The Congenital Dyserythropoietic Anemia (CDA) Registry was established with the goal to facilitate investigations of natural history, biology, and molecular pathogenetic mechanisms of CDA. Three unrelated individuals enrolled in the registry had a syndrome characterized by CDA and severe neurodevelopmental delay. They were found to have missense mutations in VPS4A, a gene coding for an ATPase that regulates the ESCRT-III machinery in a variety of cellular processes including cell division, endosomal vesicle trafficking, and viral budding. Bone marrow studies showed binucleated erythroblasts and erythroblasts with cytoplasmic bridges indicating abnormal cytokinesis and abscission. Circulating red blood cells were found to retain transferrin receptor (CD71) in their membrane, demonstrating that VPS4A is critical for normal reticulocyte maturation. Using proband-derived induced pluripotent stem cells (iPSCs), we have successfully modeled the hematologic aspects of this syndrome in vitro, recapitulating their dyserythropoietic phenotype. Our findings demonstrate that VPS4A mutations cause cytokinesis and trafficking defects leading to a human disease with detrimental effects to erythropoiesis and neurodevelopment.

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.