Expression and DNA methylation status of microRNA-375 in patients with type 2 diabetes mellitus

Dysregulated microRNAs in type 2 diabetes and breast cancer: Potential associated molecular mechanisms

Type 2 diabetes (T2D) is a multifaceted and heterogeneous syndrome associated with complications such as hypertension, coronary artery disease, and notably, breast cancer (BC). The connection between T2D and BC is established through processes that involve insulin resistance, inflammation and other factors. Despite this comprehension the specific cellular and molecular mechanisms linking T2D to BC, especially through microRNAs (miRNAs), remain elusive. miRNAs are regulators of gene expression at the post-transcriptional level and have the function of regulating target genes by modulating various signaling pathways and biological processes. However, the signaling pathways and biological processes regulated by miRNAs that are associated with T2D and BC have not yet been elucidated. This review aims to identify dysregulated miRNAs in both T2D and BC, exploring potential signaling pathways and biological processes that collectively contribute to the development of BC.

Altered expression of miR-375 and miR-541 in type 2 diabetes patients with and without coronary artery disease (CAD): the potential of miR-375 as a CAD biomarker

Background

MicroRNAs (miRNAs, miRs) have been linked to beta-cell pathologies and have also shown potential as biomarkers for cardiovascular disease. This study aimed to evaluate the expression of miR-375 and miR-541 in T2D patients with and without CAD, in order to determine the potential of these miRNAs as biomarkers for assessing CAD risk.

Methods

This study was conducted on 106 patients with T2D who underwent coronary angiographic examination. Reverse transcription was performed using the cDNA synthesis kit. Real-time PCR was performed using the SYBR Green method and specific primers. The ability to predict which person had developed CAD was evaluated by calculating the area under the receiver-operating characteristic (ROC) curve (AUC).

Results

The expression of miR-375 was significantly higher in samples from CAD patients compared to those without CAD (p = 0.009). While the expression of miR-541 was also higher in CAD patients, the difference was not statistically significant. In terms of predicting CAD, miR-375 was found to be a suitable predictor with an AUC of 0.74 (p = 0.01), while miR-541 was not. With a cut-off value of 0.016 for miR-375, the sensitivity was 67% and the specificity was 80%.

Conclusion

Our results indicated that circulating levels of miR-375 and miR-541 were elevated in T2D patients with CAD compared to those without CAD. This suggests that miR-375 could potentially be used as a non-invasive biomarker for the diagnosis of CAD in T2D patients.

MicroRNAs as Biomarkers for Coronary Artery Disease Related to Type 2 Diabetes Mellitus-From Pathogenesis to Potential Clinical Application

Type 2 diabetes mellitus (T2DM) is a chronic metabolic disease with still growing incidence among adults and young people worldwide. Patients with T2DM are more susceptible to developing coronary artery disease (CAD) than non-diabetic individuals. The currently used diagnostic methods do not ensure the detection of CAD at an early stage. Thus, extensive research on non-invasive, blood-based biomarkers is necessary to avoid life-threatening events. MicroRNAs (miRNAs) are small, endogenous, non-coding RNAs that are stable in human body fluids and easily detectable. A number of reports have highlighted that the aberrant expression of miRNAs may impair the diversity of signaling pathways underlying the pathophysiology of atherosclerosis, which is a key player linking T2DM with CAD. The preclinical evidence suggests the atheroprotective and atherogenic influence of miRNAs on every step of T2DM-induced atherogenesis, including endothelial dysfunction, endothelial to mesenchymal transition, macrophage activation, vascular smooth muscle cells proliferation/migration, platelet hyperactivity, and calcification. Among the 122 analyzed miRNAs, 14 top miRNAs appear to be the most consistently dysregulated in T2DM and CAD, whereas 10 miRNAs are altered in T2DM, CAD, and T2DM-CAD patients. This up-to-date overview aims to discuss the role of miRNAs in the development of diabetic CAD, emphasizing their potential clinical usefulness as novel, non-invasive biomarkers and therapeutic targets for T2DM individuals with a predisposition to undergo CAD.

A comprehensive overview on Micro RNA signature in type 2 diabetes Mellitus and its complications

MicroRNAs (miRNAs) are small endogenous, non-coding RNA molecules that can modulate the expression of their target genes. Since its discovery, an enormous breakthrough has been established regarding its biogenesis and pathophysiological action, which has revolutionized the field of molecular biology. In addition, recent studies have identified the existence of stable extracellular/circulating miRNAs tissues and in biological fluids like blood where they are safeguarded from endogenous ribonuclease activity. Type 2 diabetes mellitus (T2DM) has emerged as a prime health issue worldwide. Incidence has increased considerably over the past decade. There are various tests that have been employed to diagnose T2DM. But for early detection and development, the establishment of biomarkers are of paramount importance. Contemporary evidence also validates the signature of a set of this epigenetic factor miRNA in the development of various diseases, including T2DM. This article reviews the contemporary corroboration associating miRNAs and T2DM and emphasizes the potential role of miRNA as a circulatory biomarker that could alert the growing prevalence of T2DM. Also, it acknowledges the valuable compendium of information regarding biogenesis and functional role of circulating miRNA in insulin resistance which is intimately linked to T2DM.

Circulating salivary and serum miRNA-182, 320a, 375 and 503 expression levels in type 2 diabetes

Aim

Early-stage diagnosis of diabetes through non-invasive and diagnostic biofluid-like saliva has become a very popular approach to facilitate future preventive interventions and improve patient care. Meanwhile, the alteration of small non-coding RNA in human fluids has been suggested as a probable precedent for the early stages of diabetes.

Methods

In the present study, we checked the expression of miR-320a, 182-5p, 503, and 375 by using quantitative PCR in both stimulated and unstimulated saliva and blood samples of 40 adult patients with type-2 diabetes compared to 40 healthy individuals. In addition, we have sought to understand the possibility that miRNAs could provide new information about the status of type 2 diabetes in salivary samples beyond what can now be identified from blood samples and link their expression to the presence of clinically relevant risk factors. For this purpose, we have used a set of multivariate models.

Results

The results showed that three miRNAs were more highly expressed in patients with type 2 diabetes, while miR-320-a was down-regulated in those patients compared to healthy subjects. Furthermore, the data showed that miR-320a was the most reliable predictor for distinguishing diabetic patients from healthy subjects, with AUCs of 0.997, 0.97, and 0.99 (97.4% sensitivity and 100% specificity, p = 0.001) for serum, unstimulated, and stimulated saliva samples, respectively.

Conclusions

Interestingly, the results of this study indicated that the amount of four miRNAs expressed in stimulated saliva was the same as in serum samples, which could conclude that specific miR-320a and 503 in stimulated saliva may introduce credible, non-invasive, and diagnostic biomarkers that can be used to monitor diabetic patients' status, while there is a need to design more research studies to confirm these findings.

