Loss of Protease-Activated Receptor 4 Prevents Inflammation Resolution and Predisposes the Heart to Cardiac Rupture After Myocardial Infarction.

BACKGROUND: Cardiac rupture is a major lethal complication of acute myocardial infarction (MI). Despite significant advances in reperfusion strategies, mortality from cardiac rupture remains high. Studies suggest that cardiac rupture can be accelerated by thrombolytic therapy, but the relevance of this risk factor remains controversial. METHODS: We analyzed protease-activated receptor 4 (Par4) expression in mouse hearts with MI and investigated the effects of Par4 deletion on cardiac remodeling and function after MI by echocardiography, quantitative immunohistochemistry, and flow cytometry. RESULTS: Par4 mRNA and protein levels were increased in mouse hearts after MI and in isolated cardiomyocytes in response to hypertrophic and inflammatory stimuli. Par4-deficient mice showed less myocyte apoptosis, reduced infarct size, and improved functional recovery after acute MI relative to wild-type (WT). Conversely, Par4-/- mice showed impaired cardiac function, greater rates of myocardial rupture, and increased mortality after chronic MI relative to WT. Pathological evaluation of hearts from Par4-/- mice demonstrated a greater infarct expansion, increased cardiac hemorrhage, and delayed neutrophil accumulation, which resulted in impaired post-MI healing compared with WT. Par4 deficiency also attenuated neutrophil apoptosis in vitro and after MI in vivo and impaired inflammation resolution in infarcted myocardium. Transfer of Par4-/- neutrophils, but not of Par4-/- platelets, in WT recipient mice delayed inflammation resolution, increased cardiac hemorrhage, and enhanced cardiac dysfunction. In parallel, adoptive transfer of WT neutrophils into Par4-/- mice restored inflammation resolution, reduced cardiac rupture incidence, and improved cardiac function after MI. CONCLUSIONS: These findings reveal essential roles of Par4 in neutrophil apoptosis and inflammation resolution during myocardial healing and point to Par4 inhibition as a potential therapy that should be limited to the acute phases of ischemic insult and avoided for long-term treatment after MI.

Cardiac Expression of Factor X Mediates Cardiac Hypertrophy and Fibrosis in Pressure Overload.

Activated factor X is a key component of the coagulation cascade, but whether it directly regulates pathological cardiac remodeling is unclear. In mice subjected to pressure overload stress, cardiac factor X mRNA expression and activity increased concurrently with cardiac hypertrophy, fibrosis, inflammation and diastolic dysfunction, and responses blocked with a low coagulation-independent dose of rivaroxaban. In vitro, neurohormone stressors increased activated factor X expression in both cardiac myocytes and fibroblasts, resulting in activated factor X-mediated activation of protease-activated receptors and pro-hypertrophic and -fibrotic responses, respectively. Thus, inhibition of cardiac-expressed activated factor X could provide an effective therapy for the prevention of adverse cardiac remodeling in hypertensive patients.

Inflammatory Serine Proteases Play a Critical Role in the Early Pathogenesis of Diabetic Cardiomyopathy.

BACKGROUND/AIMS: Diabetic cardiomyopathy (DCM) is characterized by structural and functional alterations that can lead to heart failure. Several mechanisms are known to be involved in the pathogenesis of DCM, however, the molecular mechanism that links inflammation to DCM is incompletely understood. To learn about this mechanism, we investigated the role of inflammatory serine proteases (ISPs) during the development of DCM. METHODS: Eight weeks old mice with deletion of dipeptidyl peptidase I (DPPI), an enzyme involved in the maturation of major ISPs, and wild type (WT) mice controls were injected with streptozotocin (50 mg/kg for 5 days intraperitoneally) and studied after 4, 8, 16, and 20 week after induction of type 1 diabetes mellitus (T1DM). Induction of diabetes was followed by echocardiographic measurements, glycemic and hemoglobulin A1c profiling, immunoblot, qPCR, enzyme activity assays, and immunohistochemistry (IHC) analysis of DPPI, ISPs, and inflammatory markers. Fibrosis was determined from left ventricular heart by Serius Red staining and qPCR. Apoptosis was determined by TUNEL assay and immunoblot analysis. RESULTS: In the diabetic WT mice, DPPI expression increased along with ISP activation, and DPPI accumulated abundantly in the left ventricle mainly from infiltrating neutrophils. In diabetic DPPI-knockout (DPPI-KO) mice, significantly decreased activation of ISPs, myocyte apoptosis, fibrosis, and cardiac function was improved compared to diabetic WT mice. In addition, DPPI-KO mice showed a decrease in overall inflammatory status mediated by diabetes induction which was manifested by decreased production of pro-inflammatory cytokines like TNF-α, IL-1ß and IL-6. CONCLUSION: This study elucidates a novel role of ISPs in potentiating the immunological responses that lead to the pathogenesis of DCM in T1DM. To the best of our knowledge, this is the first study to report that DPPI expression and activation promotes the inflammation that enhances myocyte apoptosis and contributes to the adverse cardiac remodeling that subsequently leads to DCM.

