Induction of Apoptosis in Fish Cells by Hypertonic Stress

Abstract

Effects of osmotic stresses on apoptotic cell death of a fish cell line (Epithelioma Papulosum Cyprini, EPC) were investigated. EPC showed DNA fragmentation, which is a biochemical feature of apoptosis, under hypertonic stress, when exposed to 400-600 mOsm/kg media with sodium chloride supplementation. Similar results were obtained upon exposure to 450mOsm/kg medium with sorbitol. DNA fragmentation increased significantly within 3 h after exposure to the hypertonic stress. Nuclear condensation, which is a morphological hallmark of apoptosis, was also observed in the culture of EPC exposed to hypertonic stress. The amount of native nucleosomal DNA was evaluated to find whether the whole cell population undergoes apoptosis. As a result, hypertonicity below 500 mOsm/kg triggered apoptotic cell death only in a part of the whole cell population, while 600 mOsm/kg brought about cell death in a large proportion of the population by necrosis as well as apoptosis. In contrast, hypotonic media (150 and 200 mOsm/kg) did not induce DNA fragmentation. DNA fragmentation of EPC induced by hypertonic stress was suppressed in the presence of Zn2+, suggesting that a Zn2+-susceptible endonuclease(s) may be responsible for cleavage of nucleosomal DNA.