M o l e c u l a r Ba s i s o f R e c o v e r i n g o n M e c h a n i c a l C i rc u l a t o r y Support Ali Nsair, MD, David A. Liem, MD, PhD, Martin Cadeiras, MD, Richard K. Cheng, MD, Mrudula Allareddy, MD, Murray Kwon, MD, Richard Shemin, MD, Mario C. Deng, MD, FESC* KEYWORDS Reverse remodeling Molecular mechanisms Advanced heart failure Mechanical circulatory support
KEY POINTS
INTRODUCTION The number of patients with heart failure (HF) is increasing. In 2010, 6.6 million US adults 18 years of age or older (2.8%) had HF. In 2008, 1 in 9 death certificates (281,437 deaths) in the United States mentioned HF. It is estimated that by 2030, an additional 3 million people will have HF, a 25.0% increase in prevalence from 2010. HF contributes to more than 250,000 deaths a year, results in 2.4 to 3.5 million hospitalizations a year, 12 million to 15 million outpatient office visits a year, and total costs estimated at 39.2 billion dollars a year.1 The prevalence of advanced HF (AdHF), constituting between 1% and 10% of the population
with HF, is estimated to total between 30,000 and 300,000 patients in the United States. From a regional HF care perspective, for example, in the Greater Los Angeles area with a population of more than 10,000,000, the prevalence of HF is estimated at more than 100,000 people, and those with AdHF at more than 10,000 people. AdHF carries a prognosis similar to cancer. Over the past decade, mechanical circulatory support device (MCSD) therapy has been beneficial as a bridge to cardiac transplantation, and anecdotal evidence suggests that patients with HF with mechanical assist devices experience direct cardiac benefits. Moreover, recent trials on
The authors have nothing to disclose. University of California, Ahmanson-UCLA Cardiomyopathy Center, 100 Medical Plaza, Suite 630, Los Angeles, CA 90095, USA * Corresponding author. E-mail address: [email protected] Heart Failure Clin 10 (2014) S57–S62 http://dx.doi.org/10.1016/j.hfc.2013.08.007 1551-7136/14/$ – see front matter Ó 2014 Elsevier Inc. All rights reserved.
heartfailure.theclinics.com
The goal of developing a molecular/cellular profile to predict responders to left ventricular assist device (LVAD) support as a bridge to recovery in patients with heart failure (HF) will be important and complementary to clinical parameters to help identify and target this patient population. Our insights into different system levels of mechanisms by LVAD support are increasing and suggest a complex regulatory system of overlapping biological processes. To develop novel decision-making strategies and patient selection criteria, HF and reverse cardiac remodeling will be conceptualized and explored by a multifaceted research strategy of transcriptomics, metabolomics, proteomics, molecular biology, and bioinformatics. Knowledge of the molecular mechanisms of reverse cardiac remodeling is in its early stages, and comprehensive reconstruction of the underlying networks is necessary.
S58
Nsair et al limited numbers and subpopulations of patients (notably REMATCH [Randomized Evaluation of Mechanical Assistance for the Treatment of Congestive Heart Failure]) support earlier observations of improved cardiac function and point toward the use of assist devices as destination therapy. Therefore, the role of long-term MCSD is increasing and gaining importance relative to heart transplantation.2 To investigate mechanisms of myocardial recovery during long-term MCSD, the National Heart, Lung, and Blood Institute convened the working group Recovery from Heart Failure with Circulatory Assist. The team included cardiac surgeons, cardiologists, and experts in experimental research. The goal was to prioritize recommendations to guide future programs in: (1) elucidating the mechanisms leading to reverse remodeling associated with a left ventricular assist device (LVAD); (2) exploring advanced treatments, including novel pharmacologies, tissue engineering, and cell therapies, to optimize recovery with LVAD therapy; and (3) identifying target genes, proteins, and cellular pathways to focus on production of novel therapies for myocardial recovery and cardiovascular disease. The working group also made research and clinical recommendations to translate findings into improved therapeutic strategies and device design: (1) support collaborations among clinical and basic scientists with an emphasis on clinical/translational research, which might lead to clinical trials; (2) identify candidate patients most likely to benefit from LVAD as a destination therapy; (3) explore potential biomarkers indicating when patients could most successfully be weaned from devices; and (4) promote clinical and experimental study of mechanically assisted organs and the tissue derived from them.3 In this review, the data that have accrued over the past decade on molecular mechanisms of recovery during mechanical circulatory support are summarized and evaluated.
