Studies on extracellular matrix proteins in vascular disease

Abstract: The composition of the vascular extracellular matrix (ECM) is altered during remodeling conditions such as atherosclerosis. The changed ECM regulates events that are important for the progression of disease including smooth muscle cell (SMC) behaviour and collagen fiber formation. The overall aim of this project was to relate changes in the composition of ECM in the arterial wall to processes during atherosclerosis. The first part includes a characterisation of ECM components in atherosclerotic arteries of ApoE/LDLr double deficient mice. The second part involves functional studies on individual ECM components with focus on osteopontin (OPN) as well as on versican and fibulin-2. Experiments have been performed both in vivo in an atherosclerotic mouse model and in vitro on cultured rat aortic smooth muscle cells (SMC). Paper I. This immunohistochemical study demonstrated presence of the cell and/or collagen binding ECM components OPN, COMP, decorin, PRELP and fibromodulin in atherosclerotic arteries of ApoE/LDLr deficient mice. Paper II. The importance of osteopontin during the atherosclerotic process was studied by crossing OPN deficient mice with ApoE/LDLr deficient mice (AL) generating a mouse which lacks expression of ApoE, LDLR and OPN (ALO). The results demonstrated that OPN deficiency reduced atherogenesis in atherosclerotic mice. Furthermore, the data indicated that OPN might be involved in the regulation of vascular remodeling, inflammation and lipid metabolism. Paper III. In an attempt to clarify the role of OPN during the atherosclerotic process, the effect of OPN on SMC functions was studied. Mutated forms of OPN were generated lacking two integrin binding sites and the cleavage site for thrombin. The effect of thrombin cleavage of OPN was also studied and cell culture experiments showed decreased adhesion of SMC to thrombin-cleaved OPN compared to intact OPN. Paper IV. The presence of versican and fibulin-2 was studied in atherosclerotic arteries of ApoE/LDLr deficient mice and in cultured SMC. Versican and fibulin-2 were present in lesions and fibulin-2 was upregulated in SMC during phenotypic modulation. Blocking the interaction between versican and fibulin-2 inhibited SMC migration. The results indicate that fibulin-2 is produced by SMC as a response to injury and participates in the ECM organisation during vessel wall repair.