Proteomic analysis of metabolic, cytoskeletal and stress response proteins in human heart failure

Mitochondrial heterogeneity in diseases

As key organelles involved in cellular metabolism, mitochondria frequently undergo adaptive changes in morphology, components and functions in response to various environmental stresses and cellular demands. Previous studies of mitochondria research have gradually evolved, from focusing on morphological change analysis to systematic multiomics, thereby revealing the mitochondrial variation between cells or within the mitochondrial population within a single cell. The phenomenon of mitochondrial variation features is defined as mitochondrial heterogeneity. Moreover, mitochondrial heterogeneity has been reported to influence a variety of physiological processes, including tissue homeostasis, tissue repair, immunoregulation, and tumor progression. Here, we comprehensively review the mitochondrial heterogeneity in different tissues under pathological states, involving variant features of mitochondrial DNA, RNA, protein and lipid components. Then, the mechanisms that contribute to mitochondrial heterogeneity are also summarized, such as the mutation of the mitochondrial genome and the import of mitochondrial proteins that result in the heterogeneity of mitochondrial DNA and protein components. Additionally, multiple perspectives are investigated to better comprehend the mysteries of mitochondrial heterogeneity between cells. Finally, we summarize the prospective mitochondrial heterogeneity-targeting therapies in terms of alleviating mitochondrial oxidative damage, reducing mitochondrial carbon stress and enhancing mitochondrial biogenesis to relieve various pathological conditions. The possibility of recent technological advances in targeted mitochondrial gene editing is also discussed.

Emerging role of heat shock proteins in cardiovascular diseases

Heat Shock Proteins (HSPs) are evolutionarily conserved proteins from prokaryotes to eukaryotes. They are ubiquitous proteins involved in key physiological and cellular pathways (viz. inflammation, immunity and apoptosis). Indeed, the survivability of the cells under various stressful conditions depends on appropriate levels of HSP expression. There is a growing line of evidence for the role of HSPs in regulating cardiovascular diseases (CVDs) (viz. hypertension, atherosclerosis, atrial fibrillation, cardiomyopathy and heart failure). Furthermore, studies indicate that a higher concentration of circulatory HSP antibodies correlate to CVDs; some are even potential markers for CVDs. The multifaceted roles of HSPs in regulating cellular signaling necessitate unraveling their links to pathophysiology of CVDs. This review aims to consolidate our understanding of transcriptional (via multiple transcription factors including HSF-1, NF-κB, CREB and STAT3) and post-transcriptional (via microRNAs including miR-1, miR-21 and miR-24) regulation of HSPs. The cytoprotective nature of HSPs catapults them to the limelight as modulators of cell survival. Yet another attractive prospect is the development of new therapeutic strategies against cardiovascular diseases (from hypertension to heart failure) by targeting the regulation of HSPs. Moreover, this review provides insights into how genetic variation of HSPs can contribute to the manifestation of CVDs. It would also offer a bird's eye view of the evolving role of different HSPs in the modulation and manifestation of cardiovascular disease.

Proteomic and phosphoproteomic profiling in heart failure with preserved ejection fraction (HFpEF)

Although the prevalence of heart failure with preserved ejection fraction (HFpEF) is increasing, evidence-based therapies for HFpEF remain limited, likely due to an incomplete understanding of this disease. This study sought to identify the cardiac-specific features of protein and phosphoprotein changes in a murine model of HFpEF using mass spectrometry. HFpEF mice demonstrated moderate hypertension, left ventricle (LV) hypertrophy, lung congestion and diastolic dysfunction. Proteomics analysis of the LV tissue showed that 897 proteins were differentially expressed between HFpEF and Sham mice. We observed abundant changes in sarcomeric proteins, mitochondrial-related proteins, and NAD-dependent protein deacetylase sirtuin-3 (SIRT3). Upregulated pathways by GSEA analysis were related to immune modulation and muscle contraction, while downregulated pathways were predominantly related to mitochondrial metabolism. Western blot analysis validated SIRT3 downregulated cardiac expression in HFpEF vs. Sham (0.8 ± 0.0 vs. 1.0 ± 0.0; P < 0.001). Phosphoproteomics analysis showed that 72 phosphosites were differentially regulated between HFpEF and Sham LV. Aberrant phosphorylation patterns mostly occurred in sarcomere proteins and nuclear-localized proteins associated with contractile dysfunction and cardiac hypertrophy. Seven aberrant phosphosites were observed at the z-disk binding region of titin. Additional agarose gel analysis showed that while total titin cardiac expression remained unaltered, its stiffer N2B isoform was significantly increased in HFpEF vs. Sham (0.144 ± 0.01 vs. 0.127 ± 0.01; P < 0.05). In summary, this study demonstrates marked changes in proteins related to mitochondrial metabolism and the cardiac contractile apparatus in HFpEF. We propose that SIRT3 may play a role in perpetuating these changes and may be a target for drug development in HFpEF.

