Placenta (2002), 23, 232–235 doi:10.1053/plac.2001.0760, available online at http://www.idealibrary.com on SHORT COMMUNICATION Trophoblast Invasion of Spiral Arteries: a Novel In Vitro Model J. E. Cartwright a,c , L. C. Kenny b , P. R. Dash a , I. P. Crocker b , J. D. Aplin b , P. N. Baker b and G. St J. Whitley a a Department of Biochemistry and Immunology, St George’s Hospital Medical School, Cranmer Terrace, London, SW17 0RE and b Maternal and Fetal Health Research Centre, St Mary’s Hospital, Whitworth Park, Manchester, M13 0JH Paper accepted 29 October 2001 Extravillous trophoblasts invade the uterine wall (interstitial invasion) and the spiral arteries (endovascular invasion), replacing the cells of the vessel wall and creating a high-flow low-resistance vessel. We have developed a novel model to allow the interactions between the invading trophoblast cells and the cells of the spiral artery to be directly examined. Unmodified (non-placental bed) spiral arteries were obtained from uterine biopsies at caesarean section. Fluorescently labelled trophoblasts were seeded on top of artery segments embedded in fibrin gels (to study interstitial invasion) or perfused into the lumen of arteries mounted on a pressure myograph (to study endovascular invasion). Trophoblasts were incubated with the vessels for 3–5 days prior to cryo-sectioning. Both interstitial and endovascular interactions/invasion could clearly be detected and a comparison of the extravillous trophoblast cell line, SGHPL-4 and primary first trimester cytotrophoblasts showed both to be invasive in this model. This novel method will prove useful in an area where in vitro studies have been hampered by the lack of suitable models directly examining cellular interactions during invasion.  2002 Elsevier Science Ltd Placenta (2002), 23, 232–235 INTRODUCTION Within the placenta in early gestation, trophoblasts differenti- ate and give rise to sub-populations of cells. One of these, the extravillous trophoblast, invades the uterine wall (interstitial invasion) and its blood vessels (endovascular invasion). During normal pregnancy, the trophoblasts destined to be endovascu- lar adopt a more endothelial cell (EC)-like phenotype and invade the uterine spiral arteries as far as the myometrial segments. Immunohistochemical studies of placental bed biop- sies suggest that trophoblasts and EC transiently coexist on the walls of partially modified spiral arteries (Pijnenborg et al., 1980; Zhou et al., 1997) where they migrate along the luminal surfaces of EC, invading the vessels and partially replacing the EC and most of the musculoelastic tissue in the vessel walls (Pijnenborg et al., 1980; Enders and King, 1991; Blankenship et al., 1993; Meekins et al., 1997). This creates a high-flow, low-resistance circulation that maximizes maternal blood flow to the placental villi at the maternal–fetal interface. There is contrasting evidence as to whether trophoblasts themselves are important in arterial remodelling. Although it has been sug- gested that some changes in the decidual vessels occur inde- pendently (Craven et al., 1998) as part of the maternal response to pregnancy, there is also strong evidence to suggest that invasive interstitial trophoblasts prepare the decidual spiral arteries for endovascular trophoblast migration (Pijnenborg et al., 1983; Blankenship and Enders, 1997; Kam et al., 1999). The invasive trophoblast may play an important role in inducing further changes either by interactions or factors produced by the interstitial trophoblast or by direct cellular interactions of the endovascular trophoblast with the cells of the vessel that they subsequently replace. The pathogenesis of both pre-eclampsia (PE) and intrauter- ine growth restriction (IUGR) is associated with trophoblasts failing to adopt an EC-like phenotype and endovascular inva- sion failing to proceed beyond the superficial portions of the spiral arteries in early pregnancy (Meekins et al., 1994; Lim et al., 1997; Zhou et al., 1997) although Divers et al. (1995) failed to find any clear phenotypic differences. Since there is still abundant interstitial migration of trophoblasts in the placental bed (Pijnenborg et al., 1998), the ability of trophoblasts to enter and transform the spiral arteries appears to be a signifi- cant difference between normal and PE/IUGR pregnancies (Khong et al., 1986). The importance of interactions between trophoblasts and the vascular cells of the spiral arteries, which may account for these differences, have yet to be determined in normal or PE/IUGR pregnancies. Studies of spiral arteries are confined primarily to immuno- histochemical analysis of placental bed biopsies (Genbacev et al., 1996; Zhou et al., 1997; Lyall et al., 1999, 2000) while in vitro studies have been hampered by the lack of suitable models to directly examine cellular interactions during c To whom correspondence should be addressed at: Department of Biochemistry and Immunology, St George’s Hospital Medical School, Cranmer Terrace, London, SW17 0RE. Tel: 020 8725 0803; Fax: 020 8725 2992. E-mail: j.cartwright@sghms.ac.uk 0143–4004/02/020232+04 $35.00/0  2002 Elsevier Science Ltd