Saturated fatty acids-induced miR-424-5p aggravates insulin resistance via targeting insulin receptor in hepatocytes

Dietary modulation of microRNAs in insulin resistance and type 2 diabetes

The prevalence of type 2 diabetes is increasing worldwide. Various molecular mechanisms have been proposed to interfere with the insulin signaling pathway. Recent advances in proteomics and genomics indicate that one such mechanism involves the post-transcriptional regulation of insulin signaling by microRNA (miRNA). These noncoding RNAs typically induce messenger RNA (mRNA) degradation or translational repression by interacting with the 3' untranslated region (3'UTR) of target mRNA. Dietary components and patterns, which can either enhance or impair the insulin signaling pathway, have been found to regulate miRNA expression in both in vitro and in vivo studies. This review provides an overview of the current knowledge of how dietary components influence the expression of miRNAs related to the control of the insulin signaling pathway and discusses the potential application of these findings in precision nutrition.

Palmitic acid promotes miRNA release from adipocyte exosomes by activating NF-κB/ER stress

OBJECTIVE

The release of adipose tissue-derived miRNAs is increased under conditions of obesity, but the exact molecular mechanisms involved have not been elucidated. This study investigated whether obesity-induced increases in palmitic acid (PA) content could activate the NF-κB/endoplasmic reticulum stress (ER stress) pathway and promote the expression and release of exosomal miRNAs in adipocytes.

METHODS

Abdominal adipose tissue and serum samples were collected from normal weight individuals and people with obesity to clarify the correlation of serum PA content with NF-κB/ER stress and the release of exosomal miRNAs. NF-κB and ER stress were blocked in obese mice and in vitro cultured adipocytes to demonstrate the molecular mechanisms by which PA promotes the release of exosomal miRNAs.The morphology, particle size and distribution of the exosomes were observed via transmission electron microscopy and NTA.

RESULTS

Accompanied by increased serum PA levels, the NF-κB/ER stress pathway was activated in the adipose tissue of people with obesity and in high-fat diet (HFD)-induced obese mice; moreover, the levels of miRNAs in both adipose tissue and serum were increased. P-p65 (Bay11-7082) and ER stress (TUDCA) blockers significantly reduced the levels of miRNAs in abdominal adipose tissue and serum, decreased blood glucose levels, and improved glucose tolerance and insulin sensitivity in obese mice. In 3T3-L1 adipocytes, high concentrations of PA activated the NF-κB/ER stress pathway and increased the expression and release of miRNAs in exosomes. P-p65 (Bay11-7082) and ER stress (TUDCA) blockers significantly reversed the increased release exosomal miRNAs cause by PA.

CONCLUSIONS

Obesity-induced increases in PA content increase the expression and release of miRNAs in adipocyte exosomes by activating the NF-κB/ER stress pathway.

Genetic interaction in the association between oxidative stress and diabetes in the Spanish population

Oxidative stress (OS) is a relevant intermediate mechanism involved in Type 2 Diabetes Mellitus (T2D) development. To date, the interaction between OS parameters and variations in genes related to T2D has not been analyzed.

AIMS

To study the genetic interaction of genes potentially related to OS levels (redox homeostasis, renin-angiotensin-aldosterone system, endoplasmic stress response, dyslipidemia, obesity and metal transport) and OS and T2D risk in a general population from Spain (the Hortega Study) in relation to the risk of suffering from T2D.

MATERIALS AND METHODS

One thousand five hundred and two adults from the University Hospital Rio Hortega area were studied and 900 single nucleotide polymorphisms (SNPs) from 272 candidate genes were analyzed.

RESULTS

There were no differences in OS levels between cases and controls. Some polymorphisms were associated with T2D and with OS levels. Significant interactions were observed between OS levels and two polymorphisms in relation to T2D presence: rs196904 (ERN1 gene) and rs2410718 (COX7C gene); and between OS levels and haplotypes of the genes: SP2, HFF1A, ILI8R1, EIF2AK2, TXNRD2, PPARA, NDUFS2 and ERN1.

CONCLUSIONS

Our results indicate that genetic variations of the studied genes are associated with OS levels and that their interaction with OS parameters may contribute to the risk of developing T2D in the Spanish general population. These data support the importance of analyzing the influence of OS levels and their interaction with genetic variations in order to establish their real impact in T2D risk. Further studies are required to identify the real relevance of interactions between genetic variations and OS levels and the mechanisms involved in them.