STAGED HF INTERVENTIONS ASSOCIATED WITH MULTILEVEL REVERSE REMODELING Lifestyle changes such as moderate endurance training and continuous positive airway pressure therapy in patients with HF with sleep apnea induce reverse remodeling. Therapies aimed at neurohormonal blockade, also termed neurohormonal modulation therapy, such as angiotensinconverting enzyme (ACE) inhibitors, b-blockers, and aldosterone antagonists improve organ level markers for reverse remodeling, including ejection fraction, ventricular volumes, and mass. For b-blockers, reverse molecular remodeling was also shown in biopsy specimens on the cellular
and subcellular level. Aldosterone has a central role in promoting cardiac fibrosis which may be partially independent of angiotensin II, because it has also been shown in animal models, humans, and isolated cardiac fibroblasts exposed to aldosterone.4 Hence, an aldosterone antagonist may be antifibrotic. Cardiac resynchronization therapy improves exercise capacity and quality of life in patients with ventricular dyssynchrony and is associated with geometric and functional reverse remodeling over time. Surgical approaches for reverse remodeling, such as mitral valve replacement, aneurysmectomy, and volume reduction have been developed, but may also be associated with high perioperative mortality. More recent methods under exploration include percutaneous approaches to ventricular partitioning of dysfunctional segments. Mechanical unloading of the failing ventricles by LVADs induces well-characterized reverse remodeling on the cellular and subcellular level. Whether this reverse remodeling translates into sustained organ recovery and patient survival remains to be shown.5 This article focuses on the systematic review of molecular evidence of reverse remodeling related to the key domains of heart functions (ie, structural maintenance, systemic neuroimmunoendocrine regulation, muscle mechanics [contraction/relaxation], electrophysiology, perfusion, and energy metabolism).
REVERSE REMODELING OF STRUCTURAL BIOLOGY Several histology studies analyzing the morphology and size of cardiomyocytes in patients with HF supported by LVAD described a strong decrease of cell volume, cell profile area, and cell length. These effects in HF were more profound in the most distorted areas and strongly correlated with the duration of LVAD support. Mechanical unloading of the ventricle has also shown a reversal of cardiomyocyte damage by reduction of necrosis, contraction bands, and myocytolysis. LVAD support also induces normalization of cardiac sarcomeric proteins, vinculin, desmin, and tubulin. Whether and to what extent interstitial connective tissue deposits can be reversed after LVAD support is still a matter of dispute, with several contradicting reports to date.6–9 The Harefield group reported a seminal experience using clenbuterol. A total of 15 patients with nonischemic cardiomyopathy who required LVAD implantation were studied; 6 recovered sufficiently to allow explantation of the device compared with 9 who did not recover and required transplantation. Left ventricular myocardial samples were
Molecular Basis of Recovering on MCSD collected at implantation and explantation/transplantation. Affymetrix microarray analysis was performed on the paired samples and analyzed with reference to sarcomeric and nonsarcomeric cytoskeletal proteins. In the recovery group, of the nonsarcomeric proteins, lamin A/C increased 1.5-fold and spectrin 1.6-fold between the times of implantation and explantation. Integrins b1, b6, and a7 decreased 1.7-fold, 2.4-fold, and 1.5-fold, respectively, but integrins a5 and b5 increased 2.3-fold and 1.2-fold at explantation. The following sarcomeric proteins changed in the recovered group only: b-actin increased 1.4-fold; a-tropomyosin, 1.3-fold; a1-actinin, 1.8-fold; and a-filamin A, 1.6fold. Both troponin T3 and a2-actinin decreased by 1.6-fold at the time of explantation. Vinculin decreased 1.7-fold in the recovered group but increased by 1.7-fold in the nonrecovered group. Vinculin protein levels decreased 4.1-fold in the recovered group. The investigators concluded that myocardial recovery using clenbuterol was associated with a specific pattern of changes in sarcomeric, nonsarcomeric, and membraneassociated proteins, which could have important implications in understanding the mechanisms involved.10
REVERSE REMODELING OF NEUROIMMUNOENDOCRINE BIOLOGY Proinflammatory Cytokine Pathways Proinflammatory cytokine cascades such as tumor necrosis factor and interleukin 6 (IL-6) have been implicated in the progression of HF. Individual case reports show (1) the existence of an intracardiac IL-6 and IL-6 receptor system, (2) a dynamic regulation of this system in myocarditisassociated low-output syndrome, (3) the temporal association of increased plasma levels of IL-6 with myocardial gene expression and left ventricular dysfunction, and (4) synchronicity of improvement of left ventricular function with reversal of plasma levels and myocardial IL-6 mRNA expression, the cause of which might have been LVAD unloading, resolution of myocarditis, or both. These data support the concept of a pathophysiologic role of IL-6 in myocarditis and advanced HF, potentially based on its intrinsic negative inotropic or hypertrophogenic properties.11 The proinflammatory cytokine tumor necrosis factor a (TNF-a) stimulates cardiac growth and ventricular remodeling and is not present in the heart under normal conditions. However, cardiac expression of TNF-a is upregulated during both ischemia-reperfusion injury and HF progression. This upregulation can be reversed during long-term ventricular unloading by LVAD implantation.7 Chronic left ventricular
unloading with either pulsatile or continuous-flow devices decreases right ventricular total collagen and myocardial TNF-a content, suggesting that the decreased fibrosis and normalization of cytokine milieu observed may contribute to the recovery of right-sided cardiac function associated with chronic mechanical circulatory support.12 Certain heat shock proteins such as heme oxygenase and metallothioneins are also upregulated during HF progression and by certain stress stimuli, such as ischemia-reperfusion injury. After LVAD treatment, increased expression of several heat shock proteins returned to normal values.9,13 Cell death by apoptosis, which strongly contributes to HF progression, is also attenuated by LVAD support, although not all study results have been consistent, because some of the data showed increased apoptosis. The transcription factor nuclear factor kb (NF-kb) may play an important role as a key factor in the progression of HF and subsequently in reverse ventricular remodeling. NF-kb is a crucial regulator of genes that are involved in the cellular response to stressful stimuli and specifically regulates genes involved in apoptosis such as Bcl-2 protein family