Molecular and structural transition mechanisms in long-term volume overload

Contributions of mechanical loading and hormonal changes to eccentric hypertrophy during volume overload: a Bayesian analysis using logic-based network models

Primary mitral regurgitation (MR) is a pathology that alters mechanical loading on the left ventricle and induces a distinctive ventricular remodeling response known as eccentric hypertrophy. Drug therapies may alleviate symptoms, but only mitral valve repair can provide significant recovery of cardiac function and dimensions. However, 20% of patients still develop systolic dysfunction post-operatively despite being treated according to the current guidelines. Thus, better understanding of the hypertrophic process in the setting of ventricular volume overload (VO) is needed to improve and better personalize the management of MR. To address this knowledge gap, we employ a Bayesian approach to combine data from 70 studies on experimental volume overload in dogs and rats and use it to calibrate a logic-based network model of hypertrophic signaling in myocytes. The calibrated model suggests that growth in experimental VO is mostly driven by the neurohormonal response, with an initial increase in myocardial tissue stretch being compensated by subsequent remodeling fairly early in the time course of VO. This observation contrasts with a common perception that volume-overload hypertrophy is driven primarily by increased myocyte strain. The model suggests that Endothelin1 receptor activity plays a central role in driving hypertrophic responses and the activation of the fetal gene program. The model reproduces a number of responses to drug therapy not used in its calibration, and predicts that a combination of endothelin receptor antagonist and angiotensin receptor blockers would have the greatest potential to dampen cardiomyocyte hypertrophy and dysfunction in VO.

A Need to Preserve Ejection Fraction during Heart Failure

Heart failure (HF) is a significant global healthcare burden with increasing prevalence and high morbidity and mortality rates. The diagnosis and management of HF are closely tied to ejection fraction (EF), a crucial parameter for evaluating disease severity and determining treatment plans. This paper emphasizes the urgent need to maintain EF during heart failure, highlighting the distinct phenotypes of HF with preserved ejection fraction (HFpEF) and HF with reduced ejection fraction (HFrEF). It discusses the complexities of HFrEF pathophysiology and its negative impact on patient outcomes, stressing the importance of ongoing research and the development of effective therapeutic interventions to slow down the progression from preserved to reduced ejection fraction. Additionally, it explores the potential role of renal denervation in preserving ejection fraction and its implications for HFrEF management. This comprehensive review aims to offer valuable insights into the critical role of EF preservation in enhancing outcomes for patients with heart failure.

Abnormal phosphorylation / dephosphorylation and Ca2+ dysfunction in heart failure

Heart failure (HF) can be caused by a variety of causes characterized by abnormal myocardial systole and diastole. Ca2+ current through the L-type calcium channel (LTCC) on the membrane is the initial trigger signal for a cardiac cycle. Declined systole and diastole in HF are associated with dysfunction of myocardial Ca2+ function. This disorder can be correlated with unbalanced levels of phosphorylation / dephosphorylation of LTCC, endoplasmic reticulum (ER), and myofilament. Kinase and phosphatase activity changes along with HF progress, resulting in phased changes in the degree of phosphorylation / dephosphorylation. It is important to realize the phosphorylation / dephosphorylation differences between a normal and a failing heart. This review focuses on phosphorylation / dephosphorylation changes in the progression of HF and summarizes the effects of phosphorylation / dephosphorylation of LTCC, ER function, and myofilament function in normal conditions and HF based on previous experiments and clinical research. Also, we summarize current therapeutic methods based on abnormal phosphorylation / dephosphorylation and clarify potential therapeutic directions.

Association between estimated plasma volume status and acute kidney injury in patients who underwent coronary revascularization: A retrospective cohort study from the MIMIC-IV database

BACKGROUND

Acute kidney injury (AKI) remains a common complication of coronary revascularization and increases poor outcomes in critically ill surgical patients. Compared to the plasma volume status (PVS), estimated plasma volume status (ePVS) has the advantages of being noninvasive and simple and has been shown to be associated with worse prognosis in patients undergoing coronary revascularization. This study was to evaluate the association of ePVS with the risk of AKI in patients who underwent coronary revascularization.

METHODS

In this retrospective cohort study, data of patients who underwent coronary revascularization were extracted from the Medical Information Mart for Intensive Care (MIMIC)-IV database (2008-2019). The outcome was the occurrence of AKI after ICU admission. The covariates were screened via the LASSO regression method. Univariate and multivariate Logistic regression models were performed to assess the association of ePVS and PVS and the odds of AKI in patients who underwent coronary revascularization, with results shown as odds ratios (ORs) and 95% confidence intervals (CIs). Subgroup analyses of age, surgery, and anticoagulation agents and sequential organ failure assessment (SOFA) score were performed to further explore the association of ePVS with AKI.

RESULTS

A total of 3,961 patients who underwent coronary revascularization were included in this study, of whom 2,863 (72.28%) had AKI. The high ePVS was associated with the higher odds of AKI in patients who received coronary revascularization (OR = 1.06, 95%CI: 1.02-1.10), after adjusting for the covariates such as age, race, SAPS-II score, SOFA score, CCI, weight, heart rate, WBC, RDW-CV, PT, BUN, glucose, calcium, PH, PaO2, mechanical ventilation, vasopressors, and diuretic. Similar results were found in patients who underwent the CABG (OR = 1.07, 95%CI: 1.02-1.11), without anticoagulation agents use (OR = 1.07, 95%CI: 1.03-1.12) and with high SOFA score (OR = 1.10, 95%CI: 1.04-1.17). No relationship was found between PVS and the odds of AKI in patients who underwent the coronary revascularization.

CONCLUSION

The ePVS may be a promising parameter to evaluate the risk of AKI in patients undergoing coronary revascularization, which provides a certain reference for the risk stratification management of ICU patients who underwent coronary revascularization.

Cerium oxide nanoparticles-carrying human umbilical cord mesenchymal stem cells counteract oxidative damage and facilitate tendon regeneration

BACKGROUND

Tendon injuries have a high incidence and limited treatment options. Stem cell transplantation is essential for several medical conditions like tendon injuries. However, high local concentrations of reactive oxygen species (ROS) inhibit the activity of transplanted stem cells and hinder tendon repair. Cerium oxide nanoparticles (CeONPs) have emerged as antioxidant agents with reproducible reducibility.

RESULTS

In this study, we synthesized polyethylene glycol-packed CeONPs (PEG-CeONPs), which were loaded into the human umbilical cord mesenchymal stem cells (hUCMSCs) to counteract oxidative damage. H2O2 treatment was performed to evaluate the ROS scavenging ability of PEG-CeONPs in hUCMSCs. A rat model of patellar tendon defect was established to assess the effect of PEG-CeONPs-carrying hUCMSCs in vivo. The results showed that PEG-CeONPs exhibited excellent antioxidant activity both inside and outside the hUCMSCs. PEG-CeONPs protect hUCMSCs from senescence and apoptosis under excessive oxidative stress. Transplantation of hUCMSCs loaded with PEG-CeONPs reduced ROS levels in the tendon injury area and facilitated tendon healing. Mechanistically, NFκB activator tumor necrosis factor α and MAPK activator dehydrocrenatine, reversed the therapeutic effect of PEG-CeONPs in hUCMSCs, indicating that PEG-CeONPs act by inhibiting the NFκB and MAPK signaling pathways.

CONCLUSIONS

The carriage of the metal antioxidant oxidase PEG-CeONPs maintained the ability of hUCMSCs in the injured area, reduced the ROS levels in the microenvironment, and facilitated tendon regeneration. The data presented herein provide a novel therapeutic strategy for tendon healing and new insights into the use of stem cells for disease treatment.

DNA Methylation Analysis Identifies Novel Epigenetic Loci in Dilated Murine Heart upon Exposure to Volume Overload

Left ventricular (LV) dilatation, a prominent risk factor for heart failure (HF), precedes functional deterioration and is used to stratify patients at risk for arrhythmias and cardiac mortality. Aberrant DNA methylation contributes to maladaptive cardiac remodeling and HF progression following pressure overload and ischemic cardiac insults. However, no study has examined cardiac DNA methylation upon exposure to volume overload (VO) despite being relatively common among HF patients. We carried out global methylome analysis of LV harvested at a decompensated HF stage following exposure to VO induced by aortocaval shunt. VO resulted in pathological cardiac remodeling, characterized by massive LV dilatation and contractile dysfunction at 16 weeks after shunt. Although methylated DNA was not markedly altered globally, 25 differentially methylated promoter regions (DMRs) were identified in shunt vs. sham hearts (20 hypermethylated and 5 hypomethylated regions). The validated hypermethylated loci in Junctophilin-2 (Jph2), Signal peptidase complex subunit 3 (Spcs3), Vesicle-associated membrane protein-associated protein B (Vapb), and Inositol polyphosphate multikinase (Ipmk) were associated with the respective downregulated expression and were consistently observed in dilated LV early after shunt at 1 week after shunt, before functional deterioration starts to manifest. These hypermethylated loci were also detected peripherally in the blood of the shunt mice. Altogether, we have identified conserved DMRs that could be novel epigenetic biomarkers in dilated LV upon VO exposure.