Biomarkers of obesity-mediated insulin resistance: focus on microRNAs

Obesity and metabolic syndromes are becoming increasingly prevalent worldwide. Insulin resistance (IR) is a common complication of obesity. However, IR occurrence varies across individuals with obesity and may involve epigenetic factors. To rationalize the allocation of healthcare resources, biomarkers for the early risk stratification of individuals with obesity should be identified. MicroRNAs (miRNAs) are closely associated with metabolic diseases and involved in epigenetic regulation. In this review, we have summarized the changes in miRNA expression in the peripheral circulation and tissues of patients and animals with obesity-associated IR over the last 5 years and identified several candidate biomarkers that predict obesity-related IR. There are areas for improvement in existing studies. First, more than the predictive validity of a single biomarker is required, and a biomarker panel needs to be formed. Second, miRNAs are often studied in isolation and do not form a network of signaling pathways. We believe that early biomarkers can help clinicians accurately predict individuals prone to obesity-related IR at an early stage. Epigenetic regulation may be one of the underlying causes of different clinical outcomes in individuals with obesity. Future studies should focus on objectively reflecting the differences in miRNA profile expression in individuals with obesity-related IR, which may help identify more reliable biomarkers. Understanding the metabolic pathways of these miRNAs can help design new metabolic risk prevention and management strategies, and support the development of drugs to treat obesity and metabolic disorders.

Novel insights regarding the role of noncoding RNAs in diabetes

Diabetes mellitus (DM) is a group of metabolic disorders defined by hyperglycemia induced by insulin resistance, inadequate insulin secretion, or excessive glucagon secretion. In 2021, the global prevalence of diabetes is anticipated to be 10.7% (537 million people). Noncoding RNAs (ncRNAs) appear to have an important role in the initiation and progression of DM, according to a growing body of research. The two major groups of ncRNAs implicated in diabetic disorders are miRNAs and long noncoding RNAs. miRNAs are single-stranded, short (17–25 nucleotides), ncRNAs that influence gene expression at the post-transcriptional level. Because DM has reached epidemic proportions worldwide, it appears that novel diagnostic and therapeutic strategies are required to identify and treat complications associated with these diseases efficiently. miRNAs are gaining attention as biomarkers for DM diagnosis and potential treatment due to their function in maintaining physiological homeostasis via gene expression regulation. In this review, we address the issue of the gradually expanding global prevalence of DM by presenting a complete and up-to-date synopsis of various regulatory miRNAs involved in these disorders. We hope this review will spark discussion about ncRNAs as prognostic biomarkers and therapeutic tools for DM. We examine and synthesize recent research that used novel, high-throughput technologies to uncover ncRNAs involved in DM, necessitating a systematic approach to examining and summarizing their roles and possible diagnostic and therapeutic uses.

Capturing the Kidney Transcriptome by Urinary Extracellular Vesicles-From Pre-Analytical Obstacles to Biomarker Research

Urinary extracellular vesicles (uEV) hold non-invasive RNA biomarkers for genitourinary tract diseases. However, missing knowledge about reference genes and effects of preanalytical choices hinder biomarker studies. We aimed to assess how preanalytical variables (urine storage temperature, isolation workflow) affect diabetic kidney disease (DKD)-linked miRNAs or kidney-linked miRNAs and mRNAs (kidney-RNAs) in uEV isolates and to discover stable reference mRNAs across diverse uEV datasets. We studied nine raw and normalized sequencing datasets including healthy controls and individuals with prostate cancer or type 1 diabetes with or without albuminuria. We focused on kidney-RNAs reviewing literature for DKD-linked miRNAs from kidney tissue, cell culture and uEV/urine experiments. RNAs were analyzed by expression heatmaps, hierarchical clustering and selecting stable mRNAs with normalized counts (>200) and minimal coefficient of variation. Kidney-RNAs were decreased after urine storage at -20 °C vs. -80 °C. Isolation workflows captured kidney-RNAs with different efficiencies. Ultracentrifugation captured DKD -linked miRNAs that separated healthy and diabetic macroalbuminuria groups. Eleven mRNAs were stably expressed across the datasets. Hence, pre-analytical choices had variable effects on kidney-RNAs-analyzing kidney-RNAs complemented global correlation, which could fade differences in some relevant RNAs. Replicating prior DKD-marker results and discovery of candidate reference mRNAs encourages further uEV biomarker studies.

