A cardiac amino-terminal GRK2 peptide inhibits insulin resistance yet enhances maladaptive cardiovascular and brown adipose tissue remodeling in females during diet-induced obesity

Obesity and metabolic disorders are increasing in epidemic proportions, leading to poor outcomes including heart failure. With a growing recognition of the effect of adipose tissue dysfunction on heart disease, it is less well understood how the heart can influence systemic metabolic homeostasis. Even less well understood is sex differences in cardiometabolic responses. Previously, our lab investigated the role of the amino-terminus of GRK2 in cardiometabolic remodeling using transgenic mice with cardiac restricted expression of a short peptide, βARKnt. Male mice preserved insulin sensitivity, enhanced metabolic flexibility and adipose tissue health, elicited cardioprotection, and improved cardiac metabolic signaling. To examine the effect of cardiac βARKnt expression on cardiac and metabolic function in females in response to diet-induced obesity, we subjected female mice to high fat diet (HFD) to trigger cardiac and metabolic adaptive changes. Despite equivalent weight gain, βARKnt mice exhibited improved glucose tolerance and insulin sensitivity. However, βARKnt mice displayed a progressive reduction in energy expenditure during cold challenge after acute and chronic HFD stress. They also demonstrated reduced cardiac function and increased markers of maladaptive remodeling and tissue injury, and decreased or aberrant metabolic signaling. βARKnt mice exhibited reduced lipid deposition in the brown adipose tissue (BAT), but delayed or decreased markers of BAT activation and function suggested multiple mechanisms contributed to the decreased thermogenic capacity. These data suggest a non-canonical cardiac regulation of BAT lipolysis and function that highlights the need for studies elucidating the mechanisms of sex-specific responses to metabolic dysfunction.

Decreased FAM13B Expression Increases Atrial Fibrillation Susceptibility by Regulating Sodium Current and Calcium Handling

A specific genetic variant associated with atrial fibrillation risk, rs17171731, was identified as a regulatory variant responsible for controlling FAM13B expression. The atrial fibrillation risk allele decreases FAM13B expression, whose knockdown alters the expression of many genes in stem cell-derived cardiomyocytes, including SCN2B, and led to pro-arrhythmogenic changes in the late sodium current and Ca2+ cycling. Fam13b knockout mice had increased P-wave and QT interval duration and were more susceptible to pacing-induced arrhythmias vs control mice. FAM13B expression, its regulation, and downstream effects are potential targets for investigation of patient-specific therapeutics.

Pepducin ICL1-9-Mediated β2-Adrenergic Receptor-Dependent Cardiomyocyte Contractility Occurs in a Gi Protein/ROCK/PKD-Sensitive Manner

PURPOSE

β-Adrenergic receptors (βAR) are essential targets for the treatment of heart failure (HF); however, chronic use of βAR agonists as positive inotropes to increase contractility in a Gs protein-dependent manner is associated with increased mortality. Alternatively, we previously reported that allosteric modulation of β2AR with the pepducin intracellular loop (ICL)1-9 increased cardiomyocyte contractility in a β-arrestin (βarr)-dependent manner, and subsequently showed that ICL1-9 activates the Ras homolog family member A (RhoA). Here, we aimed to elucidate both the proximal and downstream signaling mediators involved in the promotion of cardiomyocyte contractility in response to ICL1-9.

METHODS

We measured adult mouse cardiomyocyte contractility in response to ICL1-9 or isoproterenol (ISO, as a positive control) alone or in the presence of inhibitors of various potential components of βarr- or RhoA-dependent signaling. We also assessed the contractile effects of ICL1-9 on cardiomyocytes lacking G protein-coupled receptor (GPCR) kinase 2 (GRK2) or 5 (GRK5).

RESULTS

Consistent with RhoA activation by ICL1-9, both Rho-associated protein kinase (ROCK) and protein kinase D (PKD) inhibition were able to attenuate ICL1-9-mediated contractility, as was inhibition of myosin light chain kinase (MLCK). While neither GRK2 nor GRK5 deletion impacted ICL1-9-mediated contractility, pertussis toxin attenuated the response, suggesting that ICL1-9 promotes downstream RhoA-dependent signaling in a Gi protein-dependent manner.

CONCLUSION

Altogether, our study highlights a novel signaling modality that may offer a new approach to the promotion, or preservation, of cardiac contractility during HF via the allosteric regulation of β2AR to promote Gi protein/βarr-dependent activation of RhoA/ROCK/PKD signaling.

A Cardiac Amino-Terminal GRK2 Peptide Inhibits Maladaptive Adipocyte Hypertrophy and Insulin Resistance During Diet-Induced Obesity

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Heart disease remains the leading cause of death, in part due to increasing diabetes and obesity, though the exact mechanisms linking these disorders are not fully understood.

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In a diet-induced obesity model, we found that cardiac expression of an amino-terminal peptide of GRK2, βARKnt, preserves systemic glucose tolerance and insulin sensitivity despite normal weight gain.

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βARKnt enhanced metabolic flexibility, increased energy expenditure, protected against maladaptive visceral adipocyte hypertrophy, and induced visceral fat browning.

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βARKnt further elicited cardioprotection and increased insulin-mediated AS160 signaling during metabolic stress.

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These data point to a noncanonical cardiac regulation of systemic metabolic homeostasis that may lead to new treatment modalities for metabolic syndrome.

Heart disease remains the leading cause of death, and mortality rates positively correlate with the presence of obesity and diabetes. Despite the correlation between cardiac and metabolic dysregulation, the mechanistic pathway(s) of interorgan crosstalk still remain undefined. This study reveals that cardiac-restricted expression of an amino-terminal peptide of GRK2 (βARKnt) preserves systemic and cardiac insulin responsiveness, and protects against adipocyte maladaptive hypertrophy in a diet-induced obesity model. These data suggest a cardiac-driven mechanism to ameliorate maladaptive cardiac remodeling and improve systemic metabolic homeostasis that may lead to new treatment modalities for cardioprotection in obesity and obesity-related metabolic syndromes.