Multi-omics integration identifies key upstream regulators of pathomechanisms in hypertrophic cardiomyopathy due to truncating MYBPC3 mutations

BACKGROUND

Hypertrophic cardiomyopathy (HCM) is the most common genetic disease of the cardiac muscle, frequently caused by mutations in MYBPC3. However, little is known about the upstream pathways and key regulators causing the disease. Therefore, we employed a multi-omics approach to study the pathomechanisms underlying HCM comparing patient hearts harboring MYBPC3 mutations to control hearts.

RESULTS

Using H3K27ac ChIP-seq and RNA-seq we obtained 9310 differentially acetylated regions and 2033 differentially expressed genes, respectively, between 13 HCM and 10 control hearts. We obtained 441 differentially expressed proteins between 11 HCM and 8 control hearts using proteomics. By integrating multi-omics datasets, we identified a set of DNA regions and genes that differentiate HCM from control hearts and 53 protein-coding genes as the major contributors. This comprehensive analysis consistently points toward altered extracellular matrix formation, muscle contraction, and metabolism. Therefore, we studied enriched transcription factor (TF) binding motifs and identified 9 motif-encoded TFs, including KLF15, ETV4, AR, CLOCK, ETS2, GATA5, MEIS1, RXRA, and ZFX. Selected candidates were examined in stem cell-derived cardiomyocytes with and without mutated MYBPC3. Furthermore, we observed an abundance of acetylation signals and transcripts derived from cardiomyocytes compared to non-myocyte populations.

CONCLUSIONS

By integrating histone acetylome, transcriptome, and proteome profiles, we identified major effector genes and protein networks that drive the pathological changes in HCM with mutated MYBPC3. Our work identifies 38 highly affected protein-coding genes as potential plasma HCM biomarkers and 9 TFs as potential upstream regulators of these pathomechanisms that may serve as possible therapeutic targets.

Membrane proteomic profiling of the heart: past, present, and future

Cardiovascular diseases remain the most rapidly rising contributing factor of all-cause mortality and the leading cause of inpatient hospitalization worldwide, with costs exceeding $30 billion annually in North America. Cell surface and membrane-associated proteins play an important role in cardiomyocyte biology and are involved in the pathogenesis of many human heart diseases. In cardiomyocytes, membrane proteins serve as critical signaling receptors, Ca²⁺ cycling regulators, and electrical propagation regulators, all functioning in concert to maintain spontaneous and synchronous contractions of cardiomyocytes. Membrane proteins are excellent pharmaceutical targets due to their uniquely exposed position within the cell. Perturbations in cardiac membrane protein localization and function have been implicated in the progression and pathogenesis of many heart diseases. However, previous attempts at profiling the cardiac membrane proteome have yielded limited results due to poor technological developments for isolating hydrophobic, low-abundance membrane proteins. Comprehensive mapping and characterization of the cardiac membrane proteome thereby remains incomplete. This review will focus on recent advances in mapping the cardiac membrane proteome and the role of novel cardiac membrane proteins in the healthy and the diseased heart.

The inflammatory markers sST2, HSP27 and hsCRP as a prognostic biomarker panel in chronic heart failure patients

BACKGROUND

The inflammatory markers sST2, HSP27 and hsCRP have already been identified as prognostic markers in chronic heart failure (HF). Though individual biomarkers have proven their value in mortality risk prediction, the role of a multimarker strategy needs further evaluation.

MATERIALS AND METHODS

This is an exploratory reanalysis in chronic HF patients. Plasma HSP27, sST2 and hsCRP in outpatients with chronic HF were analysed. Patients were followed for a minimum of twelve months for the endpoint cardiovascular mortality and unplanned HF associated hospitalisation (=event). 15 year overall mortality was assessed retrospectively. The prognostic impact was assessed using a Cox proportional hazard model.

RESULTS

113 chronic HF patients were included. Median follow up time was 614 days and 37 patients (32.7%) experienced an event. A Kaplan-Meier analysis revealed that patients with increased sST2, HSP27 and hsCRP levels have significantly worse prognosis (p < 0.001). The use of a three-biomarker combination was superior in an independent risk prediction of an event (one high vs. two high: HR = 4.5, 95% CI: 1.3-15.5, p = 0.018; and one high vs. all high: HR = 9.8, 95% CI: 2.8-34.3, p < 0.001) as shown in a multivariable cox proportional hazard model. However, the biomarker panel did not predict 15 year overall mortality, in contrast to elevated HSP27 levels (p = 0.012).

