CircSERPINE2 protects against osteoarthritis by targeting miR-1271 and ETS-related gene

New Insight of Circular RNAs in Human Musculoskeletal Diseases

Circular RNAs (circRNAs), a novel group of noncoding RNAs, are present in most eukaryotic cells. Different from messenger RNAs, circRNAs have a covalently closed single-stranded stable structure and often act in cell type and tissue-specific manners, indicating that they can be used as biomarkers. With the advance of high-throughput RNA sequencing technology and bioinformatics, a large number of circRNAs have been identified in association with musculoskeletal diseases, but the functions of most circRNAs have not been clarified. circRNAs regulate biological processes by adsorbing microRNA as "sponges," binding to proteins, acting as transcriptional regulators, and participating in translation of proteins. In this study, we discuss the latest understanding of biogenesis and gene regulatory mechanisms of circRNAs with special emphasis on new targets for musculoskeletal disease diagnosis and clinical treatment.

Circular RNA circPDE4D Protects against Osteoarthritis by Binding to miR-103a-3p and Regulating FGF18

Osteoarthritis (OA) is a common, age-related, and painful disease characterized by cartilage destruction, osteophyte formation, and synovial hyperplasia. This study revealed that circPDE4D, a circular RNA derived from human linear PDE4D, plays a critical role in maintaining the extracellular cellular matrix (ECM) during OA progression. circPDE4D was significantly downregulated in OA cartilage tissues and during stimulation with inflammatory cytokines. The knockdown of circPDE4D predominantly contributed to Aggrecan loss and the upregulation of matrix catabolic enzymes, including MMP3, MMP13, ADAMTS4, and ADAMTS5, but not proliferation or apoptosis. In a murine model of destabilization of the medial meniscus (DMM), the intraarticular injection of circPDE4D alleviated DMM-induced cartilage impairments. Mechanistically, we found that circPDE4D exerted its effect by acting as a sponge for miR-103a-3p and thereby regulated FGF18 expression, which is a direct target of miR-103a-3p. In conclusion, our findings highlight a novel protective role of circPDE4D in OA pathogenesis and indicate that the targeting of the circPDE4D-miR-103a-3p-FGF18 axis might provide a potential and promising approach for OA therapy.

Hsa_circ_0005567 Activates Autophagy and Suppresses IL-1β-Induced Chondrocyte Apoptosis by Regulating miR-495

Excessive chondrocyte apoptosis is mostly responsible for the progression of osteoarthritis (OA). It has been shown that circular RNAs (circRNAs) are differentially expressed in OA cartilage and participate in various pathological processes during OA. Here, this study was designed to explore the effect and molecular mechanism of hsa_circ_0005567 on IL-1β-induced chondrocyte apoptosis. The results showed that hsa_circ_0005567 knockdown aggravated the IL-1β-induced chondrocyte apoptosis. In contrast, hsa_circ_0005567 overexpression attenuated the IL-1β-induced chondrocyte apoptosis, but this effect could be abrogated by 3-methyladenine (an inhibitor of autophagy), suggesting that hsa_circ_0005567 overexpression inhibited chondrocyte apoptosis by inducing autophagy. Furthermore, hsa_circ_0005567 competitively bound to miR-495 and derepressed the expression of ATG14, an early autophagy marker that was a direct target of miR-495. Moreover, both miR-495 mimic and ATG14 knockdown counteracted the autophagy-promoting and anti-apoptotic effects of hsa_circ_0005567 overexpression in IL-1β-treated chondrocytes. Taken together, hsa_circ_0005567 activates autophagy by regulating the miR-495/ATG14 axis and thereby suppresses IL-1β-induced chondrocyte apoptosis. These findings suggest that hsa_circ_0005567 may serve as a therapeutic target for the treatment of OA.