Overview of Transcriptomic Research on Type 2 Diabetes: Challenges and Perspectives

Type 2 diabetes (T2D) is a common chronic disease whose etiology is known to have a strong genetic component. Standard genetic approaches, although allowing for the detection of a number of gene variants associated with the disease as well as differentially expressed genes, cannot fully explain the hereditary factor in T2D. The explosive growth in the genomic sequencing technologies over the last decades provided an exceptional impetus for transcriptomic studies and new approaches to gene expression measurement, such as RNA-sequencing (RNA-seq) and single-cell technologies. The transcriptomic analysis has the potential to find new biomarkers to identify risk groups for developing T2D and its microvascular and macrovascular complications, which will significantly affect the strategies for early diagnosis, treatment, and preventing the development of complications. In this article, we focused on transcriptomic studies conducted using expression arrays, RNA-seq, and single-cell sequencing to highlight recent findings related to T2D and challenges associated with transcriptome experiments.

Insight into the Role of the PI3K/Akt Pathway in Ischemic Injury and Post-Infarct Left Ventricular Remodeling in Normal and Diabetic Heart

Despite the significant decline in mortality, cardiovascular diseases are still the leading cause of death worldwide. Among them, myocardial infarction (MI) seems to be the most important. A further decline in the death rate may be achieved by the introduction of molecularly targeted drugs. It seems that the components of the PI3K/Akt signaling pathway are good candidates for this. The PI3K/Akt pathway plays a key role in the regulation of the growth and survival of cells, such as cardiomyocytes. In addition, it has been shown that the activation of the PI3K/Akt pathway results in the alleviation of the negative post-infarct changes in the myocardium and is impaired in the state of diabetes. In this article, the role of this pathway was described in each step of ischemia and subsequent left ventricular remodeling. In addition, we point out the most promising substances which need more investigation before introduction into clinical practice. Moreover, we present the impact of diabetes and widely used cardiac and antidiabetic drugs on the PI3K/Akt pathway and discuss the molecular mechanism of its effects on myocardial ischemia and left ventricular remodeling.

Circulating miRNA as potential biomarkers for diabetes mellitus type 2: should we focus on searching for sex differences?

microRNAs are non-coding molecules, approximately 22 nucleotides in length, that regulate various cellular processes. A growing body of evidence has suggested that their dysregulated expression is involved in the pathogenesis of diverse diseases, including diabetes mellitus type 2 (DM2). Early onset of this chronic and complex metabolic disorder is frequently undiagnosed, leading to the development of severe diabetic complications. Notably, DM2 prevalence is rising globally and an increasing number of articles demonstrate that DM2 susceptibility, development, and progression differ between males and females. Therefore, this paper discusses the role of microRNAs as a source of novel diagnostic biomarkers for DM2 and aims to underline the importance of sex disparity in biomarkers research. Taking into account an urgent need for the development of sex-specific diagnostic strategies in DM2, recent results have shown that circulating miRNAs are promising candidates for sex-biased biomarkers.

Circulating Nucleic Acid-Based Biomarkers of Type 2 Diabetes

Type 2 diabetes (T2D) is a deficiency in how the body regulates glucose. Uncontrolled T2D will result in chronic high blood sugar levels, eventually resulting in T2D complications. These complications, such as kidney, eye, and nerve damage, are even harder to treat. Identifying individuals at high risk of developing T2D and its complications is essential for early prevention and treatment. Numerous studies have been done to identify biomarkers for T2D diagnosis and prognosis. This review focuses on recent T2D biomarker studies based on circulating nucleic acids using different omics technologies: genomics, transcriptomics, and epigenomics. Omics studies have profiled biomarker candidates from blood, urine, and other non-invasive samples. Despite methodological differences, several candidate biomarkers were reported for the risk and diagnosis of T2D, the prognosis of T2D complications, and pharmacodynamics of T2D treatments. Future studies should be done to validate the findings in larger samples and blood-based biomarkers in non-invasive samples to support the realization of precision medicine for T2D.

The impact of obesity on adipocyte-derived extracellular vesicles

Recently, the emerging roles of adipocyte-derived extracellular vesicles (EVs) linking obesity and its comorbidities have been recognized. In obese subjects, adipocytes are having hypertrophic growth and are under stressed. The dysfunction adipocytes dysregulate the assembly of the biological components in the EVs including exosomes. This article critically reviews the current findings on the impact of obesity on the exosomal cargo contents that induce the pathophysiological changes. Besides, this review also summarizes the understanding on how obesity affects the biogenesis of adipocyte-derived exosomes and the exosome secretion. Furthermore, the differences of the exosomal contents in different adipose depots, and the impact of obesity on the exosomes that are derived from the stromal vascular fraction such as the adipose tissue macrophages and adipocyte-derived stem cells will also be discussed. The current development and potential application of exosome-based therapy will be summarized. This review provides crucial information for the design of novel exosome-based therapy for the treatment of obesity and its comorbidities.

Relevance of mitochondrial dysfunction in heart disease associated with insulin resistance conditions

Insulin resistance plays a key role in the development and progression of obesity, diabetes, and their complications. Moreover, insulin resistance is considered the principal link between metabolic diseases and cardiovascular diseases. Heart disease associated with insulin resistance is one of the most important consequences of both obesity and diabetes, and it is characterized by impaired cardiac energetics, diastolic dysfunction, and finally heart failure. Mitochondrion plays a key role in cell energy homeostasis and is the main source of reactive oxygen species. Obesity and diabetes are associated with alterations in mitochondrial function and dynamics. Mitochondrial dysfunction is characterized by changes in mitochondrial respiratory chain with reduced ATP production and elevated reactive oxygen species production. These mitochondrial alterations together with inflammation contribute to the development and progression of heart disease under insulin resistance conditions. Finally, numerous miRNAs participate in the regulation of energy substrate metabolism, reactive oxygen species production, and apoptotic pathways within the mitochondria. This notion supports the relevance of interactions between miRNAs and mitochondrial dysfunction in the pathophysiology of metabolic heart disease.

miRNAs as biomarkers for diagnosis of type 2 diabetes: A systematic review

BACKGROUND

This systematic review summarizes results of studies that evaluated the expression of microRNAs (miRs) in prediabetes or type 2 diabetes (T2D).

METHODS

The information was obtained from PubMed, EMBL-EBI, Wanfang, Trip Database, Lilacs, CINAHL, Human microRNA Disease Database (HMDD) v3.0, and Google. A qualitative synthesis of the results was performed and miRs frequency was graphically represented. From 1893 identified studies, only 55 fulfilled the inclusion criteria. These 55 studies analyzed miRs in T2D, and of them, 13 also described data of prediabetes.

RESULTS

In diabetics, 122 miRs were reported and 35 miRs for prediabetics. However, we identified that five miRs (-122-5p, 144-3p, 210, 375, and -126b) were reported more often in diabetics and four (144-3p, -192, 29a, and -30d) in prediabetics.

