Embryo biosensing by uterine natural killer cells determines endometrial fate decisions at implantation.

Decidualizing endometrial stromal cells (EnSC) critically determine the maternal response to an implanting conceptus, triggering either menstruation-like disposal of low-fitness embryos or creating an environment that promotes further development. However, the mechanism that couples maternal recognition of low-quality embryos to tissue breakdown remains poorly understood. Recently, we demonstrated that successful transition of the cycling endometrium to a pregnancy state requires selective elimination of pro-inflammatory senescent decidual cells by activated uterine natural killer (uNK) cells. Here we report that uNK cells express CD44, the canonical hyaluronan (HA) receptor, and demonstrate that high molecular weight HA (HMWHA) inhibits uNK cell-mediated killing of senescent decidual cells. In contrast, low molecular weight HA (LMWHA) did not attenuate uNK cell activity in co-culture experiments. Killing of senescent decidual cells by uNK cells was also inhibited upon exposure to medium conditioned by IVF embryos that failed to implant, but not successful embryos. Embryo-mediated inhibition of uNK cell activity was reversed by recombinant hyaluronidase 2 (HYAL2), which hydrolyses HMWHA. We further report a correlation between the levels of HYAL2 secretion by human blastocysts, morphological scores, and implantation potential. Taken together, the data suggest a pivotal role for uNK cells in embryo biosensing and endometrial fate decisions at implantation.

Steroid regulation of secreted phosphoprotein 1 (SPP1) expression in ovine endometrium.

Secreted phosphoprotein 1 (SPP1) is an extracellular matrix glycoprotein that is highly expressed at the maternal-fetal interface and is a critical mediator of embryo implantation. The objectives of this study were to examine the spatial and temporal cyclical expression patterns and steroid regulation of SPP1 mRNA and protein in ovine endometrium, which may be further indicative of their functionality in embryo implantation. Uterine tissue was obtained following hysterectomy from ovariectomised ewes treated with ovarian steroids. In parallel, invitro culture of endometrial cells was used to investigate the effects of ovarian steroids on SPP1 expression in endometrial and luminal epithelial (LE) cells. A significant sustained mid-luteal phase increase in SPP1 mRNA in intercaruncular regions of the endometrium was observed, indicating that glandular epithelium is likely to be the primary source of SPP1 production. This increase in SPP1 was induced by progesterone treatment and was shown at the protein level by immunohistochemistry analysis. Similarly, treatment of stromal cells with 10ng mL-1 progesterone or in combination with 1ng mL-1 oestradiol significantly increased SPP1 expression (P<0.05). Collectively, expression levels of SPP1 are cycle-dependent and peak in the progesterone-dominant luteal phase. They are dependent on the interaction of uterine LE and stromal cells and may involve paracrine signalling by progesterone receptor-positive stromal cells.

Hyaluronan and hyaluronidase, which is better for embryo development?

Our aim was to examine size-specific effects of Hyaluronan (HA) on preimplantation embryo development. We investigated the effects of Hyalovet (HA, 500-750 kDa; the size produced by HA synthase-3, which is abundant in the oviduct), or HA treated with Hyaluronidase-2 (Hyal2; also expressed in the oviduct that breaks down HA into 20 kDa fragments). In experiment 1 (in vivo), oviducts of synchronized and superovulated ewes (n = 20) were surgically exposed on Day 2 post-mating, ligated, and infused with either Hyalovet, Hyalovet + Hyal2, Hyal2, or PBS (control). Ewes were killed 5 days later for recovery of embryos and oviductal epithelial cells (OEC). Blastocyst rates were significantly higher in Hyal2 and Hyalovet + Hyal2 oviducts. Hyaluronidase-2 infusion resulted in higher blastocyst cell numbers and hatching rates. This was associated with increased HSP70 expression in OEC. In contrast, Hyalovet resulted in the lowest development to blastocyst stage and lowest hatching rates, and decreased IGF2 and IGFBP2 expression in OEC. IGF1 and IL1α expression were not affected. In experiment 2, to rule out indirect effects of oviductal factors, ovine embryos were produced and cultured with the same treatments in vitro from Day 2 to 8. Hyaluronidase-2, but not Hyalovet, enhanced blastocyst formation and reduced inner cell mass apoptosis. Hyalovet inhibited hatching. In conclusion, the presence of large-size HA (500-750 kDa) in the vicinity of developing embryos appears to disturb the oviductal environment and embryo development in vivo and in vitro. In contrast, we show evidence that breakdown of HA into smaller fragments is required to maximize embryo development and blastocyst quality.

Elafin (SKALP/Trappin-2/proteinase inhibitor-3) is produced by the cervix in pregnancy and cervicovaginal levels are diminished in bacterial vaginosis.

OBJECTIVES: To examine cervicovaginal elafin production in pregnancy and determine its relationship in bacterial vaginosis. STUDY DESIGN: Samples of cervicovaginal secretions were collected from women with uncomplicated singleton pregnancies (n = 112) below 20 weeks gestation. Bacterial flora was assessed using Nugent's criteria, and levels of elafin were measured by enzyme-linked immunosorbent serologic assay (ELISA). Elafin expression in the cervix was also examined by immunohistochemistry. In vitro expression of elafin was examined using cervix and vaginal cell lines. RESULTS: Elafin is expressed in the cervical glandular epithelium. Elafin was found in all 112 samples of cervicovaginal secretions and levels were diminished in women with bacterial vaginosis (P < .05). Interleukin 1beta (IL-1beta) stimulated elafin expression in cells derived from the endocervix, but not in those derived from the vaginal epithelium. CONCLUSIONS: Elafin is a component of cervicovaginal secretions in pregnancy, and levels are diminished in bacterial vaginosis. It may be an important component of innate immunity in the lower genital tract.