MicroRNA expression in alpha and beta cells of human pancreatic islets

Extracellular vesicles derived from stressed beta cells mediate monocyte activation and contribute to islet inflammation

Objective

Beta cell destruction in type 1 diabetes (T1D) results from the combined effect of inflammation and recurrent autoimmunity. In recent years, the role played by beta cells in the development of T1D has evolved from passive victims of the immune system to active contributors in their own destruction. We and others have demonstrated that perturbations in the islet microenvironment promote endoplasmic reticulum (ER) stress in beta cells, leading to enhanced immunogenicity. Among the underlying mechanisms, secretion of extracellular vesicles (EVs) by beta cells has been suggested to mediate the crosstalk with the immune cell compartment.

Methods

To study the role of cellular stress in the early events of T1D development, we generated a novel cellular model for constitutive ER stress by modulating the expression of HSPA5, which encodes BiP/GRP78, in EndoC-βH1 cells. To investigate the role of EVs in the interaction between beta cells and the immune system, we characterized the EV miRNA cargo and evaluated their effect on innate immune cells.

Results

Analysis of the transcriptome showed that HSPA5 knockdown resulted in the upregulation of signaling pathways involved in the unfolded protein response (UPR) and changes the miRNA content of EVs, including reduced levels of miRNAs involved in IL-1β signaling. Treatment of primary human monocytes with EVs from stressed beta cells resulted in increased surface expression of CD11b, HLA-DR, CD40 and CD86 and upregulation of IL-1β and IL-6.

Conclusion

These findings indicate that the content of EVs derived from stressed beta cells can be a mediator of islet inflammation.

MicroRNA-7 regulates endocrine progenitor delamination and endocrine cell mass in developing pancreatic islets

β-cell replenishment in patients with diabetes through cadaveric islet transplantation has been successful; however, it requires long-term immunosuppression and suitable islet donors are scarce. Stepwise in vitro differentiation of pluripotent stem cells into β-cells represents a viable alternative, but limitations in our current understanding of in vivo islet endocrine differentiation constrains its clinical use. Here, we show that microRNA-7 (miR-7) is highly expressed in embryonic pancreatic endocrine progenitors. Genetic deletion of the miR-7 gene family in endocrine progenitors leads to reduced islet endocrine cell mass, due to endocrine progenitors failing to delaminate from the epithelial plexus. This is associated with a reduction in neurogenin-3 levels and increased expression of Sry-box transcription factor 9. Further, we observe that a significant number of endocrine progenitors lacking miR-7 differentiate into ductal cells. Our study suggests that increasing miR-7 expression could improve efficiency of in vitro differentiation and augment stem cell-derived β-cell terminal maturity.

miR-200c-3p regulates α4 integrin-mediated T cell adhesion and migration

A microRNA miR-200c-3p is a regulator of epithelial-mesenchymal transition to control adhesion and migration of epithelial and mesenchymal cells. However, little is known about whether miR-200c-3p affects lymphocyte adhesion and migration mediated by integrins. Using TK-1 (a T lymphoblast cell) as a model of T cell, here we show that repressed expression of miR-200c-3p upregulated α4 integrin-mediated adhesion to and migration across mucosal addressin cell adhesion molecule-1 (MAdCAM-1). Conversely, overexpression of miR-200c-3p downregulated α4 integrin-mediated adhesion and migration. Unlike in epithelial cells, miR-200c-3p did not target talin, a conformation activator of integrin, but, targeted E26-transformation-specific sequence 1 (ETS1), a transcriptional activator of α4 integrin, in T cells. Treatment of the miR-200c-3p-low-expressing TK-1 cells that possessed elevated α4 integrin with ETS1 small interfering RNA (siRNA) resulted in the reversion of the α4 integrin expression, supporting that ETS1 is a target of miR-200c-3p. A potential proinflammatory immune-modulator retinoic acid (RA) treatment of TK-1 cells elicited a significant reduction of miR-200c-3p and simultaneously a marked increase in ETS1 and α4 integrin expression. An anti-inflammatory cytokine TGF-β1 treatment elevated miR-200c-3p, thereby downregulating ETS1 and α4 integrin expression. These results suggest that miR-200c-3p is an important regulator of α4 integrin expression and functions and may be controlled by RA and TGF-β1 in an opposite way. Overexpression of miR-200c-3p could be a novel therapeutic option for treatment of gut inflammation through suppressing α4 integrin-mediated T cell migration.

A set of circulating microRNAs belonging to the 14q32 chromosome locus identifies two subgroups of individuals with recent-onset type 1 diabetes

Circulating microRNAs (miRNAs) are linked to the onset and progression of type 1 diabetes mellitus (T1DM), thus representing potential disease biomarkers. In this study, we employed a multiplatform sequencing approach to analyze circulating miRNAs in an extended cohort of prospectively evaluated recent-onset T1DM individuals from the INNODIA consortium. Our findings reveal that a set of miRNAs located within T1DM susceptibility chromosomal locus 14q32 distinguishes two subgroups of individuals. To validate our results, we conducted additional analyses on a second cohort of T1DM individuals, confirming the identification of these subgroups, which we have named cluster A and cluster B. Remarkably, cluster B T1DM individuals, who exhibit increased expression of a set of 14q32 miRNAs, show better glycemic control and display a different blood immunomics profile. Our findings suggest that this set of circulating miRNAs can identify two different T1DM subgroups with distinct blood immunomics at baseline and clinical outcomes during follow-up.

MicroRNA regulation of islet and enteroendocrine peptides: Physiology and therapeutic implications for type 2 diabetes

The pathogenesis of type 2 diabetes (T2D) is associated with dysregulation of glucoregulatory hormones, including both islet and enteroendocrine peptides. Microribonucleic acids (miRNAs) are short noncoding RNA sequences which post transcriptionally inhibit protein synthesis by binding to complementary messenger RNA (mRNA). Essential for normal cell activities, including proliferation and apoptosis, dysregulation of these noncoding RNA molecules have been linked to several diseases, including diabetes, where alterations in miRNA expression within pancreatic islets have been observed. This may occur as a compensatory mechanism to maintain beta-cell mass/function (e.g., downregulation of miR-7), or conversely, lead to further beta-cell demise and disease progression (e.g., upregulation of miR-187). Thus, targeting miRNAs has potential for novel diagnostic and therapeutic applications in T2D. This is reinforced by the success seen to date with miRNA-based therapeutics for other conditions currently in clinical trials. In this review, differential expression of miRNAs in human islets associated with T2D will be discussed along with further consideration of their effects on the production and secretion of islet and incretin hormones. This analysis further unravels the therapeutic potential of miRNAs and offers insights into novel strategies for T2D management.

Reassessing the Abundance of miRNAs in the Human Pancreas and Rodent Cell Lines and Its Implication

miRNAs are critical for pancreas development and function. However, we found that there are discrepancies regarding pancreatic miRNA abundance in published datasets. To obtain a more relevant profile that is closer to the true profile, we profiled small RNAs from human islets cells, acini, and four rodent pancreatic cell lines routinely used in diabetes and pancreatic research using a bias reduction protocol for small RNA sequencing. In contrast to the previous notion that miR-375-3p is the most abundant pancreatic miRNA, we found that miR-148a-3p and miR-7-5p were also abundant in islets. In silico studies using predicted and validated targets of these three miRNAs revealed that they may work cooperatively in endocrine and exocrine cells. Our results also suggest, compared to the most-studied miR-375, that both miR-148a-3p and miR-7-5p may play more critical roles in the human pancreas. Moreover, according to in silico-predicted targets, we found that miR-375-3p had a much broader target spectrum by targeting the coding sequence and the 5' untranslated region, rather than the conventional 3' untranslated region, suggesting additional unexplored roles of miR-375-3p beyond the pancreas. Our study provides a valuable new resource for studying miRNAs in pancreata.

