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

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.

Circular RNA PTP4A2 regulates microglial polarization through STAT3 to promote neuroinflammation in ischemic stroke

OBJECTIVE

Microglial polarization plays a critical role in neuroinflammation and may be a potential therapeutic target for ischemic stroke. This study was to explore the role and underlying molecular mechanism of Circular RNA PTP4A2 (circPTP4A2) in microglial polarization after ischemic stroke.

METHODS

C57BL/6J mice underwent transient middle cerebral artery occlusion (tMCAO), while primary mouse microglia and BV2 microglial cells experienced oxygen glucose deprivation/reperfusion (OGD/R) to mimic ischemic conditions. CircPTP4A2 shRNA lentivirus and Colivelin were used to knock down circPTP4A2 and upregulate signal transducer and activator of transcription 3 (STAT3) phosphorylation, respectively. Microglial polarization was assessed using immunofluorescence staining and Western blot. RNA pull-down and RNA binding protein immunoprecipitation (RIP) were applied to detect the binding between circPTP4A2 and STAT3.

RESULTS

The levels of circPTP4A2 were significantly increased in plasma and peri-infarct cortex in tMCAO mice. CircPTP4A2 knockdown reduced infarct volume, increased cortical cerebral blood flow (CBF), and attenuated neurological deficits. It also decreased pro-inflammatory factors levels in peri-infarct cortex and plasma, and increased anti-inflammatory factors concentrations 24 h post-stroke. In addition, circPTP4A2 knockdown suppressed M1 microglial polarization and promoted M2 microglial polarization in both tMCAO mice and OGD/R-induced BV2 microglial cells. Moreover, circPTP4A2 knockdown inhibited the phosphorylation of STAT3 induced by oxygen-glucose deprivation. In contrast, increased phosphorylation of STAT3 partly counteracted the effects of circPTP4A2 knockdown. RNA pull-down and RIP assays further certified the binding between circPTP4A2 and STAT3.

CONCLUSION

These results revealed regulatory mechanisms of circPTP4A2 that stimulated neuroinflammation by driving STAT3-dependent microglial polarization in ischemic brain injury. CircPTP4A2 knockdown reduced cerebral ischemic injury and promoted microglial M2 polarization, which could be a novel therapeutic target for ischemic stroke.

Physiological and pathological functions of circular RNAs in the nervous system

Circular RNAs (circRNAs) are a class of covalently closed single-stranded RNAs that are expressed during the development of specific cells and tissues. CircRNAs play crucial roles in physiological and pathological processes by sponging microRNAs, modulating gene transcription, controlling the activity of certain RNA-binding proteins, and producing functional peptides. A key focus of research at present is the functionality of circRNAs in the nervous system and several advances have emerged over the last 2 years. However, the precise role of circRNAs in the nervous system has yet to be comprehensively reviewed. In this review, we first summarize the recently described roles of circRNAs in brain development, maturity, and aging. Then, we focus on the involvement of circRNAs in various diseases of the central nervous system, such as brain cancer, chronic neurodegenerative diseases, acute injuries of the nervous system, and neuropathic pain. A better understanding of the functionality of circRNAs will help us to develop potential diagnostic, prognostic, and therapeutic strategies to treat diseases of the nervous system.

Circ_0006640 transferred by bone marrow-mesenchymal stem cell-exosomes suppresses lipopolysaccharide-induced apoptotic, inflammatory and oxidative injury in spinal cord injury

BACKGROUND

Emerging proofs have shown that differentially expressed circular RNAs (circRNAs) are closely associated with the pathophysiological process of spinal cord injury (SCI). Mesenchymal stem cell (MSC)-exosomes have been demonstrated to possess favorable therapeutic effects in diseases. Herein, this work aimed to investigate the action of circ_0006640 transferred by MSC-exosomes functional recovery after SCI.

METHODS

SCI animal models were established by spinal cord contusion surgery in mice and lipopolysaccharide (LPS)-stimulated mouse microglial cell line BV2. Levels of genes and proteins were detected by qRT-PCR and Western blot. Properties of BV2 cells were characterized using CCK-8 assay, flow cytometry and ELISA analysis. The oxidative stress was evaluated. Dual-luciferase reporter assay was used for verifying the binding between miR-382-5p and circ_0006640 or IGF-1 (Insulin-like Growth Factor 1). Exosome separation was conducted by using the commercial kit.

