Differential Expression Profiles of Circular RNAs During Osteogenic Differentiation of Mouse Adipose-Derived Stromal Cells

Circular RNAs in human diseases

Circular RNAs (circRNAs) are a unique class of RNA molecules formed through back-splicing rather than linear splicing. As an emerging field in molecular biology, circRNAs have garnered significant attention due to their distinct structure and potential functional implications. A comprehensive understanding of circRNAs' functions and potential clinical applications remains elusive despite accumulating evidence of their involvement in disease pathogenesis. Recent research highlights their significant roles in various human diseases, but comprehensive reviews on their functions and applications remain scarce. This review provides an in-depth examination of circRNAs, focusing first on their involvement in non-neoplastic diseases such as respiratory, endocrine, metabolic, musculoskeletal, cardiovascular, and renal disorders. We then explore their roles in tumors, with particular emphasis on exosomal circular RNAs, which are crucial for cancer initiation, progression, and resistance to treatment. By detailing their biogenesis, functions, and impact on disease mechanisms, this review underscores the potential of circRNAs as diagnostic biomarkers and therapeutic targets. The review not only enhances our understanding of circRNAs' roles in specific diseases and tumor types but also highlights their potential as novel diagnostic and therapeutic tools, thereby paving the way for future clinical investigations and potential therapeutic interventions.

CircRNA ARHGAP10 promotes osteogenic differentiation through the miR-335-3p/RUNX2 pathway in aortic valve calcification

BACKGROUND

Calcific aortic valve disease (CAVD) is a common cardiovascular disease with high morbidity and mortality, and no effective prevention or treatment is available. In recent years, increasing evidence has shown that noncoding RNAs (ncRNAs) play an important role in the pathogenesis and prognosis of CAVD. Several associated circular RNAs (circRNAs) have been reported to be involved in CAVD, such as circRIC3 and TGFBR2. However, the limited number of circRNAs identified in CAVD warrants further in-depth investigation, and the comprehensive elucidation of their role in the key mechanisms of this disease is needed.

METHODS

The expression of circRNAs and microRNAs (miRNAs) were analyzed by RNA sequencing. Quantitative real-time polymerase chain reaction (qRT-PCR) was conducted to analyze the expression of circRNA ARHGAP10 (circARHGAP10), miR-335-3p, and RUNX2. Luciferase reporter assay, pull-down assay, and RNA binding protein immunoprecipitation (RIP) assay were performed to evaluate the binding of miR-335-3p to circARHGAP10 or RUNX2. Alizarin red S staining showed the formation of calcified nodules in valve interstitial cells (VICs). The expression of circARHGAP10 and miR-335-3p was altered through lentivirus infection. Alkaline phosphatase (ALP) activity was used to verify the correlation between circARHGAP10 and miR-335-3p. The expression of proteins was assessed via Western blot. RNA fluorescence in situ hybridization (FISH) was used to confirm the localization of circARHGAP10 in the cytoplasm of VICs. Immunofluorescence was used to detect the expression level of RUNX2. ApoE-/- mice were used to construct a CAVD model, circARHGAP10 short hairpin RNA (shRNA) and miR-335-3p inhibitor lentivirus were intraperitoneally injected, and scramble and inhibitor normal control (NC) lentivirus were injected as controls, followed by hematoxylin and eosin (HE) staining.

RESULTS

Through RNA sequencing, we found that circARHGAP10 (hsa_circ_0008975) was highly expressed in calcific aortic valves. CircARHGAP10 knockdown effectively inhibited the extent of osteogenic differentiation of VICs. We then found that circARHGAP10 was a competing endogenous RNA (ceRNA) of miR-355-3p and that miR-355-3p targeted RUNX2. In vitro experiments confirmed that circARHGAP10 regulated the osteogenic differentiation of VICs through the miR-355-3p/RUNX2 pathway, and this was validated in vivo using an ApoE-/- mouse model.

CONCLUSIONS

These findings provide a foundation for circRNA-directed diagnostics and therapeutics for CAVD.

Circ_0000888 regulates osteogenic differentiation of periosteal mesenchymal stem cells in congenital pseudarthrosis of the tibia

Congenital pseudarthrosis of the tibia (CPT) is a refractory condition characterized by the decreased osteogenic ability in tibial pseudarthrosis repair. Periosteal mesenchymal stem cells (PMSCs) are multipotent cells involved in bone formation regulation. However, the mechanisms underlying its role in CPT remain unclear. In this study, we observed downregulation of circ_0000888 and pleiotrophin (PTN), as well as upregulation of miR-338-3p in CPT derived PMSCs (CPT-dPMSCs). Our results demonstrated that circ_0000888 and PTN likely enhanced the viability, proliferation, and osteogenic ability of PMSCs, while miR-338-3p had the opposite effect. Further analysis confirmed the regulatory relationship circ_0000888 suppressed the activity of miR-338-3p and upregulated the expression of its downstream target PTN by binding to miR-338-3p, consequently promoting the viability and osteogenic differentiation ability of CPT-dPMSCs. Our findings unveil an unexpected link between circ_0000888/miR-338-3p/PTN in promoting osteogenic ability and indicate the potential pathogenic mechanisms of CPT.

