Interleukin-1 receptor-associated kinase 4 (IRAK4) is a key kinase downstream of the interleukin-1 receptor (IL-1R) and Toll-like receptors (TLRs) signaling pathway, whose overexpression and hyperactivation have been associated with several inflammatory diseases or cancer. Therefore, targeting IRAK4 has emerged as a promising therapeutic strategy. A range of potent and selective IRAK4 inhibitors and degraders based on draggability have been designed and developed. This article provides a comprehensive summary of the IRAK4 inhibitors and degraders that have been developed and discusses the challenges and opportunities for research in this area. (c) 2025 Published by Elsevier B.V. on behalf of Chinese Chemical Society and Institute of Materia Medica, Chinese Academy of Medical Sciences.

Synovial tissue infiltration by pro-inflammatory macrophages is a critical factor in the pathogenesis of rheumatoid arthritis (RA), correlating strongly with high disease activity scores in affected joints and often lead to progressive joint damage and disability. Methotrexate (MTX) is the frontline therapeutic drug for RA, but its efficacy is hampered by short plasma half-life, reduced bioavailability, and severe adverse effects. To address these limitations, we developed an injectable polymer-nanomedicine supramolecular hydrogel (PNSH) with dynamic mechanical properties and morphology tailored for intra-articular administration and sustained drug release with minimized off-target toxicity. The hydrogel was assembled from MTX-loaded polymeric nanoparticles chemically conjugated with partially oxidized glucomannan. In vitro and in vivo studies demonstrate that PNSH exhibits low cytotoxicity and superior biocompatibility. It supports the sustained release of MTX, which promotes M1 macrophage remodeling towards the M2 macrophage via switching IRF5 and IRF8 to IRF3 and IRF4 through the adenosine A2A receptor (A2AR) signaling pathway. In a rat arthritis model, PNSH effectively mitigated tissue-damaging inflammation and restored the articular immune homeostasis, thereby inhibiting arthritis progression. Notably, PNSH also upregulated CD73 and A2AR, key components of the extracellular purinergic signaling pathway, promoted the transcriptional expression of IRF3 and IRF4, and significantly decreased the transcriptional expression of IRF5 and IRF8, driving macrophage re-polarization towards M2 phenotype. These findings suggest that PNSH has the potential to serve as a novel drug delivery system for regulating inflammation and treating RA.

Systemic lupus erythematosus (SLE) is a chronic systemic autoimmune disorder involving multiple organs and systems. There is growing evidence that autoreactive B cells occupy a central role in the occurrence and progression of SLE due to their ability to generate pathogenic autoantibodies. Small molecule inhibitors targeting Bruton’s tyrosine kinase (BTK), a crucial intracellular kinase regulating B cell development and function, emerge as a new strategy to treat SLE in recent years and are superior to biologic agents depleting B cells in many aspects. Supportive data obtained from lupus-prone mice preliminarily demonstrated the promising therapeutic potential of BTK inhibition. However, these BTK inhibitors, including elsubrutinib, evobrutinib, etc., mostly face with unsatisfactory efficacy and certain safety issues during clinical use, driving the quest for new-generation inhibitors with improved potency and higher selectivity. This paper elaborates the importance of BTK involvement in SLE pathogenesis, reviews the clinical research progress of BTK inhibitors for SLE and discusses limitations and challenges the drugs met in development, in order to contribute to a deeper understanding of disease mechanism and provide a reference for new-generation BTK inhibitor research.

Pulmonary hypertension (PH) is a progressive cardiovascular disease, which may lead to severe cardiopulmonary dysfunction. As one of the main PH disease groups, pulmonary artery hypertension (PAH) is characterized by pulmonary vascular remodeling and right ventricular dysfunction. Increased pulmonary artery resistance consequently causes right heart failure, which is the major reason for morbidity and mortality in this disease. Although various treatment strategies have been available, the poor clinical prognosis of patients with PAH reminds us that further studies of the pathological mechanism of PAH are still needed. Inflammation has been elucidated as relevant to the initiation and progression of PAH, and plays a crucial and functional role in vascular remodeling. Many immune cells and cytokines have been demonstrated to be involved in the pulmonary vascular lesions in PAH patients, with the activation of downstream signaling pathways related to inflammation. Consistently, this influence has been found to correlate with the progression and clinical outcome of PAH, indicating that immunity and inflammation may have significant potential in PAH therapy. Therefore, we reviewed the pathogenesis of inflammation and immunity in PAH development, focusing on the potential targets and clinical application of anti-inflammatory and immunosuppressive therapy.

Monocytes are key effectors in autoimmunity-related diseases in the central nervous system (CNS) due to the critical roles of these cells in the production of proinflammatory cytokines, differentiation of T-helper (Th) cells, and antigen presentation. The JAK–STAT signaling is crucial for initiating monocytes induced immune responses by relaying cytokines signaling. However, the role of this pathway in modulating the communication between monocytes and Th cells in the pathogenesis of multiple sclerosis (MS) is unclear. Here, we show that the JAK1/2/3 and STAT1/3/5/6 subtypes involved in the demyelination mediated by the differentiation of pathological Th1 and Th17 and the CNS-infiltrating inflammatory monocytes in experimental autoimmune encephalomyelitis (EAE), a model for MS. JAK inhibition prevented the CNS-infiltrating CCR2-dependent Ly6Chi monocytes and monocyte-derived dendritic cells in EAE mice. In parallel, the proportion of GM-CSF+CD4+ T cells and GM-CSF secretion were decreased in pathological Th17 cells by JAK inhibition, which in turns converted CNS-invading monocytes into antigen-presenting cells to mediate tissue damage. Together, our data highlight the therapeutic potential of JAK inhibition in treating EAE by blocking the GM-CSF-driven inflammatory signature of monocytes.

Tolerogenic dendritic cells (tolDCs) facilitate the suppression of autoimmune responses by differentiating regulatory T cells (Treg). The dysfunction of immunotolerance results in the development of autoimmune diseases, such as rheumatoid arthritis (RA). As multipotent progenitor cells, mesenchymal stem cells (MSCs), can regulate dendritic cells (DCs) to restore their immunosuppressive function and prevent disease development. However, the underlying mechanisms of MSCs in regulating DCs still need to be better defined. Simultaneously, the delivery system for MSCs also influences their function. Herein, MSCs are encapsulated in alginate hydrogel to improve cell survival and retention in situ, maximizing efficacy in vivo. The three-dimensional co-culture of encapsulated MSCs with DCs demonstrates that MSCs can inhibit the maturation of DCs and the secretion of pro-inflammatory cytokines. In the collagen-induced arthritis (CIA) mice model, alginate hydrogel encapsulated MSCs induce a significantly higher expression of CD39+CD73+ on MSCs. These enzymes hydrolyze ATP to adenosine and activate A2A/2B receptors on immature DCs, further promoting the phenotypic transformation of DCs to tolDCs and regulating naïve T cells to Tregs. Therefore, encapsulated MSCs obviously alleviate the inflammatory response and prevent CIA progression. This finding clarifies the mechanism of MSCs-DCs crosstalk in eliciting the immunosuppression effect and provides insights into hydrogel-promoted stem cell therapy for autoimmune diseases.

