Vasoinhibins are a family of peptides that act on endothelial cells to suppress angiogenesis and promote apoptosis-mediated vascular regression. Vasoinhibins include the N-terminal fragments from prolactin (PRL), GH, and placental lactogen. One of the vasoinhibins, the N-terminal PRL fragment of 16 kDa, is generated by the lysosomal representative protease cathepsin D (Cath D). Because the normal growth and involution of the mammary gland (MG) are profoundly affected by the expansion and regression of blood vessels and also because PRL stimulates the growth and differentiation of MG, we proposed that intact PRL produced during lactation contributes to MG angiogenesis and increased blood flow, whereas during involution, the N-terminal PRL fragment would have proapoptotic effects on mammary epithelial cells (MECs). Therefore, we investigated the production of the N-terminal PRL fragment and its direct effect on the MG. Mouse PRL (mPRL) was proteolytically cleaved by Cath D between amino acids 148 and 149. N-terminal PRL fragment and Cath D expression increased during MG involution. Furthermore, incubation of MG fragments and MCF7 with recombinant 16 kDa mPRL revealed a proapoptotic effect in MECs. Ectopic mPRL in MECs was cleaved to 16 kDa PRL by Cath D in the MG lysosomal fraction. The majority of PRL derived from pituitary gland was cleaved to 16 kDa PRL in culture medium. Therefore, N-terminal PRL fragment increases during the involution period, has a proapoptotic effect on MECs, and is mainly generated by secreted Cath D in the extracellular space of MG.
Michiyo Ishida, Midori Maehara, Tsukasa Watanabe, Yu Yanagisawa, Yukiko Takata, Ryojun Nakajima, Mika Suzuki and Toshio Harigaya
D J Tisdall, K Watanabe, N L Hudson, P Smith and K P McNatty
A key question in elucidating the role of FSH in ovarian function is to determine when during follicular growth the FSH receptor first appears. The aim of this study was to examine the site and time of FSH receptor gene expression during early follicular growth. This study was carried out on ovaries of adult sheep during the luteal and prostaglandin-induced follicular phase of the oestrous cycle and also on ovaries of fetal sheep at 90, 100, 120 and 135 days of gestation (term=day 147).
Using reverse transcription-PCR and a set of PCR primers spanning exons 8/9/10, two partial FSH receptor cDNAs (500 and 310 bp) were isolated from adult sheep ovary. It was shown by sequencing that exon 8 was deleted in the 310 bp cDNA, implying that this was part of an alternatively spliced FSH receptor transcript. Using RNA in situ hybridisation on ovaries of adult sheep, FSH receptor mRNA was observed in granulosa cells of early preantral follicles with one to two cell layers and it was seen that gene expression continued throughout folliculogenesis into advanced stages of atresia. Moreover, in the fetus, FSH receptor gene expression was detected in follicles with two or more layers of granulosa cells in ovaries taken at 100, 120 and 135 days of gestation.
These results suggest that the FSH receptor gene is expressed after the granulosa cells of a folllicle have begun to divide but not during the earliest stages of follicle growth, namely the transformation of a primordial follicle to a primary follicle.
XiaoFeng Li, Bei Shao, ChengCheng Lin, Kevin T O'Byrne and YuanShao Lin
Stress exerts profound inhibitory effects on reproductive function by suppression of the pulsatile release of GnRH and therefore LH. Besides the corticotrophin-releasing factor (CRF), this effect also might be mediated via GABAergic signaling within the arcuate nucleus (ARC) since its inhibitory effects on LH pulses and increased activity during stress. In the present study, we investigated the role of endogenous GABAergic signaling within the ARC in stress-induced suppression of LH pulses. Ovariectomised oestradiol-replaced rats were implanted with bilateral and unilateral cannulae targeting toward the ARC and lateral cerebral ventricle respectively. Blood samples (25 μl) were taken via chronically implanted cardiac catheters every 5 min for 6 h for measurement of LH pulses. Intra-ARC infusion of GABAA receptor antagonist, bicuculline (0.2 pmol in 200 nl artificial cerebrospinal fluid (aCSF) each side, three times at 20-min intervals) markedly attenuated the inhibitory effect of lipopolysaccharide (LPS; 25 μg/kg i.v.) but not restraint (1 h) stress on pulsatile LH secretion. In contrast, restraint but not LPS stress-induced suppression of LH pulse frequency was reversed by intra-ARC administration of GABABR antagonist, CGP-35348 (1.5 nmol in 200 nl aCSF each side, three times at 20-min intervals). Moreover, intra-ARC application of either bicuculline or CGP-35348 attenuated the inhibitory effect of CRF (1 nmol in 4 μl aCSF, i.c.v.) on the LH pulses. These data indicate a pivotal and differential role of endogenous GABAA and GABAB signaling mechanisms in the ARC with respect to mediating immunological and psychological stress-induced suppression of the GnRH pulse generator respectively.
