Nava Dekel

Local injury to the endometrium doubles the incidence of successful pregnancies in patients undergoing in vitro fertilization

OBJECTIVE Exploration of the possibility that local injury of the endometrium increases the incidence of implantation. DESIGN Prospective study. SETTING Clinical IVF unit. PATIENT(S) A group of 134 patients, defined as good responders to hormonal stimulation, who failed to conceive during one or more cycles of IVF and embryo transfer (ET). INTERVENTION(S) The IVF treatment and ET were preceded by repeated endometrial biopsies, in a randomly selected 45 of a total of 134 patients. MAIN OUTCOME MEASURES Outcome of IVF-ET treatments. RESULT(S) Transfer of a similar number of embryos (3.4 +/- 1.0 and 3.1 +/- 0.9 in the experimental and control patients, respectively) resulted in rates of implantation (27.7% vs. 14.2%, P =.00011), clinical pregnancy (66.7% vs. 30.3%, P =.00009), and live births per ET (48.9% vs. 22.5%, P =.016) that were more than twofold higher in the experimental group as compared to controls. CONCLUSION(S) These results suggest that IVF treatment that is preceded by endometrial biopsy doubles the chance for a take-home baby.

Uterine DCs are crucial for decidua formation during embryo implantation in mice

Implantation is a key stage during pregnancy, as the fate of the embryo is often decided upon its first contact with the maternal endometrium. Around this time, DCs accumulate in the uterus; however, their role in pregnancy and, more specifically, implantation, remains unknown. We investigated the function of uterine DCs (uDCs) during implantation using a transgenic mouse model that allows conditional ablation of uDCs in a spatially and temporally regulated manner. Depletion of uDCs resulted in a severe impairment of the implantation process, leading to embryo resorption. Depletion of uDCs also caused embryo resorption in syngeneic and T cell-deficient pregnancies, which argues against a failure to establish immunological tolerance during implantation. Moreover, even in the absence of embryos, experimentally induced deciduae failed to adequately form. Implantation failure was associated with impaired decidual proliferation and differentiation. Dynamic contrast-enhanced MRI revealed perturbed angiogenesis characterized by reduced vascular expansion and attenuated maturation. We suggest therefore that uDCs directly fine-tune decidual angiogenesis by providing two critical factors, sFlt1 and TGF-beta1, that promote coordinated blood vessel maturation. Collectively, uDCs appear to govern uterine receptivity, independent of their predicted role in immunological tolerance, by regulating tissue remodeling and angiogenesis. Importantly, our results may aid in understanding the limited implantation success of embryos transferred following in vitro fertilization.

Modulation of cell-to-cell communication in the cumulus-oocyte complex and the regulation of oocyte maturation by LH.

Prior to ovulation, cell-to-cell communication between the oocyte and the cells of the cumulus oophorus is terminated (N. B. Gilula, M. L. Epstein, and W. H. Beers, 1978, J. Cell Biol. 78, 58–75; R. M. Moor, M. W. Smith, and R. M. C. Dawson, 1980, Exp. Cell Res. 126, 15–29). In this paper we report that LH, Bt2-cAMP, and the cyclic nucleotide phosphodiesterase inhibitor, 3-isobutyl-1-methylxanthine, are all capable of interrupting communication in vitro in rat follicle-enclosed cumulus-oocyte complexes. Moreover, the breakdown of communication appears to be closely correlated with the ability of hyaluronidase to disperse the cumulus cell mass. This observation allows simple screening of the effects of various agents on cumulus-oocyte communication. The in vitro system employed in this study has also been used to investigate the relationship between communication and oocyte maturation. The findings presented indicate that the interruption of communication between the cumulus and the oocyte leads to relief of meiotic arrest, and are consistent with the possibility that cAMP, transmitted from the cumulus to the oocyte, may be the inhibitor of oocyte maturation in vivo.

