Inducible expression of active protein phosphatase-1 inhibitor-1 enhances basal cardiac function and protects against ischemia/reperfusion injury

Constitutive phosphorylation of inhibitor-1 at Ser67 and Thr75 depresses calcium cycling in cardiomyocytes and leads to remodeling upon aging

The activity of protein phosphatase-1 (PP1) inhibitor-1 (I-1) is antithetically modulated by the cAMP-protein kinase A (PKA) and Ca(2+)-protein kinase C (PKC) signaling axes. β-adrenergic (β-AR) stimulation results in PKA-phosphorylation of I-1 at threonine 35 (Thr35) and depressed PP1 activity, while PKC phosphorylation at serine 67 (Ser67) and/or Thr75 increases PP1 activity. In heart failure, pThr35 is decreased while pSer67 and pThr75 are elevated. However, the role of Ser67/Thr75 phosphorylation in vivo and its effects on Ca(2+)-cycling are not known. Thus, our aim was to investigate the functional significance of Ser67 and Thr75 phosphorylation in intact hearts. We generated transgenic mice (TG) with cardiac-specific overexpression of constitutively phosphorylated I-1 at Ser67 and Thr75 (S67D/T75D) and evaluated cardiac function. The S67D/T75D cardiomyocytes exhibited significantly depressed Ca(2+)-kinetics and contractile parameters, compared with wild-type (WT) cells. The decreased Ca(2+)-cycling was associated with a 27 % increase in PP1 activity, no alterations in PP2 activity and impaired phosphorylation of myosin-binding protein-C (MyBPC). Upon aging, there was cardiac remodeling associated with increases in systolic and diastolic left ventricular internal diameter dimensions (at 16 months), compared with WTs. The results indicate that phosphorylation of I-1 at Ser67 and Thr75 is associated with increased PP1 activity and depressed cardiomyocyte Ca(2+)-cycling, which manifests in geometrical alterations over the long term. Thus, hyperphosphorylation of these sites in failing hearts may contribute to deteriorative remodeling.

Novel Ser/Thr protein phosphatases in cell death regulation

Cell death is regulated by a myriad of intracellular molecular pathways, with many involving protein phosphorylation and dephosphorylation. In this review, we will focus on Ser/Thr phosphatases-mediated regulation in cell apoptosis as well as on their potential roles in cell necrosis. The emerging functional importance of Ser/Thr protein phosphatases in cell death regulation adds new dimension to the signaling mechanisms of cellular function, physiology, and diseases.

Gene therapy for heart failure

Congestive heart failure accounts for half a million deaths per year in the United States. Despite its place among the leading causes of morbidity, pharmacological and mechanic remedies have only been able to slow the progression of the disease. Today's science has yet to provide a cure, and there are few therapeutic modalities available for patients with advanced heart failure. There is a critical need to explore new therapeutic approaches in heart failure, and gene therapy has emerged as a viable alternative. Recent advances in understanding of the molecular basis of myocardial dysfunction, together with the evolution of increasingly efficient gene transfer technology, have placed heart failure within reach of gene-based therapy. The recent successful and safe completion of a phase 2 trial targeting the sarcoplasmic reticulum calcium ATPase pump (SERCA2a), along with the start of more recent phase 1 trials, opens a new era for gene therapy for the treatment of heart failure.

Heart failure-inducible gene therapy targeting protein phosphatase 1 prevents progressive left ventricular remodeling

Background

The targeting of Ca²⁺ cycling has emerged as a potential therapy for the treatment of severe heart failure. These approaches include gene therapy directed at overexpressing sarcoplasmic reticulum (SR) Ca²⁺ ATPase, or ablation of phospholamban (PLN) and associated protein phosphatase 1 (PP1) protein complexes. We previously reported that PP1β, one of the PP1 catalytic subunits, predominantly suppresses Ca²⁺ uptake in the SR among the three PP1 isoforms, thereby contributing to Ca²⁺ downregulation in failing hearts. In the present study, we investigated whether heart-failure-inducible PP1β-inhibition by adeno-associated viral-9 (AAV9) vector mediated gene therapy is beneficial for preventing disease progression in genetic cardiomyopathic mice.