Human pancreatic islet microRNAs implicated in diabetes and related traits by large-scale genetic analysis

Genetic studies have identified ≥240 loci associated with the risk of type 2 diabetes (T2D), yet most of these loci lie in non-coding regions, masking the underlying molecular mechanisms. Recent studies investigating mRNA expression in human pancreatic islets have yielded important insights into the molecular drivers of normal islet function and T2D pathophysiology. However, similar studies investigating microRNA (miRNA) expression remain limited. Here, we present data from 63 individuals, the largest sequencing-based analysis of miRNA expression in human islets to date. We characterized the genetic regulation of miRNA expression by decomposing the expression of highly heritable miRNAs into cis- and trans-acting genetic components and mapping cis-acting loci associated with miRNA expression [miRNA-expression quantitative trait loci (eQTLs)]. We found i) 84 heritable miRNAs, primarily regulated by trans-acting genetic effects, and ii) 5 miRNA-eQTLs. We also used several different strategies to identify T2D-associated miRNAs. First, we colocalized miRNA-eQTLs with genetic loci associated with T2D and multiple glycemic traits, identifying one miRNA, miR-1908, that shares genetic signals for blood glucose and glycated hemoglobin (HbA1c). Next, we intersected miRNA seed regions and predicted target sites with credible set SNPs associated with T2D and glycemic traits and found 32 miRNAs that may have altered binding and function due to disrupted seed regions. Finally, we performed differential expression analysis and identified 14 miRNAs associated with T2D status-including miR-187-3p, miR-21-5p, miR-668, and miR-199b-5p-and 4 miRNAs associated with a polygenic score for HbA1c levels-miR-216a, miR-25, miR-30a-3p, and miR-30a-5p.

Circulating biomarkers during progression to type 1 diabetes: A systematic review

AIM

Progression to type 1 diabetes (T1D) is defined in stages and clinical disease is preceded by a period of silent autoimmunity. Improved prediction of the risk and rate of progression to T1D is needed to reduce the prevalence of diabetic ketoacidosis at presentation as well as for staging participants for clinical trials. This systematic review evaluates novel circulating biomarkers associated with future progression to T1D.

METHODS

PubMed, Ovid, and EBSCO databases were used to identify a comprehensive list of articles. The eligibility criteria included observational studies that evaluated the usefulness of circulating markers in predicting T1D progression in at-risk subjects <20 years old.

RESULTS

Twenty-six studies were identified, seventeen were cohort studies and ten were case control studies. From the 26 studies, 5 found evidence for protein and lipid dysregulation, 11 identified molecular markers while 12 reported on changes in immune parameters during progression to T1D. An increased risk of T1D progression was associated with the presence of altered gene expression, immune markers including regulatory T cell dysfunction and higher short-lived effector CD8⁺ T cells in progressors.

DISCUSSION

Several circulating biomarkers are dysregulated before T1D diagnosis and may be useful in predicting either the risk or rate of progression to T1D. Further studies are required to validate these biomarkers and assess their predictive accuracy before translation into broader use.

SYSTEMATIC REVIEW REGISTRATION

https://www.crd.york.ac.uk/prospero, identifier (CRD42020166830).

miRNAs as Biomarkers in Diabetes: Moving towards Precision Medicine

Diabetes mellitus (DM) is a complex metabolic disease with many specifically related complications. Early diagnosis of this disease could prevent the progression to overt disease and its related complications. There are several limitations to using existing biomarkers, and between 24% and 62% of people with diabetes remain undiagnosed and untreated, suggesting a large gap in current diagnostic practices. Early detection of the percentage of insulin-producing cells preceding loss of function would allow for effective therapeutic interventions that could delay or slow down the onset of diabetes. MicroRNAs (miRNAs) could be used for early diagnosis, as well as for following the progression and the severity of the disease, due to the fact of their pancreatic specific expression and stability in various body fluids. Thus, many studies have focused on the identification and validation of such groups or "signatures of miRNAs" that may prove useful in diagnosing or treating patients. Here, we summarize the findings on miRNAs as biomarkers in diabetes and those associated with direct cellular reprogramming strategies, as well as the relevance of miRNAs that act as a bidirectional switch for cell therapy of damaged pancreatic tissue and the studies that have measured and tracked miRNAs as biomarkers in insulin resistance are addressed.

Knockdown of miR-214 Alleviates Renal Interstitial Fibrosis by Targeting the Regulation of the PTEN/PI3K/AKT Signalling Pathway

The microRNA-214 (miR-214) precursor is formed by the DNM3 gene on human chromosome 1q24.3, which is encoded and transcribed in the nucleus and processed into mature miR-214 in the cytoplasm. Association of miR-214 with the interstitial fibrosis of the kidney has been reported in existing research. Renal interstitial fibrosis is considered necessary during the process of various renal injuries in chronic kidney disease (CKD). One of the important mechanisms is the TGF- (transforming growth factor-) β1-stimulated epithelial interstitial transformation (EMT). The specific mechanisms of miR-214-3p in renal interstitial fibrosis and whether it participates in EMT are worthy of further investigation. In this paper, we first demonstrated modulation of the downstream PI3K/AKT axis by miR-214-3p through targeting phosphatase and tension protein homologues (PTEN), indicating the miRNA's participation in unilateral ureteral obstruction (UUO) nephropathy and TGF-β1-induced EMT. We overexpressed or silenced miR-214-3p and PTEN for probing into the correlation of miR-214-3p with PTEN and the downstream PI3K/AKT signalling pathways. According to the results of the study, miR-214-3p overexpression silenced PTEN, activated the PI3K/AKT signalling pathway, and exacerbated EMT induced by TGF-β1, while miR-214-3p knockdown had the opposite effect. In miR-214-3p knockdown mice, the expression of PTEN was increased, the PI3K/AKT signalling pathway was inhibited, and fibrosis was alleviated. In conclusion, miR-214-3p regulates the EMT of renal tubular cells induced by TGF-β1 by targeting PTEN and regulating the PI3K/AKT signalling pathway. Furthermore, miR-214-3p knockdown can reduce renal interstitial fibrosis through the PTEN/PI3K/AKT pathway.

miR204 potentially promotes non-alcoholic fatty liver disease by inhibition of cpt1a in mouse hepatocytes

Non-alcoholic fatty liver disease (NAFLD) is associated with hepatic metabolism dysfunction. However, the mechanistic role of miR204 in the development of NAFLD is unknown. We investigate the functional significance of miR204 in the evolution of NAFLD. IDH2 KO mice feed a normal diet (ND) or HFD increased body weight, epididymal fat-pad weight, lipid droplet in liver, blood parameter and inflammation compared to WT mice fed a ND or HFD. Moreover, the expression of miR204 is increased in mice with IDH2 deficiency. Increased miR204 by IDH2 deficiency regulates carnitine palmitoyltransferase 1a (cpt1a) synthesis, which inhibits fatty acid β-oxidation. Inhibition of miR204 prevents the disassembly of two fatty acid-related genes by activating CPT1a expression, which decreases lipid droplet in liver, inflammatory cytokines, epididymal fat pad weight, blood parameters. Increased miR204 by IDH2 deficiency promotes the pathogenesis of HFD-induced NAFLD by regulating hepatic fatty acid metabolism and inflammation.

miR204 is found to inhibit cpt1a in mouse hepatocytes, which could play a role in promoting non-alcoholic fatty liver disease.

Progression of Type 1 Diabetes: Circulating MicroRNA Expression Profiles Changes from Preclinical to Overt Disease

Objectives

To evaluate the potential biological involvement of miRNA expression in the immune response and beta cell function in T1D.

Methods

We screened 377 serum miRNAs of 110 subjects divided into four groups: healthy individuals (control group) and patients at different stages of T1D progression, from the initial immunological manifestation presenting islet autoantibodies (AbP group) until partial and strong beta cell damage in the recent (recent T1D group) and long-term T1D, with 2 to 5 years of disease (T1D 2-5y group).

