Disruption of desmin-mitochondrial architecture in patients with regurgitant mitral valves and preserved ventricular function

Gene expression and ultra-structural evidence for metabolic derangement in the primary mitral regurgitation heart

Aims

Chronic neurohormonal activation and haemodynamic load cause derangement in the utilization of the myocardial substrate. In this study, we test the hypothesis that the primary mitral regurgitation (PMR) heart shows an altered metabolic gene profile and cardiac ultra-structure consistent with decreased fatty acid and glucose metabolism despite a left ventricular ejection fraction (LVEF) > 60%.

Methods and results

Metabolic gene expression in right atrial (RA), left atrial (LA), and left ventricular (LV) biopsies from donor hearts (n = 10) and from patients with moderate-to-severe PMR (n = 11) at surgery showed decreased mRNA glucose transporter type 4 (GLUT4), GLUT1, and insulin receptor substrate 2 and increased mRNA hexokinase 2, O-linked N-acetylglucosamine transferase, and O-linked N-acetylglucosaminyl transferase, rate-limiting steps in the hexosamine biosynthetic pathway. Pericardial fluid levels of neuropeptide Y were four-fold higher than simultaneous plasma, indicative of increased sympathetic drive. Quantitative transmission electron microscopy showed glycogen accumulation, glycophagy, increased lipid droplets (LDs), and mitochondrial cristae lysis. These findings are associated with increased mRNA for glycogen synthase kinase 3β, decreased carnitine palmitoyl transferase 2, and fatty acid synthase in PMR vs. normals. Cardiac magnetic resonance and positron emission tomography for 2-deoxy-2-[18F]fluoro-D-glucose ([18F]FDG) uptake showed decreased LV [18F]FDG uptake and increased plasma haemoglobin A1C, free fatty acids, and mitochondrial damage-associated molecular patterns in a separate cohort of patients with stable moderate PMR with an LVEF > 60% (n = 8) vs. normal controls (n = 8).

Conclusion

The PMR heart has a global ultra-structural and metabolic gene expression pattern of decreased glucose uptake along with increased glycogen and LDs. Further studies must determine whether this presentation is an adaptation or maladaptation in the PMR heart in the clinical evaluation of PMR.

Desmin gene expression is not ubiquitous in all upper airway myofibers and the pattern differs between healthy and sleep apnea subjects

BACKGROUND

Desmin is a major cytoskeletal protein considered ubiquitous in mature muscle fibers. However, we earlier reported that a subgroup of muscle fibers in the soft palate of healthy subjects and obstructive sleep apnea patients (OSA) lacked immunoexpression for desmin. This raised the question of whether these fibers also lack messenger ribonucleic acid (mRNA) for desmin and can be considered a novel fiber phenotype. Moreover, some fibers in the OSA patients had an abnormal distribution and aggregates of desmin. Thus, the aim of the study was to investigate if these desmin protein abnormalities are also reflected in the expression of desmin mRNA in an upper airway muscle of healthy subjects and OSA patients.

METHODS

Muscle biopsies from the musculus uvulae in the soft palate were obtained from ten healthy male subjects and six male patients with OSA. Overnight sleep apnea registrations were done for all participants. Immunohistochemistry, in-situ hybridization, and reverse transcription-quantitative polymerase chain reaction (RT-qPCR) techniques were used to evaluate the presence of desmin protein and its mRNA.

RESULTS

Our findings demonstrated that a group of muscle fibers lacked expression for desmin mRNA and desmin protein in healthy individuals and OSA patients (12.0 ± 5.6% vs. 23.1 ± 10.8%, p = 0.03). A subpopulation of these fibers displayed a weak subsarcolemmal rim of desmin accompanied by a few scattered mRNA dots in the cytoplasm. The muscles of OSA patients also differed from healthy subjects by exhibiting muscle fibers with reorganized or accumulated aggregates of desmin protein (14.5 ± 6.5%). In these abnormal fibers, the density of mRNA was generally low or concentrated in specific regions. The overall quantification of desmin mRNA by RT-qPCR was significantly upregulated in OSA patients compared to healthy subjects (p = 0.01).

CONCLUSIONS

Our study shows evidence that muscle fibers in the human soft palate lack both mRNA and protein for desmin. This indicates a novel cytoskeletal structure and challenges the ubiquity of desmin in muscle fibers. Moreover, the observation of reorganized or accumulated aggregates of desmin mRNA and desmin protein in OSA patients suggests a disturbance in the transcription and translation process in the fibers of the patients.

Desmin and its molecular chaperone, the αB-crystallin: How post-translational modifications modulate their functions in heart and skeletal muscles?

