Inhibition and reversal of myocardial infarction-induced hypertrophy and heart failure by NHE-1 inhibition

Astragaloside IV derivative HHQ16 ameliorates infarction-induced hypertrophy and heart failure through degradation of lncRNA4012/9456

Reversing ventricular remodeling represents a promising treatment for the post-myocardial infarction (MI) heart failure (HF). Here, we report a novel small molecule HHQ16, an optimized derivative of astragaloside IV, which effectively reversed infarction-induced myocardial remodeling and improved cardiac function by directly acting on the cardiomyocyte to reverse hypertrophy. The effect of HHQ16 was associated with a strong inhibition of a newly discovered Egr2-affiliated transcript lnc9456 in the heart. While minimally expressed in normal mouse heart, lnc9456 was dramatically upregulated in the heart subjected to left anterior descending coronary artery ligation (LADL) and in cardiomyocytes subjected to hypertrophic stimulation. The critical role of lnc9456 in cardiomyocyte hypertrophy was confirmed by specific overexpression and knockout in vitro. A physical interaction between lnc9456 and G3BP2 increased NF-κB nuclear translocation, triggering hypertrophy-related cascades. HHQ16 physically bound to lnc9456 with a high-affinity and induced its degradation. Cardiomyocyte-specific lnc9456 overexpression induced, but knockout prevented LADL-induced, cardiac hypertrophy and dysfunction. HHQ16 reversed the effect of lnc9456 overexpression while lost its protective role when lnc9456 was deleted, further confirming lnc9456 as the bona fide target of HHQ16. We further identified the human ortholog of lnc9456, also an Egr2-affiliated transcript, lnc4012. Similarly, lnc4012 was significantly upregulated in hypertrophied failing hearts of patients with dilated cardiomyopathy. HHQ16 also specifically bound to lnc4012 and caused its degradation and antagonized its hypertrophic effects. Targeted degradation of pathological increased lnc4012/lnc9456 by small molecules might serve as a novel promising strategy to regress infarction-induced cardiac hypertrophy and HF.

Pharmacological Inhibition of NHE1 Protein Increases White Matter Resilience and Neurofunctional Recovery after Ischemic Stroke

To date, recanalization interventions are the only available treatments for ischemic stroke patients; however, there are no effective therapies for reducing stroke-induced neuroinflammation. We recently reported that H+ extrusion protein Na+/H+ exchanger-1 (NHE1) plays an important role in stroke-induced inflammation and white matter injury. In this study, we tested the efficacy of two potent NHE1 inhibitors, HOE642 and Rimeporide, with a delayed administration regimen starting at 24 h post-stroke in adult C57BL/6J mice. Post-stroke HOE642 and Rimeporide treatments accelerated motor and cognitive function recovery without affecting the initial ischemic infarct, neuronal damage, or reactive astrogliosis. However, the delayed administration of NHE1 blockers after ischemic stroke significantly reduced microglial inflammatory activation while enhanced oligodendrogenesis and white matter myelination, with an increased proliferation and decreased apoptosis of the oligodendrocytes. Our findings suggest that NHE1 protein plays an important role in microglia-mediated inflammation and white matter damage. The pharmacological blockade of NHE1 protein activity reduced microglia inflammatory responses and enhanced oligodendrogenesis and white matter repair, leading to motor and cognitive function recovery after stroke. Our study reveals the potential of targeting NHE1 protein as a therapeutic strategy for ischemic stroke therapy.

Potential traditional Chinese medicines with anti-inflammation in the prevention of heart failure following myocardial infarction

Inflammation plays an important role in the development of heart failure (HF) after myocardial infarction (MI). Suppression of post-infarction inflammatory cascade has become a new strategy to delay or block the progression of HF. At present, there are no approved anti-inflammatory drugs used to prevent HF following MI. Traditional Chinese medicine (TCM) has been used clinically for cardiovascular disease for a long time. Here, we summarized the recent progress about some TCM which could both improve cardiac function and inhibit inflammation in patients or experimental models with MI or HF, in order to provide evidence for their potential application in reducing the onset of HF following MI. Among them, single Chinese medicinal herbs (eg. Astragalus and Salvia miltiorrhiza) and Chinese herbal formulas (eg. Gualou Xiebai Decoction and Sini Tang) are discussed separately. The main targets for their anti-inflammation effect are mainly involved the TLR4/NF-κB signaling, as well as pro-inflammatory cytokines IL-1β, IL-6 or TNF-α. It is worthy of further evaluating their potential, experimentally or clinically, in the prevention or delay of HF following MI.

PLCβ2 Promotes VEGF-Induced Vascular Permeability

BACKGROUND

Regulation of vascular permeability is critical to maintaining tissue metabolic homeostasis. VEGF (vascular endothelial growth factor) is a key stimulus of vascular permeability in acute and chronic diseases including ischemia reperfusion injury, sepsis, and cancer. Identification of novel regulators of vascular permeability would allow for the development of effective targeted therapeutics for patients with unmet medical need.

METHODS

In vitro and in vivo models of VEGFA-induced vascular permeability, pathological permeability, quantitation of intracellular calcium release and cell entry, and phosphatidylinositol 4,5-bisphosphate levels were evaluated with and without modulation of PLC (phospholipase C) β2.

RESULTS

Global knock-out of PLCβ2 in mice resulted in blockade of VEGFA-induced vascular permeability in vivo and transendothelial permeability in primary lung endothelial cells. Further work in an immortalized human microvascular cell line modulated with stable knockdown of PLCβ2 recapitulated the observations in the mouse model and primary cell assays. Additionally, loss of PLCβ2 limited both intracellular release and extracellular entry of calcium following VEGF stimulation as well as reduced basal and VEGFA-stimulated levels of phosphatidylinositol 4,5-bisphosphate compared to control cells. Finally, loss of PLCβ2 in both a hyperoxia-induced lung permeability model and a cardiac ischemia:reperfusion model resulted in improved animal outcomes when compared with wild-type controls.

CONCLUSIONS

The results implicate PLCβ2 as a key positive regulator of VEGF-induced vascular permeability through regulation of both calcium flux and phosphatidylinositol 4,5-bisphosphate levels at the cellular level. Targeting of PLCβ2 in a therapeutic setting may provide a novel approach to regulating vascular permeability in patients.

