Beta1-adrenergic receptors promote focal adhesion signaling downregulation and myocyte apoptosis in acute volume overload.
ABSTRACT: 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 (?(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. ?(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 ?(1)-AR agonists or adenoviral expression of ?(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 ?(1)-ARs. Collectively, these data show that ?(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.
Project description: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.
Project description:An alpha1-adrenergic receptor (alpha1-AR) antagonist increased heart failure in the Antihypertensive and Lipid-Lowering Treatment to Prevent Heart Attack Trial (ALLHAT), but it is unknown whether this adverse result was due to alpha1-AR inhibition or a nonspecific drug effect. We studied cardiac pressure overload in mice with double KO of the 2 main alpha1-AR subtypes in the heart, alpha 1A (Adra1a) and alpha 1B (Adra1b). At 2 weeks after transverse aortic constriction (TAC), KO mouse survival was only 60% of WT, and surviving KO mice had lower ejection fractions and larger end-diastolic volumes than WT mice. Mechanistically, final heart weight and myocyte cross-sectional area were the same after TAC in KO and WT mice. However, KO hearts after TAC had increased interstitial fibrosis, increased apoptosis, and failed induction of the fetal hypertrophic genes. Before TAC, isolated KO myocytes were more susceptible to apoptosis after oxidative and beta-AR stimulation, and beta-ARs were desensitized. Thus, alpha1-AR deletion worsens dilated cardiomyopathy after pressure overload, by multiple mechanisms, indicating that alpha1-signaling is required for cardiac adaptation. These results suggest that the adverse cardiac effects of alpha1-antagonists in clinical trials are due to loss of alpha1-signaling in myocytes, emphasizing concern about clinical use of alpha1-antagonists, and point to a revised perspective on sympathetic activation in heart failure.
Project description: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.
Project description:RATIONALE:The role of interleukin (IL)-6 in the pathogenesis of cardiac myocyte hypertrophy remains controversial. OBJECTIVE:To conclusively determine whether IL-6 signaling is essential for the development of pressure overload-induced left ventricular (LV) hypertrophy and to elucidate the underlying molecular pathways. METHODS AND RESULTS:Wild-type and IL-6 knockout (IL-6(-/-)) mice underwent sham surgery or transverse aortic constriction (TAC) to induce pressure overload. Serial echocardiograms and terminal hemodynamic studies revealed attenuated LV hypertrophy and superior preservation of LV function in IL-6(-/-) mice after TAC. The extents of LV remodeling, fibrosis, and apoptosis were reduced in IL-6(-/-) hearts after TAC. Transcriptional and protein assays of myocardial tissue identified Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) and signal transducer and activator of transcription 3 (STAT3) activation as important underlying mechanisms during cardiac hypertrophy induced by TAC. The involvement of these pathways in myocyte hypertrophy was verified in isolated cardiac myocytes from wild-type and IL-6(-/-) mice exposed to prohypertrophy agents. Furthermore, overexpression of CaMKII in H9c2 cells increased STAT3 phosphorylation, and exposure of H9c2 cells to IL-6 resulted in STAT3 activation that was attenuated by CaMKII inhibition. Together, these results identify the importance of CaMKII-dependent activation of STAT3 during cardiac myocyte hypertrophy via IL-6 signaling. CONCLUSIONS:Genetic deletion of IL-6 attenuates TAC-induced LV hypertrophy and dysfunction, indicating a critical role played by IL-6 in the pathogenesis of LV hypertrophy in response to pressure overload. CaMKII plays an important role in IL-6-induced STAT3 activation and consequent cardiac myocyte hypertrophy. These findings may have significant therapeutic implications for LV hypertrophy and failure in patients with hypertension.
Project description:RATIONALE:It is unknown whether every ventricular myocyte expresses all 5 of the cardiac adrenergic receptors (ARs), ?1, ?2, ?3, ?1A, and ?1B. The ?1 and ?2 are thought to be the dominant myocyte ARs. OBJECTIVE:Quantify the 5 cardiac ARs in individual ventricular myocytes. METHODS AND RESULTS:We studied ventricular myocytes from wild-type mice, mice with ?1A and ?1B knockin reporters, and ?1 and ?2 knockout mice. Using individual isolated cells, we measured knockin reporters, mRNAs, signaling (phosphorylation of extracellular signal-regulated kinase and phospholamban), and contraction. We found that the ?1 and ?1B were present in all myocytes. The ?1A was present in 60%, with high levels in 20%. The ?2 and ?3 were detected in only ?5% of myocytes, mostly in different cells. In intact heart, 30% of total ?-ARs were ?2 and 20% were ?3, both mainly in nonmyocytes. CONCLUSION:The dominant ventricular myocyte ARs present in all cells are the ?1 and ?1B. The ?2 and ?3 are mostly absent in myocytes but are abundant in nonmyocytes. The ?1A is in just over half of cells, but only 20% have high levels. Four distinct myocyte AR phenotypes are defined: 30% of cells with ?1 and ?1B only; 60% that also have the ?1A; and 5% each that also have the ?2 or ?3. The results raise cautions in experimental design, such as receptor overexpression in myocytes that do not express the AR normally. The data suggest new paradigms in cardiac adrenergic signaling mechanisms.