Maintenance of the highly organized striated muscle tissue requires a cell-wide dynamic network through protein-protein interactions providing an effective mechanochemical integrator of morphology and function. Through a continuous and complex trans-cytoplasmic network, desmin intermediate filaments ensure this essential role in heart and in skeletal muscle. Besides their role in the maintenance of cell shape and architecture (permitting contractile activity efficiency and conferring resistance towards mechanical stress), desmin intermediate filaments are also key actors of cell and tissue homeostasis. Desmin participates to several cellular processes such as differentiation, apoptosis, intracellular signalisation, mechanotransduction, vesicle trafficking, organelle biogenesis and/or positioning, calcium homeostasis, protein homeostasis, cell adhesion, metabolism and gene expression. Desmin intermediate filaments assembly requires αB-crystallin, a small heat shock protein. Over its chaperone activity, αB-crystallin is involved in several cellular functions such as cell integrity, cytoskeleton stabilization, apoptosis, autophagy, differentiation, mitochondria function or aggresome formation. Importantly, both proteins are known to be strongly associated to the aetiology of several cardiac and skeletal muscles pathologies related to desmin filaments disorganization and a strong disturbance of desmin interactome. Note that these key proteins of cytoskeleton architecture are extensively modified by post-translational modifications that could affect their functional properties. Therefore, we reviewed in the herein paper the impact of post-translational modifications on the modulation of cellular functions of desmin and its molecular chaperone, the αB-crystallin.

Elevated cardiac hemoglobin expression is associated with a pro-oxidative and inflammatory environment in primary mitral regurgitation

BACKGROUND

Primary mitral regurgitation (PMR) is associated with oxidative and inflammatory myocardial damage. We reported greater exosome hemoglobin (Hb) in pericardial fluid (PCF) versus plasma, suggesting a cardiac source of Hb.

OBJECTIVE

Test the hypothesis that Hb is produced in the PMR heart and is associated with increased inflammation.

METHODS AND RESULTS

Hb gene expression for subunits alpha (HBA) and beta (HBB) was assessed in right atria (RA), left atria (LA) and left ventricular (LV) tissue from donor hearts (n = 10) and PMR patient biopsies at surgery (n = 11). PMR patients (n = 22) had PCF and blood collected for macrophage markers, pro-inflammatory cytokines, and matrix metalloproteinases (MMPs). In-situ hybridization for HBA mRNA and immunohistochemistry for Hb-alpha (Hbα) and Hb-beta (Hbβ) protein was performed on PMR tissue.

RESULTS

HBA and HBB genes are significantly increased (>4-fold) in RA, LA, and LV in PMR vs. normal hearts. In PMR tissue, HBA mRNA is expressed in both LV cardiomyocytes and interstitial cells by in-situ hybridization; however, Hbα and Hbβ protein is only expressed in interstitial cells by immunohistochemistry. PCF oxyHb is significantly increased over plasma along with low ratios (<1.0) of haptoglobin:oxyHb and hemopexin:heme supporting a highly oxidative environment. Macrophage chemotactic protein-1, tumor necrosis factor-α, interleukin-6, and MMPs are significantly higher in PCF vs. plasma.

CONCLUSION

There is increased Hb production in the PMR heart coupled with the inflammatory state of the heart, suggests a myocardial vulnerability of further Hb delivery and/or production during cardiac surgery that could adversely affect LV functional recovery.

Different heart failure phenotypes of valvular heart disease: the role of mitochondrial dysfunction

Valvular heart disease (VHD)-related heart failure (HF) is a special subtype of HF with an increasingly concerned heterogeneity in pathophysiology, clinical phenotypes, and outcomes. The mechanism of VHD-related HF involves not only mechanical damage to the valve itself but also valve lesions caused by myocardial ischemia. The interactions between them will lead to the occurrence and development of VHD-related HF subtypes. Due to the spatial (combination of different valvular lesions) and temporal effects (sequence of valvular lesions) of valvular damages, it can make the patient's condition more complicated and also make the physicians deal with a dilemma when deciding on a treatment plan. This indicates that there is still lack of deep understanding on the pathogenic mechanism of VHD-related HF subtypes. On the other hand, mitochondrial dysfunction (MitD) is not only associated with the development of numerous cardiac diseases such as atherosclerosis, hypertension, diabetes, and HF but also occurs in VHD. However, the role of MitD in VHD-related HF is still not fully recognized. In this comprehensive review, we aim to discuss the current findings and challenges of different valvular damages derived from HF subtypes as well as the role of MitD in VHD-related HF subtypes.

Understanding post-surgical decline in left ventricular function in primary mitral regurgitation using regression and machine learning models

Background

Class I echocardiographic guidelines in primary mitral regurgitation (PMR) risks left ventricular ejection fraction (LVEF) < 50% after mitral valve surgery even with pre-surgical LVEF > 60%. There are no models predicting LVEF < 50% after surgery in the complex interplay of increased preload and facilitated ejection in PMR using cardiac magnetic resonance (CMR).

Objective

Use regression and machine learning models to identify a combination of CMR LV remodeling and function parameters that predict LVEF < 50% after mitral valve surgery.

Methods

CMR with tissue tagging was performed in 51 pre-surgery PMR patients (median CMR LVEF 64%), 49 asymptomatic (median CMR LVEF 63%), and age-matched controls (median CMR LVEF 64%). To predict post-surgery LVEF < 50%, least absolute shrinkage and selection operator (LASSO), random forest (RF), extreme gradient boosting (XGBoost), and support vector machine (SVM) were developed and validated in pre-surgery PMR patients. Recursive feature elimination and LASSO reduced the number of features and model complexity. Data was split and tested 100 times and models were evaluated via stratified cross validation to avoid overfitting. The final RF model was tested in asymptomatic PMR patients to predict post-surgical LVEF < 50% if they had gone to mitral valve surgery.