Methods

We created an adeno-associated virus 9 (AAV9) vector encoding PP1β short-hairpin RNA (shRNA) or negative control (NC) shRNA. A heart failure inducible gene expression system was employed using the B-type natriuretic protein (BNP) promoter conjugated to emerald-green fluorescence protein (EmGFP) and the shRNA sequence. AAV9 vectors (AAV9-BNP-EmGFP-PP1βshRNA and AAV9-BNP-EmGFP-NCshRNA) were injected into the tail vein (2×10¹¹ GC/mouse) of muscle LIM protein deficient mice (MLPKO), followed by serial analysis of echocardiography, hemodynamic measurement, biochemical and histological analysis at 3 months.

Results

In the MLPKO mice, BNP promoter activity was shown to be increased by detecting both EmGFP expression and the induced reduction of PP1β by 25% in the myocardium. Inducible PP1βshRNA delivery preferentially ameliorated left ventricular diastolic function and mitigated adverse ventricular remodeling. PLN phosphorylation was significantly augmented in the AAV9-BNP-EmGFP-PP1βshRNA injected hearts compared with the AAV9-BNP-EmGFP-NCshRNA group. Furthermore, BNP production was reduced, and cardiac interstitial fibrosis was abrogated at 3 months.

Conclusion

Heart failure-inducible molecular targeting of PP1β has potential as a novel therapeutic strategy for heart failure.

Ablation of junctin or triadin is associated with increased cardiac injury following ischaemia/reperfusion

AIMS

Junctin and triadin are calsequestrin-binding proteins that regulate sarcoplasmic reticulum (SR) Ca(2+) release by interacting with the ryanodine receptor. The levels of these proteins are significantly down-regulated in failing human hearts. However, the significance of such decreases is currently unknown. Here, we addressed the functional role of these accessory proteins in the heart's responses to ischaemia/reperfusion (I/R) injury.

METHODS AND RESULTS

Isolated mouse hearts were subjected to global I/R, and contractile parameters were assessed in wild-type (WT), junctin-knockout (JKO), and triadin-knockout (TKO) hearts. Both JKO and TKO were associated with significantly depressed post-I/R contractile recovery. However, ablation of triadin resulted in the most severe post-I/R phenotype. The additional contractile impairment of TKO hearts was not related to a mitochondrial death pathway, but attributed to endoplasmic reticulum (ER) stress-mediated apoptosis. Activation of the X-box-binding protein-1 and transcriptional up-regulation of C/EBP-homologous protein (CHOP) provided a molecular mechanism of caspase-12-dependent apoptosis in myocytes. In addition, elevation of cytosolic Ca(2+) during reperfusion was associated with the activation of calpain proteases and troponin I breakdown. Accordingly, treatment with the calpain inhibitor MDL-28170 significantly ameliorated post-I/R impairment of contractile recovery in intact hearts.

CONCLUSION

These findings indicate that deficiency of either junctin or triadin impairs the contractile recovery in post-ischaemic hearts, which appears to be primarily attributed to increased ER stress and activation of calpain.

Clusters of conserved beta cell marker genes for assessment of beta cell phenotype

Background and Methodology

The aim of this study was to establish a gene expression blueprint of pancreatic beta cells conserved from rodents to humans and to evaluate its applicability to assess shifts in the beta cell differentiated state. Genome-wide mRNA expression profiles of isolated beta cells were compared to those of a large panel of other tissue and cell types, and transcripts with beta cell-abundant and -selective expression were identified. Iteration of this analysis in mouse, rat and human tissues generated a panel of conserved beta cell biomarkers. This panel was then used to compare isolated versus laser capture microdissected beta cells, monitor adaptations of the beta cell phenotype to fasting, and retrieve possible conserved transcriptional regulators.

