MicroRNA-205 regulates the expression of Parkinson's disease-related leucine-rich repeat kinase 2 protein

A comprehensive profile of the tilapia (Oreochromis niloticus) circular RNA and circRNA-miRNA network in the pathogenesis of meningoencephalitis of teleosts

The pathogenesis of tilapia meningoencephalitis is still unclear, where the involvement of circRNA is considered for its active role as a "miRNA sponge". Therefore, we aimed to investigate the profile of circRNA in tilapia meningoencephalitis further by constructing the circRNA-miRNA network for in-depth mechanism exploration. Briefly, a nile tilapia model of meningitis was established by injecting Streptococcus agalactiae (1.0 × 10⁷ cfu per mL) and we evaluated the infected tilapia brain for the expression profile of circRNAs, their potential functions and their correlation with genes involved in inflammatory pathways. A total of 11 263 circRNAs were identified from RNA sequencing (RNA-seq) data in nile tilapia (Oreochromis niloticus), a commercially important fish in China and East Asia. GO and KEGG analyses revealed that the biological functions of genes hosting the circRNAs were enriched in the progression of metabolism and binding. Notably, we found that 99% circRNAs in tilapia had abundant miRNA-binding sites and a total of 2136 of the identified circRNAs had two to six miRNA-binding sites. Six circRNAs were validated by qRT-PCR and the final circRNA-miRNA network was constructed. This is the first report of comprehensive identification of O. niloticus circRNAs being differentially regulated in the brain in normal conditions relating to S. agalactiae infection. This work will shed novel light on gene expression mechanisms under disease conditions and may identify circRNAs as new biomarkers for meningoencephalitis and neurodegenerative disorders.

Small Non-coding RNAs: New Class of Biomarkers and Potential Therapeutic Targets in Neurodegenerative Disease

Neurodegenerative diseases (NDs) are becoming increasingly prevalent in the world, with an aging population. In the last few decades, due to the devastating nature of these diseases, the research of biomarkers has become crucial to enable adequate treatments and to monitor the progress of disease. Currently, gene mutations, CSF and blood protein markers together with the neuroimaging techniques are the most used diagnostic approaches. However, despite the efforts in the research, conflicting data still exist, highlighting the need to explore new classes of biomarkers, particularly at early stages. Small non-coding RNAs (MicroRNA, Small nuclear RNA, Small nucleolar RNA, tRNA derived small RNA and Piwi-interacting RNA) can be considered a "relatively" new class of molecule that have already proved to be differentially regulated in many NDs, hence they represent a new potential class of biomarkers to be explored. In addition, understanding their involvement in disease development could depict the underlying pathogenesis of particular NDs, so novel treatment methods that act earlier in disease progression can be developed. This review aims to describe the involvement of small non-coding RNAs as biomarkers of NDs and their potential role in future clinical applications.

Involvement of aberrant regulation of epigenetic mechanisms in the pathogenesis of Parkinson's disease and epigenetic-based therapies

Parkinson's disease (PD) is known as a progressive neurodegenerative disorder associated with the reduction of dopamine-secreting neurons and the formation of Lewy bodies in the substantia nigra and basal ganglia routes. Aging, as well as environmental and genetic factors, are considered as disease risk factors that can make PD as a complex one. Epigenetics means studying heritable changes in gene expression or function, without altering the underlying DNA sequence. Multiple studies have shown the association of epigenetic variations with onset or progression of various types of diseases. DNA methylation, posttranslational modifications of histones and presence of microRNA (miRNA) are among epigenetic processes involved in regulating pathways related to the development of PD. Unlike genetic mutations, most epigenetic variations may be reversible or preventable. Therefore, the return of aberrant epigenetic events in different cells is a growing therapeutic approach to treatment or prevention. Currently, there are several methods for treating PD patients, the most important of which are drug therapies. However, detection of genes and epigenetic mechanisms involved in the disease can develop appropriate diagnosis and treatment of the disease before the onset of disabilities and resulting complications. The main purpose of this study was to review the most important epigenetic molecular mechanisms, epigenetic variations in PD, and epigenetic-based therapies.

Nucleic Acid-Based Therapeutics for Parkinson's Disease

Parkinson's disease (PD) is a progressive neurodegenerative disorder that is diagnosed largely on clinical grounds due to characteristic motor manifestations that result from the loss of nigrostriatal dopaminergic neurons. While traditional pharmacological approaches to enhance dopamine levels, such as with L-dopa, can be very effective initially, the chronic use of this dopamine precursor is commonly plagued with motor response complications. Additionally, with advancing disease, non-motor manifestations emerge, including psychosis and dementia that compound patient disability. The pathology includes hallmark intraneuronal inclusions known as Lewy bodies and Lewy neurites that contain fibrillar α-synuclein aggregates. Evidence has also accumulated that these aggregates can propagate across synaptically connected brain regions, a phenomenon that can explain the progressive nature of the disease and the emergence of additional symptoms over time. The level of α-synuclein is believed to play a critical role in its fibrillization and aggregation. Accordingly, nucleic acid-based therapeutics for PD include strategies to deliver dopamine biosynthetic enzymes to boost dopamine production or modulate the basal ganglia circuitry in order to improve motor symptoms. Delivery of trophic factors that might enhance the survival of dopamine neurons is another strategy that has been attempted. These gene therapy approaches utilize viral vectors and are delivered stereotaxically in the brain. Alternative disease-modifying strategies focus on downregulating the expression of the α-synuclein gene using various techniques, including modified antisense oligonucleotides, short hairpin RNA, short interfering RNA, and microRNA. The latter approaches also have implications for dementia with Lewy bodies. Other PD genes can also be targeted using nucleic acids. In this review, we detail these various strategies that are still experimental, and discuss the challenges and opportunities of nucleic acid-based therapeutics for PD.

Mesenchymal Stem Cells-derived Exosomes: A New Possible Therapeutic Strategy for Parkinson's Disease?

Parkinson’s disease (PD) is the second most prevalent neurodegenerative disorder worldwide. Clinically, it is characterized by severe motor complications caused by a progressive degeneration of dopaminergic neurons (DAn) and dopamine loss. Current treatment is focused on mitigating the symptoms through administration of levodopa, rather than on preventing DAn damage. Therefore, the use and development of neuroprotective/disease-modifying strategies is an absolute need, which can lead to promising gains on PD translational research. Mesenchymal stem cells (MSCs)–derived exosomes have been proposed as a promising therapeutic tool, since it has been demonstrated that they can act as biological nanoparticles with beneficial effects in different pathological conditions, including PD. Thus, considering their potential protective action in lesioned sites, MSCs-derived exosomes might also be active modulators of the neuroregeneration processes, opening a door for their future use as therapeutical strategies in human clinical trials. Therefore, in this review, we analyze the current understanding of MSCs-derived exosomes as a new possible therapeutic strategy for PD, by providing an overview about the potential role of miRNAs in the cellular and molecular basis of PD.

Lrrk promotes tau neurotoxicity through dysregulation of actin and mitochondrial dynamics

Mutations in leucine-rich repeat kinase 2 (LRRK2) are the most common cause of familial Parkinson disease. Genetics and neuropathology link Parkinson disease with the microtubule-binding protein tau, but the mechanism of action of LRRK2 mutations and the molecular connection between tau and Parkinson disease are unclear. Here, we investigate the interaction of LRRK and tau in Drosophila and mouse models of tauopathy. We find that either increasing or decreasing the level of fly Lrrk enhances tau neurotoxicity, which is further exacerbated by expressing Lrrk with dominantly acting Parkinson disease-associated mutations. At the cellular level, altering Lrrk expression promotes tau neurotoxicity via excess stabilization of filamentous actin (F-actin) and subsequent mislocalization of the critical mitochondrial fission protein dynamin-1-like protein (Drp1). Biochemically, monomeric LRRK2 exhibits actin-severing activity, which is reduced as increasing concentrations of wild-type LRRK2, or expression of mutant forms of LRRK2 promote oligomerization of the protein. Overall, our findings provide a potential mechanistic basis for a dominant negative mechanism in LRRK2-mediated Parkinson disease, suggest a common molecular pathway with other familial forms of Parkinson disease linked to abnormalities of mitochondrial dynamics and quality control, and raise the possibility of new therapeutic approaches to Parkinson disease and related disorders.

