| Gene |
[GRN](/genes/grn) |
| UniProt |
P28799 |
| Length |
593 amino acids |
| Molecular Weight |
~63 kDa (full-length) |
| Signal Peptide |
Yes (1-18 aa) |
| Localization |
Secreted, lysosomes |
| Family |
Granulin family, Progranulin |
| Diseases |
[Frontotemporal Dementia](/diseases/ftd), [Alzheimer's Disease](/diseases/alzheimers-disease), [Parkinson's Disease](/diseases/parkinsons-disease) |
Progranulin (PGRN) is a secreted glycoprotein encoded by the GRN gene that functions as a multifunctional growth factor and lysosomal regulator. The protein plays critical roles in neuronal survival, microglial function, and protein homeostasis. Loss-of-function mutations in GRN cause Frontotemporal Dementia (FTD) through haploinsufficiency, making progranulin a major therapeutic target.
Progranulin is a 593-amino acid secreted glycoprotein with a unique architecture:
- N-terminal signal peptide (1-20 aa): Directs secretion via the secretory pathway
- Granulin domain repeats (21-585 aa): 7.5 tandem repeats of a highly conserved 12-cysteine granulin domain
- Each granulin domain: ~90 amino acids with 12 conserved cysteines forming 6 disulfide bonds
The crystal structure reveals that granulin domains fold into compact, cysteine-knot motifs that are highly resistant to proteolysis[^crystal2022]. Multiple granulin domains can stack together, creating a "beads-on-a-string" architecture.
- N-glycosylation: Multiple N-linked glycosylation sites in the granulin domains
- Secretion: Processed through the secretory pathway and released as a full-length protein
- Proteolytic processing: Cleaved by extracellular proteases (neutrophil elastase, proteinase 3, MMP-9) into functional granulin peptides (GRN A-G)[^proteolytic2021]
- UniProt ID: P28799
- Molecular weight: ~63 kDa (full-length, unglycosylated)
- Subcellular localization: Secreted, lysosomal lumen
- Tissue specificity: High expression in brain (neurons, microglia), lung, kidney
Progranulin promotes neuronal survival through multiple signaling pathways:
- AKT activation: Progranulin binding to unidentified receptors activates PI3K/AKT signaling[^akt2020]
- ERK/MAPK pathway: Progranulin stimulates ERK1/2 phosphorylation promoting neuronal viability
- Neurotrophic effects: Supports neurite outgrowth and dendritic arborization
Progranulin localizes to lysosomes where it:
- Regulates cathepsin activity: Binds to and modulates lysosomal proteases
- Maintains autophagic flux: Required for proper autophagosome-lysosome fusion[^lysosomal2017]
- Coordinates trafficking: Associates with LAMP-2A in lysosomal membranes
Progranulin modulates microglial function:
- Anti-inflammatory: Reduces microglial activation and pro-inflammatory cytokine production
- Phagocytosis regulation: Controls complement-mediated synaptic pruning[^complement2018]
- Survival support: Promotes microglial viability under stress conditions
| Partner |
Interaction Type |
Functional Consequence |
| Sortilin |
Receptor-mediated endocytosis |
Lysosomal targeting and degradation[^sortilin2020] |
| LAMP-2A |
Lysosomal membrane association |
Lysosomal trafficking |
| Cathepsins (B, D, L) |
Protease binding |
Lysosomal protease regulation |
| TDP-43 |
Genetic interaction |
Nuclear import regulation |
GRN mutations cause FTD through haploinsufficiency—loss-of-function mutations reduce progranulin levels by ~50%, leading to:
- TDP-43 pathology: Accumulation of hyperphosphorylated, ubiquitinated TDP-43 in cytoplasmic inclusions[^tdp432019]
- Lysosomal dysfunction: Impaired autophagic flux and lipofuscin accumulation
- Synaptic loss: Enhanced complement-mediated pruning by astrocytes[^complement2018]
- Neuroinflammation: Dysregulated microglial activation[^microglial2019]
flowchart TD
A["GRN Mutation<br/> Haploinsufficiency"] --> B["50% Reduced<br/>Progranulin"]
B --> C["Lysosomal<br/>Dysfunction"]
B --> D["TDP-43<br/>Pathology"]
B --> E["Microglial<br/>Dysregulation"]
C --> F["Autophagy<br/>Impairment"]
C --> G["Lipofuscin<br/>Accumulation"]
D --> H["Cytoplasmic<br/>Inclusions"]
D --> I["Nuclear TDP-43<br/>Depletion"]
E --> J["Excessive<br/>Synaptic Pruning"]
E --> K["Pro-inflammatory<br/>Cytokines"]
F --> L["Neuronal<br/>Dysfunction"]
G --> L
H --> L
I --> L
J --> L
K --> L
L --> M["Frontotemporal<br/>Dementia"]
style A fill:#f3e5f5,stroke:#333
style M fill:#ffcdd2,stroke:#333
- AAV gene therapy: AAV-mediated GRN delivery to restore progranulin expression[^progranulin2024]
- Protein replacement: Recombinant progranulin administration
- Small molecule upregulators: Compounds that increase GRN transcription
- Anti-sortilin antibodies: Block sortilin-mediated progranulin endocytosis and degradation[^sortilin2020]
- Protease inhibitors: Prevent progranulin cleavage into granulin peptides
- CSF progranulin: Reduced in GRN mutation carriers; diagnostic for FTD
- Plasma progranulin: Biomarker for monitoring treatment response
- Neurofilament light chain (NfL): Elevated in GRN-FTD progression
- Latozinemab (PRV-102): Anti-sortilin antibody to increase progranulin levels; Phase 1 completed 2024[^phase2024]
- AAV-GRN (YL-001): Gene therapy for GRN-FTD; preclinical/Phase 1
- Progranulin: a growth factor for neurodegenerative diseases. Experimental & Molecular Medicine. 2024.
- The role of progranulin in frontotemporal dementia. Lancet Neurology. 2023.
- Crystal structure of progranulin domains. Nature Structural & Molecular Biology. 2022.
- Progranulin activates AKT and ERK signaling. Cellular and Molecular Neurobiology. 2020.
- Progranulin deficiency leads to lysosomal dysfunction. Nature Neuroscience. 2017.
- TDP-43 pathology in frontotemporal dementia with GRN mutations. Brain. 2015.
- Phase 1 study of latozinemab in progranulin-associated FTD. Neurology. 2024.