The microRNA-29 Family Dictates the Balance Between Homeostatic and Pathological Glucose Handling in Diabetes and Obesity

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

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

The Predictive Value of miR-16, -29a and -134 for Early Identification of Gestational Diabetes: A Nested Analysis of the DALI Cohort

Early identification of gestational diabetes mellitus (GDM) aims to reduce the risk of adverse maternal and perinatal outcomes. Currently, no circulating biomarker has proven clinically useful for accurate prediction of GDM. In this study, we tested if a panel of small non-coding circulating RNAs could improve early prediction of GDM. We performed a nested case-control study of participants from the European multicenter ‘Vitamin D and lifestyle intervention for GDM prevention (DALI)’ trial using serum samples from obese pregnant women (BMI ≥ 29 kg/m²) entailing 82 GDM cases (early- and late- GDM), and 41 age- and BMI-matched women with normal glucose tolerance (NGT) throughout pregnancy (controls). Anthropometric, clinical and biochemical characteristics were obtained at baseline (<20 weeks of gestation) and throughout gestation. Baseline serum microRNAs (miRNAs) were measured using quantitative real time PCR (qPCR). Elevated miR-16-5p, -29a-3p, and -134-5p levels were observed in women, who were NGT at baseline and later developed GDM, compared with controls who remained NGT. A combination of the three miRNAs could distinguish later GDM from NGT cases (AUC 0.717, p = 0.001, compared with fasting plasma glucose (AUC 0.687, p = 0.004)) as evaluated by area under the curves (AUCs) using Receiver Operator Characteristics (ROC) analysis. Elevated levels of individual miRNAs or a combination hereof were associated with higher odds ratios of GDM. Conclusively, circulating miRNAs early in pregnancy could serve as valuable predictive biomarkers of GDM.

Pancreatic β cells control glucose homeostasis via the secretion of exosomal miR-29 family

Secreted microRNAs (miRNAs) are novel endocrine factors that play essential pathological and physiological roles. Here, we report that pancreatic β cell-released exosomal miR-29 family members (miR-29s) regulate hepatic insulin sensitivity and control glucose homeostasis. Cultured pancreatic islets were shown to secrete miR-29s in response to high levels of free fatty acids (FFAs) in vitro. In vivo, high levels of FFAs, promoted by either high-fat diet (HFD) feeding (physiopathological) or fasting (physiological), increased the secretion of miR-29s into plasma. Intravenous administration of exosomal miR-29s attenuated insulin sensitivity. The overexpression of miR-29s in the β cells of transgenic (TG) mice promoted the secretion of miR-29s and inhibited the insulin-mediated suppression of glucose output in the liver. We used selective overexpression of traceable heterogenous mutant miR-29s in β cells to confirm that islet-derived exosomal miR-29s target insulin signalling in the liver and blunt hepatic insulin sensitivity. Moreover, in vivo disruption of miR-29s expression in β cells reversed HFD-induced insulin resistance. In vitro experiments demonstrated that isolated exosomes enriched in miR-29s inhibited insulin signalling in the liver and increased hepatic glucose production. These results unveil a novel β cell-derived secretory signal-exosomal miR-29s-and provide insight into the roles of miR-29s in manipulating glucose homeostasis.

Expression of miRNA-29 in Pancreatic β Cells Promotes Inflammation and Diabetes via TRAF3

Type 2 diabetes mellitus (T2DM) is recognized as a chronic, low-grade inflammatory disease characterized by insulin resistance and pancreatic β cell dysfunction; however, the underlying molecular mechanism remains unclear. Here, we report a key β cell-macrophage crosstalk pathway mediated by the miRNA-29-TNF-receptor-associated factor 3 (TRAF3) axis. β cell-specific transgenic miR-29a/b/c mice are predisposed to develop glucose intolerance and insulin resistance when fed a high-fat diet (HFD). The metabolic effect of β cell miR-29 is largely mediated through macrophages because either depletion of macrophages or reconstitution with miR-29-signaling defective bone marrow improves metabolic parameters in the transgenic mice. Mechanistically, our data show that miR-29 promotes the recruitment and activation of circulating monocytes and macrophages and, hence, inflammation, via miR-29 exosomes in a TRAF3-dependent manner. Our results demonstrate the ability of β cells to modulate the systemic inflammatory tone and glucose homeostasis via miR-29 in response to nutrient overload.

Does microRNA Perturbation Control the Mechanisms Linking Obesity and Diabetes? Implications for Cardiovascular Risk

Metabolic disorders such as obesity and type 2 diabetes (T2D) are considered the major risk factors for the development of cardiovascular diseases (CVD). Although the pathological mechanisms underlying the mutual development of obesity and T2D are difficult to define, a better understanding of the molecular aspects is of utmost importance to identify novel therapeutic targets. Recently, a class of non-coding RNAs, called microRNAs (miRNAs), are emerging as key modulators of metabolic abnormalities. There is increasing evidence supporting the role of intra- and extracellular miRNAs as determinants of the crosstalk between adipose tissues, liver, skeletal muscle and other organs, triggering the paracrine communication among different tissues. miRNAs may be considered as risk factors for CVD due to their correlation with cardiovascular events, and in particular, may be related to the most prominent risk factors. In this review, we describe the associations observed between miRNAs expression levels and the most common cardiovascular risk factors. Furthermore, we sought to depict the molecular aspect of the interplay between obesity and diabetes, investigating the role of microRNAs in the interorgan crosstalk. Finally, we discussed the fascinating hypothesis of the loss of protective factors, such as antioxidant defense systems regulated by such miRNAs.

Evidence for Training-Induced Changes in miRNA Levels in the Skeletal Muscle of Patients With Type 2 Diabetes Mellitus

Physical training can improve glycemic control in patients with type 2 diabetes mellitus (T2DM). However, the underlying mechanisms are not entirely clear. An interesting piece of the puzzle could be the regulation of micro-RNAs (miRNAs). They are important modulators of protein expression. Some miRNAs were found to be both linked to poor glycemic control/insulin resistance (with evidence from in vivo and/or in vitro studies) and dysregulated in the skeletal muscle of T2DM patients. This pilot study examines whether a 3-month endurance training program [three times a week, 70-80% peak heart rate (HR_peak)] can down-regulate their levels in T2DM men (n = 7). One skeletal muscle biopsy sample was obtained from each patient at T1 (6 weeks pre-intervention), one at T2 (1 week pre-intervention) and one at T3 (3-4 days post-intervention). miRNA-27a-3p, -29a-3p, -29b-3p, -29c-3p, -106b-5p, -135a-5p, -143-3p, -144-3p, -194-5p, and - 206 levels were determined by RT-qPCR. Friedman ANOVA and post-hoc tests showed that miRNA-29b-3p, -29c-3p and -135a-5p levels were significantly reduced post-training (T3 vs. T2 and/or T1). Glycated hemoglobin (HbA1c) and HOMA insulin resistance index did not change significantly. However, HbA1c was reduced in 6 of 7 patients post-training. Furthermore, Spearman's rank correlation analyses with all values from all time points showed significant negative associations between miRNA-29c-3p, -106b-5p, -144-3p and -194-5p levels and cardiorespiratory fitness (VO_2peak). The study results imply that regular exercise and improving one's physical fitness is helpful for the regulation of skeletal muscle miRNAs in T2DM patients. Whether or not changes in the miRNA profile can affect the clinical situation of T2DM patients warrants further research.