Adverse effects and potential mechanisms of fluxapyroxad in Xenopus laevis on carbohydrate and lipid metabolism

Fungicides are one of significant contributing factors to the rapid decline of amphibian species worldwide. Fluxapyroxad (FLX), an effective and broad-spectrum succinate dehydrogenase inhibitor fungicide, has attracted major concerns due to its long-lasting in the environment. However, the potential toxicity of FLX in the development of amphibians remains mostly unknown. In this research, the potential toxic effects and mechanisms of FLX on Xenopus laevis were investigated. In the acute toxicity test, the 96 h median lethal concentration (LC₅₀) of FLX to X. laevis tadpoles was 1.645 mg/L. Based on the acute toxicity result, tadpoles at the stage 51 were exposed to 0, 0.00822, 0.0822, and 0.822 mg/L FLX during 21 days. Results demonstrated that FLX exposure led to an apparent delay in the growth and development of tadpoles and associated with severe liver injury. Additionally, FLX induced glycogen depletion and lipid accumulation in the liver of X. laevis. The biochemical analysis of plasma and liver indicated that FLX exposure could perturb liver glucose and lipid homeostasis by altering enzyme activity related to glycolysis, gluconeogenesis, fatty acid synthesis, and oxidation. Consistent with the biochemical result, FLX exposure altered the liver transcriptome profile, and the enrichment analysis of differential expression genes highlighted the adverse effects of FLX exposure on steroid biosynthesis, PPAR signaling pathway, glycolysis/gluconeogenesis, and fatty acid metabolism in the tadpole liver. Overall, our study was the first to reveal that sub-lethal concentrations of FLX could induce liver damage and produce obvious interference effects on carbohydrate and lipid metabolism of Xenopus, providing new insight into the potential chronic hazards of FLX for amphibians.

Therapeutic Potential of miRNAs for Type 2 Diabetes Mellitus: An Overview

MicroRNA(miRNA)s have been identified as an emerging class for therapeutic interventions mainly due to their extracellularly stable presence in humans and animals and their potential for horizontal transmission and action. However, treating Type 2 diabetes mellitus using this technology has yet been in a nascent state. MiRNAs play a significant role in the pathogenesis of Type 2 diabetes mellitus establishing the potential for utilizing miRNA-based therapeutic interventions to treat the disease. Recently, the administration of miRNA mimics or antimiRs in-vivo has resulted in positive modulation of glucose and lipid metabolism. Further, several cell culture-based interventions have suggested beta cell regeneration potential in miRNAs. Nevertheless, few such miRNA-based therapeutic approaches have reached the clinical phase. Therefore, future research contributions would identify the possibility of miRNA therapeutics for tackling T2DM. This article briefly reported recent developments on miRNA-based therapeutics for treating Type 2 Diabetes mellitus, associated implications, gaps, and recommendations for future studies.

Up-regulation of miR-133a-3p promotes ovary insulin resistance on granulosa cells of obese PCOS patients via inhibiting PI3K/AKT signaling

Background

MicroRNAs are a type of non-coding single-stranded RNA, which is involved in the regulation of ovary insulin resistance (IR). This study aims to explore the underlying mechanisms of miR-133a-3p regulating ovary IR in obese polycystic ovary syndrome (PCOS).

Methods

Granulosa cells (GCs) were extracted from follicular fluids of PCOS patients (obese PCOS group and non-obese PCOS group) and healthy women (control group). The expression of miR-133a-3p in GCs was detected by qRT-PCR. The targets and pathways of miR-133a-3p were predicted by bioinformatics analyses. The protein levels of PI3K, p-AKT, GLUT4, p-GSK-3β, and p-FOXO1 were measured by Western blotting.

Results

MiR-133a-3p was highly expressed in GCs from PCOS patients, especially in obese PCOS patients. The protein levels of PI3K and p-AKT was downregulated in GCs from PCOS patients. There were 11 target genes of miR-133a-3p enriching in PI3K/AKT signaling pathway. miR-133a-3p mimic downregulated the expression of PI3K, p-AKT, and GLUT4, and upregulated the protein levels of p-GSK-3β and p-FOXO1. miR-133a-3p inhibitor presented the opposite effect of miR-133a-3p mimic.

Conclusion

MiR-133a-3p promotes ovary IR on GCs of obese PCOS patients via inhibiting PI3K/AKT signaling pathway. This study lays a foundation for further research on the mechanism of ovary IR in obese PCOS patients.

Oligosaccharides derived from Lycium barbarum ameliorate glycolipid metabolism and modulate the gut microbiota community and the faecal metabolites in a type 2 diabetes mouse model: metabolomic bioinformatic analysis

Herein, we assessed the effects of Lycium barbarum oligosaccharides (LBO) on the intestinal microenvironment of a type 2 diabetes (T2D) mouse model through gut microbiome and metabolomics analysis. We set high (300 mg kg^-1), medium (200 mg kg^-1), and low (100 mg kg^-1) doses of LBO for intervention once a day for 4 weeks. The results showed that the intervention effect of the medium-dose group was the most significant. It reduced the symptoms of hyperglycemia, inflammation, insulin resistance, and lipid accumulation in the T2D mouse model. It restored the structure of damaged tissues and cells, such as the pancreas, liver, and kidneys. LBO increased the relative abundance of beneficial bacteria, such as Lactobacillus, Bacteroides, Prevotella, and Akkermansia, and maintained intestinal barrier integrity. The faecal metabolic map showed that the contents of glycogen amino acids, such as proline, serine, and leucine, increased. The contents of cholic, capric, and dodecanoic acid decreased. In summary, we may suggest that LBO can be used as a prebiotic for treating T2D.

