rocesses, such as inclusion formation, remains debated. However, alterations in 17568748 TDP-43 levels alter SG dynamics, suggesting that SG changes could occur in disease. ER stress and induction of the unfolded protein response are central to ALS pathophysiology. When the UPR is induced three distinct signalling pathways are activated, mediated by inositol requiring kinase 1, activating transcription factor 6, and protein-kinase-like endoplasmic reticulum kinase . IRE1 activation leads to the splicing of X-box binding protein 1 mRNA within the nucleus to produce a functional transcription factor. When ATF6 is activated, it is transported to the cis-Golgi compartment and is cleaved to produce an active transcription factor. In addition, activation of PERK causes general translational repression by stimulating SG formation via phosphorylation of eIF2a. Other consequences of UPR induction include up-regulation of ER chaperones, such as protein disulphide isomerise . Although initially protective, if unresolved, the UPR triggers apoptosis by ER stress-specific cell death signals, 22576162 including induction of C/EBP-homologous protein via the PERK and ATF6 pathways. ER stress precedes the appearance of clinical features in ALSlinked mutant superoxide dismutase 1 transgenic rodents, and genetic manipulation of ER stress mediators modulates disease in these animals. ER stress is present in sporadic and familial forms of ALS, including those cases caused by mutations in fused in sarcoma, which bears structural and functional similarities to TDP-43. Increased genetic susceptibility to ER stress has also been linked with ALS. Although TDP-43 is C-terminally fragmented and hyper-phosphorylated in disease, the factors which trigger these changes remain poorly defined. However, ER stress also causes TDP-43 fragmentation in cell culture and over-expression of TDP43 causes changes in CHOP and XBP-1 signalling in cell culture and rat models of TDP-43-linked disease. The chaperone protein disulphide isomerase is induced by ER stress and is up-regulated in human sporadic ALS and in animal models of mutant SOD1-linked ALS. PDI may protect against ER stress, inclusion formation and cell death associated with mutant SOD1 expression by modulating abnormal disulphide bond formation. In addition, the cellular distribution of PDI in mutant SOD1 transgenic mice modifies disease processes and PDI is a constituent of TDP-43-positive or FUS-positive inclusions found in motor neurons of ALS patients. Cross-linking of TDP-43 via disulphide bonds alters its conformation and function, suggesting that PDI is a potential candidate for proteins that interact with TDP-43 and prevent TDP-43 misfolding. In this study we examined whether ER stress could act as a stressor that leads to cytoplasmic accumulation of TDP-43 and subsequent incorporation of TDP-43 into SGs. Six different ALSlinked TDP-43 mutants were examined: A315T and M337V, which have been reported in multiple familial ALS pedigrees; D169G, the only ALS-linked mutation identified that lies outside the C-terminal region; and G294A, Q331K and N390D, which have been identified in sporadic ALS patients. Pharmacological induction of 
ER stress in cell culture led to cytoplasmic accumulation of wildtype TDP-43 and all six TDP-43 mutants. Furthermore, ER stress caused the rapid incorporation of TDP-43 into cytoplasmic SGs. This process was enhanced by pharmacological treatment with salubrinal to LBH589 supplier inhibit the deactivation of eIF2a, a ke
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