¹Discipline of Pathology, School of Medical Sciences and Bosch Institute, University of Sydney, Sydney, New South Wales, Australia

Correspondence: Dr BD Hambly, Discipline of Pathology, School of Medical Sciences, University of Sydney, Blackburn Building D06, Sydney, New South Wales 2006, Australia. E-mail: bretth@med.usyd.edu.au

Received 13 September 2007; Revised 25 August 2008; Accepted 1 September 2008; Published online 7 October 2008.

Abstract

Granulocyte-macrophage colony-stimulating factor (GM-CSF) has been implicated in atherogenesis and has been shown to have both pro- and antiatherogenic properties. Neointimal thickening is a prominent feature of early atherogenesis. This study aimed to examine the role of GM-CSF in neointimal formation induced by endothelial injury using a GM-CSF^-/- mouse model. Neointimal thickening was induced by endothelial damage in the common iliac arteries of normolipidemic C57Bl/6 (wild-type) and GM-CSF^-/- mice. Arteries were collected weekly for 3–7 weeks following surgery. A significant delay in neointimal formation in the GM-CSF^-/- compared with wild-type mice was detected by morphometric analysis of the intimal area. Neointimal size was 10% smaller in GM-CSF^-/- mice at 4–6 weeks post-surgery, compared with wild-type mice. The neointima was composed predominantly of smooth muscle cells and there was no difference in the extent of endothelial cell coverage between the wild-type and GM-CSF^-/- mice. Using immunohistochemistry, reduced macrophages (F4/80⁺ cells), proliferating cells (proliferating cell nuclear antigen (PCNA)⁺ cells) and platelet-derived growth factor-B were detected within the arteries of GM-CSF^-/- mice compared with wild types at 4 weeks post-surgery. GM-CSF^-/- mice had reduced connective tissue within the neointima compared with wild types at 5 weeks post-surgery, determined by trichrome staining. We conclude that GM-CSF deficiency reduces neointimal formation in a normolipidemic model, primarily due to reduced macrophage recruitment.