Functional role of circRNAs in osteogenesis: A review

The extracellular matrixes (ECM), as well as the microenvironmental signals, play an essential role in osteogenesis by regulating intercellular pathways. Recently, it has been demonstrated that a newly identified RNA, circular RNA, contributes to the osteogenesis process. Circular RNA (circRNA), the most recently identified RNA, is involved in the regulation of gene expression at transcription to translation levels. The dysregulation of circRNAs has been observed in several tumors and diseases. Also, various studies have shown that circRNAs expression is changed during osteogenic differentiation of progenitor cells. Therefore, understanding the role of circRNAs in osteogenesis might help the diagnosis as well as treatment of bone diseases such as bone defects and osteoporosis. In this review, circRNA functions and the related pathways in osteogenesis have been discussed.

Epigenetic Regulations in Autoimmunity and Cancer: from Basic Science to Translational Medicine

Epigenetics, as a discipline that aims to explain the differential expression of phenotypes arising from the same gene sequence and the heritability of epigenetic expression, has received much attention in medicine. Epigenetic mechanisms are constantly being discovered, including DNA methylation, histone modifications, noncoding RNAs and m6A. The immune system mainly achieves an immune response through the differentiation and functional expression of immune cells, in which epigenetic modification will have an important impact. Because of immune infiltration in the tumor microenvironment, immunotherapy has become a research hotspot in tumor therapy. Epigenetics plays an important role in autoimmune diseases and cancers through immunology. An increasing number of drugs targeting epigenetic mechanisms, such as DNA methyltransferase inhibitors, histone deacetylase inhibitors, and drug combinations, are being evaluated in clinical trials for the treatment of various cancers (including leukemia and osteosarcoma) and autoimmune diseases (systemic lupus erythematosus, rheumatoid arthritis, systemic sclerosis). This review summarizes the progress of epigenetic regulation for cancers and autoimmune diseases to date, shedding light on potential therapeutic strategies.

Identification of circRNAs Associated with Adipogenesis Based on RNA-seq Data in Pigs

Adipocytes or fat cells play a vital role in the storage and release of energy in pigs, and many circular RNAs (circRNAs) have emerged as important regulators in various tissues and cell types in pigs. However, the spatio-temporal expression pattern of circRNAs between different adipose deposition breeds remains elusive. In this study, RNA sequencing (RNA-seq) produced transcriptome profiles of Western Landrace (lean-type) and Chinese Songliao black pigs (obese-type) with different thicknesses of subcutaneous fat tissues and were used to identify circRNAs involved in the regulation of adipogenesis. Gene expression analysis revealed 883 circRNAs, among which 26 and 11 circRNAs were differentially expressed between Landrace vs. Songliao pigs and high- vs. low-thickness groups, respectively. We also analyzed the interaction between circRNAs and microRNAs (miRNAs) and constructed their interaction network in adipogenesis; gene ontology classification and pathway analysis revealed two vital circRNAs, with the majority of their target genes enriched in biological functions such as fatty acids biosynthesis, fatty acid metabolism, and Wnt/TGF-β signaling pathways. These candidate circRNAs can be taken as potential targets for further experimental studies. Our results show that circRNAs are dynamically expressed and provide a valuable basis for understanding the molecular mechanism of circRNAs in pig adipose biology.

Comprehensive analysis of lncRNA-miRNA-mRNA networks during osteogenic differentiation of bone marrow mesenchymal stem cells

Background

Long non-coding RNA (lncRNA) plays crucial role in osteogenic differentiation of bone marrow mesenchymal stem cells (BMMSCs), involving in regulation of competing endogenous RNA (ceRNA) mechanisms and conduction of signaling pathways. However, its mechanisms are poorly understood. This study aimed to investigate lncRNAs, miRNAs and mRNAs expression profiles in rat BMMSCs (rBMMSCs) osteogenic differentiation, screen the potential key lncRNA-miRNA-mRNA networks, explore the putative functions and identify the key molecules, as the basis of studying potential mechanism of rBMMSCs osteogenic differentiation driven by lncRNA, providing molecular targets for the management of bone defect.

Methods

High-throughput RNA sequencing (RNA-seq) was used to determine lncRNAs, miRNAs, and mRNAs expression profiles at 14-day rBMMSCs osteogenesis. The pivotal lncRNA-miRNA and miRNA-mRNA networks were predicted from sequencing data and bioinformatic analysis, and the results were exported by Cytoscape 3.9.0 software. Gene Ontology (GO) analysis and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis were used for functional exploration. Real-time quantitative reverse transcription-polymerase chain reaction (qRT-PCR) was performed to validate lncRNAs, miRNAs and mRNAs.