Specific and behaviorally consequential astrocyte Gq GPCR signaling attenuation in vivo with iβARK

Astrocytes respond to neurotransmitters and neuromodulators using G-protein-coupled receptors (GPCRs) to mediate physiological responses. Despite their importance, there has been no method to genetically, specifically, and effectively attenuate astrocyte Gq GPCR pathways to explore consequences of this prevalent signaling mechanism in vivo. We report a 122-residue inhibitory peptide from β-adrenergic receptor kinase 1 (iβARK; and inactive D110A control) to attenuate astrocyte Gq GPCR signaling. iβARK significantly attenuated Gq GPCR Ca2+ signaling in brain slices and, in vivo, altered behavioral responses, spared other GPCR responses, and did not alter astrocyte spontaneous Ca2+ signals, morphology, electrophysiological properties, or gene expression in the striatum. Furthermore, brain-wide attenuation of astrocyte Gq GPCR signaling with iβARK using PHP.eB adeno-associated viruses (AAVs), when combined with c-Fos mapping, suggested nuclei-specific contributions to behavioral adaptation and spatial memory. iβARK extends the toolkit needed to explore functions of astrocyte Gq GPCR signaling within neural circuits in vivo.

Characterization of βARKct engineered cellular extracellular vesicles and model specific cardioprotection

Recent data supporting any benefit of stem cell therapy for ischemic heart disease have suggested paracrine-based mechanisms via extracellular vesicles (EVs) including exosomes. We have previously engineered cardiac-derived progenitor cells (CDCs) to express a peptide inhibitor, βARKct, of G protein-coupled receptor kinase 2, leading to improvements in cell proliferation, survival, and metabolism. In this study, we tested whether βARKct-CDC EVs would be efficacious when applied to stressed myocytes in vitro and in vivo. When isolated EVs from βARKct-CDCs and control GFP-CDCs were added to cardiomyocytes in culture, they both protected against hypoxia-induced apoptosis. We tested whether these EVs could protect the mouse heart in vivo, following exposure either to myocardial infarction (MI) or acute catecholamine toxicity. Both types of EVs significantly protected against ischemic injury and improved cardiac function after MI compared with mice treated with EVs from mouse embryonic fibroblasts; however, βARKct EVs treated mice did display some unique beneficial properties including significantly altered pro- and anti-inflammatory cytokines. Importantly, in a catecholamine toxicity model of heart failure (HF), myocardial injections of βARKct-containing EVs were superior at preventing HF compared with control EVs, and this catecholamine toxicity protection was recapitulated in vitro. Therefore, introduction of the βARKct into cellular EVs can have improved reparative properties in the heart especially against catecholamine damage, which is significant as sympathetic nervous system activity is increased in HF.NEW & NOTEWORTHY βARKct, the peptide inhibitor of GRK2, improves survival and metabolic functions of cardiac-derived progenitor cells. As any benefit of stem cells in the ischemic and injured heart suggests paracrine mechanisms via secreted EVs, we investigated whether CDC-βARKct engineered EVs would show any benefit over control CDC-EVs. Compared with control EVs, βARKct-containing EVs displayed some unique beneficial properties that may be due to altered pro- and anti-inflammatory cytokines within the vesicles.

A peptide of the amino-terminus of GRK2 induces hypertrophy and yet elicits cardioprotection after pressure overload

G protein-coupled receptor (GPCR) kinase 2 (GRK2) expression and activity are elevated early on in response to several forms of cardiovascular stress and are a hallmark of heart failure. Interestingly, though, in addition to its well-characterized role in regulating GPCRs, mounting evidence suggests a GRK2 "interactome" that underlies a great diversity in its functional roles. Several such GRK2 interacting partners are important for adaptive and maladaptive myocyte growth; therefore, an understanding of domain-specific interactions with signaling and regulatory molecules could lead to novel targets for heart failure therapy. Herein, we subjected transgenic mice with cardiac restricted expression of a short, amino terminal fragment of GRK2 (βARKnt) to pressure overload and found that unlike their littermate controls or previous GRK2 fragments, they exhibited an increased left ventricular wall thickness and mass prior to cardiac stress that underwent proportional hypertrophic growth to controls after acute pressure overload. Importantly, despite this enlarged heart, βARKnt mice did not undergo the expected transition to heart failure observed in controls. Further, βARKnt expression limited adverse left ventricular remodeling and increased cell survival signaling. Proteomic analysis to identify βARKnt binding partners that may underlie the improved cardiovascular phenotype uncovered a selective functional interaction of both endogenous GRK2 and βARKnt with AKT substrate of 160 kDa (AS160). AS160 has emerged as a key downstream regulator of insulin signaling, integrating physiological and metabolic cues to couple energy demand to membrane recruitment of Glut4. Our preliminary data indicate that in βARKnt mice, cardiomyocyte insulin signaling is improved during stress, with a coordinate increase in spare respiratory activity and ATP production without metabolite switching. Surprisingly, these studies also revealed a significant decrease in gonadal fat weight, equivalent to human abdominal fat, in male βARKnt mice at baseline and following cardiac stress. These data suggest that the enhanced AS160-mediated signaling in the βARKnt mice may ameliorate pathological cardiac remodeling through direct modulation of insulin signaling within cardiomyocytes, and translate these to beneficial effects on systemic metabolism.

