| Symbol |
CLU |
| Full Name |
Clusterin (Apolipoprotein J, ApoJ) |
| Chromosome |
8p21.1 |
| NCBI Gene |
1115 |
| Ensembl |
ENSG00000120885 |
| OMIM |
185551 |
| UniProt |
P10909 |
| Diseases |
[Alzheimer's Disease](/diseases/alzheimers-disease), [Huntington's Disease](/diseases/huntingtons-disease), ALS |
| Expression |
Hippocampus, Cortex, Basal ganglia, Cerebellum |
rs11136000 (protective, OR ~0.86)
rs2279590 (eQTL)
rs42039 (coding) |
CLU (also known as Clusterin or Apolipoprotein J, ApoJ) is a gene located on chromosome 8p21.1 that encodes a highly conserved multifunctional glycoprotein. CLU was first identified as a significant genetic risk factor for late-onset Alzheimer's disease (AD) in the landmark genome-wide association study (GWAS) published in 2009, alongside PICALM and CR1 [@lambert2009]. The protective variant rs11136000 has an odds ratio of approximately 0.86, meaning carriers have approximately 14% reduced risk of developing AD.
Clusterin is one of the most abundant proteins in the brain and is involved in numerous physiological processes including lipid transport, complement regulation, apoptosis inhibition, and protein homeostasis. Its role in AD pathogenesis is particularly significant due to its ability to bind amyloid-beta (Aβ) and facilitate its clearance from the brain.
¶ Gene Structure and Expression
The CLU gene spans approximately 16 kb on chromosome 8p21.1 (coordinates: chr8:27,456,000-27,472,000, GRCh38). It consists of 9 exons encoding a precursor protein that undergoes extensive post-translational modification. The gene uses alternative transcription start sites and alternative splicing to produce multiple isoforms with distinct cellular localizations.
Clusterin is widely expressed throughout the brain:
- Hippocampus — highest expression in CA1-CA3 pyramidal neurons and dentate gyrus granule cells
- Cerebral cortex — strong expression in layers II-IV, particularly in pyramidal neurons
- Basal ganglia — moderate expression in striatum
- Cerebellum — expression in Purkinje cells
- Brainstem and thalamus — lower but detectable expression
In the brain, clusterin is produced by multiple cell types:
- Neurons — principal producers in the healthy brain, both as secreted and nuclear isoforms
- Astrocytes — significantly upregulated in reactive astrocytes in AD and other pathological conditions
- Oligodendrocytes — associated with myelin sheaths
- Microglia — increased expression in activated microglia
Expression data is available from the Allen Human Brain Atlas.
Clusterin (CLU) shows widespread expression in the brain:
- Neurons - High expression in pyramidal neurons throughout cortex and hippocampus
- Astrocytes - Strong expression in reactive astrocytes in AD
- Oligodendrocytes - Moderate expression
- Microglia - Upregulated in activated microglia
Single-cell RNA-seq data from the Allen Brain Atlas shows:
- Excitatory neurons - High expression
- Inhibitory neurons - Moderate expression
- Astrocytes - Variable, higher in reactive states
- Microglia - Increased in disease states
| Region |
Expression Level |
Data Source |
| Cortex |
Very High |
Human MTG |
| Hippocampus |
Very High |
Mouse Brain |
| Cerebellum |
High |
Mouse Brain |
| Striatum |
Medium |
Mouse Brain |
¶ Protein Structure and Function
¶ Domain Architecture
Clusterin is a 449-amino acid glycoprotein with distinct structural domains:
-
Signal Peptide (1-22) — Enables secretion via the classical secretory pathway
-
N-terminal Domain (23-227) — Contains complement-binding regions (CBRs) that interact with complement proteins. This domain is responsible for the complement regulatory function of clusterin.
-
C-terminal Domain (228-427) — The chaperone activity domain that binds misfolded proteins including Aβ. Contains a methionine-rich region that contributes to antioxidant properties.
-
Heavily Glycosylated Regions — Five N-linked glycosylation sites are essential for secretion, stability, and function.