Intracardiac administration of neutrophil protease cathepsin G activates noncanonical inflammasome pathway and promotes inflammation and pathological remodeling in non-injured heart.

BACKGROUND: Inflammatory serine proteases (ISPs) play an important role in cardiac repair after injury through hydrolysis of dead cells and extracellular matrix (ECM) debris. Evidence also suggests an important role of ISPs in the coordination of the inflammatory response. However, the effect of ISPs on inflammation is obfuscated by the confounding factors associated with cell death and inflammatory cell infiltration induced after cardiac injury. This study investigated whether neutrophil-derived cathepsin G (Cat.G) influences inflammation and remodeling in the absence of prior cardiac injury and cell death. METHODS AND RESULTS: Intracardiac catheter delivery of Cat.G (1 mg/kg) in rats induced significant left ventricular (LV) dilatation and cardiac contractile dysfunction at day 5, but not at day 2, post-delivery compared to vehicle-treated animals. Cat.G delivery also significantly increased matrix metalloprotease activity and collagen and fibronectin degradation at day 5 compared to vehicle-treated rats and these changes were associated with increased death signaling pathways and myocyte apoptosis. Mechanistic analysis shows that Cat.G-treatment induced potent chemotactic activity in hearts at day 2 and 5 post-delivery, characterized by processing and activation of interleukin (IL)-1ß and IL-18, stimulation of inflammatory signaling pathways and accumulation of myeloid cells when compared to vehicle-treated rats. Cat.G-induced processing of IL-1ß and IL-18 was independent of the canonical NLRP-3 inflammasome pathway and treatment of isolated cardiomyocytes with inhibitors of NLRP-3 or caspase-1 failed to reduce Cat.G-induced cardiomyocyte death. Notably, rats treated with IL-1 receptor antagonist (IL-1Ra) show reduced inflammation and improved cardiac remodeling and function following Cat.G delivery. CONCLUSIONS: Cat.G exerts potent chemoattractant and pro-inflammatory effects in non-stressed or injured heart in part through processing and activation of IL-1 family cytokines, subsequently leading to adverse cardiac remodeling and function. Thus, targeting ISPs could be a novel therapeutic strategy to reduce cardiac inflammation and improve cardiac remodeling and function after injury or stress.

Hyperglycemia-Driven Neuroinflammation Compromises BBB Leading to Memory Loss in Both Diabetes Mellitus (DM) Type 1 and Type 2 Mouse Models.

End organ injury in diabetes mellitus (DM) is driven by microvascular compromise (including diabetic retinopathy and nephropathy). Cognitive impairment is a well-known complication of DM types 1 and 2; however, its mechanism(s) is(are) not known. We hypothesized that blood-brain barrier (BBB) compromise plays a key role in cognitive decline in DM. Using a DM type 1 model (streptozotocin injected C57BL/6 mice) and type 2 model (leptin knockout obese db/db mice), we showed enhanced BBB permeability and memory loss (Y maze, water maze) that are associated with hyperglycemia. Gene profiling in isolated microvessels from DM type 1 animals demonstrated deregulated expression of 54 genes related to angiogenesis, inflammation, vasoconstriction/vasodilation, and platelet activation pathways by at least 2-fold (including eNOS, TNFα, TGFß1, VCAM-1, E-selectin, several chemokines, and MMP9). Further, the magnitude of gene expression was linked to degree of cognitive decline in DM type 1 animals. Gene analysis in brain microvessels of DM type 2 db/db animals showed alterations of similar genes as in DM 1 model, some to an even greater extent. Neuropathologic analyses of brain tissue derived from DM mice showed microglial activation, expression of ICAM-1, and attenuated coverage of pericytes compared to controls. There was a significant upregulation of inflammatory genes in brain tissue in both DM models. Taken together, our findings indicate that BBB compromise in DM in vivo models and its association with memory deficits, gene alterations in brain endothelium, and neuroinflammation. Prevention of BBB injury may be a new therapeutic approach to prevent cognitive demise in DM.

