PLACENTAL REMODELING OF THE UTERINE VASCULATURE

In eutherian mammals, the first functional organ is the placenta, a transient structure that is rapidly assembled in the extraembryonic compartment. By necessity the placenta develops in advance of the embryo, which it supports in utero, by performing many of the same functions that the lungs, gastrointestinal tract, and urinary system carry out after birth. Specialized epithelial cells that arise from the placenta, termed cytotrophoblasts (CTBs), are responsible for redirecting maternal blood to the developing conceptus, which occurs as a result of the cells' aggressive invasion through the maternal endometrial stroma (interstitial invasion) and resident blood vessels (endovascular invasion). The latter process involves displacement of maternal endothelium and induction of apoptosis in the surrounding smooth muscle. Together, these events result in a reduction of blood vessel elasticity and increased blood flow. In the past, investigations of human CTB endovascular invasion have been limited to immunohistochemical examination of tissue sections. In this chapter, we will discuss the use of in vitro and in vivo techniques that have been recently adapted for the study of the complex events that occur during CTB endovascular invasion. As an introduction, we provide background on placental anatomy and the molecular basis of CTB behaviors. To follow, we present techniques used in the isolation and culture of primary CTBs and chorionic villous explants. Approaches for identifying trophoblast-modified blood vessels in placental tissue sections are also described. Next, we review methods used by other groups to study CTB/endothelial interactions in culture focusing on techniques that employ isolated cells and chorionic explants. Finally, we conclude with methods devised by our group and others to explore the complex heterotypic cell-cell interactions that occur as CTBs invade blood vessels in vivo in the nude mouse.