members (eg, Bcl-2, BclxL, and Bax). Several studies have observed that the antiapoptotic protein Bcl-xL is upregulated after mechanical unloading with LVAD support. The susceptibility of human cardiomyocytes to apoptosis during HF may be diminished by the activation of Bcl-xL.7–9 Cardiac dysfunction can be substantially reversed by MCSD in selected patients with end-stage idiopathic dilated cardiomyopathy. The degree of preoperative myocardial fibrosis may be an indicator for outcome. Anti-b1adrenoceptor autoantibodies can be used to monitor myocyte recovery.14 The group of the world’s largest MCSD program, the Heart Center in Bad Oeynhausen, Germany, have reported on children and adolescents in fulminant myocarditis undergoing prolonged circulatory support with different assist devices. Between 1994 and 2004, of 7 children and adolescents (aged 7–18 years, mean age 13.5 years) who were treated with ventricular assist devices (VADs), 4 patients (3 LVADs, 1 biventricular assist device) could be successfully bridged to heart transplantation after a mean support time of 163 days (56–258 days). Atrial and brain natriuretic peptides reached normal values after recovery of myocardial function.15 At Advocate Christ Medical Center in Oak Lawn, Illinois, 6 patients with advanced HF and severe mitral regurgitation underwent successful bridge to recovery using a Thoratec LVAD. Normalization of clinical data collected during the recovery phase including chest roentgenogram, echocardiography, plasma norepinephrine, TNF-a, bioimpedance,
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Nsair et al and cardiopulmonary exercise testing (peak oxygen consumption), including a 10% increase in peak oxygen consumption before weaning.16
REVERSE REMODELING OF CONTRACTION/ RELAXATION, ELECTROPHYSIOLOGY, AND PERFUSION BIOLOGY Unloading of the heart by LVAD support leads to contraction strength enhancement in conjunction with an improved contraction and relaxation timing.7 This improved strength generation is correlated to a higher calcium (Ca21) content in the sarcoplasmic reticulum, thereby improving cardiac contractility. Altered regulation and density of L-type Ca21 channels, calcium cycling genes, and the Ca21 adenosine triphosphatase (ATPase) subtype 2a (SERCA 2a) and the sarcolemmal Na1-Ca21 exchanger are also normalized by mechanical unloading of the failing heart.8 In contrast, levels of the Ca21 regulatory proteins phospholamban and ryanodine receptors showed inconsistent results. b-Adrenergic receptor density and response to stimulation can be restored during LVAD support, most likely mediated by intracellular rather than hemodynamic factors.17 Other important key players in maintaining arterial blood pressure and volume homeostasis are cardiac natriuretic peptide (ANP) and B-type natriuretic peptides (BNP). Both act through guanylcyclaseA signaling, initiating antihypertrophic and antifibrotic effects. Reverse remodeling of the failing heart by LVAD support led to restoration of the impaired response of guanylcyclase-A signaling to ANP, whereas cardiac hypertrophy did not completely reverse.7–9 Expression of the sarcoplasmic endoreticular Ca21-ATPase subtype 2a, the ryanodine receptor, and the sarcolemmal Na1-Ca21 exchanger are upregulated after LVAD support. Genes known to be involved in myocardial hypertrophy and cardiovascular signaling are downregulated in reverse remodeling by LVAD.18,19 Some studies did not show a normalized gene expression during mechanical unloading and are contradictory. Transcript changes did not clearly respond to LVAD support, which opens the possibility that several molecular changes that occur during HF are an epiphenomenon or represent nonspecific responses of the myocardium.20 It is also possible that the observed changes in messenger RNA localization, efficiency of translation, and posttranslational modifications are more important for the regulation of myocardial structure and function rather than left ventricular remodeling per se. Microarray gene-chip platforms have been used to detect transcription changes of HF hearts in response to LVAD support.21 Reverse
cardiac remodeling by LVAD support may be mediated by specific regulation of certain kinases in patients with HF. The activation of Akt and GSK-3b in patients with HF is downregulated after LVAD support.22 In addition, it was reported that Erk is downregulated by mechanical unloading, whereas JNK signal transduction showed no change.23 Contradictory to previous reports, this study also observed a change of P38 by mechanical unloading.7–9 The transmission of hypertrophic and survival signals in the cardiomyocyte is partly also mediated by receptor tyrosine kinases (RTKs). Neuregulins are a family of growth-promoting proteins characterized as ligands of RTKs of the ErB family. Conditional inactivation of ErB family RTKs in ventricular muscle cells leads to severe dilated cardiomyopathy. Furthermore, the interactions of neuregulin growth factors with 2 other RTKs, Her2/neu and Her4, promote cell survival and inhibit apoptosis in cardiac myocytes. Unloading of the heart resulted in an upregulation of Her2/ neu and Her4, particularly in patients with ischemic cardiomyopathy. Glycoprotein 130, which also plays an important role in RTK signal transduction, as well as IL-6 family signal transduction,11 was decreased after LVAD implantation.24
REVERSE REMODELING OF ENERGY METABOLISM Progression of HF is associated with extremely low respiratory control indexes (RCIs) as depicted by state 3/state 4 and state 3/state 2. Using reduced nicotinamide adenine dinucleotide– dependent substrates (ie, pyruvate/malate and glutamate), RCIs are significantly improved after LVAD support, suggesting an important role of the device in benefiting oxidative phosphorylation and electron transport.25 Chronic LVAD support potentiates endogenous nitric oxide (NO)-mediated regulation of mitochondrial respiration as measured by improved MVO2 consumption, which can be abrogated by NO synthase inhibition.26 Both failing and LVAD supported hearts showed a reduction in cardiolipin content, whereas reverse remodeling by LVAD results in an improved composition of the lipid.18 Because the mitochondrial proteome is significantly modulated after cardiac resynchronization therapy in failing porcine hearts, as indicated by 31 altered mitochondrial proteins,27 it is reasonable to hypothesize that the pathologic proteomic mitochondrial phenotype is reversible in the failing heart, which may be an important underlying mechanism in reverse ventricular remodeling. The 20S proteasome activity is increased by mechanical unloading.28 The
Molecular Basis of Recovering on MCSD ubiquitin-proteasome system is depressed during HF, a disadvantageous event reversed by ventricular unloading, and may play a significant role in ventricular hypertrophy and HF as well as in reverse cardiac remodeling.29
3.