CONCLUSIONS

The combination of all three markers is an independent predictor of cardiovascular death and unplanned HF associated hospitalisation but not overall mortality. Our findings suggest that adding those markers in combination to well established risk assessment parameters may improve risk stratification.

Defining decreased protein succinylation of failing human cardiac myofibrils in ischemic cardiomyopathy

Succinylation is a post-translational modification of protein lysine residues with succinyl groups derived from succinyl CoA. Succinylation is considered a significant post-translational modification with the potential to impact protein function which is highly conserved across numerous species. The role of succinylation in the heart, especially in heart failure and myofibril mechanics, remains largely unexplored. Mechanical parameters were measured in myofibrils isolated from failing hearts of ischemic cardiomyopathy patients and non-failing donor controls. We employed mass spectrometry to quantify differential protein expression in myofibrils from failing ischemic cardiomyopathy hearts compared to non-failing hearts. In addition, we combined peptide enrichment by immunoprecipitation with liquid chromatography tandem mass spectrometry to quantitatively analyze succinylated lysine residues in these myofibrils. Several key parameters of sarcomeric mechanical interactions were altered in myofibrils isolated from failing ischemic cardiomyopathy hearts, including lower resting tension and a faster rate of activation. Of the 100 differentially expressed proteins, 46 showed increased expression in ischemic heart failure, while 54 demonstrated decreased expression in ischemic heart failure. Our quantitative succinylome analysis identified a total of 572 unique succinylated lysine sites located on 181 proteins, with 307 significantly changed succinylation events. We found that 297 succinyl-Lys demonstrated decreased succinylation on 104 proteins, while 10 residues demonstrated increased succinylation on 4 proteins. Investigating succinyl CoA generation, enzyme activity assays demonstrated that α-ketoglutarate dehydrogenase and succinate dehydrogenase activities were significantly decreased in ischemic heart failure. An activity assay for succinyl CoA synthetase demonstrated a significant increase in ischemic heart failure. Taken together, our findings support the hypothesis that succinyl CoA production is decreased and succinyl CoA turnover is increased in ischemic heart failure, potentially resulting in an overall decrease in the mitochondrial succinyl CoA pool, which may contribute to decreased myofibril protein succinylation in heart failure.

Landscape of heart proteome changes in a diet-induced obesity model

Obesity is a pandemic associated with a high incidence of cardiovascular disease; however, the mechanisms are not fully elucidated. Proteomics may provide a more in-depth understanding of the pathophysiological mechanisms and contribute to the identification of potential therapeutic targets. Thus, our study evaluated myocardial protein expression in healthy and obese rats, employing two proteomic approaches. Male Wistar rats were established in two groups (n = 13/group): control diet and Western diet fed for 41 weeks. Obesity was determined by the adipose index, and cardiac function was evaluated in vivo by echocardiogram and in vitro by isolated papillary muscle analysis. Proteomics was based on two-dimensional gel electrophoresis (2-DE) along with mass spectrometry identification, and shotgun proteomics with label-free quantification. The Western diet was efficient in triggering obesity and impaired contractile function in vitro; however, no cardiac dysfunction was observed in vivo. The combination of two proteomic approaches was able to increase the cardiac proteomic map and to identify 82 differentially expressed proteins involved in different biological processes, mainly metabolism. Furthermore, the data also indicated a cardiac alteration in fatty acids transport, antioxidant defence, cytoskeleton, and proteasome complex, which have not previously been associated with obesity. Thus, we define a robust alteration in the myocardial proteome of diet-induced obese rats, even before functional impairment could be detected in vivo by echocardiogram.

Different Transcriptomic Responses to Thermal Stress in Heat-Tolerant and Heat-Sensitive Pacific Abalones Indicated by Cardiac Performance

The Pacific abalone Haliotis discus hannai is one of the most economically important mollusks in China. Even though it has been farmed in southern China for almost 20 years, summer mortality remains the most challengeable problem for Pacific abalone aquaculture recently. Here, we determined the different heat tolerance ability for five selective lines of H. discus hannai by measuring the cardiac performance and Arrhenius breakpoint temperature (ABT). The Red line (RL) and Yangxia line (YL) were determined as the most heat-sensitive and most heat-tolerant line, respectively. Heart rates for RL were significantly lower than those of the YL at the same temperature (p < 0.05). The differentially expressed genes (DEGs), which were enriched in several pathways including cardiac muscle contraction, glutathione metabolism and oxidative phosphorylation, were identified between RL and YL at control temperature (20°C) and heat stress temperature (28.5°C, the ABT of the RL) by RNA-seq method. In the RL, 3370 DEGs were identified between the control and the heat-stress temperature, while only 1351 DEGs were identified in YL between these two temperature tests. Most of these DEGs were enriched in the pathways such as protein processing in endoplasmic reticulum, nucleotide binding and oligomerization domain (NOD) like receptor signaling, and ubiquitin mediated proteolysis. Notably, the most heat-tolerant line YL used an effective heat-protection strategy based on moderate transcriptional changes and regulation on the expression of key genes.

