amino acid transfer and reduced fetal growth mediated by down-regula- tion of Cdc42 and Rac1. http://dx.doi.org/10.1016/j.placenta.2017.07.100 P1.10. IN VITRO CHARACTERIZATION OF THE TROPHOBLASTIC STEROIDOGENESIS IN NORMAL AND TRISOMY 21 AFFECTED PREGNANCY Camille Fraichard 1 , Marylise Hebert-Schuster 1,2 , S.O.N.G. Marie- Delphine 1 , Pascale Gerbaud 1 , Edouard Lecarpentier 1,3 , Thierry Fournier 1 , Jean Guibourdenche 1,2 . 1 INSERM 1139-Paris Descartes University, Paris, France; 2 SDBA/Hormonology Department, Cochin Hospital, APHP, Paris, France; 3 Port-Royal Maternity, Cochin Hospital, APHP, Paris, France Objectifs: The placenta is an endocrine organ, secreting both steroids (progesterone [P4], estradiol [E2] and estriol [E3]) and proteins (hCG, pGH), thanks to villous cytotrophoblasts (VCT) and syncytiotrophoblast (ST). P4 allows the implantation and the maintenance of pregnancy. E2 and E3 which are involved in the maternal metabolic adaptation, are decreased in maternal serum in trisomy 21 (T21). We aimed to study the in vitro steroids production in normal and in T21 trophoblast. Methods: VCTs isolated from human T21 placenta (n¼4, 14 WG to 22 WG) and controls (n¼7) were cultured for 72h. hCG, P4 and E2 secretions were measured in supernatants at 24h and 72h of culture by immuno-assay. Intracellular expression of enzymes involved in the steroidogenesis (HSD3B1, P450SCC, aromatase, steroid sulfatase) was studied by immu- nocytofluorescence, western-blot and RT-qPCR. Results: In controls, P4 increases (x 8) during VCT differentiation into ST while estradiol decreased (x 2). HSD3B1, aromatase and steroid sulfatase are expressed in VCT and ST, and increased during trophoblast differenti- ation. P450SCC is expressed at a constant level in VCT and ST. RT-qPCR experiments demonstrate that the increase in HSD3B1 is also observed at the mRNA level while there is no change in P450SCC, aromatase and ste- roid sulfatase mRNA during trophoblast differentiation. Two groups are observed in T21: one with a good ST formation associated with an increase in hCG secretion and the other with low trophoblastic differentiation (no increase in hCG). Regardless of gestational age, the progesterone and estradiol secretions are not changed whatever the trophoblastic differentiation status. Conclusion: Our results highlight that steroidogenesis begins in mono- nucleated VCT, before the differentiation into ST. Only the progesterone synthesis is physiologically associated with trophoblast differentiation. In T21, progesterone secretion is likely to be defective, which could explain the increased rate in pregnancy loose during the first half of pregnancy. http://dx.doi.org/10.1016/j.placenta.2017.07.101 P1.11. EFFECT OF ENDOPLASMIC RETICULUM STRESS ON TROPHOBLAST CELL LINEAGE DIFFERENTIATION Nadejda Capatina 1, 2 , Myriam Hemberger 1, 3 , Graham Burton 1, 2 , Hong Wa Yung 1, 2 . 1 Centre for Trophoblast Research, University of Cambridge, Cambridge, UK; 2 Department of Physiology, Development and Neuroscience, University of Cambridge, Cambridge, UK; 3 Epigenetics Programme, The Babraham Institute, Babraham Research Campus, Cambridge, UK Objectives: Endoplasmic reticulum (ER) stress and subsequent activation of Unfolded Protein Response (UPR) pathways regulate differentiation of cardiac and liver stem cells, and decidualization of endometrial stromal cells. Yung et al. (J Pathol 2012: 228: 554-564) reported that conditioned medium from Eif2s1 tm1RjK mouse embryonic fibroblast cells that suffer chronic ER stress induces differentiation of trophoblast stem cells (TSCs) into specialized subpopulations. Hence, the aim was to provide a mecha- nistic understanding of the effects of ER stress on differentiation of TSCs. Methods: In vitro model: Mouse TSCs were cultured for 48h in proliferative conditions (control and 0.1% DMSO), followed by 48h treatment with either tunicamycin or thapsigargin. The dose-response effect was quanti- fied using RT-qPCR to monitor stemness (Essrb), and differentiation (Gcm1, Tpbpa, Pl1, Pl2, Plf, Ctsq). As a positive control, TSCs were cultured in me- dium (TS base) promoting differentiation. In vivo model: Eif2s1 tm1RjK heterozygous mice were crossed, and 3.5 dpc blastocysts collected. Blastocyst developmental stage was determined by morphology and immunostaining against Cdx2/Nanog/Oct4/E-cadherin. Lastly, single-blastocyst genotyping was performed. Results: In vitro model: Both tunicamycin and thapsigargin activated all three UPR pathways: PERK, ATF6a and IRE1a. Tunicamycin induced TSC differentiation into spongiotrophoblast and all trophoblast giant cell (TGC) subtypes, while thapsigargin induced differentiation into syncytio- trophoblast, channel and spiral artery-associated TGCs only (Fig. 1). In vivo model: Pilot data show that blastocysts form two distinct pop- ulations at 3.5 dpc: morphologically normal and abnormal blastocysts. The latter are flat-shaped, have no distinct inner cell mass or trophectoderm, and lack a blastocoel (Fig. 2). Conclusion: Pharmacological induction of ER stress causes TSC differen- tiation, dependent on the agent used. The morphological disruption of 3.5 dpc blastocysts from Eif2s1 tm1RjK heterozygous crosses observed could explain the low number of homozygous pups born, possibly due to defective implantation of homozygous blastocysts. Supported by the Centre for Trophoblast Research. Ă http://dx.doi.org/10.1016/j.placenta.2017.07.102 P1.12. PLACENTAL-HOMING PEPTIDES ATTACHED TO LIQUID CRYSTAL NANOPARTICLES FOR SELECTIVE TARGETING OF THE PLACENTA Maitham Bahman 1 , Mark Wareing 1 , Alan Christy Hunter 2 , Lynda Harris 1 . 1 University of Manchester, Manchester, UK; 2 De Montfort University, Leicester, UK Objectives: To investigate the effect of attaching the placental-homing peptide CGKRK to liquid crystal nanoparticles on their original structures and to determine the ability of the peptide-labelled nanoparticles to attach to human term placental tissue. Methods: Nanoparticles composed of soy phosphatidylcholine and citrem (1:1) were prepared using a top-down approach. The final dispersions were 5% (w/v) total lipid concentration dispersed in PBS. Targeted nano- particles were functionalised with fluorescently-labelled CGKRK peptide, and non-targeted nanoparticles were labelled with 5(6)-carboxy- fluorescein. Villous explants from human term placenta were incubated for up to 48h with the different liquid crystal formulations. Individual explants were then fixed in OCT, frozen, cryosectioned and viewed under a fluorescence microscope. Size and zeta potential measurements were obtained using a Zetasizer instrument and the nanostructures were characterised by small angle X-ray scattering and cryogenic transmission electron microscopy. Abstracts / Placenta 57 (2017) 225e335 252