Altered Inflammatory Signature in a C9ORF72 -ALS iPSC-Derived Motor Neuron and Microglia Coculture Model.

Amyotrophic lateral sclerosis (ALS) is a complex neurodegenerative disorder involving multiple cell types in the central nervous system. The key pathological features of ALS include the degeneration of motor neurons and the initiation and propagation of neuroinflammation mediated by nonneuronal cell types such as microglia. Currently, the specific mechanisms underlying the involvement of microglia in neuroinflammation in ALS are unclear. Consequently, we generated several human-induced pluripotent stem cell (iPSC) derived motor neuron and microglia cocultures. We utilized ALS patient-derived iPSCs carrying a common genetic variant, the hexanucleotide repeat expansion (HRE) in C9ORF72, as well as C9ORF72 knockout (KO) iPSC lines. iPSC-derived motor neurons and microglia demonstrated expression of cell type-specific markers and were functional. Phenotypic assessments on motor neurons and microglia in mono- and cocultures identified dysfunction in the expression and secretion of inflammatory cytokines and chemokines in lipopolysaccharide (LPS)-stimulated C9ORF72 HRE and C9ORF72 KO microglia. Analysis of single-cell RNA sequencing data from microglia and motor neuron cocultures revealed cell type-specific transcriptomic changes. Specifically, we detected the removal of an LPS-responsive microglia subpopulation, correlating with a dampened inflammatory response in C9ORF72 HRE and C9ORF72 KO microglia. Overall, our results support the critical role of microglia-mediated neuroinflammation in ALS pathology, and our iPSC-derived models should prove a valuable platform for further mechanistic studies of ALS-associated pathways.