Results

Thirteen pre-surgery PMR had LVEF < 50% after mitral valve surgery. In addition to LVEF (P = 0.005) and LVESD (P = 0.13), LV sphericity index (P = 0.047) and LV mid systolic circumferential strain rate (P = 0.024) were predictors of post-surgery LVEF < 50%. Using these four parameters, logistic regression achieved 77.92% classification accuracy while RF improved the accuracy to 86.17%. This final RF model was applied to asymptomatic PMR and predicted 14 (28.57%) out of 49 would have post-surgery LVEF < 50% if they had mitral valve surgery.

Conclusions

These preliminary findings call for a longitudinal study to determine whether LV sphericity index and circumferential strain rate, or other combination of parameters, accurately predict post-surgical LVEF in PMR.

Mitochondrial haplotype modulates genome expression and mitochondrial structure/function in cardiomyocytes following volume overload

Mitochondrial DNA (mtDNA) haplotype regulates mitochondrial structure/function and reactive oxygen species in aortocaval fistula (ACF) in mice. Here, we unravel the mitochondrial haplotype effects on cardiomyocyte mitochondrial ultrastructure and transcriptome response to ACF in vivo. Phenotypic responses and quantitative transmission electron microscopy (TEM) and RNA sequence at 3 days were determined after sham surgery or ACF in vivo in cardiomyocytes from wild-type (WT) C57BL/6J (C57n:C57mt) and C3H/HeN (C3Hn:C3Hmt) and mitochondrial nuclear exchange mice (C57n:C3Hmt or C3Hn:C57mt). Quantitative TEM of cardiomyocyte mitochondria C3HWT hearts have more electron-dense compact mitochondrial cristae compared with C57WT. In response to ACF, mitochondrial area and cristae integrity are normal in C3HWT; however, there is mitochondrial swelling, cristae lysis, and disorganization in both C57WT and MNX hearts. Tissue analysis shows that C3HWT hearts have increased autophagy, antioxidant, and glucose fatty acid oxidation-related genes compared with C57WT. Comparative transcriptomic analysis of cardiomyocytes from ACF was dependent upon mtDNA haplotype. C57mtDNA haplotype was associated with increased inflammatory/protein synthesis pathways and downregulation of bioenergetic pathways, whereas C3HmtDNA showed upregulation of autophagy genes. In conclusion, ACF in vivo shows a protective response of C3Hmt haplotype that is in large part driven by mitochondrial nuclear genome interaction.NEW & NOTEWORTHY The results of this study support the effects of mtDNA haplotype on nuclear gene expression in cardiomyocytes. Currently, there is no acceptable therapy for volume overload due to mitral regurgitation. The findings of this study could suggest that mtDNA haplotype activates different pathways after ACF warrants further investigations on human population of heart disease from different ancestry backgrounds.

Mitochondrial dysfunction in human hypertrophic cardiomyopathy is linked to cardiomyocyte architecture disruption and corrected by improving NADH-driven mitochondrial respiration

AIMS

Genetic hypertrophic cardiomyopathy (HCM) is caused by mutations in sarcomere protein-encoding genes (i.e. genotype-positive HCM). In an increasing number of patients, HCM occurs in the absence of a mutation (i.e. genotype-negative HCM). Mitochondrial dysfunction is thought to be a key driver of pathological remodelling in HCM. Reports of mitochondrial respiratory function and specific disease-modifying treatment options in patients with HCM are scarce.

METHODS AND RESULTS

Respirometry was performed on septal myectomy tissue from patients with HCM (n = 59) to evaluate oxidative phosphorylation and fatty acid oxidation. Mitochondrial dysfunction was most notably reflected by impaired NADH-linked respiration. In genotype-negative patients, but not genotype-positive patients, NADH-linked respiration was markedly depressed in patients with an indexed septal thickness ≥10 compared with <10. Mitochondrial dysfunction was not explained by reduced abundance or fragmentation of mitochondria, as evaluated by transmission electron microscopy. Rather, improper organization of mitochondria relative to myofibrils (expressed as a percentage of disorganized mitochondria) was strongly associated with mitochondrial dysfunction. Pre-incubation with the cardiolipin-stabilizing drug elamipretide and raising mitochondrial NAD+ levels both boosted NADH-linked respiration.

CONCLUSION

Mitochondrial dysfunction is explained by cardiomyocyte architecture disruption and is linked to septal hypertrophy in genotype-negative HCM. Despite severe myocardial remodelling mitochondria were responsive to treatments aimed at restoring respiratory function, eliciting the mitochondria as a drug target to prevent and ameliorate cardiac disease in HCM. Mitochondria-targeting therapy may particularly benefit genotype-negative patients with HCM, given the tight link between mitochondrial impairment and septal thickening in this subpopulation.

