Differentially Expressed Circular RNAs in Peripheral Blood Mononuclear Cells of Patients with Parkinson's Disease

Exploring circular RNAs as biomarkers for Parkinson's disease and their expression changes after aerobic exercise rehabilitation

Circular RNAs (circRNAs) are circularized single-stranded ribonucleic acids that interacts with DNA, RNA, and proteins to play critical roles in cell biology. CircRNAs regulate microRNA content, gene expression, and may code for specific peptides. Indeed, circRNAs are differentially expressed in neurodegenerative disorders like Parkinson's disease (PD), playing a potential role in the mechanisms of brain pathology. The RNA molecules with aberrant expression in the brain can cross the blood-brain barrier and reach the bloodstream, which enable their use as non-invasive PD disease biomarker. Promising targets with valuable discriminatory ability in combined circRNA signatures include MAPK9_circ_0001566, SLAIN1_circ_0000497, SLAIN2_circ_0126525, PSEN1_circ_0003848, circ_0004381, and circ_0017204. On the other hand, regular exercises are effective therapy for mitigating PD symptoms, promoting neuroprotective effects with epigenetic modulation. Aerobic exercises slow symptom progression in PD by improving motor control, ameliorating higher functions, and enhancing brain activity and neuropathology. These improvements are accompanied by changes circRNA expression, including hsa_circ_0001535 (circFAM13B) and hsa_circ_0000437 (circCORO1C). The sensitivity of current methods for detecting circulating circRNAs is considered a limitation. While amplification kits already exist for low-abundant microRNAs, similar kits are needed for circRNAs. Alternatively, the use of digital PCR can help overcome this constraint. The current review examines the potential use of circRNAs as non-invasive biomarkers of PD and to assess the effects of rehabilitation. Although circRNAs hold promise as targets for PD diagnosis and therapeutics, further validation is needed before their clinical implementation.

Autophagy-associated non-coding RNAs: Unraveling their impact on Parkinson's disease pathogenesis

BACKGROUND

Parkinson's disease (PD) is a degenerative neurological condition marked by the gradual loss of dopaminergic neurons in the substantia nigra pars compacta. The precise etiology of PD remains unclear, but emerging evidence suggests a significant role for disrupted autophagy-a crucial cellular process for maintaining protein and organelle integrity.

METHODS

This review focuses on the role of non-coding RNAs (ncRNAs) in modulating autophagy in PD. We conducted a comprehensive review of recent studies to explore how ncRNAs influence autophagy and contribute to PD pathophysiology. Special attention was given to the examination of ncRNAs' regulatory impacts in various PD models and patient samples.

RESULTS

Findings reveal that ncRNAs are pivotal in regulating key processes associated with PD progression, including autophagy, α-synuclein aggregation, mitochondrial dysfunction, and neuroinflammation. Dysregulation of specific ncRNAs appears to be closely linked to these pathogenic processes.

CONCLUSION

ncRNAs hold significant therapeutic potential for addressing autophagy-related mechanisms in PD. The review highlights innovative therapeutic strategies targeting autophagy-related ncRNAs and discusses the challenges and prospective directions for developing ncRNA-based therapies in clinical practice. The insights from this study underline the importance of ncRNAs in the molecular landscape of PD and their potential in novel treatment approaches.

CircHIVEP2 alleviates Parkinson's nerve damage and inflammatory response by targeting miR-485-3p

OBJECTIVE

Dysregulation of covalently closed circular RNAs (circRNAs) has been associated with neurological disorders, the role of circHIVP2 in Parkinson's disease (PD) and its molecular mechanism is not well understood.

METHODS

127 patients with PD and 85 healthy people were enrolled. RT-qPCR was employed to examine the levels of circHIVEP2. ROC curve to explore the diagnostic. Mpp+ induced the SH-SY5Y to construct an in vitro PD cell model. Cell viability, apoptosis, and secretion levels of inflammatory factors were analyzed by CCK-8, flow cytometry, and ELISA assay. CircHIVEP2 targets miRNA predicted by bioinformatics database and validated by the dual luciferase reporter and RIP assays.

RESULTS

CircHIVEP2 was typically lower in PD patients than in controls. CircHIVEP2 has certain specificity and sensitivity to recognize PD patients from healthy individuals. miR-485-3p, a target miRNA of circHIVEP2, was significantly elevated in PD patients. Additionally, MPP+ induction reduced cell viability and promoted apoptosis and inflammatory factor overproduction. However, overexpression of circHIVEP2 significantly inhibited the effects of MPP+, but this inhibition was significantly attenuated by elevated miR-485-3p.

CONCLUSION

circHIVEP2 is a potential diagnostic biomarker for PD, and its upregulation mitigated MPP+-induced nerve damage and inflammation and this may be through targeted by the miR-485-3p.

Transcriptome sequencing of circular RNA reveals the involvement of hsa-SCMH1_0001 in the pathogenesis of Parkinson's disease

BACKGROUND

Parkinson's disease (PD) is the second most common neurodegenerative disease. Exosomes are endosome-derived extracellular vesicles that can take part in intercellular communication. Circular RNAs (circRNAs) are noncoding RNAs characterized by covalently closed-loop structures, which perform a crucial function in many diseases.

AIM

To clarify the expression and function of exosomal circRNSs of PD patients and look for circRNAs that might be related to the pathogenesis of PD.

MATERIALS AND METHODS

We examined circRNA and mRNA expression profiles in peripheral exosomes from PD patients (n = 23) and healthy controls (n = 15) using next-generation sequencing (NGS) technology, functional annotation, and quantitative polymerase chain reaction. Correlation analysis was performed between the expression levels of the circRNAs and the clinical characteristics of PD patients. The binding miRNAs and target genes were predicted using TargetScanHuman, miRDB, and miRTarBase. The predicted target genes were compared with the differentially expressed mRNAs in sequencing results.

