Deciphering the molecular signaling cascade in neuronal death

Hydrogen sulphide (H2S), an important physiological gaso-neurotransmitter involved in neuronal long-term potentiation, is a mediator of cerebral ischemic injury. Previous study has identified H2S neuropathological implication in aggravation of ionotropic glutamate receptors (iGluRs) -induced excitotoxicity injury. Excitotoxicity is one of the earliest events in stroke, a leading cause of adult permanent disability globally. Despite extensive efforts to deduce effective therapeutic interventions, the only clinically approved stroke treatment yields limited efficacy and potential risk to intracranial hemorrhage. The purpose of my project is to formulate screening platforms and define potential manipulative targets for stroke intervention via comparative global transcriptional profiling of in vitro and in vivo models. This facilitates identification of common mechanistic pathways governing ischemic progression. Cultured primary cortical neurons treated with selective iGluRs agonists were used as in vitro cerebral ischemia representations. Comparative microarray analysis revealed occurrence of inflammation, oxidative stress and particularly cell cycle re-activation during excitotoxicity. Since cerebral ischemia does not limit at excitotoxicity but also involves critical focal hypoperfusion to a localized brain region causing oxygen-glucose deprivation that leads to further complications (e.g. microvascular injury, blood-brain barrier impairment and post-ischemic inflammation), microarray analysis was performed on in vivo cerebral ischemia rodent models (hypoxic ischemia, transient and permanent focal ischemia). Again, oxidative stress and neuroinflammation were confirmed as primary events. Transient cerebral ischemia induces a secondary damage called ischemia/reperfusion (I/R) injury, mediated by release of oxidative stressors into the bloodstream upon perfusion to the occluded artery. In order to accentuate the significance of oxidative stress during I/R injury, transgenic glutathione peroxidase-1 (a major antioxidant enzyme)-knockout mice were subjected to transient middle cerebral artery occlusion with observed downplay of Nrf2 (a cytoprotective transcription factor)-mediated anti-oxidative response, ubiquitin-proteasomal dysfunction and recruitment of additional cell death pathways mediated by p53 and Fas ligand. As observed in the in vitro models, cell cycle re-activation is a major upstream signaling pathway in neuronal injury mediation, and in particular a group of cell cycle protein kinases known as aurora kinases (AURKs), has been identified to be up-regulated for the first time in stroke. A selective AURKs inhibitor was applied to permanent focal ischemia model to determine if cell cycle impediment could abrogate ischemic progression. Unprecedentedly, AURKs inhibition successfully attenuated infarct damage via down-regulation of the neuroinflammation particularly the chemokine signaling pathway. Overall, my research facilitates a tremendous step in understanding stroke pathogenesis and identified a novel target which manipulation has achieved promising therapeutic efficacy.