Signaling network model of cardiomyocyte morphological changes in familial cardiomyopathy

Familial cardiomyopathy is a precursor of heart failure and sudden cardiac death. Over the past several decades, researchers have discovered numerous gene mutations primarily in sarcomeric and cytoskeletal proteins causing two different disease phenotypes: hypertrophic (HCM) and dilated (DCM) cardiomyopathies. However, molecular mechanisms linking genotype to phenotype remain unclear. Here, we employ a systems approach by integrating experimental findings from preclinical studies (e.g., murine data) into a cohesive signaling network to scrutinize genotype to phenotype mechanisms. We developed an HCM/DCM signaling network model utilizing a logic-based differential equations approach and evaluated model performance in predicting experimental data from four contexts (HCM, DCM, pressure overload, and volume overload). The model has an overall prediction accuracy of 83.8%, with higher accuracy in the HCM context (90%) than DCM (75%). Global sensitivity analysis identifies key signaling reactions, with calcium-mediated myofilament force development and calcium-calmodulin kinase signaling ranking the highest. A structural revision analysis indicates potential missing interactions that primarily control calcium regulatory proteins, increasing model prediction accuracy. Combination pharmacotherapy analysis suggests that downregulation of signaling components such as calcium, titin and its associated proteins, growth factor receptors, ERK1/2, and PI3K-AKT could inhibit myocyte growth in HCM. In experiments with patient-specific iPSC-derived cardiomyocytes (MLP-W4R;MYH7-R723C iPSC-CMs), combined inhibition of ERK1/2 and PI3K-AKT rescued the HCM phenotype, as predicted by the model. In DCM, PI3K-AKT-NFAT downregulation combined with upregulation of Ras/ERK1/2 or titin or Gq protein could ameliorate cardiomyocyte morphology. The model results suggest that HCM mutations that increase active force through elevated calcium sensitivity could increase ERK activity and decrease eccentricity through parallel growth factors, Gq-mediated, and titin pathways. Moreover, the model simulated the influence of existing medications on cardiac growth in HCM and DCM contexts. This HCM/DCM signaling model demonstrates utility in investigating genotype to phenotype mechanisms in familial cardiomyopathy.

Molecular perspectives in hypertrophic heart disease: An epigenetic approach from chromatin modification

Epigenetic changes induced by environmental factors are increasingly relevant in cardiovascular diseases. The most frequent molecular component in cardiac hypertrophy is the reactivation of fetal genes caused by various pathologies, including obesity, arterial hypertension, aortic valve stenosis, and congenital causes. Despite the multiple investigations performed to achieve information about the molecular components of this pathology, its influence on therapeutic strategies is relatively scarce. Recently, new information has been taken about the proteins that modify the expression of fetal genes reactivated in cardiac hypertrophy. These proteins modify the DNA covalently and induce changes in the structure of chromatin. The relationship between histones and DNA has a recognized control in the expression of genes conditioned by the environment and induces epigenetic variations. The epigenetic modifications that regulate pathological cardiac hypertrophy are performed through changes in genomic stability, chromatin architecture, and gene expression. Histone 3 trimethylation at lysine 4, 9, or 27 (H3-K4; -K9; -K27me3) and histone demethylation at lysine 9 and 79 (H3-K9; -K79) are mediators of reprogramming in pathologic hypertrophy. Within the chromatin architecture modifiers, histone demethylases are a group of proteins that have been shown to play an essential role in cardiac cell differentiation and may also be components in the development of cardiac hypertrophy. In the present work, we review the current knowledge about the influence of epigenetic modifications in the expression of genes involved in cardiac hypertrophy and its possible therapeutic approach.

Hemodynamic stress-induced cardiac remodelling is not modulated by ablation of phosphodiesterase 4D interacting protein

Adrenergic stimulation in the heart activates the protein kinase A (PKA), which phosphorylates key proteins involved in intracellular Ca²⁺ handling. PKA is held in proximity to its substrates by protein scaffolds, the A kinase anchoring proteins (AKAPs). We have previously identified the transcript of phosphodiesterase 4D interacting protein (Pde4dip; also known as myomegalin), one of the sarcomeric AKAPs, as being differentially expressed following hemodynamic overload, a condition inducing hyperadrenergic state in the heart. Here, we addressed whether PDE4DIP is involved in the adverse cardiac remodelling following hemodynamic stress. Homozygous Pde4dip knockout (KO) mice, generated by CRISPR-Cas9 technology, and wild-type (WT) littermates were exposed to aortocaval shunt (shunt) or transthoracic aortic constriction (TAC) to induce hemodynamic volume overload (VO) or pressure overload (PO), respectively. The mortality, cardiac structure, function and pathological cardiac remodelling were followed up after hemodynamic injuries. The PDE4DIP protein level was markedly downregulated in volume-overloaded- but upregulated in pressure-overloaded-WT hearts. Following shunt or TAC, mortality rates were comparably increased in both genotypes. Twelve weeks after shunt or TAC, Pde4dip-KO animals showed a similar degree of cardiac hypertrophy, dilatation and dysfunction as WT mice. Cardiomyocyte hypertrophy, myocardial fibrosis, reactivation of cardiac stress genes and downregulation of ATPase, Ca²⁺ transporting, cardiac muscle, slow twitch 2 transcript did not differ between WT and Pde4dip-KO hearts following shunt or TAC. In summary, despite a differential expression of PDE4DIP protein in remodelled WT hearts, Pde4dip deficiency does not modulate adverse cardiac remodelling after hemodynamic VO or PO.

Passive mechanical properties of the left ventricular myocardium and extracellular matrix in hearts with chronic volume overload from mitral regurgitation

Cardiac volume overload from mitral regurgitation (MR) is a trigger for left ventricular dilatation, remodeling, and ultimate failure. While the functional and structural adaptations to this overload are known, the adaptation of myocardial mechanical properties remains unknown. Using a rodent model of MR, in this study, we discern changes in the passive material properties of the intact and decellularized myocardium. Eighty Sprague-Dawley rats (350-400 g) were assigned to two groups: (1) MR (n = 40) and (2) control (n = 40). MR was induced in the beating heart by perforating the mitral leaflet with a 23G needle, and rats were terminated at 2, 10, 20, or 40 weeks (n = 10/time-point). Echocardiography was performed at baseline and termination, and explanted hearts were used for equibiaxial mechanical testing of the intact myocardium and after decellularization. Two weeks after inducing severe MR, the myocardium was more extensible compared to control, however, stiffness and extensibility of the extracellular matrix did not differ from control at this timepoint. By 20 weeks, the myocardium was stiffer with a higher elastic modulus of 1920 ± 246 kPa, and a parallel rise in extracellular matrix stiffness. Despite some matrix stiffening, it only contributed to 31% and 36% of the elastic modulus of the intact tissue in the circumferential and longitudinal directions. At 40 weeks, similar trends of increasing stiffness were observed, but the contribution of extracellular matrix remained relatively low. Chronic MR induces ventricular myocardial stiffening, which seems to be driven by the myocyte compartment of the muscle, and not the extracellular matrix.

Different activation of MAPKs and Akt/GSK3β after preload vs. afterload elevation

Aims

Pressure overload (PO) and volume overload (VO) lead to concentric or eccentric hypertrophy. Previously, we could show that activation of signalling cascades differ in in vivo mouse models. Activation of these signal cascades could either be induced by intrinsic load sensing or neuro‐endocrine substances like catecholamines or the renin‐angiotensin‐aldosterone system.

Methods and results

We therefore analysed the activation of classical cardiac signal pathways [mitogen‐activated protein kinases (MAPKs) (ERK, p38, and JNK) and Akt‐GSK3β] in in vitro of mechanical overload (ejecting heart model, rabbit and human isolated muscle strips). Selective elevation of preload in vitro increased AKT and GSK3β phosphorylation after 15 min in isolated rabbit muscles strips (AKT 49%, GSK3β 26%, P < 0.05) and in mouse ejecting hearts (AKT 51%, GSK49%, P < 0.05), whereas phosphorylation of MAPKs was not influenced by increased preload. Selective elevation of afterload revealed an increase in ERK phosphorylation in the ejecting heart (43%, P < 0.05), but not in AKT, GSK3β, and the other MAPKs. Elevation of preload and afterload in the ejecting heart induced a significant phosphorylation of ERK (95%, P < 0.001) and showed a moderate increased AKT (P = 0.14) and GSK3β (P = 0.21) phosphorylation, which did not reach significance. Preload and afterload elevation in muscles strips from human failing hearts showed neither AKT nor ERK phosphorylation changes.

