Marijuana smokers and animals treated with Δ9-tetrahydrocannabinol, the principal component of marijuana, show alterations of sperm morphology suggesting a role for cannabinoids in sperm differentiation and/or maturation. Because the cannabinoid receptor 1 (CNR1) activation appears to play a pivotal role in spermiogenesis, the developmental stage where DNA is remodeled, we hypothesized that CNR1 receptors might also influence chromatin quality in sperm. We used Cnr1 null mutant (Cnr1-/-) mice to study the possible role of endocannabinoids on sperm chromatin during spermiogenesis. We demonstrated that CNR1 activation regulated chromatin remodeling of spermatids by either increasing Tnp2 levels or enhancing histone displacement. Comparative analysis of wild-type, Cnr1+/-, and Cnr1-/- animals suggested the possible occurrence of haploinsufficiency for Tnp2 turnover control by CNR1, whereas histone displacement was disrupted to a lesser extent. Furthermore, flow cytometry analysis demonstrated that the genetic loss of Cnr1 decreased sperm chromatin quality and was associated with sperm DNA fragmentation. This damage increased during epididymal transit, from caput to cauda. Collectively, our results show that the expression/activity of CNR1 controls the physiological alterations of DNA packaging during spermiogenesis and epididymal transit. Given the deleterious effects of sperm DNA damage on male fertility, we suggest that the reproductive function of marijuana users may also be impaired by deregulation of the endogenous endocannabinoid system.

Spermatozoa (SPZ) are motile cells, characterized by a cargo of epigenetic information including histone post-translational modifications (histone PTMs) and non-coding RNAs. Specific histone PTMs are present in developing germ cells, with a key role in spermatogenic events such as self-renewal and commitment of spermatogonia (SPG), meiotic recombination, nuclear condensation in spermatids (SPT). Nuclear condensation is related to chromatin remodeling events and requires a massive histone-to-protamine exchange. After this event a small percentage of chromatin is condensed by histones and SPZ contain nucleoprotamines and a small fraction of nucleohistone chromatin carrying a landascape of histone PTMs. Circular RNAs (circRNAs), a new class of non-coding RNAs, characterized by a nonlinear back-spliced junction, able to play as microRNA (miRNA) sponges, protein scaffolds and translation templates, have been recently characterized in both human and mouse SPZ. Since their abundance in eukaryote tissues, it is challenging to deepen their biological function, especially in the field of reproduction. Here we review the critical role of histone PTMs in male germ cells and the profile of circRNAs in mouse and human SPZ. Furthermore, we discuss their suggested role as novel epigenetic biomarkers to assess sperm quality and improve artificial insemination procedure.

Endocannabinoids are lipidic modulators able to bind cannabinoid receptors (CNRs). Two types of CNRs have been cloned, CNR1 (central) and CNR2 (peripheral). The objectives of the present study were to investigate the expression pattern of CNR1 in the rat testis during prepubertal development and to define the CNR1 spatiotemporal pattern. From 31 to 60 days of age, CNR1 was immunolocalized in round elongating spermatids and spermatozoa, suggesting an important role for this receptor in spermatogenesis. From 14 to 60 days of age, adult Leydig cells (ALCs) at different developmental stages were positive for CNR1. In particular, CNR1 expression in differentiating ALCs was negatively correlated to cell division. Bromodeoxyuridine uptake experiments on serial sections showed that immature Leydig cells in mitosis were negative for CNR1; in contrast, immature nonmitotic Leydig cells were positive for CNR1. A further observation of few ALCs in CNR1KO mice validates the role of CNR1 during proliferative activity involved in ALC differentiation. In addition, starting from 41 days of age, a faint CNR1 signal was also observed in Sertoli cells. Taken together, these results demonstrate the first clear evidence (to our knowledge) of CNR1 in mammalian germinal epithelium, ALCs, and Sertoli cells and indicate that differentiation of ALCs may depend on the endocannabinoid system.

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During transit through the epididymis, spermatozoa are normally kept immotile and do not attain the ability to become motile until they reach the caudal epididymis. This study was undertaken to determine whether endocannabinoids play a role in the epididymis and in particular in suppressing the ability of spermatozoa to become motile. We show that the levels of the endocannabinoid 2-arachidonoylglycerol (2-AG) are high in mouse spermatozoa isolated from the caput (head) of the epididymis, where these cells do not move (or possess sluggish and irregular motility) and decrease dramatically in spermatozoa isolated from the cauda (tail). The subsequent gradient regulates, via autocrine communication, the activity of cannabinoid receptor CNR1 (previously known as CB1) present on the sperm cell membrane and induces caudal spermatozoa to acquire the potential to become motile ("start-up"). Accordingly, the genetic or pharmacological inactivation of CNR1 increases number of motile spermatozoa in caput. Also, blockers of endocannabinoid cellular uptake inhibit the potential to move of spermatozoa and destroy the 2-AG gradient throughout the epididymis. This gradient-regulated mechanism may encourage further research for future therapies related to male infertility.