Comparative proteomic analysis of mouse models of pathological and physiological cardiac hypertrophy, with selection of biomarkers of pathological hypertrophy by integrative Proteogenomics

To determine fundamental characteristics of pathological cardiac hypertrophy, protein expression profiles in two widely accepted models of cardiac hypertrophy (swimming-trained mouse for physiological hypertrophy and pressure-overload-induced mouse for pathological hypertrophy) were compared using a label-free quantitative proteomics approach. Among 3955 proteins (19,235 peptides, false-discovery rate < 0.01) identified in these models, 486 were differentially expressed with a log2 fold difference ≥ 0.58, or were detected in only one hypertrophy model (each protein from 4 technical replicates, p < .05). Analysis of gene ontology biological processes and KEGG pathways identified cellular processes enriched in one or both hypertrophy models. Processes unique to pathological hypertrophy were compared with processes previously identified in cardiac-hypertrophy models. Individual proteins with differential expression in processes unique to pathological hypertrophy were further confirmed using the results of previous targeted functional analysis studies. Using a proteogenomic approach combining transcriptomic and proteomic analyses, similar patterns of differential expression were observed for 23 proteins and corresponding genes associated with pathological hypertrophy. A total of 11 proteins were selected as early-stage pathological-hypertrophy biomarker candidates, and the results of western blotting for five of these proteins in independent samples confirmed the patterns of differential expression in mouse models of pathological and physiological cardiac hypertrophy.

Titin isoforms are increasingly protected against oxidative modifications in developing rat cardiomyocytes

During the perinatal adaptation process N2BA titin isoforms are switched for N2B titin isoforms leading to an increase in cardiomyocyte passive tension (F_passive). Here we attempted to reveal how titin isoform composition and oxidative insults (i.e. sulfhydryl (SH)-group oxidation or carbonylation) influence F_passive of left ventricular (LV) cardiomyocytes during rat heart development. Moreover, we also examined a hypothetical protective role for titin associated small heat shock proteins (sHSPs), Hsp27 and αB-crystallin in the above processes. Single, permeabilized LV cardiomyocytes of the rat (at various ages following birth) were exposed either to 2,2'-dithiodipyridine (DTDP) to provoke SH-oxidation or Fenton reaction reagents (iron(II), hydrogen peroxide (H₂O₂), ascorbic acid) to induce protein carbonylation of cardiomyocytes in vitro. Thereafter, cardiomyocyte force measurements for F_passive determinations and Western immunoblot assays were carried out for the semiquantitative determination of oxidized SH-groups or carbonyl-groups of titin isoforms and to monitor sHSPs' expressions. DTDP or Fenton reagents increased F_passive in 0- and 7-day-old rats to relatively higher extents than in 21-day-old and adult animals. The degrees of SH-group oxidation or carbonylation declined with cardiomyocyte age to similar extents for both titin isoforms. Moreover, the above characteristics were mirrored by increasing levels of HSP27 and αB-crystallin expressions during cardiomyocyte development. Our data implicate a gradual build-up of a protective mechanism against titin oxidation through the upregulation of HSP27 and αB-crystallin expressions during postnatal cardiomyocyte development.

Screening for key genes and transcription factors in ankylosing spondylitis by RNA-Seq

Ankylosing spondylitis (AS) is a chronic inflammatory arthritis and autoimmune disease, the etiology and pathogenesis of which remain largely unknown. In the present study, blood samples were harvested from patients with AS and from healthy volunteers as a normal control (NC) for RNA-sequencing. Differentially expressed genes (DEGs) in the AS group compared with the NC group were identified, and gene ontology (GO) term and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses were subsequently performed. Protein-protein interaction (PPI) network and AS-specific transcriptional regulatory network construction was performed for the DEGs. A total of 503 DEGs, including 338 upregulated and 165 downregulated DEGs, were identified in patients with AS compared with the NC group. Three upregulated DEGs identified, interferon-induced protein with tetratricopeptide repeats (IFIT)1, IFIT3 and radical S-adenosyl methionine domain containing (RSAD)2, are interferon (IFN)-stimulated genes that serve a role in the IFN signaling pathway. The most significantly enriched GO term was response to other organisms. Osteoclast differentiation was a significantly enriched pathway for eight DEGs [High affinity immunoglobulin gamma Fc receptor (FCGR)1A, FCGR2B, four and a half LIM domains 2, integrin β3, signal transducer and activator of transcription 2 (STAT2), suppressor of cytokine signaling 3 (SOCS3), leukocyte immunoglobulin like receptor (LILR)A4 and LILRA6]. The six hub genes in the PPI network constructed were interferon-stimulated gene 15, heat shock protein β1, microtubule-associated proteins 1A/1B light chain 3A, IFIT1, IFIT3 and SOCS3. POU domain class 2 transcription factor 1 (1-Oct) and ecotropic virus integration site-1 (Evi-1) were identified as two important transcription factors (TFs) in AS according to the AS-specific transcriptional regulatory network constructed. In addition, IFIT1 and IFIT3 were identified as targets of 1-Oct. The results of the present study indicate that osteoclast differentiation, the IFN signaling pathway and genes associated with these two signaling pathways, particularly FCGR2B, STAT2, SOCS3, IFIT1 and IFIT3, may serve a role in AS. In addition, Evi-1 and 1-Oct may be two important TFs associated with AS. These results may provide a basis for elucidating the underlying mechanisms of and developing novel treatments for AS.

