Pregnancy

Apoptosis Contributes to Vascular Lumen Formation and Vascular Branching in Human Placental Vasculogenesis

Abstract
Placental vasculogenesis consists of several stages including appearance of hemangioblasts and angiogenic cell islands, setting up a primitive vascular network and transition from vasculogenesis to sprouting and non-sprouting angiogenesis. In this study, we hypothesized that placental vasculogenesis and angiogenesis require apoptosis during the formation of primitive vascular pattern, vessel elongation, and angiogenic branching. Vasculogenesis and apoptotic cells were identified using CD31 immunohistochemistry, hematoxylin-eosin (H-E) staining, CD31-TUNEL double-labeling and transmission electron microscopy (TEM) techniques. No TUNEL-positive cell was detected in angiogenic cell islands. However, several TUNEL-positive cells were observed during the primitive lumen formation. Interestingly, some of the stromal cells located between vasculogenic areas during the endothelial tube elongation and angiogenic branching were also TUNEL-positive. The presence of morphological aspects of apoptosis such as nuclear shrinkage and nuclear bodies (apoptotic bodies) were also confirmed in H&E and electron microscopy sections. Quantitative analysis showed that higher ratios for apoptotic cells were found in the core stroma of villi among the vascular branching areas and in the primitive capillary lumen, compared to angiogenic cell cords and vasculatures with advanced lumens (p<0.05). In conclusion, our results suggest that apoptosis is likely to be involved in the physiologic mechanisms of placental vasculogenesis and angiogenesis such as lumen formation and angiogenic branching.

Key words: Apoptosis • Developmental biology • Early development • Placenta

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