Javier Riancho

Neuroprotective Effect of Bexarotene in the SOD1G93A Mouse Model of Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease characterized by progressive weakness and muscle atrophy related to the loss of upper and lower motor neurons (MNs) without a curative treatment. There is experimental evidence suggesting that retinoids may be involved in ALS pathogenesis. Bexarotene (Bxt) is a retinoid-X receptor agonist used in the treatment of cutaneous lymphoma with a favorable safety profile whose effects have been recently investigated in other neurodegenerative diseases. In this study, we analyze the potential therapeutic effect of Bxt in the SOD1G93A mouse model of ALS. Mice were treated with Bxt or vehicle five times per week from day 60 onward. Survival, weight, and neuromuscular function studies together with histological and biochemical analyses were performed. Bxt significantly delayed motor function deterioration, ameliorated the loss of body weight, and extended mice survival up to 30% of the symptomatic period. Histological analyses of the lumbosacral spinal cord revealed that Bxt markedly delayed the early motor-neuron degeneration occurring at presymptomatic stages in ALS-transgenic mice. Bxt treatment contributed to preserve the MN homeostasis in the SOD1G93A mice. Particularly, it reduced the neuronal loss and the chromatolytic response, induced nucleolar hypertrophy, decreased the formation of ubiquitylated inclusions, and modulated the lysosomal response. As an agonist of the retinoic-X receptor (RXR) pathway, Bxt notably increased the nuclear expression of the RXRα throughout transcriptionally active euchromatin domains. Bxt also contributed to protect the MN environment by reducing reactive astrogliosis and preserving perisomatic synapsis. Overall, these neuroprotective effects suggest that treatment with Bxt could be useful in ALS, particularly in those cases related to SOD1 mutations.

Compensatory Motor Neuron Response to Chromatolysis in the Murine hSOD1(G93A) Model of Amyotrophic Lateral Sclerosis

We investigated neuronal self-defense mechanisms in a murine model of amyotrophic lateral sclerosis (ALS), the transgenic hSOD1G93A, during both the asymptomatic and symptomatic stages. This is an experimental model of endoplasmic reticulum (ER) stress with severe chromatolysis. As a compensatory response to translation inhibition, chromatolytic neurons tended to reorganize the protein synthesis machinery at the perinuclear region, preferentially at nuclear infolding domains enriched in nuclear pores. This organization could facilitate nucleo-cytoplasmic traffic of RNAs and proteins at translation sites. By electron microscopy analysis, we observed that the active euchromatin pattern and the reticulated nucleolar configuration of control motor neurons were preserved in ALS chromatolytic neurons. Moreover the 5′-fluorouridine (5′-FU) transcription assay, at the ultrastructural level, revealed high incorporation of the RNA precursor 5′-FU into nascent RNA. Immunogold particles of 5′-FU incorporation were distributed throughout the euchromatin and on the dense fibrillar component of the nucleolus in both control and ALS motor neurons. The high rate of rRNA transcription in ALS motor neurons could maintain ribosome biogenesis under conditions of severe dysfunction of proteostasis. Collectively, the perinuclear reorganization of protein synthesis machinery, the predominant euchromatin architecture, and the active nucleolar transcription could represent compensatory mechanisms in ALS motor neurons in response to the disturbance of ER proteostasis. In this scenario, epigenetic activation of chromatin and nucleolar transcription could have important therapeutic implications for neuroprotection in ALS and other neurodegenerative diseases. Although histone deacetylase inhibitors are currently used as therapeutic agents, we raise the untapped potential of the nucleolar transcription of ribosomal genes as an exciting new target for the therapy of some neurodegenerative diseases.

MicroRNA Profile in Patients with Alzheimer’s Disease: Analysis of miR-9-5p and miR-598 in Raw and Exosome Enriched Cerebrospinal Fluid Samples

BACKGROUND MicroRNAs have been postulated as potential biomarkers for Alzheimers disease (AD). Exosomes are nanovesicles which transport microRNAs, proteins, and other cargos. It has been hypothesized that the exosome traffic might be increased in neurodegenerative disorders. OBJECTIVE i) To assess the cerebrospinal fluid (CSF) microRNA profile in a group of AD patients and control subjects and to validate a group of microRNAs previously reported by other authors. ii) To compare microRNA levels in whole CSF and in the exosome-enriched fraction in AD patients. METHODS A panel of 760 microRNAs was analyzed in the CSF of 10 AD patients and 10 healthy subjects. Among microRNAs differently expressed, we selected those that had been previously reported by other authors. Candidates were validated in a larger group by individual qPCR assays. MicroRNA expression was also evaluated in exosome-enriched CSF samples of patients with AD and controls. RESULTS Fifteen microRNAs were differently expressed in AD. MiR-9-5p, miR-134, and miR-598 were selected as candidates for further analysis. MiR-9-5p and miR-598 were detected in 50 and 75% of control CSF samples, respectively, while they were not detected in any AD CSF samples. We observed an opposite pattern when we evaluated the microRNA expression in the exosome-enriched CSF AD samples. No pattern variations were noted among healthy subjects. CONCLUSION These data propose miR-9-5p and miR-598 as potential biomarkers for AD. Further studies in plasma and other body fluids will confirm their potential role as easily accessible biomarkers. In addition, our data suggest that exosome trafficking is different between AD and control subjects raising the need to take this phenomenon into consideration in future studies of AD biomarkers.

