Ubiquitin Activity Following Forebrain Ischemia/Reperfusion in the Rat

Abstract

Domorakova I., E. Mechirova, J. Burda, M. Ferikova: Ubiquitin Activity Following Forebrain Ischemia/Reperfusion in the Rat. Acta Vet. Brno 2004, 73: 45-49. Cerebral ischemia/reperfusion leads to selective neuronal death in specific brain areas. The effects of forebrain ischemia produced by four-vessel occlussion were investigated in rats. Immunohistochemical localization of ubiquitin in the brain cortex and hippocampus was studied. Using antibodies against ubiquitin we have found that ubiquitin immunoreactivity (UIR) was normally present in all neurons of hippocampus and in the cerebral cortex. After 20 min of ischemia and 24 h of reperfusion the number of ubiquitin positive cells was decreased in CA2 and CA3 regions of hippocampus and ubiquitin-negative neurons were found in the most vulnerable region of CA1 subfield. Cerebral cortex showed significant changes of ubiquitin immunoreactivity in the nuclei and perikarya of pyramidal neurons. Seven days of reperfusion after 20 min of ischemia showed recovery of UIR in the hippocampal CA2, CA3 regions and in granule cells layer of the dentate gyrus. The most vulnerable CA1 pyramidal cells showed morphological changes of the cell bodies and irregularities of the cell membrane. Interestingly, number of those cells display intensive UIR in their perikarya and in the nuclei as well . Comparison of UIR in CA1 pyramidal cells after ischemia/reperfusion with those in the control sections showed increase in ubiquitin reaction. Remarkable UIR was also found in all layers in the cerebral cortex. These data suggest that recovery of ubiquitin immunoreactivity in some regions of hippocampus and cerebral cortex may be a prerequisite to neuronal survival after ischemia /reperfusion. In CA1 region the accumulation of ubiquitinated proteins in pyramidal cells was visualized without their degradation. The stress protein ubiquitin is one of the regulatory proteins playing a role in ischemic tolerance. Ischemia, hippocampus, cerebral cortex, ubiquitin, rat Specific neuronal populations in the brain are selectively vulnerable to ischemic insults. Ischemic cell death is characterized by a delay between the insult and manifestation of major cell damage. This delay varies greatly, depending on the nature of the insult and of the brain region being affected (Lipton 1999). Two different types of cell death can be discerned. One type progresses rapidly over a period of hours whereas the second type requires several days to mature (Kirino 1982). The hippocampus is a brain structure displaying both these features. Following transient periods of cerebral ischemia in the rat a rapid degeneration of the neurons in the dentate gyrus takes place. The CA1 neurons, on the other hand, show light microscopical signs of degeneration during the first days following the insult, demonstrating delayed neuronal death (Kirino 1982; Pulsinelli and Brierley 1982). Although total protein synthesis of the brain during ischemia/reperfusion is severely inhibited ( Araki et al. 1990), synthesis of specific proteins, such as heat shock proteins (HSP70) is induced. Protective role of HSP in ischemic tolerance has been reported by Kirino et al. (1991) and Liu et al. (1992). Ubiquitin, a low molecular weight heat shock protein found in all eukaryotic cells, is bound to short-lived and denatured proteins produced by various forms of injury. Ubiquitin