Genetic Background Dramatically Changed Whether Cannabinoid Receptor Knockouts Affected MS-Like Disease in Mice | Research

The takeaway

The immune-modulating effects of CB2 receptor deletion on MS-like disease were completely dependent on mouse genetic background, disappearing when the knockout was bred into a different strain, with major implications for translating animal cannabinoid research to humans.

Read this if you follow cannabinoid research and want to understand the limitations of animal studies.

CB2 knockout effects completely disappeared when bred into a different mouse strain

What the researchers found

CB2 receptor knockout mice on a C57BL/6 background developed more severe EAE (MS model), consistent with prior reports. However, when the same CB2 knockout was bred into the Biozzi ABH background, the immune-enhancing effect of CB2 deletion was completely lost. Similarly, CB1 receptor and TRPV1 knockouts on the ABH background showed no disease alteration.

GPR55 knockout mice showed less severe disease on the C57BL/6 background (especially females) but only marginal effects on the ABH background. The authors concluded that non-psychoactive doses of medicinal cannabis have marginal influence on the MS immune response, with THC immunosuppression occurring only at sedative doses through CB1 rather than CB2 receptors.

Why it matters

This study is a cautionary tale for cannabinoid research. Many conclusions about cannabinoid receptor roles in immunity come from one mouse strain. The finding that genetic background completely changes the outcome challenges the reliability of these conclusions and their translation to genetically diverse human populations.

The numbers in context

CB2 KO on C57BL/6: augmented EAE. CB2 KO on ABH: no effect. CB1 KO on ABH: no effect. TRPV1 KO on ABH: no effect. GPR55 KO on C57BL/6: reduced EAE (females). GPR55 KO on ABH: marginal effect.

How the study worked

EAE induction in multiple knockout mouse strains on two genetic backgrounds (C57BL/6 and Biozzi ABH). Gene knockouts: CB2 (two distinct knockouts), CB1, TRPV1, GPR55. Disease incidence and severity measured. Pharmacological THC challenge in both backgrounds.

What this study cannot tell us

Mouse EAE is an imperfect model of human MS. The ABH background may be more resistant to genetic perturbation generally. The knockout approach creates lifelong absence rather than acute modulation. Only EAE disease scores were used, not detailed immunological characterization on both backgrounds.

How to read the evidence

Comprehensive multi-strain study with definitive negative findings; moderate evidence for the limitations of single-strain studies.

When this study was published

Published in 2013. This study has influenced how cannabinoid researchers design and interpret knockout studies.

The bigger picture

This study has profound implications for cannabinoid drug development. If receptor knockout effects vary this dramatically between mouse strains, predicting human responses from any single animal model is hazardous. It also suggests that the immune effects of cannabinoids in MS may be more modest than some preclinical studies suggest.

Questions still open

Which mouse background better predicts human cannabinoid immune responses? Should all cannabinoid knockout studies be replicated on multiple backgrounds? Does the marginal immune effect mean cannabinoid treatments for MS work through mechanisms other than immune modulation?

Common questions

Does this mean cannabinoids do not help MS?

Not exactly. Sativex is approved for MS spasticity and clearly helps some patients. What this study shows is that the immune-modulating effects attributed to cannabinoid receptors in mouse models may be strain-specific and may not explain how cannabis helps MS patients. The benefits may be more symptomatic (anti-spastic, pain relief) than immune-modulating.

Why does genetic background matter so much?

Different mouse strains have different immune system characteristics, metabolism, and receptor expression patterns. When a gene is deleted, these background differences determine whether the loss is critical or compensated. This is why the same CB2 deletion caused more disease in one strain and had zero effect in another. Humans are far more genetically diverse than any mouse strain, making predictions even more challenging.

Read the original research

Genetic background can result in a marked or minimal effect of gene knockout (GPR55 and CB2 receptor) in experimental autoimmune encephalomyelitis models of multiple sclerosis.

PloS one, 8(10), e76907

View on PubMed ↗Publisher’s paper ↗

Citation

Sisay, Sofia; Pryce, Gareth; Jackson, Samuel J; Tanner, Carolyn; Ross, Ruth A; Michael, Gregory J; Selwood, David L; Giovannoni, Gavin; Baker, David. (2013). Genetic background can result in a marked or minimal effect of gene knockout (GPR55 and CB2 receptor) in experimental autoimmune encephalomyelitis models of multiple sclerosis.. PloS one, 8(10), e76907. https://doi.org/10.1371/journal.pone.0076907