Subarachnoid hemorrhage triggers neuroinflammation of the entire cerebral cortex, leading to neuronal cell death

BACKGROUND

Subarachnoid hemorrhage (SAH) is a fatal disease, with early brain injury (EBI) occurring within 72 h of SAH injury contributes to its poor prognosis. EBI is a complicated phenomenon involving multiple mechanisms. Although neuroinflammation has been shown to be important prognosis factor of EBI, whether neuroinflammation spreads throughout the cerebrum and the extent of its depth in the cerebral cortex remain unknown. Knowing how inflammation spreads throughout the cerebrum is also important to determine if anti-inflammatory agents are a future therapeutic strategy for EBI.

METHODS

In this study, we induced SAH in mice by injecting hematoma into prechiasmatic cistern and created models of mild to severe SAH. In sections of the mouse cerebrum, we investigated neuroinflammation and neuronal cell death in the cortex distal to the hematoma injection site, from anterior to posterior region 24 h after SAH injury.

RESULTS

Neuroinflammation caused by SAH spread to all layers of the cerebral cortex from the anterior to the posterior part of the cerebrum via the invasion of activated microglia, and neuronal cell death increased in correlation with neuroinflammation. This trend increased with the severity of the disease.

CONCLUSIONS

Neuroinflammation caused by SAH had spread throughout the cerebrum, causing neuronal cell death. Considering that the cerebral cortex is responsible for long-term memory and movement, suppressing neuroinflammation in all layers of the cerebral cortex may improve the prognosis of patients with SAH.

Temporal Pattern and Crosstalk of Necroptosis Markers with Autophagy and Apoptosis Associated Proteins in Ischemic Hippocampus

Necroptosis, a novel type of programmed cell death, has been recently implicated as a possible mechanism for cerebral ischemia-reperfusion (I/R) injury. We herein studied time-dependent changes of necroptosis markers along with apoptosis- and autophagy-associated proteins in rat hippocampus at 1, 3, 6, 12, 24, and 48 h after global cerebral I/R injury. Furthermore, to determine the cross talk between autophagy and necroptosis, we examined the effects of pretreatment with bafilomycin-A1 (Baf-A1), as a late-stage autophagy inhibitor, on necroptosis. Highest levels of receptor-interacting protein 1 and 3 (RIP1 and RIP3), as key mediators of necroptosis, were observed at 24 h after reperfusion. Alongside, activity of glutamate dehydrogenase (GLUD1), downstream enzyme of RIP3, was increased. Peak time of necroptosis was subsequent to caspase-3-dependent cell death that peaked at 12 h of reperfusion but concurrent with autophagy. Administration of Baf-A1 could attenuate necroptosis, verified by decrease in RIP1 and RIP3 protein levels, as well as GLUD1 activity. However, there was no significant change in caspase-3-dependent cell death. Taken together, our results highlight that global cerebral I/R activates necroptosis that could be triggered by autophagy and interacts reversely with caspase-3-dependent apoptosis.

Stroke and cardiac cell death: Two peas in a pod

A close pathological link between stroke brain and heart failure may exist. Here, we discuss relevant laboratory and clinical reports demonstrating neural and cardiac myocyte cell death following ischemic stroke. Although various overlapping risk factors exist between cerebrovascular incidents and cardiac incidents, stroke therapy has largely neglected the cardiac pathological consequences. Recent preclinical stroke studies have implicated an indirect cell death pathway, involving toxic molecules, that originates from the stroke brain and produces cardiac cell death. In concert, previous laboratory reports have revealed a reverse cell death cascade, in that cardiac arrest leads to ischemic cell death in the brain. A deeper understanding of the crosstalk of cell death pathways between stroke and cardiac failure will facilitate the development of novel treatments designed to arrest the global pathology of both diseases thereby improving the clinical outcomes of patients diagnosed with stroke and heart failure.

Apitoxin protects rat pups brain from propionic acid-induced oxidative stress: The expression pattern of Bcl-2 and Caspase-3 apoptotic genes

The primary aim of this study was to determine the potential modulatory role of the apitoxin (bee venom; BV) against propionic acid (PPA)-induced neurotoxicity. The biochemical responses to PPA exposure in rat pups were assayed, including changes in the antioxidant barrier systems and lipid peroxidation and protein oxidation biomarkers in the brain tissue. DNA damage was measured by single-cell gel electrophoresis and differences in Bcl-2 and Caspase-3 mRNA expression were assessed using real-time PCR. Changes in amygdala complex ultrastructure were visually assessed using electron microscopy. Sixty rat pups were assigned into six groups: a control group, a PPA-treated group, a BV-treated group, a protective co-treated group, a therapeutic co-treated group, and a protective/therapeutic co-treated group. The results indicate that PPA induced a pronounced increase (64.6%) in malondialdehyde (MDA), and in DNA damage (73.3%) with three-fold increase in protein carbonyl concentration. A significant reduction was observed in the enzyme activities of superoxide dismutase (SOD) (48.7%) and catalase (CAT) (74.8%) and reduced glutathione (GSH) level (52.6%). BV significantly neutralized the PPA-induced oxidative stress effects, especially in the BV protective/therapeutic co-treated group. In this group, GSH levels were restored to 64.5%, and MDA, protein carbonyl levels and tail moment % were diminished by 69.5, 21.1 and 18.8% relative to the control, respectively. Furthermore, while PPA induced significant apoptotic neural cell death, BV markedly inhibited apoptosis by promoting Bcl-2 expression and blocking Caspase-3 expression. BV markedly restored the normal ultrastructural morphology of the amygdala complex neurons. These results conclusively demonstrate that BV administration provides both protective and therapeutic effects in response to the PPA-induced deleterious effects, including oxidative stress, DNA damage, and neuronal death in the brains of rat pups.

Disruption of neurogenesis and cortical development in transgenic mice misexpressing Olig2, a gene in the Down syndrome critical region

The basic helix-loop-helix (bHLH) transcription factor Olig2 is crucial for mammalian central nervous system development. Human ortholog OLIG2 is located in the Down syndrome critical region in trisomy 21. To investigate the effect of Olig2 misexpression on brain development, we generated a developmentally regulated Olig2-overexpressing transgenic line with a Cre/loxP system. The transgenic mice with Olig2 misexpression in cortical neural stem/progenitor cells exhibited microcephaly, cortical dyslamination, hippocampus malformation, and profound motor deficits. Ectopic misexpression of Olig2 impaired cortical progenitor proliferation and caused precocious cell cycle exit. Massive neuronal cell death was detected in the developing cortex of Olig2-misexpressing mice. In addition, Olig2 misexpression led to a significant downregulation of neuronal specification factors including Ngn1, Ngn2 and Pax6, and a defect in cortical neurogenesis. Chromatin-immunoprecipitation and sequencing (ChIP-Seq) analysis indicates that Olig2 directly targets the promoter and/or enhancer regions of Nfatc4, Dscr1/Rcan1 and Dyrk1a, the critical neurogenic genes that contribute to Down syndrome phenotypes, and inhibits their expression. Together, our study suggests that Olig2 misexpression in neural stem cells elicits neurogenesis defects and neuronal cell death, which may contribute to developmental disorders including Down syndrome, where OLIG2 is triplicated on chromosomal 21.