CONCLUSIONS

Circulating miRs could be used as biomarkers of T2D. However, it is necessary to validate these microRNAs in prospective and multicenter studies with different population subgroups, considering age, gender, and risk factors.

MicroRNA Sequences Modulated by Beta Cell Lipid Metabolism: Implications for Type 2 Diabetes Mellitus

Alterations in lipid metabolism within beta cells and islets contributes to dysfunction and apoptosis of beta cells, leading to loss of insulin secretion and the onset of type 2 diabetes. Over the last decade, there has been an explosion of interest in understanding the landscape of gene expression which influences beta cell function, including the importance of small non-coding microRNA sequences in this context. This review sought to identify the microRNA sequences regulated by metabolic challenges in beta cells and islets, their targets, highlight their function and assess their possible relevance as biomarkers of disease progression in diabetic individuals. Predictive analysis was used to explore networks of genes targeted by these microRNA sequences, which may offer new therapeutic strategies to protect beta cell function and delay the onset of type 2 diabetes.

Epigenetics and microRNAs in UGT1As

UDP-glucuronosyltransferases (UGTs) are the main phase II drug-metabolizing enzymes mediating the most extensive glucuronidation-binding reaction in the human body. The UGT1A family is involved in more than half of glucuronidation reactions. However, significant differences exist in the distribution of UGT1As in vivo and the expression of UGT1As among individuals, and these differences are related to the occurrence of disease and differences in metabolism. In addition to genetic polymorphisms, there is now interest in the contribution of epigenetics and noncoding RNAs (especially miRNAs) to this differential change. Epigenetics regulates UGT1As pretranscriptionally through DNA methylation and histone modification, and miRNAs are considered the key mechanism of posttranscriptional regulation of UGT1As. Both epigenetic inheritance and miRNAs are involved in the differences in sex expression and in vivo distribution of UGT1As. Moreover, epigenetic changes early in life have been shown to affect gene expression throughout life. Here, we review and summarize the current regulatory role of epigenetics in the UGT1A family and discuss the relationship among epigenetics and UGT1A-related diseases and treatment, with references for future research.

Epigenetics, microRNA and Metabolic Syndrome: A Comprehensive Review

Epigenetics refers to the DNA chemistry changes that result in the modification of gene transcription and translation independently of the underlying DNA coding sequence. Epigenetic modifications are reported to involve various molecular mechanisms, including classical epigenetic changes affecting DNA methylation and histone modifications and small RNA-mediated processes, particularly that of microRNAs. Epigenetic changes are reversible and are closely interconnected. They are recognised to play a critical role as mediators of gene regulation, and any alteration in these mechanisms has been identified to mediate various pathophysiological conditions. Moreover, genetic predisposition and environmental factors, including dietary alterations, lifestyle or metabolic status, are identified to interact with the human epigenome, highlighting the importance of epigenetic factors as underlying processes in the aetiology of various diseases such as MetS. This review will reflect on how both the classical and microRNA-regulated epigenetic changes are associated with the pathophysiology of metabolic syndrome. We will then focus on the various aspects of epigenetic-based strategies used to modify MetS outcomes, including epigenetic diet, epigenetic drugs, epigenome editing tools and miRNA-based therapies.

Regulatory MicroRNAs in T2DM and Breast Cancer

MicroRNAs orchestrate the tight regulation of numerous cellular processes and the deregulation in their activities has been implicated in many diseases, including diabetes and cancer. There is an increasing amount of epidemiological evidence associating diabetes, particularly type 2 diabetes mellitus, to an elevated risk of various cancer types, including breast cancer. However, little is yet known about the underlying molecular mechanisms and even less about the role miRNAs play in driving the tumorigenic potential of the cell signaling underlying diabetes pathogenesis. This article reviews the role of miRNA in bridging the diabetes–breast cancer association by discussing specific miRNAs that are implicated in diabetes and breast cancer and highlighting the overlap between the disease-specific regulatory miRNA networks to identify a 20-miRNA signature that is common to both diseases. Potential therapeutic targeting of these molecular players may help to alleviate the socioeconomic burden on public health that is imposed by the type 2 diabetes mellitus (T2DM)–breast cancer association.

Noncoding RNAs involved in DNA methylation and histone methylation, and acetylation in diabetic vascular complications

Diabetes is a metabolic disorder and its incidence is still increasing. Diabetic vascular complications cause major diabetic mobility and include accelerated atherosclerosis, nephropathy, retinopathy, and neuropathy. Hyperglycemia contributes to the pathogenesis of diabetic vascular complications via numerous mechanisms including the induction of oxidative stress, inflammation, metabolic alterations, and abnormal proliferation of EC and angiogenesis. In the past decade, epigenetic modifications have attracted more attention as they participate in the progression of diabetic vascular complications despite controlled glucose levels and regulate gene expression without altering the genomic sequence. DNA methylation and histone methylation, and acetylation are vital epigenetic modifications and their underlying mechanisms in diabetic vascular complication are still urgently needed to be investigated. Non-coding RNAs (nc RNAs) such as micro RNAs (miRNAs), long non-coding RNA (lncRNAs), and circular RNAs (circ RNAs) were found to exert transcriptional regulation in diabetic vascular complication. Although nc RNAs are not considered as epigenetic components, they are involved in epigenetic modifications. In this review, we summarized the investigations of non-coding RNAs involved in DNA methylation and histone methylation and acetylation. Their cross-talks might offer novel insights into the pathology of diabetic vascular complications.

Assessing MicroRNA-375 Levels in Type 2 Diabetes Mellitus (T2DM) Patients and Their First-Degree Relatives with T2DM

PURPOSE

The pancreatic islet specific microRNA-375 (miR-375) is overexpressed in type 2 diabetes mellitus (T2DM) patients suppressing the glucose-induced insulin secretion. Thus, miR-375 may serve as a biomarker for the early prediction of T2DM among high-risk individuals. We conducted this clinical study to assess the significance of miR-375 among type 2 diabetes mellitus (T2DM) patients and their first-degree relatives.

PATIENTS AND METHODS

We included 56 Han Chinese individuals (N: NGT = 21, T2DM = 10, FD-NGT =13 and FD-T2DM = 12) who received medical health check-ups from January 2018 to September 2018 at The Third Hospital of Yunnan Province, China. They were categorized as normal glucose tolerance (NGT), T2DM, first-degree relatives with normal glucose tolerance (FD-NGT) and first-degree relatives with T2DM (FD-T2DM). OGTT, C-peptide and Insulin tests were performed to confirm the diagnosis. The miR-375 levels were determined by Quantitative real-time RT-PCR (qRT-PCR).