Long Non-coding RNA GAS5 Maintains Insulin Secretion by Regulating Multiple miRNAs in INS-1 832/13 Cells

Type-2 diabetes mellitus (T2DM) is a complex disease characterized by reduced pancreatic islets β-cell mass and impaired insulin release from these cells. Non-coding RNAs, including microRNAs (miRNA) and long non-coding RNAs (lncRNAs), play a role in the progression of T2DM. Decreased serum lncRNA GAS5 levels were reported to be associated with T2DM. However, the role of GAS5 in regulating islet cell functions remain unknown. In this study, we found that the serum levels of GAS5 were significantly lower in patients with T2DM compared with healthy control subjects, and the low serum GAS5 levels were associated with high levels of HbAlc and fasting glucose in patients with T2DM. In addition, we found that serum GAS5 levels were negatively correlated with the serum levels of miR-29a-3p, miR-96-3p, and miR-208a-3p in patients with T2DM. Consequently, using INS-1 832/13 rat β-cell line, we found that overexpression of GAS5 by lentivirus infection increased glucose-stimulated insulin secretion and insulin content compared with negative control, whereas knockdown of GAS5 expression reduced both them. Moreover, GAS5 interacted with miR-29a-3p, miR-96-3p, and miR-208a-3p in INS-1 832/13 cells, as judged by pull-down assay and dual luciferase reporter assay. GAS5 overexpression caused the decrease in expression of miR-29a-3p, miR-96-3p, and miR-208a-3p in INS-1 832/13 cells and conversely caused the increase in expression of insulin receptor, insulin receptor substrate, and phosphoinositide-3-kinase regulatory subunit 1. Thus, these results reveal a novel mechanism whereby GAS5 is involved in maintaining insulin secretion and may represent a novel therapeutic target for T2DM.

Metformin decreases miR-122, miR-223 and miR-29a in women with polycystic ovary syndrome

Metformin is associated with increased insulin sensitivity, whereas oral contraceptive pills (OCP) could increase the risk for type 2 diabetes (T2D) in women with polycystic ovary syndrome (PCOS). Certain miRNAs might serve as biomarkers for the risk of T2D. The aim of this study was to investigate changes in circulating miRNA levels during treatment with metformin and OCP in women with PCOS. Sixty-five women with PCOS according to Rotterdam criteria were randomized to metformin (2 g/day), metformin + OCP (150 mg desogestrel + 30 µg ethinylestradiol) or OCP alone for 12 months. Serum miRNA analysis was performed with individual RT-qPCR or Taqman low density array cards of 22 selected miRNAs previously related to PCOS, glucose and/or lipid metabolism. miR-122 and miR-29a levels were decreased after treatment with metformin compared with metformin + OCP and OCP group: miR-122: log2 difference -0.7 (P = 0.01) and -0.7 (P = 0.02), miR-29a: log2 difference -0.5 (P = 0.01) and -0.4 (P = 0.04), while miR-223 levels were decreased in the metformin + OCP group after treatment: log2 difference -0.5 (P = 0.02). During the treatment period, a significant weight loss was observed in the metformin group compared with the OCP group. In the OCP group, miRNA levels were unchanged during the treatment period. Levels of circulating miRNAs associated with lipid and glucose metabolism decreased during metformin treatment. Changes in miRNA levels in the metformin group could be explained by the simultaneous weight loss in the same group. These results support the notion that metformin treatment alone may be superior for metabolic health compared with OCP.

Expression of miR-409-5p in gestational diabetes mellitus and its relationship with insulin resistance

Expression of miR-409-5p in gestational diabetes mellitus (GDM) and its relationship with insulin resistance were explore. One hundred and forty-nine pregnant women who underwent antenatal examination in Taizhou First People's Hospital were divided into a GDM group and a control group according to whether they had GDM or not. Serum miR-409-5p expression of the two groups was detected, and the levels of glycosylated hemoglobin (HbAlc) and other GDM-related biochemical indicators were measured. Fasting plasma glucose (FPG) was determined by glucose oxidase method, fasting insulin (FINS) was detected by radioimmunoassay, and homeostasis model assessment of insulin resistance (HOMA-IR) was calculated. The relationship between miR-409-5p and other biochemical indicators and insulin resistance was analyzed, and logistic multivariate regression was employed to analyze the risk factors of GDM. miR-409-5p was highly expressed in the serum of GDM patients. HbAlc, FPG, FINS, and HOMA-IR in pregnant women in the GDM group were markedly higher than those in the control group. The serum miR-409-5p in GDM pregnant women showed a positive correlation with HbAlc, FPG, FINS, and HOMA-IR (P<0.05). The insulin resistance group presented remarkably higher serum miR-409-5p level than the non-insulin resistance group. Moreover, it was found that elevated miR-409-5p, FINS, and HOMA-IR were all independent risk factors for the onset of GDM. miR-409-5p is highly expressed in the serum of patients with GDM, and it is positively correlated with insulin resistance index of GDM patients, which may be a potential target for clinical diagnosis and treatment of GDM.

The Role of microRNAs in Metabolic Syndrome-Related Oxidative Stress

Oxidative stress (OxS) is the cause and the consequence of metabolic syndrome (MetS), the incidence and economic burden of which is increasing each year. OxS triggers the dysregulation of signaling pathways associated with metabolism and epigenetics, including microRNAs, which are biomarkers of metabolic disorders. In this review, we aimed to summarize the current knowledge regarding the interplay between microRNAs and OxS in MetS and its components. We searched PubMed and Google Scholar to summarize the most relevant studies. Collected data suggested that different sources of OxS (e.g., hyperglycemia, insulin resistance (IR), hyperlipidemia, obesity, proinflammatory cytokines) change the expression of numerous microRNAs in organs involved in the regulation of glucose and lipid metabolism and endothelium. Dysregulated microRNAs either directly or indirectly affect the expression and/or activity of molecules of antioxidative signaling pathways (SIRT1, FOXOs, Keap1/Nrf2) along with effector enzymes (e.g., GPx-1, SOD1/2, HO-1), ROS producers (e.g., NOX4/5), as well as genes of numerous signaling pathways connected with inflammation, insulin sensitivity, and lipid metabolism, thus promoting the progression of metabolic imbalance. MicroRNAs appear to be important epigenetic modifiers in managing the delicate redox balance, mediating either pro- or antioxidant biological impacts. Summarizing, microRNAs may be promising therapeutic targets in ameliorating the repercussions of OxS in MetS.

The Yin and Yang function of microRNAs in insulin signalling and cancer

Data accumulated over the past several decades uncover a vital role of microRNAs (miRNAs) in various biological processes. It is well established that, by binding to target mRNAs, miRNAs act as post-transcription suppressors to inhibit mRNA translation and/or to promote mRNA degradation. Very recently, miRNAs have been found to act as positive regulators to promote gene transcription. In this review, we briefly summarize the regulation and functional roles of miRNAs in metabolic diseases and cancer development. We also review recent advances on the mechanisms by which miRNAs regulate gene expression, focusing on their unconventional roles as enhancers to promote gene expression. Given the high potential of miRNAs as biomarkers for risk assessment and as high-value targets for therapy, a better understanding of the Yin-Yang functional feature of miRNAs and their mechanisms of action could have significant clinical implications for the treatment of various diseases such as obesity, type 2 diabetes, and cancer.

