Islet-expressed circular RNAs are associated with type 2 diabetes status in human primary islets and in peripheral blood

Single-cell transcriptomic profiling of human pancreatic islets reveals genes responsive to glucose exposure over 24 h

AIMS/HYPOTHESIS

Disruption of pancreatic islet function and glucose homeostasis can lead to the development of sustained hyperglycaemia, beta cell glucotoxicity and subsequently type 2 diabetes. In this study, we explored the effects of in vitro hyperglycaemic conditions on human pancreatic islet gene expression across 24 h in six pancreatic cell types: alpha; beta; gamma; delta; ductal; and acinar. We hypothesised that genes associated with hyperglycaemic conditions may be relevant to the onset and progression of diabetes.

METHODS

We exposed human pancreatic islets from two donors to low (2.8 mmol/l) and high (15.0 mmol/l) glucose concentrations over 24 h in vitro. To assess the transcriptome, we performed single-cell RNA-seq (scRNA-seq) at seven time points. We modelled time as both a discrete and continuous variable to determine momentary and longitudinal changes in transcription associated with islet time in culture or glucose exposure. Additionally, we integrated genomic features and genetic summary statistics to nominate candidate effector genes. For three of these genes, we functionally characterised the effect on insulin production and secretion using CRISPR interference to knock down gene expression in EndoC-βH1 cells, followed by a glucose-stimulated insulin secretion assay.

RESULTS

In the discrete time models, we identified 1344 genes associated with time and 668 genes associated with glucose exposure across all cell types and time points. In the continuous time models, we identified 1311 genes associated with time, 345 genes associated with glucose exposure and 418 genes associated with interaction effects between time and glucose across all cell types. By integrating these expression profiles with summary statistics from genetic association studies, we identified 2449 candidate effector genes for type 2 diabetes, HbA1c, random blood glucose and fasting blood glucose. Of these candidate effector genes, we showed that three (ERO1B, HNRNPA2B1 and RHOBTB3) exhibited an effect on glucose-stimulated insulin production and secretion in EndoC-βH1 cells.

CONCLUSIONS/INTERPRETATION

The findings of our study provide an in-depth characterisation of the 24 h transcriptomic response of human pancreatic islets to glucose exposure at a single-cell resolution. By integrating differentially expressed genes with genetic signals for type 2 diabetes and glucose-related traits, we provide insights into the molecular mechanisms underlying glucose homeostasis. Finally, we provide functional evidence to support the role of three candidate effector genes in insulin secretion and production.

DATA AVAILABILITY

The scRNA-seq data from the 24 h glucose exposure experiment performed in this study are available in the database of Genotypes and Phenotypes (dbGap; https://www.ncbi.nlm.nih.gov/gap/ ) with accession no. phs001188.v3.p1. Study metadata and summary statistics for the differential expression, gene set enrichment and candidate effector gene prediction analyses are available in the Zenodo data repository ( https://zenodo.org/ ) under accession number 11123248. The code used in this study is publicly available at https://github.com/CollinsLabBioComp/publication-islet_glucose_timecourse .

CircCamsap1 is dispensable for male fertility in mice

Background

Circular RNAs (circRNAs) are a large class of RNAs present in mammals. Among these, circCamsap1 is a well-acknowledged circRNA with significant implications, particularly in the development and progression of diverse tumors. However, the potential consequences of circCamsap1 depletion in vivo on male reproduction are yet to be thoroughly investigated.

Methods

The presence of circCamsap1 in the mouse testes was confirmed, and gene expression analysis was performed using reverse transcription quantitative polymerase chain reaction. CircCamsap1 knockout mice were generated utilizing the CRISPR/Cas9 system. Phenotypic analysis of both the testes and epididymis was conducted using histological and immunofluorescence staining. Additionally, fertility and sperm motility were assessed.

Results

Here, we successfully established a circCamsap1 knockout mouse model without affecting the expression of parental gene. Surprisingly, male mice lacking circCamsap1 (circCamsap1-/-) exhibited normal fertility, with no discernible differences in testicular and epididymal histology, spermatogenesis, sperm counts or sperm motility compared to circCamsap1+/+ mice. These findings suggest that circCamsap1 may not play an essential role in physiological spermatogenesis. Nonetheless, this result also underscores the complexity of circRNA function in male reproductive biology. Therefore, further research is necessary to elucidate the precise roles of other circRNAs in regulating male fertility.