Results

The results revealed 69 differentially expressed miRNAs (DEMs) in relation to controls. Several miRNAs were correlated with islet autoantibodies (IA2A, GADA, and Znt8A), age, and C-peptide levels, mainly from AbP, and recent T1D groups pointing these miRNAs as relevant to T1D pathogenesis and progression. Several miRNAs were related to metabolic derangements, inflammatory pathways, and several other autoimmune diseases. Pathway analysis of putative DEM targets revealed an enrichment in pathways related to metabolic syndrome, inflammatory response, apoptosis and insulin signaling pathways, metabolic derangements, and decreased immunomodulation. One of the miRNAs' gene targets was DYRK2 (dual-specificity tyrosine-phosphorylation-regulated kinase 2), which is an autoantigen targeted by an antibody in T1D. ROC curve analysis showed hsa-miR-16 and hsa-miR-200a-3p with AUCs greater than for glucose levels, with discriminating power for T1D prediction greater than glucose levels. Conclusions/Interpretation. Our data suggests a potential influence of DEMs on disease progression from the initial autoimmune lesion up to severe beta cell dysfunction and the role of miRNAs hsa-miR-16 and hsa-miR-200a-3p as biomarkers of T1D progression.

Development of a beta cell-specific expression control element for rAAV

Diabetes mellitus, caused by loss or dysfunction of the insulin producing beta cells of the pancreas, is a promising target for rAAV-mediated gene therapy. To target potential therapeutic payloads specifically to beta cells, a cell-type specific expression control element is needed. Here, we tested a series of rAAV vectors designed to express transgenes specifically in human beta cells using the islet-tropic rAAV-KP1 capsid. A small promoter, consisting of only 84 bp of the insulin core promoter was not beta cell-specific in AAV, but highly active in multiple cell types, including tissues outside the pancreas. A larger 363 bp fragment of the insulin promoter (INS) also lacked beta cell specificity. However, beta cell-specific expression was achieved by combining two regulatory elements, a promoter consisting of two copies of INS (INSx2) and microRNA (miRNA) regulatory elements (MREs). The INSx2 promoter alone showed some beta cell preference, but not tight specificity. To reduce unspecific transgene expression in alpha cells, negative regulation by miRNAs was applied. MREs that are recognized by miRNAs abundant in alpha cells effectively downregulated the transgene expression in these cells. The INS2x-MRE expression vector was highly specific to human beta cells and stem cell derived beta cells.

Human Islet MicroRNA-200c Is Elevated in Type 2 Diabetes and Targets the Transcription Factor ETV5 to Reduce Insulin Secretion

MicroRNAs (miRNAs) are part of deregulated insulin secretion in type 2 diabetes (T2D) development. Rodent models have suggested miR-200c to be involved, but the role and potential as therapeutic target of this miRNA in human islets are not clear. Here we report increased expression of miR-200c in islets from T2D as compared with nondiabetic (ND) donors and display results showing reduced glucose-stimulated insulin secretion in EndoC-βH1 cells overexpressing miR-200c. We identify transcription factor ETV5 as the top rank target of miR-200c in human islets using TargetScan in combination with Pearson correlation analysis of miR-200c and mRNA expression data from the same human donors. Among other targets were JAZF1, as earlier shown in miR-200 knockout mice. Accordingly, linear model analysis of ETV5 and JAZF1 gene expression showed reduced expression of both genes in islets from human T2D donors. Western blot analysis confirmed the reduced expression of ETV5 on the protein level in EndoC-βH1 cells overexpressing miR-200c, and luciferase assay validated ETV5 as a direct target of miR-200c. Finally, LNA knockdown of miR-200c increased glucose-stimulated insulin secretion in islets from T2D donors approximately threefold. Our data reveal a vital role of the miR-200c-ETV5 axis in β-cell dysfunction and pathophysiology of T2D.

Let7b-5p inhibits insulin secretion and decreases pancreatic β-cell mass in mice

MicroRNAs are crucial regulators for the development, mass and function of pancreatic β-cells. MiRNA dysregulation is associated with β-cell dysfunction and development of diabetes. The members of let7 family are important players in regulating cellular growth and metabolism. In this study we investigated the functional role of let7b-5p in the mouse pancreatic β-cells. We generated pancreatic β-cell-specific let7b-5p transgenic mouse model and analyzed the glucose metabolic phenotype, β-cells mass and insulin secretion in vivo. Luciferase reporter assay, immunofluorescence staining and western blot were carried out to study the target genes of let7b-5p in β-cells. Let7b-5p overexpression impaired the insulin production and secretion of β-cells and resulted impaired glucose tolerance in mice. The overexpressed let7b-5p inhibited pancreatic β-cell proliferation and decreased the expression of cyclin D1 and cyclin D2. Our findings demonstrated that let7b-5p was critical in regulating the proliferation and insulin secretion of pancreatic β-cells.

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

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

MiR-205 is up-regulated in islets of diabetes-susceptible mice and targets the diabetes gene Tcf7l2

AIM

MicroRNAs play an important role in the maintenance of cellular functions by fine-tuning gene expression levels. The aim of the current study was to identify genetically caused changes in microRNA expression which associate with islet dysfunction in diabetic mice.

METHODS

To identify novel microRNAs involved in islet dysfunction, transcriptome and miRNome analyses were performed in islets of obese, diabetes-susceptible NZO and diabetes-resistant B6-ob/ob mice and results combined with quantitative trait loci (QTL) and functional in vitro analysis.

RESULTS

In islets of NZO and B6-ob/ob mice, 94 differentially expressed microRNAs were detected, of which 11 are located in diabetes QTL. Focusing on conserved microRNAs exhibiting the strongest expression difference and which have not been linked to islet function, miR-205-5p was selected for further analysis. According to transcriptome data and target prediction analyses, miR-205-5p affects genes involved in Wnt and calcium signalling as well as insulin secretion. Over-expression of miR-205-5p in the insulinoma cell line INS-1 increased insulin expression, left-shifted the glucose-dependence of insulin secretion and supressed the expression of the diabetes gene TCF7L2. The interaction between miR-205-5p and TCF7L2 was confirmed by luciferase reporter assay.

CONCLUSION

MiR-205-5p was identified as relevant microRNA involved in islet dysfunction by interacting with TCF7L2.

The MicroRNA Landscape of Acute Beta Cell Destruction in Type 1 Diabetic Recipients of Intraportal Islet Grafts

Ongoing beta cell death in type 1 diabetes (T1D) can be detected using biomarkers selectively discharged by dying beta cells into plasma. microRNA-375 (miR-375) ranks among the top biomarkers based on studies in animal models and human islet transplantation. Our objective was to identify additional microRNAs that are co-released with miR-375 proportionate to the amount of beta cell destruction. RT-PCR profiling of 733 microRNAs in a discovery cohort of T1D patients 1 h before/after islet transplantation indicated increased plasma levels of 22 microRNAs. Sub-selection for beta cell selectivity resulted in 15 microRNAs that were subjected to double-blinded multicenter analysis. This led to the identification of eight microRNAs that were consistently increased during early graft destruction: besides miR-375, these included miR-132/204/410/200a/429/125b, microRNAs with known function and enrichment in beta cells. Their potential clinical translation was investigated in a third independent cohort of 46 transplant patients by correlating post-transplant microRNA levels to C-peptide levels 2 months later. Only miR-375 and miR-132 had prognostic potential for graft outcome, and none of the newly identified microRNAs outperformed miR-375 in multiple regression. In conclusion, this study reveals multiple beta cell-enriched microRNAs that are co-released with miR-375 and can be used as complementary biomarkers of beta cell death.

Deciphering the Variants Located in the MIR196A2, MIR146A, and MIR423 with Type-2 Diabetes Mellitus in Pakistani Population

MicroRNAs (miRNAs) are small non-coding RNA molecules that control the post-transcriptional gene expression. They play a pivotal role in the regulation of important physiological processes. Variations in miRNA genes coding for mature miRNA sequences have been implicated in several diseases. However, the association of variants in miRNAs genes with Type 2 Diabetes Mellitus (T2DM) in the Pakistani population is rarely reported. Therefore, the current study was designed to investigate the association of rs11614913 T/C (MIR196A2), rs2910164 G/C (MIR146A), and rs6505162 C/A (MIR423) in clinicopathological proven T2DM patients and gender-matched healthy controls. The tetra-primer amplification refractory mutation system-polymerase chain (ARMS-PCR) reaction method was used to determine the genotypes and to establish the association of each variant with T2DM through inherited models. In conclusion, the present study showed that variants rs11614913 T/C and rs2910164 G/C were linked with the risk of T2DM. The data suggested that rs11614913 T/C and rs2910164 G/C could be considered as novel risk factors in the pathogenesis of T2DM in the Pakistani population.

