In vivo gene delivery of HSP70i by adenovirus and adeno-associated virus preserves contractile function in mouse heart following ischemia-reperfusion

Development of the cardioprotective drugs class based on pathophysiology of myocardial infarction: A comprehensive review

The cardiovascular system is mainly responsible for the transport of substances necessary to cellular metabolism. However, for the good performance of this function, there is need for adequate control of blood pressure levels of tissue perfusion and systemic arterial. Acute myocardial infarction is one of the complications of the cardiovascular system, that most affects the population around the world. This condition can be defined as a disease generated by an imbalance of oxygen concentrations used in cardiovascular metabolism, this change usually occurs because coronary occlusion, which prevents myocardial blood flow. The diagnosis is based on the set of clinical and laboratory investigations, which are in the release of cardiac enzyme biomarkers, cardiovascular and hemodynamic changes and cardiac accommodations. The treatment consists in the use of concomitant cardiovascular drugs, such as: antihypertensive, antiplatelet and hypolipidemic. Despite improvements in clinical and pharmacological management, acute myocardial infarction remains the leading cause of death worldwide. This finding encourages the scientific research of new drugs for the treatment of myocardial infarction or supporting therapies aimed at reducing the levels of deaths and comorbities generated by cardiovascular diseases.

RyR2 Serine-2030 PKA Site Governs Ca2+ Release Termination and Ca2+ Alternans

BACKGROUND

PKA (protein kinase A)-mediated phosphorylation of cardiac RyR2 (ryanodine receptor 2) has been extensively studied for decades, but the physiological significance of PKA phosphorylation of RyR2 remains poorly understood. Recent determination of high-resolution 3-dimensional structure of RyR2 in complex with CaM (calmodulin) reveals that the major PKA phosphorylation site in RyR2, serine-2030 (S2030), is located within a structural pathway of CaM-dependent inactivation of RyR2. This novel structural insight points to a possible role of PKA phosphorylation of RyR2 in CaM-dependent inactivation of RyR2, which underlies the termination of Ca²⁺ release and induction of cardiac Ca²⁺ alternans.

METHODS

We performed single-cell endoplasmic reticulum Ca²⁺ imaging to assess the impact of S2030 mutations on Ca²⁺ release termination in human embryonic kidney 293 cells. Here we determined the role of the PKA site RyR2-S2030 in a physiological setting, we generated a novel mouse model harboring the S2030L mutation and carried out confocal Ca²⁺ imaging.

RESULTS

We found that mutations, S2030D, S2030G, S2030L, S2030V, and S2030W reduced the endoplasmic reticulum luminal Ca²⁺ level at which Ca²⁺ release terminates (the termination threshold), whereas S2030P and S2030R increased the termination threshold. S2030A and S2030T had no significant impact on release termination. Furthermore, CaM-wild-type increased, whereas Ca²⁺ binding deficient CaM mutant (CaM-M [a loss-of-function CaM mutation with all 4 EF-hand motifs mutated]), PKA, and Ca²⁺/CaMKII (CaM-dependent protein kinase II) reduced the termination threshold. The S2030L mutation abolished the actions of CaM-wild-type, CaM-M, and PKA, but not CaMKII, in Ca²⁺ release termination. Moreover, we showed that isoproterenol and CaM-M suppressed pacing-induced Ca²⁺ alternans and accelerated Ca²⁺ transient recovery in intact working hearts, whereas CaM-wild-type exerted an opposite effect. The impact of isoproterenol was partially and fully reversed by the PKA inhibitor N-[2-(p-bromocinnamylamino)ethyl]-5-isoquinoline-sulfonamide and the CaMKII inhibitor N-[2-[N-(4-chlorocinnamyl)-N-methylaminomethyl]phenyl]-N-(2-hydroxyethyl)-4-methoxybenzenesulfonamide individually and together, respectively. S2030L abolished the impact of CaM-wild-type, CaM-M, and N-[2-(p-bromocinnamylamino)ethyl]-5-isoquinoline-sulfonamide-sensitive component, but not the N-[2-[N-(4-chlorocinnamyl)-N-methylaminomethyl]phenyl]-N-(2-hydroxyethyl)-4-methoxybenzenesulfonamide-sensitive component, of isoproterenol.

Ca2+-CaM Dependent Inactivation of RyR2 Underlies Ca2+ Alternans in Intact Heart

RATIONALE

Ca²⁺ alternans plays an essential role in cardiac alternans that can lead to ventricular fibrillation, but the mechanism underlying Ca²⁺ alternans remains undefined. Increasing evidence suggests that Ca²⁺ alternans results from alternations in the inactivation of cardiac RyR2 (ryanodine receptor 2). However, what inactivates RyR2 and how RyR2 inactivation leads to Ca²⁺ alternans are unknown.