MiR-183-5p Induced by Saturated Fatty Acids Hinders Insulin Signaling by Downregulating IRS-1 in Hepatocytes

Excessive saturated fatty acids (SFA) uptake is known to be a primary cause of obesity, a widely acknowledged risk factor of insulin resistance and type 2 diabetes. Although specific microRNAs (miRNAs) targeting insulin signaling intermediates are dysregulated by SFA, their effects on insulin signaling and sensitivity are largely unknown. Here, we investigated the role of SFA-induced miR-183-5p in the regulation of proximal insulin signaling molecules and the development of hepatic insulin resistance. HepG2 hepatocytes treated with palmitate and the livers of high-fat diet (HFD)-fed mice exhibited impaired insulin signaling resulting from dramatic reductions in the protein expressions of insulin receptor (INSR) and insulin receptor substrate-1 (IRS-1). Differential expression analysis showed the level of miR-183-5p, which tentatively targets the 3'UTR of IRS-1, was significantly elevated in palmitate-treated HepG2 hepatocytes and the livers of HFD-fed mice. Dual-luciferase analysis showed miR-183-5p bound directly to the 3'UTR of IRS-1 and reduced IRS-1 expression at the post-transcriptional stage. Moreover, transfection of HepG2 hepatocytes with miR-183-5p mimic significantly inhibited IRS-1 expression and hindered insulin signaling, consequently inhibiting insulin-stimulated glycogen synthesis. Collectively, this study reveals a novel mechanism whereby miR-183-5p induction by SFA impairs insulin signaling and suggests miR-183-5p plays a crucial role in the pathogenesis of hepatic insulin resistance in the background of obesity.

MicroRNAs in obesity, sarcopenia, and commonalities for sarcopenic obesity: a systematic review

Sarcopenic obesity is a distinct condition of sarcopenia in the context of obesity, with the cumulative health risks of both phenotypes. Differential expression of microRNAs (miRNAs) has been reported separately in people with obesity and sarcopenia and may play a role in the pathogenesis of sarcopenic obesity. However, this has not been explored to date. This study aimed to identify differentially expressed miRNAs reported in serum, plasma, and skeletal muscle of people with obesity and sarcopenia and whether there are any commonalities between these conditions. We performed a systematic review on Embase and MEDLINE (PROSPERO, CRD42020224486) for differentially expressed miRNAs (fold change >1.5 or P-value <0.05) in (i) sarcopenia or frailty and (ii) obesity or metabolic syndrome. The functions and targets of miRNAs commonly changed in both conditions, in the same direction, were searched using PubMed. Following deduplication, 247 obesity and 42 sarcopenia studies were identified for full-text screening. Screening identified 36 obesity and 6 sarcopenia studies for final inclusion. A total of 351 miRNAs were identified in obesity and 157 in sarcopenia. Fifty-five miRNAs were identified in both obesity and sarcopenia-by sample type, 48 were found in plasma and one each in serum and skeletal muscle. Twenty-four miRNAs were identified from 10 of the included studies as commonly changed in the same direction (22 in plasma and one each in serum and skeletal muscle) in obesity and sarcopenia. The majority of miRNA-validated targets identified in the literature search were members of the phosphoinositide 3-kinase/protein kinase B and transforming growth factor-β signalling pathways. The most common targets identified were insulin-like growth factor 1 (miR-424-5p, miR-483-3p, and miR-18b-5p) and members of the SMAD family (miR-483-3p, miR-92a-3p, and miR-424-5p). The majority of commonly changed miRNAs were involved in protein homeostasis, mitochondrial dynamics, determination of muscle fibre type, insulin resistance, and adipogenesis. Twenty-four miRNAs were identified as commonly dysregulated in obesity and sarcopenia with functions and targets implicated in the pathogenesis of sarcopenic obesity. Given the adverse health outcomes associated with sarcopenic obesity, understanding the pathogenesis underlying this phenotype has the potential to lead to effective screening, monitoring, or treatment strategies. Further research is now required to confirm whether these miRNAs are differentially expressed in older adults with sarcopenic obesity.