Interstitial Collagen Loss, Myocardial Remodeling, and Function in Primary Mitral Regurgitation

•

The stretch of volume overload in PMR initiates interstitial collagen loss and decrease in LV sphericity index.

•

LV chamber diastolic function is normal whereas LA function, LV twist/volume slope, early LV untwist, and myocardial circumferential strain are impaired.

•

There is increased oxidative stress in the cardiomyocyte with cytoskeletal breakdown and myofibrillar loss in PMR.

Interstitial collagen loss and cardiomyocyte ultrastructural damage accounts for left ventricular (LV) sphericity and decrease in LV twist and circumferential strain. Normal LV diastolic function belies significantly abnormal left atrial (LA) function and early LV diastolic untwist rate. This underscores the complex interplay of LV and LA myocardial remodeling and function in the pathophysiology of primary mitral regurgitation. In this study, we connect LA function with LV systolic and diastolic myocardial remodeling and function using cardiac magnetic resonance tissue tagging in primary mitral regurgitation.

Post-translational protein deimination signatures in sea lamprey (Petromyzon marinus) plasma and plasma-extracellular vesicles

Lampreys are a jawless vertebrate species belonging to an ancient vertebrate lineage that diverged from a common ancestor with humans ~500 million years ago. The sea lamprey (Petromyzon marinus) has a filter feeding ammocoete larval stage that metamorphoses into a parasitic adult, feeding both on teleost and elasmobranch fish. Lampreys are a valuable comparative model species for vertebrate immunity and physiology due to their unique phylogenetic position, unusual adaptive immune system, and physiological adaptions such as tolerance to salinity changes and urea. Peptidylarginine deiminases (PADs) are a phylogenetically conserved enzyme family which catalyses post-translational deimination/citrullination in target proteins, enabling proteins to gain new functions (moonlighting). The identification of deiminated protein targets in species across phylogeny may provide novel insights into post-translational regulation of physiological and pathophysiological processes. Extracellular vesicles (EVs) are membrane vesicles released from cells that carry cargos of small molecules and proteins for cellular communication, involved in both normal and pathological processes. The current study identified deimination signatures in proteins of both total plasma and plasma-EVs in sea lamprey and furthermore reports the first characterisation of plasma-EVs in lamprey. EVs were poly-dispersed in the size range of 40-500 nm, similar to what is observed in other taxa, positive for CD63 and Flotillin-1. Plasma-EV morphology was confirmed by transmission electron microscopy. Assessment of deimination/citrullination signatures in lamprey plasma and plasma-EVs, revealed 72 deimination target proteins involved in immunity, metabolism and gene regulation in whole plasma, and 37 target proteins in EVs, whereof 24 were shared targets. Furthermore, the presence of deiminated histone H3, indicative of gene-regulatory mechanisms and also a marker of neutrophil extracellular trap formation (NETosis), was confirmed in lamprey plasma. Functional protein network analysis revealed some differences in KEGG and GO pathways of deiminated proteins in whole plasma compared with plasma-EVs. For example, while common STRING network clusters in plasma and plasma-EVs included Peptide chain elongation, Viral mRNA translation, Glycolysis and gluconeogenesis, STRING network clusters specific for EVs only included: Cellular response to heat stress, Muscle protein and striated muscle thin filament, Nucleosome, Protein processing in endoplasmic reticulum, Nucleosome and histone deacetylase complex. STRING network clusters specific for plasma were: Adipokinetic hormone receptor activity, Fibrinogen alpha/beta chain family, peptidase S1A, Glutathione synthesis and recycling-arginine, Fructose 1,6-bisphosphate metabolic process, Carbon metabolism and lactate dehydrogenase activity, Post-translational protein phosphorylation, Regulation of insulin-like growth factor transport and clotting cascade. Overall, for the EV citrullinome, five STRING network clusters, 10 KEGG pathways, 15 molecular GO pathways and 29 Reactome pathways were identified, compared with nine STRING network clusters, six KEGG pathways, two Molecular GO pathways and one Reactome pathway specific for whole plasma; while further pathways were shared. The reported findings indicate that major pathways relevant for immunity and metabolism are targets of deimination in lamprey plasma and plasma-EVs, with some differences, and may help elucidating roles for the conserved PAD enzyme family in regulation of immune and metabolic function throughout phylogeny.