Principal Findings

A panel of 332 conserved beta cell biomarker genes was found to discriminate both isolated and laser capture microdissected beta cells from all other examined cell types. Of all conserved beta cell-markers, 15% were strongly beta cell-selective and functionally associated to hormone processing, 15% were shared with neuronal cells and associated to regulated synaptic vesicle transport and 30% with immune plus gut mucosal tissues reflecting active protein synthesis. Fasting specifically down-regulated the latter cluster, but preserved the neuronal and strongly beta cell-selective traits, indicating preserved differentiated state. Analysis of consensus binding site enrichment indicated major roles of CREB/ATF and various nutrient- or redox-regulated transcription factors in maintenance of differentiated beta cell phenotype.

Conclusions

Conserved beta cell marker genes contain major gene clusters defined by their beta cell selectivity or by their additional abundance in either neural cells or in immune plus gut mucosal cells. This panel can be used as a template to identify changes in the differentiated state of beta cells.

Calcium cycling proteins and their association with heart failure

Heart failure (HF) has reached epidemic proportions in the United States and is one of the most important challenges to public health. Severe congestive HF is associated with substantial morbidity and mortality. HF afflicts approximately 5 million patients and contributes to 3 million hospitalizations and 300,000 deaths yearly. Late-stage HF has a poor prognosis, and therapeutic options are limited. Defective excitation–contraction (EC) coupling in HF may result from altered density or function of proteins relevant for Ca2+ homeostasis.

Rescuing the failing heart by targeted gene transfer

Congestive heart failure is a major cause of morbidity and mortality in the United States. Although progress in conventional treatments is making steady and incremental gains to decrease heart failure mortality, there is a critical need to explore new therapeutic approaches. Gene therapy was initially applied in the clinical setting for inherited monogenic disorders. It is now apparent that gene therapy has broader potential that also includes acquired polygenic diseases, such as congestive heart failure. Recent advances in understanding of the molecular basis of myocardial dysfunction, together with the evolution of increasingly efficient gene transfer technology, have placed heart failure within the reach of gene-based therapy. Furthermore, the recent successful and safe completion of a phase 2 trial targeting the sarcoplasmic reticulum Ca(2+) ATPase pump along with the start of more recent phase 1 trials are ushering in a new era of gene therapy for the treatment of heart failure.

Targeted gene therapy for the treatment of heart failure

Chronic heart failure is one of the leading causes of morbidity and mortality in Western countries and is a major financial burden to the health care system. Pharmacologic treatment and implanting devices are the predominant therapeutic approaches. They improve survival and have offered significant improvement in patient quality of life, but they fall short of producing an authentic remedy. Cardiac gene therapy, the introduction of genetic material to the heart, offers great promise in filling this void. In-depth knowledge of the underlying mechanisms of heart failure is, obviously, a prerequisite to achieve this aim. Extensive research in the past decades, supported by numerous methodological breakthroughs, such as transgenic animal model development, has led to a better understanding of the cardiovascular diseases and, inadvertently, to the identification of several candidate genes. Of the genes that can be targeted for gene transfer, calcium cycling proteins are prominent, as abnormalities in calcium handling are key determinants of heart failure. A major impediment, however, has been the development of a safe, yet efficient, delivery system. Nonviral vectors have been used extensively in clinical trials, but they fail to produce significant gene expression. Viral vectors, especially adenoviral, on the other hand, can produce high levels of expression, at the expense of safety. Adeno-associated viral vectors have emerged in recent years as promising myocardial gene delivery vehicles. They can sustain gene expression at a therapeutic level and maintain it over extended periods of time, even for years, and, most important, without a safety risk.

