Amyotrophic lateral sclerosis (ALS) Cell Models for Research

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease affecting motor neurons, leading to muscle weakness, paralysis, and death typically within 2-5 years of symptom onset. The global incidence is approximately 1.5-2.5 per 100,000 person-years, with a prevalence of about 4-6 per 100,000. The male-to-female ratio is about 1.3:1. Most cases are sporadic (90-95%), while familial forms account for 5-10%. The disease is more common in individuals aged 55-75, but early-onset cases exist. There is no cure, and current treatments (riluzole, edaravone) only modestly extend survival. The economic burden is significant, with high care costs. Research is critical to understand disease mechanisms and develop effective therapies.

ALS is an ideal model for studying neurodegeneration, protein aggregation, RNA metabolism, and oxidative stress. The disease has well-defined genetic causes in familial cases, enabling the creation of isogenic cell models with specific mutations. Public datasets, such as those from the ALS Consortium and GEO, provide transcriptomic and proteomic data. Key open questions include the role of TDP-43 pathology, the contribution of glial cells, and the mechanisms of selective motor neuron vulnerability. Gene-edited cell models are essential for dissecting these pathways and testing potential therapeutics.

ALS pathogenesis involves multiple interconnected pathways:

• • Protein aggregation: Misfolded proteins (e.g., TDP-43, SOD1, FUS) accumulate in cytoplasmic inclusions, leading to proteotoxic stress.
• • RNA metabolism defects: Mutations in TARDBP, FUS, and C9orf72 disrupt RNA splicing, transport, and translation.
• • Oxidative stress: Impaired antioxidant defenses cause reactive oxygen species (ROS) accumulation, damaging cellular components.
• • Mitochondrial dysfunction: Defective mitochondrial dynamics and bioenergetics contribute to motor neuron death.
• • Glutamate excitotoxicity: Excessive glutamate signaling leads to calcium overload and neuronal injury.
• • Neuroinflammation: Activated microglia and astrocytes release pro-inflammatory cytokines, exacerbating neuronal damage.

Data from ALS databases and literature (e.g., ALSoD, ClinVar).

Key signaling networks implicated in ALS:

• • Autophagy-lysosomal pathway: Mutations in OPTN, TBK1, VCP, and C9orf72 impair autophagic flux, leading to protein accumulation.
• • Unfolded protein response (UPR): ER stress activates PERK, IRE1, and ATF6, which can trigger apoptosis if unresolved.
• • NF-κB signaling: Chronic activation in glial cells promotes neuroinflammation.
• • MAPK/ERK pathway: Aberrant activation contributes to oxidative stress and apoptosis.
• • PI3K/AKT/mTOR pathway: Dysregulation affects cell survival and autophagy.
• • Wnt signaling: Altered in motor neurons and glia, influencing neurogenesis and inflammation.

Organoids: 3D motor neuron organoids derived from iPSCs recapitulate ALS pathology, including TDP-43 aggregation and axonal degeneration. They provide a more physiologically relevant model than 2D cultures.

• • Transgenic mice: SOD1-G93A, TDP-43-A315T, C9orf72 repeat-expansion mice are widely used.
• • Knock-in mice: For point mutations (e.g., SOD1-D90A) to better mimic human disease.
• • Zebrafish: Transgenic models for high-throughput drug screening.
• • Drosophila: Models for genetic screens.
• • Induced models: Use of toxins (e.g., LPS) to induce neuroinflammation.

CRISPR-Cas9 technology enables the creation of isogenic cell lines with precise genetic modifications, such as:

• • Knockout lines: For genes like SOD1, TARDBP, or C9orf72 to study loss-of-function effects.
• • Knock-in lines: Introducing disease-associated point mutations (e.g., SOD1-A4V, TARDBP-M337V) into wild-type cells.
• • Reporter lines: Tagging endogenous proteins (e.g., TDP-43-GFP) for live-cell imaging.

These models are commercially available and sequence-verified, ensuring reproducibility. They are essential for studying disease mechanisms and drug screening.

Knockout and knock-in lines are used to validate the role of genes in ALS pathogenesis. For example:

• • SOD1 knockout cells show increased oxidative stress and reduced viability.
• • TARDBP knockout cells exhibit abnormal RNA splicing and TDP-43 aggregation.
• • C9orf72 knockout cells display impaired autophagy and increased inflammation.

These models allow researchers to study gene function in a controlled genetic background.

Isogenic pairs (wild-type vs. mutant) are used in high-throughput screens to identify compounds that selectively kill mutant cells or rescue their phenotype. For example:

• • Screening for compounds that reduce TDP-43 aggregation in TARDBP-mutant cells.
• • Testing drugs that alleviate oxidative stress in SOD1-mutant cells.
• • Modeling drug resistance by exposing cells to increasing concentrations of a compound and selecting resistant clones.

CRISPR-engineered cells are used to identify biomarkers for diagnosis and prognosis. For example:

• • Secreted proteins from mutant cells can be analyzed to find potential biomarkers.
• • Synthetic lethality screens: knocking out genes in combination with disease mutations to identify vulnerabilities that can be targeted therapeutically.