Glial proliferation and activation are associated with disease progression in amyotrophic lateral sclerosis (ALS) and frontotemporal lobar dementia. In this study, we describe a unique platform to address the question of cell autonomy in transactive response DNAbinding protein (TDP-43) proteinopathies. We generated functional astroglia from human induced pluripotent stem cells carrying an ALScausing TDP-43 mutation and show that mutant astrocytes exhibit increased levels of TDP-43, subcellular mislocalization of TDP-43, and decreased cell survival. We then performed coculture experiments to evaluate the effects of M337V astrocytes on the survival of wild-type and M337V TDP-43 motor neurons, showing that mutant TDP-43 astrocytes do not adversely affect survival of cocultured neurons. These observations reveal a significant and previously unrecognized glial cell-autonomous pathological phenotype associated with a pathogenic mutation in TDP-43 and show that TDP-43 proteinopathies do not display an astrocyte non-cell-autonomous component in cell culture, as previously described for SOD1 ALS. This study highlights the utility of induced pluripotent stem cell-based in vitro disease models to investigate mechanisms of disease in ALS and other TDP-43 proteinopathies.glia | motor neuron disease | disease modeling T ransactive response DNA-binding protein (TDP-43) is the major component of ubiquitinated cytoplasmic and nuclear inclusions in neurons and astroglia in amyotrophic lateral sclerosis (ALS) and a subgroup of frontotemporal lobar degeneration (FTLD-TDP) (1-3). These pathological hallmarks provide a unifying description of a range of conditions defined as TDP-43 proteinopathies (4). At present, >30 mutations in the TDP-43 gene (TARDBP) have been linked to familial ALS (fALS) (5), strongly suggesting a causative role for TDP-43 in the pathogenesis of ALS.Accumulating evidence from experimental systems implicating non-cell-autonomous mechanisms in ALS has highlighted the importance of the glial cellular environment to motor neuron (MN) degeneration (1,3,(6)(7)(8)(9). In vivo rodent models of ALS with lineage-specific SOD1 expression have particularly influenced our understanding of the nonneuronal contribution to disease progression. Glial expression of mutant SOD1 cannot initiate MN disease on its own, but is necessary for disease progression (6, 7). Furthermore, astrogliosis precedes MN degeneration in some animal models and is a dominant feature of all human ALS pathology (4, 6, 10). Collectively, these observations highlight the need to better understand the nature of astroglial pathology in ALS. Combining developmental neurobiological principles of cell fate determination with human induced pluripotent stem cell (iPSC) lines derived from patients carrying ALS disease-causing mutations may provide important insights into astroglia pathology.We recently generated human MNs from iPSC lines derived from a fALS patient and demonstrated that the M337V TDP-43 mutation confers cell-autonomous toxicity to MNs (11). More...

Amyotrophic lateral sclerosis (ALS) is a devastating neurodegenerative disease for which a greater understanding of early disease mechanisms is needed to reveal novel therapeutic targets. We report the use of human induced pluripotent stem cell (iPSC)-derived motoneurons (MNs) to study the pathophysiology of ALS. We demonstrate that MNs derived from iPSCs obtained from healthy individuals or patients harbouring TARDBP or C9ORF72 ALS-causing mutations are able to develop appropriate physiological properties. However, patient iPSC-derived MNs, independent of genotype, display an initial hyperexcitability followed by progressive loss of action potential output and synaptic activity. This loss of functional output reflects a progressive decrease in voltage-activated Na+ and K+ currents, which occurs in the absence of overt changes in cell viability. These data implicate early dysfunction or loss of ion channels as a convergent point that may contribute to the initiation of downstream degenerative pathways that ultimately lead to MN loss in ALS.