Fibroblast Growth Factor 2 Induces the Precocious Development of Endothelial Cell Networks in Bovine Luteinising Follicular Cells

The transition from follicle to corpus luteum represents a period of intense angiogenesis; however, the exact roles of angiogenic factors during this time remain to be elucidated. Thus, the roles of vascular endothelial growth factor (VEGF) A, fibroblast growth factor (FGF) 2 and LH in controlling angiogenesis were examined in the present study. A novel serum-free luteinising follicular angiogenesis culture system was developed in which progesterone production increased during the first 5 days and was increased by LH (P<0.01). Blockade of signalling from FGF receptors (SU5402; P<0.001) and, to a lesser extent, VEGF receptors (SU1498; P<0.001) decreased the development of endothelial cell (EC) networks. Conversely, FGF2 dose-dependently (P<0.001) induced the precocious transition of undeveloped EC islands into branched networks associated with a twofold increase in the number of branch points (P<0.001). In contrast, VEGFA had no effect on the area of EC networks or the number of branch points. LH had no effect on the area of EC networks, but it marginally increased the number of branch points (P<0.05) and FGF2 production (P<0.001). Surprisingly, progesterone production was decreased by FGF2 (P<0.01) but only on Day 5 of culture. Progesterone production was increased by SU5402 (P<0.001) and decreased by SU1498 (P<0.001). These results demonstrate that FGF and VEGF receptors play a fundamental role in the formation of luteal EC networks in vitro, which includes a novel role for FGF2 in induction of EC sprouting.