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Urokinase-type plasminogen activator (uPA) is expressed at elevated levels in atherosclerotic human arteries, primarily in macrophages. Plasminogen (Plg), the primary physiologic substrate of uPA, is present at significant levels in blood and interstitial fluid. Both uPA and Plg have activities that could affect atherosclerosis progression. Moreover, correlations between increased Plg activation and accelerated atherosclerosis are reported in several human studies. However, a coherent picture of the role of the uPA/Plg system in atherogenesis has not yet emerged, with at least one animal study suggesting that Plg is atheroprotective. We used a transgenic mouse model of macrophage-targeted uPA overexpression in apolipoprotein E-deficient mice to investigate the roles of uPA and Plg in atherosclerosis. We found that macrophageexpressed uPA accelerated atherosclerotic plaque growth and promoted aortic root dilation through Plg-dependent pathways. These pathways appeared to affect lesion progression rather than initiation and to include actions that disproportionately increase lipid accumulation in the artery wall. In addition, loss of Plg was protective against atherosclerosis both in the presence and absence of uPA overexpression. Transgenic mice with macrophagetargeted uPA overexpression reveal atherogenic roles for both uPA and Plg and are a useful experimental setting for investigating the molecular mechanisms that underlie clinically established relationships between uPA expression, Plg activation, and atherosclerosis progression.proteolysis ͉ aorta ͉ aneurysm

Human hearts with end-stage failure and fibrosis have macrophage accumulation and elevated plasminogen activator activity. However, the mechanisms that link macrophage accumulation and plasminogen activator activity with cardiac fibrosis are unclear. We previously reported that mice with macrophage-targeted overexpression of urokinase plasminogen activator (SR-uPA Cardiac fibrosis, the accumulation of excess extracellular matrix in the heart, is a common feature of end-stage heart disease independent of etiology. Cardiac fibrosis may contribute to impaired systolic and diastolic function and is associated with both atrial and ventricular arrhythmias (1, 2). Fibrotic cardiac tissue is relatively avascular (3), and cardiac fibroblasts are unable to propagate cardiac action potentials (for review see Ref. 4). For these reasons, cardiac fibrosis will likely interfere with implementation of cell-based therapies for heart disease (5). Despite the importance of cardiac fibrosis, the mechanisms through which it develops are incompletely understood.Human and animal studies suggest that both macrophage accumulation and increased plasminogen activator (PA) 2 activity contribute to the pathogenesis of cardiac fibrosis. Macrophage accumulation is present in fibrotic, end-stage human hearts (6, 7). Macrophages express urokinase-type plasminogen activator (uPA) (8), and increased PA activity is present, along with macrophages and fibrosis, in failing human hearts (9). Mice with increased macrophage PA activity have early cardiac macrophage accumulation and develop cardiac fibrosis later in life (10). Moreover, mice that lack uPA are resistant to the development of cardiac fibrosis (11, 12).The pathways through which macrophage accumulation and increased cardiac PA activity could lead to cardiac fibrosis in both mice and humans are unknown. These pathways could include PA-mediated conversion of plasminogen to plasmin. Alternatively, cardiac fibrosis could be caused by plasminogen-independent actions of either PAs or macrophages. Definition of the pathways through which increased cardiac macrophage accumulation and PA activity lead to cardiac fibrosis may clarify the basic mechanisms of cardiac fibrosis and suggest new therapeutic approaches.Here we report the use of mice with macrophage-targeted expression of uPA (SR-uPA ϩ/o mice (13)) to investigate the mechanisms through which increased macrophage PA activity causes cardiac macrophage accumulation and fibrosis. SR-uPA ϩ/o mice are an appropriate animal model for these investigations because, in the absence of infarction or any other overt cardiac injury, they develop cardiac macrophage accumulation by 5 weeks of age and cardiac fibrosis by 15 weeks (10). We hypothesized that the uPA receptor (uPAR) (which can facilitate cell migration by focusing uPA and plasmin proteolytic activity to the leading edge of migrating cells (14)) is required for both cardiac macrophage accumulation and the subsequent development of fibrosis in SR-uPA

ObjectiveInflammation and fibrosis are intertwined in multiple disease processes. We have previously found that over-expression of urokinase plasminogen activator in macrophages induces spontaneous macrophage accumulation and fibrosis specific to the heart in mice. Understanding the relationship between inflammation and fibrosis in the heart is critical to developing therapies for diverse myocardial diseases. Therefore, we sought to determine if uPA induces changes in macrophage function that promote cardiac collagen accumulation.Methods and ResultsWe analyzed the effect of the uPA transgene on expression of pro-inflammatory (M1) and pro-fibrotic (M2) genes and proteins in hearts and isolated macrophages of uPA overexpressing mice. We found that although there was elevation of the pro-inflammatory cytokine IL-6 in hearts of transgenic mice, IL-6 is not a major effector of uPA induced cardiac fibrosis. However, uPA expressing bone marrow-derived macrophages are polarized to express M2 genes in response to IL-4 stimulation, and these M2 genes are upregulated in uPA expressing macrophages following migration to the heart. In addition, while uPA expressing macrophages express a transcriptional profile that is seen in tumor–associated macrophages, these macrophages promote collagen expression in cardiac but not embryonic fibroblasts.ConclusionsUrokinase plasminogen activator induces an M2/profibrotic phenotype in macrophages that is fully expressed after migration of macrophages into the heart. Understanding the mechanisms by which uPA modulates macrophage function may reveal insights into diverse pathologic processes.

This retrospective chart review suggests the feasibility of a novel protocol for medically supervised opioid withdrawal and transition to relapse prevention strategies, including injectable ER naltrexone. This withdrawal protocol does not utilize opioid agonists or other controlled substances.‬‬‬‬.