Small heat shock protein 20 interacts with protein phosphatase-1 and enhances sarcoplasmic reticulum calcium cycling

BACKGROUND

Heat shock proteins (Hsp) are known to enhance cell survival under various stress conditions. In the heart, the small Hsp20 has emerged as a key mediator of protection against apoptosis, remodeling, and ischemia/reperfusion injury. Moreover, Hsp20 has been implicated in modulation of cardiac contractility ex vivo. The objective of this study was to determine the in vivo role of Hsp20 in the heart and the mechanisms underlying its regulatory effects in calcium (Ca) cycling.

METHODS AND RESULTS

Hsp20 overexpression in intact animals resulted in significant enhancement of cardiac function, coupled with augmented Ca cycling and sarcoplasmic reticulum Ca load in isolated cardiomyocytes. This was associated with specific increases in phosphorylation of phospholamban (PLN) at both Ser16 and Thr17, relieving its inhibition of the apparent Ca affinity of SERCA2a. Accordingly, the inotropic effects of Hsp20 were abrogated in cardiomyocytes expressing nonphosphorylatable PLN (S16A/T17A). Interestingly, the activity of type 1 protein phosphatase (PP1), a known regulator of PLN signaling, was significantly reduced by Hsp20 overexpression, suggesting that the Hsp20 stimulatory effects are partially mediated through the PP1-PLN axis. This hypothesis was supported by cell fractionation, coimmunoprecipitation, and coimmunolocalization studies, which revealed an association between Hsp20, PP1, and PLN. Furthermore, recombinant protein studies confirmed a physical interaction between AA 73 to 160 in Hsp20 and AA 163 to 330 in PP1.

CONCLUSIONS

Hsp20 is a novel regulator of sarcoplasmic reticulum Ca cycling by targeting the PP1-PLN axis. These findings, coupled with the well-recognized cardioprotective role of Hsp20, suggest a dual benefit of targeting Hsp20 in heart disease.

Phosphatase-1 inhibitor-1 in physiological and pathological β-adrenoceptor signalling

Control of protein phosphorylation-dephosphorylation events occurs through regulation of protein kinases and phosphatases. Phosphatase type 1 (PP-1) provides the main activity of serine/threonine protein phosphatases in the heart. Inhibitor-1 (I-1) was the first endogenous molecule found to inhibit PP-1 specifically. Notably, I-1 is activated by cAMP-dependent protein kinase A (PKA), and the subsequent prevention of target dephosphorylation by PP-1 provides distal amplification of β-adrenoceptor (β-AR) signalling. I-1 was found to be down-regulated and hypo-phosphorylated in human and experimental heart failure but hyperactive in human atrial fibrillation, implicating I-1 in the pathogenesis of heart failure and arrhythmias. Consequently, the therapeutic potential of I-1 in heart failure and arrhythmias has recently been addressed by the generation and analysis of several I-1 genetic mouse models. This review summarizes and discusses these data, highlights partially controversial issues on whether I-1 should be therapeutically reinforced or inhibited and suggests future directions to better understand the functional role of I-1 in physiological and pathological β-AR signalling.

The large isoforms of A-kinase anchoring protein 18 mediate the phosphorylation of inhibitor-1 by protein kinase A and the inhibition of protein phosphatase 1 activity

Inhibitor-1 (I-1) is phosphorylated on threonine residue 35 (Thr35) by the cAMP-dependent protein kinase (PKA), inducing the potent inhibition of the serine-threonine-specific protein phosphatase 1 (PP1). We now report that the formation of a signaling complex containing PKA and I-1 by the A-kinase anchoring protein 18 (AKAP18) facilitates this regulation in cells. AKAP18 directly bound I-1, and AKAP18/I-1 complexes were isolated from both rat heart extract and transfected heterologous cells. It is noteworthy that prevention of PKA binding to the AKAP18 scaffold decreased I-1 phosphorylation by 48% in cells. Moreover, the I-1 target PP1 was also associated with AKAP18 complexes. The cAMP-mediated inhibition of phosphatase activity was contingent on PKA binding to the scaffold. These observations reveal an additional level of complexity in PP1 regulation because of its association with AKAP18 multimolecular signaling complexes and suggest that targeting of AKAP18 complexes may be an alternative method to alter phosphatase activity and modulate specific substrate dephosphorylation.