SUMMARY Although all established evidence-based therapies for HF have been shown to have a reverse remodeling effect on both the clinical and the molecular level (moderate endurance training, continuous positive airway pressure therapy, ACE inhibitors, b-blockers, cardiac resynchronization, mitral valve replacement, aneurysmectomy, left ventricular volume reduction, mechanical unloading of the failing ventricles by LVAD), the challenges to be addressed include the following: (1) how consistently do reverse remodeling changes on the molecular level translate into clinical reverse remodeling effects and benefits? (2) Do acute reverse remodeling changes during ongoing HF interventions translate into sustained long-term reverse remodeling effects after discontinuation of the causative HF therapy? (3) If so, what validated predictors do we have? The goal of developing a molecular/cellular profile to predict responders to LVAD support as a bridge to recovery in patients with HF will be important and complementary to clinical parameters to help identify and target this patient population. Our insights into different system levels of mechanisms by LVAD support are increasing and suggest a complex regulatory system of overlapping biological processes. In the framework of systems biology, we believe that to develop novel decision-making strategies and patient selection criteria, HF and reverse cardiac remodeling will be conceptualized and explored by a multifaceted research strategy of transcriptomics, metabolomics, proteomics, molecular biology, and bioinformatics. Knowledge of the molecular mechanisms of reverse cardiac remodeling is in its early stages, and comprehensive reconstruction of the underlying networks is necessary. We have the unique potential of organizing truly bidirectional bedsideto-bench research to achieve this goal.30
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REFERENCES 1. Roger VL, Go AS, Lloyd-Jones DM, et al. Heart disease and stroke statistics–2012 update: a report from the American Heart Association. Circulation 2012;125:e2–220. 2. Deng MC, Ardehali A, Shemin R, et al. Relative roles of heart transplantations and long term mechanical circulatory support in contemporary management
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of advanced heart failure–a critical appraisal ten years after REMATCH. Eur J Cardiothorac Surg 2011;40:781–2. Reinlib L, Abraham W, Working Group of the National, Heart, Lung, and Blood Institute. Recovery from heart failure with circulatory assist: a working group of the National, Heart, Lung, and Blood Institute. J Card Fail 2003;9:459–63. Everett AD, Tufro-McReddie A, Fisher A, et al. Angiotensin receptor regulates cardiac hypertrophy and transforming growth factor-beta 1 expression. Hypertension 1994;23:587–92. Pieske B. Reverse remodeling in heart failure–fact or fiction? Eur Heart J 2004;6(Suppl D):D66. Rose AG, Park SJ. Pathology in patients with ventricular assist devices: a study of 21 autopsies, 24 ventricular apical core biopsies and 24 explanted hearts. Cardiovasc Pathol 2005;14:19–23. Klotz S, Jan Danser AH, Burkhoff D. Impact of left ventricular assist device (LVAD) support on the cardiac reverse remodeling process. Prog Biophys Mol Biol 2008;97:479–96. Ambardekar AV, Buttrick PM. Reverse remodeling with left ventricular assist devices: a review of clinical, cellular, and molecular effects. Circ Heart Fail 2011;4:224–33. Drakos SG, Kfoury AG, Selzman CH, et al. Left ventricular assist device unloading effects on myocardial structure and function: current status of the field and call for action. Curr Opin Cardiol 2011;26:245–55. Birks EJ, Hall JL, Barton PJ, et al. Gene profiling changes in cytoskeletal proteins during clinical recovery after left ventricular-assist device support. Circulation 2005;112(Suppl 9):I57–64. Plenz G, Baba HA, Erren M, et al. Reversal of myocardial interleukin-6-mRNA expression following longterm left ventricular assist device support for myocarditis-associated low output syndrome [letter]. J Heart Lung Transplant 1999;18:923–4. Kucuker SA, Stetson SJ, Becker KA, et al. Evidence of improved right ventricular structure after LVAD support in patients with end-stage cardiomyopathy. J Heart Lung Transplant 2004;23(1):28–35. Baba HA, Schmid C, August C, et al. Reversal of metallothionein expression of the human myocardium after prolonged left ventricular mechanical support. J Heart Lung Transplant 2000;19:668–74. Mueller J, Wallukat G, Weng YG, et al. Weaning from mechanical cardiac support in patients with idiopathic dilated cardiomyopathy. Circulation 1997;96:542–9. Reiss N, El-Banayosy A, Arusoglu L, et al. Acute fulminant myocarditis in children and adolescents: the role of mechanical circulatory assist. ASAIO J 2006;52:211–4. Slaughter MS, Bostic R, Tong K, et al. Temporal changes in hospital costs for left ventricular assist device implantation. J Card Surg 2011;26:535–41.