Results

rBMMSCs were identified, and the osteogenic and adipogenic differentiation ability were detected. A total of 8634 lncRNAs were detected by RNA-seq, and 1524 differential expressed lncRNAs, of which 812 up-regulated and 712 down-regulated in osteo-inductive groups compared with control groups. 30 up-regulated and 61 down-regulated miRNAs, 91 miRNAs were differentially expressed in total. 2453 differentially expressed mRNAs including 1272 up-expressed and 1181 down-expressed were detected. 10 up-regulated lncRNAs were chosen to predict 21 down-regulated miRNAs and 650 up-regulated mRNAs. 49 lncRNA-miRNA and 1515 miRNA–mRNA interactive networks were constructed. GO analysis showed the most important enrichment in cell component and molecular function were “cytoplasm” and “protein binding”, respectively. Biological process related to osteogenic differentiation such as “cell proliferation”, “wound healing”, “cell migration”, “osteoblast differentiation”, “extracellular matrix organization” and “response to hypoxia” were enriched. KEGG analysis showed differentially expressed genes were mainly enriched in “PI3K-Akt signaling pathway”, “Signaling pathway regulating pluripotency of stem cells”, “cGMP-PKG signaling pathway”, “Axon guidance” and “Calcium signaling pathway”. qRT-PCR verified that lncRNA Tug1, lncRNA AABR07011996.1, rno-miR-93-5p, rno-miR-322-5p, Sgk1 and Fzd4 were consistent with the sequencing results, and 4 lncRNA-miRNA-mRNA networks based on validations were constructed, and enrichment pathways were closely related to “PI3K-Akt signaling pathway”, “Signaling pathway regulating pluripotency of stem cells” and “Wnt signaling pathway”.

Conclusions

lncRNAs, miRNAs and mRNAs expression profiles provide clues for future studies on their roles for BMMSCs osteogenic differentiation. Furthermore, lncRNA–miRNA–mRNA networks give more information on potential new mechanisms and targets for management on bone defect.

Supplementary information

The online version contains supplementary material available at 10.1186/s12864-022-08646-x.

Emerging functions of circular RNA in the regulation of adipocyte metabolism and obesity

As noncoding RNAs, circular RNAs (circRNAs) are covalently enclosed endogenous biomolecules in eukaryotes that have tissue specificity and cell specificity. circRNAs were once considered a rare splicing byproduct. With the development of high-throughput sequencing, it has been confirmed that they are expressed in thousands of mammalian genes. To date, only a few circRNA functions and regulatory mechanisms have been verified. Adipose is the main tissue for body energy storage and energy supply. Adipocyte metabolism is a physiological process involving a series of genes and affects biological activities in the body, such as energy metabolism, immunity, and signal transmission. When adipocyte formation is dysregulated, it will cause a series of diseases, such as atherosclerosis, obesity, fatty liver, and diabetes. In recent years, many noncoding RNAs involved in adipocyte metabolism have been revealed. This review provides a comprehensive overview of the basic structure and biosynthetic mechanism of circRNAs, and further discusses the circRNAs related to adipocyte formation in adipose tissue and liver. Our review will provide a reference for further elucidating the genetic regulation mechanism of circRNAs involved in adipocyte metabolism.

Identification and Characterization of Circular RNAs in Association With the Deposition of Intramuscular Fat in Aohan Fine-Wool Sheep

Aohan fine-wool sheep (AFWS) is a high-quality fine-wool sheep breed that supplies wool and meat. Research is needed on the molecular mechanism behind intramuscular fat (IMF) deposition that greatly improves mutton quality. The widely expressed non-coding RNA is physiologically used in roles such as competitive endogenous RNA (ceRNA) that includes circular RNAs (circRNAs). Although circRNAs were studied in many fields, little research was devoted to IMF in sheep. We used the longissimus dorsi muscle of 2 and 12-month-old AWFS as research material to identify circRNAs related to IMF deposition in these sheep by RNA-seq screening for differentially expressed circRNAs in the two age groups. A total of 11,565 candidate circRNAs were identified, of which the 104 differentially expressed circRNAs in the two age groups were analyzed. Enrichment analysis was performed using Gene Ontology and the Kyoto Encyclopedia of Genes and Genomes. The enriched pathways included lipid transport (GO:0006869), negative regulation of canonical Wnt signaling pathway (GO:0090090), fat digestion and absorption (ko04975), and sphingolipid metabolism (ko00600). The differentially expressed circRNAs included ciRNA455, circRNA9086, circRNA7445, circRNA4557, and others. The source genes involved in these pathways might regulate IMF deposition. We used the TargetScan and miRanda software for interaction analysis, and a network diagram of circRNA-miRNA interactions was created. CircRNA455-miR-127, circRNA455-miR-29a, circRNA455-miR-103, circRNA4557-mir149-5p, and circRNA2440-mir-23a might be involved in the IMF deposition process. The targeting relationship of circRNA4557-miR-149-5p was verified by a dual-luciferase reporter assay. The RT-qPCR results of seven randomly selected circRNAs were consistent with the sequencing results. This study provides additional information on circRNA regulation of IMF deposition in AFWS and is a useful resource for future research on this sheep breed.

Circular RNAs as potential regulators in bone remodeling: a narrative review

Objective

In this review, we focus on the recent progress of circular ribonucleic acids (circRNAs)-related molecular mechanisms in the processes of osteogenesis and osteoclastogenesis, and explore their roles in the development of bone-remodeling disorders.

Background

The well-coupled bone-formation and bone-resorption processes are vital in bone remodeling. Once the balance is disrupted, bone-remodeling disorders (e.g., osteoporosis and osteopetrosis) occur, severely affecting patients’ quality of life. CircRNAs, the newly discovered members of the non-coding RNA family, have been reported to act as key checkpoints of various signaling pathways that influence osteoblasts and osteoclasts functions, thus regulating the physiological and pathological processes of bone homeostasis.