RESULTS

According to the NGS, 62 upregulated and 37 downregulated circRNAs in the PD group were screened out. Correlation analysis revealed that hsa-SCMH1_0001 has strong clinical relevance. We identified 17 potential binding miRNAs of hsa-SCMH1_0001 with 149 potential target genes. ARID1A and C1orf115 belong to the intersection of the predicted target genes and the differentially expressed mRNAs obtained by sequencing.

CONCLUSION

This study suggested that hsa-SCMH1_0001 and its target genes ARID1A and C1orf115 are downregulated in PD patients and may be involved in the occurrence of PD.

Transcriptomic analysis reveals associations of blood-based A-to-I editing with Parkinson's disease

BACKGROUND

Adenosine-to-inosine (A-to-I) editing is the most common type of RNA editing in humans and the role of A-to-I RNA editing remains unclear in Parkinson's disease (PD).

OBJECTIVE

We aimed to explore the potential causal association between A-to-I editing and PD, and to assess whether changes in A-to-I editing were associated with cognitive progression in PD.

METHODS

The RNA-seq data from 380 PD patients and 178 healthy controls in the Parkinson's Progression Marker Initiative cohort was used to quantify A-to-I editing sites. We performed cis-RNA editing quantitative trait loci analysis and a two-sample Mendelian Randomization (MR) study by integrating genome-wide association studies to infer the potential causality between A-to-I editing and PD pathogenesis. The potential causal A-to-I editing sites were further confirmed by Summary-data-based MR analysis. Spearman's correlation analysis was performed to characterize the association between longitudinal A-to-I editing and cognitive progression in patients with PD.

RESULTS

We identified 17 potential causal A-to-I editing sites for PD and indicated that genetic risk variants may contribute to the risk of PD through A-to-I editing. These A-to-I editing sites were located in genes NCOR1, KANSL1 and BST1. Moreover, we observed 57 sites whose longitudinal A-to-I editing levels correlated with cognitive progression in PD.

CONCLUSIONS

We found potential causal A-to-I editing sites for PD onset and longitudinal changes of A-to-I editing were associated with cognitive progression in PD. We anticipate this study will provide new biological insights and drive the discovery of the epitranscriptomic role underlying Parkinson's disease.

Circulating blood circular RNA in Parkinson's Disease; a systematic study

We aimed to identify circRNAs associated with Parkinson's disease (PD) by leveraging 1,848 participants and 1,789 circRNA from two of the largest publicly available studies with longitudinal clinical and blood transcriptomic data. To comprehensively understand changes in circRNAs we performed a cross-sectional study utilizing the last visit of each participant, and a longitudinal (mix model) analysis that included 1,166 participants with at least two time points. We identified 192 circRNAs differentially expressed in PD participants compared to healthy controls, with effects that were consistent in the mixed models, mutation carriers, and diverse ancestry. Finally, we included the 149 circRNA in a model with a ROC AUC of 0.825, showing that have the potential to aid the diagnosis of PD. Overall, we demonstrated that circRNAs play an important role in PD and can be leveraged as biomarkers.

Early-stage idiopathic Parkinson's disease is associated with reduced circular RNA expression

Neurodegeneration in Parkinson's disease (PD) precedes diagnosis by years. Early neurodegeneration may be reflected in RNA levels and measurable as a biomarker. Here, we present the largest quantification of whole blood linear and circular RNAs (circRNA) in early-stage idiopathic PD, using RNA sequencing data from two cohorts (PPMI = 259 PD, 161 Controls; ICICLE-PD = 48 PD, 48 Controls). We identified a replicable increase in TMEM252 and LMNB1 gene expression in PD. We identified novel differences in the expression of circRNAs from ESYT2, BMS1P1 and CCDC9, and replicated trends of previously reported circRNAs. Overall, using circRNA as a diagnostic biomarker in PD did not show any clear improvement over linear RNA, minimising its potential clinical utility. More interestingly, we observed a general reduction in circRNA expression in both PD cohorts, accompanied by an increase in RNASEL expression. This imbalance implicates the activation of an innate antiviral immune response and suggests a previously unknown aspect of circRNA regulation in PD.

Neuronal dysfunction and gene modulation by non-coding RNA in Parkinson's disease and synucleinopathies

Over the last few decades, emerging evidence suggests that non-coding RNAs (ncRNAs) including long-non-coding RNA (lncRNA), microRNA (miRNA) and circular-RNA (circRNA) contribute to the molecular events underlying progressive neuronal degeneration, and a plethora of ncRNAs have been identified significantly misregulated in many neurodegenerative diseases, including Parkinson's disease and synucleinopathy. Although a direct link between neuropathology and causative candidates has not been clearly established in many cases, the contribution of ncRNAs to the molecular processes leading to cellular dysfunction observed in neurodegenerative diseases has been addressed, suggesting that they may play a role in the pathophysiology of these diseases. Aim of the present Review is to overview and discuss recent literature focused on the role of RNA-based mechanisms involved in different aspects of neuronal pathology in Parkinson's disease and synucleinopathy models.

Circ_UBAP2 exacerbates proliferation and metastasis of OS via targeting miR-665/miR-370-3p/HMGA1 axis

Circ_UBAP2 is extensively engaged in regulating the development of various malignancies, containing osteosarcoma (OS). However, its biological significance and function are not fully understood. In this study, we found that circ_UBAP2 and HMGA1 levels were up-regulated, and miR-370-3p and miR-665 expressions were decreased in osteosarcoma tissues. Inhibition of circ_UBAP2 or HMGA1 expression in OS cells, cell viability, invasion and migration abilitities were notably hindered, and cell apoptosis abilities were increased. Bioinformatics analysis predicted that miR-665 and miR-370-3p were the downstream targets of circ_UBAP2, and the dual luciferase experiment demonstrated the correlation between them. In addition, inhibition of miR-665 and miR-370-3p expression could significantly reverse the impact of knocking down circ_UBAP2 on OS cells. HMGA1 was discovered to become the downstream target of both miR-665 and miR-370-3p. It was shown that over-expression of miR-665 or miR-370-3p notably stimulated the cell growth, invasion, and migration of osteosarcoma cells, while hindered cell apoptosis. Nevertheless, this effect could be reversed by concurrent over-expression of HMGA1. Our data strongly prove that circ_UBAP2 makes a vital impact on promoting the proliferation, invasion as well as migration of osteosarcoma cells via down-regulating the level of miR-665 and miR-370-3p, and later up-regulating the level of HMGA1. In conclusion, circ_UBAP2 is upregulated in osteosarcoma, and it competitively adsorbs miR-370-3p and miR-665, resulting in up-regulation of HMGA1, thus promoting OS development.