SORCS2 activity in pancreatic α-cells safeguards insulin granule formation and release from glucose-stressed β-cells

Sorting receptor SORCS2 is a stress-response factor protecting neurons from acute insults, such as during epilepsy. SORCS2 is also expressed in the pancreas, yet its action in this tissue remains unknown. Combining metabolic studies in SORCS2-deficient mice with ex vivo functional analyses and single-cell transcriptomics of pancreatic tissues, we identified a role for SORCS2 in protective stress response in pancreatic islets, essential to sustain insulin release. We show that SORCS2 is predominantly expressed in islet alpha cells. Loss of expression coincides with inability of these cells to produce osteopontin, a secreted factor that facilitates insulin release from stressed beta cells. In line with diminished osteopontin levels, beta cells in SORCS2-deficient islets show gene expression patterns indicative of aggravated cell stress, and exhibit defects in insulin granule maturation and a blunted glucose response. These findings corroborate a function for SORCS2 in protective stress response that extends to metabolism.

circGlis3 promotes β-cell dysfunction by binding to heterogeneous nuclear ribonucleoprotein F and encoding Glis3-348aa protein

Circular RNAs (circRNAs) are crucial regulators of β-cell function and are involved in lipotoxicity-induced β-cell damage in type 2 diabetes mellitus (T2DM). We previously identified that circGlis3, a circRNA derived from exon 4 of the diabetes susceptibility gene Glis3, was upregulated in lipotoxic β cells. However, the functional role and molecular mechanism of circGlis3 in β cells remain largely unknown. Here, we revealed that the splicing factor CUGBP Elav-Like Family Member 1 (CELF1) facilitated the biogenesis of circGlis3. Moreover, we established a transgenic mouse model and confirmed that the overexpression of circGlis3 impaired β-cell function. Mechanistically, circGlis3 bound to heterogeneous nuclear ribonucleoprotein F (hnRNPF) and blocked its nuclear translocation, thereby reducing Sirt1 levels. Additionally, circGlis3 encoded a 348aa protein that interacted with GLIS3 and inhibited its transcriptional activity. Our data uncover a critical role of circGlis3 in β-cell dysfunction, suggesting that circGlis3 may be a potential therapeutic target for T2DM.

Decrypting the circular RNAs does a favor for us: Understanding, diagnosing and treating diabetes mellitus and its complications

Circular RNAs (circRNAs), a novel type of single-stranded noncoding RNAs with a covalently closed loop structure, are generated in a circular conformation via non-canonical splicing or back-splicing events. Functionally, circRNAs have been elucidated to soak up microRNAs (miRNAs) and RNA binding proteins (RBPs), serve as protein scaffolds, maintain mRNA stability, and regulate gene transcription and translation. Notably, circRNAs are strongly implicated in the regulation of β-cell functions, insulin resistance, adipocyte functions, inflammation as well as oxidative stress via acting as miRNA sponges and RBP sponges. Basic and clinical studies have demonstrated that aberrant alterations of circRNAs expressions are strongly associated with the initiation and progression of diabetes mellitus (DM) and its complications. Here in this review, we present a summary of the biogenesis, transportation, degradation and functions of circRNAs, and highlight the recent findings on circRNAs and their action mechanisms in DM and its complications. Overall, this review should contribute greatly to our understanding of circRNAs in DM pathogenesis, offering insights into the further perspectives of circRNAs for DM diagnosis and therapy.

Multiple novel functions of circular RNAs in diabetes mellitus

Circular RNAs (circRNAs), as an emerging group of non-coding RNAs (ncRNAs), have received the attention given evidence indicating that these novel ncRNAs are implicated in various biological processes. Due to the absence of 5' and 3' ends in circ-RNAs, their two ends are covalently bonded together, and they are synthesised from pre-mRNAs in a process called back-splicing, which makes them more stable than linear RNAs. There is accumulating evidence showing that circRNAs play a critical role in the pathogenesis of diabetes mellitus (DM). Moreover, it has been indicated that dysregulation of circRNAs has made them promising diagnostic biomarkers for the detection of DM. Recently, increasing attention has been paid to investigate the mechanisms underlying the DM process. It has been demonstrated that there is a strong correlation between the expression of circRNAs and DM. Hence, our aim is to discuss the crosstalk between circRNAs and DM and its complications.