Abstract 381: Mcur1 is a Potential Target to Modulate Cardiac Contractility and Alleviate Cardiac Function During Heart Failure

Cardiac contractility is regulated by the intracellular Ca 2+ concentration fluxes which are actively regulated by multiple channels and transporters. Ca 2+ uptake into the mitochondrial matrix is precisely controlled by the highly Ca 2+ selective channel, Mitochondrial Calcium Uniporter (MCU). Earlier studies on the cardiac-specific acute MCU knockout and a transgenic dominant-negative MCU mice have demonstrated that mitochondrial Ca 2+ ( m Ca 2+ ) signaling is necessary for cardiac ‘‘fight-or-flight’’ contractile response, however, the role of m Ca 2+ buffering to shape global cytosolic Ca 2+ levels and affect E-C coupling, particularly the Ca 2+ transient, on a beat-to-beat basis still remains to be solved. Our earlier studies have demonstrated that loss of MCU Regulator 1 (MCUR1) in cardiomyocytes results in the impaired m Ca 2+ uptake. We have now employed the cardiac-specific MCUR1 knockout mouse to dissect the precise role of MCU in regulating cytosolic Ca 2+ transients associated with excitation-contraction (E-C) coupling and cardiac function. Results from our studies including the in vivo analyses of cardiac physiology during normal and pressure-overloaded mouse models and in vitro experiments including single-cell cardiac contractility, calcium transients, and electrophysiology measurements demonstrate that MCUR1/MCU regulated m Ca 2+ buffering in cardiomyocytes, although insignificant under basal condition, becomes critical in stress induced conditions and actively participates in regulating the c Ca 2+ transients. Also, the ablation of MCUR1 in cardiomyocytes during stress conditions prevents m Ca 2+ overload and subsequent mROS overproduction. Our data indicate that MCUR1 ablation offers protection against pressure-overload cardiac hypertrophy. In summary, our results provide critical insights into the mechanisms by which the MCU channel contributes in regulating the contractile function of the cardiomyocytes and the role of m Ca 2+ in the development and progression of heart failure.

Circular RNA CircFndc3b modulates cardiac repair after myocardial infarction via FUS/VEGF-A axis

Circular RNAs are generated from many protein-coding genes, but their role in cardiovascular health and disease states remains unknown. Here we report identification of circRNA transcripts that are differentially expressed in post myocardial infarction (MI) mouse hearts including circFndc3b which is significantly down-regulated in the post-MI hearts. Notably, the human circFndc3b ortholog is also significantly down-regulated in cardiac tissues of ischemic cardiomyopathy patients. Overexpression of circFndc3b in cardiac endothelial cells increases vascular endothelial growth factor-A expression and enhances their angiogenic activity and reduces cardiomyocytes and endothelial cell apoptosis. Adeno-associated virus 9 -mediated cardiac overexpression of circFndc3b in post-MI hearts reduces cardiomyocyte apoptosis, enhances neovascularization and improves left ventricular functions. Mechanistically, circFndc3b interacts with the RNA binding protein Fused in Sarcoma to regulate VEGF expression and signaling. These findings highlight a physiological role for circRNAs in cardiac repair and indicate that modulation of circFndc3b expression may represent a potential strategy to promote cardiac function and remodeling after MI.

Circular RNAs (circRNAs) are non-coding RNAs generated from pre-mRNAs of coding genes by the splicing machinery whose function in the heart is poorly understood. Here the authors show that AAV-mediated delivery of the circRNA circFndc3b prevents cardiomyocyte apoptosis, enhances angiogenesis, and attenuates LV dysfunction post-MI in mice by regulating FUS-VEGF-A signalling.

Tumor Necrosis Factor-α in Heart Failure: an Updated Review

PURPOSE OF THE REVIEW

Proinflammatory cytokines are consistently elevated in congestive heart failure. In the current review, we provide an overview on the current understanding of how tumor necrosis factor-α (TNFα), a key proinflammatory cytokine, potentiates heart failure by overwhelming the anti-inflammatory responses disrupting the homeostasis.

RECENT FINDINGS

Studies have shown co-relationship between severity of heart failure and levels of the proinflammatory cytokine TNFα and one of its secondary mediators interleukin-6 (IL-6), suggesting their potential as biomarkers. Recent efforts have focused on understanding the mechanisms of how proinflammatory cytokines contribute towards cardiac dysfunction and failure. In addition, how unchecked proinflammatory cytokines and their cross-talk with sympathetic system overrides the anti-inflammatory response underlying failure. The review offers insights on how TNFα and IL-6 contribute to cardiac dysfunction and failure. Furthermore, this provides a forum to begin the discussion on the cross-talk between sympathetic drive and proinflammatory cytokines and its determinant role in deleterious outcomes.

Designer Approaches for G Protein-Coupled Receptor Modulation for Cardiovascular Disease

The new horizon for cardiac therapy may lie beneath the surface, with the downstream mediators of G protein–coupled receptor (GPCR) activity. Targeted approaches have shown that receptor activation may be biased toward signaling through G proteins or through GPCR kinases (GRKs) and β-arrestins, with divergent functional outcomes. In addition to these canonical roles, numerous noncanonical activities of GRKs and β-arrestins have been demonstrated to modulate GPCR signaling at all levels of receptor activation and regulation. Further, research continues to identify novel GRK/effector and β-arrestin/effector complexes with distinct impacts on cardiac function in the normal heart and the diseased heart. Coupled with the identification of once orphan receptors and endogenous ligands with beneficial cardiovascular effects, this expands the repertoire of GPCR targets. Together, this research highlights the potential for focused therapeutic activation of beneficial pathways, with simultaneous exclusion or inhibition of detrimental signaling, and represents a new wave of therapeutic development.