Characterization of the circRNA Landscape in Interleukin-4 Induced Anti-Inflammatory Microglia

Microglia are resident innate immune cells that play an essential role in the development and surveillance of the central nervous system as well as the shared pathogenesis of neurodegenerative diseases. Microglia rapidly respond to multiple inflammatory stimuli and activate towards different phenotypes, such as pro-inflammatory and anti-inflammatory phenotypes. Cytokines, epigenetic and long non-coding RNA modulations have been shown to regulate microglial activation; however, the role of circRNAs in microglia-mediated neuroinflammation remains elusive. Here, we performed circRNA sequencing in IL-4-treated anti-inflammatory microglia and discovered 120 differentially expressed circRNAs. We systemically verified the identities of circRNAs by assays of PCR, RNase R treatment and fluorescent in situ hybridization (FISH), among others. We found that circAdgre1 promoted IL-4-induced anti-inflammatory responses and further conferred neuroprotective effects upon lipopolysaccharide (LPS) stimuli. Taken together, our results show that circRNAs might be possible therapeutic targets for microglia-mediated neuroinflammation and neurodegenerative diseases.

Circular RNAs: Diagnostic and Therapeutic Perspectives in CNS Diseases

Circular RNAs (circRNAs) are a class of regulatory non-coding RNAs characterized by the presence of covalently closed ends. A growing body of evidence suggests that circRNAs play important roles in physiology and pathology. In particular, accumulating data on circRNA functions in various central nervous system (CNS) diseases and their correlations indicate that circRNAs are critical contributors to the onset and development of brain disorders. In this review, we focus on the regulatory and functional roles of circRNAs in CNS diseases, highlighting their diagnostic and therapeutic potential, with the aim of providing new insights into CNS diseases.

The common denominators of Parkinson's disease pathogenesis and methamphetamine abuse

The pervasiveness and mortality associated with methamphetamine abuse has doubled during the past decade suggesting a possible worldwide substance use crisis. Epitomizing the pathophysiology and toxicology of methamphetamine abuse proclaims severe signs and symptoms of neurotoxic and neurobehavioral manifestations in both humans and animals. Most importantly, chronic use of this drug enhances the probability of developing neurodegenerative diseases manifolds. Parkinson's disease is one such neurological disorder, which significantly and evidently not only shares a number of toxic pathogenic mechanisms induced by methamphetamine exposure but is also interlinked both structurally andgenetically. Methamphetamine-induced neurodegeneration involves altered dopamine homeostasis that promotes the aggregation of α-synuclein protofibrils in the dopaminergic neurons and drives these neurons to make them more vulnerable to degeneration as recognized in Parkinson's disease. Moreover, the pathologic mechanisms such as mitochondrial dysfunction, oxidative stress, neuroinflammation and decreased neurogenesis detected in methamphetamine abusers dramatically resemble to what is observed in Parkinson's disease cases. Therefore, the present review comprehensively cumulates a holistic illustration of various genetic and molecular mechanisms putting across the notion of how methamphetamine administration and intoxication might lead to Parkinson's disease-like pathology and Parkinsonism.

Prenatal alcohol exposure dysregulates spinal and circulating immune cell circular RNA expression in adult female rats with chronic sciatic neuropathy

Alcohol consumption during pregnancy is associated with Fetal Alcohol Spectrum Disorders (FASD) that results in a continuum of central nervous system (CNS) deficits. Emerging evidence from both preclinical and clinical studies indicate that the biological vulnerability to chronic CNS disease in FASD populations is driven by aberrant neuroimmune actions. Our prior studies suggest that, following minor nerve injury, prenatal alcohol exposure (PAE) is a risk factor for developing adult-onset chronic pathological touch sensitivity or allodynia. Allodynia in PAE rats occurs concurrently with heightened proinflammatory peripheral and spinal glial-immune activation. However, minor nerve-injured control rats remain non-allodynic, and corresponding proinflammatory factors are unaltered. A comprehensive molecular understanding of the mechanism(s) that underlie PAE-induced proinflammatory bias during adulthood remains elusive. Non-coding circular RNAs (circRNAs) are emerging as novel modulators of gene expression. Here, we hypothesized that PAE induces dysregulation of circRNAs that are linked to immune function under basal and nerve-injured conditions during adulthood. Utilizing a microarray platform, we carried out the first systematic profiling of circRNAs in adult PAE rats, prior to and after minor nerve injury. The results demonstrate a unique circRNA profile in adult PAE rats without injury; 18 circRNAs in blood and 32 spinal circRNAs were differentially regulated. Following minor nerve injury, more than 100 differentially regulated spinal circRNAs were observed in allodynic PAE rats. Bioinformatic analysis identified that the parental genes of these circRNAs are linked to the NF-κB complex, a central transcription factor for pain-relevant proinflammatory cytokines. Quantitative real-time PCR was employed to measure levels of selected circRNAs and linear mRNA isoforms. We have validated that circVopp1 was significantly downregulated in blood leukocytes in PAE rats, concurrent with downregulation of Vopp1 mRNA levels. Spinal circVopp1 levels were upregulated in PAE rats, regardless of nerve injury. Additionally, PAE downregulated levels of circItch and circRps6ka3, which are linked to immune regulation. These results demonstrate that PAE exerts long-lasting dysregulation of circRNA expression in blood leukocytes and the spinal cord. Moreover, the spinal circRNA expression profile following peripheral nerve injury is differentially modulated by PAE, potentially contributing to PAE-induced neuroimmune dysregulation.

