Roles of CircRNAs in Autoimmune Diseases

New Therapeutic Strategies for the Inflammatory Rheumatoid Arthritis Disease: Emphasizing Mesenchymal Stem Cells and Associated exo-miRNA or exo-lncRNA

The most prevalent inflammatory arthritis and a leading contributor to disability is rheumatoid arthritis (RA). Although it may not have arrived in Europe until the 17th century, it was present in early Native American communities several thousand years ago. Exosomes released by mesenchymal stem cells (MSCs) are highly immunomodulatory due to the origin of the cell. As a cell-free therapy, MSCs-exosomes are less toxic and elicit a weakened immune response than cell-based therapies. Exosomal noncoding RNAs (ncRNAs) are closely associated with a number of biological and functional facets of human health, especially microRNAs (miRNAs) and long noncoding RNAs (lncRNAs). Various exo-miRNAs and lncRNAs such as HAND2-AS1, miR-150-5p, miRNA-124a, and miR-320a lodged with MSC could be appropriate therapeutic ways for RA treatment. These MSC-derived exosomes affect RA disorders via different molecular pathways such as NFK-β, MAPK, and Wnt. The purpose of this review is to review the research that has been conducted since 2020 so far in the field of RA disease treatment with MSC-loaded exo-miRNAs and exo-lncRNAs.

Exosomes derived from cancer-associated fibroblasts promote tumorigenesis, metastasis and chemoresistance of colorectal cancer by upregulating circ_0067557 to target Lin28

BACKGROUND

Cancer associated fibroblasts (CAFs) can remodel tumor microenvironment by secreting exosomes. This study aimed to investigate the role of exosomes derived from cancer-associated fibroblasts in colorectal cancer (CRC) progression.

METHODS

Circular RNA (circRNA) array was used to identify differentially expressed circRNAs in exosomes from normal fibroblasts (NFs) and CAFs, and confirmed one differentially expressed circRNA circ_0067557 by real-time PCR. The effect of circ_0067557 on proliferation, metastasis, chemoresistance and apoptosis was verified by wound heal, tranwell, CCK8, sphere-forming and flow cytometry assay.

RESULTS

Circ_0067557 expression in exosomes from CAFs was higher than those from NFs. CAF-derived exosomes promoted the proliferation, migration, invasion and chemoresistance of CRC cells while suppressed apoptosis. Silencing of circ_0067557 inhibited malignant phenotypes of CRC cells by targeting Lin28A and Lin28B. Moreover, CAF-derived exosomes enhanced the growth of CRC xenograft tumors.

CONCLUSION

Circ_0067557/Lin28A and Lin28B signal axis may be a potential therapy target for CRC.

A novel link between melatonin and circ_0005753/PTBP1/TXNIP regulatory network in the modulation of osteogenic potential in mesenchymal stem cells

Labeled with pluripotent potential, the transplantation of bone marrow mesenchymal stem cells (BMSCs) is considered as a promising strategy for treating osteoporosis (OP). Melatonin (MEL) has been investigated to be an essential regulator involved in bone metabolism, as well as BMSCs differentiation. Circular RNAs (circRNAs) are a unique kind of non-coding RNA and play an important regulatory role in OP. However, whether circRNAs are implicated in the effects of MEL on BMSCs osteogenic differentiation remains largely indeterminate. Expression of circ_0005753 in human BMSCs with MEL treatment, clinical specimens diagnosed with OP, either with ovariectomy (OVX)-induced mice, was measured by RT-qPCR. Western blot was conducted to analyze protein levels of osteogenesis-related molecules (Opg, RUNX2, ALP, BMP4) and TXNIP. RNA immunoprecipitation (RIP) and RNA pull-down assays were performed to validate the binding relationship among circ_0005753, PTBP1, and TXNIP. Alkaline phosphatase (ALP) and alizarin red staining (ARS) were performed to evaluate osteogenic capacity of BMSCs. OP mouse model was established by ovariectomy, as evaluated pathologic changes via hematoxylin-eosin (HE), Masson, and Immunohistochemistry (IHC) staining. Expression of circ_0005753 was remarkably decreased during MEL-induced osteogenic differentiation of BMSCs. Interestingly, not only circ_0005753 knockdown significantly promoted osteogenic differentiation of BMSCs, but circ_0005753 overexpression also weakened osteogenic differentiation induced by MEL treatment. Mechanistically, circ_0005753 maintained the stabilization of TXNIP mRNA via recruiting PTBP1. Additionally, reinforced circ_0005753 abrogated MEL-mediated protective effects on OP pathogenesis in a mouse model. This work shows that MEL facilitates osteogenic differentiation of BMSCs via the circ_0005753/PTBP1/TXNIP axis, which may shed light on the development of a novel therapeutic strategy to prevent OP.

Exploring the Multifaceted Biologically Relevant Roles of circRNAs: From Regulation, Translation to Biomarkers

CircRNAs are a category of regulatory RNAs that have garnered significant attention in the field of regulatory RNA research due to their structural stability and tissue-specific expression. Their circular configuration, formed via back-splicing, results in a covalently closed structure that exhibits greater resistance to exonucleases compared to linear RNAs. The distinctive regulation of circRNAs is closely associated with several physiological processes, as well as the advancement of pathophysiological processes in several human diseases. Despite a good understanding of the biogenesis of circular RNA, details of their biological roles are still being explored. With the steady rise in the number of investigations being carried out regarding the involvement of circRNAs in various regulatory pathways, understanding the biological and clinical relevance of circRNA-mediated regulation has become challenging. Given the vast landscape of circRNA research in the development of the heart and vasculature, we evaluated cardiovascular system research as a model to critically review the state-of-the-art understanding of the biologically relevant functions of circRNAs. We conclude the review with a discussion of the limitations of current functional studies and provide potential solutions by which these limitations can be addressed to identify and validate the meaningful and impactful functions of circRNAs in different physiological processes and diseases.

Recent advances of exosomal circRNAs in cancer and their potential clinical applications

Circular RNA (circRNA) is a type of non-coding RNA that forms a covalently closed, uninterrupted loop. The expression of circRNA differs among cell types and tissues, and various circRNAs are aberrantly expressed in a variety of diseases, including cancer. Aberrantly expressed circRNAs contribute to disease progression by acting as microRNA sponges, functional protein sponges, or novel templates for protein translation. Recent studies have shown that circRNAs are enriched in exosomes. Exosomes are spherical bilayer vesicles released by cells into extracellular spaces that mediate intercellular communication by delivering cargoes. These cargoes include metabolites, proteins, lipids, and RNA molecules. Exosome-mediated cell-cell or cell-microenvironment communications influence the progression of carcinogenesis by regulating cell proliferation, angiogenesis, metastasis as well as immune escape. In this review, we summarize the current knowledge about exosomal circRNAs in cancers and discuss their specific functions in tumorigenesis. Additionally, we discuss the potential value of exosomal circRNAs as diagnostic biomarkers and the potential applications of exosomal circRNA-based cancer therapy.

A spotlight on the interplay between Wnt/β-catenin signaling and circular RNAs in hepatocellular carcinoma progression

Hepatocellular carcinoma (HCC) is one of the deadliest cancers due to multifocal development and distant metastasis resulting from late diagnosis. Consequently, new approaches to HCC diagnosis and treatment are required to reduce mortality rates. A large body of evidence suggests that non-coding RNAs (ncRNAs) are important in cancer initiation and progression. Cancer cells release many of these ncRNAs into the blood or urine, enabling their use as a diagnostic tool. Circular RNAs (CircRNAs) are as a members of the ncRNAs that regulate cancer cell expansion, migration, metastasis, and chemoresistance through different mechanisms such as the Wnt/β-catenin Signaling pathway. The Wnt/β-catenin pathway plays prominent roles in several biological processes including organogenesis, stem cell regeneration, and cell survival. Aberrant signaling of both pathways mentioned above could affect the progression and metastasis of many cancers, including HCC. Based on several studies investigated in the current review, circRNAs have an effect on HCC formation and progression by sponging miRNAs and RNA-binding proteins (RBPs) and regulating the Wnt/β-catenin signaling pathway. Therefore, circRNAs/miRNAs or RBPs/Wnt/β-catenin signaling pathway could be considered promising prognostic and therapeutic targets in HCC.