Clinical relevance of circulating non-coding RNAs in metabolic diseases: Emphasis on obesity, diabetes, cardiovascular diseases and metabolic syndrome

Non-coding RNAs (ncRNAs) participate in the regulation of several cellular processes including transcription, RNA processing and genome rearrangement. The aberrant expression of ncRNAs is associated with several pathological conditions. In this review, we focused on recent information to elucidate the role of various regulatory ncRNAs i.e., micro RNAs (miRNAs), circular RNAs (circRNAs) and long-chain non-coding RNAs (lncRNAs), in metabolic diseases, e.g., obesity, diabetes mellitus (DM), cardiovascular diseases (CVD) and metabolic syndrome (MetS). The mechanisms by which ncRNAs participated in disease pathophysiology were also highlighted. miRNAs regulate the expression of genes at transcriptional and translational levels. circRNAs modulate the regulation of gene expression via miRNA sponging activity, interacting with RNA binding protein and polymerase II transcription regulation. lncRNAs regulate the expression of genes by acting as a protein decoy, miRNA sponging, miRNA host gene, binding to miRNA response elements (MRE) and the recruitment of transcriptional element or chromatin modifiers. We examined the role of ncRNAs in the disease pathogenesis and their potential role as molecular markers for diagnosis, prognosis and therapeutic targets. We showed the involvement of ncRNAs in the onset of obesity and its progression to MetS and CVD. miRNA-192, miRNA-122, and miRNA-221 were dysregulated in all these metabolic diseases. Other ncRNAs, implicated in at least three diseases include miRNA-15a, miRNA-26, miRNA-27a, miRNA-320, and miRNA-375. Dysregulation of ncRNAs increased the risk of development of DM and MetS and its progression to CVD in obese individuals. Hence, these molecules are potential targets to arrest or delay the progression of metabolic diseases.

Circular RNA as a Novel Regulator and Promising Biomarker in Polycystic Ovary Syndrome

Polycystic ovary syndrome (PCOS) is a prevalent metabolic and reproductive disorder that causes low fertility in females. Despite its detrimental effects on women's health, care for PCOS has been impeded by its undefined pathogenesis. Thus, there is an urgent need to explore novel biomarkers and therapeutic targets for the diagnosis and treatment of PCOS. Circular RNAs (circRNAs) are a class of noncoding RNAs with covalently closed cyclic structures, present in high abundance, and show development-stage specific expression patterns. Recent studies have demonstrated that circRNAs participate in PCOS progression by modulating various biological functions, including cell proliferation, apoptosis, and steroidogenesis. In addition, circRNAs are widely present in the follicular fluid of women with PCOS, indicating their potential as diagnostic biomarkers and therapeutic targets for PCOS. This review provides the current knowledge of circRNAs in PCOS, including their regulatory functions and molecular mechanisms, and explores their potential as diagnostic biomarkers and therapeutic targets.

CircRNA and Ageing

Circular RNAs (circRNAs) are closed-loop RNA transcripts formed by a noncanonical back splicing mechanism. circRNAs are expressed in various tissues and cell types in a temporospatially regulated manner and have diverse molecular functions including their ability to act as miRNA sponges, transcriptional and splicing regulators, protein traps, and even templates for polypeptide synthesis. Emerging evidence suggests that circRNAs are themselves dynamically regulated throughout development in various organisms, with a substantial accumulation during ageing. Their regulatory roles in cellular pathways associated with ageing and senescence, as well as their implications in ageing-related diseases, such as neurological disease, cancer, and cardiovascular disease, suggest that circRNAs are key molecular determinants of the ageing process. Their unique structure, expression specificity, and biological functions highlight a potential capacity for use as novel biomarkers for diagnosis, prognosis, and treatment outcomes in a variety of conditions including pathological ageing. CircRNA may also have potential as target for interventions that manipulate ageing and longevity. In this chapter, we discuss the most recent advances in circRNA changes in ageing and ageing-associated disease.

circRAB3IP modulates cell proliferation by reorganizing gene expression and mRNA processing in a paracrine manner

Circular RNAs are an endogenous long-lived and abundant noncoding species. Despite their prevalence, only a few circRNAs have been dissected mechanistically to date. Here, we cataloged nascent RNA-enriched circRNAs from primary human cells and functionally assigned a role to circRAB3IP in sustaining cellular homeostasis. We combined "omics" and functional experiments to show how circRAB3IP depletion deregulates hundreds of genes, suppresses cell cycle progression, and induces senescence-associated gene expression changes. Conversely, excess circRAB3IP delivered to endothelial cells via extracellular vesicles suffices for accelerating their division. We attribute these effects to an interplay between circRAB3IP and the general splicing factor SF3B1, which can affect transcript variant expression levels of cell cycle-related genes. Together, our findings link the maintenance of cell homeostasis to the presence of a single circRNA.