Dual inhibition of cathepsin G and chymase reduces myocyte death and improves cardiac remodeling after myocardial ischemia reperfusion injury.

Early reperfusion of ischemic cardiac tissue increases inflammatory cell infiltration which contributes to cardiomyocyte death and loss of cardiac function, referred to as ischemia/reperfusion (IR) injury. Neutrophil- and mast cell-derived proteases, cathepsin G (Cat.G) and chymase, are released early after IR, but their function is complicated by potentially redundant actions and targets. This study investigated whether a dual inhibition of Cat.G and chymase influences cardiomyocyte injury and wound healing after experimental IR in mice. Treatment with a dual Cat.G and chymase inhibitor (DCCI) immediately after reperfusion blocked cardiac Cat.G and chymase activity induced after IR, which resulted in decreased immune response in the infarcted heart. Mice treated with DCCI had less myocardial collagen deposition and showed preserved ventricular function at 1 and 7 days post-IR compared with vehicle-treated mice. DCCI treatment also significantly attenuated focal adhesion (FA) complex disruption and myocyte degeneration after IR. Treatment of isolated cardiomyocytes with Cat.G or chymase significantly promoted FA signaling downregulation, myofibril degeneration and myocyte apoptosis. Conversely, treatment of cardiac fibroblasts with Cat.G or chymase induced FA signaling activation and increased their migration and differentiation to myofibroblasts. These opposite responses in cardiomyocytes and fibroblasts were blocked by treatment with DCCI. These findings show that Cat.G and chymase are key mediators of myocyte apoptosis and fibroblast migration and differentiation that play a role in adverse cardiac remodeling and function post-IR. Thus, dual targeting of neutrophil- and mast cell-derived proteases could be used as a novel therapeutic strategy to reduce post-IR inflammation and improve cardiac remodeling.

Platelet microparticles infiltrating solid tumors transfer miRNAs that suppress tumor growth.

Platelet-derived microparticles (PMPs) are associated with enhancement of metastasis and poor cancer outcomes. Circulating PMPs transfer platelet microRNAs (miRNAs) to vascular cells. Solid tumor vasculature is highly permeable, allowing the possibility of PMP-tumor cell interaction. Here, we show that PMPs infiltrate solid tumors in humans and mice and transfer platelet-derived RNA, including miRNAs, to tumor cells in vivo and in vitro, resulting in tumor cell apoptosis. MiR-24 was a major species in this transfer. PMP transfusion inhibited growth of both lung and colon carcinoma ectopic tumors, whereas blockade of miR-24 in tumor cells accelerated tumor growth in vivo, and prevented tumor growth inhibition by PMPs. Conversely, Par4-deleted mice, which had reduced circulating microparticles (MPs), supported accelerated tumor growth which was halted by PMP transfusion. PMP targeting was associated with tumor cell apoptosis in vivo. We identified direct RNA targets of platelet-derived miR-24 in tumor cells, which included mitochondrial mt-Nd2, and Snora75, a noncoding small nucleolar RNA. These RNAs were suppressed in PMP-treated tumor cells, resulting in mitochondrial dysfunction and growth inhibition, in an miR-24-dependent manner. Thus, platelet-derived miRNAs transfer in vivo to tumor cells in solid tumors via infiltrating MPs, regulate tumor cell gene expression, and modulate tumor progression. These findings provide novel insight into mechanisms of horizontal RNA transfer and add multiple layers to the regulatory roles of miRNAs and PMPs in tumor progression. Plasma MP-mediated transfer of regulatory RNAs and modulation of gene expression may be a common feature with important outcomes in contexts of enhanced vascular permeability.

Protease-activated receptor 4 deficiency offers cardioprotection after acute ischemia reperfusion injury.