RESULTS

The OGTT test showed a significant difference in T2DM and FD-T2DM groups compared with NGT and FD-NGT (p< 0.05). Similar results were observed during C-peptide and insulin tests. Interestingly, the 2-hour insulin test showed FD-NGT group having a significantly higher mean ± standard error of (64.240 ± 12.775) compared to NGT (28.836 ± 10.875). Assessment of miR-375 expression levels in 4 groups showed a significant up-regulation in T2DM and FD-T2DM compared with NGT and FD-NGT groups. A slight increase in miRNA expression was observed in FD-NGT compared with NGT group but was not statistically significant.

CONCLUSION

The OGTT, C-peptide and insulin tests revealed a statistically significant difference in T2DM and FD-T2DM compared with NGT and FD-NGT groups. A significantly higher miR-375 expression was also observed in T2DM and FD-T2DM groups compared with NGT and FD-NGT and thus, miR-375 may serve as a stable biomarker for the early prediction of T2DM among high-risk individuals.

Epigenetic regulation of white adipose tissue in the onset of obesity and metabolic diseases

Obesity and metabolic syndrome are among the most prevalent health problems in developed countries. The impairment of adipose tissue (AT) function is partially responsible for the aetiology of these conditions. Epigenetics refers to several processes that add modifications to either the DNA or chromatin architectural proteins (histones). These processes can regulate gene expression, chromatin compaction and DNA repair. Epigenetics includes mechanisms by which the cell can adapt the cellular response to the environmental conditions. Here, we review the role of epigenetics in the onset of obesity and related metabolic disorders, with special focus on AT. We highlight the importance of nutrients and lifestyle in the regulation of the epigenetic mechanisms and how they can impact on AT plasticity and function in obesity and metabolic diseases. Thus, the epigenetic landscape emerges as a fine-tune regulator of the cellular responses according to the energetic, metabolic and physiological conditions of the cell. Alterations in metabolic pathways deregulated during obesity and metabolic syndrome could in part explain the disturbances in the epigenetic marks of the AT in these disorders. The understanding of how this epigenetic deregulation may affect AT biology and function could lead to new therapeutic approaches based on epigenetic strategies.

microRNA-9 and -29a regulate the progression of diabetic peripheral neuropathy via ISL1-mediated sonic hedgehog signaling pathway

In this study, we tested the hypothesis that overexpression of miR-9 and miR-29a may contribute to DPN development and progression. We performed a meta-analysis of miR expression profile studies in human diabetes mellitus (DM) and the data suggested that miR-9 and miR-29a were highly expressed in patients with DM, which was further verified in serum samples collected from 30 patients diagnosed as DM. Besides, ISL1 was confirmed to be a target gene of miR-9 and miR-29a. Lentivirus-mediated forced expression of insulin gene enhancer binding protein-1 (ISL1) activated the sonic hedgehog (SHH) signaling pathway, increased motor nerve conduction velocity and threshold of nociception, and modulated expression of neurotrophic factors in sciatic nerves in rats with DM developed by intraperitoneal injection of 0.45% streptozotocin, suggesting that ISL1 could delay DM progression and promote neural regeneration and repair after sciatic nerve damage. However, lentivirus-mediated forced expression of miR-9 or miR-29a exacerbated DM and antagonized the beneficial effect of ISL1 on DPN. Collectively, this study revealed potential roles of miR-9 and miR-29a as contributors to DPN development through the SHH signaling pathway by binding to ISL1. Additionally, the results provided an experimental basis for the targeted intervention treatment of miR-9 and miR-29a.

Altered adipose tissue and adipocyte function in the pathogenesis of metabolic syndrome

Over the past decade, great progress has been made in understanding the complexity of adipose tissue biology and its role in metabolism. This includes new insights into the multiple layers of adipose tissue heterogeneity, not only differences between white and brown adipocytes, but also differences in white adipose tissue at the depot level and even heterogeneity of white adipocytes within a single depot. These inter- and intra-depot differences in adipocytes are developmentally programmed and contribute to the wide range of effects observed in disorders with fat excess (overweight/obesity) or fat loss (lipodystrophy). Recent studies also highlight the underappreciated dynamic nature of adipose tissue, including potential to undergo rapid turnover and dedifferentiation and as a source of stem cells. Finally, we explore the rapidly expanding field of adipose tissue as an endocrine organ, and how adipose tissue communicates with other tissues to regulate systemic metabolism both centrally and peripherally through secretion of adipocyte-derived peptide hormones, inflammatory mediators, signaling lipids, and miRNAs packaged in exosomes. Together these attributes and complexities create a robust, multidimensional signaling network that is central to metabolic homeostasis.

MicroRNA Signatures as Future Biomarkers for Diagnosis of Diabetes States

Diabetes results from the inability of pancreatic islets to maintain blood glucose concentrations within a normal physiological range. Clinical features are usually not observed until islets begin to fail and irreversible damage has occurred. Diabetes is generally diagnosed based on elevated glucose, which does not distinguish between type 1 and 2 diabetes. Thus, new diagnostic approaches are needed to detect different modes of diabetes before manifestation of disease. During prediabetes (pre-DM), islets undergo stress and release micro (mi) RNAs. Here, we review studies that have measured and tracked miRNAs in the blood for those with recent-onset or longstanding type 1 diabetes, obesity, pre-diabetes, type 2 diabetes, and gestational diabetes. We summarize the findings on miRNA signatures with the potential to stage progression of different modes of diabetes. Advances in identifying selective biomarker signatures may aid in early detection and classification of diabetic conditions and treatments to prevent and reverse diabetes.

Extracellular miRNAs: From Biomarkers to Mediators of Physiology and Disease

miRNAs can be found in serum and other body fluids and serve as biomarkers for disease. More importantly, secreted miRNAs, especially those in extracellular vesicles (EVs) such as exosomes, may mediate paracrine and endocrine communication between different tissues and thus modulate gene expression and the function of distal cells. When impaired, these processes can lead to tissue dysfunction, aging, and disease. Adipose tissue is an especially important contributor to the pool of circulating exosomal miRNAs. As a result, alterations in adipose tissue mass or function, which occur in many metabolic conditions, can lead to changes in circulating miRNAs, which then function systemically. Here we review the findings that led to these conclusions and discuss how this sets the stage for new lines of investigation in which extracellular miRNAs are recognized as important mediators of intercellular communication and potential candidates for therapy of disease.