Decipher the Immunopathological Mechanisms and Set Up Potential Therapeutic Strategies for Patients with Lupus Nephritis

Lupus nephritis (LN) is one of the most severe complications in patients with systemic lupus erythematosus (SLE). Traditionally, LN is regarded as an immune complex (IC) deposition disease led by dsDNA-anti-dsDNA-complement interactions in the subendothelial and/or subepithelial basement membrane of glomeruli to cause inflammation. The activated complements in the IC act as chemoattractants to chemically attract both innate and adaptive immune cells to the kidney tissues, causing inflammatory reactions. However, recent investigations have unveiled that not only the infiltrating immune-related cells, but resident kidney cells, including glomerular mesangial cells, podocytes, macrophage-like cells, tubular epithelial cells and endothelial cells, may also actively participate in the inflammatory and immunological reactions in the kidney. Furthermore, the adaptive immune cells that are infiltrated are genetically restricted to autoimmune predilection. The autoantibodies commonly found in SLE, including anti-dsDNA, are cross-reacting with not only a broad spectrum of chromatin substances, but also extracellular matrix components, including α-actinin, annexin II, laminin, collagen III and IV, and heparan sulfate proteoglycan. Besides, the glycosylation on the Fab portion of IgG anti-dsDNA antibodies can also affect the pathogenic properties of the autoantibodies in that α-2,6-sialylation alleviates, whereas fucosylation aggravates their nephritogenic activity. Some of the coexisting autoantibodies, including anti-cardiolipin, anti-C1q, anti-ribosomal P autoantibodies, may also enhance the pathogenic role of anti-dsDNA antibodies. In clinical practice, the identification of useful biomarkers for diagnosing, monitoring, and following up on LN is quite important for its treatments. The development of a more specific therapeutic strategy to target the pathogenic factors of LN is also critical. We will discuss these issues in detail in the present article.

Circular RNA vaccine induces potent T cell responses

Circular RNAs (circRNAs) are a class of RNAs commonly found across eukaryotes and viruses, characterized by their resistance to exonuclease-mediated degradation. Their superior stability compared to linear RNAs, combined with previous work showing that engineered circRNAs serve as efficient protein translation templates, make circRNA a promising candidate for RNA medicine. Here, we systematically examine the adjuvant activity, route of administration, and antigen-specific immunity of circRNA vaccination in mice. Potent circRNA adjuvant activity is associated with RNA uptake and activation of myeloid cells in the draining lymph nodes and transient cytokine release. Immunization of mice with engineered circRNA encoding a protein antigen delivered by a charge-altering releasable transporter induced innate activation of dendritic cells, robust antigen-specific CD8 T cell responses in lymph nodes and tissues, and strong antitumor efficacy as a therapeutic cancer vaccine. These results highlight the potential utility of circRNA vaccines for stimulating potent innate and T cell responses in tissues.

Circular RNA ciRS-7 affects the propagation of Cryptosporidium parvum in HCT-8 cells via regulating miR-135a-5p/stat1 axis

Cryptosporidium spp. are protozoan parasites that mainly inhabit intestinal epithelial cells, causing diarrheal diseases in humans and a great number of animals. Cryptosporidium parvum is the most common zoonotic species, responsible for nearly 45% of human cryptosporidiosis worldwide. Understanding the interaction mechanisms between C. parvum and host gastrointestinal epithelial cells has significant implications to control cryptosporidiosis. One up-regulated circRNA ciRS-7 was found previously by our group to promote in vitro propagation of C. parvum in HCT-8 cells. In the present study, miR-135a-5p, was found to be a miRNA target of ciRS-7. Cryptosporidium parvum infection induced significantly down-regulation of miR-135a-5p and dramatic up-regulation of its potential target stat1 gene at mRNA and protein levels. Dual luciferase reporter assays validated the physical interactions between miR-135a-5p and stat1, and between ciRS-7 and miR-135a-5p. Further study revealed that ciRS-7 could sponge miR-135a-5p to positively regulate the protein levels of STAT1 and phosphorylated STAT1 (p-STAT1) and thus promote C. parvum propagation in HCT-8 cells. Our findings further reveal the mystery of regulatory roles of host circRNAs during Cryptosporidium infection, and provide a novel insight to develop strategies to control cryptosporidiosis.

Circular RNA in autoimmune diseases: special emphasis on regulation mechanism in RA and SLE

BACKGROUND

Autoimmune diseases are diseases caused by tissue damage caused by the body's immune response to autoantibodies. Circular RNAs (CircRNAs) are a kind of special endogenous non-coding RNA that play a biological role by regulating gene transcription.

METHODS

In this work, we searched the PubMed, Web of Science (SCIE), National Science and Technology Library (NSTL), and ScienceDirect Online (SDOL) databases to summarize the impact of circRNAs on autoimmune diseases, especially the results of circRNAs in rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE).

RESULTS

The study on the function of circRNAs and autoimmune diseases further deepened our understanding of the development and pathogenesis of autoimmune diseases. CircRNAs may act as miRNA sponges to regulate biological processes and affect the occurrence and development of autoimmune diseases. CircRNAs are closely related to the pathogenesis of RA and SLE and may become potential biomarkers for the diagnosis and treatment of RA and SLE.

CONCLUSION

CircRNAs play an important role in the pathogenesis of RA, SLE and other autoimmune diseases, and are expected to provide new biomarkers for the diagnosis and treatment of autoimmune diseases. However, the function and mechanism of circRNAs in autoimmune diseases need more comprehensive research.

METTL3-mediated Hsa_circ_0000390 downregulation enhances the proliferation, migration, and invasion of colorectal cancer cells by increasing Notch1 expression

Circular RNAs (circRNAs), as noncoding RNAs, have gained widespread attention in cancers. Circ_0000390 has been verified to be downregulated in gastric cancer, while its function and regulatory mechanism in cancer is largely unknown. The purpose of this study is to investigate the expression, functions, and potential mechanism of circ_0000390 in colorectal cancer (CRC). Circ_0000390 expression in CRC tissues was first identified with RT-qPCR. Besides, the function of circ_0000390 was assessed through gain-of-function and rescued experiments in CRC cells and mouse xenograft models. Our results showed that circ_0000390 was lowly expressed in CRC tissues, and circ_0000390 could downregulate Notch1 and be downregulated by METTL3. Functionally, results showed circ_0000390 overexpression suppressed the proliferation, cell migration, and invasion of CRC cells, which also could be reversed by Notch1 overexpression. Additionally, METTL3 overexpression could accelerate the proliferation, cell migration, and invasion of CRC cells, which also was weakened by circ_0000390 overexpression in CRC cells in vitro and in vivo. This study suggested that circ_0000390 might be anti-tumor factor in CRC and METTL3/Notch1 might be a therapeutic targets for CRC.

The role of non-coding RNA in lupus nephritis

Systemic lupus erythematosus (SLE) is a common autoimmune disease with multiple manifestations. The renal implication, also called lupus nephritis (LN) is the most regular type of complication and results in adverse outcomes. Multiple studies revealed the importance of non-coding RNA in diseases, likewise observed in nephropathies, particularly LN. Long-non-coding RNA (lncRNA) is a group of RNA that are more than 200 nucleotides in length. And in circular RNA (circRNA), the head and tail of RNA are connected by a 3' → 5' phosphodiester bond. Both two types of non-coding RNA play important roles in LN pathogenesis through the competitive endogenous RNA (ceRNA) effect. LncRNAs and circRNAs can sponge miRNAs and consequently act on downstream signaling pathways, which are capable to influence various aspects of LN, including cell proliferation, inflammation, and oxidative stress. And lncRNAs and circRNAs have the potential to act as biomarkers to diagnose LN and distinguish whether SLE patients with LN or not. In the future, lncRNAs and circRNAs may be accessible therapeutic targets.

