Expression of amyotrophic lateral sclerosis associated protein disulfide isomerase A3 D217N variant recapitulates early morphological alterations at the neuromuscular junction

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease characterized by neuromuscular connectivity decline followed by motoneuron loss. Altered proteostasis is suggested as a transversal pathogenic mechanism, notably involving dysfunction at the level of the endoplasmic reticulum (ER). Protein disulfide isomerases (PDIs) are key enzymes that catalyze protein folding and disulfide bond formation in the ER. Importantly, PDIs function is disrupted in ALS. We previously identified mutations in the gene encoding PDIA3 (also known as Grp58 or ERp57) as risk factors for ALS, which were associated with altered neuromuscular junction (NMJ) organization when expressed in zebrafish, a phenotype recapitulated in PDIA3-null mice. Here, we generated a transgenic mouse line overexpressing the ALS-linked PDIA3 variant D217N and performed a comprehensive characterization of ALS-like features. The transgenic line exhibited moderate overexpression of mutant PDIA3^D217N, which led to morphological alterations at the NMJ resembling those observed in ALS models and patients, along with abnormal distribution of oxidative and glycolytic muscle fibers. However, mutant PDIA3^D217N expression did not result in motor impairment, coordination deficits, or motoneuron loss. At the molecular level, we observed reduced expression of SV2 in the spinal cord, an important synaptic protein involved in NMJ function. Our findings further support the involvement of PDIA3 dysfunction as a risk factor in the emergence of early features of ALS.