Cell-type-specific miR-431 dysregulation in a motor neuron model of spinal muscular atrophy

Revealing the potential role of hsa-miR-663a in modulating the PI3K-Akt signaling pathway via miRNA microarray in spinal muscular atrophy patient fibroblast-derived iPSCs

Spinal muscular atrophy (SMA) is an autosomal recessive neuromuscular disorder due to deletion or mutation of survival motor neuron 1 (SMN1) gene. Although survival motor neuron 2 (SMN2) gene is still present in SMA patients, the production of full-length survival motor neuron (SMN) protein is insufficient owing to missing or mutated SMN1. No current disease-modifying therapies can cure SMA. The aim of this study was to explore microRNA (miRNA)-based therapies that may serve as a potential target for therapeutic intervention in delaying SMA progression or as treatment. The study screened for potentially dysregulated miRNAs in SMA fibroblast-derived iPSCs using miRNA microarray. Results from the miRNA microarray were validated using quantitative reverse transcription polymerase chain reaction. Bioinformatics analysis using various databases was performed to predict the potential putative gene targeted by hsa-miR-663a. The findings showed differential expression of hsa-miR-663a in SMA patients in relation to a healthy control. Bioinformatics analysis identified GNG7, IGF2, and TNN genes that were targeted by hsa-miR-663a to be involved in the PI3K-AKT pathway, which may be associated with disease progression in SMA. Thus, this study suggests the potential role of hsa-miR-663a as therapeutic target for the treatment of SMA patients in the near future.

Role of circulating biomarkers in spinal muscular atrophy: insights from a new treatment era

Spinal muscular atrophy (SMA) is a lower motor neuron disease due to biallelic mutations in the SMN1 gene on chromosome 5. It is characterized by progressive muscle weakness of limbs, bulbar and respiratory muscles. The disease is usually classified in four different phenotypes (1-4) according to age at symptoms onset and maximal motor milestones achieved. Recently, three disease modifying treatments have received approval from the Food and Drug Administration (FDA) and the European Medicines Agency (EMA), while several other innovative drugs are under study. New therapies have been game changing, improving survival and life quality for SMA patients. However, they have also intensified the need for accurate biomarkers to monitor disease progression and treatment efficacy. While clinical and neurophysiological biomarkers are well established and helpful in describing disease progression, there is a great need to develop more robust and sensitive circulating biomarkers, such as proteins, nucleic acids, and other small molecules. Used alone or in combination with clinical biomarkers, they will play a critical role in enhancing patients' stratification for clinical trials and access to approved treatments, as well as in tracking response to therapy, paving the way to the development of individualized therapeutic approaches. In this comprehensive review, we describe the foremost circulating biomarkers of current significance, analyzing existing literature on non-treated and treated patients with a special focus on neurofilaments and circulating miRNA, aiming to identify and examine their role in the follow-up of patients treated with innovative treatments, including gene therapy.

SMN promotes mitochondrial metabolic maturation during myogenesis by regulating the MYOD-miRNA axis

Spinal muscular atrophy (SMA) is a congenital neuromuscular disease caused by the mutation or deletion of the survival motor neuron 1 (SMN1) gene. Although the primary cause of progressive muscle atrophy in SMA has classically been considered the degeneration of motor neurons, recent studies have indicated a skeletal muscle-specific pathological phenotype such as impaired mitochondrial function and enhanced cell death. Here, we found that the down-regulation of SMN causes mitochondrial dysfunction and subsequent cell death in in vitro models of skeletal myogenesis with both a murine C2C12 cell line and human induced pluripotent stem cells. During myogenesis, SMN binds to the upstream genomic regions of MYOD1 and microRNA (miR)-1 and miR-206. Accordingly, the loss of SMN down-regulates these miRs, whereas supplementation of the miRs recovers the mitochondrial function, cell survival, and myotube formation of SMN-deficient C2C12, indicating the SMN-miR axis is essential for myogenic metabolic maturation. In addition, the introduction of the miRs into ex vivo muscle stem cells derived from Δ7-SMA mice caused myotube formation and muscle contraction. In conclusion, our data revealed novel transcriptional roles of SMN during myogenesis, providing an alternative muscle-oriented therapeutic strategy for SMA patients.

ISGylation is induced in neurons by demyelination driving ISG15-dependent microglial activation

The causes of grey matter pathology and diffuse neuron injury in MS remain incompletely understood. Axonal stress signals arising from white matter lesions has been suggested to play a role in initiating this diffuse grey matter pathology. Therefore, to identify the most upstream transcriptional responses in neurons arising from demyelinated axons, we analyzed the transcriptome of actively translating neuronal transcripts in mouse models of demyelinating disease. Among the most upregulated genes, we identified transcripts associated with the ISGylation pathway. ISGylation refers to the covalent attachment of the ubiquitin-like molecule interferon stimulated gene (ISG) 15 to lysine residues on substrates targeted by E1 ISG15-activating enzyme, E2 ISG15-conjugating enzymes and E3 ISG15-protein ligases. We further confirmed that ISG15 expression is increased in MS cortical and deep gray matter. Upon investigating the functional impact of neuronal ISG15 upregulation, we noted that ISG15 expression was associated changes in neuronal extracellular vesicle protein and miRNA cargo. Specifically, extracellular vesicle-associated miRNAs were skewed toward increased frequency of proinflammatory and neurotoxic miRNAs and decreased frequency of anti-inflammatory and neuroprotective miRNAs. Furthermore, we found that ISG15 directly activated microglia in a CD11b-dependent manner and that microglial activation was potentiated by treatment with EVs from neurons expressing ISG15. Further study of the role of ISG15 and ISGylation in neurons in MS and neurodegenerative diseases is warranted.

