Beyond Weight Loss: the Emerging Role of Incretin-Based Treatments in Cardiometabolic HFpEF

PURPOSE OF REVIEW

Incretin-based drugs are potent weight-lowering agents, emerging as potential breakthrough therapy for the treatment of obesity-related phenotype of heart failure with preserved ejection fraction (HFpEF). In this review article, we will discuss the contribution of weight loss as part of the benefits of incretin-based medications in obese patients with HFpEF. Furthermore, we will describe the potential effects of glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) receptor agonists on the heart, particularly in relation to HFpEF pathophysiology.

RECENT FINDINGS

In the STEP-HFpEF trial, the GLP-1 receptor agonist semaglutide significantly improved quality of life outcomes in obese HFpEF patients. Whether the beneficial effects of semaglutide in obese patients with HFpEF are merely a consequence of body weight reduction is unclear. Considering the availability of other weight loss strategies (e.g., caloric restriction, exercise training, bariatric surgery) to be used in obese HFpEF patients, answering this question is crucial to provide tailored therapeutic options in these subjects.

SUMMARY

Incretin-based drugs may represent a milestone in the treatment of obesity in HFpEF. Elucidating the contribution of weight loss in the overall benefit observed with these drugs is critical in the management of obese HFpEF patients, considering that other weight-lowering strategies are available and might represent potential alternative options for these patients.

A roadmap for therapeutic discovery in pulmonary hypertension associated with left heart failure. A scientific statement of the Heart Failure Association (HFA) of the ESC and the ESC Working Group on Pulmonary Circulation & Right Ventricular Function

Pulmonary hypertension (PH) associated with left heart failure (LHF) (PH-LHF) is one of the most common causes of PH. It directly contributes to symptoms and reduced functional capacity and negatively affects right heart function, ultimately leading to a poor prognosis. There are no specific treatments for PH-LHF, despite the high number of drugs tested so far. This scientific document addresses the main knowledge gaps in PH-LHF with emphasis on pathophysiology and clinical trials. Key identified issues include better understanding of the role of pulmonary venous versus arteriolar remodelling, multidimensional phenotyping to recognize patient subgroups positioned to respond to different therapies, and conduct of rigorous pre-clinical studies combining small and large animal models. Advancements in these areas are expected to better inform the design of clinical trials and extend treatment options beyond those effective in pulmonary arterial hypertension. Enrichment strategies, endpoint assessments, and thorough haemodynamic studies, both at rest and during exercise, are proposed to play primary roles to optimize early-stage development of candidate therapies for PH-LHF.

Impairment of the adrenergic reserve associated with exercise intolerance in a murine model of heart failure with preserved ejection fraction

AIM

Exercise intolerance is the central symptom in patients with heart failure with preserved ejection fraction. In the present study, we investigated the adrenergic reserve both in vivo and in cardiomyocytes of a murine cardiometabolic HFpEF model.

METHODS

12-week-old male C57BL/6J mice were fed regular chow (control) or a high-fat diet and L-NAME (HFpEF) for 15 weeks. At 27 weeks, we performed (stress) echocardiography and exercise testing and measured the adrenergic reserve and its modulation by nitric oxide and reactive oxygen species in left ventricular cardiomyocytes.

RESULTS

HFpEF mice (preserved left ventricular ejection fraction, increased E/e', pulmonary congestion [wet lung weight/TL]) exhibited reduced exercise capacity and a reduction of stroke volume and cardiac output with adrenergic stress. In ventricular cardiomyocytes isolated from HFpEF mice, sarcomere shortening had a higher amplitude and faster relaxation compared to control animals. Increased shortening was caused by a shift of myofilament calcium sensitivity. With addition of isoproterenol, there were no differences in sarcomere function between HFpEF and control mice. This resulted in a reduced inotropic and lusitropic reserve in HFpEF cardiomyocytes. Preincubation with inhibitors of nitric oxide synthases or glutathione partially restored the adrenergic reserve in cardiomyocytes in HFpEF.

CONCLUSION

In this murine HFpEF model, the cardiac output reserve on adrenergic stimulation is impaired. In ventricular cardiomyocytes, we found a congruent loss of the adrenergic inotropic and lusitropic reserve. This was caused by increased contractility and faster relaxation at rest, partially mediated by nitro-oxidative signaling.

Mitophagy modulation for the treatment of cardiovascular diseases

BACKGROUND

Defects of mitophagy, the selective form of autophagy for mitochondria, are commonly observed in several cardiovascular diseases and represent the main cause of mitochondrial dysfunction. For this reason, mitophagy has emerged as a novel and potential therapeutic target.

METHODS

In this review, we discuss current evidence about the biological significance of mitophagy in relevant preclinical models of cardiac and vascular diseases, such as heart failure, ischemia/reperfusion injury, metabolic cardiomyopathy and atherosclerosis.

RESULTS

Multiple studies have shown that cardiac and vascular mitophagy is an adaptive mechanism in response to stress, contributing to cardiovascular homeostasis. Mitophagy defects lead to cell death, ultimately impairing cardiac and vascular function, whereas restoration of mitophagy by specific compounds delays disease progression.

CONCLUSIONS

Despite previous efforts, the molecular mechanisms underlying mitophagy activation in response to stress are not fully characterized. A comprehensive understanding of different forms of mitophagy active in the cardiovascular system is extremely important for the development of new drugs targeting this process. Human studies evaluating mitophagy abnormalities in patients at high cardiovascular risk also represent a future challenge.

Impaired T cell IRE1α/XBP1 signaling directs inflammation in experimental heart failure with preserved ejection fraction

Heart failure with preserved ejection fraction (HFpEF) is a widespread syndrome with limited therapeutic options and poorly understood immune pathophysiology. Using a 2-hit preclinical model of cardiometabolic HFpEF that induces obesity and hypertension, we found that cardiac T cell infiltration and lymphoid expansion occurred concomitantly with cardiac pathology and that diastolic dysfunction, cardiomyocyte hypertrophy, and cardiac phospholamban phosphorylation were T cell dependent. Heart-infiltrating T cells were not restricted to cardiac antigens and were uniquely characterized by impaired activation of the inositol-requiring enzyme 1α/X-box-binding protein 1 (IRE1α/XBP1) arm of the unfolded protein response. Notably, selective ablation of XBP1 in T cells enhanced their persistence in the heart and lymphoid organs of mice with preclinical HFpEF. Furthermore, T cell IRE1α/XBP1 activation was restored after withdrawal of the 2 comorbidities inducing HFpEF, resulting in partial improvement of cardiac pathology. Our results demonstrated that diastolic dysfunction and cardiomyocyte hypertrophy in preclinical HFpEF were T cell dependent and that reversible dysregulation of the T cell IRE1α/XBP1 axis was a T cell signature of HFpEF.