Objective: Although guidelines have recommended standardized drug treatment for heart failure (HF), there are still many challenges in making the correct clinical decisions due to the complicated clinical situations of HF patients. Each patient would satisfy several recommendations, meaning the decision tree of HF treatment should be nonmutually exclusive, and the same patient would be allocated to several leaf nodes in the decision tree. In the current study, we aim to propose a way to ensemble a nonmutually exclusive decision tree for recommendation system for complicated diseases, such as HF. Methods: The nonmutually exclusive decision tree was constructed via knowledge rules summarized from the HF clinical guidelines. Then similar patients were defined as those who followed the same pattern of leaf node allocation according to the decision tree. The frequent medication patterns for each similar patient were mined using the Apriori algorithms, and we also carried out the outcome prognosis analyses to show the capability for the evidence-based medication recommendations of our nonmutually exclusive decision tree. Results: Based on a large database that included 29,689 patients with 84,705 admissions, we tested the framework for HF treatment recommendation. In the constructed decision tree, the HF treatment recommendations were grouped into two independent parts. The first part was recommendations for new cases, and the second part was recommendations when patients had different historical medication. There are 14 leaf nodes in our decision tree, and most of the leaf nodes had a guideline adherence of around 90%. We reported the top 10 popular similar patients, which accounted for 32.84% of the whole population. In addition, the multiple outcome prognosis analyses were carried out to assess the medications for one of the subgroups of similar patients. Our results showed even for the subgroup of the same similar patients that no one medication pattern would benefit all outcomes. Conclusion: In the present study, the methodology to construct a nonmutually exclusive decision tree for medication recommendations for HF and its application in CDSS was proposed. Our framework is universal for most diseases and could be generally applied in developing the CDSS for treatment.

Quercetin (QU) is one of the most abundant flavonoids in plants and has attracted the attention of researchers because of its remarkable antirheumatoid arthritis (RA) effects and extremely low adverse reactions. However, the underlying mechanism needs further study.Flow cytometry, immunofluorescence, enzyme linked immunosorbent assay （ELISA）, and quantitative real-time polymerase chain reaction （qRT-PCR） reveal the obvious inhibitory effects of QU on Th17 cell differentiation in arthritic mice. More importantly, QU markedly limits the development of Th17 cell polarization, which is virtually compromised by the treatment with peroxisome proliferator activated receptor γ (PPARγ) inhibitor GW9662 and knockdown of PPARγ. Additionally, molecular dynamics simulation and immunofluorescence exhibit QU directly binds to PPARγ and increases PPARγ nuclear translocation. Besides, QU confers its moderation effect on suppressor of cytokine signaling protein (SOCS3)/signal transducer and activator of transcription 3 (STAT3) axis partially depending on PPARγ. Furthermore, coimmunoprecipitation shows QU redistributes the corepressor silencing mediator for retinoid and thyroid-hormone receptors (SMRT) from PPARγ to STAT3. Finally, the inhibition of Th17 response and the antiarthritic effect of QU are nullified by GW9662 treatment in arthritic mice.QU targets PPARγ and consequently inhibits Th17 cell differentiation by dual inhibitory activity of STAT3 to exert antiarthritic effect. The findings facilitate its development and put forth a stage for uncovering the mechanism of other naturally occurring compounds with chemical structures similar to QU.

Pregnancy with pulmonary hypertension (PH) seriously threatens the life and safety of mothers and infants. Here, the long-term effect of maternal PH on the postpartum growth of rat offspring was focused for the first time, as well as explored the role of Myadm in PH rats before pregnancy based upon the previous findings. Patients with PH are prone to hypoxemia, leading to insufficient placental structure and function, which affects the organ function of fetuses, followed by evidence that differently expressed genes (DEGs) existed in the heart of maternal PH newborn rats and enriched in pathways related to cardiac and nerve development on human infants with similar birth outcome: low birth weight (LBW). LBW was one of the possible birth outcomes of pregnancy with PH, especially severe PH, accompanied by evidence that offspring derived from mothers with PH presented lower birth weights and slower growth rates than those derived from normal control mothers in a rat model. Besides, maternal PH rat offspring showed cardiac remodeling and a significant elevation of the expression levels of hypoxia- and inflammation-related markers in the cerebral cortex at both 10 and 14 weeks of age, respectively. What is more, the previous studies found that the overexpression of Myadm could result in the remodeling of the pulmonary artery. And targeting Myadm to intervene PH before pregnancy could alleviate sustained low weight growth in maternal PH rat offspring, and the pathological changes of the cardiac–cerebral system caused by maternal PH, including enlarged right heart cavity, loss of cardiomyocytes, abnormal heart index, as well as cerebral cortex hypoxia and the inflammatory state as they grew up to a certain extent. The findings show the pathological significance of maternal PH on offspring growth and the cardiac–cerebral development in a rat model, as well as point out the potential treatment target, which may provide a further reference for pregnancy outcomes in women with PH and healthy development of offspring to some extent.

Janus kinases (JAKs) play a critical role in immune responses by relaying signals from more than 50 cytokines, making them attractive therapeutic targets for autoimmune diseases. Although approved JAK inhibitors have demonstrated clinical efficacy, they target a broad spectrum of cytokines, which results in side effects. Therefore, next-generation inhibitors maintain efficacy, while sparing adverse events need to be developed. Among members of the JAK family, JAK3 only regulates a narrow spectrum of γc cytokines and becomes a potentially ideal target. Here, a highly JAK3-selective inhibitor Z583 is developed, which showed a potent inhibition of JAK3 with an IC 50 of 0.1 nM and exhibited a 4500-fold selectivity for JAK3 than other JAK subtypes. Furthermore, Z583 completely inhibited the γc cytokine signaling and sufficiently blocked the development of inflammatory response in RA model, while sparing hematopoiesis. Collectively, the highly selective JAK3 inhibitor Z583 is a promising candidate with significant therapeutic potential for autoimmune diseases.

Although pituitary adenomas are histologically benign, they are often accompanied by multiple complications, such as cardiovascular disease and metabolic dysfunction. In the present study, we repositioned the Food and Drug Administration -approved immune regulator tamoxifen to target STAT6 based on the genomics analysis of PAs. Tamoxifen inhibited the proliferation of GH3 and AtT-20 cells with respective IC50 values of 9.15 and 7.52 μM and increased their apoptotic rates in a dose-dependent manner. At the molecular level, tamoxifen downregulated phosphorylated PI3K, phosphorylated AKT and the anti-apoptotic protein Bcl-2 and increased the expression of pro-apoptotic proteins p53 and Bax in GH3 and AtT-20 cells. Furthermore, tamoxifen also inhibited the migration of both cell lines by reprogramming tumor-associated macrophages to the M1 phenotype through STAT6 inactivation and inhibition of the macrophage-specific immune checkpoint SHP1/SHP. Finally, administration of tamoxifen (20, 50, 100 mg·kg−1·d−1, for 21 days) inhibited the growth of pituitary adenomas xenografts in nude mice in a dose-dependent manner. Taken together, tamoxifen is likely to be a promising combination therapy for pituitary adenomas and should be investigated further.

