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.
Background
Amyotrophic lateral sclerosis (ALS) is a multifactorial fatal motoneuron disease without a cure. Ten percent of ALS cases can be pointed to a clear genetic cause, while the remaining 90% is classified as sporadic. Our study was aimed to uncover new connections within the ALS network through a bioinformatic approach, by which we identified C13orf18, recently named Pacer, as a new component of the autophagic machinery and potentially involved in ALS pathogenesis.
Methods
Initially, we identified Pacer using a network-based bioinformatic analysis. Expression of Pacer was then investigated in vivo using spinal cord tissue from two ALS mouse models (SOD1
G93A
and TDP43
A315T
) and sporadic ALS patients. Mechanistic studies were performed in cell culture using the mouse motoneuron cell line NSC34. Loss of function of Pacer was achieved by knockdown using short-hairpin constructs. The effect of Pacer repression was investigated in the context of autophagy, SOD1 aggregation, and neuronal death.
Results
Using an unbiased network-based approach, we integrated all available ALS data to identify new functional interactions involved in ALS pathogenesis. We found that Pacer associates to an ALS-specific subnetwork composed of components of the autophagy pathway, one of the main cellular processes affected in the disease. Interestingly, we found that Pacer levels are significantly reduced in spinal cord tissue from sporadic ALS patients and in tissues from two ALS mouse models. In vitro, Pacer deficiency lead to impaired autophagy and accumulation of ALS-associated protein aggregates, which correlated with the induction of cell death.
Conclusions
This study, therefore, identifies Pacer as a new regulator of proteostasis associated with ALS pathology.
Electronic supplementary material
The online version of this article (10.1186/s13024-019-0313-9) contains supplementary material, which is available to authorized users.
Amyotrophic lateral sclerosis (ALS) is an adult onset and fatal neurodegenerative disease. A major histophatological hallmark of the disease patient-derived tissue and ALS mouse models is the presence of protein aggregates containing misfolded specific proteins. Strategies to clear out these abnormal protein species are proposed as a possible target for disease intervention. Autophagy, a catabolic route that selective degradates abnormally-folded proteins by the lysosomal pathway, has emerged as an attractive target to treat neurodegenerative diseases, like ALS. Accumulating evidence indicates that autophagy impairment also occurs in ALS and can contribute to the neurodegenerative condition. In this article we discuss the evidence involving autophagy alteration associated to ALS phenotype and the evidence that place autophagy as a therapeutic opportunity to treat this neurodegenerative disease.
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