Machine learning workflows identify a microRNA signature of insulin transcription in human tissues

Dicer knockout mouse models demonstrated a key role for microRNAs in pancreatic β-cell function. Studies to identify specific microRNA(s) associated with human (pro-)endocrine gene expression are needed. We profiled microRNAs and key pancreatic genes in 353 human tissue samples. Machine learning workflows identified microRNAs associated with (pro-)insulin transcripts in a discovery set of islets (n = 30) and insulin-negative tissues (n = 62). This microRNA signature was validated in remaining 261 tissues that include nine islet samples from individuals with type 2 diabetes. Top eight microRNAs (miR-183-5p, -375-3p, 216b-5p, 183-3p, -7-5p, -217-5p, -7-2-3p, and -429-3p) were confirmed to be associated with and predictive of (pro-)insulin transcript levels. Use of doxycycline-inducible microRNA-overexpressing human pancreatic duct cell lines confirmed the regulatory roles of these microRNAs in (pro-)endocrine gene expression. Knockdown of these microRNAs in human islet cells reduced (pro-)insulin transcript abundance. Our data provide specific microRNAs to further study microRNA-mRNA interactions in regulating insulin transcription.

MicroRNA-27a targets Sfrp1 to induce renal fibrosis in diabetic nephropathy by activating Wnt/β-Catenin signalling

Diabetic nephropathy (DN) commonly causes end-stage renal disease (ESRD). Increasing evidence indicates that abnormal miRNA expression is tightly associated with chronic kidney disease (CKD). This work aimed to investigate whether miR-27a can promote the occurrence of renal fibrosis in DN by suppressing the expression of secreted frizzled-related protein 1 (Sfrp1) to activate Wnt/β-catenin signalling. Therefore, we assessed the expression levels of miR-27a, Sfrp1, Wnt signalling components, and extracellular matrix (ECM)-related molecules in vitro and in vivo. Sfrp1 was significantly down-regulated in a high-glucose environment, while miR-27a levels were markedly increased. A luciferase reporter assay confirmed that miR-27a down-regulated Sfrp1 by binding to the 3′ untranslated region directly. Further, NRK-52E cells under high-glucose conditions underwent transfection with miR-27a mimic or the corresponding negative control, miR-27a inhibitor or the corresponding negative control, si-Sfrp1, or combined miR-27a inhibitor and si-Sfrp1. Immunoblotting and immunofluorescence were performed to assess the relative expression levels of Wnt/β-catenin signalling and ECM components. The mRNA levels of Sfrp1, miR-27a, and ECM-related molecules were also detected by quantitative real-time PCR (qPCR). We found that miR-27a inhibitor inactivated Wnt/β-catenin signalling and reduced ECM deposition. Conversely, Wnt/β-catenin signalling was activated, while ECM deposition was increased after transfection with si-Sfrp1. Interestingly, miR-27a inhibitor attenuated the effects of si-Sfrp1. We concluded that miR-27a down-regulated Sfrp1 and activated Wnt/β-catenin signalling to promote renal fibrosis.

New insight into the role of isorhamnetin as a regulator of insulin signaling pathway in type 2 diabetes mellitus rat model: Molecular and computational approach

We intended to examine the molecular mechanism of action of isorhamnetin (IHN) to regulate the pathway of insulin signaling. Molecular analysis, immunofluorescence, and histopathological examination were used to assess the anti-hyperglycemic and insulin resistance lowering effects of IHN in streptozotocin /high fat diet-induced type 2 diabetes using Wistar rats. At the microscopic level, treatment with IHN resulted in the restoration of myofibrils uniform arrangement and adipose tissue normal architecture. At the molecular level, treatment with IHN at three different doses showed a significant decrease in m-TOR, IGF1-R & LncRNA-RP11-773H22.4. expression and it up-regulated the expression of AKT2 mRNA, miR-1, and miR-3163 in both skeletal muscle and adipose tissue. At the protein level, IHN treated group showed a discrete spread with a moderate faint expression of m-TOR in skeletal muscles as well as adipose tissues. We concluded that IHN could be used in the in ameliorating insulin resistance associated with type 2 diabetes mellitus.

Diagnostic value of dysregulated microribonucleic acids in the placenta and circulating exosomes in gestational diabetes mellitus

Aims/Introduction

Differentially expressed microribonucleic acids (miRNAs) in the placenta and circulating exosomes are of diagnostic value for gestational diabetes mellitus (GDM). In a cross‐sectional study, we identified miRNAs expressed both in the placenta and circulating exosomes of pregnant women with GDM, and estimated their diagnostic value.

Materials and Methods

Next‐generation sequencing was used to identify miRNAs in the placenta that were differentially expressed between GDM and normal glucose tolerance pregnancies. Quantitative polymerase chain reaction was used to validate the identified targets. Western blot and transmission electron microscopy were used to validate exosomes. Univariate logistic regression analysis was used to establish diagnostic models based on miRNAs expression, and the diagnostic value was estimated using the receiver operator characteristic curve.

Results

We identified 157 dysregulated miRNAs in the placental tissue obtained from GDM pregnancies. Of these, miRNA‐125b was downregulated (P < 0.001), whereas miRNA‐144 was upregulated (P < 0.001). The patterns of these two miRNAs remained the same in circulating exosomes from GDM pregnancies (all P < 0.001). miRNA‐144 levels in the circulating exosomes negatively correlated with body mass index both before pregnancy (P = 0.018) and before delivery (P = 0.039), and positively correlated with blood glucose at 1 h, estimated using the oral glucose tolerance test (P = 0.044). The area under curve for the established diagnostic model was 0.898, which was higher than blood glucose levels at 0 h.

Conclusions

These findings suggest that miRNA‐125b and miRNA‐144 are consistently dysregulated in circulating exosomes and the placenta from GDM pregnancies, and are of excellent diagnostic value for GDM.

Baseline Assessment of Circulating MicroRNAs Near Diagnosis of Type 1 Diabetes Predicts Future Stimulated Insulin Secretion

Type 1 diabetes is an autoimmune disease resulting in severely impaired insulin secretion. We investigated whether circulating microRNAs (miRNAs) are associated with residual insulin secretion at diagnosis and predict the severity of its future decline. We studied 53 newly diagnosed subjects enrolled in placebo groups of TrialNet clinical trials. We measured serum levels of 2,083 miRNAs, using RNA sequencing technology, in fasting samples from the baseline visit (<100 days from diagnosis), during which residual insulin secretion was measured with a mixed meal tolerance test (MMTT). Area under the curve (AUC) C-peptide and peak C-peptide were stratified by quartiles of expression of 31 miRNAs. After adjustment for baseline C-peptide, age, BMI, and sex, baseline levels of miR-3187-3p, miR-4302, and the miRNA combination of miR-3187-3p/miR-103a-3p predicted differences in MMTT C-peptide AUC/peak levels at the 12-month visit; the combination miR-3187-3p/miR-4723-5p predicted proportions of subjects above/below the 200 pmol/L clinical trial eligibility threshold at the 12-month visit. Thus, miRNA assessment at baseline identifies associations with C-peptide and stratifies subjects for future severity of C-peptide loss after 1 year. We suggest that miRNAs may be useful in predicting future C-peptide decline for improved subject stratification in clinical trials.