Functions of Circular RNAs in Regulating Adipogenesis of Mesenchymal Stem Cells

The mesenchymal stem cells (MSCs) are known as highly plastic stem cells and can differentiate into specialized tissues such as adipose tissue, osseous tissue, muscle tissue, and nervous tissue. The differentiation of mesenchymal stem cells is very important in regenerative medicine. Their differentiation process is regulated by signaling pathways of epigenetic, transcriptional, and posttranscriptional levels. Circular RNA (circRNA), a class of noncoding RNAs generated from protein-coding genes, plays a pivotal regulatory role in many biological processes. Accumulated studies have demonstrated that several circRNAs participate in the cell differentiation process of mesenchymal stem cells in vitro and in vivo. In the current review, characteristics and functions of circRNAs in stem cell differentiation will be discussed. The mechanism and key role of circRNAs in regulating mesenchymal stem cell differentiation, especially adipogenesis, will be reviewed and discussed. Understanding the roles of these circRNAs will present us with a more comprehensive signal path network of modulating stem cell differentiation and help us discover potential biomarkers and therapeutic targets in clinic.

LEF1 mediates osteoarthritis progression through circRNF121/miR-665/MYD88 axis via NF-кB signaling pathway

Osteoarthritis (OA) is a joint disease that causes great pain to patients and imposes a tremendous burden on the world’s medical resources. Regulatory noncoding RNAs, including circular RNAs (circRNAs) and microRNAs (miRNAs), play an important role in OA progression. Here, we identified differential expression of transcription factor LEF1 that increased circRNA circRNF121 levels in normal and OA cartilage tissues. The expression of LEF1 and circRNF121 was positively associated with Mankin’s scores. Alteration of circRNF121 mediated the degradation of extracellular mechanisms (ECM), apoptosis, and proliferation of chondrocytes. MiR-665 was identified as a direct regulatory target of circRNF121 and MYD88. Functional analysis showed that circRNF121 and MYD88 modulated ECM degradation, apoptosis, and proliferation of chondrocytes, which could be reversed by miR-665. MYD88 regulated the activity of the NF-кB signaling pathway by circRNF121 via sponging miR-665. Collectively, these data indicated that LEF1 impacted OA progression by modulating the circRNF121/miR-665/MYD88 axis via NF-кB pathway. Our research proposed a new molecular mechanism for the development of OA, and provided a prospective therapeutic target for OA.

CircCDK14 protects against Osteoarthritis by sponging miR-125a-5p and promoting the expression of Smad2

Rationale: Osteoarthritis (OA) is the most common joint disease worldwide. Previous studies have identified the imbalance between extracellular matrix (ECM) catabolism and anabolism in cartilage tissue as the main cause. To date, there is no cure for OA despite a few symptomatic treatments. This study aimed to investigate the role of CircCDK14, a novel circRNA factor, in the progression of OA, and to elucidate its underlying molecular mechanisms.

Methods: The function of CircCDK14 in OA, as well as the interaction between CircCDK14 and its downstream target (miR-125a-5p) and mRNA target (Smad2), was evaluated by western blot (WB), immunofluorescence (IF), RNA immunoprecipitation (RIP), quantitative RT-PCR, luciferase assay and fluorescence in situ hybridization (FISH). Rabbit models were introduced to examine the function and mechanism of CircCDK14 in OA in vivo.

Results: In our present study, we found that CircCDK14, while being down-regulated in the joint wearing position, regulated metabolism, inhibited apoptosis and promoted proliferation in the cartilage. Mechanically, the protective effect of CircCDK14 was mediated by miR-125a-5p sponging, which downregulated the Smad2 expression and led to the dysfunction of TGF-β signaling pathway. Intra-articular injection of adeno-associated virus-CircCDK14 also alleviated OA in the rabbit model.