Assessment of cerebral spinal fluid biomarkers and microRNA-mediated disease mechanisms in spinal muscular atrophy patient samples

Cerebral spinal fluid (CSF) is a promising biospecimen for the detection of central nervous system biomarkers to monitor therapeutic efficacy at the cellular level in neurological diseases. Spinal muscular atrophy (SMA) patients receiving intrathecal antisense oligonucleotide (nusinersen) therapy tend to show improved motor function, but the treatment effect on cellular health remains unknown. The objective of this study was to assess the potential of extracellular RNAs and microRNAs in SMA patient CSF as indicators of neuron and glial health following nusinersen treatment. Extracellular RNA analysis of CSF samples revealed ongoing cellular stress related to inflammation and glial differentiation, even after treatment administration. Downregulated microRNA expression associated with SMA-specific or general motor neuron dysfunction in animal and cellular models, tended to increase in nusinersen treated patient CSF samples and correlated with SMA Type 1 and 2 motor functioning improvements. However, miR-146a, known to be upregulated in SMA induced pluripotent stem cell (iPSC)-derived astrocytes, showed increased expression in nusinersen treated CSF samples. We then used mRNA sequencing and multi-electrode arrays to assess the transcriptional and functional effects of miR-146a on healthy and SMA iPSC-derived motor neurons. miR-146a treatment on iPSC-derived motor neurons led to a downregulation of extracellular matrix genes associated with synaptic perineuronal net and alterations in spontaneous electrophysiological activity. Together, this study suggests that extracellular RNAs and microRNAs may serve as useful biomarkers to monitor cellular health during nusinersen treatment. Moreover, these data highlight the importance of addressing astrocyte health and response to nusinersen in SMA pathogenesis and treatment strategies.

SMA-miRs (miR-181a-5p, -324-5p, and -451a) are overexpressed in spinal muscular atrophy skeletal muscle and serum samples

Background:

Spinal muscular atrophy (SMA) is a neuromuscular disorder characterized by the degeneration of the second motor neuron. The phenotype ranges from very severe to very mild forms. All patients have the homozygous loss of the SMN1 gene and a variable number of SMN2 (generally 2–4 copies), inversely related to the severity. The amazing results of the available treatments have made compelling the need of prognostic biomarkers to predict the progression trajectories of patients. Besides the SMN2 products, few other biomarkers have been evaluated so far, including some miRs.

Methods:

We performed whole miRNome analysis of muscle samples of patients and controls (14 biopsies and 9 cultures). The levels of muscle differentially expressed miRs were evaluated in serum samples (51 patients and 37 controls) and integrated with SMN2 copies, SMN2 full-length transcript levels in blood and age (SMA-score).

Results:

Over 100 miRs were differentially expressed in SMA muscle; 3 of them (hsa-miR-181a-5p, -324-5p, -451a; SMA-miRs) were significantly upregulated in the serum of patients. The severity predicted by the SMA-score was related to that of the clinical classification at a correlation coefficient of 0.87 (p<10^-5).

Conclusions:

miRNome analyses suggest the primary involvement of skeletal muscle in SMA pathogenesis. The SMA-miRs are likely actively released in the blood flow; their function and target cells require to be elucidated. The accuracy of the SMA-score needs to be verified in replicative studies: if confirmed, its use could be crucial for the routine prognostic assessment, also in presymptomatic patients.

Funding:

Telethon Italia (grant #GGP12116).

Functional roles of non-coding RNAs in atrophy

Atrophy is defined as a reduction in cell, organ, or tissue size after reaching their normal mature sizes because of loss of organelles, cytoplasmic compartments, and proteins. This process is also involved in the pathogenesis of human disorders. Inadequate nourishment, poor circulation, inadequate hormonal support, defects in nerve supply of the tissue, disproportionate induction of apoptosis in the tissue, and absence of exercise are some underlying causes of atrophy. Recently, several non-coding RNAs (ncRNAs) have been identified that regulate atrophy, thus participating in the pathobiology of related disorders such as neurodegenerative/ neuromuscular diseases, age-related muscle atrophy, and cardiac tissue atrophy. In the current review, we have focused on two classes of ncRNAs namely long ncRNAs (lncRNAs) and microRNAs (miRNAs) to unravel their participation in atrophy-associated disorders.