RESULTS

Circ_0006640 expression was lower in SCI mice and LPS-induced microglial cells. Circ_0006640 overexpression protected microglial cells from LPS-induced apoptotic, inflammatory and oxidative injury. Mechanistically, circ_0006640 directly sponged miR-382-5p, which targeted IGF-1. MiR-382-5p was increased, while IGF-1 was decreased in SCI mice and LPS-induced microglial cells. Knockdown of miR-382-5p suppressed apoptosis, inflammation and oxidative stress in LPS-induced microglial cells, which were reversed by IGF-1 deficiency. Moreover, miR-382-5p up-regulation abolished the protective functions of circ_0006640 in LPS-induced microglial cells. Additionally, circ_0006640 was packaged into MSC-exosomes and could be transferred by exosomes. Exosomal circ_0006640 also had protective effects on microglial cells via miR-382-5p/IGF-1 axis.

CONCLUSION

Circ_0006640 transferred by BMSC-exosomes suppressed LPS-induced apoptotic, inflammatory and oxidative injury via miR-382-5p/IGF-1 axis, indicating a new insight into the clinical application of exosomal circRNA-based therapeutic in the function recovery after SCI.

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.

An update to pain management after spinal cord injury: from pharmacology to circRNAs

Neuropathic pain (NP) following a spinal cord injury (SCI) is often hard to control and therapies should be focused on the physical, psychological, behavioral, social, and environmental factors that may contribute to chronic sensory symptoms. Novel therapeutic treatments for NP management should be based on the combination of pharmacological and nonpharmacological options. Some of them are addressed in this review with a focus on mechanisms and novel treatments. Several reports demonstrated an aberrant expression of non-coding RNAs (ncRNAs) that may represent key regulatory factors with a crucial role in the pathophysiology of NP and as potential diagnostic biomarkers. This review analyses the latest evidence for cellular and molecular mechanisms associated with the role of circular RNAs (circRNAs) in the management of pain after SCI. Advantages in the use of circRNA are their stability (up to 48 h), and specificity as sponges of different miRNAs related to SCI and nerve injury. The present review discusses novel data about deregulated circRNAs (up or downregulated) that sponge miRNAs, and promote cellular and molecular interactions with mRNAs and proteins. This data support the concept that circRNAs could be considered as novel potential therapeutic targets for NP management especially after spinal cord injuries.

Non-Coding RNAs Regulate Spinal Cord Injury-Related Neuropathic Pain via Neuroinflammation

Secondary chronic neuropathic pain (NP) in addition to sensory, motor, or autonomic dysfunction can significantly reduce quality of life after spinal cord injury (SCI). The mechanisms of SCI-related NP have been studied in clinical trials and with the use of experimental models. However, in developing new treatment strategies for SCI patients, NP poses new challenges. The inflammatory response following SCI promotes the development of NP. Previous studies suggest that reducing neuroinflammation following SCI can improve NP-related behaviors. Intensive studies of the roles of non-coding RNAs in SCI have discovered that ncRNAs bind target mRNA, act between activated glia, neuronal cells, or other immunocytes, regulate gene expression, inhibit inflammation, and influence the prognosis of NP.

Analysis and verification of the circRNA regulatory network RNO_CIRCpedia_ 4214/RNO-miR-667-5p/Msr1 axis as a potential ceRNA promoting macrophage M2-like polarization in spinal cord injury

BACKGROUND

CircRNAs are involved in the pathogenesis of several central nervous system diseases. However, their functions and mechanisms in spinal cord injury (SCI) are still unclear. Therefore, the purpose of this study was to evaluate circRNA and mRNA expression profiles in the pathological setting of SCI and to predict the potential function of circRNA through bioinformatics.

METHODS

A microarray-based approach was used for the simultaneous measurement of circRNAs and mRNAs, together with qPCR, fluorescence in situ hybridization, western immunoblotting, and dual-luciferase reporter assays to investigate the associated regulatory mechanisms in a rat SCI model.