Conclusions

Our data show that preload activates the AKT–GSK3β and afterload the ERK pathway in vitro, indicating an intrinsic mechanism independent of endocrine signalling.

Ultrastructural Adaptation of the Cardiomyocyte to Chronic Mitral Regurgitation

Introduction: Mitral regurgitation (MR) imposes volume overload on the left ventricle (LV) and elevates wall stress, triggering its adverse remodeling. Pronounced LV dilation, minimal wall thinning, and a gradual decline in cardiac ejection fraction (EF) are observed. The structural changes in the myocardium that define these gross, organ level remodeling are not known. Cardiomyocyte elongation and slippage have both been hypothesized, but neither are confirmed, nor are the changes to the cardiomyocyte structure known. Using a rodent model of MR, we used immunohistochemistry and transmission electron microscopy (TEM) to describe the ultrastructural remodeling of the cardiomyocyte.

Methods: Twenty-four male Sprague-Dawley rats (350–400 g) were assigned to two groups: group (1) rats induced with severe MR (n = 18) and group (2) control rats that were healthy and age and weight matched (n = 6). MR was induced in the beating heart using a 23-G ultrasound-guided, transapical needle to perforate the anterior mitral leaflet, and the rats were followed to 2, 10, and 20 weeks (n = 6/time-point). Echocardiography was performed to quantify MR severity and to measure LV volume and function at each time-point. Explanted myocardial tissue were examined with TEM and immunohistochemistry to investigate the ultrastructural changes.

Results: MR induced rapid and significant increase in end-diastolic volume (EDV), with a 50% increase by 2 weeks, compared with control. Rise in end-systolic volume (ESV) was more gradual; however, by 20 weeks, both EDV and ESV in MR rats were increased by 126% compared with control. A significant decline in EF was measured at 10 weeks of MR. At the ultrastructural level, as early as 2 weeks after MR, cardiomyocyte elongation and increase in cross-sectional area were observed. TEM depicted sarcomere shortening, with loss of Z-line and I-band. Desmin, a cytoskeletal protein that is uniformly distributed along the length of the cardiomyocyte, was disorganized and localized to the intercalated disc, in the rats induced with MR and not in the controls. In the rats with MR, the linear registry of the mitochondrial arrangement along the sarcomeres was lost, with mitochondrial fragmentation, aggregation around the nucleus, and irregularities in the cristae.

Discussion: In the setting of chronic mitral regurgitation, LV dilatation occured by cardiomyocyte elongation, which manifests at the subcellular level as distinct ultrastructural alterations of the sarcomere, cytoskeleton, and mitochondria. Since the cytoskeleton not only provides tensegrity but has functional consequences on myocyte function, further investigation into the impact of cytoskeletal remodeling on progressive heart failure or recovery of function upon correcting the valve lesion are needed.

Haematopoietic and cardiac GPR55 synchronize post-myocardial infarction remodelling

While classical cannabinoid receptors are known to crucially impact on myocardial infarction (MI) repair, a function of the cannabinoid-sensitive receptor GPR55 herein is poorly understood. We investigated the role of GPR55 in cardiac physiology and post-MI inflammation and remodelling. Global GPR55-/- and wildtype (WT) mice were basally characterized or assigned to 1, 3 or 28 days permanent MI and subsequently analysed via pro-inflammatory and pro-hypertrophic parameters. GPR55-/- deficiency was basally associated with bradycardia, increased diastolic LV volume and sarcomere length and a subtle inflammatory phenotype. While infarct size and myeloid cell infiltration were unaffected by GPR55 depletion, acute cardiac chemokine production was prolonged post-MI. Concurrently, GPR55-/- hearts exhibited a premature expansion of pro-reparative and phagocytic macrophages paralleled by early up-regulation of extracellular matrix (ECM) factors 3 days post-MI, which could be mimicked by sole haematopoietic GPR55 depletion. Moreover, global GPR55 deficiency mitigated MI-induced foetal gene re-programming and cardiomyocyte hypertrophy, culminating in aggravated LV dilatation and infarct expansion. GPR55 regulates cardiac homeostasis and ischaemia responses by maintaining adequate LV filling and modulating three crucial processes post-MI: wound healing kinetics, cardiomyocyte hypertrophy and maladaptive remodelling.

Prognostic significance of liver stiffness assessed by fibrosis-4 index in patients with heart failure

BACKGROUND

Heart failure (HF)-related congestive hepatopathy is a well-recognized problem in management of HF. The fibrosis-4 (FIB4) index calculated by [age × aspartate aminotransferase (IU/L)/platelet count (10⁹ /L) × square root of alanine aminotransferase (IU/L)] is useful for evaluating liver stiffness. We aimed to investigate the impact of the FIB4 index on prognosis in patients with HF.

METHODS AND RESULTS

Consecutive HF patients referred for hospitalization at Kumamoto University Hospital, Japan, were registered between 2006 and 2015. We observed cardiovascular outcomes in each type of HF [HF with reduced left ventricular ejection fraction (LVEF) (HFrEF), HF with mid-range LVEF (HFmrEF) and with preserved LVEF (HFpEF)] according to their FIB4 index; Group 1 (FIB4 index <1.3), Group 2 (FIB4 index: 1.3-2.67), and Group 3 (FIB4 index >2.67). This study enrolled 83 HFrEF patients, 117 HFmrEF patients, and 504 HFpEF patients. In HFpEF patients, the Kaplan-Meier curve revealed that Group 3 had a significantly higher rate of total cardiovascular events compared with the other two groups. By contrast, the occurrences of total cardiovascular events were not different among three groups in HFrEF and HFmrEF patients. Multivariate Cox proportional hazard analysis with significant factors in univariate analysis identified that the FIB4 index as an independent and significant predictor for future total cardiovascular events in HFpEF patients (hazard ratio: 1.09, 95% confidence interval: 1.03-1.15, P = 0.001).

CONCLUSIONS

The FIB4 index was a significant predictor for total cardiovascular events in HFpEF.

Volume Load-Induced Right Ventricular Failure in Rats Is Not Associated With Myocardial Fibrosis

Background

Right ventricular (RV) function and failure are key determinants of morbidity and mortality in various cardiovascular diseases. Myocardial fibrosis is regarded as a contributing factor to heart failure, but its importance in RV failure has been challenged. This study aims to assess whether myocardial fibrosis drives the transition from compensated to decompensated volume load-induced RV dysfunction.

Methods

Wistar rats were subjected to aorto-caval shunt (ACS, n = 23) or sham (control, n = 15) surgery, and sacrificed after 1 month, 3 months, or 6 months. Echocardiography, RV pressure-volume analysis, assessment of gene expression and cardiac histology were performed.

Results

At 6 months, 6/8 ACS-rats (75%) showed clinical signs of RV failure (pleural effusion, ascites and/or liver edema), whereas at 1 month and 3 months, no signs of RV failure had developed yet. Cardiac output has increased two- to threefold and biventricular dilatation occurred, while LV ejection fraction gradually decreased. At 1 month and 3 months, RV end-systolic elastance (Ees) remained unaltered, but at 6 months, RV Ees had decreased substantially. In the RV, no oxidative stress, inflammation, pro-fibrotic signaling (TGFβ1 and pSMAD2/3), or fibrosis were present at any time point.

Conclusions

In the ACS rat model, long-term volume load was initially well tolerated at 1 month and 3 months, but induced overt clinical signs of end-stage RV failure at 6 months. However, no myocardial fibrosis or increased pro-fibrotic signaling had developed. These findings indicate that myocardial fibrosis is not involved in the transition from compensated to decompensated RV dysfunction in this model.

Mechanotranduction Pathways in the Regulation of Mitochondrial Homeostasis in Cardiomyocytes

Mitochondria are one of the most important organelles in cardiomyocytes. Mitochondrial homeostasis is necessary for the maintenance of normal heart function. Mitochondria perform four major biological processes in cardiomyocytes: mitochondrial dynamics, metabolic regulation, Ca2+ handling, and redox generation. Additionally, the cardiovascular system is quite sensitive in responding to changes in mechanical stress from internal and external environments. Several mechanotransduction pathways are involved in regulating the physiological and pathophysiological status of cardiomyocytes. Typically, the extracellular matrix generates a stress-loading gradient, which can be sensed by sensors located in cellular membranes, including biophysical and biochemical sensors. In subsequent stages, stress stimulation would regulate the transcription of mitochondrial related genes through intracellular transduction pathways. Emerging evidence reveals that mechanotransduction pathways have greatly impacted the regulation of mitochondrial homeostasis. Excessive mechanical stress loading contributes to impairing mitochondrial function, leading to cardiac disorder. Therefore, the concept of restoring mitochondrial function by shutting down the excessive mechanotransduction pathways is a promising therapeutic strategy for cardiovascular diseases. Recently, viral and non-viral protocols have shown potentials in application of gene therapy. This review examines the biological process of mechanotransduction pathways in regulating mitochondrial function in response to mechanical stress during the development of cardiomyopathy and heart failure. We also summarize gene therapy delivery protocols to explore treatments based on mechanical stress-induced mitochondrial dysfunction, to provide new integrative insights into cardiovascular diseases.