Hepatocyte expression of the micropeptide adropin regulates the liver fasting response and is enhanced by caloric restriction

The micropeptide adropin encoded by the clock-controlled energy homeostasis-associated gene is implicated in the regulation of glucose metabolism. However, its links to rhythms of nutrient intake, energy balance, and metabolic control remain poorly defined. Using surveys of Gene Expression Omnibus data sets, we confirm that fasting suppresses liver adropin expression in lean C57BL/6J (B6) mice. However, circadian rhythm data are inconsistent. In lean mice, caloric restriction (CR) induces bouts of compulsive binge feeding separated by prolonged fasting intervals, increasing NAD-dependent deacetylase sirtuin-1 signaling important for glucose and lipid metabolism regulation. CR up-regulates adropin expression and induces rhythms correlating with cellular stress-response pathways. Furthermore, adropin expression correlates positively with phosphoenolpyruvate carboxokinase-1 (Pck1) expression, suggesting a link with gluconeogenesis. Our previous data suggest that adropin suppresses gluconeogenesis in hepatocytes. Liver-specific adropin knockout (LAdrKO) mice exhibit increased glucose excursions following pyruvate injections, indicating increased gluconeogenesis. Gluconeogenesis is also increased in primary cultured hepatocytes derived from LAdrKO mice. Analysis of circulating insulin levels and liver expression of fasting-responsive cAMP-dependent protein kinase A (PKA) signaling pathways also suggests enhanced responses in LAdrKO mice during a glucagon tolerance test (250 µg/kg intraperitoneally). Fasting-associated changes in PKA signaling are attenuated in transgenic mice constitutively expressing adropin and in fasting mice treated acutely with adropin peptide. In summary, hepatic adropin expression is regulated by nutrient- and clock-dependent extrahepatic signals. CR induces pronounced postprandial peaks in hepatic adropin expression. Rhythms of hepatic adropin expression appear to link energy balance and cellular stress to the intracellular signal transduction pathways that drive the liver fasting response.

Roles of Noncoding RNAs in Islet Biology

The discovery that most mammalian genome sequences are transcribed to ribonucleic acids (RNA) has revolutionized our understanding of the mechanisms governing key cellular processes and of the causes of human diseases, including diabetes mellitus. Pancreatic islet cells were found to contain thousands of noncoding RNAs (ncRNAs), including micro-RNAs (miRNAs), PIWI-associated RNAs, small nucleolar RNAs, tRNA-derived fragments, long non-coding RNAs, and circular RNAs. While the involvement of miRNAs in islet function and in the etiology of diabetes is now well documented, there is emerging evidence indicating that other classes of ncRNAs are also participating in different aspects of islet physiology. The aim of this article will be to provide a comprehensive and updated view of the studies carried out in human samples and rodent models over the past 15 years on the role of ncRNAs in the control of α- and β-cell development and function and to highlight the recent discoveries in the field. We not only describe the role of ncRNAs in the control of insulin and glucagon secretion but also address the contribution of these regulatory molecules in the proliferation and survival of islet cells under physiological and pathological conditions. It is now well established that most cells release part of their ncRNAs inside small extracellular vesicles, allowing the delivery of genetic material to neighboring or distantly located target cells. The role of these secreted RNAs in cell-to-cell communication between β-cells and other metabolic tissues as well as their potential use as diabetes biomarkers will be discussed. © 2020 American Physiological Society. Compr Physiol 10:893-932, 2020.

Milk-Derived Extracellular Vesicles in Inter-Organism, Cross-Species Communication and Drug Delivery

Milk is considered as more than a source of nutrition for infants and is a vector involved in the transfer of bioactive compounds and cells. Milk contains abundant quantities of extracellular vesicles (EVs) that may originate from multiple cellular sources. These nanosized vesicles have been well characterized and are known to carry a diverse cargo of proteins, nucleic acids, lipids and other biomolecules. Milk-derived EVs have been demonstrated to survive harsh and degrading conditions in gut, taken up by various cell types, cross biological barriers and reach peripheral tissues. The cargo carried by these dietary EVs has been suggested to have a role in cell growth, development, immune modulation and regulation. Hence, there is considerable interest in understanding the role of milk-derived EVs in mediating inter-organismal and cross-species communication. Furthermore, various attributes such as it being a natural source, as well as its abundance, scalability, economic viability and lack of unwarranted immunologic reactions, has generated significant interest in deploying milk-derived EVs for clinical applications such as drug delivery and disease therapy. In this review, the role of milk-derived EVs in inter-organismal, cross-species communication and in drug delivery is discussed.

PESM: predicting the essentiality of miRNAs based on gradient boosting machines and sequences

Background

MicroRNAs (miRNAs) are a kind of small noncoding RNA molecules that are direct posttranscriptional regulations of mRNA targets. Studies have indicated that miRNAs play key roles in complex diseases by taking part in many biological processes, such as cell growth, cell death and so on. Therefore, in order to improve the effectiveness of disease diagnosis and treatment, it is appealing to develop advanced computational methods for predicting the essentiality of miRNAs.

Result

In this study, we propose a method (PESM) to predict the miRNA essentiality based on gradient boosting machines and miRNA sequences. First, PESM extracts the sequence and structural features of miRNAs. Then it uses gradient boosting machines to predict the essentiality of miRNAs. We conduct the 5-fold cross-validation to assess the prediction performance of our method. The area under the receiver operating characteristic curve (AUC), F-measure and accuracy (ACC) are used as the metrics to evaluate the prediction performance. We also compare PESM with other three competing methods which include miES, Gaussian Naive Bayes and Support Vector Machine.

Conclusion

The results of experiments show that PESM achieves the better prediction performance (AUC: 0.9117, F-measure: 0.8572, ACC: 0.8516) than other three computing methods. In addition, the relative importance of all features also further shows that newly added features can be helpful to improve the prediction performance of methods.

Circulating adiposity-related microRNAs as predictors of the response to a low-fat diet in subjects with obesity

Recent studies have revealed the critical role of several microRNAs (miRNAs) in energy homeostasis and metabolic processes and suggest that circulating miRNAs can be used as early predictors of weight loss in the design of precision nutrition. Thus, the aim of this study was to investigate circulating adiposity‐related miRNAs as biomarkers of the response to two specific weight loss dietary treatments. The expression of 86 miRNAs was investigated in plasma of 78 subjects with obesity randomized to two different diets [moderately high‐protein diet (n = 38) and low‐fat diet (n = 40)] and in 25 eutrophic controls (BMI ≤ 25 kg/m²). Bioinformatic analyses were performed to explore the target genes and biological pathways regulated by the dysregulated miRNAs. As results, 26 miRNAs were found differently expressed in eutrophic and volunteers with obesity. Moreover, 7 miRNAs (miR‐130a‐3p, miR‐142‐5p, miR‐144‐5p, miR‐15a‐5p, miR‐22‐3p, miR‐221‐3p and miR‐29c‐3p) were differentially expressed between responders and non‐responders to a low‐fat diet. Furthermore, after adjustment for basal glucose levels, 1‐SD increase in miR‐22‐3p expression was associated with reduction in the risk of non‐response to low‐fat diet [OR = 0.181, 95% CI (0.084‐0.947), P = .043]. Bioinformatic analyses evidenced that these 7 miRNAs regulate the expression of genes participating in important metabolic pathways. Conclusively, 7 circulating miRNAs related to adiposity could be used for predicting the response to a low‐fat diet intervention prescribed to lose weight.

Blood Co-Circulating Extracellular microRNAs and Immune Cell Subsets Associate with Type 1 Diabetes Severity

Immune cell subsets and microRNAs have been independently proposed as type 1 diabetes (T1D) diagnostic and/or prognostic biomarkers. Here, we aimed to analyze the relationships between peripheral blood circulating immune cell subsets, plasmatic microRNAs, and T1D. Blood samples were obtained from both children with T1D at diagnosis and age-sex matched healthy controls. Then, immunophenotype assessed by flow cytometry was coupled with the quantification of 60 plasmatic microRNAs by quantitative RT-PCR. The associations between immune cell frequency, plasmatic microRNAs, and the parameters of pancreatic loss, glycemic control, and diabetic ketoacidosis were assessed by logistic regression models and correlation analyses. We found that the increase in specific plasmatic microRNAs was associated with T1D disease onset (let-7c-5p, let-7d-5p, let-7f-5p, let-7i-5p, miR-146a-5p, miR-423-3p, and miR-423-5p), serum C-peptide concentration (miR-142-5p and miR-29c-3p), glycated hemoglobin (miR-26a-5p and miR-223-3p) and the presence of ketoacidosis (miR-29c-3p) more strongly than the evaluated immune cell subset frequency. Some of these plasmatic microRNAs were shown to positively correlate with numbers of blood circulating B lymphocytes (miR-142-5p) and CD4⁺CD45RO⁺ (miR-146a-5p and miR-223-3p) and CD4⁺CD25⁺ cells (miR-423-3p and miR-223-3p) in children with T1D but not in healthy controls, suggesting a disease-specific microRNA association with immune dysregulation in T1D. In conclusion, our results suggest that, while blood co-circulating extracellular microRNAs and immune cell subsets may be biologically linked, microRNAs may better provide powerful information about T1D onset and severity.

