Redox signaling and cardiac sarcomeres

Dysregulation of metalloproteins in ischemic heart disease patients with systolic dysfunction

Ischemic heart disease (IHD) is the leading cause of mortality worldwide. Metalloproteins have been linked to human health and diseases. The molecular functions of metalloproteins in IHD is not well understood and require further exploration. The objective of this study was to find out the role of metalloproteins in the pericardial fluid of IHD patients having normal (EF > 45) and impaired (EF < 45) left ventricular ejection fraction (LVEF). IHD patients were grouped into two categories: LVEF<45 (n = 12) and LVEF >45 (n = 33). Pooled samples of pericardial fluid were fractionated by using ZOOM-isoelectric focusing (IEF) followed by further processing using one-dimensional gel electrophoresis (1D SDS-PAGE) and filter-aided sample preparation (FASP). Tryptic peptides of each fraction and differential bands were then analyzed by nano-LC-ESI-MS/MS. Protein identification was performed through a Mascot search engine using NCBI-Prot and SwissProt databases. A total of 1082 proteins including 154 metalloproteins were identified. In the differential bands, 60 metalloproteins were identified, while 115 metalloproteins were identified in all ZOOM-IEF fractions. Twelve differentially expressed metalloproteins were selected in the intense bands according to their molecular weight (MW) and isoelectric point (pI). The 12 differentially expressed metalloprotein includes ceruloplasmin, Prothrombin, Vitamin K-dependent protein, Fibulin-1, Ribosomal protein S6 kinase alpha-6, nidogen, partial, Serum albumin, Hemopexin, C-reactive protein, Serum amyloid P-component, and Intelectin-1 protein which were all up-regulated while serotransferrin is the only metalloprotein that was down-regulated in impaired (LVEF<45) group. Among the metalloproteins, Zn-binding proteins are 36.5 % followed by Ca-binging 32.2 %, and Fe-binging 12.2 %. KEGG, pathway analysis revealed the association of ceruloplasmin and serotransferrin with the ferroptosis pathway. In conclusion, 154 metalloproteins were identified of them the Zn-binding protein followed by Ca-binding and Fe-binding proteins were the most abundant metalloproteins. The two metalloproteins, the Cu-binding protein ceruloplasmin, and Fe-binding protein serotransferrin are involved in the ferroptosis pathway, an iron-dependent form of regulated cell death that has been linked to cardiac pathology, especially in IHD patients having impaired systolic (LVEF<45) dysfunction. However, further research is required to validate these findings.

Metformin Acutely Mitigates Oxidative Stress in Human Atrial Tissue: A Pilot Study in Overweight Non-Diabetic Cardiac Patients

Metformin, the first-line drug in type 2 diabetes mellitus, elicits cardiovascular protection also in obese patients via pleiotropic effects, among which the anti-oxidant is one of the most investigated. The aim of the present study was to assess whether metformin can acutely mitigate oxidative stress in atrial tissue harvested from overweight non-diabetic patients. Right atrial appendage samples were harvested during open-heart surgery and used for the evaluation of reactive oxygen species (ROS) production by means of confocal microscopy (superoxide anion) and spectrophotometry (hydrogen peroxide). Experiments were performed after acute incubation with metformin (10 µM) in the presence vs. absence of angiotensin II (AII, 100 nM), lipopolysaccharide (LPS, 1 μg/mL), and high glucose (Gluc, 400 mg/dL). Stimulation with AII, LPS, and high Gluc increased ROS production. The magnitude of oxidative stress correlated with several echocardiographic parameters. Metformin applied in the lowest therapeutic concentration (10 µM) was able to decrease ROS generation in stimulated but also non-stimulated atrial samples. In conclusion, in a pilot group of overweight non-diabetic cardiac patients, acute incubation with metformin at a clinically relevant dose alleviated oxidative stress both in basal conditions and conditions that mimicked the activation of the renin-angiotensin-aldosterone system, acute inflammation, and uncontrolled hyperglycemia.

Post-translational modification patterns on β-myosin heavy chain are altered in ischemic and nonischemic human hearts

Phosphorylation and acetylation of sarcomeric proteins are important for fine-tuning myocardial contractility. Here, we used bottom-up proteomics and label-free quantification to identify novel post-translational modifications (PTMs) on β-myosin heavy chain (β-MHC) in normal and failing human heart tissues. We report six acetylated lysines and two phosphorylated residues: K34-Ac, K58-Ac, S210-P, K213-Ac, T215-P, K429-Ac, K951-Ac, and K1195-Ac. K951-Ac was significantly reduced in both ischemic and nonischemic failing hearts compared to nondiseased hearts. Molecular dynamics (MD) simulations show that K951-Ac may impact stability of thick filament tail interactions and ultimately myosin head positioning. K58-Ac altered the solvent-exposed SH3 domain surface - known for protein-protein interactions - but did not appreciably change motor domain conformation or dynamics under conditions studied. Together, K213-Ac/T215-P altered loop 1's structure and dynamics - known to regulate ADP-release, ATPase activity, and sliding velocity. Our study suggests that β-MHC acetylation levels may be influenced more by the PTM location than the type of heart disease since less protected acetylation sites are reduced in both heart failure groups. Additionally, these PTMs have potential to modulate interactions between β-MHC and other regulatory sarcomeric proteins, ADP-release rate of myosin, flexibility of the S2 region, and cardiac myofilament contractility in normal and failing hearts.

Indirect evidence that anoxia exposure and cold acclimation alter transarcolemmal Ca2+ flux in the cardiac pacemaker, right atrium and ventricle of the red-eared slider turtle (Trachemys scripta)

We indirectly assessed if altered transarcolemmal Ca²⁺ flux accompanies the decreased cardiac activity displayed by Trachemys scripta with anoxia exposure and cold acclimation. Turtles were first acclimated to 21 °C or 5 °C and held under normoxic (21N; 5N) or anoxic conditions (21A; 5A). We then compared the response of intrinsic heart rate (f_H) and maximal developed force of spontaneously contracting right atria (F_max,RA), and maximal developed force of isometrically-contracting ventricular strips (F_max,V), to Ni²⁺ (0.1-10 mM), which respectively blocks T-type Ca²⁺ channels, L-type Ca²⁺ channels and the Na⁺-Ca²⁺-exchanger at the low, intermediate and high concentrations employed. Dose-response curves were established in simulated in vivo normoxic (Sim Norm) or simulated in vivo anoxic extracellular conditions (Sim Anx; 21A and 5A preparations). Ni²⁺ decreased intrinsic f_H, F_max,RA and F_max,V of 21N tissues in a concentration-dependent manner, but the responses were blunted in 21A tissues in Sim Norm. Similarly, dose-response curves for F_max,RA and F_max,V of 5N tissues were right-shifted, whereas anoxia exposure at 5 °C did not further alter the responses. The influence of Sim Anx was acclimation temperature-, cardiac chamber- and contractile parameter-dependent. Combined, the findings suggest that: (1) reduced transarcolemmal Ca²⁺ flux in the cardiac pacemaker is a potential mechanism underlying the slowed intrinsic f_H of anoxic turtles at 21 °C, but not 5 °C, (2) a downregulation of transarcolemmal Ca²⁺ flux may aid cardiac anoxia survival at 21 °C and prime the turtle myocardium for winter anoxia and (3) confirm that altered extracellular conditions with anoxia exposure can modify turtle cardiac transarcolemmal Ca²⁺ flux.

