Conditional Deletion of Focal Adhesion Kinase Leads to Defects in Ventricular Septation and Outflow Tract Alignment

Abstract

To examine a role for focal adhesion kinase (FAK) in cardiac morphogenesis, we generated a line of mice with a conditional deletion of FAK in nkx2-5-expressing cells (herein termed FAK nk mice). FAK nk mice died shortly after birth, likely resulting from a profound subaortic ventricular septal defect and associated malalignment of the outflow tract. Additional less penetrant phenotypes included persistent truncus arteriosus and thickened valve leaflets. Thus, conditional inactivation of FAK in nkx2-5-expressing cells leads to the most common congenital heart defect that is also a subset of abnormalities associated with tetralogy of Fallot and the DiGeorge syndrome. No significant differences in proliferation or apoptosis between control and FAK nk hearts were observed. However, decreased myocardialization was observed for the conal ridges of the proximal outflow tract in FAK nk hearts. Interestingly, chemotaxis was significantly attenuated in isolated FAK-null cardiomyocytes in comparison to genetic controls, and these effects were concomitant with reduced tyrosine phosphorylation of Crk-associated substrate (CAS). Thus, it is possible that ventricular septation and appropriate outflow tract alignment is dependent, at least in part, upon FAK-dependent CAS activation and subsequent induction of polarized myocyte movement into the conal ridges. Future studies will be necessary to determine the precise contributions of the additional nkx2-5-derived lineages to the phenotypes observed.The heart is the first organ to form, and its development involves an intricate and complex series of events that must occur in a coordinated spatial and temporal fashion (44,60,75). The heart develops from bilaterally symmetric cardiogenic primordia that migrate and fuse at the embryonic midline to form a functional primitive heart tube that subsequently undergoes rightward looping to orient the atrial and ventricular chambers and properly align the outflow tract (OFT). As the chambers mature, the trabecular layer within the ventricles is elaborated, endocardial cushions form and fuse, and the chamber walls grow and thicken as the cardiomyocytes continue to proliferate and differentiate. A critical event in cardiac development related to human congenital heart defects (CHD) is septal morphogenesis, which commences during midgestation. The single ventricle becomes septated by a process involving fusion of the muscular interventricular septum (IVS) with the endocardial cushions, and further septation and valve formation continues until birth to ensure unidirectional flow of blood. Since multiple cell types, including those derived from the myocardium, endocardium, epicardium, and neural crest, contribute to the complex process of valvuloseptal morphogenesis, it is not surprising that CHD associated with aberrant septation of the OFT are quite common. Indeed, CHD afflict nearly 1% of newborn infants each year, and defective valvuloseptal morphogenesis is the leading cause of preterm mortality in the United States (22,23,53,59). Thus, und...

TGFβ1 antagonistic peptides inhibit TGFβ1-dependent angiogenesis

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α5 and αv integrins cooperate to regulate vascular smooth muscle and neural crest functions in vivo

“…Focal adhesions are essential for maintaining structural integrity of vessels by inducing cytoskeletal rearrangements and alignment of vSMCs in response to mechanical strain. Previous studies have shown that genetic deletion of FAK (Ptk2) in vSMC precursors leads to defects in the patterning of the aortic arch arteries and septation of the heart and outflow tract (Hakim et al, 2007;Vallejo-Illarramendi et al, 2009;Cheng et al, 2011). These defects, however, are caused by abnormal recruitment (Hakim et al, 2007;Cheng et al, 2011) and/or impaired differentiation of vSMCs (Vallejo-Illarramendi et al, 2009), neither of which was seen in our mutants.…”

IGF signaling directs ventricular cardiomyocyte proliferation during embryonic heart development

“…Nkx2.5Cre is active in ventricular and atrial myocardium and also in the endocardium and epicardium, and achieves very high efficiency recombination (see Fig. S8 in the supplementary material); several previous studies have confirmed that Nkx2.5Cre and certain other Cre drivers cause more severe heart phenotypes than does MLC2vCre when crossed to the same target genes (Shai et al, 2002;Hakim et al, 2007;Peng et al, 2008;Ieda et al, 2009).…”