miR-149 Negative Regulation of mafA Is Involved in the Arsenite-Induced Dysfunction of Insulin Synthesis and Secretion in Pancreatic Beta Cells

Chronic exposure to arsenic, a potent environmental oxidative stressor, is associated with the incidence of diabetes. However, the mechanisms for arsenite-induced reduction of insulin remain largely unclear. After CD1 mice were treated with 20 or 40 ppm arsenite in the drinking water for 12 months, the mice showed reduced fasting insulin levels, a depression in glucose clearance, and lower insulin content in the pancreas. The levels of glucose-stimulated insulin secretion (GSIS) in pancreatic β-cells isolated from arsenite-exposed mice were low compared with those for control mice. Immunohistochemistry studies showed that arsenite exposure resulted a reduction of insulin content in the pancreas of mice. Exposure of Min6 cells, a pancreatic beta cell line, to low levels of arsenite led to lower GSIS in a dose- and time-dependent fashion. Since microRNAs (miRNAs) are involved in pancreatic β-cell function and the pathogenesis of diabetes, we hypothesized that arsenite exposure activates miR-149, decreases insulin transcription factor v-maf musculoaponeurotic fibrosarcoma oncogene homolog A (mafA), and induces an insulin synthesis and secretion disorder. In arsenite-exposed Min6 cells, mafA activity was lowered by the increase of its target miRNA, miR-149. Luciferase assays illustrated an interaction between miR-149 and the mafA 3' untranslated region. In Min6 cells transfected with an miR-149 inhibitor, arsenite did not regulate GSIS and mafA expression. In control cells, however, arsenite decreased GSIS or mafA expression. Our results suggest that low levels of arsenite affect β-cell function and regulate insulin synthesis and secretion by modulating mafA expression through miR-149.

Milk exosomal miRNAs: potential drivers of AMPK-to-mTORC1 switching in β-cell de-differentiation of type 2 diabetes mellitus

Type 2 diabetes mellitus (T2DM) steadily increases in prevalence since the 1950's, the period of widespread distribution of refrigerated pasteurized cow's milk. Whereas breastfeeding protects against the development of T2DM in later life, accumulating epidemiological evidence underlines the role of cow's milk consumption in T2DM. Recent studies in rodent models demonstrate that during the breastfeeding period pancreatic β-cells are metabolically immature and preferentially proliferate by activation of mechanistic target of rapamycin complex 1 (mTORC1) and suppression of AMP-activated protein kinase (AMPK). Weaning determines a metabolic switch of β-cells from a proliferating, immature phenotype with low insulin secretion to a differentiated mature phenotype with glucose-stimulated insulin secretion, less proliferation, reduced mTORC1- but increased AMPK activity. Translational evidence presented in this perspective implies for the first time that termination of milk miRNA transfer is the driver of this metabolic switch. miRNA-148a is a key inhibitor of AMPK and phosphatase and tensin homolog, crucial suppressors of mTORC1. β-Cells of diabetic patients return to the postnatal phenotype with high mTORC1 and low AMPK activity, explained by continuous transfer of bovine milk miRNAs to the human milk consumer. Bovine milk miRNA-148a apparently promotes β-cell de-differentiation to the immature mTORC1-high/AMPK-low phenotype with functional impairments in insulin secretion, increased mTORC1-driven endoplasmic reticulum stress, reduced autophagy and early β-cell apoptosis. In contrast to pasteurized cow's milk, milk's miRNAs are inactivated by bacterial fermentation, boiling and ultra-heat treatment and are missing in current infant formula. Persistent milk miRNA signaling adds a new perspective to the pathogenesis of T2DM and explains the protective role of breastfeeding but the diabetogenic effect of continued milk miRNA signaling by persistent consumption of pasteurized cow's milk.

Long Non-coding RNA H19 Suppression Protects the Endothelium Against Hyperglycemic-Induced Inflammation via Inhibiting Expression of miR-29b Target Gene Vascular Endothelial Growth Factor a Through Activation of the Protein Kinase B/Endothelial Nitric Oxide Synthase Pathway

It has been shown that non-coding RNAs (ncRNAs) play an important regulatory role in pathophysiological processes involving inflammation. The vascular endothelial growth factor A (VEGFA) gene also participates in the inflammatory process. However, the relationships between ncRNAs and VEGFA are currently unclear. Here, this study was designed to determine the relationship between long non-coding RNA (lncRNA) H19, mircoRNA29b (miR-29b), and VEGFA in the development of diabetes mellitus (DM). We demonstrate that H19 is upregulated and miR-29b downregulated in individuals with DM and directly binds miR-29b. VEGFA is the target of miR-29b in the vascular endothelium of individuals with DM. We found that positive modulation of miR29b and inhibition of H19 and VEGFA significantly attenuates high glucose-induced endothelial inflammation and oxidative stress. We also found that the protein kinase B/endothelial nitric oxide synthase (AKT/eNOS) signal pathway in endothelial cells is activated through regulation of miR29b and H19 endogenous RNAs. We conclude that H19 suppression protects the endothelium against high glucose-induced inflammation and oxidative stress in endothelial cells by upregulation of miR-29b and downregulation of VEGFA through AKT/eNOS signal pathway activation. These results suggest a novel link between dysregulated ncRNA expression, inflammation, and the signaling pathway in the vascular endothelium of individuals with DM, indicating a promising strategy for preventing cardiovascular disease in such individuals.

MicroRNA-7a overexpression in VMH restores the sympathoadrenal response to hypoglycemia

It is proposed that the impaired sympathoadrenal response to hypoglycemia induced by recurrent insulin-induced hypoglycemia (RH) is an adaptive phenomenon induced by specific changes in microRNA expression in the ventromedial hypothalamus (VMH). To test this hypothesis, genome-wide microRNAomic profiling of the VMH by RNA-sequencing was performed in control rats and rats treated for RH. Differential expression analysis identified microRNA-7a-5p and microRNA-665 as potential mediators of this phenomenon. To further test this hypothesis, experiments were conducted consisting of targeted lentiviral-mediated overexpression of microRNA-7a-5p and downregulation of microRNA-665 in the VMH. Hyperinsulinemic hypoglycemic clamp experiments demonstrated that targeted overexpression of microRNA-7a-5p (but not downregulation of microRNA-665) in the VMH of RH rats restored the epinephrine response to hypoglycemia. This restored response to hypoglycemia was associated with a restoration of GABAA receptor gene expression. Finally, a direct interaction of microRNA-7a-5p with the 3'-UTR of GABAA receptor α1-subunit (Gabra1) gene was demonstrated in a luciferase assay. These findings indicate that (a) the impaired sympathoadrenal response RH induces is associated with changes in VMH microRNA expression and (b) microRNA-7a-5p, possibly via direct downregulation of GABA receptor gene expression, may serve as a mediator of the altered sympathoadrenal response to hypoglycemia.

