Identificación, caracterización y aislamiento de células madre somáticas en los miomas humanos

Human uterine fibroids or leiomyomas are the most common benign tumor of the female genital tract affecting 25-30% of women worldwide. They are estrogen-dependent tumors within the myometrium composed by high extracellular matrix content. Typical leiomyoma symptoms, such as pain, menstrual disorders and infertility (1), tend to increase with age and tumor size, constituting the main cause of hysterectomy (2) since no effective long-term medical treatment is available. Despite its high prevalence, knowledge about the cells initiating these uterine tumors is scarce (3), although their origin is associated with disorders in the function, proliferation and fate of a subset of myometrial cells (4, 5). A large body of evidence points to its clonal origin (6) and high proliferation features under hypoxic conditions (7, 8). The cancer stem cells (CSC) or cell initiators of tumors (CIT) hypothesis suggests that tumor cells are organized hierarchically, similarly to normal tissues, with a small self-renewing population of stem cells (SC) generating a large population of proliferative cells that differ from the rest. Thus, they are initiated through a small subset of tumor cells that are ultimately responsible for their formation and growth. CSC/CIT have been identified in a variety of solid tumors, including breast (9), prostate (10), colorectal (11), pancreatic (12), brain (13, 14), and ovarian cancer (15-19). Side population (SP) cells have been successfully used as a tool to identify somatic SC in different organs and tissues, such as bone marrow (20,21), mammary gland (22), skin (23), lung (24), dental pulp (25), endometrium (26-28) and uterine myometrium (29), and also in tumors such as ovarian cancer (18). However, accumulated evidences also demonstrate that tumor progression could result from the interaction between CSC/CIT and their microenvironment (30), specifically with the stromal compartment (31, 32). In this context, our aim was to isolate and characterize the SP population from human leiomyomas, analyzing its clonogenic activity under hypoxic conditions and establishing two MyoSP cell lines (MyoSP1 and MyoSP2). Here we report in vitro and in vivo assays demonstrating the ability of these cell lines to differentiate into mesenchymal lineages cell types, and to form a tissues-like leiomyoma in an animal model.