Na+/H+ Exchanger 1, a Potential Therapeutic Drug Target for Cardiac Hypertrophy and Heart Failure

Cardiac hypertrophy is defined as increased heart mass in response to increased hemodynamic requirements. Long-term cardiac hypertrophy, if not counteracted, will ultimately lead to heart failure. The incidence of heart failure is related to myocardial infarction, which could be salvaged by reperfusion and ultimately invites unfavorable myocardial ischemia-reperfusion injury. The Na⁺/H⁺ exchangers (NHEs) are membrane transporters that exchange one intracellular proton for one extracellular Na⁺. The first discovered NHE isoform, NHE1, is expressed almost ubiquitously in all tissues, especially in the myocardium. During myocardial ischemia-reperfusion, NHE1 catalyzes increased uptake of intracellular Na⁺, which in turn leads to Ca²⁺ overload and subsequently myocardial injury. Numerous preclinical research has shown that NHE1 is involved in cardiac hypertrophy and heart failure, but the exact molecular mechanisms remain elusive. The objective of this review is to demonstrate the potential role of NHE1 in cardiac hypertrophy and heart failure and investigate the underlying mechanisms.

MSC Pretreatment for Improved Transplantation Viability Results in Improved Ventricular Function in Infarcted Hearts

Many clinical studies utilizing MSCs (mesenchymal stem cells, mesenchymal stromal cells, or multipotential stromal cells) are underway in multiple clinical settings; however, the ideal approach to prepare these cells in vitro and to deliver them to injury sites in vivo with maximal effectiveness remains a challenge. Here, pretreating MSCs with agents that block the apoptotic pathways were compared with untreated MSCs. The treatment effects were evaluated in the myocardial infarct setting following direct injection, and physiological parameters were examined at 4 weeks post-infarct in a rat permanent ligation model. The prosurvival treated MSCs were detected in the hearts in greater abundance at 1 week and 4 weeks than the untreated MSCs. The untreated MSCs improved ejection fraction in infarcted hearts from 61% to 77% and the prosurvival treated MSCs further improved ejection fraction to 83% of normal. The untreated MSCs improved fractional shortening in the infarcted heart from 52% to 68%, and the prosurvival treated MSCs further improved fractional shortening to 77% of normal. Further improvements in survival of the MSC dose seems possible. Thus, pretreating MSCs for improved in vivo survival has implications for MSC-based cardiac therapies and in other indications where improved cell survival may improve effectiveness.

Current Pharmacological Strategies for Duchenne Muscular Dystrophy

Duchenne muscular dystrophy (DMD) is a lethal, X-linked neuromuscular disorder caused by the absence of dystrophin protein, which is essential for muscle fiber integrity. Loss of dystrophin protein leads to recurrent myofiber damage, chronic inflammation, progressive fibrosis, and dysfunction of muscle stem cells. There is still no cure for DMD so far and the standard of care is principally limited to symptom relief through glucocorticoids treatments. Current therapeutic strategies could be divided into two lines. Dystrophin-targeted therapeutic strategies that aim at restoring the expression and/or function of dystrophin, including gene-based, cell-based and protein replacement therapies. The other line of therapeutic strategies aims to improve muscle function and quality by targeting the downstream pathological changes, including inflammation, fibrosis, and muscle atrophy. This review introduces the important developments in these two lines of strategies, especially those that have entered the clinical phase and/or have great potential for clinical translation. The rationale and efficacy of each agent in pre-clinical or clinical studies are presented. Furthermore, a meta-analysis of gene profiling in DMD patients has been performed to understand the molecular mechanisms of DMD.

Role of Genetic Mutations of the Na+/H+ Exchanger Isoform 1, in Human Disease and Protein Targeting and Activity

The mammalian Na⁺/H⁺ exchanger isoform one (NHE1) is a plasma membrane protein that is ubiquitously present in human cells. It functions to regulate intracellular pH removing an intracellular proton in exchange for one extracellular sodium and is involved in heart disease and in promoting metastasis in cancer. It is made of a 500 amino acid membrane domain plus a 315 amino acid, regulatory cytosolic tail. The membrane domain is thought to have 12 transmembrane segments and a large membrane-associated extracellular loop. Early studies demonstrated that in mice, disruption of the NHE1 gene results in locomotor ataxia and a phenotype of slow-wave epilepsy. Defects included a progressive neuronal degeneration. Growth and reproductive ability were also reduced. Recent studies have identified human autosomal homozygous recessive mutations in the NHE1 gene (SLC9A1) that result in impaired development, ataxia and other severe defects, and explain the cause of the human disease Lichtenstein-Knorr syndrome. Other human mutations have been identified that are stop codon polymorphisms. These cause short non-functional NHE1 proteins, while other genetic polymorphisms in the NHE1 gene cause impaired expression of the NHE1 protein, reduced activity, enhanced protein degradation or altered kinetic activation of the protein. Since NHE1 plays a key role in many human physiological functions and in human disease, genetic polymorphisms of the protein that significantly alter its function and are likely play significant roles in varying human phenotypes and be involved in disease.

Protective effects of rimeporide on left ventricular function in golden retriever muscular dystrophy dogs

BACKGROUND

Alterations in intracellular Na+ and Ca2+ have been observed in patients with Duchenne muscular dystrophy (DMD) and in animal models of DMD, and inhibition of Na+-H+ exchanger 1 (NHE1) by rimeporide has previously demonstrated cardioprotective effects in animal models of myocardial ischemia and heart failure. Since heart failure is becoming a predominant cause of death in DMD patients, this study aimed to demonstrate a cardioprotective effect of chronic administration of rimeporide in a canine model of DMD.

METHODS

Golden retriever muscular dystrophy (GRMD) dogs were randomized to orally receive rimeporide (10 mg/kg, twice a day) or placebo from 2 months to 1 year of age. Left ventricular (LV) function was assessed by conventional and advanced echocardiography.

RESULTS

Compared with placebo-treated GRMD, LV function deterioration with age was limited in rimeporide-treated GRMD dogs as indicated by the preservation of LV ejection fraction as well as overall cardiac parameters different from placebo-treated dogs, as revealed by composite cardiac scores and principal component analysis. In addition, principal component analysis clustered rimeporide-treated GRMD dogs close to healthy control dogs.

CONCLUSIONS

Chronic administration of the NHE1 inhibitor rimeporide exerted a protective effect against LV function decline in GRMD dogs. This study provides proof of concept to explore the cardiac effects of rimeporide in DMD patients.