Methods

Three English and three Chinese databases [i.e., PubMed, Embase, MEDLINE (via Ovid), Chinese Biomedical Literature, China National Knowledge Infrastructure, and VIP databases] were searched to June 2021 without language restrictions. Studies exploring the roles of circRNAs in key bone remodeling mediators, such as Smad-dependent bone morphogenetic protein (BMP)/transforming growth factor beta (TGF-β), Wnts, runt-related transcription factor (RUNX), forkhead boxes (FOXs), colony-stimulating factor 1 (CSF-1), receptor activator of nuclear factor kappa B ligand (RANKL)/osteoprotegerin (OPG), and circRNA-related bone-remodeling disorders, were included.

Conclusions

Many circRNAs have been shown to promote osteogenesis and facilitate osteoclast differentiation via diverse mechanisms, and thus modulate the process of bone homeostasis. The imbalance or impairment of these two parts causes diseases, such as osteoporosis, and osteonecrosis of the femoral head, which are also closely correlated to the aberrant presence of circRNAs. Current evidence provides us with promising diagnosis and treatment methods for some bone homeostasis disorders.

CircRNA TGFBR2/MiR-25-3p/TWIST1 axis regulates osteoblast differentiation of human aortic valve interstitial cells

INTRODUCTION

Calcified aortic valve disease (CAVD) is characterized by valve thickening and calcification. Osteoblast differentiation is one of the key steps of valve calcification. CircRNAs is involved in osteogenic differentiation of multiple mesenchymal cells. However, the function of circRNA TGFBR2 (TGFBR2) in CAVD remained unclear. We explored the effect and mechanism of TGFBR2 in modulating CAVD.

MATERIALS AND METHODS

Human aortic valve interstitial cells (VICs) were subjected to osteogenic induction, and transfected with TGFBR2, miR-25-3p mimic and siTWIST1. The relationship between miR-25-3p and GFBR2 was predicted by starBase and confirmed by luciferase reporter and Person's correlation test. The relationship between miR-25-3p and TWIST1 was predicted by TargetScan and confirmed by luciferase reporter assay. The expressions of TGFBR2, miR-25-3p, TWIST1, osteoblast markers (RUNX2 and OPN) were detected by Western blot or/and qRT-PCR. Alkaline phosphatase (ALP) activity and calcium nodule was determined by colorimetric method and Alizarin Red S staining.

RESULTS

The expression of TGFBR2 was down-regulated and that of miR-25-3p was up-regulated in calcific valves and osteogenic VICs. TGFBR2 was inversely correlated with miR-25-3p expression in calcific valves. TGFBR2 sponged miR-25-3p to regulate TWIST1 expression in osteogenic VICs. During osteogenic differentiation, ALP activity, calcium nodule, the levels of osteoblast markers were increased in VICs. MiR-25-3p overexpression or TWIST1 knockdown reversed the inhibitory effect of TGFBR2 overexpression on ALP activity, calcium nodule, the expressions of RUNX2 and OPN in osteogenic VICs.

CONCLUSION

The findings indicated that TGFBR2/miR-25-3p/TWIST1 axis regulates osteoblast differentiation in VICs, supporting the fact that TGFBR2 is a miRNA sponge in CAVD.

Functions and mechanisms of circular RNAs in regulating stem cell differentiation

Stem cells are a class of undifferentiated cells with great self-renewal and differentiation capabilities that can differentiate into mature cells in specific tissue types. Stem cell differentiation plays critical roles in body homoeostasis, injury repair and tissue generation. The important functions of stem cell differentiation have resulted in numerous studies focusing on the complex molecular mechanisms and various signalling pathways controlling stem cell differentiation. Circular RNAs (circRNAs) are a novel class of noncoding RNAs with a covalently closed structure present in eukaryotes. Numerous studies have highlighted important biological functions of circRNAs, and they play multiple regulatory roles in various physiological and pathological processes. Importantly, multiple lines of evidence have shown the abnormal expression of numerous circRNAs during stem cell differentiation, and some play a role in regulating stem cell differentiation, highlighting the role of circRNAs as novel biomarkers of stem cell differentiation and novel targets for stem cell-based therapy. In this review, we systematically summarize and discuss recent advances in our understanding of the roles and underlying mechanisms of circRNAs in modulating stem cell differentiation, thus providing guidance for future studies to investigate stem cell differentiation and stem cell-based therapy.Abbreviations: CircRNAs: circular RNAs; ESCs: embryonic stem cells; ADSCs: adipose-derived mesenchymal stem cells; ecircRNAs: exonic circRNAs; EIciRNAs: exon-intron circRNAs; eiRNAs: circular intronic RNAs; tricRNAs: tRNA intronic circRNAs; pol II: polymerase II; snRNP: small nuclear ribonucleoprotein; m6A: N6-methyladenosine; AGO2: Argonaute 2; RBPs: RNA-binding proteins; MBNL: muscleblind-like protein 1; MSCs: mesenchymal stem cells; hiPSCs: human induced pluripotent stem cells; hiPSC-CMs: hiPSC-derived cardiomyocytes; hBMSCs: human bone marrow mesenchymal stem cells; hADSCs: human adipose-derived mesenchymal stem cells; hDPSCs: human dental pulp stem cells; RNA-seq: high-throughput RNA sequencing; HSCs: haematopoietic stem cells; NSCs: neural stem cells; EpSCs: epidermal stem cells; hESCs: human embryonic stem cells; mESCs: murine embryonic stem cells; MNs: motor neurons; SSUP: small subunit processome; BMSCs: bone marrow-derived mesenchymal stem cells; OGN: osteoglycin; GIOP: glucocorticoid‑induced osteoporosis; CDR1as: cerebellar degeneration-related protein 1 transcript; SONFH: steroid-induced osteogenesis of the femoral head; rBMSCs: rat bone marrow-derived mesenchymal stem cells; QUE: quercetin; AcvR1b: activin A receptor type 1B; BSP: bone sialoprotein; mADSCs: mouse ADSCs; PTBP1: polypyrimidine tract-binding protein; ER: endoplasmic reticulum; hUCMSCs: MSCs derived from human umbilical cord; MSMSCs: maxillary sinus membrane stem cells; SCAPs: stem cells from the apical papilla; MyoD: myogenic differentiation protein 1; MSTN: myostatin; MEF2C: myocyte enhancer factor 2C; BCLAF1: BCL2-associated transcription factor 1; EpSCs: epidermal stem cells; ISCs: intestinal stem cells; NSCs: neural stem cells; Lgr5+ ISCs: crypt base columnar cells; ILCs: innate lymphoid cells.

