Apoptosis in Rat Liver Development: tTG and TGF beta1 Expression Related to Apoptotic Mechanism

Lim, Kyung Taek; Chae, Hee Sun; Yoon, Suk Hwan; Kim, Sung Su; Kim, Kyung Yong; Lee, Won Bok

Abstract

This study was designed to investigate the apoptosis and the roles of TGF beta1 and tTG in apoptosis in fetal and postnatal rat livers using TUNEL and immunohistochemical staining. Results obtained were as follows: 1. Apoptosis began to appear in gestation day 15, reached the peak in gestation day 16 showing the highest activity of hepatic hemopoiesis, and gradually decreased after gestation day 18. But apoptosis repeatedly increased after postnatal day 1. 2. The cells showing apoptosis were mainly hemopoietic cells during gestation period, but were mainly hepatocytes after birth. In addition, apoptosis increased in sinusoidal endothelial cells after birth. 3. Apoptotic bodies rarely appeared in gestation day 16, increased in gestation day 18, and partly decreased after gestation day 20. Thereafter, the frequency of apoptotic bodies was relatively constant untill postnatal day 10. 4. TGF b1 began to be expressed from gestation day 14 when apoptosis occurred, was strongly expressed from gestation day 16, and became to be expressed weakly after gestation day 18. The expression of TGF beta1 was increased in sinusoidal endothelial cells after birth. 5. tTG began to be expressed in gestation day 16 during the highest activity of hemopoietic stage, and became to be expressed weakly in apoptotic bodies after gestation day 18. The expression of tTG increased again mainly in sinusoidal endothelial cells after birth. In summary, it is suggested that apoptosis is related to the control of hemopoiesis in prenatal period and the maintenance of the physiological balance of hepatic tissue after birth, and that TGF beta1 is related to the induction of the apoptosis during liver development and to the formation of apoptotic bodies through the control of the expression of tTG.