|dc.description.abstract||Efferocytosis, the clearance of apoptotic cells including apoptotic neutrophils by macrophage
phagocytosis, is a key cellular mechanism for resolution of inflammation and tissue repair.
Cyclin-dependent kinases (CDKs) 7 and 9 phosphorylate RNA polymerase II that is vital for
neutrophil transcriptional capacity. CDK inhibitors such as R-roscovitine, and the more
selective inhibitor AT7519, induce neutrophil apoptosis and promote resolution of several
mouse models of inflammation including acute lung inflammation.
The hypothesis investigated here was that AT7519 would promote neutrophil apoptosis (i) in
the infarcted heart, leading to macrophage polarisation, angiogenesis, reduced infarct
expansion and retention of cardiac function and (ii) in the peritoneum, enhancing resolution
of sterile peritonitis.
AT7519 (1μM) induced apoptosis of mouse unstimulated-bone marrow derived neutrophils
and thioglycollate-stimulated neutrophils in vitro in a time- and caspase-dependent manner,
but did not alter activation assessed by calcium flux in response to the synthetic formyl
peptide (fMLF) or platelet-activating factor (PAF). Only high concentrations of AT7519 (10
μM) induced monocyte/macrophage apoptosis and this was likely due to saturated
phagocytosis of apoptotic neutrophils induced by high concentration of AT7519.
Myocardial infarction (MI) was induced by coronary artery ligation in adult male mice and
infarct volume was assessed 7 or 21 days later by in vitro optical projection tomography
(OPT). The novel use of OPT for this purpose was validated by demonstrating correlation
with infarct volume obtained by late-gadolinium enhanced magnetic resonance imaging in
vivo and with infarct area assessed by histological staining (Masson’s Trichrome) in tissue
AT7519 (30 mg/kg i.p.) increased the number of apoptotic neutrophils (cleaved caspase-3 and
Ly6G +ve) in the heart when administered after MI, but this was not associated with any
subsequent alteration in macrophage polarisation, vessel density, infarct expansion or
structural and functional remodelling of the left ventricle.
In contrast, induction of neutrophil apoptosis by AT7519 (30mg/kg i.p.) successfully
promoted macrophage polarisation and the resolution of inflammation associated with
peritonitis elicited by either 10% thioglycollate or by 1mg zymosan. AT7519 treatment also
reduced the number of CD19+ B cells, Foxp3+CD4+ T cells and eosinophils in peritoneal
lavage, and prolonged the phase of monocyte recruitment in zymosan-induced peritonitis.
In conclusion, AT7519 successfully induced mouse neutrophil apoptosis in vitro, as well as in
vivo in experimental MI and peritonitis. Subsequent promotion of inflammation resolution in
peritonitis was not matched by improved outcome following MI. Unexpected effects of CDK
inhibition on monocytes, T cells and eosinophils that are necessary for myocardial infarct
repair may have compromised any beneficial effects resulting from promotion of in situ
neutrophil apoptosis. CDK inhibition may therefore have therapeutic potential for the
treatment of peritonitis, but not for prevention of infarct expansion and detrimental
ventricular remodelling after MI.||en
|dc.publisher||The University of Edinburgh||en
|dc.relation.hasversion||Zhao X, Wu J, Gray CD, McGregor K, Rossi AG, Morrison H, Jansen MA, and Gray GA. Optical projection tomography permits efficient assessment of infarct volume in the murine heart post-myocardial infarction. Am J Physiol Heart Circ Physiol, 309, H702-10.||en
|dc.title||Can promotion of neutrophil apoptosis enhance repair in the infarcted myocardium and resolution of sterile peritonitis?||en
|dc.type||Thesis or Dissertation||en
|dc.type.qualificationname||PhD Doctor of Philosophy||en