Immune-mediated denervation of the pineal gland underlies sleep disturbance in cardiac disease

Disruption of the physiologic sleep-wake cycle and low melatonin levels frequently accompany cardiac disease, yet the underlying mechanism has remained enigmatic. Immunostaining of sympathetic axons in optically cleared pineal glands from humans and mice with cardiac disease revealed their substantial denervation compared with controls. Spatial, single-cell, nuclear, and bulk RNA sequencing traced this defect back to the superior cervical ganglia (SCG), which responded to cardiac disease with accumulation of inflammatory macrophages, fibrosis, and the selective loss of pineal gland-innervating neurons. Depletion of macrophages in the SCG prevented disease-associated denervation of the pineal gland and restored physiological melatonin secretion. Our data identify the mechanism by which diurnal rhythmicity in cardiac disease is disturbed and suggest a target for therapeutic intervention.

The Lure of Cardiac Metabolism in the Diagnosis, Prevention, and Treatment of Heart Failure

Energy substrate metabolism and contractile function are tightly coupled in the heart. Within this framework, heart failure may be viewed as a state of impaired energy transfer. The metabolic changes in the failing heart are linked to functional and structural changes. A worthwhile goal is to measure metabolic flux and its regulation quantitatively, and to do this in a manner that leads to targeted interventions. For several good reasons, this goal has been elusive until now. The development of new analytical and imaging techniques offers the potential of exploring the landscape of metabolic changes across the different stages of heart failure. In this Review Topic of the Month, we focus on concepts and brevity to provide a strategic overview of cardiac metabolism in the diagnosis, prevention, and treatment of nonischemic heart failure.

Cardiac metabolism in HFpEF: from fuel to signalling

Heart failure (HF) is marked by distinctive changes in myocardial uptake and utilization of energy substrates. Among the different types of HF, HF with preserved ejection fraction (HFpEF) is a highly prevalent, complex, and heterogeneous condition for which metabolic derangements seem to dictate disease progression. Changes in intermediate metabolism in cardiometabolic HFpEF-among the most prevalent forms of HFpEF-have a large impact both on energy provision and on a number of signalling pathways in the heart. This dual, metabolic vs. signalling, role is played in particular by long-chain fatty acids (LCFAs) and short-chain carbon sources [namely, short-chain fatty acids (SCFAs) and ketone bodies (KBs)]. LCFAs are key fuels for the heart, but their excess can be harmful, as in the case of toxic accumulation of lipid by-products (i.e. lipotoxicity). SCFAs and KBs have been proposed as a potential major, alternative source of energy in HFpEF. At the same time, both LCFAs and short-chain carbon sources are substrate for protein post-translational modifications and other forms of direct and indirect signalling of pivotal importance in HFpEF pathogenesis. An in-depth molecular understanding of the biological functions of energy substrates and their signalling role will be instrumental in the development of novel therapeutic approaches to HFpEF. Here, we summarize the current evidence on changes in energy metabolism in HFpEF, discuss the signalling role of intermediate metabolites through, at least in part, their fate as substrates for post-translational modifications, and highlight clinical and translational challenges around metabolic therapy in HFpEF.

Molecular mechanisms underlying the beneficial effects of exercise and dietary interventions in the prevention of cardiometabolic diseases

Cardiometabolic diseases still represent a major cause of mortality worldwide. In addition to pharmacological approaches, lifestyle interventions can also be adopted for the prevention of these morbid conditions. Lifestyle changes include exercise and dietary restriction protocols, such as calorie restriction and intermittent fasting, which were shown to delay cardiovascular ageing and elicit health-promoting effects in preclinical models of cardiometabolic diseases. Beneficial effects are mediated by the restoration of multiple molecular mechanisms in heart and vessels that are compromised by metabolic stress. Exercise and dietary restriction rescue mitochondrial dysfunction, oxidative stress and inflammation. They also improve autophagy. The result of these effects is a marked improvement of vascular and heart function. In this review, we provide a comprehensive overview of the molecular mechanisms involved in the beneficial effects of exercise and dietary restriction in models of diabetes and obesity. We also discuss clinical studies and gap in animal-to-human translation.

High-Resolution Transthoracic Echocardiography Accurately Detects Pulmonary Arterial Pressure and Decreased Right Ventricular Contractility in a Mouse Model of Pulmonary Fibrosis and Secondary Pulmonary Hypertension

Background To date, assessment of right ventricular (RV) function in mice has relied extensively on invasive measurements. Echocardiographic advances have allowed adaptation of measures used in humans for serial, noninvasive RV functional assessment in mice. We evaluated the diagnostic performance of tricuspid annular plane systolic excursion (TAPSE), RV peak systolic myocardial velocity (s'), RV myocardial performance index (MPI), and RV fractional area change (FAC) in a mouse model of pulmonary hypertension. Methods and Results Echocardiography was performed on mice at baseline and 3 weeks after induction of pulmonary hypertension using inhaled bleomycin or saline, including adapted measures of TAPSE, s', MPI, and FAC. RV systolic pressure was measured by invasive catheterization, and RV contractility was measured as the peak slope of the RV systolic pressure recording (maximum change pressure/change time). Postmortem morphological assessment of RV hypertrophy was performed. RV systolic pressure was elevated and maximum change pressure/change time was reduced in bleomycin versus control (n=8; P=0.002). Compared with controls, bleomycin mice had reduced TAPSE (0.79±0.05 versus 1.06±0.04 mm; P=0.003), s' (21.3±1.2 versus 29.2±1.3 mm/s; P<0.001), and FAC (20.3±0.7% versus 31.0±1.3%; P<0.001), whereas MPI was increased (0.51±0.03 versus 0.37±0.01; P=0.006). All measures correlated with RV systolic pressure and maximum change pressure/change time. Intraobserver and interobserver variability were minimal. Receiver operating characteristic curves demonstrated that TAPSE (<0.84 mm), s'(<23.3 mm/s), MPI (0.42), and FAC (<23.3%) identified maximum change pressure/change time ≤2100 mm Hg/s with high accuracy. Conclusions TAPSE, s', MPI, and FAC are measurable consistently using high-resolution echocardiography in mice, and are sensitive and specific measures of pulmonary pressure and RV function. This validation opens the opportunity for serial noninvasive measures in mouse models of pulmonary hypertension, enhancing the statistical power of preclinical studies of novel therapeutics.

Nitro-oxidative stress impairs single cardiomyocyte adrenergic reserve in a murine model of HFpEF

Background

Exercise intolerance is the central symptom of patients with heart failure and preserved ejection fraction (HFpEF). Underlying reduced cardiac functional reserve in response to adrenergic stimuli (stress testing) has been suggested but the molecular mechanisms are insufficiently understood. In cardiomyocytes, nitric oxide (NO) modifies contractility and is required to achieve a full adrenergic response. Recently, dysregulation of NO release has been described to contribute to HFpEF. In a murine model of HFpEF, we investigated cardiomyocyte's adrenergic functional reserve and the role of NO in cardiomyocyte contractility, calcium handling and adrenergic reserve.

