Identification of particular groups of microRNAs that positively or negatively impact on beta cell function in obese models of type 2 diabetes

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

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

Potential value of circulating microRNA-126 and microRNA-210 as biomarkers for type 2 diabetes with coronary artery disease

BACKGROUND

Macrovascular complications are the main cause of morbidity and mortality among the diabetic patients. MicroRNAs (miRNAs), a family of small non-coding RNAs, play vital roles in the regulation of blood glucose level and the concurrent cardiovascular complications of type 2 diabetes. We hypothesized that plasma miR-126 and miR-210 are linked to coronary artery disease (CAD) in these diabetes patients.

METHODS

Fasting blood samples were collected from 20 healthy volunteers and 100 patients with diabetes (54 patients without CAD and 46 patients with CAD). Plasma miR-126 and miR-210 expressions were assessed by quantitative real time PCR. Specificity and sensitivity of miR-126 and miR-210 to discriminate CAD with diabetes was determined by receiver operating characteristic curve analysis. Correlations between miR-126 and miR-210 and studied characteristics in diabetes patients with and without CAD were compared.

RESULTS

Plasma relative expressions of miR-126 and miR-210 were 0.38 ± 0.03 and 5.3 ± 0.56 in diabetes alone vs. 0.08 ± 0.03 and 21.44 ± 0.97 in diabetes with CAD, respectively (both p < 0.0001). Levels of miR-126 and miR-210 significantly correlated with certain glycemic and lipid indices. The miRNAs significantly discriminated between diabetes with and without CAD at cut-off values of 0.055 (sensitivity 91.3%, specificity 100%) for miR-126 and of 17.59 (sensitivity 93.5%, specificity 100%) for miR-210.

CONCLUSION

Plasma miR-126 and miR-210 levels may be biomarkers for diabetes with or without CAD.

Mechanisms of β-cell dedifferentiation in diabetes: recent findings and future research directions

Like all the cells of an organism, pancreatic β-cells originate from embryonic stem cells through a complex cellular process termed differentiation. Differentiation involves the coordinated and tightly controlled activation/repression of specific effectors and gene clusters in a time-dependent fashion thereby giving rise to particular morphological and functional cellular features. Interestingly, cellular differentiation is not a unidirectional process. Indeed, growing evidence suggests that under certain conditions, mature β-cells can lose, to various degrees, their differentiated phenotype and cellular identity and regress to a less differentiated or a precursor-like state. This concept is termed dedifferentiation and has been proposed, besides cell death, as a contributing factor to the loss of functional β-cell mass in diabetes. β-cell dedifferentiation involves: (1) the downregulation of β-cell-enriched genes, including key transcription factors, insulin, glucose metabolism genes, protein processing and secretory pathway genes; (2) the concomitant upregulation of genes suppressed or expressed at very low levels in normal β-cells, the β-cell forbidden genes; and (3) the likely upregulation of progenitor cell genes. These alterations lead to phenotypic reconfiguration of β-cells and ultimately defective insulin secretion. While the major role of glucotoxicity in β-cell dedifferentiation is well established, the precise mechanisms involved are still under investigation. This review highlights the identified molecular mechanisms implicated in β-cell dedifferentiation including oxidative stress, endoplasmic reticulum (ER) stress, inflammation and hypoxia. It discusses the role of Foxo1, Myc and inhibitor of differentiation proteins and underscores the emerging role of non-coding RNAs. Finally, it proposes a novel hypothesis of β-cell dedifferentiation as a potential adaptive mechanism to escape cell death under stress conditions.

Dysfunctional Wound Healing in Diabetic Foot Ulcers: New Crossroads

PURPOSE OF REVIEW

Diabetic foot ulcerations (DFU) affect 25% of patients with diabetes mellitus during their lifetime and constitute a major health problem as they are often recalcitrant to healing due to a constellation of both intrinsic and extrinsic factors. The purpose of this review is to (1) detail the current mechanistic understanding of DFU formation and (2) highlight future therapeutic targets.

RECENT FINDINGS

From a molecular perspective, DFUs exhibit a chronic inflammatory predisposition. In addition, increased local hypoxic conditions and impaired cellular responses to hypoxia are pathogenic factors that contribute to delayed wound healing. Finally, recent evidence suggests a role for epigenetic alterations, including microRNAs, in delayed DFU healing due to the complex interplay between genes and the environment. In this regard, notable progress has been made in the molecular and genetic understanding of DFU formation. However, further studies are needed to translate preclinical investigations into clinical therapies.

MiR-184 expression is regulated by AMPK in pancreatic islets

AMPK is a critical energy sensor and target for widely used antidiabetic drugs. In β cells, elevated glucose concentrations lower AMPK activity, and the ablation of both catalytic subunits [β-cell–specific AMPK double-knockout (βAMPKdKO) mice] impairs insulin secretion in vivo and β-cell identity. MicroRNAs (miRNAs) are small RNAs that silence gene expression that are essential for pancreatic β-cell function and identity and altered in diabetes. Here, we have explored the miRNAs acting downstream of AMPK in mouse and human β cells. We identified 14 down-regulated and 9 up-regulated miRNAs in βAMPKdKO vs. control islets. Gene ontology analysis of targeted transcripts revealed enrichment in pathways important for β-cell function and identity. The most down-regulated miRNA was miR-184 (miR-184-3p), an important regulator of β-cell function and compensatory expansion that is controlled by glucose and reduced in diabetes. We demonstrate that AMPK is a potent regulator and an important mediator of the negative effects of glucose on miR-184 expression. Additionally, we reveal sexual dimorphism in miR-184 expression in mouse and human islets. Collectively, these data demonstrate that glucose-mediated changes in AMPK activity are central for the regulation of miR-184 and other miRNAs in islets and provide a link between energy status and gene expression in β cells.—Martinez-Sanchez, A., Nguyen-Tu, M.-S., Cebola, I., Yavari, A., Marchetti, P., Piemonti, L., de Koning, E., Shapiro, A. M. J., Johnson, P., Sakamoto, K., Smith, D. M., Leclerc, I., Ashrafian, H., Ferrer, J., Rutter, G. A. MiR-184 expression is regulated by AMPK in pancreatic islets.

Change in circulating microRNA profile of obese children indicates future risk of adult diabetes

PURPOSE

Childhood obesity increases susceptibility to type 2 diabetes (T2D) in adults. Circulating microRNAs (miRNAs) in serum have been proposed as potential diagnostic biomarkers, and they may contribute to the progression toward T2D. Here, we investigated the possibility of predicting the future risk of adult T2D in obese children by using circulating miRNAs.

