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