microRNA and circRNA in Parkinson's Disease and atypical parkinsonian syndromes

Multiple System Atrophy (MSA) and Progressive Supranuclear Palsy (PSP) are atypical parkinsonian syndromes (APS) with various clinical phenotypes and considerable clinical overlap with idiopathic Parkinson's disease (iPD). This disease heterogeneity makes ante-mortem diagnosis extremely challenging with up to 24% of patients misdiagnosed. Because diagnosis is predominantly clinical, there is great interest in identifying biomarkers for early diagnosis and differentiation of the different types of parkinsonism. Compared to protein biomarkers, microRNAs (miRNAs) and circularRNAs (circRNAs) are stable tissue-specific molecules that can be accurately measured by reverse transcription-quantitative polymerase chain reaction (RT-qPCR). This chapter critically reviews miRNAs and circRNAs as diagnostic biomarkers and therapeutics to differentiate atypical parkinsonian disorders and their role in disease pathogenesis.

Research progress of circular RNA molecules in aging and age-related diseases

Circular RNAs (circRNAs) are a class of single-chain endogenous closed circular RNAs that do not have a poly(A) tail at the 3' end and a cap structure at the 5' end and are connected end-to-end by covalent bonds. CircRNAs, which are pervasive, diverse, stable, and conversed, have functions in transcriptional control and protein translation and play vital roles in modulating cell senescence, individual aging, as well as the occurrence and development of age-related diseases. Studies in recent years were reviewed from aspects including the biosynthesis mechanisms, classification, expression, biomedical functions, associations with aging and age-related diseases, and potential clinical applications of circRNAs. It will provide the theoretic basis for exploring the molecular biological mechanisms of aging, using circRNA as the therapeutic target to delay aging, and finding therapeutic strategies to prevent and treat age-related diseases.

Circular RNAs in Parkinson's Disease: Reliable Biological Markers and Targets for Rehabilitation

In clinical practice, the underlying pathogenesis of Parkinson's disease (PD) remains unknown. Circular RNAs (circRNAs) have good biological properties and can be used as biological marker. Rehabilitation as a third treatment alongside drug and surgery has been shown to be clinically effective, but biomarkers of rehabilitation efficiency at genetic level is still lacking. In this study, we identified differentially expressed circRNAs in peripheral blood exosomes between PD patients and health controls (HCs) and determined whether these circRNAs changed after rehabilitation, to explore the competing RNA networks and epigenetic mechanisms affected. We found that there were 558 upregulated and 609 downregulated circRNAs in PD patients compared to HCs, 3398 upregulated and 479 downregulated circRNAs in PD patients after rehabilitation compared to them before rehabilitation, along with 3721 upregulated and 635 downregulated circRNAs in PD patients after rehabilitation compared to HCs. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis revealed that differentially expressed circRNAs may affect the stability of the cellular actin backbone and synaptic structure by influencing the aggregation of α-synuclein (a-syn). We selected two circRNAs overexpressed in PD patients for validation (hsa_circ_0001535 and hsa_circ_0000437); the results revealed that their expression levels were all reduced to varying degrees (p < 0.05) after rehabilitation. After network analysis, we believe that hsa_circ_0001535 may be related to the aggregation of a-syn, while hsa_circ_0000437 may act on hsa-let-7b-5p or hsa-let-7c-5p through sponge effect to cause inflammatory response. Our findings suggest that rehabilitation can mitigate the pathological process of PD by epigenetic means.

Diagnostic accuracy of novel mRNA blood biomarkers of infection to predict outcomes in emergency department patients with undifferentiated abdominal pain

Abdominal pain represents greater than 20% of US Emergency Department (ED) visits due to a wide range of illnesses. There are currently no reliable blood biomarkers to predict serious outcomes in patients with abdominal pain. Our previous studies have identified three mRNA transcripts related to innate immune activation: alkaline phosphatase (ALPL), interleukin-8 receptor-β (IL8RB), and defensin-1 (DEFA1) as promising candidates to detect an intra-abdominal infection. The objective of this study was to evaluate the accuracy of these mRNA biomarkers to predict likely infection, hospitalization and surgery in Emergency Department patients with undifferentiated abdominal pain. We prospectively enrolled Emergency Department patients with undifferentiated abdominal pain who received an abdominal CT scan as part of their evaluation. Clinical outcomes were abstracted from the CT scan and medical records. mRNA biomarker levels were calculated independent of the clinical outcomes and their accuracy was assessed to predict infectious diagnoses, surgery and hospital admission. 89 patients were enrolled; 21 underwent surgery; 47 underwent hospital admission; and, no deaths were observed within 30 days. In identifying which cases were likely infectious, mRNA biomarkers' AUC values were: ALPL, 0.83; DEFA1 0.51; IL8RB, 0.74; and ALPL + IL8RB, 0.79. In predicting which Emergency Department patients would receive surgery, the AUC values were: ALPL, 0.75; DEFA1, 0.58; IL8RB, 0.75; and ALPL + IL8RB, 0.76. In predicting hospital admission, the AUC values were: ALPL, 0.78; DEFA1, 0.52; IL8RB, 0.74; and, ALPL + IL8RB, 0.77. For predicting surgery, ALPL + IL8RB's positive likelihood ratio (LR) was 3.97; negative LR (NLR) was 0.70. For predicting hospital admission, the same marker's positive LR was 2.80 with an NLR of 0.45. Where the primary cause for admission was a potentially infectious disorder, 33 of 34 cases (97%) had positive RNA scores. In a pragmatic, prospective diagnostic accuracy trial in Emergency Department patients with undifferentiated abdominal pain, mRNA biomarkers showed good accuracy to identify patients with potential infection, as well as those needing surgery or hospital admission.