A Lard and Soybean Oil Mixture Alleviates Low-Fat-High-Carbohydrate Diet-Induced Nonalcoholic Fatty Liver Disease in Mice

Dietary habit is highly related to nonalcoholic fatty liver disease (NAFLD). Low-fat–high-carbohydrate (LFHC) diets could induce lean NAFLD in Asians. Previously, we found that a lard and soybean oil mixture reduced fat accumulation with a medium-fat diet; therefore, in this study, we evaluated the effect of a lard and soybean oil mixture (LFHC diet) on NAFLD and its underlying mechanisms. Mice in groups were fed with lard, soybean oil, or a lard and soybean oil mixture—an LFHC diet—separately. Our results showed that mixed oil significantly inhibited serum triglyceride, liver triglyceride, serum free fatty acids (FFAs), and liver FFAs compared with soybean oil or lard, and we found fewer inflammatory cells in mice fed with mixed oil. RNA-seq results indicate that mixed oil reduced FFAs transportation into the liver via decreasing liver fatty acid-binding protein 2 expression, inhibited oxidative phosphorylation via tumor necrosis factor receptor superfamily member 6 downregulation, and alleviated inflammation via downregulating inflammatory cytokine. The liquid chromatography–mass spectrometry results showed that the mixed oil promoted bile acid conjugated with taurine and glycine, thus activating G-protein-coupled bile acid receptor 1 for improved lipids metabolism. In conclusion, the lard and soybean oil mixture alleviated NAFLD.

Potential role of microRNAs in selective hepatic insulin resistance: From paradox to the paradigm

The paradoxical action of insulin on hepatic glucose metabolism and lipid metabolism in the insulin-resistant state has been of much research interest in recent years. Generally, insulin resistance would promote hepatic gluconeogenesis and demote hepatic de novo lipogenesis. The underlying major drivers of these mechanisms were insulin-dependent, via FOXO-1-mediated gluconeogenesis and SREBP1c-mediated lipogenesis. However, insulin-resistant mouse models have shown high glucose levels as well as excess lipid accumulation. As suggested, the inert insulin resistance causes the activation of the FOXO-1 pathway promoting gluconeogenesis. However, it does not affect the SREBP1c pathway; therefore, cells continue de novo lipogenesis. Many hypotheses were suggested for this paradoxical action occurring in insulin-resistant rodent models. A "downstream branch point" in the insulin-mediated pathway was suggested to act differentially on the FOXO-1 and SREBP1c pathways. MicroRNAs have been widely studied for their action of pathway mediation via suppressing the intermediate protein expressions. Many in vitro studies have postulated the roles of hepato-specific expressions of miRNAs on insulin cascade. Thus, miRNA would play a pivotal role in selective hepatic insulin resistance. As observed, there were confirmations and contradictions between the outcomes of gene knockout studies conducted on selective hepatic insulin resistance and hepato-specific miRNA expression studies. Furthermore, these studies had evaluated only the effect of miRNAs on glucose metabolism and few on hepatic de novo lipogenesis, limiting the ability to conclude their role in selective hepatic insulin resistance. Future studies conducted on the role of miRNAs on selective hepatic insulin resistance warrant the understanding of this paradoxical action of insulin.

Circulating microRNAs are associated with variability in fasting blood glucose over 12-months and target pathways related to type 2 diabetes: A pilot study

INTRODUCTION

MicroRNAs (miRs) may be important regulators of risk for type 2 diabetes (T2D). Circulating miRs may provide information about which individuals are at risk for T2D. The purpose of this study was to assess longitudinal associations between circulating miR expression and variability in fasting blood glucose (FBG) and to identify miR-targeted genes and biological pathways.

METHODS

Variability in FBG was estimated using standard deviation from participants (n = 20) in a previously completed yoga trial. Expression of 402 miRs was measured using hydrogel particle lithography. MirTarBase was used to identify mRNAs, and miRPathDB was used to identify pathways targeted by differentially expressed miRs.

RESULTS

Six circulating miRs (miR-192, miR-197, miR-206, miR-424, miR-486, and miR-93) were associated with variability in FBG and targeted 143 genes and 23 Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways. Six mRNAs (AKT1, CCND1, ESR1, FASN, SMAD7, and VEGFA) were targeted by at least two miRs and four of those were located in miR-targeted KEGG pathways.

CONCLUSIONS

Circulating miRs are associated with variability in FBG in individuals at risk for T2D. Further studies are needed to determine whether miRs may be prodromal biomarkers that can identify which individuals are at greatest risk to progress to T2D and which biological pathways underlie this risk.