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Nsair et al 17. Ogletree-Hughes ML, Stull LB, Sweet WE, et al. Mechanical unloading restores beta-adrenergic responsiveness and reverses receptor downregulation in the failing human heart. Circulation 2001;104:881–6. 18. Heerdt PM, Schlame M, Jehle R, et al. Disease-specific remodeling of cardiac mitochondria after a left ventricular assist device. Ann Thorac Surg 2002; 73:1216–21. 19. Rodrigue-Way A, Burkhoff D, Geesaman BJ, et al. Sarcomeric genes involved in reverse remodeling of the heart during left ventricular assist device support. J Heart Lung Transplant 2005;24:73–80. 20. Margulies KB, Matiwala S, Cornejo C, et al. Mixed messages: transcription patterns in failing and recovering human myocardium. Circ Res 2005;96:592–9. 21. Hall JL, Birks EJ, Grindle S, et al. Molecular signature of recovery following combination left ventricular assist device (LVAD) support and pharmacologic therapy. Eur Heart J 2007;28:613–27. 22. Baba HA, Stypmann J, Grabellus F, et al. Dynamic regulation of MEK/Erks and Akt/GSK-3beta in human end-stage heart failure after left ventricular mechanical support: myocardial mechanotransduction-sensitivity as a possible molecular mechanism. Cardiovasc Res 2003;59:390–9. 23. Flesch M, Margulies KB, Mochmann HC, et al. Differential regulation of mitogen-activated protein kinases in the failing human heart in response to mechanical unloading. Circulation 2001;104:2273–6.
24. Chien KR. Genomic circuits and the integrative biology of cardiac diseases. Nature 2000;407: 227–32. 25. Lee SH, Doliba N, Osbakken M, et al. Improvement of myocardial mitochondrial function after hemodynamic support with left ventricular assist devices in patients with heart failure. J Thorac Cardiovasc Surg 1998;116:344–9. 26. Mital S, Loke KE, Addonizio LJ, et al. Left ventricular assist device implantation augments nitric oxide dependent control of mitochondrial respiration in failing human hearts. J Am Coll Cardiol 2000;36: 1897–902. 27. Agnetti G, Kaludercic N, Kane LA, et al. Modulation of mitochondrial proteome and improved mitochondrial function by biventricular pacing of dyssynchronous failing hearts. Circ Cardiovasc Genet 2010;3: 78–87. 28. Kassiotis C, Ballal K, Wellnitz K, et al. Markers of autophagy are downregulated in failing human heart after mechanical unloading. Circulation 2009;120: S191–7. 29. Wohlschlaeger J, Sixt SU, Stoeppler T, et al. Ventricular unloading is associated with increased 20s proteasome protein expression in the myocardium. J Heart Lung Transplant 2010;29:125–32. 30. Weiss JN, Karma A, MacLellan WR, et al. “Good enough solutions” and the genetics of complex diseases. Circ Res 2012;111:493–504.
KEY POINTS
INTRODUCTION The number of patients with heart failure (HF) is increasing. In 2010, 6.6 million US adults 18 years of age or older (2.8%) had HF. In 2008, 1 in 9 death certificates (281,437 deaths) in the United States mentioned HF. It is estimated that by 2030, an additional 3 million people will have HF, a 25.0% increase in prevalence from 2010. HF contributes to more than 250,000 deaths a year, results in 2.4 to 3.5 million hospitalizations a year, 12 million to 15 million outpatient office visits a year, and total costs estimated at 39.2 billion dollars a year.1 The prevalence of advanced HF (AdHF), constituting between 1% and 10% of the population
with HF, is estimated to total between 30,000 and 300,000 patients in the United States. From a regional HF care perspective, for example, in the Greater Los Angeles area with a population of more than 10,000,000, the prevalence of HF is estimated at more than 100,000 people, and those with AdHF at more than 10,000 people. AdHF carries a prognosis similar to cancer. Over the past decade, mechanical circulatory support device (MCSD) therapy has been beneficial as a bridge to cardiac transplantation, and anecdotal evidence suggests that patients with HF with mechanical assist devices experience direct cardiac benefits. Moreover, recent trials on
The authors have nothing to disclose. University of California, Ahmanson-UCLA Cardiomyopathy Center, 100 Medical Plaza, Suite 630, Los Angeles, CA 90095, USA * Corresponding author. E-mail address: [email protected] Heart Failure Clin 10 (2014) S57–S62 http://dx.doi.org/10.1016/j.hfc.2013.08.007 1551-7136/14/$ – see front matter Ó 2014 Elsevier Inc. All rights reserved.
heartfailure.theclinics.com
The goal of developing a molecular/cellular profile to predict responders to left ventricular assist device (LVAD) support as a bridge to recovery in patients with heart failure (HF) will be important and complementary to clinical parameters to help identify and target this patient population. Our insights into different system levels of mechanisms by LVAD support are increasing and suggest a complex regulatory system of overlapping biological processes. To develop novel decision-making strategies and patient selection criteria, HF and reverse cardiac remodeling will be conceptualized and explored by a multifaceted research strategy of transcriptomics, metabolomics, proteomics, molecular biology, and bioinformatics. Knowledge of the molecular mechanisms of reverse cardiac remodeling is in its early stages, and comprehensive reconstruction of the underlying networks is necessary.
