Link protein as an enhancer of cumulus cell-oocyte complex expansion

Recombinant human follicle-stimulating hormone and transforming growth factor-alpha enhance in vitro maturation of porcine oocytes

The biological functions of recombinant human follicle-stimulating hormone (FSH) and transforming growth factor-α (TGF-α) on in vitro maturation of porcine oocytes were investigated. Cumulus-oocyte complexes were matured in defined porcine oocyte medium containing 0-0.1 IU/ml FSH in the presence or absence of 10 ng/ml TGF-α. The percentage of oocytes reaching metaphase II was significantly higher with the addition of 0.01-0.1 IU/ml FSH compared with no addition, and was further enhanced in the presence of TGF-α. The rates of sperm penetration and blastocyst formation were significantly higher with the addition of 0.05-0.1 IU/ml FSH compared with no addition after in vitro fertilization and embryo culture. There was no beneficial effect of FSH and TGF-α on nuclear maturation of denuded oocytes. The specific EGF receptor inhibitor, AG1478, completely inhibited TGF-α-induced meiotic resumption, but did not completely prevent the stimulatory effect of FSH. Addition of both FSH and TGF-α significantly enhanced cumulus expansion compared with no addition. When cumulus expansion-related genes (HAS2, HAPLN1, and VCAN) mRNA expression in COCs was measured during in vitro maturaiton, addition of both of FSH and TGF-α upregulated the expression of HAS2 mRNA after 20 hr culture and HAPLN1 mRNA after 44 hr culture compared with no addition. Expression of VCAN mRNA was significantly higher in the presence of FSH compared with addition of TGF-α alone. These results suggest that FSH and TGF-α synergistically enhance porcine oocyte maturation via cumulus cells, and act through different signaling pathways.

Detection of RUNX2 gene expression in cumulus cells in women undergoing controlled ovarian stimulation

BACKGROUND

RUNX2 is a transcription factor, whose expression has been recently identified in the mouse ovary. Regulation of RUNX2 expression and its function in the human ovary have not been determined yet. The aim of the present study is the investigation of the possible correlation between RUNX2 gene expression in cumulus cells and controlled ovarian stimulation and pregnancy outcomes after ART treatment.

METHODS

A total of 41 patients undergoing ICSI treatment for male factor infertility were enrolled into a specific ART program, during which cumulus cells were collected. The expression of RUNX2 gene in cumulus cells was examined by real-time PCR.

RESULTS

Concerning RUNX2 gene expression, 12 out of 41 women were detected with RUNX2 expression, with ratios ranging from 0.84 to 1.00, while 28 out of 41 women had no expression (ratio = 0). Only 1 woman presented a weak RUNX2 gene expression (ratio = 0.52). From 8 women that proceeded to pregnancy, 7 of them did not express RUNX2 gene in cumulus cells, while one was the woman with weak gene expression that also achieved pregnancy. The group of women without RUNX2 expression presented higher number of follicles (p = 0.013), higher number of retrieved oocytes (p = 0.016), higher basal LH serum levels (p = 0.016) and higher peak estradiol levels (p = 0.013), while the number of fertilized oocytes differed marginally between the two groups (p = 0.089). Moreover, RUNX2 expression was negatively associated with LH levels (OR = 0.22, p = 0.021) and E2 levels (OR = 0.25, p = 0.026).

CONCLUSIONS

Consequently, based on the preliminary findings of the present pilot study a potential inhibitory mechanism of RUNX2 gene is observed in the ovary when high mRNA levels are detected, suggesting that RUNX2 could possibly be used as a candidate genetic marker in the monitoring of the outcome of an ART treatment.

Periovulatory expression of hyaluronan and proteoglycan link protein 1 (Hapln1) in the rat ovary: hormonal regulation and potential function

Periovulatory follicular matrix plays an important role in cumulus-oocyte complex (COC) expansion, ovulation, and luteal formation. Hyaluronan and proteoglycan link protein 1 (HAPLN1), a component of follicular matrix, was shown to enhance COC expansion in vitro. However, the regulatory mechanisms of periovulatory expression of Hapln1 and its role in periovulatory granulosa cells have not been elucidated. We first determined the periovulatory expression pattern of Hapln1 using pregnant mare serum gonadotropin/human chorionic gonadotropin (PMSG/hCG)-primed immature rat ovaries. Hapln1 expression was transiently induced both in intact ovaries and granulosa cells at 8 h and 12 h after hCG injection. This in vivo expression of Hapln1 was recapitulated by culturing preovulatory granulosa cells with hCG. The stimulatory effect of hCG was blocked by inhibition of protein kinase A, phosphatidylinositol-dependent kinase, p38 MAPK, epidermal growth factor signaling, and prostaglandin synthesis, revealing key mediators involved in LH-induced Hapln1 expression. In addition, knockdown of Runx1 and Runx2 expression by small interfering RNA or inhibition of RUNX activities by dominant-negative RUNX decreased hCG or agonist-induced Hapln1 expression. Chromatin immunoprecipitation assays verified the in vivo binding of RUNX1 and RUNX2 to the Hapln1 promoter in periovulatory granulosa cells. Luciferase reporter assays revealed that mutation of the RUNX binding sites completely obliterated the agonist-induced activity of the Hapln1 promoter. These data conclusively identified RUNX proteins as the crucial transcription regulators for LH-induced Hapln1 expression. Functionally, treatment with HAPLN1 increased the viability of cultured granulosa cells and decreased the number of the cells undergoing apoptosis, whereas knockdown of Hapln1 expression decreased granulosa cells viability. This novel finding indicates that HAPLN1 may promote periovulatory granulosa cell survival, which would facilitate their differentiation into luteal cells.