The role of LRRK2 in cytoskeletal dynamics

Leucine-rich repeat kinase 2 (LRRK2), a complex kinase/GTPase mutated in Parkinson's disease, has been shown to physically and functionally interact with cytoskeletal-related components in different brain cells. Neurons greatly rely on a functional cytoskeleton for many homeostatic processes such as local and long-distance vesicle transport, synaptic plasticity, and dendrites/axons growth and remodeling. Here, we will review the available data linking LRRK2 and the cytoskeleton, and discuss how this may be functionally relevant for the well-established roles of LRRK2 in intracellular trafficking pathways and outgrowth of neuronal processes in health and disease conditions.

Prior Knowledge Driven Joint NMF Algorithm for ceRNA Co-Module Identification

MRNA and lncRNA serve as a type of endogenous RNA in cell, which can competitively bind to the same miRNA through miRNA response elements (MREs), thereby regulating their respective expression levels, playing an important role in post-transcriptional regulation, and regulating the progress of tumors. The proposed competing endogenous RNA (ceRNA) hypothesis provides novel clues for the occurrence and development of tumors, but the integrative analysis methods of diverse RNA data are significantly limited. In order to find out the relationship among miRNA, mRNA and lncRNA, the previous studies only used individual dataset as seeds to search two other related data in the database to construct ceRNA network, but it was difficult to identify the synchronized effects from multiple regulatory levels. Here, we developed the joint matrix factorization method integrating prior knowledge to map the three types of RNA data of lung cancer to the common coordinate system and construct the ceRNA network corresponding to the common module. The results show that more than 90% of the modules are closely related to cancer, including lung cancer. Furthermore, the resulting ceRNA network not only accurately excavates the known correlation of the three types of RNA molecular, but also further discovers the potential biological associations of them. Our work provides support and foundation for future biological validation how competitive relationships of multiple RNAs affects the development of tumors.

The Parkinson's disease gene product DJ-1 modulates miR-221 to promote neuronal survival against oxidative stress

DJ-1 is a highly conserved protein that protects neurons against oxidative stress and whose loss of function mutations are linked to recessively inherited Parkinson's disease (PD). While a number of signaling pathways have been shown to be regulated by DJ-1, its role in controlling cell survival through non-coding RNAs remains poorly understood. Here, using a microarray screen, we found that knocking down DJ-1 in human neuroblastoma cells results in down-regulation of microRNA-221 (miR-221). This is one of the most abundant miRNAs in the human brain and promotes neurite outgrowth and neuronal differentiation. Yet the molecular mechanism linking miR-221 to genetic forms of PD has not been studied. Consistent with the microarray data, miR-221 expression is also decreased in DJ-1-/- mouse brains. Re-introduction of wild-type DJ-1, but not its PD-linked pathogenic M26I mutant, restores miR-221 expression. Notably, over-expression of miR-221 is protective against 1-methyl-4-phenylpyridinium (MPP+)-induced cell death, while inhibition of endogenous miR-221 sensitizes cells to this toxin. Additionally, miR-221 down-regulates the expression of several pro-apoptotic proteins at basal conditions and prevents oxidative stress-induced up-regulation of bcl-2-like protein 11 (BIM). Accordingly, miR-221 protects differentiated DJ-1 knock-down ReNcell VM human dopaminergic neuronal cells from MPP+-induced neurite retraction and cell death. DJ-1 is a known activator of the mitogen-activated protein kinase (MAPK)/extracellular-regulated kinase (ERK) pathway and may modulate miR-221 levels in part through this pathway. We found that inhibiting ERK1/2 decreases miR-221 levels, whereas over-expressing ERK1 in DJ-1 knock-down cells increases miR-221 levels. These findings point to a new cytoprotective mechanism by which DJ-1 may increase miR-221 expression through the MAPK/ERK pathway, subsequently leading to repression of apoptotic molecules. The inability of a pathogenic DJ-1 mutant to modulate miR-221 further supports the relevance of this mechanism in neuronal health and its failure in DJ-1-linked PD.

Epigenetic Study in Parkinson's Disease: A Pilot Analysis of DNA Methylation in Candidate Genes in Brain

Efforts have been made to understand the pathophysiology of Parkinson’s disease (PD). A significant number of studies have focused on genetics, despite the fact that the described pathogenic mutations have been observed only in around 10% of patients; this observation supports the fact that PD is a multifactorial disorder. Lately, differences in miRNA expression, histone modification, and DNA methylation levels have been described, highlighting the importance of epigenetic factors in PD etiology. Taking all this into consideration, we hypothesized that an alteration in the level of methylation in PD-related genes could be related to disease pathogenesis, possibly due to alterations in gene expression. After analysing promoter regions of five PD-related genes in three brain regions by pyrosequencing, we observed some differences in DNA methylation levels (hypo and hypermethylation) in substantia nigra in some CpG dinucleotides that, possibly through an alteration in Sp1 binding, could alter their expression.

Elevated microRNA-520d-5p in the serum of patients with Parkinson's disease, possibly through regulation of cereloplasmin expression

Iron metabolism dysfunction and redox-active iron-induced oxidative stress in the brain may contribute to the pathogenesis of Parkinson's disease. We have previously demonstrated that reduced serum ceruloplasmin level exacerbates nigral iron deposition in Parkinson's disease, although the underlying cause of the low serum ceruloplasmin level in Parkinson's disease remains unknown. Fluorescent quantitative real-time polymerase chain reaction analysis revealed that patients with Parkinson's disease had higher serum levels of microRNA (miR)-520d-5p than controls (p = 0.0011). Patients with Alzheimer's disease or multiple system atrophy did not have significantly elevated miR-520d-5p levels. Expression of miR-520d-5p did not correlate with disease severity or the motor phenotype of Parkinson's disease. Luciferase assays confirmed that miR-520d-5p was associated with ceruloplasmin gene expression, as predicted by the TargetScan tool and miRBase. In vitro experiments showed that miR-520d-5p reduced ceruloplasmin gene expression in the U251 astrocyte cell line. Our data suggest that miR-520d-5p may be a potential regulator of ceruloplasmin gene expression in vitro.

MicroRNAs to differentiate Parkinsonian disorders: Advances in biomarkers and therapeutics

Parkinsonian disorders are a set of progressive neurodegenerative movement disorders characterized by rigidity, tremor, bradykinesia, postural instability and their distinction has significant implications in terms of management and prognosis. Parkinson's disease (PD) is the most common among them. Its clinical diagnosis is challenging and, it can be misdiagnosed in the early stages. Multiple system atrophy and progressive supranuclear palsy are the close mimickers in early stages, due to overlapping clinical features. MicroRNAs are a class of stable non-coding small RNA molecules implicated in post-transcriptional gene regulation. Current studies propose that miRNAs play an essential role in the pathobiology of multiple neurodegenerative disorders including Parkinsonism, and they seem to be one of the reasonably available methods to aid in the differential diagnosis between PD and related disorders. MicroRNA-based diagnostic biomarkers and therapeutics are a powerful tool to understand and explore the function of the pathogenic gene/s, their mechanism in the disease pathobiology, and to validate drug targets. In this review, we emphasize on the recent developments in the usage of miRNAs as diagnostic biomarkers to identify PD and to differentiate it from atypical parkinsonian conditions, their role in disease pathogenesis, and their possible utility in the therapy of these disorders.