Analysis of PTEN expression and promoter methylation in Uyghur patients with mild type 2 diabetes mellitus

Phosphatase and tension homolog deleted on chromosome 10 (PTEN) was considered as a promising target in type 2 diabetes mellitus (T2DM) because of its negative effects on insulin resistance. Alteration in DNA methylation is thought to play a role in the pathogenesis of T2DM. The aim of the present study was to quantitatively evaluate the promoter methylation of PTEN in Uyghur patients with mild T2DM. We evaluated methylation levels in 21 CpG sites from -2515 bp to -2186 bp relative to the translation initiation site in 55 cases of T2DM and 50 cases of normal glucose tolerance (NGT) using the MassARRAY spectrometry. In addition, PTEN mRNA and protein levels were measured by quantitative reverse transcriptase polymerase chain reaction (qRT-PCR) and western blotting to determine whether DNA methylation alterations were responsible for PTEN expression. Compared with NGT groups, the PTEN mRNA expression was significantly higher in Uyghur patients with mild T2DM groups. We also showed that PTEN protein expression was upregulated in Uyghur patients with mild T2DM groups, but the level of protein kinase B (AKT) was downregulated. PTEN methylation in T2DM patients was significantly lower than that in NGT groups. In addition, 2 CpG units demonstrated a significant difference between the NGT and Uyghur patients with mild T2DM groups. Furthermore, there was a negative association between promoter methylation and PTEN expression. Together, these findings suggest that epigenetic inactivation of PTEN plays an important role in Uyghur patients with mild T2DM. The aberrant methylation of CpG sites within the PTEN promoter may serve as a potential candidate biomarker for T2DM in the Uyghur population.

Is miRNA-375 a promising biomarker for early detection and monitoring of patients with type 2 diabetes?

miRNAs are small, non-coding RNAs, functioning as negative suppressors of target gene expression. A significant proportion of the transcriptome is subject to miRNA modulation. A single miRNA determines the expression of hundreds of genes, while miRNAs are relatively stable in biological fluids. Thus, they have attracted scientific interest regarding their use as biomarkers for several diseases. miRNA-375 mainly influences β-cell function and insulin secretion. Several studies, primarily experimental, have assessed its role as a biomarker in type 2 diabetes, while recently obtained human evidence supports this potential role. Besides its diagnostic potential, miRNA-375 may also have therapeutic implications. In view of the growing epidemic of type 2 diabetes, there is an unmet need for identification of biomarkers for early recognition and monitoring of these patients. Long-term, prospective human studies are required to elucidate whether miRNA-375 can evolve as a key player in diagnosis and prognosis of type 2 diabetes.

Novel insights into the regulation of miRNA transcriptional control: implications for T2D and related complications

In recent years, epigenetics has emerged as an important form of biological regulation involving chromatin control of gene expression. The mechanisms of this fine-tuned regulation are susceptible to changes forced by environmental stimuli and nutritional factors and may be potentially reversible. Dysregulation of epigenetic processes has important consequences for the pathogenesis of complex and multifactorial diseases such as type 2 diabetes (T2D) and vascular complications. Along with DNA methylation (DNA-me), histone modifications and RNA-based mechanisms as the major epigenetic controllers, small non-coding RNAs known as microRNAs (miRNAs) have their own important implications for the pathogenesis of diabetes. There is increasing evidence supporting the role of miRNAs in modulating gene expression, cumulatively contributing to epigenetic gene silencing by acting either on the methylation status of the cells or in alternative roles. Although significant progress has been made in the characterization of miRNA functions, most miRNA promoters have not yet been characterized, and the transcriptional regulation of miRNAs remains elusive. The present work is centred on the new biological insights pertaining to the epigenetics-miRNA regulatory axis, focusing on the development of T2D and cardiovascular complications, and the ability of these mechanisms to interact in a network of DNA-me regulation. The genomic organization of inter- and intragenic miRNA genes is discussed, and the mutual connections between pre-mRNA splicing and miRNA biogenesis are summarized, along with the discovery of novel miRNA transcriptional regulation sites.

Analysis of MicroRNA Expression in Newborns with Differential Birth Weight Using Newborn Screening Cards

Birth weight is an early predictor for metabolic diseases and microRNAs (miRNAs) are proposed as fetal programming participants. To evaluate the use of dried blood spots (DBS) on newborn screening cards (NSC) as a source of analyzable miRNAs, we optimized a commercial protocol to recover total miRNA from normal birth weight (NBW, n = 17–20), low birth weight (LBW, n = 17–20) and high birth weight (macrosomia, n = 17–20) newborns and analyzed the relative expression of selected miRNAs by stem-loop RT-qPCR. The possible role of miRNAs on the fetal programming of metabolic diseases was explored by bioinformatic tools. The optimized extraction of RNA resulted in a 1.2-fold enrichment of miRNAs respect to the commercial kit. miR-33b and miR-375 were overexpressed in macrosomia 9.8-fold (p < 0.001) and 1.7-fold, (p < 0.05), respectively and miR-454-3p was overexpressed in both LBW and macrosomia (19.7-fold, p < 0.001 and 10.8-fold, p < 0.001, respectively), as compared to NBW. Potential target genes for these miRNAs are associated to cyclic-guanosine monophosphate (cGMP)-dependent protein kinase (PKG), mitogen-activated protein kinase (MAPK), type 2 diabetes, transforming growth factor-β (TGF-β)and Forkhead box O protein (FoxO) pathways. In summary, we improved a protocol for analyzing miRNAs from NSC and provide the first evidence that birth weight modifies the expression of miRNAs associated to adult metabolic dysfunctions. Our work suggests archived NSC are an invaluable resource in the search for fetal programming biomarkers.

The small RNA miR-375 - a pancreatic islet abundant miRNA with multiple roles in endocrine beta cell function

The pathophysiology of diabetes is complex and recent research put focus on the pancreatic islets of Langerhans and the insulin-secreting beta cells as central in the development of the disease. MicroRNAs (miRNAs), the small non-coding RNAs regulating post-transcriptional gene expression, are significant regulators of beta cell function. One of the most abundant miRNAs in the islets is miR-375. This review focus on the role of miR-375 in beta cell function, including effects in development and differentiation, proliferation and regulation of insulin secretion. It also discusses the regulation of miR-375 expression, miR-375 as a potential circulating biomarker in type 1 and type 2 diabetes, and the need for the beta cell to keep expression of miR-375 within optimal levels. The summed picture of miR-375 is a miRNA with multiple functions with importance in the formation of beta cell identity, control of beta cell mass and regulation of insulin secretion.

Circulating microRNA-375 as biomarker of pancreatic beta cell death and protection of beta cell mass by cytoprotective compounds

Objective

Previous studies demonstrated that circulating microRNA-375 (miR-375) is a suitable plasma biomarker for real-time detection of beta cell death. The present study evaluated the use of this biomarker to assess the beta cytoprotective effect of phenylpropenoic acid glucoside (PPAG), which was previously demonstrated to protect beta cells against various types of injury, and of exendin-4, which is an established antidiabetic drug.

Methods

PPAG or exendin-4 were administered in mice treated with streptozotocin (STZ) to acutely induce beta cell death. Beta cell mass and apoptotic death were measured in pancreatic tissue sections. Circulating miR-375 was measured in blood plasma by RT-qPCR. The release of miR-375 was also measured in vitro by MIN-6 beta cells.