Local injury of the endometrium induces an inflammatory response that promotes successful implantation

OBJECTIVE To study whether an injury-induced inflammation might be the mechanism underlying the favorable effect of endometrial biopsy on the implantation rate in in vitro fertilization (IVF) patients. DESIGN Controlled clinical study. SETTING A medical center IVF unit and a research institute. PATIENT(S) Women undergoing IVF who had previous failed treatment cycles. INTERVENTION(S) Endometrial samples were collected from two groups of patients on day 21 of their spontaneous menstrual cycle. The experimental, but not the control group underwent prior biopsy treatment on days 8 or/and 11 to 13 of that same cycle. MAIN OUTCOME MEASURE(S) Abundance of immune cells, cytokines/chemokines level, correlation between these parameters and pregnancy outcome. RESULT(S) A statistically significantly higher amount of macrophages/dendritic cells (HLA-DR+ CD11c+ cells) and elevated proinflammatory cytokines, tumor necrosis factor-α (TNF-α), growth-regulated oncogene-α (GRO-α), interleukin-15 (IL-15), and macrophage inflammatory protein 1B (MIP-1B), were detected in day-21 endometrial samples of the experimental group. A direct stimulatory effect of TNF-α on MIP-1B, GRO-α, and IL-15 messenger RNA (mRNA) expression was demonstrated. A positive correlation was found between the levels of macrophages/dendritic cells, MIP-1B expression, and TNF-α expression and the pregnancy outcome. CONCLUSION(S) A biopsy-induced inflammatory response may facilitate the preparation of the endometrium for implantation. Increased MIP-1B expression could possibly serve for prediction of implantation competence.

Inflammation and Implantation

Approximately half of all human embryo implantations result in failed pregnancy. Multiple factors may contribute to this failure, including genetic or metabolic abnormalities of the embryo. However, many of these spontaneous early abortion cases are attributed to poor uterine receptivity. Furthermore, although many fertility disorders have been overcome by a variety of assisted reproductive techniques, implantation remains the rate‐limiting step for the success of the in vitro fertilization (IVF) treatments. It has been demonstrated that endometrial biopsies performed either during the spontaneous, preceding cycle, or during the IVF cycle itself, significantly improve the rate of implantation, clinical pregnancies and live births. These observations suggest that mechanical injury of the endometrium may enhance uterine receptivity by provoking the immune system to generate an inflammatory reaction. In strong support of this idea, we recently found that dendritic cells (DCs), an important cellular component of the innate immune system, play a critical role in successful implantation in a mouse model. In this review, we discuss the hypothesis that the injury‐derived inflammation in the biopsy‐treated patients generates a focus for uterine DCs accumulation that, in turn, enhances the endometrial expression of essential molecules, which facilitate the interaction between the embryo and the uterine epithelium.

Reactive oxygen species are indispensable in ovulation

Ovulation is stimulated by the preovulatory surge of the pituitary luteinizing hormone (LH). Because the ovulatory response is commonly identified with inflammation, we explored the involvement of reactive oxygen species (ROS) in this process. Our experiments show that administration of broad-range scavengers of oxidative species into the ovarian bursa of mice, hormonally induced to ovulate, significantly reduced the rate of ovulation. LH-induced cumulus mucification/expansion, a necessary requirement for ovulation, was prevented by antioxidants both in vivo and in an ex vivo system of isolated intact ovarian follicles. Along this line, H2O2 fully mimicked the effect of LH, bringing about an extensive mucification/expansion of the follicle-enclosed cumulus–oocyte complexes. Impaired progesterone production was observed in isolated follicles incubated with LH in the presence of the antioxidant agents. Furthermore, LH-stimulated up-regulation of genes, the expression of which is crucial for ovulation, was substantially attenuated upon ROS ablation. This system was also used for demonstrating the role of ROS in phosphorylation and activation of the EGF receptor as well as its downstream effector, p42/44 MAPK. Together, our results provide evidence that ovarian production of ROS is an essential preovulatory signaling event, most probably transiently triggered by LH.