Neuroepigenetics of Aging and Age-Related Neurodegenerative Disorders

Neurodegenerative diseases are complex, progressive disorders and affect millions of people worldwide, contributing significantly to the global burden of disease. In recent years, research has begun to investigate epigenetic mechanisms for a potential role in disease etiology. In this chapter, we describe the current state of play for epigenetic research into neurodegenerative disorders including Alzheimer's disease, Parkinson's disease and Huntington's disease. We focus on the recent evidence for a potential role of DNA modifications, histone modifications and non-coding RNA in the etiology of these disorders. Finally, we discuss how new technological and bioinformatics advances in the field of epigenetics could further progress our understanding about the underlying mechanisms of neurodegenerative diseases.

Regulation of MicroRNAs-Mediated Autophagic Flux: A New Regulatory Avenue for Neurodegenerative Diseases With Focus on Prion Diseases

Prion diseases are fatal neurological disorders affecting various mammalian species including humans. Lack of proper diagnostic tools and non-availability of therapeutic remedies are hindering the control strategies for prion diseases. MicroRNAs (miRNAs) are abundant endogenous short non-coding essential RNA molecules that negatively regulate the target genes after transcription. Several biological processes depend on miRNAs, and altered profiles of these miRNAs are potential biomarkers for various neurodegenerative diseases, including prion diseases. Autophagic flux degrades the misfolded prion proteins to reduce chronic endoplasmic reticulum stress and enhance cell survival. Recent evidence suggests that specific miRNAs target and regulate the autophagic mechanism, which is critical for alleviating cellular stress. miRNAs-mediated regulation of these specific proteins involved in the autophagy represents a new target with highly significant therapeutic prospects. Here, we will briefly describe the biology of miRNAs, the use of miRNAs as potential biomarkers with their credibility, the regulatory mechanism of miRNAs in major neurodegenerative diseases such as Alzheimer’s, Parkinson’s, and prion diseases, degradation pathways for aggregated prion proteins, the role of autophagy in prion diseases. Finally, we will discuss the miRNAs-modulated autophagic flux in neurodegenerative diseases and employ them as potential therapeutic intervention strategy in prion diseases.

MiR-19b alleviates MPP+-induced neuronal cytotoxicity via targeting the HAPLN4/MAPK pathway in SH-SY5Y cells

Background: miR-19b has been reported to be involved in nervous system disease including Parkinson's disease (PD). However its molecular basis has not been exhaustively elucidated. Materials and Methods: SH-SY5Y cells were treated with 1-methyl-4-phenylpyridinium (MPP+) to construct PD model in vitro. RT-qPCR was performed to detect the expression of miR-19b and proteoglycan link protein 4 (HAPLN4) mRNA. Western blot analysis was used to measure the level of HAPLN4 and mitogen activated protein kinase (MAPK)-related protein. Cell viability and apoptosis were determined by MTT and flow cytometry. Commercial ELISA kits were applied to quantify caspase-3 activity, lactate dehydrogenase (LDH), reactive oxygen species (ROS), superoxide dismutase (SOD), tumor necrosis factor-α (TNF-α) and interleukin-1 beta (IL-1β). Dual-luciferase reporter assay was applied to assess the relationship between miR-19b and HAPLN4. Results: miR-19b was downregulated in MPP+-induced SH-SY5Y cells. miR-19b overexpression reversed MPP+-induced suppression of cell viability and promotion of cell apoptosis in SH-SY5Y cells. Moreover, miR-19b alleviated MPP+-induced cytotoxicity of SH-SY5Y cells, embodied by the decrease of LDH release, caspase-3 activity, ROS expression, TNF-α and IL-1β secretion, as well as the increase of SOD level. HAPLN4 was identified as a direct target of miR-19b and miR-19b repressed HAPLN4 expression in a post-transcriptional manner. In addition, miR-19b-mediated anti-apoptosis effect was abated following HAPLN4 expression restoration in MPP+-induced SH-SY5Y cells. Furthermore, MAPK signaling participated in miR-19b/HAPLN4-mediated regulation in MPP+-treated SH-SY5Y cells. Conclusion: the neuroprotective effect of miR-19b might be mediated by HAPLN4/MAPK pathway in SH-SY5Y cells.

MicroRNA expressing profiles in A53T mutant alpha-synuclein transgenic mice and Parkinsonian

α-synuclein gene mutations can cause α-synuclein protein aggregation in the midbrain of Parkinson's disease (PD) patients. MicroRNAs (miRNAs) play a key role in the metabolism of α-synuclein but the mechanism involved in synucleinopathy remains unclear. In this study, we investigated the miRNA profiles in A53T-α-synuclein transgenic mice and analyzed the candidate miRNAs in the cerebrospinal fluid (CSF) of PD patients. The 12-month A53T-transgenic mouse displayed hyperactive movement and anxiolytic-like behaviors with α-synuclein aggregation in midbrain. A total of 317,759 total and 289,207 unique small RNA sequences in the midbrain of mice were identified by high-throughput deep sequencing. We found 644 miRNAs were significantly changed in the transgenic mice. Based on the conserved characteristic of miRNAs, we selected 11 candidates from the 40 remarkably expressed miRNAs and explored their expression in 44 CSF samples collected from PD patients. The results revealed that 11 microRNAs were differently expressed in CSF, emphatically as miR-144-5p, miR-200a-3p and miR-542-3p, which were dramatically up-regulated in both A53T-transgenic mice and PD patients, and had a helpful accuracy for the PD prediction. The ordered logistic regression analysis showed that the severity of PD has strong correlation with an up-expression of miR-144-5p, miR-200a-3p and miR-542-3p in CSF. Taken together, our data suggested that miRNAs in CSF, such as miR-144-5p, miR-200a-3p and miR-542-3p, may be useful to the PD diagnosis as potential biomarkers.

lncRNA MALAT1/miR-205-5p axis regulates MPP+-induced cell apoptosis in MN9D cells by directly targeting LRRK2

Metastasis-associated lung adenocarcinoma transcript 1 (MALAT1), as a long chain non-coding RNA (lncRNA), has been reported to be upregulated in Parkinson's disease (PD). However, the mechanisms underlying this process remain unknown. Hence, to investigate the role of MALAT1 in PD, N-methyl-4-phenylpyridinium (MPP⁺) was used to induce PD in vitro in the MN9D dopaminergic neuronal cell line and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) was used to induce PD in vivo in C57BL/6 mice. Quantitative Real-Time PCR (qRT-PCR) and western blot assay showed that the expression levels of MALAT1 and leucine-rich repeat kinase (LRRK2) were increased, and that of miR-205-5p was decreased in the midbrains of mice in which PD was induced by MPTP. MALAT1 suppressed the expression of miR-205-5p in MN9D cells. The results of luciferase reporter assay indicated that LRRK2 was a direct target of miR-205-5p. Transfection with the miR-205-5p mimics decreased, whereas transfection with miR-205-5p inhibitor increased the expression levels of LRRK2 mRNA and protein. The cell counting kit-8 (CCK-8) and flow cytometry assays showed that overexpression of LRRK2 reduced the viability and promoted apoptosis in MN9D cells treated with MPP⁺. MALAT1 knockdown exerted a protective effect on the viability and apoptosis of MN9D cells treated with MPP⁺, which was abrogated by LRRK2 overexpression and miR-205-5p inhibition. Our study demonstrates that the MALAT1/miR-205-5p axis regulates MPP⁺-induced apoptosis in MN9D cells by targeting LRRK2, thereby improving our understanding of the molecular pathogenesis of PD.

microRNAs in Neurodegeneration: Current Findings and Potential Impacts

Significant advancements have been made in unraveling and understanding the non-coding elements of the human genome. New insights into the structure and function of noncoding RNAs have emerged. Their relevance in the context of both physiological cellular homeostasis and human diseases is getting appreciated. As a result, exploration of noncoding RNAs, in particular microRNAs (miRs), as therapeutic agents or targets of therapeutic strategies is under way. This review summarizes and discusses in depth the current literature on the role of miRs in neurodegenerative diseases.

