The cannabinoid receptor CB1 regulates differentiation of spermatids. We recently characterized spermatozoa from caput epididymis of CB1-knock-out mice and identified a considerable number of sperm cells with chromatin abnormality such as elevated histone content and poorly condensed chromatin. In this paper, we extended our findings and studied the role of CB1 in the epididymal phase of chromatin condensation of spermatozoa by analysis of spermatozoa from caput and cauda epididymis of wild-type and CB1-knock-out mouse in both a homozygous or heterozygous condition. Furthermore, we studied the impact of CB1-gene deletion on histone displacement mechanism by taking into account the hyperacetylation of histone H4 and players of displacement such as Chromodomain Y Like protein (CDYL) and Bromodomain testis-specific protein (BRDT). Our results show that CB1, via local and/or endocrine cell-to-cell signaling, modulates chromatin remodeling mechanisms that orchestrate a nuclear condensation extent of mature spermatozoa. We show that CB1-gene deletion affects the epididymal phase of chromatin condensation by interfering with inter-/intra-protamine disulphide bridges formation, and deranges the efficiency of histone removal by reducing the hyper-acetylation of histone H4. This effect is independent by gene expression of Cdyl and Brdt mRNA. Our results reveal a novel and important role for CB1 in sperm chromatin condensation mechanisms.
Keywords: bromodomain protein BRDT; caput and cauda epididymis; chromatin remodeling and histone displacement; chromodomain protein CDYL; estrogens and endocannabinoids; post-translational modification of histone H4 (histone H4 acetylation); protamine thiol oxidation; sperm chromatin condensation and maturation; spermiogenesis; type-1 cannabinoid receptor (CB1).