Mice lacking the main 2-AG enzyme still had CB1 receptor signaling through backup pathways | Research

The takeaway

Even when the primary enzyme for producing the brain endocannabinoid 2-AG was genetically deleted, mouse brain tissue generated enough 2-AG through alternative pathways to activate CB1 receptors.

Read this if you want to understand the complexity and redundancy of the brain endocannabinoid system.

CB1 signaling remained largely unchanged despite deletion of primary 2-AG enzymes

What the researchers found

Researchers studied brain tissue from mice genetically engineered to lack DAGLa or DAGLb, the two main enzymes thought to produce the endocannabinoid 2-AG. Despite deletion of these primary production pathways, CB1 receptor signaling (measured by G-protein activation) remained largely unchanged across brain regions.

When researchers blocked 2-AG breakdown (allowing produced 2-AG to accumulate), sufficient 2-AG was generated through alternative enzymatic pathways to activate CB1 receptors throughout the brain. Mass spectrometry confirmed that this pool of 2-AG was produced by pathways distinct from either DAGLa or DAGLb.

Why it matters

The endocannabinoid system is more complex than previously thought. The existence of backup pathways for 2-AG production means that blocking a single enzyme may not be sufficient to fully suppress endocannabinoid signaling, which has implications for drug development targeting this system.

The numbers in context

Brain regional CB1 receptor activity was largely unaltered in both DAGLa-knockout and DAGLb-knockout mice. Alternative pathways produced sufficient 2-AG to activate CB1 receptors throughout the brain when 2-AG breakdown was blocked.

How the study worked

Functional autoradiography was used to measure CB1 receptor G-protein activity across brain regions in DAGLa-knockout, DAGLb-knockout, and wild-type mice. Following pharmacological blockade of 2-AG hydrolysis, 2-AG levels were measured using liquid chromatography tandem mass spectrometry (LC/MS/MS).

What this study cannot tell us

Brain cryosection experiments may not fully reflect in vivo conditions. Genetic knockout animals may develop compensatory changes during development. The alternative 2-AG pathways were identified pharmacologically but not fully characterized enzymatically.

How to read the evidence

Well-designed knockout mouse study with multiple analytical methods, but findings are preclinical and may involve compensatory developmental changes.

When this study was published

Published in 2014.

The bigger picture

This study revealed redundancy in the endocannabinoid system. From an evolutionary perspective, multiple pathways for producing 2-AG suggest this signaling molecule is critically important for brain function. For researchers developing drugs targeting the endocannabinoid system, this redundancy means simple enzyme inhibition strategies may face limitations.

Questions still open

What are the specific enzymes in these alternative 2-AG production pathways? Would acute pharmacological inhibition of DAGLa (rather than lifelong genetic deletion) produce different results? Do these backup pathways operate in humans?

Common questions

What is 2-AG?

2-arachidonoylglycerol (2-AG) is the primary endocannabinoid in the brain. It is produced by neurons and activates CB1 receptors to regulate synaptic signaling. This study showed that the brain has backup ways to produce it beyond the primary known enzymes.

Why do backup pathways for endocannabinoid production matter?

The existence of alternative 2-AG production pathways suggests the endocannabinoid system is highly important and protected by redundancy. It also means that drugs designed to block a single production enzyme may not fully suppress endocannabinoid signaling.

Read the original research

Brain regional cannabinoid CB(1) receptor signalling and alternative enzymatic pathways for 2-arachidonoylglycerol generation in brain sections of diacylglycerol lipase deficient mice.

European journal of pharmaceutical sciences : official journal of the European Federation for Pharmaceutical Sciences, 51, 87-95

View on PubMed ↗Publisher’s paper ↗

Citation

Aaltonen, Niina; Riera Ribas, Casandra; Lehtonen, Marko; Savinainen, Juha R; Laitinen, Jarmo T. (2014). Brain regional cannabinoid CB(1) receptor signalling and alternative enzymatic pathways for 2-arachidonoylglycerol generation in brain sections of diacylglycerol lipase deficient mice.. European journal of pharmaceutical sciences : official journal of the European Federation for Pharmaceutical Sciences, 51, 87-95. https://doi.org/10.1016/j.ejps.2013.08.035