Table 5.

ALS models for C9orf72, SOD1, TARDBP and FUS mutations using hiPSC technology

Mutation	Cell types	Purpose and application	Key findings/take home messages	Reference
SOD1	MNs	Defining phenotypes directly linked to SOD1A4V mutation	SOD1A4V hiPSC-MNs exhibit decreased cell survival that is rescued by gene correction SOD1A4V MNs show mitochondrial dysfunction and evidence of oxidative and ER stress	(Kiskinis et al., 2014)
SOD1	MNs	Studying role of protein inclusions	SOD1 hiPSC-MNs display neurofilament aggregation followed by neurite degeneration in the absence of glia Mutant SOD1 binds to 3'UTR of NF-L mRNA and changes proportion of NF subunitsn	(Chen et al., 2014)
SOD1; C9orf72; FUS	MNs	Electrophysiological properties of MNs	Hyperexcitabilty of ALS hiPSC-MNs	(Wainger et al., 2014)
SOD1; FUS	MNs	Determining whether divergent causal mutations exhibit common dysfunctional pathways	SOD1 induces degeneration via ERK and JNK signaling in hiPSC-MNs, which is reverted by gene correction FUS hiPSC-MNs exhibit activated p38 and ERK indicating overlapping pathway	(Bhinge et al., 2017)
SOD1; TARDBP; C9orf72	MNs	Screen to repurpose existing drugs for ALS	Src/c-Abl inhibition increased survival of ALS MNs One inhibitor (Bosutinib) increased autophagy and decreased misfolded SOD1 load	(Imamura et al., 2017)
C9orf72	MNs	Studying mechanisms of C9 HRE pathology	C9orf72 hiPSC-MNs exhibit RNA foci, differential expression of genes-related to membrane excitability, and decreased firing capacity that were reversed by antisense oligonucleotides targeting C9orf72	(Sareen et al., 2013)
C9orf72 (FTD)	Neurons	Understanding C9orf72 pathology in FTD	C9orf72 hiPSC-neurons display RNA foci and RAN protein expression as well as sensitivity towards autophagy inhibition	(Almeida et al., 2013)
C9orf72	MNs	Studying the toxic gain-of-function role of C9orf72 in ALS	C9orf72 hiPSC MNs show RNA foci and repeat RNA sequesters ADARB2 C9orf72 hiPSC-MNs have increased susceptibility to excitotoxic stress	(Donnelly et al., 2013)
C9orf72	Neurons	Investigating HRE RNA-induced toxicity	RanGAP1 interacts with HRE RNA and suppresses neurodegeneration C9orf72 hiPSC neurons show RanGAP1 mislocalization and impaired nuclear import	(Zhang et al., 2015a)
C9orf72	Neurons	Studying RAN mediated toxicity	C9orf72 hiPSC neurons display dysfunctional RNA export out of nucleus	(Freibaum et al., 2015)
C9orf72; TARDBP	MNs	Characterization of electrophysiological properties of ALS MNs	Comparison of electrophysiological properties of hiPSC MNs shows a transition from initial hyperexcitability to hypoexcitability after prolonged culture	(Devlin et al., 2015)
C9orf72	Cortical neurons, MNs	Phenotypic characterization of cortical and spinal MNs	Both C9orf72 hiPSC cortical neurons and MNs exhibit stress granule formation and abnormal protein aggregation Decreased survival of C9orf72 hiPSC-MNs is associated with Ca2+ dysregulation and ER stress	(Dafinca et al., 2016)
C9orf72	MNs; Neurons	Understanding C9ORF72 HRE-mediated toxicity	C9orf72 hiPSC-MNs and hiPSC neurons ectopically expressing dipeptide repeat (DPR) protein (GR)80 have increased oxidative stress and DNA damage GR(80) preferentially binds to mitochondrial ribosomal proteins and induces mitochondrial dysfunction	(Lopez-Gonzalez et al., 2016)
C9orf72; sALS	Astrocytes, MNs	Investigating mechanisms of impaired proteostasis in MNs	ALS hiPSC astrocytes impair autophagy in MNs via soluble factors	(Madill et al., 2017)
C9orf72	Astrocytes, MNs	Role of astrocytes in humanized system	hiPSC C9orf72 astrocytes show RNA foci and poly-GP DPRs Co-culture with MNs reduces MN functional output	(Zhao et al., 2020)
C9orf72	Astrocytes, MNs	Studying astrocyte-mediated toxicity	C9orf72 hiPSCs display toxicity to MNs via soluble factor Astrocyte conditioned media induces oxidative stress in MNs	(Birger et al., 2019)
C9orf72	MNs	Investigating proteins with altered nucleocytoplasmic distribution in C9ORF72 HRE-ALS	C9orf72 hiPSC-MNs show redistribution of eRF1 in nuclear invaginations C9orf72 hiPSC-MNs show reduced translation and hyperactive nonsense-mediated decay	(Ortega et al., 2020)
C9orf72; SOD1; sALS	MNs	Cross comparison of multiOMIC datasets in hiPSC-MNs and patient tissues	Transcriptomic and proteomic signatures of C9orf72 hiPSC-MNs corroborated in MNs from C9orf72 and sALS patients SOD1 hiPSC-MNs have different transcriptomic signature	(Wong and Venkatachalam, 2019)
TARDBP	MNs, neurons	Investigating cell-autonomous mechanisms of TARDBP pathology	TARDBP hiPSC-MNs show increased soluble and detergent-resistant TDP-43 and selective degeneration over time that can be reversed by PI3K inhibition	(Bilican et al., 2012)
