Endometrial Cell-Type Specific Regulation of the Endocannabinoids System and the Impact of Menstrual Cycle and Endometriosis

Introduction: Anandamide (AEA) and 2-arachidonoylglycerol are endogenous agonists of the cannabinoid receptors and regulate and control many cellular functions. Their activities are governed by enzymes and proteins that regulate their synthesis, receptor binding, transport, and degradation, which are known as the endocannabinoid system (ECS). The aim of this study was to investigate the regulation of endocannabinoid activity in the endometrium by studying the RNA and protein expression of the ECS within endometrial cell types and during different menstrual cycle stages and the impact of endometriosis.

Materials and Methods: The RNA expression of 70 ECS genes was assessed using RNA sequencing of isolated endometrial epithelial and stromal cells. Subsequent immunofluorescence-stained endometrial samples on ECS components of interest were objectively analyzed via an agnostic and automated image analysis pipeline to extract quantitative information. Differential gene and protein expression was investigated between the two cell types, menstrual cycle phases, and endometriosis cases and controls.

Results: Sufficient RNA expression was detected for 45 genes, and 17 (38%) genes were significantly different between epithelial and stromal cells. FAAH RNA was significantly higher in epithelial cells compared with stromal cells. Protein expression analysis of the main synthesizing (NAPE-PLD) and catabolizing (FAAH and NAAA) enzymes of AEA revealed a significantly stronger epithelial expression compared to stromal cells. The RNA and protein expression of CB1 receptors was very low with no significant difference between epithelial and stromal cells. Eleven ECS genes were regulated across the menstrual cycle, and there was no gene with significant difference between endometriosis cases and controls in epithelial cells.

Discussion: Differential expression of ECS genes supports a cell type-specific endocannabinoid activity in the endometrium. As endocannabinoids are short-lived signaling molecules, higher RNA and protein expression of FAAH in the epithelial cells suggests an active regulation of endocannabinoid activity in epithelial cells within the endometrium.