Amyotrophic Lateral Sclerosis (ALS) is a fatal neurodegenerative disorder characterized by progressive loss of upper and lower motor neurons. This pathway models the molecular mechanisms underlying motor neuron degeneration in ALS[@cleveland2001].
Overview
ALS mechanisms involve multiple interconnected processes: [@boillee2006]
Protein Aggregation: TDP-43, SOD1, FUS, C9orf72 DPR proteins form cytoplasmic inclusions
RNA Metabolism Dysregulation: Defects in RNA processing, splicing, and transport
Mitochondrial Dysfunction: Energy deficits, oxidative stress, mitophagy impairment
Excitotoxicity: Glutamate-induced calcium dysregulation, EAAT2 loss
Neuroinflammation: Activated microglia and astrocytes releasing pro-inflammatory cytokines
Axonal Transport Defects: Impaired transport of proteins, organelles
Neuronal Death: Progressive loss of cortical and spinal motor neurons
Pathway Diagram
Mechanism
flowchart TD
A["Genetic Mutations"] --> B["SOD1 Misfolding"]
A --> C["TDP-43 Mislocalization"]
A --> D["C9orf72 Repeat Expansion"]
A --> E["FUS Aggregation"]
C --> F["RNA Processing Defects"]
D --> G["Dipeptide Repeat Toxicity"]
B --> H["Protein Aggregation"]
E --> F
F --> H
G --> H
H --> I["Motor Neuron Stress"]
J["EAAT2 Loss"] --> K["Glutamate Excitotoxicity"]
K --> I
I --> L["Mitochondrial Dysfunction"]
I --> M["Axonal Transport Failure"]
L --> N["Motor Neuron Death"]
M --> N
...
ALS Mechanistic Pathway
Introduction
Amyotrophic Lateral Sclerosis (ALS) is a fatal neurodegenerative disorder characterized by progressive loss of upper and lower motor neurons. This pathway models the molecular mechanisms underlying motor neuron degeneration in ALS[@cleveland2001].
Overview
ALS mechanisms involve multiple interconnected processes: [@boillee2006]
Protein Aggregation: TDP-43, SOD1, FUS, C9orf72 DPR proteins form cytoplasmic inclusions
RNA Metabolism Dysregulation: Defects in RNA processing, splicing, and transport
Mitochondrial Dysfunction: Energy deficits, oxidative stress, mitophagy impairment
Excitotoxicity: Glutamate-induced calcium dysregulation, EAAT2 loss
Neuroinflammation: Activated microglia and astrocytes releasing pro-inflammatory cytokines
Axonal Transport Defects: Impaired transport of proteins, organelles
Neuronal Death: Progressive loss of cortical and spinal motor neurons
Pathway Diagram
Mechanism
Mermaid diagram (expand to render)
Key Molecular Players
| Protein/Gene | Role in ALS | Therapeutic Target | [@ilieva2009] |--------------|-------------|-------------------| [@ling2013] | TDP-43 | RNA-binding protein; forms cytoplasmic inclusions in 95% of ALS | ASO, aggregation inhibitors | [@taylor2016] | SOD1 | Superoxide dismutase; mutant causes familial ALS | Gene silencing, copper chelators | [@van2017] | FUS | RNA-binding protein; mutations cause FUS-ALS | ASO, modulators | [@mejzini2019] | C9orf72 | Hexanucleotide repeat causes ALS/FTD | ASO, gene therapy | [@ghasemi2018] | EAAT2 | Glutamate transporter; loss causes excitotoxicity | Ceftriaxone, gene therapy | [@liu2022] | OPTN | Autophagy receptor; mutations cause ALS | Autophagy modulators | | UBQLN2 | Autophagy receptor; mutations cause ALS | Proteostasis enhancers |
Disease Mechanisms
Protein Aggregation
TDP-43 Pathology (95% of ALS cases)
TDP-43 mislocalizes from nucleus to cytoplasm
Forms phosphorylated, ubiquitinated inclusions
Sequesters RNA and RNA-binding proteins
Causes loss of nuclear TDP-43 function
SOD1 Mutations (20% of familial ALS)
Gain-of-toxic-function through misfolding
Forms insoluble aggregates
Impaired axonal transport