Project description:Cardiac myocyte hypertrophy is regulated by an extensive intracellular signal transduction network. In vitro evidence suggests that the scaffold protein muscle A-kinase anchoring protein ? (mAKAP?) serves as a nodal organizer of hypertrophic signaling. However, the relevance of mAKAP? signalosomes to pathological remodeling and heart failure in vivo remains unknown.Using conditional, cardiac myocyte-specific gene deletion, we now demonstrate that mAKAP? expression in mice is important for the cardiac hypertrophy induced by pressure overload and catecholamine toxicity. mAKAP? targeting prevented the development of heart failure associated with long-term transverse aortic constriction, conferring a survival benefit. In contrast to 29% of control mice (n=24), only 6% of mAKAP? knockout mice (n=31) died in the 16 weeks of pressure overload (P=0.02). Accordingly, mAKAP? knockout inhibited myocardial apoptosis and the development of interstitial fibrosis, left atrial hypertrophy, and pulmonary edema. This improvement in cardiac status correlated with the attenuated activation of signaling pathways coordinated by the mAKAP? scaffold, including the decreased phosphorylation of protein kinase D1 and histone deacetylase 4 that we reveal to participate in a new mAKAP signaling module. Furthermore, mAKAP? knockout inhibited pathological gene expression directed by myocyte-enhancer factor-2 and nuclear factor of activated T-cell transcription factors that associate with the scaffold.mAKAP? orchestrates signaling that regulates pathological cardiac remodeling in mice. Targeting of the underlying physical architecture of signaling networks, including mAKAP? signalosome formation, may constitute an effective therapeutic strategy for the prevention and treatment of pathological remodeling and heart failure.
Project description:Mammalian sterile 20-like kinase (Mst)1 plays an important role in mediating apoptosis and inhibiting hypertrophy in the heart. Because Hippo, a Drosophila homolog of Mst1, forms a signaling complex with Warts, a serine/threonine kinase, which in turn stimulates cell death and inhibits cell proliferation, mammalian homologs of Warts, termed Lats1 and Lats2, may mediate the function of Mst1. We here show that Lats2, but not Lats1, dose-dependently increased apoptosis in cultured cardiac myocytes. Lats2 also dose-dependently reduced [(3)H]phenylalanine incorporation and cardiac myocyte size, whereas dominant negative Lats2 (DN-Lats2) increased them, suggesting that endogenous Lats2 negatively regulates myocyte growth. DN-Lats2 significantly attenuated induction of apoptosis and inhibition of hypertrophy by Mst1, indicating that Lats2 mediates the function of Mst1 in cardiac myocytes. Cardiac specific overexpression of Lats2 in transgenic mice significantly reduced the size of left and right ventricles, whereas that of DN-Lats2 caused hypertrophy in both ventricles. Overexpression of Lats2 reduced left ventricular systolic and diastolic function without affecting baseline levels of myocardial apoptosis. Expression of endogenous Lats2 was significantly upregulated in response to transverse aortic constriction. Overexpression of DN-Lats2 significantly enhanced cardiac hypertrophy and inhibited cardiac myocyte apoptosis induced by transverse aortic constriction. These results suggest that Lats2 is necessary and sufficient for negatively regulating ventricular mass in the heart. Although Lats2 is required for cardiac myocyte apoptosis in response to pressure overload, it was not sufficient to induce apoptosis at baseline. In conclusion, Lats2 affects both growth and death of cardiac myocytes, but it primarily regulates the size of the heart and acts as an endogenous negative regulator of cardiac hypertrophy.
