Characterizing an iPSC-Derived Microglial Model of TDP-43 Dysfunction

The RNA-binding protein TDP-43 is a key pathological factor in multiple neurodegenerative disorders including Amyotrophic Lateral Sclerosis (ALS) and Frontotemporal Dementia (FTD). TDP-43 dysfunction is known to cause neuronal degradation; however, if and/or how physiological levels of TDP-43 dysfunction alter microglial function is unknown. We therefore developed an iPSC-derived microglial model expressing CRISPR-induced ALS/FTD-associated mutations, TDP-43 Q331K and M337V. TMRE staining revealed diminished mitochondrial function in the homozygous mutants, independent of major changes in mitochondrial protein abundance or viability. Considering TDP-43’s involvement in RNA processing, we hypothesized that altered splicing events may underpin this mitochondrial dysfunction. MAJIQ and LeafCutter analyses identified numerous altered splicing events in mutant cells, including in mitochondria-associated TDP-43 targets. Inflammatory responses were largely unchanged in the mutant iMGs; however, Q331K+/+ did induce elevated CCL5 secretion 24 hours after TLR-4 activation. Interestingly, a knock-in mouse model of the same genotype also showed elevated Ccl5 expression 24 hours after traumatic brain injury. Taken together, we have demonstrated that physiological levels of ALS/FTD-associated TDP-43 mutations are sufficient to cause mitochondrial dysfunction, differential splicing, and altered CCL5 response in an iMG model. This work describes distinct transcriptomic and functional changes in human microglia-like cells that could have significant implications for the innate immune response associated with ALS/FTD.