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Title: Mechanisms underlying the endogenous neuroprotection of hamartin in ischaemic stroke
Author: Hadley, Gina Louise
ISNI:       0000 0004 5922 0745
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 2016
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Introduction: Hamartin has been shown to mediate the endogenous resistance of Cornu Ammonis 3 (CA3) neurons to ischaemia. Proposed mechanisms concern the inhibition of mammalian target of rapamycin (mTOR) which could promote productive autophagy and prevent endoplasmic reticulum (ER) stress. A small molecule targeted at these pathways could protect neurons and buy valuable time for recanalization therapy for stroke. Methods: In vivo, the modified four vessel occlusion model of global cerebral ischaemia was used in male Wistar rats. A temporal and spatial profile for hamartin and mTOR proteins and their downstream mechanisms of autophagy and ER stress was characterised using Western blotting. In vitro, small molecules were assessed in E18 neuronal cultures exposed to oxygen and glucose deprivation (OGD) in an attempt to replicate hamartin’s protective effect. Results: Time course experiments revealed that global ischaemia selectively induced hamartin expression in the membrane fraction of the hippocampal CA3 region, peaking at 12 hours of reperfusion. Autophagy-associated proteins were differentially expressed in CA1 and CA3 after global ischaemia. Decreased levels of ER stress proteins were observed in CA3 neurons while increased ER stress was found in CA1 neurons after global ischaemia. In vitro, hamartin’s neuroprotective effect appeared to be due to the induction of productive autophagy. The mTOR inhibitor rapamycin did not replicate hamartin’s protective effect. Induction of autophagy with metformin and attenuation of the ER stress response with salubrinal also failed to afford neuroprotection. A novel mTORC1/2 inhibitor, AZD2014, currently in clinical trials for cancer, caused increased neurotoxicity following OGD which was associated with increased ER stress. Conclusions: The selective dynamic response of hamartin is involved in the endogenous resistance of CA3 neurons to global ischaemia. The temporal association between increased hamartin expression, induction of productive autophagy and decreased ER stress levels in CA3 neurons may contribute to the mechanism of hamartin’s endogenous protective effect. None of the pharmacological agents that targeted downstream mechanisms of hamartin replicated these neuroprotective effects. Further research is needed to fully understand the neuroprotection elicited by hamartin and discover a small molecule that can mimic these effects.
Supervisor: Not available Sponsor: Oxford University Clinical Academic Graduate School
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available