Rheumatoid arthritis and non-coding RNAs; how to trigger inflammation

Rheumatoid arthritis (RA) is a systemic and chronic inflammatory disease categorized by continuous synovitis in the joints and systemic inflammatory responses that can cause lifelong disability. The major cause of RA is the dysregulation of the immune response. The development of RA disease includes multiplex association of several interleukins and cells, which leads to synovial cell growth, cartilage and bone damage. The primary stage of RA disease is related to the modification of both the innate and adaptive immune systems, which leads to the formation of autoantibodies. This process results in many damaged molecules and epitope spreading. Both the innate (e.g., dendritic cells, macrophages, and neutrophils) and acquired immune cells (e.g., T and B lymphocytes) will increase and continue the chronic inflammatory condition in the next stages of the RA disease. In recent years, non-coding RNAs have been proved as significant controllers of biological functions, especially immune cell expansion and reactions. Non-coding RNAs were primarily containing microRNA (miRNA), long non-coding RNA (lncRNA), and circular RNA (circRNA). Various studies confirmed non-coding RNAs as hopeful markers for diagnosing and curing RA. This review will describe and cover existing knowledge about RA pathogenesis, which might be favorable for discovering possible ncRNA markers for RA.

CircVAPA contributes to hyper-proliferation and inflammation of keratinocytes through miR-125b-5p/sirt6 axis in psoriasis

Psoriasis is an autoimmune skin disease with abnormal keratinocyte hyperproliferation. The important roles of circular RNAs (circRNAs) in various inflammatory diseases have been revealed. The present study aimed to investigate the roles of circVAPA and its molecular mechanisms in psoriasis. Quantitative real-time polymerase chain reaction was performed to measure the RNA expression. Enzyme-linked immunosorbent assays were employed to examine the production of inflammatory factors. Cell-counting kit-8, EDU and flow cytometry assay were conducted to examine the cell viability, proliferation and apoptosis respectively. Dual-luciferase reporter assay and ribonucleoprotein immunoprecipitation (RIP) were conducted to verify the target relationship between miR-125b-5p and circVAPA or Sirt6. Herein our findings showed increased expression of circVAPA and Sirt6 and decreased level of miR-125b-5p in psoriatic lesional tissues and M5-stimulated keratinocytes. Mechanistically, circVAPA knockdown significantly suppressed the promotion of M5 on cell viability, proliferation, and inflammation of HaCaT cells. circVAPA was verified to interact with miR-125b-5p, while inhibition of miR-125b-5p counteracted circVAPA knockdown-mediated effects in M5-stimulated HaCaT cells. Sirt6 was confirmed as a target of miR-125b-5p, and miR-125b-5p overexpression inhibited cell growth and inflammation partly by targeting Sirt6 in M5-stimulated HaCaT cells. Moreover, circVAPA was featured as a competing endogenous RNA by directly sponging miR-125b-5p to up-regulate the expression of Sirt6. CircVAPA participate in the progression of psoriasis through miR-125b-5p/sirt6 axis by regulating proliferation and inflammation of keratinocytes, highlighting a potential therapeutic target for psoriasis.

Dysregulation of miR-193a serves as a potential contributor to MS pathogenesis via affecting RhoA and Rock1

BACKGROUND

Multiple sclerosis (MS) is one of the most common neurological diseases that cause chronic inflammation of the central nervous system and demyelination of the myelin sheath. At present, microRNAs (miRNAs) are considered not only a diagnostic and prognostic indicator of diseases but also a new goal in gene therapy. This study aims to find a simple, non-invasive, valuable biomarker for early detection and potential treatment of MS.

METHODS

In the present study, 30 patients with MS were included. The qRT-PCR method was performed to evaluate the expression level of miR-193a, RhoA, and ROCK1. Besides, western blotting was performed to determine the expression level of RhoA and ROCK1 at protein levels. Moreover, we aimed to clarify the possible correlation between miR-193a-5p and its-regulated target genes so that miR-193a-5p mimic was transfected into MS-derived cultured PBMSs, and the expression level of RhoA and ROCK1 were then evaluated by qRT-PCR and Western blotting. In the final step, the correlation between miR-193a-5p and clinicopathological features of patients was investigated.

RESULTS

Results showed that miR-193a was decreased while RhoA and ROCK1 were up-regulated in PBMCs obtained from patients with MS compared to the control group. It was also revealed that miR-193a transfection reduced RhoA and ROCK1 expression at mRNA and protein levels. The results from the Chi-square analysis showed that down-regulation of miR-193a was associated with increased CRP level, CSF IgG positivity, and MSSS (Multiple Sclerosis Severity Score), suggesting miR-193a is a potential diagnostic and prognostic indicator.

CONCLUSION

We implied that miR-193a could modulate RhoA and ROCK 1 expression in MS patients, in which its down-regulation leads to increased expression of RhoA and ROCK1 and poor prognosis of patients with MS. Therefore, miR-193a and its associated targets could serve potential prognostic, diagnostic, and therapeutic efficacy in MS patients.

Biomarkers (mRNAs and non-coding RNAs) for the diagnosis and prognosis of rheumatoid arthritis

In recent years, diagnostic and therapeutic approaches for rheumatoid arthritis (RA) have continued to improve. However, in the advanced stages of the disease, patients are unable to achieve long-term clinical remission and often suffer from systemic multi-organ damage and severe complications. Patients with RA usually have no overt clinical manifestations in the early stages, and by the time a definitive diagnosis is made, the disease is already at an advanced stage. RA is diagnosed clinically and with laboratory tests, including the blood markers C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR) and the autoantibodies rheumatoid factor (RF) and anticitrullinated protein antibodies (ACPA). However, the presence of RF and ACPA autoantibodies is associated with aggravated disease, joint damage, and increased mortality, and these autoantibodies have low specificity and sensitivity. The etiology of RA is unknown, with the pathogenesis involving multiple factors and clinical heterogeneity. The early diagnosis, subtype classification, and prognosis of RA remain challenging, and studies to develop minimally invasive or non-invasive biomarkers in the form of biofluid biopsies are becoming more common. Non-coding RNA (ncRNA) molecules are composed of long non-coding RNAs, small nucleolar RNAs, microRNAs, and circular RNAs, which play an essential role in disease onset and progression and can be used in the early diagnosis and prognosis of RA. In this review of the diagnostic and prognostic approaches to RA disease, we provide an overview of the current knowledge on the subject, focusing on recent advances in mRNA-ncRNA as diagnostic and prognostic biomarkers from the biofluid to the tissue level.

CircRNA expression profiles and functional analysis in a mouse model of chronic intermittent hypoxia-induced renal injury: new insight into pathogenesis

Increasing evidence has demonstrated that circular RNAs (circRNAs) play crucial roles in the pathogenesis of multiple diseases. However, the functions of circRNAs in renal injury induced by obstructive sleep apnea (OSA) are poorly understood. The aim of this current study is to identify the global changes of circRNAs expression in OSA-induced renal damage. The mouse model of OSA treated by chronic intermittent hypoxia (CIH) was established. We assessed the expression profiles of circRNAs in CIH caused renal injury by microarray analysis. Bioinformatic analyses were further performed by us to assess those differentially expressed circRNAs. Quantitative realtime PCR (qRT-PCR) were then conducted to assure the data of microarray. Finally, a circRNA-miRNA -mRNA competing endogenous RNA (ceRNA) regulatory network was constructed. We found 11 upregulated and 13 downregulated circRNAs in CIH-induced renal injury. The qRT-PCR validated that the six selected circRNAs were identical to the results of microarray. Both Gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis were further employed to annotate the potential functions of dysregulated circRNAs. Finally, we established a ceRNA network to predict the target genes of circRNAs. In general, our results first illustrate that circRNAs are aberrantly expressed in OSA-induced renal injury, which might aid in offering novel genetic insights into this disease and potential therapeutic targets for OSA-associated chronic kidney disease.

