Retinal ischemia-induced apoptosis is associated with alteration in Bax and Bcl-xL expression rather than modifications in Bak and Bcl-2

[摘要] Purpose: Apoptosis is known to play akey role in cell death after retinal ischemia. However, little is knownabout the kinetics of the signaling pathways involved and theircontribution to this process. The aim of this study was to determinewhether changes in the expression of molecules in the mitochondrialapoptotic pathway might explain the progression of retinal damagefollowing ischemia/reperfusion. Methods: Retinal ischemia was induced byelevating intraocular pressure in the vitreous cavity to 150 mmHgfor a period of 60 min. At time 0, 3 h (early phase), and 24 h (latephase) after reperfusion, the retinas were harvested and modificationsin the expression of Bax, Bak, Bcl-2, and Bcl-xL as well ascaspase-3 and −7, were examined by qPCR and, in some cases, by westernblot. Results: qPCR analysis performed at theearly phase after ischemia revealed a time dependent decrease in Bax,Bak, and Bcl-xL and no alteration in Bcl-2mRNA expression in response to retinal ischemia. At the protein level,proapoptotic Bax and Bak were not modulated while Bcl-2 and Bcl-xLwere significantly upregulated. At this stage, the Bax per Bcl-2 andBax:Bcl-xL ratios were not modified. At the late phase ofrecovery, Bax and Bcl-xL mRNAs weredownregulated while Bak was increased. Increased Bax:Bcl-2 andBax:Bcl-xL ratios at both the mRNA and protein levels wereobserved 24 h after the ischemic insult. Analysis of caspasesassociated with mitochondria-mediated apoptosis revealed a specificincrease in the expression of caspase-3 in the ischemic retinas24 h after reperfusion, and a decrease in the expression of caspase-7.Conclusions: This study revealed thatBcl-2-related family members were differently regulated in the earlyand late phases after an ischemic insult. We showed that the Bax:Bcl-2and Bax:Bcl-xL balances were not affected in the initialphases, but the Bax:Bcl-xL ratio shifted toward apoptosisduring the late phase of recovery. This shift was reinforced by caspase-3upregulation.

[学科分类] 生物化学/生物物理