Clusterin
Clusterin (apolipoprotein J, CLU)
Written by Aaron CuhaReviewed Sep 2026
Also known as: CLU, Apolipoprotein J, ApoJ, Complement lysis inhibitor
An exercise-induced plasma protein that reduced brain inflammation in aged and Alzheimer-model mice, and is higher in people who exercise. The only human interventional clusterin trials lowered it, for cancer, and one was terminated.
Overview
A 2021 Nature paper collected plasma from voluntarily running mice and infused it into sedentary mice, which reduced baseline neuroinflammatory gene expression and experimentally induced brain inflammation. Proteomic analysis found a coordinated increase in complement cascade inhibitors, clusterin among them. Intravenously injected clusterin bound to brain endothelial cells and reduced neuroinflammatory gene expression in a mouse model of acute brain inflammation and in a mouse Alzheimer model. The same paper reports a human observation: patients with cognitive impairment who took part in six months of structured exercise had higher plasma clusterin.
Clusterin also has a genuine human genetic literature that predates all of this. CLU is one of the established Alzheimer disease risk loci from genome-wide association studies, and variants in CLU have been studied for their interaction with other risk genes in modulating that risk. That is human evidence about clusterin, though it is about disease susceptibility rather than about giving anyone the protein.
The human interventional record runs in the opposite direction to the exercise hypothesis and should never be quoted as supporting it. The only clusterin-directed drug that has been through human trials is custirsen, an antisense oligonucleotide that lowers clusterin, developed in oncology. Its phase 3 in metastatic castration-resistant prostate cancer, NCT01083615, was terminated after enrolling 14 of its planned participants, with the registry giving the reason as inability to enrol due to the stable baseline pain criterion. Lowering clusterin in cancer patients tells you nothing about raising it in older people, and a terminated trial tells you little about either.
No human has received clusterin as a therapy.
Mechanism of action
In mice, intravenously injected clusterin binds brain endothelial cells and reduces neuroinflammatory gene expression, in both an acute brain inflammation model and an Alzheimer model. The broader context in the same paper is a coordinated rise in complement cascade inhibitors in the plasma of exercising animals, which fits clusterin's long-established role as a complement lysis inhibitor and extracellular chaperone. In humans, clusterin's established biology is as a secreted chaperone, a complement regulator and a lipoprotein-associated protein, and the CLU locus is an established Alzheimer disease risk gene. The mouse anti-inflammatory mechanism has not been tested in a person.
Human evidence
No human has been given clusterin. The human data are observational measurement in exercise and metabolic cohorts, human genetics linking the CLU locus to Alzheimer disease risk, and an oncology programme that lowered clusterin rather than raising it.
- Nature 2021 human component: patients with cognitive impairment who participated in six months of structured exercise had higher plasma clusterin levels. An observational measurement within an otherwise mouse study.
- NCT04133896: an observational case-control study of 176 participants measuring circulating interleukin-6, clusterin and irisin, completed. Measurement only.
- Human genetics: CLU is an established Alzheimer disease risk locus from genome-wide association work, with variant interactions studied against other risk genes.
- The only clusterin-directed human interventional programme is custirsen, an antisense oligonucleotide that lowers clusterin, developed in prostate and breast cancer. Its registered phase 3 NCT01083615 was terminated after 14 participants, for an enrolment criterion problem rather than for a safety or efficacy result. Lowering clusterin is the opposite of the exerkine hypothesis and must not be cited as support for it.
What this does not tell you: Higher clusterin in people who exercised for six months does not tell you whether clusterin caused anything; exercise changes hundreds of plasma proteins at once. The genetic association tells you the CLU locus influences Alzheimer risk, not that giving someone clusterin would help. And the only interventional human experience with this protein went in the other direction, in cancer patients, and stopped early. There is no human safety data for administering clusterin.
Reading the research record
The clusterin literature is a clean example of why a page has to name the direction of an intervention. A reader searching for clusterin trials will find a real clinical programme with phase 1, phase 2 and phase 3 records attached. All of it is custirsen, an antisense drug designed to lower clusterin in cancer, and the exercise hypothesis is that higher clusterin is protective. Citing the oncology record as clinical support for the exerkine idea would be the reverse of what the data say, and that mistake is easy to make from a registry search alone.