Na+/H+ exchanger and cardiac hypertrophy

Reactive cardiac hypertrophy (CH) is an increase in heart mass in response to hemodynamic overload. Exercise-induced CH emerges as an adaptive response with improved cardiac function, in contrast to pathological CH that represents a risk factor for cardiovascular health. The Na⁺/H⁺ exchanger (NHE-1) is a membrane transporter that not only regulates intracellular pH but also intracellular Na⁺ concentration. In the scenario of cardiovascular diseases, myocardial NHE-1 is activated by a variety of stimuli, such as neurohumoral factors and mechanical stress, leading to intracellular Na⁺ overload and activation of prohypertrophic cascades. NHE-1 hyperactivity is intimately linked to heart diseases, including ischemia-reperfusion injury, maladaptive CH and heart failure. In this review, we will present evidence to support that the NHE-1 hyperactivity constitutes a "switch on/off" for the pathological phenotype during CH development. We will also discuss some classical and novel strategies to avoid NHE-1 hyperactivity, and that are therefore worthwhile to improve cardiovascular health.

A high-throughput ratiometric method for imaging hypertrophic growth in cultured primary cardiac myocytes

Maladaptive hypertrophy of cardiac myocytes increases the risk of heart failure. The underlying signaling can be triggered and interrogated in cultured neonatal ventricular myocytes (NRVMs) using sophisticated pharmacological and genetic techniques. However, the methods for quantifying cell growth are, by comparison, inadequate. The lack of quantitative, calibratable and computationally-inexpensive high-throughput technology has limited the scope for using cultured myocytes in large-scale analyses. We present a ratiometric method for quantifying the hypertrophic growth of cultured myocytes, compatible with high-throughput imaging platforms. Protein biomass was assayed from sulforhodamine B (SRB) fluorescence, and image analysis calculated the quotient of signal from extra-nuclear and nuclear regions. The former readout relates to hypertrophic growth, whereas the latter is a reference for correcting protein-independent (e.g. equipment-related) variables. This ratiometric measure, when normalized to the number of cells, provides a robust quantification of cellular hypertrophy. The method was tested by comparing the efficacy of various chemical agonists to evoke hypertrophy, and verified using independent assays (myocyte area, transcripts of markers). The method's high resolving power and wide dynamic range were confirmed by the ability to generate concentration-response curves, track the time-course of hypertrophic responses with fine temporal resolution, describe drug/agonist interactions, and screen for novel anti-hypertrophic agents. The method can be implemented as an end-point in protocols investigating hypertrophy, and is compatible with automated plate-reader platforms for generating high-throughput data, thereby reducing investigator-bias. Finally, the computationally-minimal workflow required for obtaining measurements makes the method simple to implement in most laboratories.

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Maladaptive hypertrophy of myocytes can lead to heart failure.

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Common methods for tracking growth in cultured myocytes are inadequate.

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We design and test a method for tracking myocyte hypertrophy in vitro.

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The method provides a ratiometric index of growth for high throughput analyses.

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Using the method, we characterize further details of (anti)hypertrophic responses.

Reversal of ApoE4-induced recycling block as a novel prevention approach for Alzheimer's disease

ApoE4 genotype is the most prevalent and also clinically most important risk factor for late-onset Alzheimer’s disease (AD). Available evidence suggests that the root cause for this increased risk is a trafficking defect at the level of the early endosome. ApoE4 differs from the most common ApoE3 isoform by a single amino acid that increases its isoelectric point and promotes unfolding of ApoE4 upon endosomal vesicle acidification. We found that pharmacological and genetic inhibition of NHE6, the primary proton leak channel in the early endosome, in rodents completely reverses the ApoE4-induced recycling block of the ApoE receptor Apoer2/Lrp8 and the AMPA- and NMDA-type glutamate receptors that are regulated by, and co-endocytosed in a complex with, Apoer2. Moreover, NHE6 inhibition restores the Reelin-mediated modulation of excitatory synapses that is impaired by ApoE4. Our findings suggest a novel potential approach for the prevention of late-onset AD.

Alzheimer’s disease is a degenerative condition that destroys connections between brain cells leading to memory loss, confusion and difficulties in thinking. Apolipoprotein E is a protein that carries fatty substances called lipids and cholesterol around the brain, and plays an important role in repair mechanisms. There are three major forms of Apolipoprotein E, and individuals who carry a version known as ApoE4 are up to 10 times more likely to develop Alzheimer’s disease than those who carry other variations.

In nerve cells, or neurons, Apolipoprotein E binds to a specific family of receptors. One of these receptors, called Apoer2, is found in the synaptic gap between neurons, where it regulates their activities. Both Apolipoprotein E and Apoer2 are taken into the cell within compartments known as endosomal vesicles. Usually, the Apoer2 receptor is quickly recycled back to the surface of the cell, but this recycling process is delayed in individuals with the ApoE4 version of Apolipoprotein E.

Apoer2 is just one of many different receptors on the surface of neurons that are taken into vesicles before being recycled back to the cell surface. The fluid inside these vesicles becomes progressively more acidic as they move through the cell. This process helps to control the interaction of these receptors with their binding partners and to regulate their movement and recycling. Here, Xian, Pohlkamp et al. investigated whether changing the acidity of vesicles in rat neurons could overcome the block in recycling Apoer2 – and other receptors that travel with Apoer2 in the same compartments – in the presence of ApoE4.

A protein called NHE6 is embedded in the membrane of vesicles called early endosomes and acts to make the vesicles less acidic. Xian, Pohlkamp et al. used drugs to block the activity of NHE6, which led to the vesicles becoming more acidic and allowed Apoer2 to be recycled faster. Using a genetic approach known as siRNA knockdown to decrease the amount of NHE6 produced in neurons also had a similar effect on Apoer2 recycling.

Together these findings suggest that drugs that make vesicles in neurons more acidic may have the potential to help prevent individuals that carry the ApoE4 protein from developing Alzheimer’s disease. Current drugs that target NHE6 also affect other molecules, which can often lead to side effects. A next step will be to develop tailor-made, small molecule drugs that can enter the brain efficiently and selectively block NHE6.

