The cannabinoid receptor CB1 is expressed and functional in isolated nuclei of rat cerebral cortex

Abstract

Lipids in nuclei are membrane components as well as signaling molecules with a potential role in regulating gene transcription. Former studies from our lab demonstrated an active nuclear glycerolipid metabolism in the central nervous system. We detected diacylglycerol lipase, monoacylglycerol lipase, and lysophosphate phosphatase enzymatic activities, which are responsible for maintaining the levels of endocannabinoid 2-arachidonoyl-glycerol (2-AG), a bioactive lipid mediator. The endocannabinoid system is a cellular signaling mechanism with a protective role in many pathophysiological processes, especially in the nervous system. 2-AG activates CB1 and CB2 GPCR receptors and triggers different signaling cascades, modulating intracellular Ca2+ levels, ERK1/2 phosphorylation, and other second messengers. Different studies have reported that CB1 is expressed not only in plasma membrane but also in intracellular compartments where they also seem to be functional. Therefore, the aim of this work was to study CB1 expression and function in isolated nuclei from rat cerebral cortex (CC). To this end, CC from Wistar rats were dissected, homogenized and highly purified nuclei (CCN) were isolated on a sucrose-density ultracentrifugation. CB1 protein expression was observed in CCN as well as in isolated cerebellum nuclei by Western Blot, which was confirmed by immunocytochemistry. In order to evaluate if CB1 is functional, CCN were incubated at 37 °C with a CB1 agonist (WIN 55-212-2) and ERK1/2 and Akt signaling cascades were studied by Western Blot. Interestingly, it was observed that ERK1/2 phosphorylation increased in nuclei treated with WIN 5 µM for 30 min with respect to controls (p<0.01) while no changes were seen in Akt phosphorylation. Taken together, these results demonstrate that CB1 has also a nuclear localization in the cerebral cortex where it could have a potential role in chromatin regulation and gene expression.