BASIC PROCEDURES

We performed miRNA high-throughput sequencing to screen relevant circulating miRNAs in obese children. The expression patterns of targeted miRNAs were further explored in obese children and adults with T2D. To investigate the underlying contributions of these miRNAs to the development of T2D, we detected the impacts of the candidate miRNAs on preadipocyte proliferation, insulin secretion by pancreatic β-cell, and glucose uptake by skeletal muscle cells.

MAIN FINDINGS

Three miRNAs (miR-486, miR-146b and miR-15b), whose expression in the circulation was most dramatically augmented in obese children and adult T2D patients, were selected for further investigation. Of these 3 miRNAs, miR-486 was implicated in accelerating preadipocyte proliferation and myotube glucose intolerance, miR-146b and miR-15b were engaged in the suppression of high concentration glucose-induced pancreatic insulin secretion, and they all contributed to the pathological processes of obesity and T2D.

PRINCIPAL CONCLUSIONS

Our results provide a better understanding of the role of circulating miRNAs, particularly miR-486, miR-146b and miR-15b, in predicting the future risk of T2D in obese children.

MicroRNAs and the metabolic hallmarks of aging

Aging, the natural process of growing older, is characterized by a progressive deterioration of physiological homeostasis at the cellular, tissue, and organismal level. Metabolically, the aging process is characterized by extensive changes in body composition, multi-tissue/multi-organ insulin resistance, and physiological declines in multiple signaling pathways including growth hormone, insulin/insulin-like growth factor 1, and sex steroids regulation. With this review, we intend to consolidate published information about microRNAs that regulate critical metabolic processes relevant to aging. In certain occasions we uncover relationships likely relevant to aging, which has not been directly described before, such as the miR-451/AMPK axis. We have also included a provocative section highlighting the potential role in aging of a new designation of miRNAs, namely fecal miRNAs, recently discovered to regulate intestinal microbiota in mammals.

miR-34a and miR-125b are upregulated in peripheral blood mononuclear cells from patients with type 2 diabetes mellitus

Type 2 diabetes mellitus (T2DM) is a leading cause of blindness, non-traumatic amputation and end-stage renal disease, as well as a major cardiovascular risk factor. To determine whether miR-125b and miR-34a serve an important role in the development of T2DM, the current study investigated the expression profile of two microRNAs (miR-34a and miR-125b) and their relative genes in peripheral blood mononuclear cells from 73 patients with T2DM and 52 healthy donors by reverse transcription-quantitative polymerase chain reaction In addition, the association between miR-34a, miR-125b and their relevant genes expression profile were analyzed with respect to the pathogenesis of T2DM. The present study demonstrated that the expression levels of miR-125b and miR-34a were elevated in peripheral blood mononuclear cell samples from patients with T2DM. Furthermore, miR-34a and miR-125b were positively correlated with low-density lipoprotein/high-density lipoprotein (HDL) and Foxp3 and negatively related to triglyceride/HDL. However, no correlation among miR-34a, miR-125b and the value of homeostasis model assessment of insulin resistance, homeostasis model assessment of β-cell function and the genes of B lymphocyte-induced maturation protein-1, interferon regulatory factor-4, P53 and retinoid-related orphan receptor γt were observed. These results indicate that the alteration of miR-34a and miR-125b exists in patients with T2DM, which may be involved in the pathogenesis of T2DM, and could be a potential novel biomarker of T2DM.

miRNA Signatures of Insulin Resistance in Obesity

OBJECTIVE

Extracellular microRNAs (miRNAs) represent functional biomarkers for obesity and related disorders; this study investigated plasma miRNAs in insulin resistance phenotypes in obesity.

METHODS

One hundred seventy-five miRNAs were analyzed in females with obesity (insulin sensitivity, n = 11; insulin resistance, n = 19; type 2 diabetes, n = 15) and without obesity (n = 12). Correlations between miRNA level and clinical parameters and levels of 15 miRNAs in a murine obesity model were investigated.

RESULTS

One hundred six miRNAs were significantly (adjusted P ≤ 0.05) different between controls and at least one obesity phenotype, including miRNAs with the following attributes: previously reported roles in obesity and altered circulating levels (e.g., miR-122, miR-192); known roles in obesity but no reported changes in circulating levels (e.g., miR-378a); and no current reported role in, or association with, obesity (e.g., miR-28-5p, miR-374b, miR-32). The miRNAs in the latter group were found to be associated with extracellular vesicles. Forty-eight miRNAs showed significant correlations with clinical parameters; stepwise regression retained let-7b, miR-144-5p, miR-34a, and miR-532-5p in a model predictive of insulin resistance (R²  = 0.57, P = 7.5 × 10^-8 ). Both miR-378a and miR-122 were perturbed in metabolically relevant tissues in a murine model of obesity.

CONCLUSIONS

This study expands on the role of extracellular miRNAs in insulin-resistant phenotypes of obesity and identifies candidate miRNAs not previously associated with obesity.

Exosomes as new players in metabolic organ cross-talk

Blood glucose homeostasis requires a constant communication between insulin-secreting and insulin-sensitive cells. A wide variety of circulating factors, including hormones, cytokines and chemokines work together to orchestrate the systemic response of metabolic organs to changes in the nutritional state. Failure in the coordination between these organs can lead to a rise in blood glucose levels and to the appearance of metabolic disorders such as diabetes mellitus. Exosomes are small extracellular vesicles (EVs) that are produced via the endosomal pathway and are released from the cells upon fusion of multivesicular bodies with the plasma membrane. There is emerging evidence indicating that these EVs play a central role in cell-to-cell communication. The interest in exosomes exploded when they were found to transport bioactive proteins, messenger RNA (mRNAs) and microRNA (miRNAs) that can be transferred in active form to adjacent cells or to distant organs. In this review, we will first outline the mechanisms governing the biogenesis, the cargo upload and the release of exosomes by donor cells as well as the uptake by recipient cells. We will then summarize the studies that support the novel concept that miRNAs and other exosomal cargo components are new important vehicles for metabolic organ cross-talk.

miR-199a-3p affects adipocytes differentiation and fatty acid composition through targeting SCD

