New therapies to improve stroke outcome

Stroke remains a leading cause of long-term disability and mortality worldwide, yet no viable treatment is readily available to the majority of stroke patients. New effective strategies for therapy are therefore urgently required to aid in limiting brain injury and/or promoting functional recovery after stroke. The experiments described in this Thesis have used models of stroke in vivo and in vitro to explore and identify some of the novel therapeutic targets against ischemic stroke. In Chapter 3, we demonstrated for the first time that direct stimulation of angiotensin II type 2 receptors (AT₂R) using a selective agonist, CGP42112, exerts neuroprotection in mice following cerebral ischemia in vitro and in vivo. We found that CGP42112 can directly protect neurons from injury following glucose deprivation. Furthermore, administration of CGP42112 reduced infarct volume and improved behavioural outcomes at 24 h after stroke. Interestingly, we also found that CGP42112 treatment in vivo enhanced regional cerebral blood flow during reperfusion and reduced cleaved/activated caspase 3 immunoreactivity in the ischemic hemisphere compared to vehicle-treated mice suggesting that the protective effect may be associated with enhanced vasodilatation and reduced neuronal apoptosis. In Chapter 4, we examined the effect of direct Mas receptor (MasR) activation using AVE0991, a selective MasR agonist, in our in vitro and in vivo models of stroke. In this study, we showed for the first time that AVE0991 can directly protect neurons subjected to glucose deprivation in vitro, but this protective effect failed to successfully translate to our in vivo model of stroke. In Chapter 5, we tested whether targeting a broad spectrum of chemokines using a novel type of chemokine binding protein (CBP) can reduce infiltration of leukocytes into the brain and improve stroke outcomes. We found that intravenous administration of CBP can effectively block increases in plasma levels of chemokines CCL2/MCP-1 and CXCL2/MIP-2 for at least the first 48 h after stroke. We also found that CBP treatment attenuated leukocyte infiltration into brain, neurological deficit and infarct volume at 24 h, but CBP was no longer protective at 48 h after stroke. These findings suggest that post-stroke CBP treatment exert temporary neuroprotection by retarding but not preventing leukocyte infiltration into the brain, thereby delaying infarct development and neurological deficits. In Chapter 6, we examined changes in the brain expression of numerous miRNA and their target genes after stroke, and particularly focused on changes in miR-367 following ischemia with or without reperfusion. Our main findings reveal miR-367 as a critical player in mediating gene expression and regulation that are associated with neuronal activation and oxidative stress. Interestingly, the study also demonstrated for the first time that miR-367 may play an important role in chemerin-signaling network after stroke. However, the underlying mechanism and clinical relevance remain unclear. Collectively, the findings of this Thesis provide novel insights into some mechanisms of injury and potential therapeutic targets in the ischemic brain, revealing new strategies that could be developed for use in combination with vessel recanalization.