Distinct Functions of MEKK3 and MEKK4 in Heart Valve Morphogenesis

Persistent Link:
http://hdl.handle.net/10150/194848
Title:
Distinct Functions of MEKK3 and MEKK4 in Heart Valve Morphogenesis
Author:
Stevens, Mark V.
Issue Date:
2008
Publisher:
The University of Arizona.
Rights:
Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
Abstract:
Congenital heart defects (CHDs) occur in 5% of births. While gene mutations have been identified in CHD patients, not much is known about coordinated signaling mechanisms during heart morphogenesis. Endocardial cushions of the atrioventricular canal and outflow tract contribute to the formation of valves and septa in the heart. Epithelial cell to mesenchymal cell transition (EMT) is a key process in cardiac cushions before this tissue undergoes remodeling into valves and septa. Defining complex signaling networks directing cardiac cushion epithelial to mesenchymal transition is essential for understanding the etiology of CHDs. We identified the MAP3Kinases, MEKK3 and MEKK4, as signaling components present during cardiovascular development. MEKK3 is detected in myocardium and endocardium surrounding the cardiac cushions of the atrioventricular canal during heart morphogenesis, while MEKK4 is found in the myocardium, endocardium, and cushion mesenchyme. Functional assays were employed to examine how MEKK3 and MEKK4 kinase activity contributes to endocardial EMT. Addition of dominant negative (dn)-MEKK3 or dn-MEKK4 to endocardial cushion explants, cultures that recapitulate in vivo EMT, causes a significant decrease in mesenchyme formation as compared to controls. Ventricular explant cultures, where the endocardial cells do not normally undergo EMT, provided with constitutively active (ca) MEKK3 activates mesenchyme production. ca-MEKK4 is not sufficient to cause EMT in ventricular endocardium. Furthermore, ca-MEKK3 expression in ventricular explants leads to increased secreted TGFβ2, which mediates mesenchyme formation. Blockade of TGFβ2 in ventricular explant cultures provided with ca-MEKK3 ablates the activation of EMT. In addition to in vitro studies, we show that mice expressing kinase inactive MEKK4 have myxomatous valves characterized by increased proliferation and changes in extracellular matrix molecules such as hyaluronan. We next investigated whether signal transduction is affected in cushions and valves of the MEKK4 kinase inactive mice. Abnormal TGFβ signaling is observed in MEKK4 mutant hearts, which is also seen with Marfan's sydrome. Remarkably, activated MEKK3 is maintained in cardiac cushions of these mice after EMT indicating compensation by MEKK3 for loss of MEKK4 catalytic activity. Our observations define MEKK3 and MEKK4 expression during cardiovascular development and suggest that MEKK3 and MEKK4 have diverse functions during development of heart valves.
Type:
text; Electronic Dissertation
Keywords:
Endocardial cushion; Epithelial to Mesenchymal Transition; Heart; MEKK3; MEKK4; Valve
Degree Name:
Ph.D.
Degree Level:
doctoral
Degree Program:
Pharmacology & Toxicology; Graduate College
Degree Grantor:
University of Arizona
Advisor:
Camenisch, Todd D.
Committee Chair:
Camenisch, Todd D.

Full metadata record

DC FieldValue Language
dc.language.isoENen_US
dc.titleDistinct Functions of MEKK3 and MEKK4 in Heart Valve Morphogenesisen_US
dc.creatorStevens, Mark V.en_US
dc.contributor.authorStevens, Mark V.en_US
dc.date.issued2008en_US
dc.publisherThe University of Arizona.en_US
dc.rightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.en_US
dc.description.abstractCongenital heart defects (CHDs) occur in 5% of births. While gene mutations have been identified in CHD patients, not much is known about coordinated signaling mechanisms during heart morphogenesis. Endocardial cushions of the atrioventricular canal and outflow tract contribute to the formation of valves and septa in the heart. Epithelial cell to mesenchymal cell transition (EMT) is a key process in cardiac cushions before this tissue undergoes remodeling into valves and septa. Defining complex signaling networks directing cardiac cushion epithelial to mesenchymal transition is essential for understanding the etiology of CHDs. We identified the MAP3Kinases, MEKK3 and MEKK4, as signaling components present during cardiovascular development. MEKK3 is detected in myocardium and endocardium surrounding the cardiac cushions of the atrioventricular canal during heart morphogenesis, while MEKK4 is found in the myocardium, endocardium, and cushion mesenchyme. Functional assays were employed to examine how MEKK3 and MEKK4 kinase activity contributes to endocardial EMT. Addition of dominant negative (dn)-MEKK3 or dn-MEKK4 to endocardial cushion explants, cultures that recapitulate in vivo EMT, causes a significant decrease in mesenchyme formation as compared to controls. Ventricular explant cultures, where the endocardial cells do not normally undergo EMT, provided with constitutively active (ca) MEKK3 activates mesenchyme production. ca-MEKK4 is not sufficient to cause EMT in ventricular endocardium. Furthermore, ca-MEKK3 expression in ventricular explants leads to increased secreted TGFβ2, which mediates mesenchyme formation. Blockade of TGFβ2 in ventricular explant cultures provided with ca-MEKK3 ablates the activation of EMT. In addition to in vitro studies, we show that mice expressing kinase inactive MEKK4 have myxomatous valves characterized by increased proliferation and changes in extracellular matrix molecules such as hyaluronan. We next investigated whether signal transduction is affected in cushions and valves of the MEKK4 kinase inactive mice. Abnormal TGFβ signaling is observed in MEKK4 mutant hearts, which is also seen with Marfan's sydrome. Remarkably, activated MEKK3 is maintained in cardiac cushions of these mice after EMT indicating compensation by MEKK3 for loss of MEKK4 catalytic activity. Our observations define MEKK3 and MEKK4 expression during cardiovascular development and suggest that MEKK3 and MEKK4 have diverse functions during development of heart valves.en_US
dc.typetexten_US
dc.typeElectronic Dissertationen_US
dc.subjectEndocardial cushionen_US
dc.subjectEpithelial to Mesenchymal Transitionen_US
dc.subjectHearten_US
dc.subjectMEKK3en_US
dc.subjectMEKK4en_US
dc.subjectValveen_US
thesis.degree.namePh.D.en_US
thesis.degree.leveldoctoralen_US
thesis.degree.disciplinePharmacology & Toxicologyen_US
thesis.degree.disciplineGraduate Collegeen_US
thesis.degree.grantorUniversity of Arizonaen_US
dc.contributor.advisorCamenisch, Todd D.en_US
dc.contributor.chairCamenisch, Todd D.en_US
dc.contributor.committeememberVaillancourt, Richard R.en_US
dc.contributor.committeememberSchroeder, Joyce A.en_US
dc.contributor.committeememberFutscher, Bernard W.en_US
dc.contributor.committeememberRunyan, Raymond B.en_US
dc.identifier.proquest10073en_US
dc.identifier.oclc659750490en_US
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