Sestrin2 is an endogenous antioxidant that improves contractile function in the heart during exposure to ischemia and reperfusion stress

Sestrin2 (Sesn2) is a stress-inducible protein that plays a critical role in the response to ischemic stress. We recently recognized that Sesn2 may protect the heart against ischemic insults by reducing the generation of reactive oxygen species (ROS). After 45 min of ischemia followed by 24 h of reperfusion, myocardial infarcts were significantly larger in Sesn2 KO hearts than in wild-type hearts. Isolated cardiomyocytes from wild-type hearts treated with hypoxia and reoxygenation (H/R) stress showed significantly greater Sesn2 levels, compared with normoxic hearts (p < 0.05). Intriguingly, the administration of adeno-associated virus 9-Sesn2 into Sesn2 knockout (KO) hearts rescued Sesn2 protein levels and significantly improved the cardiac function of Sesn2 KO mice exposed to ischemia and reperfusion. The rescued levels of Sesn2 in Sesn2 KO hearts significantly ameliorated ROS generation and the activation of ROS-related stress signaling pathways during ischemia and reperfusion. Moreover, the rescued Sesn2 levels in Sesn2 KO cardiomyocytes improved the maximal velocity of cardiomyocyte shortening by H/R stress. Rescued Sesn2 levels also improved peak height, peak shortening amplitude, and maximal velocity of the re-lengthening of Sesn2 KO cardiomyocytes subjected to H/R. Finally, the rescued Sesn2 levels significantly augmented intracellular calcium levels and reduced the mean time constant of transient calcium decay in Sesn2 KO cardiomyocytes exposed to H/R. Overall, these findings indicated that Sesn2 can act as an endogenous antioxidant to maintain intracellular redox homeostasis under ischemic stress conditions.

Network integration and modelling of dynamic drug responses at multi-omics levels

Uncovering cellular responses from heterogeneous genomic data is crucial for molecular medicine in particular for drug safety. This can be realized by integrating the molecular activities in networks of interacting proteins. As proof-of-concept we challenge network modeling with time-resolved proteome, transcriptome and methylome measurements in iPSC-derived human 3D cardiac microtissues to elucidate adverse mechanisms of anthracycline cardiotoxicity measured with four different drugs (doxorubicin, epirubicin, idarubicin and daunorubicin). Dynamic molecular analysis at in vivo drug exposure levels reveal a network of 175 disease-associated proteins and identify common modules of anthracycline cardiotoxicity in vitro, related to mitochondrial and sarcomere function as well as remodeling of extracellular matrix. These in vitro-identified modules are transferable and are evaluated with biopsies of cardiomyopathy patients. This to our knowledge most comprehensive study on anthracycline cardiotoxicity demonstrates a reproducible workflow for molecular medicine and serves as a template for detecting adverse drug responses from complex omics data.

Using a network propagation approach with integrated multi-omic data, Selevsek et al. develop a reproducible workflow for identifying drug toxicity effects in cellular systems. This is demonstrated with the analysis of anthracycline cardiotoxicity in cardiac microtissues under the effect of multiple drugs.

Screening for in-vivo regional contractile defaults to predict the delayed Doxorubicin Cardiotoxicity in Juvenile Rat

Anthracyclines are key chemotherapeutic agents used in various adult and pediatric cancers, however, their clinical use is limited due to possible congestive heart failure (HF) caused by acute and irreversible cardiotoxicity. Currently, there is no method to predict the future development of the HF in these patients. In order to identify early biomarkers to predict anthracycline cardiotoxicity in long-term survivors of childhood cancer, this longitudinal study aimed to analyze early and late in-vivo regional myocardial anthracycline-induced cardiotoxicity, related to in-vitro cardiac myocytes dysfunction, in a juvenile rat model. Methods: Young male Wistar rats (4 weeks-old) were treated with different cumulative doses of doxorubicin (7.5, 10 or 12.5 mg/kg) or NaCl (0.9%) once a week for 6 weeks by intravenous injection. Cardiac function was evaluated in-vivo by conventional (left ventricular ejection fraction, LVEF) and regional two-dimensional (2D) speckle tracking echocardiography over the 4 months after the last injection. The animals were assigned to preserved (pEF) or reduced EF (rEF) groups at the end of the protocol and were compared to controls. Results: We observed a preferential contractile dysfunction of the base of the heart, further altered in the posterior segment, even in pEF group. The first regional alterations appeared 1 month after chemotherapy. Functional investigation of cardiomyocytes isolated from the LV base 1 month after doxorubicin treatment showed that early in-vivo contractile alterations were associated with both decreased myofilament Ca²⁺ sensitivity and length-dependent activation. Changes in post-translational modifications (phosphorylation; S-glutathionylation) and protein degradation of the cardiac myosin binding protein-C may contribute to these alterations. Conclusion: Our data suggest that screening of the contractile defaults of the base of the heart by regional 2D strain echocardiography is useful to detect subclinical myocardial dysfunction prior to the development of delayed anthracycline-induced cardiomyopathy in pediatric onco-cardiology.

Myocardial injection of a thermoresponsive hydrogel with reactive oxygen species scavenger properties improves border zone contractility

The decrease in contractility in myocardium adjacent (border zone; BZ) to a myocardial infarction (MI) is correlated with an increase in reactive oxygen species (ROS). We hypothesized that injection of a thermoresponsive hydrogel, with ROS scavenging properties, into the MI would decrease ROS and improve BZ function. Fourteen sheep underwent antero-apical MI. Seven sheep had a comb-like copolymer synthesized from N-isopropyl acrylamide (NIPAAm) and 1500 MW methoxy poly(ethylene glycol) methacrylate, (NIPAAm-PEG1500), injected (20 × 0.5 mL) into the MI zone 40 min after MI (MI + NIPAAm-PEG1500) and seven sheep were MI controls. Cardiac MRI was performed 2 weeks before and 6 weeks after MI + NIPAAm-PEG1500. BZ wall thickness at end systole was significantly higher for MI + NIPAAm-PEG1500 (12.32 ± 0.51 mm/m² MI + NIPAAm-PEG1500 vs. 9.88 ± 0.30 MI; p = .023). Demembranated muscle force development for BZ myocardium 6 weeks after MI was significantly higher for MI + NIPAAm-PEG1500 (67.67 ± 2.61 mN/m² MI + NIPAAm-PEG1500 vs. 40.53 ± 1.04 MI; p < .0001) but not significantly different from remote myocardium or BZ or non-operated controls. Levels of ROS in BZ tissue were significantly lower in the MI + NIPAAm-PEG1500 treatment group (hydroxyl p = .0031; superoxide p = .0182). We conclude that infarct injection of the NIPAAm-PEG1500 hydrogel with ROS scavenging properties decreased ROS and improved contractile protein function in the border zone 6 weeks after MI.

The Role of Signaling Pathways of Inflammation and Oxidative Stress in Development of Senescence and Aging Phenotypes in Cardiovascular Disease

The ASK1-signalosome→p38 MAPK and SAPK/JNK signaling networks promote senescence (in vitro) and aging (in vivo, animal models and human cohorts) in response to oxidative stress and inflammation. These networks contribute to the promotion of age-associated cardiovascular diseases of oxidative stress and inflammation. Furthermore, their inhibition delays the onset of these cardiovascular diseases as well as senescence and aging. In this review we focus on whether the (a) ASK1-signalosome, a major center of distribution of reactive oxygen species (ROS)-mediated stress signals, plays a role in the promotion of cardiovascular diseases of oxidative stress and inflammation; (b) The ASK1-signalosome links ROS signals generated by dysfunctional mitochondrial electron transport chain complexes to the p38 MAPK stress response pathway; (c) the pathway contributes to the sensitivity and vulnerability of aged tissues to diseases of oxidative stress; and (d) the importance of inhibitors of these pathways to the development of cardioprotection and pharmaceutical interventions. We propose that the ASK1-signalosome regulates the progression of cardiovascular diseases. The resultant attenuation of the physiological characteristics of cardiomyopathies and aging by inhibition of the ASK1-signalosome network lends support to this conclusion. Importantly the ROS-mediated activation of the ASK1-signalosome p38 MAPK pathway suggests it is a major center of dissemination of the ROS signals that promote senescence, aging and cardiovascular diseases. Pharmacological intervention is, therefore, feasible through the continued identification of potent, non-toxic small molecule inhibitors of either ASK1 or p38 MAPK activity. This is a fruitful future approach to the attenuation of physiological aspects of mammalian cardiomyopathies and aging.