Chronic cardiac structural damage, diastolic and systolic dysfunction following acute myocardial injury due to bromine exposure in rats

Accidental bromine spills are common and its large industrial stores risk potential terrorist attacks. The mechanisms of bromine toxicity and effective therapeutic strategies are unknown. Our studies demonstrate that inhaled bromine causes deleterious cardiac manifestations. In this manuscript we describe mechanisms of delayed cardiac effects in the survivors of a single bromine exposure. Rats were exposed to bromine (600 ppm for 45 min) and the survivors were sacrificed at 14 or 28 days. Echocardiography, hemodynamic analysis, histology, transmission electron microscopy (TEM) and biochemical analysis of cardiac tissue were performed to assess functional, structural and molecular effects. Increases in right ventricular (RV) and left ventricular (LV) end-diastolic pressure and LV end-diastolic wall stress with increased LV fibrosis were observed. TEM images demonstrated myofibrillar loss, cytoskeletal breakdown and mitochondrial damage at both time points. Increases in cardiac troponin I (cTnI) and N-terminal pro brain natriuretic peptide (NT-proBNP) reflected myofibrillar damage and increased LV wall stress. LV shortening decreased as a function of increasing LV end-systolic wall stress and was accompanied by increased sarcoendoplasmic reticulum calcium ATPase (SERCA) inactivation and a striking dephosphorylation of phospholamban. NADPH oxidase 2 and protein phosphatase 1 were also increased. Increased circulating eosinophils and myocardial 4-hydroxynonenal content suggested increased oxidative stress as a key contributing factor to these effects. Thus, a continuous oxidative stress-induced chronic myocardial damage along with phospholamban dephosphorylation are critical for bromine-induced chronic cardiac dysfunction. These findings in our preclinical model will educate clinicians and public health personnel and provide important endpoints to evaluate therapies.

Mitigating cardiac dysfunction by TOE-guided cardioplegia and mitral valve repair

Based on current guidelines, 15% to 20% of patients undergoing mitral valve repair for regurgitation develop left ventricular dysfunction (ejection fraction < 50%-55%) despite a normal baseline. Two schools of thought have been debated: preexisting myocardial disease or suboptimal intraoperative myocardial protection. In our view, they could be reconciled. It is well recognized that left ventricular ejection fraction with a standard cut off at 50%-55% has limited sensitivity in detecting early systolic impairment in mitral regurgitation patients. Mitral regurgitation also leads to mitochondrial oxidative stress, thus rendering the myocardium more susceptible to ischemia-reperfusion injury and precipitating postoperative cardiac dysfunction. The fall in left ventricular ejection fraction early after mitral valve repair was shown to be caused by the reduction in both myocardial contractility and left ventricular stroke volume. To mitigate the risk to myocardial reperfusion injury, appropriate cardioplegia volume and distribution and well-defined surgical repair processes are equally important. We use transesophageal echocardiography-guided cardioplegia delivery, imaging the intramyocardial flow and ensuring adequate protection of the subendocardium during mitral valve repair. Mild aortic regurgitation on a beating heart often leads to left ventricular dilatation with diminished cardioplegia flow in the myocardium, thus requiring direct ostia cardioplegia. Systematic transesophageal echocardiography assessment before surgery is essential for establishing the mitral regurgitation mechanisms and translating them into precise surgical repair strategies. The benefits of transesophageal echocardiography-guided cardioplegia delivery warrant further clinical trials in order to evolve into part of a high surgical standard.

Ubiquitin Pathway Is Associated with Worsening Left Ventricle Function after Mitral Valve Repair: A Global Gene Expression Study

The molecular mechanism for worsening left ventricular (LV) function after mitral valve (MV) repair for chronic mitral regurgitation remains unknown. We wished to assess the LV transcriptome and identify determinants associated with worsening LV function post-MV repair. A total of 13 patients who underwent MV repair for chronic primary mitral regurgitation were divided into two groups, preserved LV function (N = 8) and worsening LV function (N = 5), for the study. Specimens of LV from the patients taken during surgery were used for the gene microarray study. Cardiomyocyte cell line HL-1 cells were transfected with gene-containing plasmids and further evaluated for mRNA and protein expression, apoptosis, and contractile protein degradation. Of 67,258 expressed sequence tags, microarrays identified 718 genes to be differentially expressed between preserved-LVF and worsening-LVF, including genes related to the protein ubiquitination pathway, bone morphogenetic protein (BMP) receptors, and regulation of eIF4 and p70S6K signaling. In addition, worsening-LVF was associated with altered expressions of genes pathologically relevant to heart failure, such asdownregulated apelin receptors and upregulated peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PPARGC1A). HL-1 cardiomyocyte cells transfected with ubiquitination-related genes demonstrated activation of the protein ubiquitination pathwaywith an increase in the ubiquitin activating enzyme E1 (UAE-E1). It also led to increased apoptosis, downregulated and ubiquitinated X-linked inhibitor of apoptosis protein (XIAP), and reduced cell viability. Overexpression of ubiquitination-related genes also resulted in degradation and increased ubiquitination of α-smooth muscle actin (SMA). In conclusion, worsening-LVF presented differential gene expression profiles from preserved-LVF after MV repair. Upregulation of protein ubiquitination-related genes associated with worsening-LVF after MV repair may exert adverse effects on LV through increased apoptosis and contractile protein degradation.

Long-term risk of heart failure and mortality following mitral valve surgery in patients with and without right ventricular pacemaker

OBJECTIVES

Patients undergoing mitral valve surgery are at risk of developing postoperative conduction blocks and have a high incidence of heart failure (HF). Mitral valve surgery often results in reduced left ventricular systolic ejection fraction following surgery and the imposition of dyssynchrony with right ventricular (RV) pacing may further compromise stroke volume. Our aim was to investigate the risks of HF and mortality in patients with vs without RV pacemaker placement (PPM) after mitral valve surgery.

