The regulatory roles of microRNAs toward pathogenesis and treatments in Huntington's disease

Therapeutic advances in neural regeneration for Huntington's disease

Huntington's disease is a neurodegenerative disease caused by the expansion mutation of a cytosine-adenine-guanine triplet in the exon 1 of the HTT gene which is responsible for the production of the huntingtin (Htt) protein. In physiological conditions, Htt is involved in many cellular processes such as cell signaling, transcriptional regulation, energy metabolism regulation, DNA maintenance, axonal trafficking, and antiapoptotic activity. When the genetic alteration is present, the production of a mutant version of Htt (mHtt) occurs, which is characterized by a plethora of pathogenic activities that, finally, lead to cell death. Among all the cells in which mHtt exerts its dangerous activity, the GABAergic Medium Spiny Neurons seem to be the most affected by the mHtt-induced excitotoxicity both in the cortex and in the striatum. However, as the neurodegeneration proceeds ahead the neuronal loss grows also in other brain areas such as the cerebellum, hypothalamus, thalamus, subthalamic nucleus, globus pallidus, and substantia nigra, determining the variety of symptoms that characterize Huntington's disease. From a clinical point of view, Huntington's disease is characterized by a wide spectrum of symptoms spanning from motor impairment to cognitive disorders and dementia. Huntington's disease shows a prevalence of around 3.92 cases every 100,000 worldwide and an incidence of 0.48 new cases every 100,000/year. To date, there is no available cure for Huntington's disease. Several treatments have been developed so far, aiming to reduce the severity of one or more symptoms to slow down the inexorable decline caused by the disease. In this context, the search for reliable strategies to target the different aspects of Huntington's disease become of the utmost interest. In recent years, a variety of studies demonstrated the detrimental role of neuronal loss in Huntington's disease condition highlighting how the replacement of lost cells would be a reasonable strategy to overcome the neurodegeneration. In this view, numerous have been the attempts in several preclinical models of Huntington's disease to evaluate the feasibility of invasive and non-invasive approaches. Thus, the aim of this review is to offer an overview of the most appealing approaches spanning from stem cell-based cell therapy to extracellular vesicles such as exosomes in light of promoting neurogenesis, discussing the results obtained so far, their limits and the future perspectives regarding the neural regeneration in the context of Huntington's disease.

Huntington's Disease: Complex Pathogenesis and Therapeutic Strategies

Huntington's disease (HD) arises from the abnormal expansion of CAG repeats in the huntingtin gene (HTT), resulting in the production of the mutant huntingtin protein (mHTT) with a polyglutamine stretch in its N-terminus. The pathogenic mechanisms underlying HD are complex and not yet fully elucidated. However, mHTT forms aggregates and accumulates abnormally in neuronal nuclei and processes, leading to disruptions in multiple cellular functions. Although there is currently no effective curative treatment for HD, significant progress has been made in developing various therapeutic strategies to treat HD. In addition to drugs targeting the neuronal toxicity of mHTT, gene therapy approaches that aim to reduce the expression of the mutant HTT gene hold great promise for effective HD therapy. This review provides an overview of current HD treatments, discusses different therapeutic strategies, and aims to facilitate future therapeutic advancements in the field.

Intranuclear inclusions of polyQ-expanded ATXN1 sequester RNA molecules

Spinocerebellar ataxia type 1 (SCA1) is an autosomal dominant neurodegenerative disease caused by a trinucleotide (CAG) repeat expansion in the ATXN1 gene. It is characterized by the presence of polyglutamine (polyQ) intranuclear inclusion bodies (IIBs) within affected neurons. In order to investigate the impact of polyQ IIBs in SCA1 pathogenesis, we generated a novel protein aggregation model by inducible overexpression of the mutant ATXN1(Q82) isoform in human neuroblastoma SH-SY5Y cells. Moreover, we developed a simple and reproducible protocol for the efficient isolation of insoluble IIBs. Biophysical characterization showed that polyQ IIBs are enriched in RNA molecules which were further identified by next-generation sequencing. Finally, a protein interaction network analysis indicated that sequestration of essential RNA transcripts within ATXN1(Q82) IIBs may affect the ribosome resulting in error-prone protein synthesis and global proteome instability. These findings provide novel insights into the molecular pathogenesis of SCA1, highlighting the role of polyQ IIBs and their impact on critical cellular processes.

