title: The role of mineralocorticoid receptor and stress in ischaemic stroke: pre-clinical and clinical studies
Creators: name: Martin, Hannah
Publisher: name: University of Glasgow
Year: 2018

description: Ischaemic stroke is a leading cause of death with a complex pathophysiology. There are several important modifiable risk factors for stroke such as high blood pressure (hypertension), but high levels of the hormone aldosterone have been found to significantly increase risk, independent of blood pressure. Antagonism of the mineralocorticoid receptor (MR), upon which aldosterone exerts its effects, is protective in experimental models of stroke. However, the MR is a transcription factor and despite characterisation of its downstream effects in the kidney, its action in the brain has yet to be elucidated. Furthermore, the main stress hormone cortisol is also able to activate the MR. Stress has long been identified as both a risk factor for stroke, and a key determinant of stroke recovery, but stress is not routinely reported in animal models of experimental stroke. The aims of this thesis were therefore to determine the level of stress experienced by rats undergoing experimental stroke surgery and to evaluate a welfare package designed to reduce stress, to investigate the expression and activation of the MR following transient middle cerebral artery occlusion (tMCAO), and to identify a list of microRNAs (miRNAs) that are altered post-tMCAO and have the potential to regulate the MR. This thesis shows that SHRSPs undergoing tMCAO surgery do experience an increase in stress, as evidenced by significant increases in faecal corticosterone level and loss of body weight post-tMCAO. However, reassurance handling resulted in an even greater increase in stress hormone level in the acute hours post-tMCAO and a failure to re-gain lost body weight, indicating a detrimental effect of the enhanced welfare package on stress levels in SHRSPs undergoing tMCAO. Furthermore, tMCAO surgery has significant effects on cardiovascular properties post-tMCAO, including an immediate loss of diurnal rhythm which did not return within the first 7 days post-surgery. However, reassurance handling had no significant effects on cardiovascular properties compared to control animals. When investigating the expression, activation and action of the MR in SHRSPs in the context of experimental stroke and salt-loading, this thesis has shown that there are strain-specific responses to salt-loading, with significant differences in both MR expression and activation in SHRSPs compared to the normotensive Wistar-Kyoto (WKY) strain. Similarly, there were cell- and region- specific changes in MR expression following hypoxic challenge or tMCAO. Interestingly, MR activation was significantly upregulated in SHRSP brains post-tMCAO even from an early time-point, providing supporting evidence for the beneficial effect of antagonism or regulation of the MR in the context of ischaemic stroke. Lastly, 247 miRNAs were identified as being potential MR regulators, and these were cross-referenced with data from a previous microarray which profiled miRNAs altered following tMCAO, revealing several miRNAs that were found to be altered post-tMCAO and were predicted to regulate the MR. However, none validated in rat brain tissue, or rat and human stroke patient serum extracellular vesicles. Despite this, 9 miRNAs were found to be significantly altered in a different direction or at a different time-point in rat or human tissues, and were predicted to bind the MR. This is the first study to evaluate an enhanced welfare package for SHRSPs undergoing tMCAO, and the first to both characterise the expression, activation and potential regulation by miRNAs of the MR in the context of ischaemic stroke. Further research dissecting the role and regulation of the MR in ischaemic stroke will deepen our understanding of stroke pathophysiology and may lead to the identification of novel stroke therapeutics or prevention methods.