RESULTS

SCI was found to be associated with the differential expression of 414 and 5337 circRNAs and mRNAs, respectively. Pathway enrichment analyses were used to predict the primary function of these circRNAs and mRNAs. GSEA analysis showed that differentially expressed mRNAs were primarily associated with inflammatory immune response activity. Further screening of these inflammation-associated genes was used to construct and analyze a competing endogenous RNA network. RNO_CIRCpedia_4214 was knocked down in vitro, resulting in reduced expression of Msr1, while the expression of RNO-miR-667-5p and Arg1 was increased. Dual-luciferase assays demonstrated that RNO_CIRCpedia_4214 bound to RNO-miR-667-5p. The RNO_CIRCpedia_4214/RNO-miR-667-5p/Msr1 axis may be a potential ceRNA that promotes macrophage M2-like polarization in SCI.

CONCLUSION

Overall, these results highlighted the critical role that circRNAs may play in the pathophysiology of SCI and the discovery of a potential ceRNA mechanism based on novel circRNAs that regulates macrophage polarization, providing new targets for the treatment of SCI.

The Implications of Microglial Regulation in Neuroplasticity-Dependent Stroke Recovery

Stroke causes varying degrees of neurological deficits, leading to corresponding dysfunctions. There are different therapeutic principles for each stage of pathological development. Neuroprotection is the main treatment in the acute phase, and functional recovery becomes primary in the subacute and chronic phases. Neuroplasticity is considered the basis of functional restoration and neurological rehabilitation after stroke, including the remodeling of dendrites and dendritic spines, axonal sprouting, myelin regeneration, synapse shaping, and neurogenesis. Spatiotemporal development affects the spontaneous rewiring of neural circuits and brain networks. Microglia are resident immune cells in the brain that contribute to homeostasis under physiological conditions. Microglia are activated immediately after stroke, and phenotypic polarization changes and phagocytic function are crucial for regulating focal and global brain inflammation and neurological recovery. We have previously shown that the development of neuroplasticity is spatiotemporally consistent with microglial activation, suggesting that microglia may have a profound impact on neuroplasticity after stroke and may be a key therapeutic target for post-stroke rehabilitation. In this review, we explore the impact of neuroplasticity on post-stroke restoration as well as the functions and mechanisms of microglial activation, polarization, and phagocytosis. This is followed by a summary of microglia-targeted rehabilitative interventions that influence neuroplasticity and promote stroke recovery.

Regulation of Glial Function by Noncoding RNA in Central Nervous System Disease

Non-coding RNAs (ncRNAs) are a class of functional RNAs that play critical roles in different diseases. NcRNAs include microRNAs, long ncRNAs, and circular RNAs. They are highly expressed in the brain and are involved in the regulation of physiological and pathophysiological processes of central nervous system (CNS) diseases. Mounting evidence indicates that ncRNAs play key roles in CNS diseases. Further elucidating the mechanisms of ncRNA underlying the process of regulating glial function that may lead to the identification of novel therapeutic targets for CNS diseases.

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.

The emerging power and promise of non-coding RNAs in chronic pain

Chronic pain (CP) is an unpleasant sensory and emotional experience associated with, or resembling that associated with, actual or potential tissue damage lasting longer than 3 months. CP is the main reason why people seek medical care and exerts an enormous economic burden. Genome-wide expression analysis has revealed that diverse essential genetic elements are altered in CP patients. Although many possible mechanisms of CP have been revealed, we are still unable to meet all the analgesic needs of patients. In recent years, non-coding RNAs (ncRNAs) have been shown to play essential roles in peripheral neuropathy and axon regeneration, which is associated with CP occurrence and development. Multiple key ncRNAs have been identified in animal models of CP, such as microRNA-30c-5p, ciRS-7, and lncRNA MRAK009713. This review highlights different kinds of ncRNAs in the regulation of CP, which provides a more comprehensive understanding of the pathogenesis of the disease. It mainly focuses on the contributions of miRNAs, circRNAs, and lncRNAs to CP, specifically peripheral neuropathic pain (NP), diabetic NP, central NP associated with spinal cord injury, complex regional pain syndrome, inflammatory pain, and cancer-induced pain. In addition, we summarize some potential ncRNAs as novel biomarkers for CP and its complications. With an in-depth understanding of the mechanism of CP, ncRNAs may provide novel insight into CP and could become new therapeutic targets in the future.

circ_0041795 Induces YAP1 Upregulation to Accelerate the Progression of Diabetic Retinopathy through Binding to miR-589-5p

Background

Circular RNAs (circRNAs) are involved in the pathogenesis of many diseases, and circ_0041795 was shown to promote the progression of diabetic retinopathy (DR). The aim of this study was to explore the molecular mechanism of circ_0041795 in DR.

