Localization of the cannabinoid type‐1 receptor in subcellular astrocyte compartments of mutant mouse hippocampus

• Published in: Glia Vol. 66; no. 7; pp. 1417 - 1431
• Main Authors: Gutiérrez‐Rodríguez, Ana, Bonilla‐Del Río, Itziar, Puente, Nagore, Gómez‐Urquijo, Sonia M., Fontaine, Christine J., Egaña‐Huguet, Jon, Elezgarai, Izaskun, Ruehle, Sabine, Lutz, Beat, Robin, Laurie M., Soria‐Gómez, Edgar, Bellocchio, Luigi, Padwal, Jalindar D., van der Stelt, Mario, Mendizabal‐Zubiaga, Juan, Reguero, Leire, Ramos, Almudena, Gerrikagoitia, Inmaculada, Marsicano, Giovanni, Grandes, Pedro
• Format: Journal Article
• Language: English
• Published: United States Wiley Subscription Services, Inc 01-07-2018
• Subjects: Astrocytes; Brain; Cannabinoid CB1 receptors; cannabinoids; Fluorescence; glia; Glial fibrillary acidic protein; Gold; Green fluorescent protein; Hippocampus; Immunoelectron microscopy; intracellular receptors; Localization; Membranes; Mice; Microscopy; Mitochondria; Molecular chains; Plasma membranes; Proteins; Receptors; Rodents; Synaptic plasticity; Synaptic transmission; tripartite synapse; Viruses; cannabinoids; tripartite synapse; immunoelectron microscopy; intracellular receptors; glia; mitochondria
• ISSN: 0894-1491; 1098-1136
• DOI: 10.1002/glia.23314

Astroglial type‐1 cannabinoid (CB1) receptors are involved in synaptic transmission, plasticity and behavior by interfering with the so‐called tripartite synapse formed by pre‐ and post‐synaptic neuronal elements and surrounding astrocyte processes. However, little is known concerning the subcellular distribution of astroglial CB1 receptors. In particular, brain CB1 receptors are mostly localized at cells' plasmalemma, but recent evidence indicates their functional presence in mitochondrial membranes. Whether CB1 receptors are present in astroglial mitochondria has remained unknown. To investigate this issue, we included conditional knock‐out mice lacking astroglial CB1 receptor expression specifically in glial fibrillary acidic protein (GFAP)‐containing astrocytes (GFAP‐CB1‐KO mice) and also generated genetic rescue mice to re‐express CB1 receptors exclusively in astrocytes (GFAP‐CB1‐RS). To better identify astroglial structures by immunoelectron microscopy, global CB1 knock‐out (CB1‐KO) mice and wild‐type (CB1‐WT) littermates were intra‐hippocampally injected with an adeno‐associated virus expressing humanized renilla green fluorescent protein (hrGFP) under the control of human GFAP promoter to generate GFAPhrGFP‐CB1‐KO and ‐WT mice, respectively. Furthermore, double immunogold (for CB1) and immunoperoxidase (for GFAP or hrGFP) revealed that CB1 receptors are present in astroglial mitochondria from different hippocampal regions of CB1‐WT, GFAP‐CB1‐RS and GFAPhrGFP‐CB1‐WT mice. Only non‐specific gold particles were detected in mouse hippocampi lacking CB1 receptors. Altogether, we demonstrated the existence of a precise molecular architecture of the CB1 receptor in astrocytes that will have to be taken into account in evaluating the functional activity of cannabinergic signaling at the tripartite synapse.
Main Points
Intracellular CB1 receptors are localized in astroglial mitochondria.
About 12% of the mitochondria in the hippocampal astrocytes express the receptor.
This novel finding extends the subcellular compartmentalization of the CB1 receptor in the brain.