Retinoids and motor neuron disease: Potential role in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is the most common neurodegenerative disease affecting motor neurons (MN). This fatal disease is characterized by progressive muscular atrophy and unfortunately it does not have an effective treatment. Although a small proportion of ALS cases have a familiar origin, the vast majority of them are thought to have a sporadic origin. Although the pathogenesis of ALS has not been fully elucidated, various disorders in different cellular functions such as gene expression, protein metabolism, axonal transport and glial cell disorders have been linked to MN degeneration. Among them, proteostasis is one of the best studied. Retinoids are vitamin A-derived substances that play a crucial role in embryogenesis, development, programmed cell death and other cellular functions. Retinoid agonists behave as transcription factors throughout the activation of the nuclear retinoid receptors. Several reports in the literature suggest that retinoids are involved in proteostasis regulation, by modulating its two major pathways, the ubiquitin-proteasome system and the autophagy-lysosome response. Additionally, there are some evidences for a role of retinoids themselves, in ALS pathogenesis. In this review, we discuss the importance of proteostasis disruption as a trigger for MN degeneration and the capability of retinoids to modulate it, as well as the potential therapeutic role of retinoids as a new therapy in ALS.

Why do motor neurons degenerate? Actualization in the pathogenesis of amyotrophic lateral sclerosis.

Abstract Introduction Amyotrophic lateral sclerosis (ALS) is the most common neurodegenerative disease affecting motor neurons. Although a small proportion of ALS cases are familial in origin and linked to mutations in specific genes, most cases are sporadic and have a multifactorial aetiology. Some recent studies have increased our knowledge of ALS pathogenesis and raised the question of whether this disorder is a proteinopathy, a ribonucleopathy, an axonopathy, or a disease related to the neuronal microenvironment. Development This article presents a review of ALS pathogenesis. To this end, we have reviewed published articles describing either ALS patients or ALS animal models and we discuss how the main cellular pathways (gene processing, protein metabolism, oxidative stress, axonal transport, relationship with neuronal microenvironment) may be involved in motor neurons degeneration. Conclusions ALS pathogenesis has not been fully elucidated. Recent studies suggest that although initial triggers may differ among patients, the final motor neurons degeneration mechanisms are similar in most patients once the disease is fully established.

How to interpret epigenetic association studies: a guide for clinicians

Epigenetic mechanisms are able to alter gene expression, without altering DNA sequence, in a stable manner through cell divisions. They include, among others, the methylation of DNA cytosines and microRNAs and allow the cells to adapt to changing environmental conditions. In recent years, epigenetic association studies are providing new insights into the pathogenesis of complex disorders including prevalent skeletal disorders. Unlike the genome, the epigenome is cell and tissue specific and may change with age and a number of acquired factors. This poses particular difficulties for the design and interpretation of epigenetic studies, particularly those exploring the association of genome-wide epigenetic marks with disease phenotypes. In this report, we propose a framework to help in the critical appraisal of epigenetic association studies. In line with previous suggestions, we focus on the questions critical to appraise the validity of the study, to interpret the results and to assess the generalizability and relevance of the information.

¿Por qué degeneran las motoneuronas? Actualización en la patogenia de la esclerosis lateral amiotrófica

INTRODUCTION Amyotrophic lateral sclerosis (ALS) is the most common neurodegenerative disease affecting motor neurons. Although a small proportion of ALS cases are familial in origin and linked to mutations in specific genes, most cases are sporadic and have a multifactorial aetiology. Some recent studies have increased our knowledge of ALS pathogenesis and raised the question of whether this disorder is a proteinopathy, a ribonucleopathy, an axonopathy, or a disease related to the neuronal microenvironment. DEVELOPMENT This article presents a review of ALS pathogenesis. To this end, we have reviewed published articles describing either ALS patients or ALS animal models and we discuss how the main cellular pathways (gene processing, protein metabolism, oxidative stress, axonal transport, relationship with neuronal microenvironment) may be involved in motor neurons degeneration. CONCLUSIONS ALS pathogenesis has not been fully elucidated. Recent studies suggest that although initial triggers may differ among patients, the final motor neurons degeneration mechanisms are similar in most patients once the disease is fully established.

Amyotrophic Lateral Sclerosis in Northern Spain 40 Years Later: What Has Changed?

