The role of endogenous free radical signalling in human endometrium

Abstract

Differentiation of human endometrial stromal cells (HESCs) into specialized decidual cells is critical for embryo implantation and maintenance of a successful pregnancy. Initiation of this differentiation process, termed decidualization, is strictly dependent on elevated cAMP levels, whereas its maintenance requires continuous progesterone signalling. Here I show that NADPH oxidase-dependent reactive oxygen species (ROS) play a critical role in initiating and maintaining the decidual process. I first show that cAMP-dependent induction of decidual marker genes can be attenuated or enhanced upon inhibition or activation of the NADPH oxidase complex, respectively. Time-course analysis demonstrated that cAMP enhances endogenous ROS production, apparent after 12 hours of stimulation, which coincides with a marked induction of differentiation markers. By a process of elimination, I identified NOX4 as the main catalytic subunit involved in decidualization. Silencing of NOX4, or its cofactor p22PHOX, impaired the decidual process. I then show that the NOX4/p22PHOX complex regulates the transcriptional activity of CCAAT/enhancer binding protein β, a key regulator of HESC differentiation. Furthermore, microarray analysis revealed that the NOX4/p22PHOX complex functions downstream FOXO1, a multifaceted transcription factor involved in antioxidant defences, DNA repair and cell cycle regulation. In agreement, knockdown of NOX4/p22PHOX complex disrupted endogenous ROS production and resulted in a paradoxical prooxidant stress response further characterized by activation of the DNA repair pathway in the absence of primary DNA damage or cell death. Finally, I provide preliminary data that p22PHOX is downregulated at the transcript and protein level in the eutopic endometrium of patients with endometriosis. In summary, endogenous ROS signalling is critical for the differentiation and redox homeostasis of HESCs. Furthermore, deregulation of endometrial NADPH oxidase-dependent ROS production and signalling may be a hallmark of endometriosis, a prevalent and debilitating reproductive disorder.EThOS - Electronic Theses Online ServiceGBUnited Kingdo