Brain-protective mechanisms of autophagy associated circRNAs: Kick starting self-cleaning mode in brain cells via circRNAs as a potential therapeutic approach for neurodegenerative diseases

Altered autophagy is a hallmark of neurodegeneration but how autophagy is regulated in the brain and dysfunctional autophagy leads to neuronal death has remained cryptic. Being a key cellular waste-recycling and housekeeping system, autophagy is implicated in a range of brain disorders and altering autophagy flux could be an effective therapeutic strategy and has the potential for clinical applications down the road. Tight regulation of proteins and organelles in order to meet the needs of complex neuronal physiology suggests that there is distinct regulatory pattern of neuronal autophagy as compared to non-neuronal cells and nervous system might have its own separate regulator of autophagy. Evidence has shown that circRNAs participates in the biological processes of autophagosome assembly. The regulatory networks between circRNAs, autophagy, and neurodegeneration remains unknown and warrants further investigation. Understanding the interplay between autophagy, circRNAs and neurodegeneration requires a knowledge of the multiple steps and regulatory interactions involved in the autophagy pathway which might provide a valuable resource for the diagnosis and therapy of neurodegenerative diseases. In this review, we aimed to summarize the latest studies on the role of brain-protective mechanisms of autophagy associated circRNAs in neurodegenerative diseases (including Alzheimer's disease, Parkinson's disease, Huntington's disease, Spinal Muscular Atrophy, Amyotrophic Lateral Sclerosis, and Friedreich's ataxia) and how this knowledge can be leveraged for the development of novel therapeutics against them. Autophagy stimulation might be potential one-size-fits-all therapy for neurodegenerative disease as per considerable body of evidence, therefore future research on brain-protective mechanisms of autophagy associated circRNAs will illuminate an important feature of nervous system biology and will open the door to new approaches for treating neurodegenerative diseases.

Circular RNAs: emerging players in brain aging and neurodegenerative diseases

Brain aging is closely related to neurodegenerative diseases. Circular RNAs (circRNAs) are a type of conserved RNAs with covalently closed continuous loops. Emerging evidence has shown that circRNAs are implicated in the biology of brain aging and the pathology of age-related neurodegenerative diseases. Here, we summarize current studies on circRNAs associated with brain aging and neurodegenerative diseases by discussing their expression features, pathophysiological roles, and mechanisms of action. We also discuss the potential challenges of circRNA-based therapy against brain aging and neurodegenerative diseases, as well as their potential as diagnostic biomarkers of neurodegenerative diseases. The review provides insights into current progress in the functions of circRNAs in the process of brain aging and neurodegenerative diseases. © 2022 The Pathological Society of Great Britain and Ireland.

The emerging role of circular RNAs in Parkinson's disease

Parkinson's disease (PD) is the second most prevalent neurodegenerative disease and the most common movement disorder. It involves a gradual loss of dopaminergic neurons in the substantia nigra. Although many studies have been conducted, the underlying molecular pathways of PD remain largely unknown. Circular RNAs (circRNAs), a novel class of non-coding RNAs with a covalently closed loop structure, are common in the brain. They are stable, conserved molecules that are widely expressed in eukaryotes in tissue-, cell-, and development-specific patterns. Many circRNAs have recently been identified in nervous system diseases, and some circRNA expression profiles have been linked to PD. Given that recent research has indicated the essential roles of various circRNAs in the development and progression of neurodegenerative diseases, the identification of individual circRNAs may be a promising strategy for finding new treatment targets for PD. Moreover, the search for circRNAs with high specificity and sensitivity will open up new avenues for the early diagnosis and treatment of PD. Herein, we address the biogenesis, properties, and roles of circRNAs and review their potential utility as biomarkers and therapeutic targets in PD.

The Role of Non-Coding RNAs in the Pathogenesis of Parkinson’s Disease: Recent Advancement

Parkinson’s disease (PD) is a prevalent neurodegenerative aging disorder that manifests as motor and non-motor symptoms, and its etiopathogenesis is influenced by non-coding RNAs (ncRNAs). Signal pathway and gene sequence studies have proposed that alteration of ncRNAs is relevant to the occurrence and development of PD. Furthermore, many studies on brain tissues and body fluids from patients with PD indicate that variations in ncRNAs and their target genes could trigger or exacerbate neurodegenerative pathogenesis and serve as potential non-invasive biomarkers of PD. Numerous ncRNAs have been considered regulators of apoptosis, α-syn misfolding and aggregation, mitochondrial dysfunction, autophagy, and neuroinflammation in PD etiology, and evidence is mounting for the determination of the role of competing endogenous RNA (ceRNA) mechanisms in disease development. In this review, we discuss the current knowledge regarding the regulation and function of ncRNAs as well as ceRNA networks in PD pathogenesis, focusing on microRNAs, long ncRNAs, and circular RNAs to increase the understanding of the disease and propose potential target identification and treatment in the early stages of PD.

Circular RNA hsa_circ_0004381 Promotes Neuronal Injury in Parkinson's Disease Cell Model by miR-185-5p/RAC1 Axis

The study aims to explore the molecular mechanism involved in Parkinson's disease (PD). Hsa_circ_0004381, microRNA-185-5p (miR-185-5p), and Rac family small GTPase 1 (RAC1) level were measured by real-time quantitative polymerase chain reaction (RT-qPCR). Furthermore, cell viability and apoptosis rate were assessed by Cell Counting Kit-8 (CCK-8) and flow cytometry assays, respectively. Protein levels of B cell lymphoma-2 (Bcl-2), Bcl-2-related X protein (Bax), cleaved-caspase 3 (c-caspase 3), and RAC1 were determined by western blot assay. The levels of tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), and IL-6 were detected by enzyme-linked immunosorbent assay (ELISA). The ROS generation and LDH and SOD activity were detected by the corresponding kits. The binding relationship between miR-185-5p and hsa_circ_0004381 or RAC1 was predicted by Starbase and then verified by a dual-luciferase reporter and RNA Immunoprecipitation (RIP) assays. Hsa_circ_0004381 and RAC1 were increased, and miR-185-5p was decreased in MPP⁺-triggered SK-N-SH cells. Moreover, hsa_circ_0004381 silencing promoted cell viability, and repressed apoptosis, inflammatory response, and oxidative stress in MPP⁺-treated SK-N-SH cells. The mechanical analysis suggested that hsa_circ_0004381 served as a sponge of miR-185-5p to affect RAC1 expression. Hsa_circ_0004381 could contribute to MPP⁺-triggered neuron injury by targeting the miR-185-5p/RAC1 axis, which provided a novel insight into the pathogenesis and treatment of PD.

