Deleterious Sequestosome 1 mutations G262R and P438L in amyotrophic lateral sclerosis cause autophagy and oxidative stress imbalance.

Amyotrophic Lateral Sclerosis (ALS) is a severe neurodegenerative disease (NDD) prevalent across the world. It is known that mutations in ALS associated genes can cause imbalances between cellular processes such as apoptosis, necroptosis, autophagy and proteasomal degradation that remove dysfunctional and aggregating proteins. Two rare missense variants namely G262R (G > A) and P438L (C > T) in Sequestosome 1 (SQSTM1), were identified by our group in a cohort of Indian ALS patients. SQSTM1 codes for p62, which is an autophagy adaptor protein involved in several signaling pathways. In this study, we investigated how these SQSTM1 mutations affect autophagy and the oxidative stress response pathway in SH-SY5Y cells through quantitative RT-PCR, immunoblotting and confocal microscopy. In addition, we examined how changes in the downstream signaling pathways alters nuclear-cytoplasmic localization of TDP-43 protein, a marker protein usually found in cytoplasmic inclusions in ALS patient tissues. We observed up-regulation of autophagy marker proteins LC3-II and ubiquitin, and down-regulation of oxidative stress marker protein Nrf2. Along with LC3-II, p-OPTN and ATG5, proteins that are also associated with autophagy were up-regulated. We also observed an increase in cytoplasmic localization of TDP-43 protein in cells expressing these p62 mutant proteins. Overall, our study provides evidence that the G262R (G > A) and P438L (C > T) mutations are deleterious through mechanisms that increase cytoplasmic localization of TDP-43, and adversely affect the autophagy and oxidative stress response pathway.