Insulin-Like Growth Factor Binding Proteins and IGFBP Proteases: A Dynamic System Regulating the Ovarian Folliculogenesis. Mazerbourg S et al. (2018) The aim of the present article is to update our understanding of the expression of the insulin-like growth factor binding proteins (IGFBPs), IGFBP proteases and their implication in the different processes of ovarian folliculogenesis in mammals. In the studied species, IGFs and several small-molecular weight IGFBPs (in particular IGFBP-2 and IGFBP-4) are considered, respectively, as stimulators and inhibitors of follicular growth and maturation. IGFs play a key role in sensitizing ovarian granulosa cells to FSH action during terminal follicular growth. Concentrations of IGFBP-2 and IGFBP-4 in follicular fluid strongly decrease during follicular growth, leading to an increase in IGF bioavailability. Inversely, atresia is characterized by an increase of IGFBP-2 and IGFBP-4 levels, leading to a decrease in IGF bioavailability. Changes in intrafollicular IGFBPs content are due to variations in mRNA expression and/or proteolytic degradation by the pregnancy-associated plasma protein-A (PAPP-A), and likely participates in the selection of dominant follicles. The identification of PAPP-A2, as an IGFBP-3 and -5 protease, and stanniocalcins (STCs) as inhibitors of PAPP-A activity extends the IGF system. Studies on their implication in folliculogenesis in mammals are still in the early stages.//////////////////
NCBI Summary:
The protein encoded by this gene is one of six similar proteins that bind insulin-like growth factors I and II (IGF-I and IGF-II). The encoded protein can be secreted into the bloodstream, where it binds IGF-I and IGF-II with high affinity, or it can remain intracellular, interacting with many different ligands. High expression levels of this protein promote the growth of several types of tumors and may be predictive of the chances of recovery of the patient. Several transcript variants, one encoding a secreted isoform and the others encoding nonsecreted isoforms, have been found for this gene. [provided by RefSeq, Sep 2015]
General function
Extracellular binding protein
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Cellular localization
Secreted
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Regulation of insulin-like growth factor binding protein secretion by human granulosa luteal cells in a polycystic ovary-like environment. Greisen S et al. (2002) To determine the effect of androstenedione (A), insulin, and LH on secretion of insulin-like growth factor binding proteins (IGFBPs) from human granulosa luteal cells. Human granulosa cells were cultured for a total of 4 days in serum-free medium containing A (10(-6) mol/L), with or without insulin (100 microU/mL-800 microU/mL), LH (1 microU/mL-10 microg/L), and A (10(-5) mol/L). Granulosa cells were obtained from IVF procedures. Women undergoing IVF for tubal disease. None. Immunoassay and autoradiographs of Western ligand blotting detected IGFBP accumulations in the medium. Cultured granulosa cells secreted IGFBP-1 through IGFBP-4. Insulin (100 microU/mL-800 microU/mL), LH (1 microg/L-10 microg/L), and A (10(-5) mol/L) caused a significant decrease in IGFBP-1 accumulation in the medium both alone and when added in combination. The release of IGFBP-2 and IGFBP-4 was significantly stimulated by insulin, whereas LH had no effect. Elevated levels of androgen (10(-5) mol/L) significantly stimulated the secretion of IGFBP-2, whereas the release of IGFBP-4 was reduced. These results demonstrate that androgen and insulin are important regulators of IGFBP release and that elevated levels of the two hormones may contribute to the altered IGFBP profile found in PCOS follicles, compared with the case of estrogen-dominant follicles.//////////////////
Ovarian function
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Influence of insulin-like growth factor-binding proteins-2 and -3 in the pathogenesis of cystic ovarian disease in cattle. Rodr?ez FM et al. Ovarian cysts are one of the major causes of infertility in dairy cows. The development is associated with an endocrine imbalance in the hypothalamo-hypophyseal-gonadal axis in which endocrine factors participate in follicular growth and differentiation and in the secretion of ovarian hormones. Insulin-like growth factor family are essential local regulators of ovarian follicle development and functionality and actions are mediated by binding protein activity. The aim of the present study was to analyze the expression of IGFBP-2 and IGFBP-3 in developing follicles of normal estrous cycling animals and with spontaneous and induced cystic ovarian disease (COD) to determine IGF bioavailability. The mRNA of IGFBP-2 and IGFBP-3 in follicular walls was quantified by reverse transcription-polymerase chain reaction (RT-PCR) and in situ hybridization. Protein expression was analyzed by immunohistochemistry. The results demonstrated reduced amounts of mRNA of both IGFBPs in the granulosa cells of ovarian follicles of animals with COD (P<0.05). The present study suggests that the IGF system or imbalances between IGFs and IGFBPs may be involved in COD of cattle.
Expression regulated by
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Ovarian localization
Oocyte, Granulosa, Surface epithelium
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Arraztoa JA, et al 2002
analyzed IGFBP mRNA expression patterns in ovaries from mid-cycle rhesus monkeys using in situ hybridization. IGFBP-1 mRNA was concentrated in theca-interstitial cells and was present at low levels in granulosa cells of atretic follicles. IGFBP-2 mRNA was expressed in the ovarian surface epithelium and granulosa cells of all antral follicles, including obviously atretic as well as dominant follicles. IGFBP-3 mRNA was localized in oocytes and in the ovarian vascular endothelium; this mRNA was also concentrated in the superficial cortical stroma in which it was distinctly more abundant in the nondominant ovary. Granulosa cells of mature dominant and ovulatory follicles selectively expressed IGFBP-5 mRNA. IGFBP-5 mRNA was also widely expressed in the ovarian stroma, in which, in contrast to IGFBP-3, it was distinctly more abundant in dominant, compared with nondominant, ovary. IGFBP-6 mRNA was present at low levels in the ovary interstitium and theca externa and was more abundant in the ovary surface epithelium. These novel data reveal distinctive cellular expression patterns for IGFBPs 1, 2, 3, 5, and 6 in the nonhuman primate ovary, suggesting distinct roles for each binding protein in ovarian function.
Follicle stages
Antral
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Genomewide discovery and classification of candidate ovarian fertility genes in the mouse. Gallardo TD et al. Female infertility syndromes are among the most prevalent chronic health disorders in women, but their genetic basis remains unknown because of uncertainty regarding the number and identity of ovarian factors controlling the assembly, preservation, and maturation of ovarian follicles. To systematically discover ovarian fertility genes en masse, we employed a mouse model (Foxo3) in which follicles are assembled normally but then undergo synchronous activation. We developed a microarray-based approach for the systematic discovery of tissue-specific genes and, by applying it to Foxo3 ovaries and other samples, defined a surprisingly large set of ovarian factors (n = 348, approximately 1% of the mouse genome). This set included the vast majority of known ovarian factors, 44% of which when mutated produce female sterility phenotypes, but most were novel. Comparative profiling of other tissues, including microdissected oocytes and somatic cells, revealed distinct gene classes and provided new insights into oogenesis and ovarian function, demonstrating the utility of our approach for tissue-specific gene discovery. This study will thus facilitate comprehensive analyses of follicle development, ovarian function, and female infertility. This is an oocyte-specific gene.