S58
Nsair et al limited numbers and subpopulations of patients (notably REMATCH [Randomized Evaluation of Mechanical Assistance for the Treatment of Congestive Heart Failure]) support earlier observations of improved cardiac function and point toward the use of assist devices as destination therapy. Therefore, the role of long-term MCSD is increasing and gaining importance relative to heart transplantation.2 To investigate mechanisms of myocardial recovery during long-term MCSD, the National Heart, Lung, and Blood Institute convened the working group Recovery from Heart Failure with Circulatory Assist. The team included cardiac surgeons, cardiologists, and experts in experimental research. The goal was to prioritize recommendations to guide future programs in: (1) elucidating the mechanisms leading to reverse remodeling associated with a left ventricular assist device (LVAD); (2) exploring advanced treatments, including novel pharmacologies, tissue engineering, and cell therapies, to optimize recovery with LVAD therapy; and (3) identifying target genes, proteins, and cellular pathways to focus on production of novel therapies for myocardial recovery and cardiovascular disease. The working group also made research and clinical recommendations to translate findings into improved therapeutic strategies and device design: (1) support collaborations among clinical and basic scientists with an emphasis on clinical/translational research, which might lead to clinical trials; (2) identify candidate patients most likely to benefit from LVAD as a destination therapy; (3) explore potential biomarkers indicating when patients could most successfully be weaned from devices; and (4) promote clinical and experimental study of mechanically assisted organs and the tissue derived from them.3 In this review, the data that have accrued over the past decade on molecular mechanisms of recovery during mechanical circulatory support are summarized and evaluated.
STAGED HF INTERVENTIONS ASSOCIATED WITH MULTILEVEL REVERSE REMODELING Lifestyle changes such as moderate endurance training and continuous positive airway pressure therapy in patients with HF with sleep apnea induce reverse remodeling. Therapies aimed at neurohormonal blockade, also termed neurohormonal modulation therapy, such as angiotensinconverting enzyme (ACE) inhibitors, b-blockers, and aldosterone antagonists improve organ level markers for reverse remodeling, including ejection fraction, ventricular volumes, and mass. For b-blockers, reverse molecular remodeling was also shown in biopsy specimens on the cellular
and subcellular level. Aldosterone has a central role in promoting cardiac fibrosis which may be partially independent of angiotensin II, because it has also been shown in animal models, humans, and isolated cardiac fibroblasts exposed to aldosterone.4 Hence, an aldosterone antagonist may be antifibrotic. Cardiac resynchronization therapy improves exercise capacity and quality of life in patients with ventricular dyssynchrony and is associated with geometric and functional reverse remodeling over time. Surgical approaches for reverse remodeling, such as mitral valve replacement, aneurysmectomy, and volume reduction have been developed, but may also be associated with high perioperative mortality. More recent methods under exploration include percutaneous approaches to ventricular partitioning of dysfunctional segments. Mechanical unloading of the failing ventricles by LVADs induces well-characterized reverse remodeling on the cellular and subcellular level. Whether this reverse remodeling translates into sustained organ recovery and patient survival remains to be shown.5 This article focuses on the systematic review of molecular evidence of reverse remodeling related to the key domains of heart functions (ie, structural maintenance, systemic neuroimmunoendocrine regulation, muscle mechanics [contraction/relaxation], electrophysiology, perfusion, and energy metabolism).
REVERSE REMODELING OF STRUCTURAL BIOLOGY Several histology studies analyzing the morphology and size of cardiomyocytes in patients with HF supported by LVAD described a strong decrease of cell volume, cell profile area, and cell length. These effects in HF were more profound in the most distorted areas and strongly correlated with the duration of LVAD support. Mechanical unloading of the ventricle has also shown a reversal of cardiomyocyte damage by reduction of necrosis, contraction bands, and myocytolysis. LVAD support also induces normalization of cardiac sarcomeric proteins, vinculin, desmin, and tubulin. Whether and to what extent interstitial connective tissue deposits can be reversed after LVAD support is still a matter of dispute, with several contradicting reports to date.6–9 The Harefield group reported a seminal experience using clenbuterol. A total of 15 patients with nonischemic cardiomyopathy who required LVAD implantation were studied; 6 recovered sufficiently to allow explantation of the device compared with 9 who did not recover and required transplantation. Left ventricular myocardial samples were
Molecular Basis of Recovering on MCSD collected at implantation and explantation/transplantation. Affymetrix microarray analysis was performed on the paired samples and analyzed with reference to sarcomeric and nonsarcomeric cytoskeletal proteins. In the recovery group, of the nonsarcomeric proteins, lamin A/C increased 1.5-fold and spectrin 1.6-fold between the times of implantation and explantation. Integrins b1, b6, and a7 decreased 1.7-fold, 2.4-fold, and 1.5-fold, respectively, but integrins a5 and b5 increased 2.3-fold and 1.2-fold at explantation. The following sarcomeric proteins changed in the recovered group only: b-actin increased 1.4-fold; a-tropomyosin, 1.3-fold; a1-actinin, 1.8-fold; and a-filamin A, 1.6fold. Both troponin T3 and a2-actinin decreased by 1.6-fold at the time of explantation. Vinculin decreased 1.7-fold in the recovered group but increased by 1.7-fold in the nonrecovered group. Vinculin protein levels decreased 4.1-fold in the recovered group. The investigators concluded that myocardial recovery using clenbuterol was associated with a specific pattern of changes in sarcomeric, nonsarcomeric, and membraneassociated proteins, which could have important implications in understanding the mechanisms involved.10
