Abstract
BackgroundAmyotrophic 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.MethodsInitially, 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 (SOD1G93A and TDP43A315T) 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.ResultsUsing 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.ConclusionsThis study, therefore, identifies Pacer as a new regulator of proteostasis associated with ALS pathology.
Highlights
Amyotrophic lateral sclerosis (ALS) is a multifactorial fatal motoneuron disease without a cure
Mutations in several genes coding for proteins involved in autophagy or other membrane trafficking pathways have been found in ALS patients, including SQSTM1 and OPTN, which encode the selective autophagy receptors SQSTM1/p62 and optineurin, respectively, and ALS2 that encodes alsin2, which participates in membrane trafficking, as well as TBK1 (TANK-binding kinase 1), a kinase involved in autophagy-mediated degradation of ubiquitinated cargos [17,18,19]
We selected Pacer (C13orf18) for further experimental studies, mainly because it was displayed as a component of a subnetwork composed of itself and Beclin1 (Fig. 1a and Additional file 3: Figure S1h), an interaction previously reported in a proteomic study [30]
Summary
Amyotrophic lateral sclerosis (ALS) is a multifactorial fatal motoneuron disease without a cure. Most cell types, including neurons, operate under constitutive autophagy [11], which is thought to have a vital role in maintaining their metabolic and proteostatic balance [12,13,14]. In this context, defects in the endolysosomal pathway or autophagy-related genes have been associated with diverse neurodegenerative diseases, including Alzheimer’s disease (AD), Huntington’s disease (HD), Parkinson’s disease (PD), as well as ALS [15, 16]. Defects in autophagy and endolysosomal pathways may underlay an important part of the etiology of the disease
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