Molecular mechanisms of insulin-like growth factor 1 promoted synthesis and retention of hyaluronic acid in porcine oocyte-cumulus complexes

The purpose of the present study was to elucidate signaling pathways by which insulin like-growth factor 1 (IGF1) promotes FSH-stimulated synthesis and retention of hyaluronic acid (HA) in pig oocyte-cumulus complexes (OCCs) cultured in serum-free medium. We found that IGF1 had no effects on FSH-stimulated production of cAMP and activation of protein kinase A in the OCCs. Immunoblotting with phospho-specific antibodies showed that FSH moderately phosphorylated v-akt murine thymoma viral oncogene homolog (AKT) and mitogen-activated kinase 3 and 1 (MAPK3/1) in cumulus cells. The exposure of OCCs to both FSH and IGF1 resulted in a significant (P < 0.05) increase in AKT and MAPK3/1 phosphorylation. An inhibitor of phosphoinositide-3-kinase (PIK3), LY 294002, significantly (P < 0.05) reduced the IGF1-enhanced phosphorylation of AKT, and inhibitors of AKT (SH6) and MAPK3/1 (U0126) significantly (P < 0.05) decreased the synthesis and retention of HA stimulated by concomitant exposure of OCCs to both FSH and IGF1. The IGF1-promoted synthesis of HA was not accompanied by an increase in the relative abundance of hyaluronan synthase 2 (HAS2) mRNA in the cumulus cells. We conclude that IGF1 promotes the FSH-stimulated synthesis and retention of HA in pig OCCs by PIK3/AKT- and MAPK3/1-dependent mechanisms.

Molecular mechanisms of ovulation: co-ordination through the cumulus complex

Successful ovulation requires that developmentally competent oocytes are released with appropriate timing from the ovarian follicle. Somatic cells of the follicle sense the ovulatory stimulus and guide resumption of meiosis and release of the oocyte, as well as structural remodelling and luteinization of the follicle. Complex intercellular communication co-ordinates critical stages of oocyte maturation and links this process with release from the follicle. To achieve these outcomes, ovulation is controlled through multiple inputs, including endocrine hormones, immune and metabolic signals, as well as intrafollicular paracrine factors from the theca, mural and cumulus granulosa cells and the oocyte itself. This review focuses on the recent advances in understanding of molecular mechanisms that commence after the gonadotrophin surge and culminate with release of the oocyte. These mechanisms include intracellular signalling, gene regulation and remodelling of tissue structure in each of the distinct ovarian compartments. Most critical ovulatory mediators exert effects through the cumulus cell complex that surrounds and connects with the oocyte. The convergence of ovulatory signals through the cumulus complex co-ordinates the key mechanistic processes that mediate and control oocyte maturation and ovulation.

Effect of homologous follicular fluid from medium-sized and large follicles on in vitro maturation of equine cumulus - oocyte complexes

The in vitro maturation (IVM) of equine oocytes is typically performed using various synthetic media; however, an optimal IVM system for equine oocytes has not been developed. The aim of the present study was to evaluate the effects of two types of follicular fluid (FF) obtained from cyclic mares and two incubation intervals for the IVM of equine cumulus–oocyte complexes (COCs). Follicular fluid was collected from medium-sized (20–29 mm diameter) and large (≥30 mm; post-human chorionic gonadotrophin administration) follicles using transvaginal ultrasound-guided follicle aspiration. Compact (n = 232) and non-compact (n = 183) COCs obtained from a slaughterhouse were incubated separately in the following groups: (1) FF from medium follicles for 24 h; (2) FF from large follicles for 24 h; (3) control (synthetic) medium for 24 h; (4) FF from medium follicles for 24 h then FF from large follicles for an additional 24 h; (5) FF from large follicles for 48 h; and (6) control medium for 48 h. For compact COCs, there was a tendency (P = 0.06) for more COCs incubated in FF from large follicles for 24 h to reach metaphase II compared with those incubated in control medium for 24 h (58% v. 35%, respectively). More (P < 0.05) compact COCs had degenerated after incubation in control medium for 48 h compared with all other groups (51% v. 14–24%, respectively). For non-compact COCs, incubation in FF from medium follicles for 24 h resulted in more (P = 0.05) COCs at metaphase II compared with control medium for 48 h (58% v. 29%, respectively). These results indicate that homologous FF from cyclic mares is a suitable alternative for the IVM of equine COCs and that it may be superior to conventional media for longer (i.e. >24 h) incubation intervals.

