Publications

Searchable abstracts of presentations at key conferences in endocrinology ISSN 1470-3947 (print) | ISSN 1479-6848 (online)

Abstract Plasmin, the primary fibrinolytic enzyme, has a broad substrate spectrum and is implicated in biologic processes dependent upon proteolytic activity, such as tissue remodeling and cell migration. Active plasmin is generated from proteolytic cleavage of the zymogen plasminogen (Plg) by urokinase-type plasminogen activator (uPA) and tissue-type plasminogen activator (tPA). Here, we have investigated the role of plasmin in C2C12 myoblast fusion and differentiation in vitro, as well as in skeletal muscle regeneration in vivo, in wild-type and Plg-deficient mice. Wild-type mice completely repaired experimentally damaged skeletal muscle. In contrast, Plg−/− mice presented a severe regeneration defect with decreased recruitment of blood-derived monocytes and lymphocytes to the site of injury and persistent myotube degeneration. In addition, Plg-deficient mice accumulated fibrin in the degenerating muscle fibers; however, fibrinogen depletion of Plg-deficient mice resulted in a correction of the muscular regeneration defect. Because we found that uPA, but not tPA, was induced in skeletal muscle regeneration, and persistent fibrin deposition was also reproducible in uPA-deficient mice following injury, we propose that fibrinolysis by uPA-dependent plasmin activity plays a fundamental role in skeletal muscle regeneration. In summary, we identify plasmin as a critical component of the mammalian skeletal muscle regeneration process, possibly by preventing intramuscular fibrin accumulation and by contributing to the adequate inflammatory response after injury. Finally, we found that inhibition of plasmin activity with α2-antiplasmin resulted in decreased myoblast fusion and differentiation in vitro. Altogether, these studies demonstrate the requirement of plasmin during myogenesis in vitro and muscle regeneration in vivo.

The importance of vascular endothelial growth factor-A (VEGF) and subsequent Notch signaling in cardiac outflow tract development is generally recognized. Although genetic heterogeneity and mutations of these genes in both humans and mouse models relate to a high susceptibility to develop outflow tract malformations such as tetralogy of Fallot and peripheral pulmonary stenosis, no etiology has been proposed so far. Using immunohistochemistry, in situ hybridization, and quantitative RT-PCR on embryonic hearts, we have shown spatiotemporal increase and abnormal patterning of Vegf /VEGF/(phosphorylated) VEGFR-2, (cleaved) Notch1, and Jagged2 in the outflow tract of Vegf120/120 mouse embryos. This coincides with hyperplasia of specifically the outflow tract cushions and a high degree of subpulmonary myocardial apoptosis that, in later stages, manifest as pulmonary stenosis and ventricular septal defects. We postulate that increase of VEGF and Notch signaling during right ventricular outflow tract development can lead to abnormal development of both cushion and myocardial structures. Defective right ventricular outflow tract development as presented provides new insight in the etiology of tetralogy of Fallot.

Abstract —Although the serine protease, tissue plasminogen activator (tPA), is approved by the US Food and Drug Administration for therapy to combat focal cerebral infarction, the basic concept of thrombolytic tPA therapy for stroke was challenged by recent studies that used genetically manipulated tPA-deficient (tPA−/−) mice, which suggested that tPA mediates ischemic neuronal damage. However, those studies were potentially flawed because the genotypes of tPA−/− and wild-type control mice were not entirely clear, and ischemic neuronal injury was evaluated in isolation of tPA effects on brain thrombosis. Using mice with appropriate genetic backgrounds and a middle cerebral artery occlusion stroke model with nonsiliconized thread, which does lead to microvascular thrombus formation, in the present study we determined the risk for cerebrovascular thrombosis and neuronal injury in tPA−/− and genetically matched tPA+/+ mice subjected to transient focal ischemia. Cerebrovascular fibrin deposition and the infarction volume were increased by 8.2- and 6.7-fold in tPA−/− versus tPA+/+ mice, respectively, and these variables were correlated with reduced cerebral blood flow up to 58% ( P <0.05) and impaired motor neurological score by 70% ( P <0.05). Our findings indicate that tPA deficiency exacerbates ischemia-induced cerebrovascular thrombosis and that endogenous tPA protects the brain from an ischemic insult, presumably through its thrombolytic action. In addition, our study emphasizes the importance of appropriate genetic controls in murine stroke research.

