Knockdown of CREB1 promotes apoptosis and decreases estradiol synthesis in mouse granulosa cells

Cyclic AMP response element-binding protein 1 (CREB1), a member of the CREB family, is known to be involved in follicular growth, ovulation, and ovarian disease. However, the physiological function of CREB1 in mouse granulosa cells (mGCs) remains lagerly unknown. The aim of this study was to determine the role of CREB1 in mGCs by knocking down CREB1 expression. CREB1 knock-down in mGCs at the mRNA and protein levels, was confirmed by quantitative real-time polymerase chain reaction and western blot. Results of enzyme linked immunosorbent assay revealed that CREB1 knockdown significantly decreased the concentrations of estradiol (E2) and progesterone (P4) in mGCs. Furthermore, the CREB1 knockdown in mGCs promoted cell proliferation and apoptosis, and arrested the cell cycle in S-phase. To elucidate the regulatory mechanism underlying the effects of CREB1 knockdown on steroid synthesis, cell cycle, and apoptosis, we measured the protein expression levels of several related genes in mGCs knocked down CREB1. When CREB1 was knocked down, the expression of Cyp1b1 and Cyp19a1, which encode steroidogenic enzymes, was down-regulated; the expression of the cell cycle factors CyclinA1, CyclinB1, and CyclinD2 were significantly decreased. Among apoptosis-related genes, Bcl-2 was down-regulated, whereas Bax and cleaved Caspase3 were upregulated. Moreover, CREB1 knockdown significantly decreased expression level of Has2, Ptgs2, and Igfbp4, which are essential genes for folliculogenesis in mGCs. Taken together, these findings suggested that CREB1 might be a key regulator of mGCs through regulating steroid synthesis, cell proliferation, cell cycle, apoptosis, and other regulators of folliculogenesis.

The regulated expression of the pregnancy-associated plasma protein-A in the rodent ovary: a proposed role in the development of dominant follicles and of corpora lutea

Compelling evidence exists displaying that the intrafollicular IGF-I system constitutes an obligatory mediator of FSH action in the murine ovary. Within this system, the ovarian IGF binding protein-4-directed protease (IGFBP-4ase) may have a critical role. Human IGFBP-4ase has been proved identical to the previously well-characterized pregnancy-associated plasma protein-A (PAPP-A). This communication reports the cloning and sequencing of the mouse PAPP-A cDNA as well as its expression and cellular localization in the mouse ovary. PAPP-A mRNA was undetectable in ovaries of untreated immature 25-d-old mice. Treatment with PMSG led to a marked time-dependent increase in PAPP-A expression in well-defined subsets of granulosa cells and follicles. Specifically, PAPP-A expression was detectable exclusively in centrifugally residing membrana granulosa cells of antral follicles during a 3- to 36-h period post PMSG. PAPP-A expression then fell to nondetectable levels in dominant preovulatory follicles at 48 h post PMSG. Treatment of PMSG-primed mice with human CG caused a rapid reinduction of PAPP-A expression in granulosa cells of dominant follicles and was sustained at relatively high levels throughout the ovulation and luteinization. These results suggest a role for gonadotropin-stimulated PAPP-A gene expression in the physiologic processes of dominant follicle development, ovulation, and luteogenesis in the mammalian ovary. The early onset and extended duration of gonadotropin-dependent PAPP-A expression in granulosa cells may serve to degrade the antigonadotropin IGFBP-4. Accordingly, successful antral follicle development, ovulation, and corpus luteum formation may be contingent on an IGFBP-4-deplete/PAPP-A-replete circumstance, hence resulting in an IGF-I-replete intrafollicular microenvironment.

IGF-binding protein-4 expression and IGF-binding protein-4 protease activity are regulated coordinately in smooth muscle during postnatal development and after vascular injury

Recent studies support a critical role for the paracrine IGF/IGF-binding protein system in the regulation of vascular smooth muscle cell growth. In this study we have explored the hypothesis that the abundance of individual IGF-binding proteins in smooth muscle is subject to regulation during postnatal life and in response to injury. IGF-binding protein-2 was the predominant binding protein secreted by neonatal rat vascular smooth muscle cells, whereas IGF-binding protein-4 was most prevalent in adult vascular smooth muscle cells coincident with increased IGF-binding protein-4 protease activity. After arterial injury, IGF-binding protein-4 mRNA increased, associated with greater IGF-binding protein-4 proteolytic activity, resulting in stable steady state levels of the IGF-binding protein-4 protein. Expression of pregnancy-associated plasma protein A mRNA, recently identified as an IGF-binding protein-4 protease, was expressed at higher levels in adult than neonatal vascular smooth muscle cell lines, but did not change significantly after arterial injury. The peak of immunoreactive pregnancy-associated plasma protein A from hydrophobic interaction chromatography fractions of smooth muscle cell-conditioned medium coincided, but did not fully overlap, with the fractions containing maximal IGF-binding protein-4 protease activity. In conclusion, our data point to a developmental switch from IGF-binding protein-2 to IGF-binding protein-4 in vascular smooth muscle cells postnatally. Moreover, IGF-binding protein-4 expression is coregulated with IGF-binding protein-4 protease activity, suggesting that biosynthesis and degradation of this binding protein are coordinated events important for regulating biological activity of IGF-I.

