Emerging roles of circular RNAs in stem cells

Circular RNAs in glioblastoma

Glioblastoma multiforme (GBM) is the most malignant and common form of brain cancer in adults. The molecular mechanisms underlying GBM progression and resistance are complex and poorly understood. Circular RNAs (circRNAs) are a new class of non-coding RNAsformed by covalently closed loopstructures with no free ends. Their circular structure makes them more stable than linear RNA and resistant to exonuclease degradation. In recent years, they have received significant attention due to their diverse functions in gene regulation and their association with various diseases, including cancer. Therefore, understanding the functions and applications of circRNAs is critical to developing targeted therapeutic interventions and advancing the field of glioblastoma cancer research. In this review, we summarized the main functions of circRNAs and their potential applications in the diagnosis, prognosis and targeted therapy of GBM.

Selection and Regulatory Network Analysis of Differential CircRNAs in the Hypothalamus of Goats with High and Low Reproductive Capacity

The objectives of this investigation were to identify differentially expressed circular RNAs (circRNAs) in the hypothalamus of goats with high and low prolificacy and construct a circRNA-mRNA regulatory network to uncover key potential circRNAs that influence goat prolificacy. Transcriptome analysis was performed on hypothalamus samples from low-prolificacy (n = 5) and high-prolificacy (n = 6) Chuanzhong black goats to identify circRNAs that influence prolificacy in these goats. Differential expression analysis identified a total of 205 differentially expressed circRNAs, comprising 100 upregulated and 105 downregulated circRNAs in the high-prolificacy group compared with the low-prolificacy group. Enrichment analysis of these differentially expressed circRNAs indicated significant enrichment in Gene Ontology terms associated with mammalian oogenesis, negative regulation of neurotransmitter secretion, reproductive developmental processes, hormone-mediated signaling pathways, and negative regulation of hormone secretion. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis highlighted significant enrichment in the oxytocin signaling pathway, GnRH signaling pathway, and hormone-mediated oocyte maturation. The hypothalamus of low- and high-prolificacy goats contains circular RNAs (circRNAs), including chicirc_063269, chicirc_097731, chicirc_017440, chicirc_049641, chicirc_008429, chicirc_145057, chicirc_030156, chicirc_109497, chicirc_030156, chicirc_176754, and chicirc_193363. Chuanzhong black goats have the potential to influence prolificacy by modulating the release of serum hormones from the hypothalamus. A circRNA-miRNA regulatory network was constructed, which determined that miR-135a, miR-188-3p, miR-101-3p, and miR-128-3p may interact with differentially expressed circRNAs, thereby regulating reproductive capacity through the hypothalamic-pituitary-gonadal axis. The results of this study enhance our knowledge of the molecular mechanisms that regulate prolificacy in Chuanzhong black goats at the hypothalamic level.

Circ-ZNF236 mediates stem cells from apical papilla differentiation by regulating LGR4-induced autophagy

AIM

Human stem cells from the apical papilla (SCAPs) are an appealing stem cell source for tissue regeneration engineering. Circular RNAs (circRNAs) are known to exert pivotal regulatory functions in various cell differentiation processes, including osteogenesis of mesenchymal stem cells. However, few studies have shown the potential mechanism of circRNAs in the odonto/osteogenic differentiation of SCAPs. Herein, we identified a novel circRNA, circ-ZNF236 (hsa_circ_0000857) and found that it was remarkably upregulated during the SCAPs committed differentiation. Thus, in this study, we showed the significance of circ-ZNF236 in the odonto/osteogenic differentiation of SCAPs and its underlying regulatory mechanisms.

METHODOLOGY

The circular structure of circ-ZNF236 was identified via Sanger sequencing, amplification of convergent and divergent primers. The proliferation of SCAPs was detected by CCK-8, flow cytometry analysis and EdU incorporation assay. Western blotting, qRT-PCR, Alkaline phosphatase (ALP) and Alizarin red staining (ARS) were performed to explore the regulatory effect of circ-ZNF236/miR-218-5p/LGR4 axis in the odonto/osteogenic differentiation of SCAPs in vitro. Fluorescence in situ hybridization, as well as dual-luciferase reporting assays, revealed that circ-ZNF236 binds to miR-218-5p. Transmission electron microscopy (TEM) and mRFP-GFP-LC3 lentivirus were performed to detect the activation of autophagy.