Novel insights into the role of circular RNAs in Parkinson disease: An emerging renaissance in the management of neurodegenerative diseases

Parkinson's disease (PD), as a debilitating neurodegenerative disease, particularly affects the elderly population, and is clinically identified by resting tremor, rigidity, and bradykinesia. Pathophysiologically, PD is characterized by an early loss of dopaminergic neurons in the Substantia nigra pars compacta, accompanied by the extensive aggregation of alpha-synuclein (α-Syn) in the form of Lewy bodies. The onset of PD has been reported to be influenced by multiple biological molecules. In this context, circular RNAs (circRNAs), as tissue-specific noncoding RNAs with closed structures, have been recently demonstrated to involve in a set of PD's pathogenic processes. These RNA molecules can either up- or downregulate the expression of α-Syn, as well as moderating its accumulation through different regulatory mechanisms, in which targeting microRNAs (miRNAs) is considered the most common pathway. Since circRNAs have prominent structural and biological characteristics, they could also be considered as promising candidates for PD diagnosis and treatment. Unfortunately, PD has become a global health concern, and a large number of its pathogenic processes are still unclear; thus, it is crucial to elucidate the ambiguous aspects of PD pathophysiology to improve the efficiency of diagnostic and therapeutic strategies. In line with this fact, the current review aims to highlight the interplay between circRNAs and PD pathogenesis, and then discusses the diagnostic and therapeutic potential of circRNAs in PD progression. This study will thus be the first of its kind reviewing the relationship between circRNAs and PD.

Circular RNA circTLK1 regulates dopaminergic neuron injury during Parkinson's disease by targeting miR-26a-5p／DAPK1

BACKGROUND

Parkinson's disease (PD) is a neurodegenerative disorder that is featured by the elevated loss of substantia nigra pars compacta dopaminergic neurons and the disruption of motor functions. Aberrant expression of circular RNAs (circRNAs) is correlated with neurodegenerative diseases. This study aimed to explore the role of circTLK1 in PD pathology.

METHODS

MPTP-stimulated in vivo PD mouse model and MPP+ and rotenone-induced in vitro PD model were established to investigate the function of circTLK1/miR-26a-5p/DAPK1 axis during dopaminergic neuron injury. The motor function of mice was evaluated by using the Rotarod test. Brain tissue damage was checked by hematoxylin and eosin, TdT-mediated dUTP-biotin nick end labeling. Cell viability, apoptosis, and cytotoxicity were evaluated by cell counting kit 8 (CCK-8), flow cytometry, and LDH activity. The interaction between circTLK1 and miR-26a-5p as well as miR-26a-5p and DAPK1 was detected by luciferase reporter assay.

RESULTS

The expression of circTLK1 was notably elevated in in vitro and in vivo PD models. Knockdown of circTLK1 significantly improved cell viability, suppressed apoptosis and cytotoxicity, whereas inhibition of miR-16a-5p and overexpression of DAPK1 abolished these effects. MiR-26a-5p acts as a sponge of DAPK1 to mediate circTLK1 functions. Luciferase reporter gene assay confirmed the interaction between circTLK1 and miR-26a-5p as well as miR-26a-5p and DAPK1.

CONCLUSION

Depletion of circTLK1 mitigates dopaminergic neuron injury in vitro and in vivo, via releasing miR-26a-5p to target DAPK1 expression. Targeting circTLK1 may contribute to improving PD therapy.

Circular RNAs: Emblematic Players of Neurogenesis and Neurodegeneration

In the fascinating landscape of non-coding RNAs (ncRNAs), circular RNAs (circRNAs) are peeping out as a new promising and appreciated class of molecules with great potential as diagnostic and prognostic biomarkers. They come from circularization of single-stranded RNA molecules covalently closed and generated through alternative mRNA splicing. Dismissed for many years, similar to aberrant splicing by-products, nowadays, their role has been regained. They are able to regulate the expression of linear mRNA transcripts at different levels acting as miRNA sponges, interacting with ribonucleoproteins or exerting a control on gene expression. On the other hand, being extremely conserved across phyla and stable, cell and tissue specific, mostly abundant than the linear RNAs, it is not surprising that they should have critical biological functions. Curiously, circRNAs are particularly expressed in brain and they build up during aging and age-related diseases. These extraordinary peculiarities make circRNAs potentially suitable as promising molecular biomarkers, especially of aging and neurodegenerative diseases. This review aims to explore new evidence on circRNAs, emphasizing their role in aging and pathogenesis of major neurodegenerative disorders, Alzheimer's disease, frontotemporal dementia, and Parkinson's diseases with a look toward their potential usefulness in biomarker searching.

Circular RNA detection identifies circPSEN1 alterations in brain specific to autosomal dominant Alzheimer's disease

BACKGROUND

Autosomal-dominant Alzheimer's disease (ADAD) is caused by pathogenic mutations in APP, PSEN1, and PSEN2, which usually lead to an early age at onset (< 65). Circular RNAs are a family of non-coding RNAs highly expressed in the nervous system and especially in synapses. We aimed to investigate differences in brain gene expression of linear and circular transcripts from the three ADAD genes in controls, sporadic AD, and ADAD.

METHODS

We obtained and sequenced RNA from brain cortex using standard protocols. Linear counts were obtained using the TOPMed pipeline; circular counts, using python package DCC. After stringent quality control (QC), we obtained the counts for PSEN1, PSEN2 and APP genes. Only circPSEN1 passed QC. We used DESeq2 to compare the counts across groups, correcting for biological and technical variables. Finally, we performed in-silico functional analyses using the Circular RNA interactome website and DIANA mirPath software.

