Afterload Stress Research Articles

Dissecting contributions of pulmonary arterial remodeling to right ventricular afterload in pulmonary hypertension.

Pulmonary hypertension (PH) is defined as an elevation in the right ventricle (RV) afterload, characterized by increased hemodynamic pressure in the main pulmonary artery (PA). Elevations in RV afterload increase RV wall stress, resulting in RV remodeling and potentially RV failure. From a biomechanical standpoint, the primary drivers for RV afterload elevations include increases in pulmonary vascular resistance (PVR) in the distal vasculature and decreases in vessel compliance in the proximal PA. However, the individual contributions of the various vascular remodeling events toward the progression of PA pressure elevations and altered vascular hemodynamics remain elusive. In this study, we used a subject-specific one-dimensional (1D) fluid-structure interaction (FSI) model to investigate the alteration of pulmonary hemodynamics in PH and to quantify the contributions of vascular stiffening and increased resistance towards increased main pulmonary artery (MPA) pressure. We used a combination of subject-specific hemodynamic measurements, ex-vivo mechanical testing of arterial tissue specimens, and ex-vivo X-ray micro-tomography imaging to develop the 1D-FSI model and dissect the contribution of PA remodeling events towards alterations in the MPA pressure waveform. Both the amplitude and pulsatility of the MPA pressure waveform were analyzed. Our results indicated that increased distal resistance has the greatest effect on the increase in maximum MPA pressure, while increased stiffness caused significant elevations in the characteristic impedance. The method presented in this study will serve as an essential step toward understanding the complex interplay between PA remodeling events that leads to the most severe adverse effect on RV dysfunction.

Abstract Tu110: CD36-Mediated Transendothelial Fatty Acid Transport Determines Cardiomyocyte Uptake and is Critical to Limiting a Lipotoxic Ceramide Profile and Supporting Cardiac Function during Pathological Stress.

The heart primarily relies on long chain fatty acid oxidation (LCFA) to meet ATP demand. CD36, is a transmembrane glycoprotein transferase for LCFA uptake widely expressed in several cell types including endothelial cells (ECs), cardiomyocytes (CMs), skeletal myocytes, adipocytes, and monocyte/macrophages. Notably, genetic deficiency of CD36 in humans is associated with hypertrophic cardiomyopathy. The role of CD36 in transendothelial LCFA delivery to CMs under physiologic vs pathologic conditions is unknown. We explored consequences of EC-specific CD36 deletion (EC-CD36 KO mice) on the cardiac response to pressure overload. Lack of EC-CD36 increased severity of left ventricular hypertrophy (LVH), and systolic and diastolic dysfunction at 8 weeks of pressure overload via transverse aortic constriction (TAC), with increases in HW:TL ratio, LV mass by echo, reduced EF (p<0.05), and elevated E/E’ in EC-CD36-KO vs. flox/flox littermate controls (f/f) (p<0.5) (Fig 1). Dynamic mode 13 C NMR revealed delayed 13 C LCFA uptake kinetics (time constant, τ) in CMs of isolated, sham and TAC EC-CD36 KO hearts provided 13 C palmitate + 13 C oleate (0.02 mM each) + 10 mM glucose + 1 mM lactate (Fig 2). 13 C LCFA esterification into triglyceride (TG) was also reduced in EC-CD36-KO vs f/f controls, but without evidence for an additional effect of TAC. The contribution of 13 C LCFA to acetyl CoA entry into oxidation via the TCA cycle, was reduced by lack of EC-CD36 in sham and TAC hearts (p<0.0001) (Fig 2). Consistent with diminished LCFA oxidation, phosphocreatine (PCr) to ATP ratio was also compromised in EC-CD36-KO-TAC hearts (p<0.05). Lack of EC-CD36 during TAC increased 13 C LCFA trafficking to lipotoxic C16 ceramide in EC-CD36 KO hearts (Fig 3). CD36 in ECs is critical to LCFA delivery to CMs during pathological stress on the heart. The imbalance in intramyocellular LCFA dynamics due to restricted transendothelial delivery of LCFA to CMs increased lipotoxic ceramide formation. Thus, EC CD36 is critical to the adaptive cardiac response to pathological stress, and the absence of EC CD36-dependent delivery of LCFA to CMs exacerbates reduced energy potential, adverse cardiac remodeling, and dysfunction during afterload stress.