METHODS

Using Danish nationwide databases, we identified all patients undergoing mitral valve repair or replacement surgery between 1997 and 2017, who were free from HF at baseline. The association of PPM implanted within 30 days following surgery with long-term risks of HF and mortality was investigated by multivariable Cox regression models.

RESULTS

Of 4072 patients (33% female), 248 (6%) had a PPM implanted at 30-day postsurgery. Patients with PPM were older (68 vs 63 years), had a higher prevalence of concomitant aortic valve surgery (15% vs 11%), ischemic heart disease (13% vs 8%), and atrial fibrillation (19% vs 12%), compared with patients without PPM. Over a median follow-up of 5 years, 68 (27%) vs 825 (22%) patients with vs without PPM developed HF and 74 (30%) vs 1018 (27%) died. In multivariable-adjusted models, the hazard ratios associated with PPM were 1.00 (0.78-1.30), P = .93 for HF, and .96 (0.76-1.21), P = .72 for mortality.

CONCLUSIONS

Postoperative implantation of a permanent RV pacemaker does not alter the long-term risks of HF and mortality following mitral valve surgery.

Priming the Proteasome to Protect against Proteotoxicity

Increased proteotoxic stress (IPTS) resulting from the increased production or decreased removal of abnormally folded proteins is recognized as an important pathogenic factor for a large group of highly disabling and life-threatening human diseases, such as neurodegenerative disorders and many heart diseases. The proteasome is pivotal to the timely removal of abnormal proteins but its functional capacity often becomes inadequate in the disease conditions; consequently, proteasome functional insufficiency in return exacerbates IPTS. Recent research in proteasome biology reveals that the proteasome can be activated by endogenous protein kinases, making it possible to pharmacologically prime the proteasome for treating diseases with IPTS.

Reduced Left Atrial Emptying Fraction and Chymase Activation in Pathophysiology of Primary Mitral Regurgitation

Increasing left atrial (LA) size predicts outcomes in patients with isolated mitral regurgitation (MR). Chymase is plentiful in the human heart and affects extracellular matrix remodeling. Chymase activation correlates to LA fibrosis, LA enlargement, and a decreased total LA emptying fraction in addition to having a potential intracellular role in mediating myofibrillar breakdown in LA myocytes. Because of the unreliability of the left ventricular ejection fraction in predicting outcomes in MR, LA size and the total LA emptying fraction may be more suitable indicators for timing of surgical intervention.

Highly Dynamic Changes in the Activity and Regulation of Macroautophagy in Hearts Subjected to Increased Proteotoxic Stress

Macroautophagy (referred to as autophagy hereafter) plays an important role in the quality control of cellular proteins and organelles. Transcription Factor EB (TFEB) globally activates the expression of genes in the autophagic-lysosomal pathway (ALP) to replenish lysosomes and ALP machineries. We previously reported that myocardial TFEB signaling was impaired in advanced cardiac proteinopathy; however, myocardial ALP status and TFEB activity at earlier stages of cardiac proteinopathy remain uncharacterized. Here a stable line of CryAB^R120G transgenic (R120G) and non-transgenic (NTG) littermate mice with cardiomyocyte-restricted overexpression of CryAB^R120G were used at 1, 3, and 6 months of age. At 1 month when no cardiac phenotypes other than aberrant protein aggregation are discernible, R120G mice displayed a 5-fold increase in myocardial LC3-II flux. Interestingly, the LC3-II flux increase co-existed with increases in mTOR complex 1 (mTORC1) activities as well as cytoplasmic, but not nuclear, TFEB proteins. This increase in cytoplasmic TFEB proteins occurred without any discernible alteration in TFEB activity as reflected by unchanged mRNA levels of representative TFEB target genes (Mcoln1, M6pr, Sqstm1, Vps18, and Uvrag). At 3 months of age when hypertrophy and diastolic malfunction start to develop, the LC3-II flux remained significantly increased but to a lesser degree (2-fold) than at 1 month. The LC3-II flux increase was associated with decreased mTORC1 activities and with increased nuclear TFEB proteins and TFEB activities. At 6 months of age when congestive heart failure is apparent in R120G mice, both LC3-II flux and TFEB activities were severely suppressed, while mTORC1 activity increased. We conclude that changes in both autophagy and TFEB signaling are highly dynamic during the progression of cardiac proteinopathy. Increases in autophagy occur before increases in TFEB activities but both increase in the compensatory stage of cardiac proteinopathy. Once congestive heart failure develops, both autophagy and TFEB signaling become impaired. Our results suggest that TFEB signaling is regulated by both mTORC1-dependent and -independent mechanisms in hearts subjected to increased proteotoxic stress. For therapeutic exploration, it will be important to test the effect of TFEB stimulation at the early, intermediate, and late stages of cardiac proteinopathy.