The role of microRNAs in the pathophysiology of human central nervous system: A focus on neurodegenerative diseases

microRNAs (miRNAs) are suggested to play substantial roles in regulating the development and various physiologic functions of the central nervous system (CNS). These include neurogenesis, cell fate and differentiation, morphogenesis, formation of dendrites, and targeting non-neural mRNAs. Notably, deregulation of an increasing number of miRNAs is associated with several neurodegenerative diseases including Alzheimer's disease, Parkinson's disease, multiple sclerosis, amyotrophic lateral sclerosis and CNS tumors. They are particularly known to affect the amyloid β (Aβ) cleavage and accumulation, tau protein homeostasis, and expression of alpha-synuclein (α-syn), Parkin, PINK1, and brain-derived neurotrophic factor (BDNF) that play pivotal roles in the pathogenesis of neurodegenerative diseases. These include miR-16, miR-17-5p, miR-20a, miR-106a, miR-106b, miR-15a, miR-15b, miR-103, miR-107, miR-298, miR-328, miR-195, miR-485, and miR-29. In CNS tumors, several miRNAs, including miR-31, miR-16, and miR-21 have been identified to modulate tumorigenesis through impacting tumor invasion and apoptosis. In this review article, we have a look at the recent advances on our knowledge about the role of miRNAs in human brain development and functions, neurodegenerative diseases, and their clinical potentials.

miR-196a provides antioxidative neuroprotection via USP15/Nrf2 regulation in Huntington's disease

Huntington's disease (HD) is a devastating neurodegenerative disorder characterized by the accumulation of mutant Huntingtin protein (mHTT) and oxidative stress-induced neuronal damage. Based on previous reports, microRNA-196a (miR-196a) has emerged as a potential therapeutic target due to its neuroprotective effects in various neurodegenerative diseases. However, whether miR-196a functions through antioxidative effects is still unknown. In this study, we demonstrated that HD models, both in vitro and in vivo, exhibit elevated levels of reactive oxygen species (ROS) and increased neuronal death, and miR-196a mitigates ROS levels and reduces cell death in HD cells. Moreover, we elucidated that miR-196a facilitates the translocation of nuclear factor erythroid 2 (Nrf2) into the nucleus, enhancing the transcription of antioxidant genes, including heme oxygenase-1 (HO-1). We further identified ubiquitin-specific peptidase 15 (USP15), a direct target of miR-196a related to the Nrf2 pathway, and USP15 exacerbates mHTT aggregate formation while partially counteracting miR-196a-induced reductions in mHTT levels. Taken together, these findings shed light on the multifaceted role of miR-196a in HD, highlighting its potential as a therapeutic avenue for ameliorating oxidative stress and neurodegeneration in this debilitating disease.

Repressor Element-1 Binding Transcription Factor (REST) as a Possible Epigenetic Regulator of Neurodegeneration and MicroRNA-Based Therapeutic Strategies

Neurodegenerative disorders (NDD) have grabbed significant scientific consideration due to their fast increase in prevalence worldwide. The specific pathophysiology of the disease and the amazing changes in the brain that take place as it advances are still the top issues of contemporary research. Transcription factors play a decisive role in integrating various signal transduction pathways to ensure homeostasis. Disruptions in the regulation of transcription can result in various pathologies, including NDD. Numerous microRNAs and epigenetic transcription factors have emerged as candidates for determining the precise etiology of NDD. Consequently, understanding by what means transcription factors are regulated and how the deregulation of transcription factors contributes to neurological dysfunction is important to the therapeutic targeting of pathways that they modulate. RE1-silencing transcription factor (REST) also named neuron-restrictive silencer factor (NRSF) has been studied in the pathophysiology of NDD. REST was realized to be a part of a neuroprotective element with the ability to be tuned and influenced by numerous microRNAs, such as microRNAs 124, 132, and 9 implicated in NDD. This article looks at the role of REST and the influence of various microRNAs in controlling REST function in the progression of Alzheimer's disease (AD), Parkinson's disease (PD), and Huntington's disease (HD) disease. Furthermore, to therapeutically exploit the possibility of targeting various microRNAs, we bring forth an overview of drug-delivery systems to modulate the microRNAs regulating REST in NDD.