Acute Effect in Mechanical Efficiency by Pressure-Volume Loop Analysis after Transcatheter Aortic Valve Implantation.

This study aimed to evaluate the immediate effect of transcatheter aortic valve implantation (TAVI) on mechanical efficiency. A total of 46 patients (25 females) with an average age of 83 ± 6.4 years underwent TAVI using the CoreValve system. During the same hospitalization, we conducted a comprehensive comparison of the patients before and after TAVI without inotropic support using echocardiography. The parameters encompassed left ventricular (LV) geometry, valvular load, global LV afterload and ventricular hemodynamics. The analysis using pressure-volume loops enabled the determination of load-independent contractility (Ees) and afterload, in addition to assessing potential energy, stroke work, and mechanical efficiency. The immediate effect was an augmented aortic valve area accompanied by a reduction in the transvalvular pressure gradient. We observed reductions in left ventricular end-systolic volume and end-diastolic volume, and also reductions in global afterload and end-systolic meridional wall stress. The Ea index decreased, while the Ees index remained relatively stable. We noted increases in stroke volume and systemic arterial compliance, indicating more efficient blood transfer from the ventricle to aorta. These changes contributed to the normalization of ventricular-arterial coupling. In terms of mechanical work of the chamber, we observed significant decreases in potential energy, stroke work, and pressure-volume area. There was an increase in the mechanical efficiency of the chamber. The TAVI procedure immediately reduced global afterload and improved diastolic compliance of the chamber, resulting in enhanced ventricular function and mechanical efficiency.

Alterations of pulmonary vascular afterload in exercise‐induced pre‐ and post‐capillary pulmonary hypertension

Exercise imposes increased pulmonary vascular afterload based on rises in pulmonary artery (PA) wedge pressure, declines in PA compliance, and resistance-compliance time. In health, afterload stress stabilizes during steady-state exercise. Our objective was to examine alterations of these exercise-associated stresses in states of pre- and post-capillary pulmonary hypertension (PH). PA hemodynamics were evaluated at rest, 2 and 7min of steady-state exercise at moderate intensity in patients who exhibited Pre-capillary (n=22) and post-capillary PH (n=22). Patients with normal exercise hemodynamics (NOR-HD) (n=32) were also studied. During exercise in all groups, PA wedge pressure increased at 2min, with no further change at 7min. In post-capillary PH and NOR-HD, increases in PA diastolic pressure and diastolic pressure gradient remained stable at 2 and 7min of exercise, while in pre-capillary PH, both continued to increase at 7 min. The behavior of the diastolic pressure gradient was linearly related to the duration of resistance-compliance time at rest (r2 =0.843) and exercise (r2 =0.760). Exercise resistance-compliance time was longer in pre-capillary PH associated with larger increases in diastolic pressure gradient. Conversely, resistance-compliance time was shortest in post-capillary PH compared to pre-capillary PH and NOR-HD and associated with limited increases in exercise diastolic pressure gradient. During steady-state, modest-intensity exercise-specific patterns of pulmonary vascular afterload responses were observed in pre- and post-capillary PH relative to NOR-HD. Longer resistance-compliance time related to greater increases in PA diastolic pressure and diastolic pressure gradients in pre-capillary PH, while shorter resistance-compliance time appeared to limit these increases in post-capillary PH.

Chronic intermittent hypoxia accelerates cardiac dysfunction and cardiac remodeling during cardiac pressure overload in mice and can be alleviated by PHD3 overexpression.

Obstructive sleep apnea (OSA) accelerates the progression of chronic heart failure (CHF). OSA is characterized by chronic intermittent hypoxia (CIH), and CIH exposure accelerates cardiac systolic dysfunction and cardiac remodeling in a cardiac afterload stress mouse model. Mechanistic experiments showed that long-term CIH exposure activated hypoxia-inducible factor 1α (HIF-1α) expression in the mouse heart and upregulated miR-29c expression and that both HIF-1α and miR-29c simultaneously inhibited sarco-/endoplasmic reticulum calcium ATPase 2a (SERCA2a) expression in the mouse heart. Cardiac HIF-1α activation promoted cardiomyocyte hypertrophy. SERCA2a expression was suppressed in mouse heart in middle- and late-stage cardiac afterload stress, and CIH exposure further downregulated SERCA2a expression and accelerated cardiac systolic dysfunction. Prolyl hydroxylases (PHDs) are physiological inhibitors of HIF-1α, and PHD3 is most highly expressed in the heart. Overexpression of PHD3 inhibited CIH-induced HIF-1α activation in the mouse heart while decreasing miR-29c expression, stabilizing the level of SERCA2a. Although PHD3 overexpression did not reduce mortality in mice, it alleviated cardiac systolic dysfunction and cardiac remodeling induced by CIH exposure.