Mitochondrial quality control mechanisms as molecular targets in cardiac ageing

Cardiovascular disease is the leading cause of morbidity and mortality worldwide. Advancing age is a major risk factor for developing cardiovascular disease because of the lifelong exposure to cardiovascular risk factors and specific alterations affecting the heart and the vasculature during ageing. Indeed, the ageing heart is characterized by structural and functional changes that are caused by alterations in fundamental cardiomyocyte functions. In particular, the myocardium is heavily dependent on mitochondrial oxidative metabolism and is especially susceptible to mitochondrial dysfunction. Indeed, primary alterations in mitochondrial function, which are subsequently amplified by defective quality control mechanisms, are considered to be major contributing factors to cardiac senescence. In this Review, we discuss the mechanisms linking defective mitochondrial quality control mechanisms (that is, proteostasis, biogenesis, dynamics, and autophagy) to organelle dysfunction in the context of cardiac ageing. We also illustrate relevant molecular pathways that might be exploited for the prevention and treatment of age-related heart dysfunction.

Developmental plasticity of cardiac anoxia-tolerance in juvenile common snapping turtles ( Chelydra serpentina)

For some species of ectothermic vertebrates, early exposure to hypoxia during embryonic development improves hypoxia-tolerance later in life. However, the cellular mechanisms underlying this phenomenon are largely unknown. Given that hypoxic survival is critically dependent on the maintenance of cardiac function, we tested the hypothesis that developmental hypoxia alters cardiomyocyte physiology in a manner that protects the heart from hypoxic stress. To test this hypothesis, we studied the common snapping turtle, which routinely experiences chronic developmental hypoxia and exploits hypoxic environments in adulthood. We isolated cardiomyocytes from juvenile turtles that embryonically developed in either normoxia (21% O₂) or hypoxia (10% O₂), and subjected them to simulated anoxia and reoxygenation, while simultaneously measuring intracellular Ca²⁺, pH and reactive oxygen species (ROS) production. Our results suggest developmental hypoxia improves cardiomyocyte anoxia-tolerance of juvenile turtles, which is supported by enhanced myofilament Ca²⁺-sensitivity and a superior ability to suppress ROS production. Maintenance of low ROS levels during anoxia might limit oxidative damage and a greater sensitivity to Ca²⁺ could provide a mechanism to maintain contractile force. Our study suggests developmental hypoxia has long-lasting effects on turtle cardiomyocyte function, which might prime their physiology for exploiting hypoxic environments.

Demembranated skeletal and cardiac fibers produce less force with altered cross-bridge kinetics in a mouse model for limb-girdle muscular dystrophy 2i

Limb-girdle muscular dystrophy 2i (LGMD2i) is a dystroglycanopathy that compromises myofiber integrity and primarily reduces power output in limb muscles but can influence cardiac muscle as well. Previous studies of LGMD2i made use of a transgenic mouse model in which a proline-to-leucine (P448L) mutation in fukutin-related protein severely reduces glycosylation of α-dystroglycan. Muscle function is compromised in P448L mice in a manner similar to human patients with LGMD2i. In situ studies reported lower maximal twitch force and depressed force-velocity curves in medial gastrocnemius (MG) muscles from male P448L mice. Here, we measured Ca²⁺-activated force generation and cross-bridge kinetics in both demembranated MG fibers and papillary muscle strips from P448L mice. Maximal activated tension was 37% lower in MG fibers and 18% lower in papillary strips from P448L mice than controls. We also found slightly faster rates of cross-bridge recruitment and detachment in MG fibers from P448L than control mice. These increases in skeletal cross-bridge cycling could reduce the unitary force output from individual cross bridges by lowering the ratio of time spent in a force-bearing state to total cycle time. This suggests that the decreased force production in LGMD2i may be due (at least in part) to altered cross-bridge kinetics. This finding is notable, as the majority of studies germane to muscular dystrophies have focused on sarcolemma or whole muscle properties, whereas our findings suggest that the disease pathology is also influenced by potential downstream effects on cross-bridge behavior.

Proteomic Identification of Protein Glutathionylation in Cardiomyocytes

Reactive oxygen species (ROS) are important signaling molecules, but their overproduction is associated with many cardiovascular diseases, including cardiomyopathy. ROS induce various oxidative modifications, among which glutathionylation is one of the significant protein oxidations that occur under oxidative stress. Despite previous efforts, direct and site-specific identification of glutathionylated proteins in cardiomyocytes has been limited. In this report, we used a clickable glutathione approach in a HL-1 mouse cardiomyocyte cell line under exposure to hydrogen peroxide, finding 1763 glutathionylated peptides with specific Cys modification sites, which include many muscle-specific proteins. Bioinformatic and cluster analyses found 125 glutathionylated proteins, whose mutations or dysfunctions are associated with cardiomyopathy, many of which include sarcomeric structural and contractile proteins, chaperone, and other signaling or regulatory proteins. We further provide functional implication of glutathionylation for several identified proteins, including CSRP3/MLP and complex I, II, and III, by analyzing glutathionylated sites in their structures. Our report establishes a chemoselective method for direct identification of glutathionylated proteins and provides potential target proteins whose glutathionylation may contribute to muscle diseases.

Stress-induced protein S-glutathionylation and phosphorylation crosstalk in cardiac sarcomeric proteins - Impact on heart function

BACKGROUND

The interplay between oxidative stress and other signaling pathways in the contractile machinery regulation during cardiac stress and its consequences on cardiac function remains poorly understood. We evaluated the effect of the crosstalk between β-adrenergic and redox signaling on post-translational modifications of sarcomeric regulatory proteins, Myosin Binding Protein-C (MyBP-C) and Troponin I (TnI).

METHODS AND RESULTS

We mimicked in vitro high level of physiological cardiac stress by forcing rat hearts to produce high levels of oxidized glutathione. This led to MyBP-C S-glutathionylation associated with lower protein kinase A (PKA) dependent phosphorylations of MyBP-C and TnI, increased myofilament Ca²⁺ sensitivity, and decreased systolic and diastolic properties of the isolated perfused heart. Moderate physiological cardiac stress achieved in vivo with a single 35 min exercise (Low stress induced by exercise, LSE) increased TnI and cMyBP-C phosphorylations and improved cardiac function in vivo (echocardiography) and ex-vivo (isolated perfused heart). High stress induced by exercise (HSE) altered strongly oxidative stress markers and phosphorylations were unchanged despite increased PKA activity. HSE led to in vivo intrinsic cardiac dysfunction associated with myofilament Ca²⁺ sensitivity defects. To limit protein S-glutathionylation after HSE, we treated rats with N-acetylcysteine (NAC). NAC restored the ability of PKA to modulate myofilament Ca²⁺ sensitivity and prevented cardiac dysfunction observed in HSE animals.

CONCLUSION

Under cardiac stress, adrenergic and oxidative signaling pathways work in concert to alter myofilament properties and are key regulators of cardiac function.

