Identification of Circular RNA Expression Profiles and their Implication in Spinal Cord Injury Rats at the Immediate Phase

Circ-KATNAL1 Knockdown Reduces Neuronal Apoptosis and Alleviates Spinal Cord Injury Through the miR-98-5p/PRDM5 Regulatory Axis

Spinal cord injury (SCI) is a common disease of the central nervous system. circRNAs play a crucial role in neurological disease. The purpose of this study was to investigate the role of circ-KATNAL1 in SCI and its regulatory mechanism. T9-L10 spinal segment of Sprague Dawley rats was compressed or contused after T10 laminectomy to establish the SCI rat model. Then, rats were divided into SCI group, si-NC group, si-circ-KATNAL1 group, si-circ-KATNAL1 + antagomir NC group, si-circ-KATNAL1 + miR-98-5p antagomir group, si-circ-KATNAL1 + oe-NC group, and si-circ-KATNAL1 + oe-PRDM5 group, with 6 rats in each group. There was another sham operation group that received no treatment. Basso, Beattie, and Bresnahan (BBB) scores were used to evaluate the neural function of rats. In addition to that, the pathological changes of spinal cord tissue, neuronal apoptosis, and inflammatory responses were correspondingly observed and analyzed. Quantitative measurements of circ-KATNAL1, miR-98-5p, and PRDM5 levels were conducted, as well as analyses of their interrelationship. Circ-KATNAL1 was up-regulated in the spinal cord tissue of SCI rats, and circ-KATNAL1 knockdown could improve neural function, alleviate pathological changes of spinal cord tissue, and inhibit neuronal apoptosis and inflammatory responses in SCI rats. For miR-98-5p, circ-KATNAL1 was an upstream factor, while PRDM5 was a downstream actor. miR-98-5p deficiency or PRDM5 restoration impaired the remission effect of circ-KATNAL1 knockdown on SCI. Circ-KATNAL1 knockdown reduces neuronal apoptosis and alleviates SCI through miR-98-5p/PRDM5 regulatory axis.

Inhibition by rno-circRNA-013017 of the apoptosis of motor neurons in anterior horn and descending axonal degeneration in rats after traumatic spinal cord injury

Introduction

Spinal cord injury (SCI) often causes continuous neurological damage to clinical patients. Circular RNAs (circRNAs) are related to a lot of diseases, including SCI. We previously found five candidate circRNAs which were likely to regulate the secondary pathophysiological changes in rat model after traumatic SCI.

Methods

In this study, we first selected and overexpressed target circRNA in rats. We then explored its functional roles using various functional assays in a rat model after SCI.

Results

We found that rno-circRNA-013017-the selected target circRNA-reduced neuron apoptosis, preserved the survival and activity of motor neurons, and regulated apoptosis-related proteins at 3 days post-SCI using western blot, immunofluorescence and polymerase chain reaction. Additionally, we found that rno-circRNA-013017 inhibited descending axonal degeneration and preserved motor neurons and descending axons at 6 weeks post-SCI using immunofluorescence, biotin dextran amine diffusion tensor imaging. Finally, the overexpression of rno-circRNA-013017 promoted the locomotor function of rats after SCI using open-field test and gait analysis.

Conclusion

Focusing on the functions of rno-circRNA-013017, this study provides new options for future studies exploring therapeutic targets and molecular mechanisms for SCI.

Circular RNAs in organ injury: recent development

Circular ribonucleic acids (circRNAs) are a class of long non-coding RNA that were once regarded as non-functional transcription byproducts. However, recent studies suggested that circRNAs may exhibit important regulatory roles in many critical biological pathways and disease pathologies. These studies have identified significantly differential expression profiles of circRNAs upon changes in physiological and pathological conditions of eukaryotic cells. Importantly, a substantial number of studies have suggested that circRNAs may play critical roles in organ injuries. This review aims to provide a summary of recent studies on circRNAs in organ injuries with respect to (1) changes in circRNAs expression patterns, (2) main mechanism axi(e)s, (3) therapeutic implications and (4) future study prospective. With the increasing attention to this research area and the advancement in high-throughput nucleic acid sequencing techniques, our knowledge of circRNAs may bring fruitful outcomes from basic and clinical research.