REVERSE REMODELING OF NEUROIMMUNOENDOCRINE BIOLOGY Proinflammatory Cytokine Pathways Proinflammatory cytokine cascades such as tumor necrosis factor and interleukin 6 (IL-6) have been implicated in the progression of HF. Individual case reports show (1) the existence of an intracardiac IL-6 and IL-6 receptor system, (2) a dynamic regulation of this system in myocarditisassociated low-output syndrome, (3) the temporal association of increased plasma levels of IL-6 with myocardial gene expression and left ventricular dysfunction, and (4) synchronicity of improvement of left ventricular function with reversal of plasma levels and myocardial IL-6 mRNA expression, the cause of which might have been LVAD unloading, resolution of myocarditis, or both. These data support the concept of a pathophysiologic role of IL-6 in myocarditis and advanced HF, potentially based on its intrinsic negative inotropic or hypertrophogenic properties.11 The proinflammatory cytokine tumor necrosis factor a (TNF-a) stimulates cardiac growth and ventricular remodeling and is not present in the heart under normal conditions. However, cardiac expression of TNF-a is upregulated during both ischemia-reperfusion injury and HF progression. This upregulation can be reversed during long-term ventricular unloading by LVAD implantation.7 Chronic left ventricular
unloading with either pulsatile or continuous-flow devices decreases right ventricular total collagen and myocardial TNF-a content, suggesting that the decreased fibrosis and normalization of cytokine milieu observed may contribute to the recovery of right-sided cardiac function associated with chronic mechanical circulatory support.12 Certain heat shock proteins such as heme oxygenase and metallothioneins are also upregulated during HF progression and by certain stress stimuli, such as ischemia-reperfusion injury. After LVAD treatment, increased expression of several heat shock proteins returned to normal values.9,13 Cell death by apoptosis, which strongly contributes to HF progression, is also attenuated by LVAD support, although not all study results have been consistent, because some of the data showed increased apoptosis. The transcription factor nuclear factor kb (NF-kb) may play an important role as a key factor in the progression of HF and subsequently in reverse ventricular remodeling. NF-kb is a crucial regulator of genes that are involved in the cellular response to stressful stimuli and specifically regulates genes involved in apoptosis such as Bcl-2 protein family members (eg, Bcl-2, BclxL, and Bax). Several studies have observed that the antiapoptotic protein Bcl-xL is upregulated after mechanical unloading with LVAD support. The susceptibility of human cardiomyocytes to apoptosis during HF may be diminished by the activation of Bcl-xL.7–9 Cardiac dysfunction can be substantially reversed by MCSD in selected patients with end-stage idiopathic dilated cardiomyopathy. The degree of preoperative myocardial fibrosis may be an indicator for outcome. Anti-b1adrenoceptor autoantibodies can be used to monitor myocyte recovery.14 The group of the world’s largest MCSD program, the Heart Center in Bad Oeynhausen, Germany, have reported on children and adolescents in fulminant myocarditis undergoing prolonged circulatory support with different assist devices. Between 1994 and 2004, of 7 children and adolescents (aged 7–18 years, mean age 13.5 years) who were treated with ventricular assist devices (VADs), 4 patients (3 LVADs, 1 biventricular assist device) could be successfully bridged to heart transplantation after a mean support time of 163 days (56–258 days). Atrial and brain natriuretic peptides reached normal values after recovery of myocardial function.15 At Advocate Christ Medical Center in Oak Lawn, Illinois, 6 patients with advanced HF and severe mitral regurgitation underwent successful bridge to recovery using a Thoratec LVAD. Normalization of clinical data collected during the recovery phase including chest roentgenogram, echocardiography, plasma norepinephrine, TNF-a, bioimpedance,
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Nsair et al and cardiopulmonary exercise testing (peak oxygen consumption), including a 10% increase in peak oxygen consumption before weaning.16
REVERSE REMODELING OF CONTRACTION/ RELAXATION, ELECTROPHYSIOLOGY, AND PERFUSION BIOLOGY Unloading of the heart by LVAD support leads to contraction strength enhancement in conjunction with an improved contraction and relaxation timing.7 This improved strength generation is correlated to a higher calcium (Ca21) content in the sarcoplasmic reticulum, thereby improving cardiac contractility. Altered regulation and density of L-type Ca21 channels, calcium cycling genes, and the Ca21 adenosine triphosphatase (ATPase) subtype 2a (SERCA 2a) and the sarcolemmal Na1-Ca21 exchanger are also normalized by mechanical unloading of the failing heart.8 In contrast, levels of the Ca21 regulatory proteins phospholamban and ryanodine receptors showed inconsistent results. b-Adrenergic receptor density and response to stimulation can be restored during LVAD support, most likely mediated by intracellular rather than hemodynamic factors.17 Other important key players in maintaining arterial blood pressure and volume homeostasis are cardiac natriuretic peptide (ANP) and B-type natriuretic peptides (BNP). Both act through guanylcyclaseA signaling, initiating antihypertrophic and antifibrotic effects. Reverse remodeling of the