Project description:BACKGROUND:Recent studies indicate that a1-adrenergic receptors (a1-ARs) are cardioprotective by preventing cardiac myocyte death and augmenting contractility in heart failure. Although G-protein-coupled receptors are assumed to localize to and signal at the plasma membrane, we previously demonstrated that endogenous a1-ARs localize to the nuclei in adult cardiac myocytes. However, the functional consequence of this nuclear localization remains unclear. Here, we attempted to reconcile nuclear localization of a1-ARs with their physiologic function by examining a1-AR-induced contractility in adult cardiac myocytes. METHODS AND RESULTS:By measuring shortening in unloaded, cultured adult cardiac myocytes, we found that the a1A-subtype regulated contractility through phosphorylation of cardiac troponin I (cTnI) at the protein kinase C (PKC) site, threonine 144. Reconstitution of an a1A-subtype nuclear localization mutant in cardiac myocytes lacking a1-ARs failed to rescue nuclear a1A-mediated phosphorylation of cTnI and myocyte contractility. Leptomycin B, the nuclear export inhibitor, also blocked a1A-mediated phosphorylation of cTnI. These data indicate that a1-AR signaling originates in the nucleus. Consistent with these observations, we localized the a1A-subtype to the inner nuclear membrane, identified PKCa, d, and e in the nucleus, and found that a1-ARs activate PKCd in nuclei isolated from adult cardiac myocytes. Finally, we found that a PKCd nuclear localization mutant blunted a1-induced phosphorylation of cTnI. CONCLUSIONS:Together, our data identify a novel, “inside-out” nuclear a1A-subtype/PKCd/cTnI-signaling pathway that regulates contractile function in adult cardiac myocytes. Importantly, these data help resolve the discrepancy between nuclear localization of a1-ARs and a1-AR-mediated physiologic function.
Project description:cAMP and protein kinase A (PKA) activation represents a key signaling mechanism upon beta-adrenergic stimulation under stress. Both beta(1)- and beta(2)-adrenoreceptor (ARs) subtypes induce cAMP accumulation, yet play distinct roles in cardiac contraction and myocyte apoptosis. Differences in controlling cAMP/PKA activities through the assembly of complexes between the receptors and cAMP-specific phosphodiesterases contribute to the distinct biological outcomes. Here, we demonstrate that beta(2)ARs form signaling complexes with a set of PDE4D isoforms expressed in cardiac myocytes. PDE4D9 and PDE4D8 bind to the beta(2)AR at resting conditions; however, agonist stimulation induces dissociation of PDE4D9 from the receptor but recruitment of PDE4D8 to the receptor. Agonist stimulation also induces recruitment of PDE4D5 to the beta(2)AR. Moreover, the receptor-associated PDE4D isoforms play distinct roles in controlling cAMP activities and regulating the PKA phosphorylation of the receptor and myocyte contraction rate responses. Knockdown of PDE4D9 with short hairpin RNA enhances the beta(2)AR-induced cAMP signaling, whereas knockdown of PDE4D8 only slightly prolongs the receptor-induced cAMP signaling in myocytes. Inhibition of PDE4D9 and PDE4D5 enhances the base-line levels of contraction rates, whereas inhibition of PDE4D9 and PDE4D8 enhances the maximal contraction rate increases upon activation of beta(2)AR. Our data underscore the complex regulation of intracellular cAMP by beta(2)AR-associated phosphodiesterase enzymes to enforce the specificity of the receptor signaling for physiological responses.
Project description:BACKGROUND:Cardiac hypertrophy and heart failure are characterized by increased late sodium current and abnormal Ca2+ handling. Ranolazine, a selective inhibitor of the late sodium current, can reduce sodium accumulation and Ca 2+ overload. In this study, we investigated the effects of ranolazine on pressure overload-induced cardiac hypertrophy and heart failure in mice. METHODS AND RESULTS:Inhibition of late sodium current with the selective inhibitor ranolazine suppressed cardiac hypertrophy and fibrosis and improved heart function assessed by echocardiography, hemodynamics, and histological analysis in mice exposed to chronic pressure overload induced by transverse aortic constriction (TAC). Ca2+ imaging of ventricular myocytes from TAC mice revealed both abnormal SR Ca 2+ release and increased SR Ca 2+ leak. Ranolazine restored aberrant SR Ca 2+ handling induced by pressure overload. Ranolazine also suppressed Na + overload induced in the failing heart, and restored Na + -induced Ca 2+ overload in an sodium-calcium exchanger (NCX)-dependent manner. Ranolazine suppressed the Ca 2+ -dependent calmodulin (CaM)/CaMKII/myocyte enhancer factor-2 (MEF2) and CaM/CaMKII/calcineurin/nuclear factor of activated T-cells (NFAT) hypertrophy signaling pathways triggered by pressure overload. Pressure overload also prolonged endoplasmic reticulum (ER) stress leading to ER-initiated apoptosis, while inhibition of late sodium current or NCX relieved ER stress and ER-initiated cardiomyocyte apoptosis. CONCLUSIONS:Our study demonstrates that inhibition of late sodium current with ranolazine improves pressure overload-induced cardiac hypertrophy and systolic and diastolic function by restoring Na+ and Ca 2+ handling, inhibiting the downstream hypertrophic pathways and ER stress. Inhibition of late sodium current may provide a new treatment strategy for cardiac hypertrophy and heart failure.