TNFα-induced IKKβ complex activation influences epithelial, but not stromal cell survival in endometriosis

STUDY QUESTION: Can the activity of the IκB kinase (IKKβ) complex in endometriotic cells contribute to endometriotic lesion survival? SUMMARY ANSWER: There is a constitutive activity of the IKKβ catalytic complex in peritoneal and deeply infiltrating lesions that can influence epithelial, but not stromal cell viability. WHAT IS KNOWN ALREADY: Endometriotic lesions exist in an inflammatory microenvironment with higher local concentrations of cytokines, such as tumour necrosis factor α (TNFα). TNFα stimulates the activation of the IKKβ complex, an important nodal point in multiple signalling pathways that influence gene transcription, proliferation and apoptosis. However, few data on the regulation of IKKβ in endometriotic tissue are currently available. STUDY DESIGN, SIZE, DURATION: A retrospective analysis of endometriotic tissue from peritoneal, ovarian and deeply infiltrating lesions from 37 women. PARTICIPANTS/MATERIALS, SETTING, METHODS: Basal and activated (phosphorylated) IKKβ concentrations were analysed by western blotting and immunohistochemistry. The relationship between the expression and activation of these proteins and peritoneal fluid (TNFα) concentrations, measured via ELISA, was examined. A subsequent in vitro analysis of TNFα treatment on the activation of IKKβ and the effect on epithelial and stromal cell viability by its inhibition with PS1145 was also performed. MAIN RESULTS AND ROLE OF CHANCE: Levels of the phosphorylated IKKβ complex in endometriotic lesions had a significant positive correlation with peritoneal fluid TNFα concentrations. Phosphorylated IKKβ complex was more prevalent in peritoneal and deeply infiltrating endometriosis lesions compared with ovarian lesions. IKKβ was present in both epithelial and stromal cells in all lesions but active IKKβ was limited to epithelial cells. TNFα stimulated an increased expression of phosphorylated IKKβ and the inhibition of this kinase with PS1145 significantly influenced ectopic epithelial cells viability but not eutopic epithelial cells, or endometrial stromal cells. LIMITATIONS, REASONS FOR CAUTION: In vitro analysis on epithelial cells was performed with immortalized cell lines and not primary cell cultures and only low sample numbers were available for the study. WIDER IMPLICATIONS OF THE FINDINGS: The regulation of aberrant signalling pathways represents a promising yet relatively unexplored area of endometriosis progression. The IKKβ complex is activated by inflammation and is critical nodal point of numerous downstream kinase-signalling pathways, including NFκB (nuclear factor κB), mTOR (mammalian target of rapamycin) and BAD (Bcl2-antagonist of cell death). This study shows a significant relationship between peritoneal fluid TNFα and IKKβ activation in epithelial cells that will have significant consequences for the continued survival of these cells at ectopic locations through the regulation of downstream pathways. LARGE SCALE DATA: None. STUDY FUNDING/COMPETING INTEREST(S): The study was funded by the Swiss National Science Foundation (Grant Number 320030_140774). The authors have no conflict of interest to declare