NADPH oxidase-4 promotes eccentric cardiac hypertrophy in response to volume overload

AIMS

Chronic pressure or volume overload induce concentric vs. eccentric left ventricular (LV) remodelling, respectively. Previous studies suggest that distinct signalling pathways are involved in these responses. NADPH oxidase-4 (Nox4) is a reactive oxygen species-generating enzyme that can limit detrimental cardiac remodelling in response to pressure overload. This study aimed to assess its role in volume overload-induced remodelling.

METHODS AND RESULTS

We compared the responses to creation of an aortocaval fistula (Shunt) to induce volume overload in Nox4-null mice (Nox4-/-) vs. wild-type (WT) littermates. Induction of Shunt resulted in a significant increase in cardiac Nox4 mRNA and protein levels in WT mice as compared to Sham controls. Nox4-/- mice developed less eccentric LV remodelling than WT mice (echocardiographic relative wall thickness: 0.30 vs. 0.27, P < 0.05), with less LV hypertrophy at organ level (increase in LV weight/tibia length ratio of 25% vs. 43%, P < 0.01) and cellular level (cardiomyocyte cross-sectional area: 323 µm2 vs. 379 μm2, P < 0.01). LV ejection fraction, foetal gene expression, interstitial fibrosis, myocardial capillary density, and levels of myocyte apoptosis after Shunt were similar in the two genotypes. Myocardial phospho-Akt levels were increased after induction of Shunt in WT mice, whereas levels decreased in Nox4-/- mice (+29% vs. -21%, P < 0.05), associated with a higher level of phosphorylation of the S6 ribosomal protein (S6) and the eIF4E-binding protein 1 (4E-BP1) in WT compared to Nox4-/- mice. We identified that Akt activation in cardiac cells is augmented by Nox4 via a Src kinase-dependent inactivation of protein phosphatase 2A.

CONCLUSION

Endogenous Nox4 is required for the full development of eccentric cardiac hypertrophy and remodelling during chronic volume overload. Nox4-dependent activation of Akt and its downstream targets S6 and 4E-BP1 may be involved in this effect.

Intrarenal Doppler ultrasonography reflects hemodynamics and predicts prognosis in patients with heart failure

We aimed to clarify clinical implications of intrarenal hemodynamics assessed by intrarenal Doppler ultrasonography (IRD) and their prognostic impacts in heart failure (HF). We performed a prospective observational study, and examined IRD and measured interlobar renal artery velocity time integral (VTI) and intrarenal venous flow (IRVF) patterns (monophasic or non-monophasic pattern) to assess intrarenal hypoperfusion and congestion in HF patients (n = 341). Seven patients were excluded in VTI analysis due to unclear imaging. The patients were divided into groups based on (A) VTI: high VTI (VTI ≥ 14.0 cm, n = 231) or low VTI (VTI < 14.0 cm, n = 103); and (B) IRVF patterns: monophasic (n = 36) or non-monophasic (n = 305). We compared post-discharge cardiac event rate between the groups, and right-heart catheterization was performed in 166 patients. Cardiac index was lower in low VTI than in high VTI (P = 0.04), and right atrial pressure was higher in monophasic than in non-monophasic (P = 0.03). In the Kaplan–Meier analysis, cardiac event rate was higher in low VTI and monophasic groups (P < 0.01, respectively). In the Cox proportional hazard analysis, the combination of low VTI and a monophasic IRVF pattern was a predictor of cardiac events (P < 0.01). IRD imaging might be associated with cardiac output and right atrial pressure, and prognosis.

Relationship between Soluble ST2 and Left Ventricular Geometry in Maintenance Hemodialysis Patients

INTRODUCTION

Left ventricular hypertrophy (LVH) is a highly prevalent presentation of cardiac structural abnormality and a strong predictor of adverse outcomes in maintenance hemodialysis (MHD) patients. Different left ventricular geometry may provide additional clinical information. Soluble ST2 is a novel cardiac prognostic biomarker in MHD patients and is closely related to cardiac remodeling.

OBJECTIVE

This study sought to evaluate the association of sST2 and left ventricular structure in a cohort of MHD patients.

METHODS

Two hundred eighty-seven patients were enrolled. Left ventricular structure was assessed via transthoracic echocardiography. Left ventricular geometric patterns were defined according to left ventricular mass index and relative wall thickness (RWT). Serum sST2 levels were measured.

RESULTS

Prevalence of LVH was 44.9% in the study population. In univariate analysis, sST2 levels were correlated with interventricular septal wall thickness, posterior wall thickness, and RWT. After multivariate adjustment, sST2 was independently correlated with only RWT (p = 0.028). Comparing sST2 concentrations across different LV geometric patterns, we found sST2 levels were significantly increased in patients with concentric cardiac remodeling and concentric LVH.

CONCLUSIONS

The present study found that sST2 were significantly increased in patients with concentric remodeling and concentric LVH. ST2/interleukin (IL)-33 signaling might participate in the process of cardiac remodeling via its pro-fibrotic action. Future studies on the mechanism of ST2/IL-33 pathway are needed.

Regulation of titin-based cardiac stiffness by unfolded domain oxidation (UnDOx)

The relationship between oxidative stress and cardiac stiffness is thought to involve modifications to the giant muscle protein titin, which in turn can determine the progression of heart disease. In vitro studies have shown that S-glutathionylation and disulfide bonding of titin fragments could alter the elastic properties of titin; however, whether and where titin becomes oxidized in vivo is less certain. Here we demonstrate, using multiple models of oxidative stress in conjunction with mechanical loading, that immunoglobulin domains preferentially from the distal titin spring region become oxidized in vivo through the mechanism of unfolded domain oxidation (UnDOx). Via oxidation type-specific modification of titin, UnDOx modulates human cardiomyocyte passive force bidirectionally. UnDOx also enhances titin phosphorylation and, importantly, promotes nonconstitutive folding and aggregation of unfolded domains. We propose a mechanism whereby UnDOx enables the controlled homotypic interactions within the distal titin spring to stabilize this segment and regulate myocardial passive stiffness.

Clinical Implications of Hepatic Hemodynamic Evaluation by Abdominal Ultrasonographic Imaging in Patients With Heart Failure

Background It has been reported that liver stiffness assessed by transient elastography are correlated with right atrial pressure, which is associated with worse outcome in patients with heart failure (HF). We aimed to clarify clinical implications of hepatic hemodynamic evaluation (liver congestion and hypoperfusion) by abdominal ultrasonography in patients with HF. Methods and Results We performed abdominal ultrasonography, right-heart catheterization, and echocardiography, then followed up for cardiac events such as cardiac death or worsening HF in patients with HF. Regarding liver congestion, liver stiffness assessed by shear wave elastography (SWE) of the liver was significantly correlated with right atrial pressure determined by right-heart catheterization (R=0.343; P<0.01), right atrial end-systolic area, and inferior vena cava diameter determined by echocardiography. Regarding liver hypoperfusion, peak systolic velocity (PSV) of the celiac artery was correlated with cardiac index determined by right-heart catheterization (R=0.291; P<0.001) and tricuspid annular plane systolic excursion determined by echocardiography. According to the Kaplan-Meier analysis, HF patients with high SWE and low PSV had the highest cardiac event rate (log-rank P=0.033). In the Cox proportional hazard analysis, high SWE and low PSV were associated with high cardiac event rate (high SWE: hazard ratio [HR], 2.039; 95% CI, 1.131-4.290; low PSV: HR, 2.211; 95% CI, 1.199-4.449), and the combination of high SWE and low PSV was a predictor of cardiac events (HR, 4.811; 95% CI, 1.562-14.818). Conclusions Intrahepatic congestion and hypoperfusion determined by abdominal ultrasonography (liver SWE and celiac PSV) are associated with adverse prognosis in patients with HF.

Cardiac remodeling secondary to chronic volume overload is attenuated by a novel MMP9/2 blocking antibody

Objective

Monoclonal antibody derivatives are promising drugs for the treatment of various diseases due to their high matrix metalloproteinases (MMP) active site specificity. We studied the effects of a novel antibody, SDS3, which specifically recognizes the mature active site of MMP9/2 during ventricular remodeling progression in a mouse model of chronic volume overload (VO).