Multifunctional Role of Chymase in Acute and Chronic Tissue Injury and Remodeling

Chymase is the most efficient Ang II (angiotensin II)-forming enzyme in the human body and has been implicated in a wide variety of human diseases that also implicate its many other protease actions. Largely thought to be the product of mast cells, the identification of other cellular sources including cardiac fibroblasts and vascular endothelial cells demonstrates a more widely dispersed production and distribution system in various tissues. Furthermore, newly emerging evidence for its intracellular presence in cardiomyocytes and smooth muscle cells opens an entirely new compartment of chymase-mediated actions that were previously thought to be limited to the extracellular space. This review illustrates how these multiple chymase-mediated mechanisms of action can explain the residual risk in clinical trials of cardiovascular disease using conventional renin-angiotensin system blockade.

Chymase uptake by cardiomyocytes results in myosin degradation in cardiac volume overload

Background

Volume overload (VO) of isolated mitral regurgitation (MR) or aortocaval fistula (ACF) is associated with extracellular matrix degradation and cardiomyocyte myofibrillar and desmin breakdown. Left ventricular (LV) chymase activity is increased in VO and recent studies demonstrate chymase presence within cardiomyocytes. Here we test the hypothesis that chymase within the cardiomyocyte coincides with myosin and desmin breakdown in VO.

Methods and results

Aortocaval fistula (ACF) was induced in Sprague Dawley (SD) rats and was compared to age-matched sham-operated rats at 24 hours, 4 and 12 weeks. Immunohistochemistry (IHC) and transmission electron microscopy (TEM) immunogold of LV tissue demonstrate chymase within cardiomyocytes at all ACF time points. IHC for myosin demonstrates myofibrillar disorganization starting at 24 hours. Proteolytic presence of chymase in cardiomyocytes is verified by in situ chymotryptic tissue activity that is inhibited by pretreatment with a chymase inhibitor. Real-time PCR of isolated cardiomyocytes at all ACF time points and in situ hybridization demonstrate endothelial cells and fibroblasts as a major source of chymase mRNA in addition to mast cells. Chymase added to adult rat cardiomyocytes in vitro is taken up by a dynamin-mediated process and myosin breakdown is attenuated by dynamin inhibitor, suggesting that chymase uptake is essential for myosin breakdown. In a previous study in the dog model of chronic MR, the intracellular changes were attributed to extracellular effects. However, we now demonstrate intracellular effects of chymase in both species.

Conclusion

In response to VO, fibroblast and endothelial cells produce chymase and subsequent cardiomyocyte chymase uptake is followed by myosin degradation. The results demonstrate a novel intracellular chymase-mediated mechanism of cardiomyocyte dysfunction and adverse remodeling in a pure VO.

Bromine inhalation mimics ischemia-reperfusion cardiomyocyte injury and calpain activation in rats

Halogens are widely used, highly toxic chemicals that pose a potential threat to humans because of their abundance. Halogens such as bromine (Br₂) cause severe pulmonary and systemic injuries; however, the mechanisms of their toxicity are largely unknown. Here, we demonstrated that Br₂ and reactive brominated species produced in the lung and released in blood reach the heart and cause acute cardiac ultrastructural damage and dysfunction in rats. Br₂-induced cardiac damage was demonstrated by acute (3-24 h) increases in circulating troponin I, heart-type fatty acid-binding protein, and NH₂-terminal pro-brain natriuretic peptide. Transmission electron microscopy demonstrated acute (3-24 h) cardiac contraction band necrosis, disruption of z-disks, and mitochondrial swelling and disorganization. Echocardiography and hemodynamic analysis revealed left ventricular (LV) systolic and diastolic dysfunction at 7 days. Plasma and LV tissue had increased levels of brominated fatty acids. 2-Bromohexadecanal (Br-HDA) injected into the LV cavity of a normal rat caused acute LV enlargement with extensive disruption of the sarcomeric architecture and mitochondrial damage. There was extensive infiltration of neutrophils and increased myeloperoxidase levels in the hearts of Br_2- or Br₂ reactant-exposed rats. Increased bromination of sarco(endo)plasmic reticulum Ca²⁺-ATPase (SERCA) and increased phosphalamban after Br₂ inhalation decreased cardiac SERCA activity by 70%. SERCA inactivation was accompanied by increased Ca²⁺-sensitive LV calpain activity. The calpain-specific inhibitor MDL28170 administered within 1 h after exposure significantly decreased calpain activity and acute mortality. Bromine inhalation and formation of reactive brominated species caused acute cardiac injury and myocardial damage that can lead to heart failure. NEW & NOTEWORTHY The present study defines left ventricular systolic and diastolic dysfunction due to cardiac injury after bromine (Br₂) inhalation. A calpain-dependent mechanism was identified as a potential mediator of cardiac ultrastructure damage. This study not only highlights the importance of monitoring acute cardiac symptoms in victims of Br₂ exposure but also defines calpains as a potential target to treat Br₂-induced toxicity.

Long-term results of mitral valve repair for severe mitral regurgitation in asymptomatic patients

BACKGROUND

In asymptomatic patients with severe degenerative mitral valve regurgitation (MR), early surgery is often performed in experienced centers. The patient- and valve-related results and the quality of life after surgery in these patients remain insufficiently explored.

