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.

The endocannabinoid anandamide impairs in vitro decidualization of human cells.

Endocannabinoids (eCBs) are endogenous mediators that along with the cannabinoid receptors (CB1 and CB2), a membrane transporter and metabolic enzymes form the endocannabinoid system (ECS). Several eCBs have been discovered with emphasis on anandamide (AEA). They are involved in several biological processes such as energy balance, immune response and reproduction. Decidualization occurs during the secretory phase of human menstrual cycle, which involves proliferation and differentiation of endometrial stromal cells into decidual cells and is crucial for the establishment and progression of pregnancy. In this study, a telomerase-immortalized human endometrial stromal cell line (St-T1b) and non-differentiated primary cultures of human decidual fibroblasts from term placenta were used to characterize the ECS using immunoblotting and qRT-PCR techniques. It was shown that St-T1b cells express CB1, but not CB2, and that both receptors are expressed in HdF cells. Furthermore, the expression of fatty acid amide hydrolase (FAAH), the main degrading enzyme of AEA, increased during stromal cell differentiation. AEA inhibited cell proliferation, through deregulation of cell cycle progression and induced polyploidy. Moreover, through CB1 binding receptor, AEA also impaired cell differentiation. Therefore, AEA is proposed as a modulator of human decidualization. Our findings may provide wider implications, as deregulated levels of AEA, due to Cannabis sativa consumption or altered expression of the metabolic enzymes, may negatively regulate human endometrial stromal cell decidualization with an impact on human (in)fertility.Free Portuguese abstract: A Portuguese translation of this abstract is freely available at http://www.reproduction-online.org/content/152/4/351/suppl/DC1.