Spatially regulated differentiation of endometrial vascular smooth muscle cells

Angiogenesis within the human endometrium involves the development of arterioles and elaboration of a capillary network. It was postulated that maturation of these arterioles involves a spatially regulated process of vascular smooth muscle cell (VSMC) differentiation. The endometrial vascular tree was therefore examined immunohistochemically for evidence of longitudinal and radial gradients of VSMC phenotype. Twenty-three hysterectomy specimens and 15 first trimester decidual tissues were studied. Five cytoskeletal markers (alpha and gamma-smooth muscle (sm) actin, sm myosin, desmin, vimentin), three endothelial markers (CD31, CD34, factor VIII related antigen) and two steroid receptors (oestrogen and progesterone) were detected immunohistochemically. alpha-sm actin was present throughout the wall of basal arterial segments and extended longitudinally towards the endometrial surface. Sm myosin expression was more restricted longitudinally and radially within in the vascular tree. The expression of gamma-sm actin was even more restricted than myosin. In first trimester decidua, however, gamma-sm actin was widely distributed within the wall of spiral arteries that were not invaded by trophoblast. Oestrogen and progesterone receptors were present in peri-vascular stromal cells but absent from vascular smooth muscle and endothelium. Endometrial VSMC differentiation involves a progressive increase in cytoskeletal complexity and occurs in a spatially regulated fashion.