AGE-induced neuronal cell death is enhanced in G2019S LRRK2 mutation with increased RAGE expression

Background

Leucine-rich repeat kinase 2 (LRRK2) mutations represent the most common genetic cause of sporadic and familial Parkinson’s disease (PD). Especially, LRRK2 G2019S missense mutation has been identified as the most prevalent genetic cause in the late-onset PD. Advanced glycation end products (AGEs) are produced in high amounts in diabetes and diverse aging-related disorders, such as cardiovascular disease, renal disease, and neurological disease. AGEs trigger intracellular signaling pathway associated with oxidative stress and inflammation as well as cell death. RAGE, receptor of AGEs, is activated by interaction with AGEs and mediates AGE-induced cytotoxicity. Whether AGE and RAGE are involved in the pathogenesis of mutant LRRK2 is unknown.

Methods

Using cell lines transfected with mutant LRRK2 as well as primary neuronal cultures derived from LRRK2 wild-type (WT) and G2019S transgenic mice, we compared the impact of AGE treatment on the survival of control and mutant cells by immunostaining. We also examined the levels of RAGE proteins in the brains of transgenic mice and PD patients by western blots.

Results

We show that LRRK2 G2019S mutant-expressing neurons were more sensitive to AGE-induced cell death compared to controls. Furthermore, we found that the levels of RAGE proteins were upregulated in LRRK2 G2019S mutant cells.

Conclusions

These data suggest that enhanced AGE-RAGE interaction contributes to LRRK2 G2019S mutation-mediated progressive neuronal loss in PD.

Integrated Analysis and Identification of Novel Biomarkers in Parkinson's Disease

Parkinson's disease (PD) is a quite common neurodegenerative disorder with a prevalence of approximately 1:800-1,000 in subjects over 60 years old. The aim of our study was to determine the candidate target genes in PD through meta-analysis of multiple gene expression arrays datasets and to further combine mRNA and miRNA expression analyses to identify more convincing biological targets and their regulatory factors. Six included datasets were obtained from the Gene Expression Omnibus database by systematical search, including five mRNA datasets (150 substantia nigra samples in total) and one miRNA dataset containing 32 peripheral blood samples. A chip meta-analysis of five microarray data was conducted by using the metaDE package and 94 differentially expressed (DE) mRNAs were comprehensively obtained. And 19 deregulated DE miRNAs were obtained through the analysis of one miRNAs dataset by Qlucore Omics Explorer software. An interaction network formed by DE mRNAs, DE miRNAs, and important pathways was discovered after we analyzed the functional enrichment, protein-protein interactions, and miRNA targetome prediction analysis. In conclusion, this study suggested that five significantly downregulated mRNAs (MAPK8, CDC42, NDUFS1, COX4I1, and SDHC) and three significantly downregulated miRNAs (miR-126-5p, miR-19-3p, and miR-29a-3p) were potentially useful diagnostic markers in clinic, and lipid metabolism (especially non-alcoholic fatty liver disease pathway) and mitochondrial dysregulation may be the keys to biochemically detectable molecular defects. However, the role of these new biomarkers and molecular mechanisms in PD requires further experiments in vivo and in vitro and further clinical evidence.

microRNAs in Parkinson's Disease: From Pathogenesis to Novel Diagnostic and Therapeutic Approaches

Parkinson’s disease (PD) is the most prevalent central nervous system (CNS) movement disorder and the second most common neurodegenerative disease overall. PD is characterized by the progressive loss of dopaminergic (DAergic) neurons in the substantia nigra pars compacta (SNpc) within the midbrain, accumulation of alpha-synuclein (α-SYN) in Lewy bodies and neurites and excessive neuroinflammation. The neurodegenerative processes typically begin decades before the appearance of clinical symptoms. Therefore, the diagnosis is achievable only when the majority of the relevant DAergic neurons have already died and for that reason available treatments are only palliative at best. The causes and mechanism(s) of this devastating disease are ill-defined but complex interactions between genetic susceptibility and environmental factors are considered major contributors to the etiology of PD. In addition to the role of classical gene mutations in PD, the importance of regulatory elements modulating gene expression has been increasingly recognized. One example is the critical role played by microRNAs (miRNAs) in the development and homeostasis of distinct populations of neurons within the CNS and, in particular, in the context of PD. Recent reports demonstrate how distinct miRNAs are involved in the regulation of PD genes, whereas profiling approaches are unveiling variations in the abundance of certain miRNAs possibly relevant either to the onset or to the progression of the disease. In this review, we provide an overview of the miRNAs recently found to be implicated in PD etiology, with particular focus on their potential relevance as PD biomarkers, as well as their possible use in PD targeted therapy.

miR-124-3p attenuates MPP+-induced neuronal injury by targeting STAT3 in SH-SY5Y cells

Ample evidence has demonstrated the involvement of microRNAs in Parkinson's disease pathogenesis. miR-124-3p was reported to be able to improve neural functional recovery. However, the underlying mechanism of miR-124-3p in Parkinson's disease progression was not well established. This study was designed to investigate the role of miR-124-3p in methyl phenyl pyridinium iodide (MPP)+-induced SH-SY5Y cells, an in vitro Parkinson's disease model. It is observed that miR-124-3p expression was decreased, and STAT3 expression was increased in MPP+-induced SH-SY5Y cells. miR-124-3p overexpression attenuated MPP+-induced neuronal injury, displayed as increased cell viability and superoxide dismutase activities, as well as reduced cell apoptosis, Caspase-3 activity, lactate dehydrogenase activity, inflammatory factors TNF-α, and IL-1β levels and reactive oxygen species generation. Moreover, STAT3 was confirmed to be a miR-124-3p target. Restored STAT3 expression reversed miR-124-3p-induced neuroprotective effects against MPP+-mediated neuronal injury. These data demonstrated that miR-124-3p contributed to neuroprotective effects in MPP+-induced Parkinson's disease cell model by targeting STAT3. Impact statement PD affects millions of people in the world, causing uncontrolled tremors. MicroRNAs, a class of endogenous single-stranded non-coding transcript with approximately 22 nucleotides, could bind to the 3″ UTR of their targets. The functional action of miR-124-3p in PD was not fully elucidated. Our study found that ectopic expression miR-124-3p attenuated MPP+-induced injury in PD model in vitro by suppressing neurotoxicity, neuronal apoptosis, neuroinflammation, and oxidative stress. Moreover, we validated that miR-124-3p could bind to STAT3 mediating the neuroprotective effect of miR-124-3p. We believe this study will be interesting for readers of this area.

Elevated LRRK2 autophosphorylation in brain-derived and peripheral exosomes in LRRK2 mutation carriers

Missense mutations in the leucine-rich repeat kinase 2 (LRRK2) gene can cause late-onset Parkinson disease (PD). LRRK2 mutations increase LRRK2 kinase activities that may increase levels of LRRK2 autophosphorylation at serine 1292 (pS1292) and neurotoxicity in model systems. pS1292-LRRK2 protein can be packaged into exosomes and measured in biobanked urine. Herein we provide evidence that pS1292-LRRK2 protein is robustly expressed in cerebral spinal fluid (CSF) exosomes. In a novel cohort of Norwegian subjects with and without the G2019S-LRRK2 mutation, with and without PD, we quantified levels of pS1292-LRRK2, total LRRK2, and other exosome proteins in urine from 132 subjects and in CSF from 82 subjects. CSF and urine were collected from the same morning clinic visit in 55 of the participants. We found that total LRRK2 protein concentration was similar in exosomes purified from either CSF or urine but the levels did not correlate. pS1292-LRRK2 levels were higher in urinary exosomes from male and female subjects with a LRRK2 mutation. Male LRRK2 mutation carriers without PD had intermediate pS1292-LRRK2 levels compared to male carriers with PD and controls. However, female LRRK2 mutation carriers without PD had the same pS1292-LRRK2 levels compared to female carriers with PD. pS1292-LRRK2 levels in CSF exosomes were near saturated in most subjects, ten-fold higher on average than pS1292-LRRK2 levels in urinary exosomes, irrespective of LRRK2 mutation status or PD diagnosis. These results provide insights into the effects of LRRK2 mutations in both the periphery and brain in a well-characterized clinical population and show that LRRK2 protein in brain exosomes may be much more active than in the periphery in most subjects.