Abstract 288: Circular RNA CircFNDC3b Modulates Cardiac Repair After Myocardial Infarction via FUS-1/VEGF-A Axis

Circular RNA (circRNA) is a new addition to the list of growing body of non-coding RNAs.Recent studies highlighted that circRNA are dysregulated in cardiovascular disease. However,knowledge of the role of circRNAs in ischemic cardiac injury is limited. Using global circRNAexpression profiling, we identified several circRNA transcripts that were differentially regulatedpost-MI in mice, including circFNDC3b (derived from 2 and 3 exons of cognate FNDC3b gene)which is significantly down regulated. Cell fractionation experiments revealed that circFNDC3bis highly enriched in endothelial cells of post-MI mice. Notably, we found a circFNDC3b orthologin humans, which was also significantly down regulated in ischemic cardiomyopathy patients.Further, gene profile analysis of circFNDC3b overexpression in cardiac endothelial cellsdemonstrated an increase in angiogenic genes. Among them, vascular endothelial growthfactor-A (VEGF-A) was significantly elevated concomitant with reduced in vitro apoptosis ofcardiomyoblasts and endothelial cells, which also exhibited enhanced tube formation. Forcardiac overexpression of circFNDC3b, we generated AAV9 viral particles and found that in vivoover expression attenuated LV dysfunction post-MI and enhanced neovascularization.Mechanistically, circFNDC3b interacts with its potential target RNA binding protein FUS-1 (fusedin sarcoma) and regulate VEGF signaling, thereby reducing cardiomyocyte apoptosis andenhancing neovascularization and cardiac function post-MI. These results indicatethat circFNDC3b is a novel potential target to prevent cardiac remodeling and highlight theimportance of circRNAs in cardiovascular diseases.

Abstract 366: The Role of Mitochondrial Calcium Uniporter Complex in Cardiac Contractility and Function

Cardiac contractility is regulated by the intracellular Ca 2+ concentration fluxes which are maintained by multiple channels and transporters. Mitochondrial Calcium Uniporter (MCU) is the highly selective Ca 2+ ion channel responsible for the electrophoretic Ca 2+ uptake into the mitochondrial matrix. Earlier studies on the cardiac-specific acute MCU knockout and transgenic dominant-negative MCU mice have demonstrated that mitochondrial Ca 2+ ( m Ca 2+ ) signaling is necessary for cardiac ‘‘fight-or-flight’’ contractile response, however, the role of m Ca 2+ in the beat-to-beat regulation of cardiac contractility is highly debated. The MCU channel function is regulated by varied molecular regulatory components as well as ROS mediated modification at the Cys-96 residue of the core MCU protein. Our earlier studies have demonstrated that loss of MCU Regulator 1 (MCUR1) in cardiomyocytes results in the impaired m Ca 2+ uptake. To dissect the precise role of MCU in regulating cytosolic Ca 2+ transients associated with excitation-contraction (E-C) coupling and cardiac functions, we have employed the loss-of-function, cardiac-specific MCUR1 knockout mouse and a gain-of-function MCU C96A knockin mouse generated by CRISPR/Cas9 approach. Using these novel mouse models, both by in vivo analyses of cardiac physiology and in vitro experiments including single-cell cardiac contractility, calcium transients, and electrophysiology measurements, our study demonstrates that m Ca 2+ buffering actively participates in E-C coupling. MCUR1/MCU regulated m Ca 2+ buffering in cardiomyocytes, although insignificant under basal condition, becomes critical in stress-induced conditions and actively participates in regulating the c Ca 2+ transients during adrenergic stimulation. Our data indicate that MCUR1 ablation offers protection against pressure-overload cardiac hypertrophy and MCU C96A KI mice exhibit significantly decreased LV ejection fraction at baseline. In summary, our results provide critical insights into the mechanisms by which the MCU channel contributes in regulating the contractile function of the cardiomyocytes and the role of m Ca 2+ in the development and progression of heart failure.

G protein-coupled receptor kinase 2 promotes cardiac hypertrophy

The increase in protein activity and upregulation of G-protein coupled receptor kinase 2 (GRK2) is a hallmark of cardiac stress and heart failure. Inhibition of GRK2 improved cardiac function and survival and diminished cardiac remodeling in various animal heart failure models. The aim of the present study was to investigate the effects of GRK2 on cardiac hypertrophy and dissect potential molecular mechanisms. In mice we observed increased GRK2 mRNA and protein levels following transverse aortic constriction (TAC). Conditional GRK2 knockout mice showed attenuated hypertrophic response with preserved ventricular geometry 6 weeks after TAC operation compared to wild-type animals. In isolated neonatal rat ventricular cardiac myocytes stimulation with angiotensin II and phenylephrine enhanced GRK2 expression leading to enhanced signaling via protein kinase B (PKB or Akt), consecutively inhibiting glycogen synthase kinase 3 beta (GSK3β), such promoting nuclear accumulation and activation of nuclear factor of activated T-cells (NFAT). Cardiac myocyte hypertrophy induced by in vitro GRK2 overexpression increased the cytosolic interaction of GRK2 and phosphoinositide 3-kinase γ (PI3Kγ). Moreover, inhibition of PI3Kγ as well as GRK2 knock down prevented Akt activation resulting in halted NFAT activity and reduced cardiac myocyte hypertrophy. Our data show that enhanced GRK2 expression triggers cardiac hypertrophy by GRK2-PI3Kγ mediated Akt phosphorylation and subsequent inactivation of GSK3β, resulting in enhanced NFAT activity.

Abstract 298: Circular Rna Mmu_circ_008396 Attenuates Cardiac Remodeling After Myocardial Infarction in Mice

Recent studies highlighted that circular RNAs (circRNA) can play an important role in cardiac hypertrophy. However, the circRNAs in cardiac diseases is still limited. Using global circRNA expression profiling, we identified several circRNA transcripts that were differentially regulated post-MI in mice, including mmu_circ_008396 that is significantly down regulated. Cell fractionation experiments indicated that mmu_circ_008396 is highly enriched in endothelial cells in post-MI mice. Interestingly, we found a mmu_circ_008396 circRNA ortholog in humans, which was also significantly down regulated in ischemic cardiomyopathy patients. Further, overexpression of mmu_circ_008396 significantly enhanced tube formation and reduced apoptosis of human umbilical vein endothelial cells. For cardiac overexpression of mmu_circ_008396 circRNA, we created AAV9 viral particles and found that in vivo over expression attenuated LV dysfunction post-MI and enhanced neovascularization. Mechanistically, mmu_circ_008396 binds to its potential target miRNAs (mmu-miR-93-3p, mmu-miR-412-3p and mmu-miR-298-5p) and regulate hemeoxygenase-1/ VEGF signaling, thereby enhancing neovascularization and cardiac repair post-MI. These results indicate that mmu_circ_008396 circRNA might be a novel potential target to prevent cardiac remodeling and also highlight the significance of circRNAs in cardiovascular diseases.

