| PICALM — Phosphatidylinositol Binding Clathrin Assembly Protein | |
|---|---|
| Symbol | PICALM |
| Full Name | Phosphatidylinositol Binding Clathrin Assembly Protein |
| Chromosome | 10q24.2 |
| NCBI Gene | 81501 |
| Ensembl | ENSG00000021762 |
| OMIM | 610004 |
| UniProt | Q7Z417 |
| Diseases | [Alzheimer's Disease](/diseases/alzheimers-disease) |
| Expression | Brain, Blood cells, Heart, Lung |
| Key Variants | |
| rs3851179 (protective, OR ~0.86) rs5942 (risk) rs12340882 (eQTL) |
|
PICALM (Phosphatidylinositol Binding Clathrin Assembly Protein, also known as CALM or CLT) is a gene located on chromosome 10q24.2 that encodes a protein critically involved in clathrin-mediated endocytosis. First identified as a significant genetic risk factor for late-onset Alzheimer's disease (AD) in the landmark 2009 genome-wide association study (GWAS), alongside CLU and CR1, PICALM remains one of the most consistently replicated AD risk loci [1][2].
The protein facilitates clathrin-coated vesicle formation, which is essential for synaptic vesicle recycling, receptor internalization, and endosomal trafficking in neurons. Through these mechanisms, PICALM influences amyloid precursor protein (APP) processing, amyloid-beta (Aβ) production, and synaptic function—all key processes in AD pathogenesis.
The PICALM gene spans approximately 54 kb on chromosome 10q24.2 (coordinates: chr10:96,200,000-96,254,000, GRCh38). It consists of 21 exons encoding a 652-amino acid protein. The gene is ubiquitously expressed with particularly high levels in the brain.
PICALM is highly expressed in the central nervous system:
In the brain, PICALM is expressed in:
Expression data is available from the Allen Human Brain Atlas.
PICALM (Phosphatidylinositol Binding Clathrin Assembly Protein) shows neuronal-enriched expression:
Single-cell RNA-seq data from the Allen Brain Atlas shows:
| Region | Expression Level | Data Source |
|---|---|---|
| Cortex | Very High | Human MTG |
| Hippocampus | High | Mouse Brain |
| Striatum | Medium | Mouse Brain |
| Cerebellum | Medium | Mouse Brain |
The PICALM protein contains several functional domains:
N-terminal Domain — Contains the phosphatidylinositol-4,5-bisphosphate (PIP2) binding site, which targets the protein to the plasma membrane
Central Region — Mediates interactions with clathrin and other endocytic proteins
Clathrin-Binding Domain — Facilitates recruitment and assembly of clathrin triskelions
C-terminal Region — Contains additional protein-protein interaction motifs
PICALM/CALM functions as an accessory protein in clathrin-mediated endocytosis through multiple mechanisms:
Membrane Recruitment — The N-terminal domain binds to phosphatidylinositol-4,5-bisphosphate (PIP2) on the plasma membrane, targeting PICALM to sites of vesicle formation [3].
Clathrin Assembly — PICALM facilitates clathrin triskelion formation and lattice polymerization at the plasma membrane. It serves as a scaffold that nucleates clathrin coat assembly [4].
Vesicle Scission — Working with dynamin and other proteins, PICALM participates in the final scission step that releases clathrin-coated vesicles into the cytoplasm [5].
Cargo Selection — PICALM participates in the selection of cargo molecules for internalization, including membrane proteins, receptors, and synaptic vesicles [6].
PICALM is essential for maintaining proper synaptic function:
Synaptic Vesicle Endocytosis — PICALM is critical for synaptic vesicle recycling during sustained neuronal activity. It ensures the rapid retrieval of synaptic vesicle components after neurotransmitter release [4:1].
AMPA Receptor Trafficking — PICALM regulates the internalization and recycling of AMPA receptors, directly affecting synaptic plasticity and strength [7].
Dendritic Spine Morphology — PICALM is required for maintaining proper dendritic spine morphology and density [8].
Neurotransmitter Homeostasis — By controlling the presynaptic vesicle cycle, PICALM ensures proper neurotransmitter homeostasis.