Transinnominate Impella 5.5 insertion as a bridge to transplantation in a pediatric patient in refractory cardiogenic shock.

Transinnominate Impella 5.5 insertion as a bridge to transplantation in a pediatric patient in refractory cardiogenic shock.

Mitochondrial Metabolism in Myocardial Remodeling and Mechanical Unloading: Implications for Ischemic Heart Disease

Ischemic heart disease refers to myocardial degeneration, necrosis, and fibrosis caused by coronary artery disease. It can lead to severe left ventricular dysfunction (LVEF ≤ 35–40%) and is a major cause of heart failure (HF). In each contraction, myocardium is subjected to a variety of mechanical forces, such as stretch, afterload, and shear stress, and these mechanical stresses are clinically associated with myocardial remodeling and, eventually, cardiac outcomes. Mitochondria produce 90% of ATP in the heart and participate in metabolic pathways that regulate the balance of glucose and fatty acid oxidative phosphorylation. However, altered energetics and metabolic reprogramming are proved to aggravate HF development and progression by disturbing substrate utilization. This review briefly summarizes the current insights into the adaptations of cardiomyocytes to mechanical stimuli and underlying mechanisms in ischemic heart disease, with focusing on mitochondrial metabolism. We also discuss how mechanical circulatory support (MCS) alters myocardial energy metabolism and affects the detrimental metabolic adaptations of the dysfunctional myocardium.

The myosin activator omecamtiv mecarbil improves wall stress in a rat model of chronic aortic regurgitation.

In patients with chronic aortic regurgitation (AR), excessive preload and afterload increase left ventricle wall stress, leading to left ventricular systolic dysfunction. Thus, the objective of the present study was to evaluate the effects of the myosin activator omecamtiv mecarbil (OM) on left ventricle wall stress in an experimental rat model of severe chronic AR. Forty adult male Wistar rats were randomized into two experimental groups: induction of AR (acute phase) by retrograde puncture (n = 34) or a sham intervention (n = 6). Rats that survived the acute phase (n = 18) were randomized into an OM group (n = 8) or a placebo group (n = 10). Equal volumes of OM (1.2 mg/kg/h) or placebo (0.9% NaCl) were continuously infused into the femoral vein over 30 min. OM significantly decreased end‐systolic and end‐diastolic and maximum wall stress in this experimental rat model of chronic severe AR (p < 0.001) and increased systolic performance assessed by fractional shortening and left ventricle end‐systolic diameter; both p < 0.05). These effects were correlated with decreased indices of global cardiac function (cardiac output and stroke volume; p < 0.05) but were not inferior to baseline pump indices. Infusion with placebo did not affect global cardiac function but decreased end‐systolic wall stress (p < 0.05) and increased systolic performance (all p < 0.001). In the sham‐operated (control) group, OM decreased diastolic wall stress (p < 0.05). Based on these results, OM had a favorable effect on left ventricle wall stress in an experimental rat model of severe chronic AR.

How to interpret right ventricular remodeling in athletes.