Objective We aimed to explore the associations between type 2 diabetes onset age and cardiovascular disease (CVD) and all-cause mortality in Chinese population. Research design and methods This study included 101,080 participants free of prevalent diabetes and CVD at baseline from the Kailuan study. All participants were followed biennially until December 31, 2017. A total of 11,384 participants were diagnosed as type 2 diabetes during follow-up. For each case, one control was randomly selected matched for age (±1 years) and sex. The final analysis comprised 10,777 case-control pairs. Weighted Cox regression models were used to evaluate the average hazard ratios (AHRs) and 95% confidence intervals (CIs) of incident CVD and all-cause mortality among patients with new-onset type 2 diabetes versus controls across age groups. Results During a median follow-up of 5.57 years, 1794 incident events (907 CVD events, of which were 725 strokes, and 887 deaths) occurred. After adjustment for potential confounders, participants with type 2 diabetes diagnosed at age < 45 years had the highest risks of CVD and all-cause mortality relative to the matched controls, with AHRs of 3.21 (95% CI 1.18–8.72) for CVD, 2.99 (95% CI 1.01–9.17) for stroke, and 4.79 (95% CI 1.95–11.76) for all-cause mortality. The risks gradually attenuated with each decade increase in type 2 diabetes onset age. Conclusions The relative risks of CVD and all-cause mortality differed across type 2 diabetes onset age groups, and the associations were more evident in younger-onset type 2 diabetes.

We recently identified oncologic miR-182 as a new regulator of pulmonary artery hypertension (PAH) that targets myeloid-associated differentiation marker (Myadm), which is expressed in bone marrow stem cells and multipotent progenitors. Both miR-182 and Myadm are expressed in the cardiopulmonary system and correlated with the balance between the bone morphogenetic protein (BMP) and the transforming growth factor (TGF)-β signalling pathways, which are disturbed in PAH. We hypothesize that miR-182/Myadm are involved in BMP-TGF-β-signalling way in PAH. Hypoxia triggered pathological progression in cardiopulmonary PAH in vivo and in vitro; these changes were accompanied by strongly dowregulated BMP/SMAD1/5/8 expression and enhanced TGF-β/SMAD2/3 signalling pathway, favouring SMAD4/SMAD2 transcript formation and inhibiting the PAH negative regulator Id1 expression. miR-182 gain-of-function significantly inhibited the pathological progression in hypoxia-induced PAH (HPH) in vivo and in vitro, with a restoration of the balance in BMP-TGF-β signalling pathway. This recovery was abrogated by overexpression of Myadm. Conversely, loss-of-function of miR-182 increased the pathological progression of HPH followed by severe disturbance of BMP and TGF-β signal transduction and reduced Id1 expression, which was restored by Myadm knockdown. We also showed that the miR-182/Myadm relate BMP-TGF-β pathway is associated with NOS3/NO/cGMP via the crosstalk between endothelial cells and smooth muscle cells. Our findings further support the therapeutic significance of miR-182/Myadm in PAH via the balance of BMP- and TGF-β-associated mechanisms.

Background Cushing's disease is a rare and little-known disease, and the individualization of drug treatment varies greatly. Studies have shown that the gene expression profile of Cushing's disease is related to its clinical characteristics. Therefore, the study aims to identify key differential genes between the age and size of tumors through bioinformatics technology, thus providing a theoretical basis for personalized targeted therapy of Cushing's disease. Methods Downloading the gene expression microarray (GSE93825) data from the Gene Expression Omnibus (GEO) database and obtaining differentially expressed genes (DEGs) of different tumor sizes and ages through GEO2R. The DAVID database, Cytoscape and String platforms were utilized for functional enrichment analysis and protein-protein interaction (PPI) network analysis on selected differential genes. Results First, 96 DEGs were identified between macroadenoma (MAC) and microadenoma (MIC), which initially proved the different gene expression characteristics between them. Second, a total of 2128 DEGs were identified in MAC age group. The top five hub genes of the PPI network were GNGT2, LPAR3, PDYN, GRM3, and HTR1D. A total of 16 DEGs were identified in MIC age group. In addition, 88 DEGs were identified in younger MAC and MIC groups. The top five hub genes included LEP, PTGS2, STAT6, CXCL12, and ITPKB. 299 DEGs were identified in senior MAC and MIC groups. The first five hub genes were CCR7, LPAR2, CXCR5, ADCY3, and TAS2R14. By virtue of DAVID and Cytoscape software, the function enrichment analysis and core module analysis were performed successfully. Conclusions In summary, our research shows through bioinformatics analysis that different gene expression profiles of Cushing's disease are related to the size and age of the tumor, which may provide new insights into the molecular pathogenesis of Cushing's disease. These hub genes may be used for accurate diagnosis and treatment of Cushing's disease.

