Spreading Depression-Induced Cyclooxygenase-2 Expression in the Cortex

Spreading depression (SD) is a wave of sustained depolarization challenging the energy metabolism of the cells without causing irreversible damage. However, brain injury, especially focal ischemic stroke, triggers SD-like waves, which in the vicinity of the original damage site contribute to enlargement of the dying brain tissue. Brain injury induces expression of several genes, which are thought to play a role in neuronal death, and therefore represent potential targets for therapy. One such gene is cyclooxygenase-2 (COX-2), an inducible prostaglandin and superoxide producing enzyme. Here we review our recent studies on the regulation of COX-2 in SD.     

Bcl-2 overexpression protects against neuron loss within the ischemic margin following experimental stroke and inhibits cytochrome c translocation and caspase-3 activity

Bcl-2 protects against both apoptotic and necrotic death induced by several cerebral insults. We and others have previously demonstrated that defective herpes simplex virus vectors expressing Bcl-2 protect against various insults in vitro and in vivo, including cerebral ischemia. Because the infarct margin may be a region that is most amenable to treatment, we first determined whether gene transfer to the infarct margin is possible using a focal ischemia model. Since ischemic injury with and without reperfusion may occur by different mechanisms, we also determined whether Bcl-2 protects against focal cerebral ischemic injury either with or without reperfusion in rats. Bax expression, cytochrome c translocation and activated caspase-3 expression were also assessed. Viral vectors overexpressing Bcl-2 were delivered to the infarct margin. Reperfusion resulted in larger infarcts than permanent occlusion. Bcl-2 overexpression significantly improved neuron survival in both ischemia models. Bcl-2 overexpression did not alter overall Bax expression, but inhibited cytosolic accumulation of cytochrome c and caspase-3 activation. Thus, we provide the first evidence that gene transfer to the infarct margin is feasible, that overexpression of Bcl-2 protects against damage to the infarct margin induced by ischemia with and without reperfusion, and that Bcl-2 overexpression using gene therapy attenuates apoptosis-related proteins. This suggests a potential therapeutic strategy for stroke.     

Pathophysiology and Therapy of Experimental Stroke

1. Stroke is the neurological evidence of a critical reduction of cerebral blood flow in a circumscribed part of the brain, resulting from the sudden or gradually progressing obstruction of a large brain artery. Treatment of stroke requires the solid understanding of stroke pathophysiology and involves a broad range of hemodynamic and molecular interventions. This review summarizes research that has been carried out in many laboratories over a long period of time, but the main focus will be on own experimental research.2. The first chapter deals with the hemodynamics of focal ischemia with particular emphasis on the collateral circulation of the brain, the regulation of blood flow and the microcirculation. In the second chapter the penumbra concept of ischemia is discussed, providing a detailed list of the physiological, biochemical and structural viability thresholds of ischemia and examples of how these thresholds can be applied for imaging the penumbra. The third chapter summarizes the pathophysiology of infarct progression, focusing on the role of peri-infarct depolarisation, the multitude of putative molecular injury pathways, brain edema and inflammation. Finally, the fourth chapter provides an overview of currently discussed therapeutic approaches, notably the effect of mechanical or thrombolytic reperfusion, arteriogenesis, pharmacological neuroprotection, ischemic preconditioning and regeneration.3. The main emphasis of the review is placed on the balanced differentiation between hemodynamic and molecular factors contributing to the manifestation of ischemic injury in order to provide a rational basis for future therapeutic interventions.     

Biochemical and Molecular Characteristics of the Brain with Developing Cerebral Infarction

1. We review the biochemical and molecular changes in brain with developing cerebral infarction, based on recent findings in experimental focal cerebral ischemia.2. Occlusion of a cerebral artery produces focal ischemia with a gradual decline of blood flow, differentiating a severely ischemic core where infarct develops rapidly and an area peripheral to the core where the blood flow reduction is moderate (called penumbra). Neuronal injury in the penumbra is essentially reversible but only for several hours. The penumbra area tolerates a longer duration of ischemia than the core and may be salvageable by pharmacological agents such as glutamate antagonists or prompt reperfusion.3. Upon reperfusion, brain cells alter their genomic properties so that protein synthesis becomes restricted to a small number of proteins such as stress proteins. Induction of the stress response is considered to be a rescue program to help to mitigate neuronal injury and to endow the cells with resistance to subsequent ischemic stress. The challenge now is to determine how the neuroprotection conferred by prior sublethal ischemia is achieved so that rational strategies can be developed to detect and manipulate gene expression in brain cells vulnerable to ischemia.4. Expansion of infarction may be caused by an apoptotic mechanism. Investigation of apoptosis may also help in designing novel molecular strategies to prevent ischemic cell death.5. Ischemia/reperfusion injury is accompanied by inflammatory reactions induced by neutrophils and monocytes/macrophages infiltrated and accumulated in ischemic areas. When the role of the inflammatory/immune systems in ischemic brain injury is revealed, new therapeutic targets and agents will emerge to complement and synergize with pharmacological intervention directed against glutamate and Ca²⁺ neurotoxicity.