Exploring miRNA-mRNA regulatory network in cardiac pathology in Na+/H+ exchanger isoform 1 transgenic mice

Numerous studies have demonstrated that Na⁺/H⁺ exchanger isoform 1 (NHE1) is elevated in myocardial diseases and its effect is detrimental. To better understand the involvement of NHE1, we have previously studied cardiac-specific NHE1 transgenic mice and shown that these mice develop cardiac hypertrophy, interstitial fibrosis, and cardiac dysfunction. The purpose of current study was to identify microRNAs and their mRNA targets involved in NHE1-mediated cardiac injury. An unbiased high-throughput sequencing study was performed on both microRNAs and mRNAs. RNA sequencing showed that differentially expressed genes were enriched in hypertrophic cardiomyopathy pathway by Kyoto Encyclopedia of Genes and Genomes annotation in NHE1 transgenic hearts. These genes were classified as contraction defects (e.g., Myl2, Myh6, Mybpc3, and Actb), impaired intracellular Ca²⁺ homeostasis (e.g., SERCA2a, Ryr2, Rcan1, and CaMKII delta), and signaling molecules for hypertrophic cardiomyopathy (e.g., Itga/b, IGF-1, Tgfb2/3, and Prkaa1/2). microRNA sequencing revealed that 15 microRNAs were differentially expressed (2-fold, P < 0.05). Six of them (miR-1, miR-208a-3p, miR-199a-5p, miR-21-5p, miR-146a-5p, and miR-30c-5p) were reported to be related to cardiac pathological functions. The integrative analysis of microRNA and RNA sequencing data identified several crucial microRNAs including miR-30c-5p, miR-199a-5p, miR-21-5p, and miR-34a-5p as well as 10 of their mRNA targets that may affect the heart via NFAT hypertrophy and cardiac hypertrophy signaling. Furthermore, important microRNAs and mRNA targets were validated by quantitative PCR. Our study comprehensively characterizes the expression patterns of microRNAs and mRNAs, establishes functional microRNA-mRNA pairs, elucidates the potential signaling pathways, and provides novel insights on the mechanisms underlying NHE1-medicated cardiac injury.

Inhibition of Na+/H+ Exchanger With EMD 87580 does not Confer Greater Cardioprotection Beyond Preconditioning on Ischemia-Reperfusion Injury in Normal Dogs

Postischemic accumulation of intracellular Na⁺ promotes calcium overload and contributes to cellular necrosis. Cardioprotection afforded by pharmacologic blockade of the sodium-hydrogen exchanger subtype 1 (NHE1) is thought to be more remarkable than that obtained by ischemic conditioning (IC). The window of protection provided by IC pretreatment is maintained even when performed up to 48 hours before ischemia. In addition, the perception exists that combined NHE1 inhibition plus IC produces greater than additive protection against ischemic injury. The current study compared the efficacy of NHE1 blockade by N-[2-methyl-4,5-bis(methylsulfonyl)-benzoyl]-guanidine (EMD 87580 5 mg/kg) combined with first- or second-window IC on ischemic tolerance in dogs subject to 90-minute acute ischemia and 180-minute reperfusion. Infarct size (tetrazolium staining), vascular responses, and myocardial perfusion (microspheres) were assessed. EMD 87580 given before ischemia or before reperfusion did not reduce infarct size (compared to vehicle-treated group). Significant protection against tissue necrosis was obtained by both first- and second-window IC, but additive cardioprotection (ie, greater than that afforded by IC) was not observed by treatment with EMD 87580. Vascular reactivity in the infarct-related artery was not preserved after ischemia-reperfusion in any of the experimental groups. Likewise, either the pharmacologic or the nonpharmacologic interventions did not modify myocardial perfusion. These data demonstrate that EMD 87580 did not protect against ischemia-reperfusion injury regardless of the time of drug administration. Combined EMD 87580 and IC did not antagonize protection that was achieved by either first- or second-window IC alone; no additive protection beyond preconditioning was obtained. Further study is necessary to assess the value of NHE1 blockers as protective agents against myocardial injury.

Na+-H+ exchanger and proton channel in heart failure associated with Becker and Duchenne muscular dystrophies

Cardiomyopathy is found in patients with Duchenne (DMD) and Becker (BMD) muscular dystrophies, which are linked muscle diseases caused by mutations in the dystrophin gene. Dystrophin defects are not limited to DMD but are also present in mild BMD. The hereditary cardiomyopathic hamster of the UM-X7.1 strain is a particular experimental model of heart failure (HF) leading to early death in muscular dystrophy (dystrophin deficiency and sarcoglycan mutation) and heart disease (δ-sarcoglycan deficiency and dystrophin mutation) in human DMD. Using this model, our previous work showed a defect in intracellular sodium homeostasis before the appearance of any apparent biochemical and histological defects. This was attributed to the continual presence of the fetal slow sodium channel, which was also found to be active in human DMD. Due to muscular intracellular acidosis, the intracellular sodium overload in DMD and BMD was also due to sodium influx through the sodium-hydrogen exchanger NHE-1. Lifetime treatment with an NHE-1 inhibitor prevented intracellular Na⁺ overload and early death due to HF. Our previous work also showed that another proton transporter, the voltage-gated proton channel (Hv1), exists in many cell types including heart cells and skeletal muscle fibers. The Hv1 could be indirectly implicated in the beneficial effect of blocking NHE-1.

Nutrigenomic effects of glucosinolates on liver, muscle and distal kidney in parasite-free and salmon louse infected Atlantic salmon

Background

Reduction of Lepeophtheirus salmonis infection in Atlantic salmon achieved by glucosinolates (GLs) from Brassica plants was recently reported. However, wider application of functional feeds based on GLs requires better knowledge of their positive and adverse effects.

Methods

Liver, distal kidney and muscle transcriptomes of salmon exposed to the extreme dose of GLs were profiled by microarray, while qPCR analysis followed up selected hepatic and renal responses under the extreme and moderate GLs dose during the L. salmonis challenge. Transcriptional analysis were complemented with measurements of organ indices, liver steatosis and plasma profiling, including indicators of cytolysis and bilirubin. Finally, the third trial was performed to quantify the effect of lower GLs doses on growth.

Results

The extreme GLs dose caused a decrease in hepatic fat deposition and growth, in line with microarray findings, which suggested tissue remodeling and reduction of cellular proliferation in the skeletal muscle and liver. Lower GLs inclusion levels in a follow-up trial did not show negative effects on growth. Microarray analysis of the distal kidney pointed to activation of anti-fibrotic responses under the overexposure. However, analyses of ALT, CK and AST enzymes in plasma provided no evidence of increased cytolysis and organ damage. Prevalent activation of phase-2 detoxification genes that occurred in all three tissues could be considered part of beneficial effects caused by the extreme dose of GLs. In addition, transcriptomic evidence suggested GLs-mediated iron and heme withdrawal response, including increased heme degradation in muscle (upregulation of heme oxygenase-1), decrease of its synthesis in liver (downregulation of porphobilinogen deaminase) and increased iron sequestration from blood (hepatic induction of hepcidin-1 and renal induction of intracellular storage protein ferritin). This response could be advantageous for salmon upon encountering lice, which depend on the host for the provision of iron carrying heme. Most of the hepatic genes studied by qPCR showed similar expression levels in fish exposed to GLs, lice and their combination, while renal induction of leptin suggested heightened stress by the combination of extreme dose of GLs and lice. High expression of interferonγ (cytokine considered organ-protective in mammalian kidney) was detected at the moderate GLs level. This fish also showed highest plasma bilirubin levels (degradation product of heme), and had lowest number of attached lice, further supporting hypothesis that making heme unavailable to lice could be part of an effective anti-parasitic strategy.