Methods

VO was induced by creating an aortocaval fistula (ACF) in 10- to 12-week-old C57BL male mice. The VO-induced mice were treated with either vehicle control (PBS) or with SDS3 twice weekly by intraperitoneal (ip) injection. The relative changes in cardiac parameters between baseline (day 1) and end-point (day 30), were evaluated by echocardiography. The effects of SDS3 treatment on cardiac fibrosis, cardiomyocyte volume, and cardiac inflammation were tested by cardiac staining with Masson's trichrome, wheat Germ Agglutinin (WGA), and CD45, respectively. Serum levels of TNFα and IL-6 with and without SDS3 treatment were tested by ELISA.

Results

SDS3 significantly reduced cardiac dilatation, left ventricular (LV) mass, and cardiomyocyte hypertrophy compared to the vehicle treated animals. The antibody also reduced the heart-to-body weight ratio of the ACF animals to values comparable to those of the controls. Interestingly, the SDS3 group underwent significant reduction of cardiac inflammation and pro-inflammatory cytokine production, indicating a regulatory role for MMP9/2 in tissue remodeling, possibly by tumor necrosis factor alpha (TNFα) activation. In addition, significant changes in the expression of proteins related to mitochondrial function were observed in ACF animals, these changes were reversed following treatment with SDS3.

Conclusion

The data suggest that MMP9/2 blockage with SDS3 attenuates myocardial remodeling associated with chronic VO by three potential pathways: downregulating the extracellular matrix proteolytic cleavage, reducing the cardiac inflammatory responses, and preserving the cardiac mitochondrial structure and function.

Left ventricular response in the transition from hypertrophy to failure recapitulates distinct roles of Akt, β-arrestin-2, and CaMKII in mice with aortic regurgitation

Background

Although aortic regurgitation (AR) is a clinically important condition that is becoming increasingly common, few relevant murine models and mechanistic studies exist for this condition. In this study, we attempted to delineate the pathological and molecular changes and address the roles of some potentially relevant molecules in an animal model of surgically induced AR.

Methods

AR was induced by puncturing the aortic valve leaflets in C57BL/6J mice under echocardiographic guidance.

Results

As early as 1 week following AR, the left ventricles (LV) displayed marked impairments in diastolic function and coronary flow reserve (CFR), as well as cardiac hypertrophy and chamber dilatation at both end-systole and end-diastole. LV free wall thickening and cardiomyocyte hypertrophy in LV were observed 2 weeks following of AR while a decline in ejection fraction was not seen until after 4 weeks. Nppa (natriuretic peptide A) and Nppb (natriuretic peptide B) increased over time, in conjunction with prominent Akt activation as well as slight CaMKII (Ca²⁺/calmodulin-dependent protein kinase II) activation and biphasic changes in β-arrestin-2 expression. Treatment of AR mice with Akt inhibition exacerbated the eccentric hypertrophy, while neither inhibition of CaMKII nor β-arrestin-2 overexpression influenced the response to AR.

Conclusions

Our structural, functional, molecular and therapeutic analyses reveal that Akt, but not CaMKII or β-arrestin-2, plays a regulatory role in the development of LV remodeling after AR in Mice. These results may shed important light on therapeutic targets for volume overloaded cardiomyopathy.

Estimated plasma volume and mortality: analysis from NHANES 1999-2014

BACKGROUND

While estimated plasma volume (ePV) has been studied in some diseases, such as heart failure, the relationship between ePV and all-cause or cause-specific mortality remains unexplored. Therefore, we investigated the association between ePV and all-cause, cardiovascular (CV), and cancer-related mortality among adults in the US.

METHOD

We used the National Health and Nutrition Examination Survey (NHANES) from 1999 to 2014 and included participants older than 18 years. Mortality data were obtained from the National Death Index and matched to the NHANES participants. ePV was derived using Strauss formula. Cox proportional hazard models were fit to estimate hazard ratios for all-cause and cause-specific mortality without and with adjustment for potential confounders.

RESULTS

Of the 42,705 participants, 5194 died (1121 CV deaths) during mean follow-up of 8.0 (range 0-16.7) years. Mean ± SD age and ePV of the participants were 47.2 ± 19.4 years and 4.2 ± 0.84, respectively. In unadjusted models, 1 unit increase in ePV was associated with 29%, 32%, and 16% increased risk in all-cause (HR 1.29; 95% CI 1.24, 1.35), CV (HR 1.32; 95% CI 1.22, 1.43), and cancer-related (HR 1.16; 95% CI 1.05, 1.27) mortality. Risk remained high in adjusted models (all-cause HR 1.24; 95% CI 1.18, 1.30; CV HR 1.22; 95% CI 1.11, 1.34; cancer-specific HR 1.24; 95% CI 1.10, 1.39). When comparing the highest and lowest ePV quartiles, similar results were noted (adjusted all-cause HR 1.64; 95% CI 1.45, 1.86; CV HR 1.52; 95% CI 1.19, 1.93; cancer HR 1.85; 95% CI 1.38, 2.49).

CONCLUSION

An increase in ePV was associated with increased all-cause and cause-specific mortality. Further studies are needed to explore the mechanism of this relationship and translation into a better outcome.

Circulating Biomarkers Predicting Longitudinal Changes in Left Ventricular Structure and Function in a General Population

Background Serial imaging studies in the general population remain important to evaluate the usefulness of pathophysiologically relevant biomarkers in predicting progression of left ventricular (LV) remodeling and dysfunction. Here, we assessed in a general population whether these circulating biomarkers at baseline predict longitudinal changes in LV structure and function. Methods and Results In 592 participants (mean age, 50.8 years; 51.4% women; 40.5% hypertensive), we derived echocardiographic indexes reflecting LV structure and function at baseline and after 4.7 years. At baseline, we measured alkaline phosphatase, markers of collagen turnover (procollagen type I, C-terminal telopeptide, matrix metalloproteinase-1) and high-sensitivity cardiac troponin T. We regressed longitudinal changes in LV indexes on baseline biomarker levels and reported standardized effect sizes as a fraction of the standard deviation of LV change. After full adjustment, a decline in LV longitudinal strain (-14.2%) and increase in E/e' ratio over time (+18.9%; P≤0.019) was associated with higher alkaline phosphatase activity at baseline. Furthermore, longitudinal strain decreased with higher levels of collagen I production and degradation at baseline (procollagen type I, -14.2%; C-terminal telopeptide, -16.4%; P≤0.029). An increase in E/e' ratio over time was borderline associated with lower matrix metalloproteinase-1 (+9.8%) and lower matrix metalloproteinase-1/tissue inhibitor of metalloproteinase-1 ratio (+11.9%; P≤0.041). Higher high-sensitivity cardiac troponin T levels at baseline correlated significantly with an increase in relative wall thickness (+23.1%) and LV mass index (+18.3%) during follow-up ( P≤0.035). Conclusions We identified a set of biomarkers predicting adverse changes in LV structure and function over time. Circulating biomarkers reflecting LV stiffness, injury, and collagen composition might improve the identification of subjects at risk for subclinical cardiac maladaptation.

[Role of apoptosis signal-regulating kinase 1 in left ventricular remodeling in mice]

OBJECTIVE

To study the changes and significance of apoptosis signal-regulating kinase 1 (ASK1) in left ventricular remodeling in FVB/N mice.

METHODS

A total of 54 FVB/N mice were randomly divided into 4 groups: 0 d group with 8 mice, 7 d group with 10 mice, 14 d group with 16 mice, and 21 d group with 20 mice. A model of cardiac remodeling was established by intraperitoneal injection of isoproterenol (ISO) at a daily dose of 30 mg/kg, and the 7 d, 14 d, and 21 d groups were injected for 7, 14, and 21 consecutive days respectively. The 0 d group was given intraperitoneal injection of an equal volume of normal saline. Echocardiography was used to measure left ventricular posterior wall thickness at end diastole (dLVPW) and the ratio of heart weight to tibia length (HW/TL) was measured. Hematoxylin-eosin staining was used to measure left ventricular myocardial fiber diameter. Picric-Sirius red staining was used to measure myocardial collagen deposition area in the left ventricle. Quantitative real-time PCR was used to measure the mRNA expression of ASK1, type I collagen (collagen I), and B-type natriuretic peptide (BNP). The mortality rate was observed for each group.

RESULTS

There were gradual increases in HW/TL, myocardial fiber diameter, and dLVPW after 0, 7, and 14 days of ISO injection (P<0.05). There were no significant changes in HW/TL ratio and dLVPW from days 14 to 21 of ISO injection (P>0.05), while there was a significant reduction in myocardial fiber diameter (P<0.05), which was similar to the value on day 7 (P>0.05). There were significant increases in myocardial collagen deposition area and the mRNA expression of collagen I, ASK1, and BNP after 0, 7, 14, and 21 days of ISO injection, which reached the peaks on day 21 (P<0.01). The mRNA expression of ASK1 was positively correlated with myocardial collagen deposition area and the mRNA expression of collagen I and BNP and had a weak correlation with HW/TL, myocardial fiber diameter, and dLVPW. There was a significant increase in the mortality rate of the mice over the time of ISO injection.

