Mutations in the gene encoding fused in sarcoma (FUS) are linked to amyotrophic lateral sclerosis (ALS), but the mechanisms by which these mutants trigger neurodegeneration remain unknown. Endoplasmic reticulum (ER) stress is increasingly recognized as an important and early pathway to motor neuron death in ALS. FUS is normally located in the nucleus but in ALS, FUS redistributes to the cytoplasm and forms inclusions. In this study, we investigated whether FUS induces ER stress in a motor neuron like cell line (NSC-34). We demonstrate that ER stress is triggered in cells expressing mutant FUS, and this is closely associated with redistribution of mutant FUS to the cytoplasm. Mutant FUS also colocalized with protein disulfide-isomerase (PDI), an important ER chaperone, in NSC-34 cells and PDI was colocalized with FUS inclusions in human ALS lumbar spinal cords, in both sporadic ALS and mutant FUS-linked familial ALS tissues. These findings implicate ER stress in the pathophysiology of FUS, and provide evidence for common pathogenic pathways in ALS linked to the ER.

Objective: To investigate the imaging and biodistribution of a novel zirconium-89 (89Zr)-labeled mouse anti-cd20 monoclonal antibody (mAb) in control and experimental autoimmune encephalomyelitis (EAE) mice following subcutaneous (s. c.) and intravenous (i.v.) administration. Background: Anti-cd20-mediated B-cell depletion using mAbs is a promising therapy for multiple sclerosis. Recombinant human myelin oligodendrocyte glycoprotein (rhMOG)-induced EAE involves B-cell-mediated inflammation and demyelination in mice. Design/Methods: C57BL/6J mice (n = 39) were EAE-induced using rhMOG. On Day 14 post EAE induction, 89Zr-labeled-anti-cd20 mAb was injected in control and EAE mice in the right lower flank (s.c.) or tail vein (i.v.). Positron emission tomography/computed tomography (PET/CT) imaging and gamma counting (ex vivo) were performed on Days 1, 3, and 7 to quantify tracer accumulation in the major organs, lymphatics, and central nervous system (CNS). A preliminary study was conducted in healthy mice to elucidate full and early kinetics of the tracer that were subsequently applied in the EAE and control mice study. Results:89Zr-labeled anti-cd20 mAb was effectively absorbed from s.c. and i.v. injection sites and distributed to all major organs in the EAE and control mice. There was a good correlation between in vivo PET/CT data and ex vivo quantification of biodistribution of the tracer. From gamma counting studies, initial tracer uptake within the lymphatic system was found to be higher in the draining lymph nodes (inguinal or subiliac and sciatic) following s.c. vs. i.v. administration; within the CNS a significantly higher tracer uptake was observed at 24 h in the cerebellum, cerebrum, and thoracic spinal cord (p < 0.05 for all) following s.c. vs. i.v. administration. Conclusions: The preclinical data suggest that initial tracer uptake was significantly higher in the draining lymph nodes (subiliac and sciatic) and parts of CNS (the cerebellum and cerebrum) when administered s.c. compared with i.v in EAE mice.