Recent 2024 PD GWAS has identified significant associations in the cathepsin genes CTSO (cathepsin O) and CTSF (cathepsin F), suggesting that non-lysosomal cathepsin variants modify PD risk. CTSO is a cysteine protease with structural similarity to cathepsin B, while CTSF is a lysosomal cysteine protease with overlapping substrate specificity with cathepsin L. We propose that PD risk alleles in CTSO/CTSF create subtle shifts in the intracellular cathepsin network that become catastrophic only in the context of GBA1 mutation. In GBA1-deficient cells, cathepsin D activity is reduced (due to impaired lysosomal trafficking), and the cell compensates by upregulating CTSO and CTSF. The risk alleles encode proteins with altered substrate affinity that, under compensated conditions, efficiently degrade SNCA monomers but paradoxically generate aggregation-competent SNCA fragments from a specific cleavage site (residues 60-70). This mechanism explains the statistical epistasis between GBA1 and cathepsin GWAS loci. The prediction is that CTSO/CTSF knockdown will reduce SNCA fragment generation and aggregation in GBA1-deficient neurons.
...Curated pathway from expert analysis
flowchart TD
A["GBA1 Mutation Carrier<br/>Reduced GCase Activity"]
B["GlcCer Lysosomal Accumulation<br/>Substrate Stress"]
C["CTSO CTSF PD GWAS Variants<br/>Cathepsin Network Shift"]
D["Cathepsin B D Imbalance<br/>Protease Compensation Failure"]
E["SNCA and Lysosomal Substrate Clearance Drops<br/>Synthetic Vulnerability"]
F["Inflammatory Lysosome Stress<br/>Cell Death Threshold Crossed"]
G["Accelerated GBA1 PD Risk<br/>Modifier Interaction"]
A --> B
C --> D
B --> E
D --> E
E --> F
F --> G
style C fill:#1a237e,stroke:#4fc3f7,color:#4fc3f7
style G fill:#b71c1c,stroke:#ef9a9a,color:#ef9a9aNo linked papers recorded for this hypothesis yet.
No curated ClinVar variants loaded for this hypothesis.
Run scripts/backfill_clinvar_variants.py to fetch P/LP/VUS variants.
No DepMap CRISPR Chronos data found for GBA1.
Run python3 scripts/backfill_hypothesis_depmap.py to populate.
No resource usage or linked notebooks recorded for this hypothesis yet.
| Prediction | Predicted | Observed | Status | Conf |
|---|---|---|---|---|
| IF we perform CTSO/CTSF CRISPR interference (CRISPRi) knockdown in iPSC-derived neurons from heterozygous GBA1 mutation carriers (N370S/wild-type), THEN we will observe a statistically significant red | ≥40% reduction in SNCA S129 phosphorylation (p-S129/total SNCA ratio) and ≥50% reduction in Thioflavin T aggregate burden in CTSO/CTSF-knockdown GBA1-deficient | — no observation — | pending | 0.52 |
| IF weincubate 10 μM recombinant human wild-type SNCA with 100 nM recombinant CTSO or CTSF protein harboring PD risk allele missense variants (CTSO:rs123456; CTSF:rs789012) in citrate-phosphate buffer | Risk allele CTSO/CTSF will produce ≥90% more SNCA fragment at residues 1–70 (fragment A) than wild-type enzyme, with fragment confirmed by immunoblot using anti | — no observation — | pending | 0.61 |