Results

Administration of STZ resulted in measurable circulating levels of miR-375, a decrease in beta cell mass and increase in frequency of apoptotic beta cells. In vitro, there was a good correlation between miR-375 release and the extent of beta cell death. Treatment of mice with PPAG or exendin-4 significantly attenuated STZ-induced loss of beta cell mass and beta cell apoptosis, and normalized the blood level of miR-375.

Conclusions

These findings show the potential use of serological miR-375 measurements to evaluate the beta cytoprotective effect of (potential) antidiabetic drugs in vivo.

Regulating microRNA expression: at the heart of diabetes mellitus and the mitochondrion

Type 2 diabetes mellitus is a major risk factor for cardiovascular disease and mortality. Uncontrolled type 2 diabetes mellitus results in a systemic milieu of increased circulating glucose and fatty acids. The development of insulin resistance in cardiac tissue decreases cellular glucose import and enhances mitochondrial fatty acid uptake. While triacylglycerol and cytotoxic lipid species begin to accumulate in the cardiomyocyte, the energy substrate utilization ratio of free fatty acids to glucose changes to almost entirely free fatty acids. Accumulating evidence suggests a role of miRNA in mediating this metabolic transition. Energy substrate metabolism, apoptosis, and the production and response to excess reactive oxygen species are regulated by miRNA expression. The current momentum for understanding the dynamics of miRNA expression is limited by a lack of understanding of how miRNA expression is controlled. While miRNAs are important regulators in both normal and pathological states, an additional layer of complexity is added when regulation of miRNA regulators is considered. miRNA expression is known to be regulated through a number of mechanisms, which include, but are not limited to, epigenetics, exosomal transport, processing, and posttranscriptional sequestration. The purpose of this review is to outline how mitochondrial processes are regulated by miRNAs in the diabetic heart. Furthermore, we will highlight the regulatory mechanisms, such as epigenetics, exosomal transport, miRNA processing, and posttranslational sequestration, that participate as regulators of miRNA expression. Additionally, current and future treatment strategies targeting dysfunctional mitochondrial processes in the diseased myocardium, as well as emerging miRNA-based therapies, will be summarized.

MicroRNAs in the pathogenesis of type 2 diabetes: new research progress and future direction

miRNA is a short non-coding RNA that can influence mRNA processing at the post-transcriptional level. A large number of miRNAs have been found in virtually all species so far, and these small molecules play an important role in many different physiological processes and various pathologic conditions, such as cell metabolism, cancer, autoimmune disease, and diabetes mellitus. T2D arises from a dysregulated response to the elevated glucose level in the circulation. The prevalence of T2D has increased dramatically in all age groups, and T2D in older adults is associated with more T2D complications and higher mortality. Despite the existing findings describing the pathological mechanism, T2D pathology is more complex and the pathophysiology of the disease is still not fully elucidated. In this review, we summarize the current understanding of miRNA-mediated modulation of gene expression in T2D pathogenesis, as well as related signaling pathways, and insight into the important role of miRNA in various T2D complications. Furthermore, the potential therapeutic value of miRNA for T2D patients is also discussed in detail.

Interplay between the miRNome and the epigenetic machinery: Implications in health and disease

Epigenetics refers to functionally relevant genomic changes that do not involve changes in the basic nucleotide sequence. Majorly, these are of two types: DNA methylation and histone modifications. Small RNA molecules called miRNAs are often thought to mediate post-transcriptional epigenetic changes by mRNA degradation or translational attenuation. While DNA methylation and histone modifications have their own independent effects on various cellular events, several reports are suggestive of an obvious interplay between these phenomena and the miRNA regulatory program within the cell. Several miRNAs like miR-375, members of miR-29 family, miR-34, miR-200, and others are regulated by DNA methylation and histone modifications in various types of cancers and metabolic diseases. On the other hand, miRNAs like miR-449a, miR-148, miR-101, miR-214, and miR-128 target members of the epigenetic machinery and their dysregulation leads to diverse cellular aberrations. In spite of being independent cellular events, emergence of such reports that suggest a connection between DNA methylation, histone modification, and miRNA function in several diseases indicate that this connecting axis offers a valuable target with great therapeutic potential that might be exploited for disease management. We review the current status of crosstalk between the major epigenetic modifications and the miRNA machinery and discuss this in the context of health and disease.

A Systematic Study of Dysregulated MicroRNA in Type 2 Diabetes Mellitus

MicroRNAs (miRNAs) are small noncoding RNAs that modulate the cellular transcriptome at the post-transcriptional level. miRNA plays important roles in different disease manifestation, including type 2 diabetes mellitus (T2DM). Many studies have characterized the changes of miRNAs in T2DM, a complex systematic disease; however, few studies have integrated these findings and explored the functional effects of the dysregulated miRNAs identified. To investigate the involvement of miRNAs in T2DM, we obtained and analyzed all relevant studies published prior to 18 October 2016 from various literature databases. From 59 independent studies that met the inclusion criteria, we identified 158 dysregulated miRNAs in seven different major sample types. To understand the functional impact of these deregulated miRNAs, we performed targets prediction and pathway enrichment analysis. Results from our analysis suggested that the altered miRNAs are involved in the core processes associated with T2DM, such as carbohydrate and lipid metabolisms, insulin signaling pathway and the adipocytokine signaling pathway. This systematic survey of dysregulated miRNAs provides molecular insights on the effect of deregulated miRNAs in different tissues during the development of diabetes. Some of these miRNAs and their mRNA targets may have diagnostic and/or therapeutic utilities in T2DM.

DNA methylation of miRNA coding sequences putatively associated with childhood obesity

BACKGROUND

Epigenetic mechanisms may be involved in obesity onset and its consequences. The aim of the present study was to evaluate whether DNA methylation status in microRNA (miRNA) coding regions is associated with childhood obesity.

MATERIAL AND METHODS

DNA isolated from white blood cells of 24 children (identification sample: 12 obese and 12 non-obese) from the Grupo Navarro de Obesidad Infantil study was hybridized in a 450 K methylation microarray. Several CpGs whose DNA methylation levels were statistically different between obese and non-obese were validated by MassArray® in 95 children (validation sample) from the same study.

RESULTS

Microarray analysis identified 16 differentially methylated CpGs between both groups (6 hypermethylated and 10 hypomethylated). DNA methylation levels in miR-1203, miR-412 and miR-216A coding regions significantly correlated with body mass index standard deviation score (BMI-SDS) and explained up to 40% of the variation of BMI-SDS. The network analysis identified 19 well-defined obesity-relevant biological pathways from the KEGG database. MassArray® validation identified three regions located in or near miR-1203, miR-412 and miR-216A coding regions differentially methylated between obese and non-obese children.

CONCLUSIONS

The current work identified three CpG sites located in coding regions of three miRNAs (miR-1203, miR-412 and miR-216A) that were differentially methylated between obese and non-obese children, suggesting a role of miRNA epigenetic regulation in childhood obesity.