MicroRNAs and Target Genes As Biomarkers for the Diagnosis of Early Onset of Parkinson Disease

Among the neurodegenerative disorders, Parkinson's disease (PD) ranks as the second most common disorder with a higher prevalence in individuals aged over 60 years old. Younger individuals may also be affected with PD which is known as early onset PD (EOPD). Despite similarities between the characteristics of EOPD and late onset PD (LODP), EOPD patients experience much longer disease manifestations and poorer quality of life. Although some individuals are more prone to have EOPD due to certain genetic alterations, the molecular mechanisms that differentiate between EOPD and LOPD remains unclear. Recent findings in PD patients revealed that there were differences in the genetic profiles of PD patients compared to healthy controls, as well as between EOPD and LOPD patients. There were variants identified that correlated with the decline of cognitive and motor symptoms as well as non-motor symptoms in PD. There were also specific microRNAs that correlated with PD progression, and since microRNAs have been shown to be involved in the maintenance of neuronal development, mitochondrial dysfunction and oxidative stress, there is a strong possibility that these microRNAs can be potentially used to differentiate between subsets of PD patients. PD is mainly diagnosed at the late stage, when almost majority of the dopaminergic neurons are lost. Therefore, identification of molecular biomarkers for early detection of PD is important. Given that miRNAs are crucial in controlling the gene expression, these regulatory microRNAs and their target genes could be used as biomarkers for early diagnosis of PD. In this article, we discussed the genes involved and their regulatory miRNAs, regarding their roles in PD progression, based on the findings of significantly altered microRNAs in EOPD studies. We also discussed the potential of these miRNAs as molecular biomarkers for early diagnosis.

Let's make microglia great again in neurodegenerative disorders

All of the common neurodegenerative disorders-Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis and prion diseases-are characterized by accumulation of misfolded proteins that trigger activation of microglia; brain-resident mononuclear phagocytes. This chronic form of neuroinflammation is earmarked by increased release of myriad cytokines and chemokines in patient brains and biofluids. Microglial phagocytosis is compromised early in the disease process, obfuscating clearance of abnormal proteins. This review identifies immune pathologies shared by the major neurodegenerative disorders. The overarching concept is that aberrant innate immune pathways can be targeted for return to homeostasis in hopes of coaxing microglia into clearing neurotoxic misfolded proteins.

Tiny But Mighty: Promising Roles of MicroRNAs in the Diagnosis and Treatment of Parkinson's Disease

Parkinson's disease (PD) is the second most common age-related neurodegenerative disorder after Alzheimer's disease. To date, the clinical diagnosis of PD is primarily based on the late onset of motor impairments. Unfortunately, at this stage, most of the dopaminergic neurons may have already been lost, leading to the limited clinical benefits of current therapeutics. Therefore, early identification of PD, especially at the prodromal stage, is still a main challenge in the diagnosis and management of this disease. Recently, microRNAs (miRNAs) in cerebrospinal fluid or peripheral blood have been proposed as putative biomarkers to assist in PD diagnosis and therapy. In this review, we systematically summarize the changes of miRNA expression profiles in PD patients, and highlight their putative roles in the diagnosis and treatment of this devastating disease.

Loss of MicroRNA-7 Regulation Leads to α-Synuclein Accumulation and Dopaminergic Neuronal Loss In Vivo

Abnormal alpha-synuclein (α-synuclein) expression and aggregation is a key characteristic of Parkinson's disease (PD). However, the exact mechanism(s) linking α-synuclein to the other central feature of PD, dopaminergic neuron loss, remains unclear. Therefore, improved cell and in vivo models are needed to investigate the role of α-synuclein in dopaminergic neuron loss. MicroRNA-7 (miR-7) regulates α-synuclein expression by binding to the 3' UTR of the Synuclein Alpha Non A4 Component of Amyloid Precursor (SNCA) gene and inhibiting its translation. We show that miR-7 is decreased in the substantia nigra of patients with PD and, therefore, may play an essential role in the regulation of α-synuclein expression. Furthermore, we have found that lentiviral-mediated expression of miR-7 complementary binding sites to stably induce a loss of miR-7 function results in an increase in α-synuclein expression in vitro and in vivo. We have also shown that depletion of miR-7 using a miR-decoy produces a loss of nigral dopaminergic neurons accompanied by a reduction of striatal dopamine content. These data suggest that miR-7 has an important role in the regulation of α-synuclein and dopamine physiology and may provide a new paradigm to study the pathology of PD.

LRRK2 detection in human biofluids: potential use as a Parkinson's disease biomarker?

Leucine-rich repeat kinase 2 (LRRK2) is a complex signalling protein that is a key therapeutic target, particularly in Parkinson's disease (PD). In addition, there is now evidence showing that LRRK2 expression and phosphorylation levels have potential as markers of disease or target engagement. Indeed, reports show increases in LRRK2 protein levels in the prefrontal cortex of PD patients relative to controls, suggesting that increase in total LRRK2 protein expression is correlated with disease progression. LRRK2 phosphorylation levels are reduced in experimental systems for most disease mutants, and LRRK2 is also rapidly dephosphorylated upon LRRK2 inhibitor treatment, considered potential therapeutics. Recently, the presence of LRRK2 was confirmed in exosomes from human biofluids, including urine and cerebrospinal fluid. Moreover, phosphorylation of LRRK2 at phosphosites S910, S935, S955 and S973, as well as at the autophosphoryation site S1292, was found in urinary exosomes. In this review, we summarize knowledge on detection of LRRK2 in human biofluids and the relevance of these findings for the development of PD-related biomarkers.

MicroRNAs in Parkinson's disease

Parkinson's disease is the second most common neurodegenerative disease commonly affecting the older population. Loss of dopaminergic neurons in the substantia nigra of brain leads to impairment of motor activities as well as cognitive defects. There are many underlying causes to this disease, both genetic and epigenetic, which are yet to be fully explored. Non-coding RNAs are significant part of our genome and are involved in various cellular processes. MicroRNAs, which are small non-coding RNAs having 20-22 nucleotides, are involved in many underlying mechanisms of pathogenesis of several neurodegenerative diseases including Parkinson's. This review focuses on the role played by microRNAs in regulating various genes responsible for the onset and pathogenesis of Parkinson's disease and various literature evidences pointing at the usefulness of targeting specific microRNAs as a potential alternate therapeutic strategy for successful impairment of the disease progression. This review also discusses about various biofluid-based microRNA markers which may be potentially utilized for diagnostic purposes.

MicroRNA biomarkers of Parkinson's disease in serum exosome-like microvesicles

Parkinson's disease (PD) is a progressive age-related debilitating motor disorder and the second most common neurodegenerative disease after Alzheimer's disease. In this study, we aimed to investigate the expression of 24 candidate miRNAs in PD and to assess their diagnostic value in patients with PD. We collected serum samples from 109 patients with PD and 40 age- and sex-matched healthy volunteers (control group). RNAs encapsulated in exosome-like microvesicles in serum were extracted and reverse transcribed. Serum miRNAs were analyzed by quantitative reverse transcription polymerase chain reaction (qRT-PCR), and the ability of the miRNAs to accurately discriminate PD was analyzed by receiver operating characteristic curves. Based on our analysis, we further validated the downregulation of miR-19b and the upregulation of miR-195 and miR-24 in patients with PD. When compared with the control group, the area under the curve (AUC) values for miR-19b, miR-24, and miR-195 were 0.753, 0.908, and 0.697, respectively. Therefore, analysis of the expression levels of miR-19b, miR-24, and miR-195 in serum may be useful for the diagnosis of PD.