Heat-shock protein B1 upholds the cytoplasm reduced state to inhibit activation of the Hippo pathway in H9c2 cells

Heat-shock protein B1 (HSPB1) is a multifunctional protein that protects against oxidative stress; however, its function in antioxidant pathways remains largely unknown. Here, we sought to determine the roles of HSPB1 in H9c2 cells subjected to oxidative stress. Using nonreducing sodium dodecyl sulfate polyacrylamide gel electrophoresis, we found that increased HSPB1 expression promoted the reduced states of glutathione reductase (GR), peroxiredoxin 1 (Prx1), and thioredoxin 1, whereas knockdown of HSPB1 attenuated these responses following oxidative stress. Increased HSPB1 expression promoted the activation of GR and thioredoxin reductase. Conversely, knockdown of HSPB1 attenuated these responses following oxidative stress. Importantly, overexpression of HSPB1 promoted the complex formation between HSPB1 and oxidized Prx1, leading to dephosphorylation of STE-mammalian STE20-like kinase 1 (MST1) in H9c2 cells exposed to H₂ O ₂ , whereas downregulation of HSPB1 induced the opposite results. Mechanistically, HSPB1 regulated the Hippo pathway by enhancing the dephosphorylation of MST1, resulting in reduced phosphorylation of LATS1 and Yes-associated protein (YAP). Moreover, HSPB1 regulated YAP-dependent gene expression. Thus, HSPB1 promoted the reduced state of endogenous antioxidant pathways following oxidative stress in H9c2 cells and improved the redox state of the cytoplasm via modulation of the Hippo signaling pathway.

Role of superoxide ion formation in hypothermia/rewarming induced contractile dysfunction in cardiomyocytes

Rewarming following accidental hypothermia is associated with circulatory collapse due primarily to impaired cardiac contractile (systolic) function. Previously, we found that reduced myofilament Ca²⁺ sensitivity underlies hypothermia/rewarming (H/R)-induced cardiac contractile dysfunction. This reduced Ca²⁺ sensitivity is associated with troponin I (cTnI) phosphorylation. We hypothesize that H/R induces reactive oxygen species (ROS) formation in cardiomyocytes, which leads to cTnI phosphorylation and reduced myofilament Ca²⁺ sensitivity. To test this hypothesis, we exposed isolated rat cardiomyocytes to a 2-h period of severe hypothermia (15 °C) followed by rewarming (35 °C) with and without antioxidant (TEMPOL) treatment. Simultaneous measurements of cytosolic Ca²⁺ ([Ca²⁺]_cyto) and contractile (sarcomere shortening) responses indicated that H/R-induced contractile dysfunction and reduced Ca²⁺ sensitivity was prevented in cardiomyocytes treated with TEMPOL. In addition, TEMPOL treatment blunted H/R-induced cTnI phosphorylation. These results support our overall hypothesis and suggest that H/R disrupts excitation-contraction coupling of the myocardium through a cascade of event triggered by excessive ROS formation during hypothermia. Antioxidant treatment may improve successful rescue of accidental hypothermia victims.

The effect of reactive oxygen species on cardiomyocyte differentiation of pluripotent stem cells

The coordination of metabolic shift with genetic circuits is critical to cell specification, but the metabolic mechanisms that drive cardiac development are largely unknown. Reactive oxygen species (ROS) are not only the by-product of mitochondrial metabolism, but play a critical role in signalling cascade of cardiac development as a second messenger. Various levels of ROS appear differential and even oppose effect on selfrenewal and cardiac differentiation of pluripotent stem cells (PSCs) at each stage of differentiation. The intracellular ROS and redox balance are meticulous regulated by several systems of ROS generation and scavenging, among which mitochondria and the NADPH oxidase (NOX) are major sources of intracellular ROS involved in cardiomyocyte differentiation. Some critical signalling modulators are activated or inactivated by oxidation, suggesting ROS can be involved in regulation of cell fate through these downstream targets. In this review, the literatures about major sources of ROS, the effect of ROS level on cardiac differentiation of PSCs, as well as the underlying mechanism of ROS in the control of cardiac fate of PSC are summarised and discussed.

Hemopexin counteracts systolic dysfunction induced by heme-driven oxidative stress

Heart failure is a leading cause of morbidity and mortality in patients affected by different disorders associated to intravascular hemolysis. The leading factor is the presence of pathologic amount of pro-oxidant free heme in the bloodstream, due to the exhaustion of the natural heme scavenger Hemopexin (Hx). Here, we evaluated whether free heme directly affects cardiac function, and tested the therapeutic potential of replenishing serum Hx for increasing serum heme buffering capacity. The effect of heme on cardiac function was assessed in vitro, on primary cardiomyocytes and H9c2 myoblast cell line, and in vivo, in Hx^-/- mice and in genetic and acquired mouse models of intravascular hemolysis. Purified Hx or anti-oxidants N-Acetyl-L-cysteine and α-tocopherol were used to counteract heme cardiotoxicity. In mice, Hx loss/depletion resulted in heme accumulation and enhanced reactive oxygen species (ROS) production in the heart, which ultimately led to severe systolic dysfunction. Similarly, high ROS reduced systolic Ca²⁺ transient amplitudes and fractional shortening in primary cardiomyocytes exposed to free heme. In keeping with these Ca²⁺ handling alterations, oxidation and CaMKII-dependent phosphorylation of Ryanodine Receptor 2 were higher in Hx^-/- hearts than in controls. Administration of anti-oxidants prevented systolic failure both in vitro and in vivo. Intriguingly, Hx rescued contraction defects of heme-treated cardiomyocytes and preserved cardiac function in hemolytic mice. We show that heme-mediated oxidative stress perturbs cardiac Ca²⁺ homeostasis and promotes contractile dysfunction. Scavenging heme, Hx counteracts cardiac heme toxicity and preserves left ventricular function. Our data generate the rationale to consider the therapeutic use of Hx to limit the cardiotoxicity of free heme in hemolytic disorders.

Hydrogen-Rich Saline as an Innovative Therapy for Cataract: A Hypothesis

Cataract is the leading cause of irreversible blindness worldwide. Increasing evidence indicates that oxidative stress is an important risk factor contributing to the development of cataract. Moreover, the enhancement of the antioxidant defense system may be beneficial to prevent or delay the cataractogenesis. The term oxidative stress has been defined as a disturbance in the equilibrium status of oxidant/antioxidant systems with progressive accumulation of reactive oxygen species (ROS) in intact cells. Superfluous ROS can damage proteins, lipids, polysaccharides, and nucleic acids within ocular tissues that are closely correlated with cataract formation. Therefore, prevention of oxidative stress damage by antioxidants might be considered as a viable means of medically offsetting the progression of this vision-impairing disease. Molecular hydrogen has recently been verified to have protective and therapeutic value as an antioxidant through its ability to selectively reduce cytotoxic ROS such as hydroxyl radical (OH). Hitherto, hydrogen has been used as a therapeutic element against multiple pathologies in both animal models and human patients. Unlike most well-known antioxidants, which are unable to successfully target organelles, hydrogen has advantageous distribution characteristics enabling it to penetrate biomembranes and diffuse into the cytosol, mitochondria, and nucleus. Consequently, we speculate that hydrogen might be an effective antioxidant to protect against lens damage, and it is important to further explore the biological mechanism underlying its potential therapeutic effects.