The extracellular matrix of porcine mature oocytes: origin, composition and presumptive roles

The extracellular matrix (ECM) of porcine mature oocytes was revealed by transmission electron microscopy (TEM) after treatment with tannic acid and ruthenium red. Present in the perivitelline space (PVS) and on the surface of the zona pellucida (ZP), it appeared to be composed of thin filaments and granules at the interconnections of the filaments, which were interpreted respectively as hyaluronic acid chains and bound proteoglycans. In order to determine whether this material is produced by the corona cells (the same ECM was found also on the surface of the zona pellucida and between cumulus cells) or by the oocyte itself, the synthesis of glycoproteins and glycosaminoglycans was checked by autoradiography on semi-thin and thin sections observed by light and electron microscopy. Immature oocytes within or without cumulus cells, were incubated with L [3H-] fucose or L [3H-] glucosamine--precursors respectively of glycoproteins and hyaluronic acid or hyaluronan (HA) bound to proteoglycans--for various times (with or without chase) and at different stages during in vitro maturation. In the first case, incorporation was found in both cumulus cells and ooplasm (notably in the Golgi area for 3H-fucose) and labeled material accumulated in the ECM of the PVS and of the ZP surface. Labeling in the PVS with both precursors was maximum between metaphase I (MI) and metaphase II (MII) and was partially extracted by hyaluronidase but not by neuraminidase. Tunicamycin, an inhibitor of glycoprotein synthesis, significantly decreased the amount of 3H-fucose labeled molecules in the PVS and increased the incidence of polyspermic penetration during subsequent in vivo fertilization. Since cumulus-free oocytes also secreted 3H-glucosamine containing compounds, both oocyte and cumulus cells probably contribute to the production of the ECM found in the PVS of mature oocytes. ECM and particularly its HA moiety present on both sides of the ZP may constitute a favourable factor for sperm penetration.

Genetic rescue of chondrodysplasia and the perinatal lethal effect of cartilage link protein deficiency

The targeted disruption of cartilage link protein gene (Crtl1) in homozygous mice resulted in a severe chondrodysplasia and perinatal lethality. This raised the question of whether the abnormalities seen in Crtl1 null mice are all caused by the absence of link protein in cartilage or whether the deficiency of the protein in other tissues and organs contributed to the phenotype. To address this question we have generated transgenic mice overexpressing cartilage link protein under the control of a cartilage-specific promoter, and then these transgenic mice were used for a genetic rescue of abnormalities in Crtl1 null mice. While the overexpression of cartilage link protein resulted in no abnormal phenotype, the cartilage-specific transgene expression of link protein could completely prevent the perinatal mortality of link protein-deficient mice and, depending on the level of the link protein expression, rescue skeletal abnormalities. Although link protein was originally isolated from cartilage, we found and determined Crtl1 transcripts and corresponding proteins in every organ tested from mouse embryos to aging animals. We also identified three additional members of the link protein family, all co-localized with hyaluronic acid-binding proteoglycans in the mouse genome. The ubiquitous presence of link protein suggests a general and systemic function of link protein in the organization of extracellular matrix in a number of tissues, possibly interacting with other proteoglycans, such as versican, brevican, and neurocan.

Follicle-stimulating hormone and insulin-like growth factor I synergistically induce up-regulation of cartilage link protein (Crtl1) via activation of phosphatidylinositol-dependent kinase/Akt in rat granulosa cells

FSH and IGF-I are both important determinants of follicle development and the process of cumulus cell-oocyte complex expansion. FSH stimulates the phosphorylation of Akt by mechanisms involving phosphatidylinositol 3-kinase (PI3-K), a pattern of response mimicking that of IGF-I. Cartilage link protein (Crtl1) is confined to the cartilaginous lineage and is assembled into a macroaggregate complex essential for hyaluronan-rich matrix stabilization. The present studies were performed to determine the actions of FSH and IGF-I on Crtl1 production in rat granulosa cells. Primary cultures of granulosa cells were prepared from 24-d-old rats. After treatments, cell extracts and media were prepared, and the Crtl1 level was determined by immunoblotting analysis using anti-Crtl1 antibodies. Here we showed that 1) treatment with FSH (> or = 25 ng/ml) or IGF-I (> or = 25 ng/ml) for 4 h increased Crtl1 production; 2) maximal stimulatory effects of FSH or IGF-I were observed at 100 or 50 ng/ml, respectively; 3) FSH caused a concentration-dependent increase in IGF-I-induced Crtl1 production and vice versa; 4) FSH and IGF-I also up-regulate the expression of Crtl1 mRNA; 5) FSH- and IGF-I-dependent Crtl1 production were abrogated by PI3-K inhibitors (LY294002 and wortmannin), and inhibition of Crtl1 production by p38 mitogen-activated protein kinase inhibitor (SB202190) was partial (approximately 30%), suggesting that PI3-K and, to a lesser extent, p38 mitogen-activated protein kinase are critical for the response. Our study represents the first report that FSH amplifies IGF-I-mediated Crtl1 production, possibly via PI3-K-Akt signaling cascades in rat granulosa cells.