Potential value of differentially expressed circular RNAs derived from circulating exosomes in the pathogenesis of rat spinal cord injury

Spinal cord injury (SCI) remains one kind of devastating neurological damage, and specific molecular mechanisms involved need to be understood deeply. Currently, circular RNAs (circRNAs), as a newly discovered type of non-coding RNAs (ncRNAs), have been under active investigation. Through functional interactions with disease-associated microRNAs (miRNAs), exosome-derived circRNAs have been extensively implicated in various organ pathogenesis. Nevertheless, the functional involvement of circulating circRNAs in SCI onset, progression as well as repair remains poorly explored until now. Of note, there still lacks clinical and experimental evidence in this regard. To obtain some relevant knowledge in this field, this study was originally designed to have a general overview of differentially expressed circRNAs derived from circulating exosomes in SCI rats in comparison with the control rats. It turned out that 709 types of downregulated circRNAs and 346 kinds of upregulated circRNAs were preliminarily screened out. Functional enrichment analyses including kyoto encyclopedia of genes and genomes (KEGG) pathway and gene ontology (GO) were performed to evaluate the possible biological functions of upregulated as well as downregulated circRNAs involved in SCI. Furthermore, five types of upregulated circulating circRNAs including chr4:208359914–208362182+, chr15:20088296–20092102+, chr1:175098934– 175134845–, chr1:175099657– 175128203–, and chr1:175104454– 175134845–, and plus five kinds of downregulated circulating circRNAs including chr11:74154652– 74159524–, chr12:45412398– 45412635–, chr7:137630261– 137648924–, chr6:6280974–6281188+, and chr4:225251864–225254087+, were verified through reverse transcription-polymerase chain reaction (RT-PCR). At last, taking these differentially expressed circRNAs in the center, the circRNA-miRNA-mRNA gene interaction network was constructed to predict the possible functionalities of circRNAs in SCI through anticipating specific interactive miRNAs, giving new insights into how circRNAs contribute to this pathological process. Taken together, these findings suggest the possible involvement and functional significance of circRNAs in SCI.

Circular RNA Hecw1 Regulates the Inflammatory Imbalance in Spinal Cord Injury via miR-3551-3p/LRRTM1 Axis

Spinal cord injury (SCI) is a neurological disease having devastating effect and results in the development of systemic inflammation. However, the molecular mechanisms of SCI remain not entirely elucidated. This study was directed toward exploring the circ Hecw1 involved in the mechanism of lipopolysaccharide (LPS)-triggered inflammation damage in neuronal cells. The in vitro model of SCI based on PC12 cells were established with lipopolysaccharide. The cell proliferation was determined by the use of cell counting kit-8 (CCK8). The expressions of circHecw1, miR-3551-3p, and inflammatory factors were measured by quantitative real-time PCR and ELISA assay. Flow cytometry was used to assess apoptosis. Western blot analysis was performed for the purpose of determining LRRTM1 and NF-kB signaling. The expression of circ Hecw1, TNF-α, IL-6, and IL-1β in LPS-triggered PC12 cells and the expression of miR-3551-3p and IL-10 were significantly decreased. Knockdown of circHecw1 promoted proliferation and inhibited apoptosis and reduction in the inflammatory cytokine expression. Our study revealed that circHecw1 regulates SCI neuronal cell inflammation imbalance by regulating the miR-3551-3p/LRRTM1 signaling.

Exosomes Secreted from circZFHX3-modified Mesenchymal Stem Cells Repaired Spinal Cord Injury Through mir-16-5p/IGF-1 in Mice

BACKGROUND

Spinal cord injury (SCI) is a devastating neurological event that leads to severe motor and sensory dysfunction. Exosome-mediated transfer of circular RNAs (circRNAs) was associated with SCI, and exosomes have been reported to be produced by mesenchymal stem cells (MSCs). This study is designed to explore the mechanism of exosomal circZFHX3 on LPS-induced MSCs injury in SCI.