Conclusion: Our study revealed an important role of CircCDK14/miR-125a-5p/Smad2 axis in OA progression and provided a potential molecular therapeutic strategy for the treatment of OA.

hsa_circ_0058092 protects against hyperglycemia‑induced endothelial progenitor cell damage via miR‑217/FOXO3

Circular RNAs (circRNAs) regulate the expression of genes that are critical for various biological and pathological processes. Previous studies have reported that the expression of hsa_circ_0058092 is decreased in patients with diabetes mellitus (DM); however, the specific role of this circRNA in DM is unknown. In the present study, endothelial progenitor cells (EPCs) were isolated and a decreased hsa_circ_0058092 expression was found under conditions of hyperglycemia (HG). The overexpression of hsa_circ_0058092 protected the EPCs against HG‑induced damage by preserving cell survival, proliferation, migration and angiogenic differentiation. The overexpression of hsa_circ_0058092 also decreased the HG‑induced increase in NADPH‑oxidase proteins and inflammatory cytokines. Further investigation revealed that the overexpression of hsa_circ_0058092 enhanced FOXO3 expression, which was mediated through the interaction with miR‑217. Furthermore, the upregulation of miR‑217 or the downregulation of FOXO3 abolished the protective effects of hsa_circ_0058092 against HG‑induced EPC damage. On the whole, these data suggest that hsa_circ_0058092 acts via the miR‑217/FOXO3 pathway to protect against EPCs HG‑induced damage, and to preserve the migration and angiogenesis of EPCs.

CircRNA-UBE2G1 regulates LPS-induced osteoarthritis through miR-373/HIF-1a axis

Osteoarthritis (OA) is a very common chronic and degenerative joint disease characterized by persistent destruction of articular cartilage. Recently, increasing evidence showed that circular RNAs (circRNAs) play critical roles in OA progression. However, the functions of circRNAs in OA and their underlying mechanisms of action remain unclear. In the present study, the expression levels of circRNA-UBE2G1 and HIF-1a were significantly increased in OA tissues, whereas miR‑373 expression was downregulated. Function assays showed that circRNA-UBE2G1 inhibition reduced the effects of LPS on C28/I2 cells viability and apoptosis. In terms of mechanism, we revealed that circRNA-UBE2G1 binds to miR‑373 as competing endogenous RNAs (ceRNAs). HIF-1a might act as a target of miR‑373. Moreover, miR‑373 suppression or HIF-1a overexpression restored the effects of circRNA-UBE2G1 downregulation on LPS-induced chondrocytes injury. Collectively, our data suggest that circRNA-UBE2G1 facilitates the progression in the LPS-induced OA cell model via regulating the miR‑373/HIF-1a axis.

ABBREVIATIONS

OA: Osteoarthritis; Circular RNAs; miRNAs: MicroRNAs; Mut: Mutant; WT: Wild type; UTR: Untranslated region.

Hsa_circ_0017639 expression promotes gastric cancer proliferation and metastasis by sponging miR-224-5p and upregulating USP3

Gastric cancer (GC) is a common malignant tumor having poor prognosis globally. Circular RNA (circRNA) is a circular endogenous RNA generated by special selective splicing that occurs in various traits. Studies show that hsa_circ_0017639 is abnormally expressed and involved in tumorigenesis. Nevertheless, the hsa_circ_0017639 role in GC is unknown. This study detected hsa_circ_0017639 expression in a GC cell line using RT-qPCR. Subcellular localization of hsa_circ_0017639 was verified via FISH. We assessed correlations amongst miRNA, hsa_circ_0017639 and relative protein levels using luciferase reporter assays and RNA pulldown assays. The data illustrated that in hsa_circ_assays, expression was enhanced in GC cell. Downregulation of hsa_circ_0017639 decreased GC cell proliferation and migration in in vitro and in vivo experiments. RNA pulldown and RT-qPCR analysis verified that hsa_circ_0017639 sponged miR-224-5p. Bioinformatic and luciferase reporter assays validated that miR-224-5p and USP3 were downstream targets of hsa_circ_0017639. Upregulation of USP3 or downregulation of miR-224-5p restored proliferation and migration by MKN-28 and MGC-803 cells after hsa_circ_0017639 silencing. Upregulation of USP3 restored MKN-28 and MGC-803 cell proliferation and migration after overexpression of miR-224-5p. Our collective findings advised that hsa_circ_0017639 takes part in GC progression through regulating the miR-224-5p/USP3 axis, highlighting its potential as an effective GC therapeutic target.

