Extracellular matrix in uterine leiomyoma pathogenesis: a potential target for future therapeutics

BACKGROUND: Uterine leiomyoma (also known as fibroid or myoma) is the most common benign tumor of the uterus found in women of reproductive age. It is not usually fatal but can produce serious clinical symptoms, including excessive uterine bleeding, pelvic pain or pressure, infertility and pregnancy complications. Due to lack of effective medical treatments surgery has been a definitive choice for the management of this tumor. OBJECTIVE AND RATIONALE: Extracellular matrix (ECM) accumulation and remodeling are thought to be crucial for fibrotic diseases such as uterine leiomyoma. Indeed, ECM plays important role in forming the bulk structure of leiomyoma, and the ECM-rich rigid structure within these tumors is thought to be a cause of abnormal bleeding and pelvic pain. Therefore, a better understanding of ECM accumulation and remodeling is critical for developing new therapeutics for uterine leiomyoma. SEARCH METHODS: PubMed and Google Scholar were searched for all original and review articles/book chapters related to ECM and medical treatments of uterine leiomyoma published in English until May 2017. OUTCOMES: This review discusses the involvement of ECM in leiomyoma pathogenesis as well as current and future medical treatments that target ECM directly or indirectly. Uterine leiomyoma is characterized by elevated levels of collagens, fibronectin, laminins and proteoglycans. They can induce the mechanotransduction process, such as activation of the integrin-Rho/p38 MAPK/ERK pathway, resulting in cellular responses that are involved in pathogenesis and altered bidirectional signaling between leiomyoma cells and the ECM. ECM accumulation is affected by growth factors (TGF-β, activin-A and PDGF), cytokines (TNF-α), steroid hormones (estrogen and progesterone) and microRNAs (miR-29 family, miR-200c and miR-93/106b). Among these, TGF-βs (1 and 3) and activin-A have been suggested as key players in the accumulation of excessive ECM (fibrosis) in leiomyoma. The presence of elevated levels of ECM and myofibroblasts in leiomyoma supports the fibrotic character of these tumors. Interestingly, ECM may serve as a reservoir of profibrotic growth factors and enhance their activity by increasing their stability and extending their duration of signaling. At present, several classes of compounds, including gonadotropin-releasing hormone (GnRH) agonist (leuprolide acetate), GnRH antagonist (cetrorelix acetate), selective progesterone receptor modulators (ulipristate acetate and asoprisnil), antiprogestin (mifepristone) and natural compounds like vitamin D and resveratrol have been studied as medical treatments that target ECM in uterine leiomyoma. WIDER IMPLICATIONS: Although several types of drugs (mostly antiproliferative agents) are available for leiomyoma treatment, none of them were introduced specifically as antifibrotic agents. In light of its critical role in the process of fibrosis in leiomyoma, we propose that ECM should be considered as a crucial target for future therapeutics. Thus, the introduction of drugs that are specifically antifibrotic could be a good solution to control abnormal leiomyoma growth and associated clinical symptoms. The antifibrotic compounds can be introduced based on their ability to regulate ECM components and their receptors, as well as growth factors, cytokines, steroid hormones and their corresponding receptors and intracellular signaling pathways, as well as microRNAs, involved in ECM production in leiomyoma.