The Proteasome Is Involved in the First Metaphase-to-Anaphase Transition of Meiosis in Rat Oocytes

Abstract The proteasome engages in protein degradation as a regulatory process in biological transactions. Among other cellular processes, the proteasome participates in degradation of ubiquinated cyclins in mitosis. However, its role in meiosis has not been established. Resumption of meiosis in the oocyte involves the activation of maturation promoting factor (MPF), a complex of p34cdc2 and cyclin B. Inactivation of this factor, occurring between the two meiotic divisions, is associated with degradation of cyclin B. In this study, we examined the possible involvement of the proteasome in regulation of the exit from metaphase I in spontaneously maturing rat oocytes. We found that upon resumption of meiosis, proteasomes translocate to the spindle apparatus. We further demonstrated that specific inhibitors of proteasome catalytic activity, MG132 and lactacystin, blocked polar body extrusion. Chromosome and microtubule fluorescent staining verified that MG132-treated oocytes were arrested at metaphase I. Intervention of proteasomal action with this inhibitor also resulted in accumulation of cyclin B and elevated activity of MPF. These data demonstrate that proteasomal catalytic activity is absolutely essential for the decrease in MPF activity and completion of the first meiotic division. Its translocation to the spindle apparatus may facilitate the timely degradation of cyclin B.

Cellular, biochemical and molecular mechanisms regulating oocyte maturation

The original model for regulation of oocyte maturation proposed by us in 1978 postulated that gap junction-mediated transmission of cAMP from the follicle cells to the oocyte inhibits meiosis and that luteinizing hormone (LH) terminates the flux of the follicle cAMP to the oocyte. A decrease in oocyte cAMP below inhibitory threshold occurs since oocytes lack the ability to generate sufficient amounts of cAMP to compensate for the phosphodiesterase activity. Our previous studies provided evidence to support this model. More recent studies in our laboratory were directed at identification of the cellular biochemical and molecular events initiated within rat oocytes upon the relief of cAMP inhibition. These studies: (i) identified an oocyte specific A kinase anchoring protein (AKAP) that is phosphorylated in oocytes resuming meiosis, (ii) confirmed that cdc25B governs meiosis reinitiation and demonstrated that its expression is translationally regulated, (iii) substantiated the indispensable role of proteasomal degradation at completion of the first meiotic division in a mammalian system, (iv) elucidated the role of MPF reactivation in suppressing interphase between the two meiotic divisions and (v) provided evidence that mos translation is negatively regulated by a protein kinase A (PKA)-mediated action of cAMP and is dependent on an active MPF. A detailed account on each of these findings is presented in this chapter.

Gap junctions in the ovary: expression, localization and function.

Gap junctions that allow the direct communication between cytoplasmic compartments of neighboring cells are present in a variety of tissues and organs and play pivotal roles in a wide range of physiological processes. In the ovary, gap junctions consist mainly of connexin (Cx) 43 and Cx37, and their indispensable role in regulating folliculogenesis and oogenesis is well established. The ovarian Cx43 is regulated by gonadotropins at the transcriptional, translational and post-translational levels whereas the regulation of the ovarian Cx37 is yet unknown. In addition to their involvement in normal ovarian functions, gap junction proteins, particularly Cx43, seem to act as cancer suppressors. A summary of our present knowledge regarding gap junctional communication (GJC) and the ovarian gap junction proteins in normally developing ovaries and under pathological conditions is presented in this review.

Regulation of Oocyte Maturation

Meiotic maturation in the mammalian oocyte is initiated during fetal life. It proceeds through the prophase of the first meiotic division and is arrested at the diplotene stage. The arrest of meiosis is maintained until shortly before ovulation. By this time meiosis is reinitiated and oocyte maturation is resumed. Reinitiation of meiosis in the oocyte is morphologically indicated by the disappearance of the nuclear structure known as the germinal vesicle (germinal vesicle breakdown — GVB).