Body fat mass is closely associated to diseases related to obesity. MicroRNAs (miRNAs, miR) are important regulatory molecules that function as post-transcriptional gene regulators of adipocyte development. In the current study, we revealed that reduced expression of miR-199a-3p in adipose tissue resulting from high fat diet (HFD)-induced obesity in mice. Overexpression of miR-199a-3p promoted adipocyte proliferation by regulating the expression of regulating factors of the cell cycle. Furthermore, miR-199a-3p blunted lipid accumulation in 3T3-L1 adipocytes. This was accompanied by a marked decrease in the expression of adipocyte-specific genes involved in lipogenic transcription, fatty acid synthesis, and fatty acid transportation. Furthermore, the fatty acid oxidation process was enhanced. Luciferase activity assays confirmed that miR-199a-3p regulates adipocyte differentiation by directly targeting the 3'-untranslated region (3'-UTR) of stearoyl-CoA desaturase (SCD). Moreover, miR-199a-3p regulates fatty acid composition by decreasing the ratio of unsaturated fatty acids (UFAs) in adipocytes transfected with miR-199a-3p mimics. These results suggest that miR-199a-3p may promote adipocyte proliferation, while also repressing adipocyte differentiation by down-regulating SCD and changing fatty acid composition during adipogenesis.

MiR-338 controls BPA-triggered pancreatic islet insulin secretory dysfunction from compensation to decompensation by targeting Pdx-1

Bisphenol A (BPA) can disrupt glucose homeostasis and impair pancreatic islet function; however, the mechanisms behind these effects are poorly understood. Male mice (4 wk old) were treated with BPA (50 or 500 μg/kg/d) for 8 wk. Whole-body glucose homeostasis, pancreatic islet morphology and function, and miR-338-mediated molecular signal transduction analyses were examined. We showed that BPA treatment led to a disruption of glucose tolerance and a compensatory increase of pancreatic islets insulin secretion and pancreatic and duodenal homeobox 1 (Pdx1) expression in mice. Inhibition of Pdx1 reduced glucose-stimulated insulin secretion and ATP production in the islets of BPA-exposed mice. Based on primary pancreatic islets, we also confirmed that miR-338 regulated Pdx1 and thus contributed to BPA-induced insulin secretory dysfunction from compensation to decompensation. Short-term BPA exposure downregulated miR-338 through activation of G-protein-coupled estrogen receptor 1 (Gpr30), whereas long-term BPA exposure upregulated miR-338 through suppression of glucagon-like peptide 1 receptor (Glp1r). Taken together, our results reveal a molecular mechanism, whereby BPA regulates Gpr30/Glp1r to mediate the expression of miR-338, which acts to control Pdx1-dependent insulin secretion. The Gpr30/Glp1r-miR-338-Pdx1 axis should be represented as a novel mechanism by which BPA induces insulin secretory dysfunction in pancreatic islets.-Wei, J., Ding, D., Wang, T., Liu, Q., Lin, Y. MiR-338 controls BPA-triggered pancreatic islet insulin secretory dysfunction from compensation to decompensation by targeting Pdx-1.

Characterization and predicted role of microRNA expression profiles associated with early childhood obesity

MicroRNAs (miRNAs) are implicated in the pathogenesis of obesity. The aim of the present study was to characterize the miRNA profile associated with early childhood obesity in peripheral blood mononuclear cells (PBMCs). A total of 12 children (6 obese and 6 lean controls) aged 36 months old to 48 months old were recruited. The miRNA expression profile from PBMCs was detected using the multiplexed NanoString nCounter system. Bioinformatics was employed to detect target genes and miRNA-regulated biological function. A total of 9 differentially expressed miRNAs were identified in obese children compared with lean children (P<0.05). Among the 9 miRNAs, miR-199a-3p/miR-199b-3p and miR-4454 presented at least a 1.5-fold change in expression. A total of 643 potential target genes were regulated by the three miRNAs, and 291 of the potential genes were involved in a protein interaction network. Gene ontology annotation indicated that 291 potential genes were enriched in 14 biological process annotations and 2 molecular function annotations. miRNA dysregulation may be involved in early childhood obesity.

Altered levels of circulating cytokines and microRNAs in lean and obese individuals with prediabetes and type 2 diabetes

Today obesity and type 2 diabetes (T2D) have both reached epidemic proportions. However, our current understanding of the primary mechanisms leading to these diseases is still limited due to the complex multifactorial nature of the underlying phenomena. We hypothesize that the levels of specific cytokines and miRNAs vary across the diabetes spectrum and unique signatures associated with them may serve as early biomarkers of the disease and provide insights into respective pathogenetic mechanisms. In this study, we measured the circulating levels of cytokines and microRNAs (miRNAs) in lean and obese humans with prediabetes (n = 21), T2D (n = 17), and healthy controls (n = 20) (ORIGINS trial, NCT02226640). Data were analyzed by fitting linear models adjusted for confounding variables (BMI, age, and gender in the diabetes context and age, gender, and diabetes status in the obesity context) and implementing nonparametric randomization-based tests for statistical inference. Group differences and correlations (r > 0.3) between variables with P < 0.05 were considered significant. False discovery rates (FDR) correcting for multiple testing were calculated using the Benjamini-Hochberg correction. We found a number of circulating cytokines and miRNAs deregulated in subjects with obesity, prediabetes, and T2D. Specifically, cytokines IL-6, IL-8, IL-10, IL-12, and SFRP4, as well as miRNAs miR-21, miR-24.1, miR-27a, miR-28-3p, miR-29b, miR-30d, miR-34a, miR-93, miR-126, miR-146a, miR-148, miR-150, miR-155, and miR-223, significantly changed across the diabetes spectrum, and were associated with measures of pancreatic islet β cell function and glycemic control, among others. Notably, SFRP4 was the only studied cytokine that was significantly associated with obesity, prediabetes, and T2D, which underscores the important role of this molecule during disease development and progression. Our data suggest that changes in circulating miRNAs and cytokines may have clinical utility as biomarkers of prediabetes.

MicroRNAs as stress regulators in pancreatic beta cells and diabetes

Background

MicroRNAs have emerged as important regulatory non-coding RNAs that tune cellular responses to physiological perturbations and disease conditions. An increasing body of literature underlines the important roles of miRNA function in pancreatic β-cells in response to metabolic, genetic and inflammatory stress. Lessons from genetic loss- and gain-of-function studies have implicated several highly expressed and evolutionary conserved miRNAs in stress signal modulation, resolution and buffering, thereby forming stabilizing miRNA networks that preserve β-cell differentiation, function, proliferation and cell survival.

