Administration of cannabinoid receptor 2 (CB2R) agonists in inflammatory and autoimmune disease and CNS injury models results in significant attenuation of clinical disease, and reduction of inflammatory mediators. Previous studies reported that CB2R signaling also reduces leukocyte migration. Migration of dendritic cells (DCs) to various sites is required for their activation and for the initiation of adaptive immune responses. Here, we report for the first time that CB2R signaling affects DC migration in vitro and in vivo, primarily through the inhibition of matrix metalloproteinase 9 (MMP-9) expression. Reduced MMP-9 production by DCs results in decreased migration to draining lymph nodes in vivo and in vitro in the matrigel migration assay. The effect on Mmp-9 expression is mediated through CB2R, resulting in reduction in cAMP levels, subsequent decrease in ERK activation, and reduced binding of c-Fos and c-Jun to Mmp-9 promoter activator protein 1 sites. We postulate that, by dampening production of MMP-9 and subsequent MMP-9-dependent DC migration, cannabinoids contribute to resolve acute inflammation and to reestablish homeostasis. Selective CB2R agonists might be valuable future therapeutic agents for the treatment of chronic inflammatory conditions by targeting activated immune cells, including DCs.
IntroductionThe cannabinoid system consists of cannabinoid receptors and their ligands, including endocannabinoids, synthetic cannabinoid receptor agonists and antagonists, and phytocannabinoids. Several cannabinoid receptors have been described, that is, the classic cannabinoid receptor 1 (GPR) and GPR, the previously orphaned G-protein receptors GPR18 and GPR55, various ion channels, and intracellular peroxisome proliferator-activated receptor-␥ (reviewed in Pertwee et al 1 and Console-Bram 2 ). The 2 classic cannabinoid receptors, CB1R and CB2R, have different distribution and functions (reviewed in Kubajewska and Constantinescu 3 and Basu and Dittel 4 ). CB1R is abundantly expressed on CNS and peripheral neurons and involved in neural functions. In contrast, CB2R is mostly expressed on immune cells and involved in immunoregulation. Administration of CB2R-selective agonists in models of inflammatory and autoimmune diseases such as systemic sclerosis, experimental autoimmune uveoretinitis, inflammatory bowel diseases, and experimental autoimmune encephalomyelitis (EAE) resulted in attenuation of clinical disease (reviewed in Basu and Dittel 4 ). CB2R agonists also have been reported to have a beneficial effect in models of CNS injury such as cerebral infarction and spinal cord injury. [5][6][7][8] In addition to effects on clinical outcome, CB2R agonists reduced the levels of inflammatory mediators in various experimental models. [8][9][10] A possible mechanism for the anti-inflammatory effect of CB2R signaling is the direct action of CB2R agonists on immune cells. In vitro studies indicated that CB2R signaling inhibited the production of proinflammatory cytokines such as TNF␣, IL-6, IL-2, and IFN-␥ by ac...