Effects of magnesium supplementation on electrophysiological remodeling of cardiac myocytes in L-NAME induced hypertensive rats

Hypertension is one of the major risk factors of cardiac hypertrophy and magnesium deficiency is suggested to be a contributing factor in the progression of this complication. In this study, we aimed to investigate the relationship between intracellular free Mg(2+) levels and electrophysiological changes developed in the myocardium of L-NAME induced hypertensive rats. Hypertension was induced by administration of 40 mg/kg of L-NAME for 6 weeks, while magnesium treated rats fed with a diet supplemented with 1 g/kg of MgO for the same period. L-NAME administration for 6 weeks elicited a significant increase in blood pressure which was corrected with MgO treatment; thereby cardiac hypertrophy developing secondary to hypertension was prevented. Cytosolic free magnesium levels of ventricular myocytes were significantly decreased with hypertension and magnesium administration restored these changes. Hypertension significantly decreased the fractional shortening with slowing of shortening kinetics in left ventricular myocytes whereas magnesium treatment was capable of restoring hypertension-induced contractile dysfunction. Long-term magnesium treatment significantly restored the hypertension-induced prolongation in action potentials of ventricular myocytes and suppressed Ito and Iss currents. In contrast, hypertension dependent decrement in intracellular Mg(2+) level did not cause a significant change in L-type Ca(2+) currents, SR Ca(2+) content and NCX activity. Nevertheless, hypertension mediated increase in superoxide anion, hydrogen peroxide and protein oxidation mitigated with magnesium treatment. In conclusion, magnesium administration improves mechanical abnormalities observed in hypertensive rat ventricular myocytes due to reduced oxidative stress. It is likely that, changes in intracellular magnesium balance may contribute to the pathophysiology of chronic heart diseases.

Lessons from mammalian hibernators: molecular insights into striated muscle plasticity and remodeling

Striated muscle shows an amazing ability to adapt its structural apparatus based on contractile activity, loading conditions, fuel supply, or environmental factors. Studies with mammalian hibernators have identified a variety of molecular pathways which are strategically regulated and allow animals to endure multiple stresses associated with the hibernating season. Of particular interest is the observation that hibernators show little skeletal muscle atrophy despite the profound metabolic rate depression and mechanical unloading that they experience during long weeks of torpor. Additionally, the cardiac muscle of hibernators must adjust to low temperature and reduced perfusion, while the strength of contraction increases in order to pump cold, viscous blood. Consequently, hibernators hold a wealth of knowledge as it pertains to understanding the natural capacity of myocytes to alter structural, contractile and metabolic properties in response to environmental stimuli. The present review outlines the molecular and biochemical mechanisms which play a role in muscular atrophy, hypertrophy, and remodeling. In this capacity, four main networks are highlighted: (1) antioxidant defenses, (2) the regulation of structural, contractile and metabolic proteins, (3) ubiquitin proteosomal machinery, and (4) macroautophagy pathways. Subsequently, we discuss the role of transcription factors nuclear factor (erythroid-derived 2)-like 2 (Nrf2), Myocyte enhancer factor 2 (MEF2), and Forkhead box (FOXO) and their associated posttranslational modifications as it pertains to regulating each of these networks. Finally, we propose that comparing and contrasting these concepts to data collected from model organisms able to withstand dramatic changes in muscular function without injury will allow researchers to delineate physiological versus pathological responses.

Hydrogen Sulfide and Cellular Redox Homeostasis

Intracellular redox imbalance is mainly caused by overproduction of reactive oxygen species (ROS) or weakness of the natural antioxidant defense system. It is involved in the pathophysiology of a wide array of human diseases. Hydrogen sulfide (H₂S) is now recognized as the third “gasotransmitters” and proved to exert a wide range of physiological and cytoprotective functions in the biological systems. Among these functions, the role of H₂S in oxidative stress has been one of the main focuses over years. However, the underlying mechanisms for the antioxidant effect of H₂S are still poorly comprehended. This review presents an overview of the current understanding of H₂S specially focusing on the new understanding and mechanisms of the antioxidant effects of H₂S based on recent reports. Both inhibition of ROS generation and stimulation of antioxidants are discussed. H₂S-induced S-sulfhydration of key proteins (e.g., p66Shc and Keap1) is also one of the focuses of this review.

Heme-induced contractile dysfunction in human cardiomyocytes caused by oxidant damage to thick filament proteins

Intracellular free heme predisposes to oxidant-mediated tissue damage. We hypothesized that free heme causes alterations in myocardial contractility via disturbed structure and/or regulation of the contractile proteins. Isometric force production and its Ca(2+)-sensitivity (pCa50) were monitored in permeabilized human ventricular cardiomyocytes. Heme exposure altered cardiomyocyte morphology and evoked robust decreases in Ca(2+)-activated maximal active force (Fo) while increasing Ca(2+)-independent passive force (F passive). Heme treatments, either alone or in combination with H2O2, did not affect pCa50. The increase in F passive started at 3 µM heme exposure and could be partially reversed by the antioxidant dithiothreitol. Protein sulfhydryl (SH) groups of thick myofilament content decreased and sulfenic acid formation increased after treatment with heme. Partial restoration in the SH group content was observed in a protein running at 140 kDa after treatment with dithiothreitol, but not in other proteins, such as filamin C, myosin heavy chain, cardiac myosin binding protein C, and α-actinin. Importantly, binding of heme to hemopexin or alpha-1-microglobulin prevented its effects on cardiomyocyte contractility, suggesting an allosteric effect. In line with this, free heme directly bound to myosin light chain 1 in human cardiomyocytes. Our observations suggest that free heme modifies cardiac contractile proteins via posttranslational protein modifications and via binding to myosin light chain 1, leading to severe contractile dysfunction. This may contribute to systolic and diastolic cardiac dysfunctions in hemolytic diseases, heart failure, and myocardial ischemia-reperfusion injury.

Counteracting Protein Kinase Activity in the Heart: The Multiple Roles of Protein Phosphatases

Decades of cardiovascular research have shown that variable and flexible levels of protein phosphorylation are necessary to maintain cardiac function. A delicate balance between phosphorylated and dephosphorylated states of proteins is guaranteed by a complex interplay of protein kinases (PKs) and phosphatases. Serine/threonine phosphatases, in particular members of the protein phosphatase (PP) family govern dephosphorylation of the majority of these cardiac proteins. Recent findings have however shown that PPs do not only dephosphorylate previously phosphorylated proteins as a passive control mechanism but are capable to actively control PK activity via different direct and indirect signaling pathways. These control mechanisms can take place on (epi-)genetic, (post-)transcriptional, and (post-)translational levels. In addition PPs themselves are targets of a plethora of proteinaceous interaction partner regulating their endogenous activity, thus adding another level of complexity and feedback control toward this system. Finally, novel approaches are underway to achieve spatiotemporal pharmacologic control of PPs which in turn can be used to fine-tune misleaded PK activity in heart disease. Taken together, this review comprehensively summarizes the major aspects of PP-mediated PK regulation and discusses the subsequent consequences of deregulated PP activity for cardiovascular diseases in depth.

Contractile apparatus dysfunction early in the pathophysiology of diabetic cardiomyopathy

Diabetes mellitus significantly increases the risk of cardiovascular disease and heart failure in patients. Independent of hypertension and coronary artery disease, diabetes is associated with a specific cardiomyopathy, known as diabetic cardiomyopathy (DCM). Four decades of research in experimental animal models and advances in clinical imaging techniques suggest that DCM is a progressive disease, beginning early after the onset of type 1 and type 2 diabetes, ahead of left ventricular remodeling and overt diastolic dysfunction. Although the molecular pathogenesis of early DCM still remains largely unclear, activation of protein kinase C appears to be central in driving the oxidative stress dependent and independent pathways in the development of contractile dysfunction. Multiple subcellular alterations to the cardiomyocyte are now being highlighted as critical events in the early changes to the rate of force development, relaxation and stability under pathophysiological stresses. These changes include perturbed calcium handling, suppressed activity of aerobic energy producing enzymes, altered transcriptional and posttranslational modification of membrane and sarcomeric cytoskeletal proteins, reduced actin-myosin cross-bridge cycling and dynamics, and changed myofilament calcium sensitivity. In this review, we will present and discuss novel aspects of the molecular pathogenesis of early DCM, with a special focus on the sarcomeric contractile apparatus.

