Analysis of organoid-derived microglia implicates microglial dysfunction in C9ORF72 ALS/FTD

Amyotrophic lateral sclerosis (ALS) is an adult-onset neurodegenerative disease characterized by loss of upper and lower motor neurons and progressive muscle wasting. Accumulating evidence indicates a role for non-neuronal cells in ALS pathogenesis, but their exact role and mechanism-of-action remain incompletely understood. A hexanucleotide (GGGGCC) repeat expansion (HRE) in C9ORF72 is the most common genetic cause of ALS (C9-ALS) and a frequent cause of frontotemporal dementia (FTD). Several lines of experimental evidence support a role for the immune system and microglia in C9-ALS/FTD, and, dependent on experimental settings and species used, both reduced and increased microglial activity have been reported. To further study microglia in C9-ALS/FTD in the context of a complex, three-dimensional disease environment, we developed cerebral organoids that innately develop microglia derived from induced pluripotent stem cells (iPSCs) of C9ORF72 patients and controls. To define changes in C9-organoid derived microglia (oMG) activational state due to C9-HRE, we performed RNA sequencing from four C9 iPSC lines and four healthy controls (HC).