TARDBP	MNs	Developing platform for disease modeling and screening	TARDBP hiPSC-MNs display cytosolic TDP-43 aggregates and fewer neurites TDP-43 in detergent insoluble fraction interacts with SNRPB2 Histone acetyltransferase inhibitor anacardic acid reversed the phenotype	(Egawa et al., 2012)
TARDBP	astrocytes, MNs	Investigating non-cell autonomous contribution to TARDBP ALS	TARDBP hiPSC-astrocytes have increased TARDBP expression and TDP-43 aggregation and decreased cell survival Co-culture with MNs does not induce MN cell death	(Serio et al., 2013)
TARDBP	MNs	Investigate composition and role of TDP-43 aggregates in ALS	TDP-43 aggregates sequester nuclear pore proteins and affect nucleocytoplasmic transport	(Chou et al., 2018)
TARDBP	MNs	Studying mechanisms of TARDBP pathology	TARDBP hiPSC-MNs display neurofilament abnormalities along with mitochondrial and lysosomal dysfunction and neuron loss independent of TDP-43 mislocalization or aggregation	(Kreiter et al., 2018)
TARDBP	MNs	Comparing calcium dysregulation in C9orf72 and TDP-43 iPS-derived MNs	Glutamate stimulation leads to high recovery times of normal cytosolic calcium levels in TDP-43 MNs Calcium-permeable receptors are upregulated in TDP-43 MNs Reduced mitochondrial calcium uptake is observed in TDP-43 MNs TDP-43 MNs have low ER calcium release and high levels of Bcl-2	(Dafinca et al., 2020)
TARDBP	MNs	Gaining insights into the role of SGs in pathophysiology	20 planar compounds decreased stress granule formation by preventing TDP-43 from entering the stress granules Generated MNs from TARDBP ALS patients and control family members. After stimulating MNs with toxins, stress granule formation increased and TDP-43 entered the stress granules TDP-43 formed more permanent clumps in TARDBP MNs compared to controls. Planar compounds reduced the formation of TDP-43 permanent clumps and increased TARDBP MN survival	(Fang et al., 2019)
FUS	MNs	Studying FUS-induced pathology	Compared mild and severe FUS mutations at baseline or under stress conditions Under stress conditions, FUS hiPSC-MNs show FUS mislocalization to cytoplasm and larger FUS+ stress granules At baseline, FUS hiPSC-MNs show DNA damage Degree of FUS mislocalization correlated with disease onset	(Higelin et al., 2016)
FUS	MNs	Mechanisms of FUS pathology	Mutant FUS hiPSC-MNs exhibit increased FUS mislocalization to cytoplasm and in stress granules under stress conditions compared to isogenic counterparts MN precursor cells display differential splicing and gene expression	(Ichiyanagi et al., 2016)
FUS	MNs	Mechanisms of FUS pathology	Mutant FUS hiPSC-MNs show FUS mislocalization, hypoexcitability, and axonal transport deficits Treatment of FUS hiPSC-MNs with HDAC6 inhibitors and ASOs rescues axonal transport deficits	(Guo et al., 2017b)
FUS	MNs; Neurons	Investigating the role of stress granules in ALS	Generated wild type- and P525L-FUS-GFP isogenic hiPSC lines P525L mutation alters dynamics of FUS-GFP incorporation in stress granules Screen reveals inhibition of PI3K/AKT/mTOR promotes autophagy and reduces P525L-FUS recruitment to stress granules	(Marrone et al., 2018)
FUS	hiPSCs; MNs	Understanding nuclear-cytoplasmic transport defects due to FUS mutations	In hiPSC-MNs, FUS mutations in the nuclear localization sequence cause dysfunction of poly(ADP-ribose) polymerase (PARP)-dependent DNA damage response (DDR) signaling This causes FUS mislocalization and subsequent FUS aggregation and cell death	(Naumann et al., 2018)
FUS	MNs	Understanding the effect of FUS mutations on neuromuscular junction	Co-cultures of FUS patient-derived hiPSC-MNs and myotubes show endplate maturation defects	(Picchiarelli et al., 2019)
sALS	MNs	Modeling sALS	sALS hiPSC MNs exhibit TDP-43 aggregation Identified Digoxin modulates TDP-43 aggregation in high content chemical screen	(Burkhardt et al., 2013)
sALS	astrocytes, MNs	Investigating astrocyte-mediated toxicity to MNs in human system	sALS patient postmortem-derived astrocytes induce death of hiPSC-MNs via necroptosis	(Re et al., 2014)
sALS	MNs	Studying non-genetic forms of ALS	sALS hiPSC-MNs gene expression signature reveals mitochondrial dysfunction and degeneration	(Alves et al., 2015)
sALS	MN; SkM	Developing platform for NMJ studies	Developed 3D skeletal muscle/MN "ALS-on-a-chip technology" ALS motor unit showed fewer SkM contractions, MN degeneration, and SkM apoptosis	(Osaki et al., 2018)
sALS; FUS; TARDBP; SOD1	MNs	Develop multi-phenotypic screen to cluster heterogeneous sALS lines	Stratified sALS hiPSC-MNs Identified ropinirole as therapeutic target for non-SOD1 ALS	(Fujimori et al., 2018)