The mouse evidence itself is reasonably careful: plasma transfer first, then the proteomic identification, then administration of the isolated protein reproducing the anti-inflammatory effect in two different models. What is missing is what is missing for every factor in this batch: nobody has given it to a person.
One feature of clusterin makes a human programme less likely than it looks. Because the CLU locus is an established Alzheimer risk gene, clusterin biology in humans is already known to be complicated and bidirectional, with the protein appearing in amyloid plaques and its genetic variants associated with risk in ways that do not map simply onto more is better.
The evidence, charted
Fig. 1 · evidence composition
3of 4 citations (75%) are in people
Counted from the citation list on this page. The Human count is the same number shown in the badge at the top. Both understate any literature larger than the sources we cite.
Fig. 2 · evidence over time
Evidence spans 4 distinct years, 2010 to 2021, counted from the citation list on this page.
Fig. 3 · legal status at a glance
US
Not approved
UK
Approved
AU
Approved
CA
Not approved
Approved in 2 of 4, prescription route in 0, not approved in 2. A jurisdiction's classification is a regulatory fact, not a verdict on the science; see Legal status below for the full text and any notes.
Fig. 4 · dose response
No human dose response curve exists
We draw this figure where the data supports it. For this compound in humans it does not, so the panel stays empty rather than borrowing an animal curve and implying it transfers.
Key studies & citations
- Animal2021
Exercise plasma boosts memory and dampens brain inflammation via clusterin
Mouse, with a human observational component. Plasma from voluntarily running mice infused into sedentary mice reduced baseline neuroinflammatory gene expression and experimentally induced brain inflammation. Proteomics showed a coordinated increase in complement cascade inhibitors including clusterin. Intravenous clusterin bound brain endothelial cells and reduced neuroinflammatory gene expression in acute brain inflammation and Alzheimer models. Separately, patients with cognitive impairment who completed six months of structured exercise had higher plasma clusterin. NIH funded.
Nature - Human2016
Interaction between variants in CLU and MS4A4E modulates Alzheimer's disease risk
Human genetics. CLU, the clusterin gene, is an established Alzheimer disease risk locus, and this study examines how variants in CLU interact with variants in MS4A4E to modulate that risk. Human evidence about clusterin biology, but about inherited disease risk rather than about administering the protein.
Alzheimer's and Dementia - Human2018
Circulating IL-6, Clusterin and Irisin in Obese Subjects
Registry record for human clusterin measurement. Observational case-control study with a cross-sectional time perspective, 176 participants enrolled, completed, start February 2018. Measurement in people, not administration.
ClinicalTrials.gov - Human2010
A Study Evaluating the Pain Palliation Benefit of Adding Custirsen to Docetaxel Retreatment or Cabazitaxel as Second Line Therapy in Men With Metastatic Castrate Resistant Prostate Cancer
The human interventional clusterin record, and it runs the opposite way to the exercise hypothesis. Custirsen is an antisense oligonucleotide that LOWERS clusterin. This phase 3 was TERMINATED with the registry reason given as inability to enrol due to criteria for stable baseline pain, after 14 participants. Sponsor Achieve Life Sciences, start March 2010.
ClinicalTrials.gov
Frequently asked questions
Does clusterin reduce brain inflammation in people?
Not shown. In mice, intravenous clusterin bound brain endothelial cells and reduced neuroinflammatory gene expression in acute inflammation and Alzheimer models. In humans, the only related observation is that people with cognitive impairment who exercised for six months had higher plasma clusterin, which is an association within an exercise study.
Are there clusterin trials in humans?
There are trials of a drug that lowers clusterin, which is the opposite direction. Custirsen, an antisense oligonucleotide, was developed in prostate and breast cancer; its registered phase 3 NCT01083615 was terminated after 14 participants because of an enrolment criterion problem. No trial has given clusterin to anyone.
Is clusterin linked to Alzheimer disease?
Yes, genetically. CLU is one of the established Alzheimer disease risk loci from genome-wide association studies, and variants in it have been studied for interaction with other risk genes. That is a risk association in human populations, not evidence that administering clusterin would treat anything.