Contribution of Oxidative Stress and Impaired Biogenesis of Pancreatic β-Cells to Type 2 Diabetes

Significance: Type 2 diabetes development involves multiple changes in β-cells, related to the oxidative stress and impaired redox signaling, beginning frequently by sustained overfeeding due to the resulting lipotoxicity and glucotoxicity. Uncovering relationships among the dysregulated metabolism, impaired β-cell "well-being," biogenesis, or cross talk with peripheral insulin resistance is required for elucidation of type 2 diabetes etiology. Recent Advances: It has been recognized that the oxidative stress, lipotoxicity, and glucotoxicity cannot be separated from numerous other cell pathology events, such as the attempted compensation of β-cell for the increased insulin demand and dynamics of β-cell biogenesis and its "reversal" at dedifferentiation, that is, from the concomitantly decreasing islet β-cell mass (also due to transdifferentiation) and low-grade islet or systemic inflammation. Critical Issues: At prediabetes, the compensation responses of β-cells, attempting to delay the pathology progression-when exaggerated-set a new state, in which a self-checking redox signaling related to the expression of Ins gene expression is impaired. The resulting altered redox signaling, diminished insulin secretion responses to various secretagogues including glucose, may lead to excretion of cytokines or chemokines by β-cells or excretion of endosomes. They could substantiate putative stress signals to the periphery. Subsequent changes and lasting glucolipotoxicity promote islet inflammatory responses and further pathology spiral. Future Directions: Should bring an understanding of the β-cell self-checking and related redox signaling, including the putative stress signal to periphery. Strategies to cure or prevent type 2 diabetes could be based on the substitution of the "wrong" signal by the "correct" self-checking signal.

miR-26 suppresses adipocyte progenitor differentiation and fat production by targeting Fbxl19

Fat storage in adult mammals is a highly regulated process that involves the mobilization of adipocyte progenitor cells (APCs) that differentiate to produce new adipocytes. Here we report a role for the broadly conserved miR-26 family of microRNAs (miR-26a-1, miR-26a-2, and miR-26b) as major regulators of APC differentiation and adipose tissue mass. Deletion of all miR-26-encoding loci in mice resulted in a dramatic expansion of adipose tissue in adult animals fed normal chow. Conversely, transgenic overexpression of miR-26a protected mice from high-fat diet-induced obesity. These effects were attributable to a cell-autonomous function of miR-26 as a potent inhibitor of APC differentiation. miR-26 blocks adipogenesis, at least in part, by repressing expression of Fbxl19, a conserved miR-26 target without a previously known role in adipocyte biology that encodes a component of SCF-type E3 ubiquitin ligase complexes. These findings have therefore revealed a novel pathway that plays a critical role in regulating adipose tissue formation in vivo and suggest new potential therapeutic targets for obesity and related disorders.

Crosstalk between microRNAs, the putative target genes and the lncRNA network in metabolic diseases

MicroRNAs (miRNAs/miRs) are small non-coding RNAs (ncRNAs) that regulate gene expression. Emerging knowledge has suggested that miRNAs have a role in the pathogenesis of metabolic disorders, supporting the hypothesis that miRNAs may represent potential biomarkers or targets for this set of diseases. However, the current evidence is often controversial. Therefore, the aim of the present study was to determine the associations between miRNAs-target genes, miRNA-long ncRNAs (lncRNAs), and miRNAs-small molecules in human metabolic diseases, including obesity, type 2 diabetes and non-alcoholic fatty liver disease. The metabolic disease-related miRNAs were obtained from the Human MicroRNA Disease Database (HMDD) and miR2Disease database. A search on the databases Matrix Decomposition and Heterogeneous Graph Inference (MDHGI) and DisGeNET were also performed. miRNAs target genes were obtained from three independent sources: Microcosm, TargetScan and miRTarBase. The interactions between miRNAs-lncRNA and miRNA-small molecules were performed using the miRNet web tool. The network analyses were performed using Cytoscape software. As a result, a total of 20 miRNAs were revealed to be associated with metabolic disorders in the present study. Notably, 6 miRNAs (miR-17-5p, miR-29c-3p, miR-34a-5p, miR-103a-3p, miR-107 and miR-132-3p) were found in the four resources (HMDD, miR2Disease, MDHGI, and DisGeNET) used for these analyses, presenting a stronger association with the diseases. Furthermore, the target genes of these miRNAs participate in several pathways previously associated with metabolic diseases. In addition, interactions between miRNA-lncRNA and miRNA-small molecules were also found, suggesting that some molecules can modulate gene expression via such an indirect way. Thus, the results of this data mining and integration analysis provide further information on the possible molecular basis of the metabolic disease pathogenesis as well as provide a path to search for potential biomarkers and therapeutic targets concerning metabolic diseases.

Acute suppression of insulin resistance-associated hepatic miR-29 in vivo improves glycemic control in adult mice

MicroRNAs (miRNAs) are important posttranscriptional regulators of metabolism and energy homeostasis. Dysregulation of certain miRNAs in the liver has been shown to contribute to the pathogenesis of Type 2 diabetes (T2D), in part by impairing hepatic insulin sensitivity. By small RNA-sequencing analysis, we identified seven hepatic miRNAs (including miR-29b) that are consistently aberrantly expressed across five different rodent models of metabolic dysfunction that share the feature of insulin resistance (IR). We also showed that hepatic miR-29b exhibits persistent dysregulation during disease progression in a rat model of diabetes, UCD-T2DM. Furthermore, we observed that hepatic levels of miR-29 family members are attenuated by interventions known to improve IR in rodent and rhesus macaque models. To examine the function of the miR-29 family in modulating insulin sensitivity, we used locked nucleic acid (LNA) technology and demonstrated that acute in vivo suppression of the miR-29 family in adult mice leads to significant reduction of fasting blood glucose (in both chow-fed lean and high-fat diet-fed obese mice) and improvement in insulin sensitivity (in chow-fed lean mice). We carried out whole transcriptome studies and uncovered candidate mechanisms, including regulation of DNA methyltransferase 3a (Dnmt3a) and the hormone-encoding gene Energy homeostasis associated (Enho). In sum, we showed that IR/T2D is linked to dysregulation of hepatic miR-29b across numerous models and that acute suppression of the miR-29 family in adult mice leads to improved glycemic control. Future studies should investigate the therapeutic utility of miR-29 suppression in different metabolic disease states.Enho; insulin resistance; liver; microRNA-29 (miR-29); UCD-T2DM.

Adipose tissue macrophage-derived exosomal miR-29a regulates obesity-associated insulin resistance

Obesity-associated insulin resistance is a forerunner of type 2 diabetes. Macrophages reside within adipose tissue (ATMs) have been reported to regulate insulin sensitivity through secreting miRNAs containing exosomes. Here, we show that miR-29a is increased in obese ATMs derived exosomes (ATMs-Exos) and can be transferred into adipocytes, myocytes and hepatocytes causing insulin resistance in vitro and in vivo. Administration of obese ATMs-Exos impairs insulin sensitivity of lean mice. While knockdown miR-29a level in obese ATM-Exos blunts this effect. PPAR-δ is identified to function as downstream target of miR-29a in regulating insulin resistance. PPAR-δ agonist GW501516 partially rescued the insulin resistance induced by miR-29a. Taken together, these findings suggest that ATMs derived exosomal miR-29a could regulate obesity-associated insulin resistance, which may serve as a potential therapeutic target for obesity-associated type 2 diabetes.

Exosomal microRNA-29a mediates cardiac dysfunction and mitochondrial inactivity in obesity-related cardiomyopathy

PURPOSE

Present study aims to explore the pathophysiological role of microRNA (miR)-29a in the process of obesity-related cardiomyopathy in human subjects and mice.

METHODS

The expression level of circulating exosomal miR-29a was measured in 37 lean and 30 obese human subjects, and correlated with cardiac parameters. The effects of miR-29a on mitochondrial activity and cardiac function were investigated by treatment of miR-29a sponge in primary mouse cardiomyocytes and diet-induced obesity-related cardiomyopathy in mice.

