Regulation of Fas receptor/Fas-asssociated protein with death domain apoptotic complex and associated signalling systems by cannabinoid receptors in the mouse brain

Abstract

Background and purpose: Natural and synthetic cannabinoids (CBs) induce deleterious or beneficial actions on neuronal survival. The Fas-associated protein with death domain (FADD) promotes apoptosis, and its phosphorylated form (p-FADD) mediates non-apoptotic actions. The regulation of Fas/FADD, mitochondrial apoptotic proteins and other pathways by CB receptors was investigated in the mouse brain. Experimental approach: Wild-type, CB1 and CB2 receptor knock-out (KO) mice were used to assess differences in receptor genotypes. CD1 mice were used to evaluate the effects of CB drugs on canonical apoptotic pathways and associated signalling systems. Target proteins were quantified by Western blot analysis. Key results: In brain regions of CB1 receptor KO mice, Fas/FADD was reduced, but p-Ser191 FADD and the p-FADD/FADD ratio were increased. In CB2 receptor KO mice, Fas/FADD was increased, but the p-FADD/FADD ratio was not modified. In mutant mice, cleavage of poly(ADP-ribose)-polymerase (PARP) did not indicate alterations in brain cell death. In CD1 mice, acute WIN55212-2 (CB1 receptor agonist), but not JWH133 (CB2 receptor agonist), inversely modulated brain FADD and p-FADD. Chronic WIN55212-2 induced FADD down-regulation and p-FADD up-regulation. Acute and chronic WIN55212-2 did not alter mitochondrial proteins or PARP cleavage. Acute, but not chronic, WIN55212-2 stimulated activation of anti-apoptotic (ERK, Akt) and pro-apoptotic (JNK, p38 kinase) pathways. Conclusions and implications: CB1 receptors appear to exert a modest tonic activation of Fas/FADD complexes in brain. However, chronic CB1 receptor stimulation decreased pro-apoptotic FADD and increased non-apoptotic p-FADD. The multifunctional protein FADD could participate in the mechanisms of neuroprotection induced by CBs.