Proteomics landscape of radiation-induced cardiovascular disease: somewhere over the paradigm

INTRODUCTION

Epidemiological studies clearly show that thoracic or whole body exposure to ionizing radiation increases the risk of cardiac morbidity and mortality. Radiation-induced cardiovascular disease (CVD) has been intensively studied during the last ten years but the underlying molecular mechanisms are still poorly understood. Areas covered: Heart proteomics is a powerful tool holding promise for the future research. The central focus of this review is to compare proteomics data on radiation-induced CVD with data arising from proteomics of healthy and diseased cardiac tissue in general. In this context we highlight common and unique features of radiation-related and other heart pathologies. Future prospects and challenges of the field are discussed. Expert commentary: Data from comprehensive cardiac proteomics have deepened the knowledge of molecular mechanisms involved in radiation-induced cardiac dysfunction. State-of-the-art proteomics has the potential to identify novel diagnostic and therapeutic markers of this disease.

Monoamine Oxidase Is Overactivated in Left and Right Ventricles from Ischemic Hearts: An Intriguing Therapeutic Target

Growing evidence indicates that reactive oxygen species (ROS) may play a key role in human heart failure (HF). Monoamine oxidase (MAO) is emerging as a major ROS source in several cardiomyopathies. However, little is known about MAO activity in human failing heart and its relationship with redox imbalance. Therefore, we measured MAO activity in the left (LV) and in the right (RV) ventricle of human nonfailing (NF) and in end-stage ischemic (IHD) and nonischemic failing hearts. We found that both MAO isoforms (MAO-A/B) significantly increased in terms of activity and expression levels only in IHD ventricles. Catalase and aldehyde dehydrogenase-2 activities (ALDH-2), both implicated in MAO-catalyzed catecholamine catabolism, were significantly elevated in the failing LV, whereas, in the RV, statistical significance was observed only for ALDH-2. Oxidative stress markers levels were significantly increased only in the failing RV. Actin oxidation was significantly elevated in both failing ventricles and related to MAO-A activity and to functional parameters. These data suggest a close association between MAO-A-dependent ROS generation, actin oxidation, and ventricular dysfunction. This latter finding points to a possible pathogenic role of MAO-A in human myocardial failure supporting the idea that MAO-A could be a new therapeutic target in HF.

Right ventricular protein expression profile in end-stage heart failure

Little is known about the right ventricular (RV) proteome in human heart failure (HF), including possible differences compared to the left ventricular (LV) proteome. We used 2-dimensional differential in-gel electrophoresis (pH: 4-7, 10-150 kDa), followed by liquid chromatography tandem mass spectrometry, to compare the RV and LV proteomes in 12 explanted human hearts. We used Western blotting and multiple-reaction monitoring for protein verification and RNA sequencing for messenger RNA and protein expression correlation. In all 12 hearts, the right ventricles (RVs) demonstrated differential expression of 11 proteins relative to the left ventricles (LVs), including lesser expression of CRYM, TPM1, CLU, TXNL1, and COQ9 and greater expression of TNNI3, SAAI, ERP29, ACTN2, HSPB2, and NDUFS3. Principal-components analysis did not suggest RV-versus-LV proteome partitioning. In the nonischemic RVs (n = 6), 7 proteins were differentially expressed relative to the ischemic RVs (n = 6), including increased expression of CRYM, B7Z964, desmin, ANXA5, and MIME and decreased expression of SERPINA1 and ANT3. Principal-components analysis demonstrated partitioning of the nonischemic and ischemic RV proteomes, and gene ontology analysis identified differences in hemostasis and atherosclerosis-associated networks. There were no proteomic differences between RVs with echocardiographic dysfunction (n = 8) and those with normal function (n = 4). Messenger RNA and protein expression did not correlate consistently, suggesting a major role for RV posttranscriptional protein expression regulation. Differences in contractile, cytoskeletal, metabolic, signaling, and survival pathways exist between the RV and the LV in HF and may be related to the underlying HF etiology and differential posttranscriptional regulation.