Current Insights into miRNA and lncRNA Dysregulation in Diabetes: Signal Transduction, Clinical Trials and Biomarker Discovery

Diabetes is one of the most frequently occurring metabolic disorders, affecting almost one tenth of the global population. Despite advances in antihyperglycemic therapeutics, the management of diabetes is limited due to its complexity and associated comorbidities, including diabetic neuropathy, diabetic nephropathy and diabetic retinopathy. Noncoding RNAs (ncRNAs), including microRNAs (miRNAs) and long noncoding RNAs (lncRNAs), are involved in the regulation of gene expression as well as various disease pathways in humans. Several ncRNAs are dysregulated in diabetes and are responsible for modulating the expression of various genes that contribute to the 'symptom complex' in diabetes. We review various miRNAs and lncRNAs implicated in diabetes and delineate ncRNA biological networks as well as key ncRNA targets in diabetes. Further, we discuss the spatial regulation of ncRNAs and their role(s) as prognostic markers in diabetes. We also shed light on the molecular mechanisms of signal transduction with diabetes-associated ncRNAs and ncRNA-mediated epigenetic events. Lastly, we summarize clinical trials on diabetes-associated ncRNAs and discuss the functional relevance of the dysregulated ncRNA interactome in diabetes. This knowledge will facilitate the identification of putative biomarkers for the therapeutic management of diabetes and its comorbidities. Taken together, the elucidation of the architecture of signature ncRNA regulatory networks in diabetes may enable the identification of novel biomarkers in the discovery pipeline for diabetes, which may lead to better management of this metabolic disorder.

Newly discovered circRNAs in rheumatoid arthritis, with special emphasis on functional roles in inflammatory immunity

Circular RNA (circRNA) is a unique type of endogenous RNA. It does not have free 3 ′or 5′ ends, but forms covalently closed continuous rings. Rheumatoid arthritis (RA) is a common chronic autoimmune joint disease, characterized by chronic inflammation of the joint synovial membrane, joint destruction, and the formation of pannus. Although the pathogenesis of rheumatoid arthritis remains incompletely understood, a growing amount of research shows that circRNA has a close relationship with RA. Researchers have found that abnormally expressed circRNAs may be associated with the occurrence and development of RA. This article reviews the inflammatory immune, functions, mechanisms, and values of the circRNAs in RA to provide new ideas and novel biomarkers for the diagnosis and treatment of RA.

High-throughput analysis of ANRIL circRNA isoforms in human pancreatic islets

The antisense non-coding RNA in the INK locus (ANRIL) is a hotspot for genetic variants associated with cardiometabolic disease. We recently found increased ANRIL abundance in human pancreatic islets from donors with certain Type II Diabetes (T2D) risk-SNPs, including a T2D risk-SNP located within ANRIL exon 2 associated with beta cell proliferation. Recent studies have found that expression of circular species of ANRIL is linked to the regulation of cardiovascular phenotypes. Less is known about how the abundance of circular ANRIL may influence T2D phenotypes. Herein, we sequence circular RNA in pancreatic islets to characterize circular isoforms of ANRIL. We identify several consistently expressed circular ANRIL isoforms whose expression is correlated across dozens of individuals and characterize ANRIL splice sites that are commonly involved in back-splicing. We find that samples with the T2D risk allele in ANRIL exon 2 had higher ratios of circular to linear ANRIL compared to protective-allele carriers, and that higher circular:linear ANRIL was associated with decreased beta cell proliferation. Our study points to a combined involvement of both linear and circular ANRIL species in T2D phenotypes and opens the door for future studies of the molecular mechanisms by which ANRIL impacts cellular function in pancreatic islets.