OBJECTIVE

To determine the role of CaM (calmodulin) on Ca²⁺ alternans in intact working mouse hearts.

METHODS AND RESULTS

We used an in vivo local gene delivery approach to alter CaM function by directly injecting adenoviruses expressing CaM-wild type, a loss-of-function CaM mutation, CaM (1-4), and a gain-of-function mutation, CaM-M37Q, into the anterior wall of the left ventricle of RyR2 wild type or mutant mouse hearts. We monitored Ca²⁺ transients in ventricular myocytes near the adenovirus-injection sites in Langendorff-perfused intact working hearts using confocal Ca²⁺ imaging. We found that CaM-wild type and CaM-M37Q promoted Ca²⁺ alternans and prolonged Ca²⁺ transient recovery in intact RyR2 wild type and mutant hearts, whereas CaM (1-4) exerted opposite effects. Altered CaM function also affected the recovery from inactivation of the L-type Ca²⁺ current but had no significant impact on sarcoplasmic reticulum Ca²⁺ content. Furthermore, we developed a novel numerical myocyte model of Ca²⁺ alternans that incorporates Ca²⁺-CaM-dependent regulation of RyR2 and the L-type Ca²⁺ channel. Remarkably, the new model recapitulates the impact on Ca²⁺ alternans of altered CaM and RyR2 functions under 9 different experimental conditions. Our simulations reveal that diastolic cytosolic Ca²⁺ elevation as a result of rapid pacing triggers Ca²⁺-CaM dependent inactivation of RyR2. The resultant RyR2 inactivation diminishes sarcoplasmic reticulum Ca²⁺ release, which, in turn, reduces diastolic cytosolic Ca²⁺, leading to alternations in diastolic cytosolic Ca²⁺, RyR2 inactivation, and sarcoplasmic reticulum Ca²⁺ release (ie, Ca²⁺ alternans).

CONCLUSIONS

Our results demonstrate that inactivation of RyR2 by Ca²⁺-CaM is a major determinant of Ca²⁺ alternans, making Ca²⁺-CaM dependent regulation of RyR2 an important therapeutic target for cardiac alternans.

Biology of Tissue Inhibitor of Metalloproteinase 3 (TIMP3), and Its Therapeutic Implications in Cardiovascular Pathology

Tissue inhibitor of metalloproteinase 3 (TIMP3) is unique among the four TIMPs due to its extracellular matrix (ECM)-binding property and broad range of inhibitory substrates that includes matrix metalloproteinases (MMPs), a disintegrin and metalloproteinases (ADAMs), and ADAM with thrombospondin motifs (ADAMTSs). In addition to its metalloproteinase-inhibitory function, TIMP3 can interact with proteins in the extracellular space resulting in its multifarious functions. TIMP3 mRNA has a long 3' untranslated region (UTR) which is a target for numerous microRNAs. TIMP3 levels are reduced in various cardiovascular diseases, and studies have shown that TIMP3 replenishment ameliorates the disease, suggesting a therapeutic potential for TIMP3 in cardiovascular diseases. While significant efforts have been made in identifying the effector targets of TIMP3, the regulatory mechanism for the expression of this multi-functional TIMP has been less explored. Here, we provide an overview of TIMP3 gene structure, transcriptional and post-transcriptional regulators (transcription factors and microRNAs), protein structure and partners, its role in cardiovascular pathology and its application as therapy, while also drawing reference from TIMP3 function in other diseases.

Celastrol-type HSP90 modulators allow for potent cardioprotective effects

AIMS

Cardiac ischemic conditioning has been shown to decrease ischemic injury in experimental models and clinically. Activation of survival pathways leading to heat shock proteins (HSP) modulation is an important contributor to this effect. We have previously shown that celastrol, an HSP90 modulator, achieves cardioprotection through activation of cytoprotective HSP's and heme-oxygenase-1 (HO-1). This is the first comparative evaluation of several modulators of HSP90 activity for cardioprotection. Furthermore, basic celastrol structure-activity relationship was characterized in order to develop novel potent infarct sparing agents suitable for clinical development.

MAIN METHODS

Combining in vitro cell culture using rat myocardial cell line exposed to ischemic and ischemia/reperfusion (I/R) stresses, and ex vivo Langendorff rat heart perfusion I/R model, we evaluated cardioprotective effects of various compounds. Selected signalling pathways were evaluated by western blot and reporter gene activation.

