Early nuclear phenotypes and reactive transformation in human iPSC‐derived astrocytes from ALS patients with SOD1 mutations

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease characterized by the progressive death of motor neurons (MNs). Glial cells play roles in MN degeneration in ALS. More specifically, astrocytes with mutations in the ALS‐associated gene Cu/Zn superoxide dismutase 1 (SOD1) promote MN death. The mechanisms by which SOD1‐mutated astrocytes reduce MN survival are incompletely understood. To characterize the impact of SOD1 mutations on astrocyte physiology, we generated astrocytes from human induced pluripotent stem cell (iPSC) derived from ALS patients carrying SOD1 mutations, together with control isogenic iPSCs. We report that astrocytes harboring SOD1(A4V) and SOD1(D90A) mutations exhibit molecular and morphological changes indicative of reactive astrogliosis when compared to isogenic astrocytes. We show further that a number of nuclear phenotypes precede, or coincide with, reactive transformation. These include increased nuclear oxidative stress and DNA damage, and accumulation of the SOD1 protein in the nucleus. These findings reveal early cell‐autonomous phenotypes in SOD1‐mutated astrocytes that may contribute to the acquisition of a reactive phenotype involved in alterations of astrocyte‐MN communication in ALS. Main Points Astrocytes generated from iPSCs carrying ALS‐associated SOD1(A4V) and SOD1(D90A) mutations undergo reactive transformation Astrocytes with SOD1(A4V) and SOD1(D90A) mutations display increased nuclear oxidation, DNA damage, and nuclear SOD1 accumulation