Long‐lasting athletic training induces an overload on the heart that leads to structural, functional, and electrical adaptive changes known as the “athlete's heart.” The amount of this heart remodeling has been traditionally considered balanced between the left and the right heart chambers. However, during intense exercise, the right heart is exposed to a disproportional afterload and wall stress which over a long period of time could lead to more pronounced exercise‐induced changes. Highly trained athletes, especially those involved in endurance sport disciplines, can develop marked right ventricular (RV) remodeling that could raise the suspicion of an underlying RV pathology including arrhythmogenic cardiomyopathy (ACM). The distinction between physiological and pathological RV remodeling is essential as ACM is a common cause of sudden cardiac death in athletes, and high‐intensity exercise training has demonstrated to accelerate its phenotypic expression and worsen its prognosis. The distinction between physiological and pathological RV remodeling is essential since ACM is a common cause of sudden cardiac death in athletes, and high‐intensity exercise training has demonstrated to accelerate the phenotypic expression and worsen the prognosis. This article outlines the physiological adaptation of the RV to acute exercise, the subsequent physiological structural and functional changes induced by athletic training and provides useful tips of how to differentiate between physiological RV remodeling and a cardiomyopathy phenotype.

Abstract 026: Eicosapentaenoic Acid is a Strong Predictor of Risk for Heart Failure in the Multi-ethnic Study of Atherosclerosis

Introduction: In animal models of afterload stress, eicosapentaenoic acid (EPA) prevents interstitial myocardial fibrosis and preserves diastolic dysfunction. Hypothesis: We hypothesized that EPA is similarly protective in humans. Methods: In the Multi-Ethnic Study of Atherosclerosis, we tested for an effect of plasma phospholipid EPA percent of total fatty acids on primary heart failure incidence across heart failure types including, heart failure with reduced ejection fraction (HFrEF; &lt;45% EF), and with preserved ejection fraction (HFpEF) using Cox proportional hazards modeling in 6566 subjects. Results are mean [95% CI]. Results: A total of 6566 subjects had measured baseline EPA, including 1797 black, 794 Chinese, 1444 Hispanic, and 2531 white participants; 52% were female. Over a median follow-up of 13.0 years, 293 heart failure events occurred in subjects with measured EPA: 129 had HFrEF, 110 had HFpEF, and the remaining 54 had unknown ejection fraction status. Mean EPA in HF-free subjects was 0.77% (0.76 - 0.79), and was lower in heart failure subjects 0.70% (0.65 - 0.74), p=0.002. EPA was associated with lower incidence of HF, having a hazard ratio of 0.73 (0.60 - 0.89) per unit change in percentage of total fatty acids, p=0.001. Adjusting for age, sex, race, BMI, smoking, diabetes mellitus, blood pressure, lipids and lipid-lowering drugs, and albuminuria did not change this relationship. Sensitivity analysis showed no dependence on heart failure type. Adjusting for other fatty acids with clustering did not change hazards. In animals, &gt;2.5% EPA is required for prevention of HF, between 2.5% and 1% is marginal, and &lt;1% EPA is insufficient. Most subjects had insufficient EPA levels (n=4794), fewer had marginal levels (n=1471), and fewer still had sufficient levels (n=301). Subjects with sufficient EPA levels were at 0.40 (0.15 - 0.81) fold risk compared to insufficient EPA (p=0.008). Conclusion: High abundance of EPA is robustly associated with reduced risk for heart failure, independent of established risk factors and regardless of ejection fraction status.

Exercise and the right ventricle: a potential Achilles' heel.

Exercise is associated with unequivocal health benefits and results in many structural and functional changes of the myocardium that enhance performance and prevent heart failure. However, intense exercise also presents a significant hemodynamic challenge in which the right-sided heart chambers are exposed to a disproportionate increase in afterload and wall stress that can manifest as myocardial fatigue or even damage if intense exercise is sustained for prolonged periods. This review focuses on the physiological factors that result in a disproportionate load on the right ventricle during exercise and the long-term consequences. The changes in cardiac structure and function that define 'athlete's heart' disproportionately affect the right-sided heart chambers and this can raise important diagnostic overlap with some cardiac pathologies, particularly some inherited cardiomyopathies. The interaction between exercise and arrhythmogenic right ventricular cardiomyopathy (ARVC) will be highlighted as an important example of how hemodynamic stressors can combine with deficiencies in cardiac structural elements to cause cardiac dysfunction predisposing to arrhythmias. The extent to which extreme exercise can cause adverse remodelling in the absence of a genetic predisposition remains controversial. In the athlete with profound changes in heart structure, it can be extremely challenging to determine whether common symptoms such as palpitations may be a marker of more sinister arrhythmias. This review discusses some of the techniques that have recently been proposed to identify pathology in these circumstances. Finally, we will discuss recent evidence defining the role of exercise restriction as a therapeutic intervention in individuals predisposed to arrhythmogenic cardiomyopathy.

