Dysregulation of Amyloid-β Protein Precursor, β-Secretase, Presenilin 1 and 2 Genes in the Rat Selectively Vulnerable CA1 Subfield of Hippocampus Following Transient Global Brain Ischemia

Sevoflurane Post-conditioning Enhanced Hippocampal Neuron Resistance to Global Cerebral Ischemia Induced by Cardiac Arrest in Rats through PI3K/Akt Survival Pathway

The purpose of this current study was to evaluate whether improvement of mitochondrial dysfunction was involved in the therapeutic effect of sevoflurane post-conditioning in global cerebral ischemia after cardiac arrest (CA) via the PI3K/Akt pathway. In the first experiment, animals were randomly divided into three groups: a sham group, a CA group, a CA+sevoflurane post-conditioning group (CA+SE). Sevoflurane post-conditioning was achieved by administration of 2.5% sevoflurane for 30 min after resuscitation. Sevoflurane post-conditioning has a significant neuroprotective effect by increasing survival rates and reducing neuronal apoptosis. Additionally, the gene and protein expression of PGC-1α, NRF-1, and TFAM, the master regulators of mitochondrial biogenesis, were up-regulated in the CA+SE group, when compared to the CA group. Similarly, in contrast to the CA group, mitochondria-specific antioxidant enzymes, including heat-shock protein 60 (HSP60), peroxiredoxin 3 (Prx3), and thioredoxin 2 (Trx2) were also increased in the CA+SE group. Finally, administration of sevoflurane ameliorated mitochondrial reactive oxygen species (ROS) formation and maintained mitochondrial integrity. In the second experiment, we investigated the relationship between the PI3K/Akt pathway and mitochondrial biogenesis and mitochondria-specific antioxidant enzymes in sevoflurane-induced neuroprotection. The selective PI3K inhibitor wortmannin not only eliminated the beneficial biochemical processes of sevoflurane by reducing the level of mitochondrial biogenesis-related proteins and aggravating mitochondrial integrity, but also reversed the elevation of mitochondria-specific antioxidant enzymes induced by sevoflurane. Therefore, our data suggested that sevoflurane post-conditioning provides neuroprotection via improving mitochondrial biogenesis and integrity, as well as increasing mitochondria-specific antioxidant enzymes by a mechanism involving the PI3K/Akt pathway.

Expression of Alzheimer's disease risk genes in ischemic brain degeneration

We review the Alzheimer-related expression of genes following brain ischemia as risk factors for late-onset of sporadic Alzheimer's disease and their role in Alzheimer's disease ischemia-reperfusion pathogenesis. More recent advances in understanding ischemic etiology of Alzheimer's disease have revealed dysregulation of Alzheimer-associated genes including amyloid protein precursor, β-secretase, presenilin 1 and 2, autophagy, mitophagy and apoptosis. We review the relationship between these genes dysregulated by brain ischemia and the cellular and neuropathological characteristics of Alzheimer's disease. Here we summarize the latest studies supporting the theory that Alzheimer-related genes play an important role in ischemic brain injury and that ischemia is a needful and leading supplier to the onset and progression of sporadic Alzheimer's disease. Although the exact molecular mechanisms of ischemic dependent neurodegenerative disease and neuronal susceptibility finally are unknown, a downregulated expression of neuronal defense genes like alfa-secretase in the ischemic brain makes the neurons less able to resist injury. The recent challenge is to find ways to raise the adaptive reserve of the brain to overcome such ischemic-associated deficits and support and/or promote neuronal survival. Understanding the mechanisms underlying the association of these genes with risk for Alzheimer's disease will provide the most meaningful targets for therapeutic development to date.

Brain ischemia with Alzheimer phenotype dysregulates Alzheimer's disease-related proteins

There are evidences for the influence of Alzheimer's proteins on postischemic brain injury. We present here an overview of the published evidence underpinning the relationships between β-amyloid peptide, hyperphosphorylated tau protein, presenilins, apolipoproteins, secretases and neuronal survival/death decisions after ischemia and development of postischemic dementia. The interactions of above molecules and their influence and contribution to final ischemic brain degeneration resulting in dementia of Alzheimer phenotype are reviewed. Generation and deposition of β-amyloid peptide and tau protein pathology are essential factors involved in Alzheimer's disease development as well as in postischemic brain dementia. Postischemic injuries demonstrate that ischemia may stimulate pathological amyloid precursor protein processing by upregulation of β- and γ-secretases and therefore are capable of establishing a vicious cycle. Functional postischemic brain recovery is always delayed and incomplete by an injury-related increase in the amount of the neurotoxic C-terminal of amyloid precursor protein and β-amyloid peptide. Finally, we present here the concept that Alzheimer's proteins can contribute to and/or precipitate postischemic brain neurodegeneration including dementia with Alzheimer's phenotype.

Alzheimer-associated presenilin 2 gene is dysregulated in rat medial temporal lobe cortex after complete brain ischemia due to cardiac arrest

BACKGROUND

Brain ischemia may be causally related with Alzheimer's disease. Probably, presenilin gene dysregulation may be associated with Alzheimer's disease neuropathology. Consequently, we have examined quantitative changes in both presenilin 1 and 2 genes in the medial temporal lobe cortex following 10-min global brain ischemia in rats.

METHODS

Global brain ischemia was induced by cardiac arrest in female rats that were allowed to survive for 2, 7 and 30 days. The expression of presenilin genes was evaluated in the rat medial temporal lobe cortex with the use of quantitative RT-PCR analysis.

RESULTS

Presenilin 1 gene expression tended to be downregulated from days 2 to 7 postischemia but at day 30, there was a reverse tendency. The greatest overexpression of presenilin 2 gene was noted at 2-nd day whilst on day 7, the expression of this gene was only modestly elevated. Eventually, at day 30 expression of presenilin 2 gene was modestly downregulated. Alterations of presenilin 2 gene expression between 2 and 7 days and between 2 and 30 days were statistically significant.

CONCLUSIONS

Thus, presented changes suggest that the significant dysregulation of presenilin 2 gene may be connected with a response of neuronal cells to transient global brain ischemia due to cardiac arrest. Finally, the ischemia-induced gene dysregulation may play a key role in the late onset of Alzheimer's-type dementia.