Protease-activated receptor (PAR)4 is a low affinity thrombin receptor with less understood function relative to PAR1. PAR4 is involved in platelet activation and hemostasis, but its specific actions on myocyte growth and cardiac function remain unknown. This study examined the role of PAR4 deficiency on cardioprotection after myocardial ischemia-reperfusion (IR) injury in mice. When challenged by in vivo or ex vivo IR, PAR4 knockout (KO) mice exhibited increased tolerance to injury, which was manifest as reduced infarct size and a more robust functional recovery compared to wild-type mice. PAR4 KO mice also showed reduced cardiomyocyte apoptosis and putative signaling shifts in survival pathways in response to IR. Inhibition of PAR4 expression in isolated cardiomyocytes by shRNA offered protection against thrombin and PAR4-agonist peptide-induced apoptosis, while overexpression of wild-type PAR4 significantly enhanced the susceptibility of cardiomyocytes to apoptosis, even under low thrombin concentrations. Further studies implicate Src- and epidermal growth factor receptor-dependent activation of JNK on the proapoptotic effect of PAR4 in cardiomyocytes. These findings reveal a pivotal role for PAR4 as a regulator of cardiomyocyte survival and point to PAR4 inhibition as a therapeutic target offering cardioprotection after acute IR injury.

Intracoronary Cytoprotective Gene Therapy: A Study of VEGF-B167 in a Pre-Clinical Animal Model of Dilated Cardiomyopathy.

BACKGROUND: Vascular endothelial growth factor (VEGF)-B activates cytoprotective/antiapoptotic and minimally angiogenic mechanisms via VEGF receptors. Therefore, VEGF-B might be an ideal candidate for the treatment of dilated cardiomyopathy, which displays modest microvascular rarefaction and increased rate of apoptosis. OBJECTIVES: This study evaluated VEGF-B gene therapy in a canine model of tachypacing-induced dilated cardiomyopathy. METHODS: Chronically instrumented dogs underwent cardiac tachypacing for 28 days. Adeno-associated virus serotype 9 viral vectors carrying VEGF-B167 genes were infused intracoronarily at the beginning of the pacing protocol or during compensated heart failure. Moreover, we tested a novel VEGF-B167 transgene controlled by the atrial natriuretic factor promoter. RESULTS: Compared with control subjects, VEGF-B167 markedly preserved diastolic and contractile function and attenuated ventricular chamber remodeling, halting the progression from compensated to decompensated heart failure. Atrial natriuretic factor-VEGF-B167 expression was low in normally functioning hearts and stimulated by cardiac pacing; it thus functioned as an ideal therapeutic transgene, active only under pathological conditions. CONCLUSIONS: Our results, obtained with a standard technique of interventional cardiology in a clinically relevant animal model, support VEGF-B167 gene transfer as an affordable and effective new therapy for nonischemic heart failure.

c-Cbl inhibition improves cardiac function and survival in response to myocardial ischemia.

BACKGROUND: The proto-oncogene Casitas b-lineage lymphoma (c-Cbl) is an adaptor protein with an intrinsic E3 ubiquitin ligase activity that targets receptor and nonreceptor tyrosine kinases, resulting in their ubiquitination and downregulation. However, the function of c-Cbl in the control of cardiac function is currently unknown. In this study, we examined the role of c-Cbl in myocyte death and cardiac function after myocardial ischemia. METHODS AND RESULTS: We show increased c-Cbl expression in human ischemic and dilated cardiomyopathy hearts and in response to pathological stress stimuli in mice. c-Cbl-deficient mice demonstrated a more robust functional recovery after myocardial ischemia/reperfusion injury and significantly reduced myocyte apoptosis and improved cardiac function. Ubiquitination and downregulation of key survival c-Cbl targets, epidermal growth factor receptors and focal adhesion kinase, were significantly reduced in c-Cbl knockout mice. Inhibition of c-Cbl expression or its ubiquitin ligase activity in cardiac myocytes offered protection against H2O2 stress. Interestingly, c-Cbl deletion reduced the risk of death and increased cardiac functional recovery after chronic myocardial ischemia. This beneficial effect of c-Cbl deletion was associated with enhanced neoangiogenesis and increased expression of vascular endothelial growth factor-a and vascular endothelial growth factor receptor type 2 in the infarcted region. CONCLUSIONS: c-Cbl activation promotes myocyte apoptosis, inhibits angiogenesis, and causes adverse cardiac remodeling after myocardial infarction. These findings point to c-Cbl as a potential therapeutic target for the maintenance of cardiac function and remodeling after myocardial ischemia.

Beta1-adrenergic receptors promote focal adhesion signaling downregulation and myocyte apoptosis in acute volume overload.

