Anandamide oxidative metabolism-induced endoplasmic reticulum stress and apoptosis

The Endocannabinoid System (ECS) has been recognized as a crucial player in human reproduction. Changes in the levels of anandamide (AEA), the main endocannabinoid (eCB), negatively affect reproductive events, such as implantation, decidualization and placentation. Cyclooxygenase-2 (COX-2) is a major enzyme expressed in the endometrium and its involvement in female reproductive system has evolved over the last few years. Currently, COX-2 oxidative metabolism is emerging as a key mediator of AEA-induced actions. In this study, we aimed to disclose the mechanisms underlying the effects of AEA in human endometrial stromal cell fate, using a human-derived endometrial cell line (St-T1b). We found that AEA has an anti-proliferative activity through a direct effect on cell cycle progression by inducing G₂/M arrest. Moreover, high levels of AEA increased COX-2 activity, triggering apoptotic cell death, with loss of mitochondrial membrane potential, induction of caspase -9 and -3/-7 activities, and cleavage of poly (ADP-ribose) polymerase (PARP). In addition, the involvement of intracellular reactive oxygen species (ROS) and endoplasmic reticulum (ER) stress was verified. These effects were prevented by pre-incubation with a selective COX-2 inhibitor. Therefore, we hypothesize that, in response to altered levels of this eCB, COX-2 oxidative metabolism of AEA may deregulate endometrial cell turnover and, consequently, interfere with cellular events crucial for implantation and decidualization, with a negative impact on human fertility.