Heart mitochondrial proteome study elucidates changes in cardiac energy metabolism and antioxidant PRDX3 in human dilated cardiomyopathy

Background

Dilated cardiomyopathy (DCM) is a public health problem with no available curative treatment, and mitochondrial dysfunction plays a critical role in its development. The present study is the first to analyze the mitochondrial proteome in cardiac tissue of patients with DCM to identify potential molecular targets for its therapeutic intervention.

Methods and Results

16 left ventricular (LV) samples obtained from explanted human hearts with DCM (n = 8) and control donors (n = 8) were extracted to perform a proteomic approach to investigate the variations in mitochondrial protein expression. The proteome of the samples was analyzed by quantitative differential electrophoresis and Mass Spectrometry. These changes were validated by classical techniques and by novel and precise selected reaction monitoring analysis and RNA sequencing approach increasing the total heart samples up to 25. We found significant alterations in energy metabolism, especially in molecules involved in substrate utilization (ODPA, ETFD, DLDH), energy production (ATPA), other metabolic pathways (AL4A1) and protein synthesis (EFTU), obtaining considerable and specific relationships between the alterations detected in these processes. Importantly, we observed that the antioxidant PRDX3 overexpression is associated with impaired ventricular function. PRDX3 is significantly related to LV end systolic and diastolic diameter (r = 0.73, p value<0.01; r = 0.71, p value<0.01), fractional shortening, and ejection fraction (r = −0.61, p value<0.05; and r = −0.62, p value<0.05, respectively).

Conclusion

This work could be a pivotal study to gain more knowledge on the cellular mechanisms related to the pathophysiology of this disease and may lead to the development of etiology-specific heart failure therapies. We suggest new molecular targets for therapeutic interventions, something that up to now has been lacking.

ATP synthase subunit alpha and LV mass in ischaemic human hearts

Mitochondrial dysfunction plays a critical role in the development of ischaemic cardiomyopathy (ICM). In this study, the mitochondrial proteome in the cardiac tissue of ICM patients was analysed by quantitative differential electrophoresis (2D-DIGE) and mass spectrometry (MS) for the first time to provide new insights into cardiac dysfunction in this cardiomyopathy. We isolated mitochondria from LV samples of explanted hearts of ICM patients (n = 8) and control donors (n = 8) and used a proteomic approach to investigate the variations in mitochondrial protein expression. We found that most of the altered proteins were involved in cardiac energy metabolism (82%). We focused on ATPA, which is involved in energy production, and dihydrolipoyl dehydrogenase, implicated in substrate utilization, and observed that these molecules were overexpressed and that the changes detected in the processes mediated by these proteins were closely related. Notably, we found that ATPA overexpression was associated with reduction in LV mass (r = −0.74, P < 0.01). We also found a substantial increase in the expression of elongation factor Tu, a molecule implicated in protein synthesis, and PRDX3, involved in the stress response. All of these changes were validated using classical techniques and by using novel and precise selected reaction monitoring analysis and an RNA sequencing approach, with the total heart samples being increased to 24. This study provides key insights that enhance our understanding of the cellular mechanisms related to the pathophysiology of ICM and could lead to the development of aetiology-specific heart failure therapies. ATPA could serve as a molecular target suitable for new therapeutic interventions.

Human myocytes are protected from titin aggregation-induced stiffening by small heat shock proteins

Small heat shock proteins translocate to unfolded titin Ig domains under stress conditions to prevent titin aggregation and myocyte stiffening.

In myocytes, small heat shock proteins (sHSPs) are preferentially translocated under stress to the sarcomeres. The functional implications of this translocation are poorly understood. We show here that HSP27 and αB-crystallin associated with immunoglobulin-like (Ig) domain-containing regions, but not the disordered PEVK domain (titin region rich in proline, glutamate, valine, and lysine), of the titin springs. In sarcomeres, sHSP binding to titin was actin filament independent and promoted by factors that increased titin Ig unfolding, including sarcomere stretch and the expression of stiff titin isoforms. Titin spring elements behaved predominantly as monomers in vitro. However, unfolded Ig segments aggregated, preferentially under acidic conditions, and αB-crystallin prevented this aggregation. Disordered regions did not aggregate. Promoting titin Ig unfolding in cardiomyocytes caused elevated stiffness under acidic stress, but HSP27 or αB-crystallin suppressed this stiffening. In diseased human muscle and heart, both sHSPs associated with the titin springs, in contrast to the cytosolic/Z-disk localization seen in healthy muscle/heart. We conclude that aggregation of unfolded titin Ig domains stiffens myocytes and that sHSPs translocate to these domains to prevent this aggregation.