CircRNA-23525 regulates osteogenic differentiation of adipose-derived mesenchymal stem cells via miR-30a-3p

Adipose-derived mesenchymal stem cells (ADSCs) are considered to be seed cells in bone tissue engineering and emerging evidence indicates that circular RNAs (circRNAs) function in the osteogenic differentiation of ADSCs. The mechanisms of osteoblastic differentiation of ADSCs from the perspective of circRNA modulation are examined in this study. First, circRNA-23525 was upregulated during osteoblastic differentiation of ADSCs. Second, overexpression of circRNA-23525 increased Runx2, ALP and OCN at both mRNA and protein levels. Alkaline phosphatase (ALP) and Alizarin Red staining indicated a similar tendency. Silencing circRNA-23525 produced the opposite effect. Bioinformatics analysis with luciferase assays confirmed that circRNA-23525 functioned as a sponge for miR-30a-3p. In the osteoblastic differentiation of ADSCs, the dynamic expression of miR-30a-3p and circRNA-23525 resulted in an opposite trend at 3, 7 and 14 days. Overexpression of circRNA-23525 downregulated miR-30a-3p and knockdown of circRNA-23525 promoted the expression of miR-30a-3p. Bioinformatics methods and luciferase assays suggested that miR-30a-3p modulated Runx2 expression by targeting 3'UTR. Knockdown of miR-30a-3p facilitated osteogenesis in ADSCs and enhancing miR-30a-3p interfered with the osteogenic process. Finally, circRNA-23525 overexpression significantly increased Runx2 expression, while co-transfection of miR-30a-3p mimics reversed it. Runx2 expression was decreased in circRNA-23525-knockdown ADSCs but expression was rescued by including the miR-30a-3p inhibitor in the osteoblastic process. ALP activity and mineralized bone matrix confirmed the function of circRNA-23525/miR-30a-3p in osteogenesis. Taken together, the current study demonstrated that circRNA-23525 regulates Runx2 expression via targeting miR-30a-3p and is thus a positive regulator in the osteoblastic differentiation of ADSCs.

The circular RNAs differential expression profiles in the metastasis of salivary adenoid cystic carcinoma cells

In order to reveal circular RNAs (circRNAs) differential expression profiles and investigate the function and mechanism of circRNAs in the metastasis of salivary adenoid cystic carcinoma (SACC), microarray was used to detect differentially expressed circRNAs in SACC-83 and SACC-lung metastasis (LM) cell lines. Up-regulated circRNAs were analyzed using Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses to further predict their function. Expression of candidate circRNA and microRNA (miRNA) was determined using quantitative real-time polymerase chain reaction (qRT-PCR). Constructed circRNA-miRNA-mRNA co-expression network was based on TargetScan, miRanda databases. Wound healing and transwell assays were completed to examine the effects of hsa_circRNA_001982 and miR-181a-5p on cell migration and invasion. qRT-PCR confirmed hsa_circRNA_092556, hsa_circRNA_101379, and hsa_circRNA_001982 up-regulation in SACC-LM. miR-181a-5p was down-regulated in SACC-LM and correlated with up-regulated hsa_circRNA_001982. Wound healing and transwell assays indicated that silencing hsa_circRNA_001982 inhibited the migration and invasion of the SACC-LM cells. Furthermore, over-expression of hsa_circRNA_001982 promoted the migration and invasion of SACC-83 cells. Interestingly, up-regulation or down-regulation of miR-181a-5p led to the opposite result in wound healing and transwell assays. Overall, differential expression circRNA profiles in SACC-83 and SACC-LM cells may reveal potential targets and a novel mechanism of circRNAs in the metastasis of SACC. Moreover, the interaction of hsa_circRNA_001982/miR-181a-5p is closely related to the metastasis of SACC cells.

