Increased expression of integrin-linked kinase during decidualization regulates the morphological transformation of endometrial stromal cells

OBJECTIVE:To study the impact of integrin-linked kinase (ILK) in endometrial stromal cells (ESCs) during decidualization. DESIGN:Laboratory study with the use of human endometrium. SETTING:University hospital. PATIENT(S):Fertile reproductive-age women who had not received hormonal treatment for 3 months before tissue collection. INTERVENTION(S):Endometrium tissue collection, in vitro decidualization of isolated ESCs, and small interfering (si) RNA transfection. MAIN OUTCOME MEASURE(S):Immunohistochemistry, ELISA, Western blot analysis, methylthiazolyl tetrazolium assay, and immunofluorescence staining. RESULT(S):In vivo expression of ILK is significantly increased in distended-fusiform stromal cells of late secretory endometrium and in cobblestone-shaped decidual cells of early pregnancy. During in vitro decidualization for up to 8 days, confluent cultures of isolated ESCs consistently displayed increased ILK expression and morphologic transformation from fibroblast-like to polygonal cells. Subsequent ILK knockdown by siRNA transfection reversed this transformation, accompanied by decreased phosphorylation of glycogen synthase kinase (GSK) 3β and decreased viable cell numbers. Immunofluorescence staining of the decidualized ESCs demonstrated linkage of increased levels of ILK at the tips of the fan-shaped organization of actin stress fibers located in the submembranous area, which expanded the decidual cells into a typical polygonal appearance. Knock-down of ILK abrogated the polymerization and organization of actin fibers, which reverted the cells to their undecidualized morphology. CONCLUSION(S):During human endometrial decidualization, ILK is essential for morphologic transformation of ESCs through organization of the actin cytoskeleton; it may also function through subsequent GSK3β signaling, which requires further studies.