Since 1995, discovered mammalian STC 1, several studies have been aimed to unravel the biological significance of this hormone in mammals.Analyses of STC 1 gene expression showed that, at least in the mouse, the ovary displays the highest levels of STC 1 mRNA . This observation would suggest a potential involvement of STC 1 in regulating ovarian function. To the best of our knowledge, the present study identifies STC 1 in swine ovary for the first time. In particular, we have demonstrated that STC 1 protein is present in swine ovarian follicles, is present in follicular fluid and is produced by granulosa cells.As for gene expression, transcription was detected in the theca layer from antral follicles. This is in agreement with the findings inthe mouse, rat and bovine.Moreover, our data showed that STC 1 expression in theca layer cells decrease during follicle growth. In addition, our experiments showed that STC 1 is also expressed in granulosa cells, with an increasing trend during follicular development. This result is surprising as STC 1 expression in the mouse, rat and bovine ovary has been reported to be confined to theca-interstitial cells, with no apparent expression elsewhere . At the moment, there is no information concerning STC 1 expression in granulosa cells in other mammalian species. In particular, as shown in the mouse our study showed that STC 1 protein is strongly concentrated and its gene is also expressed in the swine oocyte. These findings are partly in contrast with the sequestering hypothesis formulated in the kidney by whereby STC 1 appeared to be synthesized and released by one cell type and heavily sequestered by its target cells. This hypothesis was further reinforced by the findings obtained in the ovary
and in the developing mouse embryo and it was assumed that the process was receptormediated.
However, the underlying purpose for the sequestering has not been
clarified yet.These data, along with the evidence of STC 1 presence in swine follicular fluid, lead us to suppose that STC 1 may be involved in different aspects of ovarian follicle maturation. The exact role of STC 1 in ovarian dynamics is still mostly unknown, even if experimental evidence suggest its involvement in the regulation of follicular development (Luo et al., 2004). Since lipid and cholesterol storage droplets represent preferential subcellular targets of STC
1 a modulation of the steroidogenetic pathway by this hormone could be assumed (Baioni et al., 2009).Interestingly, earlier experimental data have also demonstrated a role of STC 1 in the angiogenic process.Therefore, the presence of STC 1 in the ovarian follicle in this
context may be relevant, since neovascularization is closely associated with oocyte growth and development . In particular, we have previously demonstrated that, among the various triggers of angiogenesis, low oxygen tension appears as a particularly important stimulus . The present data demonstrate that STC 1 secretion by granulosa cells is increased by oxygen deprivation. Moreover, severalauthors have demonstrated that the activation of STC 1 expression is increased in cells
exposed to hypoxic stress. These results are therefore suggestive of a potential role for STC 1 in ovarian follicle physiology where progressive hypoxia is established during follicle growth.
Further studies are in due course in our laboratory to get an insight on the physiological significance of STC 1 in swine ovarian follicle.
Since 1995, discovered mammalian STC 1, several studies have been aimed to unravel the biological significance of this hormone in mammals.Analyses of STC 1 gene expression showed that, at least in the mouse, the ovary displays the highest levels of STC 1 mRNA . This observation would suggest a potential involvement of STC 1 in regulating ovarian function. To the best of our knowledge, the present study identifies STC 1 in swine ovary for the first time. In particular, we have demonstrated that STC 1 protein is present in swine ovarian follicles, is present in follicular fluid and is produced by granulosa cells.As for gene expression, transcription was detected in the theca layer from antral follicles. This is in agreement with the findings inthe mouse, rat and bovine.Moreover, our data showed that STC 1 expression in theca layer cells decrease during follicle growth. In addition, our experiments showed that STC 1 is also expressed in granulosa cells, with an increasing trend during follicular development. This result is surprising as STC 1 expression in the mouse, rat and bovine ovary has been reported to be confined to theca-interstitial cells, with no apparent expression elsewhere . At the moment, there is no information concerning STC 1 expression in granulosa cells in other mammalian species. In particular, as shown in the mouse our study showed that STC 1 protein is strongly concentrated and its gene is also expressed in the swine oocyte. These findings are partly in contrast with the sequestering hypothesis formulated in the kidney by whereby STC 1 appeared to be synthesized and released by one cell type and heavily sequestered by its target cells. This hypothesis was further reinforced by the findings obtained in the ovary and in the developing mouse embryo and it was assumed that the process was receptormediated. However, the underlying purpose for the sequestering has not beenclarified yet.These data, along with the evidence of STC 1 presence in swine follicular fluid, lead us to suppose that STC 1 may be involved in different aspects of ovarian follicle maturation. The exact role of STC 1 in ovarian dynamics is still mostly unknown, even if experimental evidence suggest its involvement in the regulation of follicular development (Luo et al., 2004). Since lipid and cholesterol storage droplets represent preferential subcellular targets of STC1 a modulation of the steroidogenetic pathway by this hormone could be assumed (Baioni et al., 2009).Interestingly, earlier experimental data have also demonstrated a role of STC 1 in the angiogenic process.Therefore, the presence of STC 1 in the ovarian follicle in thiscontext may be relevant, since neovascularization is closely associated with oocyte growth and development . In particular, we have previously demonstrated that, among the various triggers of angiogenesis, low oxygen tension appears as a particularly important stimulus . The present data demonstrate that STC 1 secretion by granulosa cells is increased by oxygen deprivation. Moreover, severalauthors have demonstrated that the activation of STC 1 expression is increased in cellsexposed to hypoxic stress. These results are therefore suggestive of a potential role for STC 1 in ovarian follicle physiology where progressive hypoxia is established during follicle growth. Further studies are in due course in our laboratory to get an insight on the physiological significance of STC 1 in swine ovarian follicle.
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