Wildtype sigma-1 receptor and the receptor agonist improve ALS-associated mutation-induced insolubility and toxicity.

Genetic mutations related to amyotrophic lateral sclerosis (ALS), a progressive neurological disease, have been discovered in the gene encoding sigma-1 receptor (σ1R). We previously reported that σ1RE102Q elicits toxicity in cells. The σ1R forms oligomeric states that are regulated by ligands. Nevertheless, little is known about the effect of ALS-related mutations on oligomer formation. Here, we transfected NSC-34 cells, a motor neuronal cell line, and HEK293T cells with σ1R-mCherry (mCh), σ1RE102Q-mCh or non-tagged forms to investigate detergent solubility and subcellular distribution using immunocytochemistry and fluorescence recovery after photobleaching (FRAP). The oligomeric state was determined using crosslinking procedure. σ1Rs were solubleto detergents, whereas the mutants accumulated in the insoluble fraction. Within the soluble fraction, peak distribution of mutants appeared in higher sucrose density fractions. Mutants formed intracellular aggregates that were costained with p62, ubiquitin, and phosphorylated pancreatic eukaryotic translation initiation factor-2-alpha kinase in NSC-34 cells but not in HEK293T cells. The aggregates had significantly lower recovery in FRAP. Acute treatment with σ1R agonist SA4503 failed to improve recovery, while prolonged treatment for 48 h significantly decreased σ1RE102Q-mCh insolubility and inhibited apoptosis. While σ1R-mCh formed monomers and dimers, σ1RE102Q-mCh also formed trimers and tetramers. SA4503 reduced accumulation of the four types in the insoluble fraction and increased monomers in the soluble fraction. The σ1RE102Q insolubility was diminished by σ1R-mCh co-expression. These results suggest the agonist and wildtype σ1R modify the detergent insolubility, toxicity, and oligomeric state of σ1RE102Q which may lead to promising new treatments for σ1R-related ALS.