Focal adhesion kinase in cardiac development and disease

In the United States, nearly 80 million adults are affected by cardiovascular disease. The spectrum of disease range from congenital structural defects to acquired structural changes in response to an increased hemodynamic load on the heart, myocardial infarction, or hormonal imbalance. Cardiovascular disease accounts for significant amounts of morbidity and mortality and is currently the number one cause of death in the U.S. Congenital heart disease is the most common cause of infant death from birth defects. Genetic studies in lower vertebrates have been critical to the understanding of the specific factors required for heart development. These studies suggest that cardiac abnormalities may be mediated by abnormal regulation of transcription factors. Although several transcription factors involved in cardiac development have been elucidated, much regarding specific signaling pathways implicated in abnormal cardiogenesis is still unknown. Acquired cardiac disease can occur in response to various stimuli. For example, an increased hemodynamic load can result in compensatory hypertrophic remodeling and may progress to pathologic hypertrophy. A common manifestation of this pathologic process is a constellation of symptoms known as congestive heart failure. Focal Adhesion Kinase (FAK) is responsible for a variety of biological functions including cell adhesion, migration, proliferation, and survival. Several studies demonstrated a role for FAK binding partners and/or for upstream activators of FAK throughout cardiac development and disease. However, since germline deletion of FAK results in early embryonic lethality, it is difficult to study the specific role for FAK in cardiac development and disease. Therefore, we addressed this issue by creating several mouse models which express tissue specific expression of FAK, or its dominant negative FAK-related non-kinase (FRNK). We used these mice to investigate the role of FAK in cardiogenesis, anabolic growth, and cardiac disease. Collectively, these conditional mouse models demonstrated that FAK activity and/or its expression is required for cardiomyocyte proliferation throughout development, is dispensable for anabolic growth of the heart, and is necessary and sufficient for the induction of cardiac hypertrophy. Further characterization of the precise signaling pathways downstream of FAK may lead to targets for future therapeutic intervention to treat congenital and acquired heart disease

FAK regulates cardiomyocyte survival following ischemia/reperfusion

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

The LIM Protein Leupaxin Is Enriched in Smooth Muscle and Functions As an Serum Response Factor Cofactor to Induce Smooth Muscle Cell Gene Transcription

Leupaxin is a LIM-domain containing adapter protein belonging to the paxillin family that has been previously reported to be preferentially expressed in hematopoeitic cells. Herein, we identified leupaxin in a screen for FAK binding partners in aortic smooth muscle, show that leupaxin is enriched in human and mouse vascular smooth muscle, and that leupaxin expression is dynamically regulated during development. In addition, our studies reveal that leupaxin can undergo cytoplasmic/nuclear shuttling and functions as an SRF-cofactor in the nucleus. We found that leupaxin forms a complex with SRF, associates with CArG-containing regions of SM promoters, and that ectopic expression of leupaxin induces SM marker gene expression in both 10T1/2 cells and rat aortic smooth muscle cells (SMC). Subsequent studies indicated that enhanced FAK activity (induced by fibronectin or expression of constitutively active FAK) attenuates the nuclear accumulation of leupaxin and limits the ability of leupaxin to enhance SRF-dependent gene transcription. Thus, these studies indicate that modulation of the sub-cellular localization of SRF-cofactors is one mechanism by which extracellular matrix-dependent signals might regulate phenotypic switching of SMC

Myocyte-Restricted Focal Adhesion Kinase Deletion Attenuates Pressure Overload-Induced Hypertrophy

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

Transient Expression of FRNK Reveals Stage-Specific Requirement for Focal Adhesion Kinase Activity in Cardiac Growth

Focal adhesion kinase (FAK) is strongly activated by integrins and growth factors and is essential for embryonic development. We previously showed that the C terminus of FAK is expressed as a separate protein termed FAK-related nonkinase (FRNK) in a smooth muscle cell–selective fashion and that FRNK functions to buffer FAK-dependent signals. We now show that FRNK is also transiently expressed in the neonatal myocardium, with peak levels occurring 5 to 7 days postnatal, just before cell cycle withdrawal. Using novel mouse models, we demonstrate that cardiac-selective expression of FRNK (leading to inhibition of FAK) starting at embryonic day 10.5 leads to a severe ventricular noncompaction defect associated with reduced cardiomyocyte proliferation. Remarkably, postnatal expression of nearly identical levels of FRNK is well tolerated and does not affect viability or anabolic cardiac growth. Nonetheless, FRNK expression in the adult heart does attenuate pathological cardiac hypertrophy following aortic banding, confirming and extending our previous data that this compensatory response is blunted in FAK null hearts. Our mechanistic studies in cultured neonatal cardiomyocytes reveal that FRNK expression induces p38/p27kip-dependent cell cycle withdrawal and attenuates extracellular signal-regulated kinase–dependent hypertrophic growth. These findings indicate that dynamic expression of FRNK in the neonatal heart may function to promote cardiomyocyte quiescence in an environment that is particularly rich in growth factors and growth promoting extracellular matrices