Analysis of circRNA-mRNA expression profiles and functional enrichment in diabetes mellitus based on high throughput sequencing

To study the pathogenesis of diabetes mellitus (DM) and identify new biomarkers, high‐throughput RNA sequencing provides a technical means to explore the regulatory network of MD gene expression. To better elucidate the genetic basis of DM, we analysed the circRNA and mRNA expression profiles in serum samples from diabetic patients. The circRNAs and mRNAs with abnormal expression in the DM group and non‐diabetic group (NDM) were classified by RNA sequencing and differential expression analysis. The circRNA‐miRNA‐mRNA regulatory network reveals the mechanism by which competitive endogenous RNAs (ceRNAs) regulate gene expression. The biological functions and interactions of circRNA and mRNA were analysed by gene ontology (GO) enrichment and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis. Differential expression analysis showed that 441 circRNAs (366 up‐regulated, 75 down‐regulated) and 683 mRNAs (354 up‐regulated, 329 down‐regulated) were significantly differentially expressed in the DM group compared with the NDM group. Screening of the differential genes at the nodes of the interaction network showed that a single circRNA could interact with multiple miRNAs and then jointly regulate more mRNAs. In addition, the expressions of circRNA CNOT6 and AXIN1 as well as mRNA STAT3, MYD88, and B2M were associated with the progression of diabetes. Enrichment pathway analysis indicated that differentially expressed circRNA and mRNA may participate in Nod‐like receptor signalling pathway, insulin signalling pathway, sphinolipid metabolism pathway, and ribosome pathway, and play a role in the pathogenesis of diabetes. This study provides a theoretical basis for elucidating the molecular mechanism of DM occurrence and development at circRNA and mRNA levels.

Emergent Roles of Circular RNAs in Metabolism and Metabolic Disorders

Circular RNAs (circRNAs) are an emerging group of long non-coding RNAs (lncRNAs) and have attracted attention again according to the progress in high-throughput sequencing in recent years. circRNAs are genome transcripts produced from pre-messenger (m)RNA regions in a specific process called “back-splicing,” which forms covalently closed continuous loops. Due to their lack of a 5’ cap and 3’ poly-adenylated tails, circRNAs are remarkably more stable than linear RNAs. Functionally, circRNAs can endogenously sponge to microRNAs, interact with RNA-binding proteins (RBPs), or translate themselves. Moreover, circRNAs can be expressed in cell type- or tissue-specific expression patterns. Therefore, they are proposed to play essential roles in fine-tuning our body’s homeostasis by regulating transcription and translation processes. Indeed, there has been accumulating emergent evidence showing that dysregulation of circRNAs can lead to metabolic disorders. This study explored the current knowledge of circRNAs that regulate molecular processes associated with glucose and lipid homeostasis and related pathogeneses of metabolic disorders. We also suggest the potential role of circRNAs as disease biomarkers and therapeutic targets.

Research progress on the mechanism of beta-cell apoptosis in type 2 diabetes mellitus

Type 2 diabetes mellitus(T2DM) is regarded as one of the most severe chronic metabolic diseases worldwide, which poses a great threat to human safety and health. The main feature of T2DM is the deterioration of pancreatic beta-cell function. More and more studies have shown that the decline of pancreatic beta-cell function in T2DM can be attributable to beta-cell apoptosis, but the exact mechanisms of beta-cell apoptosis in T2DM are not yet fully clarified. Therefore, in this review, we will focus on the current status and progress of research on the mechanism of pancreatic beta-cell apoptosis in T2DM, to provide new ideas for T2DM treatment strategies.

Circular RNAs in diabetes mellitus and its complications

Diabetes mellitus (DM) is an endocrine disorder characterized by a relative or absolute lack of insulin due to the dysfunction or destruction of β-cells. DM is one of the fastest growing challenges to global health in the 21^st century and places a tremendous burden on affected individuals and their families and countries. Although insulin and antidiabetic drugs have been used to treat DM, a radical cure for the disease is unavailable. The pathogenesis of DM remains unclear. Emerging roles of circular RNAs (circRNAs) in DM have become a subject of global research. CircRNAs have been verified to participate in the onset and progression of DM, implying their potential roles as novel biomarkers and treatment tools. In the present review, we briefly introduce the characteristics of circRNAs. Next, we focus on specific roles of circRNAs in type 1 diabetes mellitus, type 2 diabetes mellitus, gestational diabetes mellitus and diabetes-associated complications.