Scope of Review

This review will summarize our current knowledge of how biologically relevant miRNAs regulate stress responses in pancreatic β-cells, discuss the challenges and opportunities associated with using secreted miRNAs as biomarkers and forecast how mechanistic knowledge of miRNA function can be exploited in developing miRNA-based therapeutics.

Major Conclusions

miRNAs play important roles in the function, differentiation, proliferation, and survival of pancreatic β-cells. Many miRNA families that are regulated by metabolic, genetic, and inflammatory stressors have been found to coordinate the adaptive responses of β-cells in vivo in conditions such as obesity and diabetes.

Maternal chromium restriction modulates miRNA profiles related to lipid metabolism disorder in mice offspring

Increasing evidence shows that maternal nutrition status has a vital effect on offspring susceptibility to obesity. MicroRNAs are related to lipid metabolism processes. This study aimed to evaluate whether maternal chromium restriction could affect miRNA expression involved in lipid metabolism in offspring. Weaning C57BL/6J mice born from mothers fed with normal control diet or chromium-restricted diet were fed for 13 weeks. The adipose miRNA expression profile was analyzed by miRNA array analysis. At 16 weeks old, pups from dams fed with chromium-restricted diet exhibit higher body weight, fat weight, and serum TC, TG levels. Six miRNAs were identified as upregulated in the RC group compared with the CC group, whereas eight miRNAs were lower than the threshold level set in the RC group. In the validated target genes of these differentially expressed miRNA, the MAPK signaling pathway serves an important role in the influence of early life chromium-restricted diet on lipid metabolism through miRNA. Long-term programming on various specific miRNA and MAPK signaling pathway may be involved in maternal chromium restriction in the adipose of female offspring. Impact statement For the first time, our study demonstrates important miRNA differences in the effect of maternal chromium restriction in offspring. These miRNAs may serve as "bridges" between the mother and the offspring by affecting the MAPK pathway.

Interplay between miRNAs and human diseases

MicroRNAs (miRNAs) are endogenous, non-coding RNAs, which have evoked a great deal of interest due to their importance in many aspects of homeostasis and diseases. MicroRNAs are stable and are essential components of gene regulatory networks. They play a crucial role in healthy individuals and their dysregulations have also been implicated in a wide range of diseases, including diabetes, cardiovascular disease, kidney disease, and cancer. This review summarized the current understanding of interactions between miRNAs and different diseases and their role in disease diagnosis and therapy.

NutrimiRAging: Micromanaging Nutrient Sensing Pathways through Nutrition to Promote Healthy Aging

Current sociodemographic predictions point to a demographic shift in developed and developing countries that will result in an unprecedented increase of the elderly population. This will be accompanied by an increase in age-related conditions that will strongly impair human health and quality of life. For this reason, aging is a major concern worldwide. Healthy aging depends on a combination of individual genetic factors and external environmental factors. Diet has been proved to be a powerful tool to modulate aging and caloric restriction has emerged as a valuable intervention in this regard. However, many questions about how a controlled caloric restriction intervention affects aging-related processes are still unanswered. Nutrient sensing pathways become deregulated with age and lose effectiveness with age. These pathways are a link between diet and aging. Thus, fully understanding this link is a mandatory step before bringing caloric restriction into practice. MicroRNAs have emerged as important regulators of cellular functions and can be modified by diet. Some microRNAs target genes encoding proteins and enzymes belonging to the nutrient sensing pathways and, therefore, may play key roles in the modulation of the aging process. In this review, we aimed to show the relationship between diet, nutrient sensing pathways and microRNAs in the context of aging.

Downregulation of miR-139-5p contributes to the antiapoptotic effect of liraglutide on the diabetic rat pancreas and INS-1 cells by targeting IRS1

Liraglutide is administered as glucagon-like peptide-1 (GLP-1) receptor agonist for diabetic patients and can protect pancreatic β-cells by inhibiting their apoptosis. MicroRNA-139-5p (miRNA-139-5p) participates in the regulation of cancer cell apoptosis. However, it is not clear whether miR-139-5p contributes to the anti-apoptotic effect of liraglutide in β-cells. The objective of the present study was to investigate the role of miR-139-5p on apoptosis of pancreatic β-cells. MicroRNA levels in pancreatic tissue from diabetic rats and INS-1 cells treated with liraglutide were measured by real-time quantitative RT-PCR. The role of miR-139-5p on apoptosis was studied by transfecting INS-1 cells with miR-139-5p mimics. The mRNA and protein expression of the target gene, insulin receptor substrate-1 (IRS1), were measured by qRT-PCR and Western blot, respectively. Apoptosis in rat pancreatic tissue and INS-1 cells was detected by TUNEL and annexin V/propidium iodide costaining. Apoptosis of pancreatic tissue from diabetic rats and INS-1 cells was decreased by administration of liraglutide. The expression of miR-139-5p increased in the pancreas of diabetic rats and decreased with liraglutide treatment. Incubation with liraglutide (100 nM) for 48 h attenuated the expression of miR-139-5p and increased the mRNA and protein levels of IRS1. Direct regulatory effects of miR-139-5p on IRS1 were found by a dual-luciferase reporter assay. Transfection of INS-1 cells with miR-139-5p mimics led to decreases in the mRNA and protein expression of IRS1. In conclusion, our observations suggest that decreased miR-139-5p expression contributes to the anti-apoptotic effect of liraglutide on the diabetic rat pancreas and INS-1 cells by targeting IRS1.

Elevated miR-130a/miR130b/miR-152 expression reduces intracellular ATP levels in the pancreatic beta cell

MicroRNAs have emerged as important players of gene regulation with significant impact in diverse disease processes. In type-2 diabetes, in which impaired insulin secretion is a major factor in disease progression, dysregulated microRNA expression in the insulin-secreting pancreatic beta cell has been widely-implicated. Here, we show that miR-130a-3p, miR-130b-3p, and miR-152-3p levels are elevated in the pancreatic islets of hyperglycaemic donors, corroborating previous findings about their upregulation in the islets of type-2 diabetes model Goto-Kakizaki rats. We demonstrated negative regulatory effects of the three microRNAs on pyruvate dehydrogenase E1 alpha (PDHA1) and on glucokinase (GCK) proteins, which are both involved in ATP production. Consequently, we found both proteins to be downregulated in the Goto-Kakizaki rat islets, while GCK mRNA expression showed reduced trend in the islets of type-2 diabetes donors. Overexpression of any of the three microRNAs in the insulin-secreting INS-1 832/13 cell line resulted in altered dynamics of intracellular ATP/ADP ratio ultimately perturbing fundamental ATP-requiring beta cell processes such as glucose-stimulated insulin secretion, insulin biosynthesis and processing. The data further strengthen the wide-ranging influence of microRNAs in pancreatic beta cell function, and hence their potential as therapeutic targets in type-2 diabetes.