Type 1 Diabetes Mellitus-Related circRNAs Regulate CD4+ T Cell Functions

Circular RNAs (circRNAs) participate in development of malignancies through its active role as a “miRNA sponge.” Their roles in type 1 diabetes mellitus (T1DM) pathogenesis are elusive. Here, the important role of circRNAs in T1DM was explored. circRNA profiling was performed for isolated CD4+ T cells from blood of T1DM and healthy volunteers. There were 257 differentially expressed circRNAs. Only three upregulated DEcircRNAs (hsa_circ_0000324, hsa_circ_0001853, and hsa_circ_0068797) were consistent with the GEO database. Through KEGG analyses, it was found that the three DEcircRNAs were associated with 11 miRNAs and 8 immune-related target genes (mRNA). Further analysis found that four miRNAs, two circRNAs, and four mRNAs were associated with nine circRNA-miRNA-mRNA networks. This confirmed the requirements of sponge mechanisms. The qRT-PCR analysis revealed that circRNA000324/miRNA675-5p/MAPK14 and circRNA000324/miRNA-675-5p/SYK may be potential mechanisms in regulation of differentiation and proliferation of CD4+ T cell in patients with T1DM. Therefore, targeting circRNA to regulate cellular immune responses by regulating CD4+ T cell differentiation may be a new strategy for the treatment of T1DM.

Stem cell-derived exosomal transcriptomes for wound healing

Wound healing is a complex and integrated process of the interaction of various components within the injured tissue. Accumulating evidence suggested that stem cell-derived exosomal transcriptomes could serve as key regulatory molecules in wound healing in stem cell therapy. Stem cell-derived exosomal transcriptomes mainly consist of long noncoding RNAs (lncRNAs), microRNAs (miRNAs), circular RNAs (circRNAs) and messenger RNAs (mRNAs). In this article we presented a brief introduction on the wound repair process and exosomal transcriptomes. Meanwhile, we summarized our current knowledge of the involvement of exosomal transcriptomes in physiological and pathological wound repair process including inflammation, angiogenesis, and scar formation.

CircDCLRE1C Regulated Lipopolysaccharide-Induced Inflammatory Response and Apoptosis by Regulating miR-214b-3p/STAT3 Pathway in Macrophages

The immune cell inflammation response is closely related to the occurrence of disease, and much evidence has shown that circular RNAs (circRNAs) play vital roles in the occurrence of disease. However, the biological function and regulatory mechanisms of circRNAs in the immune cell inflammation response remain poorly understood. In this study, we constructed an inflammatory model using lipopolysaccharide (LPS)-stimulated chicken macrophage lines (also known as HD11) to verify the function and mechanism of the novel circDCLRE1C (ID: gga_circ_0001674), which was significantly upregulated in spleen tissues infected by coccidia and the macrophage cells exposed to LPS. The results showed that circDCLRE1C aggravated LPS-induced inflammation and apoptosis in HD11 cells. Systemically, circDCLRE1C acted as a sponge for miR-214b-3p binding sites thereby regulating the expression of STAT3. The overexpression of miR-214b-3p rescued the pro-inflammatory effect of circDCLRE1C in HD11 cells stimulated with LPS, and rescued the high expression of STAT3. In conclusion, our study showed that circDCLRE1C could aggravate LPS-induced inflammation and apoptosis through competitive adsorption of miR-214b-3p, thereby increasing the expression of STAT3.

Exosome circRNAs and ceRNA network profiles in different ANA sera

Increasing evidences show that circRNAs are associated with some autoimmunity diseases either as a biomarker or therapeutic target. Exosomes containing nucleic acids and proteins are found in sera of series diseases and could serve as either diagnostic or therapeutic target. ANA serves as first common diagnostic test for autoimmunity disease, different ANA staining reflecting different types of autoimmunity disease. Till now, whether different ANA sera exosomes express different circRNAs and relevant ceRNA networks are still shortage of investigation. This study analyzed circRNAs, miRNAs, and their interaction networks in different ANA sera exosomes by high-throughput sequencing. It found no significant difference of total circRNAs and miRNAs amount across different ANA sera exosomes. However, significant differences were found of circRNAs, miRNA constituents, function analysis by KEGG and GO, and their ceRNA networks including miRNA-circRNA and miRNA-mRNA among different ANA sera exosomes, suggesting sera exosome circRNAs as either biomarker or mechanism of autoimmunity diseases.

CircEIF5 contributes to hyperproliferation and inflammation of keratinocytes in psoriasis via p-NFκB and p-STAT3 signalling pathway

Psoriasis is a chronic, immune-mediated skin disease accompanied by hyperproliferation and inflammation of keratinocytes. Circular RNAs (circRNAs) as new players regulating the development of psoriasis have been reported in recent years. However, its mechanism has not yet been fully revealed. In this study, we identified that hsa_circ_0033469 (circEIF5) was highly expressed in psoriasis tissues compared with the normal skin. We investigated the functional roles of circEIF5 in proliferation and inflammatory of HaCat cells under M5-stimulated inflammatory condition. By using a approach of knockdown and overexpression of circEIF5, we showed that circEIF5 could promote proliferation by facilitating the G1/S transition and increase secretion of chemokines in HaCat cells. These moderating effects of circEIF5 were associated with the activating of the NF-κB and STAT3 signalling pathways. Moreover, NF-κB and STAT3 inhibition abrogated circEIF5-induced promotion of cell proliferation and chemokine secretion. These results indicated that through NF-κB and STAT3 signalling pathways, circEIF5 regulated the proliferation and chemokine secretion of HaCat cells and contributed to the pathogenesis of psoriasis, which might become a potent target for psoriasis treatment.

[Role of circular RNAs in immune-related diseases]

Objective Circular RNAs (circRNAs) are non-coding RNAs (ncRNA) circularized without a 3′ polyadenylation [poly-(A)] tail or a 5′ cap, resulting in a covalently closed loop structure. circRNAs were first discovered in RNA viruses in the 1970s, but only a small number of circRNAs were discovered at that time due to limitations in traditional polyadenylated transcriptome analyses. With the development of specific biochemical and computational methods, recent studies have shown the presence of abundant circRNAs in eukaryotic transcriptomes. circRNAs play vital roles in many physiological and pathological processes, such as acting as miRNA sponges, binding to RNA-binding proteins (RBPs), acting as transcriptional regulatory factors, and even serving as translation templates. Current evidence has shown that circRNAs can be potentially used as excellent biomarkers for diagnosis, therapeutic effect evaluation, and prognostic assessment of a variety of diseases, and they may also provide effective therapeutic targets due to their stability and tissue and development-stage specificity. This review focuses on the properties of circRNAs and their immune relationship to disease, and explores the role of circRNAs in immune-related diseases and the directions of future research.

Functional Interactions Between lncRNAs/circRNAs and miRNAs: Insights Into Rheumatoid Arthritis

Rheumatoid arthritis (RA) is one of the most common autoimmune diseases that affect synovitis, bone, cartilage, and joint. RA leads to bone and cartilage damage and extra-articular disorders. However, the pathogenesis of RA is still unclear, and the lack of effective early diagnosis and treatment causes severe disability, and ultimately, early death. Accumulating evidence revealed that the regulatory network that includes long non-coding RNAs (lncRNAs)/circular RNAs (circRNAs), micro RNAs (miRNAs), and messenger RNAs (mRNA) plays important roles in regulating the pathological and physiological processes in RA. lncRNAs/circRNAs act as the miRNA sponge and competitively bind to miRNA to regulate the expression mRNA in synovial tissue, FLS, and PBMC, participate in the regulation of proliferation, apoptosis, invasion, and inflammatory response. Thereby providing new strategies for its diagnosis and treatment. In this review, we comprehensively summarized the regulatory mechanisms of lncRNA/circRNA-miRNA-mRNA network and the potential roles of non-coding RNAs as biomarkers and therapeutic targets for the diagnosis and treatment of RA.

