Accumulation of motor neuron diseases associated misfolded proteins is counteracted by dynein inhibition

Spinobulbar muscular atrophy (SBMA) and amyotrophic lateral sclerosis (ALS) are two motor neuron diseases (MNDs) characterized by selective death of motor neuron localized in cerebral cortex and in spinal cord. The hallmark of SBMA and ALS is the presence of aggregates of mutant proteins (androgen receptors (AR) and superoxide dismutase 1(SOD1), TDP43, etc. respectively) with aberrant conformation (misfolding). Altered protein quality control system cannot correctly remove toxic aggregates of misfolding proteins. These species may lead to cell death. Dynein motor complex seems play a crucial role to maintain an efficient removal of these toxic species by autophagy: i) through aggregate transport near MTOC, ii) by autophagosome nucleation, iii) by assisting the fusion of autophagosome to lysosome. Treatment of NSC34 cell line with a selective inhibitor of dynein (EHNA), drastically reduce the autophagy marker LC3 when autophagy is induced by trehalose. In NSC34 transfected with mutant proteins: i) immunofluorescence (IF) analysis showed that dynein is sequestered into mutant AR aggregates. ii) EHNA treatment, unexpectedly, reduces aggregates of mutant AR, SOD1 and TDP43 retained on cellulose acetate membrane in filter retardation assay (FTA) also in presence of autophagy inhibitor (3-MA), but not in presence of proteasome inhibitor (MG132). iii) EHNA increases the solubility of mutated AR. iv) BAG1, which routes misfolding proteins to proteasome degradation or chaperone-mediated-autophagy, is increases after EHNA treatment. These data suggest that dynein impairment may induces proteasome targeting of misfolded proteins involve in MNDs.