Methods

Firstly, the effects of NO on sarcomere shortening and calcium handling (Fura-2) were studied in isolated, adult ventricular cardiomyocytes (AMVMs) from 8–10 weeks old, male C57BL/6J mice. Secondly, male C57BL/6J mice (12w) were fed regular CHOW (Sham) or a high fat diet (D12492, Research Diet) and L-NAME (1g/l, via the drinking water) for 15 weeks to induce HFpEF. At week 27, mice underwent echocardiography and exercise testing (treadmill). In AMVMs isolated from HFpEF and Sham mice, we quantified sarcomere shortening, calcium handling (Fura-2), release of NO (CuFL2) and reactive oxygen species (DCF) before and after the addition of isoproterenol (ISO, 1μM), in the absence and presence (40 min preincubation) of an inhibitor of inducible NO Synthase (1400W) or a denitrosylating agent (glutathione).

Results

In AMVMs, addition of the NO donor SNAP (10μM) increased calcium transient amplitude and accelerated relaxation time. Inhibition of NO synthesis with L-NAME (100μM) impaired adrenergic response upon exposure to ISO. HFpEF mice (evident by diastolic dysfunction (e/e' ratio) and lung edema (wet lung weight / TL)) exhibited significantly reduced exercise capacity (running distance). In AMVMs isolated from HFpEF mice, NO and ROS release were increased at baseline, associated with an increased sarcomere shortening amplitude and faster relaxation and calcium removal as compared to Sham. Strikingly, after the addition of ISO, the adrenergic functional reserve (cellular inotropy and lusitropy) was significantly lower in HFpEF vs. Sham AMVMs. Preincubation with the iNOS inhibitor 1400W or glutathione restored adrenergic inotropic and lusitropic reserve in HFpEF AMVMs.

Conclusion

In HFpEF, adrenergic reserve is impaired on a single cardiomyocyte level. This is at least partially related to an increase in NO release. Pharmacologic inhibition of iNOS improved adrenergic reserve in HFpEF.

Funding Acknowledgement

Type of funding sources: Public grant(s) – National budget only. Main funding source(s): DFG

Abstract P3016: Role Of AMPK/Sirtuin3 Signaling In HFpEF-associated Atrial Myopathy

Background: Patients with heart failure with preserved ejection fraction (HFpEF) are uniquely predisposed to atrial fibrillation (AF), which significantly worsens clinical outcomes. Pathological atrial remodeling, i.e. atrial myopathy, usually precedes clinical AF and is deemed to be an underlying cause of AF. However, little is known about its molecular features, and no effective treatments have been identified.

Method: Wild type C57Bl6 mice were fed a high fat diet (HFD) and received L-NAME via drinking water (5-8 weeks). Atrial morphology and function were assessed by echocardiography. AF was induced by transesophageal pacing.

Results: We discovered that HFpEF mice manifest prominent sinoatrial node (SAN) dysfunction and are highly susceptible to pacing-induced AF, suggesting that this is an ideal model for studying HFpEF-associated atrial changes. Our findings revealed that atrial hypertrophy, contractile dysfunction, and conduction abnormalities are key features of HFpEF-associated atrial myopathy. Interestingly, we did not observe significant atrial fibrosis in this model, a prominent feature of other AF models. Importantly, we discovered impaired AMPK/Sirt3 signaling in the atria of HFpEF mice, and similar atrial defects were observed in mice with cardiomyocyte-specific loss of sirtuin3 (Sirt3) or AMPK, indicating a critical role of AMPK/Sirt3 signaling in HFpEF-associated atrial myopathy. Lastly, we found that metformin, a widely used clinical AMPK agonist, significantly attenuated AF inducibility and SAN dysfunction in HFpEF mice.

Conclusion: Our “two-hit” HFpEF model successfully recapitulates HFpEF-associated atrial phenotypes. Using this model, we unveiled molecular features of a distinct atrial myopathy. We identified a critical role of AMPK/Sirt3 signaling in HFpEF-associated atrial remodeling and demonstrated the therapeutic effect of metformin. As next steps, confirming this benefit in a clinical trial is warranted.

Long COVID and the cardiovascular system - elucidating causes and cellular mechanisms in order to develop targeted diagnostic and therapeutic strategies: A joint Scientific Statement of the ESC Working Groups on Cellular Biology of the Heart and Myocardial & Pericardial Diseases

Long COVID has become a world-wide, non-communicable epidemic, caused by long-lasting multi-organ symptoms that endure for weeks or months after SARS-CoV-2 infection has already subsided. This scientific document aims to provide insight into the possible causes and therapeutic options available for the cardiovascular manifestations of long COVID. In addition to chronic fatigue, which is a common symptom of long COVID, patients may present with chest pain, ECG abnormalities, postural orthostatic tachycardia, or newly developed supraventricular or ventricular arrhythmias. Imaging of the heart and vessels has provided evidence of chronic, post-infectious peri-myocarditis with consequent left or right ventricular failure, arterial wall inflammation or micro-thrombosis in certain patient populations. Better understanding of the underlying cellular and molecular mechanisms of long COVID will aid in the development of effective treatment strategies for its cardiovascular manifestations. A number of mechanisms have been proposed, including those involving direct effects on the myocardium, micro-thrombotic damage to vessels or endothelium, or persistent inflammation. Unfortunately, existing circulating biomarkers, coagulation and inflammatory markers, are not highly predictive for either the presence or outcome of long COVID when measured 3 months after SARS-CoV-2 infection. Further studies are needed to understand underlying mechanisms, identify specific biomarkers and guide future preventive strategies or treatments to address long COVID and its cardiovascular sequelae.

Immunometabolic Mechanisms of Heart Failure with Preserved Ejection Fraction

Heart failure with preserved ejection fraction (HFpEF) is increasing in prevalence worldwide, already accounting for at least half of all heart failure (HF). As most patients with HFpEF are obese with metabolic syndrome, metabolic stress has been implicated in syndrome pathogenesis. Recently, compelling evidence for bidirectional crosstalk between metabolic stress and chronic inflammation has emerged, and alterations in systemic and cardiac immune responses are held to participate in HFpEF pathophysiology. Indeed, based on both preclinical and clinical evidence, comorbidity-driven systemic inflammation, coupled with metabolic stress, have been implicated together in HFpEF pathogenesis. As metabolic alterations impact immune function(s) in HFpEF, major changes in immune cell metabolism are also recognized in HFpEF and in HFpEF-predisposing conditions. Both arms of immunity - innate and adaptive - are implicated in the cardiomyocyte response in HFpEF. Indeed, we submit that crosstalk among adipose tissue, the immune system, and the heart represents a critical component of HFpEF pathobiology. Here, we review recent evidence in support of immunometabolic mechanisms as drivers of HFpEF pathogenesis, discuss pivotal biological mechanisms underlying the syndrome, and highlight questions requiring additional inquiry.

Small nucleolar RNA SNORD3A: a potential new biomarker and molecular player in heart failure

Background

Despite optimal therapy, heart failure (HF) remains a relentless and deadly disease. Given the relative inaccessibility of myocardial human tissues, identification of circulating biomarkers mirroring myocardial pathological signaling pathways, especially in peripheral blood mononuclear cells (PBMC) is expected to be extremely relevant. Small Nucleolar RNAs (snoRNAs) have been shown to play important roles in various cellular physiological processes. However, the connection between snoRNAs and pathological dysfunction in the heart or peripheral blood mononuclear cells (PBMC) is still poorly understood.