Quercetin regulates ERα mediated differentiation of BMSCs through circular RNA

Circular RNA (circRNA) participates in regulation of gene transcription, while estrogen receptor alpha (ERα) and quercetin (QUE) positively regulate bone formation, but little is known about the correlation among circRNA, ERα and QUE. In this experiment, we created an ERα-deficient rBMSC model treated with QUE and evaluated the effects of ERα or QUE on rBMSCs, then analyzed differentially-expressed circRNAs by RNA-Seq and bioinformatics. The results showed that ERα deficiency constrained osteogenic differentiation and stimulated adipocytic differentiation of rBMSCs, while QUE abrogated those effects. We identified 136 differentially-expressed circRNAs in the Lv-shERα group and 120 differentially-expressed circRNAs in the Lv-shERα + QUE group. Thirty-two circRNAs retroregulated by ERα and QUE were involved in Rap1 and Wnt signaling, and four of them together sponged miR-326-5p, the target genes of which are osteogenic and adipogenic differentiation factors. Further study showed that over-expressed miR-326-5p could stimulate osteogenic differentiation, while attenuating adipogenic differentiation of rBMSCs. Therefore, we concluded that ERα and QUE might regulate the differentiation of rBMSCs through the circRNA-miR-326-5p-mRNA axis.

CircFOXP1/FOXP1 promotes osteogenic differentiation in adipose-derived mesenchymal stem cells and bone regeneration in osteoporosis via miR-33a-5p

Osteoporosis (OP) is defined by bone mass loss and structural bone deterioration. Currently, there are no effective therapies for OP treatment. Circular RNAs (circRNAs) have been reported to have an important function in stem cell osteogenesis and to be associated with OP. Most circRNA roles in OP remain unclear. In the present study, we employed circRNA microarray to investigate circRNA expression patterns in OP and non‐OP patient bone tissues. The circRNA‐miRNA‐mRNA interaction was predicted using bioinformatic analysis and confirmed by RNA FISH, RIP and dual‐luciferase reporter assays. ARS and ALP staining was used to detect the degree of osteogenic differentiation in human adipose‐derived mesenchymal stem cells (hASCs) in vitro. In vivo osteogenesis in hASCs encapsulated in collagen‐based hydrogels was tested with heterotopic bone formation assay in nude mice. Our research found that circFOXP1 was significantly down‐regulated in OP patient bone tissues and functioned like a miRNA sponge targeting miR‐33a‐5p to increase FOXP1 expression. In vivo and in vitro analyses showed that circFOXP1 enhances hASC osteogenesis by sponging miR‐33a‐5p. Conversely, miR‐33a‐5p inhibits osteogenesis by targeting FOXP1 3′‐UTR and down‐regulating FOXP1 expression. These results determined that circFOXP1 binding to miR‐33a‐5p promotes hASC osteogenic differentiation by targeting FOXP1. Therefore, circFOXP7ay prevent OP and can be used as a candidate OP therapeutic target.

Exosomal circLPAR1 Promoted Osteogenic Differentiation of Homotypic Dental Pulp Stem Cells by Competitively Binding to hsa-miR-31

Human dental pulp stem cells (DPSCs) hold great promise in bone regeneration. However, the exact mechanism of osteogenic differentiation of DPSCs remains unknown, especially the role of exosomes played in. The DPSCs were cultured and received osteogenic induction; then, exosomes from osteogenic-induced DPSCs (OI-DPSC-Ex) at different time intervals were isolated and sequenced for circular RNA (circRNA) expression profiles. Gradually, increased circular lysophosphatidic acid receptor 1 (circLPAR1) expression was found in the OI-DPSC-Ex coincidentally with the degree of osteogenic differentiation. Meanwhile, results from osteogenic differentiation examinations showed that the OI-DPSC-Ex had osteogenic effect on the recipient homotypic DPSCs. To investigate the mechanism of exosomal circLPAR1 on osteogenic differentiation, we verified that circLPAR1 could competently bind to hsa-miR-31, by eliminating the inhibitory effect of hsa-miR-31 on osteogenesis, therefore promoting osteogenic differentiation of the recipient homotypic DPSCs. Our study showed that exosomal circRNA played an important role in osteogenic differentiation of DPSCs and provided a novel way of utilization of exosomes for the treatment of bone deficiencies.

CircCDK8 regulates osteogenic differentiation and apoptosis of PDLSCs by inducing ER stress/autophagy during hypoxia

Mounting evidence indicates that circular RNAs (circRNAs) have essential roles in several diseases, including periodontitis. Periodontal ligament stem cells (PDLSCs) exhibit potential for treating periodontitis accompanied by hypoxia. However, it is unclear how circRNA affects the osteogenesis of PDLSCs under hypoxia. In this study, a novel circRNA, hsa_circ_0003489, was found located at the gene for cyclin-dependent kinase 8 (CDK8) and referred to as circCDK8. The expression levels of circCDK8 and hypoxia-inducible factor-1α were significantly increased in periodontitis tissues, and the expression of circCDK8 was further confirmed in a hypoxia model using cobalt chloride (CoCl₂ ). Interestingly, the results showed that the expression levels of osteoblast markers (RUNX2, ALP, OCN, and COL1A1) were increased in CoCl₂ -treated PDLSCs at 6 and 12 h, but decreased at 24, 48, and 72 h. On the basis of bioinformatics and functional experiments, CoCl₂ also induced endoplasmic reticulum stress, autophagy, and apoptosis of PDLSCs; the inhibition of autophagy promoted the osteogenic differentiation of CoCl₂ -treated PDLSCs. Furthermore, circCDK8 overexpression induced autophagy and apoptosis through mTOR signaling, and circCDK8 silencing reversed the inhibitory effects of CoCl₂ on osteogenic differentiation of PDLSCs. In conclusion, our results indicate that circCDK8 represses the osteogenic differentiation of PDLSCs by triggering autophagy activation in a hypoxic microenvironment. CircCDK8 could be a new therapeutic target of periodontitis.