CONCLUSIONS

The expression of ASK1 in the myocardium is closely associated with left ventricular remodeling. The increase of ASK1 expression may lead to the aggravation of left ventricular remodeling, and the mechanism of which needs further study.

Therapeutic targeting of mitochondrial ROS ameliorates murine model of volume overload cardiomyopathy

Concomitant heart failure is associated with poor clinical outcome in dialysis patients. The arteriovenous shunt, created as vascular access for hemodialysis, increases ventricular volume-overload, predisposing patients to developing cardiac dysfunction. The integral function of mitochondrial respiration is critically important for the heart to cope with hemodynamic overload. The involvement, however, of mitochondrial activity or reactive oxygen species (ROS) in the pathogenesis of ventricular-overload-induced heart failure has not been fully elucidated. We herein report that disorganization of mitochondrial respiration increases mitochondrial ROS production in the volume-overloaded heart, leading to ventricular dysfunction. We adopted the murine arteriovenous fistula (AVF) model, which replicates the cardinal features of volume-overload-induced ventricular dysfunction. Enzymatic assays of cardiac mitochondria revealed that the activities of citrate synthase and NADH-quinone reductase (complex Ⅰ) were preserved in the AVF heart. In contrast, the activity of NADH oxidase supercomplex was significantly compromised, resulting in elevated ROS production. Importantly, the antioxidant N-acetylcysteine prevented the development of ventricular dilatation and cardiac dysfunction, suggesting a pathogenic role for ROS in dialysis-related cardiomyopathy. A cardioprotective effect was also observed in metformin-treated mice, illuminating its potential use in the management of heart failure complicating diabetic patients on dialysis.

Assessing the role of extracellular signal-regulated kinases 1 and 2 in volume overload-induced cardiac remodelling

AIMS

Volume overload (VO) and pressure overload (PO) induce differential cardiac remodelling responses including distinct signalling pathways. Extracellular signal-regulated kinases 1 and 2 (ERK1/2), key signalling components in the mitogen-activated protein kinase (MAPK) pathways, modulate cardiac remodelling during pressure overload (PO). This study aimed to assess their role in VO-induced cardiac remodelling as this was unknown.

METHODS AND RESULTS

Aortocaval fistula (Shunt) surgery was performed in mice to induce cardiac VO. Two weeks of Shunt caused a significant reduction of cardiac ERK1/2 activation in wild type (WT) mice as indicated by decreased phosphorylation of the TEY (Thr-Glu-Tyr) motif (-28% as compared with Sham controls, P < 0.05). Phosphorylation of other MAPKs was unaffected. For further assessment, transgenic mice with cardiomyocyte-specific ERK2 overexpression (ERK2tg) were studied. At baseline, cardiac ERK1/2 phosphorylation in ERK2tg mice remained unchanged compared with WT littermates, and no overt cardiac phenotype was observed; however, cardiac expression of the atrial natriuretic peptide was increased on messenger RNA (3.6-fold, P < 0.05) and protein level (3.1-fold, P < 0.05). Following Shunt, left ventricular dilation and hypertrophy were similar in ERK2tg mice and WT littermates. Left ventricular function was maintained, and changes in gene expression indicated reactivation of the foetal gene program in both genotypes. No differences in cardiac fibrosis and kinase activation was found amongst all experimental groups, whereas apoptosis was similarly increased through Shunt in ERK2tg and WT mice.

CONCLUSIONS

VO-induced eccentric hypertrophy is associated with reduced cardiac ERK1/2 activation in vivo. Cardiomyocyte-specific overexpression of ERK2, however, does not alter cardiac remodelling during VO. Future studies need to define the pathophysiological relevance of decreased ERK1/2 signalling during VO.

Genetic deletion of calcium/calmodulin-dependent protein kinase type II delta does not mitigate adverse myocardial remodeling in volume-overloaded hearts

Calcium/calmodulin-dependent protein kinase type II delta (CaMKIIδ), the predominant CaMKII isoform expressed in the heart, has been implicated in the progression of myocardial infarction- and pressure overload-induced pathological remodeling. However, the role of CaMKIIδ in volume overload (VO) has not been explored. We have previously reported an activation of CaMKII during transition to HF in long-term VO. Here, we address whether CaMKIIδ is critically involved in the mortality, myocardial remodeling, and heart failure (HF) progression in response to VO. CaMKIIδ knockout (δ-KO) and wild-type (WT) littermates were exposed to aortocaval shunt-induced VO, and the progression of adverse myocardial remodeling was assessed by serial echocardiography, histological and molecular analyses. The mortality rates during 10 weeks of VO were similar in δ-KO and WT mice. Both genotypes displayed comparable eccentric myocardial hypertrophy, altered left ventricle geometry, perturbed systolic and diastolic functions after shunt. Additionally, cardiomyocytes hypertrophy, augmented myocyte apoptosis, and up-regulation of hypertrophic genes were also not significantly different in δ-KO versus WT hearts after shunt. Therefore, CaMKIIδ signaling seems to be dispensable for the progression of VO-induced maladaptive cardiac remodeling. Accordingly, we hypothesize that CaMKIIδ-inhibition as a therapeutic approach might not be helpful in the context of VO-triggered HF.

Posttranslational modifications of titin from cardiac muscle: how, where, and what for?

Titin is a giant elastic protein expressed in the contractile units of striated muscle cells, including the sarcomeres of cardiomyocytes. The last decade has seen enormous progress in our understanding of how titin molecular elasticity is modulated in a dynamic manner to help cardiac sarcomeres adjust to the varying hemodynamic demands on the heart. Crucial events mediating the rapid modulation of cardiac titin stiffness are post‐translational modifications (PTMs) of titin. In this review, we first recollect what is known from earlier and recent work on the molecular mechanisms of titin extensibility and force generation. The main goal then is to provide a comprehensive overview of current insight into the relationship between titin PTMs and cardiomyocyte stiffness, notably the effect of oxidation and phosphorylation of titin spring segments on titin stiffness. A synopsis is given of which type of oxidative titin modification can cause which effect on titin stiffness. A large part of the review then covers the mechanically relevant phosphorylation sites in titin, their location along the elastic segment, and the protein kinases and phosphatases known to target these sites. We also include a detailed coverage of the complex changes in phosphorylation at specific titin residues, which have been reported in both animal models of heart disease and in human heart failure, and their correlation with titin‐based stiffness alterations. Knowledge of the relationship between titin PTMs and titin elasticity can be exploited in the search for therapeutic approaches aimed at softening the pathologically stiffened myocardium in heart failure patients.

Cardiac Tissue Chips (CTCs) for Modeling Cardiovascular Disease

OBJECTIVE

Cardiovascular research and regenerative strategies have been significantly limited by the lack of relevant cell culture models that can recreate complex hemodynamic stresses associated with pressure-volume changes in the heart.

METHODS

To address this issue, we designed a biomimetic cardiac tissue chip (CTC) model where encapsulated cardiac cells can be cultured in three-dimensional (3-D) fibres and subjected to hemodynamic loading to mimic pressure-volume changes seen in the left ventricle. These 3-D fibres are suspended within a microfluidic chamber between two posts and integrated within a flow loop. Various parameters associated with heart function, like heart rate, peak-systolic pressure, end-diastolic pressure and volume, end-systolic pressure and volume, and duration ratio between systolic and diastolic, can all be precisely manipulated, allowing culture of cardiac cells under developmental, normal, and disease states.

RESULTS

We describe two examples of how the CTC can significantly impact cardiovascular research by reproducing the pathophysiological mechanical stresses associated with pressure overload and volume overload. Our results using H9c2 cells, a cardiomyogenic cell line, clearly show that culture within the CTC under pathological hemodynamic loads accurately induces morphological and gene expression changes, similar to those seen in both hypertrophic and dilated cardiomyopathy. Under pressure overload, the cells within the CTC see increased hypertrophic remodeling and fibrosis, whereas cells subject to prolonged volume overload experience significant changes to cellular aspect ratio through thinning and elongation of the engineered tissue.

CONCLUSIONS

These results demonstrate that the CTC can be used to create highly relevant models where hemodynamic loading and unloading are accurately reproduced for cardiovascular disease modeling.

