Pathogenesis of ALS: Multi-System Cellular Mechanisms

Introduction

The neurodegenerative cascade in ALS is a multifactorial process where diverse genetic defects converge on interconnected cellular pathways. Understanding these pathogenetic pathways is key to developing targetable disease-modifying therapies.

┌────────────────────────────────────────────────────────────────────────┐
│                   MOTOR NEURON DEGENERATION PATHWAYS                  │
├───────────────────┬───────────────────┬────────────────────────────────┤
│ Protein           │ Aberrant RNA      │ Oxidative Stress &             │
│ Aggregation       │ Processing        │ Mitochondrial Disruption       │
│ (SOD1, VCP, OPTN) │ (TARDBP, FUS, SETX│ (SOD1, ALSIN, APEX1)           │
├───────────────────┼───────────────────┼────────────────────────────────┤
│ Axonal            │ Microglia         │ Apoptosis &                    │
│ Dysfunction       │ Activation        │ Metabolic Disturbance          │
│ (SOD1, DCTN, PRPH)│ (SOD1, PGRN)      │ (VAPB, FIG4, SIGMAR1)          │
└───────────────────┴───────────────────┴────────────────────────────────┘

Dominant Pathogenetic Pathways

1. Protein Aggregation & Proteostatic Stress Mutations in genes like SOD1, VCP, UBQLN2, and OPTN lead to misfolded protein accumulation, overwhelming cellular ubiquitin-proteasome and autophagic clearance mechanisms.

2. Aberrant RNA Processing Mutations in TARDBP (TDP-43), FUS, SETX, and ANG disrupt transcription, alternative splicing, and RNA transport, directly impacting neuronal survival.

3. Mitochondrial Disruption & Oxidative Stress Defects in SOD1, ALSIN, and APEX1 cause structural mitochondrial alterations, electron transport chain uncoupling, decreased ATP production, impaired calcium buffering, and excessive reactive oxygen species (ROS) production.

4. Axonal Transport & Cytoskeletal Dysfunction Mutations in DCTN1 (Dynactin), PRPH, and SPG disrupt anterograde and retrograde axonal transport, depriving distant synapses of essential structural proteins and neurotrophic support.

5. Non-Neuronal Toxicity & Neuroinflammation Microglial activation (PGRN, SOD1) and metabolic disturbances (SIGMAR1, VAPB) promote inflammatory cytokine cascades that accelerate motor neuron cell death.

Key Takeaways

• ALS pathogenesis is multifactorial, involving protein aggregation, altered RNA metabolism, and axonal dysfunction.

• Mitochondrial decay leads to energy failure, impaired calcium handling, and ROS accumulation.

• Non-neuronal cells, including activated microglia and reactive astrocytes, drive motor neuron toxicity.