Ubiquitination Links DNA Damage and Repair Signaling to Cancer Metabolism

Changes in the DNA damage response (DDR) and cellular metabolism are two important factors that allow cancer cells to proliferate. DDR is a set of events in which DNA damage is recognized, DNA repair factors are recruited to the site of damage, the lesion is repaired, and cellular responses associated with the damage are processed. In cancer, DDR is commonly dysregulated, and the enzymes associated with DDR are prone to changes in ubiquitination. Additionally, cellular metabolism, especially glycolysis, is upregulated in cancer cells, and enzymes in this metabolic pathway are modulated by ubiquitination. The ubiquitin-proteasome system (UPS), particularly E3 ligases, act as a bridge between cellular metabolism and DDR since they regulate the enzymes associated with the two processes. Hence, the E3 ligases with high substrate specificity are considered potential therapeutic targets for treating cancer. A number of small molecule inhibitors designed to target different components of the UPS have been developed, and several have been tested in clinical trials for human use. In this review, we discuss the role of ubiquitination on overall cellular metabolism and DDR and confirm the link between them through the E3 ligases NEDD4, APC/C^CDH1, FBXW7, and Pellino1. In addition, we present an overview of the clinically important small molecule inhibitors and implications for their practical use.

MicroRNA schizophrenia: Etiology, biomarkers and therapeutic targets

The three sets of symptoms associated with schizophrenia-positive, negative, and cognitive-are burdensome and have serious effects on public health, which affects up to 1% of the population. It is now commonly believed that in addition to the traditional dopaminergic mesolimbic pathway, the etiology of schizophrenia also includes neuronal networks, such as glutamate, GABA, serotonin, BDNF, oxidative stress, inflammation and the immune system. Small noncoding RNA molecules called microRNAs (miRNAs) have come to light as possible participants in the pathophysiology of schizophrenia in recent years by having an impact on these systems. These small RNAs regulate the stability and translation of hundreds of target transcripts, which has an impact on the entire gene network. There may be improved approaches to treat and diagnose schizophrenia if it is understood how these changes in miRNAs alter the critical related signaling pathways that drive the development and progression of the illness.

Non-coding RNAs as key players in the neurodegenerative diseases: Multi-platform strategies and approaches for exploring the Genome's dark matter

A growing amount of evidence in the last few years has begun to unravel that non-coding RNAs have a myriad of functions in gene regulation. Intensive investigation on non-coding RNAs (ncRNAs) has led to exploring their broad role in neurodegenerative diseases (NDs) owing to their regulatory role in gene expression. RNA sequencing technologies and transcriptome analysis has unveiled significant dysregulation of ncRNAs attributed to their biogenesis, upregulation, downregulation, aberrant epigenetic regulation, and abnormal transcription. Despite these advances, the understanding of their potential as therapeutic targets and biomarkers underpinning detailed mechanisms is still unknown. Advancements in bioinformatics and molecular technologies have improved our knowledge of the dark matter of the genome in terms of recognition and functional validation. This review aims to shed light on ncRNAs biogenesis, function, and potential role in NDs. Further deepening of their role is provided through a focus on the most recent platforms, experimental approaches, and computational analysis to investigate ncRNAs. Furthermore, this review summarizes and evaluates well-studied miRNAs, lncRNAs and circRNAs concerning their potential role in pathogenesis and use as biomarkers in NDs. Finally, a perspective on the main challenges and novel methods for the future and broad therapeutic use of ncRNAs is offered.