Mitochondrial dysfunction
FUS Pathology
FUS inclusions in cytoplasm
Impaired RNA splicing
Defects in RNA transport
C9orf72 DPR Toxicity
Hexanucleotide repeat expansion
RNA foci sequester RNA-binding proteins
Dipeptide repeat (DPR) proteins are toxic
Nucleolar stress
RNA Metabolism Dysregulation
Splicing Defects: Aberrant mRNA splicing due to TDP-43/FUS loss
Transport Defects: Impaired RNA granule transport
Translation Dysregulation: Altered protein synthesis
[Cleveland DW, Rothstein JD. From Charcot to Lou Gehrig: deciphering selective motor neuron vulnerability in ALS (2001)](https://pubmed.ncbi.nlm.nih.gov/11737005/) — Nat Rev Neurosci[@cleveland2001]
[Boillee S, Vande Velde C, Cleveland DW. ALS: a disease of motor neurons and their nonneuronal neighbors (2006)](https://pubmed.ncbi.nlm.nih.gov/16815314/) — Neuron[@boillee2006]
[Ilieva H, Polymenidou M, Cleveland DW. Non-cell autonomous toxicity in neurodegenerative disorders: ALS and beyond (2009)](https://pubmed.ncbi.nlm.nih.gov/19635952/) — J Cell Biol[@ilieva2009]
[Ling SC, Polymenidou M, Cleveland DW. Converging mechanisms in ALS and FTD: disrupted RNA and protein homeostasis (2013)](https://pubmed.ncbi.nlm.nih.gov/24288922/) — Neuron[@ling2013]
[Taylor JP, Brown RH Jr, Cleveland DW. Decoding ALS: from genes to mechanism (2016)](https://pubmed.ncbi.nlm.nih.gov/28029927/) — Nature[@taylor2016]
[Van Es MA, Hardiman O, Chio A, et al. Amyotrophic lateral sclerosis (2017)](https://pubmed.ncbi.nlm.nih.gov/28542893/) — Lancet[@van2017]
[Mejzini R, Flynn LL, Pitout IL, et al. ALS genetics, mechanisms, and therapeutics: where are we now? (2019)](https://pubmed.ncbi.nlm.nih.gov/31849657/) — Front Neurosci[@mejzini2019]
[Ghasemi M, Brown RH Jr. Genetics of amyotrophic lateral sclerosis (2018)](https://pubmed.ncbi.nlm.nih.gov/29507226/) — Cold Spring Harb Perspect Med[@ghasemi2018]
[Liu J, et al. Therapeutic strategies for amyotrophic lateral sclerosis: from small molecules to disease-modifying therapies (2022)](https://pubmed.ncbi.nlm.nih.gov/35231969/) — Nat Rev Drug Discov[@liu2022]
Replication and Evidence
Multiple independent laboratories have validated this mechanism in neurodegeneration. Studies from major research institutions have confirmed key findings through replication in independent cohorts. Quantitative analyses show significant effect sizes in relevant model systems.
However, there remains some controversy regarding certain aspects of this mechanism. Some studies report conflicting results, suggesting the need for additional research to resolve outstanding questions.
Recent Research Updates (2024-2026)
Recent publications:
[Elevated serum trimethylamine N-oxide (TMAO) and trimethyllysine in patients with ALS. (2026)](https://pubmed.ncbi.nlm.nih.gov/41705073/) — IBRO neuroscience reportsPMID: 41705073(https://pubmed.ncbi.nlm.nih.gov/41705073/)
[Neuromodulatory role and therapeutic potential of N6-methyladenosine RNA methylation in neurodegenerative diseases. (2026)](https://pubmed.ncbi.nlm.nih.gov/40618260/) — Neural regeneration researchPMID: 40618260(https://pubmed.ncbi.nlm.nih.gov/40618260/)
[The role of gut microbiota-mitochondria crosstalk in neurodegeneration. (2026)](https://pubmed.ncbi.nlm.nih.gov/40314217/) — Neural regeneration researchPMID: 40314217(https://pubmed.ncbi.nlm.nih.gov/40314217/)
[Neuroinflammation in neurodegenerative diseases: Focusing on the mediation of T lymphocytes. (2026)](https://pubmed.ncbi.nlm.nih.gov/40536931/) — Neural regeneration researchPMID: 40536931(https://pubmed.ncbi.nlm.nih.gov/40536931/)