Changes in fibroblast mechanostat set point and mechanosensitivity: an adaptive response to mechanical stress in floppy eyelid syndrome

PURPOSE

Floppy eyelid syndrome (FES) is an acquired hyperelasticity disorder affecting the upper eyelid. The tarsal plate becomes hyperelastic with a loss of intrinsic rigidity. As a result, the eyelid is subjected to cyclic mechanical stress. This condition was used as a model to investigate changes in dynamic fibroblast contractility in the context of chronic cyclic mechanical stress.

METHODS

Contractile efficiency was investigated in a free-floating, three-dimensional collagen matrix model. Intrinsic cellular force measurements and responses to changes in gel tension were explored using a tensioning culture force monitor (t-CFM). Gene expression differences between cell lines exhibiting differences in contractile phenotype were explored with a genome level microarray platform and RT-PCR.

RESULTS

FES tarsal plate fibroblasts (TFs) showed an increased contractile efficiency compared with the control, and t-CFM measurements confirmed a higher intrinsic cellular force at plateau levels. Cyclic stretch/relaxation experiments determined that TFs in FES maintained a functional tensional homeostasis response but with an altered sensitivity, operating around a higher mechanostat set point. Gene expression array and RT-PCR analysis identified V-CAM1 and PPP1R3C as being upregulated in FES TFs.

CONCLUSIONS

These changes may represent an adaptive response that allows tensional homeostasis to be maintained at the high levels of tissue stress experienced in FES. Gene expression studies point to a role for V-CAM1 and PPP1R3C in mediating changes in the dynamic range of mechanosensitivity of TFs. This work identifies FES as a useful model for the study of adaptive physiological responses to mechanical stress.

Genetic inhibition of PKA phosphorylation of RyR2 prevents dystrophic cardiomyopathy

Aberrant intracellular Ca(2+) regulation is believed to contribute to the development of cardiomyopathy in Duchenne muscular dystrophy. Here, we tested whether inhibition of protein kinase A (PKA) phosphorylation of ryanodine receptor type 2 (RyR2) prevents dystrophic cardiomyopathy by reducing SR Ca(2+) leak in the mdx mouse model of Duchenne muscular dystrophy. mdx mice were crossed with RyR2-S2808A mice, in which PKA phosphorylation site S2808 on RyR2 is inactivated by alanine substitution. Compared with mdx mice that developed age-dependent heart failure, mdx-S2808A mice exhibited improved fractional shortening and reduced cardiac dilation. Whereas application of isoproterenol severely depressed cardiac contractility and caused 95% mortality in mdx mice, contractility was preserved with only 19% mortality in mdx-S2808A mice. SR Ca(2+) leak was greater in ventricular myocytes from mdx than mdx-S2808A mice. Myocytes from mdx mice had a higher incidence of isoproterenol-induced diastolic Ca(2+) release events than myocytes from mdx-S2808A mice. Thus, inhibition of PKA phosphorylation of RyR2 reduced SR Ca(2+) leak and attenuated cardiomyopathy in mdx mice, suggesting that enhanced PKA phosphorylation of RyR2 at S2808 contributes to abnormal Ca(2+) homeostasis associated with dystrophic cardiomyopathy.

Gene therapy for heart failure

Despite the progress achieved in conventional treatment modalities, heart failure remains a major cause of mortality and morbidity. The identification of novel signaling pathways has provided a solid scientific rationale which has stimulated preclinical development of gene-based therapies for heart failure. Advances in somatic gene transfer technologies have been crucial to the advent of the first human clinical trials which are currently in progress. As these and other trials of gene transfer-based therapies are initiated, these approaches have generated excitement and hope for novel treatments for cardiovascular disease. In this review, we present a summary of advancements in construction of different vectors and methods of delivery that have been used for specific myocardial gene delivery. In addition, we will show results from studies focusing on the use of gene therapy to target heart failure mechanisms in animal models of cardiac dysfunction. Finally, we discuss the limited but highly promising results from clinical studies that have served as catalysts to translate preclinical achievements towards new treatment modalities for heart failure.