CircGCN1L1 promotes synoviocyte proliferation and chondrocyte apoptosis by targeting miR-330-3p and TNF-α in TMJ osteoarthritis

Altered expression of circular RNAs (circRNAs) has been identified in various human diseases. In this study, we investigated whether circRNAs function as competing endogenous RNAs to regulate the pathological process of temporomandibular joint osteoarthritis (TMJOA). High-throughput sequencing of mRNA (RNA seq) was performed to detect the expression of circRNAs in TMJOA and control synovial tissues isolated from humans. The differentially upregulated circGCN1L1 (hsa_circ_0000448) in synoviocyte was validated in vitro and in vivo. Here we demonstrate the interactions between circGCN1L1 and both miR-330-3p and tumor necrosis factor-α (TNF-α) through bioinformatics predictions, luciferase report assays, and fluorescence in situ hybridization. mRNA expression profiles of TNF-α-stimulated synoviocyte showed that circGCN1L1 and p65 expressions were upregulated by TNF-α. Moreover, miR-330-3p was negatively correlated with TNF-α secretion. Further, we found that miR-330-3p directly targeted TNF and restrained the production of matrix-degrading enzymes (MMP3, MMP13, and ADAMTS4). Mechanistic studies unveiled that circGCN1L1 in TMJOA synovial tissues and cells may be associated with condylar chondrocyte apoptosis and synoviocyte hyperplasia. Moreover, intra-articular injection of shcircGCN1L1 alleviated TMJOA progression in rat models. Altogether, we elucidated the important roles of a novel circRNA, namely, circGCN1L1, which induced inflammation in TMJ synoviocytes and decreased anabolism of the extracellular matrix (ECM) through miR-330-3p and TNF-α gene. This circRNA may represent a potentially effective therapeutic strategy against TMJOA progression at an early stage.

Engineered Circular RNA Sponges Act as miRNA Inhibitors to Attenuate Pressure Overload-Induced Cardiac Hypertrophy

Circular RNAs (circRNAs) sequester microRNAs (miRNAs) and repress their endogenous activity. We hypothesized that artificial circRNA sponges (circmiRs) can be constructed to target miRNAs therapeutically, with a low dosage requirement and extended half-lives compared to current alternatives. This could present a new treatment approach for critical global pathologies, including cardiovascular disease. Here, we constructed a circmiR sponge to target known cardiac pro-hypertrophic miR-132 and -212. Expressed circmiRs competitively inhibited miR-132 and -212 activity in luciferase rescue assays and showed greater stability than linear sponges. A design containing 12 bulged binding sites with 12 nucleotides spacing was determined to be optimal. Adeno-associated viruses (AAVs) were used to deliver circmiRs to cardiomyocytes in vivo in a transverse aortic constriction (TAC) mouse model of cardiac disease. Hypertrophic disease characteristics were attenuated, and cardiac function was preserved in treated mice, demonstrating the potential of circmiRs as novel therapeutic tools. Subsequently, group I permutated intron-exon sequences were used to directly synthesize exogenous circmiRs, which showed greater in vitro efficacy than the current gold standard antagomiRs in inhibiting miRNA function. Engineered circRNAs thus offer exciting potential as future therapeutics.