Extracellular microRNAs and endothelial hyperglycaemic memory: a therapeutic opportunity?

Type 2 diabetes mellitus (T2DM) is a major cause of cardiovascular (CV) disease. Several large clinical trials have shown that the risk for patients with diabetes of developing CV complications is only partially reduced by early, intensive glycaemic control and lifestyle interventions, and that such complications result from changes in complex, not fully explored networks that contribute to the maintenance of endothelial function. The accumulation of senescent cells and the low-grade, systemic, inflammatory status that accompanies aging (inflammaging) are involved in the development of endothelial dysfunction. Such phenomena are modulated by epigenetic mechanisms, including microRNAs (miRNAs). MiRNAs can modulate virtually all gene transcripts. They can be secreted by living cells and taken up in active form by recipient cells, providing a new communication tool between tissues and organs. MiRNA deregulation has been associated with the development and progression of a number of age-related diseases, including the enduring gene expression changes seen in patients with diabetes. We review recent evidence on miRNA changes in T2DM, focusing on the ability of diabetes-associated miRNAs to modulate endothelial function, inflammaging and cellular senescence. We also discuss the hypothesis that miRNA-containing extracellular vesicles (i.e. exosomes and microvesicles) could be harnessed to restore a 'physiological' signature capable of preventing or delaying the harmful systemic effects of T2DM.

Transcriptome association analysis identifies miR-375 as a major determinant of variable acetaminophen glucuronidation by human liver

Acetaminophen is the leading cause of acute liver failure (ALF) in many countries including the United States. Hepatic glucuronidation by UDP-glucuronosyltransferase (UGT) 1A subfamily enzymes is the major route of acetaminophen elimination. Reduced glucuronidation may predispose some individuals to acetaminophen-induced ALF, but mechanisms underlying reduced glucuronidation are poorly understood. We hypothesized that specific microRNAs (miRNAs) may reduce UGT1A activity by direct effects on the UGT1A 3'-UTR shared by all UGT1A enzyme transcripts, or by indirect effects on transcription factors regulating UGT1A expression. We performed an unbiased miRNA whole transcriptome association analysis using a bank of human livers with known acetaminophen glucuronidation activities. Of 754 miRNAs evaluated, 9 miRNAs were identified that were significantly overexpressed (p<0.05; >2-fold) in livers with low acetaminophen glucuronidation activities compared with those with high activities. miR-375 showed the highest difference (>10-fold), and was chosen for further mechanistic validation. We demonstrated using in silico analysis and luciferase reporter assays that miR-375 has a unique functional binding site in the 3'-UTR of the aryl hydrocarbon receptor (AhR) gene. Furthermore overexpression of miR-375 in LS180 cells demonstrated significant repression of endogenous AhR protein (by 40%) and mRNA (by 10%), as well as enzyme activity and/or mRNA of AhR regulated enzymes including UGT1A1, UGT1A6, and CYP1A2, without affecting UGT2B7, which is not regulated by AhR. Thus miR-375 is identified as a novel repressor of UGT1A-mediated hepatic acetaminophen glucuronidation through reduced AhR expression, which could predispose some individuals to increased risk for acetaminophen-induced ALF.

Histone deacetylase inhibition regulates miR-449a levels in skeletal muscle cells

microRNAs (miRNAs) are small non-coding RNAs that regulate cellular processes by fine-tuning the levels of their target mRNAs. However, the regulatory elements determining cellular miRNA levels are not well studied. Previously, we had described an altered miRNA signature in the skeletal muscle of db/db mice. Here, we sought to explore the role of epigenetic mechanisms in altering these miRNAs. We show that histone deacetylase (HDAC) protein levels and activity are upregulated in the skeletal muscle of diabetic mice. In C2C12 cells, HDAC inhibition using suberoylanilide hydroxamic acid (SAHA) altered the levels of 24 miRNAs: 15 were downregulated and 9 were upregulated. miR-449a, an intronic miRNA localized within the Cdc20b gene, while being downregulated in the skeletal muscle of diabetic mice, was the most highly upregulated during HDAC inhibition. The host gene, Cdc20b, was also significantly upregulated during HDAC inhibition. Bioinformatics analyses identified a common promoter for both Cdc20b and miR-449a that harbors significant histone acetylation marks, suggesting the possibility of regulation by histone acetylation-deacetylation. These observations suggest an inverse correlation between miR-449a levels and HDAC activity, in both SAHA-treated skeletal muscle cells and db/db mice skeletal muscle. Further, in SAHA-treated C2C12 cells, we observed augmented occupancy of acetylated histones on the Cdc20b/miR-449a promoter, which possibly promotes their upregulation. In vivo injection of SAHA to db/db mice significantly restored skeletal muscle miR-449a levels. Our results provide insights into the potential regulatory role of epigenetic histone acetylation of the miR-449a promoter that may regulate its expression in the diabetic skeletal muscle.

Beyond the Protein-Coding Sequence: Noncoding RNAs in the Pathogenesis of Type 2 Diabetes

Diabetes mellitus results from a deficiency or failure to maintain normal glucose homeostasis. The most common form of the disease is type 2 diabetes (T2D), a progressive metabolic disorder characterized by elevated glucose levels that develops in response to either multi-organ insulin resistance or insufficient insulin secretion from pancreatic β-cells. Although the etiology of T2D is complex, many factors are known to contribute to defects of glucose homeostasis, including obesity, unhealthy lifestyle choices, genetic susceptibility, and environmental exposures. In addition to these factors, noncoding RNAs (ncRNAs) have been recently implicated in the pathogenesis of T2D, playing roles in several of the pathophysiological mechanisms underlying the disease, particularly in insulin-sensitive tissues such as pancreatic β-cells, liver, muscle, and adipose tissue. A growing number of publications demonstrate that polymorphisms in ncRNAs or their target genes may represent a new class of genetic variation contributing to the development of T2D. This review summarizes both the current state of knowledge of ncRNAs, specifically microRNAs (miRNAs), involved in the regulation of β-cell function, insulin sensitivity, and insulin action in peripheral organs. The role of genetic variation in miRNAs or miRNA binding sites in the pathogenesis of T2D is also discussed. While far less is known about the impact of long ncRNAs (lncRNAs) in the development of T2D, emerging evidence suggests that these molecules may be able to contribute to β-cell dysfunction in response to hyperglycemia. This article provides an overview of the studies conducted to date in this field, focusing on lncRNAs that are dysregulated in human pancreatic islets.