Interleukin-10 Inhibits Bone Marrow Fibroblast Progenitor Cell-Mediated Cardiac Fibrosis in Pressure-Overloaded Myocardium

BACKGROUND

Activated fibroblasts (myofibroblasts) play a critical role in cardiac fibrosis; however, their origin in the diseased heart remains unclear, warranting further investigation. Recent studies suggest the contribution of bone marrow fibroblast progenitor cells (BM-FPCs) in pressure overload-induced cardiac fibrosis. We have previously shown that interleukin-10 (IL10) suppresses pressure overload-induced cardiac fibrosis; however, the role of IL10 in inhibition of BM-FPC-mediated cardiac fibrosis is not known. We hypothesized that IL10 inhibits pressure overload-induced homing of BM-FPCs to the heart and their transdifferentiation to myofibroblasts and thus attenuates cardiac fibrosis.

METHODS

Pressure overload was induced in wild-type (WT) and IL10 knockout (IL10KO) mice by transverse aortic constriction. To determine the bone marrow origin, chimeric mice were created with enhanced green fluorescent protein WT mice marrow to the IL10KO mice. For mechanistic studies, FPCs were isolated from mouse bone marrow.

RESULTS

Pressure overload enhanced BM-FPC mobilization and homing in IL10KO mice compared with WT mice. Furthermore, WT bone marrow (from enhanced green fluorescent protein mice) transplantation in bone marrow-depleted IL10KO mice (IL10KO chimeric mice) reduced transverse aortic constriction-induced BM-FPC mobilization compared with IL10KO mice. Green fluorescent protein costaining with α-smooth muscle actin or collagen 1α in left ventricular tissue sections of IL10KO chimeric mice suggests that myofibroblasts were derived from bone marrow after transverse aortic constriction. Finally, WT bone marrow transplantation in IL10KO mice inhibited transverse aortic constriction-induced cardiac fibrosis and improved heart function. At the molecular level, IL10 treatment significantly inhibited transforming growth factor-β-induced transdifferentiation and fibrotic signaling in WT BM-FPCs in vitro. Furthermore, fibrosis-associated microRNA (miRNA) expression was highly upregulated in IL10KO-FPCs compared with WT-FPCs. Polymerase chain reaction-based selective miRNA analysis revealed that transforming growth factor-β-induced enhanced expression of fibrosis-associated miRNAs (miRNA-21, -145, and -208) was significantly inhibited by IL10. Restoration of miRNA-21 levels suppressed the IL10 effects on transforming growth factor-β-induced fibrotic signaling in BM-FPCs.

CONCLUSIONS

Our findings suggest that IL10 inhibits BM-FPC homing and transdifferentiation to myofibroblasts in pressure-overloaded myocardium. Mechanistically, we show for the first time that IL10 suppresses Smad-miRNA-21-mediated activation of BM-FPCs and thus modulates cardiac fibrosis.

Abstract 278: Domain-specific Roles for GRK2 in Cardiac Hypertrophy and Heart Failure

During heart failure (HF), cardiac levels and activity of the G protein-coupled receptor (GPCR) kinase (GRK) GRK2 are elevated and contribute to adverse remodeling and contractile dysfunction, while inhibition via a carboxyl-terminal peptide, βARKct, enhances heart function and can prevent HF. Mounting evidence supports the idea of a dynamic “interactome” in which GRK2 can uncouple GPCRs via novel protein-protein interactions. Several GRK2 interacting partners are important for adaptive and maladaptive myocyte growth; therefore, an understanding of domain-specific interactions with signaling and regulatory molecules could lead to novel targets for HF therapy. For instance, GRK2 contains a putative amino-terminal R egulator of G protein S ignaling (RGS) domain (βARKrgs) that directly interacts with Gαq and inhibits signaling. Previously, our lab investigated cardiac-specific transgenic expression of a fragment of this RGS domain (βARKnt), that did not reduce acute hypertrophy after pressure overload or demonstrate RGS activity in vivo against Gαq-mediated signaling. In contrast, βARKnt induced hypertrophy and elevated β-adrenergic receptor (βAR) density without altering agonist-induced contractility or adenylyl cyclase activity, due to a compensatory increase in GRK2 activity. Importantly, βAR downregulation in response to chronic agonist administration was attenuated by βARKnt expression, indicating a novel regulation of βAR receptor density. Herein, we investigated the effect of βARKnt expression during chronic pressure overload post trans-aortic constriction (TAC). Echocardiographic analysis revealed increased posterior wall thickness and left-ventricular mass 4 weeks post-TAC compared to non-transgenic littermate controls. Importantly, despite enhanced hypertrophy, the progression to HF was inhibited in βARKnt mice 14 weeks post-TAC. Histological analysis of interstitial fibrosis and cross-sectional area is underway to determine alterations in maladaptive remodeling. Further, cardiomyocyte signaling and βARKnt protein-binding partners are a focus, since our data indicate that βARKnt-mediated regulation of βAR density may provide a novel means of cardioprotection during pressure-overload induced HF.