Purpose

To identify novel circulating PBMC biomarkers linked to myocardial dysfunction and HF.

Methods

Myocardial left ventricle (LV) samples and PBMC were obtained from patients affected by ischemic HF (HF, n=13) undergoing heart transplantation and control donors (CD, n=7) and analyzed by RNA sequencing analysis (RNASeq). SNORD3A expression levels in the different groups were evaluated by quantitative real-time PCR. HF was induced in 8-week-old wild type C57BL/6 mice by transverse aortic constriction (TAC). Sham-operated mice (sham) were used as controls. After twelve-week-TAC (12w) or sham operation, mice were anesthetized, cardiac function was analyzed by echocardiography, and cardiac/PBMC samples were collected after sacrifice. In order to test the role of SNORD3A in cardiomyocyte hypoxia, H9C2 cardiomyoblasts were transfected with SNORD3A-targeted antisense oligonucleotides (ASO) and cell survival was analyzed by cleaved caspase-3 and PARP1 immunoblotting.

Results

RnaSeq analysis identified a small set of genes differentially expressed in the heart and PBMC from HF patients. Among these, SNORD3A was up-regulated in cardiac and PBMC samples from HF patients compared to CD (Figure 1A-B). Similarly, in murine HF induced by 12w TAC, SNORD3A levels were increased by rtPCR, both in the heart and PBMC (Figure 1C-D). SNORD3A expression levels were also significantly increased in H9C2 cells exposed to in vitro hypoxia (Figure 1E). Interestingly, H9C2 transfection with SNORD3A-specific ASO significantly reduced hypoxia-induced SNORD3A upregulation and reduced hypoxia-induced cell death (Figure 1F-G).

Conclusions

In this study, we identify SNORD3A as a novel possible biomarker in human HF, similarly up-regulated in the heart and PBMC, induced by hypoxia in vitro and modulating cell survival.

Funding Acknowledgement

Type of funding sources: Public grant(s) – National budget only. Main funding source(s): STAR GRANT Figure 1

Abstract P464: Cardiac Dysfunction In A Mouse Model For Autosomal Dominant Polycystic Kidney Disease

Mutations in polycystin-1 (PC1) cause autosomal dominant polycystic kidney disease (ADPKD), a disorder that manifests with cardiac hypertrophy and dysfunction. We recently showed that cardiomyocyte-specific PC1 KO mice exhibit both systolic and diastolic dysfunction without signs of cardiac hypertrophy. The purpose of this study was to determine the effects of ADPKD-causing PC1 mutations on cardiac function using a mouse model for ADPKD harboring a mutation in PC1 R3277C (RC/RC). We used echocardiography to determine cardiac function and Western blot analysis to explore signaling pathways in WT and RC/RC mice (2-4 months of age).We observed a slight but significant decrease in ejection fraction (77.2±0.7 vs 86.2±2.4 %, N=5, 4, P=0.015) without signs of left ventricular hypertrophy (LV mass 78.4±5.5 vs 93.5±4.2 mg, N=5, 4, P>0.05) in RC/RC compared to WT mice. Western blot analysis from total heart lysates (WT and RC/RC; N=5) revealed no changes in protein levels of hypertrophic markers: beta myosin heavy chain (β-MHC) and regulator of calcineurin 1 (RCAN1). In addition, we studied multiple signaling pathways involved in cardiac hypertrophy by analyzing their phosphorylation status by Western blot (phosphorylated/total protein). We observed no changes in mTOR, S6K1 and S6 phosphorylation. However, a decrease in p-4EBP1 and p-eIF4B was observed in RC/RC compared to WT. Moreover, we observed a significant increase in p-ERK and p-CaMKII. Our data suggest that alterations in PC1 signaling promote cardiac dysfunction but do not promote hypertrophy in young mice (2-4 months of age). Published evidence (PMID: 32730856) suggest that RC/RC hearts become hypertrophic at 6 months of age. However, our data suggest there may be dysfunction prior to cardiac hypertrophy. This warrants further investigation into the more primary role of ADPKD-associated co-morbidities. More studies, with a larger animal cohort, are necessary to unveil the effects of mutant PC1 on cardiac function.

Heart failure with preserved ejection fraction in humans and mice: embracing clinical complexity in mouse models

Heart failure (HF) with preserved ejection fraction (HFpEF) is a multifactorial disease accounting for a large and increasing proportion of all clinical HF presentations. As a clinical syndrome, HFpEF is characterized by typical signs and symptoms of HF, a distinct cardiac phenotype and raised natriuretic peptides. Non-cardiac comorbidities frequently co-exist and contribute to the pathophysiology of HFpEF. To date, no therapy has proven to improve outcomes in HFpEF, with drug development hampered, at least partly, by lack of consensus on appropriate standards for pre-clinical HFpEF models. Recently, two clinical algorithms (HFA-PEFF and H₂FPEF scores) have been developed to improve and standardize the diagnosis of HFpEF. In this review, we evaluate the translational utility of HFpEF mouse models in the context of these HFpEF scores. We systematically recorded evidence of symptoms and signs of HF or clinical HFpEF features and included several cardiac and extra-cardiac parameters as well as age and sex for each HFpEF mouse model. We found that most of the pre-clinical HFpEF models do not meet the HFpEF clinical criteria, although some multifactorial models resemble human HFpEF to a reasonable extent. We therefore conclude that to optimize the translational value of mouse models to human HFpEF, a novel approach for the development of pre-clinical HFpEF models is needed, taking into account the complex HFpEF pathophysiology in humans.

Activation of Autophagic Flux Blunts Cardiac Ischemia/Reperfusion Injury

[Figure: see text].

Impact of chronic kidney disease on platelet aggregation in patients with acute coronary syndrome

AIMS

Chronic kidney disease (CKD) is associated with increased thrombotic events and seems to influence platelet reactivity. Conflicting results have been published on platelet response in CKD patients with stable coronary artery disease. The aim of our study was to investigate the impact of CKD on platelet aggregation in acute coronary syndrome (ACS) patients receiving dual antiplatelet therapy, included the more potent P2Y12 inhibitors.

METHODS

We enrolled 206 patients with ACS, divided in two groups, according to the presence or the absence of moderate/severe CKD. Platelet aggregation was performed with light transmission aggregometry and results are expressed as percentage of maximum platelet aggregation. High residual platelet reactivity (HRPR) was defined as maximum platelet aggregation more than 59%.

RESULTS

Patients with CKD [estimate glomerular filtration rate (eGFR) < 60 ml/min/1.73 m, n = 28] were prevalent older, diabetic, had previous coronary revascularization. In these patients, platelet aggregation was significantly higher than in those with eGFR ≥ 60 ml/min/1.73 m (ADP 10 μmol/l: 28.46 ± 26.19 vs. 16.64 ± 12.79, P < 0.001; ADP 20 μmol/l: 30.07 ± 25.89 vs. 17.46 ± 12.82, P < 0.001). HRPR was observed in 4.4% of patients, with higher prevalence in those with eGFR less than 60 ml/min/1.73 m [21.4 vs. 1.7%, P < 0.001, odds ratio (OR) [95% confidence interval (CI)] = 15.91 (3.71-68.17), P < 0.001]. At multivariate analysis, after correction for baseline confounders, eGFR [adjusted OR (95% CI) = 0.95 (0.91-0.98), P = 0.007], together with the use of clopidogrel [adjusted OR (95% CI) = 23.59 (4.01-138.82), P < 0.001], emerged as determinants of HRPR.

