Steroidogenesis and apoptosis in the mammalian ovary
Abraham Amsterdam∗ , Iris Keren-Tal, Dorit Aharoni, Ada Dantes, Abigail Land-Bracha, Eli Rimon, Ravid Sasson, Liron Hirsh
Department of Molecular Cell Biology, Weizmann Institute of Science, Rehovot 76100, Israel
Abstract Ovarian cell death is an essential process for the homeostasis of ovarian function inhuman and other mammalian species. It ensures the selection of the dominant follicle and the demise of excess follicles. In turn, this process minimizes the possibility of multiple embryo development during pregnancy and assures the development of few, but healthy embryos. Degeneration of the old corpora lutea in each estrous/menstrual cycle by programmed cell death is essential to maintain thenormal cyclicity of ovarian steroidogenesis. Although there are multiple pathways that can determine cell death or survival, crosstalk among endocrine, paracrine and autocrine factors, as well as among protooncogenes, tumor suppressor genes, survival genes and death genes, plays an important role in determining the fate of ovarian somatic and germ cells. The establishment of immortalized rat and humansteroidogenic granulosa cell lines and the investigation of pure populations of primary granulosa cells allows systematic studies of the mechanisms that control steroidogenesis and apoptosis in granulosa cells. We have discovered that during initial stages of granulosa cell apoptosis progesterone production does not decrease. In contrast, we found that it is elevated up to 24 h following the onsetof the apoptotic stimuli exerted by starvation, cAMP, p53 or TNF- stimulation, before total cell collapse. These observations raise the possibility for an alternative unique apoptotic pathway, one not involving mitochondrial Cyt C release associated with the destruction of mitochondrial structure and steroidogenic function. Using mRNA from apoptotic cells and affymetrix DNA microarray technologywe discovered that granzyme B, a protease that normally resides in T cytotoxic lymphocytes and natural killer cells of the immune system is expressed and activated in granulosa cells. Thus, the apoptotic signals could bypass mitochondrial signals for apoptosis, which can preserve their steroidogenic activity until complete cell destruction. This unique apoptotic pathway assures cyclicity ofestradiol and progesterone release in the estrous/menstruous cycle even during the initial stages of apoptosis. © 2003 Elsevier Inc. All rights reserved.
Keywords: Ovary; Granulosa cells; Granztme B
1. Introduction Ovarian cell death is a crucial event in maintaining ovarian homeostasis in mammals. It ensures that in every estrus/menstrous cycle only one or very few follicle-enclosed oocytes willreach the stage of a Graaﬁan follicle and will ovulate. This is essential in the prevention of multiple embryos during pregnancy. The rest of the follicles are gradually eliminated during the fertility period of the female. The apoptotic process of the old corpora lutea is essential for maintaining the cyclicity and the release of progesterone during the estrous/menstrous cycle (reviewed in [1–5]).There are several factors that may control apoptosis of granulosa cells. In each stage of the cycle about 50% of the large preantral and antral follicles will be in the process of apoptotic death . In most antral follicles apoptosis will initiate at inner layers of the membrana granulosa, border∗
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ing the follicle antrum (Fig. 1) Apoptosis is protected by the basement membrane which can sequester basic ﬁbroblastic growth factor (bFGF) where both laminin the main component of the basement membrane, and bFGF serve as survival factors [7,8]. Interestingly, laminin protects against apoptosis without affecting steroidogenesis while bFGF enhances formation...