Abstract 97: Induction of Hexosamine Biosynthetic Pathway Promotes Cardiac Hypertrophy through Activation of O-GlcNAcylation

Background &amp; significance: Heart failure affects approximately 6 million Americans, with 5-year survival of 50%, which is responsible for a huge burden on the US economy and healthcare system. The relevance and significance of the metabolic alteration to the pathogenesis of pressure overload-induced cardiac hypertrophy and heart failure are largely unknown. The hexosamine biosynthetic pathway (HBP) that is linked to metabolism of glucose, fatty acids and amino acids, has been implicated in the pathophysiology of heart diseases. Methods &amp; results: Thoracic aortic constriction (TAC) was performed to induce heart failure by pressure overload in mice. At the in vitro levels, treatment of phenylephrine (PE, 50 μM) was used to induce cellular hypertrophy in neonatal rat ventricular myocytes (NRVM). Our data revealed that all the enzymes of the HBP were upregulated while induction of hypertrophy at both in vivo and in vitro levels. Consistently, the intermediate product of the HBP was elevated in heart by afterload stress, as measured by metabolomics analyses. In the transgenic mice model for Gfat1, the rate-limiting enzyme of the HBP, we found more profound cardiac hypertrophy and cardiac remodeling in response to pressure overload. The increase of O-GlcNAc was also observed. In addition, the regulation of O-GlcNAcylation by specific targeting of two enzymes of the HBP (1 mM Alloxan, an inhibitor of OGT and 10 μM PUGNAc, an inhibitor of OGA) in NRVM suggested an involvement of the mTOR signaling in the activation of O-GlcNAc levels and the hypertrophy response. Targeting of the HBP by either specific siRNA or Gfat1 inhibitor (Azaserine, 5 μM) led to decrease in cellular hypertrophic response. Conclusions: Together, our data strongly suggest that the HBP participates in cardiac hypertrophic growth and pharmacologic targeting of the HBP may represent a novel approach to ameliorate pathological remodeling.

Low-Level Laser Application in the Early Myocardial Infarction Stage Has No Beneficial Role in Heart Failure.

Low-level laser therapy (LLLT) has been targeted as a promising approach that can mitigate post-infarction cardiac remodeling. There is some interesting evidence showing that the beneficial role of the LLLT could persist long-term even after the end of the application, but it remains to be systematically evaluated. Therefore, the present study aimed to test the hypothesis that LLLT beneficial effects in the early post-infarction cardiac remodeling could remain in overt heart failure even with the disruption of irradiations. Female Wistar rats were subjected to the coronary occlusion to induce myocardial infarction or Sham operation. A single LLLT application was carried out after 60 s and 3 days post-coronary occlusion, respectively. Echocardiography was performed 3 days and at the end of the experiment (5 weeks) to evaluate cardiac function. After the last echocardiographic examination, LV hemodynamic evaluation was performed at baseline and on sudden afterload increases. Compared with the Sham group, infarcted rats showed increased systolic and diastolic internal diameter as well as a depressed shortening fraction of LV. The only benefit of the LLLT was a higher shortening fraction after 3 days of infarction. However, treated-LLLT rats show a lower shortening fraction in the 5th week of study when compared with Sham and non-irradiated rats. A worsening of cardiac function was confirmed in the hemodynamic analysis as evidenced by the higher LV end-diastolic pressure and lower +dP/dt and −dP/dt with five weeks of study. Cardiac functional reserve was also impaired by infarction as evidenced by an attenuated response of stroke work index and cardiac output to a sudden afterload stress, without LLLT repercussions. No significant differences were found in the myocardial expression of Akt1/VEGF pathway. Collectively, these findings illustrate that LLLT improves LV systolic function in the early post-infarction cardiac remodeling. However, this beneficial effect may be dependent on the maintenance of phototherapy. Long-term studies with LLLT application are needed to establish whether these effects ultimately translate into improved cardiac remodeling.