KEY FINDINGS

From a variety of HSP90 modulator chemotypes, the celastrol family was most efficient in inducing cytoprotective HSP70 and HO-1 protein overexpression and cell survival in vitro. Celastrol and two synthetic analogs were protective against ischemia and prevented ischemia/reperfusion (I/R) injury when given as pre-treatment or at time of reperfusion, increasing viability and reducing mitochondrial permeability transition pore opening. Ex vivo experiments demonstrated that the two synthetic analogs show cardioprotective activity at lower concentrations compared to celastrol, with activation of multiple survival pathways.

SIGNIFICANCE

Celastrol backbone is essential for cardioprotection through HSP90 activity modulation. These compounds hold promise as novel adjunct treatment to improve outcome in the clinical management of I/R injury.

Thyroid hormones and cardiac remodeling

Thyroid hormones have many cardioprotective actions expressed mainly through the action of T3 on thyroid receptors α1 and β1. They are procontractile anti-apoptotic, anti-inflammatory, and anti-fibrotic, promote angiogenesis and regeneration, and have beneficial effects on microRNA profiles. They have proven to be anti-remodeling in numerous animal studies, mostly in rodents; a specific action on the border zone has been described. Studies in humans with DIPTA have been in conclusion. Remodeling can be defined as an increase of ≥20 % of the end-diastolic or end-systolic volume, together with a return to the fetal phenotype. An overview of animal and clinical studies is given.

The Mitochondrial Unfolded Protein Response Protects against Anoxia in Caenorhabditis elegans

The mitochondrial unfolded protein response (UPR^mt) is a surveillance pathway that defends proteostasis in the “powerhouse” of the cell. Activation of the UPR^mt protects against stresses imposed by reactive oxygen species, respiratory chain deficits, and pathologic bacteria. Consistent with the UPR^mt’s role in adaption, we found that either its pharmacological or genetic activation by ethidium bromide (EtBr) or RNAi of the mitochondrial AAA-protease spg-7 was sufficient to reduce death in an anoxia-based Caenorhabditis elegans model of ischemia-reperfusion injury. The UPR^mt-specific transcription factor atfs-1 was necessary for protection and atfs-1 gain-of-function (gf) mutants were endogenously protected from both death and dysfunction. Neurons exhibited less axonal degeneration following non-lethal anoxia-reperfusion (A-R) when the UPR^mt was pre-activated, and consistent with the concept of mitochondrial stress leading to cell non-autonomous (ie. “remote”) effects, we found that restricted activation of the UPR^mt in neurons decreased A-R death. However, expression of the atfs-1(gf) mutant in neurons, which resulted in a robust activation of a neuronal UPR^mt, did not upregulate the UPR^mt in distal tissues, nor did it protect the worms from A-R toxicity. These findings suggest that remote signaling requires additional component(s) acting downstream of de facto mitochondrial stress.

Novel therapeutic strategies for cardioprotection

The morbidity and mortality from ischemic heart disease (IHD) remain significant worldwide. The treatment for acute myocardial infarction has improved over the past decades, including early reperfusion of occluded coronary arteries. Although it is essential to re-open the artery as soon as possible, paradoxically this leads to additional myocardial injury, called acute ischemia-reperfusion injury (IRI), for which currently no effective therapy is available. Therefore, novel therapeutic strategies are required to protect the heart from acute IRI in order to reduce myocardial infarction size, preserve cardiac function and improve clinical outcomes in patients with IHD. In this review article, we will first outline the pathophysiology of acute IRI and review promising therapeutic strategies for cardioprotection. These include novel aspects of mitochondrial function, epigenetics, circadian clocks, the immune system, microvesicles, growth factors, stem cell therapy and gene therapy. We discuss the therapeutic potential of these novel cardioprotective strategies in terms of pharmacological targeting and clinical application.

Mst1 promotes cardiac myocyte apoptosis through phosphorylation and inhibition of Bcl-xL

The Hippo pathway, evolutionarily conserved from flies to mammals, promotes cell death and inhibits cell proliferation to regulate organ size. The core component of this cascade, Mst1 in mammalian cells, is sufficient to promote apoptosis. However, the mechanisms underlying both its activation and its ability to elicit cell death remain largely undefined. We here identify a signaling cassette in cardiac myocytes consisting of K-Ras, the scaffold RASSF1A, and Mst1 that is localized to mitochondria and promotes Mst1 activation in response to oxidative stress. Activated Mst1 phosphorylates Bcl-xL at Ser14, which resides in the BH4 domain, thereby antagonizing Bcl-xL-Bax binding. This, in turn, causes activation of Bax and subsequent mitochondria-mediated apoptotic death. Our findings demonstrate mitochondrial localization of Hippo signaling and identify Bcl-xL as a target that is directly modified to promote apoptosis.