Cardiac protein changes in ischaemic and dilated cardiomyopathy: a proteomic study of human left ventricular tissue

The development of heart failure (HF) is characterized by progressive alteration of left ventricle structure and function. Previous works on proteomic analysis in cardiac tissue from patients with HF remain scant. The purpose of our study was to use a proteomic approach to investigate variations in protein expression of left ventricle tissue from patients with ischaemic (ICM) and dilated cardiomyopathy (DCM). Twenty-four explanted human hearts, 12 from patients with ICM and 12 with DCM undergoing cardiac transplantation and six non-diseased donor hearts (CNT) were analysed by 2DE. Proteins of interest were identified by mass spectrometry and validated by Western blotting and immunofluorescence. We encountered 35 differentially regulated spots in the comparison CNT versus ICM, 33 in CNT versus DCM, and 34 in ICM versus DCM. We identified glyceraldehyde 3-phophate dehydrogenase up-regulation in both ICM and DCM, and alpha-crystallin B down-regulation in both ICM and DCM. Heat shock 70 protein 1 was up-regulated only in ICM. Ten of the eleven differentially regulated proteins common to both aetiologies are interconnected as a part of a same network. In summary, we have shown by proteomics analysis that HF is associated with changes in proteins involved in the cellular stress response, respiratory chain and cardiac metabolism. Although we found altered expression of eleven proteins common to both ischaemic and dilated aetiology, we also observed different proteins altered in both groups. Furthermore, we obtained that seven of these eleven proteins are involved in cell death and apoptosis processes, and therefore in HF progression.

Proteomic analysis of right and left cardiac ventricles under aerobic conditions and after ischemia/reperfusion

Ischemia/reperfusion (I/R) injury is a major consequence of a cardiovascular intervention. The study of changes of the left and right ventricle proteomes from hearts subjected to I/R may be a key to revealing the pathological mechanisms underlying I/R-induced heart contractile dysfunction. Isolated rat hearts were perfused under aerobic conditions or subjected to 25 min global ischemia and 30 min reperfusion. At the end of perfusion, right and left ventricular homogenates were analyzed by 2DE. Contractile function and coronary flow were significantly reduced by I/R. 2DE followed by mass spectrometry identified ten protein spots whose levels were significantly different between aerobic left and right ventricles, eight protein spots whose levels were different between aerobic and I/R left ventricle, ten protein spots whose levels were different between aerobic and I/R right ventricle ten protein spots whose levels were different between the I/R groups. Among these protein spots were ATP synthase beta subunit, myosin light chain 2, myosin heavy chain fragments, peroxiredoxin-2, and heat shock proteins, previously associated with cardiovascular disease. These results reveal differences between proteomes of left and right ventricle both under aerobic conditions and in response to I/R that contribute to a better understanding of I/R injury.

Novel proteins associated with human dilated cardiomyopathy: selective reduction in α(1A)-adrenergic receptors and increased desensitization proteins

Abstract Therapeutics to treat human heart failure (HF) and the identification of proteins associated with HF are still limited. We analyzed α(1)-adrenergic receptor (AR) subtypes in human HF and performed proteomic analysis on more uniform samples to identify novel proteins associated with human HF. Six failing hearts with end-stage dilated cardiomyopathy (DCM) and four non-failing heart controls were subjected to proteomic analysis. Out of 48 identified proteins, 26 proteins were redundant between samples. Ten of these 26 proteins were previously reported to be associated with HF. Of the newly identified proteins, we found several muscle proteins and mitochondrial/electron transport proteins, while novel were functionally similar to previous reports. However, we also found novel proteins involved in functional classes such as β-oxidation and G-protein coupled receptor signaling and desensitization not previously associated with HF. We also performed radioligand-binding studies on the heart samples and not only confirmed a large loss of β(1)-ARs in end-stage DCM, but also found a selective decrease in the α(1A)-AR subtype not previously reported. We have identified new proteins and functional categories associated with end-stage DCM. We also report that similar to the previously characterized loss of β(1)-AR in HF, there is also a concomitant loss of α(1A)-ARs, which are considered cardioprotective proteins.