Calculated plasma volume status and outcomes in patients undergoing coronary bypass graft surgery

OBJECTIVES

Congestion is associated with worse outcomes in critically ill surgical patients but can be difficult to quantify noninvasively. We hypothesised that plasma volume status (PVS), estimated preoperatively using a validated formula that enumerates percentage change from ideal plasma volume (PV), would provide incremental prognostic utility after coronary artery bypass graft (CABG) surgery.

METHODS

In this retrospective cohort study, patients who underwent CABG surgery (1999-2010) were identified from a prospectively collected database. Actual ([1-haematocrit] x [a+(b x weight [kg])]) and ideal (c x weight [kg]) PV were obtained from equations where a, b and c are sex-dependent constants. Calculated PVS was then derived (100% x [(actual-ideal)/ideal]).

RESULTS

In 1887 patients (mean age 67±10 years; 79% male; median European System for Cardiac Operative Risk Evaluation [EuroSCORE] 4), mean PVS was -8.2±9%. While 8% of subjects had clinical evidence of congestion, a relatively increased PV (PVS >0%) was estimated in 17% and correlated with lower serum sodium, higher EuroSCORE and a diagnosis of diabetes mellitus. A PVS≥5.6% was optimally prognostic and associated with greater mortality (HR: 2.31, p=0.009), independently of, and incremental to, EuroSCORE, New York Heart Association class and serum sodium. A PVS≥5.6% also independently predicted longer intensive care (β: 0.65, p=0.007) and hospital (β: 2.01, p=0.006) stays, and greater postoperative renal (OR: 1.61, p=0.008) and arrhythmic (OR: 1.29, p=0.03) complications.

CONCLUSIONS

Higher PVS values, calculated simply from weight and haematocrit, are associated with worse inpatient outcomes after CABG. PVS could help refine risk stratification and further investigations are warranted to evaluate the potential clinical utility of PVS-guided management in patients undergoing CABG.

Treating oxidative stress in heart failure: past, present and future

Advances in cardiovascular research have identified oxidative stress as an important pathophysiological pathway in the development and progression of heart failure. Oxidative stress is defined as the imbalance between the production of reactive oxygen species (ROS) and the endogenous antioxidant defence system. Under physiological conditions, small quantities of ROS are produced intracellularly, which function in cell signalling, and can be readily reduced by the antioxidant defence system. However, under pathophysiological conditions, the production of ROS exceeds the buffering capacity of the antioxidant defence system, resulting in cell damage and death. Over the last decades several studies have tried to target oxidative stress with the aim to improve outcome in patients with heart failure, with very limited success. The reasons as to why these studies failed to demonstrate any beneficial effects remain unclear. However, one plausible explanation might be that currently employed strategies, which target oxidative stress by exogenous inhibition of ROS production or supplementation of exogenous antioxidants, are not effective enough, while bolstering the endogenous antioxidant capacity might be a far more potent avenue for therapeutic intervention. In this review, we provide an overview of oxidative stress in the pathophysiology of heart failure and the strategies utilized to date to target this pathway. We provide novel insights into modulation of endogenous antioxidants, which may lead to novel therapeutic strategies to improve outcome in patients with heart failure.

Sarcoplasmic reticulum calcium leak contributes to arrhythmia but not to heart failure progression

Increased sarcoplasmic reticulum (SR) Ca2+ leak via the cardiac ryanodine receptor (RyR2) has been suggested to play a mechanistic role in the development of heart failure (HF) and cardiac arrhythmia. Mice treated with a selective RyR2 stabilizer, rycal S36, showed normalization of SR Ca2+ leak and improved survival in pressure overload (PO) and myocardial infarction (MI) models. The development of HF, measured by echocardiography and molecular markers, showed no difference in rycal S36– versus placebo-treated mice. Reduction of SR Ca2+ leak in the PO model by the rycal-unrelated RyR2 stabilizer dantrolene did not mitigate HF progression. Development of HF was not aggravated by increased SR Ca2+ leak due to RyR2 mutation (R2474S) in volume overload, an SR Ca2+ leak–independent HF model. Arrhythmia episodes were reduced by rycal S36 treatment in PO and MI mice in vivo and ex vivo in Langendorff-perfused hearts. Isolated cardiomyocytes from murine failing hearts and human ventricular failing and atrial nonfailing myocardium showed reductions in delayed afterdepolarizations, in spontaneous and induced Ca2+ waves, and in triggered activity in rycal S36 versus placebo cells, whereas the Ca2+ transient, SR Ca2+ load, SR Ca2+ adenosine triphosphatase function, and action potential duration were not affected. Rycal S36 treatment of human induced pluripotent stem cells isolated from a patient with catecholaminergic polymorphic ventricular tachycardia could rescue the leaky RyR2 receptor. These results suggest that SR Ca2+ leak does not primarily influence contractile HF progression, whereas rycal S36 treatment markedly reduces ventricular arrhythmias, thereby improving survival in mice.

Alterations in Titin Properties and Myocardial Fibrosis Correlate With Clinical Phenotypes in Hemodynamic Subgroups of Severe Aortic Stenosis

•

The extent of myocardial fibrosis and the degree of isoform-expression and phosphorylation changes in cardiomyocyte titin were unknown in different hemodynamic subgroups of AS, including “paradoxical” low-flow, low-gradient AS with preserved ejection fraction.

•

Hemodynamic subtypes of AS were found to exhibit increased cardiac fibrosis, titin-isoform transition toward more compliant N2BA variants, and both total and site-specific titin (N2Bus) hypophosphorylation compared with donor heart controls.

•

A significant shift toward N2BA titin appeared in “paradoxical” AS, whereas alterations in total-titin phosphorylation and cardiac fibrosis were similar in all hemodynamic subtypes of AS, suggesting increased myocardial passive stiffness.

•

The unfavorable prognosis of “paradoxical” AS could be explained by the pronounced myocardial remodeling, which is no less severe than in other AS subtypes.

Titin-isoform expression, titin phosphorylation, and myocardial fibrosis were studied in 30 patients with severe symptomatic aortic stenosis (AS). Patients were grouped into “classical” high-gradient, normal-flow AS with preserved ejection fraction (EF); “paradoxical” low-flow, low-gradient AS with preserved EF; and AS with reduced EF. Nonfailing donor hearts served as controls. AS was associated with increased fibrosis, titin-isoform switch toward compliant N2BA, and both total and site-specific titin hypophosphorylation compared with control hearts. All AS subtypes revealed titin and matrix alterations. The extent of myocardial remodeling in “paradoxical” AS was no less severe than in other AS subtypes, thus explaining the unfavorable prognosis.

Modeling Human Cardiac Hypertrophy in Stem Cell-Derived Cardiomyocytes

Cardiac hypertrophy accompanies many forms of cardiovascular diseases. The mechanisms behind the development and regulation of cardiac hypertrophy in the human setting are poorly understood, which can be partially attributed to the lack of a human cardiomyocyte-based preclinical test system recapitulating features of diseased myocardium. The objective of our study is to determine whether human embryonic stem cell-derived cardiomyocytes (hESC-CMs) subjected to mechanical stretch can be used as an adequate in vitro model for studying molecular mechanisms of cardiac hypertrophy. We show that hESC-CMs subjected to cyclic stretch, which mimics mechanical overload, exhibit essential features of a hypertrophic state on structural, functional, and gene expression levels. The presented hESC-CM stretch approach provides insight into molecular mechanisms behind mechanotransduction and cardiac hypertrophy and lays groundwork for the development of pharmacological approaches as well as for discovering potential circulating biomarkers of cardiac dysfunction.

Cardiomyocyte proliferation prevents failure in pressure overload but not volume overload

Induction of the cell cycle is emerging as an intervention to treat heart failure. Here, we tested the hypothesis that enhanced cardiomyocyte renewal in transgenic mice expressing cyclin D2 would be beneficial during hemodynamic overload. We induced pressure overload by transthoracic aortic constriction (TAC) or volume overload by aortocaval shunt in cyclin D2-expressing and WT mice. Although cyclin D2 expression dramatically improved survival following TAC, it did not confer a survival advantage to mice following aortocaval shunt. Cardiac function decreased following TAC in WT mice, but was preserved in cyclin D2-expressing mice. On the other hand, cardiac structure and function were compromised in response to aortocaval shunt in both WT and cyclin D2-expressing mice. The preserved function and improved survival in cyclin D2-expressing mice after TAC was associated with an approximately 50% increase in cardiomyocyte number and exaggerated cardiac hypertrophy, as indicated by increased septum thickness. Aortocaval shunt did not further impact cardiomyocyte number in mice expressing cyclin D2. Following TAC, cyclin D2 expression attenuated cardiomyocyte hypertrophy, reduced cardiomyocyte apoptosis, fibrosis, calcium/calmodulin-dependent protein kinase IIδ phosphorylation, brain natriuretic peptide expression, and sustained capillarization. Thus, we show that cyclin D2-induced cardiomyocyte renewal reduced myocardial remodeling and dysfunction after pressure overload but not after volume overload.

