Effect of Ischemic Preconditioning on Mitochondrial Dysfunction and Mitochondrial P53 Translocation after Transient Global Cerebral Ischemia in Rats

Abstract

Transient global brain ischemia induces dysfunctions of mitochondria including disturbance in mitochondrial protein synthesis and inhibition of respiratory chain complexes. Due to capacity of mitochondria to release apoptogenic proteins, ischemia-induced mitochondrial dysfunction is considered to be a key event coupling cerebral blood flow arrest to neuronal cell death. Ischemic preconditioning (IPC) represents an important phenomenon of adaptation of central nervous system (CNS) to sub-lethal short-term ischemia, which results in increased tolerance of CNS to the lethal ischemia. In this study we have determined the effect of ischemic preconditioning on ischemia/reperfusion-associated inhibition of mitochondrial protein synthesis and activity of mitochondrial respiratory chain complexes I and IV in the hippocampus of rats. Global brain ischemia was induced by 4-vessel occlusion in duration of 15 min. Rats were preconditioned by 5 min of sub-lethal ischemia and 2 days later, 15 min of lethal ischemia was induced. Our results showed that IPC affects ischemia-induced dysfunction of hippocampal mitochondria in two different ways. Repression of mitochondrial translation induced during reperfusion of the ischemic brain is significantly attenuated by IPC. Slight protective effect of IPC was documented for complex IV, but not for complex I. Despite this, protective effect of IPC on ischemia/reperfusion-associated changes in integrity of mitochondrial membrane and membrane proteins were observed. Since IPC exhibited also inhibitory effect on translocation of p53 to mitochondria, our results indicate that IPC affects downstream processes connecting mitochondrial dysfunction to neuronal cell death.

Mechanisms of Ischemic Induced Neuronal Death and Ischemic Tolerance

“…In addition, IPC had significant protective effect on ischemia-induced DNA fragmentation, as well as on number of positive Fluoro-Jade C staining cells. Thus, it indicates that IPC abolished almost completely both initiation and execution of mitochondrial apoptosis induced by global brain ischemia in vulnerable CA1 layer of rat hippocampus (Racay et al, 2007(Racay et al, , 2009b. The studies showed that ischemia induced inhibition of mitochondrial complexes I and IV, however inhibition is not accompanied by a decrease of mitochondrial Ca 2+ uptake rate apparently due to the excess capacity of the complex I and complex IV.…”

“…Collective studies confirm, that reactive oxygen species (ROS) contribute to neuronal cell injuries secondary to ischemia and reperfusion (Lehotsky et al, 2004;Burda et al, 2005;Danielisova et al, 2005;Shi and Liu, 2007) and might initiate cell death signaling pathways after cerebral ischemia and parallels with selective post-ischemic vulnerability of the brain (Valko et al, 2007;Shi and Liu, 2007;Otani, 2008;Dirnagl et al, 2009). As shown by measurement of steady state fluorescence of ANS in hippocampal mitochondria (Racay et al, 2007(Racay et al, , 2009a, naive IRI induced significant increase in ANS flurescence (it binds to hydrophobic part of membrane lipids and proteins) of the forebrain in both ischemic and reperfusion periods. These results support data from previous experiments (Lehotsky et al, 2004;Babusikova et al, 2008), which showed that IRI induced structural changes on hippocampal membrane lipids and both, the lipoperoxidation dependent and the direct www.intechopen.com oxidative modifications of membrane proteins.…”

“…In a series of recent papers (Racay et al, 2007(Racay et al, , 2009a, authors have studied the effect of global cerebral ischemia/reperfusion injury (IRI) and ischemic tolerance developed by prior ischemic non-injurious stimulus -preconditioning-ischemic preconditioning (IPC) on mitochondrial Ca 2+ homeostasis and mitochondrial way of apoptosis. As documented by Racay et al (2007Racay et al ( , 2009a, global ischemia led to progressive decrease of complex I activity after IRI to 65.7% of control at 24 h after reperfusion. In preconditioned animals, the activity of complex I was also significantly inhibited after ischemia (to 65.4% of control) and ischemia/reperfusion for 1, 3, and 24 h (62-78% of control).…”

“…As shown by experimental and clinical studies, IRI -induced mitochondrial pathway of apoptosis is an important event leading to neuronal cell death after blood flow arrest. Impact of IRI and ischemic preconditioning on the level of apoptotic and anti-apoptotic proteins was assessed in both cortical and hippocampal mitochondria by Western blot analysis of p53, bax, and bcl-x (Racay et al, 2007(Racay et al, , 2009b. Remarkably, IRI led to increase of p53 level in hippocampal mitochondria, with significant differences after 3 h (217.1 ± 42.2% of control), 24 h (286.8 ± 65% of control), and 72 h (232.9 ± 37.3% of control) of reperfusion.…”

Mitochondrial complex I in the network of known and unknown facts

“…Moreover, it is believed that CI dysfunction and the subsequent impairment of mitochondrial respiration provoke the activation of the mitochondrial-dependent apoptotic machinery by directly triggering the release of apoptogenic molecule cytochrome c from defective mitochondria (Green and Kroemer 2004;Clayton et al 2005;Perier et al 2007). Finally, loss of mitochondrial CI catalytic activity in the electron transport chain is associated with a wide spectrum of neurodegenerative disorders (Table 1) or acute pathophysiological processes such as ischemia-reperfusion injury (Almeida et al 1995;Tompkins et al 2006;Racay et al 2007) and heart failure as well as with normal aging process (Petrosillo et al 2008). …”