Astrocytes display cell autonomous and diverse early reactive states in familial amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a rapidly progressive and fatal disease. Although astrocytes are increasingly recognized contributors to the underlying pathogenesis, the uniformity of their reactive transformation in different genetic forms of ALS remains unresolved. Here we begin to systematically examine this issue by using highly enriched and serum-free human induced pluripotent stem cell derived astrocytes from patients with VCP and SOD1 mutations. We show that VCP mutant astrocytes undergo cell autonomous reactive transformation characterized by increased expression of complement component 3 (C3) in addition to several characteristic gene expression changes. In contrast, we find that isochronic SOD1 mutant astrocytes undergo a molecularly distinct reactive transformation in their basal state. Importantly, through transcriptome-wide analyses we identify divergent gene expression profiles and activation of key transcription factors in SOD1 and VCP mutant hiPSC-derived astrocytes. Finally, we show functional differences in the basal cytokine secretome between VCP and SOD1 hiPSC-derived astrocytes. Our data therefore reveal that early reactive transformation can occur cell autonomously in human ALS astrocytes and with a striking degree of molecular and functional heterogeneity when comparing different disease-causing mutations. These insights may be important when considering astrocyte reactivity as a putative therapeutic target in familial ALS.