C. Azuma, K. Miyai, F. Saji, S. Kamiura, Y. Tokugawa, T. Kimura, K. Ohashi, M. Koyama, Y. Iijima, T. Kashiwai, Y. Hayashizaki and O. Tanizawa
The heterodimeric glycoprotein hormones, human chorionic gonadotrophin (hCG), LH, TSH and FSH, consist of two non-covalently linked subunits, the α and β subunits. The β subunit is specific for each hormone and is responsible for the biological specificity, but the β subunits of different hormones show some degree of structural homology. The CAGY (cysteine-alanine-glycine-tyrosine) region is one of the amino acid sequences that is homologous in different β subunits and is highly conserved between species. In the present study, site-specific in-vitro mutagenesis was used to change three individual nucleotides in the centre of the CAGY region of the hCG-β subunit, and the effects of these mutations on hCG production was determined by in-vitro transcription and then translation in Xenopus laevis oocytes. The results indicate that the CAGY region, particularly the glycine residue at position 36 in the β subunit, is essential for the production of hCG. This finding is consistent with previous studies showing that this region is necessary for the biological activity of human TSH.
M Zhang, Y Tao, B Zhou, H Xie, F Wang, L Lei, L Huo, Q Sun and G Xia
Atrial natriuretic peptide (ANP) as well as its receptors is found in mammalian ovary and follicular cells and its function in oocyte meiotic maturation has also been reported in Xenopus, hamster and rat. But the results are controversial and the physiological mechanism of ANP on oocyte maturation is not clear, especially the relationship between gonadotrophin and ANP as well as the signal transduction, and these need further study. The present study conducted experiments to examine these questions by using drug treatment and Western blot analysis and focused on pig oocyte meiotic maturation and cumulus expansion in vitro. The results revealed that ANP could inhibited FSH-induced pig oocyte maturation and cumulus expansion and prevent the full phosphorylation of mitogen-activated protein kinase in both oocytes and cumulus cells, and that these inhibitory effects could be mimicked by 8-Br-cyclic guanosine 5′-monophosphate (8-Br-cGMP), but blocked by a protein kinase G (PKG) inhibitor KT5823. Zaprinast, a cGMP-specific phosphodiesterase inhibitor, could enhance the inhibitory effect of ANP on oocyte maturation. A specific analogue of ANP, C-ANP-(4–23), which binds to the natriuretic peptide receptor-C (NPRC), had no effect in either FSH-induced or spontaneous oocyte maturation. Treatment with forskolin, a stimulator of adenylate cyclase, had a biphasic effect; 44 h treatment induced cumulus expansion but inhibited oocyte maturation while 2 h treatment induced maturation of cumulus-enclosed oocytes (CEOs). Both ANP and C-ANP-(4–23) could inhibit the effect of forskolin on CEO maturation, and these inhibitory effects of ANP/C-ANP-(4–23) could be blocked by preincubation with pertussis toxin (PT), consistent with mediation by a Gi protein(s) in the cumulus cells. All these results suggest that ANP is a multifunctional regulator of FSH and forskolin on pig CEO maturation by two signalling mechanisms: one is via a cGMP/PKG pathway, the other is via NPRC receptors in cumulus cells and the activation of the PT-sensitive Gi protein(s).
J Quirk and P Brown
The homeobox repressor Hesx1, expressed throughout Rathke's pouch and required for normal pituitary development, has been implicated in anterior pituitary pathogenesis in man. Prolonged expression of Hesx1 delays the appearance of anterior pituitary terminal differentiation markers in mice, particularly the gonadotroph hormones. We tested if Hesx1 could modulate gonadotrophin gene expression directly, and found that Hesx1 repressed both common alpha subunit (alpha GSU) and luteinising hormone beta-subunit (LH beta) gene promoters. Repression mapped to the Pitx1 homeodomain protein transactivation site in the proximal alpha GSU promoter, but did not map to the equivalent site on LH beta. Hesx1 repression of the alpha GSU Pitx1 site was overridden by co-transfection of Pitx1. In contrast, Hesx1 antagonised Pitx1 transactivation of LH beta in a dose-dependent manner. This was due to monomeric binding of Hesx1 on alpha GSU and homodimerisation on LH beta. The homodimerisation site comprises the Pitx1 DNA binding site and a proximal binding site, and mutation of either inhibited homodimer formation. Conversion of the LH beta Pitx1 DNA binding site to an alpha GSU-type did not promote homodimer formation, arguing that Hesx1 has pronounced site selectivity. Furthermore, mutation of the proximal half of the homodimerisation site blocked Hesx1 antagonisation of Pitx1 transactivation. We conclude that Hesx1 monomers repress gene expression, and homodimers block specific transactivation sites.