Epigenetic modulation of autophagy genes linked to diabetic nephropathy by administration of isorhamnetin in Type 2 diabetes mellitus rats

Aim: To assess isorhamnetin efficacy for diabetic kidney disease in a Type 2 diabetes mellitus rat model, through investigating its effect at the epigenetic, mRNA and protein levels. Materials & methods: Type 2 diabetes mellitus was induced in rats by streptozotocin and high-fat diet. Rats were treated with isorhamnetin (50 mg/kg/d) for 4 or 8 weeks. Fasting blood glucose, renal and lipid profiles were evaluated. Renal tissues were examined by light and electron microscopy. Autophagy genes (FYCO1, ULK, TECPR1 and WIPI2) and miR-15b, miR-34a and miR-633 were assessed by qRT-PCR, and LC3A/B by immunoblotting. Results: Isorhamnetin improved fasting blood glucose, renal and lipid profiles with increased autophagosomes in renal tissues. It suppressed miRNA regulation of autophagy genes. Conclusion: We propose a molecular mechanism for the isorhamnetin renoprotective effect by modulation of autophagy epigenetic regulators.

The Landscape of microRNAs in βCell: Between Phenotype Maintenance and Protection

Diabetes mellitus is a group of heterogeneous metabolic disorders characterized by chronic hyperglycaemia mainly due to pancreatic β cell death and/or dysfunction, caused by several types of stress such as glucotoxicity, lipotoxicity and inflammation. Different patho-physiological mechanisms driving β cell response to these stresses are tightly regulated by microRNAs (miRNAs), a class of negative regulators of gene expression, involved in pathogenic mechanisms occurring in diabetes and in its complications. In this review, we aim to shed light on the most important miRNAs regulating the maintenance and the robustness of β cell identity, as well as on those miRNAs involved in the pathogenesis of the two main forms of diabetes mellitus, i.e., type 1 and type 2 diabetes. Additionally, we acknowledge that the understanding of miRNAs-regulated molecular mechanisms is fundamental in order to develop specific and effective strategies based on miRNAs as therapeutic targets, employing innovative molecules.

Integration of single-cell datasets reveals novel transcriptomic signatures of β-cells in human type 2 diabetes

Pancreatic islet β-cell failure is key to the onset and progression of type 2 diabetes (T2D). The advent of single-cell RNA sequencing (scRNA-seq) has opened the possibility to determine transcriptional signatures specifically relevant for T2D at the β-cell level. Yet, applications of this technique have been underwhelming, as three independent studies failed to show shared differentially expressed genes in T2D β-cells. We performed an integrative analysis of the available datasets from these studies to overcome confounding sources of variability and better highlight common T2D β-cell transcriptomic signatures. After removing low-quality transcriptomes, we retained 3046 single cells expressing 27 931 genes. Cells were integrated to attenuate dataset-specific biases, and clustered into cell type groups. In T2D β-cells (n = 801), we found 210 upregulated and 16 downregulated genes, identifying key pathways for T2D pathogenesis, including defective insulin secretion, SREBP signaling and oxidative stress. We also compared these results with previous data of human T2D β-cells from laser capture microdissection and diabetic rat islets, revealing shared β-cell genes. Overall, the present study encourages the pursuit of single β-cell RNA-seq analysis, preventing presently identified sources of variability, to identify transcriptomic changes associated with human T2D and underscores specific traits of dysfunctional β-cells across different models and techniques.

The Potential Role of Zinc Oxide Nanoparticles in MicroRNAs Dysregulation in STZ-Induced Type 2 Diabetes in Rats

Diabetes mellitus (DM) is a group of metabolic disorders that are characterized by a loss of glucose homeostasis and insufficiency in production or action of insulin. Development of newly antidiabetic molecules using a variety of organic compounds and biomolecules has been in practice for a long time. Recently, nanomaterials are also being used in antidiabetic studies for their unique properties. In this context, zinc nanoparticles have drawn attention due to the relationship between diabetes and imbalance of zinc homeostasis. Few studies have attempted to investigate the effect of zinc oxide nanoparticles (ZON) in microRNA dysregulations in diabetes. To evaluate the therapeutic effect of ZON on streptozotocin (STZ)-induced diabetic rats as well as its role in microRNA dysregulations. Diabetes was induced in rats by 60 mg/kg body weight (bwt) of STZ and then treated with ZON (5 mg/kg bwt) for 15 consecutive days. The levels of glucose, insulin, oxidative stress markers, and microRNAs expression were measured in liver and pancreas tissues. Intraperitoneal injection of 60 mg/kg bwt of STZ to Wistar rats caused significant decreases in the body weight and Zn contents of pancreas, liver, and kidney. Also, STZ injection increased the blood glucose level and oxidative stress (lipid peroxidation (LPO) and nitric oxide (NO). Meanwhile, STZ decreased blood insulin and pancreatic anti-oxidants. STZ also resulted in β cell dysfunction and destruction and altered the expression of certain pancreatic and liver microRNAs. ZON treatment for 15 days, at a dose of 5 mg/kg bwt resulted in marked improvements in the blood insulin, glucose tolerance, and structure and function of the pancreatic β cells. Furthermore, ZON administration reduced LPO and NO, and increased the levels of enzymatic and non-enzymatic anti-oxidants in STZ-induced diabetic rats. It was found also that ZON specifically regulated the expression of pancreatic and liver microRNAs that involved in diabetes development. The obtained results revealed that ZON is a promising antidiabetic agent. The antidiabetic effect of ZON was partially mediated by restoring the oxidants/antioxidants balance and by modulating the alerted microRNAs.

Genetic deletion of miR-204 improves glycemic control despite obesity in db/db mice

MicroRNAs (miRs) are small non-coding RNAs that regulate the target gene expression. A change in miR profile in the pancreatic islets during diabetes is known, and multiple studies have demonstrated that miRs influence the pancreatic β-cell function. The miR-204 is highly expressed in the β-cells and reported to regulate insulin synthesis. Here we investigated whether the absence of miR-204 rescues the impaired glycemic control and obesity in the genetically diabetic (db/db) mice. We found that the db/db mice overexpressed miR-204 in the islets. The db/db mice lacking miR-204 (db/db-204^-/-) initially develops hyperglycemia and obesity like the control (db/db) mice but later displayed a gradual improvement in glycemic control despite remaining obese. The db/db-204^-/- mice had a lower fasting blood glucose and higher serum insulin level compared to the db/db mice. A homeostatic model assessment (HOMA) suggests the improvement of β-cell function contributes to the improvement in glycemic control in db/db-204^-/- mice. Next, we examined the cellular proliferation and endoplasmic reticulum (ER) stress and found an increased frequency of proliferating cells (PCNA + ve) and a decreased CHOP expression in the islets of db/db-204^-/- mice. Next, we determined the effect of systemic miR-204 inhibition in improving glycemic control in the high-fat diet (HFD)-fed insulin-resistant mice. MiR-204 inhibition for 6 weeks improved the HFD-triggered impairment in glucose disposal. In conclusion, the absence of miR-204 improves β-cell proliferation, decreases islet ER stress, and improves glycemic control with limited change in body weight in obese mice.

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

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Role of miRNAs in the pathogenesis of T2DM, insulin secretion, insulin resistance, and β cell dysfunction: the story so far

Diabetes, the most common endocrine disorder, also known as a silent killer disease, is characterized by uncontrolled hyperglycemia. According to the International Diabetes Federation, there were 451 million people with diabetes mellitus worldwide in 2017. It is a multifactorial syndrome caused by genetic as well as environmental factors. Noncoding RNAs, especially the miRNAs, play a significant role in the development as well as the progression of the disease. This is on account of insulin resistance or defects in β cell function. Various miRNAs including miR-7, miR-9, miR-16, miR-27, miR-24, miR-29, miR-124a, miR-135, miR-130a, miR-144, miR-181a, and miR-375 and many more have been associated with insulin resistance and other pathogenic conditions leading to the development of the disease. These miRNAs play significant roles in various pathways underlying insulin resistance such as PI3K, AKT/GSK, and mTOR. The main target genes of these miRNAs are FOXO1, FOXA2, STAT3, and PTEN. The miRNAs carry out important functions in insulin target tissues like the adipose tissue, liver, and muscle. MiRNAs miR-9, miR-375, and miR-124a, are also associated with the secretion of insulin from pancreatic cells. There is an interplay between the miRNAs and pancreatic cell growth, especially the miRNAs affecting development and proliferation of these cells. Most of the miRNAs target more than one gene which not only justifies their use as biomarkers but also their therapeutic potential. The current review has been compiled with an aim to discuss the role of various miRNAs involved in various pathogenic mechanisms including insulin resistance, insulin secretion, and the β cell dysfunction.

