Apoptotic DNA fragmentation and upregulation of Bax induced by transient ischemia of the rat retina

This study was performed to examine the involvement of apoptosis and the ex pression of bcl-2 family genes in ischemia-induced retinal injury. Retinal ischemia was induced in adult rats by raising the intraocular pressure to 1 30 mmHg for 45 min. Selective damage to the inner retina was observed 7 day s after ischemia. No terminal deoxynucleotidyl-transferase (TdT)-mediated d UTP nick end-labeling (TUNEL) positive cells were observed in the normal re tina, but there was a significant number of TUNEL positive cells 6-48 h aft er transient ischemia followed by a decrease at 96 and 168 h. The number of TUNEL positive cells reached a maximum at 24 h after ischemia. DNA ladderi ng was observed on agarose gel electrophoresis with the retinas 24 and 48 h after ischemia but not in the normal retina. Semiquantitative reverse tran scription-polymerase chain reaction (RT-PCR) revealed that bax gene express ion did not change immediately after cessation of ischemia, but gradually i ncreased as early as 6 h, reached a peak at 24 h, then decreased to near ba seline levels at 168 h. On the other hand, bcl-2 gene expression showed no obvious changes at any time after transient ischemia. Moreover, intense Bax protein immunoreactivity was detected in the retinal sections at 24 h afte r ischemia although little immunoreactivity was present in the normal secti ons. These results suggest that apoptosis associated with the expression of Bax is involved in retinal cell loss after ischemic insult. (C) 1999 Elsev ier Science B.V. All rights reserved.