Birgit C.G. Faber

Disruption of the Cathepsin K Gene Reduces Atherosclerosis Progression and Induces Plaque Fibrosis but Accelerates Macrophage Foam Cell Formation

Background— Cathepsin K (catK), a lysosomal cysteine protease, was identified in a gene-profiling experiment that compared human early plaques, advanced stable plaques, and advanced atherosclerotic plaques containing a thrombus, where it was highly upregulated in advanced stable plaques. Methods and Results— To assess the function of catK in atherosclerosis, catK−/−/apolipoprotein (apo) E−/− mice were generated. At 26 weeks of age, plaque area in the catK−/−/apoE−/− mice was reduced (41.8%) owing to a decrease in the number of advanced lesions as well as a decrease in individual advanced plaque area. This suggests an important role for catK in atherosclerosis progression. Advanced plaques of catK−/−/apoE−/− mice showed an increase in collagen content. Medial elastin fibers were less prone to rupture than those of apoE−/− mice. Although the relative macrophage content did not differ, individual macrophage size increased. In vitro studies of bone marrow derived–macrophages confirmed this observation. Scavenger receptor–mediated uptake (particularly by CD36) of modified LDL increased in the absence of catK, resulting in an increased macrophage size because of increased cellular storage of cholesterol esters, thereby enlarging the lysosomes. Conclusions— A deficiency of catK reduces plaque progression and induces plaque fibrosis but aggravates macrophage foam cell formation in atherosclerosis.

The dynamic extracellular matrix: intervention strategies during heart failure and atherosclerosis

The extracellular matrix is no longer seen as the static embedding in which cells reside; it has been shown to be involved in cell proliferation, migration and cell–cell interactions. Turnover of the different extracellular matrix components is an active process with multiple levels of regulation. Collagen, a major extracellular matrix constituent of the myocardium and the arterial vascular wall, is synthesized by (myo)fibroblasts in the myocardium and smooth muscle cells in the medial arterial vascular wall. Its degradation is controlled by proteinases, which include matrix metalloproteinases. This review will focus on the impact of fibrosis and especially collagen turnover on the progression of heart failure and atherosclerosis, two of the main cardiovascular pathologies. We will discuss data from human studies and animal models, with an emphasis on the effects of interventions on collagen synthesis and degradation. We conclude that there is a dynamic (dis)balance in the rate of collagen synthesis and degradation during heart failure and atherosclerosis, which makes the outcome of interventions not always predictable. Alternative approaches for intervening in collagen metabolism will be discussed as possible therapeutic intervention strategies. Copyright

Gene Profiling in Atherosclerosis Reveals a Key Role for Small Inducible Cytokines Validation Using a Novel Monocyte Chemoattractant Protein Monoclonal Antibody

Background—Pathological aspects of atherosclerosis are well described, but gene profiles during atherosclerotic plaque progression are largely unidentified. Methods and Results—Microarray analysis was performed on mRNA of aortic arches of ApoE−/− mice fed normal chow (NC group) or Western-type diet (WD group) for 3, 4.5, and 6 months. Of 10 176 reporters, 387 were differentially (>2×) expressed in at least 1 group compared with a common reference (ApoE−/−, 3- month NC group). The number of differentially expressed genes increased during plaque progression. Time-related expression clustering and functional grouping of differentially expressed genes suggested important functions for genes involved in inflammation (especially the small inducible cytokines monocyte chemoattractant protein [MCP]-1, MCP-5, macrophage inflammatory protein [MIP]-1&agr;, MIP-1&bgr;, MIP-2, and fractalkine) and matrix degradation (cathepsin-S, matrix metalloproteinase-2/12). Validation experiments focused on the gene cluster of small inducible cytokines. Real-time polymerase chain reaction revealed a plaque progression–dependent increase in mRNA levels of MCP-1, MCP-5, MIP-1&agr;, and MIP-1&bgr;. ELISA for MCP-1 and MCP-5 showed similar results. Immunohistochemistry for MCP-1, MCP-5, and MIP-1&agr; located their expression to plaque macrophages. An inhibiting antibody for MCP-1 and MCP-5 (11K2) was designed and administered to ApoE−/− mice for 12 weeks starting at the age of 5 or 17 weeks. 11K2 treatment reduced plaque area and macrophage and CD45+ cell content and increased collagen content, thereby inducing a stable plaque phenotype. Conclusions—Gene profiling of atherosclerotic plaque progression in ApoE−/− mice revealed upregulation of the gene cluster of small inducible cytokines. Further expression and in vivo validation studies showed that this gene cluster mediates plaque progression and stability.

Genes potentially involved in plaque rupture.

Purpose of review Rupture of an atherosclerotic plaque is the predominant underlying event in the pathogenesis of acute coronary syndromes and stroke. While ruptured plaques are morphologically well described, the precise molecular mechanisms involved in plaque rupture are still incompletely understood. Over the last few years, techniques like microarray, suppression subtractive hybridization and differential display enabled us to study complex gene expression profiles that occur during the process of atherogenesis. In this review we focus on recent large-scale gene expression profiles performed on whole mount vascular specimens. Recent findings The gene expression profiles on whole mount vascular tissue confirmed that at least three mechanisms are involved in plaque rupture: (1) a disturbed balance in extracellular matrix turnover, (2) disturbed regulation of cell turnover and (3) processes involved in lipid metabolism. Animal models exhibiting features of plaque rupture reflect the involvement of these three mechanisms. The most dramatic mouse phenotypes were observed after interventions in at least two of these mechanisms. Summary The observation of plaque rupture in recent mice models is indicative of the multifactorial process of plaque rupture. This multifactorial character of plaque rupture suggests that interventions may be most effective when they influence more than one mechanisms at a time.

Noninvasive diagnosis of ruptured peripheral atherosclerotic lesions and myocardial infarction by antibody profiling

Novel biomarkers, such as circulating (auto)antibody signatures, may improve early detection and treatment of ruptured atherosclerotic lesions and accompanying cardiovascular events, such as myocardial infarction. Using a phage-display library derived from cDNAs preferentially expressed in ruptured peripheral human atherosclerotic plaques, we performed serological antigen selection to isolate displayed cDNA products specifically interacting with antibodies in sera from patients with proven ruptured peripheral atherosclerotic lesions. Two cDNA products were subsequently evaluated on a validation series of patients with peripheral atherosclerotic lesions, healthy controls, and patients with coronary artery disease at different stages. Our biomarker set was able to discriminate between patients with peripheral ruptured lesions and patients with peripheral stable plaques with 100% specificity and 76% sensitivity. Furthermore, 93% of patients with an acute myocardial infarction (AMI) tested positive for our biomarkers, whereas all patients with stable angina pectoris tested negative. Moreover, 90% of AMI patients who initially tested negative for troponin T, for which a positive result is known to indicate myocardial infarction, tested positive for our biomarkers upon hospital admission. In conclusion, antibody profiling constitutes a promising approach for noninvasive diagnosis of atherosclerotic lesions, because a positive serum response against a set of 2 cDNA products showed a strong association with the presence of ruptured peripheral atherosclerotic lesions and myocardial infarction.