CONCLUSION

In patients with ACS receiving dual antiplatelet therapy, CKD is associated with an increasing ADP-induced platelet aggregation and higher prevalence of HRPR, which is mainly correlated to clopidogrel use.

NAD+ Repletion Reverses Heart Failure With Preserved Ejection Fraction

[Figure: see text].

Cooperative Binding of ETS2 and NFAT Links Erk1/2 and Calcineurin Signaling in the Pathogenesis of Cardiac Hypertrophy

Supplemental Digital Content is available in the text.

Cardiac hypertrophy is an independent risk factor for heart failure, a leading cause of morbidity and mortality globally. The calcineurin/NFAT (nuclear factor of activated T cells) pathway and the MAPK (mitogen-activated protein kinase)/Erk (extracellular signal-regulated kinase) pathway contribute to the pathogenesis of cardiac hypertrophy as an interdependent network of signaling cascades. How these pathways interact remains unclear and few direct targets responsible for the prohypertrophic role of NFAT have been described.

Xbp1s-FoxO1 axis governs lipid accumulation and contractile performance in heart failure with preserved ejection fraction

Heart failure with preserved ejection fraction (HFpEF) is now the dominant form of heart failure and one for which no efficacious therapies exist. Obesity and lipid mishandling greatly contribute to HFpEF. However, molecular mechanism(s) governing metabolic alterations and perturbations in lipid homeostasis in HFpEF are largely unknown. Here, we report that cardiomyocyte steatosis in HFpEF is coupled with increases in the activity of the transcription factor FoxO1 (Forkhead box protein O1). FoxO1 depletion, as well as over-expression of the Xbp1s (spliced form of the X-box-binding protein 1) arm of the UPR (unfolded protein response) in cardiomyocytes each ameliorates the HFpEF phenotype in mice and reduces myocardial lipid accumulation. Mechanistically, forced expression of Xbp1s in cardiomyocytes triggers ubiquitination and proteasomal degradation of FoxO1 which occurs, in large part, through activation of the E3 ubiquitin ligase STUB1 (STIP1 homology and U-box-containing protein 1) a novel and direct transcriptional target of Xbp1s. Our findings uncover the Xbp1s-FoxO1 axis as a pivotal mechanism in the pathogenesis of cardiometabolic HFpEF and unveil previously unrecognized mechanisms whereby the UPR governs metabolic alterations in cardiomyocytes.

Immunoglobulins G modulate endothelial function and affect insulin sensitivity in humans

BACKGROUND AND AIMS

Data from animals suggest that immunoglobulins G (IgG) play a mechanistic role in atherosclerosis and diabetes through endothelial dysfunction and insulin resistance. Patients with common variable immunodeficiency (CVID), who have low circulating levels of IgG and are treated with intravenous polyclonal IgG (IVIgG), may provide an ideal model to clarify whether circulating IgG modulate endothelial function and affect insulin sensitivity in humans.

METHODS AND RESULTS

We studied 24 patients with CVID and 17 matched healthy controls (HC). Endothelial function was evaluated as flow mediated dilation (FMD) of the brachial artery at baseline and 1, 7, 14, and 21 days after IVIgG infusion in the CVID patients. We measured also plasma glucose, insulin, and calculated the HOMA-IR index. We also investigated the role of human IgG on the production of Nitric Oxide (NO) in vitro in Human Coronary Artery Endothelial Cells (HCAEC). Compared to HC, FMD of CVID patients was significantly impaired at baseline (9.4 ± 0.9 and 7.6 ± 0.6% respectively, p < 0.05) but rose above normal levels 1 and 7 days after IVIgG infusion to return at baseline at 14 and 21 days. Serum insulin concentration and HOMA-IR index dropped by 50% in CVID patients after IVIgG (p < 0.002 vs. baseline). In vitro IgG stimulated NO production in HCAEC.

CONCLUSIONS

Reduced IgG levels are associated with endothelial dysfunction and IVIgG stimulates endothelial function directly while improving insulin sensitivity. The current findings may suggest an anti-atherogenic role of human IgG.

Epigenetic Reader BRD4 (Bromodomain-Containing Protein 4) Governs Nucleus-Encoded Mitochondrial Transcriptome to Regulate Cardiac Function

BACKGROUND

BET (bromodomain and extraterminal) epigenetic reader proteins, in particular BRD4 (bromodomain-containing protein 4), have emerged as potential therapeutic targets in a number of pathological conditions, including cancer and cardiovascular disease. Small-molecule BET protein inhibitors such as JQ1 have demonstrated efficacy in reversing cardiac hypertrophy and heart failure in preclinical models. Yet, genetic studies elucidating the biology of BET proteins in the heart have not been conducted to validate pharmacological findings and to unveil potential pharmacological side effects.

METHODS

By engineering a cardiomyocyte-specific BRD4 knockout mouse, we investigated the role of BRD4 in cardiac pathophysiology. We performed functional, transcriptomic, and mitochondrial analyses to evaluate BRD4 function in developing and mature hearts.

RESULTS

Unlike pharmacological inhibition, loss of BRD4 protein triggered progressive declines in myocardial function, culminating in dilated cardiomyopathy. Transcriptome analysis of BRD4 knockout mouse heart tissue identified early and specific disruption of genes essential to mitochondrial energy production and homeostasis. Functional analysis of isolated mitochondria from these hearts confirmed that BRD4 ablation triggered significant changes in mitochondrial electron transport chain protein expression and activity. Computational analysis identified candidate transcription factors participating in the BRD4-regulated transcriptome. In particular, estrogen-related receptor α, a key nuclear receptor in metabolic gene regulation, was enriched in promoters of BRD4-regulated mitochondrial genes.

CONCLUSIONS

In aggregate, we describe a previously unrecognized role for BRD4 in regulating cardiomyocyte mitochondrial homeostasis, observing that its function is indispensable to the maintenance of normal cardiac function.