Long Noncoding RNA and Circular RNA Expression Profiles of Monocyte-Derived Dendritic Cells in Autoimmune Hepatitis

Autoimmune hepatitis (AIH) is a chronic liver disease caused by disruption of liver immune homeostasis. The effect of dendritic cells (DCs) on the pathogenesis of AIH is not fully understood. Long noncoding RNAs (lncRNAs), circular RNAs (circRNAs), and microRNAs (miRNAs) have been shown to play critical roles in the regulation of cell function. In this study, we analyzed the immunophenotypic characteristics of DCs in the peripheral blood. The percentage of mature DCs was higher in AIH patients than in healthy controls (HCs), and the proportion of mature DCs decreased after treatment. We isolated monocyte-derived DCs (moDCs) from the peripheral blood, obtained whole RNA-sequencing (RNA-seq) data for the moDCs from the two groups, and identified differentially expressed (DE) lncRNAs, circRNAs, miRNAs and mRNAs. In addition, we performed Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses for the DE mRNAs and constructed competing endogenous RNA (ceRNA) networks. ENST00000543334, hsa_circ_0000279, and hsa_circ_0005076 were selected and validated by RT-qPCR. These results provide a possible molecular mechanism of DCs in the pathogenesis of AIH and identify some potential therapeutic targets.

Circular RNA CREBBP Suppresses Hepatic Fibrosis Via Targeting the hsa-miR-1291/LEFTY2 Axis

CircRNAs (circRNAs) are commonly dysregulated in a variety of human diseases and are involved in the development and progression of cancer. However, the role of circRNAs in hepatic fibrosis (HF) is still unclear. Our previous high throughput screen revealed changes in many circRNAs in mice with carbon tetrachloride (CCl4)-induced HF. For example, circCREBBP was significantly down-regulated in primary hepatic stellate cells (HSCs) and liver tissue of HF mice induced by CCl4 compared to those in the vehicle group. Overexpression of circCREBBP with AAV8-circCREBBP in vivo prevented CCl4-induced HF worsening by reducing serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) contents, liver hydroxyproline levels, collagen deposition, and levels of pro-fibrosis genes and pro-inflammatory cytokines. Furthermore, in vitro function loss and function gain analysis showed that circCREBBP inhibited HSCs activation and proliferation. Mechanically, circCREBBP acts as a sponge for hsa-miR-1291 and subsequently promotes LEFTY2 expression. In conclusion, our current results reveal a novel mechanism by which circCREBBP alleviates liver fibrosis by targeting the hsa-miR-1291/LEFTY2 axis, and also suggest that circCREBBP may be a potential biomarker for heart failure.

RNA-Seq profiling of leukocytes reveals a sex-dependent global circular RNA upregulation in multiple sclerosis and 6 candidate biomarkers

Multiple sclerosis (MS) is a chronic autoimmune disease of the central nervous system, with higher prevalence in women, that leads to neurological disability. The disease course and clinical phenotype are highly variable, and therefore, biomarkers for the diagnosis, classification, monitoring of the disease and treatment assessment are needed. Studies have shown a dysregulation in the coding and non-coding RNAs and proposed some as biomarkers. However, still none of them have reached the clinical practice. Recently, circular RNAs (circRNAs) have emerged as new players in the transcriptome that hold a great potential as biomarkers in several diseases. Leukocytes from 30 MS patients and 20 healthy controls (HCs) were RNA-sequenced to study the linear and circular transcriptome. Differential expression analysis was performed by DESeq, and circRNA candidates were studied in a second cohort (70 MS and 46 HC) by RT-qPCR and in paired samples drawn during the relapse and remission phases (20 patients). Among the differentially expressed circRNAs, 96.1% are upregulated in patients compared with controls, but similar circRNA profiles are found between MS types. The same upregulation trend was observed in females but not in males or in the linear transcriptome. The upregulation of 6 circRNAs was validated, and a change in their expression was found between relapse and remission. The 6 circRNAs showed a good performance to discriminate patients from HC with a combined area under the curve of 0.852. There is global, specific and sex-dependent increase of circRNA expression in MS, and 6 circRNAs are proposed as potential biomarkers.

Paeoniflorin Suppresses Rheumatoid Arthritis Development via Modulating the Circ-FAM120A/miR-671-5p/MDM4 Axis

Paeoniflorin is an active ingredient derived from Paeonia, which has an anti-inflammatory effect. However, the potential role and basis of paeoniflorin in rheumatoid arthritis (RA) are indistinct. Cell viability, cycle distribution, migration, and invasion were evaluated via Cell Counting Kit-8 (CCK-8), flow cytometry, and transwell assays. The contents of inflammatory cytokines were examined using enzyme-linked immunosorbent assay (ELISA). RNA expression levels were determined via qRT-PCR and western blot. The targeting relationship between miR-671-5p and circ-FAM120A (hsa_circ_0003972) or murine double minute 4 (MDM4) was validated via dual-luciferase reporter assay. Paeoniflorin restrained proliferation, migration, invasion, and inflammation and accelerated cell cycle arrest in RA fibroblast-like synoviocytes (RA-FLSs). Circ-FAM120A was boosted in RA synovial tissues and RA-FLSs. Circ-FAM120A upregulation, miR-671-5p knockdown, or MDM4 augmentation reversed the repressive effect of paeoniflorin on RA-FLS progression. Moreover, paeoniflorin attenuated RA-FLS progression by regulating the circ-FAM120A/miR-671-5p/MDM4 axis. Paeoniflorin inhibited RA-FLS proliferation, mobility, and inflammation and triggered cell cycle arrest via mediating the circ-FAM120A/miR-671-5p/MDM4 pathway.

Circ_0087862 promotes the progression of colorectal cancer by sponging miR-142-3p and up-regulating BACH1 expression

Circular RNAs (circRNAs) feature prominently in regulating the malignant biological behaviors of colorectal cancer (CRC), including cell viability, cell cycle progression, apoptosis, migration, invasion, and so on. This study is performed to probe into the biological function and molecular mechanism of circ_0087862 in CRC. The expression profile of GSE138589 was available from Gene Expression Omnibus (GEO), and the differentially expressed circRNAs were analyzed by GEO2R. The expression of circ_0087862, miR-142-3p, and BACH1 mRNA in CRC tissues and cells was measured by qRT-PCR. CCK-8 assay was employed to determine the proliferation of CRC cells. Scratch wound healing and transwell assays were used to examine the migration and invasion of CRC cells. The targeting relationships between circ_0087862 and miR-142-3p, and between miR-142-3p and BACH1 3'UTR were verified by dual-luciferase reporter gene assay and RIP assay. BACH1 protein expression was probed by western blot. Circ_0087862 was highly expressed in CRC tissues and cell lines. Knocking down circ_0087862 significantly restrained the multiplication, migration and invasion of CRC cells. miR-142-3p inhibition weakened the impact of circ_0087862 knockdown on CRC cells. Circ_0087862 regulated BACH1 expressions by targeting miR-142-3p. Circ_0087862 regulates BACH1 expressions through sponging miR-142-3p, and promotes the proliferation, migration, and invasion of CRC cells.

Promising Therapeutic Targets for Treatment of Rheumatoid Arthritis

Rheumatoid arthritis (RA) is a systemic poly-articular chronic autoimmune joint disease that mainly damages the hands and feet, which affects 0.5% to 1.0% of the population worldwide. With the sustained development of disease-modifying antirheumatic drugs (DMARDs), significant success has been achieved for preventing and relieving disease activity in RA patients. Unfortunately, some patients still show limited response to DMARDs, which puts forward new requirements for special targets and novel therapies. Understanding the pathogenetic roles of the various molecules in RA could facilitate discovery of potential therapeutic targets and approaches. In this review, both existing and emerging targets, including the proteins, small molecular metabolites, and epigenetic regulators related to RA, are discussed, with a focus on the mechanisms that result in inflammation and the development of new drugs for blocking the various modulators in RA.

