MOLECULAR ANATOMY OF THE PERIVASCULAR SHEATH IN HUMAN PLACENTAL STEM VILLI - THE CONTRACTILE APPARATUS AND ITS ASSOCIATION TO THE EXTRACELLULAR-MATRIX

In previous studies, we have shown that smooth muscle cells and myofib roblast subpopulations of the perivascular stem villous sheath of the human placenta contain focal adhesion plaques and talin immunoreactivi ty. The close association of these cells to elastic and collagen fibre s have led to the assumption of a functional myofibroelastic unit with in the perivascular stem villous sheath. Interactions between the extr acellular matrix and smooth muscle cells depend on a variety of struct ural protein assemblies. In the present study, we examined, by immunoc ytochemistry, whether the molecular assembly of extracellular matrix p roteins and molecules of focal adhesions, known to be essential for si gnal transduction in smooth muscle cells, are also found in smooth mus cle cells of the perivascular stem villous sheath of the human placent a. Vascular and extravascular smooth muscle cells were immunoreactive for alpha-actinin, vinculin, paxillin and tensin, the integrin chains alpha 1 and beta 1, and the basement membrane components laminin and h eparan/-chondroitin sulfate proteoglycan perlecan. pp125(FAK) not reac t. In did the extracellular matrix of blood vessel walls and the periv ascular stem villous sheath, we found immunoreactivity of fibronectin and collagen types I, VI and undulin (collagen type XIV). From our dat a we conclude that within the perivascular stem villous sheath, there exists a system of signal transduction molecules, indicating a cross t alk between the smooth muscle cells of this sheath and their surroundi ng extracellular matrix.