Reversible inactivation of dihydrolipoamide dehydrogenase by mitochondrial hydrogen peroxide

Under oxidative stress conditions, mitochondria are the major site for cellular production of reactive oxygen species (ROS) such as superoxide anion and H2O2 that can attack numerous mitochondrial proteins including dihydrolipoamide dehydrogenase (DLDH). While DLDH is known to be vulnerable to oxidative inactivation, the mechanisms have not been clearly elucidated. The present study was therefore designed to investigate the mechanisms of DLDH oxidative inactivation by mitochondrial reactive oxygen species (ROS). Mitochondria, isolated from rat brain, were incubated with mitochondrial respiratory substrates such as pyruvate/malate or succinate in the presence of electron transport chain inhibitors such as rotenone or antimycin A. This is followed by enzyme activity assay and gel-based proteomic analysis. The present study also examined whether ROS-induced DLDH oxidative inactivation could be reversed by reducing reagents such as DTT, cysteine, and glutathione. Results show that DLDH could only be inactivated by complex III- but not complex I-derived ROS; and the accompanying loss of activity due to the inactivation could be restored by cysteine and glutathione, indicating that DLDH oxidative inactivation by complex III-derived ROS was a reversible process. Further studies using catalase indicate that it was H2O2 instead of superoxide anion that was responsible for DLDH inactivation. Moreover, using sulfenic acid-specific labeling techniques in conjunction with two-dimensional Western blot analysis, we show that protein sulfenic acid formation (also known as sulfenation) was associated with the loss of DLDH enzymatic activity observed under our experimental conditions. Additionally, such oxidative modification was shown to be associated with preventing DLDH from further inactivation by the thiol-reactive reagent N-ethylmaleimide. Taken together, the present study provides insights into the mechanisms of DLDH oxidative inactivation by mitochondrial H2O2.

Characterization of hsp27 kinases activated by elevated aortic pressure in heart

Chronic hemodynamic overload results in left ventricular hypertrophy, fibroblast proliferation, and interstitial fibrosis. The small heat shock protein hsp27 has been shown to be cardioprotective and this requires a phosphorylatable form of this protein. To further understand the regulation of hsp27 in heart in response to stress, we investigated the ability of elevated aortic pressure to activate hsp27-kinase activities. Isolated hearts were subjected to retrograde perfusion and then snap frozen. Hsp27-kinase activity was measured in vitro as hsp27 phosphorylation. Immune complex assays revealed that MK2 activity was low in non-perfused hearts and increased following crystalline perfusion at 60 or 120 mmHg. Hsp27-kinase activities were further studied following ion-exchange chromatography. Anion exchange chromatography on Mono Q revealed 2 peaks (b and c) of hsp27-kinase activity. A third peak a was detected upon chromatography of the Mono Q flow-through fractions on the cation exchange resin, Mono S. The hsp27-kinase activity underlying peaks a and c increased as perfusion pressure was increased from 40 to 120 mmHg. In contrast, peak b increased over pressures 60-100 mmHg but was decreased at 120 mmHg. Peaks a, b, and c contained MK2 immunoreactivity, whereas MK3 and MK5 immunoreactivity was detected in peak a. p38 MAPK and phospho-p38 MAPK were also detected in peaks b and c but absent from peak a. Hsp27-kinase activity in peaks b and c (120 mmHg) eluted from a Superose 12 gel filtration column with an apparent molecular mass of 50 kDa. Hence, peaks b and c were not a result of MK2 forming complexes. In-gel hsp27-kinase assays revealed a single 49-kDa renaturable hsp27-kinase activity in peaks b and c at 60 mmHg, whereas several hsp27-kinases (p43, p49, p54, p66) were detected in peaks b and c from hearts perfused at 120 mmHg. Thus, multiple hsp27-kinases were activated in response to elevated aortic pressure in isolated, perfused rat hearts and hence may be implicated in regulating the cardioprotective effects of hsp27 and thus may represent targets for cardioprotective therapy.

Effect of the myosin light chain kinase inhibitor ML-7 on the proteome of hearts subjected to ischemia-reperfusion injury

In the development of ischemia/reperfusion (I/R) injury, the role of the myosin light chain (MLC) phosphorylation has been given increased consideration. ML-7, a MLC kinase inhibitor, has been shown to protect cardiac function from I/R, however the exact mechanism remains unclear. Isolated rat hearts were perfused under aerobic conditions (controls) or subjected to I/R in the presence or absence of ML-7. Continuous administration of ML-7 (5 μM) from 10 min before onset of ischemia to the first 10 min of reperfusion resulted in significant recovery of heart contractility. Analysis of gels from two-dimensional electrophoresis revealed eight proteins with decreased levels in I/R hearts. Six proteins are involved in energy metabolism:ATP synthase beta subunit, cytochrome b-c1 complex subunit 1, 24-kDa mitochondrial NADH dehydrogenase, NADH dehydrogenase [ubiquinone] iron-sulfur protein 8, cytochrome c oxidase subunit, and succinyl-CoA ligase subunit. The other two proteins with decreased levels in I/R hearts are: peroxiredoxin-2 and tubulin. Administration of ML-7 increased level of succinyl-CoA ligase, key enzyme involved in the citric acid cycle. The increased level of succinyl-CoA ligase in I/R hearts perfused with ML-7 suggests that the cardioprotective effect of ML-7, at least partially, also may involve increase of energy production.