Transcriptional and posttranscriptional regulation of intraovarian insulin-like growth factor-binding proteins by interleukin-1beta (IL-1beta): evidence for IL-1beta as an antiatretic principal

Intraovarian interleukin-1 (IL-1), a putative intermediary in the ovulatory cascade, has recently been implicated as an antiatretic agent. Given the reported antigonadotropic and thus atretogenic potential of granulosa cell-derived insulin-like growth factor-binding proteins (IGFBPs), we evaluated the ability of IL-1beta to regulate ovarian IGFBP-4 and -5, the IGFBP species elaborated by the rat granulosa cell. Treatment of whole ovarian dispersates of immature rat origin with increasing concentrations of IL-1beta for 96 h resulted in substantial and significant time-dependent inhibition of IGFBP-4 and IGFBP-5 transcripts compared with that in untreated controls. The IL-1 effect proved relatively specific in that no significant alterations in IGFBP transcripts were observed in the presence of select ovarian agonists, including transforming growth factor-alpha, tumor necrosis factor-alpha, endothelin-1, hepatocyte growth factor, keratinocyte growth factor, or basic fibroblast growth factor. The inhibitory effect of IL-1beta on ovarian IGFBP-4 and -5 expression was almost completely reversed in the presence of IL-1 receptor antagonist, suggesting mediation via a specific IL-1 receptor. The addition of actinomycin D to IL-1beta-pretreated whole ovarian dispersates produced a pattern of (IGFBP-4 and -5) messenger RNA decay indistinguishable from that noted for the untreated control group. Medium conditioned by IL-1beta-treated (but not untreated) whole ovarian dispersates displayed a marked diminution in the relative content of the IGFBP-4 and IGFBP-5 proteins (24- and 28- to 29-kDa proteins, respectively). Medium conditioned by IL-1beta-treated (but not untreated) whole ovarian dispersates proteolyzed [125I]IGFBP-5 (but not IGFBP-4) into fragments with apparent molecular masses of 18 and 14 kDa, respectively. In conclusion, our present observations demonstrate the ability of IL-1 to 1) inhibit the steady state levels of transcripts corresponding to IGFBP-4 and -5 in a time-dependent, relatively specific, and receptor-mediated fashion; 2) suppress the accumulation of the corresponding IGFBP proteins; and 3) stimulate the activity of the IGFBP-5-directed (but not IGFBP-4) endopeptidase, a posttranscriptional phenomenon. Our findings also suggest, by inference, that the IL-1beta-mediated inhibition of IGFBP-4 and -5 transcripts is due in part to a decrease in the rate of transcription of the corresponding genes and not to a change in the stability of the relevant messenger RNAs. Consequently, the ability of IL-1 to influence ovarian IGFBP economy appears multifaceted, comprising both transcriptional and posttranscriptional effects. To the extent that IGFBP-4 and -5 constitute atretogenic agents, our present findings support the view that IL-1beta may play an antiatretic role in the context of ovarian physiology.

Expression of mouse ovarian insulin growth factor system components during follicular development and atresia

Insulin growth factor I (IGF-I) appears necessary for the completion of follicular development in mice. However, little is known about changes in the IGF system components during follicular development and luteinization. This study determined the relation between gene expression of specific IGF system components and follicular growth, survival, or atresia in mice. Immature mice from three different strains (129, C57, and MF1), with or without gonadotropin treatment (2.5 IU PMSG/2.5 IU human CG (hCG)], were used. The strains were similar in all parameters measured. Apoptosis, as detected by in situ labeling of nicked DNA, preceded the appearance of morphological signs of atresia. In healthy follicles, IGF-I transcripts were low during the primary follicular stage but increased to a maximum in the late preantral and early antral stages (P < 0.001) irrespective of hormone treatment. Occasionally, IGF-I transcripts were also detected in apoptotic follicles but decreased (P < 0.05) as a function of atresia as assessed by morphological criteria. IGF binding protein-4 (IGFBP-4) messenger RNA (mRNA) expression in granulosa cells was restricted to apoptotic and atretic follicles (P < 0.001). IGFBP-5 transcript levels, on the other hand, were elevated in granulosa cells of healthy primary and secondary follicles but decreased in subsequent follicular stages and in atretic follicles (P < 0.001). Conversely, IGFBP-2 mRNA was constitutively expressed in granulosa cells. PMSG/hCG treatment induced the appearance of IGFBP-2 transcripts in the ovarian interstitium. Following PMSG/hCG-induced ovulation, IGFBP-2 and -4 and IGF type-I receptor mRNAs were strongly expressed in virtually all luteal cells, whereas IGFBP-3 and -5 transcripts were selectively localized to some cell types in the corpus luteum. Conversely, IGF-I mRNA was essentially undetectable in the corpus luteum. This study represents the most comprehensive and detailed analysis of the physiology and anatomy of the mouse ovarian IGF system, and shows that 1) IGFBP-5-is linked to the survival of the slow growing and immature preantral follicles; 2) IGF-I is associated with the growth and survival of the rapidly growing large preantral and antral follicles; 3) IGFBP-4 is an atretogenic candidate for mouse ovarian follicles; 4) ovulatory doses of PMSG/hCG up-regulate IGFBP-2 mRNA expression in the ovarian interstitium; and 5) transcripts of IGF type-I receptor and IGFBP-2 through -5, but not those of IGF-I are highly expressed in the mouse corpus luteum.