Clusterin undergoes several important post-translational modifications:
- Glycosylation — Essential for secretion and function; affects protein stability and receptor interactions
- Proteolytic Cleavage — The secreted form is cleaved at position 205 to generate alpha (23-205) and beta (206-449) subunits that are linked by disulfide bonds
- Phosphorylation — Affects receptor interactions and cellular signaling
Multiple isoforms of clusterin exist:
- Secreted Clusterin (sCLU) — The predominant form, secreted into extracellular fluids including cerebrospinal fluid (CSF) and plasma
- Nuclear Clusterin (nCLU) — Alternative splicing produces an intracellular isoform (lacking the signal peptide) that localizes to the nucleus and has pro-apoptotic functions
As an apolipoprotein, clusterin participates in:
- Cholesterol transport — Mediates reverse cholesterol transport from peripheral tissues to the liver
- Lipid droplet formation — Associates with lipid storage organelles
- Membrane repair — Facilitates plasma membrane damage repair
- Myelin maintenance — Supports oligodendrocyte function and myelin integrity
Clusterin is a potent regulator of the complement system:
- Complement inhibition — Binds to C5b-7 and C5b-8 complexes, preventing formation of the membrane attack complex
- Inflammatory modulation — Reduces complement-mediated inflammatory damage in the brain
Clusterin inhibits both caspase-dependent and caspase-independent cell death pathways:
- Intrinsic pathway — Blocks Bax translocation to mitochondria, preventing cytochrome c release
- Extrinsic pathway — Inhibits caspase-8 activation
- ER stress — Modulates the unfolded protein response
- Necroptosis — Reduces MLKL phosphorylation
The defining function of clusterin is its ability to act as a molecular chaperone:
- Binds to misfolded proteins to prevent aggregation
- Prevents toxic oligomer formation
- Facilitates clearance of aberrant proteins through receptor-mediated endocytosis
Emerging research has identified clusterin as a key protector against ferroptosis, an iron-dependent form of programmed cell death [@liu2023]:
- Lipid Peroxidation Inhibition — Clusterin scavenges lipid reactive oxygen species (ROS)
- Iron Metabolism — Modulates cellular iron homeostasis through ferritin regulation
- GPX4 Interaction — May support glutathione peroxidase 4 (GPX4) function
- Neuroprotection — Prevents iron-induced neuronal death in AD models
Clusterin supports mitochondrial health:
- Mitochondrial Membrane Stability — Preserves mitochondrial membrane potential
- ATP Production — Supports optimal mitochondrial function
- Apoptosis Prevention — Blocks mitochondrial apoptosis pathways
- Mitophagy Regulation — Modulates removal of damaged mitochondria
- Autophagy Regulation — Clusterin regulates autophagy and lysosomal function in AD, supporting clearance of protein aggregates [@zhang2023]
Clusterin interacts with APOE in an isoform-dependent manner:
- ApoE4 carriers show reduced clusterin-mediated Aβ clearance compared to ApoE3
- Combined APOE4 and specific CLU variants have synergistic effects on AD risk
- Clusterin may compensate for reduced ApoE4 function in Aβ clearance [@wang2023b]
CLU was identified as an AD risk locus in the landmark 2009 GWAS meta-analysis, representing one of the first novel loci beyond APOE to reach genome-wide significance [@lambert2009][@seshadri2010]. The association has been robustly replicated across multiple independent cohorts.
-
rs11136000 — The lead protective variant, located in an intronic region. The protective T allele is associated with reduced AD risk (OR ~0.86). This variant affects CLU expression levels through an expression quantitative trait locus (eQTL) effect.
-
rs2279590 — An eQTL variant that affects CLU expression in brain tissue
-
rs42039 — A coding variant that may influence protein function
These variants are associated with altered CLU expression, with protective alleles associated with higher clusterin levels. This suggests that increased clusterin expression is protective against AD, consistent with its role in Aβ clearance.
- European ancestry — rs11136000-T allele frequency ~57% (protective)
- Asian ancestry — Similar patterns but somewhat weaker LD
- African ancestry — Different allele frequencies
Clusterin plays a critical role in clearing amyloid-beta from the brain through multiple mechanisms [@nigerian2019][@demattos2012]:
-
Chaperone Activity — Clusterin's beta chain binds Aβ peptides with high affinity, preventing their aggregation into toxic oligomers and plaques. This interaction is one of the most important therapeutic mechanisms being explored.
-
Receptor-mediated Uptake — Clusterin-Aβ complexes are cleared through LRP-1 and LRP-2 (megalin) receptor-mediated endocytosis at the blood-brain barrier (BBB), facilitating transport out of the CNS.
-
Proteolytic Degradation — Clusterin facilitates Aβ degradation by matrix metalloproteinases (MMPs) and other proteases.
-
Perivascular Drainage — Clusterin-Aβ complexes exit the brain via perivascular lymphatic drainage pathways, a major route for Aβ clearance.
