Apoptosis Contributes to Vascular Lumen Formation and Vascular Branching in Human Placental Vasculogenesis1

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 nonsprouting angiogenesis. In the present 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). 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 also were TUNEL-positive. The presence of morphological aspects of apoptosis, such as nuclear shrinkage and nuclear bodies (apoptotic bodies), also was confirmed in H-E-stained and TEM-depicted 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 likely is involved in the physiologic mechanisms of placental vasculogenesis and angiogenesis, such as lumen formation and angiogenic branching.

Potential of fibroblasts to regulate the formation of three-dimensional vessel-like structures from endothelial cells in vitro

“…For example, high proportions of ECs lead to cluster formation accompanied or followed by apoptotic EC death. This massive cell death, which is not found in areas of EC tubular structures in the spheroid cocultures, clearly does not reflect the process of EC apoptosis found in the middle of a cord interpreted to contribute to lumen formation and maturation of patent small blood vessels (15,51). Both culture strategies applied in the present study imply an optimum fibroblast-to-EC ratio for EC attachment, survival, and network formation that is in the range of 10 to 1.…”

Inhibition of P38 MAPK Reduces Tumor Conditioned Medium-Induced Angiogenesis in Co-Cultured Human Umbilical Vein Endothelial Cells and Fibroblasts

“…The fact that capillary-like structure formed in all groups indicates that apoptosis occuring in HUVECs does not prevent HUVECs from differentiating into capillary-like structures. Other reports have also suggested that the occurrence of apoptosis in the endothelium is required during the formation of capillary network structure, [34][35][36] since inhibition of apoptosis weakens the potential of angiogenesis by HUVECs. 37) Yilmaz recently reported that inhibition of p38 MAPK by SB203580 prevented serum starvation-induced apoptosis in HUVECs.…”

Regulation of vascular growth and function in the human placenta

“…These precursor endothelial cells are united by either desmosomes or tight junctions, and the cords gradually acquire lumens and unite to form vessels (Dempsey 1972, Demir et al 1989. The first signs of lumen formation are seen around 23 days pc, and immunohistochemical and morphological evidences suggest that apoptosis is involved in the process (Tertemiz et al 2005). Early erythrocytes, still containing a nucleus, are often seen within the newly formed lumen, having differentiated from the inner aspect of the hemangioblastic cluster.…”