A role for retinoids in human oocyte fertilization: regulation of connexin 43 by retinoic acid in cumulus granulosa cells.

Retinoids are essential for ovarian steroid production and oocyte maturation in mammals. Oocyte competency is known to positively correlate with efficient gap junction intercellular communication (GJIC) among granulosa cells in the cumulus-oocyte complex. Connexin 43 (C x 43) is the main subunit of gap junction channels in human cumulus granulosa cells (CGC) and is regulated by all-trans retinoic acid (ATRA) in other hormone responsive cell types. The objectives of this study were to quantify retinoid levels in human CGC obtained during IVF oocyte retrievals, to investigate the potential relationship between CGC ATRA levels and successful oocyte fertilization, and to determine the effects of ATRA on C x 43 protein expression in CGC. Results showed that CGC cultures actively metabolize retinol to produce ATRA. Grouped according to fertilization rate tertiles, mean ATRA levels were 2-fold higher in pooled CGC from women in the highest versus the lowest tertile (P < 0.05). ATRA induced a rapid dephosphorylation of C x 43 in CGC and granulosa cell line (KGN) cultures resulting in a >2-fold increase in the expression of the functional non-phosphorylated (P0) species (P < 0.02). Similar enhancement of P0 by ATRA was shown in CGC and KGN cultures co-treated with LH or hCG which, by themselves, enhanced the protein levels of C x 43 without altering its phosphorylation profile. Correspondingly, the combination of ATRA+hCG treatment of KGN caused a significant increase in GJIC compared with single agent treatments (P < 0.025) and a doubling of GJIC from that seen in untreated cells (P < 0.01). These findings indicate that CGC are a primary site of retinoid uptake and ATRA biosynthesis. Regulation of C x 43 by ATRA may serve an important role in folliculogenesis, development of oocyte competency, and successful fertilization by increasing GJIC in CGC.

Vascular endothelial growth factor receptor 2-mediated angiogenesis is essential for gonadotropin-dependent follicle development.

Gonadotropins induce ovarian follicle growth that is coincident with increased follicular vasculature, suggesting a role of angiogenesis in follicle development. Functional studies performed in nonhuman primates show that administration of substances that inactivate VEGF block the development and function of preovulatory follicles as demonstrated by histological analysis or hormone measurements. Blockage of function of VEGF receptor 2 (VEGFR-2) alters follicular hormone secretion, suggesting that the intraovarian effect of VEGF might be mediated by this receptor. The specific mechanism by which follicular development was blocked in these previous studies remains unclear, however. Here we characterize the intraovarian role of VEGFR-2 activity on follicular development by choosing a model in which active feedback is absent, the prepuberally hypophysectomized mouse. Hypophysectomy prevents advanced follicle growth and maturation; however, follicle development to the preovulatory stage can be stimulated by administration of gonadotropins. We report that exogenously administered gonadotropins are unable to drive follicle development to the preovulatory stage in the presence of antiangiogenic agent, VEGFR-2-neutralizing Ab's. This inhibition of follicular development is caused by arrests to both angiogenesis and antrum formation. We conclude that the intraovarian VEGF/VEGFR-2 pathway is critical for gonadotropin-dependent angiogenesis and follicular development.

The vascular endothelial growth factor (VEGF)/VEGF receptor 2 pathway is critical for blood vessel survival in corpora lutea of pregnancy in the rodent.

