Abstract-The transition from stable to rupture-prone and ruptured atherosclerotic plaques involves many processes, including an altered balance between inflammation and fibrosis. An important mediator of both is transforming growth factor (TGF)-␤, and a pivotal role for TGF-␤ in atherogenesis has been postulated. Here, we determine the in vivo effects of TGF-␤ inhibition on plaque progression and phenotype in atherosclerosis. Recombinant soluble TGF-␤ receptor II (TGF␤RII:Fc), which inhibits TGF-␤ signaling, was injected in apolipoprotein E-deficient mice for 12 weeks (50 g, twice a week intraperitoneally) as early treatment (treatment age 5 to 17 weeks) and delayed treatment (age 17 to 29 weeks). In the early treatment group, inhibition of TGF-␤ signaling treatment resulted in a prominent increase in CD3-and CD45-positive cells in atherosclerotic lesions. Most profound effects were found in the delayed treatment group. Plaque area decreased 37.5% after TGF␤RII:Fc treatment. Moreover, plaque morphology changed into an inflammatory phenotype that was low in fibrosis: lipid cores were 64.6% larger, and inflammatory cell content had increased 2.7-fold. The amount of fibrosis decreased 49.6%, and intraplaque hemorrhages and iron and fibrin deposition were observed frequently. TGF␤RII:Fc treatment did not result in systemic effects. These results reveal a pivotal role for TGF-␤ in the maintenance of the balance between inflammation and fibrosis in atherosclerotic plaques.

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 Ϫ/Ϫ /apolipoprotein (apo) E Ϫ/Ϫ mice were generated. At 26 weeks of age, plaque area in the catK Ϫ/Ϫ /apoE Ϫ/Ϫ 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 Ϫ/Ϫ /apoE Ϫ/Ϫ mice showed an increase in collagen content. Medial elastin fibers were less prone to rupture than those of apoE Ϫ/Ϫ 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.

The hematopoietic deficiency of Hck and Fgr led to attenuated atherosclerotic plaque formation by abrogating endothelial adhesion and transmigration; paradoxically, it also promoted plaque instability by causing monocyte subset imbalance and subendothelial accumulation, raising a note of caution regarding src kinase-targeted intervention in plaque inflammation.