Conclusions

Modulation of detoxification and iron metabolism in Atlantic salmon tissues could be beneficial prior and during lice infestations. Investigation of anti-lice functional feeds based on low and moderate GLs inclusion levels thus deserves further attention.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-016-1921-7) contains supplementary material, which is available to authorized users.

P2Y2 purinergic receptors are highly expressed in cardiac and diaphragm muscles of mdx mice, and their expression is decreased by suramin

INTRODUCTION

In Duchenne muscular dystrophy (DMD) and in the mdx mouse model of DMD, the lack of dystrophin leads to increased calcium influx and muscle necrosis. Patients suffer progressive muscle loss, and cardiomyopathy is an important determinant of morbidity. P2 purinergic receptors participate in the increased calcium levels in dystrophic skeletal muscles.

METHODS

In this study, we evaluated whether P2 receptors are involved in cardiomyopathy in mdx mice at later stages of the disease.

RESULTS

Western blotting revealed that P2Y₂ receptor levels were upregulated (54%) in dystrophic heart compared with a normal heart. Suramin reduced the levels of P2Y₂ to almost normal values. Suramin also decreased heart necrosis (reduced CK-MB) and the expression of the stretch-activated calcium channel TRPC1.

CONCLUSIONS

This study suggests that P2Y₂ may participate in cardiomyopathy in mdx mice. P2-selective drugs with specific actions in the dystrophic heart may ameliorate cardiomyopathy in dystrophinopathies. Muscle Nerve 55: 116-121, 2017.

Na+–H+ exchanger inhibitor prevents early death in hereditary cardiomyopathy

Using the UM-X7.1 hereditary cardiomyopathic and muscular dystrophy hamsters (HCMH), we tested the effects of lifelong preventive or curative treatments during the heart failure phase with the NHE-1 inhibitor EMD 87580 (EMD) or with the angiotensin-converting enzyme inhibitor cilazapril on the intracellular Na+ and Ca2+ overloads, elevated level of NHE-1, necrosis, hypertrophy, heart failure, and early death. Our results showed that 310-day pretreatment of 30-day-old HCMHs with EMD significantly prevented cardiac necrosis, cardiomyocyte hypertrophy, and reduced the heart to body mass ratio. This treatment significantly prevented Na+ and Ca2+ overloads and the increase in NHE-1 protein level observed in HCMHs. Importantly, this lifelong preventive treatment significantly decreased the levels of creatine kinase and prevented early death of HCMHs. Curative treatment of hypertrophic 275-day-old HCMHs for 85 days with EMD significantly prevented hypertrophy and early death of HCMHs. However, treatments with cilazapril did not have any significant effects on the cardiac parameters studied or on early death of HCMHs. Our results suggest that the increase in the NHE-1 level and the consequent Na+ and Ca2+ overloads are implicated in the pathological process leading to heart failure and early death in HCMHs, and treatment with the NHE-1 inhibitor is promising for preventing early death in hereditary cardiomyopathy.

Targeting osteopontin, the silent partner of Na+/H+ exchanger isoform 1 in cardiac remodeling

Cardiac hypertrophy (CH), characterized by the enlargement of cardiomyocytes, fibrosis and apoptosis, contributes to cardiac remodeling, which if left unresolved results in heart failure. Understanding the signaling pathways underlying CH is necessary to identify potential therapeutic targets. The Na(+) /H(+) -exchanger isoform I (NHE1), a ubiquitously expressed glycoprotein and cardiac specific isoform, regulates intracellular pH. Recent studies have demonstrated that enhanced expression/activity of NHE1 contributes to cardiac remodeling and CH. Inhibition of NHE1 in both in vitro and in vivo models have suggested that inhibition of NHE1 protects against hypertrophy. However, clinical trials using NHE1 inhibitors have proven to be unsuccessful, suggesting that additional factors maybe contributing to cardiac remodeling. Recent studies have indicated that the upregulation of NHE1 is associated with enhanced levels of osteopontin (OPN) in the setting of CH. OPN has been demonstrated to be upregulated in left ventricular hypertrophy, dilated cardiomyopathy and in diabetic cardiomyopathy. The cellular interplay between OPN and NHE1 in the setting of CH remains unknown. This review focuses on the role of NHE1 and OPN in cardiac remodeling and emphasizes the signaling pathways implicating OPN in the NHE1-induced hypertrophic response.

Alpha-lipoic acid attenuates cardiac hypertrophy via inhibition of C/EBPβ activation

Alpha-lipoic acid (ALA), a naturally occurring compound, exerts powerful protective effects in numerous cardiovascular disease models. However, the pharmacological property of ALA on cardiac hypertrophy has not been well investigated. The present study was carried out to determine whether ALA exerts a direct anti-hypertrophic effect in cultured cardiomyocytes and whether it modifies the hypertrophic process in vivo. Furthermore, we determined the potential underlying mechanisms for these actions. Treatment of cardiomyocytes with phenylephrine (PE) for 24 h produced a marked hypertrophic effect as evidenced by significantly increased in ANF and BNP mRNA levels, as well as cell surface area. These effects were attenuated by ALA in a concentration-dependent manner with a complete inhibition of hypertrophy at a concentration of 100 µg/mL. PE-induced cardiomyocyte hypertrophy was associated with increased mRNA and protein levels of C/EBPβ, which were inhibited by pretreatment with ALA. However, when cardiomyocytes were co-transfected with C/EBPβ, ALA failed to inhibit hypertrophic responses. Upregulation of C/EBPβ expression was also evident in rats subjected to 4 weeks of coronary artery ligation (CAL). However, rats treated with ALA demonstrated markedly reduced hemodynamic and hypertrophic responses, which were accompanied by attenuation of upregulation of C/EBPβ. Taken together, our results revealed a robust anti-hypertrophic and anti-remodeling effect of ALA, which is mediated by inhibition of C/EBPβ activation.

Up-regulation of heme oxygenase-1 after infarct initiation reduces mortality, infarct size and left ventricular remodeling: experimental evidence and proof of concept

BACKGROUND

Up-regulation of HO-1 by genetic manipulation or pharmacological pre-treatment has been reported to provide benefits in several animal models of myocardial infarction (MI). However, its efficacy following MI initiation (as in clinical reality) remains to be tested. Therefore, this study investigated whether HO-1 over-expression, by cobalt protoporphyrin (CoPP) administered after LAD ligation, is still able to improve functional and structural changes in left ventricle (LV) in a rat model of 4-week MI.

