Csx/Nkx2-5 Is Required for Homeostasis and Survival of Cardiac Myocytes in the Adult Heart

Abstract

Csx/Nkx2-5, which is essential for cardiac development of the embryo, is abundantly expressed in the adult heart. We here examined the role of Csx/Nkx2-5 in the adult heart using two kinds of transgenic mice. Transgenic mice that overexpress a dominant negative mutant of Csx/Nkx2-5 (DN-TG mice) showed degeneration of cardiac myocytes and impairment of cardiac function. Doxorubicin induced more marked cardiac dysfunction in DN-TG mice and less in transgenic mice that overexpress wild type Csx/Nkx2-5 (WT-TG mice) compared with non-transgenic mice. Doxorubicin induced cardiomyocyte apoptosis, and the number of apoptotic cardiomyocytes was high in the order of DN-TG mice, non-transgenic mice, and WT-TG mice. Overexpression of the dominant negative mutant of Csx/Nkx2-5 induced apoptosis in cultured cardiomyocytes, while expression of wild type Csx/Nkx2-5 protected cardiomyocytes from doxorubicin-induced apoptotic death. These results suggest that Csx/Nkx2-5 plays a critical role in maintaining highly differentiated cardiac phenotype and in protecting the heart from stresses including doxorubicin.The cardiac homeobox gene Csx/Nkx2-5 starts to be expressed at embryonic day 7.5 in the heart primordia of mice (1, 2), and targeted disruption of murine Csx/Nkx2-5 results in embryonic lethality (3). Many mutations in human Csx/Nkx2-5 have been reported to cause a variety of congenital heart diseases and atrioventricular conduction delay (4, 5). These observations indicate that Csx/Nkx2-5 plays a critical role in cardiac morphogenesis and contributes to diverse cardiac developmental pathways at the embryonic stage.Knockout experiments have suggested that many genes such as Hand1, myocyte enhancer factor-2, atrial natriuretic peptide (ANP), 1 brain natriuretic peptide (BNP), cardiac ␣-actin, cardiac ankyrin repeat protein (CARP), N-myc, and MSX2 are genetically located downstream of Csx/Nkx2-5 at the embryonic stage (2, 6 -8). Although Csx/Nkx2-5 continues to be expressed in the adult heart (1, 2), the function of Csx/Nkx2-5 in the later stage of development is unknown because of embryonic lethality of null mutant mice (3, 8). In our recently generated transgenic mice that overexpress human Csx/Nkx2-5 (WT-TG mice), mRNA levels of many cardiac genes such as ANP, BNP, CARP, and sarcoplasmic reticulum calcium ATPase 2 (SERCA2) genes were up-regulated (9). These results suggest that Csx/Nkx2-5 regulates expression of cardiac-specific genes also in the adult heart. However, because there was no difference in phenotype between WT-TG and non-transgenic (non-TG) mice (9), the significance of these gene up-regulations remains unknown. Csx/Nkx2-5 itself is also differentially regulated by different stimuli. In response to hypertrophic stimuli such as isoproterenol, phenylephrine, and pressure overload, Csx/Nkx2-5 is upregulated (10, 11), whereas it is down-regulated by treatment with doxorubicin (DOX) (12). These results suggest that Csx/ Nkx2-5 has certain roles in the adult heart. In this study, we generated transgenic mice that over...

The enigmatic role of the ankyrin repeat domain 1 gene in heart development and disease

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Epidemiology and Etiology of Congenital Heart Diseases

“…Transcription Factor Genes transcribe and translate proteins that serve to interact cooperatively with each other to control gene expression.  NKX2-5, the NK family, on chromosome 5q35; Homeobox-containing genes play critical roles in regulating tissue-specific gene expression essential for specification of heart muscle progenitors (Komuro & Izumo, 1993;Toko et al, 2002). Mutations in NKX2-5 result in loss of heart formation in the embryo and have been found in sporadic www.intechopen.com CCVM.…”

Zebrafish early cardiac connexin, Cx36.7/Ecx, regulates myofibril orientation and heart morphogenesis by establishing Nkx2.5 expression

“…Studies have uncovered that several transcription factors, including TBX5, NKX2.5, GATA4, and SALL4, cooperate to direct the cardiac cell lineage commitment and/or morphogenesis through the regulation of proteins characteristic of cardiomyocytes and that mutations in these transcription factors are responsible for many cases of CHD (3)(4)(5)(6)(7). Recent data have also suggested the significant roles of these transcription factors for maintenance of the functional heart in postnatal life as well (8)(9)(10)(11)(12). In the past decade, zebrafish (Danio rerio) has emerged as a valuable model system to study many developmental processes, including heart development, and a number of important insights have been gained from analyses of zebrafish mutants (13)(14)(15)(16)(17).…”