Hyperbilirubinemia modulates myocardial function, aortic ejection, and ischemic stress resistance in the Gunn rat

Mildly elevated circulating unconjugated bilirubin (UCB) is associated with protection against hypertension and ischemic heart disease. We assessed whether endogenously elevated bilirubin in Gunn rats modifies cardiovascular function and resistance to ischemic insult. Hearts were assessed ex vivo (Langendorff perfusion) and in vivo (Millar catheterization and echocardiography), and left ventricular myocardial gene expression was measured via quantitative real-time PCR. Ex vivo analysis revealed reduced intrinsic contractility in the Gunn myocardium (+dP/d t: 1,976 ± 622 vs. 2,907 ± 334 mmHg/s, P < 0.01; −dP/d t: −1,435 ± 372 vs. −2,234 ± 478 mmHg/s, P < 0.01), which correlated positively with myocardial UCB concentration ( P < 0.05). In vivo analyses showed no changes in left ventricular contractile parameters and ejection (fractional shortening and ejection fraction). However, Gunn rats exhibited reductions in the rate of aortic pressure development (3,008 ± 461 vs. 4,452 ± 644 mmHg/s, P < 0.02), mean aortic velocity (439 ± 64 vs. 644 ± 62 mm/s, P < 0.01), and aortic volume time integral pressure gradient (2.32 ± 0.65 vs. 5.72 ± 0.74 mmHg, P < 0.01), in association with significant aortic dilatation (12–24% increase in aortic diameter, P < 0.05). Ex vivo Gunn hearts exhibited improved ventricular function after 35 min of ischemia and 90 min of reperfusion (63 ± 14 vs. 35 ± 12%, P < 0.01). These effects were accompanied by increased glutathione peroxidase and reduced superoxide dismutase and phospholamban gene expression in Gunn rat myocardium ( P < 0.05). These data collectively indicate that hyperbilirubinemia in Gunn rats 1) reduces intrinsic cardiac contractility, which is compensated for in vivo; 2) induces aortic dilatation, which may beneficially influence aortic ejection velocities and pressures; and 3) may improve myocardial stress resistance in association with beneficial transcriptional changes. These effects may contribute to protection from cardiovascular disease with elevated bilirubin.

Redox-sensitive residue in the actin-binding interface of myosin

We have examined the chemical and functional reversibility of oxidative modification in myosin. Redox regulation has emerged as a crucial modulator of protein function, with particular relevance to aging. We previously identified a single methionine residue in Dictyostelium discoideum (Dicty) myosin II (M394, near the myosin cardiomyopathy loop in the actin-binding interface) that is functionally sensitive to oxidation. We now show that oxidation of M394 is reversible by methionine sulfoxide reductase (Msr), restoring actin-activated ATPase activity. Sequence alignment reveals that M394 of Dicty myosin II is a cysteine residue in all human isoforms of skeletal and cardiac myosin. Using Dicty myosin II as a model for site-specific redox sensitivity of this Cys residue, the M394C mutant can be glutathionylated in vitro, resulting in reversible inhibition of actin-activated ATPase activity, with effects similar to those of methionine oxidation at this site. This work illustrates the potential for myosin to function as a redox sensor in both non-muscle and muscle cells, modulating motility/contractility in response to oxidative stress.

Mitochondrial ion channels/transporters as sensors and regulators of cellular redox signaling

SIGNIFICANCE

Mitochondrial ion channels/transporters and the electron transport chain (ETC) serve as key sensors and regulators for cellular redox signaling, the production of reactive oxygen species (ROS) and nitrogen species (RNS) in mitochondria, and balancing cell survival and death. Although the functional and pharmacological characteristics of mitochondrial ion transport mechanisms have been extensively studied for several decades, the majority of the molecular identities that are responsible for these channels/transporters have remained a mystery until very recently.

RECENT ADVANCES

Recent breakthrough studies uncovered the molecular identities of the diverse array of major mitochondrial ion channels/transporters, including the mitochondrial Ca2+ uniporter pore, mitochondrial permeability transition pore, and mitochondrial ATP-sensitive K+ channel. This new information enables us to form detailed molecular and functional characterizations of mitochondrial ion channels/transporters and their roles in mitochondrial redox signaling.

CRITICAL ISSUES

Redox-mediated post-translational modifications of mitochondrial ion channels/transporters and ETC serve as key mechanisms for the spatiotemporal control of mitochondrial ROS/RNS generation.

FUTURE DIRECTIONS

Identification of detailed molecular mechanisms for redox-mediated regulation of mitochondrial ion channels will enable us to find novel therapeutic targets for many diseases that are associated with cellular redox signaling and mitochondrial ion channels/transporters.

Aggregate-prone R120GCRYAB triggers multifaceted modifications of the thioredoxin system

AIMS

The human mutation R120G in the αB-crystallin (CRYAB) causes a multisystemic disease that is characterized by hypertrophic cardiomyopathy and cytoplasmic protein aggregates. In transgenic mice, human R120GCRYAB (hR120GTg) expression in heart sequentially modifies the REDOX status, in part by the activation of the nuclear factor, erythroid derived 2, like 2 (Nrf2). Thioredoxin system (TS) components are NRF2 target genes, so it could be hypothesized that TS was affected in hR120GTg mice.

RESULTS

Transgenic hearts overexpressed thioredoxin 1 (Trx1), which was identified by isotope coded affinity tag-mass spectrometry, among hundreds of peptides displaying an increased reduced/oxidized ratio. Coupled to this higher level of reduced cysteines, the activity of thioredoxin reductase 1 (TrxR1) was augmented by 2.5-fold. Combining mutiple experimental approaches, the enzymatic regulation of TrxR1 by a histone deacetylase 3 (HDAC3)-dependent level of acetylation was confirmed. In vitro and in vivo functional tests established that TrxR1 activity is required to mitigate aggregate development, and this could be mediated by Bcl-2-associated athanogene 3 (BAG3) as a potential TS substrate.

INNOVATION AND CONCLUSIONS

This study uncovers the compartmentalized changes and the involvement of TS in the cardiac stress response elicited by misfolded proteins such as R120GCRYAB. Our work suggests that R120GCRYAB triggers a defensive pathway acting through the newly identified interacting partners HDAC3, TrxR1, and BAG3 to counter aggregate growth. Therefore, those interactors may function as modifier genes contributing to the variable onset and expressivity of such human diseases. Furthermore, our work underscores the potential organismal effects of pharmacological interventions targeting TS and HDAC.

Reactive oxygen species and excitation-contraction coupling in the context of cardiac pathology

Reactive oxygen species (ROS) are highly reactive oxygen-derived chemical compounds that are by-products of aerobic cellular metabolism as well as crucial second messengers in numerous signaling pathways. In excitation-contraction-coupling (ECC), which links electrical signaling and coordinated cardiac contraction, ROS have a severe impact on several key ion handling proteins such as ion channels and transporters, but also on regulating proteins such as protein kinases (e.g. CaMKII, PKA or PKC), thereby pivotally influencing the delicate balance of this finely tuned system. While essential as second messengers, ROS may be deleterious when excessively produced due to a disturbed balance in Na(+) and Ca(2+) handling, resulting in Na(+) and Ca(2+) overload, SR Ca(2+) loss and contractile dysfunction. This may, in the end, result in systolic and diastolic dysfunction and arrhythmias. This review aims to provide an overview of the single targets of ROS in ECC and to outline the role of ROS in major cardiac pathologies, such as heart failure and arrhythmogenesis. This article is part of a Special Issue entitled "Redox Signalling in the Cardiovascular System"

Folic acid reverses nitric oxide synthase uncoupling and prevents cardiac dysfunction in insulin resistance: role of Ca2+/calmodulin-activated protein kinase II