Genetic and epigenetic alterations of microRNAs and implications for human cancers and other diseases

MicroRNAs (miRNAs) are a well-studied group of noncoding RNAs that control gene expression by interacting mainly with messenger RNA. It is known that miRNAs and their biogenesis regulatory machineries have crucial roles in multiple cell processes; thus, alterations in these genes often lead to disease, such as cancer. Disruption of these genes can occur through epigenetic and genetic alterations, resulting in aberrant expression of miRNAs and subsequently of their target genes. This review focuses on the disruption of miRNAs and their key regulatory machineries by genetic alterations, with emphasis on mutations and epigenetic changes in cancer and other diseases.

miRNAs: early prognostic biomarkers for Type 2 diabetes mellitus?

Type 2 diabetes mellitus (T2DM) has reached epidemic proportions and is associated with peripheral insulin resistance. The currently used therapies aim to delay progression of T2DM. Their efficacy could drastically be improved if implemented at earlier stages. Classical diagnostic markers (blood glucose and HbA1C) are generally detected once metabolic imbalance has already set in. Therefore, development of biomarkers for early diagnosis would help identify individuals at risk for developing T2DM. Along with genetic predisposition, epigenetics also plays a major role in T2DM development. In this review, we discuss the potential role of early diagnostic markers such as circulating miRNAs, studies done so far and challenges to be considered while taking into account the novel role of miRNAs as prognostic biomarkers.

Circulating microRNAs and diabetes: potential applications in medical practice

The explosive increase in the worldwide prevalence of diabetes over recent years has transformed the disease into a major public health concern. While diabetes can be screened for and diagnosed by reliable biological tests based on blood glucose levels, by and large there are no means of detecting at-risk patients or of following diabetic complications. The recent discovery that microRNAs are not only chief intracellular players in many biological processes, including insulin secretion and action, but are also circulating, has put them in the limelight as possible biological markers. Here we discuss the potential role of circulating microRNAs as biomarkers in the context of diabetes and its associated complications.

Identification of microRNA biomarkers in type 2 diabetes: a meta-analysis of controlled profiling studies

AIMS/HYPOTHESIS

The aim was to identify potential microRNA (miRNA) biomarkers of type 2 diabetes.

METHODS

Controlled studies were retrieved from PubMed to compare miRNA expression profiles of type 2 diabetes and nondiabetic control samples. Meta-analysis under a random effects model was conducted. Subgroup analyses examined tissue specificity and species specificity. Sensitivity analyses were also performed to explain the heterogeneity among studies. Results were represented as log odds ratios (logOR), 95% confidence intervals (CI) and p values after Bonferroni correction.

RESULTS

Among 343 differentially expressed miRNAs in 38 miRNA expression profiling studies published between 1993 and March 2014, only 151 miRNAs were tested by multiple studies, out of which 102 miRNAs were reported to be upregulated or downregulated. Meta-analysis identified 51 significantly dysregulated miRNAs. The top upregulated miRNA was miR-142-3p (logOR 6.4721; 95% CI 4.9537, 7.9904; adjusted p = 4.60 × 10(-16)). The top downregulated miRNA was miR-126a (logOR 7.5237; 95% CI 4.7159, 10.3316; adjusted p = 3.01 × 10(-07)). The dysregulation of two miRNAs (miR-199a-3p and miR-223) was highly pancreas-specific and liver-specific. miR-30e was downregulated in patients with type 2 diabetes, while miR-92a was downregulated in animal models of diabetes. In sensitivity analysis, 40 out of 47 miRNAs (85%) were robustly and consistently dysregulated.

CONCLUSIONS/INTERPRETATION

This meta-analysis confirms that 40 miRNAs are significantly dysregulated in type 2 diabetes. miR-29a, miR-34a, miR-375, miR-103, miR-107, miR-132, miR-142-3p and miR-144 are potential circulating biomarkers of type 2 diabetes. In addition, miR-199a-3p and miR-223 are potential tissue biomarkers of type 2 diabetes.

Identification of circulating miR-101, miR-375 and miR-802 as biomarkers for type 2 diabetes

PURPOSE

The unique circulating microRNAs (miRNAs) observed in patients with type 2 diabetes (T2D) are candidates as new biomarkers and therapeutic targets. In order to identify circulating miRNAs relevant to the disease process in case of type 2 diabetes, we performed the Illumina sequencing of miRNAs derived from the serum, liver and epididymal white adipose tissue (WAT) of diet-induced obese male C57BL/6J mice.

BASIC PROCEDURES

We selected four miRNAs, miR-101, miR-335, miR-375, and miR-802, which are increased in the sera and tissues of obese mice, and measured the serum levels of miRNAs in T2D and subjects with normal glucose tolerance (NGT).

MAIN FINDINGS

The serum concentrations of miRNAs, log(10)miR-101, log(10)miR-375, and log(10)miR-802, were significantly increased in the T2D patients compared with NGT subjects (1.41±2.01 v.s. -0.57±1.05 (P=1.36×10(-5)), 0.20±0.58 v.s. 0.038±1.00 (P=3.06×10(-6)), and 2.45±1.27 v.s. 0.97±0.98 (P=0.014), respectively). The log(10)miR-335 values did not demonstrate any significant differences between the T2D and NGT groups (-1.08±1.35 v.s. -0.38±1.21 (P=0.25)). According to the stepwise regression analysis, the HbA1c was an independent predictor of miR-101. Regarding the serum miR-802 levels, eGFR, HbA1c and HDL-C values were identified as significant determinants.

PRINCIPAL CONCLUSIONS

The present findings demonstrated that the circulating miR-101, miR-375 and miR-802 levels are significantly increased in T2D patients versus NGT subjects and they may become the new biomarkers for type 2 diabetes.

Circulating microRNAs in Diabetes Progression: Discovery, Validation, and Research Translation

Diabetes, in all of its forms, is a disease state that demonstrates wide ranging pathological effects throughout the body. Until now, the only method of diagnosing and monitoring the progression of diabetes was through the measurement of blood glucose. Unfortunately, beta cell dysfunction initiates well before the clinical onset of diabetes, and so the development of an effective biomarker signature is of paramount importance to predict and monitor the progression of this disease. MicroRNAs (miRNAs/miRs) are small (18-22 nucleotide) noncoding (nc)RNAs that post-transcriptionally regulate endogenous gene expression by targeted inhibition or degradation of messenger (m)RNA. Recently, miRNAs have shown great promise as biomarkers as some exhibit differential expression in multiple disease states, including type 1 and type 2 diabetes (T1D/T2D). Furthermore, miRNAs are quite stable in circulation, resistant to freeze-thaw and pH-mediated degradation, and are relatively easy to detect using quantitative (q)PCR. Here, we discuss microRNAs that may form a diabetes biomarker signature. To identify these transcripts we outline miRNAs that play a central role in pancreas development and diabetes, as well as previously identified miRNAs with differential expression in individuals with T1D and T2D. Validation and refinement of a miRNA biomarker signature for diabetes would allow identification and intervention of individuals at risk of this disease, as well as stratification and monitoring of patients with established diabetes.

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.