Circular RNAs (circRNAs) are a new class of noncoding single-stranded RNAs that differ from linear microRNAs (miRNAs), since they form covalently closed loop structures without free 3′ poly(A) tails or 5′ caps. circRNAs are the competitive endogenous RNAs (ceRNAs) by binding to miRNA through miRNA response elements (MREs) (i.e., “miRNA sponge”), thereby reducing the quantity of miRNA available to target mRNA, subsequently promoting mRNA stability or protein expression, which involves the initiation and progress of human diseases. Owing to these features of abundance, stability, conservative property, and tissue and stage specificity, widely distributing in the extracellular space and in various bodily fluids, circRNAs can be considered as potential biomarkers for various diseases. Here, we reviewed the promising circRNAs being disease biomarkers, focused on their regulatory function by acting as miRNA sponges, and described their roles in cancer, cardiovascular or neurodegenerative diseases, osteoarthritis, rheumatoid arthritis, diabetes, and other human aging-related diseases, which provide a new direction for pathogenesis, diagnosis, and treatment of human aging-related diseases. Circular RNAs (circRNAs) are a new class of noncoding single-stranded RNAs that differ from linear microRNAs (miRNAs), since they form covalently closed loop structures without free 3′ poly(A) tails or 5′ caps. circRNAs are the competitive endogenous RNAs (ceRNAs) by binding to miRNA through miRNA response elements (MREs) (i.e., “miRNA sponge”), thereby reducing the quantity of miRNA available to target mRNA, subsequently promoting mRNA stability or protein expression, which involves the initiation and progress of human diseases. Owing to these features of abundance, stability, conservative property, and tissue and stage specificity, widely distributing in the extracellular space and in various bodily fluids, circRNAs can be considered as potential biomarkers for various diseases. Here, we reviewed the promising circRNAs being disease biomarkers, focused on their regulatory function by acting as miRNA sponges, and described their roles in cancer, cardiovascular or neurodegenerative diseases, osteoarthritis, rheumatoid arthritis, diabetes, and other human aging-related diseases, which provide a new direction for pathogenesis, diagnosis, and treatment of human aging-related diseases. Circular RNAs (circRNAs) are a new class of noncoding single-stranded RNA,1Holdt L.M. Kohlmaier A. Teupser D. Molecular roles and function of circular RNAs in eukaryotic cells.Cell. Mol. Life Sci. 2018; 75: 1071-1098Crossref PubMed Scopus (119) Google Scholar characterized by covalently closed loop structures without free 3′ poly(A) tails or 5′ caps. These features differentiate them from linear RNAs,2Chen Y. Li C. Tan C. Liu X. Circular RNAs: a new frontier in the study of human diseases.J. Med. Genet. 2016; 53: 359-365Crossref PubMed Scopus (146) Google Scholar long noncoding RNAs (lncRNAs), and microRNAs (miRNAs).3Song Y.Z. Li J.F. Circular RNA hsa_circ_0001564 regulates osteosarcoma proliferation and apoptosis by acting miRNA sponge.Biochem. Biophys. Res. Commun. 2018; 495: 2369-2375Crossref PubMed Scopus (87) Google Scholar Although circRNAs were first discovered in the 1990s in viruses, viroids, and tetrahymena,4Hu J. Li P. Song Y. Ge Y.X. Meng X.M. Huang C. Li J. Xu T. Progress and prospects of circular RNAs in Hepatocellular carcinoma: Novel insights into their function.J. Cell. Physiol. 2018; 233: 4408-4422Crossref PubMed Scopus (30) Google Scholar little attention has been paid to their function.4Hu J. Li P. Song Y. Ge Y.X. Meng X.M. Huang C. Li J. Xu T. Progress and prospects of circular RNAs in Hepatocellular carcinoma: Novel insights into their function.J. Cell. Physiol. 2018; 233: 4408-4422Crossref PubMed Scopus (30) Google Scholar,5Yang Y. Gao X. Zhang M. Yan S. Sun C. Xiao F. Huang N. Yang X. Zhao K. Zhou H. et al.Novel Role of FBXW7 Circular RNA in Repressing Glioma Tumorigenesis.J. Natl. Cancer Inst. 2018; 110: 304-315Crossref Scopus (367) Google Scholar At that time, they were considered abnormal products, resulting from splicing errors.3Song Y.Z. Li J.F. Circular RNA hsa_circ_0001564 regulates osteosarcoma proliferation and apoptosis by acting miRNA sponge.Biochem. Biophys. Res. Commun. 2018; 495: 2369-2375Crossref PubMed Scopus (87) Google Scholar,6Xu Y. Yao Y. Zhong X. Leng K. Qin W. Qu L. Cui Y. Jiang X. Downregulated circular RNA hsa_circ_0001649 regulates proliferation, migration and invasion in cholangiocarcinoma cells.Biochem. Biophys. Res. Commun. 2018; 496: 455-461Crossref PubMed Scopus (39) Google Scholar In addition, circRNAs are often found in low abundance, and the traditional methods used to study linear RNAs are not applicable. With recent developments in biochemical-enrichment methods, especially high-throughput RNA sequencing and circRNAs microarray, more than 30,000 circRNAs have been discovered.7Yang F. Zhu P. Guo J. Liu X. Wang S. Wang G. Liu W. Wang S. Ge N. Circular RNAs in thoracic diseases.J. Thorac. Dis. 2017; 9: 5382-5389Crossref PubMed Scopus (6) Google Scholar They are widely expressed in yeasts, plants, protists, fruit flies, worms, zebrafish, mice, rats, and humans.8Li M. Ding W. Sun T. Tariq M.A. Xu T. Li P. Wang J. Biogenesis of circular RNAs and their roles in cardiovascular development and pathology.FEBS J. 2018; 285: 220-232Crossref PubMed Scopus (54) Google Scholar Compared with the levels of their linear isomers, circRNA expression levels can be increased by 10-fold or more,9Jeck W.R. Sorrentino J.A. Wang K. Slevin M.K. Burd C.E. Liu J. Marzluff W.F. Sharpless N.E. Circular RNAs are abundant, conserved, and associated with ALU repeats.RNA. 2013; 19: 141-157Crossref PubMed Scopus (1832) Google Scholar an indication of their potential abundance. Owing to their distinctive structure, they can resist exonuclease activity and are extremely stable.1Holdt L.M. Kohlmaier A. Teupser D. Molecular roles and function of circular RNAs in eukaryotic cells.Cell. Mol. Life Sci. 2018; 75: 1071-1098Crossref PubMed Scopus (119) Google Scholar The average lifetime of a 3′ → 5′-linked circRNA is 2∼5 times longer than that of a linear mRNA.1Holdt L.M. Kohlmaier A. Teupser D. Molecular roles and function of circular RNAs in eukaryotic cells.Cell. Mol. Life Sci. 2018; 75: 1071-1098Crossref PubMed Scopus (119) Google Scholar In addition, the expression levels of circRNAs are tissue and stage specific, and a number of highly abundant circRNAs have been found to exist in human peripheral blood (PB),10Memczak S. Papavasileiou P. Peters O. Rajewsky N. Identification and Characterization of Circular RNAs As a New Class of Putative Biomarkers in Human Blood.PLoS ONE. 2015; 10: e0141214Crossref PubMed Scopus (345) Google Scholar indicating that circRNAs can act as biomarkers to screen, diagnose, characterize, and monitor various diseases. circRNAs have many biological functions, including regulating host gene splicing and transcription,11Ashwal-Fluss R. Meyer M. Pamudurti N.R. Ivanov A. Bartok O. Hanan M. Evantal N. Memczak S. Rajewsky N. Kadener S. circRNA biogenesis competes with pre-mRNA splicing.Mol. Cell. 2014; 56: 55-66Abstract Full Text Full Text PDF PubMed Scopus (1222) Google Scholar acting as miRNA12Wang X. Zhu X. Zhang H. Wei S. Chen Y. Chen Y. Wang F. Fan X. Han S. Wu G. Increased circular RNA hsa_circ_0012673 acts as a sponge of miR-22 to promote lung adenocarcinoma proliferation.Biochem. Biophys. Res. Commun. 2018; 496: 1069-1075Crossref PubMed Scopus (2) Google Scholar and protein sponges,8Li M. Ding W. Sun T. Tariq M.A. Xu T. Li P. Wang J. Biogenesis of circular RNAs and their roles in cardiovascular development and pathology.FEBS J. 2018; 285: 220-232Crossref PubMed Scopus (54) Google Scholar reacting with proteins,13Du W.W. Yang W. Chen Y. Wu Z.K. Foster F.S. Yang Z. Li X. Yang B.B. Foxo3 circular RNA promotes cardiac senescence by modulating multiple factors associated with stress and senescence responses.Eur. Heart J. 2017; 38: 1402-1412Crossref PubMed Google Scholar and serving as protein-coding circRNAs.14Yang Y. Fan X. Mao M. Song X. Wu P. Zhang Y. Jin Y. Yang Y. Chen L.L. Wang Y. et al.Extensive translation of circular RNAs driven by N6-methyladenosine.Cell Res. 2017; 27: 626-641Crossref PubMed Scopus (539) Google Scholar Many studies15Panda A.C. Circular RNAs Act as miRNA Sponges.Adv. Exp. Med. Biol. 2018; 1087: 67-79Crossref PubMed Scopus (121) Google Scholar, 16Hsiao K.Y. Sun H.S. Tsai S.J. Circular RNA - New member of noncoding RNA with novel functions.Exp. Biol. Med. (Maywood). 2017; 242: 1136-1141Crossref PubMed Scopus (129) Google Scholar, 17Qu S. Yang X. Li X. Wang J. Gao Y. Shang R. Sun W. Dou K. Li H. Circular RNA: A new star of noncoding RNAs.Cancer Lett. 2015; 365: 141-148Crossref PubMed Scopus (773) Google Scholar have indicated that circRNAs contain a large number of miRNA binding sites. As competitive endogenous RNAs (ceRNAs), circRNAs can function as an miRNA sponge and competitively combine with the same miRNAs by miRNA response elements (MREs), removing or reducing the inhibition of genes targeted by the miRNAs and regulating the expression of the target genes.18Gao J. Xu W. Wang J. Wang K. Li P. The Role and Molecular Mechanism of Non-Coding RNAs in Pathological Cardiac Remodeling.Int. J. Mol. Sci. 2017; 18: 608Crossref PubMed Scopus (0) Google Scholar,19Salmena L. Poliseno L. Tay Y. Kats L. Pandolfi P.P. A ceRNA hypothesis: the Rosetta Stone of a hidden RNA language?.Cell. 2011; 146: 353-358Abstract Full Text Full Text PDF PubMed Scopus (3057) Google Scholar circRNA not only participates in the proliferation, differentiation, and aging of normal cells but also plays an important role in the pathogenesis of diseases via a large regulatory network of sponge.20Poliseno L. Salmena L. Zhang J. Carver B. Haveman W.J. Pandolfi P.P. A coding-independent function of gene and pseudogene mRNAs regulates tumour biology.Nature. 2010; 465: 1033-1038Crossref PubMed Scopus (1592) Google Scholar,21Hansen T.B. Jensen T.I. Clausen B.H. Bramsen J.B. Finsen B. Damgaard C.K. Kjems J. Natural RNA circles function as efficient microRNA sponges.Nature. 2013; 495: 384-388Crossref PubMed Scopus (3266) Google Scholar Concerning an important pathway, the novel pathological functions of these circRNA-miRNA-mRNA axes in diseases have been expanded over the last few years,22Su Q. Lv X. Revealing new landscape of cardiovascular disease through circular RNA-miRNA-mRNA axis.Genomics. 2020; 112: 1680-1685Crossref PubMed Scopus (6) Google Scholar and circRNA-miRNA-mRNA axes cannot only provide a new direction for pathogenesis, diagnosis, and treatment of diseases but also can act as an advanced molecular technology to simulate or manufacture therapeutic agents, which indicates that this regulatory function of circRNAs, by acting as miRNA sponges, should be a focus of research. With the gradual aging of the population, the exploration of the biological basis of aging and related molecular mechanisms has become an important topic in modern scientific research.23Bruins M.J. Van Dael P. Eggersdorfer M. The Role of Nutrients in Reducing the Risk for Noncommunicable Diseases during Aging.Nutrients. 2019; 11: 85-108Crossref Scopus (11) Google Scholar Aging can cause the decay of multiple organ functions, leading to the occurrence and development of various aging-related diseases. These include tumors, heart failure, coronary artery disease (CAD), Alzheimer’s disease (AD), osteoporosis, and diabetes. Recently, accumulating evidence has supported the notion that circRNAs are involved in the development of multiple diseases, especially aging-related diseases, such as cancer,24Zhou Z. Du D. Chen A. Zhu L. Circular RNA expression profile of articular chondrocytes in an IL-1β-induced mouse model of osteoarthritis.Gene. 2018; 644: 20-26Crossref PubMed Scopus (37) Google Scholar,25Qu S. Liu Z. Yang X. Zhou J. Yu H. Zhang R. Li H. The emerging functions and roles of circular RNAs in cancer.Cancer Lett. 2018; 414: 301-309Crossref PubMed Scopus (109) Google Scholar cardiovascular diseases,8Li M. Ding W. Sun T. Tariq M.A. Xu T. Li P. Wang J. Biogenesis of circular RNAs and their roles in cardiovascular development and pathology.FEBS J. 2018; 285: 220-232Crossref PubMed Scopus (54) Google Scholar neurological disorders,2Chen Y. Li C. Tan C. Liu X. Circular RNAs: a new frontier in the study of human diseases.J. Med. Genet. 2016; 53: 359-365Crossref PubMed Scopus (146) Google Scholar osteoarthritis,26Ji Q. Zhang C. Sun X. Li Q. Circular RNAs function as competing endogenous RNAs in multiple types of cancer.Oncol. Lett. 2018; 15: 23-30PubMed Google Scholar,27Zhou Z.B. Du D. Huang G.X. Chen A. Zhu L. Circular RNA Atp9b, a competing endogenous RNA, regulates the progression of osteoarthritis by targeting miR-138-5p.Gene. 2018; 646: 203-209Crossref PubMed Scopus (42) Google Scholar inflammatory diseases,28Zheng F. Yu X. Huang J. Dai Y. Circular RNA expression profiles of peripheral blood mononuclear cells in rheumatoid arthritis patients, based on microarray chip technology.Mol. Med. Rep. 2017; 16: 8029-8036Crossref PubMed Scopus (56) Google Scholar and diabetes.29Zhao Z. Li X. Jian D. Hao P. Rao L. Li M. Hsa_circ_0054633 in peripheral blood can be used as a diagnostic biomarker of pre-diabetes and type 2 diabetes mellitus.Acta Diabetol. 2017; 54: 237-245Crossref PubMed Scopus (121) Google Scholar Here, we highlight recent advances in our understanding of circRNA biogenesis and expression, focusing on the function of miRNA sponges, which serve as biomarkers in these human diseases. circRNAs are widespread in the eukaryotic genome. In eukaryotes, RNA polymerase II (RNA Pol II) catalyzes the synthesis of precursor mRNAs (pre-mRNAs). The pre-mRNAs undergo spliceosome-mediated splicing to generate linear mRNAs.30Darnell Jr., J.E. Reflections on the history of pre-mRNA processing and highlights of current knowledge: a unified picture.RNA. 2013; 19: 443-460Crossref PubMed Scopus (64) Google Scholar Currently, we do not understand the correlation between RNA circularization and alternative splicing, but several sequence features, such as intron/exon length, hyperdebited RNA, and sequence content, affect the formation of circRNAs.11Ashwal-Fluss R. Meyer M. Pamudurti N.R. Ivanov A. Bartok O. Hanan M. Evantal N. Memczak S. Rajewsky N. Kadener S. circRNA biogenesis competes with pre-mRNA splicing.Mol. Cell. 2014; 56: 55-66Abstract Full Text Full Text PDF PubMed Scopus (1222) Google Scholar It is important to note that the expression levels of circRNAs do not always correlate with those of their linear counterparts, suggesting that the spliceosome can discriminate between linear splicing and RNA circularization, although the mechanism is still unclear. In terms of their genomic origin, circRNAs can be divided into three classes: circular intronic RNA (ciRNA), exonic circRNA (ecircRNA), and exon-intron circRNA (EIciRNA), all of which possess a covalently closed loop structure. These molecules share multiple features, including stability, abundance, conserved properties, and tissue specificity.31Tang C.M. Zhang M. Huang L. Hu Z.Q. Zhu J.N. Xiao Z. Zhang Z. Lin Q.X. Zheng X.L. -Yang M. et al.CircRNA_000203 enhances the expression of fibrosis-associated genes by derepressing targets of miR-26b-5p, Col1a2 and CTGF, in cardiac fibroblasts.Sci. Rep. 2017; 7: 40342-40350Crossref PubMed Scopus (132) Google Scholar ciRNAs, derived from 2′ → 5′-linked intronic lariats, are generated by canonical splicing32Xie L. Mao M. Xiong K. Jiang B. Circular RNAs: A Novel Player in Development and Disease of the Central Nervous System.Front. Cell. Neurosci. 