Plasma microRNAs biomarkers in mild cognitive impairment among patients with type 2 diabetes mellitus

Objectives

To assess the potential value of some miRNAs as diagnostic biomarkers for mild cognitive impairment (MCI) among patients with type2 diabetes mellitus (T2DM) and to identify other risk factors for MCI among them.

Methods

This study enrolled 163 adults with T2DM using face to face interview. Cognitive function with its domains was assessed using Adenbrooke’s Cognitive Examination III (ACE III). Lipid profile, glycated hemoglobin, and miR-128, miR-132, miR- 874, miR-134, miR-323, and miR-382 expressions, using quantitative real-time PCR, were assessed.

Results

MCI was detected among 59/163 (36.2%) patients with T2DM. Plasma expression of miR-132 was significantly higher in T2DM patients with MCI compared to those without MCI and to normal cognitive healthy individuals (median = 2, 1.1 and 1.2 respectively, P < 0.05. Logistic regression analysis showed that higher miR-132 expression with adjusted odds ratio (AOR): 1.2 (95% CI 1.0–1.3), female gender (AOR:2.1; 95%CI 1.0–4.3), education below postgraduate (secondary and university education with AOR: 9.5 & 19.4 respectively) were the significant predicting factors for MCI among T2DM patients. Using ROC curve, miR-132 was the only assayed miRNA that significantly differentiates T2DM patients with MCI from those with normal cognition with 72.3% sensitivity, 56.2% specificity, and 63.8% accuracy (P < 0.05). Other studied miRNAs showed lower sensitivity and specificity for detecting MCI among studied T2DM participants.

Conclusion

MCI affects nearly one-third of adult patients with T2DM. A significantly over expression of miR-132 was detected among T2DM with MCI compared to those with normal cognition.

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.

Microbiota-governed microRNA-204 impairs endothelial function and blood pressure decline during inactivity in db/db mice

An impaired decline in blood pressure at rest is typical in people with diabetes, reflects endothelial dysfunction, and increases the risk of end-organ damage. Here we report that microRNA-204 (miR-204) promotes endothelial dysfunction and impairment in blood pressure decline during inactivity. We show that db/db mice overexpress miR-204 in the aorta, and its absence rescues endothelial dysfunction and impaired blood pressure decline during inactivity despite obesity. The vascular miR-204 is sensitive to microbiota, and microbial suppression reversibly decreases aortic miR-204 and improves endothelial function, while the endothelial function of mice lacking miR-204 remained indifferent to the microbial alterations. We also show that the circulating miR-122 regulates vascular miR-204 as miR-122 inhibition decreases miR-204 in endothelial cells and aorta. This study establishes that miR-204 impairs endothelial function, promotes impairment in blood pressure decline during rest, and opens avenues for miR-204 inhibition strategies against vascular dysfunction.

MiR-542-3p drives renal fibrosis by targeting AGO1 in vivo and in vitro

AIMS

Renal fibrosis is the typical manifestation of progressive kidney disease and causes a severe threat to human health. Surging evidence has illustrated that miRNA plays a core role in the genesis and development of kidney fibrosis. MiR-542-3p has been testified to function as a facilitator in hepatic stellate cell activation and fibrosis. The purpose of study is to investigate the potential of miR-542-3p in renal tubulointerstitial fibrosis.

MATERIALS AND METHODS

In this study, to establish renal fibrosis model in vivo and in vitro, we first conducted unilateral ureteral obstruction (UUO) on rats and high glucose (HG) treatment on the HK-2 cells. Histological and western blot analyses were utilized for assessment of renal fibrosis model. Luciferase reporter assay was carried out to explore the regulatory mechanism underlying miR-542-3p in renal fibrosis.

KEY FINDINGS

MiR-542-3p was found to be highly expressed in renal fibrosis. Functional experiments revealed that overexpression of miR-542-3p accelerated the deterioration of kidney fibrosis and inhibition of miR-542-3p led to the opposite result. Through the aid of bioinformatics tool, the speculated miR-542-3p binding sites were uncovered in the 3'UTR of argonaute RISC component 1 (AGO1). Mechanism study elucidated that AGO1 was a direct target of miR-542-3p. Lastly, our findings suggested that miR-542-3p played a promoting role in renal fibrosis via repression of AGO1.

SIGNIFICANCE

We justified that miR-542-3p induced kidney fibrogenesis both in vivo and in vitro through targeting AGO1, unveiling that miR-542-3p might be a promising option for the treatment of patients with renal fibrosis.

MicroRNA Networks in Pancreatic Islet Cells: Normal Function and Type 2 Diabetes

Impaired insulin secretion from the pancreatic β-cells is central in the pathogenesis of type 2 diabetes (T2D), and microRNAs (miRNAs) are fundamental regulatory factors in this process. Differential expression of miRNAs contributes to β-cell adaptation to compensate for increased insulin resistance, but deregulation of miRNA expression can also directly cause β-cell impairment during the development of T2D. miRNAs are small noncoding RNAs that posttranscriptionally reduce gene expression through translational inhibition or mRNA destabilization. The nature of miRNA targeting implies the presence of complex and large miRNA-mRNA regulatory networks in every cell, including the insulin-secreting β-cell. Here we exemplify one such network using our own data on differential miRNA expression in the islets of T2D Goto-Kakizaki rat model. Several biological processes are influenced by multiple miRNAs in the β-cell, but so far most studies have focused on dissecting the mechanism of action of individual miRNAs. In this Perspective we present key islet miRNA families involved in T2D pathogenesis including miR-200, miR-7, miR-184, miR-212/miR-132, and miR-130a/b/miR-152. Finally, we highlight four challenges and opportunities within islet miRNA research, ending with a discussion on how miRNAs can be utilized as therapeutic targets contributing to personalized T2D treatment strategies.

β-Cell Stress Shapes CTL Immune Recognition of Preproinsulin Signal Peptide by Posttranscriptional Regulation of Endoplasmic Reticulum Aminopeptidase 1

The signal peptide of preproinsulin is a major source for HLA class I autoantigen epitopes implicated in CD8 T cell (CTL)-mediated β-cell destruction in type 1 diabetes (T1D). Among them, the 10-mer epitope located at the C-terminal end of the signal peptide was found to be the most prevalent in patients with recent-onset T1D. While the combined action of signal peptide peptidase and endoplasmic reticulum (ER) aminopeptidase 1 (ERAP1) is required for processing of the signal peptide, the mechanisms controlling signal peptide trimming and the contribution of the T1D inflammatory milieu on these mechanisms are unknown. Here, we show in human β-cells that ER stress regulates ERAP1 gene expression at posttranscriptional level via the IRE1α/miR-17-5p axis and demonstrate that inhibition of the IRE1α activity impairs processing of preproinsulin signal peptide antigen and its recognition by specific autoreactive CTLs during inflammation. These results underscore the impact of ER stress in the increased visibility of β-cells to the immune system and position the IRE1α/miR-17 pathway as a central component in β-cell destruction processes and as a potential target for the treatment of autoimmune T1D.

Fine-tuning of microRNAs in Type 2 Diabetes Mellitus

Type 2 diabetes mellitus is a metabolic disease widely spread across industrialized countries. Sedentary lifestyle and unhealthy alimentary habits lead to obesity, boosting both glucose and fatty acid in the bloodstream and eventually, insulin resistance, pancreas inflammation and faulty insulin production or secretion, all of them very well-defined hallmarks of type 2 diabetes mellitus. miRNAs are small sequences of non-coding RNA that may regulate several processes within the cells, fine-tuning protein expression, with an unexpected and subtle precision and in time-frames ranging from minutes to days. Since the discovery of miRNA and their possible implication in pathologies, several groups aimed to find a relationship between type 2 diabetes mellitus and miRNAs. Here we discuss the pattern of expression of different miRNAs in cultured cells, animal models and diabetic patients. We summarize the role of the most important miRNAs involved in pancreas growth and development, insulin secretion and liver, skeletal muscle or adipocyte insulin resistance in the context of type 2 diabetes mellitus.

