Arthur M. Feldman

Paroxetine-mediated GRK2 inhibition reverses cardiac dysfunction and remodeling after myocardial infarction

GRK2 inhibition with paroxetine improves cardiac function independent of its central nervous system effects. Taking antidepressants to heart Drug repurposing—extending currently Food and Drug Administration (FDA)–approved drugs to treat additional diseases—has both economic and safety advantages over new drug development. The selective serotonin reuptake inhibitor (SSRI) paroxetine, which is used as an antidepressant, has been shown to selectively inhibit G protein (heterotrimeric guanine nucleotide–binding protein)–coupled receptor kinase 2 (GRK2), which is thought to contribute to heart failure progression. Now Schumacher et al. report that paroxetine can block or even reverse heart damage after myocardial infarction in a mouse model. These affects are separate from its SSRI functions and are further enhanced in the presence of current standard-of-care β-blockers. If these data hold true in humans, paroxetine therapy could be an additional or even additive strategy for treating heart failure. Heart failure (HF) is a disease of epidemic proportion and is associated with exceedingly high health care costs. G protein (heterotrimeric guanine nucleotide–binding protein)–coupled receptor (GPCR) kinase 2 (GRK2), which is up-regulated in the failing human heart, appears to play a critical role in HF progression in part because enhanced GRK2 activity promotes dysfunctional adrenergic signaling and myocyte death. Recently, we found that the selective serotonin reuptake inhibitor (SSRI) paroxetine could inhibit GRK2 with selectivity over other GRKs. Wild-type mice were treated for 4 weeks with paroxetine starting at 2 weeks after myocardial infarction (MI). These mice were compared with mice treated with fluoxetine, which does not inhibit GRK2, to control for the SSRI effects of paroxetine. All mice exhibited similar left ventricular (LV) dysfunction before treatment; however, although the control and fluoxetine groups had continued degradation of function, the paroxetine group had considerably improved LV function and structure, and several hallmarks of HF were either inhibited or reversed. Use of genetically engineered mice indicated that paroxetine was working through GRK2 inhibition. The beneficial effects of paroxetine were markedly greater than those of β-blocker therapy, a current standard of care in human HF. These data demonstrate that paroxetine-mediated inhibition of GRK2 improves cardiac function after MI and represents a potential repurposing of this drug, as well as a starting point for innovative small-molecule GRK2 inhibitor development.

Gi-Biased β2AR Signaling Links GRK2 Upregulation to Heart Failure

Rationale: Phosphorylation of &bgr;2-adrenergic receptor (&bgr;2AR) by a family of serine/threonine kinases known as G protein–coupled receptor kinase (GRK) and protein kinase A (PKA) is a critical determinant of cardiac function. Upregulation of G protein–coupled receptor kinase 2 (GRK2) is a well-established causal factor of heart failure, but the underlying mechanism is poorly understood. Objective: We sought to determine the relative contribution of PKA- and GRK-mediated phosphorylation of &bgr;2AR to the receptor coupling to Gi signaling that attenuates cardiac reserve and contributes to the pathogenesis of heart failure in response to pressure overload. Methods and Results: Overexpression of GRK2 led to a Gi-dependent decrease of contractile response to &bgr;AR stimulation in cultured mouse cardiomyocytes and in vivo. Importantly, cardiac-specific transgenic overexpression of a mutant &bgr;2AR lacking PKA phosphorylation sites (PKA-TG) but not the wild-type &bgr;2AR (WT-TG) or a mutant &bgr;2AR lacking GRK sites (GRK-TG) led to exaggerated cardiac response to pressure overload, as manifested by markedly exacerbated cardiac maladaptive remodeling and failure and early mortality. Furthermore, inhibition of Gi signaling with pertussis toxin restores cardiac function in heart failure associated with increased &bgr;2AR to Gi coupling induced by removing PKA phosphorylation of the receptor and in GRK2 transgenic mice, indicating that enhanced phosphorylation of &bgr;2AR by GRK and resultant increase in Gi-biased &bgr;2AR signaling play an important role in the development of heart failure. Conclusions: Our data show that enhanced &bgr;2AR phosphorylation by GRK, in addition to PKA, leads the receptor to Gi-biased signaling, which, in turn, contributes to the pathogenesis of heart failure, marking Gi-biased &bgr;2AR signaling as a primary event linking upregulation of GRK to cardiac maladaptive remodeling, failure and cardiodepression.

