Alterations in the vascular extracellular matrix of granulocyte macrophage colony-stimulating factor (GM-CSF)-deficient mice

GM-CSF takes part in the cytokine network regulating the metabolism of extracellular matrix (ECM) during atherogenesis. Since data also point to an effect of GM-CSF on the vascular ECM in general, the vascular collagenous matrix was studied in wild-type and GM-CSF-deficient mice. Histological examination revealed a disorganized vascular ECM in GM-CSF-deficient mice involving the collagenous matrix and elastic fiber system. As shown by electron microscopy, collagen bundles were disrupted and reduced. The diameter of fibrils varied widely. mRNA expression of collagens and related molecules was studied. Fibrillar collagens were markedly reduced, alpha1 (I) procollagen to 16.5% of control levels alpha1 (III) procollagen was abolished whereas the expression level of network-forming alpha1 (VIII) procollagen was not altered. As shown by in situ hybridization, the number of collagen-expressing cells was reduced. Matrix metalloproteinases and their inhibitor 1 were not affected by GM-CSF deficiency. Our studies demonstrate that GM-CSF plays a major role in the cytokine network regulating the metabolism of vascular collagens. GM-CSF deficiency leads to an altered composition of the vascular collagenous matrix, i.e., reduced amount of fibrillar collagen, altered ratio of fibrillar and network-forming collagen, and failures in the fibrillogenesis. We suggest that GM-CSF is a basic requirement for the maintenance of vessel wall integrity and resilience.