METHODS

A total of 144 adult male Wistar rats were subjected to either left anterior coronary artery ligation or sham-operation. The effect of CoPP treatment (5 mg/kg i.p. at the end of the surgical session and, then, once a week for 4 weeks) was evaluated on the basis of survival, electro- and echocardiography, plasma levels of B-type natriuretic peptide (BNP), endothelin-1 and prostaglandin E2, coronary microvascular reactivity, MI size, LV wall thickness and vascularity. Besides, the expression of HO-1 and connexin-43 in different LV territories was assessed by western blot analysis and immunohistochemistry, respectively.

RESULTS

CoPP induced an increased expression of HO-1 protein with >16 h delay. CoPP treatment significantly reduced mortality, MI size, BNP concentration, ECG alterations, LV dysfunction, microvascular constriction, capillary rarefaction and restored connexin-43 expression as compared to untreated MI. These functional and structural changes were paralleled by increased HO-1 expression in all LV territories. HO activity inhibition by tin-mesoporphyrin abolished the differences between CoPP-treated and untreated MI animals.

CONCLUSIONS

This is the first report demonstrating the putative role of pharmacological induction of HO-1 following coronary occlusion to benefit infarcted and remote territories, leading to better cardiac function in a 4-week MI outcome.

The therapeutic effect of 2-cyclohexylthio-AMP in heart failure

AIM

: The aim of this study was to investigate the therapeutic effect of 2-cyclohexylthio-adenosine 5'-monophosphate (AMP) in mice with heart failure (HF).

METHODS

: 2-Cyclohexylthio-AMP was dissolved in phosphate-buffered saline and infused in mice with ischemic HF after permanent left coronary [left anterior descending (LAD)] ligation and in calsequestrin (CSQ) mice with HF. Myocardial function ex vivo was determined in the working heart model. Cardiac function in vivo was assessed by echocardiography.

RESULTS

: Injection of 2-cyclohexylthio-AMP induced a dose-dependent increase in +dP/dt, -dP/dt, and left ventricular developed pressure in normal wild-type mice and in CSQ mice with HF using the ex vivo working heart model. Spontaneous heart rate did not change after the injection of 2-cyclohexylthio-AMP. Compared with normal saline-treaded mice, chronic infusion of 2-cyclohexylthio-AMP in mice with ischemic HF after left coronary artery (LAD) ligation and in CSQ mice resulted in improved +dP/dt, -dP/dt, left ventricular developed pressure, and fractional shortening, restored the β-adrenergic response and decreased heart weight/body weight ratios.

CONCLUSIONS

: 2-Cyclohexylthio-AMP improved the cardiac contractile performance and rescued mice from HF. This salutary action may result from the reduction of myocardial hypertrophy and the restoration of the β-adrenergic response in both LAD ligation and CSQ mouse models of HF. The fact that this agent can increase contractile performance without heart rate increase should be desirable in HF therapy.

Aberrant dynamin 2-dependent Na(+) /H(+) exchanger-1 trafficking contributes to cardiomyocyte apoptosis

Sarcolemmal Na⁺/H⁺ exchanger 1 (NHE1) activity is essential for the intracellular pH (pH_i) homeostasis in cardiac myocytes. Emerging evidence indicates that sarcolemmal NHE1 dysfunction was closely related to cardiomyocyte death, but it remains unclear whether defective trafficking of NHE1 plays a role in the vital cellular signalling processes. Dynamin (DNM), a large guanosine triphosphatase (GTPase), is best known for its roles in membrane trafficking events. Herein, using co-immunoprecipitation, cell surface biotinylation and confocal microscopy techniques, we investigated the potential regulation on cardiac NHE1 activity by DNM. We identified that DNM2, a cardiac isoform of DNM, directly binds to NHE1. Overexpression of a wild-type DNM2 or a dominant-negative DNM2 mutant with defective GTPase activity in adult rat ventricular myocytes (ARVMs) facilitated or retarded the internalization of sarcolemmal NHE1, whereby reducing or increasing its activity respectively. Importantly, the increased NHE1 activity associated with DNM2 deficiency led to ARVMs apoptosis, as demonstrated by cell viability, terminal deoxynucleotidyl transferase–mediated dUTP nick-end labelling assay, Bcl-1/Bax expression and caspase-3 activity, which were effectively rescued by pharmacological inhibition of NHE1 with zoniporide. Thus, our results demonstrate that disruption of the DNM2-dependent retrograde trafficking of NHE1 contributes to cardiomyocyte apoptosis.

Inhibition of carbonic anhydrase prevents the Na(+)/H(+) exchanger 1-dependent slow force response to rat myocardial stretch

Myocardial stretch is an established signal that leads to hypertrophy. Myocardial stretch induces a first immediate force increase followed by a slow force response (SFR), which is a consequence of an increased Ca(2+) transient that follows the NHE1 Na(+)/H(+) exchanger activation. Carbonic anhydrase II (CAII) binds to the extreme COOH terminus of NHE1 and regulates its transport activity. We aimed to test the role of CAII bound to NHE1 in the SFR. The SFR and changes in intracellular pH (pHi) were evaluated in rat papillary muscle bathed with CO2/HCO3(-) buffer and stretched from 92% to 98% of the muscle maximal force development length for 10 min in the presence of the CA inhibitor 6-ethoxzolamide (ETZ, 100 μM). SFR control was 120 ± 3% (n = 8) of the rapid initial phase and was fully blocked by ETZ (99 ± 4%, n = 6). The SFR corresponded to a maximal increase in pHi of 0.18 ± 0.02 pH units (n = 4), and pHi changes were blocked by ETZ (0.04 ± 0.04, n = 6), as monitored by epifluorescence. NHE1/CAII physical association was examined in the SFR by coimmunoprecipitation, using muscle lysates. CAII immunoprecipitated with an anti-NHE1 antibody and the CAII immunoprecipitated protein levels increased 58 ± 9% (n = 6) upon stretch of muscles, assessed by immunoblots. The p90(RSK) kinase inhibitor SL0101-1 (10 μM) blocked the SFR of heart muscles after stretch 102 ± 2% (n = 4) and reduced the binding of CAII to NHE1, suggesting that the stretch-induced phosphorylation of NHE1 increases its binding to CAII. CAII/NHE1 interaction constitutes a component of the SFR to heart muscle stretch, which potentiates NHE1-mediated H(+) transport in the myocardium.