BAG3: a new player in the heart failure paradigm

BAG3 is a cellular protein that is expressed predominantly in skeletal and cardiac muscle but can also be found in the brain and in the peripheral nervous system. BAG3 functions in the cell include: serving as a co-chaperone with members of the heat-shock protein family of proteins to facilitate the removal of misfolded and degraded proteins, inhibiting apoptosis by interacting with Bcl2 and maintaining the structural integrity of the Z-disk in muscle by binding with CapZ. The importance of BAG3 in the homeostasis of myocytes and its role in the development of heart failure was evidenced by the finding that single allelic mutations in BAG3 were associated with familial dilated cardiomyopathy. Furthermore, significant decreases in the level of BAG3 have been found in end-stage failing human heart and in animal models of heart failure including mice with heart failure secondary to trans-aortic banding and in pigs after myocardial infarction. Thus, it becomes relevant to understand the cellular biology and molecular regulation of BAG3 expression in order to design new therapies for the treatment of patients with both hereditary and non-hereditary forms of dilated cardiomyopathy.

Decreased Levels of BAG3 in a Family With a Rare Variant and in Idiopathic Dilated Cardiomyopathy

The most common cause of dilated cardiomyopathy and heart failure (HF) is ischemic heart disease; however, in a third of all patients the cause remains undefined and patients are diagnosed as having idiopathic dilated cardiomyopathy (IDC). Recent studies suggest that many patients with IDC have a family history of HF and rare genetic variants in over 35 genes have been shown to be causative of disease. We employed whole‐exome sequencing to identify the causative variant in a large family with autosomal dominant transmission of dilated cardiomyopathy. Sequencing and subsequent informatics revealed a novel 10‐nucleotide deletion in the BCL2‐associated athanogene 3 (BAG3) gene (Ch10:del 121436332_12143641: del. 1266_1275 [NM 004281]) that segregated with all affected individuals. The deletion predicted a shift in the reading frame with the resultant deletion of 135 amino acids from the C‐terminal end of the protein. Consistent with genetic variants in genes encoding other sarcomeric proteins there was a considerable amount of genetic heterogeneity in the affected family members. Interestingly, we also found that the levels of BAG3 protein were significantly reduced in the hearts from unrelated patients with end‐stage HF undergoing cardiac transplantation when compared with non‐failing controls. Diminished levels of BAG3 protein may be associated with both familial and non‐familial forms of dilated cardiomyopathy. J. Cell. Physiol. 229: 1697–1702, 2014.

The second member of transient receptor potential-melastatin channel family protects hearts from ischemia-reperfusion injury.

The second member of the transient receptor potential-melastatin channel family (TRPM2) is expressed in the heart and vasculature. TRPM2 channels were expressed in the sarcolemma and transverse tubules of adult left ventricular (LV) myocytes. Cardiac TRPM2 channels were functional since activation with H2O2 resulted in Ca(2+) influx that was dependent on extracellular Ca(2+), was significantly higher in wild-type (WT) myocytes compared with TRPM2 knockout (KO) myocytes, and inhibited by clotrimazole in WT myocytes. At rest, there were no differences in LV mass, heart rate, fractional shortening, and +dP/dt between WT and KO hearts. At 2-3 days after ischemia-reperfusion (I/R), despite similar areas at risk and infarct sizes, KO hearts had lower fractional shortening and +dP/dt compared with WT hearts. Compared with WT I/R myocytes, expression of the Na(+)/Ca(2+) exchanger (NCX1) and NCX1 current were increased, expression of the α1-subunit of Na(+)-K(+)-ATPase and Na(+) pump current were decreased, and action potential duration was prolonged in KO I/R myocytes. Post-I/R, intracellular Ca(2+) concentration transients and contraction amplitudes were equally depressed in WT and KO myocytes. After 2 h of hypoxia followed by 30 min of reoxygenation, levels of ROS were significantly higher in KO compared with WT LV myocytes. Compared with WT I/R hearts, oxygen radical scavenging enzymes (SODs) and their upstream regulators (forkhead box transcription factors and hypoxia-inducible factor) were lower, whereas NADPH oxidase was higher, in KO I/R hearts. We conclude that TRPM2 channels protected hearts from I/R injury by decreasing generation and enhancing scavenging of ROS, thereby reducing I/R-induced oxidative stress.