Nitric oxide synthase (NOS) may be uncoupled to produce superoxide rather than nitric oxide (NO) under pathological conditions such as diabetes mellitus and insulin resistance, leading to cardiac contractile anomalies. Nonetheless, the role of NOS uncoupling in insulin resistance-induced cardiac dysfunction remains elusive. Given that folic acid may produce beneficial effects for cardiac insufficiency partially through its NOS recoupling capacity, this study was designed to evaluate the effect of folic acid on insulin resistance-induced cardiac contractile dysfunction in a sucrose-induced insulin resistance model. Mice were fed a sucrose or starch diet for 8 weeks before administration of folic acid in drinking water for an additional 4 weeks. Cardiomyocyte contractile and Ca(2+) transient properties were evaluated and myocardial function was assessed using echocardiography. Our results revealed whole body insulin resistance after sucrose feeding associated with diminished NO production, elevated peroxynitrite (ONOO(-)) levels, and impaired echocardiographic and cardiomyocyte function along with a leaky ryanodine receptor (RYR) and intracellular Ca(2+) handling derangement. Western blot analysis showed that insulin resistance significantly promoted Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) phosphorylation, which might be responsible for the leaky RYR and cardiac mechanical dysfunction. NOS recoupling using folic acid reversed insulin resistance-induced changes in NO and ONOO(-), CaMKII phosphorylation, and cardiac mechanical abnormalities. Taken together, these data demonstrated that treatment with folic acid may reverse cardiac contractile and intracellular Ca(2+) anomalies through ablation of CaMKII phosphorylation and RYR Ca(2+) leak.

Myosin heads are displaced from actin filaments in the in situ beating rat heart in early diabetes

Diabetes is independently associated with a specific cardiomyopathy, characterized by impaired cardiac muscle relaxation and force development. Using synchrotron radiation small-angle x-ray scattering, this study investigated in the in situ heart and in real-time whether changes in cross-bridge disposition and myosin interfilament spacing underlie the early development of diabetic cardiomyopathy. Experiments were conducted using anesthetized Sprague-Dawley rats 3 weeks after treatment with either vehicle (control) or streptozotocin (diabetic). Diffraction patterns were recorded during baseline and dobutamine infusions simultaneous with ventricular pressure-volumetry. From these diffraction patterns myosin mass transfer to actin filaments was assessed as the change in intensity ratio (I(1,0)/I(1,1)). In diabetic hearts cross-bridge disposition was most notably abnormal in the diastolic phase (p < 0.05) and to a lesser extent the systolic phase (p < 0.05). In diabetic rats only, there was a transmural gradient of contractile depression. Elevated diabetic end-diastolic intensity ratios were correlated with the suppression of diastolic function (p < 0.05). Furthermore, the expected increase in myosin head transfer by dobutamine was significantly blunted in diabetic animals (p < 0.05). Interfilament spacing did not differ between groups. We reveal that impaired cross-bridge disposition and radial transfer may thus underlie the early decline in ventricular function observed in diabetic cardiomyopathy.

Pulmonary hypertension associated with diffuse deposition of pentosidine in pulmonary arterioles

Diabetes induces advanced glycation end products (AGEs) that per se are not only a major cause of oxidative stress but also reduce the plasticity of connective tissue by pathological collagen cross-linking. We describe a case of severe pulmonary hypertension manifesting as a major diabetic complication. Impaired pulmonary arteriolar plasticity attributed to pentosidine, together with increased circulation volume by hyperosmotic pressure and reduction in myocardial compliance by multiple patchy fibrosis, may contribute to the clinical manifestation of severe pulmonary hypertension.

Reductive stress linked to small HSPs, G6PD, and Nrf2 pathways in heart disease

SIGNIFICANCE

Aerobic organisms must exist between the dueling biological metabolic processes for energy and respiration and the obligatory generation of reactive oxygen species (ROS) whose deleterious consequences can reduce survival. Wide fluctuations in harmful ROS generation are circumvented by endogenous countermeasures (i.e., enzymatic and nonenzymatic antioxidants systems) whose capacity decline with aging and are enhanced by disease states.

RECENT ADVANCES

Substantial efforts on the cellular and molecular underpinnings of oxidative stress has been complemented recently by the discovery that reductive stress similarly predisposes to inheritable cardiomyopathy, firmly establishing that the biological extremes of the redox spectrum play essential roles in disease pathogenesis.

CRITICAL ISSUES

Because antioxidants by nutritional or pharmacological supplement to prevent or mitigate disease states have been largely disappointing, we hypothesize that lack of efficacy of antioxidants might be related to adverse outcomes in responders at the reductive end of the redox spectrum. As emerging concepts, such as reductive, as opposed, oxidative stress are further explored, there is an urgent and critical gap for biochemical phenotyping to guide the targeted clinical applications of therapeutic interventions.

FUTURE DIRECTIONS

New approaches are vitally needed for characterizing redox states with the long-term goal to noninvasively assess distinct clinical states (e.g., presymptomatic, end-stage) with the diagnostic accuracy to guide personalized medicine.

Subendocardial increase in reactive oxygen species production affects regional contractile function in ischemic heart failure

AIMS

Heart failure (HF) is characterized by regionalized contractile alterations resulting in loss of the transmural contractile gradient across the left ventricular free wall. We tested whether a regional alteration in mitochondrial oxidative metabolism during HF could affect myofilament function through protein kinase A (PKA) signaling.

RESULTS

Twelve weeks after permanent left coronary artery ligation that induced myocardial infarction (MI), subendocardial (Endo) cardiomyocytes had decreased activity of complex I and IV of the mitochondrial electron transport chain and produced twice more superoxide anions than sham Endo and subepicardial cells. This effect was associated with a reduced antioxidant activity of superoxide dismutase and Catalase only in MI Endo cells. The myofilament contractile properties (Ca(2+) sensitivity and maximal tension), evaluated in skinned cardiomyocytes, were also reduced only in MI Endo myocytes. Conversely, in MI rats treated with the antioxidant N-acetylcysteine (NAC) for 4 weeks, the generation of superoxide anions in Endo cardiomyocytes was normalized and the contractile properties of skinned cardiomyocytes restored. This effect was accompanied by improved in vivo contractility. The beneficial effects of NAC were mediated, at least, in part, through reduction of the PKA activity, which was higher in MI myofilaments, particularly, the PKA-mediated hyperphosphorylation of cardiac Troponin I.

INNOVATION

The Transmural gradient in the mitochondrial content/activity is lost during HF and mediates reactive oxygen species-dependent contractile dysfunction.

CONCLUSIONS

Regionalized alterations in redox signaling affect the contractile machinery of sub-Endo myocytes through a PKA-dependent pathway that contributes to the loss of the transmural contractile gradient and impairs global contractility.

Integration of troponin I phosphorylation with cardiac regulatory networks

We focus here on the modulation of thin filament activity by cardiac troponin I phosphorylation as an integral and adaptive mechanism in cardiac homeostasis and as a mechanism vulnerable to maladaptive response to stress. We discuss a current concept of cardiac troponin I function in the A-band region of the sarcomere and potential signaling to cardiac troponin I in a network involving the ends of the thin filaments at the Z-disk and the M-band regions. The cardiac sarcomere represents a remarkable set of interacting proteins that functions not only as a molecular machine generating the heartbeat but also as a hub of signaling. We review how phosphorylation signaling to cardiac troponin I is integrated, with parallel signals controlling excitation-contraction coupling, hypertrophy, and metabolism.