Preeclampsia remains a clinical challenge due to its poorly understood pathogenesis. A prevailing notion is that increased placental production of soluble fms-like tyrosine kinase-1 (sFlt-1) causes the maternal syndrome by inhibiting proangiogenic placental growth factor (PlGF) and VEGF. However, the significance of PlGF suppression in preeclampsia is uncertain. To test whether preeclampsia results from the imbalance of angiogenic factors reflected by an abnormal sFlt-1/PlGF ratio, we studied PlGF KO (Pgf-/-) mice and noted that the mice did not develop signs or sequelae of preeclampsia despite a marked elevation in circulating sFLT-1. Notably, PlGF KO mice had morphologically distinct placentas, showing an accumulation of junctional zone glycogen. We next considered the role of placental PlGF in an established model of preeclampsia (pregnant catechol-O-methyltransferase-deficient [COMT-deficient] mice) by generating mice with deletions in both the Pgf and Comt genes. Deletion of placental PlGF in the context of COMT loss resulted in a reduction in maternal blood pressure and increased placental glycogen, indicating that loss of PlGF might be protective against the development of preeclampsia. These results identify a role for PlGF in placental development and support a complex model for the pathogenesis of preeclampsia beyond an angiogenic factor imbalance.

Background: Mutations in the cardiac sodium channel, SCN5A, have been associated with one type of long-QT syndrome, with isolated cardiac conduction defects and Brugada syndrome. The sodium channelopathies exhibit marked variation in clinical phenotypes. The mechanisms underlying the phenotypical diversity, however, remain unknown. Exonic SCN5A mutations can be detected in 20% of Brugada syndrome patients. Results: An intronic mutation (c.4810+3_4810+6dupGGGT) in the SCN5A gene, located outside the consensus splice site, was detected in this study in a family with a highly variable clinical phenotype of Brugada syndrome and/or conduction disease and in a patient with Brugada syndrome. The mutation was not found in a control panel of 100 (200 alleles) ethnically matched normal control subjects. We provide in vivo and in vitro evidence that the mutation can disrupt the splice donor site, activate a cryptic splice site, and create a novel splice site. Notably, our data show that normal transcripts can be also derived from the mutant allele. Conclusions: This is the first report of an unconventional intronic splice site mutation in the SCN5A gene leading to cardiac sodium channelopathy. We speculate that its phenotypical diversity might be determined by the ratio of normal/abnormal transcripts derived from the mutant allele.

The middle T antigen of murine Polyomavirus (PymT) rapidly transforms endothelial cells, leading to the formation of vascular tumors in newborn mice. Transformed endothelial (End.) cell lines established from such tumors exhibit altered proteolytic activity as a result of increased expression of urokinase-type plasminogen activator (uPA) and are capable of inducing vascular tumors efficiently when injected into adult mice. In this study we have used mice lacking components of the PA/plasmin system to analyze the role of this system in the transformation process and in tumor growth. We found that the proteolytic status of the host is not a critical determinant for PymT-induced vascular tumor formation. In addition, the lack of either uPA or tissue-type PA (tPA) activity is not limiting for the establishment and proliferation of End. cells in vitro, although the combined loss of both PA activities leads to a marked reduction in proliferation rates. Furthermore, the in vitro morphogenetic properties of mutant End. cells in fibrin gels could only be correlated with an altered proteolytic status in cells lacking both uPA and tPA. However, in contrast with tumors induced by PymT itself, the tumorigenic potential of mutant and wild-type End. cell lines was found to be highly dependent on the proteolytic status of both the tumor cells and the host. Thus, genetic alterations in the PA/plasmin system affect vascular tumor development, indicating that this system is a causal component in PymTmediated oncogenesis.