Evolutionary conservation in noncoding genomic regions

Humans may share more genomic commonalities with other species than previously thought. According to current estimates, ~5% of the human genome is functionally constrained, which is a much larger fraction than the ~1.5% occupied by annotated protein-coding genes. Hence, ~3.5% of the human genome comprises likely functional conserved noncoding elements (CNEs) preserved among organisms, whose common ancestors existed throughout hundreds of millions of years of evolution. As whole-genome sequencing emerges as a standard procedure in genetic analyses, interpretation of variations in CNEs, including the elucidation of mechanistic and functional roles, becomes a necessity. Here, we discuss the phenomenon of noncoding conservation via four dimensions (sequence, regulatory conservation, spatiotemporal expression, and structure) and the potential significance of CNEs in phenotype variation and disease.

Dysregulation of circRNA expression in the peripheral blood of individuals with schizophrenia and bipolar disorder

Circular RNAs (circRNAs) are head-to-tail back-spliced RNA transcripts that have been linked to several biological processes and their perturbation is evident in human disease, including neurological disorders. There is also emerging research suggesting circRNA expression may also be altered in psychiatric and behavioural syndromes. Here, we provide a comprehensive analysis of circRNA expression in peripheral blood mononuclear cells (PBMCs) from 39 patients with schizophrenia and bipolar disorder as well as 20 healthy individuals using deep RNA-seq. We observed systematic alternative splicing leading to a complex and diverse profile of RNA transcripts including 8762 high confidence circRNAs. More specific scrutiny of the circular transcriptome in schizophrenia and bipolar disorder, compared to a non-psychiatric control group, revealed significant dysregulation of 55 circRNAs with a bias towards downregulation. These molecules were predicted to interact with a large number of miRNAs that target genes enriched in psychiatric disorders. Further replication and cross-validation to determine the specificity of these circRNAs across broader diagnostic groups and subgroups in psychiatry will enable their potential utility as biomarkers to be established. KEY MESSAGES: • We identified 8762 high confidence circRNAs with systematic alternative splicing in human PBMCs. • CircRNAs were dysregulated in schizophrenia and bipolar disorder, compared to a non-psychiatric control group. • The DE circRNAs were predicted to interact with miRNAs with target genes enriched in psychiatric disorders. • Some circRNAs have the potential to serve as biomarkers in psychiatry.

CircMAPK9 promotes the progression of fibroblast-like synoviocytes in rheumatoid arthritis via the miR-140-3p/PPM1A axis

Background

Rheumatoid arthritis (RA) is a chronic inflammatory joint disease, and fibroblast-like synoviocytes (FLSs) are key effector cells in RA development. Mounting evidence indicates that circular RNAs (circRNAs) participate in the occurrence and development of RA. However, the precise mechanism of circRNA mitogen-activated protein kinase (circMAPK9) in the cell processes of FLSs has not been reported.

Methods

The expression levels of circMAPK9, microRNA-140-3p (miR-140-3p), and protein phosphatase magnesium-dependent 1A (PPM1A) were determined by quantitative real-time polymerase chain reaction (qRT-PCR) or western blot assay. Cell proliferation was examined by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Cell apoptosis and cycle distribution were assessed by flow cytometry. Cell migration and invasion were tested by transwell assay. All the proteins were inspected by western blot assay. Inflammatory response was evaluated by enzyme-linked immunosorbent assay (ELISA). The interaction between miR-140-3p and circMAPK9 or PPM1A was verified by dual-luciferase reporter assay.

Results

CircMAPK9 and PPM1A were upregulated and miR-140-3p was downregulated in RA patients and FLSs from RA patients (RA-FLSs). CircMAPK9 silence suppressed cell proliferation, migration, invasion, inflammatory response, and promoted apoptosis in RA-FLSs. MiR-140-3p was a target of circMAPK9, and miR-140-3p downregulation attenuated the effects of circMAPK9 knockdown on cell progression and inflammatory response in RA-FLSs. PPM1A was targeted by miR-140-3p, and circMAPK9 could regulate PPM1A expression by sponging miR-140-3p. Furthermore, miR-140-3p could impede cell biological behaviors in RA-FLSs via targeting PPM1A.

Conclusion

CircMAPK9 knockdown might inhibit cell proliferation, migration, invasion, inflammatory response, and facilitate apoptosis in RA-FLSs via regulating miR-140-3p/PPM1A axis, offering a new mechanism for the comprehension of RA development and a new insight into the potential application of circMAPK9 in RA treatment.

The functions of fluoxetine and identification of fluoxetine-mediated circular RNAs and messenger RNAs in cerebral ischemic stroke

Fluoxetine is used to improve cognition, exercise ability, depression, and neurological functions in patients with cerebral ischemic stroke. Circular RNAs (circRNAs) play important regulatory roles in multiple diseases. However, studies regarding the fluoxetine-mediated circRNA-microRNA-messenger RNA (mRNA) axis have not been conducted. This study is aim to investigate the functions of fluoxetine and identification of fluoxetine-mediated circRNAs and mRNAs in cerebral ischemic stroke. The middle cerebral artery occlusion (MCAO) rat models were successfully established at fisrt, and then rats were intraperitoneally injected with 10-mg/kg fluoxetine hydrochloride for 14 d. Afterward, the cerebral infarction area was evaluated using triphenyltetrazolium chloride staining. High-throughput sequencing was adopted to screen the differential circRNAs and mRNAs. The candidate circRNAs, mRNAs, and potential microRNAs were verified using quantitative reverse transcriptase polymerase chain reaction (qRT-PCR). In addtion, microRNA and circRNA binding was verified using the dual-luciferase reporter assay. Results revealed that fluoxetine markedly diminished the cerebral infarction area in rats after MCAO. The circRNAs and mRNAs were differentially expressed, which includes 879 circRNAs and 815 mRNAs between sham and MCAO groups, respectively, and 958 circRNAs and 838 mRNAs between MCAO and fluoxetine groups, respectively. In which, circMap2k1 and Pidd1 expression was significantly increased in the MCAO group but suppressed after fluoxetine treatment. Moreover, circMap2k1 directly binds with miR-135b-5p. Taken together, we verified that fluoxetine could improve brain injury after cerebral ischemic stroke. Moreover, the circMap2k1/miR-135b-5p/Pidd1 axis is potentially involved in cerebral ischemic stroke.

CircELK4 Contributes to Lupus Nephritis by Acting as a miR-27b-3p Sponge to Regulate STING/IRF3/IFN-I Signaling

Systemic lupus erythematosus (SLE) is a prototypic autoimmune disease and a common complication of SLE is lupus nephritis (LN) during which lupus autoantibodies and proinflammatory cytokines attack the kidney and cause renal dysfunction. The current treatments to LN are limited due to a poor understanding of the pathogenesis. Here, we studied the molecular mechanisms of LN by investigating the function of circELK4/miR-27b-3p axis. MRL/lpr mice and LPS-treated HK-2 cells were used as the mouse model and cell model of LN, respectively. Blood samples were collected from LN patients. qRT-PCR and western blot were used to measure expression levels of circELK4, miR-27b-3p, apoptosis-related proteins, cytokines, and STING/IRF-3/IFN-I signaling. ELISA was performed to examine levels of cytokines including IL-6 and TNF-α. H&E staining was used to examine kidney morphology. TUNEL staining and flow cytometry were used to determine cell apoptosis. Dual luciferase activity assay and RNA pull down were employed to validate the interactions of circELK4/miR-27b-3p and miR-27b-3p/STING. CircELK4 was elevated in LN mice, patients, and LPS-treated HK-2 cells. Knockdown of circELK4 attenuated renal injury in LN mice and LPS-induced HK-2 cell injury. CircELK4 directly bound to miR-27b-3p while miR-27b-3p targeted STING. Moreover, overexpression of circELK4 could partially reverse the effects of miR-27b-3p mimics on cell apoptosis and inflammation. Furthermore, circELK4/miR-27b-3p regulated renal cell damage via modulating STING/IRF3/IFN-I signaling. CircELK4 contributes to renal injury by promoting inflammation and cell apoptosis via acting as a miR-27b-3p sponge to modulate STING/IRF3/IFN-I signaling in LN.