RESULTS

Our results show significant differences in gene counts of circPSEN1 in ADAD individuals, when compared to sporadic AD and controls (ADAD = 21, AD = 253, Controls = 23-ADADvsCO: log2FC = 0.794, p = 1.63 × 10-04, ADADvsAD: log2FC = 0.602, p = 8.22 × 10-04). The high gene counts are contributed by two circPSEN1 species (hsa_circ_0008521 and hsa_circ_0003848). No significant differences were observed in linear PSEN1 gene expression between cases and controls, indicating that this finding is specific to the circular forms. In addition, the high circPSEN1 levels do not seem to be specific to PSEN1 mutation carriers; the counts are also elevated in APP and PSEN2 mutation carriers. In-silico functional analyses suggest that circPSEN1 is involved in several pathways such as axon guidance (p = 3.39 × 10-07), hippo signaling pathway (p = 7.38 × 10-07), lysine degradation (p = 2.48 × 10-05) or Wnt signaling pathway (p = 5.58 × 10-04) among other KEGG pathways. Additionally, circPSEN1 counts were able to discriminate ADAD from sporadic AD and controls with an AUC above 0.70.

CONCLUSIONS

Our findings show the differential expression of circPSEN1 is increased in ADAD. Given the biological function previously ascribed to circular RNAs and the results of our in-silico analyses, we hypothesize that this finding might be related to neuroinflammatory events that lead or that are caused by the accumulation of amyloid-beta.

Circular RNA circ_0070441 regulates MPP+-triggered neurotoxic effect in SH-SY5Y cells via miR-626/IRS2 axis

Circular RNAs (circRNAs) was suggested to play crucial regulatory roles in various human diseases, including Parkinson's disease (PD). This research aimed to investigate the function and potential mechanism of circ_0070441 in PD. MPP⁺ (1-methyl-4-phenylpyridinium)-treated SH-SY5Y cells was used as an in vitro cellular PD model. The expressions of circ_0070441, microRNA (miR)-626 and insulin receptor substrate 2 (IRS2) were measured by quantitative real-time polymerase chain reaction (RT-qPCR) or western blot. Cell Counting Kit-8 (CCK-8) assay, Cytotoxicity Detection Kit (Lactate Dehydrogenase), flow cytometry and Caspase-3 Assay Kit were used to detect cell viability, LDH release, cell apoptosis and caspase-3 activity, respectively. The levels of inflammation-related factors were detected by enzyme-linked immunosorbent assay (ELISA). The correlation among circ_0070441, miR-626 and IRS2 were confirmed by dual-luciferase reporter assay, RNA immunoprecipitation (RIP) assay and RNA pull-down assay. The levels of circ_0070441 and IRS2 were increased while miR-626 expression was decreased in MPP⁺-treated SH-SY5Y cells in dose- and time-dependent manners. Depletion of circ_0070441 alleviated MPP⁺-triggered neuronal damage by regulating cell apoptosis and inflammation. Circ_0070441 acted as a sponge for miR-626, and IRS2 was a target of miR-626. Besides, the neuroprotective effects of circ_0070441 knockdown or miR-626 overexpression were partly overturned by the suppression of miR-626 or IRS2 overexpression. Moreover, circ_0070441 upregulated IRS2 expression by interacting with miR-626. In summary, circ_0070441 aggravated MPP⁺-triggered neurotoxic effect in SH-SY5Y cells by regulating miR-626/IRS2 axis.

Insights into the multifaceted role of circular RNAs: implications for Parkinson's disease pathogenesis and diagnosis

Parkinson's disease (PD) is a complex, age-related, neurodegenerative disease whose etiology, pathology, and clinical manifestations remain incompletely understood. As a result, care focuses primarily on symptoms relief. Circular RNAs (circRNAs) are a large class of mostly noncoding RNAs that accumulate with aging in the brain and are increasingly shown to regulate all aspects of neuronal and glial development and function. They are generated by the spliceosome through the backsplicing of linear RNA. Although their biological role remains largely unknown, they have been shown to regulate transcription and splicing, act as decoys for microRNAs and RNA binding proteins, used as templates for translation, and serve as scaffolding platforms for signaling components. Considering that they are stable, diverse, and detectable in easily accessible biofluids, they are deemed promising biomarkers for diagnosing diseases. CircRNAs are differentially expressed in the brain of patients with PD, and growing evidence suggests that they regulate PD pathogenetic processes. Here, the biogenesis, expression, degradation, and detection of circRNAs, as well as their proposed functions, are reviewed. Thereafter, research linking circRNAs to PD-related processes, including aging, alpha-synuclein dysregulation, neuroinflammation, and oxidative stress is highlighted, followed by recent evidence for their use as prognostic and diagnostic biomarkers for PD.

Roles of Non-Coding RNAs as Novel Diagnostic Biomarkers in Parkinson's Disease

Parkinson's disease (PD) is the second most common neurodegenerative disorder, affecting 5%of the elderly population. Currently, the diagnosis of PD is mainly based on clinical features and no definitive diagnostic biomarkers have been identified. The discovery of biomarkers at the earliest stages of PD is of extreme interest. This review focuses on the current findings in the field of circulating non-coding RNAs in PD. We briefly describe the more established circulating biomarkers in PD and provide a more thorough review of non-coding RNAs, in particular microRNAs, long non-coding RNAs and circular RNAs, differentially expressed in PD, highlighting their potential for being considered as biomarkers for diagnosis. Together, these studies hold promise for the use of peripheral biomarkers for the diagnosis of PD.

