The Mutual Modulation of Endocannabinoid and Kisspeptin Systems in Rat Testis

Background: The endocannabinoid system (ECS) and the Kisspeptin system (KS) play crucial roles in the central and peripheral regulation of male reproduction. The KS comprises Kisspeptins, the cleavage product of the Kiss1 protein, and its receptor Kiss1R; it is a critical central regulatory factor of the Gonadotropin Releasing Hormone (GnRH), but its role in the testis in sustaining spermatogenesis is not fully understood. Similarly, in addition to the brain, the ECS is widely expressed in the testis, where it regulates spermatogenesis, steroidogenesis, and the production of high-quality gametes. Since the possible crosstalk between KS and ECS at the gonadal level is poorly understood, this study investigates the possible mutual modulation between ECS and KS in rat testis. Methods: Experiment 1: Testis pieces collected from adult rats were treated ex vivo for 1 h with the endocannabinoid anandamide (AEA, 10−8 M) ± SR141716A (10−7 M, a cannabinoid receptor (CB) 1 antagonist), or with SR141716A alone. Experiment 2: Testis pieces were treated for 4 h with decreasing doses of Kisspeptin-10 (Kp10, 10−6–10−9 M) ± Kp234 (a Kiss1R antagonist). Proteins extracted from the treated tissues were analyzed by Western blot for Kiss1R, Kiss1, CB1, CB2, AEA-hydrolyzing enzyme Fatty Acid Amide Hydrolase (FAAH), and AEA-biosynthetic enzyme N-acylphosphatidylethanolamine-specific phospholipase D (NAPE-PLD) proteins. Results: AEA treatment, via CB1, reduced Kiss1R protein in testis. Kp10 treatment increased the expression of CBs and NAPE-PLD at all doses and increased FAAH at 10−9 M dose only. Pre-incubation with Kp234 abolished Kp10 effects on CB1, NAPE-PLD, and FAAH, suggesting a direct Kp10-dependent modulation; on the other hand, pre-incubation with Kp234 did not abolish Kp10’s effects on CB2, suggesting an indirect action of Kp10 on CB2. Conclusions: Mutual modulation between ECS and KS exists in the testis: AEA, via CB1, suppresses Kisspeptin signaling, while Kisspeptin regulates the ECS through both Kiss1R-dependent and independent mechanisms. These local interactions identify new potential mechanisms in the intratesticular communications sustaining spermatogenesis via ECS and suggest that KS might be a new therapeutic target to rescue ECS impairment in male reproductive dysfunction.