Abstract 301: Initial Increase of Klf5 and Ppara Expression After Myocardial Ischemia/Reperfusion in Mice Appears to be Critical for Survival

Krüppel-like factors (KLF) have important roles in metabolism. We previously found that KLF5 is a positive transcriptional regulator of peroxisome proliferator-activated receptor α ( Ppara) , a central regulator of cardiac fatty acid oxidation (FAO). Mice with cardiomyocyte-specific Klf5 ablation ( α MHC-Klf5 -/- ) had reduced cardiac Ppara expression and FAO. At age 6-12 months these mice develop distinct cardiac dysfunction. The role of PPARα activation in I/R injury is unclear as both beneficial and detrimental effects have been reported. We aimed to study if Ppara expression changes during I/R are driven by KLF5 and explore its protective or detrimental role. Wild type mice were subjected to in vivo I/R or sham surgery. I/R resulted in an initial increase in Ppara , and its target gene pyruvate dehydrogenase kinase 4 ( Pdk4) mRNA after 2h reperfusion, followed by decreased expression after 24h reperfusion. The Ppara expression is associated with parallel changes in cardiac Klf5 mRNA expression. Concurrent, there was a decrease of cardiac FAO-related genes carnitine palmitoyl-transferase 1β ( Cpt1b), very long chain acyl-CoA dehydrogenase (Vlcad), and acyl-CoA oxidase ( Aox) in mice with I/R. To define the cell type causing the temporal changes in Klf5 and Ppara after I/R we isolated primary cardiomyocytes and fibroblasts. Our data suggest a similar effect in primary isolated cardiomyocytes only. Klf5 mRNA expression is increased after 2 hour hypoxia and normalized after 4 hour re-oxygenation in cardiomyocytes, whereas there are no changes after hypoxia/normoxia in fibroblasts. To assess the importance of cardiomyocyte KLF5 in I/R we used α MHC-Klf5 -/- mice. Interestingly, despite reduced FAO, 7 month old αMHC-Klf5 -/- mice subjected to I/R had a marked increase in mortality; 4 of 7 αMHC-Klf5 -/- mice died within the first 24h of reperfusion while no mortality was observed in age-matched wild type mice that underwent I/R. In conclusion, I/R is associated with an increase in Klf5 and Ppara in the first hours of reperfusion followed by a decrease in Klf5 and Ppara , likely accounted for by cardiomyocytes. Increased mortality for α MHC-Klf5 -/- mice with I/R injury suggests that the initial increase may be an adaptive response that is critical for survival.

A peptide of the RGS domain of GRK2 binds and inhibits Gα(q) to suppress pathological cardiac hypertrophy and dysfunction

G protein-coupled receptor (GPCR) kinases (GRKs) play a critical role in cardiac function by regulating GPCR activity. GRK2 suppresses GPCR signaling by phosphorylating and desensitizing active GPCRs, and through protein-protein interactions that uncouple GPCRs from their downstream effectors. Several GRK2 interacting partners, including Gα(q), promote maladaptive cardiac hypertrophy, which leads to heart failure, a leading cause of mortality worldwide. The regulator of G protein signaling (RGS) domain of GRK2 interacts with and inhibits Gα(q) in vitro. We generated TgβARKrgs mice with cardiac-specific expression of the RGS domain of GRK2 and subjected these mice to pressure overload to trigger adaptive changes that lead to heart failure. Unlike their nontransgenic littermate controls, the TgβARKrgs mice exhibited less hypertrophy as indicated by reduced left ventricular wall thickness, decreased expression of genes linked to cardiac hypertrophy, and less adverse structural remodeling. The βARKrgs peptide, but not endogenous GRK2, interacted with Gα(q) and interfered with signaling through this G protein. These data support the development of GRK2-based therapeutic approaches to prevent hypertrophy and heart failure.

Science Signaling Podcast for 22 March 2016: Preventing heart failure with GRK2

A GRK2-derived peptide reduces pathological cardiac hypertrophy in mice.

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

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.

Comparative effects of urocortins and stresscopin on cardiac myocyte contractility

RATIONALE

There is a current need for the development of new therapies for patients with heart failure.

OBJECTIVE

We test the effects of members of the corticotropin-releasing factor (CRF) family of peptides on myocyte contractility to validate them as potential heart failure therapeutics.

METHODS AND RESULTS

Adult feline left ventricular myocytes (AFMs) were isolated and contractility was assessed in the presence and absence of CRF peptides Urocortin 2 (UCN2), Urocortin 3 (UCN3), Stresscopin (SCP), and the β-adrenergic agonist isoproterenol (Iso). An increase in fractional shortening and peak Ca(2+) transient amplitude was seen in the presence of all CRF peptides. A decrease in Ca(2+) decay rate (Tau) was also observed at all concentrations tested. cAMP generation was measured by ELISA in isolated AFMs in response to the CRF peptides and Iso and significant production was seen at all concentrations and time points tested.

CONCLUSIONS

The CRF family of peptides effectively increases cardiac contractility and should be evaluated as potential novel therapeutics for heart failure patients.

Abstract 365: Domain-specific Roles for GRK2 in Cardiac Hypertrophy and Heart Failure

During heart failure (HF), cardiac levels and activity of the G protein-coupled receptor (GPCR) kinase (GRK) GRK2 are elevated and contribute to adverse remodeling and contractile dysfunction, while inhibition via a carboxyl-terminal peptide, βARKct, enhances heart function and can prevent HF development. Mounting evidence supports the idea of a dynamic “interactome” in which GRK2 can uncouple GPCRs via novel protein-protein interactions. Several GRK2 interacting partners are important for adaptive and maladaptive myocyte growth; therefore, an understanding of domain-specific interactions with signaling and regulatory molecules could lead to novel targets for HF therapy. For instance, GRK2 contains a putative amino-terminal Regulator of G protein Signaling (RGS) domain (βARK-RGS) that directly interacts with Gq and appears to inhibit signaling without altering Gq enzymatic activity. Previously, our lab investigated cardiac-specific transgenic (Tg) expression of a fragment of this RGS domain (βARKnt). This fragment did not alter acute hypertrophy after pressure overload or demonstrate RGS activity in vivo against Gq-mediated signaling. In contrast, βARKnt induced hypertrophy and elevated β-adrenergic receptor (βAR) density without altering agonist-induced contractility or adenylyl cyclase activity, due to a compensatory increase in GRK2 activity. Importantly, though, βAR downregulation in response to chronic agonist administration was attenuated by βARKnt expression, indicating a novel regulation of βAR receptor density. Given these findings we have recently investigated the effect of βARKnt expression during chronic pressure overload post trans-aortic constriction (TAC). Echocardiographic analysis revealed increased posterior wall thickness and left-ventricular mass 4 weeks post-TAC compared to non-transgenic littermate controls (NLC). Importantly, despite enhanced hypertrophy, the progression to HF was inhibited in βARKnt mice 14 weeks post-TAC (%LV Ejection Fraction of 36.1 ± 0.2 in NLC versus 56.6 ± 0.9 in Tg mice). While mechanistic characterization is underway, these data indicate that βARKnt-mediated regulation of βAR density may provide a novel means of cardioprotection during pressure-overload induced HF.

