The fibrinolytic system includes a broad spectrum of proteolytic enzymes with physiological and pathophysiological functions in several processes, such as haemostatic balance, tissue remodeling, tumor invasion, angiogenesis and reproduction. The main enzyme of the plasminogen activator system is plasmin, which is responsible for the degradation of fibrin into soluble degradation products. The activation of plasminogen into plasmin is mediated by two types of activators, urokinase-type plasminogen activator (uPA) and tissue-type plasminogen activator (tPA). The activity of both is regulated by specific plasminogen activator inhibitors (PAIs). There are 3 types of PAIs described so far but the most important fibrinolytic inhibitor in vivo is PAI type 1 (PAI-1). Among others, the presence of metabolic syndrome and the -675 4G/5G promoter polymorphism are known to be modulators of PAI-1 levels. Besides their fibrinolytic profile, plasmin and plasminogen activators are implicated in tissue proliferation and cellular adhesion, as they can proteolytically degrade the extracellular matrix and regulate the activation of both growth factors and matrix metalloproteinases. By all these means, the fibrinolytic system is also involved in physiological processes, and in pathological situations such as thrombosis, arteriosclerosis, endometriosis and cancer. PAI 1 has been studied in different settings with thrombotic pathophysiology, such as coronary artery disease and ischaemic stroke. Controversial results have been published and concerns about study designs or presence of confounders have been claimed to be responsible of them. Recently, its involvement in adverse thrombotic events related to the modern drug-eluting coronary stents has renewed the interest of its study. PAI-1 also plays an important role in signal transduction, cell adherence, and migration. Indeed, studies of several types of cancers, including breast cancer, have shown that increased uPA and PAI-1 levels are associated with aggressive tumor behavior and poor prognosis. Endometriosis is defined by the presence of endometrial glands and stroma outside the uterus with marked ability to attach and invade the peritoneum. It is one of the most frequent benign gynecological diseases that affect women with pelvic pain or infertility during their reproductive age. Immune system disorders, genetic predisposition, altered peritoneal environment and endometrial alterations are believed to increase the susceptibility to endometriosis. The plasminogen activator system may be involved in this process, where local extracellular proteolysis plays a crucial role. Altered expression of several components of the fibrinolytic system in both eutopic and ectopic endometrium and peritoneal fluid of women with the disease has been implicated not only in the onset, but also in the progression of the endometriotic lesions.

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.

microRNAs (miRNAs) are 21-22 nucleotide non-coding RNAs that regulate gene expression and play fundamental roles in biological processes. These small molecules bind to target mRNAs, leading to translational repression and/or mRNA degradation. Aberrant miRNA expression is associated with several human diseases such as cancer, cardiovascular disorders, inflammatory diseases and gynecological pathology. The present article reviews the role of miRNAs in four gynecological disorders that affect the ovary or the uterus, one benign and frequent disease (endometriosis) that is classified as a tumor-like lesion and three malignant gynecological diseases (endometrial, cervical and ovarian cancers). Endometriosis, defined as the presence of endometrium outside the uterus, is one of the most frequent benign gynecological diseases. Similarly to tumor metastasis, endometriotic implants require neovascularization to proliferate, invade the extracellular matrix and establish an endometriotic lesion. Despite its high prevalence and incapacitating symptoms, the exact pathogenic mechanism of endometriosis remains unsolved. A relationship between endometriosis and gynecological cancer, especially ovarian cancer, has been reported. Endometriosis is a multifactorial and polygenic disease, and emerging data provide evidence that a dysregulation of miRNA expression may be involved. miRNAs appear to be potent regulators of gene expression in endometriosis, raising the prospect of using miRNAs as biomarkers and therapeutic tools in this disease. In cancer, miRNAs have an important role as regulatory molecules, acting as oncogenes (oncomiRs) or tumor suppressors. Endometrial cancer is one of the most frequent gynecological malignancies in the developed countries. Cervical cancer, also one of the most common cancers in women, is associated with high-risk human papillomaviruses although this infection alone may not be enough to induce the malignant transformation. Ovarian cancer is the fifth leading cause of all cancer-related deaths among women. Over 80% of cases are diagnosed at an advanced stage, with a reduced five-year survival rate. Recent studies have shown that miRNAs are aberrantly expressed in different human cancer types, including endometrial, cervical and ovarian cancer, and that specific dysregulated miRNAs may act as biomarkers of patients' outcome. Recently, miRNAs have been detected in serum and plasma, and circulating miRNA expression profiles have now been associated with a range of different tumor types. Their accessibility in peripheral blood and stability given the fact that miRNAs circulate confined within exosomes, make researchers foster hope in their role as emerging biomarkers of cancer and other disorders. The development of therapies that might block the expression or mimic the functions of miRNAs could represent new therapeutic strategies for any of the aforementioned gynecological disorders.

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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.