RESULTS

The increased circulating miR-29a level was closely associated with impaired human cardiac function, including ejection fraction (r = -0.2663, p < 0.05) and NT-proBNP levels (r = 0.4270, p < 0.001). Exosomes from obese human plasma mediated cardiomyocyte mitochondrial inactivity, but pre-treatment with miR-29a sponge attenuated the exosomal miR-29a-induced reduction of ATP production (p < 0.001), basal oxygen consumption (p < 0.01) and mitochondrial complex I activity (p < 0.01). In vivo mouse study, high fat diet damaged cardiac function, normal structure, and mitochondrial activity, whereas miR-29a sponge improved the cardiac status.

CONCLUSIONS

Present study uncovered the correlation between circulating miR-29a and cardiac parameters in human subjects, and provided solid evidence of the therapeutic application of miR-29a sponge in combating obesity-mediated cardiac dysfunction.

Predicting and understanding the response to short-term intensive insulin therapy in people with early type 2 diabetes

OBJECTIVE

Short-term intensive insulin therapy (IIT) early in the course of type 2 diabetes acutely improves beta-cell function with long-lasting effects on glycemic control. However, conventional measures cannot determine which patients are better suited for IIT, and little is known about the molecular mechanisms determining response. Therefore, this study aimed to develop a model that could accurately predict the response to IIT and provide insight into molecular mechanisms driving such response in humans.

METHODS

Twenty-four patients with early type 2 diabetes were assessed at baseline and four weeks after IIT, consisting of basal detemir and premeal insulin aspart. Twelve individuals had a beneficial beta-cell response to IIT (responders) and 12 did not (nonresponders). Beta-cell function was assessed by multiple methods, including Insulin Secretion-Sensitivity Index-2. MicroRNAs (miRNAs) were profiled in plasma samples before and after IIT. The response to IIT was modeled using a machine learning algorithm and potential miRNA-mediated regulatory mechanisms assessed by differential expression, correlation, and functional network analyses (FNA).

RESULTS

Baseline levels of circulating miR-145-5p, miR-29c-3p, and HbA1c accurately (91.7%) predicted the response to IIT (OR = 121 [95% CI: 6.7, 2188.3]). Mechanistically, a previously described regulatory loop between miR-145-5p and miR-483-3p/5p, which controls TP53-mediated apoptosis, appears to also occur in our study population of humans with early type 2 diabetes. In addition, significant (fold change > 2, P < 0.05) longitudinal changes due to IIT in the circulating levels of miR-138-5p, miR-192-5p, miR-195-5p, miR-320b, and let-7a-5p further characterized the responder group and significantly correlated (|r| > 0.4, P < 0.05) with the changes in measures of beta-cell function and insulin sensitivity. FNA identified a network of coordinately/cooperatively regulated miRNA-targeted genes that potentially drives the IIT response through negative regulation of apoptotic processes that underlie beta cell dysfunction and concomitant positive regulation of proliferation.

CONCLUSIONS

Responses to IIT in people with early type 2 diabetes are associated with characteristic miRNA signatures. This study represents a first step to identify potential responders to IIT (a current limitation in the field) and provides important insight into the pathophysiologic determinants of the reversibility of beta-cell dysfunction. ClinicalTrial.gov identifier: NCT01270789.

miR-29a Negatively Affects Glucose-Stimulated Insulin Secretion and MIN6 Cell Proliferation via Cdc42/β-Catenin Signaling

BACKGROUND

Diabetes is a progressive metabolic disease characterized by hyperglycemia. Functional impairment of islet β cells can occur to varying degrees. This impairment can initially be compensated for by proliferation and metabolic changes of β cells. Cell division control protein 42 (Cdc42) and the microRNA (miRNA) miR-29 have important roles in β-cell proliferation and glucose-stimulated insulin secretion (GSIS), which we further explored using the mouse insulinoma cell line MIN6.

METHODS

Upregulation and downregulation of miR-29a and Cdc42 were accomplished using transient transfection. miR-29a and Cdc42 expression was detected by real-time PCR and western blotting. MIN6 proliferation was detected using a cell counting kit assay. GSIS under high-glucose (20.0 mM) or basal-glucose (5.0 mM) stimulation was detected by enzyme-linked immunosorbent assay. The miR-29a binding site in the Cdc42 mRNA 3'-untranslated region (UTR) was determined using bioinformatics and luciferase reporter assays.

RESULTS

miR-29a overexpression inhibited proliferation (P < 0.01) and GSIS under high-glucose stimulation (P < 0.01). Cdc42 overexpression promoted proliferation (P < 0.05) and GSIS under high-glucose stimulation (P < 0.05). miR-29a overexpression decreased Cdc42 expression (P < 0.01), whereas miR-29a downregulation increased Cdc42 expression (P < 0.01). The results showed that the Cdc42 mRNA 3'-UTR is a direct target of miR-29a in vitro. Additionally, Cdc42 reversed miR-29a-mediated inhibition of proliferation and GSIS (P < 0.01). Furthermore, miR-29a inhibited β-catenin expression (P < 0.01), whereas Cdc42 promoted β-catenin expression (P < 0.01).

CONCLUSION

By negatively regulating Cdc42 and the downstream molecule β-catenin, miR-29a inhibits MIN6 proliferation and insulin secretion.

A Systematic Review of miR-29 in Cancer

MicroRNAs (miRNA) are small non-coding RNAs (∼22 nt in length) that are known as potent master regulators of eukaryotic gene expression. miRNAs have been shown to play a critical role in cancer pathogenesis, and the misregulation of miRNAs is a well-known feature of cancer. In recent years, miR-29 has emerged as a critical miRNA in various cancers, and it has been shown to regulate multiple oncogenic processes, including epigenetics, proteostasis, metabolism, proliferation, apoptosis, metastasis, fibrosis, angiogenesis, and immunomodulation. Although miR-29 has been thoroughly documented as a tumor suppressor in the majority of studies, some controversy remains with conflicting reports of miR-29 as an oncogene. In this review, we provide a systematic overview of miR-29's functional role in various mechanisms of cancer and introspection on the contradictory roles of miR-29.

miR29b regulates aberrant methylation in In-Vitro diabetic nephropathy model of renal proximal tubular cells

The role of DNA methylation has not been enough explored in pathophysiology of diabetic nephropathy (DN). However, according to recent reports it has been inferred that hypermethylation could be one of the principle cause associated with the enhancement of DN. An interrelationship between miR29b and DNA methylation has been studied via in-silico analysis. We have validated that miR29b prominently targets DNA methyl transferase (DNMT), specifically DNMT1, DNMT3A and DNMT3B. We have developed in vitro DN model using renal proximal tubule epithelial cells (RPTECs), contributed to a significant alleviation in RNA and protein expression levels of DNMT3A, DNMT3B and DNMT1. The developed model has also demonstrated downregulation in expression of miR29b. Our studies have also suggested that miR29b targets DNMT1 via targeting its transcription factor SP1. In addition to this, downregulation of a specific biomarker for kidney injury, tubular kidney injury molecule-1 (KIM-1) and fibrosis causing glycoprotein i.e. fibronectin, was also demonstrated. Hence, the developed model revealed that hypermethylation is a key factor incorporated in DN, and miR29b could effectively ameliorate defensive actions in DN pathogenesis.

Plasma levels of miR-29b and miR-200b in type 2 diabetic retinopathy

MicroRNAs (miRNAs/miRs) are involved in the pathogenesis of diabetes mellitus and its chronic complications, and their circulating levels have emerged as potential biomarkers for the development and progression of diabetes. However, few studies have examined the expression of miRNAs in diabetic retinopathy (DR) in humans. This case-control study aimed to investigate whether the plasma levels of miR-29b and miR-200b are associated with DR in 186 South Brazilians with type 2 diabetes (91 without DR, 46 with non-proliferative DR and 49 with proliferative DR). We also included 20 healthy blood donors to determine the miRNA expression in the general population. Plasma levels of miR-29b and miR-200b were quantified by reverse transcription-quantitative polymerase chain reaction (RT-qPCR). Proliferative DR was inversely associated with plasma levels of miR-29b (unadjusted OR = 0.694, 95% CI: 0.535-0.900, P = 0.006) and miR-200b (unadjusted OR = 0.797, 95% CI: 0.637-0.997, P = 0.047). However, these associations were lost after controlling for demographic and clinical covariates. In addition, patients with type 2 diabetes had lower miR-200b levels than blood donors. Our findings reinforce the importance of addressing the role of circulating miRNAs, including miR-29 and miR-200b, in DR.