Circular versus linear RNA topology: different modes of RNA-RNA interactions in vitro and in human cells

Circular RNA is progressively reported to occur in various species including mammals where it is thought to be involved in the post-transcriptional regulation of gene expression, partly via interactions with microRNA. Here, we asked whether the circular topology causes functional differences to linear forms when interacting with short RNA strands in vitro and in human cells. Kinetic studies with human bladder cancer-derived synthetic circular RNA versus linear transcripts, respectively, with short oligoribonucleotides showed similar association rates for both topologies. Conversely, a substantial topology-related difference was measured for the activation entropy and the activation enthalpy of RNA–RNA annealing. This finding strongly indicates a significant difference of the mechanism of RNA–RNA interactions. To investigate whether these characteristics of circular RNA are biologically meaningful we performed transient transfection experiments with a microRNA-regulated expression system for luciferase in bladder cancer-derived cells. We co-transfected linear or circular RNA containing one microRNA binding site for the target-suppressing microRNA mlet7a. Here, the circular isoform showed a strongly increased competition with microRNA function versus linear versions. In summary, this study suggests novel topology-related characteristics of RNA–RNA interactions involving circRNA in vitro and in living cells.

Evolutionary dynamics of circular RNAs in primates

Many primate genes produce circular RNAs (circRNAs). However, the extent of circRNA conservation between closely related species remains unclear. By comparing tissue-specific transcriptomes across over 70 million years of primate evolution, we identify that within 3 million years circRNA expression profiles diverged such that they are more related to species identity than organ type. However, our analysis also revealed a subset of circRNAs with conserved neural expression across tens of millions of years of evolution. By comparing to species-specific circRNAs, we identified that the downstream intron of the conserved circRNAs display a dramatic lengthening during evolution due to the insertion of novel retrotransposons. Our work provides comparative analyses of the mechanisms promoting circRNAs to generate increased transcriptomic complexity in primates.

Circular RNAs in metabolism and metabolic disorders

Metabolic syndrome (MetS) is a serious health condition triggered by hyperglycemia, dyslipidemia, and abnormal adipose deposition. Recently, circular RNAs (circRNAs) have been proposed as key molecular players in metabolic homeostasis due to their regulatory effects on genes linked to the modulation of multiple aspects of metabolism, including glucose and lipid homeostasis. Dysregulation of circRNAs can lead to metabolic disorders, indicating that circRNAs represent plausible potential targets to alleviate metabolic abnormalities. More recently, a series of circulating circRNAs have been identified to act as both essential regulatory molecules and biomarkers for the progression of metabolism-related disorders, including type 2 diabetes mellitus (T2DM or T2D) and cardiovascular disease (CVD). The findings of this study highlight the function of circRNAs in signaling pathways implicated in metabolic diseases and their potential as future therapeutics and disease biomarkers.

Function of Circular RNAs in Fish and Their Potential Application as Biomarkers

Circular RNAs (circRNAs) are an emerging class of regulatory RNAs with a covalently closed-loop structure formed during pre-mRNA splicing. Recent advances in high-throughput RNA sequencing and circRNA-specific computational tools have driven the development of novel approaches to their identification and functional characterization. CircRNAs are stable, developmentally regulated, and show tissue- and cell-type-specific expression across different taxonomic groups. They play a crucial role in regulating various biological processes at post-transcriptional and translational levels. However, the involvement of circRNAs in fish immunity has only recently been recognized. There is also broad evidence in mammals that the timely expression of circRNAs in muscle plays an essential role in growth regulation but our understanding of their expression and function in teleosts is still very limited. Here, we discuss the available knowledge about circRNAs and their role in growth and immunity in vertebrates from a comparative perspective, with emphasis on cultured teleost fish. We expect that the interest in teleost circRNAs will increase substantially soon, and we propose that they may be used as biomarkers for selective breeding of farmed fish, thus contributing to the sustainability of the aquaculture sector.

Diagnostic Biomarker Hsa_circ_0126218 and Functioning Prediction in Peripheral Blood Monocular Cells of Female Patients With Major Depressive Disorder

Introduction

Although major depressive diroder (MDD) has brought huge burden and challenges to society globally, effective and accurate diagnoses and treatments remain inadequate. The pathogenesis that for women are more likely to suffer from depression than men needs to be excavated as well. The function of circRNAs in pathological process of depression has not been widely investigated. This study aims to explore potential diagnostic biomarker circRNA of female patients with MDD and to investigate its role in pathogenesis.

Methods

First, an expression profile of circRNAs in the peripheral blood monocular cells of MDD patients and healthy peripherals were established based on high-throughput sequencing analysis. In addition, the top 10 differentially expressed circRNAs were quantified by quantitative real-time PCR to explore diagnostic biomarkers. To further investigate the function of biomarkers in the pathogenesis of MDD, bioinformatics analysis on downstream target genes of the biomarkers was carried out.