Methods

Human retinal pigment epithelial cells ARPE-19 were treated with high glucose (HG). circ_0041795, miR-589-5p, and Yes-associated protein 1 (YAP1) levels were measured by reverse transcription-quantitative polymerase chain reaction assay. Biological behaviors were examined by Cell Counting Kit-8 assay for cell viability, EdU assay for cell proliferation, flow cytometry for cell apoptosis, and enzyme-linked immunosorbent assay for cell inflammation. Oxidative stress was assessed via the commercial kits. Western blot was performed for analysis of protein expression. The molecular binding was assessed via dual-luciferase reporter assay and pull-down assay.

Results

HG-induced inhibiting effects on cell viability and proliferation but promoting effects on cell apoptosis, inflammation, and oxidative stress were ameliorated by silence of circ_0041795. circ_0041795 was identified to act as a miR-589-5p sponge. The regulation of circ_0041795 in HG-induced cell injury was achieved by inhibiting miR-589-5p. miR-589-5p targeted YAP1 and relieved HG-induced cell dysfunction via downregulating YAP1. circ_0041795 sponged miR-589-5p to regulate YAP1 level and activated the NF-κB pathway through the miR-589-5p/YAP1 axis.

Conclusion

All these results elucidated that circ_0041795 facilitated the development of DR by inducing miR-589-5p-mediated YAP1 upregulation.

Exosomal miR-152-5p and miR-3681-5p function as potential biomarkers for ST-segment elevation myocardial infarction

BACKGROUND

The strain parameters of Real-Time Three-Dimensional Spot Tracking Echocardiography (RT3D-STE) are GLS, GAS, GRS, and GCS, while each index can significantly diagnose Acute Myocardial Infarction (AMI) patients, but none of them can distinguish between NSTEMI and STEMI. MicroRNAs (miRNAs) play essential roles in Acute Myocardial Infarction (AMI), but little is known about the value of exosome miRNA combined with Real-Time Three-Dimensional Spot Tracking Echocardiography (RT3D-STE) between ST-segment Elevation Myocardial Infarction (STEMI) and Non-ST-segment Elevation Myocardial Infarction (NSTEMI).

AIM

To estimate the exosomal miRNAs related to strain parameters of RT3D-STE as biomarkers for early detection of STEMI and NSTEMI.

METHODS

The present study collected plasma samples from thirty-four (34) patients with AMI (including STEMI and NSTEMI) and employed high-throughput sequence technology and real-time quantitative polymerase chain reaction (RT-qPCR) to identify the differentially expressed miRNAs. The Pearson correlation coefficient is used to measure the strength of a linear association between differentially expressed miRNAs and strain parameters of RT3D-STE.

RESULTS

Twenty-eight (28) differentially expressed exosomal miRNAs were universally identified between STEMI, NSTEM, and normal groups. Among them, there are 10 miRNAs (miR-152-5p, miR-3681-5p, miR-193a-5p, miR-193b-5p miR-345-5p, miR-125a-5p, miR-365a-3p, miR-4520-2-3p, hsa-miR-193b-3p and hsa-miR-5579-5p) with a Pearson correlation greater than 0.6 with RT3D-STE strain parameters. Especially, miR-152-5p and miR-3681-5p showed the most significant correlation with RT3D-STE strain parameters. Target genes of these 10 miRNAs are analyzed for Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways enrichment, and they were found to be mainly involved in the cellular metabolism processes and HIF-1 signaling pathway. RT-qPCR verified the significant differential expression of miR-152-5p and miR-3681-5p between STEMI and NSTEM groups.

CONCLUSION

RT3D-STE and exosome miRNAs can be used as a hierarchical diagnostic system in AMI. If the RT3D-STE is abnormal, the exosome miRNAs can be detected again to obtain more detailed and accurate diagnostic results between STEMI and NSTEM groups. Exosomal miR-152-5p and miR-3681-5p may serve as potential biomarkers for ST-segment elevation myocardial infarction.