Patient iPSC-Derived Neurons for Disease Modeling of Frontotemporal Dementia with Mutation in CHMP2B

The truncated mutant form of the charged multivesicular body protein 2B (CHMP2B) is causative for frontotemporal dementia linked to chromosome 3 (FTD3). CHMP2B is a constituent of the endosomal sorting complex required for transport (ESCRT) and, when mutated, disrupts endosome-to-lysosome trafficking and substrate degradation. To understand the underlying molecular pathology, FTD3 patient induced pluripotent stem cells (iPSCs) were differentiated into forebrain-type cortical neurons. FTD3 neurons exhibited abnormal endosomes, as previously shown in patients. Moreover, mitochondria of FTD3 neurons displayed defective cristae formation, accompanied by deficiencies in mitochondrial respiration and increased levels of reactive oxygen. In addition, we provide evidence for perturbed iron homeostasis, presenting an in vitro patient-specific model to study the effects of iron accumulation in neurodegenerative diseases. All phenotypes observed in FTD3 neurons were rescued in CRISPR/Cas9-edited isogenic controls. These findings illustrate the relevance of our patient-specific in vitro models and open up possibilities for drug target development.

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FTD3 neurons show abnormalities in endosomes and mitochondria

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Parkinson's and Alzheimer's disease core genes are altered in FTD3 neurons

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Iron homeostasis is perturbed in FTD3 neurons

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Impairments in FTD3 neurons are rescued in CRISPR/Cas9-edited isogenic controls

Plasma levels of miR-137 and miR-124 are associated with Parkinson's disease but not with Parkinson's disease with depression

MicroRNAs (miRNAs) are a class of small, non-coding RNAs that regulate gene expression at the post-transcriptional level. Recently, it was reported that miR-137, miR-124, and miR-184 were widely expressed in the central nervous system and were vital to neuronal regulation. In this study, we detected the circulating levels of miR-137, miR-124, and miR-184 in PD patients, and explored the potential role of miR-124, miR-137, and miR-184 in the diagnosis of PD. We further described the relationship between these miRNAs and PD with depression (PD-Dep). The study recruited 60 controls and 60 PD patients, which were further divided into two subgroups, PD with depression (PD-Dep, n = 24) and non-depressed group (PD-NDep, n = 36) according to Hamilton Rating Scale for Depression. Plasma levels of miR-137, miR-124, and miR-184 were detected by qRT-PCR. Receiver-operating characteristic (ROC) curve was used to evaluate miR-124 and miR-137 levels as potential diagnostic biomarkers for PD. The results demonstrated that there were no significant differences in levels of miR-184 between PD patients and controls (p > 0.05). However, miR-137 levels were increased significantly for PD patients compared to controls (p < 0.05), while miR-124 levels were down-regulated (p < 0.05). The areas under the ROC curve (AUC) of miR-137 and miR-124 were 0.707 (95% CI 0.615-0.789, p < 0.05) and 0.709 (95% CI 0.618-0.633, p < 0.05), respectively. Correlation analysis revealed that there was no relationship between these two miRNAs levels and UPDRS scores or H&Y stage. There were no significant differences in miR-137 and miR-124 levels between PD-Dep and PD-NDep (p > 0.05). Thus, plasma levels of miR-137 and miR-124 are associated with Parkinson's disease and might be potential biomarkers of the diagnosis of PD. There were no associations of plasma miR-137 and miR-124 with the severity of PD motor symptoms or PD-Dep.

miRNAs as biomarkers of neurodegenerative disorders

Neurodegenerative diseases (NDDs) are the result of progressive deterioration of neurons, ultimately leading to disabilities. There is no effective cure for NDDs at present; ongoing therapies are mainly aimed at treating the most bothersome symptoms. Since early treatment is crucial in NDDs, there is an urgent need for specific and sensitive biomarkers that can aid in early diagnosis of these disorders. Recently, altered expression of miRNAs has been implicated in several neurological disorders, including NDDs. miRNA expression has been extensively investigated in the cells, tissues and body fluids of patients with different types of NDDs. The aim of this review is to provide a comprehensive overview of miRNAs as biomarkers and therapeutic targets for NDDs.

Regulation of LRRK2 by Phosphatases

LRRK2 is a highly phosphorylated protein, and evidence of a physiological role for LRRK2 phosphorylation has accumulated in recent years for cellular phosphosites, many of which are found in the ANK-LRR interdomain region, i.e., the S910/S935/S955/S973 sites as well as recently for autophosphorylation sites, at least one of which has been confirmed in cells, S1292. LRRK2 phosphorylation is modulated in several disease or potential therapy relevant conditions such as in disease mutant variants of LRRK2 or following LRRK2 kinase inhibitor treatment. This chapter will focus on the regulation of LRRK2 phosphorylation and more specifically the role of phosphatases in LRRK2 dephosphorylation. This will include reviewing the conditions in which LRRK2 is found to be dephosphorylated, the molecular partners and phosphatases involved in regulating LRRK2 phosphorylation, as well as discussing how LRRK2 phosphatases may be therapeutic targets or biomarkers in their own right.

MicroRNAs in Neurocognitive Dysfunctions: New Molecular Targets for Pharmacological Treatments?

BACKGROUND

Neurodegenerative and cognitive disorders are multifactorial diseases (i.e., involving neurodevelopmental, genetic, age or environmental factors) characterized by an abnormal development that affects neuronal function and integrity. Recently, an increasing number of studies revealed that the dysregulation of microRNAs (miRNAs) may be involved in the etiology of cognitive disorders as Alzheimer, Parkinson, and Huntington's diseases, Schizophrenia and Autism spectrum disorders.

METHODS

From an extensive search in bibliographic databases of peer-reviewed research literature, we identified relevant published studies related to specific key words such as memory, cognition, neurodegenerative disorders, neurogenesis and miRNA. We then analysed, evaluated and summerized scientific evidences derived from these studies.

RESULTS

We first briefly summarize the basic molecular events involved in memory, a process inherent to cognitive disease, and then describe the role of miRNAs in neurodevelopment, synaptic plasticity and memory. Secondly, we provide an overview of the impact of miRNA dysregulation in the pathogenesis of different neurocognitive disorders, and lastly discuss the feasibility of miRNA-based therapeutics in the treatment of these disorders.

CONCLUSION

This review highlights the molecular basis of neurodegenerative and cognitive disorders by focusing on the impact of miRNAs dysregulation in these pathological phenotypes. Altogether, the published reports suggest that miRNAs-based therapy could be a viable therapeutic alternative to current treatment options in the future.