failing heart by LVAD support led to restoration of the impaired response of guanylcyclase-A signaling to ANP, whereas cardiac hypertrophy did not completely reverse.7–9 Expression of the sarcoplasmic endoreticular Ca21-ATPase subtype 2a, the ryanodine receptor, and the sarcolemmal Na1-Ca21 exchanger are upregulated after LVAD support. Genes known to be involved in myocardial hypertrophy and cardiovascular signaling are downregulated in reverse remodeling by LVAD.18,19 Some studies did not show a normalized gene expression during mechanical unloading and are contradictory. Transcript changes did not clearly respond to LVAD support, which opens the possibility that several molecular changes that occur during HF are an epiphenomenon or represent nonspecific responses of the myocardium.20 It is also possible that the observed changes in messenger RNA localization, efficiency of translation, and posttranslational modifications are more important for the regulation of myocardial structure and function rather than left ventricular remodeling per se. Microarray gene-chip platforms have been used to detect transcription changes of HF hearts in response to LVAD support.21 Reverse
cardiac remodeling by LVAD support may be mediated by specific regulation of certain kinases in patients with HF. The activation of Akt and GSK-3b in patients with HF is downregulated after LVAD support.22 In addition, it was reported that Erk is downregulated by mechanical unloading, whereas JNK signal transduction showed no change.23 Contradictory to previous reports, this study also observed a change of P38 by mechanical unloading.7–9 The transmission of hypertrophic and survival signals in the cardiomyocyte is partly also mediated by receptor tyrosine kinases (RTKs). Neuregulins are a family of growth-promoting proteins characterized as ligands of RTKs of the ErB family. Conditional inactivation of ErB family RTKs in ventricular muscle cells leads to severe dilated cardiomyopathy. Furthermore, the interactions of neuregulin growth factors with 2 other RTKs, Her2/neu and Her4, promote cell survival and inhibit apoptosis in cardiac myocytes. Unloading of the heart resulted in an upregulation of Her2/ neu and Her4, particularly in patients with ischemic cardiomyopathy. Glycoprotein 130, which also plays an important role in RTK signal transduction, as well as IL-6 family signal transduction,11 was decreased after LVAD implantation.24
REVERSE REMODELING OF ENERGY METABOLISM Progression of HF is associated with extremely low respiratory control indexes (RCIs) as depicted by state 3/state 4 and state 3/state 2. Using reduced nicotinamide adenine dinucleotide– dependent substrates (ie, pyruvate/malate and glutamate), RCIs are significantly improved after LVAD support, suggesting an important role of the device in benefiting oxidative phosphorylation and electron transport.25 Chronic LVAD support potentiates endogenous nitric oxide (NO)-mediated regulation of mitochondrial respiration as measured by improved MVO2 consumption, which can be abrogated by NO synthase inhibition.26 Both failing and LVAD supported hearts showed a reduction in cardiolipin content, whereas reverse remodeling by LVAD results in an improved composition of the lipid.18 Because the mitochondrial proteome is significantly modulated after cardiac resynchronization therapy in failing porcine hearts, as indicated by 31 altered mitochondrial proteins,27 it is reasonable to hypothesize that the pathologic proteomic mitochondrial phenotype is reversible in the failing heart, which may be an important underlying mechanism in reverse ventricular remodeling. The 20S proteasome activity is increased by mechanical unloading.28 The
Molecular Basis of Recovering on MCSD ubiquitin-proteasome system is depressed during HF, a disadvantageous event reversed by ventricular unloading, and may play a significant role in ventricular hypertrophy and HF as well as in reverse cardiac remodeling.29
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SUMMARY Although all established evidence-based therapies for HF have been shown to have a reverse remodeling effect on both the clinical and the molecular level (moderate endurance training, continuous positive airway pressure therapy, ACE inhibitors, b-blockers, cardiac resynchronization, mitral valve replacement, aneurysmectomy, left ventricular volume reduction, mechanical unloading of the failing ventricles by LVAD), the challenges to be addressed include the following: (1) how consistently do reverse remodeling changes on the molecular level translate into clinical reverse remodeling effects and benefits? (2) Do acute reverse remodeling changes during ongoing HF interventions translate into sustained long-term reverse remodeling effects after discontinuation of the causative HF therapy? (3) If so, what validated predictors do we have? The goal of developing a molecular/cellular profile to predict responders to LVAD support as a bridge to recovery in patients with HF will be important and complementary to clinical parameters to help identify and target this patient population. Our insights into different system levels of mechanisms by LVAD support are increasing and suggest a complex regulatory system of overlapping biological processes. In the framework of systems biology, we believe that to develop novel decision-making strategies and patient selection criteria, HF and reverse cardiac remodeling will be conceptualized and explored by a multifaceted research strategy of transcriptomics, metabolomics, proteomics, molecular biology, and bioinformatics. Knowledge of the molecular mechanisms of reverse cardiac remodeling is in its early stages, and comprehensive reconstruction of the underlying networks is necessary. We have the unique potential of organizing truly bidirectional bedsideto-bench research to achieve this goal.30
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