Numerous studies demonstrated increased expression of extracellular matrix (ECM) proteins and activation of focal adhesion (FA) signaling pathways in models of pressure overload-induced cardiac hypertrophy. However, little is known about FA signaling in response to volume overload where cardiac hypertrophy is associated with ECM loss. This study examines the role of beta1-adrenergic receptors (ß(1)-ARs) in FA signaling changes and myocyte apoptosis induced during acute hemodynamic stress of volume overload. Rats with eccentric cardiac hypertrophy induced after aorto-caval fistula (ACF) develop reduced interstitial collagen content and decreased tyrosine phosphorylation of key FA signaling molecules FAK, Pyk(2) and paxillin along with an increase in cardiac myocyte apoptosis. ACF also increased activation of PTEN, a dual lipid and protein phosphatase, and its interaction with FA proteins. ß(1)-AR blockade (extended-release of metoprolol succinate, 100mg QD) markedly attenuated PTEN activation, restored FA signaling and reduced myocyte apoptosis induced by ACF at 2days, but failed to reduce interstitial collagen loss and left ventricular dilatation. Treating cultured myocytes with ß(1)-AR agonists or adenoviral expression of ß(1)-ARs caused PTEN activation and interaction with FA proteins, thus leading to FA signaling downregulation and myocyte apoptosis. Adenoviral-mediated expression of a catalytically inactive PTEN mutant or wild-type FAK restored FA signaling downregulation and attenuated myocyte apoptosis induced by ß(1)-ARs. Collectively, these data show that ß(1)-AR stimulation in response to ACF induces FA signaling downregulation through an ECM-independent mechanism. This effect involves PTEN activation and may contribute to adverse cardiac remodeling and function in the course of volume overload.

c-Cbl ubiquitin ligase regulates focal adhesion protein turnover and myofibril degeneration induced by neutrophil protease cathepsin G.

The neutrophil-derived serine protease, cathepsin G (Cat.G), has been shown to induce myocyte detachment and apoptosis by anoikis through down-regulation of focal adhesion (FA) signaling. However, the mechanisms that control FA protein stability and turnover in myocytes are not well understood. Here, we have shown that the Casitas b-lineage lymphoma (c-Cbl), adaptor protein with an intrinsic E3 ubiquitin ligase activity, is involved in FA and myofibrillar protein stability and turnover in myocytes. Cat.G treatment induced c-Cbl activation and its interaction with FA proteins. Deletion of c-Cbl using c-Cbl knock-out derived myocytes or inhibition of c-Cbl ligase activity significantly reduced FA protein degradation, myofibrillar degeneration, and myocyte apoptosis induced by Cat.G. We also found that inhibition of the proteasome activity, but not the lysosome or the calpain activity, markedly attenuated FA and myofibrillar protein degradation induced by Cat.G. Interestingly, c-Cbl activation induced by Cat.G was mediated through epidermal growth factor receptor (EGFR) transactivation as inhibition of EGFR kinase activity markedly attenuated c-Cbl phosphorylation and FA protein degradation induced by Cat.G. These findings support a model in which neutrophil protease Cat.G promotes c-Cbl interaction with FA proteins, resulting in enhanced c-Cbl-mediated FA protein ubiquitination and degradation, myofibril degradation, and subsequent down-regulation of myocyte survival signaling.

Pleiotropic effects of neutrophils on myocyte apoptosis and left ventricular remodeling during early volume overload.

Most of the available evidence on the role of neutrophils on pathological cardiac remodeling has been pertained after acute myocardial infarction. However, whether neutrophils directly contribute to the pathogenesis of cardiac remodeling after events other than acute myocardial infarction remains unknown. Here we show that acute eccentric hypertrophy induced by aorto-caval fistula (ACF) in the rats induced an increase in the inflammatory response characterized by activation of the STAT pathway and increased infiltration of neutrophils in the myocardium. This early inflammation was associated with a decrease in interstitial collagen accumulation and an increase in myocyte apoptosis. Neutrophil infiltration blockade attenuated MMP activation, ECM degradation, and myocyte apoptosis induced by ACF at 24 hours and attenuated the development of eccentric hypertrophy induced by ACF at 2 and 3 weeks, suggesting a causal relationship between neutrophils and the ACF-induced cardiac remodeling. In contrast, sustained neutrophil depletion over 4 weeks resulted in adverse cardiac remodeling with further increase in cardiac dilatation and macrophage infiltration, but with no change in myocyte apoptosis level. These data support a functional role for neutrophils in MMP activation, ECM degradation, and myocyte apoptosis during eccentric cardiac hypertrophy and underscore the adverse effects of chronic anti-neutrophil therapy on cardiac remodeling induced by early volume overload.