2017; 11: 354-373Crossref PubMed Scopus (22) Google Scholar and are mainly found in the nucleus.33Chen B. Huang S. Circular RNA: An emerging non-coding RNA as a regulator and biomarker in cancer.Cancer Lett. 2018; 418: 41-50Crossref PubMed Google Scholar When pre-mRNAs are spliced, abundant GU elements near the 5′ splice site of the intron and C-rich elements near the branch point escape the debranching enzyme to form the intron lariat.8Li M. Ding W. Sun T. Tariq M.A. Xu T. Li P. Wang J. Biogenesis of circular RNAs and their roles in cardiovascular development and pathology.FEBS J. 2018; 285: 220-232Crossref PubMed Scopus (54) Google Scholar ecircRNAs, derived only from exons, represent more than 80% of total circRNAs and are located in the cytoplasm. Most circRNAs are generated from exons (protein-coding genes) or from exons and introns through “back-splicing,” a noncanonical splicing process.32Xie L. Mao M. Xiong K. Jiang B. Circular RNAs: A Novel Player in Development and Disease of the Central Nervous System.Front. Cell. Neurosci. 2017; 11: 354-373Crossref PubMed Scopus (22) Google Scholar,34Qian Z. Liu H. Li M. Shi J. Li N. Zhang Y. Zhang X. Lv J. Xie X. Bai Y. et al.Potential Diagnostic Power of Blood Circular RNA Expression in Active Pulmonary Tuberculosis.EBioMedicine. 2018; 27: 18-26Abstract Full Text Full Text PDF PubMed Scopus (38) Google Scholar In this process, characterized by exon skipping, with the help of RNA binding proteins (RBPs) 24Zhou Z. Du D. Chen A. Zhu L. Circular RNA expression profile of articular chondrocytes in an IL-1β-induced mouse model of osteoarthritis.Gene. 2018; 644: 20-26Crossref PubMed Scopus (37) Google Scholar or reverse complementary sequences between the flanking introns,31Tang C.M. Zhang M. Huang L. Hu Z.Q. Zhu J.N. Xiao Z. Zhang Z. Lin Q.X. Zheng X.L. -Yang M. et al.CircRNA_000203 enhances the expression of fibrosis-associated genes by derepressing targets of miR-26b-5p, Col1a2 and CTGF, in cardiac fibroblasts.Sci. Rep. 2017; 7: 40342-40350Crossref PubMed Scopus (132) Google Scholar the downstream splice donor joins the 3′ acceptor splice site of an upstream exon to form the EIciRNA or circRNA24Zhou Z. Du D. Chen A. Zhu L. Circular RNA expression profile of articular chondrocytes in an IL-1β-induced mouse model of osteoarthritis.Gene. 2018; 644: 20-26Crossref PubMed Scopus (37) Google Scholar,32Xie L. Mao M. Xiong K. Jiang B. Circular RNAs: A Novel Player in Development and Disease of the Central Nervous System.Front. Cell. Neurosci. 2017; 11: 354-373Crossref PubMed Scopus (22) Google Scholar (Figure 1). ecircRNAs, containing only exons, are found mainly in the cytoplasm, whereas EIciRNAs, containing exon and intron regions, are located in the nucleus. As shown in Figure 2, some RBPs, such as muscleblind (MBL),11Ashwal-Fluss R. Meyer M. Pamudurti N.R. Ivanov A. Bartok O. Hanan M. Evantal N. Memczak S. Rajewsky N. Kadener S. circRNA biogenesis competes with pre-mRNA splicing.Mol. Cell. 2014; 56: 55-66Abstract Full Text Full Text PDF PubMed Scopus (1222) Google Scholar quaking (QKI),35Conn S.J. Pillman K.A. Toubia J. Conn V.M. Salmanidis M. Phillips C.A. Roslan S. Schreiber A.W. Gregory P.A. Goodall G.J. The RNA binding protein quaking regulates formation of circRNAs.Cell. 2015; 160: 1125-1134Abstract Full Text Full Text PDF PubMed Scopus (831) Google Scholar fused-in-sarcoma (FUS),36Errichelli L. Dini Modigliani S. Laneve P. Colantoni A. Legnini I. Capauto D. Rosa A. De Santis R. Scarfò R. Peruzzi G. et al.FUS affects circular RNA expression in murine embryonic stem cell-derived motor neurons.Nat. Commun. 2017; 8: 14741-14749Crossref PubMed Scopus (149) Google Scholar RNA binding motif (RBM)20 protein,37Khan M.A. Reckman Y.J. Aufiero S. van den Hoogenhof M.M. van der Made I. Beqqali A. Koolbergen D.R. Rasmussen T.B. van der Velden J. Creemers E.E. Pinto Y.M. RBM20 Regulates Circular RNA Production From the Titin Gene.Circ. Res. 2016; 119: 996-1003Crossref PubMed Scopus (130) Google Scholar and double-stranded RNA (dsRNA)-specific adenosine deaminase (ADAR),32Xie L. Mao M. Xiong K. Jiang B. Circular RNAs: A Novel Player in Development and Disease of the Central Nervous System.Front. Cell. Neurosci. 2017; 11: 354-373Crossref PubMed Scopus (22) Google Scholar act as splicing factors and regulate circRNA formation. circMbl is formed by back splicing after MBL binds to MBL binding sites in the flanking introns.1Holdt L.M. Kohlmaier A. Teupser D. Molecular roles and function of circular RNAs in eukaryotic cells.Cell. Mol. Life Sci. 2018; 75: 1071-1098Crossref PubMed Scopus (119) Google Scholar On the other hand, translation of MBL is inhibited by circMbl, which contains the start codon of the main coding sequence,24Zhou Z. Du D. Chen A. Zhu L. Circular RNA expression profile of articular chondrocytes in an IL-1β-induced mouse model of osteoarthritis.Gene. 2018; 644: 20-26Crossref PubMed Scopus (37) Google Scholar indicating that there is a dynamic balance between MBL and circMbl (Figure 2A). QKI is not only a splicing factor that is essential for circulatory and neural development but also a circRNA regulator that plays an important role in the generation of circRNAs.1Holdt L.M. Kohlmaier A. Teupser D. Molecular roles and function of circular RNAs in eukaryotic cells.Cell. Mol. Life Sci. 2018; 75: 1071-1098Crossref PubMed Scopus (119) Google Scholar,35Conn S.J. Pillman K.A. Toubia J. Conn V.M. Salmanidis M. Phillips C.A. Roslan S. Schreiber A.W. Gregory P.A. Goodall G.J. The RNA binding protein quaking regulates formation of circRNAs.Cell. 2015; 160: 1125-1134Abstract Full Text Full Text PDF PubMed Scopus (831) Google Scholar QKI regulates this process depending on the presence of putative QKI binding sites in the flanking introns of circularized exons. These sites are sufficient to induce circRNA biogenesis, suggesting a simple mechanism that regulates the splicing of circRNA through dimerization of flanking introns (Figure 2B).32Xie L. Mao M. Xiong K. Jiang B. Circular RNAs: A Novel Player in Development and Disease of the Central Nervous System.Front. Cell. Neurosci. 2017; 11: 354-373Crossref PubMed Scopus (22) Google Scholar As an RBP, FUS regulates circRNA biogenesis by binding to the introns flanking back-splicing junctions, promoting circRNA production (Figure 2C). Based on this mechanism of splice regulation, studies indicate that FUS participates in the pathogenesis of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia. Similarly, RBM20 also binds to introns flanking back-splicing junctions to regulate the I-band region of the titin transcript, which is known to undergo highly complex alternative splicing and can express approximately 80 circRNAs (Figure 2C).36Errichelli L. Dini Modigliani S. Laneve P. Colantoni A. Legnini I. Capauto D. Rosa A. De Santis R. Scarfò R. Peruzzi G. et al.FUS affects circular RNA expression in murine embryonic stem cell-derived motor neurons.Nat. Commun. 2017; 8: 14741-14749Crossref PubMed Scopus (149) Google Scholar,37Khan M.A. Reckman Y.J. Aufiero S. van den Hoogenhof M.M. van der Made I. Beqqali A. Koolbergen D.R. Rasmussen T.B. van der Velden J. Creemers E.E. Pinto Y.M. RBM20 Regulates Circular RNA Production From the Titin Gene.Circ. Res. 2016; 119: 996-1003Crossref PubMed Scopus (130) Google Scholar The quantity of circRNAs is negatively correlated with the expression levels of the RNA-editing enzyme ADAR1, which disrupts RNA-RNA interactions (Figure 2D). Hence, knockdown of ADAR1 significantly enhances circRNA expression in human HEK293 cells.38Rybak-Wolf A. Stottmeister C. Glažar P. Jens M. Pino N. Giusti S. Hanan M. Behm M. Bartok O. Ashwal-Fluss R. et al.Circular RNAs in the Mammalian Brain Are Highly Abundant, Conserved, and Dynamically Expressed.Mol. Cell. 2015; 58: 870-885Abstract Full Text Full Text PDF PubMed Scopus (926) Google Scholar Although the biological functions of circRNAs remain largely unknown, recent studies have demonstrated that circRNAs participate in several steps of gene expression, for example, competing with their linear cognates to regulate promoter activity,27Zhou Z.B. Du D. Huang G.X. Chen A. Zhu L. Circular RNA Atp9b, a competing endogenous RNA, regulates the progression of osteoarthritis by targeting miR-138-5p.Gene. 2018; 646: 203-209Crossref PubMed Scopus (42) Google Scholar facilitating protein interactions or encoding functional proteins,13Du W.W. Yang W. Chen Y. Wu Z.K. Foster F.S. Yang Z. Li X. Yang B.B. Foxo3 circular RNA promotes cardiac senescence by modulating multiple factors associated with stress and senescence responses.Eur. Heart J. 2017; 38: 1402-1412Crossref PubMed Google Scholar,24Zhou Z. Du D. Chen A. Zhu L. Circular RNA expression profile of articular chondrocytes in an IL-1β-induced mouse model of osteoarthritis.Gene. 2018; 644: 20-26Crossref PubMed Scopus (37) Google Scholar and sponging miRNAs.12Wang X. Zhu X. Zhang H. Wei S. Chen Y. Chen Y. Wang F. Fan X. Han S. Wu G. Increased circular RNA hsa_circ_0012673 acts as a sponge of miR-22 to promote lung adenocarcinoma proliferation.Biochem. Biophys. Res. Commun. 2018; 496: 1069-1075Crossref PubMed Scopus (2) Google Scholar In human cells, circRNAs that are located in the nucleus, such as ciRNAs and EIciRNAs,33Chen B. Huang S. Circular RNA: An emerging non-coding RNA as a regulator and biomarker in cancer.Cancer Lett. 2018; 418: 41-50Crossref PubMed Google Scholar have been found to compete with pre-mRNAs for splicing14Yang Y. Fan X. Mao M. Song X. Wu P. Zhang Y. Jin Y. Yang Y. Chen L.L. Wang Y. et al.Extensive translation of circular RNAs driven by N6-methyladenosine.Cell Res. 2017; 27: 626-641Crossref PubMed Scopus (539) Google Scholar (Figure 3A). It has been noted that knockdown of ciRNAs derived from the introns of ANKRD52, MCM5, and SIRT7, led to decreased expression of their parent genes without affecting nearby genes, suggesting that these ciRNAs act in cis.39Zhang Y. Zhang X.O. Chen T. Xiang J.F. Yin Q.F. Xing Y.H. Zhu S. Yang L. Chen L.L. Circular intronic long noncoding RNAs.Mol. Cell. 2013; 51: 792-806Abstract Full Text Full Text PDF PubMed Scopus (985) Google Scholar Another study reported that ciRNAs accumulated at the sites of transcription, interacted with the Pol II elongation complex and regulated transcriptional efficiency.40Fan X. Weng X. Zhao Y. Chen W. Gan T. Xu D. Circular RNAs in Cardiovascular Disease: An Overview.BioMed Res. Int. 2017; 2017: 5135781Crossref PubMed Scopus (102) Google Scholar Similarly, EIciRNAs could combine with U1 small nuclear ribonucleoprotein particle (snRNP) via specific RNA-RNA interactions to form EIciRNA-U1-snRNP complexes and recruit RNA Pol II, promoting RNA Pol II activity in cis and splicing to enhance host gene transcription24Zhou Z. Du D. Chen A. Zhu L. Circular RNA expression profile of articular chondrocytes in an IL-1β-induced mouse model of osteoarthritis.Gene. 2018; 644: 20-26Crossref PubMed Scopus (37) Google Scholar,41Li H. Yang J. Wei X. Song C. Dong D. Huang Y. Lan X. Plath M. Lei C. Ma Y. et al.CircFUT10 reduces proliferation and facilitates differentiation of myoblasts by sponging miR-133a.J. Cell. Physiol. 2018; 233: 4643-4651Crossref PubMed Scopus (53) Google Scholar (Figure 3B). Suppression of EIciRNA-U1-snRNP interactions blocked the transcription-enhancing effects of EIciRNAs. In addition, circRNAs have been found to sponge or interact with proteins to regulate host gene transcription.8Li M. Ding W. Sun T. Tariq M.A. Xu T. Li P. Wang J. Biogenesis of circular RNAs and their roles in cardiovascular development and pathology.FEBS J. 2018; 285: 220-232Crossref PubMed Scopus (54) Google Scholar For example, circMbl originates in the second exon of the splicing factor MBL. In Drosophila, MBL binds to MBL binding sites in the flanking introns to form circMbl.1Holdt L.M. Kohlmaier A. Teupser D. Molecular roles and function of circular RNAs in eukaryotic cells.Cell. Mol. Life Sci. 2018; 75: 1071-1098Crossref PubMed Scopus (119) Google Scholar At the same time, MBL can combine with circMbl to inhibit the production of circMbl,42Lei K. Bai H. Wei Z. Xie C. Wang J. Li J. Chen Q. The mechanism and function of circular RNAs in human diseases.Exp. Cell Res. 2018; 368: 147-158Crossref PubMed Scopus (31) Google Scholar indicating that circRNAs not only modulate alternative splicing but can also act as protein sponges (Figure 3C). Another example is circ-Foxo3 (associated with heart failure), which binds to the age-related proteins ID1 and E2F1, the stress-related protein HIF1a, and FAK in the cytoplasm, inhibiting the entry of these nuclear transcription factors (ID1, E2F1, and HIF1a) into the nucleus, thus inhibiting their function (Figure 3D).13Du W.W. Yang W. Chen Y. Wu Z.K. Foster F.S. Yang Z. Li X. Yang B.B. Foxo3 circular RNA promotes cardiac senescence by modulating multiple factors associated with stress and senescence responses.Eur. Heart J. 2017; 38: 1402-1412Crossref PubMed Google Scholar More surprisingly, some circRNAs that contain an internal ribosome entry site (IRES) and open reading frame (ORF) have been demonstrated to have protein-coding potential in a 5′ cap-independent way,8Li M. Ding W. Sun T. Tariq M.A. Xu T. Li P. Wang J. Biogenesis of circular RNAs and their roles in cardiovascular development and pathology.FEBS J. 2018; 285: 220-232Crossref PubMed Scopus (54) Google Scholar thus expanding the eukaryotic proteome. Current evidence indicates that most circRNAs originate from exons and are located in the cytoplasm, which increases the possibility that they may act as protein-coding circRNAs.43Li L.J. Leng R.X. Fan Y.G. Pan H.F. Ye D.Q. Translation of noncoding RNAs: Focus on lncRNAs, pri-miRNAs, and circRNAs.Exp. Cell Res. 2017; 361: 1-8Crossref PubMed Scopus (57) Google Scholar In gliomas, circ-FBXW7 has been found to encode a novel 21-kD protein called FBXW7-185aa through a cross-knot ORF driven by the ribosome entry site. The expression of FBXW7 and FBXW7-185aa was decreased in gliomas, and this had prognostic significance.5Yang Y. Gao X. Zhang M. Yan S. Sun C. Xiao F. Huang N. Yang X. Zhao K. Zhou H. et al.Novel Role of FBXW7 Circular RNA in Repressing Gli

