diseases and diabetes.

miRNA gene counts in chromosomes vary widely in a species and biogenesis of miRNA largely depends on transcription or post-transcriptional processing of coding genes

MicroRNAs target specific mRNA(s) to silence its expression and thereby regulate various cellular processes. We have investigated miRNA gene counts in chromosomes for 20 different species and observed wide variation. Certain chromosomes have extremely high number of miRNA gene compared with others in all the species. For example, high number of miRNA gene in X chromosome and the least or absence of miRNA gene in Y chromosome was observed in all species. To search the criteria governing such variation of miRNA gene counts in chromosomes, we have selected three parameters- length, number of non-coding and coding genes in a chromosome. We have calculated Pearson's correlation coefficient of miRNA gene counts with length, number of non-coding and coding genes in a chromosome for all 20 species. Major number of species showed that number of miRNA gene was not correlated with chromosome length. Eighty five percent of species under study showed strong positive correlation coefficient (r ≥ 0.5) between the numbers of miRNA gene vs. non-coding gene in chromosomes as expected because miRNA is a sub-set of non-coding genes. 55% species under study showed strong positive correlation coefficient (r ≥ 0.5) between numbers of miRNA gene vs. coding gene. We hypothesize biogenesis of miRNA largely depends on coding genes, an evolutionary conserved process. Chromosomes having higher number of miRNA genes will be most likely playing regulatory roles in several cellular processes including different disorders. In humans, cancer and cardiovascular disease associated miRNAs are mostly intergenic and located in Chromosome 19, X, 14, and 1.

miR-25 and miR-92a regulate insulin I biosynthesis in rats

The 3' UTR of insulin has been identified as a critical region that confers mRNA stability, which is crucial for promoting transcription in response to glucose challenge. miRNAs are endogenously encoded non-coding RNAs that function as regulators of gene expression. This regulatory function is generally mediated by complementary binding to the 3'UTR of its mRNA targets that affects subsequent translational process. Genes involved in the regulation of glucose homeostasis, particularly in insulin production, have been found as targets of several miRNAs. Yet, no direct miRNA-based regulators of insulin biosynthesis have been identified. In this study, identification of possible miRNA-based regulators of insulin production is explored. Members of a miRNA family, miR-25 and miR-92a, are found as direct modulators of insulin expression. Overexpression of miR-25 or miR-92a reduced insulin expression while inhibition of miR-25 and miR-92a expression using corresponding antagomiRs promoted insulin expression and ultimately enhanced glucose-induced insulin secretion. Furthermore, suppression of insulin secretion by pre miR-9 could be attenuated by treatment with anti-miR-25 or miR-92a. Interestingly, we found the binding site of miR-25 and miR-92a to overlap with that of PTBP1, an important RNA binding molecule that stabilizes insulin mRNA for translation. Despite the increase in PTBP1 protein in the pancreas of diabetic rats, we observed insulin expression to be reduced alongside upregulation of miR-25 and miR-92a, suggesting an intricate regulation of insulin (bio)synthesis at its mRNA level.

Seasonal variation of urinary microRNA expression in male goats (Capra hircus) as assessed by next generation sequencing

Testosterone plays a key role in preparation of a male domesticated goat (Capra hircus) to breeding season including changes in the urogenital tract of a male goat (buck). microRNAs are important regulators of cellular metabolism, differentiation and function. They are powerful intermediaries of hormonal activity in the body, including the urogenital tract. We investigated seasonal changes in expression of microRNAs in goat buck urine and their potential consequences using next generation sequencing (microRNA-Seq). We determined the location of each microRNA gene in the goat genome. Testosterone was measured by radioimmunoassay and the androgen receptor binding sites (ARBS) in the promoters of the microRNA genes were determined by MatInspector. The overall impact of regulated microRNAs on cellular physiology was assessed by mirPath. We observed high testosterone levels during the breeding season and changes in the expression of forty microRNAs. Nineteen microRNAs were upregulated, while twenty-one were downregulated. We identified several ARBS in the promoters of regulated microRNAs. Notably, the mostly inhibited microRNA, miR-1246, has a unique set of several gene copy variants associated with a cluster of androgen receptor binding sites. Concomitant changes in regulated microRNA expression could promote transcription, proliferation and differentiation of urogenital tract cells. Together, these findings indicate that in a domesticated goat (Capra hircus), there are specific changes in the microRNA expression profile in buck urine during breeding season, which could be attributable to high testosterone levels during breeding, and could help in preparation of the urogenital tract for high metabolic demands of that season.