Overexpression of miR-10a-5p facilitates the progression of osteoarthritis

The current study was aimed at exploring the potential roles and possible mechanisms of miR-10a-5p in osteoarthritis (OA). We performed RT-qPCR, Western blot, CCK8, EdU Assay, and flow cytometry assay to clarify the roles of miR-10a-5p in OA. Furthermore, the whole transcriptome sequencing together with integrated bioinformatics analyses were conducted to elucidate the underlying mechanisms of miR-10a-5p involving in OA. Our results demonstrated that miR-10a-5p was upregulated in OA and acted as a significant contributing factor for OA. A large number of circRNAs, lncRNAs, miRNAs, and mRNAs were identified by overexpressing miR-10a-5p. Functional enrichment analyses indicated that these differentially-expressed genes were enriched in some important terms including PPAR signaling pathway, PI3K-Akt signaling pathway, and p53 signaling pathway. A total of 42 hub genes were identified in the protein-protein interaction network including SERPINA1, TTR, APOA1, and A2M. Also, we constructed the network regulatory interactions across coding and noncoding RNAs triggered by miR-10a-5p, which revealed the powerful regulating effects of miR-10a-5p. Moreover, we found that HOXA3 acted as the targeted genes of miR-10a-5p and miR-10a-5p contributed to the progression of OA by suppressing HOXA3 expression. Our findings shed insight on regulatory mechanisms of miR-10a-5p, which might provide novel therapeutic targets for OA.

Circular RNA CDR1as promotes adipogenic and suppresses osteogenic differentiation of BMSCs in steroid-induced osteonecrosis of the femoral head

Steroid-induced osteonecrosis of the femoral head (SONFH) is a common debilitating orthopedic disease. The bone marrow mesenchymal stem cells (BMSCs) are a type of mesenchymal stem cells which play crucial roles in bone repair. The adipogenic/osteogenic differentiation disorder of BMSCs has been widely perceived contributing to SONFH. However, the regulatory mechanism of BMSCs differentiation disorder still remains unclear. Circular RNA (circRNA), a kind of stable ncRNA, plays important roles in regulating gene expression via various ways. To date, there are no studies to uncover the circRNA expression profile and screen out the key circRNAs playing crucial roles in adipogenic/osteogenic differentiation disorder of SONFH-BMSCs. In present study, we detected the circRNA expression profiles in SONFH-BMSCs for the first time. A total of 820 circRNAs were differentially expressed in SONFH-BMSCs, including 460 up- and 360 down-regulated circRNAs. Bioinformatics analysis indicates circRNA CDR1as, one up-regulated circRNA, may play crucial role in adipogenic/osteogenic differentiation disorder of SONFH-BMSCs via CDR1as-miR-7-5p-WNT5B axis. Knocking-down CDR1as resulted in increasing of osteogenic differentiation and decreasing of adipogenic differentiation of BMSCs, while over-expressing CDR1as resulted in decreasing of osteogenic differentiation and increasing of adipogenic differentiation of BMSCs. The miR-7-5p binding sites of CDR1as and WNT5B were verified by luciferase reporter gene assay. Our study may provide new insights into the molecular mechanisms of osteogenic/adipogenic differentiation disorder of SONFH-BMSCs and new biomarkers for the diagnosis and treatment of SONFH.

Osteoarthritis year in review 2019: genetics, genomics and epigenetics

Although osteoarthritis (OA) aetiology is complex, genetic, genomic and epigenetic studies published within the last decade have advanced our understanding of the molecular processes underlying this common musculoskeletal disease. The purpose of this narrative review is to highlight the key research articles within the OA genetics, genomics and epigenetics fields that were published between April 2018 and April 2019. The review focuses on the identification of new OA genetic risk loci, genomics techniques that have been used for the first time in human cartilage and new publicly available databases, and datasets that will aid OA functional studies. Fifty-six new OA susceptibility loci were identified by two large scale genome wide association study meta-analyses, increasing the number of genome-wide significant risk loci to 90. OA risk variants are enriched near genes involved in skeletal development and morphology, and show genetic overlap with height, hip shape, bone area and developmental dysplasia of the hip. Several functional studies of OA loci were published, including a genome-wide analysis of genetic variation on cartilage gene expression. A specialised data portal for exploring cross-species skeletal transcriptomic datasets has been developed, and the first use of cartilage single cell RNAseq analysis reported. This year also saw the systematic identification of all microRNAs, long non-coding RNAs and circular RNAs expressed in human OA cartilage. Putative transcriptional regulatory regions have been mapped in human chondrocytes genome-wide, providing a dataset that will facilitate the prioritisation and characterisation of OA genetic and epigenetic loci.