The potential role of miRNA therapies in spinal muscle atrophy

Spinal muscular atrophy (SMA) is a neurodegenerative disease caused by low levels of full-length survival motor neuron (SMN) protein due to the loss of the survival motor neuron 1 (SMN1) gene and inefficient splicing of the survival motor neuron 2 (SMN2) gene, which mostly affects alpha motor neurons of the lower spinal cord. Despite the U.S. Food and Drug Administration (FDA) approved SMN-dependent therapies including Nusinersen, Zolgensma® and Evrysdi™, SMA is still a devastating disease as these existing expensive drugs may not be sufficient and thus, remains a need for additional therapies. The involvement of microRNAs (miRNAs) in SMA is expanding because miRNAs are important mediators of gene expression as each miRNA could target a number of genes. Hence, miRNA-based therapy could be utilized in treating this genetic disorder. However, the delivery of miRNAs into the target cells remains an obstacle in SMA, as there is no effective delivery system to date. This review highlights the potential strategies for intracellular miRNA delivery into target cells and current challenges in miRNA delivery. Furthermore, we provide the future prospects of miRNA-based therapeutic strategies in SMA.

Neuronal Development-Related miRNAs as Biomarkers for Alzheimer's Disease, Depression, Schizophrenia and Ionizing Radiation Exposure

Radiation exposure may induce Alzheimer's disease (AD), depression or schizophrenia. A number of experimental and clinical studies suggest the involvement of miRNA in the development of these diseases, and also in the neuropathological changes after brain radiation exposure. The current literature review indicated the involvement of 65 miRNAs in neuronal development in the brain. In the brain tissue, blood, or cerebral spinal fluid (CSF), 11, 55, or 28 miRNAs are involved in the development of AD respectively, 89, 50, 19 miRNAs in depression, and 102, 35, 8 miRNAs in schizophrenia. We compared miRNAs regulating neuronal development to those involved in the genesis of AD, depression and schizophrenia and also those driving radiation-induced brain neuropathological changes by reviewing the available data. We found that 3, 11, or 8 neuronal developmentrelated miRNAs from the brain tissue, 13, 16 or 14 miRNAs from the blood of patient with AD, depression and schizophrenia respectively were also involved in radiation-induced brain pathological changes, suggesting a possibly specific involvement of these miRNAs in radiation-induced development of AD, depression and schizophrenia respectively. On the other hand, we noted that radiationinduced changes of two miRNAs, i.e., miR-132, miR-29 in the brain tissue, three miRNAs, i.e., miR- 29c-5p, miR-106b-5p, miR-34a-5p in the blood were also involved in the development of AD, depression and schizophrenia, thereby suggesting that these miRNAs may be involved in the common brain neuropathological changes, such as impairment of neurogenesis and reduced learning memory ability observed in these three diseases and also after radiation exposure.

Circulating microRNAs as potential biomarkers and therapeutic targets in spinal muscular atrophy

Spinal muscular atrophy (SMA), a leading genetic cause of infant death, is a neurodegenerative disease characterized by the selective loss of particular groups of motor neurons (MNs) in the anterior horn of the spinal cord with progressive muscle wasting. SMA is caused by a deficiency of the survival motor neuron (SMN) protein due to a homozygous deletion or mutation of the SMN1 gene. However, the molecular mechanisms whereby the SMN complex regulates MN functions are not fully elucidated. Emerging studies on SMA pathogenesis have turned the attention of researchers to RNA metabolism, given that increasingly identified SMN-associated modifiers are involved in both coding and non-coding RNA (ncRNA) processing. Among various ncRNAs, microRNAs (miRNAs) are the most studied in terms of regulation of posttranscriptional gene expression. Recently, the discovery that miRNAs are critical to MN function and survival led to the study of dysregulated miRNAs in SMA pathogenesis. Circulating miRNAs have drawn attention as a readily available biomarker due to their property of being clinically detectable in numerous human biofluids through non-invasive approaches. As there are recent promising findings from novel miRNA-based medicines, this article presents an extensive review of the most up-to-date studies connecting specific miRNAs to SMA pathogenesis and the potential applications of miRNAs as biomarkers and therapeutic targets for SMA.

Anti-NMDA Receptor Encephalitis, Vaccination and Virus

Anti-N-methyl-d-aspartate (Anti-NMDA) receptor encephalitis is an acute autoimmune disorder. The symptoms range from psychiatric symptoms, movement disorders, cognitive impairment, and autonomic dysfunction. Previous studies revealed that vaccination might induce this disease. A few cases were reported to be related to H1N1 vaccine, tetanus/diphtheria/pertussis and polio vaccine, and Japanese encephalitis vaccine. Although vaccination is a useful strategy to prevent infectious diseases, in a low risk, it may trigger serious neurological symptoms. In addition to anti-NMDA receptor encephalitis, other neurological diseases were reported to be associated with a number of vaccines. In this paper, the anti-NMDA receptor encephalitis cases related to a number of vaccines and other neurological symptoms that might be induced by these vaccines were reviewed. In addition, anti-NMDA receptor encephalitis cases that were induced by virus infection were also reviewed.

Current Status of microRNA-Based Therapeutic Approaches in Neurodegenerative Disorders

MicroRNAs (miRNAs) are a key gene regulator and play essential roles in several biological and pathological mechanisms in the human system. In recent years, plenty of miRNAs have been identified to be involved in the development of neurodegenerative disorders (NDDs), thus making them an attractive option for therapeutic approaches. Hence, in this review, we provide an overview of the current research of miRNA-based therapeutics for a selected set of NDDs, either for their high prevalence or lethality, such as Alzheimer's, Parkinson's, Huntington's, Amyotrophic Lateral Sclerosis, Friedreich's Ataxia, Spinal Muscular Atrophy, and Frontotemporal Dementia. We also discuss the relevant delivery techniques, pertinent outcomes, their limitations, and their potential to become a new generation of human therapeutic drugs in the near future.