METHODS

Exosomes were detected by transmission electron microscope and nanoparticle tracking analysis. CD9, CD63, CD81, and TSC101, B-cell lymphoma-2 (Bcl-2), Bcl-2 related X protein (Bax), Cleaved caspase 3, and Insulin-like growth factor 1 (IGF-1) protein levels were measured by western blot assay. CircZFHX3, microRNA-16-5p (miR-16-5p), and IGF-1 level were detected by real-time quantitative polymerase chain reaction (RT-qPCR). Cell viability and apoptosis were detected by Cell Counting Kit-8 (CCK-8) and flow cytometry assay. Levels of IL-1β, IL-6, and TNF-α were assessed using Enzyme-linked immunosorbent assays (ELISA). ROS, LDH, and SOD levels were measured by the special kits. The binding between miR-16-5p and circZFHX3 or IGF-1 was predicted by Starbase and DianaTools and then verified by a dual-luciferase reporter and RNA Immunoprecipitation (RIP) assays. The biological role of exosomal circZFHX3 on SCI mice was examined in vivo.

RESULTS

CircZFHX3 and IGF-1 were decreased, and miR-16-5p was increased in SCI mice. Also, exosomal circZFHX3 boosted cell viability and repress apoptosis, inflammation, and oxidative stress in LPS-treated BV-2 cells in vitro. Mechanically, circZFHX3 acted as a sponge of miR-16-5p to regulate IGF-1 expression. Exosomal circZFHX3 reduced cell injury of SCI in vivo.

CONCLUSIONS

Exosomal circZFHX3 inhibited LPS-induced BV-2 cell injury partly by regulating the miR-16-5p/ IGF-1 axis, hinting at a promising therapeutic strategy for the SCI treatment.

An update on the roles of circular RNAs in spinal cord injury

Spinal cord injury (SCI) is a disabling condition for which therapeutic options are limited. Increasing number of microarray and next-generation sequencing studies have demonstrated that SCI coincides with altered expression of circular RNAs (circRNAs) in the damaged tissue. Emerging functional evidence further pinpointed specific differentially expressed circRNAs (e.g., circ-HIPK3, cicRNA.7079, circRNA_01477, circRNA-2960, and circ_0001723) for their effects on cellular processes relevant to SCI repair and regeneration, including neuronal apoptosis, astrocyte activation, and neuroinflammation, via sponging SCI-related microRNAs. Although circRNAs and their target microRNAs appear to be good candidates for therapeutic exploitation in SCI, further investigation into the efficient delivery of these regulatory molecules in a cell-type specific manner is a pre-requisite for translating these basic discoveries into clinical benefits.

Mechanism underlying circularRNA_014301-mediated regulation of neuronal cell inflammation and apoptosis

Spinal cord injury (SCI) causes damage to the spinal cord owing to trauma or disease and myelinated fiber tracts that transmit sensation and motor signals to and from the brain. Circular RNAs (circRNAs) are a recently discovered class of regulatory molecules, and their roles in SCI are still unknown. circRNA_014301 was indicated to be differentially expressed in the spinal cord at the site of SCI in a rat model. To analyze the role of circRNA_014301 in SCI, we exposed rat adrenal pheochromocytoma PC12 cells were exposed to increasing concentrations of lipopolysaccharide (LPS) and to construct a PC12 cell inflammatory model. Cell Counting Kit-8 assay was used to analyze cell viability. Reverse transcription-quantitative PCR and ELISA were used to detect the expression of inflammatory factors (IL-1β, IL-6 and TNF-α). Annexin V-FITC/PI double staining was employed to detect cell apoptosis, and western blotting was performed to detect the expression of apoptotic proteins (Bax/Bcl-2/cleaved caspase-3) and NF-κB. The results demonstrated that LPS induced inflammation in PC12 cells as evidenced by the reduced cell proliferation and enhanced expression of inflammatory and apoptotic factors under increasing LPS concentrations. Western blotting analyses indicated that circRNA_014301 induced the expression of p-NF-κB/NF-κB, Bax and cleaved caspase-3, and decreased the expression of Bcl-2 following LPS-induced inflammation, and this apoptosis-promoting effect was relieved by small interfering-RNA-mediated knockdown of circRNA_014301. Thus, circRNA_014301 silencing alleviated apoptosis and inflammation in PC12 cells. SCI is invariably associated with spinal cord inflammation, and LPS was used to stimulate apoptosis and inflammatory injury in PC12 cells, and create a cell model of SCI. By promoting PC12 cell apoptosis under inflammatory conditions, it was indicated that circRNA_014301 may suppress SCI. Therefore, circRNA_014301 may represent a potential target for SCI diagnosis and therapy.