Expression of active protein phosphatase 1 inhibitor-1 attenuates chronic beta-agonist-induced cardiac apoptosis

Cardiac apoptosis has been considered an important contributing factor to heart failure. Several subcellular mechanisms, including increased protein phosphatase 1 activity, have been suggested to induce apoptosis. Protein phosphatase 1 is regulated by an endogenous inhibitor-1 (I-1) that is activated upon phosphorylation at threonine 35 via protein kinase A. Here, we tested whether cardiac-specific overexpression of a constitutively active (T35D, AA 1-65) inhibitor-1 (I-1c), could also affect cardiac apoptosis and heart failure progression induced by prolonged beta-adrenergic stimulation. We found that either acute or chronic expression of I-1c reduced isoproterenol (ISO)-induced apoptosis assessed by nuclear condensation, TUNEL staining and DNA fragmentation. The beneficial effects of I-1c were associated with increased expression of the anti-apoptotic protein Bcl-2, decreased expression of the pro-apoptotic protein Bax and reduced levels of active caspases as well as increased activation of ERK. These findings suggest that mitochondrial signaling and ERK activation may be involved in the I-1c cardioprotective effects against apoptosis induced by prolonged beta-adrenergic stimulation.

The extended PP1 toolkit: designed to create specificity

Protein Ser/Thr phosphatase-1 (PP1) catalyzes the majority of eukaryotic protein dephosphorylation reactions in a highly regulated and selective manner. Recent studies have identified an unusually diversified PP1 interactome with the properties of a regulatory toolkit. PP1-interacting proteins (PIPs) function as targeting subunits, substrates and/or inhibitors. As targeting subunits, PIPs contribute to substrate selection by bringing PP1 into the vicinity of specific substrates and by modulating substrate specificity via additional substrate docking sites or blocking substrate-binding channels. Many of the nearly 200 established mammalian PIPs are predicted to be intrinsically disordered, a property that facilitates their binding to a large surface area of PP1 via multiple docking motifs. These novel insights offer perspectives for the therapeutic targeting of PP1 by interfering with the binding of PIPs or substrates.

Constitutively active phosphatase inhibitor-1 improves cardiac contractility in young mice but is deleterious after catecholaminergic stress and with aging

Phosphatase inhibitor-1 (I-1) is a distal amplifier element of beta-adrenergic signaling that functions by preventing dephosphorylation of downstream targets. I-1 is downregulated in human failing hearts, while overexpression of a constitutively active mutant form (I-1c) reverses contractile dysfunction in mouse failing hearts, suggesting that I-1c may be a candidate for gene therapy. We generated mice with conditional cardiomyocyte-restricted expression of I-1c (referred to herein as dTGI-1c mice) on an I-1-deficient background. Young adult dTGI-1c mice exhibited enhanced cardiac contractility but exaggerated contractile dysfunction and ventricular dilation upon catecholamine infusion. Telemetric ECG recordings revealed typical catecholamine-induced ventricular tachycardia and sudden death. Doxycycline feeding switched off expression of cardiomyocyte-restricted I-1c and reversed all abnormalities. Hearts from dTGI-1c mice showed hyperphosphorylation of phospholamban and the ryanodine receptor, and this was associated with an increased number of catecholamine-induced Ca2+ sparks in isolated myocytes. Aged dTGI-1c mice spontaneously developed a cardiomyopathic phenotype. These data were confirmed in a second independent transgenic mouse line, expressing a full-length I-1 mutant that could not be phosphorylated and thereby inactivated by PKC-alpha (I-1S67A). In conclusion, conditional expression of I-1c or I-1S67A enhanced steady-state phosphorylation of 2 key Ca2+-regulating sarcoplasmic reticulum enzymes. This was associated with increased contractile function in young animals but also with arrhythmias and cardiomyopathy after adrenergic stress and with aging. These data should be considered in the development of novel therapies for heart failure.