RNA in spinal muscular atrophy: therapeutic implications of targeting

INTRODUCTION

Spinal muscular atrophy (SMA) is caused by low levels of the Survival Motor Neuron (SMN) protein due to deletions of or mutations in the SMN1 gene. Humans carry another nearly identical gene, SMN2, which mostly produces a truncated and less stable protein SMNΔ7 due to predominant skipping of exon 7. Elevation of SMN upon correction of SMN2 exon 7 splicing and gene therapy have been proven to be the effective treatment strategies for SMA.

AREAS COVERED

This review summarizes existing and potential SMA therapies that are based on RNA targeting.We also discuss the mechanistic basis of RNA-targeting molecules.

EXPERT OPINION

The discovery of intronic splicing silencer N1 (ISS-N1) was the first major step towards developing the currently approved antisense-oligonucleotide (ASO)-directed therapy (SpinrazaTM) based on the correction of exon 7 splicing of the endogenous SMN2pre-mRNA. Recently, gene therapy (Zolgensma) has become the second approved treatment for SMA. Small compounds (currently in clinical trials) capable of restoring SMN2 exon 7 inclusion further expand the class of the RNA targeting molecules for SMA therapy. Endogenous RNA targets, such as long non-coding RNAs, circular RNAs, microRNAs and ribonucleoproteins, could be potentially exploited for developing additional SMA therapies.

Multifaceted roles of microRNAs: From motor neuron generation in embryos to degeneration in spinal muscular atrophy

Two crucial questions in neuroscience are how neurons establish individual identity in the developing nervous system and why only specific neuron subtypes are vulnerable to neurodegenerative diseases. In the central nervous system, spinal motor neurons serve as one of the best-characterized cell types for addressing these two questions. In this review, we dissect these questions by evaluating the emerging role of regulatory microRNAs in motor neuron generation in developing embryos and their potential contributions to neurodegenerative diseases such as spinal muscular atrophy (SMA). Given recent promising results from novel microRNA-based medicines, we discuss the potential applications of microRNAs for clinical assessments of SMA disease progression and treatment.

miR-431-5p Knockdown Protects Against Angiotensin II-Induced Hypertension and Vascular Injury

Vascular injury is an early manifestation in hypertension and a cause of end-organ damage. MicroRNAs play an important role in cardiovascular disease, but their implication in vascular injury in hypertension remains unclear. This study revealed using an unbiased approach, microRNA and mRNA sequencing with molecular interaction analysis, a microRNA-transcription factor coregulatory network involved in vascular injury in mice made hypertensive by 14-day Ang II (angiotensin II) infusion. A candidate gene approach identified upregulated miR-431-5p encoded in the conserved 12qF1 (14q32 in humans) microRNA cluster, whose expression correlated with blood pressure, and which has been shown to be upregulated in human atherosclerosis, as a potential key regulator in Ang II-induced vascular injury. Gain- and loss-of-function in human vascular smooth muscle cells demonstrated that miR-431-5p regulates in part gene expression by targeting ETS homologous factor. In vivo miR-431-5p knockdown delayed Ang II-induced blood pressure elevation and reduced vascular injury in mice, which demonstrated its potential as a target for treatment of hypertension and vascular injury.

AAV9-mediated delivery of miR-23a reduces disease severity in Smn2B/-SMA model mice

Spinal muscular atrophy (SMA) is a neuromuscular disease caused by deletions or mutations in survival motor neuron 1 (SMN1). The molecular mechanisms underlying motor neuron degeneration in SMA remain elusive, as global cellular dysfunction obscures the identification and characterization of disease-relevant pathways and potential therapeutic targets. Recent reports have implicated microRNA (miRNA) dysregulation as a potential contributor to the pathological mechanism in SMA. To characterize miRNAs that are differentially regulated in SMA, we profiled miRNA levels in SMA induced pluripotent stem cell (iPSC)-derived motor neurons. From this array, miR-23a downregulation was identified selectively in SMA motor neurons, consistent with previous reports where miR-23a functioned in neuroprotective and muscle atrophy-antagonizing roles. Reintroduction of miR-23a expression in SMA patient iPSC-derived motor neurons protected against degeneration, suggesting a potential miR-23a-specific disease-modifying effect. To assess this activity in vivo, miR-23a was expressed using a self-complementary adeno-associated virus serotype 9 (scAAV9) viral vector in the Smn2B/- SMA mouse model. scAAV9-miR-23a significantly reduced the pathology in SMA mice, including increased motor neuron size, reduced neuromuscular junction pathology, increased muscle fiber area, and extended survival. These experiments demonstrate that miR-23a is a novel protective modifier of SMA, warranting further characterization of miRNA dysfunction in SMA.