Alpinia oxyphylla Miq. extract changes miRNA expression profiles in db-/db- mouse kidney

Background

A number of dysregulated miRNAs have been identified and are proposed to have significant roles in the pathogenesis of type 2 diabetes mellitus or renal pathology. Alpinia oxyphylla has shown significant anti-inflammatory properties and play an anti-diabetes role. The objective of this study was to detect the alteration of miRNAs underlying the anti-diabetes effects of A. oxyphylla extract (AOE) in a type II diabetic animal model (C57BIKsj db-/db-).

Results

Treatment with AOE for 8 weeks led to lower concentrations of blood glucose, urine albumin, and urine creatinine. 17 and 13 miRNAs were statistically identified as differentially regulated in the DB/DB and db-/db- AOE mice, respectively, compared to the untreated db-/db- mice. Of these, 7 miRNAs were identified in both comparison groups, and these 7 miRNAs were verified by quantitative real-time PCR. Functional bioinformatics showed that the putative target genes of 7 miRNAs were associated with several diabetes effects and signaling pathways.

Conclusions

These founding suggest that the potential of AOE as a medicinal anti-diabetes treatment through changes in the expressions of specific miRNAs. The results provide a useful resource for future investigation of the role of AOE-regulated miRNAs in diabetes mellitus.

Electronic supplementary material

The online version of this article (doi:10.1186/s40659-017-0111-1) contains supplementary material, which is available to authorized users.

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.

An 'alpha-beta' of pancreatic islet microribonucleotides

MicroRNAs (miRNAs) are cellular, short, non-coding ribonucleotides acting as endogenous posttranscriptional repressors following incorporation in the RNA-induced silencing complex. Despite being chemically and mechanistically very similar, miRNAs exert a multitude of different cellular effects by acting on mRNA species, whose gene-products partake in a wide array of processes. Here, the aim was to review the knowledge of miRNA expression and action in the islet of Langerhans. We have focused on: 1) physiological consequences of islet or beta cell specific inhibition of miRNA processing, 2) mechanisms regulating processing of miRNAs in islet cells, 3) presence and function of miRNAs in alpha versus beta cells - the two main cell types of islets, and 4) miRNA mediators of beta cell decompensation. It is clear that miRNAs regulate pancreatic islet development, maturation, and function in vivo. Moreover, processing of miRNAs appears to be altered by obesity, diabetes, and aging. A number of miRNAs (such as miR-7, miR-21, miR-29, miR-34a, miR-212/miR-132, miR-184, miR-200 and miR-375) are involved in mediating beta cell dysfunction and/or compensation induced by hyperglycemia, oxidative stress, cytotoxic cytokines, and in rodent models of fetal metabolic programming prediabetes and overt diabetes. Studies of human type 2 diabetic islets underline that these miRNA families could have important roles also in human type 2 diabetes. Furthermore, there is a genuine gap of knowledge regarding miRNA expression and function in pancreatic alpha cells. Progress in this area would be enhanced by improved in vitro alpha cell models and better tools for islet cell sorting.

MiRNAs in β-Cell Development, Identity, and Disease

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

Clinical relevance of epigenetics in the onset and management of type 2 diabetes mellitus

Epigenetics is involved in the altered expression of gene networks that underlie insulin resistance and insufficiency. Major genes controlling β-cell differentiation and function, such as PAX4, PDX1, and GLP1 receptor, are epigenetically controlled. Epigenetics can cause insulin resistance through immunomediated pro-inflammatory actions related to several factors, such as NF-kB, osteopontin, and Toll-like receptors. Hereafter, we provide a critical and comprehensive summary on this topic with a particular emphasis on translational and clinical aspects. We discuss the effect of epigenetics on β-cell regeneration for cell replacement therapy, the emerging bioinformatics approaches for analyzing the epigenetic contribution to type 2 diabetes mellitus (T2DM), the epigenetic core of the transgenerational inheritance hypothesis in T2DM, and the epigenetic clinical trials on T2DM. Therefore, prevention or reversion of the epigenetic changes occurring during T2DM development may reduce the individual and societal burden of the disease.

Pathological Effects of Exosomes in Mediating Diabetic Cardiomyopathy

Diabetic subjects are at risk of developing cardiovascular disease, which accounts for 60-80% of diabetes-related mortality. Atherosclerosis is still considered as a leading cause of heart failure in diabetic patients, but it could also be an intrinsic and long-term effect of contractile cardiac cells malfunction, known as diabetic cardiomyopathy (DCM). Pathologically, this cardiac dysfunction is manifested by inflammation, apoptosis, fibrosis, hypertrophy and altered cardiomyocytes metabolism. However, the underlying molecular mechanisms of DCM pathophysiology are not clearly understood. Recent and several studies have suggested that exosomes are contributed to the regulation of cell-to-cell communication. Therefore, their in-depth investigation can interpret the complex pathophysiology of DCM. Structurally, exosomes are membrane-bounded vesicles (10-200 nm in diameter), which are actively released from all types of cells and detected in all biological fluids. They carry a wide array of bioactive molecules, including mRNAs, none-coding RNAs (e.g., microRNAs, lncRNAs, circRNAs, etc), proteins and lipids. Importantly, the abundance and nature of loaded molecules inside exosomes fluctuate with cell types and pathological conditions. This chapter summarizes currently available studies on the exosomes' role in the regulation of diabetic cardiomyopathy. Specifically, the advances on the pathological effects of exosomes in diabetic cardiomyopathy as well as the therapeutic potentials and perspectives are also discussed.

miRNAs: Nanomachines That Micromanage the Pathophysiology of Diabetes Mellitus

Diabetes mellitus (DM) refers to a combination of heterogeneous complex metabolic disorders that are associated with episodes of hyperglycemia and glucose intolerance occurring as a result of defects in insulin secretion, action, or both. The prevalence of DM is increasing at an alarming rate, and there exists a need to develop better therapeutics and prognostic markers for earlier detection and diagnosis. In this review, after giving a brief introduction of diabetes mellitus and microRNA (miRNA) biogenesis pathway, we first describe various in vitro and animal model systems that have been developed to study diabetes. Further, we elaborate on the significant roles played by miRNAs as regulators of gene expression in the context of development of diabetes and its secondary complications. The different approaches to quantify miRNAs and their potential to be used as therapeutic targets for alleviation of diabetes have also been discussed.

