Higher fibrotic content of endometriotic lesions is associated with diminished prostaglandin E2 signaling

Purpose While the prevailing view holds that the prostaglandin E2 (PGE2) signaling plays a vital role in endometriosis, PGE2 also is known to be anti‐fibrotic. We investigated the immunostaining of COX‐2, EP2, and EP4, along with fibrotic content in ovarian endometrioma (OE) and deep endometriosis (DE) lesions, and in OE lesions from adolescent and adult patients. In addition, we evaluated the effect of substrate stiffness on the expression of COX‐2, EP2, and EP4 in endometrial stromal cells. Methods Immunohistochemistry analysis of COX‐2, EP2, and EP4, along with the quantification of lesional fibrosis, was conducted for OE and DE lesion samples and also OE lesion samples from adolescent and adult patients. The effect of substrate rigidity on fibroblast‐to‐myofibroblast transdifferentiation (FMT) and the expression of COX‐2, EP2, and EP4, with or without TGF‐β1 stimulation, were investigated. Results The immunostaining of COX‐2, EP2, and EP4 was substantially reduced in endometriotic lesions as lesions became more fibrotic. Both TGF‐β1 stimulation and stiff substrates induced FMT and reduced the expression of COX‐2, EP2, and EP4. Conclusions Since fibrosis is a common feature of endometriosis, our results thus cast doubts on the use of therapeutics that suppresses the PGE2 signaling pathway, either by inhibiting COX‐2 or EP2/EP4.