Mechanism of microRNA-431-5p-EPB41L1 interaction in glioblastoma multiforme cells

INTRODUCTION

Glioblastoma multiforme (GBM) is a kind of malignant brain tumor prevalent in adults, with the characteristics well adapted to poorly immunogenic and hypoxic conditions. Effective treatment of GBM is impeded due to the high proliferation, migration and invasion of GBM cells. GBM cells migrate by degrading the extracellular matrix, so it is difficult to have GBM cells eradicated completely by surgery. This study aims to confirm that miR-431-5p could influence the proliferation, invasion and migration of human glioblastoma multiforme cells by targeting EPB41L1 (erythrocyte membrane protein band 4.1).

MATERIAL AND METHODS

The expression levels of miR-431-5p and EPB41L1 were detected in GBM cells and tissues using qRT-PCR. Dual luciferase reporter gene assay and western blot were applied to confirm the targeting relationship between miR-431-5p and EPB41L1. GBM cell line U87 was used in MTT, flow cytometry, Transwell, and wound healing assays to determine cell proliferation, migration and invasion.

RESULTS

MiR-431-5p was overexpressed in GBM tissues while EPB41L1 was under-expressed. The results of dual luciferase reporter gene assay and western blot demonstrated that miR-431-5p could target EPB41L1 and suppress its expression. Down-regulating the expression of miR-431-5p or up-regulating the expression of EPB41L1 could inhibit the proliferation, invasion and migration but promote the apoptosis of GBM cells.

CONCLUSIONS

MiR-431-5p facilitated the progression of GBM by inhibiting EPB41L1 expression.

Hyperexcitability precedes motoneuron loss in the Smn2B/- mouse model of spinal muscular atrophy

Spinal motoneuron dysfunction and loss are pathological hallmarks of the neuromuscular disease spinal muscular atrophy (SMA). Changes in motoneuron physiological function precede cell death, but how these alterations vary with disease severity and motoneuron maturational state is unknown. To address this question, we assessed the electrophysiology and morphology of spinal motoneurons of presymptomatic Smn^2B/- mice older than 1 wk of age and tracked the timing of motor unit loss in this model using motor unit number estimation (MUNE). In contrast to other commonly used SMA mouse models, Smn^2B/- mice exhibit more typical postnatal development until postnatal day (P)11 or 12 and have longer survival (~3 wk of age). We demonstrate that Smn^2B/- motoneuron hyperexcitability, marked by hyperpolarization of the threshold voltage for action potential firing, was present at P9-10 and preceded the loss of motor units. Using MUNE studies, we determined that motor unit loss in this mouse model occurred 2 wk after birth. Smn^2B/- motoneurons were also larger in size, which may reflect compensatory changes taking place during postnatal development. This work suggests that motoneuron hyperexcitability, marked by a reduced threshold for action potential firing, is a pathological change preceding motoneuron loss that is common to multiple models of severe SMA with different motoneuron maturational states. Our results indicate voltage-gated sodium channel activity may be altered in the disease process.NEW & NOTEWORTHY Changes in spinal motoneuron physiologic function precede cell death in spinal muscular atrophy (SMA), but how they vary with maturational state and disease severity remains unknown. This study characterized motoneuron and neuromuscular electrophysiology from the Smn^2B/- model of SMA. Motoneurons were hyperexcitable at postnatal day (P)9-10, and specific electrophysiological changes in Smn^2B/- motoneurons preceded functional motor unit loss at P14, as determined by motor unit number estimation studies.

Functional characterization of SMN evolution in mouse models of SMA

Spinal Muscular Atrophy (SMA) is a monogenic neurodegenerative disorder and the leading genetic cause of infantile mortality. While several functions have been ascribed to the SMN (survival motor neuron) protein, their specific contribution to the disease has yet to be fully elucidated. We hypothesized that some, but not all, SMN homologues would rescue the SMA phenotype in mouse models, thereby identifying disease-relevant domains. Using AAV9 to deliver Smn homologs to SMA mice, we identified a conservation threshold that marks the boundary at which homologs can rescue the SMA phenotype. Smn from Danio rerio and Xenopus laevis significantly prevent disease, whereas Smn from Drosophila melanogaster, Caenorhabditis elegans, and Schizosaccharomyces pombe was significantly less efficacious. This phenotypic rescue correlated with correction of RNA processing defects induced by SMN deficiency and neuromuscular junction pathology. Based upon the sequence conservation in the rescuing homologs, a minimal SMN construct was designed consisting of exons 2, 3, and 6, which showed a partial rescue of the SMA phenotype. While a significant extension in survival was observed, the absence of a complete rescue suggests that while the core conserved region is essential, additional sequences contribute to the overall ability of the SMN protein to rescue disease pathology.

miR-155-5p Promotes Dorsal Root Ganglion Neuron Axonal Growth in an Inhibitory Microenvironment via the cAMP/PKA Pathway