The Expression of Non-Coding RNAs and Their Target Molecules in Rheumatoid Arthritis: A Molecular Basis for Rheumatoid Pathogenesis and Its Potential Clinical Applications

Rheumatoid arthritis (RA) is a typical autoimmune-mediated rheumatic disease presenting as a chronic synovitis in the joint. The chronic synovial inflammation is characterized by hyper-vascularity and extravasation of various immune-related cells to form lymphoid aggregates where an intimate cross-talk among innate and adaptive immune cells takes place. These interactions facilitate production of abundant proinflammatory cytokines, chemokines and growth factors for the proliferation/maturation/differentiation of B lymphocytes to become plasma cells. Finally, the autoantibodies against denatured immunoglobulin G (rheumatoid factors), EB virus nuclear antigens (EBNAs) and citrullinated protein (ACPAs) are produced to trigger the development of RA. Furthermore, it is documented that gene mutations, abnormal epigenetic regulation of peptidylarginine deiminase genes 2 and 4 (PADI2 and PADI4), and thereby the induced autoantibodies against PAD2 and PAD4 are implicated in ACPA production in RA patients. The aberrant expressions of non-coding RNAs (ncRNAs) including microRNAs (miRs) and long non-coding RNAs (lncRNAs) in the immune system undoubtedly derange the mRNA expressions of cytokines/chemokines/growth factors. In the present review, we will discuss in detail the expression of these ncRNAs and their target molecules participating in developing RA, and the potential biomarkers for the disease, its diagnosis, cardiovascular complications and therapeutic response. Finally, we propose some prospective investigations for unraveling the conundrums of rheumatoid pathogenesis.

Emerging roles of circular RNAs in systemic lupus erythematosus

Circular RNAs (circRNAs) are a class of non-coding RNAs with covalently closed single-stranded structures lacking 5'-3' polarity and a polyadenine tail. Over recent years, a growing body of studies have been conducted to explore the roles of circRNAs in human diseases. Systemic lupus erythematosus (SLE) is a severe autoimmune disorder characterized by the presence of autoantibodies and excessive inflammation, which impact multiple organs. Recent advances have begun to shed light on the roles of circRNAs in SLE, providing fresh insights into the pathogenesis of SLE and the latent capacity for translation into clinical applications. Here, we briefly introduce these "star molecules" and summarize their roles in SLE. In addition, we outline the limitations of the current studies and raise prospects for future research.

Epigenetics in Non-tumor Immune-Mediated Skin Diseases

Epigenetics is the study of the mechanisms that regulate gene expression without modifying DNA sequences. Knowledge of and evidence about how epigenetics plays a causative role in the pathogenesis of many skin diseases is increasing. Since the epigenetic changes present in tumor diseases have been thoroughly reviewed, we believe that knowledge of the new epigenetic findings in non-tumor immune-mediated dermatological diseases should be of interest to the general dermatologist. Hence, the purpose of this review is to summarize the recent literature on epigenetics in most non-tumor dermatological pathologies, focusing on psoriasis. Hyper- and hypomethylation of DNA methyltransferases and methyl-DNA binding domain proteins are the most common and studied methylation mechanisms. The acetylation and methylation of histones H3 and H4 are the most frequent and well-characterized histone modifications and may be associated with disease severity parameters and serve as therapeutic response markers. Many specific microRNAs dysregulated in non-tumor dermatological disease have been reviewed. Deepening the study of how epigenetic mechanisms influence non-tumor immune-mediated dermatological diseases might help us better understand the role of interactions between the environment and the genome in the physiopathogenesis of these diseases.

Current Understanding of Circular RNAs in Systemic Lupus Erythematosus

Systemic lupus erythematosus (SLE) is a common and potentially fatal autoimmune disease that affects multiple organs. To date, its etiology and pathogenesis remains elusive. Circular RNAs (circRNAs) are a novel class of endogenous non-coding RNAs with covalently closed loop structure. Growing evidence has demonstrated that circRNAs may play an essential role in regulation of gene expression and transcription by acting as microRNA (miRNA) sponges, impacting cell survival and proliferation by interacting with RNA binding proteins (RBPs), and strengthening mRNA stability by forming RNA-protein complexes duplex structures. The expression patterns of circRNAs exhibit tissue-specific and pathogenesis-related manner. CircRNAs have implicated in the development of multiple autoimmune diseases, including SLE. In this review, we summarize the characteristics, biogenesis, and potential functions of circRNAs, its impact on immune responses and highlight current understanding of circRNAs in the pathogenesis of SLE.

AUF1 ligand circPCNX reduces cell proliferation by competing with p21 mRNA to increase p21 production

Mammalian circRNAs can influence different cellular processes by interacting with proteins and other nucleic acids. Here, we used ribonucleoprotein immunoprecipitation (RIP) analysis to identify systematically the circRNAs associated with the cancer-related protein AUF1. Among the circRNAs interacting with AUF1 in HeLa (human cervical carcinoma) cells, we focused on hsa_circ_0032434 (circPCNX), an abundant target of AUF1. Overexpression of circPCNX specifically interfered with the binding of AUF1 to p21 (CDKN1A) mRNA, thereby promoting p21 mRNA stability and elevating the production of p21, a major inhibitor of cell proliferation. Conversely, silencing circPCNX increased AUF1 binding to p21 mRNA, reducing p21 production and promoting cell division. Importantly, eliminating the AUF1-binding region of circPCNX abrogated the rise in p21 levels and rescued proliferation. Therefore, we propose that the interaction of circPCNX with AUF1 selectively prevents AUF1 binding to p21 mRNA, leading to enhanced p21 mRNA stability and p21 protein production, thereby suppressing cell growth.

Effects of circular RNA Ttc3/miR-148a/Rcan2 axis on inflammation and oxidative stress in rats with acute kidney injury induced by sepsis

Aim Increasing evidence demonstrated circular RNAs (circRNAs) are involved in the development of various diseases, including sepsis-induced AKI. Although CIRC-Ttc3 has been proved to regulate cardiac function after myocardial infarction, its role in sepsis-induced AKI remains unclear.

MATERIALS AND METHODS

The AKI rat model was firstly induced by sepsis through cecal ligation puncture (CLP). Serum levels of creatinine, BUN, NGAL, TNF-α, IL-6, SOD, MDA and IL-1β were measured through appropriate kits. The pathological alteration and renal microvascular permeability in renal tissues were determined by HE staining and Evans Blue assays. Cell apoptosis was detected by TUNEL assay. The expression levels of CIRC-Ttc3, miR-148a, TNF-α, IL-1β and iNOS in rats' renal samples were tested by qRT-PCR or/and western blot. The binding ability between CIRC-Ttc3 and miR-148a was evaluated through luciferase reporter, RIP and RNA pull-down assays.

KEY FINDINGS

Kidney injury was found in CLP-treated rats. CIRC-Ttc3 expression was down-regulated, and upregulation of CIRC-Ttc3 improved inflammatory responses and oxidative stress in AKI rats. Mechanismly, CIRC-Ttc3 was confirmed to bind to and negatively regulate miR-148a. Further rescue assays revealed that overexpression of miR-148a rescued the improvement of CIRC-Ttc3 on sepsis-induced AKI. Then, it was illustrated that CIRC-Ttc3 regulated Rcan2 expression by binding to miR-148a. Finally, knockdown of Rcan2 reversed the effects of miR-148a inhibition on sepsis-induced AKI.

SIGNIFICANCE

CIRC-Ttc3 relieved inflammation and oxidative stress through regulating the miR-148a/Rcan2 axis in rats with AKI induced by sepsis. Therefore, CIRC-Ttc3 may be a potential therapeutic target for sepsis-induced AKI.

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.