Role of miRNAs in the pathogenesis and susceptibility of diabetes mellitus

MicroRNAs (miRNAs) are noncoding RNAs of ~22 nucleotides that regulate gene expression post-transcriptionally by binding to the 3' untranslated region of messenger RNA (mRNAs), resulting in inhibition of translation or mRNA degradation. miRNAs have a key role in fine-tuning cellular functions such as proliferation, differentiation and apoptosis, and they are involved in carcinogenesis, glucose homeostasis, inflammation and other biological processes. In this review, we focus on the role of miRNAs in the pathophysiology of the metabolic disease and diabetes mellitus, the hallmark of which is hyperglycemia caused by defective insulin secretion and/or action. A growing number of studies have revealed the association between miRNAs and the processes of insulin production and secretion in pancreatic β cells. In addition, aberrant expression of miRNAs in skeletal muscle, adipose tissue and liver has also been reported. Intriguingly, the tumor suppressor p53 has been implicated in the pathogenesis of diabetes in association with a number of miRNAs, suggesting that a p53/miRNA pathway might be a therapeutic target. Moreover, data from genome-wide association studies have revealed that several miRNA target sequences overlap type 2 diabetes susceptibility loci. Finally, the recent discovery of circulating miRNAs associated with diabetes onset/progression suggests the potential use of miRNAs as biomarkers.

Comparison of Transcriptome Between Type 2 Diabetes Mellitus and Impaired Fasting Glucose

Background

The aim of this study was to compare the transcriptome between impaired fasting glucose (IFG) and type 2 diabetes mellitus (T2DM), and further research their molecular mechanisms.

Material/Methods

The original microarray GSE21321, including miRNA and mRNA expression profiles, was downloaded from the GEO database. Data preprocessing was processed by limma package, and differentially expressed genes (DGs) and miRNA (DMs) were screened. Then, the regulatory relationships among miRNA, TF, and genes were screened and the regulatory network was constructed. Finally, DAVID was used for KEGG enrichment analysis.

Results

There were 11 upregulated IFG-related DMs and five upregulated T2DM-related DMs. Three of the DMs overlapped. In addition, there were eight downregulated IFG-related DMs and two downregulated T2DM-related DMs. Only one downregulated DM overlapped. Similarly, there were 264 upregulated IFG-related DGs and 331 upregulated T2DM-related DGs; and 196 overlapping genes were obtained. In addition, there were 400 downregulated IFG-related DMs and 568 downregulated T2DM-related DMs. A total of 326 downregulated DMs were overlapped. The overlapped DGs were enriched in various pathways, including hematopoietic cell lineage, Fc gamma R-mediated phagocytosis, and MAPK signaling pathway. TAF1 (upregulated gene) and MAFK (downregulated gene) were hub nodes both in IFG- and T2DM-related miRNA-TF-gene regulatory network. In addition, miRNAs, including hsa-miR-29a, hsa-miR-192, and hsa-miR-144, were upregulated hub nodes in the two regulatory networks.

Conclusions

Genes including TAF1 and MAFK, and miRNAs including hsa-miR-29a, hsa-miR-192, and hsa-miR-144 might be potential target genes and important miRNAs for IFG and T2DM.

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

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

A Presenilin/Notch1 pathway regulated by miR-375, miR-30a, and miR-34a mediates glucotoxicity induced-pancreatic beta cell apoptosis

The presenilin-mediated Notch1 cleavage pathway plays a critical role in controlling pancreatic beta cell fate and survival. The aim of the present study was to investigate the role of Notch1 activation in glucotoxicity-induced beta cell impairment and the contributions of miR-375, miR-30a, and miR-34a to this pathway. We found that the protein levels of presenilins (PSEN1 and PSEN2), and NOTCH1 were decreased in INS-1 cells after treatment with increased concentrations of glucose, whereas no significant alteration of mRNA level of Notch1 was observed. Targeting of miR-375, miR-30a, and miR-34a to the 3′utr of Psen1, Psen2, and Notch1, respectively, reduced the amounts of relevant proteins, thereby reducing NICD1 amounts and causing beta cell apoptosis. Overexpression of NICD1 blocked the effects of glucotoxicity as well as miRNA overabundance. Downregulating the expression of miR-375, miR-30a, and miR-34a restored PSEN1, PSEN2, and NICD1 production and prevented glucotoxicity-induced impairment of the beta cells. These patterns of miRNA regulation of the Notch1 cleavage pathway were reproduced in GK rats as well as in aged rats. Our findings demonstrated that miRNA-mediated suppression of NICD1 links the presenilin/Notch1 pathway to glucotoxicity in mature pancreatic beta cells.

Recent advances in exploring the genetic susceptibility to diabetic neuropathy

Diabetic polyneuropathy and cardiovascular autonomic neuropathy are common and disabling complications of diabetes. Although glycaemic control and cardiovascular risk factors are major contributory elements in its development, diabetic neuropathy recognizes a multifactorial influence and a multiplicity of pathogenetic mechanisms. Thus genetic and environmental factors may contribute to its susceptibility, each with a modest contribution, by targeting various metabolic and microvascular pathways whose alterations intervene in diabetic neuropathy pathogenesis. This review is aimed at describing major data from the available literature regarding genetic susceptibility to diabetic neuropathies. It provides an overview of the genes reported as associated with the development or progression of these complications, i.e. ACE, MTHFR, GST, GLO1, APOE, TCF7L2, VEGF, IL-4, GPX1, eNOS, ADRA2B, GFRA2, MIR146A, MIR128A. The identification of genetic susceptibility can help in both expanding the comprehension of the pathogenetic mechanisms of diabetic nerve damage and identifying biomarkers of risk prediction and response to therapeutic intervention.

miR-451 suppresses the NF-kappaB-mediated proinflammatory molecules expression through inhibiting LMP7 in diabetic nephropathy

Activation of nuclear factor -kappa B (NF-κB) is associated with inflammation in the progression of diabetic nephropathy (DN). MiR-451 is closely linked to renal damage in DN. Large multifunctional protease 7 (LMP7), an immunoproteasome subunit, can activate NF-κB. However, it remained unclear whether miR-451 affected NF-κB-induced inflammation by regulating LMP7 in DN. In this study, deep sequencing, in situ hybridization, quantitative real-time PCR, dual-luciferase reporter gene assays, western blot and chromatin immunoprecipitation were respectively used. For the results, we found that miR-451 was markedly downregulated in the kidneys of db/db mice, PBMCs of DN patients and mesangial cells (MCs) cultured in high glucose conditions. Furthermore, miR-451 directly targeted LMP7 expression to inhibit NF-κB activity, and down-regulated transcription of proinflammatory molecules in MCs. More importantly, in the kidneys of db/db DN mice, increasing miR-451 level inhibited LMP7/NF-κB activity, and attenuated the urinary microalbumin excretion, blood glucose, and glomerular injury. In conclusion, these results provide new insights into the regulation of miR-451 via the LMP7/NF-κB central inflammatory pathway during progression of DN.