The vascular endothelial growth factor (VEGF)/VEGF receptor 2 (VEGFR-2) pathway regulates proliferation, survival, and permeability of vasculature. This pathway is active during the formation of a corpus luteum, a highly vascularized, endocrine organ with a short life span during the nonpregnant state. In the pregnant state, the life span of corpora lutea is much longer because they play a critical role in supporting pregnancy development. We hypothesized that the VEGF/VEGFR-2 pathway plays a critical role in regulating angiogenic events in the corpora lutea of pregnancy. Injection of the neutralizing anti-VEGFR-2 antibody DC101 (ImClone Systems, Inc., New York, NY) on embryonic d 3.5 (preimplantation) or 6.5 (postimplantation) disrupts function of the corpora lutea of pregnancy in CD1 mice, as evidenced by a decrease in organ size, regression of luteal vessels, and a fall in progesterone secretion within 24 h postinjection. Inhibition of the VEGFR-2 caused removal of endothelial cells, mostly through endothelial cell detachment from the vascular basement membrane. Luteal steroid-producing epithelial cells were eliminated through apoptosis secondary to vasculature becoming dysfunctional. Disruption of luteal function caused arrest of embryonic development. The effect of antibody is specific to the ovary, because pregnancy progresses normally in ovariectomized, progesterone-replaced animals treated with anti-VEGFR-2 antibody. Embryonic blood vessels were not affected directly by the antibody, because it did not reach the embryo. Administration of an antibody against VE-cadherin (E4G10), which specifically blocks endothelial proliferation, did not disrupt luteal function and pregnancy development. Thus, VEGFR-2-mediated endothelial cell signals are critical to maintain functionality of luteal blood vessels during pregnancy. Potential clinical applications of inhibitors of the VEGF/VEGFR-2 pathway include emergency contraception and medical treatment of ectopic and abnormal intrauterine pregnancies.

Analysis of follicular fluid retinoids in women undergoing in vitro fertilization: retinoic acid influences embryo quality and is reduced in women with endometriosis.

Retinol (ROL) and its biologically active metabolite, all-trans retinoic acid (ATRA), are essential for a number of reproductive processes. However, there is a paucity of information regarding their roles in ovarian folliculogenesis, oocyte maturation, and early embryogenesis. The objectives of this study were to quantify and compare peripheral plasma (PP) and follicular fluid (FF) retinoid levels, including ATRA in women undergoing in vitro fertilization (IVF) and to investigate the relationship between retinoid levels and embryo quality. Retinoid levels were evaluated in PP and FF from 79 women undergoing IVF at the time of oocyte retrieval and corresponding embryo quality assessed on a daily basis after retrieval for 3 days until uterine transfer. Analysis compared the retinoid levels with day 3 embryo grades and between endometriosis versus control patients. Results demonstrated distinctive levels of retinoid metabolites and isomers in FF versus PP. There was a significantly larger percentage of high-quality grade I embryos derived from the largest versus smallest follicles. An increase in follicle size also correlated with a >50% increase in FF ROL and ATRA concentrations. Independent of follicle size, FF yielding grade I versus nongrade I embryos showed higher mean levels of ATRA but not ROL. In a nested case-control analysis, control participants had 50% higher mean levels of ATRA in their FF and PP than women with endometriosis. These findings strongly support the proposition that ATRA plays a fundamental role in oocyte development and quality, and that reduced ATRA synthesis may contribute to decreased fecundity of participants with endometriosis.

Athletic amenorrhea: energy deficit or psychogenic challenge?

Athletic women are at risk for developing ovulatory dysfunction, which presents variably as menstrual irregularity or absence. Initially characterized as an isolated disruption of hypothalamic gonadotropin-releasing hormone (GnRH) release, athletic amenorrhea, a form of hypogonadotropic hypogonadism, is invariably accompanied by additional neuroendocrine aberrations, including activation of adrenal and suppression of thyroidal axes. Exercise may elicit intermittent or chronic metabolic stress owing to increased energy expenditure and/or insufficient or imbalanced nutrient intake. In addition, athletic activities are motivated by or serve as psychogenic stressors. Prior studies dichotomized stressors as metabolic or psychogenic. Not only is this a false dichotomy because all stressors have both a metabolic and a psychogenic component, but also stressors act synergistically rather than in isolation to compromise GnRH drive and endocrine homeostasis. To ameliorate reproductive and endocrine consequences of stress, then, requires identification and amelioration of all relevant stressors. Formal psychosocial support helps individuals to develop better coping strategies and make appropriate lifestyle changes. Our research has shown that cognitive behavior therapy restores reproductive and endocrine balance.

Current status of the approach to assisted reproduction.

Assisted reproductive technologies are important tools in the clinical armamentarium used to treat both female and male infertility disorders. Pre-implantation genetic diagnosis offers couples at risk of having children with inheritable disorders the ability to analyze the genetic make-up of embryos before transfer. For patients undergoing treatment of cancer with chemotherapy or radiation therapy, these technologies offer the potential for the preservation of future fertility. As technology evolves, it is likely the clinical applications of assisted reproduction will continue to develop and expand in the future to enhance fertility.