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The heart responds to sustained overload by hypertrophic growth in which the myocytes distinctly thicken or elongate on increases in systolic or diastolic stress. Though potentially adaptive, hypertrophy itself may predispose to cardiac dysfunction in pathological settings. The mechanisms underlying the diverse morphology and outcomes of hypertrophy are uncertain. Here we used a focal adhesion kinase (FAK) cardiac-specific transgenic mice model (FAK-Tg) to explore the function of this non-receptor tyrosine kinase on the regulation of myocyte growth. FAK-Tg mice displayed a phenocopy of concentric cardiac hypertrophy, reflecting the relative thickening of the individual myocytes. Moreover, FAK-Tg mice showed structural, functional and molecular features of a compensated hypertrophic growth, and preserved responses to chronic pressure overload. Mechanistically, FAK overexpression resulted in enhanced myocardial FAK activity, which was proven by treatment with a selective FAK inhibitor to be required for the cardiac hypertrophy in this model. Our results indicate that upregulation of FAK does not affect the activity of Src/ERK1/2 pathway, but stimulated signaling by a cascade that encompasses PI3K, AKT, mTOR, S6K and rpS6. Moreover, inhibition of the mTOR complex by rapamycin extinguished the cardiac hypertrophy of the transgenic FAK mice. These findings uncover a unique role for FAK in regulating the signaling mechanisms that governs the selective myocyte growth in width, likely controlling the activity of PI3K/AKT/mTOR pathway, and suggest that FAK activation could be important for the adaptive response to increases in cardiac afterload. This article is part of a Special Issue entitled "Local Signaling in Myocytes".

Received 21 Jun 2011; first review completed 28 Jun 2011; accepted in final form 11 Aug 2011ABSTRACT—Sepsis and septic shock are associated with cardiac depression. Cardiovascular instability is a major causeof death in patients with sepsis. Focal adhesion kinase (FAK) is a potential mediator of cardiomyocyte responses tooxidative and mechanical stress. Myocardial collagen deposition can affect cardiac compliance and contractility. The aimof the present study was to determine whether the silencing of FAK is protective against endotoxemia-induced alterationsof cardiac structure and function. In male Wistar rats, endotoxemia was induced by intraperitoneal injection oflipopolysaccharide (10 mg/kg). Cardiac morphometry and function were studied in vivo by left ventricular catheterizationand histology. Intravenous injection of small interfering RNA targeting FAK was used to silence myocardial expression ofthe kinase. The hearts of lipopolysaccharide-injected rats showed collagen deposition, increased matrix metalloproteinase2 activity, and myocyte hypertrophy, as well as reduced 24-h +dP/dt and jdP/dt, together with hypotension, increased leftventricular end-diastolic pressure, and elevated levels of FAK (phosphorylated and unphosphorylated). Focal adhesionkinase silencing reduced the expression and activation of the kinase in cardiac tissue, as well as protecting against theincreased collagen deposition, greater matrix metalloproteinase 2 activity, and reduced cardiac contractility that occurduring endotoxemia. In conclusion, FAK is activated in endotoxemia, playing a role in cardiac remodeling and in theimpairment of cardiac function. This kinase represents a potential therapeutic target for the protection of cardiac function inpatients with sepsis.KEYWORDS—Focal adhesion protein-tyrosine kinases, cytokines, inflammation, sepsis, shock septic

We studied the implication of focal adhesion kinase (FAK) in cardiac mitochondrial biogenesis induced by mechanical stress. Prolonged stretching (2–12 h) of neonatal rat ventricular myocytes (NRVM) upregulated the main components of mitochondrial transcription cascade [peroxisome proliferator-activated receptor coactivator-1 (PGC-1α), nuclear respiratory factor (NRF-1), and mitochondrial transcription factor A]. Concomitantly, prolonged stretching enhanced mitochondrial biogenesis [copy number of mitochondrial DNA (mtDNA), content of the subunit IV of cytochrome oxidase, and mitochondrial staining-green fluorescence intensity of Mitotracker green] and induced the hypertrophic growth (cell size and atrial natriuretic peptide transcripts) of NRVM. Furthermore, the stretching of NRVM enhanced phosphorylation, nuclear localization, and association of FAK with PGC-1α. Recombinant FAK COOH-terminal, but not the NH2-terminal or kinase domain, precipitated PGC-1α from nuclear extracts of NRVM. Depletion of FAK by RNA interference suppressed the upregulation of PGC-1α and NRF-1 and markedly attenuated the enhanced mitochondrial biogenesis and hypertrophic growth of stretched NRVM. In the context of energy metabolism, FAK depletion became manifest by a reduction of ATP levels in stretched NRVM. Complementary studies in adult mice left ventricle demonstrated that pressure overload upregulated PGC-1α, NRF-1, and mtDNA. In vivo FAK silencing transiently attenuated the upregulation of PGC-1α, NRF-1, and mtDNA, as well as the left ventricular hypertrophy induced by pressure overload. In conclusion, activation of FAK signaling seems to be important for conferring enhanced mitochondrial biogenesis coupled to the hypertrophic growth of cardiomyocytes in response to mechanical stress, via control of mitochondrial transcription cascade.