Shaping and preserving β-cell identity with microRNAs

The highly sophisticated identity of pancreatic β-cells is geared to accomplish its unique feat of providing insulin for organismal glucose and lipid homeostasis. This requires a particular and streamlined fuel metabolism which defines mature β-cells as glucose sensors linked to an insulin exocytosis machinery. The establishment of an appropriate β-cell mass and function during development as well as the maintenance of their identity throughout life are necessary for energy homeostasis. The small non-coding RNAs, microRNAs (miRNAs), are now well-recognized regulators of gene transcripts, which in general are negatively affected by them. Convincing evidence exists to view miRNAs as major actors in β-cell development and function, suggesting an important role for them in the distinctive β-cell 'identity card'. Here, we summarize key features that associate miRNAs and the establishment of the appropriate β-cell identity and its necessary maintenance during their 'long life'.

The potential of endurance exercise-derived exosomes to treat metabolic diseases

Endurance exercise-mediated multisystemic adaptations are known to mitigate metabolism-related disorders such as obesity and type 2 diabetes mellitus (T2DM). However, the underlying molecular mechanisms that promote crosstalk between organs and orchestrate the pro-metabolic effects of endurance exercise remain unclear. Exercise-induced release of peptides and nucleic acids from skeletal muscle and other organs (collectively termed 'exerkines') has been implicated in mediating these systemic adaptations. Given that the extracellular milieu is probably not a hospitable environment for labile exerkines, a lipid vehicle-based mode of delivery has originated over the course of evolution. Two types of extracellular vesicles, exosomes and microvesicles, have been shown to contain proteins and nucleic acids that participate in a variety of physiological and pathological processes. Exosomes, in particular, have been shown to facilitate the exchange of peptides, microRNA, mRNA and mitochondrial DNA between cells and tissues. Intriguingly, circulatory extracellular vesicle content increases in an intensity-dependant manner in response to endurance exercise. We propose that the systemic benefits of exercise are modulated by exosomes and/or microvesicles functioning in an autocrine, paracrine and/or endocrine manner. Furthermore, we posit that native or modified exosomes, and/or microvesicles enriched with exerkines will have therapeutic utility in the treatment of obesity and T2DM.

Expression of miR-199a-3p in human adipocytes is regulated by free fatty acids and adipokines

Obesity is associated with a notable risk for disease, including risk of cardiovascular disorders, type 2 diabetes mellitus (T2DM) and hypertension. Adipose tissue modulates the metabolism by releasing free fatty acids (FFAs) and adipokines, including leptin, resistin, tumor necrosis factor-α (TNF-α) and interleukin 6 (IL-6). Altered secretion patterns of FFAs and adipokines have been demonstrated to result in obesity-associated insulin resistance (IR) and inflammatory responses. MicroRNA-199a-3p (miR)-199a-3p expression is significantly induced in differentiated human adipose-derived mesenchymal stem cells and indicates the association with T2DM. However, the association between miR-199a-3p levels in adipocytes and obesity-associated IR, as well as inflammatory responses remains to be elucidated. The present study observed an elevation of miR-199a-3p expression level in mature human adipocytes (visceral) compared with pre-adipocytes. In addition, miR-199a-3p expression was higher in visceral adipose deposits from obese subjects. FFA, TNF-α, IL-6 and leptin significantly induced miR-199a-3p expression in mature human adipocytes, while resistin had the opposite effect. miR-199a-3p may represent a factor in the modulation of obesity-associated IR and inflammatory responses.

Chenodeoxycholic acid significantly impacts the expression of miRNAs and genes involved in lipid, bile acid and drug metabolism in human hepatocytes

AIMS

Bile acids (BAs) are important gut signaling hormones, influencing lipid, glucose, and energy homeostasis. The exact mechanisms behind these effects are not yet fully understood. Lately, they have come to the fore as putative therapeutics in metabolic diseases, such as e.g. nonalcoholic fatty liver disease (NAFLD). We elucidate to what extent BAs impacts on the mRNAome and microRNAome in hepatocytes to gather novel insights into the mechanisms behind metabolic and toxicologic effects of bile acids.

MAIN METHODS

Five batches of primary human hepatocytes were treated with 50μmol/l chenodeoxycholic acid (CDCA) for 24 or 48h. Total RNA was extracted, size fractionated and subjected to Next Generation Sequencing to generate mRNA and miRNA profiles.

KEY FINDINGS

Expression of 738 genes and 52 miRNAs were CDCA dependently decreased, whereas 1566 genes and 29 miRNAs were significantly increased in hepatocytes. Distinct gene clusters controlling BA and lipid homeostasis (FGF(R), APO and FABP family members, HMGCS2) and drug metabolism (CYP, UGT and SULT family members) were significantly modulated by CDCA. Importantly, CDCA affected distinct microRNAs, including miR-34a, -505, -885, -1260 and -552 that systematically correlated in expression with gene clusters responsible for bile acid, lipid and drug homeostasis incorporating genes, such as e.g. SLCO1B1, SLC22A7, FGF19, CYP2E1, CYP1A2, APO family members and FOXO3.

SIGNIFICANCE

Bile acids significantly modulate metabolic and drug associated gene networks that are connected to distinct shifts in the microRNAome These findings give novel insights on how BA enfold metabolic and system toxic effects.