The Role of MicroRNAs in Diabetes-Related Oxidative Stress

Cellular stress, combined with dysfunctional, inadequate mitochondrial phosphorylation, produces an excessive amount of reactive oxygen species (ROS) and an increased level of ROS in cells, which leads to oxidation and subsequent cellular damage. Because of its cell damaging action, an association between anomalous ROS production and disease such as Type 1 (T1D) and Type 2 (T2D) diabetes, as well as their complications, has been well established. However, there is a lack of understanding about genome-driven responses to ROS-mediated cellular stress. Over the last decade, multiple studies have suggested a link between oxidative stress and microRNAs (miRNAs). The miRNAs are small non-coding RNAs that mostly suppress expression of the target gene by interaction with its 3'untranslated region (3'UTR). In this paper, we review the recent progress in the field, focusing on the association between miRNAs and oxidative stress during the progression of diabetes.

Serum miR-204 is an early biomarker of type 1 diabetes-associated pancreatic beta-cell loss

Pancreatic beta-cell death is a major factor in the pathogenesis of type 1 diabetes (T1D), but straightforward methods to measure beta-cell loss in humans are lacking, underlining the need for novel biomarkers. Using studies in INS-1 cells, human islets, diabetic mice, and serum samples of subjects with T1D at different stages, we have identified serum miR-204 as an early biomarker of T1D-associated beta-cell loss in humans. MiR-204 is a highly enriched microRNA in human beta-cells, and we found that it is released from dying beta-cells and detectable in human serum. We further discovered that serum miR-204 was elevated in children and adults with T1D and in autoantibody-positive at-risk subjects but not in type 2 diabetes or other autoimmune diseases and was inversely correlated with remaining beta-cell function in recent-onset T1D. Thus, serum miR-204 may provide a much needed novel approach to assess early T1D-associated human beta-cell loss even before onset of overt disease.

Differential expression and release of exosomal miRNAs by human islets under inflammatory and hypoxic stress

AIMS/HYPOTHESIS

Pancreatic islets produce non-coding microRNAs (miRNAs) that regulate islet cell function and survival. Our earlier investigations revealed that human islets undergo significant damage due to various types of stresses following transplantation and release miRNAs. Here, we sought to identify and validate exosomal miRNAs (exo-miRNAs) produced by human islets under conditions of cellular stress, preceding loss of cell function and death. We also aimed to identify islet stress signalling pathways targeted by exo-miRNAs to elucidate potential regulatory roles in islet cell stress.

METHODS

Human islets were subjected to proinflammatory cytokine and hypoxic cell stress and miRNA from exosomes was isolated for RNA sequencing and analysis. Stress-induced exo-miRNAs were evaluated for kinetics of expression and release by intact islets for up to 48 h exposure to cytokines and hypoxia. A subset of stress-induced exo-miRNAs were assessed for recovery and detection as biomarkers of islet cell stress in a diabetic nude mouse xenotransplant model and in patients undergoing total pancreatectomy with islet auto-transplantation (TPIAT). Genes and signalling pathways targeted by stress-induced exo-miRNAs were identified by Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis and direct interactions of miRNAs with downstream signalling targets were validated in human islet cells using the miRNA Tests for Read Analysis and Prediction (MirTrap) system.

RESULTS

Global exo-miRNA sequencing revealed that 879 miRNA species were released from human islets and 190 islet exo-miRNAs were differentially expressed in response to proinflammatory cytokines, hypoxia or both. Release of exo-miRNAs hsa-miR-29b-3p and hsa-miR-216a-5p was detected within 6 h of exposure to cytokines and hypoxia. The remaining subset of stress-induced exo-miRNAs, including hsa-miR-148a-3p and islet cell damage marker hsa-miR-375, showed delayed release at 24-48 h, correlating with apoptosis and cell death. Stress and damage exo-miRNAs were significantly elevated in the circulation in human-to-mouse xenotransplant models and in human transplant recipients. Elevated blood exo-miRNAs negatively correlated with post-transplant islet function based on comparisons of stress and damage exo-miRNA indices with Secretory Unit of Islet Transplant Objects (SUITO) indices. KEGG analysis and further validation of exo-miRNA targets by MirTrap analysis revealed significant enrichment of islet mRNAs involved in phosphoinositide 3-kinase/Akt and mitogen-activated protein kinase signalling pathways.

CONCLUSIONS/INTERPRETATION

The study identifies exo-miRNAs differentially expressed and released by islets in response to damage and stress. These exo-miRNAs could serve as potential biomarkers for assessing islet damage and predicting outcomes in islet transplantation. Notably, exo-miRNAs 29b-3p and 216a-5p could be detected in islets prior to damage-released miRNAs and indicators of cellular apoptosis and death. Thus, these stress-induced exo-miRNAs may have potential diagnostic value for detecting early islet stress prior to progressive loss of islet cell mass and function. Further investigations are warranted to investigate the utility of these exo-miRNAs as early indicators of islet cell stress during prediabetic conditions.

Increased Expression of Circulating microRNA 101-3p in Type 1 Diabetes Patients: New Insights Into miRNA-Regulated Pathophysiological Pathways for Type 1 Diabetes

MicroRNAs (miRs) are master regulators of post-transcriptional gene expression, and they are often dysregulated in individuals suffering from diabetes. We investigated the roles of miR-101-3p and miR-204-5p, both of which negatively regulate insulin secretion and cell survival and are highly expressed in pancreatic β cells, in the context of type 1 diabetes (T1D) pathogenesis. Using quantitative real time PCR, we evaluated serum levels of miR-101-3p and miR-204-5p in four groups, including recent-onset T1D patients (T1D group; n = 50), individuals with normal glucose levels expressing one islet autoantibody (Ab) (single Ab group; n = 26) or multiple autoantibodies (multiple Ab group; n = 12), and healthy controls (control group; n = 43). An in silico analysis was performed to identify potential target genes of these miRNAs and to delineate enriched pathways. The relative expression of serum miR-101-3p was approximately three times higher in the multiple Ab and T1D groups than that in the single Ab and control groups (p < 0.0001). When considering all groups together, miR-101-3p expression was positively correlated with the level of islet autoantibodies GADA (r = 0.267; p = 0.0027) and IA-2A (r = 0.291; p = 0.001), and the expression of the miRNA was not correlated with levels of ZnT8A (r = 0.125; p = 0.183). miR-101-3p expression did not correlate with HbA1c (r = 0.178; p = 0.052) or glucose levels (r = 0.177; p = 0.051). No significant differences were observed in miR-204-5p expression among the analyzed groups. Computational analysis of the miR-101-3p target gene pathways indicated a potential activation of the HGF/c-Met, Ephrin receptor, and STAT3 signaling pathways. Our study demonstrated that the circulating levels of miR-101-3p are higher in T1D patients and in individuals with normal glucose levels, testing positive for multiple autoantibodies, indicating that miR-101-3p precedes loss of glucose homeostasis. The pathogenic role of miR-101-3p in T1D may involve multiple molecular pathways.

