Danyella B. Dogini

The new world of RNAs

One of the major developments that resulted from the human genome sequencing projects was a better understanding of the role of non-coding RNAs (ncRNAs). NcRNAs are divided into several different categories according to size and function; however, one shared feature is that they are not translated into proteins. In this review, we will discuss relevant aspects of ncRNAs, focusing on two main types: i) microRNAs, which negatively regulate gene expression either by translational repression or target mRNA degradation, and ii) small interfering RNAs (siRNAs), which are involved in the biological process of RNA interference (RNAi). Our knowledge regarding these two types of ncRNAs has increased dramatically over the past decade, and they have a great potential to become therapeutic alternatives for a variety of human conditions.

MicroRNA Expression Profile in Murine Central Nervous System Development

MicroRNAs (miRNAs) regulate gene expression in a post-transcriptional sequence-specific manner. In order to better understand the possible roles of miRNAs in central nervous system (CNS) development, we examined the expression profile of 104 miRNAs during murine brain development. We obtained brain samples from animals at embryonic days (E) E15, E17, and postnatal days (P) P1 and P7. Total RNA was isolated from tissue and used to obtain mature miRNAs by reverse transcription. Our results indicate that there is a group of 12 miRNAs that show a distinct expression profile, with the highest expression during embryonic stages and decreasing significantly during development. This profile suggests key roles in processes occurring during early CNS development.

MicroRNA regulation and dysregulation in epilepsy

Epilepsy, one of the most frequent neurological disorders, represents a group of diseases that have in common the clinical occurrence of seizures. The pathogenesis of different types of epilepsy involves many important biological pathways; some of which have been shown to be regulated by microRNAs (miRNAs). In this paper, we will critically review relevant studies regarding the role of miRNAs in epilepsy. Overall, the most common type of epilepsy in the adult population is temporal lobe epilepsy (TLE), and the form associated with mesial temporal sclerosis (MTS), called mesial TLE, is particularly relevant due to the high frequency of resistance to clinical treatment. There are several target studies, as well few genome-wide miRNA expression profiling studies reporting abnormal miRNA expression in tissue with MTS, both in patients and in animal models. Overall, these studies show a fine correlation between miRNA regulation/dysregulation and inflammation, seizure-induced neuronal death and other relevant biological pathways. Furthermore, expression of many miRNAs is dynamically regulated during neurogenesis and its dysregulation may play a role in the process of cerebral corticogenesis leading to malformations of cortical development (MCD), which represent one of the major causes of drug-resistant epilepsy. In addition, there are reports of miRNAs involved in cell proliferation, fate specification, and neuronal maturation and these processes are tightly linked to the pathogenesis of MCD. Large-scale analyzes of miRNA expression in animal models with induced status epilepticus have demonstrated changes in a selected group of miRNAs thought to be involved in the regulation of cell death, synaptic reorganization, neuroinflammation, and neural excitability. In addition, knocking-down specific miRNAs in these animals have demonstrated that this may consist in a promising therapeutic intervention.

MicroRNAs-424 and 206 are potential prognostic markers in spinal onset amyotrophic lateral sclerosis.

INTRODUCTION Skeletal muscle microRNAs (miRNAs) are potential candidate biomarkers for amyotrophic lateral sclerosis (ALS) that deserve further investigation. OBJECTIVES To identify miRNAs abnormally expressed in the skeletal muscle and plasma of patients with ALS, and to correlate them with parameters of disease progression. METHODS Expression profile of miRNAs in muscle was evaluated using an array platform. Subsequently we assessed the plasmatic expression of candidate miRNAs in a set of 39 patients/39 controls. We employed generalized estimating equations to investigate correlations with clinical data. RESULTS We identified 11 miRNAs differentially expressed in the muscle of ALS patients; of these, miR424, miR-214 and miR-206 were validated by qPCR in muscle samples. In plasma, we found only miR-424 and miR 206 to be overexpressed. Baseline expression of miR-424 and 206 correlated with clinical deterioration over time. CONCLUSION MiR-424 and miR-206 are potential prognostic markers for ALS.