The role of noncoding RNAs in Parkinson's disease: biomarkers and associations with pathogenic pathways

The discovery of various noncoding RNAs (ncRNAs) and their biological implications is a growing area in cell biology. Increasing evidence has revealed canonical and noncanonical functions of long and small ncRNAs, including microRNAs, long ncRNAs (lncRNAs), circular RNAs, PIWI-interacting RNAs, and tRNA-derived fragments. These ncRNAs have the ability to regulate gene expression and modify metabolic pathways. Thus, they may have important roles as diagnostic biomarkers or therapeutic targets in various diseases, including neurodegenerative disorders, especially Parkinson's disease. Recently, through diverse sequencing technologies and a wide variety of bioinformatic analytical tools, such as reverse transcriptase quantitative PCR, microarrays, next-generation sequencing and long-read sequencing, numerous ncRNAs have been shown to be associated with neurodegenerative disorders, including Parkinson's disease. In this review article, we will first introduce the biogenesis of different ncRNAs, including microRNAs, PIWI-interacting RNAs, circular RNAs, long noncoding RNAs, and tRNA-derived fragments. The pros and cons of the detection platforms of ncRNAs and the reproducibility of bioinformatic analytical tools will be discussed in the second part. Finally, the recent discovery of numerous PD-associated ncRNAs and their association with the diagnosis and pathophysiology of PD are reviewed, and microRNAs and long ncRNAs that are transported by exosomes in biofluids are particularly emphasized.

Circular RNA circZFPM2 promotes epithelial-mesenchymal transition in endometriosis by regulating miR-205-5p/ZEB1 signalling pathway

Endometriosis is a debilitating gynecological disease affecting millions of women worldwide, but its exact pathogenesis remains unclear. Circular RNAs (circRNAs) have been demonstrated to be important regulators in multiple diseases. Nonetheless, the potential regulatory mechanism of aberrant circRNA expression in endometriosis has been elusive. The up-regulated circZFPM2 in ectopic endometrial tissues was previously screened by circRNA high-throughput sequencing and was furtherly validated by quantitative real time reverse transcriptase polymerase chain reaction (RT-qPCR). Overexpression of circZFPM2 promoted the proliferation, migration, invasion, and epithelial-mesenchymal transition (EMT) in Ishikawa and End1/E6E7 cells, whereas silencing circZFPM2 produced the opposite effect. Luciferase reporter assays validated that circZFPM2 could directly target miR-205-5p and miR-205-5p target ZEB1. RT-qPCR results showed that miR-205-5p was underexpressed while ZEB1 was overexpressed in ectopic endometrial tissues compared with their expression in eutopic endometria and non-endometriosis control endometria. The expression level of miR-205-5p was inversely proportional and that of ZEB1 was directly proportional with the proliferative, migrative, and invasive ability of endometrial cells. Further in vitro investigation indicated that miR-205-5p could inhibit EMT by targeting ZEB1. Subsequent rescue experiments confirmed that circZFPM2 could induce EMT and promote cell proliferation, migration, and invasion cascades through the miR-205-5p /ZEB1 signaling pathway. Conclusively, circZFPM2 may present a promising biomarker in the diagnosis and treatment of endometriosis.

The Emerging Role of Circular RNAs in Alzheimer's Disease and Parkinson's Disease

Alzheimer’s disease (AD) and Parkinson’s disease (PD) are two neurodegenerative diseases (NDDs) commonly found in elderly patients that are difficult to diagnose and lack effective treatment. Currently, the available diagnostic methods for these two NDDs do not meet clinical diagnostic expectations. Circular RNAs (circRNAs) are a diverse group of endogenous non-coding RNAs (ncRNAs) found in eukaryotic cells. Emerging studies suggest that altered expression of circRNAs is involved in the pathological processes of NDDs. CircRNAs could also prove to be promising biomarkers for the early diagnosis of NDDs such as AD and PD. Growing evidence has improved our knowledge of the roles of circRNAs in NDDs, which may lead to new therapeutic approaches that target transcription for preventing neurodegeneration. In this review, we describe the formation mechanisms and functions of circRNAs as well as methods of validation. We also discuss the emerging role of circRNAs in the pathophysiology of AD and PD and their potential value as biomarkers and therapeutic targets for AD and PD in the future.

Circulating CircRNAs Panel Acts as a Biomarker for the Early Diagnosis and Severity of Parkinson's Disease

Parkinson’s disease (PD) is a chronic and progressive degenerative disease of the central nervous system. Degenerative neuropathy can occur in patients with PD even before typical clinical symptoms appear in the preclinical stage. Therefore, if the early diagnosis of degenerative diseases can be timely and the correlation with the disease progression can be explored, the disease progression will be slowed down and the quality of life of patients will be improved. In this study, the circRNA microarray was employed to screen the dysregulated circRNA in plasma samples of PD. Four circRNAs (circ_0085869, circ_0004381, circ_0017204, and circ_0090668) were obtained with increased levels in PD patients by cross comparison and preliminary verification in PD comparing with healthy controls. Further validation found the circRNA panel was consistent with the training set. The ROC curve also revealed a high diagnostic ability of circ_0004381 and circ_0017204 in predicting the early stage of PD from healthy controls. circ_0085869, circ_0004381, circ_0017204, and circ_0090668 also presented a high ability to distinguish the late stage of PD from early stage. In conclusion, circulating circRNA panel might be a potential fingerprint for predicting the early diagnosis of PD and may act as a biomarker for disease progression.

Genetic and Transcriptomic Biomarkers in Neurodegenerative Diseases: Current Situation and the Road Ahead

Neurodegenerative diseases are etiologically and clinically heterogeneous conditions, often reflecting a spectrum of disease rather than well-defined disorders. The underlying molecular complexity of these diseases has made the discovery and validation of useful biomarkers challenging. The search of characteristic genetic and transcriptomic indicators for preclinical disease diagnosis, prognosis, or subtyping is an area of ongoing effort and interest. The next generation of biomarker studies holds promise by implementing meaningful longitudinal and multi-modal approaches in large scale biobank and healthcare system scale datasets. This work will only be possible in an open science framework. This review summarizes the current state of genetic and transcriptomic biomarkers in Parkinson's disease, Alzheimer's disease, and amyotrophic lateral sclerosis, providing a comprehensive landscape of recent literature and future directions.