Essential Role of Developmentally Activated Hypoxia-Inducible Factor 1α for Cardiac Morphogenesis and Function

Abstract

Abstract-Development of the mammalian heart is governed by precisely orchestrated interactions between signaling pathways integrating environmental cues and a core cardiac transcriptional network that directs differentiation, growth and morphogenesis. Here we report that in mice, at about embryonic day (E)8.5 to E10.0, cardiac development proceeds in an environment that is hypoxic and characterized by high levels of hypoxia-inducible factor (HIF)1␣ protein. Mice lacking HIF1␣ in ventricular cardiomyocytes exhibit aborted development at looping morphogenesis and embryonic lethality between E11.0 to E12.0. Intriguingly, HIF1␣-deficient hearts display reduced expression of the core cardiac transcription factors Mef2C and Tbx5 and of titin, a giant protein that serves as a template for the assembly and organization of the sarcomere. Chromatin immunoprecipitation experiments revealed that Mef2C, Tbx5, and titin are direct target genes of HIF1␣ in vivo. Thus, hypoxia signaling controls cardiac development through HIF1␣-mediated transcriptional regulation of key components of myofibrillogenesis and the cardiac transcription factor network, thereby providing a mechanistic basis of how heart development, morphogenesis, and function is coupled to low oxygen tension during early embryogenesis. Key Words: cardiac development Ⅲ hypoxia Ⅲ transcription Ⅲ myofibrillogenesis Ⅲ HIF1␣ C ardiac development is a multi-stage process governed by a network of transcription factors including Nkx2.5, Tbx5, Mef2C, and GATA4 that connect signaling pathways with the regulation of gene expression for the specification of cardiac cell fate, differentiation and morphogenesis. These transcription factors act in an interconnected and coordinated manner at specific stages of cardiogenesis. Although Nkx2.5 and GATA4 activity is predominantly associated with cardiac lineage specification and differentiation, it is also required for induction of downstream cardiogenic transcription factors such as Tbx5 and Mef2C, whose function is primarily linked to looping morphogenesis and chamber formation. 1 Thus specific transcription factors induce the expression of genes necessary for progression through the respective stages of cardiogenesis. How the expression and activity of these transcription factors are coordinated spatially and temporally in the course of cardiogenesis remains less clear.A central feature of mammalian embryogenesis is the development of intraembryonic hypoxia. 2 As the embryo increases in size, oxygenation of the avascular early postimplantation embryo by diffusion alone becomes limited, leading to a state of regional embryonic hypoxia. In normal development, regional hypoxia has been implicated to serve as a stimulus for the tissue/region-specific induction of genes required for yolk sac vasculogenesis, 3 the establishment of the maternal-fetal circulatory network 4 and the initiation of intraembryonic circulation and cardiac function. 5,6 Thus, the embryonic hypoxic phase is characterized by the coordinated development of multipl...

Disruption of spatiotemporal hypoxic signaling causes congenital heart disease in mice

“…We therefore monitored the spatial distribution of pimonidazole, a nitroimidazole derivative that incorporates into hypoxic cells when oxygen concentration is below 10 mmHg (<2%) in embryonic mouse hearts between E8.0 and E9.5. Hypoxic cells were mainly localized in the myocardium of the looping heart tube as described previously (25). Surprisingly, however, CPCs in the cardiac mesoderm and the outflow tract, which we defined by expression of Isl1, showed negligible incorporation of pimonidazole, indicating that ISL1 + CPCs are maintained in a nonhypoxic (normoxic) environment ( Figure 1A).…”

“…Physiological hypoxia (oxygen concentration <2%) and activation of HIF1α play critical roles for cardiac morphogenesis and function, but it is not clear whether hypoxia signaling is equally important for all parts of the developing heart (25). We therefore monitored the spatial distribution of pimonidazole, a nitroimidazole derivative that incorporates into hypoxic cells when oxygen concentration is below 10 mmHg (<2%) in embryonic mouse hearts between E8.0 and E9.5.…”

Cardiac Vasculature: Development and Pathology

“…The functional deletion of both HIF-1 and HIF-2 by expressing a dominant negative HIF2a led to embryonic lethality at E11.5. The conditional "knockout" of HIF-1a early in ventricular cardiomyocytes (Krishnan et al, 2008) and HIF-1 and HIF-2 by expression of a dominant negative HIF mutant in endothelial cells also resulted in early death [death by E11.5; (Licht, 2006)]. As coronary vessel development occurs at E10.5-13.5, the early death of these mice precluded determining the role of HIFs in coronary development by the use of these mice.…”

Cardiomyocyte-specific Prolyl-4-hydroxylase Domain 2 Knock Out Protects from Acute Myocardial Ischemic Injury

“…Most interestingly, these mice also develop a cardiac phenotype with symptoms of dilated cardiomyopathy. In the heart, HIF-1␣ and thereby also the PHDs are known to influence key components of heart development, morphogenesis, and function (19,20). Long term activation of HIF-1␣ in the heart seems to activate detrimental pathways resulting in the development of heart failure (21).…”