Abstract 113: Klf5 and Ppara Expression is Increased at the Early Stage and Reduced at the Late Stage of Myocardial Ischemia/Reperfusion in Mice

Inhibition of cardiac fatty acid oxidation (FAO) is considered beneficial after ischemia reperfusion (I/R). Krüppel-like factors (KLF) have an important role in metabolism. In a model of cardiac energetic deficiency (LPS-treated mice), in silico promoter analysis and whole genome array analysis indicated cardiac KLF5 as important regulator of Ppara . Gene expression analysis in human ventricular myocytes (AC16) treated with Ad-Klf5 followed by ChIP analysis confirmed that KLF5 is a positive transcriptional regulator of Ppara . Mice with cardiomyocyte-specific Klf5 ablation (αMHC-Klf5 -/- ) that we made had reduced cardiac Ppara expression and other FAO-related genes. The role of PPARα activation in I/R injury is unclear as both beneficial and detrimental effects have been reported. We aimed to gain insight in the effects of KLF5 and PPARα on acute I/R injury.

To mimic I/R in vitro , AC16 cells were subjected to hypoxia (9.5 h) followed by short (1h) or prolonged (14h) normoxia. Ppara expression was initially (1h) increased (p<0.05) and then (14 h) decreased (p<0.05). Klf5 expression pattern showed a trend of similar changes . Infarction was performed by 30 min of left coronary artery occlusion followed by 2 or 24 hours of reperfusion in wild type mice. I/R resulted in a trend for an initial increase in Klf5 (2-fold, p=0.05), Ppara (3-fold, p=0.08), and Pdk4 (8-fold, p<0.01) mRNA at 2h post-surgery. Klf5 (2-fold; p<0.01) and Ppara (9-fold; p<0.05) expression were decreased 24h post-surgery. Consistent with Ppara changes, there was a 2-fold decrease of Cpt1 (p<0.01) and Vlcad (p<0.01) and a trend for decreased Aox (2-fold), Lcad (2-fold), and Pdk4 (6-fold) compared to sham. Echocardiography indicated normal cardiac function after 24h post-surgery. Despite reduced FAO, αMHC-Klf5 -/- mice subjected to I/R had a marked increase in mortality; 40% (4 of 10) of αMHC-Klf5 -/- mice died within the first 24h of reperfusion while no mortality was observed in wild type mice that underwent I/R.

In conclusion, I/R is associated with an increase in Klf5 and Ppara in the first hours of reperfusion followed by a decrease in Klf5 and Ppara . Increased mortality for αMHC-Klf5 -/- mice with I/R injury suggests that the initial increase may be an adaptive response that is critical for survival.

Abstract 70: Domain-Specific Roles for GRK2 in Cardiac Hypertrophy and Heart Failure

During heart failure (HF), cardiac levels and activity of the G protein-coupled receptor (GPCR) kinase (GRK) GRK2 are elevated, increasing phosphorylation, desensitization and down-regulation of β-adrenergic receptors (βARs) and other cardiac GPCRs. Increased GRK2 participates in adverse remodeling and contractile dysfunction during HF, while inhibition via a carboxy-terminal peptide, βARKct, enhances heart function and can prevent HF development. Mounting evidence supports the idea of a dynamic “interactome” in which GRK2 can uncouple GPCRs via novel protein-protein interactions. Several novel GRK2 interacting partners are important for adaptive and maladaptive myocyte growth including Gq, the signaling trigger for maladaptive cardiac hypertrophy, leading to HF. Importantly, GRK2 contains a putative amino-terminal Regulator of G protein Signaling (RGS) domain (βARK-RGS). This domain directly interacts with Gq and appears to inhibit signaling without altering Gq enzymatic activity. Therefore, this domain may alter hypertrophic responses in the heart and represent a novel role for GRK2 and a potential therapeutic target to limit maladaptive cardiac hypertrophy. We have begun to address this by generation of novel transgenic (Tg) mice with cardiac-specific expression of the RGS domain of GRK2. Using a trans-aortic constriction (TAC) model of pressure overload hypertrophy, we found that expression of βARK-RGS demonstrates anti-hypertrophic effects. Echocardiographic analysis post-TAC revealed reduced left ventricular posterior wall thickness (LVPW) in βARK-RGS compared to non-transgenic littermate controls (NLC) (0.85 vs 1.0 mm LVPWd at 4 weeks). RT-PCR analysis found decreased hypertrophic factor transcripts, such as ANF for which the nearly 18-fold increase post TAC was completely inhibited in βARK-RGS mice. Further, the progression to HF was inhibited in βARK-RGS mice, but not NLCs, 14 weeks post-TAC. While mechanistic characterization is underway, these data support our hypothesis that the RGS domain of GRK2 may serve as a non-canonical inhibitor of Gq-mediated hypertrophic signaling in the heart and highlight how this research may pave the way for novel GRK2-based therapeutic approaches to prevent hypertrophy and HF.