Pharmacologic Treatment with a Melanocortin Analogue Protects Against Pressure‐Overload Induced Cardiac Hypertrophy

PurposeHypertrophic growth of the heart is a consequence of heart ability to adapt to an increased afterload and wall stress. Although left ventricular hypertrophy (LVH) may resolute with adequate therapy, this process increases the amount of irreversible cardiac fibrosis.These morphological and functional changes in the myocardium may manifests as arrhythmias and congestive heart failure (CHF).Melanocortins regulate important physiological functions such as energy balance and blood pressure, but their long‐term effects on cardiac remodeling remain unexplored.In the present study, we investigated whether melanocortins affect physiological or pathologic cardiac growth and function.MethodsFirst, we studied the effects of transgenic melanocortin overexpression (MSH‐OE) on physiological age‐related cardiac growth in mice. Second, we examined the effects of a stable melanocortin analogue (MT‐II) on pressure overload‐ induced cardiac hypertrophy. We subjected 8‐week‐old C57Bl/6N mice to pressure‐overload by transverse aortic constriction (TAC) and randomly assigned the mice to receive daily i.p. injections of either vehicle (physiological saline) or MT‐II (0.3 mg/kg) for 6 weeks starting 2 weeks after surgery.ResultsAt the age of 6 months, MSH‐OE mice (n=11) had lower heart weight and smaller myocytes with maintained cardiac function compared to their age‐matched wild‐type littermates (n=15) while no differences in heart weight were noted at the age of 3‐months, indicating that melanocortin overactivity restrains age‐related cardiac growth. Eight weeks of pressure‐overload induced significant left ventricular (LV) hypertrophy with decreased cardiac function in saline‐treated TAC mice (n=15) compared to sham‐operated control mice (n=9).This pathologic cardiac remodeling was attenuated in MT‐II‐treated TAC mice (n=9) (Figure 1. and 2.). Importantly, MT‐II‐treatment did not compromise cardiac function, but tended to maintain LV contractility of TAC mice. Using quantitative NMR scanning to analyze body composition, we demonstrate that MT‐II treatment also prevented the deterioration of body weight development associated with the hypertrophic disease state.MT‐II treatment attenuated also the expression of genes regulating cardiac remodeling related mRNAs such as NppA, NppB, MMP‐2 and Col1a2.ConclusionsAlthough the underlying mechanisms remain largely unclear, these results, for the first time, establish melanocortin signaling as an antihypertrophic regulator and suggest that melanocortin analogues may be potential therapeutic tools for the treatment of cardiac hypertrophy and heart failure.Support or Funding InformationAcademy of Finland, Finnish Cultural Foundation

Transgenic Over-Expression of Carbonic Anhydrase III in Cardiac Muscle Demonstrates a Mechanism to Resist Acidosis

Carbonic anhydrase III (CAIII) is an abundant protein in skeletal muscle, liver and adipose cells. A cytosolic enzyme that catalyzes conversions between CO2 and HCO3- in regulating intracellular pH, its physiological function in muscle is unclear. Mice lacking CAIII showed lower than wild type intracellular pH in skeletal muscle cells during fatigue treatment. To further understand the role of CAIII in muscle functions and stress adaptation, we developed transgenic mice overexpressing CAIII in the heart under the control of a cloned myosin heavy chain promoter for phenotype comparisons with wild type mouse hearts that are CAIII negative. Three months old transgenic mice showed normal cardiac phenotypes under non-stress conditions. Cardiac function was examined using ex vivo working heart preparations under normal and low pH conditions to investigate CAIII function in pH regulation of cardiac muscle. With equilibration of 5% CO2 generating pH 7.4 in normal Kreb's perfusion buffer, 10% CO2 was used to lower pH to 7.0. Functional data showed that transgenic and wild type hearts had similar pumping functions under normal pH. Perfused with low pH buffer, heart functions of both groups were decreased. In comparison with wild type controls at low pH, CAIII transgenic mouse hearts showed higher left ventricular pressure development and systolic and diastolic velocities under both baseline conditions and increased afterload stress, indicating a better tolerance to acidosis. The results suggest that CAIII may function in compensating for intracellular pH under acidotic conditions, a tractive novel approach to develop new treatment of chronic congestive heart failure.

Identifying early changes in myocardial microstructure in hypertensive heart disease.