MicroRNAs in Parkinson's disease and emerging therapeutic targets

Parkinson's disease (PD) is the second most common age-related neurodegenerative disorder, with the clinical main symptoms caused by a loss of dopaminergic neurons in the substantia nigra, corpus striatum and brain cortex. Over 90% of patients with PD have sporadic PD and occur in people with no known family history of the disorder. Currently there is no cure for PD. Treatment with medications to increase dopamine relieves the symptoms but does not slow down or reverse the damage to neurons in the brain. Increasing evidence points to inflammation as a chief mediator of PD with inflammatory response mechanisms, involving microglia and leukocytes, activated following loss of dopaminergic neurons. Oxidative stress is also recognized as one of the main causes of PD, and excessive reactive oxygen species (ROS) and reactive nitrogen species can lead to dopaminergic neuron vulnerability and eventual death. MicroRNAs control a range of physiological and pathological functions, and may serve as potential targets for intervention against PD to mitigate damage to the brain. Several studies have demonstrated that microRNAs can regulate oxidative stress and prevent ROS-mediated damage to dopaminergic neurons, suggesting that specific microRNAs may be putative targets for novel therapeutic strategies in PD. Recent human and animal studies have identified a large number of dysregulated microRNAs in PD brain tissue samples, many of which were downregulated. The dysregulated microRNAs affect downstream targets such as SNCA, PARK2, LRRK2, TNFSF13B, LTA, SLC5A3, PSMB2, GSR, GBA, LAMP-2A, HSC. Apart from one study, none of the studies reviewed had used agomirs or antagomirs to reverse the levels of downregulated or upregulated microRNAs, respectively, in mouse models of PD or with isolated human or mouse dopaminergic cells. Further large-scale studies of brain tissue samples collected with short postmortem interval from human PD patients are warranted to provide more information on the microRNA profiles in different brain regions and to test for gender differences.

MicroRNA-712 restrains macrophage pro-inflammatory responses by targeting LRRK2 leading to restoration of insulin stimulated glucose uptake by myoblasts

Chronic inflammatory diseases such as insulin resistance, Type 2 diabetes, neurodegenerative diseases etc., are shown to be caused due to imbalanced activation states of macrophages. MicroRNAs which are transcriptional/post-transcriptional regulators of gene expression drive several pathophysiological processes including macrophage polarization. However the functional role of microRNAs in regulating inflammation induced insulin resistance is ill defined. In our current study we observed that the expression of miR-712 was reduced in macrophages exposed to LPS and IFN-γ. Ectopic expression of miR-712 in RAW 264.7 mouse macrophages impaired the expression of iNOS protein and secretion of pro-inflammatory cytokines such as TNF-α, IL-6 and IFN-β which in turn led to improved insulin stimulated glucose uptake in co-cultured L6 myoblasts. Mechanistically, we identified that miR-712 targets the 3'UTR of a potent inflammatory gene LRRK2 and dampens the phosphorylation of p38 and ERK1/2 kinases. Taken together, our data underscore the regulatory role of miR-712 in restoring insulin stimulated glucose uptake by myoblasts through down-regulating macrophage mediated inflammatory responses.

Identification of therapeutic targets for Parkinson's disease via bioinformatics analysis

The present study aimed to identify molecular targets that have important roles in the progression of Parkinson's disease. The gene expression profile dataset GSE7621 and the microRNA (miRNA) expression profile dataset GSE16658 were downloaded from the Gene Expression Omnibus database. R programing software was used to identify differentially expressed genes and miRNAs. Subsequently, enriched Gene Ontology terms of differentially expressed genes were obtained using the Database for Annotation, Visualization and Integrated Discovery. Target genes of differentially expressed miRNAs were identified using the starBase database and a miRNA-gene regulatory network was constructed using Cytoscape software. A total of 391 differentially expressed genes and 88 differentially expressed miRNAs were identified. Gene Ontology terms that were associated with nervous system activity, including synapse and dopamine metabolic process, were shown to be enriched in the differentially expressed genes. A total of 620 target genes were identified from the differentially expressed miRNAs, and 10 overlaps were identified between these target genes and differentially expressed genes. Furthermore, 10 miRNA-gene regulation pairs were obtained between the overlaps and differentially expressed miRNAs. In conclusion, the present study used bioinformatics analysis of gene and miRNA expression profile datasets, and identified potential therapeutic targets for Parkinson's disease.

Recent developments in circulating biomarkers in Parkinson’s disease: the potential use of miRNAs in a clinical setting

Parkinson’s disease (PD) is the second most common neurodegenerative disorder, affecting 5% of the elderly population. PD diagnosis is still based on the identification of neuromotor symptoms although nonmotor manifestations emerge years prior to diagnosis. The discovery of biomarkers at the earliest stages of PD is of extreme interest. miRNAs have been considered potential biomarkers for neurodegenerative diseases, but only a limited number have been found to be PD related. This review focuses on the current findings in the field of circulating miRNAs in PD and the challenges surrounding clinical utility and validation. We briefly describe the more established circulating biomarkers in PD and provide a more thorough review of miRNAs differentially expressed in PD. We highlight their potential for being considered as biomarkers for diagnosis while emphasizing the challenges for adequate validation of the findings and how miRNAs can be envisioned in a clinical setting satisfying regulatory bodies.

MicroRNAs in Cerebrospinal Fluid as Potential Biomarkers for Parkinson's Disease and Multiple System Atrophy

Parkinson’s disease (PD) and multiple system atrophy (MSA) are both part of the spectrum of neurodegenerative movement disorders and α-synucleinopathies with overlap of symptoms especially at early stages of the disease but with distinct disease progression and responses to dopaminergic treatment. Therefore, having biomarkers that specifically classify patients, which could discriminate PD from MSA, would be very useful. MicroRNAs (miRNAs) regulate protein translation and are observed in biological fluids, including cerebrospinal fluid (CSF), and may therefore have potential as biomarkers of disease. The aim of our study was to determine if miRNAs in CSF could be used as biomarkers for either PD or MSA. Using quantitative PCR (qPCR), we evaluated expression levels of 10 miRNAs in CSF patient samples from PD (n = 28), MSA (n = 17), and non-neurological controls (n = 28). We identified two miRNAs (miR-24 and miR-205) that distinguished PD from controls and four miRNAs that differentiated MSA from controls (miR-19a, miR-19b, miR-24, and miR-34c). Combinations of miRNAs accurately discriminated either PD (area under the curve (AUC) = 0.96) or MSA (AUC = 0.86) from controls. In MSA, we also observed that miR-24 and miR-148b correlated with cerebellar ataxia symptoms, suggesting that these miRNAs are involved in cerebellar degeneration in MSA. Our findings support the potential of miRNA panels as biomarkers for movement disorders and may provide more insights into the pathological mechanisms related to these disorders.

Epigenetic regulation in Parkinson's disease

Recent efforts have shed new light on the epigenetic mechanisms driving gene expression alterations associated with Parkinson's disease (PD) pathogenesis. Changes in gene expression are a well-established cause of PD, and epigenetic mechanisms likely play a pivotal role in regulation. Studies in families with PD harboring duplications and triplications of the SNCA gene have demonstrated that gene dosage is associated with increased expression of both SNCA mRNA and protein, and correlates with a fulminant disease course. Furthermore, it is postulated that even subtle changes in SNCA expression caused by common variation is associated with disease risk. Of note, genome-wide association studies have identified over 30 loci associated with PD with most signals located in non-coding regions of the genome, thus likely influencing transcript expression levels. In health, epigenetic mechanisms tightly regulate gene expression, turning genes on and off to balance homeostasis and this, in part, explains why two cells with the same DNA sequence will have different RNA expression profiles. Understanding this phenomenon will be crucial to our interpretation of the selective vulnerability observed in neurodegeneration and specifically dopaminergic neurons in the PD brain. In this review, we discuss epigenetic mechanisms, such as DNA methylation and histone modifications, involved in regulating the expression of genes relevant to PD, RNA-based mechanisms, as well as the effect of toxins and potential epigenetic-based treatments for PD.

Parkinson's disease: SNCA-, PARK2-, and LRRK2- targeting microRNAs elevated in cingulate gyrus

INTRODUCTION

In order to better understand the role of epigenetic influences in the etiology of Parkinson's disease (PD), we studied the expression of microRNAs in gyri cinguli of patients and controls.

METHODS

Expression profiling of 744 well-characterized microRNAs in gyri cinguli from patients and controls using TaqMan array microRNA cards. Verification of significantly dysregulated microRNAs by SYBR Green qRT-PCR.