Rationale: There is a continued need for investigating the roles of microRNAs and their targets on the pathogenesis of pulmonary arterial hypertension (PAH) vascular remodeling. We recently identified the association of myeloid miR-182-3p and its new target, Myeloid-Associated Differentiation Marker (Myadm), with vascular remodeling. Here, we aimed to determine the role of miR-182-3p/Myadm on PAH vascular remodeling and the underlying molecular mechanism. Methods: The miR-182-3p/Myadm expression profiles were detected in PAH patients and experimental rodent models. Loss-of-function and gain-of-function studies using gene knock-in or gene knock-out and the combinations of the proteomic technology and genome-wide ChIP-Seq were employed to determine the downstream targets of miR-182-3p/Myadm in response to monocrotaline (MCT)-induced PAH. Results: The miR-182-3p/Myadm expression was altered in PAH patients and experimental rodent models. Both miR-182-3p inhibitor and overexpression of Myadm augmented the pathological progression in rats in response to MCT-induced PAH. In contrast, miR-182-3p mimic and Myadm gene knockout attenuated the changes in the hemodynamics and structure of the cardio-pulmonary system in MCT-induced PAH in rats. Myadm mediated the proliferation of pulmonary artery smooth muscle cells (PASMCs) by altering the cell cycle kinase inhibitor (p21/Cip1) expression through the transcription factor Krüppel-like factor 4 (KLF4) translocation into the cytoplasm. Conclusion: Our findings indicate the prognostic and therapeutic significance of miR-182-3p in PAH and provide a new regulatory model of the myeloid-derived miR-182-3p/Myadm/KLF4/p21 axis in PAH vascular remodeling.