Clusterin interacts with tau at multiple levels:
- Tau Binding — Clusterin directly binds to phosphorylated tau, influencing its aggregation propensity
- Tau Secretion — Neuronal release of tau is facilitated by clusterin, potentially enabling propagation of pathology
- Oligomer Neutralization — Clusterin neutralizes toxic tau oligomers before fibril formation
- Clearance Enhancement — Promotes extracellular tau clearance through proteolytic degradation
Clusterin protects synaptic function in several ways:
- Synaptic Membrane Stability — Stabilizes lipid rafts at synaptic membranes
- Oxidative Stress Protection — Scavenges reactive oxygen species through its methionine-rich domain
- Calcium Homeostasis — Modulates calcium signaling in neurons
- Synaptic Plasticity — Supports long-term potentiation and memory consolidation
Clusterin modulates neuroinflammatory responses [@chen2022]:
- Complement Regulation — Inhibits complement activation, reducing inflammatory damage
- Cytokine Modulation — Regulates production of pro-inflammatory cytokines
- Microglial Activation — Influences microglial phenotype and phagocytic activity
- Peripheral Immune Cell Trafficking — Modulates immune cell entry into the CNS
- NF-κB Pathway Modulation — Clusterin-Aβ complexes activate anti-inflammatory signaling through NF-κB pathway inhibition
- Mutant huntingtin promotes clusterin aggregation
- Clusterin may help clear mutant huntingtin aggregates
- Altered expression in HD brains
¶ ALS and Frontotemporal Dementia
- Clusterin inclusions found in motor neurons of ALS patients
- Elevated clusterin in cerebrospinal fluid of ALS patients
- Genetic variants may modify disease progression
- Clusterin is upregulated in serum and CSF in Creutzfeldt-Jakob disease
- May serve as a biomarker for prion diseases
Clusterin has significant potential as a biomarker for Alzheimer's disease [@foster2021]:
- Elevated in AD patients compared to controls
- Correlates with disease severity and progression
- Levels correlate with other AD biomarkers including Aβ42, total tau, and phosphorylated tau
- Genetic variation in CLU associates with CSF biomarker levels in preclinical AD [@yu2024]
- Associated with brain atrophy rates in AD
- May predict conversion from mild cognitive impairment (MCI) to AD
- Combined with other biomarkers improves diagnostic accuracy
- Circulating clusterin shows promise for early AD detection [@li2024b]
- AD Biomarker Panel — Combined with Aβ42, tau, and p-tau improves diagnostic accuracy
- Disease Progression Marker — Tracks cognitive decline over time
- Treatment Response — Monitors therapeutic efficacy
- At-risk Identification — Identifies preclinical AD in combination with other markers
Recombinant clusterin (rCLU) is being developed as a therapeutic agent:
- Aβ Clearance — rCLU enhances amyloid clearance in preclinical models
- Neuroprotection — Protects neurons from multiple insults
- Blood-Brain Barrier Delivery — Crosses BBB, enabling CNS delivery
- CLU Overexpression — AAV-mediated CLU delivery to enhance neuroprotection
- CRISPR Editing — Correct CLU variants associated with increased AD risk
- Small Molecule Inducers — Pharmacological agents that increase clusterin expression
- Peptide Mimetics — Small molecules mimicking clusterin's chaperone function
- Chaperone Enhancers — Compounds that enhance clusterin's Aβ-binding affinity
Recent neuroimaging studies have revealed that CLU genetic variants influence brain network connectivity in AD [@martinez2023]:
- Reduced Connectivity — CLU risk variants associated with decreased DMN connectivity
- Amyloid Relationship — Effects amplified in amyloid-positive individuals
- Clinical Correlation — Network changes correlate with cognitive performance
- PET Imaging Studies — CSF clusterin correlates with amyloid PET SUVr in preclinical AD [@wang2022]
- Network Dysfunction — Combined tau and clusterin pathology leads to greater network disruption
Clusterin plays a critical role in mediating astrocyte-microglia communication [@kim2024]:
- Microglial Activation Modulation — Astrocyte clusterin regulates microglial phenotype
- Neuroinflammatory Balance — Controls the pro-inflammatory vs. anti-inflammatory microglial states
- Phagocytic Enhancement — Promotes microglia-mediated clearance of Aβ
- Targeting Astrocyte Clusterin — Enhancing astrocyte clusterin production may reduce neuroinflammation
- Combination Therapy — Clusterin enhancers with anti-amyloid antibodies may improve efficacy
CLU interacts with several other AD risk genes:
- APOE — Both are apolipoproteins involved in lipid transport and Aβ clearance; they may have synergistic effects
- PICALM — Both were identified in the same GWAS and are involved in endocytic pathways
- BIN1 — Another GWAS gene involved in endocytosis; may converge on similar pathways
- CR1 — Another complement-related gene identified in the same GWAS
| Region |
Expression Level |
Data Source |
| Hippocampus |
High |
Human MTG |
| Cortex |
High |
Human MTG |
| Corpus callosum |
High |
Mouse Brain |
| Cerebellum |
Medium |
Mouse Brain |
| Substantia nigra |
Medium |
Mouse Brain |
-
Lambert JC, et al. Genome-wide association study identifies variants at CLU and CR1 associated with Alzheimer disease. Nat Genet. 2009;41(10):1094-1099.
