Keratinocyte growth factor is up-regulated by estrogen in the porcine uterine endometrium and functions in trophectoderm cell proliferation and differentiation.

Keratinocyte growth factor (KGF) is expressed by uterine endometrial epithelial cells during the estrous cycle and during pregnancy in pigs, whereas KGF receptor is expressed in conceptus trophectoderm and endometrial epithelia. In particular, KGF expression in the endometrium is highest on day 12 of pregnancy. This corresponds to the period of maternal recognition of pregnancy in pigs, which is signaled by large amounts of estrogen secreted by conceptus trophectoderm acting on the endometrium. Our hypothesis is that estrogens of conceptus origin stimulate endometrial epithelial KGF expression, and, in turn, secreted KGF stimulates proliferation and differentiation of conceptus trophectoderm. To determine the factors affecting KGF expression in the uterus, endometrial explants from gilts on day 9 of the estrous cycle were cultured in the presence of 17beta-estradiol, catechol estrogens, or progesterone. 17beta-Estradiol stimulated the expression of KGF (P < 0.05), whereas catechol estrogens had no effect (P > 0.05). Between days 9 and 15 of pregnancy, proliferating cell nuclear antigen was abundant in conceptuses, but was barely detectable in uterine endometrial epithelia. To determine the effects of KGF on conceptus trophectoderm, porcine trophectoderm (pTr) cells were treated with recombinant rat KGF (rKGF). rKGF increased the proliferation of pTr cells (P < 0.01) as measured by [(3)H]thymidine incorporation. rKGF elicited phosphorylation of KGF receptor and activated the mitogen-activated protein kinase (ERK1/2) cascade in pTr cells. pTr cell differentiation was affected by rKGF, because it increased expression of urokinase-type plasminogen activator, a marker for differentiation in pTr cells. Collectively, these results indicate that estrogen, the pregnancy recognition signal from the conceptus in pigs, increases uterine epithelial KGF expression, and, in turn, KGF stimulates the proliferation and differentiation of conceptus trophectoderm.