The transition from healthy myocardium to hypertensive heart disease is characterized by a series of poorly understood changes in myocardial tissue microstructure. Incremental alterations in the orientation and integrity of myocardial fibers can be assessed using advanced ultrasonic image analysis. We used a modified algorithm to investigate left ventricular myocardial microstructure based on analysis of the reflection intensity at the myocardial-pericardial interface on B-mode echocardiographic images. We evaluated the extent to which the novel algorithm can differentiate between normal myocardium and hypertensive heart disease in humans as well as in a mouse model of afterload resistance. The algorithm significantly differentiated between individuals with uncomplicated essential hypertension (N = 30) and healthy controls (N = 28), even after adjusting for age and sex (P = 0.025). There was a trend in higher relative wall thickness in hypertensive individuals compared to controls (P = 0.08), but no difference between groups in left ventricular mass (P = 0.98) or total wall thickness (P = 0.37). In mice, algorithm measurements (P = 0.026) compared with left ventricular mass (P = 0.053) more clearly differentiated between animal groups that underwent fixed aortic banding, temporary aortic banding, or sham procedure, on echocardiography at 7 weeks after surgery. Based on sonographic signal intensity analysis, a novel imaging algorithm provides an accessible, non-invasive measure that appears to differentiate normal left ventricular microstructure from myocardium exposed to chronic afterload stress. The algorithm may represent a particularly sensitive measure of the myocardial changes that occur early in the course of disease progression.

Abstract 18169: Identifying Early Changes in Myocardial Microstructure via Ultrasound in Hypertensive Heart Disease

BACKGROUND: The transition from healthy myocardium to hypertensive heart disease is characterized by a series of poorly understood changes in myocardial tissue microstructure. Incremental alterations in the orientation and deformation of myocardial fibers can now be assessed using advanced techniques in ultrasonic image analysis. METHODS: We used a modified approach to non-invasively assess left ventricular (LV) myocardial microstructure, based on sonographic signal intensity analysis of the inferolateral pericardium (viewed in the parasternal long-axis view of B-mode echocardiographic images). We defined the transmission intensity (TI), an indirect measure of the intensity reflection coefficient at the myocardial-pericardial interface, as 1 - (P/256) where P is the 25th percentile value of pericardial signal intensity on a 256 scale. We determined the extent to which TI is able to differentiate between normal myocardium and hypertensive heart disease in a mouse model and in humans. RESULTS: As shown in the Figure, 7-week echocardiographic measurements of TI were significantly different between groups of mice that underwent fixed aortic banding (n=3) versus sham procedure (n=3) at baseline. Similarly, measurements of TI were significantly different between individuals with uncomplicated essential hypertension (N=30, age 54±3 yrs, 47% women) and healthy controls (N=28, age 53±9 yrs, 60% women). Although there was a trend in higher relative wall thickness in hypertensive individuals compared to controls (P=0.09), there was no difference between these groups in LV mass (P=0.67) or LV wall thickness (P=0.26). CONCLUSION: Based on sonographic signal intensity analysis, the TI is an accessible, non-invasive measure that appears to differentiate normal LV microstructure from myocardium exposed to chronic afterload stress. The TI may be a particularly sensitive measure of myocardial changes that occur early in the course of disease progression.

PKG Primes the Proteasome

Proteostasis, the precisely orchestrated balance between protein synthesis and degradation, plays a critical role in the maintenance of cell function. This is particularly the case for postmitotic cells such as cardiomyocytes and neurons, which rarely re-enter the cell cycle to divide and hence survive for decades. Disease-related stress can promote dysregulation of proteostasis, leading to accumulation of damaged or misfolded proteins as toxic aggregates capable of triggering cell death.1,2 Indeed, in both dilated cardiomyopathy and ischemic heart disease, perturbations in proteostasis are evidenced by accumulation of polyubiquitinated proteins.3 Additionally, genetic disorders that lead to aggregate formation can trigger cardiomyopathy.4 For example, specific mutations in the coding region of the molecular chaperone αB-crystallin (CryAB) disrupt its chaperone function, leading to a distinctive myofibrillar myopathy characterized by accumulation of toxic aggregates in cardiac myocytes reminiscent of Alzheimer disease or polyglutamine expansion disorders. Article see p 365 Cells can be protected from accumulation of abnormal protein aggregates by either a decrease in their formation or an increase in their clearance. Protein aggregate clearance is accomplished by 2 major catabolic processes: the ubiquitin proteasome pathway (UPP) or the autophagy-lysosomal pathway (Figure 1). Inhibition of either pathway provokes increases in toxic, intracellular aggregates that can promote disease pathogenesis. Figure 1. Damaged or misfolded proteins are targeted primarily for degradation by the ubiquitin proteasomal pathway (UPP). When an excess of these proteins accumulates, they aggregate and are degraded by autophagic pathways. If misfolded proteins continue to accumulate, they can be ultimately sequestered by the cell into ubiquitin-rich cytoplasmic inclusions called aggresomes. Autophagy is a highly conserved catabolic process underlying bulk removal of cytoplasmic proteins and organelles. Autophagy acts as an adaptive response both under conditions of starvation, where recycling of intracellular contents is required to replenish life-sustaining nutrients, and in the setting of …