RESULTS

Circ-ZNF236 was identified as a highly stable circRNA with a covalent closed loop structure. Circ-ZNF236 had no detectable influence on cell proliferation but positively regulated SCAPs odonto/osteogenic differentiation. Furthermore, circ-ZNF236 was confirmed as a sponge of miR-218-5p in SCAPs, while miR-218-5p targets LGR4 mRNA at its 3'-UTR. Subsequent rescue experiments revealed that circ-ZNF236 regulates odonto/osteogenic differentiation by miR-218-5p/LGR4 in SCAPs. Importantly, circ-ZNF236 activated autophagy, and the activation of autophagy strengthened the committed differentiation capability of SCAPs. Subsequently, in vivo experiments showed that SCAPs overexpressing circ-ZNF236 promoted bone formation in a rat skull defect model.

CONCLUSIONS

Circ-ZNF236 could activate autophagy through increasing LGR4 expression, thus positively regulating SCAPs odonto/osteogenic differentiation. Our findings suggested that circ-ZNF236 might represent a novel therapeutic target to prompt the odonto/osteogenic differentiation of SCAPs.

Circular RNA-Mediated Regulation of Oral Tissue-Derived Stem Cell Differentiation: Implications for Oral Medicine and Orthodontic Applications

Circular RNAs (circRNAs) are a novel class of endogenous non-coding RNAs (ncRNAs) which unlike linear RNAs, have a covalently closed continuous loop structure. circRNAs are found abundantly in human cells and their biology is complex. They feature unique expression to different types of cells, tissues, and developmental stages. To the present, the functional roles of circular RNAs are not fully understood. They reportedly act as microRNA (miRNA) sponges, therefore having key regulatory functions in diverse physiological and pathological processes. As for dentistry field, lines of evidence indicate that circRNAs play vital roles in the odontogenic and osteogenic differentiation of dental pulp stem cells (DPSCs) and periodontal ligament stem cells (PDLSCs). Abnormal expression of circRNAs have been found in other areas of pathology frequently reflected also in the oral environment, such as inflammation or bone and soft tissue loss. Therefore, circRNAs could be of significant importance in various fields in dentistry, especially in bone and soft tissue engineering and regeneration. Understanding the molecular mechanisms occurring during the regulation of oral biological and tissue remodeling processes could augment the discovery of novel diagnostic biomarkers and therapeutic strategies that will improve orthodontic and other oral therapeutic protocols.

WNT/β-catenin signaling in hepatocellular carcinoma: The aberrant activation, pathogenic roles, and therapeutic opportunities

Hepatocellular carcinoma (HCC) is a liver cancer, highly heterogeneous both at the histopathological and molecular levels. It arises from hepatocytes as the result of the accumulation of numerous genomic alterations in various signaling pathways, including canonical WNT/β-catenin, AKT/mTOR, MAPK pathways as well as signaling associated with telomere maintenance, p53/cell cycle regulation, epigenetic modifiers, and oxidative stress. The role of WNT/β-catenin signaling in liver homeostasis and regeneration is well established, whereas in development and progression of HCC is extensively studied. Herein, we review recent advances in our understanding of how WNT/β-catenin signaling facilitates the HCC development, acquisition of stemness features, metastasis, and resistance to treatment. We outline genetic and epigenetic alterations that lead to activated WNT/β-catenin signaling in HCC. We discuss the pivotal roles of CTNNB1 mutations, aberrantly expressed non-coding RNAs and complexity of crosstalk between WNT/β-catenin signaling and other signaling pathways as challenging or advantageous aspects of therapy development and molecular stratification of HCC patients for treatment.