The orphan receptor TR3 participates in angiotensin II-induced cardiac hypertrophy by controlling mTOR signalling

Angiotensin II (AngII) induces cardiac hypertrophy and increases the expression of TR3. To determine whether TR3 is involved in the regulation of the pathological cardiac hypertrophy induced by AngII, we established mouse and rat hypertrophy models using chronic AngII administration. Our results reveal that a deficiency of TR3 in mice or the knockdown of TR3 in the left ventricle of rats attenuated AngII-induced cardiac hypertrophy compared with the respective controls. A mechanistic analysis demonstrates that the TR3-mediated activation of mTORC1 is associated with AngII-induced cardiac hypertrophy. TR3 was shown to form a trimer with the TSC1/TSC2 complex that specifically promoted TSC2 degradation via a proteasome/ubiquitination pathway. As a result, mTORC1, but not mTORC2, was activated; this was accompanied by increased protein synthesis, enhanced production of reactive oxygen species and enlarged cell size, thereby resulting in cardiac hypertrophy. This study demonstrates that TR3 positively regulates cardiac hypertrophy by influencing the effect of AngII on the mTOR pathway. The elimination or reduction of TR3 may reduce cardiac hypertrophy; therefore, TR3 is a potential target for clinical therapy.

AAV vectors for cardiac gene transfer: experimental tools and clinical opportunities

Since the first demonstration of in vivo gene transfer into myocardium there have been a series of advancements that have driven the evolution of cardiac gene delivery from an experimental tool into a therapy currently at the threshold of becoming a viable clinical option. Innovative methods have been established to address practical challenges related to tissue-type specificity, choice of delivery vehicle, potency of the delivered material, and delivery route. Most importantly for therapeutic purposes, these strategies are being thoroughly tested to ensure safety of the delivery system and the delivered genetic material. This review focuses on the development of recombinant adeno-associated virus (rAAV) as one of the most valuable cardiac gene transfer agents available today. Various forms of rAAV have been used to deliver "pre-event" cardiac protection and to temper the severity of hypertrophy, cardiac ischemia, or infarct size. Adeno-associated virus (AAV) vectors have also been functional delivery tools for cardiac gene expression knockdown studies and successfully improving the cardiac aspects of several metabolic and neuromuscular diseases. Viral capsid manipulations along with the development of tissue-specific and regulated promoters have greatly increased the utility of rAAV-mediated gene transfer. Important clinical studies are currently underway to evaluate AAV-based cardiac gene delivery in humans.

Induction of heat shock protein 70 inhibits ischemic renal injury

Heat shock protein 70 (Hsp70) is a potent antiapoptotic agent. Here, we tested whether it directly regulates renal cell survival and organ function in a model of transient renal ischemia using Hsp70 knockout, heterozygous, and wild-type mice. The kidney cortical Hsp70 content inversely correlated with tubular injury, apoptosis, and organ dysfunction after injury. In knockout mice, ischemia caused changes in the activity of Akt and glycogen synthase kinase 3-β (kinases that regulate the proapoptotic protein Bax), increased active Bax, and activated the proapoptotic protease caspase 3. As these changes were significantly reduced in the wild-type mice, we tested whether Hsp70 influences ischemia-induced apoptosis. An Hsp70 inducer, geranylgeranylacetone, increased Hsp70 expression in heterozygous and wild-type mice, and reduced both ischemic tubular injury and organ dysfunction. When administered after ischemia, this inducer also decreased tubular injury and organ failure in wild-type mice but did not protect the knockout mice. ATP depletion in vitro caused greater mitochondrial Bax accumulation and death in primary proximal tubule cells harvested from knockout compared with wild-type mice and altered serine phosphorylation of a Bax peptide at the Akt-specific target site. In contrast, lentiviral-mediated Hsp70 repletion decreased mitochondrial Bax accumulation and rescued Hsp70 knockout cells from death. Thus, increasing Hsp70 either before or after ischemic injury preserves renal function by attenuating acute kidney injury.

Thyroid hormone as a therapeutic option for treating ischaemic heart disease: from early reperfusion to late remodelling

Thyroid hormone (TH), apart from its "classical" actions on cardiac contractility and heart rhythm, appears to regulate various intracellular signalling pathways related to response to stress and cardiac remodelling. There is now accumulating experimental and clinical evidence showing a beneficial effect of TH on limiting myocardial ischaemic injury, preventing/reversing post infarction cardiac remodelling and improving cardiac hemodynamics. Thyroid analogs have already been developed and may allow TH use in clinical practice. However, the efficacy of TH in the treatment of cardiac diseases is now awaiting to be tested in large clinical trials.

