Rab1-dependent ER–Golgi transport dysfunction is a common pathogenic mechanism in SOD1, TDP-43 and FUS-associated ALS

Abstract

Several diverse proteins are linked genetically/pathologically to neurodegeneration in amyotrophic lateral sclerosis (ALS) including SOD1, TDP-43 and FUS. Using a variety of cellular and biochemical techniques, we demonstrate that ALS-associated mutant TDP-43, FUS and SOD1 inhibit protein transport between the endoplasmic reticulum (ER) and Golgi apparatus in neuronal cells. ER-Golgi transport was also inhibited in embryonic cortical and motor neurons obtained from a widely used animal model (SOD1(G93A) mice), validating this mechanism as an early event in disease. Each protein inhibited transport by distinct mechanisms, but each process was dependent on Rab1. Mutant TDP-43 and mutant FUS both inhibited the incorporation of secretory protein cargo into COPII vesicles as they bud from the ER, and inhibited transport from ER to the ER-Golgi intermediate (ERGIC) compartment. TDP-43 was detected on the cytoplasmic face of the ER membrane, whereas FUS was present within the ER, suggesting that transport is inhibited from the cytoplasm by mutant TDP-43, and from the ER by mutant FUS. In contrast, mutant SOD1 destabilised microtubules and inhibited transport from the ERGIC compartment to Golgi, but not from ER to ERGIC. Rab1 performs multiple roles in ER-Golgi transport, and over-expression of Rab1 restored ER-Golgi transport, and prevented ER stress, mSOD1 inclusion formation and induction of apoptosis, in cells expressing mutant TDP-43, FUS or SOD1. Rab1 also co-localised extensively with mutant TDP-43, FUS and SOD1 in neuronal cells, and Rab1 formed inclusions in motor neurons of spinal cords from sporadic ALS patients, which were positive for ubiquitinated TDP-43, implying that Rab1 is misfolded and dysfunctional in sporadic disease. These results demonstrate that ALS-mutant forms of TDP-43, FUS, and SOD1 all perturb protein transport in the early secretory pathway, between ER and Golgi compartments. These data also imply that restoring Rab1-mediated ER-Golgi transport is a novel therapeutic target in ALS.

Proteomic Analysis of Dynein-Interacting Proteins in Amyotrophic Lateral Sclerosis Synaptosomes Reveals Alterations in the RNA-Binding Protein Staufen1

“…Furthermore, ANAT predicted a few other RNAbinding proteins (Supplemental Table S4), which could be the basis for further studies into the cellular pathology of ALS. Among them are the RNA-methylating protein Mettl3 and the RNA-activated translation-initiating factor Eukaryotic translation initiation factor 2-alpha kinase 2, shown to be downregulated in skeletal muscle in ALS mice (39). The fact that most of the RNA-binding proteins including Staufen1 were not identified by MS analysis but only predicted by ANAT supports our assumption that some protein interactions might have been lost due to the non-RNA-preserving conditions during the immunoprecipitation experiments.…”

Protein Quality Control and the Amyotrophic Lateral Sclerosis/Frontotemporal Dementia Continuum

“…In addition, mutant FUS impairs the association between ER and mitochondria, which disrupts the interaction between VAPB and PTPIP51 in NSC-34 cells (Stoica et al, 2016). Furthermore, mutant FUS inhibits both autophagy and ER–Golgi transport in a Rab1 dependent manner, which can further increase ER stress (Soo et al, 2015a; Stoica et al, 2016). When comparing the binding partners of the mRNA and protein profiles of mutant and wildtype FUS, mutant FUS was found to interact more with VCP, UBA1 proteins and mRNAs that are related to the ER and ubiquitin-proteosome pathways (Hoell et al, 2011; Lagier-Tourenne et al, 2012; Wang et al, 2015a).…”

Disrupted ER‐to‐Golgi trafficking underlies anti‐HIV drugs and alcohol‐induced cellular stress and hepatic injury

“…(42,43) While other COPI- or COPII-independent routes may also be involved, our observations support the fact that the effects of drugs on COPII trafficking contribute to Golgi fragmentation, which has also been linked to downstream ER stress and apoptosis in pancreatic beta cells and patients with amyotrophic lateral sclerosis. (44,45) The observed lipid accumulation in the RL-treated hepatocytes may be a direct consequence of the blocking. In addition, we further addressed what stage of the ER-to-Golgi trafficking was affected by RL.…”