Genetic Ablation of Fgf23 or Klotho Does not Modulate Experimental Heart Hypertrophy Induced by Pressure Overload

Left ventricular hypertrophy (LVH) ultimately leads to heart failure in conditions of increased cardiac pre- or afterload. The bone-derived phosphaturic and sodium-conserving hormone fibroblast growth factor-23 (FGF23) and its co-receptor Klotho have been implicated in the development of uremic LVH. Using transverse aortic constriction (TAC) in gene-targeted mouse models, we examine the role of Fgf23 and Klotho in cardiac hypertrophy and dysfunction induced by pressure overload. TAC profoundly increases serum intact Fgf23 due to increased cardiac and bony Fgf23 transcription and downregulation of Fgf23 cleavage. Aldosterone receptor blocker spironolactone normalizes serum intact Fgf23 levels after TAC by reducing bony Fgf23 transcription. Notably, genetic Fgf23 or Klotho deficiency does not influence TAC-induced hypertrophic remodelling, LV functional impairment, or LV fibrosis. Despite the profound, aldosterone-mediated increase in circulating intact Fgf23 after TAC, our data do not support an essential role of Fgf23 or Klotho in the pathophysiology of pressure overload-induced cardiac hypertrophy.

Liver stiffness assessed by Fibrosis-4 index predicts mortality in patients with heart failure

Objective

Liver dysfunction due to heart failure (HF) is known as congestive hepatopathy. It has recently been reported that liver stiffness assessed by transient elastography reflects increased central venous pressure. The Fibrosis-4 (FIB4) index (age (years) × aspartate aminotransferase (IU/L)/platelet count (10⁹/L) × square root of alanine aminotransferase (IU/L)) is expected to be useful for evaluating liver stiffness in patients with non-alcoholic fatty liver disease. We aimed to investigate the impact of the FIB4 index on HF prognosis, with consideration for liver fibrosis markers and underlying cardiac function.

Methods

Consecutive 1058 patients with HF who were admitted to our hospital were divided into three groups based on their FIB4 index: first (FIB4 index <1.72, n=353), second (1.72≤FIB4 index <3.01, n=353) and third tertiles (3.01≤FIB4 index, n=352). We prospectively followed for all-cause mortality.

Results

During the follow-up period (mean 1047 days), 246 deaths occurred. In the Kaplan-Meier analysis, all-cause mortality progressively increased from the first to third groups (12.2%, 21.0% and 36.6%, p<0.01). In the Cox proportional hazard analysis, FIB4 index was an independent predictor of all-cause mortality in patients with HF (p<0.05). In comparisons of laboratory and echocardiographic findings, the third tertile had higher levels of type IV collagen 7S, procollagen type III peptide, hyaluronic acid, left atrial volume, mitral valve E/e’, inferior vena cava diameter and right atrial end systolic area (p<0.01, respectively).

Conclusion

The FIB4 index, a marker of liver stiffness, is associated with higher all-cause mortality in patients with HF.

Tampering with springs: phosphorylation of titin affecting the mechanical function of cardiomyocytes

Reversible post-translational modifications of various cardiac proteins regulate the mechanical properties of the cardiomyocytes and thus modulate the contractile performance of the heart. The giant protein titin forms a continuous filament network in the sarcomeres of striated muscle cells, where it determines passive tension development and modulates active contraction. These mechanical properties of titin are altered through post-translational modifications, particularly phosphorylation. Titin contains hundreds of potential phosphorylation sites, the functional relevance of which is only beginning to emerge. Here, we provide a state-of-the-art summary of the phosphorylation sites in titin, with a particular focus on the elastic titin spring segment. We discuss how phosphorylation at specific amino acids can reduce or increase the stretch-induced spring force of titin, depending on where the spring region is phosphorylated. We also review which protein kinases phosphorylate titin and how this phosphorylation affects titin-based passive tension in cardiomyocytes. A comprehensive overview is provided of studies that have measured altered titin phosphorylation and titin-based passive tension in myocardial samples from human heart failure patients and animal models of heart disease. As our understanding of the broader implications of phosphorylation in titin progresses, this knowledge could be used to design targeted interventions aimed at reducing pathologically increased titin stiffness in patients with stiff hearts.

Plasma volume status predicts prognosis in patients with acute heart failure syndromes

Background:

The intravascular compartment is known as the plasma volume, and the extravascular compartment represents fluid within the interstitial space. Plasma volume expansion is a major symptom of heart failure. The aim of the current study was to investigate the impact of plasma volume status on the prognosis of acute heart failure syndromes.

Methods and results:

We analyzed 1115 patients with acute heart failure syndromes who were admitted to our hospital. These patients were divided into three groups based on their plasma volume status at admission: first tertile (plasma volume status <41.9%, n = 371), second tertile (41.9%⩽ plasma volume status <49.0%, n = 372), and third tertile (49.0%⩽ plasma volume status, n = 372). Plasma volume status was defined as follows: actual plasma volume = (1 − hematocrit) × [ a + ( b × body weight)] ( a=1530 in males and a=864 in females, b=41.0 in males and b=47.9 in females); ideal plasma volume = c × body weight ( c=39 in males and c=40 in females); and plasma volume status = [(actual plasma volume − ideal plasma volume)/ideal plasma volume] × 100 (%). In the Kaplan–Meier analysis, all-cause mortality, cardiac mortality and cardiac events increased progressively from the first to third tertile ( p <0.001, respectively). In the Cox proportional hazard analysis, after adjusting for potential confounding factors, plasma volume status was an independent predictor of all-cause mortality (hazard ratio 1.429, p < 0.001), cardiac mortality (hazard ratio 1.416, p = 0.001) and cardiac events (hazard ratio 1.207, p = 0.004).

Conclusion:

Increased congestion is associated with increased morbidity and mortality in heart failure patients. Plasma volume status, which represents intravascular compartment and congestion, can identify poor prognosis in patients with acute heart failure syndromes.

Relevance of mouse models of cardiac fibrosis and hypertrophy in cardiac research

Heart disease causing cardiac cell death due to ischemia-reperfusion injury is a major cause of morbidity and mortality in the United States. Coronary heart disease and cardiomyopathies are the major cause for congestive heart failure, and thrombosis of the coronary arteries is the most common cause of myocardial infarction. Cardiac injury is followed by post-injury cardiac remodeling or fibrosis. Cardiac fibrosis is characterized by net accumulation of extracellular matrix proteins in the cardiac interstitium and results in both systolic and diastolic dysfunctions. It has been suggested by both experimental and clinical evidence that fibrotic changes in the heart are reversible. Hence, it is vital to understand the mechanism involved in the initiation, progression, and resolution of cardiac fibrosis to design anti-fibrotic treatment modalities. Animal models are of great importance for cardiovascular research studies. With the developing research field, the choice of selecting an animal model for the proposed research study is crucial for its outcome and translational purpose. Compared to large animal models for cardiac research, the mouse model is preferred by many investigators because of genetic manipulations and easier handling. This critical review is focused to provide insight to young researchers about the various mouse models, advantages and disadvantages, and their use in research pertaining to cardiac fibrosis and hypertrophy.

Proteomic analysis of short-term preload-induced eccentric cardiac hypertrophy

BACKGROUND

Hemodynamic load leads to cardiac hypertrophy and heart failure. While afterload (pressure overload) induces concentric hypertrophy, elevation of preload (volume overload) yields eccentric hypertrophy and is associated with a better outcome. Here we analysed the proteomic pattern of mice subjected to short-term preload.

METHODS AND RESULTS

Female FVB/N mice were subjected to aortocaval shunt-induced volume overload that leads to an eccentric hypertrophy (left ventricular weight/tibia length +31 %) with sustained systolic heart function at 1 week after operation. Two-dimensional gel electrophoresis (2-DE) followed by mass spectrometric analysis showed alteration in the expression of 25 protein spots representing 21 different proteins. 64 % of these protein spots were up-regulated and 36 % of the protein spots were consistently down-regulated. Interestingly, α-1-antitrypsin was down-regulated, indicating higher elastin degradation and possibly contributing to the early dilatation. In addition to contractile and mitochondrial proteins, polymerase I and transcript release factor protein (PTRF) was also up-regulated, possibly contributing to the preload-induced signal transduction.

CONCLUSIONS

Our findings reveal the proteomic changes of early-stage eccentric myocardial remodeling after volume overload. Induced expression of some of the respiratory chain enzymes suggests a metabolic shift towards an oxidative phosphorylation that might contribute to the favorable remodeling seen in early VO. Down-regulation of α-1-antitrypsin might contribute to extracellular matrix remodeling and left ventricular dilatation. We also identified PTRF as a potential signaling regulator of volume overload-induced cardiac hypertrophy.