Insulin action at a molecular level - 100 years of progress

The discovery of insulin 100 years ago and its application to the treatment of human disease in the years since have marked a major turning point in the history of medicine. The availability of purified insulin allowed for the establishment of its physiological role in the regulation of blood glucose and ketones, the determination of its amino acid sequence, and the solving of its structure. Over the last 50 years, the function of insulin has been applied into the discovery of the insulin receptor and its signaling cascade to reveal the role of impaired insulin signaling-or resistance-in the progression of type 2 diabetes. It has also become clear that insulin signaling can impact not only classical insulin-sensitive tissues, but all tissues of the body, and that in many of these tissues the insulin signaling cascade regulates unexpected physiological functions. Despite these remarkable advances, much remains to be learned about both insulin signaling and how to use this molecular knowledge to advance the treatment of type 2 diabetes and other insulin-resistant states.

Centennial Review: Metabolic microRNA - shifting gears in the regulation of metabolic pathways in poultry

Over 20 yr ago, a small noncoding class of RNA termed microRNA (miRNA) that was able to recognize sequences in mRNAs and inhibit their translation was discovered in Caenorhabditis elegans. In the intervening years, miRNA have been discovered in most eukaryotes and are now known to regulate the majority of protein-coding genes. It has been discovered that disruption of miRNA function often leads to the development of pathological conditions. One physiological system under extensive miRNA-mediated regulation is metabolism. Metabolism is one of the most dynamic of biological networks within multiple organs, including the liver, muscle, and adipose tissue, working in concert to respond to ever-changing nutritional cues and energy demands. Therefore, it is not surprising that miRNA regulate virtually all aspects of eukaryotic metabolism and have been linked to metabolic disorders, such as obesity, fatty liver diseases, and diabetes, just to name a few. Chickens, and birds in general, face their own unique metabolic challenges, particularly after hatching, when their metabolism must completely transform from using lipid-rich yolk to carbohydrate-rich feed as fuel in a very short period of time. Furthermore, commercial poultry breeds have undergone extensive selection over the last century for more desirable production traits, which has resulted in numerous metabolic consequences. Here, we review the current knowledge of miRNA-mediated regulation of metabolic development and function in chickens.

Influence of Obesity in the miRNome: miR-4454, a Key Regulator of Insulin Response Via Splicing Modulation in Prostate

CONTEXT

Obesity is a major health problem associated with severe comorbidities, including type 2 diabetes and cancer, wherein microRNAs (miRNAs) might be useful as diagnostic/prognostic tools or therapeutic targets.

OBJECTIVE

To explore the differential expression pattern of miRNAs in obesity and their putative role in obesity-related comorbidities such as insulin resistance.

METHODS

An Affymetrix-miRNA array was performed in plasma samples from normoweight (n = 4/body mass index < 25) and obese subjects (n = 4/body mass index > 30). The main changes were validated in 2 independent cohorts (n = 221/n = 18). Additionally, in silico approaches were performed and in vitro assays applied in tissue samples and prostate (RWPE-1) and liver (HepG2) cell-lines.

RESULTS

A total of 26 microRNAs were altered (P < 0.01) in plasma of obese subjects compared to controls using the Affymetrix-miRNA array. Validation in ampler cohorts revealed that miR-4454 levels were consistently higher in obesity, associated with insulin-resistance (Homeostatic Model Assessment of Insulin Resistance/insulin) and modulated by medical (metformin/statins) and surgical (bariatric surgery) strategies. miR-4454 was highly expressed in prostate and liver tissues and its expression was increased in prostate and liver cells by insulin. In vitro, overexpression of miR-4454 in prostate cells resulted in decreased expression levels of INSR, GLUT4, and phosphorylation of AMPK/AKT/ERK, as well as in altered expression of key spliceosome components (ESRP1/ESRP2/RBM45/RNU2) and insulin-receptor splicing variants.

CONCLUSIONS

Obesity was associated to an alteration of the plasmatic miRNA landscape, wherein miR-4454 levels were higher, associated with insulin-resistance and modulated by obesity-controlling interventions. Insulin regulated miR-4454, which, in turn may impair the cellular response to insulin, in a cell type-dependent manner (i.e., prostate gland), by modulating the splicing process.

miR-322/-503 rescues myoblast defects in myotonic dystrophy type 1 cell model by targeting CUG repeats