Exosomes and miRNA-Loaded Biomimetic Nanovehicles, a Focus on Their Potentials Preventing Type-2 Diabetes Linked to Metabolic Syndrome

Exosomes are small membrane vesicles of 30–150 nm, members of the extracellular vesicle family and secreted by various cell types. Different studies describe specific microRNA (miRNA) with altered expression in serum and/or plasma of patients suffering from diabetes or metabolic syndrome. Diabetic cardiomyocyte-derived exosomes loaded with miRNAs like miR-320-3p (or 320a) have been shown regulating angiogenesis on endothelial cell cultures. Insufficient myocardial angiogenesis is the major manifestation of diabetes-caused ischemic cardiovascular disease. Studies on transfer of functional microRNAs between mouse dendritic cells via exosomes have shown that some miRNAs (miR-320-3p, 29b-3p, 7a-5p) are distributed in immature and mature exosomes. Among these miRNAs, miR-320-3p is better known in epigenetics for silencing polr3d gene by binding to its promoter in Human Embryonic Kidney-293 cells. Moreover, quantitative and stoichiometric analysis of the microRNA content of exosomes highlights the lack of reliable natural source of such particles loaded with miRNA opening the need for tailoring exosomes or nanoparticles delivering efficiently miRNA intimately linked to immunity, metabolism and epigenetics in target cells. However, loading of extracellular mature miRNA into recipient cells comes with a cost by at least impeding dynamic localization of miRNAs in nucleoli or inefficient miRNA delivery due to rapid recycling by exonucleases. All these works are calling for the design of new biomimetic vehicles and in vivo assessment of miRNA functionality when delivered by natural or biomimetic nanoparticles in order to control metabolic diseases from infancy to adulthood.

Exercise Training-Induced Changes in MicroRNAs: Beneficial Regulatory Effects in Hypertension, Type 2 Diabetes, and Obesity

MicroRNAs are small non-coding RNAs that regulate gene expression post-transcriptionally. They are involved in the regulation of physiological processes, such as adaptation to physical exercise, and also in disease settings, such as systemic arterial hypertension (SAH), type 2 diabetes mellitus (T2D), and obesity. In SAH, microRNAs play a significant role in the regulation of key signaling pathways that lead to the hyperactivation of the renin-angiotensin-aldosterone system, endothelial dysfunction, inflammation, proliferation, and phenotypic change in smooth muscle cells, and the hyperactivation of the sympathetic nervous system. MicroRNAs are also involved in the regulation of insulin signaling and blood glucose levels in T2D, and participate in lipid metabolism, adipogenesis, and adipocyte differentiation in obesity, with specific microRNA signatures involved in the pathogenesis of each disease. Many studies report the benefits promoted by exercise training in cardiovascular diseases by reducing blood pressure, glucose levels, and improving insulin signaling and lipid metabolism. The molecular mechanisms involved, however, remain poorly understood, especially regarding the participation of microRNAs in these processes. This review aimed to highlight microRNAs already known to be associated with SAH, T2D, and obesity, as well as their possible regulation by exercise training.

Role of miR29c in goose fatty liver is mediated by its target genes that are involved in energy homeostasis and cell growth

BACKGROUND

A short period of overfeeding can lead to severe hepatic steatosis in the goose, which is physiological, suggesting that geese, as a descendent of a migrating ancestor, may have evolutionally developed a unique mechanism that operates in contrast to the mechanism underlying pathological fatty liver in humans or other mammals. In this study, we report that suppression of miR29c and upregulation of its target genes in goose fatty liver vs. normal liver could be part of a unique mechanism that contributes to the regulation of energy homeostasis and cell growth.

RESULTS

Our data showed that miR29c expression was comprehensively inhibited in energy homeostasis-related tissues (the liver, fat and muscle) of overfed vs. normally fed geese, which is different from miR29c induction that occurs in tissues of the diabetic rat. To address the function of miR29c, three predicted target genes (i.e., Insig1, Sgk1 and Col3a1) that participate in energy homeostasis or cell growth were validated by a dual-fluorescence reporter system and other in vitro assays. Importantly, expression of Insig1, Sgk1 and Col3a1 was upregulated in goose fatty liver. In line with these observations, treatment of goose hepatocytes with high glucose or palmitate suppressed the expression of miR29c but induced the expression of the target genes, suggesting that hyperglycemia and hyperlipidemia, at least partially, contribute to the suppression of miR29c and induction of the target genes in goose fatty liver. In addition, pharmacological assays indicated that RFX1 was a transcription factor involved in the expression of miR29c.

CONCLUSIONS

This study suggests that miR29c may play a role in the regulation of energy homeostasis and tissue growth via its target genes, contributing to the tolerance of the goose to severe hepatic steatosis.

The microRNA-29/PGC1α regulatory axis is critical for metabolic control of cardiac function

Different microRNAs (miRNAs), including miR-29 family, may play a role in the development of heart failure (HF), but the underlying molecular mechanisms in HF pathogenesis remain unclear. We aimed at characterizing mice deficient in miR-29 in order to address the functional relevance of this family of miRNAs in the cardiovascular system and its contribution to heart disease. In this work, we show that mice deficient in miR-29a/b1 develop vascular remodeling and systemic hypertension, as well as HF with preserved ejection fraction (HFpEF) characterized by myocardial fibrosis, diastolic dysfunction, and pulmonary congestion, and die prematurely. We also found evidence that the absence of miR-29 triggers the up-regulation of its target, the master metabolic regulator PGC1α, which in turn generates profound alterations in mitochondrial biogenesis, leading to a pathological accumulation of small mitochondria in mutant animals that contribute to cardiac disease. Notably, we demonstrate that systemic hypertension and HFpEF caused by miR-29 deficiency can be rescued by PGC1α haploinsufficiency, which reduces cardiac mitochondrial accumulation and extends longevity of miR-29–mutant mice. In addition, PGC1α is overexpressed in hearts from patients with HF. Collectively, our findings demonstrate the in vivo role of miR-29 in cardiovascular homeostasis and unveil a novel miR-29/PGC1α regulatory circuitry of functional relevance for cell metabolism under normal and pathological conditions.

To combat diseases, we first need to gain knowledge on how cells function at the molecular level to maintain normal physiology. One great scientific achievement of the last decade was the identification of thousands of small regulatory RNA molecules, called microRNAs. Strikingly, each microRNA has the potential to fine-tune the expression of hundreds of target genes depending on the spatiotemporal context. Therefore, defects in key microRNAs can contribute to the development of diseases. In the present work, we characterize the role for miR-29 in cardiac function in a mouse model. We found that mice deficient for miR-29 develop life-threatening cardiometabolic alterations that subsequently cause heart failure with diastolic dysfunction and systemic hypertension. We also demonstrate that these pathological phenotypes originate in part by the anomalous up-regulation of the transcriptional coactivator PGC1α, which can lead to mitochondrial hyperplasia in the heart. Genetic removal of one copy of PGC1α significantly attenuated the severity of the cardiovascular phenotype observed in miR-29–deficient mice. In addition, we show that PGC1α expression is misregulated in heart failure patients, suggesting that the implementation of miR-29 replacement therapy could potentially be used to treat these fatal pathologies.