Left ventricular dysfunction in heart failure with preserved ejection fraction-molecular mechanisms and impact on right ventricular function

The current classification of heart failure (HF) based on left ventricular (LV) ejection fraction (EF) identifies a large group of patients with preserved ejection fraction (HFpEF) with significant morbidity and mortality but without prognostic benefit from current HF therapy. Co-morbidities and conditions such as arterial hypertension, diabetes mellitus, chronic kidney disease, adiposity and aging shape the clinical phenotype and contribute to mortality. LV diastolic dysfunction and LV structural remodeling are hallmarks of HFpEF, and are linked to remodeling of the cardiomyocyte and extracellular matrix. Pulmonary hypertension (PH) and right ventricular dysfunction (RVD) are particularly common in HFpEF, and mortality is up to 10-fold higher in HFpEF patients with vs. without RV dysfunction. Here, we review alterations in cardiomyocyte function (i.e., ion homeostasis, sarcomere function and cellular metabolism) associated with diastolic dysfunction and summarize the main underlying cellular pathways. The contribution and interaction of systemic and regional upstream signaling such as chronic inflammation, neurohumoral activation, and NO-cGMP-related pathways are outlined in detail, and their diagnostic and therapeutic potential is discussed in the context of preclinical and clinical studies. In addition, we summarize prevalence and pathomechanisms of RV dysfunction in the context of HFpEF and discuss mechanisms connecting LV and RV dysfunction in HFpEF. Dissecting the molecular mechanisms of LV and RV dysfunction in HFpEF may provide a basis for an improved classification of HFpEF and for therapeutic approaches tailored to the molecular phenotype.

Metabolic inflammation in heart failure with preserved ejection fraction

One in 10 persons in the world aged 40 years and older will develop the syndrome of HFpEF (heart failure with preserved ejection fraction), the most common form of chronic cardiovascular disease for which no effective therapies are currently available. Metabolic disturbance and inflammatory burden contribute importantly to HFpEF pathogenesis. The interplay within these two biological processes is complex; indeed, it is now becoming clear that the notion of metabolic inflammation-metainflammation-must be considered central to HFpEF pathophysiology. Inflammation and metabolism interact over the course of syndrome progression, and likely impact HFpEF treatment and prevention. Here, we discuss evidence in support of a causal, mechanistic role of metainflammation in shaping HFpEF, proposing a framework in which metabolic comorbidities profoundly impact cardiac metabolism and inflammatory pathways in the syndrome.

FoxO1-Dio2 signaling axis governs cardiomyocyte thyroid hormone metabolism and hypertrophic growth

Forkhead box O (FoxO) proteins and thyroid hormone (TH) have well established roles in cardiovascular morphogenesis and remodeling. However, specific role(s) of individual FoxO family members in stress-induced growth and remodeling of cardiomyocytes remains unknown. Here, we report that FoxO1, but not FoxO3, activity is essential for reciprocal regulation of types II and III iodothyronine deiodinases (Dio2 and Dio3, respectively), key enzymes involved in intracellular TH metabolism. We further show that Dio2 is a direct transcriptional target of FoxO1, and the FoxO1-Dio2 axis governs TH-induced hypertrophic growth of neonatal cardiomyocytes in vitro and in vivo. Utilizing transverse aortic constriction as a model of hemodynamic stress in wild-type and cardiomyocyte-restricted FoxO1 knockout mice, we unveil an essential role for the FoxO1-Dio2 axis in afterload-induced pathological cardiac remodeling and activation of TRα1. These findings demonstrate a previously unrecognized FoxO1-Dio2 signaling axis in stress-induced cardiomyocyte growth and remodeling and intracellular TH homeostasis.

Distinctive patterns of inflammation across the heart failure syndrome

Inflammation has long been known to play a role in heart failure (HF). Earlier studies demonstrated that inflammation contributes to the pathogenesis of HF with reduced ejection fraction (HFrEF), and the knowledge about molecules and cell types specifically involved in inflammatory events has been constantly increased ever since. However, conflicting results of several trials with anti-inflammatory treatments led to the conclusions that inflammation does participate in the progression of HFrEF, but more likely it is not the primary event. Conversely, it has been suggested that inflammation drives the development of HF with preserved ejection fraction (HFpEF). Recently the pharmacological blockade of interleukin-1 has been shown to prevent HF hospitalization and mortality in patients with prior myocardial infarction, lending renewed support to the hypothesis that inflammation is a promising therapeutic target in HF. Inflammation has also been proposed to underlie both HF and commonly associated conditions, such as chronic kidney disease or cancer. Within this last paradigm, an emergent role has been ascribed to clonal hematopoiesis of indeterminate potential. Here, we summarize the recent evidence about the role of inflammation in HF, highlighting the similarities and differences in HFrEF vs. HFpEF, and discuss the diagnostic and therapeutic opportunities raised by antinflammatory-based approaches.

Fibroblast Primary Cilia Are Required for Cardiac Fibrosis

BACKGROUND

The primary cilium is a singular cellular structure that extends from the surface of many cell types and plays crucial roles in vertebrate development, including that of the heart. Whereas ciliated cells have been described in developing heart, a role for primary cilia in adult heart has not been reported. This, coupled with the fact that mutations in genes coding for multiple ciliary proteins underlie polycystic kidney disease, a disorder with numerous cardiovascular manifestations, prompted us to identify cells in adult heart harboring a primary cilium and to determine whether primary cilia play a role in disease-related remodeling.

METHODS

Histological analysis of cardiac tissues from C57BL/6 mouse embryos, neonatal mice, and adult mice was performed to evaluate for primary cilia. Three injury models (apical resection, ischemia/reperfusion, and myocardial infarction) were used to identify the location and cell type of ciliated cells with the use of antibodies specific for cilia (acetylated tubulin, γ-tubulin, polycystin [PC] 1, PC2, and KIF3A), fibroblasts (vimentin, α-smooth muscle actin, and fibroblast-specific protein-1), and cardiomyocytes (α-actinin and troponin I). A similar approach was used to assess for primary cilia in infarcted human myocardial tissue. We studied mice silenced exclusively in myofibroblasts for PC1 and evaluated the role of PC1 in fibrogenesis in adult rat fibroblasts and myofibroblasts.

RESULTS

We identified primary cilia in mouse, rat, and human heart, specifically and exclusively in cardiac fibroblasts. Ciliated fibroblasts are enriched in areas of myocardial injury. Transforming growth factor β-1 signaling and SMAD3 activation were impaired in fibroblasts depleted of the primary cilium. Extracellular matrix protein levels and contractile function were also impaired. In vivo, depletion of PC1 in activated fibroblasts after myocardial infarction impaired the remodeling response.

CONCLUSIONS

Fibroblasts in the neonatal and adult heart harbor a primary cilium. This organelle and its requisite signaling protein, PC1, are required for critical elements of fibrogenesis, including transforming growth factor β-1-SMAD3 activation, production of extracellular matrix proteins, and cell contractility. Together, these findings point to a pivotal role of this organelle, and PC1, in disease-related pathological cardiac remodeling and suggest that some of the cardiovascular manifestations of autosomal dominant polycystic kidney disease derive directly from myocardium-autonomous abnormalities.

Abstract 867: NAD + Repletion Reverses HFpEF by Attenuating Myocardial Metabolic Dysfunction

Background: Heart failure with preserved ejection fraction (HFpEF) is a highly prevalent clinical condition associated with significant morbidity, mortality and health care expenses. Yet, no effective treatment has been identified. We recently demonstrated that concomitant metabolic and hypertensive stress in mice elicited by a combination of high fat diet (HFD) and constitutive nitric oxide synthase inhibition by N [w] -nitro-l-arginine methyl ester (L-NAME) faithfully recapitulates the numerous and myriad features of human HFpEF (paper in press at Nature ).

