Search

The endothelial tyrosine kinase receptor Tie1 remains poorly characterized, largely owing to its orphan receptor status. Global Tie1 inactivation causes late embryonic lethality, thereby reflecting its importance during development. Tie1 also plays pivotal roles during pathologies such as atherosclerosis and tumorigenesis. In order to study the contribution of Tie1 to tumor progression and metastasis, we conditionally deleted Tie1 in endothelial cells at different stages of tumor growth and metastatic dissemination. Tie1 deletion during primary tumor growth in mice led to a decrease in microvessel density and an increase in mural cell coverage with improved vessel perfusion. Reduced angiogenesis and enhanced vascular normalization resulted in a progressive increase of intratumoral necrosis that caused a growth delay only at later stages of tumor progression. Concomitantly, surgical removal of the primary tumor decreased the number of circulating tumor cells, reduced metastasis, and prolonged overall survival. Additionally, Tie1 deletion in experimental murine metastasis models prevented extravasation of tumor cells into the lungs and reduced metastatic foci. Taken together, the data support Tie1 as a therapeutic target by defining its regulatory functions during angiogenesis and vascular abnormalization and identifying its role during metastasis., Introduction The high demand for oxygen and nutrients of growing tumors with substantial intratumoral hypoxia gradients stimulates the recruitment of blood vessels through the continuous production of proangiogenic molecules in [...]

Although the response of endothelial cells to the disturbed blood flowin the vicinity of atherosclerotic lesions is known to be distinct from that elicited by nonatherogenic laminar flow, the mechanisms involved are poorly understood. Our initial studies confirmed that expression of the endothelial receptor tyrosine kinase Tie1 was evident at regions of atherogenic flow in mature animals. We therefore hypothesized that Tie1 plays a role in the endothelial response to atherogenic shear stress. Consistent with this, we found that [Tie1.sup.+/-] mice bred to the apoE-deficient background displayed a 35% reduction in atherosclerosis relative to [Tie1.sup.+/+];[Apoe.sup.-/-] mice. Since deletion of Tie1 results in embryonic lethality secondary to vascular dysfunction, we used conditional and inducible mutagenesis to study the effect of endothelial-specific Tie1 attenuation on atherogenesis in [Apoe.sup.-/-] mice and found a dose-dependent decrease in atherosclerotic lesions. Analysis of primary aortic endothelial cells indicated that atheroprotective laminar flow decreased Tie1 expression in vitro. Attenuation of Tie1 was associated with an increase in eNOS expression and Tie2 phosphorylation. In addition, Tie1 attenuation increased IkBα expression while decreasing ICAM levels. In summary, we have found that shear stress conditions that modulate atherogenic events also regulate Tie1 expression. Therefore, Tie1 may play a novel proinflammatory role in atherosclerosis., Introduction Atherosclerotic lesions have a predilection for locales exposed to disturbed blood flow that can trigger inflammation and apoptosis (1-5). Disturbed flow is seen at the aortic sinus and at [...]

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.ydbio.2009.06.033 Byline: Andrew M. Misfeldt (a)(b), Scott C. Boyle (b), Kevin L. Tompkins (a), Victoria L. Bautch (d), Patricia A. Labosky (b)(c), H. Scott Baldwin (a)(b) Keywords: Endocardium; Myocardium; Heart development; NFATc1; Transcription factors; Mouse embryonic stem cells; Multipotent stem cells; Mesoderm; Embryonic stem cell differentiation; Flk1; Mouse transgenesis; Mouse embryogenesis; BAC recombination Abstract: Identification of multipotent cardiac progenitors has provided important insights into the mechanisms of myocardial lineage specification, yet has done little to clarify the origin of the endocardium. Despite its essential role in heart development, characterization of the endocardial lineage has been limited by the lack of specific markers of this early vascular subpopulation. To distinguish endocardium from other vasculature, we generated an NFATc1-nuc-LacZ BAC transgenic mouse line capable of labeling this specific endothelial subpopulation at the earliest stages of cardiac development. To further characterize endocardiogenesis, embryonic stem cells (ESCs) derived from NFATc1-nuc-LacZ blastocysts were utilized to demonstrate that endocardial differentiation in vitro recapitulates the close temporal-spatial relationship observed between myocardium and endocardium seen in vivo. Endocardium is specified as a cardiac cell lineage, independent from other vascular populations, responding to BMP and Wnt signals that enhance cardiomyocyte differentiation. Furthermore, a population of Flk1+ cardiovascular progenitors, distinct from hemangioblast precursors, represents a mesodermal precursor of the endocardial endothelium, as well as other cardiovascular lineages. Taken together, these studies emphasize that the endocardium is a unique cardiac lineage and provides further evidence that endocardium and myocardium are derived from a common precursor. Author Affiliation: (a) Department of Pediatrics, Division of Cardiology, Vanderbilt University School of Medicine, Nashville, TN 37232, USA (b) Department of Cell and Developmental Biology, Vanderbilt University School of Medicine, Nashville, TN 37232, USA (c) Center for Stem Cell Biology, Vanderbilt University School of Medicine, Nashville, TN 37232, USA (d) Department of Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA Article History: Received 18 February 2009; Revised 16 June 2009; Accepted 22 June 2009

