Congenital heart disease (CHD) is the most common type of birth defect. Valvuloseptal defects, which result from aberrant endocardial cushion development, comprise up to one third of CHD, and also are a significant cause of adult morbidity/mortality. Although progress has been made in delineating single gene defects that perturb valvulogenesis in mouse and man, how these genes regulate development, and how normal development is altered by disease-associated mutations, remain largely unknown. Protein tyrosine phosphorylation, controlled by protein-tyrosine kinases (PTKs) and protein-tyrosine phosphatases (PTP), is a key cellular regulatory mechanism., Many growth factor receptors are transmembrane PTKs, and several are implicated in valvulogenesis. Vascular endothelial growth factor (VEGF), produced by myocardjal cells, inhibits endocardial-mesechymal transition (EMT), a key initial event in which specialized endocardia! cells transform into mesenchymal cells that invade the cushion matrix and proliferate. ErbB3, most likely partnering with ErbB2 (HER2) and responding to heregulin (HRG), promotes EMT and/or mesenchymal proliferation. Conversely, heparin-binding EGF (HB-EGF), acting via the EGFR (ErbB1), terminates mesenchymal cell proliferation and plays a key role in valve remodeling. The non-receptor PTP, Shp2 (PTPN11), also plays an essential role in valve development. Shp2 deficiency enhances the effect of EGFR loss of function in mice, resulting in abnormal valve thickening. Furthermore, ~50% of cases of the autosomal dominant disorder Nponan syndrome (NS), the most common non-chromosomal cause of CHD, is caused by PTPN11 mutations. Structural, enzymologic, and biochemical studies, and a mouse NS model generated in our laboratory, indicate that NS mutations are gain-of-function alleles that enhance Erk MAP kinase activation in developing cardiac cushions. PTPN11 mutations also cause LEOPARD syndrome (LS), which exhibits an overlapping spectrum of cardiac defects. But we showed recently that unlike NS alleles, LS mutants are PTP-inactive, and act as dominant negative mutants that impair Erk activation. Based on these data, we hypothesize that NS and LS mutations cause similar cardiac valve defects by acting in opposing ways on distinct RTK pathways at different times during valvulogenesis. We propose a combined biochemical, cell biological and genetic approach to address key questions about the pathogenesis of cardiac defects caused by human PTPN11 mutations.
Aim 1 will use an inducible knock-in approach to determine the cell type and developmental interval in which NS mutants act to cause valvuloseptal defects.
In Aim 2, we will study an allelic series of Shp2 knock-in alleles, asking if the specific PTPN11 mutation affects the NS cardiac phenotype, and generate a knock-in mouse model of LS to test the hypothesis that LS mutants act later during valvulogenesis to inhibit EGFR signaling/remodeling. Finally, Aim 3 will use a combination of mouse models, explant assays, and pharmacologic agents to test the hypothesis that NS alleles enhance ErbB2/3 signaling to the Ras/Erk pathway, thereby enhancing EMT and possibly mesenchymal proliferation. Our results should yield new insights into the pathogenesis of CHD, and may have important implications for the therapy of NS and LS. ? ? ?

Agency
National Institute of Health (NIH)
Institute
National Heart, Lung, and Blood Institute (NHLBI)
Type
Research Project (R01)
Project #
1R01HL083273-01A2
Application #
7319031
Study Section
Cardiovascular Differentiation and Development Study Section (CDD)
Program Officer
Schramm, Charlene A
Project Start
2007-07-16
Project End
2011-04-30
Budget Start
2007-07-16
Budget End
2008-04-30
Support Year
1
Fiscal Year
2007
Total Cost
$425,000
Indirect Cost
Name
Beth Israel Deaconess Medical Center
Department
Type
DUNS #
071723621
City
Boston
State
MA
Country
United States
Zip Code
02215
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