IGF-1 Inhibits Apoptosis of Porcine Primary Granulosa Cell by Targeting Degradation of BimEL.

Ying Han,Shumin Wang,Shenming Zeng,Yingzheng Wang

doi:10.3390/ijms20215356

Abstract

Insulin-like growth factor-1 (IGF-1) is an intra-ovarian growth factor that plays important endocrine or paracrine roles during ovarian development. IGF-1 affects ovarian function and female fertility through reducing apoptosis of granulosa cells, yet the underlying mechanism remains poorly characterized. Here, we aimed to address these knowledge gaps using porcine primary granulosa cells and examining the anti-apoptotic mechanisms of IGF-1. IGF-1 prevented the granulosa cell from apoptosis, as shown by TUNEL and Annexin V/PI detection, and gained the anti-apoptotic index, the ratio of Bcl-2/Bax. This process was partly mediated by reducing the pro-apoptotic BimEL (Bcl-2 Interacting Mediator of Cell Death-Extra Long) protein level. Western blotting showed that IGF-1 promoted BimEL phosphorylation through activating p-ERK1/2, and that the proteasome system was responsible for degradation of phosphorylated BimEL. Meanwhile, IGF-1 enhanced the Beclin1 level and the rate of LC3 II/LC3 I, indicating that autophagy was induced by IGF-1. By blocking the proteolysis processes of both proteasome and autophagy flux with MG132 and chloroquine, respectively, the BimEL did not reduce and the phosphorylated BimEL protein accumulated, thereby indicating that both proteasome and autophagy pathways were involved in the degradation of BimEL stimulated by IGF-1. In conclusion, IGF-1 inhibited porcine primary granulosa cell apoptosis via degradation of pro-apoptotic BimEL. This study is critical for us to further understand the mechanisms of follicular survival and atresia regulated by IGF-1. Moreover, it provides a direction for the treatment of infertility caused by ovarian dysplasia, such as polycystic ovary syndrome and the improvement of assisted reproductive technology.

Highlights

The insulin-like growth factor (IGF) system includes IGFs, IGF receptors, and multiple binding proteins [1]
Granulosa cells experienced increased apoptosis signals in the untreated group, while Insulin-like growth factor-1 (IGF-1) treatment significantly reduced the percentage of apoptotic cells, as revealed by the TUNEL assay (Figure 1A)
The results suggested that autophagy, an important cellular hydrolytic process, was induced by IGF-1

Summary

Introduction

The insulin-like growth factor (IGF) system includes IGFs, IGF receptors, and multiple binding proteins [1]. IGF-1 exerts multiple physiologic effects on the systemic vasculature through endocrine, autocrine or paracrine mechanisms [2]. Many studies have reported that IGF-1 widely exists in mammalian ovarian tissues and is indispensable to follicle growth [3,4,5]. On the contrary, when the second dominant follicle, destined to be atresia, was injected with bioactive IGF-1, it became dominant and eventually showed ovulation in mares [7]. Only a small fraction of mammalian ovarian follicles can ovulate while the vast majority are destined to undergo atresia [8].

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Conclusion