The unfolded protein response in models of human mutant G93A amyotrophic lateral sclerosis

Recent studies indicate that endoplasmic reticulum (ER) stress is involved in the pathogenesis of familial and sporadic amyotrophic lateral sclerosis (ALS). ER stress occurs when the ERmitochondria calcium cycle (ERMCC) is disturbed and misfolded proteins accumulate in the ER. To cope with ER stress, the cell engages the unfolded protein response (UPR). While activation of the UPR has been shown in some ALS models and tissues, ER stress elements have not been studied directly in motor neurons. Here we investigated the expression of XBP1 and ATF6a and phosphorylation of eIF2a, and their modulation, in mutated SOD1G93A NSC34 and animal model of ALS. Expression of XBP1 and ATF6a mRNA and protein was enhanced in SOD1G93A NSC34 cells. Activation of ATF6a and XBP1 and phosphorylation of eIF2a were detectable in mutated SOD1G93A motor but not in wild-type motor neurons. Treatment with the ER stressor thapsigargin enhanced phosphorylation of eIF2a and activated proteolysis of ATF6a and splicing of XBP1 in NSC34 and motor neurons in a time-dependent manner. The present study thus provides direct evidence of activated UPR in motor neurons which overexpress human pathogenic mutant SOD1G93A, providing evidence that ER stress plays a major role in ALS.