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

CircKat6b Mediates the Antidepressant Effect of Esketamine by Regulating Astrocyte Function

The abundant expression of circular RNAs (circRNAs) in the central nervous system and their contribution to the pathogenesis of depression suggest that circRNAs are promising therapeutic targets for depression. This study explored the role and mechanism of circKat6b in esketamine's antidepressant effect. We found that intravenous administration of esketamine (5 mg/kg) treatment decreased the circKat6b expression in the astrocytes of hippocampus induced by a chronic unpredictable mild stress (CUMS) mouse model, while the overexpression of circKat6b in the hippocampus significantly attenuated the antidepressant effects of esketamine in depressed mice. RNA-sequencing, RT-PCR, and western blot experiments showed that the stat1 and p-stat1 expression were significantly upregulated in mouse astrocytes overexpressing circKat6b. In the CUMS mouse model, overexpression of circKat6b in the hippocampus significantly reversed the downregulation of p-stat1 protein expression caused by esketamine. Our findings demonstrated that a novel mechanism of the antidepressant like effect of esketamine may be achieved by reducing the expression of circKat6b in the astrocyte of the hippocampus of depressed mice.

The roles of circular RNAs in nerve injury and repair

Nerve injuries significantly impact the quality of life for patients, with severe cases posing life-threatening risks. A comprehensive understanding of the pathophysiological mechanisms underlying nerve injury is crucial to the development of effective strategies to promote nerve regeneration. Circular RNAs (circRNAs), a recently characterized class of RNAs distinguished by their covalently closed-loop structures, have been shown to play an important role in various biological processes. Numerous studies have highlighted the pivotal role of circRNAs in nerve regeneration, identifying them as potential therapeutic targets. This review aims to succinctly outline the latest advances in the role of circRNAs related to nerve injury repair and the underlying mechanisms, including peripheral nerve injury, traumatic brain injury, spinal cord injury, and neuropathic pain. Finally, we discuss the potential applications of circRNAs in drug development and consider the potential directions for future research in this field to provide insights into circRNAs in nerve injury repair.

Identification of Novel Circular RNA Targets in Key Penumbra Region of Rats After Cerebral Ischemia-Reperfusion Injury

Circular RNAs (circRNAs) are abundantly and stably expressed in the brain of mammals and humans. Some circRNAs are implicated in ischemic stroke. Therefore, we aimed to detect how circRNAs change in the key penumbra area during cerebral ischemia-reperfusion (CI/R) injury. Rats were subjected to transient middle cerebral artery occlusion (tMCAO), during which the permanent blocking period was 2 h and reperfusion time was 24 or 72 h. Then modified neurologic severity score (mNSS), triphenyl tetrazolium chloride (TTC) staining and HE staining were used to exhibiting damage between rats in different groups. The penumbra regions of all rats were dissected and total RNA was further processed for high-throughput sequencing. CircRNA expression profiles were screened and bioinformatics analyses were conducted to investigate these differentially expressed circRNAs. Some of them were verified by reverse transcription-quantitative polymerase chain reaction (RT-qPCR), followed by the establishment of a circRNA-miRNA-mRNA network and the detection of their downstream molecules. A total of 99 and 98 circRNAs were differentially expressed at CI/R 24 h and CI/R 72 h, respectively. Notably, 21 circRNAs significantly changed at both reperfusion points. Three circRNAs, namely circ.7225, circ.5415, and circ.20623 were found to be associated with CI/R injury and might be preferred targets. Common downstream miR-298-5p and Bcl-3 were found to make up the circRNA-miRNA-mRNA network. Novel circRNA targets came to light in the penumbra of rats during CI/R injury and might establish the circRNA-miRNA-mRNA relationship, thus serving as potential biomarkers for ischemic stroke treatment.

Circular RNA hsa_circ_0000690 as a potential biomarker for diagnosis and prognosis of intracranial aneurysm: Closely relating to the volume of hemorrhage

PURPOSE

This study aimed to explore circular RNA (circRNA) hsa_circ_0000690 as a potential biomarker for diagnosis and prognosis of intracranial aneurysm (IA) and its relationship with clinical factors and complications of IA.

