Evaluation of the role of the melanocortin receptor system in ischemia-reperfusion induced leukocyte endothelium interaction in the brain microcirculation

File Description SizeFormat 
Holloway-PM-2013-PhD-Thesis.pdfThesis6.19 MBAdobe PDFView/Open
Title: Evaluation of the role of the melanocortin receptor system in ischemia-reperfusion induced leukocyte endothelium interaction in the brain microcirculation
Authors: Holloway, Paul Matthew
Item Type: Thesis or dissertation
Abstract: Leukocyte recruitment following cerebral ischemia reperfusion (I/R) has been shown to amplify inflammatory processes and enhance brain injury. Potent anti-inflammatory and neuro-protective properties have been attributed to the melanocortin receptor system, thus targeting this system may provide a novel therapeutic strategy for the treatment of stroke. Melanocortin receptor (MC) subtypes MC1, MC3 and MC4 have previously been shown to mediate MC anti-inflammatory actions, however their relative importance is poorly understood and may differ with the pathophysiological environment. In this study the bilateral common carotid artery occlusion (BCCAo) mouse model of global stroke was used with intravital microscopy to investigate the potential of melanocortin targeted compounds in modulating cerebral I/R induced leukocyte recruitment. While under basal conditions the cerebral microcirculation provides a poor substrate for leukocyte recruitment, BCCAo induced significant leukocyte recruitment by 40 min of reperfusion, with leukocyte rolling increasing from 21.5 cells/mm2/min to 191.0 cells/mm2/min and adhesion from 42.1 cells/mm2/min to 282.3 cells/mm2/min. Extending reperfusion to 2 h resulted in further increases in adhesion to 1500% of sham levels. Treatment with the non-selective melanocortin agonist, α-MSH, significantly reduced I/R induced leukocyte recruitment (Rolling by 80% at 40 min and 68% at 2 h and adhesion by 68% at 40 min and 82% at 2 h). The relative contributions of the melanocortin receptor subtypes were investigated in this model using MC selective compounds and receptor mutant mice. The MC1 selective BMS-470,539 provided most potent inhibition of leukocyte recruitment at 40 min with the MC1 mutant e/e mice also showing enhanced leukocyte rolling and circulating TNF-α, while MC3-/- mice showed no inflammatory phenotype. However by 2 h the inhibitory effects of BMS-470,539 subsided and e/e mice no longer showed abnormalities in leukocyte recruitment. On the other hand MC3 targeted compounds were highly effective at this later time point. These investigations reveal an important role for MC1 immediately following BCCAo with a later shift toward MC3 mediated processes by 2 h. Due to no observed changes in receptor mRNA and that by 2 h α-MSH treatment was found to reduce NF-κβ related gene expression but not at 40min. It is likely the apparent shift in receptor importance is due to the activation of distinct signalling pathways rather than change in receptor expression.
Content Version: Open Access
Issue Date: Jul-2013
Date Awarded: Oct-2013
URI: http://hdl.handle.net/10044/1/40275
Supervisor: Getting, Stephen
Gavins, Felicity
Department: Medicine
Publisher: Imperial College London
Qualification Level: Doctoral
Qualification Name: Doctor of Philosophy (PhD)
Appears in Collections:Medicine PhD theses

Items in DSpace are protected by copyright, with all rights reserved, unless otherwise indicated.

Creative Commonsx