MicroRNA-125b-5p improves pancreatic β-cell function through inhibiting JNK signaling pathway by targeting DACT1 in mice with type 2 diabetes mellitus

Type 2 diabetes mellitus (T2DM) is a progressive disease, accompanied by increased insulin resistance and deteriorating β-cell function. Previous studies have revealed that microRNA (miRNA) plays a crucial role in the treatment of T2DM. Hence, we aim to investigate the role of microRNA-125b-5p (miR-125b-5p) in pancreatic β-cell function and insulin sensitivity of mice with T2DM with the involvement of Dishevelled antagonist Dapper1 (DACT1) and the c-Jun NH2-terminal kinases (JNK) signaling pathway. Firstly, a mouse model of T2DM was established by administering a high-fat diet plus low dosage of streptozotocin, and function of pancreatic β-cell and insulin sensitivity in the normal and T2DM mice were detected. Then, the pancreatic β-cells were collected from pancreatic islet tissues and treated with different mimics, inhibitors and siRNAs. After that, the relationship among miR-125b-5p, DACT1, and the JNK signaling-related factors in T2DM mice was determined. Finally, cell proliferation and apoptosis were determined. Mice with T2DM had lower pancreatic β-cell function and insulin sensitivity, as well as diminished expression of miR-125b-5p but enhanced expressions of DACT1, JNK and c-Jun. miR-125b-5p inhibited DACT1 expression and the activation of the JNK signaling pathway, as well as restrained cell proliferation and promoted cell apoptosis. The current results suggest that up-regulated miR-125b-5p promotes insulin sensitivity and enhances pancreatic β-cell function through inhibiting the JNK signaling pathway by negatively mediating DACT1.

miR-132-3p is a positive regulator of alpha-cell mass and is downregulated in obese hyperglycemic mice

Objective

Diabetes is a complex disease implicating several organs and cell types. Within the islets, dysregulation occurs in both alpha- and beta-cells, leading to defects of insulin secretion and increased glucagon secretion. Dysregulation of alpha-cells is associated with transcriptome changes. We hypothesized that microRNAs (miRNAs) which are negative regulators of mRNA stability and translation could be involved in alpha-cell alterations or adaptations during type 2 diabetes.

Methods

miRNA microarray analyses were performed on pure alpha- and beta-cells from high-fat diet fed obese hyperglycemic mice and low-fat diet fed controls. Then, the most regulated miRNA was overexpressed or inhibited in primary culture of mouse and human alpha-cells to determine its molecular and functional impact.

Results

16 miRNAs were significantly regulated in alpha-cells of obese hyperglycemic mice and 28 in beta-cells. miR-132-3p had the strongest regulation level in alpha-cells, where it was downregulated, while we observed an opposite upregulation in beta-cells. In vitro experiments showed that miR-132-3p, which is inversely regulated by somatostatin and cAMP, is a positive modulator of alpha-cell proliferation and implicated in their resistance to apoptosis. These effects are associated with the regulation of a series of genes, including proliferation and stress markers Mki67 and Bbc3 in mouse and human alpha-cells, potentially involved in miR-132-3p functions.

Conclusions

Downregulation of miR-132-3p in alpha-cells of obese diabetic mice may constitute a compensatory mechanism contributing to keep glucagon-producing cell number constant in diabetes.

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Alpha- and beta-cells present specific microRNA signatures.

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16 microRNAs are significantly regulated in alpha-cells of obese hyperglycemic mice.

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miR-132-3p is downregulated in alpha-cells of obese hyperglycemic mice.

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miR-132-3p stimulates alpha-cells proliferation and resistance to apoptosis.

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miR-132-3p is regulated by somatostatin in alpha-cells.

Generation of Human Stem Cell-Derived Pancreatic Organoids (POs) for Regenerative Medicine

Insulin-dependent diabetes mellitus or type 1 diabetes mellitus (T1DM) is an auto-immune condition characterized by the loss of pancreatic β-cells. The curative approach for highly selected patients is the pancreas or the pancreatic islet transplantation. Nevertheless, these options are limited by a growing shortage of donor organs and by the requirement of immunosuppression.Xenotransplantation of porcine islets has been extensively investigated. Nevertheless, the strong xenoimmunity and the risk of transmission of porcine endogenous retroviruses, have limited their application in clinic. Generation of β-like cells from stem cells is one of the most promising strategies in regenerative medicine. Embryonic, and more recently, adult stem cells are currently the most promising cell sources exploited to generate functional β-cells in vitro. A number of studies demonstrated that stem cells could generate functional pancreatic organoids (POs), able to restore normoglycemia when implanted in different preclinical diabetic models. Nevertheless, a gradual loss of function and cell dead are commonly detected when POs are transplanted in immunocompetent animals. So far, the main issue to be solved is the post-transplanted islet loss, due to the host immune attack. To avoid this hurdle, nanotechnology has provided a number of polymers currently under investigation for islet micro and macro-encapsulation. These new approaches, besides conferring PO immune protection, are able to supply oxygen and nutrients and to preserve PO morphology and long-term viability.Herein, we summarize the current knowledge on bioengineered POs and the stem cell differentiation platforms. We also discuss the in vitro strategies used to generate functional POs, and the protocols currently used to confer immune-protection against the host immune attack (micro- and macro-encapsulation). In addition, the most relevant ongoing clinical trials, and the most relevant hurdles met to move towards clinical application are revised.

Non-Coding RNA in Pancreas and β-Cell Development

In this review, we provide an overview of the current knowledge on the role of different classes of non-coding RNAs for islet and β-cell development, maturation and function. MicroRNAs (miRNAs), a prominent class of small RNAs, have been investigated for more than two decades and patterns of the roles of different miRNAs in pancreatic fetal development, islet and β-cell maturation and function are now emerging. Specific miRNAs are dynamically regulated throughout the period of pancreas development, during islet and β-cell differentiation as well as in the perinatal period, where a burst of β-cell replication takes place. The role of long non-coding RNAs (lncRNA) in islet and β-cells is less investigated than for miRNAs, but knowledge is increasing rapidly. The advent of ultra-deep RNA sequencing has enabled the identification of highly islet- or β-cell-selective lncRNA transcripts expressed at low levels. Their roles in islet cells are currently only characterized for a few of these lncRNAs, and these are often associated with β-cell super-enhancers and regulate neighboring gene activity. Moreover, ncRNAs present in imprinted regions are involved in pancreas development and β-cell function. Altogether, these observations support significant and important actions of ncRNAs in β-cell development and function.

Cell Type-Selective Expression of Circular RNAs in Human Pancreatic Islets

Understanding distinct cell-type specific gene expression in human pancreatic islets is important for developing islet regeneration strategies and therapies to improve β-cell function in type 1 diabetes (T1D). While numerous transcriptome-wide studies on human islet cell-types have focused on protein-coding genes, the non-coding repertoire, such as long non-coding RNA, including circular RNAs, remains mostly unexplored. Here, we explored transcriptional landscape of human α-, β-, and exocrine cells from published total RNA sequencing (RNA-seq) datasets to identify circular RNAs (circRNAs). Our analysis revealed that circRNAs are highly abundant in both α- and β-cells. We identified 10,830 high-confidence circRNAs expressed in human α-, β-, and exocrine cells. The most highly expressed candidates were MAN1A2, RMST, and HIPK3 across the three cell-types. Alternate circular isoforms were observed for circRNAs in the three cell-types, indicative of potential distinct functions. Highly selective α- and β-cell circRNAs were identified, which is suggestive of their potential role in regulating β-cell function.

Mapping the Pax6 3' untranslated region microRNA regulatory landscape

BACKGROUND

PAX6 is a homeodomain transcription factor that acts in a highly dosage-sensitive manner to regulate the development and function of the eyes, nose, central nervous system, gut, and endocrine pancreas. Several individual microRNAs (miRNA) have been implicated in regulating PAX6 in different cellular contexts, but a more general view of how they contribute to the fine-tuning and homeostasis of PAX6 is poorly understood.

RESULTS

Here, a comprehensive analysis of the Pax6 3' untranslated region was performed to map potential miRNA recognition elements and served as a backdrop for miRNA expression profiling experiments to identify potential cell/tissue-specific miRNA codes. Pax6 3'UTR pull-down studies identified a cohort of miRNA interactors in pancreatic αTC1-6 cells that, based on the spacing of their recognition sites in the Pax6 3'UTR, revealed 3 clusters where cooperative miRNA regulation may occur. Some of these interacting miRNAs have been implicated in α cell function but have not previously been linked to Pax6 function and may therefore represent novel PAX6 regulators.

CONCLUSIONS

These findings reveal a regulatory landscape upon which miRNAs may participate in the developmental control, fine-tuning and/or homeostasis of PAX6 levels.