Endometrium and peritoneal fluid from women with endometriosis have increased levels of VEGF, uPA and MMP-3 levels. Therefore, the development of endometriotic implants at ectopic sites may be facilitated, promoting the progress of the endometriosis.

The increase in antigenic levels of uPA and MMP-3 in endometrium of women with endometriosis might contribute to the invasive potential of endometrial cells. Once the ovarian endometriotic cyst is developed, an increase in PAI-1 and TIMP-1 is detected and significant proteolytic activity is no longer observed. This increase in inhibitors and decrease in proteolytic activity could explain the frequent clinical finding of isolated endometriotic cyst without invasion of the surrounding ovarian tissue.

The increase in mRNA and protein levels of uPA and MMP-3 observed in endometrium of women with endometriosis may facilitate the attachment of endometrial tissue to the peritoneum and ovarian surface, as well as the invasion of the extracellular matrix. This process would lead to the formation of early endometriotic lesions. Once the ovarian endometriotic cyst is developed, PAI-1 and TIMP-1 would increase which could explain the frequent clinical finding of an endometrioma without invasion of the adjacent ovarian tissue.

Expression levels of miRNAs related to angiogenesis were different in eutopic endometrium from that observed in ovarian endometrioma. This could influence the expression of angiogenic factors and play a role in the pathogenesis of endometriosis.

This work was supported by research grants from the Plan Nacional de Investigación Científica, Desarrollo e Innovación Tecnológica (Instituto de Salud Carlos III, Fondo de Investigación Sanitaria, PI080185, PI0110091) and Red RECAVA (RD06/0014/0004), by Consellería de Sanidad (AP-141/11) and Consellería de Educación (PROMETEO/2011/027), Generalitat Valenciana, by Beca Fibrinolisis 2009 and Becario 2010, 2011 from Fundación Española de Trombosis y Hemostasia and by the Fundación Investigación Hospital La Fe, Spain. None of the authors have any conflicts of interest.