Focal adhesion kinase (FAK) is a broadly expressed tyrosine kinase implicated in cellular functions such as migration, growth and survival. Emerging data support a role for FAK in cardiac development, reactive hypertrophy and failure. Data reviewed here indicate that FAK plays a critical role at the cellular level in the responses of cardiomyocytes and cardiac fibroblasts to biomechanical stress and to hypertrophic agonists such as angiotensin II and endothelin. The signaling mechanisms regulated by FAK are discussed to provide insight into its role in the pathophysiology of cardiac hypertrophy and failure.

Hypertrophy is a critical event in the onset of failure in chronically overloaded hearts. Focal adhesion kinase (FAK) has attracted particular attention as a mediator of hypertrophy induced by increased load. Here, we demonstrate increased expression and phosphorylation of FAK in the hypertrophic left ventricles (LVs) of aortic-banded mice. We used an RNA interference strategy to examine whether FAK signaling plays a role in the pathophysiology of load-induced LV hypertrophy and failure. Intrajugular delivery of specific small interfering RNA induced prolonged FAK silencing ( approximately 70%) in both normal and hypertrophic LVs. Myocardial FAK silencing was accompanied by prevention, as well as reversal, of load-induced left ventricular hypertrophy. The function of LVs was preserved and the survival rate was higher in banded mice treated with small interfering RNA targeted to FAK, despite the persistent pressure overload. Studies in cardiac myocytes and fibroblasts harvested from LVs confirmed the ability of the systemically administered specific small interfering RNA to silence FAK in both cell types. Further analysis indicated attenuation of cardiac myocyte hypertrophic growth and of the rise in the expression of beta-myosin heavy chain in overloaded LVs. Moreover, FAK silencing was demonstrated to attenuate the rise in the fibrosis, collagen content, and activity of matrix metalloproteinase-2 in overloaded LVs, as well as the rise of matrix metalloproteinase-2 protein expression in fibroblasts harvested from overloaded LVs. This study provides novel evidence that FAK may be involved in multiple aspects of the pathophysiology of cardiac hypertrophy and failure induced by pressure overload.

This study examined whether focal adhesion kinase (FAK) plays a role in the differentiation of C2C12myoblasts into myotubes. Differentiation of C2C12myoblasts induced by switch to differentiation culture medium was accompanied by a transient reduction of FAK phosphorylation at Tyr-397 (to ∼50%, at 1 and 2 h), followed by an increase thereafter (to 240% up to 5 days), although FAK protein expression remained unchanged. FAK and phosphorylated FAK were found at the edge of lamellipodia in proliferating cells, whereas the later increase in FAK phosphorylation in differentiating cells was accompanied by its preferential location at the tip of well-organized actin stress fibers. Hyperexpression of FAK autophosphorylation site (Tyr-397) mutant (MT-FAK) reduced FAK phosphorylation at Tyr-397 in proliferating cells and was accompanied by reduction of cyclin D1 and increase of myogenin expression. These cells failed to progress to myotubes in differentiation medium. In contrast, hyperexpression of a wild-type FAK construction (WT-FAK) increased baseline and abolished the transient reduction of FAK phosphorylation at Tyr-397 in serum-starved C2C12cells. Cells transfected with WT-FAK failed to reduce cyclin D1 and to increase myogenin expression, as well as to progress to terminal differentiation in differentiation medium. These data indicate that FAK signaling plays a critical role in the control of cell cycle as well as in the progression of C2C12cells to terminal differentiation. Transient inhibition of FAK phosphorylation at Tyr-397 contributes to trigger the myogenic genetic program, but its later activation is also central to terminal differentiation into myotubes.

