WINGLESS (WNT) signaling is a progesterone target for rat uterine stromal cell proliferation.

Abstract Preparation of the mammalian uterus for embryo implantation requires a precise sequence of cell proliferation. In the rodent uterus, estradiol stimulates proliferation of epithelial cells. Progesterone operates as a molecular switch and redirects proliferation to the stroma by down regulating glycogen synthase kinase 3-β (GSK-3β) and stimulating β-catenin accumulation in the periluminal stromal cells. In the present study, the WNT signal involved in the progesterone-dependent proliferative switch was investigated. Transcripts of four candidate Wnt genes were measured in uteri from ovariectomized (OVX) rats, progesterone pretreated (3 days of progesterone, 2 mg/daily) rats and progesterone pretreated rats given a single dose (0.2 µg) of estradiol. The spatial distribution of the WNT proteins was determined in uteri after the same treatments. Wnt5a increased in response to progesterone and the protein emerged in the periluminal stromal cells of progesterone pretreated rat uteri. To investigate whether WNT5a was required for proliferation, uterine stromal cell lines were stimulated with progesterone (1 µM) and fibroblast growth factor (FGF, 50 ng/ml). Proliferating stromal cells expressed a 2-fold increase in WNT5a protein at 12 h post stimulation. Stimulated stromal cells were cultured with actinomycin D (25 µg/ml) to inhibit new RNA synthesis. Relative Wnt5a expression increased at 4 and 6 h of culture suggesting progesterone plus FGF preferentially increased Wnt5a mRNA stability. Knockdown of Wnt5a in uterine stromal cell lines inhibited stromal cell proliferation and decreased Wnt5a mRNA. The results indicate that progesterone initiates and synchronizes uterine stromal cell proliferation by increasing WNT5a expression and signaling.