tetracycline and Cardiomegaly

Direct communication between arteries and veins without intervening capillary beds is the primary pathology of arteriovenous malformations (AVMs). Although Notch signaling is implicated in embryonic arteriovenous (AV) differentiation, its function in the adult mammalian vasculature has not been established due to the embryonic lethality that often occurs in both gain- and loss-of-function mutants. We expressed a constitutively active Notch4, int3, in the adult mouse endothelium by using the tetracycline-repressible system to suppress int3 during embryogenesis. int3 caused profound blood vessel enlargement and AV shunting, which are hallmarks of AVM, and led to lethality within weeks of its expression. Vessel enlargement, a manifestation of AVM, occurred in an apparently tissue-specific fashion; the liver, uterus, and skin were affected. int3-mediated vascular defects were accompanied by arterialization, including ectopic venous expression of ephrinB2, increased smooth muscle cells, and up-regulation of endogenous Notch signaling. Remarkably, the defective vessels and illness were reversed upon repression of int3 expression. Finally, endothelial expression of a constitutively active Notch1 induced similar hepatic vascular lesions. Our results provide gain-of-function evidence that Notch signaling in the adult endothelium is sufficient to render arterial characteristics and lead to AVMs.

Topics: Animals; Arteriovenous Malformations; Cardiomegaly; Echocardiography; Endothelium, Vascular; Ephrin-B2; Female; Fluorescence; Gene Expression Profiling; Gene Expression Regulation; Liver; Mice; Microspheres; Proto-Oncogene Proteins; Receptor, Notch4; Receptors, Cell Surface; Receptors, Notch; Signal Transduction; Skin; Tetracycline; Uterus

Despite the advantages of reversibly altering cardiac transgene expression, the number of successful studies with inducible cardiac-specific transgene expression remains limited. The utility of the current system is hampered by the large number of lines needed before a nonleaky inducible line is isolated and by the use of a heterologous virus-based minimal promoter in the responder line. We developed an efficient, experimentally flexible system that enables us to reversibly affect both abundant and nonabundant cardiomyocyte proteins. The use of bacterial-codon-based transactivators led to aberrant splicing, whereas other more efficient transactivators, by themselves, caused disease when expressed in the heart. The redesign of the system focused on developing stable transactivator-expressing lines in which expression was driven by the mouse alpha-myosin heavy chain promoter. A minimal responder locus was derived from the same promoter, in which the GATA sites and thyroid responsive elements responsible for robust cardiac specific expression were ablated, leading to an attenuated promoter that could be inducibly controlled. In all cases, whether activated or not, expression mimicked that of the parental promoter. By use of this system, an inducible expression of an abundant contractile protein, the atrial isoform of essential myosin light chain 1, and a powerful biological effector, glycogen synthase kinase-3beta (GSK-3beta), were obtained. Subsequently, we tested the hypothesis that GSK-3beta expression could reverse a preexisting hypertrophy. Inducible expression of GSK-3beta could both attenuate a hypertrophic response and partially reverse a pressure-overload-induced hypertrophy. The system appears to be robust and can be used to temporally control high levels of cardiac-specific transgene expression.

Topics: Animals; Cardiomegaly; DNA, Complementary; Genetic Engineering; Glycogen Synthase Kinase 3; Glycogen Synthase Kinase 3 beta; Herpes Simplex Virus Protein Vmw65; Mice; Mice, Transgenic; Myocardium; Myosin Heavy Chains; Myosin Light Chains; Promoter Regions, Genetic; RNA Splicing; Sarcomeres; Sequence Deletion; Tetracycline; Transcriptional Activation; Transgenes

Topics: Adrenocorticotropic Hormone; Cardiomegaly; Convalescence; Digitalis Glycosides; Diuretics; Endocarditis, Bacterial; Erythromycin; Glucocorticoids; Heart Failure; Humans; Injections, Intramuscular; Penicillins; Pericarditis; Rheumatic Heart Disease; Socioeconomic Factors; Streptococcal Infections; Tetracycline