Genome-wide circulating microRNA expression profiling reveals potential biomarkers for amyotrophic lateral sclerosis.

The occurrence of mutations of TDP-43, FUS, and C9ORF72 in amyotrophic lateral sclerosis (ALS) suggests pathogenic alterations to RNA metabolism and specifically to microRNA (miRNA) biology. Moreover, several ALS-related proteins impact stress granule dynamics affecting miRNA biogenesis and cellular miRNA levels. miRNAs are present in different biological fluids and have been proposed as potential biomarkers. Here we used next-generation sequencing to perform a comparative analysis of the expression profile of circulating miRNAs in the serum of 2 mutant superoxide dismutase 1 transgenic mice. Top hit candidates were then validated using quantitative real-time polymerase chain reaction, confirming significant changes for 6 miRNAs. In addition, one of these miRNAs was also altered in mutant TDP-43 mice. Then, we tested this set of miRNAs in the serum from sporadic ALS patients, observing a significant deregulation of hsa-miR-142-3p and hsa-miR-1249-3p. A negative correlation between the revised ALS functional rating scale and hsa-miR-142-3p levels was found. Bioinformatics analysis of the regulatory network governed by hsa-miR-142-3p identified TDP-43 and C9orf72 as possible targets, suggesting a connection with ALS pathogenesis. This study identifies miRNAs that are altered in ALS that may serve as potentials biomarkers.

The ER proteostasis network in ALS: Determining the differential motoneuron vulnerability.

Amyotrophic lateral sclerosis (ALS) is a fatal late-onset neurodegenerative disease characterized by the selective loss of motoneurons. The mechanisms underlying neuronal degeneration in ALS are starting to be elucidated, highlighting abnormal protein aggregation and altered mRNA metabolism as common phenomena. ALS involves the selective vulnerablility of a subpopulation of motoneurons, suggesting that intrinsic factors may determine ALS pathogenesis. Accumulating evidence indicates that alterations to endoplasmic reticulum (ER) proteostasis play a critical role on disease progression, representing one of the earliests pathological signatures of the disease. Here we discuss recent studies uncovering a fundamental role of ER stress as the driver of selective neuronal vulnerability in ALS and discuss the potential of targeting the unfolded protein response (UPR) as a therapeutic strategy to treat ALS.

Disulfide cross-linked multimers of TDP-43 and spinal motoneuron loss in a TDP-43A315T ALS/FTD mouse model.

Tar DNA binding protein 43 (TDP-43) is the principal component of ubiquitinated protein inclusions present in nervous tissue of most cases of both amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). Previous studies described a TDP-43A315T transgenic mouse model that develops progressive motor dysfunction in the absence of protein aggregation or significant motoneuron loss, questioning its validity to study ALS. Here we have further characterized the course of the disease in TDP-43A315T mice using a battery of tests and biochemical approaches. We confirmed that TDP-43 mutant mice develop impaired motor performance, accompanied by progressive body weight loss. Significant differences were observed in life span between genders, where females survived longer than males. Histopathological analysis of the spinal cord demonstrated a significant motoneurons loss, accompanied by axonal degeneration, astrogliosis and microglial activation. Importantly, histopathological alterations observed in TDP-43 mutant mice were similar to some characteristic changes observed in mutant SOD1 mice. Unexpectedly, we identified the presence of different species of disulfide-dependent TDP-43 aggregates in cortex and spinal cord tissue. Overall, this study indicates that TDP-43A315T transgenic mice develop key features resembling key aspects of ALS, highlighting its relevance to study disease pathogenesis.

ER chaperones in neurodegenerative disease: Folding and beyond.

Proteins along the secretory pathway are co-translationally translocated into the lumen of the endoplasmic reticulum (ER) as unfolded polypeptide chains. Afterwards, they are usually modified with N-linked glycans, correctly folded and stabilized by disulfide bonds. ER chaperones and folding enzymes control these processes. The accumulation of unfolded proteins in the ER activates a signaling response, termed the unfolded protein response (UPR). The hallmark of this response is the coordinated transcriptional up-regulation of ER chaperones and folding enzymes. In order to discuss the importance of the proper folding of certain substrates we will address the role of ER chaperones in normal physiological conditions and examine different aspects of its contribution in neurodegenerative disease. This article is part of a Special Issue entitled SI:ER stress.

Targeting autophagy in neurodegenerative diseases.

The most prevalent neurodegenerative disorders involve protein misfolding and the aggregation of specific proteins. Autophagy is becoming an attractive target to treat neurodegenerative disorders through the selective degradation of abnormally folded proteins by the lysosomal pathway. However, accumulating evidence indicates that autophagy impairment at different regulatory steps may contribute to the neurodegenerative process. Thus, a complex scenario is emerging where autophagy may play a dual role in neurodegenerative diseases by causing the downstream effect of promoting the degradation of misfolded proteins and an upstream effect where its deregulation perturbs global proteostasis, contributing to disease progression. Challenges in the future development of therapeutic strategies to target the autophagy pathway are discussed.