Abstract-Focal adhesion kinase (FAK) is a ubiquitously expressed cytoplasmic tyrosine kinase strongly activated by integrins and neurohumoral factors. Previous studies have shown that cardiac FAK activity is enhanced by hypertrophic stimuli before the onset of overt hypertrophy. Herein, we report that conditional deletion of FAK from the myocardium of adult mice did not affect basal cardiac performance, myocyte viability, or myofibrillar architecture. However, deletion of FAK abolished the increase in left ventricular posterior wall thickness, myocyte cross-sectional area, and hypertrophy-associated atrial natriuretic factor induction following pressure overload. Myocyte-restricted deletion of FAK attenuated the initial wave of extracellular signal-regulated kinase activation and cFos expression induced by adrenergic agonists and biomechanical stress. In addition, we found that persistent challenge of mice with myocyte-restricted FAK inactivation leads to enhanced cardiac fibrosis and cardiac dysfunction in comparison to challenged genetic controls. These studies show that loss of FAK impairs normal compensatory hypertrophic remodeling without a concomitant increase in apoptosis in response to cardiac pressure overload and highlight the possibility that FAK activation may be a common requirement for the initiation of this compensatory response. Key Words: FAK Ⅲ integrins Ⅲ heart Ⅲ hypertrophy Ⅲ heart failure Ⅲ signaling I n the face of chronic pressure or volume overload, the adult heart undergoes pathological hypertrophic growth. This response is characterized by an increase in cardiomyocyte size and myofibrillar content as well as an altered pattern of cardiac gene expression, including induction of immediate early genes and reexpression of several fetal gene transcripts. Initially these changes are compensatory, but may eventually lead to decreases in cardiac performance and heart failure. 1 The precise molecular mechanisms that regulate anabolic or pathological myocardial hypertrophy are not completely known, but studies have implicated a variety of neuroendocrine and autocrine factors, many of which act through G protein-coupled receptors (in particular those coupled to G␣ q ). 2 Extensive evidence indicates that extracellular matrix (ECM)/integrin receptor signaling is also an important regulator of myocardial hypertrophy. Upregulation of collagen III, fibronectin, osteopontin, or their cognate integrin receptors, ␤ 1 , ␣ 3 , and ␣ 5 , correlates with the advancement of cardiac hypertrophy in animal models. 3 Also transgenic mice that express a myocyte-restricted activated ␣ 5 integrin develop profound cardiac hypertrophy, 4 whereas myocyte-restricted deletion of the ␤ 1 integrin in adult mouse hearts leads to a dilated cardiomyopathy and concomitant heart failure. 5,6 In addition, mutations in the structural focal adhesion proteins muscle LIM protein and metavinculin are associated with dilated cardiomyopathy in patients. 7,8 Collectively, these studies underscore the possibility that defects in inte...

Myocyte apoptosis is central to myocardial dysfunction following ischemia/reperfusion (I/R) and during the transition from hypertrophy to heart failure. Focal adhesion kinase (FAK), a non-receptor tyrosine kinase regulates adhesion-dependent survival signals and unopposed FAK activation has been linked to tumor development. We previously showed that conditional myocyte-specific deletion of FAK (MFKO) in the adult heart did not affect basal cardiomyocyte survival or cardiac function but led to dilated cardiomyopathy and heart failure following pressure overload. In the present study, we sought to determine if FAK functions to limit stress-induced cardiomyocyte apoptosis. We reasoned that (I/R), which stimulates robust apoptotic cell death, might uncover an important cardioprotective function for FAK. We found that depletion of FAK markedly exacerbates hypoxia/re-oxygenation-induced cardiomyocyte cell death in vitro. Moreover, deletion of FAK in the adult myocardium resulted in significant increases in I/R-induced infarct size and cardiomyocyte apoptosis with a concomitant reduction in left ventricular function. Finally, our results suggest that NF-κB signaling may play a key role in modulating FAK-dependent cardioprotection, since FAK inactivation blunted activation of the NF-κB survival signaling pathway and reduced levels of the NF-κB target genes, Bcl2 and Bcl-xl. Since the toggling between pro-survival and pro-apoptotic signals remains central to preventing irreversible damage to the heart, we conclude that targeted FAK activation may be beneficial for protecting stress-dependent cardiac remodeling.

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...

OBJECTIVE We previously reported that cardiac-restricted deletion of focal adhesion kinase (FAK) exacerbated myocyte death following ischemia/reperfusion (I/R). Here we interrogated whether targeted elevation of myocardial FAK activity could protect the heart from I/R injury. METHODS AND RESULTS Transgenic mice were generated with myocyte-specific expression of a FAK variant (termed SuperFAK) that conferred elevated allosteric activation. FAK activity in unstressed transgenic hearts was modestly elevated, but this had no discernable effect on anabolic heart growth or cardiac function. Importantly, SuperFAK hearts exhibited a dramatic increase in FAK activity and a reduction in myocyte apoptosis and infarct size 24–72 hrs following I/R. Moreover, serial echocardiography revealed that the transgenic mice were protected from cardiac de-compensation for up to 8 weeks following surgery. Mechanistic studies revealed that elevated FAK activity protected cardiomyocytes from I/R-induced apoptosis by enhancing NF-κB-dependent survival signaling during the early period of reperfusion (30 and 60 minutes). Moreover, adenoviral-mediated expression of SuperFAK in cultured cardiomyocytes attenuated H2O2 or hypoxia/re-oxygenation-induced apoptosis, whereas blockade of the NF-κB pathway using a pharmacological inhibitor or small interfering RNAs completely abolished the beneficial effect of SuperFAK. CONCLUSIONS Enhancing cardiac FAK activity attenuates I/R-induced myocyte apoptosis through activation of the pro-survival NF-κB pathway and may represent a novel therapeutic strategy for ischemic heart diseases.