The emerging roles of circular RNAs in regulating the fate of stem cells

Circular RNAs(circRNAs) are a large family of RNAs shaping covalently closed ring-like molecules and have become a hotspot with thousands of newly published studies. Stem cells are undifferentiated cells and have great potential in medical treatment due to their self-renewal ability and differentiation capacity. Abundant researches have unveiled that circRNAs have unique expression profile during the differentiation of stem cells and could serve as promising biomarkers of these cells. There are key circRNAs relevant to the differentiation, proliferation, and apoptosis of stem cells with certain mechanisms such as sponging miRNAs, interacting with proteins, and interfering mRNA translation. Moreover, several circRNAs have joined in the interplay between stem cells and lymphocytes. Our review will shed lights on the emerging roles of circRNAs in regulating the fate of diverse stem cells.

Circular RNAs in cell differentiation and development

In recent years, circular RNAs (circRNAs) - a novel class of RNA molecules characterized by their covalently closed circular structure - have emerged as a complex family of eukaryotic transcripts with important biological features. Besides their peculiar structure, which makes them particularly stable molecules, they have attracted much interest because their expression is strongly tissue and cell specific. Moreover, many circRNAs are conserved across eukaryotes, localized in particular subcellular compartments, and can play disparate molecular functions. The discovery of circRNAs has therefore added not only another layer of gene expression regulation but also an additional degree of complexity to our understanding of the structure, function and evolution of eukaryotic genomes. In this Review, we summarize current knowledge of circRNAs and discuss the possible functions of circRNAs in cell differentiation and development.

Mmu_circ_003795 regulates osteoblast differentiation and mineralization in MC3T3‑E1 and MDPC23 by targeting COL15A1

Circular RNAs (circRNAs) are a class of non-coding RNAs that exhibit important regulatory roles in various biological processes. However, the role of circRNAs and their potential role in osteoblast differentiation and mineralization is unclear. The aim of the present study was to investigate the expression of mmu_circ_003795 and its effect on collagen type XV α 1 chain (COL15A1). First, it was identified that the expression levels of mmu_circ_003795 and osteopontin (OPN) were upregulated in the induced cells. Silencing of mmu_circ_003795 reduced the gene and protein levels of COL15A1 and OPN, whereas the expression level of mmu-microRNA (miR)-1249-5p was upregulated. In addition, after 7 or 14 days of induction, alkaline phosphatase and Alizarin Red-S staining were decreased in the mmu_circRNA_003795 inhibitory group compared with the negative control group. In conclusion, mmu_circ_003795 may regulate osteoblast differentiation and mineralization in MC3T3-E1 and MDPC23 cells via mmu-miR-1249-5p by targeting COL15A1.

circRNA Profiling Reveals an Abundant circFUT10 that Promotes Adipocyte Proliferation and Inhibits Adipocyte Differentiation via Sponging let-7

Adipose development is regulated by a series of complex processes, and non-coding RNAs (ncRNAs), including circular RNAs (circRNAs), play important roles in regulating proliferation and differentiation of adipocytes. In this study, we profiled circRNA expression in cattle fat tissue during calf and adult developmental stages and detected 14,274 circRNA candidates. Some circRNAs are differentially expressed between two developmental stages. We characterized circFUT10, named for its host gene FUT10, a highly expressed and abundant circRNA. Luciferase screening, an RNA-binding protein immunoprecipitation (RIP) assay, quantitative real-time PCR, and western blotting assays indicated that circFUT10 directly binds let-7c/let-e, and PPARGC1B (peroxisome proliferator-activated receptor γ coactivator 1-β) is identified as a target of let-7c. Flow cytometry, EdU (5-ethynyl-2′-deoxyuridine) incorporation, a CCK-8 (cell counting kit-8) assay, oil red O staining, and western blotting assays demonstrated that circFUT10 promotes adipocyte proliferation and inhibits cell differentiation by sponging let-7c. The results demonstrate that circFUT10 binding of let-7c promotes cell proliferation and inhibits cell differentiation by targeting PPARGC1B in cattle adipocytes.

Differential circular RNA expression profiling during osteogenic differentiation in human adipose-derived stem cells

Aim: Circular RNAs (circRNAs) are essential for stem cell differentiation. This study aimed to investigate their exact mechanism of action in human adipose-derived stem cell (hADSC) osteogenesis. Materials & methods: Isolated hADSCs were cultured in growth medium or osteogenic medium, then total RNA was extracted for circRNA microarray, hierarchical cluster, gene ontology, regulating pathway and circRNA–miRNA–mRNA network analyses. Results: A total of 171 circRNAs were upregulated and 119 were downregulated in induced groups compared with those in noninduced groups. Eight circRNAs, 40 miRNAs and 342 mRNAs were selected to construct a competing circRNA-miRNA-mRNA network. Conclusion: These findings may provide novel insight into altered and specific circRNAs that might function as competing endogenous RNAs in hADSCs during osteogenic differentiation.

