Fibroblast growth factor 2 (FGF2) is amitogen that induces proliferation, differentiation, and migration of cells, as well as angiogenesis and carcinogenesis via autocrine or paracrine actions. Fibroblast growth factor 2 expression is abundant in porcine conceptuses and endometrium during the estrous cycle and peri-implantation period of pregnancy. However, its intracellular actions in uterine epithelial cells have not been reported. The results of this study indicated abundant expression of FGFR1 and FGFR2 predominantly in uterine luminal and glandular epithelia during early pregnancy and that their expression decreased with increasing parity of the sows. Treatment of porcine uterine luminal epithelial (pLE) cells with FGF2 increased proliferation and DNA replication based on increases in proliferating cell nuclear antigen (PCNA) and initiation of G1/S phase progression. In addition, FGF2 increases phosphorylation of AKT, P70S6K, S6, ERK1/2, JNK, P38, and P90RSK in a time-dependent manner, and increases in their expression was suppressed by Wortmannin (a phosphatidylinositol 3-kinase [PI3K] inhibitor), U0126 (an ERK1/2 inhibitor), SP600125 (a JNK inhibitor), and SB203580 (a P38 inhibitor) based on western blot analyses. Also, the abundance of cytoplasmic p-AKT protein was decreased by Wortmannin and U0126, and p-ERK1/2 protein was reduced only by U0126. Furthermore, inhibition of each signal transduction protein reduced the ability of FGF2 to stimulate proliferation and migration of pLE cells. Collectively, these results indicate that activation of FGFR1 and FGFR2 by uterine- and endometrial-derived FGF2 stimulates PI3K/AKT and mitogen-activated protein kinase pathways for development of the porcine uterus and improvement of litter size.

Summary Sentence

Activation of FGFR1 and FGFR2 by uterine- and endometrial-derived FGF2 enhances uterine development for implantation and placentation and improvement of litter size.