H⁺-activated Na⁺ influx in the ventricular myocyte couples Ca²⁺-signalling to intracellular pH

Acid extrusion on Na(+)-coupled pH-regulatory proteins (pH-transporters), Na(+)/H(+) exchange (NHE1) and Na(+)-HCO3(-) co-transport (NBC), drives Na(+) influx into the ventricular myocyte. This H(+)-activated Na(+)-influx is acutely up-regulated at pHi<7.2, greatly exceeding Na(+)-efflux on the Na(+)/K(+) ATPase. It is spatially heterogeneous, due to the co-localisation of NHE1 protein (the dominant pH-transporter) with gap-junctions at intercalated discs. Overall Na(+)-influx via NBC is considerably lower, but much is co-localised with L-type Ca(2+)-channels in transverse-tubules. Through a functional coupling with Na(+)/Ca(2+) exchange (NCX), H(+)-activated Na(+)-influx increases sarcoplasmic-reticular Ca(2+)-loading and release during intracellular acidosis. This raises Ca(2+)-transient amplitude, rescuing it from direct H(+)-inhibition. Functional coupling is biochemically regulated and linked to membrane receptors, through effects on NHE1 and NBC. It requires adequate cytoplasmic Na(+)-mobility, as NHE1 and NCX are spatially separated (up to 60μm). The relevant functional NCX activity must be close to dyads, as it exerts no effect on bulk diastolic Ca(2+). H(+)-activated Na(+)-influx is up-regulated during ischaemia-reperfusion and some forms of maladaptive hypertrophy and heart failure. It is thus an attractive system for therapeutic manipulation. This article is part of a Special Issue entitled "Na(+) Regulation in Cardiac Myocytes".

Dietary Omega-3 Polyunsaturated Fatty Acids Suppress NHE-1 Upregulation in a Rabbit Model of Volume- and Pressure-Overload

BACKGROUND

Increased consumption of omega-3 polyunsaturated fatty acids (ω3-PUFAs) from fish oil (FO) may have cardioprotective effects during ischemia/reperfusion, hypertrophy, and heart failure (HF). The cardiac Na(+)/H(+)-exchanger (NHE-1) is a key mediator for these detrimental cardiac conditions. Consequently, chronic NHE-1 inhibition appears to be a promising pharmacological tool for prevention and treatment. Acute application of the FO ω3-PUFAs eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) inhibit the NHE-1 in isolated cardiomyocytes. We studied the effects of a diet enriched with ω3-PUFAs on the NHE-1 activity in healthy rabbits and in a rabbit model of HF induced by volume- and pressure-overload.

METHODS

Rabbits were allocated to four groups. The first two groups consisted of healthy rabbits, which were fed either a diet containing 1.25% (w/w) FO (ω3-PUFAs), or 1.25% high-oleic sunflower oil (ω9-MUFAs) as control. The second two groups were also allocated to either a diet containing ω3-PUFAs or ω9-MUFAs, but underwent volume- and pressure-overload to induce HF. Ventricular myocytes were isolated by enzymatic dissociation and used for intracellular pH (pH(i)) and patch-clamp measurements. NHE-1 activity was measured in HEPES-buffered conditions as recovery rate from acidosis due to ammonium prepulses.

RESULTS

In healthy rabbits, NHE-1 activity in ω9-MUFAs and ω3-PUFAs myocytes was not significantly different. Volume- and pressure-overload in rabbits increased the NHE-1 activity in ω9-MUFAs myocytes, but not in ω3-PUFAs myocytes, resulting in a significantly lower NHE-1 activity in myocytes of ω3-PUFA fed HF rabbits. The susceptibility to induced delayed afterdepolarizations (DADs), a cellular mechanism of arrhythmias, was lower in myocytes of HF animals fed ω3-PUFAs compared to myocytes of HF animals fed ω9-MUFAs. In our rabbit HF model, the degree of hypertrophy was similar in the ω3-PUFAs group compared to the ω9-MUFAs group.

CONCLUSION

Dietary ω3-PUFAs from FO suppress upregulation of the NHE-1 activity and lower the incidence of DADs in our rabbit model of volume- and pressure-overload.

Activated NHE1 is required to induce early cardiac hypertrophy in mice

The Na+/H+ exchanger isoform 1 (NHE1) has been implicated as being causal in cardiac hypertrophy and the protein level and activity are elevated in the diseased myocardium. However, it is unclear whether mere elevation of the protein is sufficient for cardiac pathology, or whether activation of the protein is required. In this study, we examined the comparative effects of elevation of wild type and activated NHE1. Two mouse transgenic models that expressed either a wild type NHE1 protein or an activated NHE1 protein were characterized. Expression of activated NHE1 caused significant increases in heart weight to body weight, apoptosis, cross-sectional area, interstitial fibrosis and decreased cardiac performance. Expression of wild type NHE1 caused a much milder pathology. When we examined 2 or 10-week-old mouse hearts, there was neither elevation of calcineurin levels nor increased phosphorylation of ERK or p38 in either NHE1 transgenic mouse line. Expression of activated NHE1 in intact mice caused an increased sensitivity to phenylephrine-induced hypertrophy. Our results show that expression of activated NHE1 promotes cardiac hypertrophy to a much greater degree than elevated levels of wild type NHE1 alone. In addition, expression of activated NHE1 promotes greater sensitivity to neurohormonal stimulation. The results suggest that activation of NHE1 is a key component that accentuates NHE1-induced myocardial pathology.

Ginseng inhibits cardiomyocyte hypertrophy and heart failure via NHE-1 inhibition and attenuation of calcineurin activation

BACKGROUND

Ginseng is a medicinal plant used widely in Asia that has gained popularity in the West during the past decade. Increasing evidence suggests a therapeutic role for ginseng in the cardiovascular system. The pharmacological properties of ginseng are mainly attributed to ginsenosides, the principal bioactive constituents in ginseng. The present study was carried out to determine whether ginseng exerts a direct antihypertrophic effect in cultured cardiomyocytes and whether it modifies the heart failure process in vivo. Moreover, we determined the potential underlying mechanisms for these actions.

METHODS AND RESULTS

Experiments were performed on cultured neonatal rat ventricular myocytes as well as adult rats subjected to coronary artery ligation (CAL). Treatment of cardiomyocytes with the α(1) adrenoceptor agonist phenylephrine (PE) for 24 hours produced a marked hypertrophic effect as evidenced by significantly increased cell surface area and ANP gene expression. These effects were attenuated by ginseng in a concentration-dependent manner with a complete inhibition of hypertrophy at a concentration of 10 μg/mL. Phenylephrine-induced hypertrophy was associated with increased gene and protein expression of the Na(+)-H(+) exchanger 1 (NHE-1), increased NHE-1 activity, increased intracellular concentrations of Na(+) and Ca(2+), enhanced calcineurin activity, increased translocation of NFAT3 into nuclei, and GATA-4 activation, all of which were significantly inhibited by ginseng. Upregulation of these systems was also evident in rats subjected to 4 weeks of CAL. However, animals treated with ginseng demonstrated markedly reduced hemodynamic and hypertrophic responses, which were accompanied by attenuation of upregulation of NHE-1 and calcineurin activity.