MATERIAL/METHODS

216 IA patients admitted to the neurosurgery department of our hospital from January 2019 to December 2020 were selected as the experimental group, and 186 healthy volunteers were selected as the control group. The expression of hsa_circ_0000690 in peripheral blood was detected by quantitative real-time PCR, and its diagnostic value was assessed by receiver operating characteristic curve. Relationship between hsa_circ_0000690 and clinical factors of IA was assessed by chi-square test. Nonparametric test was used in univariate analysis, and regression analysis was used in multivariate analysis. Multivariate Cox proportional hazards regression analysis was used to analyze the survival time.

RESULTS

CircRNA hsa_circ_0000690 of IA patients was relatively lower than that in the control group (p < .001). The AUC of hsa_circ_0000690 was 0.752, the specificity was 0.780, and sensitivity was 0.620, with diagnostic threshold of 0.0449. In addition, hsa_circ_0000690 expression was correlated with Glasgow Coma Scale, the volume of subarachnoid hemorrhage, modified Fisher scale, Hunt-Hess levels and surgical type. For hydrocephalus and delayed cerebral ischemia, hsa_circ_0000690 was significant in univariate analysis, but nonsignificant in multivariate analysis. For prognosis, hsa_circ_0000690 was significantly associated with modified Rankin Scales after surgery for 3 months, but not associated with survival time.

CONCLUSIONS

The expression of hsa_circ_0000690 can act as a diagnostic marker for IA and predict the prognosis of 3 months after operation and is closely related to the volume of hemorrhage.

circ-Ncam2 (mmu_circ_0006413) Participates in LPS-Induced Microglia Activation and Neuronal Apoptosis via the TLR4/NF-κB Pathway

Spinal cord injury (SCI) can cause permanent neurological deficits. Circular RNA Ncam2 (circ-Ncam2 also termed mmu_circ_0006413) has been reported to be overexpressed in SCI mouse models. However, the function of circ-Ncam2 in SCI has not been validated. Lipopolysaccharide (LPS) was used to activate mouse microglia (BV2 cells). Expression levels of circ-Ncam2 were determined by RT-qPCR. Relative protein levels were evaluated by western blotting. Cytokines were determined by ELISA. The regulatory mechanism of circ-Ncam2 was validated by dual-luciferase reporter and RNA pull-down assays. Effects of LPS-induced BV2 cells on mouse neuronal (HT22 cells) viability, proliferation, and apoptosis were analyzed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium Bromide (MTT), 5-ethynyl-2'-deoxyuridine (EdU), and flow cytometry assays. LPS stimulation promoted circ-Ncam2 expression in BV2 cells. Inhibition of circ-Ncam2 mitigated LPS-induced BV2 cell activation and inflammation. Mechanically, circ-Ncam2 adsorbed miR-544-3p to regulate TLR4 expression. Also, either miR-544-3p inhibition or TLR4 overexpression weakened circ-Ncam2 silencing-mediated effects on LPS-induced BV2 cell activation and inflammation. Furthermore, LPS-induced BV2 cells suppressed HT22 cell proliferation and promoted HT22 cell apoptosis through the circ-Ncam2/miR-544-3p axis. Importantly, circ-Ncam2 activated the NF-κB signaling via the miR-544-3p/TLR4axis. circ-Ncam2 silencing lowered LPS-induced microglia activation and neuronal apoptosis via blocking the TLR4/NF-κB pathway through acting as a miR-544-3p sponge, suggesting that circ-Ncam2 may be involved in secondary SCI.

Circ-Usp10 promotes microglial activation and induces neuronal death by targeting miRNA-152-5p/CD84