Distinct roles of GSK-3alpha and GSK-3beta phosphorylation in the heart under pressure overload

Glycogen synthase kinase-3 (GSK-3) is a master regulator of growth and death in cardiac myocytes. GSK-3 is inactivated by hypertrophic stimuli through phosphorylation-dependent and -independent mechanisms. Inactivation of GSK-3 removes the negative constraint of GSK-3 on hypertrophy, thereby stimulating cardiac hypertrophy. N-terminal phosphorylation of the GSK-3 isoforms GSK-3alpha and GSK-3beta by upstream kinases (e.g., Akt) is a major mechanism of GSK-3 inhibition. Nonetheless, its role in mediating cardiac hypertrophy and failure remains to be established. Here we evaluated the role of Serine(S)21 and S9 phosphorylation of GSK-3alpha and GSK-3beta in the regulation of cardiac hypertrophy and function during pressure overload (PO), using GSK-3alpha S21A knock-in (alphaKI) and GSK-3beta S9A knock-in (betaKI) mice. Although inhibition of S9 phosphorylation during PO in the betaKI mice attenuated hypertrophy and heart failure (HF), inhibition of S21 phosphorylation in the alphaKI mice unexpectedly promoted hypertrophy and HF. Inhibition of S21 phosphorylation in GSK-3alpha, but not of S9 phosphorylation in GSK-3beta, caused phosphorylation and down-regulation of G1-cyclins, due to preferential localization of GSK-3alpha in the nucleus, and suppressed E2F and markers of cell proliferation, including phosphorylated histone H3, under PO, thereby contributing to decreases in the total number of myocytes in the heart. Restoration of the E2F activity by injection of adenovirus harboring cyclin D1 with a nuclear localization signal attenuated HF under PO in the alphaKI mice. Collectively, our results reveal that whereas S9 phosphorylation of GSK-3beta mediates pathological hypertrophy, S21 phosphorylation of GSK-3alpha plays a compensatory role during PO, in part by alleviating the negative constraint on the cell cycle machinery in cardiac myocytes.

Myocardial repair: from salvage to tissue reconstruction

Cardiac tissue reconstruction following myocardial infarction represents a major challenge in cardiovascular therapy, as current clinical approaches are limited in their ability to regenerate or replace damaged myocardium. Thus, different novel treatments have been introduced aimed at myocardial salvage and repair. Here, we present a review of recent advancements in cardiac cell, gene-based and tissue engineering therapies. Selected strategies in cell therapy and new tools for myocardial gene transfer are summarized. Finally, we consider novel approaches to myocardial tissue engineering as a platform for the integration of various modalities in an attempt to rejuvenate infarcted tissue in vivo.

Adeno-associated virus-mediated expression of thyroid hormone receptor isoforms-alpha1 and -beta1 improves contractile function in pressure overload-induced cardiac hypertrophy

Pressure overload-induced cardiac hypertrophy leads to decreased contractile performance, frequently progressing to heart failure. Cardiac hypertrophy and heart failure can be accompanied by the so-called sick thyroid syndrome, resulting in decreased serum T(3) levels along with decreased expression of thyroid hormone receptors (TRalpha1 and TRbeta1) and sarco(endo)plasmic reticulum Ca-ATPase (SERCA). Because the binding of T(3) occupied receptors to the thyroid response elements in the SERCA promotor can increase gene expression, we wanted to determine whether increasing TR expression in the hypertrophied heart could also improve SERCA expression and cardiac function. Mice subjected to aortic constriction to generate pressure overload-induced hypertrophy were also subjected to gene therapy using adeno-associated virus (AAV) expressing either TRalpha1 or TRbeta1, with LacZ expressing AAV serving as control. After 8 wk of aortic constriction, a similar degree of hypertrophy was observed in all three groups; however, mice treated with TRalpha1 or TRbeta1 showed improved contractile function. Administration of a physiological dose of T(3) increased serum T(3) levels only into the lower range of normal. This T(3) dose, with or without AAV TR treatment, did not result in any significant increase in contractile performance. Calcium transients measured in isolated myocytes also exhibited an enhanced rate of decay associated with TRalpha1 or TRbeta1 treatment. Western blot analysis showed increased SERCA expression in the TRalpha1- or TRbeta1-treated groups relative to the LacZ-treated control group. These results demonstrate that increasing TR expression in the hypertrophied heart is associated with an improvement in contractile function and increased SERCA expression.