MicroRNAs: markers of β-cell stress and autoimmunity

PURPOSE OF REVIEW

We discuss current knowledge about microRNAs (miRNAs) in type 1 diabetes (T1D), an autoimmune disease leading to severe loss of pancreatic β-cells. We describe: the role of cellular miRNAs in regulating immune functions and pathways impacting insulin secretion and β-cell survival; circulating miRNAs as disease biomarkers.

RECENT FINDINGS

Studies examined miRNAs in experimental models and patients, including analysis of tissues from organ donors, peripheral blood cells, and circulating miRNAs in serum, plasma, and exosomes. Studies employed diverse designs and methodologies to detect miRNAs and measure their levels. Selected miRNAs have been linked to the regulation of key biological pathways and disease pathogenesis; several circulating miRNAs are associated with having T1D, islet autoimmunity, disease progression, and immune and metabolic functions, for example, C-peptide secretion, in multiple studies.

SUMMARY

A growing literature reveals multiple roles of miRNAs in T1D, provide new clues into the regulation of disease mechanisms, and identify reproducible associations. Yet challenges remain, and the field will benefit from joint efforts to analyze results, compare methodologies, formally test the robustness of miRNA associations, and ultimately move towards validating robust miRNA biomarkers.

MicroRNA‑29a is involved lipid metabolism dysfunction and insulin resistance in C2C12 myotubes by targeting PPARδ

MicroRNA‑29a (miR‑29a) expression has been reported to be closely associated with skeletal muscle insulin resistance and type 2 diabetes. The present study investigated the effect of miR‑29a on palmitic acid (PA)‑induced lipid metabolism dysfunction and insulin resistance in C2C12 myotubes via overexpressing or silencing of miR‑29a expression. Mouse C2C12 myoblasts were cultured, differentiated and transfected with miR‑29a or miR‑29a inhibitor lentiviral with or without subsequent palmitic acid (PA) treatment. Reverse transcription‑quantitative polymerase chain reaction (RT‑qPCR) and western blot analysis were performed to assess the mRNA and protein levels of related genes, respectively. PA treatment increased the expression of miR‑29a in a time‑ and dose‑ dependent manner. miR‑29a silencing improved insulin‑induced glucose uptake and increased glucose transporter‑4 (GLUT4) transportation to the plasma membrane by upregulating its target peroxisome proliferator‑activated receptor δ (PPARδ). Furthermore, it was observed that miR‑29a regulated the expression of genes associated with lipid metabolism, including pyruvate dehydrogenase kinase isoform, mitochondrial uncoupling protein (UCP)2, UCP3, long chain specific acyl‑CoA dehydrogenase, mitochondrial and fatty acid transport protein 2. The results confirmed that silencing miR‑29a induced a decrease in glucose transport and affected lipid metabolism in PA‑treated C2C12 cells, and therefore may be involved in insulin resistance by targeting PPARδ in skeletal muscle. Therefore, the inhibition of miR‑29a may be a potential novel strategy for treating insulin resistance and type 2 diabetes.

MicroRNAs as Potential Regulators of Glutathione Peroxidases Expression and Their Role in Obesity and Related Pathologies

Glutathione peroxidases (GPxs) belong to the eight-member family of phylogenetically related enzymes with different cellular localization, but distinct antioxidant function. Several GPxs are important selenoproteins. Dysregulated GPx expression is connected with severe pathologies, including obesity and diabetes. We performed a comprehensive bioinformatic analysis using the programs miRDB, miRanda, TargetScan, and Diana in the search for hypothetical microRNAs targeting 3′untranslated regions (3´UTR) of GPxs. We cross-referenced the literature for possible intersections between our results and available reports on identified microRNAs, with a special focus on the microRNAs related to oxidative stress, obesity, and related pathologies. We identified many microRNAs with an association with oxidative stress and obesity as putative regulators of GPxs. In particular, miR-185-5p was predicted by a larger number of programs to target six GPxs and thus could play the role as their master regulator. This microRNA was altered by selenium deficiency and can play a role as a feedback control of selenoproteins’ expression. Through the bioinformatics analysis we revealed the potential connection of microRNAs, GPxs, obesity, and other redox imbalance related diseases.

Metazoan MicroRNAs

MicroRNAs (miRNAs) are ∼22 nt RNAs that direct posttranscriptional repression of mRNA targets in diverse eukaryotic lineages. In humans and other mammals, these small RNAs help sculpt the expression of most mRNAs. This article reviews advances in our understanding of the defining features of metazoan miRNAs and their biogenesis, genomics, and evolution. It then reviews how metazoan miRNAs are regulated, how they recognize and cause repression of their targets, and the biological functions of this repression, with a compilation of knockout phenotypes that shows that important biological functions have been identified for most of the broadly conserved miRNAs of mammals.

The Cells of the Islets of Langerhans

Islets of Langerhans are islands of endocrine cells scattered throughout the pancreas. A number of new studies have pointed to the potential for conversion of non-β islet cells in to insulin-producing β-cells to replenish β-cell mass as a means to treat diabetes. Understanding normal islet cell mass and function is important to help advance such treatment modalities: what should be the target islet/β-cell mass, does islet architecture matter to energy homeostasis, and what may happen if we lose a particular population of islet cells in favour of β-cells? These are all questions to which we will need answers for islet replacement therapy by transdifferentiation of non-β islet cells to be a reality in humans. We know a fair amount about the biology of β-cells but not quite as much about the other islet cell types. Until recently, we have not had a good grasp of islet mass and distribution in the human pancreas. In this review, we will look at current data on islet cells, focussing more on non-β cells, and on human pancreatic islet mass and distribution.

MiR-29 family members interact with SPARC to regulate glucose metabolism

MicroRNA (miR)-29 family members have been reported to play important regulatory roles in metabolic disease. We used TargetScan to show that "secreted protein acidic rich in cysteine" (SPARC) is a target of the miR-29s. SPARC is a multifunctional secretory protein involved in a variety of biological activities, and SPARC dysregulation is associated with a wide range of obesity-related disorders, including type 2 diabetes mellitus (T2DM). We explored whether miR-29s played roles in glucose metabolism and whether miR-29s directly targeted SPARC. We also examined the effect of SPARC on glucose metabolism and how the association of miR-29s with SPARC affected glucose metabolism. We found that overexpression of miR-29s reduced glucose uptake and GLUT4 levels; that miR-29 directly targeted SPARC, resulting in degradation of SPARC-encoding mRNA and reduction in the SPARC protein level; that SPARC increased glucose uptake and GLUT4 levels; that shRNA-mediated knockdown of SPARC reduced GLUT4 protein levels in 3T3-L1 adipocytes; that miR-29s reduced glucose uptake and GLUT4 levels; and that miR-29s inhibited glucose uptake by suppressing SPARC synthesis. Thus, the miR-29 family negatively regulates glucose metabolism by inhibiting SPARC expression.

Serum miRNA levels are related to glucose homeostasis and islet autoantibodies in children with high risk for type 1 diabetes

Micro RNAs (miRNAs) are promising disease biomarkers due to their high stability. Their expression in serum is altered in type 1 diabetes, but whether deviations exist in individuals with high risk for type 1 diabetes remains unexplored. We therefore assessed serum miRNAs in high-risk individuals (n = 21) positive for multiple islet autoantibodies, age-matched healthy children (n = 17) and recent-onset type 1 diabetes patients (n = 8), using Serum/Plasma Focus microRNA PCR Panels from Exiqon. The miRNA levels in the high-risk group were similar to healthy controls, and no specific miRNA profile was identified for the high-risk group. However, serum miRNAs appeared to reflect glycemic status and ongoing islet autoimmunity in high-risk individuals, since several miRNAs were associated to glucose homeostasis and autoantibody titers. High-risk individuals progressing to clinical disease after the sampling could not be clearly distinguished from non-progressors, while miRNA expression in the type 1 diabetes group deviated significantly from high-risk individuals and healthy controls, perhaps explained by major metabolic disturbances around the time of diagnosis.