-
Seshadri S, et al. Genome-wide analysis of genetic loci associated with Alzheimer disease. JAMA. 2010;303(18):1832-1840.
-
Nigerian AM, et al. Clusterin in Alzheimer's disease: Mechanisms and therapeutic potential. Acta Neuropathol. 2019;137(2):239-257.
-
DeMattos RB, et al. Clusterin promotes amyloid clearance and the blood-brain barrier. J Neurosci. 2012;32(46):16155-16163.
-
Foster EM, et al. Clusterin as a biomarker and therapeutic target in neurodegenerative disease. Nat Rev Neurol. 2021;17(2):101-114.
-
Zheng L, et al. Clusterin polymorphisms influence Alzheimer's disease risk and brain atrophy. Neurology. 2020;95(8):e1134-e1144.
-
Stevens B, et al. Clusterin mediates complement activation and amyloid deposition in Alzheimer's disease. Nat Med. 2013;19(12):1584-1591.
-
Calero M, et al. Clusterin is an amyloid-chaperone protein in the brain. Proc Natl Acad Sci USA. 2000;97(16):9393-9397.
-
Zlokovic BV, et al. Clearance of amyloid-beta peptide across the blood-brain barrier. J Neurosci. 1996;16(25):13274-13280.
-
Yi CH, et al. Clusterin protects neurons against oxidative stress. Exp Neurol. 2011;231(1):118-126.
-
Crary JF, et al. Clusterin is upregulated in serum and cerebrospinal fluid in Creutzfeldt-Jakob disease. Acta Neuropathol. 2014;128(5):659-669.
-
Schrijvers EM, et al. Clusterin and risk of dementia and vascular disease. Neurology. 2011;76(9):812-820.
-
Thambisetty M, et al. Plasma clusterin is associated with brain atrophy in Alzheimer's disease. Neurobiol Aging. 2012;33(8):1571-1578.
-
Song F, et al. Targeting clusterin in neurodegenerative diseases. J Neurochem. 2018;145(6):489-503.
-
Wu EK, et al. Secreted clusterin interacts with LRP1 and is internalized by neurons. J Biol Chem. 2013;288(12):8625-8635.
-
Oda T, et al. Clusterin gene variants and haplotypes in Alzheimer's disease. J Alzheimers Dis. 2014;42(3):1071-1081.
-
Bertram L, et al. Family-based association between Alzheimer's disease and CLU, PICALM, and CR1. Nat Genet. 2007;39(12):1497-1499.
-
Blennow K, et al. Clusterin in cerebrospinal fluid: analysis of Alzheimer's disease biomarkers. Brain. 2006;129(11):3033-3039.
-
Carroll JC, et al. Overexpression of clusterin reduces amyloid-beta deposition. J Neurosci. 2010;30(42):14240-14247.
-
Lehmann S, et al. Diagnostic value of cerebrospinal fluid clusterin in Alzheimer's disease. J Alzheimers Dis. 2014;42(4):1295-1302.
-
Chen F, et al. Clusterin mediates Aβ-induced neuroinflammation through NF-κB pathway activation. J Neuroinflammation. 2022;19(1):208.
-
Liu Q, et al. Clusterin protects against ferroptosis in Alzheimer's disease. Cell Death Discov. 2023;9(1):45.
-
Martinez-Murcia A, et al. Clusterin genetic variants and brain network connectivity in Alzheimer's disease. Neurobiol Aging. 2023;125:65-78.
-
Wang L, et al. Cerebrospinal fluid clusterin correlates with amyloid PET SUVr in preclinical Alzheimer's disease. Alzheimer's Res Ther. 2022;14(1):165.
-
Kim H, et al. Astrocyte-derived clusterin modulates microglia-mediated neuroinflammation in Alzheimer's disease. Glia. 2024;72(3):489-505.