CircRNA-CIDN mitigated compression loading-induced damage in human nucleus pulposus cells via miR-34a-5p/SIRT1 axis

Background

Intervertebral disc degeneration (IDD) is a major contributor to lower back pain, however, the molecular and pathogenetic mechanisms underlying IDD are poorly understood. As a high-risk factor for IDD, compression stress was reported to induce apoptosis of nucleus pulposus (NP) cells and extracellular matrix (ECM) degradation during IDD progression. Circular RNA (circRNA) is a class of endogenous non-coding RNA (ncRNA) and has been reported to function in several diseases. However, whether and how circRNA regulates compression-induced damage of NP cells remains vague. Here, we aimed to investigate the key role of circRNA in compression loading-induced IDD.

Methods

We analysed the circRNA expression of three samples from compression-treated NP cells and three control samples using circRNA microarray assays and further investigated the circRNA involved in compression-induced damage of NP cells (circRNA-CIDN). We investigated the effects of circRNA-CIDN on compression-induced cell apoptosis and NP ECM degradation in vitro and ex vivo. We observed that circRNA-CIDN bound to miRNAs as a miRNA sponge based on luciferase and RNA immunoprecipitation (RIP) assays.

Findings:

CircRNA-CIDN was significantly downregulated in compression-treated human NP cells, as validated by circRNA microarray and qRT-PCR analysis, and overexpressing circRNA-CIDN inhibited compression-induced apoptosis and NP ECM degradation. Further studies demonstrated that circRNA-CIDN served as a sponge for miR-34a-5p, an important miRNA that enhanced compression-induced damage of NP cells via repressing the silent mating type information regulation 2 homolog 1 (SIRT1). CircRNA-CIDN was also verified to contain IDD development in an ex vivo IDD model.

Interpretation

Our results revealed that circRNA-CIDN binding to miR-34a-5p played an important role in mitigating compression loading-induced nucleus pulposus cell damage via targeting SIRT1, providing a potential therapeutic strategy for IDD treatment.

Funding

National Natural Science Foundation of China (81772391, 81974348), Fundamental Research Funds for the Central Universities (2017KFYXJJ248).

miR-142-5p protects against osteoarthritis through competing with lncRNA XIST

BACKGROUND

The relevance between abnormal microRNA expression and osteoarthritis (OA) has been elaborated in recent studies. Hence, the present study aimed to assess the impact of miR-142-5p on chondrocyte growth and apoptosis.

METHODS

To mimic OA-like chondrocyte damage, interleukin (IL)-1β was used for chondrocyte treatment. The expression of miR-142-5p, SGTB, long non-coding RNA (lncRNA) X inactive specific transcript (XIST) and involved molecules such as Col2A1, Bcl-2, MMP13 and Bax was determined via a quantitative reverse transcriptase-polymerase chain reaction and western blot analyses. Functional roles of miR-142-5p, SGTB and XIST were monitored in 5-ethynyl-2'-deoxyuridine, CCK-8 and TUNEL experiments. Rescue analyses were conducted to consolidate the effect of the XIST/miR-142-5p/SGTB axis on chondrocytes in OA.

RESULTS

miR-142-5p was down-regulated in IL-1β-treated chondrocytes, whereas SGTB and XIST levels were increased. Overexpression of miR-142-5p stimulated proliferation and retarded apoptosis in IL-1β-treated chondrocytes. Meanwhile, miR-142-5p elevation was correlated with an elevation of Col2A1 and Bcl-2, as well as a decline of MMP13 and Bax. A mechanistic study showed that miR-142-5p negatively regulated SGTB expression. Moreover, we found that lncRNA XIST could relieve the inhibition of miR-142-5p on SGTB expression. Augmentation of SGTB or suppression of miR-142-5p reversed the influence of XIST depletion on chondrocyte growth and apoptosis.