Background: In the last years different studies have reported an increase of amyotrophic lateral sclerosis (ALS) incidence, highlighting the role of the environment in this disease. This prompted us to review ALS cases diagnosed at our hospital in the last decade and to compare them with a previous ALS series reported in our region 30 years ago. Methods: We reviewed those ALS cases diagnosed at our centre between 2004 and 2013. Subsequently, we compared them with the previous series regarding clinical and epidemiological features. Results: A total of 53 patients (30 males, 23 females) were included. The annual incidence was 1.7 cases per 100,000 inhabitants (2.2 and 1.2 per 100,000 in males and females, respectively), which was significantly higher than in the previous series (1 case per 100,000 inhabitants). Otherwise, the clinical and epidemiological features were similar in both series. The median age at symptom onset was 67 years, with a median diagnosis delay of 6 months. About two thirds of the patients presented with systemic ALS, whereas the remaining had a bulbar onset. Weakness, dysphagia, and dysarthria were the most common clinical symptoms at diagnosis. The median survival from symptom onset was 22 months. Conclusion: After 3 decades, the annual incidence of ALS has almost doubled in our region. We did not find significant differences regarding other clinical or epidemiological features.

Relaunching an old drug: the potential role of bexarotene in neurodegenerative diseases

Vitamin A (retinol) and its derivatives (retinoids) play an important role in embryonic development, cellular differentiation, programmed cell death, and in other vital cellular functions. These substances exert their effects throughout the activation of their nuclear receptors. There are two main families of retinoid receptors, the retinoid acid receptors (RAR) and the retinoid X receptors (RXR) [1]. Retinoid agonists bound to RXR regulate gene transcription resulting in chromatin remodelling and transcriptional regulation of their target genes, some of them involved in protein metabolism, intracellular signalling, synaptic homeostasis, inflammation, programmed cell death, and other vital cellular functions [2]. Since protein metabolism disruption, synaptic alterations, or astroglial response are important events in the pathogenesis of neurodegeneration, several authors have hypothesized that retinoids could be useful in neurodegenerative disorders. Bexarotene (Bxt) is the only FDA approved RXR agonist. This drug is currently being used in the clinic for treating cutaneous lymphoma with a favourable safety profile [3]. For the last 3 years, this drug has been tested in different neurodegenerative diseases, comprising Alzheimeŕs disease (AD), Parkinson’s disease (PD), and amyotrophic lateral sclerosis (ALS) with promising results (Table 1). First, Cramer et al. [4] tested this drug in a murine model of AD demonstrating a marked reduction in both soluble amyloid beta (Ab) and Ab plaques that correlated with a rapid reversal of cognitive, social, and other functional capabilities. The authors showed that Bxt facilitated Ab clearance by increasing apoE expression and also stimulating Ab phagocytosis by microglial cells [4]. Subsequently, other groups were not able to reproduce completely these promising results [5–9]. Supporting a potential neuroprotective effect, Bomben et al. demonstrated that Bxt reduced cortical network excitability in a murine model of the disease [10]. In addition, Lefterov et al. reported that Bxt influenced diverse regulatory pathways that are considered critical for cognitive performance, inflammatory response, and Ab clearance, providing an explanation of the therapeutic effect of the Bxt at the molecular level [11]. However, the role of Bxt in AD remains unclear since other groups continue reporting no benefits with its use [12, 13]. To date, two clinical trials in healthy volunteers and in patients with mild to moderate AD have been initiated (registered in the clinical trials as NCT01782742 and NCT02061878). Although with limited evidence, Bxt has also been tested in other neurodegenerative diseases such as PD and ALS. In the field of PD, McFarland et al. described the ability of RXR to form heterodimers with other nuclear hormone receptors, such as nuclear receptor related 1 protein (Nurr1), which is strongly implicated in the growth, maintenance and survival of dopaminergic neurons. Remarkably, these authors demonstrated that treatment with low-dose Bxt rescued dopamine neurons and reversed the behavioural deficits in the 6-OHDA rat model of PD [14]. Regarding ALS, we have been working with Bxt as an attractive candidate for this disease because it helps to modulate some of the most important pathways related to & Javier Riancho javier.riancho86@gmail.com

The increasing importance of environmental conditions in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is the most common neurodegenerative disease affecting motor neurons (MNs). Although a small percentage of ALS has a familial origin, the vast majority of cases are sporadic in which genetic factors and environment interact with each other leading to disease onset in genetically predisposed individuals. In the current model of the disease, each individual has a determined genetic load, some degree of cell degeneration related to age and several risky environmental exposures. In this scenario, MN degeneration would occur when the sum of these factors reach a certain threshold. To date, an extensive list of environmental factors has been associated to ALS, including different categories, such as exposure to heavy metals and other toxicants, cyanotoxins or infectious agents. In addition, in recent years, lifestyle and other demographic parameters are gaining relevance in the genesis of the disease. Among them, physical activity, nutrition, body mass index, cardiovascular risk factors, autoimmune diseases and cancer are some of the conditions which have been related to the disease. In this review, we will discuss the potential mechanisms of environmental conditions in motor neuron degeneration. Understanding the role of each one of these factors as well as their interactions appears as a crucial step in order to develop new preventive, diagnostic and therapeutic approaches for ALS patients.