METHODS

Between 1/2000 and 12/2015, 83 asymptomatic patients (mean age 56.6±12.6 years, 21 female) without any complications related to long-lasting MR underwent early surgery. Follow-up clinical and echocardiographic data and health-related quality of life assessment (SF-36) were studied and matched to the general population.

RESULTS

Repair rate was 100% and early mortality was 0%. Residual MR (≥grade 2+) was seen in 1 (1%) patient who underwent a successful re-repair while 4 (5%) patients needed permanent pacemaker implantation. At a median follow-up of 7.6 (IQR 4.1-11.9) years, 6 late deaths occurred. The 10-year overall survival rate was 91.5% (95% CI 84.2-98.8%) and was comparable to the general population. The health-related quality of life (84% complete) did not differ from the general population. One patient underwent late reintervention. Median echocardiography follow-up was 5.2 years (IQR 2.4-10.4; 98% complete). The 10-year freedom from recurrent MR rate (≥grade 2+) was 86.7% (95% CI 76.1-97.3%). The 10-year freedom from any atrial tachycardia rate was 68.7% (95% CI 55.2-82.2%) while 7 (8%) patients underwent late pacemaker implantation.

CONCLUSIONS

Early surgical intervention in asymptomatic patients with severe MR can be performed safely and restores normal life expectancy and quality of life. However, the frequency of late arrhythmias and pacemaker implantation is high and needs further evaluation.

Cardiovascular magnetic resonance imaging to assess myocardial fibrosis in valvular heart disease

The left ventricular (LV) remodeling process associated with significant valvular heart disease (VHD) is characterized by an increase of myocardial interstitial space with deposition of collagen and loss of myofibers. These changes occur before LV systolic function deteriorates or the patient develops symptoms. Cardiovascular magnetic resonance (CMR) permits assessment of reactive fibrosis, with the use of T1 mapping techniques, and replacement fibrosis, with the use of late gadolinium contrast enhancement. In addition, functional consequences of these structural changes can be evaluated with myocardial tagging and feature tracking CMR, which assess the active deformation (strain) of the LV myocardium. Several studies have demonstrated that CMR techniques may be more sensitive than the conventional measures (LV ejection fraction or LV dimensions) to detect these structural and functional changes in patients with severe left-sided VHD and have shown that myocardial fibrosis may not be reversible after valve surgery. More important, the presence of myocardial fibrosis has been associated with lesser improvement in clinical symptoms and recovery of LV systolic function. Whether assessment of myocardial fibrosis may better select the patients with severe left-sided VHD who may benefit from surgery in terms of LV function and clinical symptoms improvement needs to be demonstrated in prospective studies. The present review article summarizes the current status of CMR techniques to assess myocardial fibrosis and appraises the current evidence on the use of these techniques for risk stratification of patients with severe aortic stenosis or regurgitation and mitral regurgitation.

Desmin loss and mitochondrial damage precede left ventricular systolic failure in volume overload heart failure

Heart failure due to chronic volume overload (VO) in rats and humans is characterized by disorganization of the cardiomyocyte desmin/mitochondrial network. Here, we tested the hypothesis that desmin breakdown is an early and continuous process throughout VO. Male Sprague-Dawley rats had aortocaval fistula (ACF) or sham surgery and were examined 24 h and 4 and 12 wk later. Desmin/mitochondrial ultrastructure was examined by transmission electron microscopy (TEM) and immunohistochemistry (IHC). Protein and kinome analysis were performed in isolated cardiomyocytes, and desmin cleavage was assessed by mass spectrometry in left ventricular (LV) tissue. Echocardiography demonstrated a 40% decrease in the LV mass-to-volume ratio with spherical remodeling at 4 wk with ACF and LV systolic dysfunction at 12 wk. Starting at 24 h and continuing to 4 and 12 wk, with ACF there is TEM evidence of extensive mitochondrial clustering, IHC evidence of disorganization associated with desmin breakdown, and desmin protein cleavage verified by Western blot analysis and mass spectrometry. IHC results revealed that ACF cardiomyocytes at 4 and 12 wk had perinuclear translocation of αB-crystallin from the Z disk with increased α, β-unsaturated aldehyde 4-hydroxynonelal. Use of protein markers with verification by TUNEL staining and kinome analysis revealed an absence of cardiomyocyte apoptosis at 4 and 12 wk of ACF. Significant increases in protein indicators of mitophagy were countered by a sixfold increase in p62/sequestosome-1, which is indicative of an inability to complete autophagy. An early and continuous disruption of the desmin/mitochondrial architecture, accompanied by oxidative stress and inhibition of apoptosis and mitophagy, suggests its causal role in LV dilatation and systolic dysfunction in VO.NEW & NOTEWORTHY This study provides new evidence of early onset (24 h) and continuous (4-12 wk) desmin misarrangement and disruption of the normal sarcomeric and mitochondrial architecture throughout the progression of volume overload heart failure, suggesting a causal link between desmin cleavage and mitochondrial disorganization and damage.