Circular RNAs: The Novel Actors in Pathophysiology of Spinal Cord Injury

Spinal Cord Injury (SCI) can elicit a progressive loss of nerve cells promoting disability, morbidity, and even mortality. Despite different triggering mechanisms, a cascade of molecular events involving complex gene alterations and activation of the neuroimmune system influence either cell damage or repair. Effective therapies to avoid secondary mechanisms underlying SCI are still lacking. The recent progression in circular RNAs (circRNAs) research has drawn increasing attention and opened a new insight on SCI pathology. circRNAs differ from traditional linear RNAs and have emerged as the active elements to regulate gene expression as well as to facilitate the immune response involved in pathophysiology-related conditions. In this review, we focus on the impact and possible close relationship of circRNAs with pathophysiological mechanisms following SCI, where circRNAs could be the key transcriptional regulatory molecules to define neuronal death or survival. Advances in circRNAs research provide new insight on potential biomarkers and effective therapeutic targets for SCI patients.

The emerging role of circular RNAs in spinal cord injury

Spinal cord injury (SCI) is one kind of severe diseases with high mortality and morbidity worldwide, and lacks effective therapeutic interventions currently, which leads to not only permanent neurological impairments but also heavy social and economic burden. Recent studies have proved that circRNAs are highly expressed in neural tissues, regulating the neuronal and synaptic functions. What's more, significantly altered circRNAs expression profiles are closely associated with the pathophysiology of SCI. In this review, we summarize the current advance on the role of circRNAs in SCI, which may provide a better understanding of pathogenesis and therapeutic strategies of SCI.

THE TRANSLATIONAL POTENTIAL OF THIS ARTICLE

The Translational potential of this article is that A further understanding of circRNAs in the pathogenesis of SCI will promote the circRNA-based clinical applications.

The potential roles of circular RNAs as modulators in traumatic spinal cord injury

Spinal cord injury (SCI) may cause long-term physical impairment and bring a substantial burden to both the individual patient and society. Existing therapeutic approaches for SCI have proven inadequate. This is mainly owing to the incomplete understanding of the cellular and molecular events post-injury. Circular RNAs (circRNAs) represent a new class of non-coding RNAs with a covalently closed annular structure that participates in regulating the transcription of certain genes and are linked to various biological processes and diseases. Mounting evidence is indicative that circRNAs are highly expressed in the spinal cord and they play key roles in multiple processes of neurological diseases. Recently, a role for circRNAs as effectors of SCI has emerged, leading to the continuity of relevant research. In this review, we presented current studies with regards to the abnormality of circRNAs mediating SCI by affecting mechanisms of autophagy, apoptosis, inflammation, and neural regeneration. Furthermore, the potential clinical value of circRNAs as therapeutic targets of SCI was also analyzed.

New Insight of Circular RNAs' Roles in Central Nervous System Post-Traumatic Injury

The central nervous system (CNS) post-traumatic injury can cause severe nerve damage with devastating consequences. However, its pathophysiological mechanisms remain vague. There is still an urgent need for more effective treatments. Circular RNAs (circRNAs) are non-coding RNAs that can form covalently closed RNA circles. Through second-generation sequencing technology, microarray analysis, bioinformatics, and other technologies, recent studies have shown that a number of circRNAs are differentially expressed after traumatic brain injury (TBI) or spinal cord injury (SCI). These circRNAs play important roles in the proliferation, inflammation, and apoptosis in CNS post-traumatic injury. In this review, we summarize the expression and functions of circRNAs in CNS in recent studies, as well as the circRNA–miRNA–mRNA interaction networks. The potential clinical value of circRNAs as a therapeutic target is also discussed.

Roles of Non-coding RNAs in Central Nervous System Axon Regeneration

Axons in the central nervous system often fail to regenerate after injury due to the limited intrinsic regeneration ability of the central nervous system (CNS) and complex extracellular inhibitory factors. Therefore, it is of vital importance to have a better understanding of potential methods to promote the regeneration capability of injured nerves. Evidence has shown that non-coding RNAs play an essential role in nerve regeneration, especially long non-coding RNA (lncRNA), microRNA (miRNA), and circular RNA (circRNA). In this review, we profile their separate roles in axon regeneration after CNS injuries, such as spinal cord injury (SCI) and optic nerve injury. In addition, we also reveal the interactive networks among non-coding RNAs.