The Role of Apoptosis in the Closure of Human Umbilical Vessels at Birth and Its Mechanism

Hwang, Kyung Kuk; Kim, Hyo Soo; Seo, Jung Uk; Chae, In Ho; Sohn, Dae Won; Oh, Byung Hee; Lee, Myoung Mook; Park, Young Bae; Choi, Yun Shik; Seo, Jung Don; Lee, Young Woo

Abstract

BACKGROUND: The mechanism of the closure of umbilical vessels is known to be multifactorial. In order to verify that apoptosis is one of the possible closure mechanisms, we studied to identify apoptosis in umbilical vessels and evaluate its mechanism by studying apoptosis-related gene and the relationship between the pattern of apoptosis and gestational age (GA).
METHODS
Twelve umbilical cords of GA of 37-42 weeks were obtained immediatly (less than 10 min. for minimal ongoing external influences) after birth. The presence of apoptotic cells was demonstrated by electron microscopy (EM) and terminal deoxynucleotidyl transferase- mediated dUTP nick end labeling (TUNEL). Immunohistochemical staining and Western blotting were used for the analysis of the proteins of apoptosis-related gene.
RESULTS
Apoptosis of the smooth muscle cells of media and intima of umbilical vessels was identified at EM, regardless of GA from 37 to 42 weeks. The proportion of TUNEL (+) cells was 80% in intima, 40% in media, 80% in connective tissue of umbilical cord. The expressions of bax-alpha, bcl-Xs/L were strong in intima, in media and connective tissue, but those of bcl-2 were detected in only in connective tissue, regardless of GA in immunohistochemistry. The ratios of expressions of bax-alpha to bcl-2, bcl-Xs to bcl-XL, did not change with increasing GA from 37 to 42 weeks in Western blotting.
CONCLUSION
Apoptosis was identified in umbilical vessels. The closure of umbilical vessels can be explained by apoptosis where the ratios of bax-alpha/bcl-2, bcl-Xs/ bcl-XL play an important role. The fact that there were no differences in the extent of apoptosis and the expressions of bax-alpha/bcl-2, bcl-Xs/bcl-XL according to GA, suggests that apoptosis of umbilical vessels is more dependent on the external stimuli during delivery than GA.