The signalling pathway of CaMKII-mediated apoptosis and necrosis in the ischemia/reperfusion injury

Ca(2+)-calmodulin-dependent protein kinase II (CaMKII) plays an important role mediating apoptosis/necrosis during ischemia-reperfusion (IR). We explored the mechanisms of this deleterious effect. Langendorff perfused rat and transgenic mice hearts with CaMKII inhibition targeted to sarcoplasmic reticulum (SR-AIP) were subjected to global IR. The onset of reperfusion increased the phosphorylation of Thr(17) site of phospholamban, without changes in total protein, consistent with an increase in CaMKII activity. Instead, there was a proportional decrease in the phosphorylation of Ser2815 site of ryanodine receptors (RyR2) and the amount of RyR2 at the onset of reperfusion, i.e. the ratio Ser2815/RyR2 did not change. Inhibition of the reverse Na(+)/Ca(2+)exchanger (NCX) mode (KBR7943) diminished phospholamban phosphorylation, reduced apoptosis/necrosis and enhanced mechanical recovery. CaMKII-inhibition (KN-93), significantly decreased phospholamban phosphorylation, infarct area, lactate dehydrogenase release (LDH) (necrosis), TUNEL positive nuclei, caspase-3 activity, Bax/Bcl-2 ratio and Ca(2+)-induced mitochondrial swelling (apoptosis), and increased contractile recovery when compared with non-treated IR hearts or IR hearts pretreated with the inactive analog, KN-92. Blocking SR Ca(2+) loading and release (thapsigargin/dantrolene), mitochondrial Ca(2+) uniporter (ruthenium red/RU360), or mitochondrial permeability transition pore (cyclosporine A), significantly decreased infarct size, LDH release and apoptosis. SR-AIP hearts failed to show an increase in the phosphorylation of Thr(17) of phospholamban at the onset of reflow and exhibited a significant decrease in infarct size, apoptosis and necrosis respect to controls. The results reveal an apoptotic-necrotic pathway mediated by CaMKII-dependent phosphorylations at the SR, which involves the reverse NCX mode and the mitochondria as trigger and end effectors, respectively, of the cascade.

Sarcoplasmic reticulum Ca(2+) ATPase as a therapeutic target for heart failure

The cardiac isoform of the sarco/endoplasmic reticulum Ca(2+)ATPase (SERCA2a) plays a major role in controlling excitation/contraction coupling. In both experimental and clinical heart failure, SERCA2a expression is significantly reduced which leads to abnormal Ca(2+) handling and deficient contractility. A large number of studies in isolated cardiac myocytes and in small and large animal models of heart failure showed that restoring SERCA2a expression by gene transfer corrects the contractile abnormalities and improves energetics and electrical remodeling. Following a long line of investigation, a clinical trial is underway to restore SERCA2a expression in patients with heart failure using adeno-associated virus type 1. This review addresses the following issues regarding heart failure gene therapy: i) new insights on calcium regulation by SERCA2a; ii) SERCA2a as a gene therapy target in animal models of heart failure; iii) advances in the development of viral vectors and gene delivery; and iv) clinical trials on heart failure using SERCA2a. This review focuses on the new advances in SERCA2a- targeted gene therapy made in the last three years. In conclusion, SERCA2a is an important therapeutic target in various cardiovascular disorders. Ongoing clinical gene therapy trials will provide answers on its safety and applicability.