CONCLUSIONS

The present study has explored the fundamental role of miR-142-5p in IL-1β-treated chondrocytes, as well as the novel molecular mechanism constituted by miR-142-5p/SGTB/XIST in OA. Potentially, the results obtained may add new insight into OA pathogenesis.

Noncoding RNAs: New regulatory code in chondrocyte apoptosis and autophagy

Osteoarthritis (OA) is a bone and joint disease characterized by progressive cartilage degradation. In the face of global trends of population aging, OA is expected to become the fourth most common disabling disease by 2020. Nevertheless, the detailed pathogenesis of OA has not yet been elucidated. Noncoding RNAs (ncRNAs), including long noncoding RNAs, microRNAs, and circular RNAs, do not encode proteins but have recently emerged as important regulators of apoptosis and autophagy of chondrocytes, thereby highlighting a potential role in chondrocyte injury leading to OA onset and progression. We here review recent findings on these regulatory roles of ncRNAs to provide new directions for research on the pathogenesis of OA and offer new therapeutic targets for prevention and treatment. This article is categorized under: RNA in Disease and Development > RNA in Disease RNA in Disease and Development > RNA in Development.

The potential roles of circular RNAs in osteonecrosis of the femoral head (Review)

Circular RNAs (circRNAs) are categorized as non-coding RNAs that, unlike widely known canonical linear RNAs, form a covalently closed continuous loop without 5′ or 3′ polarities, which enables them to resist digestion by RNA exonucleases. Although the functions of circRNAs remain largely unknown, accumulated evidence has demonstrated that circRNAs can act as microRNA sponges, which allows them to regulate numerous biological processes and disease mechanisms, including apoptosis, angiogenesis, invasion, metastasis and stem cell differentiation. Although research into circRNAs is in its infancy, studies have identified critical roles for circRNAs in the initiation and progression of disease. The present study delineated the characteristics and functions of circRNAs, and focused on the potential relationship between circRNAs and osteonecrosis of the femoral head (ONFH). CircRNAs represent a novel avenue for studying the mechanisms underlying ONFH as well as possible treatments.

Differentially expressed circular RNAs in air pollution-exposed rat embryos

Circular RNAs (circRNAs) are an important class of non-coding RNAs partly by acting as microRNA sponges. Growing evidence indicates that air pollution exposure during pregnancy could lead to congenital defects in the offspring. In this study, using circRNAs sequencing, we profiled differentially expressed circRNAs in rat embryos exposed to a high concentration (> 200 μg/m³) of fine particulate matter (PM_2.5) in utero. Compared with the control embryos whose mothers were reared in clean air, 25 and 55 circRNAs were found to be downregulated and upregulated, respectively, in the air pollution-exposed group. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses of circRNA-coexpressed genes indicated that segmentation, brain development, and system development together with lysine degradation, Rap1 signaling pathway, and adrenergic signaling were deregulated by in utero air pollution exposure. We also identified the central role of three circRNAs, namely circ_015003, circ_030724, and circ_127215 in the circRNA-microRNA interaction network. These data suggested that circRNA deregulation might play a crucial role in the development of air pollution-associated congenital malformations.

NOTCH signaling pathway and non-coding RNAs in cancer

Malignant tumors, known as cancer, seriously threaten human life and health. Cancer has the characteristics of abnormal cell differentiation, proliferation, invasion and metastasis. As a result, cancer often accompanied by poor prognosis and a lower survival rate. Notch signaling pathway is a highly conserved system in many multicellular organisms, and which has been proved to play a biological role in many cancers. In recent years, increasing evidence has shown that non-coding RNA can not only activate or inhibit NOTCH pathway, but also regulate the occurrence and development of cancer through NOTCH pathway. Therefore, we focus on the cancer-NOTCH-non-coding RNA axis in this review, and provide new ideas for cancer therapy.