Methods: Wild type C57Bl6 mice were fed with HFD and L-NAME via drinking water for 5-8 weeks. Myocardial mitochondrial morphology was assessed by electron microscopy. Mitochondrial function was assessed by measuring oxygen consumption rates using an oxygen electrode. Protein expression and modification were assessed by Western blotting and immunoprecipitation.

Results: Using this novel mouse model, we discovered significant impairment of mitochondrial fatty acid oxidation (FAO) associated with hyperacetylation of key FAO enzymes in HFpEF myocardium. Mechanistically, downregulation of Sirtuin3, the major mitochondrial deacetylase, and deficiency of its co-substrate nicotinamide adenine dinucleotide (NAD + ), culminated in mitochondrial protein hyperacetylation. Strikingly, supplementation with nicotinamide riboside (NR), a NAD + precursor, led to dramatic improvement of mitochondrial function, and importantly, amelioration of the HFpEF phenotype.

Conclusion: In summary, we have unveiled that protein hyperacetylation-mediated mitochondrial dysfunction is a crucial mechanism of HFpEF pathogenesis. This is, to our knowledge, the first study identifying a specific signature of metabolic remodeling in HFpEF heart. We also demonstrated the therapeutic effect of NAD + repletion in a preclinical HFpEF model. In next steps, confirming this benefit in a clinical trial is warranted.

Abstract 938: BET Bromodomain Protein 4 (BRD4) Governance of Cardiovascular Disease Stress-related Cardiomyocyte Remodeling

During the past decade, epigenetic control of cardiac remodeling has attracted attention as a major mechanism contributing to heart failure. The BET family of bromodomain proteins (BRD) functions as “readers” of acetylated chromatin. Pharmacological inhibition of BRD proteins prevents cardiac hypertrophy and heart failure in preclinical models, yet mechanistic studies elucidating the biology of BRD proteins in the heart are lacking. Here, we investigated the role(s) of BRD4 in cardiac physiology and pathophysiology. By engineering a cardiomyocyte-specific BRD4 knockout mouse, we discovered that loss of BRD4 triggered progressive decline in ventricular contractile function, culminating in dilated cardiomyopathy in both post-natal and adult hearts. To identify early transcriptomic changes in BRD4-ablated heart, we conducted a global transcriptome analysis in KO hearts prior to the onset of ventricular dysfunction. RNA sequencing analysis of BRD4 KO hearts revealed disruption of genes essential to mitochondrial energy production and homeostasis, as well as key cardiac sarcomeric components. Computational analysis identified key transcription factors involved in BRD4-mediated gene regulation, including MEF2 complex, ERR1, SRF, and Nkx2.5. By studying isolated cardiomyocytes maintained in primary culture, we confirmed that disruption of the candidate TF complexes by BRD4 ablation altered mitochondrial morphology and provoked progressive contractile dysfunction. In aggregate, we describe for the first time a critical role of BRD4 in regulating key cardiomyocyte gene networks, in particular genes involved in mitochondrial homeostasis and contractility, to maintain cardiac function. Moreover, our data suggest that BRD4 is a novel regulator of epigenetic events in dilated cardiomyopathy. Elucidating these novel roles of BRD4 in cardiomyocyte remodeling will provide critical insights into the epigenetic control of stress-related cardiac events with potential clinical relevance.

Abstract 190: Polycystin-1 Assembles With Kv Channels to Govern Cardiomyocyte Repolarization and Contractility

Mutations in the gene encoding polycystin-1 (PC1) underlie autosomal dominant polycystic kidney disease (ADPKD). ADPKD patients present with multiple cardiovascular co-morbidities believed to be caused by renal dysfunction. LV hypertrophy and diastolic dysfunction can manifest during childhood or in young adults prior to a formal diagnosis of hypertension, and evidence suggests that LV function is impaired in ADPKD patients with normal or moderately reduced kidney function. These facts suggest that cardiomyocyte-autonomous effects may contribute to the cardiovascular abnormalities seen in ADPKD. Contractile function (systolic and diastolic) measured by echo was significantly reduced in PC1 cKO ( Pkd1 F/F ;αMHC-Cre) mice compared with controls ( Pkd1 F/F ). PC1 cKO cardiomyocytes manifest impaired contractility and smaller and slower Ca 2+ transients. Using a multidimensional approach, we discovered that cardiomyocytes lacking PC1 have shorter action potentials (APD50/90) and decreased SERCA activity. These alterations impair EC-coupling and decrease SR Ca 2+ loading during pacing. Remarkably, square pulses under voltage clamp (-80 to +10 mV) produced Ca 2+ transients with similar amplitude between genotypes, which highlights that alterations in action potential (AP) duration drive most of the EC-coupling changes. PC1-deficient cardiomyocytes manifested an increase in outward K + currents (I to , I Kslow1/2 and I ss ) but not in inward currents (I K1 ). PC1 over-expression in HEK293T cells reduced the currents of heterologously expressed Kv4.3/2.1/1.5 channels. The inhibitory effects of PC1 on Kv4.3 currents were mediated by PC1-CT (C-terminus) through its coiled-coil domain (CCD). Interestingly, a naturally occurring human mutant PC1 R4228X , located in the CCD, manifested no suppressive effects on Kv4.3 channel. Finally, to begin to test for relevance to human pathology, we found that PC1 ablation reduces AP duration, and PC1-CT over-expression had the opposite effect in human stem cell-derived cardiomyocytes. Our findings uncover a novel role for PC1 controlling action potential duration and SERCA. PC1-deficient cardiomyocytes manifest impaired contractility, likely contributing to contractile dysfunction in ADPKD patients.

Remodeling of substrate consumption in the murine sTAC model of heart failure

BACKGROUND

Energy metabolism and substrate selection are key aspects of correct myocardial mechanical function. Myocardial preference for oxidizable substrates changes in both hypertrophy and in overt failure. Previous work has shown that glucose oxidation is upregulated in overpressure hypertrophy, but its fate in overt failure is less clear. Anaplerotic flux of pyruvate into the tricarboxylic acid cycle (TCA) has been posited as a secondary fate of glycolysis, aside from pyruvate oxidation or lactate production.

METHODS AND RESULTS

A model of heart failure that emulates both valvular and hypertensive heart disease, the severe transaortic constriction (sTAC) mouse, was assayed for changes in substrate preference using metabolomic and carbon-13 flux measurements. Quantitative measures of O₂ consumption in the Langendorff perfused mouse heart were paired with ¹³C isotopomer analysis to assess TCA cycle turnover. Since the heart accommodates oxidation of all physiological energy sources, the utilization of carbohydrates, fatty acids, and ketones were measured simultaneously using a triple-tracer NMR method. The fractional contribution of glucose to acetyl-CoA production was upregulated in heart failure, while other sources were not significantly different. A model that includes both pyruvate carboxylation and anaplerosis through succinyl-CoA produced superior fits to the data compared to a model using only pyruvate carboxylation. In the sTAC heart, anaplerosis through succinyl-CoA is elevated, while pyruvate carboxylation was not. Metabolomic data showed depleted TCA cycle intermediate pool sizes versus the control, in agreement with previous results.