SPG4-related hereditary spastic paraplegia: frequency and mutation spectrum in Brazil

To the Editor : Hereditary spastic paraplegia (HSP) is a heterogeneous group of neurodegenerative disorders characterized by progressive lower limb spasticity and weakness. Mutations in SPAST /SPG4 are the major cause of autosomal dominant (AD-HSP) in Europe accounting for 40–50% of all patients (1). However, there are few studies on SPG4-HSP from Latin America (2), which has a distinctive ethnic background (populations from European, African and Native American descent). Therefore, our aim was to investigate the frequency and mutation spectrum of SPG4-HSP in a cohort of 55 Brazilian patients with AD-HSP from 34 unrelated families. Patients were recruited from three centers in the south and southeast of Brazil: Universidade Estadual de Campinas (23 families), Universidade Federal do Paraná (7) and Universidade Federal do Rio Grande do Sul (4). This study was approved by our institution Ethics Committee and written informed consent was obtained from all participants. Genomic DNA was used in polymerase chain reactions with primers designed to cover the 17 exons of SPAST /SPG4 (3). Mutation screening was performed by automatic Sanger sequencing and multiplexligand probe amplification (MLPA). All variants found were checked in human single nucleotide polymorphism (SNP) and mutation databases: Ensembl (www.ensembl.org), Human Gene Mutation Database

MicroRNA hsa-miR-134 is a circulating biomarker for mesial temporal lobe epilepsy

Epilepsy is misdiagnosed in up to 25% of patients, leading to serious and long-lasting consequences. Recently, circulating microRNAs have emerged as potential biomarkers in a number of clinical scenarios. The purpose of this study was to identify and to validate circulating microRNAs that could be used as biomarkers in the diagnosis of epilepsy. Quantitative real-time PCR was used to measure plasma levels of three candidate microRNAs in two phases of study: an initial discovery phase with 14 patients with mesial temporal lobe epilepsy (MTLE), 13 with focal cortical dysplasia (FCD) and 16 controls; and a validation cohort constituted of an independent cohort of 65 patients with MTLE and 83 controls. We found hsa-miR-134 downregulated in patients with MTLE (p = 0.018) but not in patients with FCD, when compared to controls. Furthermore, hsa-miR-134 expression could be used to discriminate MTLE patients with an area under the curve (AUC) of 0.75. To further assess the robustness of hsa-miR-134 as a biomarker for MTLE, we studied an independent cohort of 65 patients with MTLE, 27 of whom MTLE patients were responsive to pharmacotherapy, and 38 patients were pharmacoresistant and 83 controls. We confirmed that hsa-miR-134 was significantly downregulated in the plasma of patients with MTLE when compared with controls (p < 0.001). In addition, hsa-miR-134 identified patients with MTLE regardless of their response to pharmacotherapy or the presence of MRI signs of hippocampal sclerosis. We revealed that decreased expression of hsa-miR-134 could be a potential non-invasive biomarker to support the diagnosis of patients with MTLE.

Dysregulation of NEUROG2 plays a key role in focal cortical dysplasia.

Focal cortical dysplasias (FCDs) are an important cause of drug‐resistant epilepsy. In this work, we aimed to investigate whether abnormal gene regulation, mediated by microRNA, could be involved in FCD type II.

MicroRNA expression profile in epilepsy: breaking molecular barriers

BACKGROUND: MicroRNAs (miRNAs) are small RNA molecules (21-24 nt) that negatively regulate gene expression, either by repression of translation or by degradation of messenger RNA. These molecules are involved in many important processes including cell differentiation, neurogenesis, formation of nervous system and others. Mesial temporal lobe epilepsy and epilepsy caused by cortical dysgenesis are among the leading causes of drug resistant epilepsy. OBJECTIVES: The objectives of this study were to characterize the expression profile of miRNAs and to investigate their regulation in mesial temporal lobe epilepsy (MTL) and in focal cortical dysplasias (FCDs). METHODS: Total RNA was extracted from hippocampal and neocortical tissue, maintained in paraffin or fresh-frozen, from patients who underwent surgery for seizure control. For comparison we used tissue obtained from autopsy. RNA was extracted and used in real time PCR reactions (157 miRNAs analyzed) or microarray chips (847 miRNAs analyzed). RESULTS: Bioinformatics analyzes identified three miRNAs with expression significantly different in patients with MTLE: let-7d, miR-29b and miR-30d; while in patients with FCDs we found 23 microRNAs differentially expressed. In addition, we found that different pathological forms of had different molecular signatures. CONCLUSIONS: The possible genes regulated by miRNAs with differential expression in tissue with mesial temporal sclerosis (MTS) are mainly related to neurogenesis and apoptosis. While in DCFs they were predominantly related to cell proliferation and migration. Our results demonstrate the importance of miRNA regulation the in molecular processes that lead to the lesions present in the MTS and the FCDs.