Spinal cord injury (SCI) is a traumatic disease resulting in neuronal injury. circRNAs are closely associated with human diseases. Nevertheless, the potential mechanism by which circRNAs impact SCI remains to be elucidated. The aim of this study was to investigate the regulatory roles of Circular RNAs (circRNAs) in SCI. The SCI mouse model and integrated bioinformatics analysis were used to identify the differentially expressed genes (DEGs). Functional enrichment analysis was conducted to study the related pathways. The circRNA-mediated ceRNA network and subnetwork was constructed based on circMir, TargetScan and miRanda. qRT–PCR, ELISA, flow cytometry, and luciferase reporter assays were carried out to validate the role of circ_0014637 (circ-Usp10) and microRNA(miR)-152-5p /CD84 in microglia. In all, 23 DE-circRNAs, 127 DE-miRNAs and 1327 DE-mRNAs were identified. We integrated these DEGs to construct a circRNA-miRNA-mRNA network. The circ-Usp10/miR-152-5p/CD84 axis was found to function in microglial activation. We also found that circ-Usp10 inhibited the secretion of proinflammatory factors in microglial BV2 cells. In addition, silencing circ-Usp10 significantly reduced the death of the neuronal cell line HT22. Taken together, we concluded that circ-Usp10 may function as a competing endogenous RNA (ceRNA) to promote microglial activation and induce neuronal death by targeting miR-152-5p/CD84. The circ-Usp10 may be a diagnostic biomarker and potential target for SCI 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.

Identification of Circular RNAs Related to Vascular Endothelial Proliferation, Migration, and Angiogenesis After Spinal Cord Injury Using Microarray Analysis in Female Mice

Background: Traumatic spinal cord injury (SCI) can result in severe disability and causes a considerable socio-economic burden worldwide. Circular RNAs (circRNAs) are important regulators of gene expression and pathological processes, and may represent therapeutic targets for SCI. To further evaluate the role of circRNAs in SCI, we elucidated circRNA expression profiles related to vascular endothelial proliferation, migration, and angiogenesis during the early stages of secondary injury in a mouse model of SCI.

Methods: Microarray analysis was performed to investigate the circRNA expression patterns in the spinal cord 3 days after SCI in female mice. Bioinformatic analyses, including GO enrichment analysis, KEGG pathway analysis, and circRNA-miRNA-mRNA network construction, were conducted to explore the role of circRNA dysregulation in vascular endothelial proliferation, migration, and angiogenesis following SCI.

Results: The expression of 1,288 circRNAs was altered (>2-fold change, p < 0.05) in the spinal cord after SCI, consisting of 991 upregulated and 297 downregulated circRNAs. We constructed a circRNA-mRNA network to predict whether these circRNAs could act as “miRNA sponges.” We next assessed the association of altered circRNAs with vascular endothelial proliferation, migration, and angiogenesis using GO and KEGG analyses. Using this analysis, we found that a total of 121 circRNAs were correlated with vascular endothelial proliferation, migration, and angiogenesis in the spinal cord after SCI.

Conclusions: Our study provides circRNA expression profiles during the early stages of SCI. circRNA.7079, circRNA.7078, and circRNA.6777 were found to play key roles in the vascular endothelial proliferation, migration, and angiogenesis, and may represent therapeutic targets for SCI.

CircTYW1 serves as a sponge for microRNA-380 in accelerating neurological recovery following spinal cord injury via regulating FGF9

As one of the most severe kinds of neurological damage, spinal cord injury (SCI) contributes to persistent motor dysfunction and involves a large repertoire of gene alterations. The participation of circular RNAs (circRNAs) in neurological recovery following SCI needs to be clarified. In the current work, we attempted to assess the function of hsa_circRNA_0003962/circTYW1 and its underlying mechanism in SCI. By accessing the GEO repository, the expression of circTYW1, microRNA-380 (miR-380), and FGF9 in SCI and sham-operated rats was evaluated. PC12 cells after oxygen-glucose deprivation (OGD) treatment were prepared to mimic the SCI model. circTYW1 and FGF9 were poorly expressed, whereas miR-380 was highly expressed in the spinal cord tissues of SCI rats. circTYW1 promoted neurological recovery in SCI rats and inhibited apoptosis in spinal cord tissues. In PC12 cells exposed to OGD, circTYW1 suppressed PC12 cell apoptosis; however, miR-380 overexpression reversed the protective effect of circTYW1 on PC12 cells. Also, circTYW1 promoted FGF9 expression through competitively binding to miR-380, which activated the ERK1/2 signaling. In summary, our results demonstrated that declines in circTYW1 prevented SCI rats from neurological recovery by regulating the miR-380/FGF9/ERK1/2 axis, which might provide new understanding for SCI treatment.