CONCLUSION

In the sTAC heart failure model, the glucose contribution to acetyl-CoA production was significantly higher, with compensatory changes in fatty acid and ketone oxidation not reaching a significant level. Anaplerosis through succinyl-CoA is also upregulated, and is likely used to preserve TCA cycle intermediate pool sizes. The triple tracer method used here is new, and can be used to assess sources of acetyl-CoA production in any oxidative tissue.

Polycystin-1 Assembles With Kv Channels to Govern Cardiomyocyte Repolarization and Contractility

BACKGROUND

Polycystin-1 (PC1) is a transmembrane protein originally identified in autosomal dominant polycystic kidney disease where it regulates the calcium-permeant cation channel polycystin-2. Autosomal dominant polycystic kidney disease patients develop renal failure, hypertension, left ventricular hypertrophy, and diastolic dysfunction, among other cardiovascular disorders. These individuals harbor PC1 loss-of-function mutations in their cardiomyocytes, but the functional consequences are unknown. PC1 is ubiquitously expressed, and its experimental ablation in cardiomyocyte-specific knockout mice reduces contractile function. Here, we set out to determine the pathophysiological role of PC1 in cardiomyocytes.

METHODS

Wild-type and cardiomyocyte-specific PC1 knockout mice were analyzed by echocardiography. Excitation-contraction coupling was assessed in isolated cardiomyocytes and human embryonic stem cell-derived cardiomyocytes, and functional consequences were explored in heterologous expression systems. Protein-protein interactions were analyzed biochemically and by means of ab initio calculations.

RESULTS

PC1 ablation reduced action potential duration in cardiomyocytes, decreased Ca²⁺ transients, and myocyte contractility. PC1-deficient cardiomyocytes manifested a reduction in sarcoendoplasmic reticulum Ca²⁺ stores attributable to a reduced action potential duration and sarcoendoplasmic reticulum Ca²⁺ ATPase (SERCA) activity. An increase in outward K⁺ currents decreased action potential duration in cardiomyocytes lacking PC1. Overexpression of full-length PC1 in HEK293 cells significantly reduced the current density of heterologously expressed Kv4.3, Kv1.5 and Kv2.1 potassium channels. PC1 C terminus inhibited Kv4.3 currents to the same degree as full-length PC1. Additionally, PC1 coimmunoprecipitated with Kv4.3, and a modeled PC1 C-terminal structure suggested the existence of 2 docking sites for PC1 within the N terminus of Kv4.3, supporting a physical interaction. Finally, a naturally occurring human mutant PC1^R4228X manifested no suppressive effects on Kv4.3 channel activity.

CONCLUSIONS

Our findings uncover a role for PC1 in regulating multiple Kv channels, governing membrane repolarization and alterations in SERCA activity that reduce cardiomyocyte contractility.

Survival and Cardiovascular Outcomes of Patients With Secondary Mitral Regurgitation: A Systematic Review and Meta-analysis

Importance

The outcomes of patients with left ventricular (LV) dysfunction and secondary mitral regurgitation (SMR) are still controversial.

Objective

To clarify the role of SMR in the outcomes of patients with ischemic or idiopathic cardiomyopathies.

Data Sources

MEDLINE, ISI Web of Science, and Scopus databases were searched for studies published up to March 2017.

Study Selection

Studies reporting data on outcomes in patients with SMR were included. Duplicate publication data, studies lacking data on SMR grade and its correlation with outcomes, mixed data on SMR and primary mitral regurgitation, studies not clearly reporting the outcome of interest, and studies with fewer than 100 patients were excluded. Of the initial 3820 articles identified, 1.4% were finally included.

Data Extraction and Synthesis

The study met PRISMA requirements. Two of us independently screened articles for fulfillment of inclusion criteria.

Main Outcomes and Measures

The primary outcome, set after data collection, was the incidence of all-cause mortality in patients with and without SMR. Secondary outcomes included hospitalization for heart failure (HF), cardiac mortality, and a composite end point of death, HF hospitalization, and cardiac transplant.

Results

Fifty-three studies and 45 900 patients were included in the meta-analysis. The mean (SD) length of follow-up was 40.8 (22.2) months. In 26 of 36 studies reporting LV function by SMR grade, increasing SMR severity was associated with worse LV function. When SMR was categorized as present or absent, all-cause mortality was significantly higher in the patients with SMR (17 studies, 26 359 patients; risk ratio [RR],1.79; 95% CI, 1.47-2.18; P < .001, I2 = 85%); when SMR was qualitatively graded, the incidence of all-cause mortality was significantly increased in patients having any degree of SMR compared with patients not having SMR (21 studies, 21 081 patients; RR, 1.96; 95% CI, 1.67-2.31; P < .001, I2 = 74%). Finally, when SMR was quantitatively graded, it remained associated with an increased all-cause mortality rate (9 studies, 3649 patients; RR, 1.97; 95% CI, 1.71-2.27; P < .001, I2 = 0%). Moreover, SMR was associated with an increased risk of hospitalization for HF (16 studies, 10 171 patients; RR, 2.26; 95% CI, 1.92-2.67; P < .001, I2 = 41%), cardiac mortality (12 studies, 11 896 patients; RR, 2.62; 95% CI, 1.87-3.69; P < .001, I2 = 74%), and death, HF, and transplant (11 studies, 8256 patients; RR, 1.63; 95% CI, 1.33-1.99; P < .001, I2 = 78%).

Conclusions and Relevance

To our knowledge, this study is the first meta-analysis to date to demonstrate that SMR, even when mild, correlates with adverse outcomes in patients with ischemic or idiopathic cardiomyopathies. Because SMR is an intrinsic consequence of LV dysfunction, causality between SMR and mortality should not be implied.

Nitrosative stress drives heart failure with preserved ejection fraction

Heart failure with preserved ejection fraction (HFpEF) is a common syndrome with high morbidity and mortality for which there are no evidence-based therapies. Here we report that concomitant metabolic and hypertensive stress in mice-elicited by a combination of high-fat diet and inhibition of constitutive nitric oxide synthase using Nω-nitro-L-arginine methyl ester (L-NAME)-recapitulates the numerous systemic and cardiovascular features of HFpEF in humans. Expression of one of the unfolded protein response effectors, the spliced form of X-box-binding protein 1 (XBP1s), was reduced in the myocardium of our rodent model and in humans with HFpEF. Mechanistically, the decrease in XBP1s resulted from increased activity of inducible nitric oxide synthase (iNOS) and S-nitrosylation of the endonuclease inositol-requiring protein 1α (IRE1α), culminating in defective XBP1 splicing. Pharmacological or genetic suppression of iNOS, or cardiomyocyte-restricted overexpression of XBP1s, each ameliorated the HFpEF phenotype. We report that iNOS-driven dysregulation of the IRE1α-XBP1 pathway is a crucial mechanism of cardiomyocyte dysfunction in HFpEF.