Results

There is a mass of dysregulated circRNAs in PBMCs between female MDD patients and healthy controls. Among the top 10 differentially expressed circRNAs, hsa_circ_0126218 is more feasible as a diagnostic biomarker. The expression level of hsa_circ_0126218 displayed upregulation in patients with MDD and the area under the operating characteristic curve of hsa_circ_0126218 was 0.801 (95% CI 0.7226–0.8791, p < 0.0001). To explain the competing endogenous RNA role of hsa_circ_0126218 in the pathogenesis of female MDD, a hsa_circ_0126218-miRNA-mRNA network was established. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathway enrichment analyses stated that some of the enriched pathways downstream of hsa_circ_0126218 are closely related to MDD. Moreover, we established a protein-protein network to further screen out the hub genes (PIK3CA, PTEN, MAPK1, CDC42, Lyn, YES1, EPHB2, SMAD2, STAT1, and ILK). The function of hsa_circ_0126218 was refined by constructing a verified circRNA-predicted miRNA-hub gene subnetwork.

Conclusion

hsa_circ_0126218 can be considered as a new female MDD biomarker, and the pathogenesis of female MDD by the downstream regulation of hsa_circ_0126218 has been predicted. These findings may help further improve the early detection, effective diagnosis, convenient monitoring of complications, precise treatment, and timely recurrence prevention of depression.

Involvement of circRNAs in Proinflammatory Cytokines-Mediated β-Cell Dysfunction

AIM

During the initial stage of type 1 diabetes, prolonged exposure of pancreatic β-cell to proinflammatory cytokines such as IL-1β, TNF-α, and IFN-γ results in a decreased capacity to produce and release insulin, as well as cell loss by apoptosis. Circular RNAs (circRNAs) are a new class of endogenous noncoding RNAs (ncRNAs) with closed loop with no free ends. circRNAs have been reported to be participated in the development of many diseases. As little is known about their role in insulin-secreting cells, this study is aimed at evaluating their contribution in the process of inflammation-induced β-cell damage.

METHODS

circRNA expression profile of MIN6 cells stimulated with a mix of cytokines, including IL-1β, IFN-γ, and TNF-α, was detected by circRNA microarrays. Four dysregulated circRNAs were validated by qRT-PCR. The involvement of the selected circRNAs in β-cell dysfunction was tested after their inhibition in MIN6 cells. MicroRNA target prediction software and multiple bioinformatic approaches were used to predict the targeting genes of circRNAs and analyze possible functions of the circRNAs.

RESULTS

1020 upregulated and 902 downregulated circRNAs were identified in cytokines-treated β-cells. Inhibition of circRNAs 000286 and 017277 in β-cells could promote β-cell apoptosis and affect insulin biosynthesis and secretion. GO analysis enriched terms such as regulation of transcription and regulation of gene expression and KEGG analysis enriched top pathways included TGF-β and MAPK signaling pathways.

CONCLUSIONS

The data shows that circRNAs may be involved in proinflammatory cytokines-mediated β-cell dysfunction and suggests the involvement of circRNAs in the development of type 1 diabetes.

Circular RNAs as Novel Regulators of β-Cell Functions under Physiological and Pathological Conditions

Circular RNAs (circRNAs) constitute a large class of non-coding RNAs characterized by a covalently closed circular structure. They originate during mRNA maturation through a modification of the splicing process and, according to the included sequences, are classified as Exonic, Intronic, or Exonic-Intronic. CircRNAs can act by sequestering microRNAs, by regulating the activity of specific proteins, and/or by being translated in functional peptides. There is emerging evidence indicating that dysregulation of circRNA expression is associated with pathological conditions, including cancer, neurological disorders, cardiovascular diseases, and diabetes. The aim of this review is to provide a comprehensive and updated view of the most abundant circRNAs expressed in pancreatic islet cells, some of which originating from key genes controlling the differentiation and the activity of insulin-secreting cells or from diabetes susceptibility genes. We will particularly focus on the role of a group of circRNAs that contribute to the regulation of β-cell functions and that display altered expression in the islets of rodent diabetes models and of type 2 diabetic patients. We will also provide an outlook of the unanswered questions regarding circRNA biology and discuss the potential role of circRNAs as biomarkers for β-cell demise and diabetes development.

