Abstract 3490: Integrin-Linked Kinase Induces Cardiomyogenesis in Human Fetal Heart
Background: Integrin-linked kinase (ILK) is a hypoxia-inducible, multifunctional kinase that regulates different signal transduction pathways, including activation of canonical Wnt signaling and induction of a compensatory form of cardiac hypertrophy. Conditional deletion of ILK in mouse heart causes spontaneous dilated cardiomyopathy and sudden death at 6 to 12 weeks of age. Here we investigate the role of ILK in the differentiation and proliferation of cardiomyocytes during cardiac morphogenesis in human fetal heart.
Results: Freshly isolated human fetal myocardial cells (19 –21 weeks gestation) were pre-cultured for 2h and separated into two fractions of adherent and non-adherent cells. Adherent cells contain a mixture of cell types, whereas non-adherent cells are comprised of homogeneous colonies of nkx2.5-positive, proliferating (Ki-67-positive) cardioblasts that contain nascent sarcomeres evident by electron microscopy. In both adherent and non-adherent cells, ILK overexpression mediated by adenoviral infection robustly increased the number of new colonies of cardioblasts with nascent sarcomeres as well as differentiated cardiomyocytes (p<0.001 vs untreated and virus vector controls). ILK-induced colonies of cardioblasts were isolated, shown to proliferate and resemble cardiomyocytes, expressing the early cardiac marker nkx2.5. This effect of ILK was accompanied by activation of β-catenin and increase in expression levels of islet-1 thus marking an early cardiac cell lineage. Moreover, transgenic mice with cardiac-specific ILK overexpression were shown to have increased myocardial islet-1 expression in vivo.
Conclusions: ILK activation can induce high frequency specification of tissue-resident, precardioblast progenitor cells into a cardiomyocyte cell type in the human fetal heart, as well as induce accelerated maturation of existing cardioblasts. Since ILK is known to be activated by hypoxia, which normally occurs during fetal heart development and in postnatal heart disease, these findings support the paradigm that stress induction of ILK might serve as a novel regulator of cardiomyogenesis.