Bexarotene (BEX), a specific retinoic acid X receptor (RXR) agonist granted by Food and Drug Administration (FDA) approval for the clinical treatment of T cell lymphoma, has now been found to exert pharmacological effects in the nervous system, with low bioavailability and poor cerebral distribution limiting its application in treatment on neurological disorders. Pharmaceutical co-crystal was a helpful method to improve the bioavailability and tissue distribution of active pharmaceutical ingredients (APIs). Here, 2bexarotene-ligustrazine (2BEX-LIG), a novel co-crystal system of BEX and ligustrazine (LIG) of which with BEX is an API, was constructed with satisfactory stability and enhanced solubility. The pharmacokinetics characteristics of BEX were detected, and the results showed that the absolute bioavailability and the cerebral concentration of BEX in rats administrated with 2BEX-LIG were enhanced from 22.89% to 42.86% and increased by 3.4-fold, respectively, compared with those in rats administrated an equivalent of BEX. Hence, our present study indicated that the novel co-crystal of 2BEX-LIG contributed to improving BEX oral bioavailability and cerebral distribution, thereby providing significant advantages for clinical application of brain tumors and other neurological diseases.

ABSTRACT Circular RNAs (circRNAs) are a new class of non-coding single-stranded RNAs which differ from linear microRNAs (miRNAs), since they form covalently closed loop structures without free 3’ poly A tails or 5’ caps. CircRNAs are the competitive endogenous RNAs (ceRNAs) by binding to miRNA through miRNA response elements (MREs) (i.e “miRNA sponge”), thereby reducing the quantity of miRNA available to target mRNA, subsequently promoting mRNA stability or protein expression which involves in the initiation and progress of human diseases. Owing to these features of abundance, stability, conservative property, tissue- and stage-specificity, widely distributing in the extracellular space and in various bodily fluids, circNRAs can be considered as potential biomarkers for various diseases. Here, we reviewed the promising circRNAs being as disease biomarkers, focused on their regulatory function by acting as miRNAs sponges, and described their roles in cancer, cardiovascular or neurodegenerative diseases, osteoarthritis, rheumatoid arthritis, diabetes and other human ageing-related diseases, which provide a new direction for pathogenesis, diagnosis and treatment of human ageing-related diseases.