Sensory dysfunction post spinal cord injury causes patients great distress. Sciatic nerve conditioning injury (SNCI) has been shown to restore sensory function after spinal cord dorsal column injury (SDCL); however, the underlying mechanism of this recovery remains unclear. We performed a microarray assay to determine the associated miRNAs that might regulate the process of SNCI promoting SDCL repair. In total, 13 miRNAs were identified according to our inclusion criteria, and RT-qPCR was used to verify the microarray results. Among the 13 miRNAs, the miR-155-5p levels were decreased at 9 h, 3 d, 7 d, 14 d, 28 d, 2 m and 3 m timepoints in the SDCL group, while the SNCI group had a smaller decrease. Thus, miR-155-5p was chosen for further study after a literature review and an analysis with the TargetScan online tool. Specifically, miR-155-5p targets PKI-α, and the expression pattern of PKI-α was opposite that of miR-155-5p in both the SDCL and SNCI groups. Interestingly, miR-155-5p could promote dorsal root ganglion (DRG) neuron axon growth via the cAMP/PKA pathway and in a TNF-α, IL-1β or MAG inhibitory microenvironment in vitro. Furthermore, miR-155-5p could regulate the cAMP/PKA pathway and promote sensory conduction function recovery post dorsal column injury as detected by NF-200 immunohistochemistry, somatosensory-evoked potentials, BBB scale and tape removal test. Collectively, our results demonstrated that miR-155-5p participates in the molecular mechanism by which SNCI promotes the repair of SDCL and that upregulated miR-155-5p can repair SDCL by enhancing DRG neuron axon growth via the cAMP/PKA pathway. These findings suggest a novel treatment target for spinal cord injury.

Biomimicking Fiber Scaffold as an Effective In Vitro and In Vivo MicroRNA Screening Platform for Directing Tissue Regeneration

MicroRNAs effectively modulate protein expression and cellular response. Unfortunately, the lack of robust nonviral delivery platforms has limited the therapeutic application of microRNAs. Additionally, there is a shortage of drug-screening platforms that are directly translatable from in vitro to in vivo. Here, a fiber substrate that provides nonviral delivery of microRNAs for in vitro and in vivo microRNA screening is introduced. As a proof of concept, difficult-to-transfect primary neurons are targeted and the efficacy of this system is evaluated in a rat spinal cord injury model. With this platform, enhanced gene-silencing is achieved in neurons as compared to conventional bolus delivery (p < 0.05). Thereafter, four well-recognized microRNAs (miR-21, miR-222, miR-132, and miR-431) and their cocktails are screened systematically. Regardless of age and origin of the neurons, similar trends are observed. Next, this fiber substrate is translated into a 3D system for direct in vivo microRNA screening. Robust nerve ingrowth is observed as early as two weeks after scaffold implantation. Nerve regeneration in response to the microRNA cocktails is similar to in vitro experiments. Altogether, the potential of the fiber platform is demonstrated in providing effective microRNA screening and direct translation into in vivo applications.

[Continuous expression of miR-431 during lung development in Sprague-Dawley rats]

OBJECTIVE

To study the role of miR-431 in lung development and morphology.

METHODS

According to the stage of lung development in rats, Sprague-Dawley rats at embryonic day 16 (E16), embryonic day (E19), embryonic day (E21), postnatal day 1 (P1), postnatal day 3 (P3), postnatal day 7 (P7), postnatal day 14 (P14) and 10 weeks after birth (P10 weeks) were selected, and lung tissue samples were collected for observation. Hematoxylin-eosin staining and transmission electron microscopy were performed to observe the morphology of lung tissue. Fluorescence in situ hybridization and real-time PCR were used to measure the expression of miR-431 during the critical stages of lung development (E19, E21 and P3).

RESULTS

The E19 group had the formation of the lamellar body and type II alveolar epithelial cells in the fetal lung tissue. The number of lamellar bodies increased with the increasing gestational age, with aggregation and excretion. Pulmonary alveoli formed rapidly, the lung interstitium became thinner, and the microvascular system became mature after birth. Fluorescence in situ hybridization and real-time PCR showed that the expression of miR-431 gradually decreased with the increasing gestational age (P<0.05).

CONCLUSIONS

The systematic and continuous morphological data of lung development is obtained in this experiment. In addition, miR-431 may play an important role in the negative regulation of lung development, which provides basis and direction for further research on the mechanism of lung development and related diseases.

Dysregulation of microRNA metabolism in motor neuron diseases: Novel biomarkers and potential therapeutics

In the last 15 years, several classes of small regulatory RNAs have been identified, uncovering the widespread impact of non-coding elements in the human genome on cell homeostasis and human diseases. MicroRNAs (miRNAs) are a family of small, non-coding RNAs, which exert silencing of mRNA targets in a sequence-dependent fashion. Many miRNAs are specifically expressed in the central nervous system, where they display roles in differentiation, neuronal survival, neuronal plasticity and learning. On the other hand, deregulated miRNA/mRNA expression networks are deeply involved in neurodegeneration. Recent findings suggest a role for miRNAs in the pathogenesis of motor neuron diseases. In particular, cell-specific changes in miRNA profile are involved in the motor neuron disease phenotype and might be implicated in their selective vulnerability. Exploitation of noncoding RNAs, in particular miRNAs, for therapeutic strategies is being assessed for implementing current therapies. In this regard, the neuroprotective potential of certain miRNAs could represent a promising potential tool to improve therapies for motor-neuron diseases. This review focuses on emerging roles of miRNAs in motor neuron diseases and on their impact on neuron life-span and integrity.