A rare SNP in pre-miR-34a is associated with increased levels of miR-34a in pancreatic beta cells

Changes in the levels of specific microRNAs (miRNAs) can reduce glucose-stimulated insulin secretion and increase beta-cell apoptosis, two causes of islet dysfunction and progression to type 2 diabetes. Studies have shown that single nucleotide polymorphisms (SNPs) within miRNA genes can affect their expression. We sought to determine whether miRNAs, with a known role in beta-cell function, possess SNPs within the pre-miRNA structure which can affect their expression. Using published literature and dbSNP, we aimed to identify miRNAs with a role in beta-cell function that also possess SNPs within the region encoding its pre-miRNA. Following transfection of plasmids, encoding the pre-miRNA and each allele of the SNP, miRNA expression was measured. Two rare SNPs located within the pre-miRNA structure of two miRNA genes important to beta-cell function (miR-34a and miR-96) were identified. Transfection of INS-1 and MIN6 cells with plasmids encoding pre-miR-34a and the minor allele of rs72631823 resulted in significantly (p < 0.05) higher miR-34a expression, compared to cells transfected with plasmids encoding the corresponding major allele. Similarly, higher levels were also observed upon transfection of HeLa cells. Transfection of MIN6 cells with plasmids encoding pre-miR-96 and each allele of rs41274239 resulted in no significant differences in miR-96 expression. A rare SNP in pre-miR-34a is associated with increased levels of mature miR-34a. Given that small changes in miR-34a levels have been shown to cause increased levels of beta-cell apoptosis this finding may be of interest to studies looking at determining the effect of rare variants on type 2 diabetes susceptibility.

Increased expression of miR-187 in human islets from individuals with type 2 diabetes is associated with reduced glucose-stimulated insulin secretion

AIMS/HYPOTHESIS

Type 2 diabetes is characterised by progressive beta cell dysfunction, with changes in gene expression playing a crucial role in its development. MicroRNAs (miRNAs) are post-transcriptional regulators of gene expression and therefore alterations in miRNA levels may be involved in the deterioration of beta cell function.

METHODS

Global TaqMan arrays and individual TaqMan assays were used to measure islet miRNA expression in discovery (n = 20) and replication (n = 20) cohorts from individuals with and without type 2 diabetes. The role of specific dysregulated miRNAs in regulating insulin secretion, content and apoptosis was subsequently investigated in primary rat islets and INS-1 cells. Identification of miRNA targets was assessed using luciferase assays and by measuring mRNA levels.

RESULTS

In the discovery and replication cohorts miR-187 expression was found to be significantly increased in islets from individuals with type 2 diabetes compared with matched controls. An inverse correlation between miR-187 levels and glucose-stimulated insulin secretion (GSIS) was observed in islets from normoglycaemic donors. This correlation paralleled findings in primary rat islets and INS-1 cells where overexpression of miR-187 markedly decreased GSIS without affecting insulin content or apoptotic index. Finally, the gene encoding homeodomain-interacting protein kinase-3 (HIPK3), a known regulator of insulin secretion, was identified as a direct target of miR-187 and displayed reduced expression in islets from individuals with type 2 diabetes.

CONCLUSIONS/INTERPRETATION

Our findings suggest a role for miR-187 in the blunting of insulin secretion, potentially involving regulation of HIPK3, which occurs during the pathogenesis of type 2 diabetes.