Types of Programmed Cell Death: Two Variants Expressed by Neonatal Murine Hepatocytes

Neonatal livers examined with the terminal transferase-mediated dUTP nick end labeling (TUNEL) method contained numerous positive cells. Although the majority of dying cells are either hematopoietic cells including erythroids and granulocytes or macrophages, a few hepatocytes were also positive. As for the ultrastructural features of these dying hepatocytes, two different types, type I and II, could be identified. The early features of type I appeared in the cytoplasm, which was characterized by dilated rough endoplasmic reticulum, and the cell fragments displayed a round, foamy appearance. Type II was characterized by nuclear compaction and margination of heterochromatin resulting in the formation of sharply circumscribed masses, followed by the condensation of the cytoplasm. The cell death of type I, characterized by the formation of massive vacuolization of the endoplasmic reticulum, corresponds to cytoplasmic type degeneration or nonapoptotic death, while that of type II corresponds to nuclear type cell death or classical apoptotic death. In the two types of programmed cell death, the incidence of nonapoptotic cell death was much higher than that of classical apoptosis in neonatal murine hepatocytes.