Cannabinoid Type 2 Receptor Activation Downregulates Stroke-Induced Classic and Alternative Brain Macrophage/Microglial Activation Concomitant to Neuroprotection

Abstract

Ischemic stroke continues to be one of the main causes of death worldwide. Inflammation accounts for a large part of damage in this pathology. The cannabinoid type 2 receptor (CB2R) has been proposed to have neuroprotective properties in neurological diseases. Therefore, our aim was to determine the effects of the activation of CB2R on infarct outcome and on ischemia-induced brain expression of classic and alternative markers of macrophage/microglial activation. Swiss wild-type and CB2R knockout male mice were subjected to a permanent middle cerebral artery occlusion. Mice were treated with either a CB2R agonist (JWH-133), with or without a CB2R antagonist (SR144528) or vehicle. Infarct outcome was determined by measuring infarct volume and neurological outcome. An additional group of animals was used to assess mRNA and protein expression of CB2R, interleukin (IL)-1β, IL-6, tumor necrosis factor α (TNF-α), monocyte chemoattractant protein-1 (MCP-1), macrophage inflammatory peptide (MIP) -1α, RANTES, inducible nitric oxide synthase (iNOS), cyclooxygenase-2, IL-4, IL-10, transforming growth factor β (TGF-β), arginase I, and Ym1. Administration of JWH-133 significantly improved infarct outcome, as shown by a reduction in brain infarction and neurological impairment. This effect was reversed by the CB2R antagonist and was absent in CB2R knockout mice. Concomitantly, administration of JWH-133 led to a lower intensity of Iba1+ microglia/macrophages and a decrease in middle cerebral artery occlusion-induced gene expression of both classic (IL-6, TNF-α, MCP-1, MIP-1α, RANTES, and iNOS) and alternative mediators/markers (IL-10, TGF-β, and Ym1) of microglial/macrophage activation after permanent middle cerebral artery occlusion. The inhibitory effect of CB2R on the activation of different subpopulations of microglia/macrophages may account for the protective effect of the selective CB2R agonist JWH-133 after stroke.