HF Vischer, JC Granneman, MH Linskens, RW Schulz and J Bogerd
LH and FSH are heterodimeric glycoprotein hormones, composed of a common alpha-subunit non-covalently associated with a hormone-specific beta-subunit. Repeated efforts to isolate catfish FSH (cfFSH) have not been successful and only catfish LH (cfLH) has been purified from catfish pituitaries. Recently, however, we succeeded in cloning the cDNA encoding the putative cfFSHbeta; the cDNAs for the alpha- and beta-subunit of cfLH have been cloned before. Here we report the expression of biologically active cfLH and cfFSH in the soil amoeba, Dictyostelium discoideum. The biological activity of the recombinant hormones was analyzed using cell lines transiently expressing either the cfLH receptor or the cfFSH receptor. Moreover, a primary testis tIssue culture system served to study the steroidogenic potency of the recombinant hormones. Our results demonstrated that Dictyostelium produced biologically active, recombinant catfish gonadotropins, with recombinant cfLH being almost indistinguishable from its native counterpart, purified from pituitaries. Although recombinant cfFSH has significant effects in the bioassays used in this study, the specific function of native cfFSH in the control of reproduction and its expression patterns are not yet understood.
M. Corbani, R. Counis, E. Wolinska-Witort, G. d'Angelo-Bernard, M. Moumni and M. Jutisz
The effects of oestradiol and progesterone on LH-subunit mRNA levels were investigated in ovariectomized rats. Four weeks after ovariectomy, rats were implanted with silicone elastomer capsules containing oestradiol and/or injected daily with progesterone in oil (5 mg/rat) for 8 days. The levels of pituitary mRNA encoding α and LH-β were determined using direct hybridization with specific [32P]cDNA probes. After oestradiol implantation in ovariectomized rats, both α and LH-β mRNA decreased with time, with maximum inhibition after 6–8 days of treatment. Progesterone injected alone did not show any effect on α and LH-β mRNA. Cytosolic progesterone receptors, determined using [3H]methyl-17α-progesterone as ligand, were undectable in control ovariectomized rats. In contrast, 2 days after oestradiol implantation, the number of receptors increased to 287·5 ± 35·4 (s.e.m.) fmol/pituitary and reached a plateau of 400 ± 21·8 fmol/pituitary after 4 days. The effects of progesterone were therefore examined by first implanting ovariectomized rats with oestradiol to induce progesterone receptors and then injecting progesterone daily for a further period of 6 days. As a result of this treatment, progesterone induced a decrease in the pituitary gland contents of both α and LH-β mRNAs, and LH release was significantly greater than that observed in the group receiving oestradiol alone. Moreover, the mRNA levels in the animals treated with oestradiol plus progesterone were lower after 8 days of treatment than those observed in ovariectomized rats treated with a tenfold higher dose of oestradiol alone.
These data demonstrate that progesterone, together with oestradiol, is capable of negatively regulating the mRNAs encoding subunits in vivo, provided that progesterone receptors are present in the pituitary gland.
HF Vischer and J Bogerd
A cDNA encoding a putative thyroid-stimulating hormone receptor (cfTSH-R) was cloned from the testis of the African catfish (Clarias gariepinus). The cfTSH-R showed the highest amino acid sequence identity with the TSH-Rs of other fish species. In addition, an insertion of approximately 50 amino acids, specific for the TSH-R subfamily, was also present in the carboxy terminus of the amino-terminal extracellular domain of the cfTSH-R. Next to the testis and thyroid follicles, abundant cfTSH-R expression was detected in cerebellum, brain, ovary, seminal vesicles and pituitary, while weaker expression was found in muscle, stomach, intestine, head-kidney, liver, kidney and heart. HEK-T 293 cells, transiently expressing the cfTSH-R, significantly increased intracellular cAMP levels in response to human TSH. Catfish LH, human choriogonadotropin and human FSH were also able to induce this cfTSH-R-mediated response, although with considerably lower efficiency than human TSH. These results indicated that a functional cfTSH-R had been cloned from the testis of African catfish.
Zhengjie Yan, Youjin Dai, Heling Fu, Yuan Zheng, Dan Bao, Yuan Yin, Qin Chen, Xiaowei Nie, Qingting Hao, Daorong Hou and Yugui Cui
This study was designed to investigate the protective effect of curcumin against d-galactose (d-gal)-induced premature ovarian failure (POF) in mice. A mouse POF model was induced by subcutaneous injection of d-gal (200 mg/kg/day) daily for 42 days. Mice in the curcumin group received both d-gal treatment and intraperitoneal injection of curcumin (100 mg/kg/day) for 42 days. Ovarian function, oxidative stress and apoptosis were evaluated. The P, E2 and SOD levels were higher, and the FSH, LH and MDA levels were significantly lower in the curcumin group than those in the d-gal group. The proportion of primordial follicles was also significantly higher in the curcumin group than that in the d-gal group. In addition, curcumin treatment after d-gal administration resulted in significantly lower Sod2, Cat, 8-OhdG, 4-HNE, NTY and senescence-associated protein P16 expression levels, higher Amh expression levels and less apoptosis in granulosa cells than was observed in the d-gal group. Moreover, the p-Akt, Nrf2 and HO-1 protein expression levels were significantly higher and the apoptosis-related cleaved caspase-3 and -9 protein expression levels were markedly lower in the curcumin group than in the d-gal group. In conclusion, curcumin effectively inhibited d-gal-induced oxidative stress, apoptosis and ovarian injury via a mechanism involving the Nrf2/HO-1 and PI3K/Akt signaling pathways, suggesting that curcumin is a potential protective agent against POF.