Valsartan/Sacubitril for Heart Failure: Reconciling Disparities Between Preclinical and Clinical Investigations

Valsartan/sacubitril (Entresto, Novartis) is a combination of the neprilysin inhibitor sacubitril and the angiotensin receptor antagonist valsartan. In July 2015, the US Food and Drug Administration (FDA) approved valsartan/sacubitril through the fast-track pathway for the treatment of patients with New York Heart Association class II through IV heart failure symptoms and a reduced ejection fraction. The approval was based on the results of a single phase 3 clinical trial (PARADIGM-HF)1 that included 8400 patients. In this trial, valsartan/sacubitril was associated with a 20% (hazard ratio, 0.80) decrease in the primary end point of death from cardiovascular cause or first hospitalization for heart failure (from 26.5% to 21.8%), when compared with the angiotensin-converting inhibitor enalapril, and a 16% (hazard ratio, 0.84) reduction in all-cause mortality (from 19.8% to 17.0%). However, recent translational science studies involving the central nervous system and the eye suggest that other effects of valsartan/sacubitril might influence its use in some patients.

G-protein beta-3 subunit genotype predicts enhanced benefit of fixed-dose isosorbide dinitrate and hydralazine: Results of A-HeFT

OBJECTIVESnThe purpose of this study was to evaluate the influence of the guanine nucleotide-binding proteins (G-proteins), beta-3 subunit (GNB3) genotype on the effectiveness of a fixed-dose combination of isosorbide dinitrate and hydralazine (FDC I/H) in A-HeFT (African American Heart Failure Trial).nnnBACKGROUNDnGNB3 plays a role in alpha2-adrenergic signaling. A polymorphism (C825T) exists, and the T allele is linked to enhanced alpha-adrenergic tone and is more prevalent in African Americans.nnnMETHODSnA total of 350 subjects enrolled in the genetic substudy (GRAHF [Genetic Risk Assessment of Heart Failure in African Americans]) were genotyped for the C825T polymorphism. The impact of FDC I/H on a composite score (CS) that incorporated death, hospital stay for heart failure, and change in quality of life (QoL) and on event-free survival were assessed in GNB3 genotype subsets.nnnRESULTSnThe GRAHF cohort was 60% male, 25% ischemic, 97% New York Heart Association functional class III, age 57 ± 13 years, with a mean qualifying left ventricular ejection fraction of 0.24 ± 0.06. For GNB3 genotype, 184 subjects were TT (53%), 137 (39%) CT, and 29 (8%) were CC. In GNB3 TT subjects, FDC I/H improved the CS (FDC I/H = 0.50 ± 1.6; placebo = -0.11 ± 1.8, p = 0.02), QoL (FDC I/H = 0.69 ± 1.4; placebo = 0.24 ± 1.5, p = 0.04), and event-free survival (hazard ratio: 0.51, p = 0.047), but not in subjects with the C allele (for CS, FDC I/H = -0.05 ± 1.7; placebo = -0.09 ± 1.7, p = 0.87; for QoL, FDC I/H = 0.28 ± 1.5; placebo = 0.14 ± 1.5, p = 0.56; and for event-free survival, p = 0.35).nnnCONCLUSIONSnThe GNB3 TT genotype was associated with greater therapeutic effect of FDC I/H in A-HeFT. The role of the GNB3 genotype for targeting therapy with FDC I/H deserves further study.

Arginine vasopressin enhances cell survival via a G protein-coupled receptor kinase 2/β-arrestin1/extracellular-regulated kinase 1/2-dependent pathway in H9c2 cells.

Circulating levels of arginine vasopressin (AVP) are elevated during hypovolemia and during cardiac stress. AVP activates arginine vasopressin type 1A (V1A)/Gαq–coupled receptors in the heart and vasculature and V2/Gαs–coupled receptors in the kidney. However, little is known regarding the signaling pathways that influence the effects of V1A receptor (V1AR) activation during cellular injury. Using hypoxia-reoxygenation (H/R) as a cell injury model, we evaluated cell survival and caspase 3/7 activity in H9c2 myoblasts after treatment with AVP. Pretreatment of H9c2 cells with AVP significantly reduced H/R-induced cell death and caspase 3/7 activity, effects that were blocked via both selective V1AR inhibition and mitogen-activated protein kinase (MEK1/2) inhibition. AVP increased extracellular-regulated kinase 1/2 (ERK1/2) phosphorylation in a concentration-dependent manner that was sensitive to MEK1/2 inhibition and V1AR inhibition, but not V1BR or V2R inhibition. Discrete elements of the V1A/Gαq-protein kinase C (PKC) and V1A/G protein–coupled receptor kinase (GRK)/β-arrestin signaling cascades were inhibited to dissect the pathways responsible for the protective effects of V1AR signaling: Gαq (overexpression of Gq-I-ires-green fluorescent protein), PKC (administration of Ro 31-82425; 2-[8-(aminomethyl)-6,7,8,9-tetrahydropyrido[1,2-a]indol-3-yl]-3-(1-methyl-1H-indol-3-yl)maleimide, HCl, bisindolylmaleimide X, HCl), GRK2 [C-terminal GRK2 peptide overexpression and small interfering RNA (siRNA) knockdown], GRK5 (siRNA knockdown), and β-arrestin1 (siRNA knockdown). These studies demonstrated that both Gαq/PKC- and GRK2/β-arrestin1–dependent V1AR signaling were capable of inducing ERK1/2 phosphorylation in response to AVP stimulation. However, AVP-mediated protection against H/R was elicited only via GRK2- and β-arrestin1–dependent signaling. These results suggest that activation of the V1AR in H9c2 cells mediates protective signaling via a GRK2/β−arrestin1/ERK1/2–dependent mechanism that leads to decreased caspase 3/7 activity and enhanced survival under conditions of ischemic stress.