Tissue proteomics in atherosclerosis: elucidating the molecular mechanisms of cardiovascular diseases

Atherosclerosis is a disease with higher levels of mortality in developed countries. Comprehension of the molecular mechanisms can yield very useful information in clinics for prevention, diagnosis and recovery monitoring. Proteomics represents an ideal methodology for this purpose, as proteins constitute the effectors of the different biological processes running during pathogenesis. To date, studies in atherosclerosis have been mainly focused on the search for plasma biomarkers. However, tissue proteomics allows going deeper into tissue secretomes, arterial layers or particular cells of interest, which, in turn, constitutes a more direct approximation to in vivo operating mechanisms. The aim of this review is to report latest advances in tissue proteomics in atherosclerosis and related diseases (e.g., aortic stenosis and ischemic injury).

Blockade of Hsp20 phosphorylation exacerbates cardiac ischemia/reperfusion injury by suppressed autophagy and increased cell death

RATIONALE

The levels of a small heat shock protein (Hsp)20 and its phosphorylation are increased on ischemic insults, and overexpression of Hsp20 protects the heart against ischemia/reperfusion injury. However, the mechanism underlying cardioprotection of Hsp20 and especially the role of its phosphorylation in regulating ischemia/reperfusion-induced autophagy, apoptosis, and necrosis remain to be clarified.

OBJECTIVE

Herein, we generated a cardiac-specific overexpression model, carrying nonphosphorylatable Hsp20, where serine 16 was substituted with alanine (Hsp20(S16A)). By subjecting this model to ischemia/reperfusion, we addressed whether: (1) the cardioprotective effects of Hsp20 are associated with serine 16 phosphorylation; (2) blockade of Hsp20 phosphorylation influences the balance between autophagy and cell death; and (3) the aggregation pattern of Hsp20 is altered by its phosphorylation.

METHODS AND RESULTS

Our results demonstrated that Hsp20(S16A) hearts were more sensitive to ischemia/reperfusion injury, evidenced by lower recovery of contractile function and increased necrosis and apoptosis, compared with non-TG hearts. Interestingly, autophagy was activated in non-TG hearts but significantly inhibited in Hsp20(S16A) hearts following ischemia/reperfusion. Accordingly, pretreatment of Hsp20(S16A) hearts with rapamycin, an activator of autophagy, resulted in improvement of functional recovery, compared with saline-treated Hsp20(S16A) hearts. Furthermore, on ischemia/reperfusion, the oligomerization pattern of Hsp20 appeared to shift to higher aggregates in Hsp20(S16A) hearts.

CONCLUSIONS

Collectively, these data indicate that blockade of Ser16-Hsp20 phosphorylation attenuates the cardioprotective effects of Hsp20 against ischemia/reperfusion injury, which may be attributable to suppressed autophagy and increased cell death. Therefore, phosphorylation of Hsp20 at serine 16 may represent a potential therapeutic target in ischemic heart disease.

Role of protein phosphatase-1 inhibitor-1 in cardiac physiology and pathophysiology

The type 1 protein phosphatase (PP1) is a critical negative regulator of Ca(2+) cycling and contractility in the cardiomyocyte. In particular, it mediates restoration of cardiac function to basal levels, after beta-adrenergic stimulation, by dephosphorylating key phospho-proteins. PP1 is a holoenzyme comprised of its catalytic and auxiliary subunits. These regulatory proteins dictate PP1's subcellular localization, substrate specificity and activity. Amongst them, inhibitor-1 is of particular importance since it has been implicated as an integrator of multiple neurohormonal pathways, which finely regulate PP1 activity, at the level of the sarcoplasmic reticulum (SR). In fact, perturbations in the regulation of PP1 by inhibitor-1 have been implicated in the pathogenesis of heart failure, suggesting that inhibitor-1-based therapeutic interventions may ameliorate cardiac dysfunction and remodeling in the failing heart. This review will discuss the current views on the role of inhibitor-1 in cardiac physiology, its possible contribution to cardiac disease and its potential as a novel therapeutic strategy.