Effect of insulin-like growth factor system on luteinising angiogenesis

Abstract

Preovulatory follicle growth and the luteal transition require intense angiogenesis. This enables progesterone production to increase sufficiently to support a pregnancy. Inadequate follicular or luteal vascularisation can lead to reduced ovarian function and thus compromise fertility. Insulin-like growth factor 1 (IGF1) and IGF2 regulate multiple ovarian processes and are key links between an animal’s reproductive and metabolic status. This study investigated the role that the IGF system plays in regulating luteinising follicular endothelial cell (EC) networks and progesterone production in vitro. Bovine luteinising follicular angiogenesis cultures were treated with (i) LR3-IGF1 (10 or 100 ng/mL) under basal and angiogenic-stimulated conditions or (ii) IGF1 receptor (IGF1R) inhibitor (picropodophyllin (PPP); 1 µM) in the presence or absence of LR3-IGF1, IGF2 or combined LR3-IGF1 + IGF2 (10 ng/mL). EC networks were quantified by von Willebrand factor immunohistochemistry. Progesterone production was analysed by ELISA, and cell proliferation was determined by MTT assay. LR3-IGF1 had limited effects on EC growth parameters, whilst PPP (P < 0.001) markedly reduced EC growth parameters (by 60–70%). Cell proliferation was slightly increased (by 3–5%) by LR3-IGF1 (P < 0.001). LR3-IGF1 had variable effects on progesterone production, whilst PPP reduced progesterone concentration (P < 0.001) with or without LR3-IGF1 or IGF2 alone or in combination. IGF1 was detected in cell-conditioned media and was increased by LH (50 ng/mL) (P < 0.001). In conclusion, exogenous IGF1 and IGF2 had minimal effects on luteinising follicular angiogenesis and progesterone production, but the inhibitory effect of the IGF1R inhibitor (PPP) suggests that IGF1R signalling is critical for the development of EC networks and progesterone production in luteinising follicular cells. Lay summary The corpus luteum is a part of the ovary responsible for producing the critical pregnancy hormone, progesterone. To fulfil this function, the corpus luteum requires an extensive blood vessel network. Here, we investigated whether an important growth factor known to act on the ovary, insulin like growth factor (IGF) 1, critically regulates the formation of this blood vessel network and progesterone production. Cells from the corpus luteum were cultured with combinations of IGF1, a closely related hormone IGF2 and a chemical which stops both IGF1 and IGF2 from working. Afterwards, we measured the size and pattern of blood vessel networks, the production of progesterone and whether cells increased in number. We found adding IGF1 had limited effects, however stopping IGF1 from working had a very negative impact on both progesterone and on the formation of the blood vessel network. This suggests that cells from the corpus luteum were producing IGF1 and that IGF1/2 are critical for both blood vessel growth and hormone production.