PICALM was first identified as an AD risk locus in the landmark 2009 GWAS meta-analysis alongside CLU, representing one of the first novel loci beyond APOE to reach genome-wide significance [1:1][2:1].
rs3851179 (5' UTR) — The lead protective variant. The A allele is associated with reduced AD risk (OR ~0.86). This variant affects PICALM expression levels, with protective alleles associated with higher expression.
rs5942 (exon) — A risk variant associated with increased AD risk through mechanisms affecting protein function.
rs12340882 — An expression quantitative trait locus (eQTL) variant that affects PICALM expression in brain tissue.
The mechanism by which PICALM variants influence AD risk involves:
Amyloid Processing — Altered endocytic function affects APP trafficking and Aβ production. PICALM influences the internalization and processing of APP, affecting the amyloidogenic pathway [9][@treurst2011].
Synaptic Dysfunction — Impaired synaptic vesicle recycling contributes to cognitive decline through loss of synaptic terminals [8:1].
Tau Pathology — PICALM may interact with tau propagation and spread, though this pathway is less well-characterized than for BIN1 [10].
PICALM shows a significant interaction with APOE genotype:
PICALM interacts with the retromer complex through VPS35:
PICALM interacts with tau pathology in multiple ways:
Recent studies have shown that PICALM reduction leads to increased tau phosphorylation and aggregation in cellular and mouse models [10:1].
PICALM plays a critical role in autophagic-lysosomal pathway regulation:
PICALM influences neuronal lipid metabolism:
PICALM regulates synaptic plasticity through multiple mechanisms:
PICALM interacts with several other AD risk genes:
PICALM expression is subject to epigenetic control:
Emerging evidence suggests sex-specific effects:
PICALM influences neuroinflammatory responses:
PICALM deficiency affects cellular metabolism:
PICALM variants show clinical correlations:
PICALM plays a role in early disease stages:
Key challenges remain in understanding PICALM:
Ongoing research focuses on:
PICALM interacts with several other AD risk genes:
PICALM influences Aβ production through its role in endocytosis:
PICALM plays a role in the autophagic-lysosomal pathway, which is critical for clearing toxic proteins:
The synaptic effects of PICALM deficiency contribute to cognitive decline:
PICALM represents a potential therapeutic target:
PICALM expression may serve as a biomarker:
PICALM interacts with several other AD risk genes:
| Region | Expression Level | Data Source |
|---|---|---|
| Cortex | High | Human MTG |
| Hippocampus | High | Human MTG |
| Basal ganglia | High | Human MTG |
| Cerebellum | Medium | Mouse Brain |
| Brainstem | Medium | Mouse Brain |
Harold D, et al. Genome-wide association study identifies variants at CLU and PICALM associated with Alzheimer's disease. Nat Genet. 2009. ↩︎ ↩︎
Lambert JC, et al. Genome-wide association study identifies variants at CLU and CR1 associated with Alzheimer's disease. Nat Genet. 2009. ↩︎ ↩︎
Tebar F, et al. Phosphatidylinositol binding clathrin assembly protein, a novel neuronal adaptor. Mol Biol Cell. 1999. ↩︎
Cousin MA, Robinson PJ. The dephosphins: dephosphorylation by calcineurin triggers synaptic vesicle endocytosis. Trends Neurosci. 2001. ↩︎ ↩︎
Ryan TA. Clathrin: anatomy. Curr Biol. 2006. ↩︎
McMahon HT, Boucrot E. Molecular mechanism and physiological functions of clathrin-mediated endocytosis. Nat Rev Mol Cell Biol. 2011. ↩︎
Lee SH, et al. PICALM regulates AMPA receptor trafficking and synaptic plasticity. Neuron. 2018. ↩︎
Gan KJ, Augustine GJ. Memory, forgetfulness, and sleep: The role of synaptic endocytosis. Neuron. 2020. ↩︎ ↩︎
Miller SE, et al. A PICALM mutation and novel therapeutic target in Alzheimer's disease. J Thromb Haemost. 2011. ↩︎
Xia Y, et al. PICALM reduction and the role of tau pathology in Alzheimer's disease. Acta Neuropathol Commun. 2017. ↩︎ ↩︎