Neuronal activity regulates DROSHA via autophagy in spinal muscular atrophy

Dysregulated miRNA expression and mutation of genes involved in miRNA biogenesis have been reported in motor neuron diseases including spinal muscular atrophy (SMA) and amyotrophic lateral sclerosis (ALS). Therefore, identifying molecular mechanisms governing miRNA expression is important to understand these diseases. Here, we report that expression of DROSHA, which is a critical enzyme in the microprocessor complex and essential for miRNA biogenesis, is reduced in motor neurons from an SMA mouse model. We show that DROSHA is degraded by neuronal activity induced autophagy machinery, which is also dysregulated in SMA. Blocking neuronal activity or the autophagy-lysosome pathway restores DROSHA levels in SMA motor neurons. Moreover, reducing DROSHA levels enhances axonal growth. As impaired axonal growth is a well described phenotype of SMA motor neurons, these data suggest that DROSHA reduction by autophagy may mitigate the phenotype of SMA. In summary, these findings suggest that autophagy regulates RNA metabolism and neuronal growth via the DROSHA/miRNA pathway and this pathway is dysregulated in SMA.

Astrocyte-produced miR-146a as a mediator of motor neuron loss in spinal muscular atrophy

Spinal muscular atrophy (SMA), the leading genetic cause of infant mortality, is caused by the loss of the survival motor neuron-1 (SMN1) gene, which leads to motor neuron loss, muscle atrophy, respiratory distress, and death. Motor neurons exhibit the most profound loss, but the mechanisms underlying disease pathogenesis are not fully understood. Recent evidence suggests that motor neuron extrinsic influences, such as those arising from astrocytes, contribute to motor neuron malfunction and loss. Here we investigated both loss-of-function and toxic gain-of-function astrocyte mechanisms that could play a role in SMA pathology. We had previously found that glial derived neurotrophic factor (GDNF) is reduced in SMA astrocytes. However, reduced GDNF expression does not play a major role in SMA pathology as viral-mediated GDNF re-expression did not improve astrocyte function or motor neuron loss. In contrast, we found that SMA astrocytes increased microRNA (miR) production and secretion compared to control astrocytes, suggesting potential toxic gain-of-function properties. Specifically, we found that miR-146a was significantly upregulated in SMA induced pluripotent stem cell (iPSC)-derived astrocytes and SMNΔ7 mouse spinal cord. Moreover, increased miR-146a was sufficient to induce motor neuron loss in vitro, whereas miR-146a inhibition prevented SMA astrocyte-induced motor neuron loss. Together, these data indicate that altered astrocyte production of miR-146a may be a contributing factor in astrocyte-mediated SMA pathology.

miRNA in spinal muscular atrophy pathogenesis and therapy

Spinal muscular atrophy (SMA) is an autosomal recessive neurodegenerative disease characterized by the selective death of lower motor neurons in the brain stem and spinal cord. SMA is caused by mutations in the survival motor neuron 1 gene (SMN1), leading to the reduced expression of the full-length SMN protein. microRNAs (miRNAs) are small RNAs that regulate post-transcriptional gene expression. Recent findings have suggested an important role for miRNAs in the pathogenesis of motor neuron diseases, including SMA. Motor neuron-specific miRNA dysregulation in SMA might be implicated in their selective vulnerability. In this study, we discuss recent findings regarding the consequences of SMN defects on miRNAs and their target mRNAs in motor neurons. Taken together, these data suggest that cell-specific changes in miRNAs are not only involved in the SMA motor neuron phenotype but can also be used as biomarkers and therapeutic targets.

SMN - A chaperone for nuclear RNP social occasions?

Survival Motor Neuron (SMN) protein localizes to both the nucleus and the cytoplasm. Cytoplasmic SMN is diffusely localized in large oligomeric complexes with core member proteins, called Gemins. Biochemical and cell biological studies have demonstrated that the SMN complex is required for the cytoplasmic assembly and nuclear transport of Sm-class ribonucleoproteins (RNPs). Nuclear SMN accumulates with spliceosomal small nuclear (sn)RNPs in Cajal bodies, sub-domains involved in multiple facets of snRNP maturation. Thus, the SMN complex forms stable associations with both nuclear and cytoplasmic snRNPs, and plays a critical role in their biogenesis. In this review, we focus on potential functions of the nuclear SMN complex, with particular emphasis on its role within the Cajal body.

MotomiRs: miRNAs in Motor Neuron Function and Disease

MiRNAs are key regulators of the mammalian transcriptome that have been increasingly linked to degenerative diseases of the motor neurons. Although many of the miRNAs currently incriminated as participants in the pathogenesis of these diseases are also important to the normal development and function of motor neurons, at present there is no knowledge of the complete miRNA profile of motor neurons. In this review, we examine the current understanding with respect to miRNAs that are specifically required for motor neuron development, function and viability, and provide evidence that these should be considered as a functional network of miRNAs which we have collectively termed MotomiRs. We will also summarize those MotomiRs currently known to be associated with both amyotrophic lateral sclerosis (ALS) and spinal muscular atrophy (SMA), and discuss their potential use as biomarkers.