Dicalcium silicate microparticles modulate the differential expression of circRNAs and mRNAs in BMSCs and promote osteogenesis via circ_1983–miR-6931–Gas7 interaction

Among C₂S-induced differentially expressed circRNAs, circ_1983 is involved in osteogenesis via circ_1983–miR-6931–Gas7 ceRNA interaction-mediated Runx2 upregulation.

CircRNA hsa_circ_0074834 promotes the osteogenesis-angiogenesis coupling process in bone mesenchymal stem cells (BMSCs) by acting as a ceRNA for miR-942-5p

Bone tissue has a strong ability to repair itself. When treated properly, most fractures will heal well. However, some fractures are difficult to heal. When a fracture does not heal, it is called nonunion. Approximately, 5% of all fracture patients have difficulty healing. Because of the continuous movement of the fracture site, bone nonunion is usually accompanied by pain, which greatly reduces the quality of life of patients. Bone marrow mesenchymal stem cells (BMSCs) play an important role in the process of nonunion. Circular RNAs (circRNAs) are a unique kind of noncoding RNA and represent the latest research hotspot in the RNA field. At present, no studies have reported a role of circRNAs in the development of nonunion. After isolation of BMSCs from patients with nonunion, the expression of circRNAs in these cells was detected by using a circRNA microarray. Alkaline phosphatase and Alizarin red staining were used to detect the regulation of osteogenic differentiation of BMSCs by hsa_circ_0074834. The target gene of hsa_circ_0074834 was detected by RNA pull-down and double-luciferase reporter assay. The ability of hsa_circ_0074834 to regulate the osteogenesis of BMSCs in vivo was tested by heterotopic osteogenesis and single cortical bone defect experiments. The results showed that the expression of hsa_circ_0074834 in BMSCs from patients with nonunion was decreased. Hsa_circ_0074834 acts as a ceRNA to regulate the expression of ZEB1 and VEGF through microRNA-942-5p. Hsa_circ_0074834 can promote osteogenic differentiation of BMSCs and the repair of bone defects. These results suggest that circRNAs may be a key target for the treatment of nonunion.

Characterization of Circular RNAs in Chinese Buffalo (Bubalus bubalis) Adipose Tissue: A Focus on Circular RNAs Involved in Fat Deposition

Circular RNAs (circRNAs) have been identified as a novel type of regulators involved in multiple biological processes. However, circRNAs with a potential function in fat deposition in buffalo are poorly understood. In this study, six RNA libraries of adipose tissue were constructed for three young and three adult Chinese buffaloes with paired-ends RNA sequencing using the Illumina HiSeq 3000 platform. A total of 5141 circRNAs were computationally identified. Among them, 252 circRNAs were differentially expressed (DE) between the young and adult buffaloes. Of these, 54 were upregulated and 198 were downregulated in the adult group. Eight DE circRNAs were further identified by quantitative real-time-PCR (qRT-PCR) and Sanger sequencing. Co-expression analysis revealed that 34 circRNAs demonstrated a strong correlation with fat deposition-associated genes (|r| > 0.980). Among these, expressional correlation between two circRNAs (19:45387150|45389986 and 21:6969877|69753491) and PR/SET domain 16 was further verified using qRT-PCR, and a strong correlation was revealed (1 > |r| > 0.8). These results strongly suggest that circRNAs 19:45387150|45389986 and 21:6969877|69753491 are potential regulators of buffalo fat deposition. In summary, this study characterized the circRNA profiles of adipose tissues at different stages for the first time and revealed two circRNAs strongly correlated with fat deposition-associated genes, which provided new candidate regulators for fat deposition in buffalo.

Influence of in vitro differentiation status on the in vivo bone regeneration of cell/chitosan microspheres using a rat cranial defect model

The aim of this study was to investigate the influence of the in vitro osteogenic differentiation status on the in vivo bone regeneration of cell/chitosan microspheres qualitatively and quantitatively. To this end, rat bone-marrow-derived mesenchymal stromal cells (BMSCs) were seeded onto apatite-coated chitosan microspheres. The constructs were osteogenically differentiated for 0, 7, 14, and 21 days followed by calvarial defect implantation in vivo for up to 8 weeks. In vitro studies showed that BMSCs in the constructs proliferated from day 0 to day 7. The activity and gene expression of alkaline phosphatise increased from day 0 to day 14 and then decreased. The gene expression of collagen type I and osteocalcin peaked at day 21. In vivo, constructs retrieved from day 0 group were filled with fibrous tissues and capillaries, but no bone formation was observed. Constructs retrieved from day 7 and day 21 groups showed progressive bone formation, whereas those retrieved from day 14 group had the highest percentage of bone formation. These data suggested that to generate a substantial amount of bone in vivo, not only the in vitro osteogenic differentiation was necessary, but also the period of pre-differentiation was important for the cell-scaffold constructs. The period of pre-differentiation for 14 days was found to be the most suitable for chitosan microspheres.