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.ydbio.2008.02.044 Byline: Xianghu Qu (a)(b), Haibo Jia (b)(c), Deborah M. Garrity (d), Kevin Tompkins (a), Lorene Batts (a), Bruce Appel (b)(e), Tao P. Zhong (b)(c), H. Scott Baldwin (a)(b) Keywords: Zebrafish; ndrg4; Cardiogenesis; Myocardium; tbx5; tbx20 Abstract: NDRG4 is a novel member of the NDRG family (N-myc downstream-regulated gene). The roles of NDRG4 in development have not previously been evaluated. We show that, during zebrafish embryonic development, ndrg4 is expressed exclusively in the embryonic heart, the central nervous system (CNS) and the sensory system. Ndrg4 knockdown in zebrafish embryos causes a marked reduction in proliferative myocytes and results in hypoplastic hearts. This growth defect is associated with cardiac phenotypes in morphogenesis and function, including abnormal heart looping, inefficient circulation and weak contractility. We reveal that ndrg4 is required for restricting the expression of versican and bmp4 to the developing atrioventricular canal. This constellation of ndrg4 cardiac defects phenocopies those seen in mutant hearts of heartstrings (hst), the tbx5 loss-of-function mutants in zebrafish. We further show that ndrg4 expression is significantly decreased in hearts with reduced tbx5 activities. Conversely, increased expression of tbx5 that is due to tbx20 knockdown leads to an increase in ndrg4 expression. Together, our studies reveal an essential role of ndrg4 in regulating proliferation and growth of cardiomyocytes, suggesting that ndrg4 may function downstream of tbx5 during heart development and growth. Author Affiliation: (a) Department of Pediatric Cardiology, Vanderbilt University Medical Center, Nashville, TN 37232, USA (b) Department of Cell and Developmental Biology, Vanderbilt University Medical Center, Nashville, TN 37232, USA (c) Department of Cardiovascular Medicine, Vanderbilt University Medical Center, Nashville, TN 37232, USA (d) Department of Biology, Colorado State University, Fort Collins, CO 80523, USA (e) Department of Biological Sciences, Vanderbilt University Medical Center, Nashville, TN 37232, USA Article History: Received 29 March 2007; Revised 1 February 2008; Accepted 20 February 2008

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.ydbio.2006.08.004 Byline: Lanying Song (a), Reinhard Fassler (b), Yuji Mishina (c), Kai Jiao (a), H. Scott Baldwin (d) Keywords: Alk3; Atrioventricular cushion; BMP; Cardiogenesis; Congenital heart diseases; Epithelial-mesenchymal transformation (EMT) Abstract: Accumulated evidence has suggested that BMP pathways play critical roles during mammalian cardiogenesis and impairment of BMP signaling may contribute to human congenital heart diseases (CHDs), which are the leading cause of infant morbidity and mortality. Alk3 encodes a BMP specific type I receptor expressed in mouse embryonic hearts. To reveal functions of Alk3 during atrioventricular (AV) cushion morphogenesis and to overcome the early lethality of Alk3.sup.-/- embryos, we applied a Cre/loxp approach to specifically inactivate Alk3 in the endothelium/endocardium. Our studies showed that endocardial depletion of Alk3 severely impairs epithelium-mesenchymal-transformation (EMT) in the atrioventricular canal (AVC) region; the number of mesenchymal cells formed in Tie1-Cre;Alk3.sup.loxp/loxp embryos was reduced to only [approximately equal to]20% of the normal level from both in vivo section studies and in vitro explant assays. We showed, for the first time, that in addition to its functions on mesenchyme formation, Alk3 is also required for the normal growth/survival of AV cushion mesenchymal cells. Functions of Alk3 are accomplished through regulating expression/activation/subcellular localization of multiple downstream genes including Smads and cell-cycle regulators. Taken together, our study supports the notion that Alk3-mediated BMP signaling in AV endocardial/mesenchymal cells plays a central role during cushion morphogenesis. Author Affiliation: (a) Division of Genetic and Translational Medicine, Department of Genetics, University of Alabama at Birmingham, Birmingham, AL 35294, USA (b) Department of Molecular Medicine, Max Planck Institute for Biochemistry, Am Klopferspitz 18, 82152 Martinsried, Germany (c) Laboratory of Reproductive and Developmental Toxicology, National Institute of Environmental Health Sciences, Research Triangle Park, NC 27709, USA (d) Division of Pediatric Cardiology, Department of Pediatrics, Vanderbilt University Medical Center, Nashville, TN 37232, USA Article History: Received 24 April 2006; Revised 11 July 2006; Accepted 1 August 2006