Abstract 317: Mast Cells Do Not Contribute to a Reduction in Vein Graft Neointima in the C-kit Mutant KitW-sh/w-sh Mice

Background: Recent evidence suggests mast cells are involved in the development of vascular diseases such as atherosclerosis. The presence of mast cells in vein grafts led us to hypothesise that mast cells may regulate the extent of vein graft neointima hyperplasia. In this study, we employed the Kit W-sh/W-sh mouse strain, a widely accepted mast cell deficient mouse model induced by a spontaneous inversion mutation in the transcriptional regulatory elements of the c-kit gene. Methods: The vein graft surgery was performed by inserting the inferior thoracic vena cava from the donor mouse into the common carotid artery of the littermate recipient. Vein grafts were harvested at 4 weeks and fixed with 4% formaldehyde for histology. In some groups, Kit W-sh/W-sh mice were reconstituted with cultured mast cells either systemically or locally 9 weeks before vein graft surgery. For primary cell culture studies, aortic endothelial cells and smooth muscle cells were isolated by collagenase digestion method and cultured in standard conditions. Results: Kit w-sh/w-sh vein grafts had a significant reduction (33%; p<0.05) in neointima area, compared to the wild type controls. The cellular composition of the Kit w-sh/w-sh neointima was similar to the wild type controls, most cells being smooth muscle alpha-actin positive. Neither the systemic nor local reconstitution of mast cells restored the neointima area to the wild type level. In the primary cell culture, Kit w-sh/w-sh vascular cells showed less migrating activity in the scratch wound healing test, which may account for the decrease in neointima formation. Conlusion: This study suggests that it is not the deficiency of mast cells in the Kit W-sh/W-sh mice which accounts for the reduction in neointima formation in vein grafts. Other cell types affected by the c-kit mutation may be responsible for the altered neointima formation in Kit W-sh/W-sh mice.