Plasma and local expressions of CircRNA CDR1as are linked with disease severity in patients with non-traumatic osteonecrosis of femoral head

Objective

To investigate the correlation of plasma and local expressions of Circ CDR1as with disease severity in patients with non-traumatic osteonecrosis of femoral head (ONFH).

Methods

Ninety-nine non-traumatic ONFH patients receiving surgery and 99 healthy individuals were enrolled in our study. Plasma and local Circ CDR1as were detected using real-time quantitative PCR (RT-qPCR). Radiographic progression was determined using Association Research Circulation Osseous (ARCO) classification system. Harris hip score (HHS) and visual analogue scale (VAS) were used to assess the clinical severity. Receiver operating characteristic (ROC) curve was carried out to evaluate the diagnostic value of plasma Circ CDR1as with regard to the radiographic severity.

Results

Plasma Circ CDR1as expressions were significantly higher in non-traumatic ONFH patients compared with healthy controls. In non-traumatic ONFH patients, there were no significant differences of CircCDR1as expressions between patients with alcohol-induced ONFH and steroid-induced ONFH. CircCDR1as in local necrotic tissue were significantly higher than adjacent non-affected tissue. Plasma and local Circ CDR1as expressions in patients with ARCO phase 4 were markedly upregulated compared with ARCO phase 3; plasma and local Circ CDR1as expressions in patients with ARCO phase 3 were markedly upregulated compared with ARCO phase 1/2. Plasma and local CircCDR1as expressions were positively associated with ARCO classification. In addition, plasma and local Circ CDR1as expressions were positively correlated with VAS and HHS scores. ROC curve analysis indicated that plasma Circ CDR1as may act as a decent marker for radiographic progression in non-traumatic ONFH patients.

Conclusions

Both plasma and local expressions of CircRNA CDR1as are linked with disease severity in patients with non-traumatic ONFH.

Roles of circular RNAs in diabetic complications: From molecular mechanisms to therapeutic potential

Diabetes is characterized by changed homeostasis of blood glucose levels, which is associated with various complications, including cardiomyopathy, atherosclerosis, endothelial dysfunction, nephropathy, retinopathy and neuropathy. In recent years, accumulative evidence has demonstrated that circular RNAs are identified as a novel type of noncoding RNAs (ncRNAs) involving in the regulation of various physiological processes and pathologic conditions. Specifically, the emergence of complications response to diabetes is finely controlled by a complex gene regulatory network in which circular RNAs play a critical role. Recently, circular RNAs are emerging as messengers that could influence cellular functions under diabetic conditions. Dysregulation of circular RNAs has been closely linked to the pathophysiology of diabetes-related complications. In this review, we aimed to summarize the current progression and underlying mechanisms of circular RNA in the development of diabetes-related complications. We will also provide an overview of circular RNA-regulated cell communications in different types of cells that have been linked to diabetic complications. We anticipated that the completion of this review will provide potential clues for developing novel circular RNAs-based biomarkers or therapeutic targets for diabetes and its associated complications.

Circ09863 Regulates Unsaturated Fatty Acid Metabolism by Adsorbing miR-27a-3p in Bovine Mammary Epithelial Cells

Fatty acid composition plays a key role in regulating flavor and quality of milk. Therefore, in order to improve milk quality, it is particularly important to investigate regulatory mechanisms of milk fatty acid metabolism. Circular RNAs (circRNAs) regulate expression genes associated with several biological processes including fatty acid metabolism. In this study, high-throughput sequencing was used to detect differentially expressed genes in bovine mammary tissue at early lactation and peak lactation. Circ09863 profiles were influenced by the lactation stage. Functional studies in bovine mammary epithelial cells (BMECs) revealed that circ09863 promotes triglyceride (TAG) synthesis together with increased content of unsaturated fatty acids (C16:1 and C18:1). These results suggested that circ09863 is partly responsible for modulating fatty acid metabolism. Additionally, software prediction identified a miR-27a-3p binding site in the circ09863 sequence. Overexpression of miR-27a-3p in BMECs led to decreased TAG synthesis. However, overexpression of circ09863 (pcDNA-circ09863) in BMECs significantly reduced expression of miR-27a-3p and enhanced gene expression of fatty acid synthase (FASN), a target of miR-27a-3p. Overall, data suggest that circ09863 relieves the inhibitory effect of miR-27a-3p on FASN expression by binding miR-27a-3p and subsequently regulating TAG synthesis and fatty acid composition. Together, these mechanisms provide new research avenues and theoretical bases to improve milk quality.