Altered ubiquitin-proteasome signaling in right ventricular hypertrophy and failure

Alterations in the ubiquitin-proteasome system (UPS) have been described in left ventricular hypertrophy and failure, although results have been inconsistent. The role of the UPS in right ventricular (RV) hypertrophy (RVH) and RV failure (RVF) is unknown. Given the greater percent increase in RV mass associated with RV afterload stress, as present in many congenital heart lesions, we hypothesized that alterations in the UPS could play an important role in RVH/RVF. UPS expression and activity were measured in the RV from mice with RVH/RVF secondary to pulmonary artery constriction (PAC). Epoxomicin and MG132 were used to inhibit the proteasome, and overexpression of the 11S PA28α subunit was used to activate the proteasome. PAC mice developed RVH (109.3% increase in RV weight to body weight), RV dilation with septal shift, RV dysfunction, and clinical RVF. Proteasomal function (26S β₅ chymotrypsin-like activity) was decreased 26% (P < 0.05). Protein expression of 19S subunit Rpt5 (P < 0.05), UCHL1 deubiquitinase (P < 0.0001), and Smurf1 E3 ubiquitin ligase (P < 0.01) were increased, as were polyubiquitinated proteins (P < 0.05) and free-ubiquitins (P = 0.05). Pro-apoptotic Bax was increased (P < 0.0001), whereas anti-apoptotic Bcl-2 decreased (P < 0.05), resulting in a sixfold increase in the Bax/Bcl-2 ratio. Proteasomal inhibition did not accelerate RVF. However, proteasome enhancement by cardiac-specific proteasome overexpression partially improved survival. Proteasome activity is decreased in RVH/RVF, associated with upregulation of key UPS regulators and pro-apoptotic signaling. Enhancement of proteasome function partially attenuates RVF, suggesting that UPS dysfunction contributes to RVF.

Regional Cardiac Dysfunction and Dyssynchrony in a Murine Model of Afterload Stress

Small animal models of afterload stress have contributed much to our present understanding of the progression from hypertension to heart failure. High-sensitivity methods for phenotyping cardiac function in vivo, particular in the setting of compensated cardiac hypertrophy, may add new information regarding alterations in cardiac performance that can occur even during the earliest stages of exposure to pressure overload. We have developed an echocardiographic analytical method, based on speckle-tracking-based strain analyses, and used this tool to rapidly phenotype cardiac changes resulting from afterload stress in a small animal model. Adult mice were subjected to ascending aortic constriction, with and without subsequent reversal of the pressure gradient. In this model of compensated hypertrophic cardiac remodeling, conventional echocardiographic measurements did not detect changes in left ventricular (LV) function at the early time points examined. Strain analyses, however, revealed a decrement in basal longitudinal myofiber shortening that was induced by aortic constriction and improved following relief of the pressure gradient. Furthermore, we observed that pressure overload resulted in LV segmental dyssynchrony that was attenuated with return of the afterload to baseline levels. Herein, we describe the use of echocardiographic strain analyses for cardiac phenotyping in a mouse model of pressure overload. This method provides evidence of dyssynchrony and regional myocardial dysfunction that occurs early with compensatory hypertrophy, and improves following relief of aortic constriction. Importantly, these findings illustrate the utility of a rapid, non-invasive method for characterizing early cardiac dysfunction, not detectable by conventional echocardiography, following afterload stress.