The updated development of blood-based biomarkers for Huntington's disease

Huntington's disease is a progressive neurodegenerative disease caused by mutation of the huntingtin (HTT) gene. The identification of mutation carriers before symptom onset provides an opportunity to intervene in the early stage of the disease course. Optimal biomarkers are of great value to reflect neuropathological and clinical progression and are sensitive to potential disease-modifying treatments. Blood-based biomarkers have the merits of minimal invasiveness, low cost, easy accessibility and safety. In this review, we summarized the updated development of blood-based biomarkers for HD from six aspects, including neuronal injuries, oxidative stress, endocrine functions, immune reactions, metabolism and differentially expressed miRNAs. The blood-based biomarkers presented and discussed in this review were close to clinical applicability and might facilitate clinical design as surrogate endpoints. Exploration and validation of robust blood-based biomarkers require further standard and systemic study design in the future.

Emerging Role of MicroRNA-30c in Neurological Disorders

MicroRNAs (miRNAs or miRs) are a class of small non-coding RNAs that negatively regulate the expression of target genes by interacting with 3' untranslated regions of target mRNAs to induce mRNA degradation and translational repression. The miR-30 family members are involved in the development of many tissues and organs and participate in the pathogenesis of human diseases. As a key member of the miR-30 family, miR-30c has been implicated in neurological disorders such as Alzheimer's disease, Parkinson's disease, multiple sclerosis, and stroke. Mechanistically, miR-30c may act as a multi-functional regulator of different pathogenic processes such as autophagy, apoptosis, endoplasmic reticulum stress, inflammation, oxidative stress, thrombosis, and neurovascular function, thereby contributing to different disease states. Here, we review and discuss the biogenesis, gene regulation, and the role and mechanisms of action of miR-30c in several neurological disorders and therapeutic potential in clinics.

Plasma microRNA-221-3p as a biomarker for POCD after non-cardiac surgery

Our previous study showed that the plasma microRNA-221-3p level could serve as a biomarker for major depression or mood. This study aimed to further investigate the role of plasma microRNA-221-3p level in postoperative cognitive dysfunction (POCD). Patients undergoing non-cardiac surgery were randomly assigned according to the inclusion and exclusion criteria. POCD was diagnosed by the Z score method. The relative level of plasma microRNA-221-3p was decided by quantitative real-time polymerase chain reaction. Multiple logistic regression analysis and receiver operating characteristic(ROC) curves were used for the analysis of plasma microRNA-221-3p prediction performance for POCD. At 7 days post-surgery, the rate of POCD was 34.04%. Patients in the POCD group had a higher preoperative depression score, older age, and longer operation duration than that in the NPOCD group. The relative level of plasma microRNA-221-3p in the POCD group was 1.78 and 2.73 times higher than that in the NPOCD group at 1 day before and 7 days after the surgery, respectively. The relative content of plasma microRNA-221-3p at 7 days after operation was an independent risk factor for POCD. The ROC curves showed that the area under the curve was 0.938 for plasma microRNA-221-3p at postoperative 7 days, and the threshold for POCD detection was 12.33 with a sensitivity and specificity of 81.3% and 96.3%, respectively. Our results indicate that the plasma postoperative microRNA-221-3p levels could be an effective predictor for POCD after non-cardiac surgery.

miR-196a enhances polymerization of neuronal microfilaments through suppressing IMP3 and upregulating IGF2 in Huntington's disease

Huntington's disease (HD) is one of the inheritable neurodegenerative diseases, and these diseases share several similar pathological characteristics, such as abnormal neuronal morphology. miR-196a is a potential target to provide neuroprotective functions, and has been reported to enhance polymerization of neuronal microtubules in HD. While microtubules and microfilaments are two important components of the neuronal cytoskeleton, whether miR-196a improves neuronal microfilaments is still unknown. Here, we identify insulin-like growth factor 2 mRNA binding protein 3 (IMP3), and show that miR-196a directly suppresses IMP3 to increase neurite outgrowth in neurons. In addition, IMP3 disturbs neurite outgrowth in vitro and in vivo, and worsens the microfilament polymerization. Moreover, insulin-like growth factor-II (IGF2) is identified as the downstream target of IMP3, and miR-196a downregulates IMP3 to upregulate IGF2, which increases microfilamental filopodia numbers and activates Cdc42 to increase neurite outgrowth. Besides, miR-196a increases neurite outgrowth through IGF2 in different HD models. Finally, higher expression of IMP3 and lower expression IGF2 are observed in HD transgenic mice and patients, and increase the formation of aggregates in the HD cell model. Taken together, miR-196a enhances polymerization of neuronal microfilaments through suppressing IMP3 and upregulating IGF2 in HD, supporting the neuroprotective functions of miR-196a through neuronal cytoskeleton in HD.