Novel circRNA discovery in sheep shows evidence of high backsplice junction conservation

Circular RNAs (circRNAs) are covalently closed circular non-coding RNAs. Due to their structure, circRNAs are more stable and have longer half-lives than linear RNAs making them good candidates for disease biomarkers. Despite the scientific relevance of these molecules, the study of circRNAs in non-model organisms is still in its infancy. Here, we analyse total RNA-seq data to identify circRNAs in sheep from peripheral blood mononuclear cells (PBMCs) and parietal lobe cortex. Out of 2510 and 3403 circRNAs detected in parietal lobe cortex and in PBMCs, a total of 1379 novel circRNAs were discovered. Remarkably, around 63% of all detected circRNAs were found to be completely homologous to a circRNA annotated in human. Functional enrichment analysis was conducted for both tissues based on GO terms and KEGG pathways. The enriched terms suggest an important role of circRNAs from encephalon in synaptic functions and the involvement of circRNAs from PBMCs in basic immune system functions. In addition to this, we investigated the role of circRNAs in repetitive vaccination experiments via differential expression analysis and did not detect any significant relationship. At last, our results support both the miRNA sponge and the miRNA shuttle functions of CDR1-AS in sheep brain. To our knowledge, this is the first study on circRNA annotation in sheep PBMCs or parietal lobe cortex samples.

Competing Endogenous RNA Networks as Biomarkers in Neurodegenerative Diseases

Protein aggregation is classically considered the main cause of neuronal death in neurodegenerative diseases (NDDs). However, increasing evidence suggests that alteration of RNA metabolism is a key factor in the etiopathogenesis of these complex disorders. Non-coding RNAs are the major contributor to the human transcriptome and are particularly abundant in the central nervous system, where they have been proposed to be involved in the onset and development of NDDs. Interestingly, some ncRNAs (such as lncRNAs, circRNAs and pseudogenes) share a common functionality in their ability to regulate gene expression by modulating miRNAs in a phenomenon known as the competing endogenous RNA mechanism. Moreover, ncRNAs are found in body fluids where their presence and concentration could serve as potential non-invasive biomarkers of NDDs. In this review, we summarize the ceRNA networks described in Alzheimer's disease, Parkinson's disease, multiple sclerosis, amyotrophic lateral sclerosis and spinocerebellar ataxia type 7, and discuss their potential as biomarkers of these NDDs. Although numerous studies have been carried out, further research is needed to validate these complex interactions between RNAs and the alterations in RNA editing that could provide specific ceRNET profiles for neurodegenerative disorders, paving the way to a better understanding of these diseases.

Whole-Transcriptome Analysis in Peripheral Blood Mononuclear Cells from Patients with Lipid-Specific Oligoclonal IgM Band Characterization Reveals Two Circular RNAs and Two Linear RNAs as Biomarkers of Highly Active Disease

The presence of anti-myelin lipid-specific oligoclonal IgM bands (LS-OCMBs) has been defined as an accurate predictor of an aggressive evolution of multiple sclerosis. However, the detection of this biomarker is performed in cerebrospinal fluid, a quite invasive liquid biopsy. In the present study we aimed at studying the expression profile of miRNA, snoRNA, circRNA and linearRNA in peripheral blood mononuclear cells (PBMCs) from patients with lipid-specific oligoclonal IgM band characterization. We included a total of 89 MS patients, 47 with negative LS-OCMB status and 42 with positive status. Microarray (miRNA and snoRNA) and RNA-seq (circular and linear RNAs) were used to perform the profiling study in the discovery cohort and candidates were validated by RT-qPCR in the whole cohort. The biomarker potential of the candidates was evaluated by ROC curve analysis. RNA-seq and RT-qPCR validation revealed that two circular (hsa_circ_0000478 and hsa_circ_0116639) and two linear RNAs (IRF5 and MTRNR2L8) are downregulated in PBMCs from patients with positive LS-OCMBs. Finally, those RNAs show a performance of a 70% accuracy in some of the combinations. The expression of hsa_circ_0000478, hsa_circ_0116639, IRF5 and MTRNR2L8 might serve as minimally invasive biomarkers of highly active disease.

hsa_circ_0003738 Inhibits the Suppressive Function of Tregs by Targeting miR-562/IL-17A and miR-490-5p/IFN-γ Signaling Pathway

Dysfunction in the suppressive function of regulatory T cells (Tregs) has been related to the pathogenesis of psoriasis. Accumulating evidence has demonstrated the importance of circular RNAs (circRNAs) in regulating various biological process, such as cell proliferation, apoptosis, etc. However, the role of circRNAs in modulating the suppressive functions of psoriatic Tregs and the underlying mechanisms have not been investigated. Here, by using circRNA microarray analysis, we discovered four upregulated and four downregulated circRNAs in psoriatic Tregs. Quantitative real-time PCR further confirmed a significant increase of circ_0003738 in psoriatic Tregs. Importantly, knockdown of circ_0003738 by lentivirus in psoriatic Tregs could restore their suppressive functions via inhibiting the secretion of proinflammatory cytokines interleukin-17A (IL-17A) and interferon (IFN)-γ. Moreover, we found that circ_0003738 could bind to miR-562 to release the inhibition of target gene IL-17RA (IL-17 receptor A), thus promoting IL-17A signaling in psoriatic Tregs. In parallel, circ_0003738 acted also as a sponge for miR-490-5p and relieved inhibition for the target gene IFNGR2, which promoted IFN-γ signaling in psoriatic Tregs. Our study demonstrated that upregulated circ_0003738 decreased the suppressive function of psoriatic Tregs via the miR-562/IL17RA and miR-490-5p/IFNGR2 (IFN-γ receptor 2) axis, which indicated the involvement of circRNAs in the pathogenesis of dysfunctional Tregs. These findings will provide new therapeutic targets for the treatment of psoriasis.

Protein-Related Circular RNAs in Human Pathologies

Circular RNAs (circRNAs) are a distinct family of RNAs derived from alternative splicing which play a crucial role in regulating gene expression by acting as microRNA (miRNA) and RNA binding protein (RBP) sponges. However, recent studies have also reported the multifunctional potential of these particles. Under different conditions, circRNAs not only regulate protein synthesis, destination, and degradation but can serve as protein scaffolds or recruiters and are also able to produce short peptides with active biological functions. circRNAs are under ongoing investigation because of their close association with the development of diseases. Some circRNAs are reportedly expressed in a tissue- and development stage-specific manner. Furthermore, due to other features of circRNAs, including their stability, conservation, and high abundance in bodily fluids, they are believed to be potential biomarkers for various diseases, including cancers. In this review, we focus on providing a summary of the current knowledge on circRNA-protein interactions. We present the properties and functions of circRNAs, the possible mechanisms of their translation abilities, and the emerging functions of circRNA-derived peptides in human pathologies.

Current State of Knowledge on Primary Sjögren's Syndrome, an Autoimmune Exocrinopathy

Primary Sjögren's syndrome (pSS) is a chronic systemic autoimmune rheumatic disease characterized by lymphoplasmacytic infiltration of the salivary and lacrimal glands, whereby sicca syndrome and/or systemic manifestations are the clinical hallmarks, associated with a particular autoantibody profile. pSS is the most frequent connective tissue disease after rheumatoid arthritis, affecting 0.3-3% of the population. Women are more prone to develop pSS than men, with a sex ratio of 9:1. Considered in the past as innocent collateral passive victims of autoimmunity, the epithelial cells of the salivary glands are now known to play an active role in the pathogenesis of the disease. The aetiology of the "autoimmune epithelitis" still remains unknown, but certainly involves genetic, environmental and hormonal factors. Later during the disease evolution, the subsequent chronic activation of B cells can lead to the development of systemic manifestations or non-Hodgkin's lymphoma. The aim of the present comprehensive review is to provide the current state of knowledge on pSS. The review addresses the clinical manifestations and complications of the disease, the diagnostic workup, the pathogenic mechanisms and the therapeutic approaches.