β-Adrenergic Receptor-Mediated Cardiac Contractility is Inhibited via Vasopressin Type 1A-Receptor-Dependent Signaling

Background— Enhanced arginine vasopressin levels are associated with increased mortality during end-stage human heart failure, and cardiac arginine vasopressin type 1A receptor (V1AR) expression becomes increased. Additionally, mice with cardiac-restricted V1AR overexpression develop cardiomyopathy and decreased &bgr;-adrenergic receptor (&bgr;AR) responsiveness. This led us to hypothesize that V1AR signaling regulates &bgr;AR responsiveness and in doing so contributes to development of heart failure. Methods and Results— Transaortic constriction resulted in decreased cardiac function and &bgr;AR density and increased cardiac V1AR expression, effects reversed by a V1AR-selective antagonist. Molecularly, V1AR stimulation led to decreased &bgr;AR ligand affinity, as well as &bgr;AR-induced Ca2+ mobilization and cAMP generation in isolated adult cardiomyocytes, effects recapitulated via ex vivo Langendorff analysis. V1AR-mediated regulation of &bgr;AR responsiveness was demonstrated to occur in a previously unrecognized Gq protein–independent/G protein receptor kinase–dependent manner. Conclusions— This newly discovered relationship between cardiac V1AR and &bgr;AR may be informative for the treatment of patients with acute decompensated heart failure and elevated arginine vasopressin.

Ca2+ entry via Trpm2 is essential for cardiac myocyte bioenergetics maintenance

Ubiquitously expressed Trpm2 channel limits oxidative stress and preserves mitochondrial function. We first demonstrated that intracellular Ca(2+) concentration increase after Trpm2 activation was due to direct Ca(2+) influx and not indirectly via reverse Na(+)/Ca(2+) exchange. To elucidate whether Ca(2+) entry via Trpm2 is required to maintain cellular bioenergetics, we injected adenovirus expressing green fluorescent protein (GFP), wild-type (WT) Trpm2, and loss-of-function (E960D) Trpm2 mutant into left ventricles of global Trpm2 knockout (gKO) or WT hearts. Five days post-injection, gKO-GFP heart slices had higher reactive oxygen species (ROS) levels but lower oxygen consumption rate (OCR) than WT-GFP heart slices. Trpm2 but not E960D decreased ROS and restored OCR in gKO hearts back to normal levels. In gKO myocytes expressing Trpm2 or its mutants, Trpm2 but not E960D reduced the elevated mitochondrial superoxide (O2(.-)) levels in gKO myocytes. After hypoxia-reoxygenation (H/R), Trpm2 but not E906D or P1018L (inactivates Trpm2 current) lowered O2(.-) levels in gKO myocytes and only in the presence of extracellular Ca(2+), indicating sustained Ca(2+) entry is necessary for Trpm2-mediated preservation of mitochondrial function. After ischemic-reperfusion (I/R), cardiac-specific Trpm2 KO hearts exhibited lower maximal first time derivative of LV pressure rise (+dP/dt) than WT hearts in vivo. After doxorubicin treatment, Trpm2 KO mice had worse survival and lower +dP/dt. We conclude 1) cardiac Trpm2-mediated Ca(2+) influx is necessary to maintain mitochondrial function and protect against H/R injury; 2) Ca(2+) influx via cardiac Trpm2 confers protection against H/R and I/R injury by reducing mitochondrial oxidants; and 3) Trpm2 confers protection in doxorubicin cardiomyopathy.