A Review of Molecular Interplay between Neurotrophins and miRNAs in Neuropsychological Disorders

Various neurotrophins (NTs), including nerve growth factor, brain-derived neurotrophic factor, neurotrophin-3, and neurotrophin-4, promote cellular differentiation, survival, and maintenance, as well as synaptic plasticity, in the peripheral and central nervous system. The function of microRNAs (miRNAs) and other small non-coding RNAs, as regulators of gene expression, is pivotal for the appropriate control of cell growth and differentiation. There are positive and negative loops between NTs and miRNAs, which exert modulatory effects on different signaling pathways. The interplay between NTs and miRNAs plays a crucial role in the regulation of several physiological and pathological brain procedures. Emerging evidence suggests the diagnostic and therapeutic roles of the interactions between NTs and miRNAs in several neuropsychological disorders, including epilepsy, multiple sclerosis, Alzheimer's disease, Huntington's disease, amyotrophic lateral sclerosis, schizophrenia, anxiety disorders, depression, post-traumatic stress disorder, bipolar disorder, and drug abuse. Here, we review current data regarding the regulatory interactions between NTs and miRNAs in neuropsychological disorders, for which novel diagnostic and/or therapeutic strategies are emerging. Targeting NTs-miRNAs interactions for diagnostic or therapeutic approaches needs to be validated by future clinical studies.

Differential Regulation of Tau Exon 2 and 10 Isoforms in Huntington's Disease Brain

Huntington's disease (HD) is an inherited neurodegenerative disorder caused by an expansion of CAG repeats in the Huntingtin (HTT) gene. Accumulating evidence suggests that the microtubule-associated tau protein participates in the pathogenesis of HD. Recently, we have identified changes in tau alternative splicing of exons 2, 3 and 10 in the putamen of HD patients (St-Amour et al, 2018). In this study, we sought to determine whether tau mis-splicing events were equally observed in other brain regions that are less prone to neurodegeneration. Using Western blot and PCR, we characterized the relationship between MAPT splicing of exons 2, 3 and 10, tauopathy and Htt pathologies, as well as neurodegeneration markers in matching putamen and cortical samples from HD (N = 48) and healthy control (N = 25) subjects. We first show that levels of 4R-tau (exon 10 inclusion) isoforms are higher in both the putamen and the cortex of individuals with HD, consistent with earlier findings. On the other hand, higher 0N-tau (exclusion of exons 2 and 3) and lower 1N-tau (exclusion of exon 3) isoforms were seen exclusively in the putamen of HD individuals. Interestingly, investigated splicing factors were deregulated in both regions whereas exon 2 differences coincided with increased tau hyperphosphorylation, aggregation and markers of neurodegeneration. Overall, these results imply a differential regulation of tau exon 2 and exon 10 alternative splicing in HD putamen that could provide a useful biomarker or therapeutic target.

Role of siRNA-based nanocarriers for the treatment of neurodegenerative diseases

Neurodegenerative disorders (NDs) lead to the progressive degeneration of the structural and physiological functions of the central and peripheral nervous systems, resulting in lifelong cognitive and motor dysfunction. Although comprehensive treatment of NDs is lacking, small interfering (si)RNA has shown therapeutic utility in the form of cellular nuclease-driven downregulation of mRNA levels. Various nanotechnologies have been used to modulate crucial physicochemical and biopharmaceutical properties of siRNA to provide protection and to enhance biomembrane interactions, residence times, tissue absorption, and cellular internalization for improved cytoplasm and/or nucleus interactions. In this review, we highlight advances in, and the role of, siRNA-based nanocarriers for the treatment of various NDs.