Immune responses against fibronectin modified by lipoprotein oxidation and their association with cardiovascular disease

Abstract

Objectives. Accumulation and subsequent oxidation of LDL in the arterial wall are considered as key events in the development of atherosclerosis. We have investigated the possibility that LDL oxidation results in release of aldehydes that modify surrounding matrix proteins and that this may target immune responses against the plaque extracellular matrix and modulate the disease progression.Results. Using custom-made ELISAs we demonstrate that human plasma contains autoantibodies against aldehyde-modified fibronectin (FN) and to a lesser extent also other extracellular matrix proteins including collagen type I, type III, and tenascin-C. Immunohistochemistry and western blot analysis showed that aldehyde-modified FN is present in human atherosclerotic plaques and that aldehydes generated by oxidation of LDL formed adducts with FN in vitro. We also demonstrate that aldehyde-modification of FN results in a loss of its ability to promote basal secretion of cytokines and growth factors from cultured macrophages without affecting the ability of the cells to respond to stimulation with LPS. A prospective clinical study demonstrated that subjects that subsequently developed acute myocardial infarction or sudden cardiac death had lower baseline levels of autoantibodies against aldehyde-modified FN than matched controls.Conclusions. These observations demonstrate that oxidation of LDL in the arterial wall may lead to aldehyde-modification of surrounding extracellular matrix proteins and that these modifications may affect macrophage function and activate autoimmune responses of pathophysiological importance for the development of atherosclerosis.

Increased aldehyde-modification of collagen type IV in symptomatic plaques – A possible cause of endothelial dysfunction

“…Indeed, by screening human plasma we found both IgM and IgG binding to several MDA-modified extracellular matrix proteins including collagen type I, collagen type III, fibronectin, and the basement membrane protein laminin. 7,8 We also showed that MDA can leak out of the LDL-particle and modify extracellular matrix proteins in vitro. 7 In addition, by using in-house produced antibodies recognizing different MDA-modified proteins, we have identified both MDA-modified fibronectin and MDA-modified laminin in atherosclerotic lesions.…”

“…7,8 We also showed that MDA can leak out of the LDL-particle and modify extracellular matrix proteins in vitro. 7 In addition, by using in-house produced antibodies recognizing different MDA-modified proteins, we have identified both MDA-modified fibronectin and MDA-modified laminin in atherosclerotic lesions. 7,8 Although previous studies identified antibodies against different modified matrix proteins, the protein levels in atherosclerotic lesions and their relation to plaque stability and 5 cardiovascular events have not been investigated.…”

“…We have previously shown that these reactive aldehydes leak out of the LDL-particle and modify surrounding extracellular matrix proteins in vitro. 7 In this study we analyzed the amount of MDA-modified and native collagen type IV in carotid plaque homogenates from symptomatic and asymptomatic patients. We found that the amount of MDA-collagen type IV, but not native collagen type IV, was increased in lesions from symptomatic patients compared to asymptomatic patients.…”

“…7,8 To test whether antibodies against MDA-modified collagen type IV were associated to the amount of MDA-modified collagen type IV in the lesions, we measured the amount of IgM and IgG against MDA-modified collagen type IV in plasma from the same patients from whom the carotid lesions were removed. Indeed, both IgM and IgG were positively associated with the amount of MDA-modified collagen type IV, but not with native collagen type IV (Supplementary table 2).…”

“…7 In addition, by using in-house produced antibodies recognizing different MDA-modified proteins, we have identified both MDA-modified fibronectin and MDA-modified laminin in atherosclerotic lesions. 7,8 Although previous studies identified antibodies against different modified matrix proteins, the protein levels in atherosclerotic lesions and their relation to plaque stability and 5 cardiovascular events have not been investigated. Modification of basement membrane components due to nearby lipid oxidation may result in decreased endothelial cell attachment, which will promote cardiovascular events.…”