Dear Editor, Cushing's disease(CD)is a rare disease manifested as Cushing's syndrome caused by adrenocorticotropic hormone(ACTH)con-sistently over-secreted by adrenocorticotropic adenomas,fol-lowed by stimulation of the adrenal gland to secrete considerable cortisol,triggering metabolic dysfunction,and leading to death from complications.However,pituitary adreno-corticotropic adenoma-directed drugs can only inhibit ACTH secretion or hamper tumour growth,which limits their clinical applications.Recently,Nur77(also known as NR4A1 and NGFI-Ba,a kind of nuclear receptor),an important positive transcription regulator of pro-opiomelanocortin(POMC),the precursor of ACTH,has been regarded as a promising CD target.1 Hence,it would be promising to identify a combination treatment that targets Nur77 and another CD target to cover hormone normalisation in the short term and tumour suppression or even elimination in the long term.

Objectives This study aimed to develop an efficient and reliable method for estimating common adulterants in saffron by detecting their characteristic components to warrant its efficacy and regular use as a highly valuable medicinal herb. Methods A selective and sensitive high-performance liquid chromatography with tandem mass spectrometry (HPLC-MS/MS) method was developed to estimate the common adulterants in saffron from corn stigma, chrysanthemum and safflower through the simultaneous determination of specific constituents including allantoin, chlorogenic acid (ChA) and hydroxysafflor yellow A (HSYA). Peak identification of each target compound was confirmed from product ions obtained using multiple reaction monitoring triggered enhanced product ions mass chromatogram. Method validation in terms of linearity, sensitivity, reproducibility, accuracy and stability was systematically performed according to official guidelines. Key findings Satisfactory separation of the three components was achieved on a C-18 column (4.6 x 250 mm, 5 mu m) with methanol-acetonitrile-ammonium acetate (3.0 mm) as the mobile phase at gradient elution. The identification of these specific constituents was accomplished using the multiple reaction monitoring mode in combination with enhanced product ion supplementary confirmation. The established method was validated in terms of linearity, sensitivity, reproducibility, accuracy and recovery, which were found satisfactory for sensitive detection of the three target compounds. Conclusions By detecting the specific constituents allantoin, ChA and HSYA in one run, the adulterants of corn stigma, chrysanthemum and safflower can be effectively identified and estimated in saffron. This is the first report on developing a simple, sensitive and operational method for the identification and estimation of common adulterants of saffron, that was forwarded for broaden application.