Myotonic dystrophy type 1 (DM1) is the most common type of adult muscular dystrophy caused by the expanded triple-nucleotides (CUG) repeats. Myoblast in DM1 displayed many defects, including defective myoblast differentiation, ribonuclear foci, and aberrant alternative splicing. Despite many were revealed to function in DM1, microRNAs that regulated DM1 via directly targeting the expanded CUG repeats were rarely reported. Here we discovered that miR-322/-503 rescued myoblast defects in DM1 cell model by targeting the expanded CUG repeats. First, we studied the function of miR-322/-503 in normal C2C12 myoblast cells. Downregulation of miR-322/-503 significantly hindered the myoblast differentiation, while miR-322/-503 overexpression promoted the process. Next, we examined the role of miR-322/-503 in the DM1 C2C12 cell model. miR-322/-503 was downregulated in the differentiation of DM1 C2C12 cells. When we introduced ectopic miR-322/-503 expression into DM1 C2C12 cells, myoblast defects were almost fully rescued, marked by significant improvements of myoblast differentiation and repressions of ribonuclear foci formation and aberrant alternative splicing. Then we investigated the downstream mechanism of miR-322/-503 in DM1. Agreeing with our previous work, Celf1 was proven to be miR-322/-503′s target. Celf1 knockdown partially reproduced miR-322/-503′s function in rescuing DM1 C2C12 differentiation but was unable to repress ribonuclear foci, suggesting other targets of miR-322/-503 existed in the DM1 C2C12 cells. As the seed regions of miR-322 and miR-503 were complementary to the CUG repeats, we hypothesized that the CUG repeats were the target of miR-322/-503. Through expression tests, reporter assays, and colocalization staining, miR-322/-503 was proved to directly and specifically target the expanded CUG repeats in the DM1 cell model rather than the shorter ones in normal cells. Those results implied a potential therapeutic function of miR-322/-503 on DM1, which needed further investigations in the future.

Role of miRNA-424 in Cancers

microRNA (miRNA) is an important part of non-coding RNA that regulates gene expression at a posttranscriptional level. miRNA has gained increasing interest in recent years, both in research and clinical fields. miRNAs have been found to play an important role in various diseases, particularly cancer. Aberrant miR-424 expression is found in several tumors where they can function as either oncogenes or tumor-suppressor genes. Meanwhile, miR-424 is also affected by the reorganization of many other non-coding RNAs such as lncRNA and cirRNA. Several studies have found that miR-424 participates in proliferation, differentiation, apoptosis, invasion, angiogenesis, and drug resistance, and plays an important role in the tumorigenesis and progression of tumors. This review will focus on the recent progress of research on miR-424 in tumors.

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.

Transcriptional Regulation of INSR, the Insulin Receptor Gene

The insulin receptor gene encodes an evolutionarily conserved signaling protein with a wide spectrum of functions in metazoan development. The insulin signaling pathway plays key roles in processes such as metabolic regulation, growth control, and neuronal function. Misregulation of the pathway features in diabetes, cancer, and neurodegenerative diseases, making it an important target for clinical interventions. While much attention has been focused on differential pathway activation through ligand availability, sensitization of overall signaling may also be mediated by differential expression of the insulin receptor itself. Although first characterized as a “housekeeping” gene with stable expression, comparative studies have shown that expression levels of the human INSR mRNA differ by tissue and in response to environmental signals. Our recent analysis of the transcriptional controls affecting expression of the Drosophila insulin receptor gene indicates that a remarkable amount of DNA is dedicated to encoding sophisticated feedback and feed forward signals. The human INSR gene is likely to contain a similar level of transcriptional complexity; here, we summarize over three decades of molecular biology and genetic research that points to a still incompletely understood regulatory control system. Further elucidation of transcriptional controls of INSR will provide the basis for understanding human genetic variation that underlies population-level physiological differences and disease.

Metabolomics for Investigating Physiological and Pathophysiological Processes

Metabolomics uses advanced analytical chemistry techniques to enable the high-throughput characterization of metabolites from cells, organs, tissues, or biofluids. The rapid growth in metabolomics is leading to a renewed interest in metabolism and the role that small molecule metabolites play in many biological processes. As a result, traditional views of metabolites as being simply the "bricks and mortar" of cells or just the fuel for cellular energetics are being upended. Indeed, metabolites appear to have much more varied and far more important roles as signaling molecules, immune modulators, endogenous toxins, and environmental sensors. This review explores how metabolomics is yielding important new insights into a number of important biological and physiological processes. In particular, a major focus is on illustrating how metabolomics and discoveries made through metabolomics are improving our understanding of both normal physiology and the pathophysiology of many diseases. These discoveries are yielding new insights into how metabolites influence organ function, immune function, nutrient sensing, and gut physiology. Collectively, this work is leading to a much more unified and system-wide perspective of biology wherein metabolites, proteins, and genes are understood to interact synergistically to modify the actions and functions of organelles, organs, and organisms.