Focal adhesion kinase in cardiac development and disease

In the United States, nearly 80 million adults are affected by cardiovascular disease. The spectrum of disease range from congenital structural defects to acquired structural changes in response to an increased hemodynamic load on the heart, myocardial infarction, or hormonal imbalance. Cardiovascular disease accounts for significant amounts of morbidity and mortality and is currently the number one cause of death in the U.S. Congenital heart disease is the most common cause of infant death from birth defects. Genetic studies in lower vertebrates have been critical to the understanding of the specific factors required for heart development. These studies suggest that cardiac abnormalities may be mediated by abnormal regulation of transcription factors. Although several transcription factors involved in cardiac development have been elucidated, much regarding specific signaling pathways implicated in abnormal cardiogenesis is still unknown. Acquired cardiac disease can occur in response to various stimuli. For example, an increased hemodynamic load can result in compensatory hypertrophic remodeling and may progress to pathologic hypertrophy. A common manifestation of this pathologic process is a constellation of symptoms known as congestive heart failure. Focal Adhesion Kinase (FAK) is responsible for a variety of biological functions including cell adhesion, migration, proliferation, and survival. Several studies demonstrated a role for FAK binding partners and/or for upstream activators of FAK throughout cardiac development and disease. However, since germline deletion of FAK results in early embryonic lethality, it is difficult to study the specific role for FAK in cardiac development and disease. Therefore, we addressed this issue by creating several mouse models which express tissue specific expression of FAK, or its dominant negative FAK-related non-kinase (FRNK). We used these mice to investigate the role of FAK in cardiogenesis, anabolic growth, and cardiac disease. Collectively, these conditional mouse models demonstrated that FAK activity and/or its expression is required for cardiomyocyte proliferation throughout development, is dispensable for anabolic growth of the heart, and is necessary and sufficient for the induction of cardiac hypertrophy. Further characterization of the precise signaling pathways downstream of FAK may lead to targets for future therapeutic intervention to treat congenital and acquired heart disease

Focal adhesion kinase antagonizes doxorubicin cardiotoxicity via p21Cip1

Clinical application of potent anthracycline anticancer drugs, especially doxorubicin (DOX), is limited by a toxic cardiac side effect that is not fully understood and preventive strategies are yet to be established. Studies in genetically modified mice have demonstrated that focal adhesion kinase (FAK) plays a key role in regulating adaptive responses of the adult myocardium to pathological stimuli through activation of intracellular signaling cascades that facilitate cardiomyocyte growth and survival. The objective of this study was to determine if targeted myocardial FAK activation could protect the heart from DOX-induced de-compensation and to characterize the underlying mechanisms. To this end, mice with myocyte-restricted FAK knock-out (MFKO) or myocyte-specific expression of an active FAK variant (termed SuperFAK) were subjected to DOX treatment. FAK depletion enhanced susceptibility to DOX-induced myocyte apoptosis and cardiac dysfunction, while elevated FAK activity provided remarkable cardioprotection. Our mec6hanistic studies reveal a heretofore unappreciated role for the protective cyclin-dependent kinase inhibitor p21 in the repression of the pro-apoptotic BH3-only protein Bim and the maintenance of mitochondrial integrity and myocyte survival. DOX treatment induced proteasomal degradation of p21, which exacerbated mitochondrial dysfunction and cardiomyocyte apoptosis. FAK was both necessary and sufficient for maintaining p21 levels following DOX treatment and depletion of p21 compromised FAK-dependent protection from DOX. These findings identify p21 as a key determinant of DOX resistance downstream of FAK in cardiomyocytes and indicate that cardiac-restricted enhancement of the FAK/p21 signaling axis might be an effective strategy to preserve myocardial function in patients receiving anthracycline chemotherapy. [Display omitted] •Cardiac FAK depletion exacerbated DOX-induced dysfunction and myocyte apoptosis.•Activation of cardiac FAK provided protection from DOX-induced toxicity.•FAK activation preserves mitochondrial integrity by inducing p21 and Bim

Targeted Focal Adhesion Kinase Activation in Cardiomyocytes Protects the Heart From Ischemia/Reperfusion Injury

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 H(2)O(2) 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

Targeted focal adhesion kinase activation in cardiomyocytes protects the heart from ischemia/reperfusion injury

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. 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 to 72 hours following I/R. Moreover, serial echocardiography revealed that the transgenic mice were protected from cardiac decompensation for up to 8 weeks following surgery. Mechanistic studies revealed that elevated FAK activity protected cardiomyocytes from I/R-induced apoptosis by enhancing nuclear factor-κB (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 H(2)O(2) or hypoxia/reoxygenation-induced apoptosis, whereas blockade of the NF-κB pathway using a pharmacological inhibitor or small interfering RNAs completely abolished the beneficial effect of SuperFAK. Enhancing cardiac FAK activity attenuates I/R-induced myocyte apoptosis through activation of the prosurvival NF-κB pathway and may represent a novel therapeutic strategy for ischemic heart diseases