In this study we investigated the role of CB1 receptor signaling in angiogenesis and the therapeutic exploitation of CB1 inactivation as an antiangiogenic strategy. We started from the observation that CB1 receptor expression is induced during angiogenesis and that the endocannabinoid anandamide stimulated bFGFinduced angiogenesis in the nanomolar physiologic range. To define the functional involvement of CB1 receptor signaling during angiogenesis, 2 different strategies have been carried out: siRNAmediated knockdown and pharmacologic antagonism of CB1 receptors. CB1 receptors inactivation resulted in the inhibition of bFGF-induced endothelial proliferation, migration, and capillary-like tube formation, through prosurvival and migratory pathways involving ERK, Akt, FAK, JNK, Rho, and MMP-2. To corroborate the potential therapeutic exploitation of CB1 blockade as an antiangiogenic strategy, we performed in vivo assays founding that CB1 blockade was able to inhibit bFGF-induced neovascular growth in the rabbit cornea assay. A relevant finding was the ability to reduce ocular pathologic neo-vascularization in mouse oxygen-induced retinopathy. These results demonstrate that CB1 signaling participates to the proliferative response elicited by proangiogenic growth factors in angiogenesis and that for this reason CB1 receptor could represent a novel target for the treatment of diseases where excessive neoangiogenesis is the underlying pathology.
IntroductionThe endocannabinoid system, composed of 2 cannabinoid receptors CB1 and CB2, their endogenous ligands (endocannabinoids, eg, anandamide), and the enzymes for their metabolism, has been pointed out to be implicated in several pathophysiologic conditions ranging from neurologic and psychiatric diseases to eating, cardiovascular, reproductive disorders, and cancer. [1][2][3] The main effects of endocannabinoids rely on the activation of CB1, a 7-transmembranedomain protein belonging to the G ␣i protein-coupled receptor family (GPCR). 4 CB1 receptors are highly expressed in the central nervous system, especially in the cortex, cerebellum, hippocampus, and basal ganglia, and their involvement in processes of memory and learning, in diseases affecting movement, mood, and anxiety and in conditions related to altered brain reward mechanisms, has been ascertained. 5 Noteworthy, CB1 receptors are expressed also by a variety of peripheral tissues and cells and in the last years a role in several physiologic functions and pathologies is emerging. CB1 deficiency was reported to be associated to age-related osteoporosis 6 and preterm birth in mice, 7 highlighting a role for CB1 signaling in bone metabolism and in early pregnancy events. On the other hand, CB1 receptor antagonism and/or inactivation through genetic engineering as in CB1-deficient mouse strains, 8 were shown to be useful in several pathologies in which the endocannabinoid system is unbalanced or CB1 more than expressed (eg, obesity, metabolic syndrome, diabetes, Alzheimer disease). 9-11 Indeed, CB1 inactivation e...
