A Narrative Review of Circular RNAs in Brain Development and Diseases of Preterm Infants

Circ-AGTPBP1 promotes white matter injury through miR-140-3p/Pcdh17 axis role of Circ-AGTPBP1 in white matter injury

White matter injury (WMI) resulting from intracerebral hemorrhage (ICH) is closely associated with adverse prognoses in ICH patients. Although Circ-AGTPBP1 has been reported to exhibit high expression in the serum of premature infants with WMI, its effects and mechanisms in ICH-induced WMI remain unclear. This study aimed to investigate the role of circ-AGTPBP1 in white matter injury after intracerebral hemorrhage. An intracerebral hemorrhage rat model was established by injecting autologous blood into rat left ventricles and circ-AGTPBP1 was knocked down at the ICH site using recombinant adeno-associated virus, AAV2/9. Magnetic resonance imaging (MRI) and gait analysis were conducted to assess long-term neurobehavioral effects. Primary oligodendrocyte progenitor cells (OPCs) were isolated from rats and overexpressed with circ-AGTPBP1. Downstream targets of circ-AGTPBP1 in OPCs were investigated using CircInteractome, qPCR, FISH analysis, and miRDB network. Luciferase gene assay was utilized to explore the relationship between miR-140-3p and Pcdh17 in OPCs and HEK-293T cells. Finally, CCK-8 assay, EdU staining, and flow cytometry were employed to evaluate the effects of mi-RNA-140-3p inhibitor or silencing of sh-pcd17 on the viability, proliferation, and apoptosis of OPCs. Low expression of circ-AGTPBP1 alleviates white matter injury and improves neurological functions in rats after intracerebral hemorrhage. Conversely, overexpression of circ-AGTPBP1 reduces the proliferative and migrative potential of oligodendrocyte progenitor cells and promotes apoptosis. CircInteractome web tool and qPCR confirmed that circ-AGTPBP1 binds with miR-140-3p in OPCs. Additionally, miRDB network predicted Pcdh17 as a downstream target of miR-140-3p. Moreover, pcdh17 expression was increased in the brain tissue of rats with intracerebral-induced white matter injury. Furthermore, inhibiting miR-140-3p suppressed the proliferation and migration of OPCs and facilitated apoptosis through Pcdh17. Circ-AGTPBP1 promotes white matter injury through modulating the miR-140-3p/Pcdh17 axis. The study provides a new direction for developing therapeutic strategies for white matter injury.

Recent insights into the roles of circular RNAs in human brain development and neurologic diseases

Circular RNAs (circRNAs) are a novel class of non-coding RNAs. They are single-stranded RNA transcripts characterized with a closed loop structure making them resistant to degrading enzymes. Recently, circRNAs have been suggested with regulatory roles in gene expression involved in controlling various biological processes. Notably, they have demonstrated abundance, dynamic expression, back-splicing events, and spatiotemporally regulation in the human brain. Accordingly, they are expected to be involved in brain functions and related diseases. Studies in animals and human brain have revealed differential expression of circRNAs in brain compartments. Interestingly, contributing roles of circRNAs in the regulation of central nervous system (CNS) development have been demonstrated in a number of studies. It has been proposed that circRNAs play role in substantial neurological functions like neurotransmitter-associated tasks, neural cells maturation, and functions of synapses. Furthermore, 3 main pathways have been identified in association with circRNAs's host genes including axon guidance, Wnt signaling, and transforming growth factor beta (TGF-β) signaling pathways, which are known to be involved in substantial functions like migration and differentiation of neurons and specification of axons, and thus play role in brain development. In this review, we have an overview to the biogenesis, biological functions of circRNAs, and particularly their roles in human brain development and the pathogenesis of neurodegenerative diseases including Alzheimer's diseases, multiple sclerosis, Parkinson's disease and brain tumors.

Expression characteristics of circular RNA in human traumatic brain injury

Traumatic brain injury (TBI) causes high rates of worldwide mortality and morbidity due to the complex secondary injury cascade. Recently, circular ribonucleic acids (circRNAs) have attracted significant attention in a variety of diseases. However, their expression characteristics in human TBI are still unclear. In this study, we examined brain injury tissues from six severe TBI patients in Jinling Hospital. The TBI tissues and adjacent brain contusion tissues were used to analyze differential expression signatures of circRNAs through full-length transcriptome sequencing, Gene Ontology (GO) analysis, Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis, and ceRNA network construction. Our results found that there were 126 differently expressed circRNAs in TBI. Among them, 64 circRNAs were up-regulated and 62 circRNAs were down-regulated. Moreover, GO and KEGG analyses revealed that the aberrantly expressed circRNAs participated in many pathophysiological processes of TBI, especially regarding microglial cell activation, protein transport, protein processing and inflammation. Furthermore, the ceRNA (circRNA-miRNA-mRNA) network predicted that there existed strong relationship among circRNA, miRNA and mRNA. Taken together, our results indicated for the first time that the expression profiles of circRNAs were different after human TBI. In addition, we found the signaling pathways that were related to circRNAs and predicted a ceRNA network, which provided new insight of circRNAs in human TBI.

Circular RNAs in Alzheimer's Disease: A New Perspective of Diagnostic and Therapeutic Targets

BACKGROUND

Circular RNAs (circRNAs), as covalently closed single-stranded noncoding RNA molecules, have been recently identified to involve in several biological processes, principally through targeting microRNAs. Among various neurodegenerative diseases (NDs), accumulating evidence has proposed key roles for circRNAs in the pathogenesis of Alzheimer's disease (AD); although the exact relationship between these RNA molecules and AD progression is not clear, they have been believed to mostly act as miRNA sponges or gene transcription modulators through correlating with multiple proteins, involved in the accumulation of Amyloid β (Aβ) peptides, as well as tau protein, as AD's pathological hallmark. More interestingly, circRNAs have also been reported to play diagnostic and therapeutic roles during AD progression.

OBJECTIVE

Literature review indicated that circRNAs could essentially contribute to the onset and development of AD. Thus, in the current review, the circRNAs' biogenesis and functions are addressed at first, and then the interplay between particular circRNAs and AD is comprehensively discussed. Eventually, the diagnostic and therapeutic significance of these noncoding RNAs is highlighted in brief.

RESULTS

A large number of circRNAs are expressed in the brain. Thereby, these RNA molecules are noticed as potential regulators of neural functions in healthy circumstances, as well as neurological disorders. Moreover, circRNAs have also been reported to have potential diagnostic and therapeutic capacities in relation to AD, the most prevalent ND.

CONCLUSION

CircRNAs have been shown to act as sponges for miRNAs, thereby regulating the function of related miRNAs, including oxidative stress, reduction of neuroinflammation, and the formation and metabolism of Aβ, all of which developed in AD. CircRNAs have also been proposed as biomarkers that have potential diagnostic capacities in AD. Despite these characteristics, the use of circRNAs as therapeutic targets and promising diagnostic biomarkers will require further investigation and characterization of the function of these RNA molecules in AD.

Emerging Role and Mechanism of circRNAs in Pediatric Malignant Solid Tumors

Circular RNAs (circRNAs) are non-coding RNAs with covalent closed-loop structures and are widely distributed in eukaryotes, conserved and stable as well as tissue-specific. Malignant solid tumors pose a serious health risk to children and are one of the leading causes of pediatric mortality. Studies have shown that circRNAs play an important regulatory role in the development of childhood malignant solid tumors, hence are potential biomarkers and therapeutic targets for tumors. This paper reviews the biological characteristics and functions of circRNAs as well as the research progress related to childhood malignant solid tumors.