RESULTS

First screen by TaqMan array identified 43 microRNAs that were upregulated in gyri cinguli from patients. Of those microRNAs, 13 are predicted to regulate at least one of six genes mutated in monogenic forms of PD (DJ-1, PARK2, PINK1, LRRK2, SNCA, and HTRA2). Five of these 13 microRNAs (-144, -199b, -221, -488, -544) were also found upregulated by SYBR Green qRT-PCR and are predicted to regulate either SNCA, PARK2, LRRK2 or combinations thereof. Consistently, expression of SNCA, PARK2, and LRRK2 was reduced in patients. An additional 5 out of ten potential target genes tested were downregulated. These are DRAM (DNA damage regulated autophagy modulator 1), predicted to be regulated by miR-144, EVC (Ellis Van Creveld Protein) by miR-221, ZNF440 (Zinc Finger Protein 440) by miR-199b, MTFMT (Mitochondrial Methionyl-tRNA Formyltransferase) by miR-488 and XIRP2 (Xin Actin Binding Repeat Containing) possibly controlled by miR-544a.

CONCLUSION

The study identified five microRNAs that play a role in the etiology of Parkinson's disease likely by modifying expression of SNCA, PARK2, LRRK2 and additional genes required for normal cellular function.

Altered microRNA profiles in cerebrospinal fluid exosome in Parkinson disease and Alzheimer disease

The differential diagnosis of Parkinson's diseases (PD) is challenging, especially in the early stages of the disease. We developed a microRNA profiling strategy for exosomal miRNAs isolated from cerebrospinal fluid (CSF) in PD and AD. Sixteen exosomal miRNAs were up regulated and 11 miRNAs were under regulated significantly in PD CSF when compared with those in healthy controls (relative fold > 2, p < 0.05). MiR-1 and miR-19b-3p were validated and significantly reduced in independent samples. While miR-153, miR-409-3p, miR-10a-5p, and let-7g-3p were significantly over expressed in PD CSF exosome. Bioinformatic analysis by DIANA-mirPath demonstrated that Neurotrophin signaling, mTOR signaling, Ubiquitin mediated proteolysis, Dopaminergic synapse, and Glutamatergic synapse were the most prominent pathways enriched in quantiles with PD miRNA patterns. Messenger RNA (mRNA) transcripts [amyloid precursor protein, APP), α-synuclein (α-syn), Tau, neurofilament, light gene (NF-L), DJ-1/PARK7, Fractalkine and Neurosin] and long non-coding RNAs (RP11-462G22.1 and PCA3) were differentially expressed in CSF exosomes in PD and AD patients. These data demonstrated that CSF exosomal RNA molecules are reliable biomarkers with fair robustness in regard to specificity and sensitivity in differentiating PD from healthy and diseased (AD) controls.

Neuroprotective Role of MicroRNA-22 in a 6-Hydroxydopamine-Induced Cell Model of Parkinson's Disease via Regulation of Its Target Gene TRPM7

Parkinson's disease (PD), the second most prevalent neurodegenerative disorder with only symptomatic treatment available, is characterized by a progressive loss of dopaminergic neurons in the midbrain. Ample evidence indicated that microRNAs (miRs) could regulate post-transcriptional gene expression and neuronal disease. In the present study, we have evaluated the effects and mechanism of miR-22 in PC12 pheochromocytoma cells treated with 6-hydroxydopamine (6-OHDA) to mimic PD. RT-PCR results showed that the expression of miR-22 is downregulated in 6-OHDA-treated PC12 cells, and the overexpression of miR-22 significantly promoted the survival and proliferation of 6-OHDA-induced PC12 cells, whereas miR-22 inhibitor reversed these effects. In addition, PC12 cells were treated with miR-22 mimics or inhibitor following 6-OHDA administration, which medicated ROS production and upregulation or downregulation of caspase-3 activity, respectively. A luciferase reporter assay revealed that transient receptor potential melastatin 7 (TRPM7) is a direct target gene of miR-22, and miR-22 overexpression markedly downregulated the level of TRPM7. Strikingly, further analysis showed that miR-22 mediated 6-OHDA-induced PC12 cell survival and proliferation by targeting TRPM7. Taken together, the present study showed that miR-22 overexpression exhibited neuroprotective and reversal effects on the 6-OHDA-induced PC12 cell growth and apoptosis by targeting TRPM7.

The roles of non-coding RNAs in Parkinson's disease

Parkinson's disease (PD) is considered as a high prevalence neurodegenerative disorders worldwide. Pathologically, the demise of dopamine-producing cells, in large part due to an abnormal accumulation of the α-synuclein in the substantia nigra, is one of the main causes of the disease. Up until now, many de novo investigations have been conducted to disclose the mechanisms underlying in PD. Among them, impacts of non-coding RNAs (ncRNAs) on the pathogenesis and/or progression of PD need to be highlighted. microRNAs (miRNAs) and long ncRNAs (lncRNAs) are more noteworthy in this context. miRNAs are small ncRNAs (with 18-25 nucleotide in length) that control the expression of multiple genes at post-transcriptional level, while lncRNAs have longer size (over 200 nucleotides) and are involved in some key biological processes through various mechanisms. Involvement of miRNAs has been well documented in the development of PD, particularly gene expression. Hence, in this current review, we will discuss the impacts of miRNAs in regulation of the expression of PD-related genes and the role of lncRNAs in the pathogenesis of PD.

miR-27a and miR-27b regulate autophagic clearance of damaged mitochondria by targeting PTEN-induced putative kinase 1 (PINK1)

Background

Loss-of-function mutations in PINK1 and PARKIN are the most common causes of autosomal recessive Parkinson’s disease (PD). PINK1 is a mitochondrial serine/threonine kinase that plays a critical role in mitophagy, a selective autophagic clearance of damaged mitochondria. Accumulating evidence suggests mitochondrial dysfunction is one of central mechanisms underlying PD pathogenesis. Therefore, identifying regulatory mechanisms of PINK1 expression may provide novel therapeutic opportunities for PD. Although post-translational stabilization of PINK1 upon mitochondrial damage has been extensively studied, little is known about the regulation mechanism of PINK1 at the transcriptional or translational levels.

Results

Here, we demonstrated that microRNA-27a (miR-27a) and miR-27b suppress PINK1 expression at the translational level through directly binding to the 3′-untranslated region (3′UTR) of its mRNA. Importantly, our data demonstrated that translation of PINK1 is critical for its accumulation upon mitochondrial damage. The accumulation of PINK1 upon mitochondrial damage was strongly regulated by expression levels of miR-27a and miR-27b. miR-27a and miR-27b prevent mitophagic influx by suppressing PINK1 expression, as evidenced by the decrease of ubiquitin phosphorylation, Parkin translocation, and LC3-II accumulation in damaged mitochondria. Consequently, miR-27a and miR-27b inhibit lysosomal degradation of the damaged mitochondria, as shown by the decrease of the delivery of damaged mitochondria to lysosome and the degradation of cytochrome c oxidase 2 (COX2), a mitochondrial marker. Furthermore, our data demonstrated that the expression of miR-27a and miR-27b is significantly induced under chronic mitophagic flux, suggesting a negative feedback regulation between PINK1-mediated mitophagy and miR-27a and miR-27b.

Conclusions

We demonstrated that miR-27a and miR-27b regulate PINK1 expression and autophagic clearance of damaged mitochondria. Our data further support a novel negative regulatory mechanism of PINK1-mediated mitophagy by miR-27a and miR-27b. Therefore, our results considerably advance our understanding of PINK1 expression and mitophagy regulation and suggest that miR-27a and miR-27b may represent potential therapeutic targets for PD.

Electronic supplementary material

The online version of this article (doi:10.1186/s13024-016-0121-4) contains supplementary material, which is available to authorized users.