Decreased microRNA levels lead to deleterious increases in neuronal M2 muscarinic receptors in Spinal Muscular Atrophy models

Spinal Muscular Atrophy (SMA) is caused by diminished Survival of Motor Neuron (SMN) protein, leading to neuromuscular junction (NMJ) dysfunction and spinal motor neuron (MN) loss. Here, we report that reduced SMN function impacts the action of a pertinent microRNA and its mRNA target in MNs. Loss of the C. elegans SMN ortholog, SMN-1, causes NMJ defects. We found that increased levels of the C. elegans Gemin3 ortholog, MEL-46, ameliorates these defects. Increased MEL-46 levels also restored perturbed microRNA (miR-2) function in smn-1(lf) animals. We determined that miR-2 regulates expression of the C. elegans M2 muscarinic receptor (m2R) ortholog, GAR-2. GAR-2 loss ameliorated smn-1(lf) and mel-46(lf) synaptic defects. In an SMA mouse model, m2R levels were increased and pharmacological inhibition of m2R rescued MN process defects. Collectively, these results suggest decreased SMN leads to defective microRNA function via MEL-46 misregulation, followed by increased m2R expression, and neuronal dysfunction in SMA.

DOI:http://dx.doi.org/10.7554/eLife.20752.001

Spinal muscular atrophy is a genetic disease that causes muscles to gradually weaken. In people with the disease, the nerve cells that control the movement of muscles – called motor neurons – deteriorate over time, hindering the person’s mobility and shortening their life expectancy. Spinal muscular atrophy is usually caused by genetic faults affecting a protein called SMN (which is short for “Survival of motor neuron”) and recent research suggested that disrupting this protein alters the function of short pieces of genetic material called microRNAs. However, the precise role that microRNAs play in the disease and their connection to the SMN protein was not clear.

MicroRNAs interfere with the production of proteins by disrupting molecules called messenger RNAs, which are temporary strings of genetic code that carry the instructions for making protein. By disrupting messenger RNAs, microRNAs can delay or halt the production of specific proteins. This is an important part of the normal behavior of a cell, but disturbing the activity of microRNAs can lead to an unwanted rise or fall in crucial proteins.

O’Hern et al. made use of engineered nematode worms and mice that share genetic features with spinal muscular atrophy patients, including disruption of the gene responsible for producing the SMN protein. These animal models of the disease were used to examine the relationship between decreased SMN levels and microRNAs in motor neurons. The experiments showed that reduced SMN activity affects a specific microRNA, which in turn causes motor neurons to produce more of a protein called m2R. This protein is a receptor for a molecule, called acetylcholine, which motor neurons use to send signals to muscle cells.

Increased m2R may be detrimental to motor neurons. As such, O’Hern et al. decreased m2R protein activity to determine whether this could reverse the defects in motor neurons that arise in the animal models of the disease. Indeed, blocking this receptor rescued some of the defects seen in the animal models, supporting the link to spinal muscular atrophy.

Several treatments that block m2R are already available to treat other conditions. As such, the next step is to determine whether these existing treatments are able to protect mice models of spinal muscular atrophy against muscle deterioration or increase their lifespan. If successful, this could open new avenues for the development of treatments in people.

DOI:http://dx.doi.org/10.7554/eLife.20752.002

Diverse role of survival motor neuron protein

The multifunctional Survival Motor Neuron (SMN) protein is required for the survival of all organisms of the animal kingdom. SMN impacts various aspects of RNA metabolism through the formation and/or interaction with ribonucleoprotein (RNP) complexes. SMN regulates biogenesis of small nuclear RNPs, small nucleolar RNPs, small Cajal body-associated RNPs, signal recognition particles and telomerase. SMN also plays an important role in DNA repair, transcription, pre-mRNA splicing, histone mRNA processing, translation, selenoprotein synthesis, macromolecular trafficking, stress granule formation, cell signaling and cytoskeleton maintenance. The tissue-specific requirement of SMN is dictated by the variety and the abundance of its interacting partners. Reduced expression of SMN causes spinal muscular atrophy (SMA), a leading genetic cause of infant mortality. SMA displays a broad spectrum ranging from embryonic lethality to an adult onset. Aberrant expression and/or localization of SMN has also been associated with male infertility, inclusion body myositis, amyotrophic lateral sclerosis and osteoarthritis. This review provides a summary of various SMN functions with implications to a better understanding of SMA and other pathological conditions.

Extrinsic and Intrinsic Regulation of Axon Regeneration by MicroRNAs after Spinal Cord Injury

Spinal cord injury is a devastating disease which disrupts the connections between the brain and spinal cord, often resulting in the loss of sensory and motor function below the lesion site. Most injured neurons fail to regenerate in the central nervous system after injury. Multiple intrinsic and extrinsic factors contribute to the general failure of axonal regeneration after injury. MicroRNAs can modulate multiple genes' expression and are tightly controlled during nerve development or the injury process. Evidence has demonstrated that microRNAs and their signaling pathways play important roles in mediating axon regeneration and glial scar formation after spinal cord injury. This article reviews the role and mechanism of differentially expressed microRNAs in regulating axon regeneration and glial scar formation after spinal cord injury, as well as their therapeutic potential for promoting axonal regeneration and repair of the injured spinal cord.