Redox signaling in cardiac physiology and pathology

Redox signaling refers to the specific and usually reversible oxidation/reduction modification of molecules involved in cellular signaling pathways. In the heart, redox signaling regulates several physiological processes (eg, excitation-contraction coupling) and is involved in a wide variety of pathophysiological and homoeostatic or stress response pathways. Reactive oxygen species involved in cardiac redox signaling may derive from many sources, but NADPH oxidases, as dedicated sources of signaling reactive oxygen species, seem to be especially important. An increasing number of specific posttranslational oxidative modifications involved in cardiac redox signaling are being defined, along with the reactive oxygen species sources that are involved. Here, we review current knowledge on the molecular targets of signaling reactive oxygen species in cardiac cells and their involvement in cardiac physiopathology. Advances in this field may allow the development of targeted therapeutic strategies for conditions such as heart failure as opposed to the general antioxidant approaches that have failed to date.

H₂O₂ lowers the cytosolic Ca²⁺ concentration via activation of cGMP-dependent protein kinase Iα

The cGMP-dependent protein kinase I (cGKI) is a key mediator of cGMP signaling, but the specific functions of its two isoforms, cGKIα and cGKIβ, are poorly understood. Recent studies indicated a novel cGMP-independent role for cGKIα in redox sensing. To dissect the effects of oxidative stress on the cGKI isoforms, we used mouse embryonic fibroblasts and vascular smooth muscle cells (VSMCs) expressing both, one, or none of them. In cGKIα-expressing cells, but not in cells expressing only cGKIβ, incubation with H₂O₂ induced the formation of a disulfide bond between the two identical subunits of the dimeric enzyme. Oxidation of cGKIα was associated with increased phosphorylation of its substrate, vasodilator-stimulated phosphoprotein. H₂O₂ did not stimulate cGMP production, indicating that it activates cGKIα directly via oxidation. Interestingly, there was a mutual influence of H₂O₂ and cGMP on cGKI activity and disulfide bond formation, respectively; preoxidation of the kinase with H₂O₂ slightly impaired its activation by cGMP, whereas preactivation of the enzyme with cGMP attenuated its oxidation by H₂O₂. To evaluate the functional relevance of the noncanonical H₂O₂-cGKIα pathway, we studied the regulation of the cytosolic Ca²⁺ concentration ([Ca²⁺](i)). H₂O₂ suppressed norepinephrine-induced Ca²⁺ transients in cGKIα-expressing VSMCs and, to a lower extent, in VSMCs expressing only cGKIβ or none of the isoforms. Thus, H₂O₂ lowers [Ca²⁺](i) mainly via a cGKIα-dependent pathway. These results indicate that oxidative stress selectively targets the cGKIα isoform, which then modulates cellular processes in a cGMP-independent manner. A decrease in [Ca²⁺](i) in VSMCs via activation of cGKIα might be a major mechanism of H₂O₂-induced vasodilation.

Small heat shock proteins in redox metabolism: implications for cardiovascular diseases

A timely review series on small heat shock proteins has to appropriately examine their fundamental properties and implications in the cardiovascular system since several members of this chaperone family exhibit robust expression in the myocardium and blood vessels. Due to energetic and metabolic demands, the cardiovascular system maintains a high mitochondrial activity but irreversible oxidative damage might ensue from increased production of reactive oxygen species. How equilibrium between their production and scavenging is achieved becomes paramount for physiological maintenance. For example, heat shock protein B1 (HSPB1) is implicated in maintaining this equilibrium or redox homeostasis by upholding the level of glutathione, a major redox mediator. Studies of gain or loss of function achieved by genetic manipulations have been highly informative for understanding the roles of those proteins. For example, genetic deficiency of several small heat shock proteins such as HSPB5 and HSPB2 is well-tolerated in heart cells whereas a single missense mutation causes human pathology. Such evidence highlights both the profound genetic redundancy observed among the multigene family of small heat shock proteins while underscoring the role proteotoxicity plays in driving disease pathogenesis. We will discuss the available data on small heat shock proteins in the cardiovascular system, redox metabolism and human diseases. From the medical perspective, we envision that such emerging knowledge of the multiple roles small heat shock proteins exert in the cardiovascular system will undoubtedly open new avenues for their identification and possible therapeutic targeting in humans. This article is part of a Directed Issue entitled: Small HSPs in physiology and pathology.

Tirapazamine-doxorubicin interaction referring to heart oxidative stress and Ca²⁺ balance protein levels

Doxorubicin (DOX) causes long-term cardiomyopathy that is dependent on oxidative stress and contractility disorders. Tirapazamine (TP), an experimental adjuvant drug, passes the same red-ox transformation as DOX. The aim of the study was to evaluate an effect of tirapazamine on oxidative stress, contractile protein level, and cardiomyocyte necrosis in rats administered doxorubicin. Rats were intraperitoneally injected six times once a week with tirapazamine in two doses, 5 (5TP) and 10 mg/kg (10TP), while doxorubicin was administered in dose 1.8 mg/kg (DOX). Subsequent two groups received both drugs simultaneously (5TP+DOX and 10TP+DOX). Tirapazamine reduced heart lipid peroxidation and normalised RyR2 protein level altered by doxorubicin. There were no significant changes in GSH/GSSG ratio, total glutathione, cTnI, AST, and SERCA2 level between DOX and TP+DOX groups. Cardiomyocyte necrosis was observed in groups 10TP and 10TP+DOX.

Physiological regulation of cardiac contractility by endogenous reactive oxygen species

Increased production of reactive oxygen species (ROS) has been linked to the pathogenesis of congestive heart failure. However, emerging evidence suggests the involvement of ROS in the regulation of various physiological cellular processes in the myocardium. In this review, we summarize the latest findings regarding the role of ROS in the acute regulation of cardiac contractility. We discuss ROS-dependent modulation of the inotropic responses to G protein-coupled receptor agonists (e.g. β-adrenergic receptor agonists and endothelin-1), the potential cellular sources of ROS (e.g. NAD(P)H oxidases and mitochondria) and the proposed end-targets and signalling pathways by which ROS affect contractility. Accumulating new data supports the fundamental role of endogenously generated ROS to regulate cardiac function under physiological conditions.

Cardiac phosphoproteome reveals cell signaling events involved in doxorubicin cardiotoxicity

The successful use of anthracyclines like doxorubicin in chemotherapy is limited by their severe cardiotoxicity. Despite decades of clinical application, a satisfying description of the molecular mechanisms involved and a preventive treatment have not yet been achieved. Here we address doxorubicin-induced changes in cell signaling as a novel potential mediator of doxorubicin toxicity by applying a non-biased screen of the cardiac phosphoproteome. Two-dimensional gel electrophoresis, phosphospecific staining, quantitative image analysis, and MALDI-TOF/TOF mass spectrometry were combined to identify (de)phosphorylation events occurring in the isolated rat heart upon Langendorff-perfusion with clinically relevant (5 μM) and supraclinical concentrations (25 μM) of doxorubicin. This approach identified 22 proteins with a significantly changed phosphorylation status and these results were validated by immunoblotting for selected phosphosites. Overrepresentation of mitochondrial proteins (>40%) identified this compartment as a prime target of doxorubicin. Identified proteins were mainly involved in energy metabolism (e.g. pyruvate dehydrogenase and acyl-CoA dehydrogenase), sarcomere structure and function (e.g. desmin) or chaperone-like activities (e.g. α-crystallin B chain and prohibitin). Changes in phosphorylation of pyruvate dehydrogenase, regulating pyruvate entry into the Krebs cycle, and desmin, maintaining myofibrillar array, are relevant for main symptoms of cardiac dysfunction related to doxorubicin treatment, namely energy imbalance and myofibrillar disorganization. This article is part of a Special Issue entitled: Translational Proteomics.

Heart development: mitochondria in command of cardiomyocyte differentiation

Continuous developmental maturation of cardiomyocytes is essential to meet the functional and metabolic demands of the growing heart. A new study (Hom et al., 2011) reports that embryonic cardiomyocytes are influenced by mitochondrial maturation, such that closure of the mitochondrial permeability transition pore results in decreased levels of reactive oxygen species, thereby inducing differentiation.