Redox-sensitive sulfenic acid modification regulates surface expression of the cardiovascular voltage-gated potassium channel Kv1.5

RATIONALE

Kv1.5 (KCNA5) is expressed in the heart, where it underlies the I(Kur) current that controls atrial repolarization, and in the pulmonary vasculature, where it regulates vessel contractility in response to changes in oxygen tension. Atrial fibrillation and hypoxic pulmonary hypertension are characterized by downregulation of Kv1.5 protein expression, as well as with oxidative stress. Formation of sulfenic acid on cysteine residues of proteins is an important, dynamic mechanism for protein regulation under oxidative stress. Kv1.5 is widely reported to be redox-sensitive, and the channel possesses 6 potentially redox-sensitive intracellular cysteines. We therefore hypothesized that sulfenic acid modification of the channel itself may regulate Kv1.5 in response to oxidative stress.

OBJECTIVE

To investigate how oxidative stress, via redox-sensitive modification of the channel with sulfenic acid, regulates trafficking and expression of Kv1.5.

METHODS AND RESULTS

Labeling studies with the sulfenic acid-specific probe DAz and horseradish peroxidase-streptavidin Western blotting demonstrated a global increase in sulfenic acid-modified proteins in human patients with atrial fibrillation, as well as sulfenic acid modification to Kv1.5 in the heart. Further studies showed that Kv1.5 is modified with sulfenic acid on a single COOH-terminal cysteine (C581), and the level of sulfenic acid increases in response to oxidant exposure. Using live-cell immunofluorescence and whole-cell voltage-clamping, we found that modification of this cysteine is necessary and sufficient to reduce channel surface expression, promote its internalization, and block channel recycling back to the cell surface. Moreover, Western blotting demonstrated that sulfenic acid modification is a trigger for channel degradation under prolonged oxidative stress.

CONCLUSIONS

Sulfenic acid modification to proteins, which is elevated in diseased human heart, regulates Kv1.5 channel surface expression and stability under oxidative stress and diverts channel from a recycling pathway to degradation. This provides a molecular mechanism linking oxidative stress and downregulation of channel expression observed in cardiovascular diseases.

Ion channel trafficking: a new therapeutic horizon for atrial fibrillation

Atrial fibrillation (AF) is a common cardiac arrhythmia with potentially life-threatening complications. Drug therapies for treatment of AF that seek long-term maintenance of normal sinus rhythm remain elusive due in large part to proarrhythmic ventricular actions. Kv1.5, which underlies the atrial specific I(Kur) current, is a major focus of research efforts seeking new therapeutic strategies and targets. Recent work has shown a novel effect of antiarrhythmic drugs where compounds that block Kv1.5 channel current also can alter ion channel trafficking. This work further suggests that the pleiotropic effects of antiarrhythmic drugs may be separable. Although this finding highlights the therapeutic potential for selective manipulation of ion channel surface density, it also reveals an uncertainty regarding the specificity of modulating trafficking pathways without risk of off-target effects. Future studies may show that specific alteration of Kv1.5 trafficking can overcome the proarrhythmic limitations of current pharmacotherapy and provide an effective method for long-term cardioversion in AF.

Antiarrhythmic drug-induced internalization of the atrial-specific k+ channel kv1.5

Conventional antiarrhythmic drugs target the ion permeability of channels, but increasing evidence suggests that functional ion channel density can also be modified pharmacologically. Kv1.5 mediates the ultrarapid potassium current (I(Kur)) that controls atrial action potential duration. Given the atrial-specific expression of Kv1.5 and its alterations in human atrial fibrillation, significant effort has been made to identify novel channel blockers. In this study, treatment of HL-1 atrial myocytes expressing Kv1.5-GFP with the class I antiarrhythmic agent quinidine resulted in a dose- and temperature-dependent internalization of Kv1.5, concomitant with channel block. This quinidine-induced channel internalization was confirmed in acutely dissociated neonatal myocytes. Channel internalization was subunit-dependent, activity-independent, stereospecific, and blocked by pharmacological disruption of the endocytic machinery. Pore block and channel internalization partially overlap in the structural requirements for drug binding. Surprisingly, quinidine-induced endocytosis was calcium-dependent and therefore unrecognized by previous biophysical studies focused on isolating channel-drug interactions. Importantly, whereas acute quinidine-induced internalization was reversible, chronic treatment led to channel degradation. Together, these data reveal a novel mechanism of antiarrhythmic drug action and highlight the possibility for new agents that selectively modulate the stability of channel protein in the membrane as an approach for treating cardiac arrhythmias.

Rab-GTPase-dependent endocytic recycling of Kv1.5 in atrial myocytes

The number of ion channels expressed on the cell surface shapes the complex electrical response of excitable cells. Maintaining a balance between anterograde and retrograde trafficking of channel proteins is vital in regulating steady-state cell surface expression. Kv1.5 is an important voltage-gated K(+) channel in the cardiovascular system underlying the ultra-rapid rectifying potassium current (Ik(ur)), a major repolarizing current in atrial myocytes, and regulating the resting membrane potential and excitability of smooth muscle cells. Defects in the expression of Kv1.5 are associated with pathological states such as chronic atrial fibrillation and hypoxic pulmonary hypertension. There is, thus, substantial interest in understanding the mechanisms regulating cell surface channel levels. Here, we investigated the internalization and recycling of Kv1.5 in the HL-1 immortalized mouse atrial myocytes. Kinetic studies indicate that Kv1.5 is rapidly internalized to a perinuclear region where it co-localizes with the early endosomal marker, EEA1. Importantly, we identified that a population of Kv1.5, originating on the cell surface, internalized and recycled back to the plasma membrane. Notably, Kv1.5 recycling processes are driven by specific Rab-dependent endosomal compartments. Thus, co-expression of GDP-locked Rab4S22N and Rab11S25N dominant-negative mutants decreased the steady-state Kv1.5 surface levels, whereas GTPase-deficient Rab4Q67L and Rab11Q70L mutants increased steady-state Kv1.5 surface levels. These data reveal an unexpected dynamic trafficking of Kv1.5 at the myocyte plasma membrane and demonstrate a role for recycling in the maintenance of steady-state ion channel surface levels.