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Sheng-Wei Chang's Thesis.pdf (8.01 MB)

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Deficits in Cardiomyocyte Proliferation: Contributors to Congenital Heart Defects

Chang, Sheng-Wei
http://rave.ohiolink.edu/etdc/view?acc_num=osu1397643835

Abstract Details

2014, Doctor of Philosophy, Ohio State University, Molecular, Cellular and Developmental Biology.
Congenital heart disease (CHD) is the most common type of birth defect with an incidence of nearly 1%. Cardiomyocyte proliferation plays an important role during heart development, and defects in cardiomyocyte proliferation can result in CHD. While the etiology for majority of CHD is unclear; multiple genes have been associated with CHD in humans. Our work has focused on elucidating the mechanisms by which mutations in CHD-causing genes disrupt normal heart development. First, we identified a patient with unbalanced atrioventricular septal defect (AVSD) and hypoplastic left ventricle with a microdeletion on chromosome 3 that encompasses gene FOXP1, which is critical for heart development and represses cardiomyocyte proliferation. To determine whether FOXP1 mutations are associated with CHD, we sequenced FOXP1 in 82 patients with AVSD or hypoplastic left heart syndrome (HLHS). We discovered two patients who harbored a heterozygous c.1702C>T variant in FOXP1 that predicted a potentially deleterious substitution of a highly conserved proline (p.Pro568Ser). The orthologous murine Foxp1 p.Pro596Ser mutation displayed decreased activity in luciferase assays and caused an increase in proliferation and Nkx2.5 expression in H9C2 cells. Our data suggested that haploinsufficiency of FOXP1 is associated with human CHD and that abnormal cardiomyocyte proliferation may contribute to CHD. Additionally, we studied two other genes, GATA4 and TBX5, which play critical roles during heart development. Mutations in GATA4 and TBX5 are associated with CHD in humans. Interaction between GATA4 and TBX5 is important for cardiac septation but the mechanisms are not well understood. We found co-expression, co-localization and in vivo interaction between Gata4 and Tbx5 in murine embryonic atria and ventricles until E15.5. However, the ventricular co-localization and interaction declines after E15.5 due to the decreased expression of Tbx5. Gata4+/-;Tbx5+/- mouse embryos revealed myocardial wall thinning prior to cardiac septation. Haploinsufficiency of Gata4 and Tbx5 in the myocardium displayed embryonic lethality, thin myocardium with reduced cell proliferation and AVSD similar to Gata4;Tbx5 compound heterozygotes. Cdk4 and Cdk2, cyclin-dependent kinases required for myocardial development and septation were reduced in Gata4+/-;Tbx5+/- hearts. Cdk4 is a known direct target of Gata4 and the regulation of Cdk2 in the developing heart has not been studied. Chromatin immunoprecipitation and transactivation studies demonstrate that Gata4 and Tbx5 directly regulate Cdk4 while only Tbx5 activates Cdk2 expression. These findings highlight the mechanisms by which disruption of the Gata4 and Tbx5 interaction in the myocardium contributes to cardiac septation by altering cardiomyocyte proliferation. miRNAs have been shown to be involved in cardiac gene regulation and cardiomyocyte proliferation. Here, we identified miR-1, a cardiac specific miRNA, as a key regulator in cardiomyocyte proliferation during heart development by microarray analysis. We found miR-1 expression is up-regulated during mouse heart development. Functional assays revealed reduced cell proliferation and decreased mRNA level of multiple cell cycle genes in H9C2 cells, which indicated the role of miR-1 in cardiomyocyte proliferation. In summary, investigation into the molecular pathways that regulate cardiomyocyte proliferation may lead to important insights into the molecular mechanisms underlying cardiac malformations which will have important implications into the genetics of CHD.
Vidu Garg (Advisor)
Brenda Lilly (Committee Member)
Susan Cole (Committee Member)
Kim McBride (Committee Member)
138 p.
Developmental Biology
Congenital heart disease; Atrioventricular septal defect; cardiomyocyte proliferation; FOXP1; Gata4; Tbx5;

Recommended Citations

Citations

  • Chang, S.-W. (2014). Deficits in Cardiomyocyte Proliferation: Contributors to Congenital Heart Defects [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1397643835

    APA Style (7th edition)

  • Chang, Sheng-Wei. Deficits in Cardiomyocyte Proliferation: Contributors to Congenital Heart Defects. 2014. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1397643835.

    MLA Style (8th edition)

  • Chang, Sheng-Wei. "Deficits in Cardiomyocyte Proliferation: Contributors to Congenital Heart Defects." Doctoral dissertation, Ohio State University, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=osu1397643835

    Chicago Manual of Style (17th edition)

osu1397643835
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This open access ETD is published by The Ohio State University and OhioLINK.