Characterization of Micro-RNA Changes during the Progression of Type 2 Diabetes in Zucker Diabetic Fatty Rats

The aim of the present pilot study was the identification of micro-RNA changes over time during the development and progression of type 2 diabetes (T2D) in Zucker diabetic fatty rats (ZDF rats). T2D is a complex metabolic disorder that is characterized, inter alia, by progressive failure of pancreatic β cells to produce insulin, but also by functional or morphological modifications of others organ, such as liver, adipose tissue and the cardiovascular system. Micro-RNAs are a novel class of biomarkers that have the potential to represent biomarkers of disease progression. In this study, the onset and progression of diabetes was followed in ZDF rats from six weeks until 17 weeks of age. After an initial phase of hyperinsulinemia, the animals developed T2D and lost the capacity to produce sufficient insulin. Circulating miRNAs were measured from plasma samples at four time points: pre-diabetes (six weeks of age), hyperinsulinemia (eight weeks), β cell failure (11 weeks) and late-stage diabetes (17 weeks) using TaqMan miRNA arrays. Bioinformatic analysis revealed distinct changes of circulating miRNAs over time. Several miRNAs were found to be increased over the course of the disease progression, such as miR-122, miR-133, miR-210 and miR-375. The most significantly decreased miRNAs were miR-140, miR-151-3p, miR-185, miR-203, miR-434-3p and miR-450a. Some of the miRNAs have also been identified in type 2 diabetic patients recently and, therefore, may have the potential to be useful biomarkers for the disease progression of T2D and/or the treatment response for anti-diabetic medications.

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.

Transcriptional regulation of the miR-212/miR-132 cluster in insulin-secreting β-cells by cAMP-regulated transcriptional co-activator 1 and salt-inducible kinases

MicroRNAs are central players in the control of insulin secretion, but their transcriptional regulation is poorly understood. Our aim was to investigate cAMP-mediated transcriptional regulation of the miR-212/miR-132 cluster and involvement of further upstream proteins in insulin secreting β-cells. cAMP induced by forskolin+IBMX or GLP-1 caused increased expression of miR-212/miR-132, and elevated phosphorylation of cAMP-response-element-binding-protein (CREB)/Activating-transcription-factor-1 (ATF1) and Salt-Inducible-Kinases (SIKs). CyclicAMP-Regulated Transcriptional Co-activator-1 (CRTC1) was concomitantly dephosphorylated and translocated to the nucleus. Silencing of miR-212/miR-132 reduced, and overexpression of miR-212 increased, glucose-stimulated insulin secretion. Silencing of CRTC1 expression resulted in decreased insulin secretion and miR-212/miR-132 expression, while silencing or inhibition of SIKs was associated with increased expression of the microRNAs and dephosphorylation of CRTC1. CRTC1 protein levels were reduced after silencing of miR-132, suggesting feed-back regulation. Our data propose cAMP-dependent co-regulation of miR-212/miR-132, in part mediated through SIK-regulated CRTC1, as an important factor for fine-tuned regulation of insulin secretion.

Could gestational diabetes mellitus be managed through dietary bioactive compounds? Current knowledge and future perspectives

Gestational diabetes mellitus (GDM) is a serious problem growing worldwide that needs to be addressed with urgency in consideration of the resulting severe complications for both mother and fetus. Growing evidence indicates that a healthy diet rich in fruit, vegetables, nuts, extra-virgin olive oil and fish has beneficial effects in both the prevention and management of several human diseases and metabolic disorders. In this review, we discuss the latest data concerning the effects of dietary bioactive compounds such as polyphenols and PUFA on the molecular mechanisms regulating glucose homoeostasis. Several studies, mostly based on in vitro and animal models, indicate that dietary polyphenols, mainly flavonoids, positively modulate the insulin signalling pathway by attenuating hyperglycaemia and insulin resistance, reducing inflammatory adipokines, and modifying microRNA (miRNA) profiles. Very few data about the influence of dietary exposure on GDM outcomes are available, although this approach deserves careful consideration. Further investigation, which includes exploring the ‘omics’ world, is needed to better understand the complex interaction between dietary compounds and GDM.

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.

Atrasentan increased the expression of klotho by mediating miR-199b-5p and prevented renal tubular injury in diabetic nephropathy

Atrasentan is a promising therapy for treating diabetic nephropathy (DN). Here we evaluated whether atrasentan down-regulated the miR-199b-5p expression, thereby increasing klotho and preventing renal tubular injury in DN. One-hundred patients with type 2 diabetes mellitus (T2DM) and 40 healthy subjects were included. A DN mice model was established by an injection of streptozotocin (STZ). Human renal proximal tubular epithelial HK-2 cells were exposed to high glucose (20 mmol/L). Treated the mice and HK-2 cells with atrasentan, and we then investigated whether and how miR-199b-5p and Klotho were involved in preventing renal tubular injury in DN. In patients, the serum miR-199b-5p level increased and the klotho concentration decreased in accordance with elevated albuminuria. Atrasentan down-regulated miR-199b-5p and up-regulated klotho of the DN mice and HK-2 cells exposed to high glucose. High glucose promoted the binding of histone H3 to the miR-199b-5p promoter, and atrasentan canceled this effect. MiR-199b-5p targeted the 3′ UTR of klotho. Overexpression of miR-199b-5p canceled the effects of atrasentan on klotho expression and apoptosis of renal tubular cells in both in vivo and in vitro. The increased serum klotho, mediated by miR-199b-5p, is a possible mechanism by which atrasentan prevents renal tubular injury in DN.

Role of microRNAs in the age-associated decline of pancreatic beta cell function in rat islets

AIMS/HYPOTHESIS

Ageing can lead to reduced insulin sensitivity and loss of pancreatic beta cell function, predisposing individuals to the development of diabetes. The aim of this study was to assess the contribution of microRNAs (miRNAs) to age-associated beta cell dysfunction.

METHODS

The global mRNA and miRNA profiles of 3- and 12-month-old rat islets were collected by microarray. The functional impact of age-associated differences in miRNA expression was investigated by mimicking the observed changes in primary beta cells from young animals.

RESULTS

Beta cells from 12-month-old rats retained normal insulin content and secretion, but failed to proliferate in response to mitotic stimuli. The islets of these animals displayed modifications at the level of several miRNAs, including upregulation of miR-34a, miR-124a and miR-383, and downregulation of miR-130b and miR-181a. Computational analysis of the transcriptomic modifications observed in the islets of 12-month-old rats revealed that the differentially expressed genes were enriched for miR-34a and miR-181a targets. Indeed, the induction of miR-34a and reduction of miR-181a in the islets of young animals mimicked the impaired beta cell proliferation observed in old animals. mRNA coding for alpha-type platelet-derived growth factor receptor, which is critical for compensatory beta cell mass expansion, is directly inhibited by miR34a and is likely to be at least partly responsible for the effects of this miRNA.

CONCLUSIONS/INTERPRETATION

Changes in the level of specific miRNAs that occur during ageing affect the proliferative capacity of beta cells. This might reduce their ability to expand under conditions of increased insulin demand, favouring the development of type 2 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.