Sympathetic activation causes focal adhesion signaling alteration in early compensated volume overload attributable to isolated mitral regurgitation in the dog.

We reported that left ventricular (LV) dilatation after 4 weeks of isolated mitral regurgitation (MR) in the dogs is marked by extracellular matrix loss and an increase in adrenergic drive. Given that extracellular matrix proteins and their receptor integrins influence beta-adrenergic receptor (beta-AR) responses in vitro, we tested whether beta1-AR activation modulates focal adhesion (FA) signaling and LV remodeling in these same dogs with isolated MR. Normal dogs were compared with dogs with MR of a 4-week duration and with MR dogs treated with beta(1)-AR blockade (beta(1)-RB) (extended-release metoprolol succinate, 100 mg QD) that was started 24 hours after MR induction. In MR LVs, a decrease in collagen accumulation compared with normal dogs was associated with a decrease in FA kinase tyrosine phosphorylation, along with FA kinase interaction with adapter and cytoskeletal proteins, p130(Cas) and paxillin, respectively, as determined by immunoprecipitation assays. There was increased phosphorylation of stress related molecules p38 mitogen-activated protein kinase (MAPK) and Hsp27 and survival signaling kinases extracellular signal-regulated kinase 1/2 and AKT, with no evidence of cardiomyocyte apoptosis. beta(1)-RB attenuated FA signaling loss and prevented p38 MAPK, Hsp27, and AKT phosphorylation induced by MR and significantly increased LV epicardial collagen content. However, beta(1)-RB did not improve LV endocardial collagen loss or LV dilatation induced by MR. Isolated myocytes from normal and MR dog hearts treated with beta(1)- or beta(2)-AR agonists demonstrated no difference in FA kinase, p38 MAPK, Hsp27, or AKT phosphorylation. These results showed that chronic stimulation of beta(1)-AR during early compensated MR impairs FA signaling that may affect myocyte/fibroblast-extracellular matrix scaffolding necessary for LV remodeling.

Role of protein-tyrosine phosphatase SHP2 in focal adhesion kinase down-regulation during neutrophil cathepsin G-induced cardiomyocytes anoikis.

Inflammatory cells and their proteases contribute to tissue reparation at site of inflammation. Although beneficial at early stages, excessive inflammatory reaction leads to cell death and tissue damage. Cathepsin G (Cat.G), a neutrophil-derived serine protease, has been shown to induce neonatal rat cardiomyocyte detachment and apoptosis by anoikis through caspase-3 dependent pathway. However the early mechanisms that trigger Cat.G-induced caspase-3 activation are not known. This study identifies focal adhesion kinase (FAK) tyrosine dephosphorylation as an early mechanism that regulates Cat.G-induced anoikis in cardiomyocytes. Both FAK tyrosine phosphorylation at Tyr-397 and kinase activity decrease rapidly upon Cat.G treatment and was associated with a decrease of FAK association with adapter and cytoskeletal proteins, p130(Cas) and paxillin, respectively. FAK-decreased tyrosine phosphorylation is required for Cat.G-induced myocyte anoikis as concurrent expression of phosphorylation-deficient FAK mutated at Tyr-397 or pretreatment with a protein-tyrosine phosphatase (PTP) inhibitor, pervanadate, blocks Cat.G-induced FAK tyrosine dephosphorylation, caspase-3 activation and DNA fragmentation. Analysis of PTPs activation shows that Cat.G treatment induces an increase of SHP2 and PTEN phosphorylation; however, only SHP2 forms a complex with FAK in response to Cat.G. Expression of dominant negative SHP2 mutant markedly attenuates FAK tyrosine dephosphorylation induced by Cat.G and protects myocytes to undergo apoptosis. In contrast, increased SHP2 expression exacerbates Cat.G-induced FAK tyrosine dephosphorylation and myocyte apoptosis. Taken together, these results show that Cat.G induces SHP2 activation that leads to FAK tyrosine dephosphorylation and promotes cardiomyocyte anoikis.