Focal adhesion kinase (FAK) regulates cellular processes that affect several aspects of development and disease. The FAK N-terminal FERM (4.1 protein-ezrin-radixin-moesin homology) domain, a compact clover-leaf structure, binds partner proteins and mediates intramolecular regulatory interactions. Combined chemical cross-linking coupled to MS, small-angle X-ray scattering, computational docking and mutational analyses showed that the FAK FERM domain has a molecular cleft (~998 A(2)) that interacts with sarcomeric myosin, resulting in FAK inhibition. Accordingly, mutations in a unique short amino acid sequence of the FERM myosin cleft, FP-1, impaired the interaction with myosin and enhanced FAK activity in cardiomyocytes. An FP-1 decoy peptide selectively inhibited myosin interaction and increased FAK activity, promoting cardiomyocyte hypertrophy through activation of the AKT-mammalian target of rapamycin pathway. Our findings uncover an inhibitory interaction between the FAK FERM domain and sarcomeric myosin that presents potential opportunities to modulate the cardiac hypertrophic response through changes in FAK activity.

BACKGROUND:The activation of the members of the myocyte enhancer factor-2 family (MEF2A, B, C and D) of transcription factors promotes cardiac hypertrophy and failure. However, the role of its individual components in the pathogenesis of cardiac hypertrophy remains unclear. METHODOLOGY/PRINCIPAL FINDINGS:In this study, we investigated whether MEF2C plays a role in mediating the left ventricular hypertrophy by pressure overload in mice. The knockdown of myocardial MEF2C induced by specific small interfering RNA (siRNA) has been shown to attenuate hypertrophy, interstitial fibrosis and the rise of ANP levels in aortic banded mice. We detected that the depletion of MEF2C also results in lowered levels of both PGC-1alpha and mitochondrial DNA in the overloaded left ventricle, associated with enhanced AMP:ATP ratio. Additionally, MEF2C depletion was accompanied by defective activation of S6K in response to pressure overload. Treatment with the amino acid leucine stimulated S6K and suppressed the attenuation of left ventricular hypertrophy and fibrosis in the aforementioned aortic banded mice. CONCLUSION/SIGNIFICANCE:These findings represent new evidences that MEF2C depletion attenuates the hypertrophic responses to mechanical stress and highlight the potential of MEF2C to be a target for new therapies to cardiac hypertrophy and failure.

FAK (focal adhesion kinase) has been shown to mediate the hypertrophic growth of the left ventricle. Experimental results also suggest that FAK may contribute to the structural and functional deterioration of the chronically overloaded left ventricle. In the present study, we postulated that FAK expression and phosphorylation may be altered in the volume-overloaded heart in humans. FAK expression and phosphorylation at Tyr397 were detected by Western blotting and immunohistochemistry in samples from endomyocardial biopsies from patients with MR (mitral regurgitation; n =21) and donor subjects ( n =4). Hearts from patients with MR had degenerated cardiac myocytes and areas of fibrosis. In this group, the myocardial collagen area was increased (18% in MR hearts compared with 3% in donor hearts respectively) and correlated negatively with left ventricular ejection fraction ( r =−0.74; P >0.001). FAK expression and phosphorylation at Tyr397 (a marker of the enzyme activity) were increased in samples from MR hearts compared with those from donor hearts (3.1- and 4.9-fold respectively). In myocardial samples from donor hearts, anti-FAK staining was almost exclusively restricted to cardiac myocytes; however, in myocardial samples from MR hearts, staining with the anti-FAK antibody was found to occur in myocytes and the interstitium. There was a positive correlation between collagen and the interstitial areas stained with the anti-FAK antibody ( r =0.76; P >0.001). Anti-FAK and anti-vimentin staining of the interstitial areas of samples from MR hearts were extensively superimposed, indicating that most of the interstitial FAK was located in fibroblasts. In conclusion, FAK expression and phosphorylation are increased and may contribute to the underlying structural and functional abnormalities in the volume-overloaded heart in humans. Abbreviations: FAK, focal adhesion kinase; LAD, left atrial diameter; LV, left ventricular; LVEDD, LV end-diastolic diameter; LVEF, LV ejection fraction; LVESD, LV end-systolic diameter; LVMI, LV mass index; MR, mitral regurgitation; PASP, pulmonary artery systolic pressure; RAP, right atrial pressure; TRITC, tetramethylrhodamine β-isothiocyanate

Cardiovasc Res (2010); 86 (3): 421–431. doi:10.1093/cvr/cvp416 The study by Dalla Costa et al. reported an analysis of the role of focal adhesion kinase in …