Differential expression of novel MicroRNAs from developing fetal heart of Gallus gallus domesticus implies a role in cardiac development

Heart development is a complex process regulated by multi-layered genetic as well epigenetic regulators many of which are still unknown. Besides their critical role during cardiac development, these molecular regulators emerge as key modulators of cardiovascular pathologies, where fetal cardiac genes' re-expression is witnessed. MicroRNAs have recently emerged as a crucial part of signalling cascade in both development and diseases. We aimed to identify, validate, and perform functional annotation of putative novel miRNAs using chicken as a cardiac development model system. Novel miRNAs were obtained through deep sequencing of small RNAs extracted from chicken embryonic cardiac tissue of different developmental stages. After filtering out real pre-miRNAs, their expression analysis, potential target gene's prediction and functional annotations were performed. Expression analysis revealed that miRNAs were differentially expressed during different developmental stages of chicken heart. The expression of selected putative novel miRNAs was further validated by real-time PCR. Our analysis indicated the presence of novel cardiac miRNAs that might be regulating critical cardiac development events such as cardiac cell growth, differentiation, cardiac action potential generation and signal transduction.

NR6A1 regulates lipid metabolism through mammalian target of rapamycin complex 1 in HepG2 cells

Background

Lipogenesis is required for the optimal growth of many types of cancer cells, it is shown to control the biosynthesis of the lipid bilayer membrane during rapid proliferation and metastasis, provides cancer cells with signaling lipid molecules to support cancer development and make cancer cells more resistant to oxidative stress-induced cell death. Though multiple lipogenic enzymes have been identified to mediate this metabolic change, how the expression of these lipogenic enzymes are transcriptionally regulated remains unclear.

Methods

Gain- and loss-of-function experiments were conducted to assess the role of transcriptional repressor, nuclear receptor sub-family 6, group A, member 1 (NR6A1) in HepG2 cells. RT-qPCR method was performed to investigate target gene of NR6A1. Western blot was employed to determine the mechanisms by which NR6A1 regulates lipid accumulation in HepG2 cells.

Results

We provide evidence that NR6A1 is a novel regulator of lipid metabolism in HepG2 cells. NR6A1 knockdown can increase lipid accumulation as well as insulin-induced proliferation and migration of HepG2 cells. The lipogenic effect correlated well with the expression of lipogenic genes, including fatty acid synthase (FAS), diglyceride acyltransferase-2 (DGAT2), malic enzyme 1 (ME1), microsomal triglyceride transfer protein (MTTP) and phosphoenolpyruvate carboxykinase (PEPCK). NR6A1 knockdown also increased the expression of carnitine palmitoyltransferase 1A (CPT1a), the rate-limiting enzyme in fatty acid oxidation. Furthermore, NR6A1 knockdown induced lipid accumulation through mammalian target of rapamycin complex 1 (mTORC1), but not mTORC2. Moreover, siRNA-mediated knockdown of NR6A1 increased expression of insulin receptor (INSR) and potentitated insulin-induced phosphorylation of mTOR and AKT partly via miR-205-5p in HepG2 cells.

Conclusions

These findings provide important new insights into the role of NR6A1 in the lipogenesis in HepG2 cells.

Graphical abstract

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Electronic supplementary material

The online version of this article (10.1186/s12964-019-0389-4) contains supplementary material, which is available to authorized users.

MicroRNAs as Regulators of Insulin Signaling: Research Updates and Potential Therapeutic Perspectives in Type 2 Diabetes

The insulin signaling pathway is composed of a large number of molecules that positively or negatively modulate insulin specific signal transduction following its binding to the cognate receptor. Given the importance of the final effects of insulin signal transduction, it is conceivable that many regulators are needed in order to tightly control the metabolic or proliferative functional outputs. MicroRNAs (miRNAs) are small non-coding RNA molecules that negatively modulate gene expression through their specific binding within the 3′UTR sequence of messenger RNA (mRNA), thus causing mRNA decoy or translational inhibition. In the last decade, miRNAs have been addressed as pivotal cellular rheostats which control many fundamental signaling pathways, including insulin signal transduction. Several studies demonstrated that multiple alterations of miRNAs expression or function are relevant for the development of insulin resistance in type 2 diabetes (T2D); such alterations have been highlighted in multiple insulin target organs including liver, muscles, and adipose tissue. Indirectly, miRNAs have been identified as modulators of inflammation-derived insulin resistance, by controlling/tuning the activity of innate immune cells in insulin target tissues. Here, we review main findings on miRNA functions as modulators of insulin signaling in physiologic- or in T2D insulin resistance- status. Additionally, we report the latest hypotheses of prospective therapies involving miRNAs as potential targets for future drugs in T2D.