CONCLUSIONS

Taken together, our results demonstrate a robust antihypertrophic and antiremodeling effect of ginseng, which is mediated by inhibition of NHE-1-dependent calcineurin activation.

Decreased Activity of the Na + /H + Exchanger by Phosphodiesterase 5A Inhibition Is Attributed to an Increase in Protein Phosphatase Activity

The beneficial effect of phosphodiesterase 5A inhibition in ischemia/reperfusion injury and cardiac hypertrophy is well established. Inhibition of the cardiac Na + /H + exchanger (NHE-1) exerts beneficial effects on these same conditions, and a possible link between these therapeutic strategies was suggested. Experiments were performed in isolated cat cardiomyocytes to gain insight into the intracellular pathway involved in the reduction of NHE-1 activity by phosphodiesterase 5A inhibition. NHE-1 activity was assessed by the rate of intracellular pH recovery from a sustained acidic load in the absence of bicarbonate. Phosphodiesterase 5A inhibition with sildenafil (1 μmol/L) did not affect basal intracellular pH; yet, it did decrease proton efflux (J H ; in millimoles per liter per minute) after the acidic load (proton efflux: 6.97±0.43 in control versus 3.31±0.58 with sildenafil; P <0.05). The blockade of both protein phosphatase 1 and 2A with 100 nmol/L of okadaic acid reverted the sildenafil effect (proton efflux: 6.77±0.82). In contrast, selective inhibition of protein phosphatase 2A (1 nmol/L of okadaic acid or 100 μmol/L of endothall) did not (3.86±1.0 and 2.61±1.2), suggesting that only protein phosphatase 1 was involved in sildenafil-induced NHE-1 inhibition. Moreover, sildenafil prevented the acidosis-induced increase in NHE-1 phosphorylation without affecting activation of the extracellular signal–regulated kinase 1/2-p90 RSK pathway. Our results suggest that phosphodiesterase 5A inhibition decreases NHE-1 activity, during intracellular pH recovery after an acidic load, by a protein phosphatase 1–dependent reduction in NHE-1 phosphorylation.

Expression of mitochondrial fusion-fission proteins during post-infarction remodeling: the effect of NHE-1 inhibition

Studies on the role of mitochondrial fission/fusion (MFF) proteins in the heart have been initiated recently due to their biological significance in cell metabolism. We hypothesized that the expression of MFF proteins is affected by post-infarction remodeling and in vitro cardiomyocyte hypertrophy, and serves as a target for the Na(+)/H(+) exchanger 1 (NHE-1) inhibition. Post-infarction remodeling was induced in Sprague-Dawley rats by coronary artery ligation (CAL) while in vitro hypertrophy was induced in cardiomyocytes by phenylephrine (PE). Mitochondrial fission (Fis1, DRP1) and fusion (Mfn2, OPA1) proteins were analyzed in heart homogenates and cell lysates by Western blotting. Our results showed that 12 and 18 weeks after CAL, Fis1 increased by 80% (P < 0.01) and 31% (P < 0.05), and Mfn2 was reduced by 17% (P < 0.05) and 22% (P < 0.05), respectively. OPA1 was not changed at 12 weeks, although its expression decreased by 18% (P < 0.05) with 18 weeks of ligation. MFF proteins were also affected by PE-induced hypertrophy that was dependent on mitochondrial permeability transition pore opening and oxidative stress. The NHE-1-specific inhibitor EMD-87580 (EMD) attenuated changes in the expression of MFF proteins in both the models of hypertrophy. The effect of EMD was likely mediated, at least in part, through its direct action on mitochondria since Percoll-purified mitochondria and mitoplasts have been shown to contain NHE-1. Our study provides the first evidence linking cardiac hypertrophy with MFF proteins expression that was affected by NHE-1 inhibition, thus suggesting that MFF proteins might be a target for pharmacotherapy with anti-hypertrophic drugs.

Elevated myocardial Na+/H+ exchanger isoform 1 activity elicits gene expression that leads to cardiac hypertrophy

In myocardial disease, elevated expression and activity of Na(+)/H(+) exchanger isoform 1 (NHE1) are detrimental. To better understand the involvement of NHE1, transgenic mice with elevated heart-specific NHE1 expression were studied. N-line mice expressed wild-type NHE1, and K-line mice expressed activated NHE1. Cardiac morphology, interstitial fibrosis, and cardiac function were examined by histological staining and echocardiography. Differences in gene expression between the N-line or K-line and nontransgenic littermates were probed with genechip analysis. We found that NHE1 K-line (but not N-line) hearts developed hypertrophy, including elevated heart weight-to-body weight ratio and increased cross-sectional area of the cardiomyocytes, interstitial fibrosis, as well as depressed cardiac function. N-line hearts had modest changes in gene expression (50 upregulations and 99 downregulations, P < 0.05), whereas K-line hearts had a very strong transcriptional response (640 upregulations and 677 downregulations, P < 0.05). In addition, the magnitude of expression alterations was much higher in K-line than N-line mice. The most significant changes in gene expression were involved in cardiac hypertrophy, cardiac necrosis/cell death, and cardiac infarction. Secreted phosphoprotein 1 and its signaling pathways were upregulated while peroxisome proliferator-activated receptor gamma signaling was downregulated in K-line mice. Our study shows that expression of activated NHE1 elicits specific pathways of gene activation in the myocardium that lead to cardiac hypertrophy, cell death, and infarction.

Anti-hypertrophic effect of NHE-1 inhibition involves GSK-3beta-dependent attenuation of mitochondrial dysfunction

Although Na(+)-H(+) exchanger 1 (NHE-1) inhibition has been demonstrated to have anti-hypertrophic effect indirectly through mitochondria, the detailed cellular mechanisms mediating this effect remain elusive. In this study we sought to determine whether NHE-1 inhibition exerts an anti-hypertrophic effect by modulating the mitochondrial permeability transition pore (mPTP) opening through the AMP-activated protein kinase (AMPK)/glycogen synthase kinase 3beta (GSK-3beta) pathway during hypertrophy in cardiomyocytes. An in vivo model of hypertrophy was induced in male Sprague-Dawley rats by subjecting them to 3, 7 or 28 days of coronary artery ligation (CAL). To induce hypertrophy in vitro, cardiomyocytes isolated from hearts of neonatal (1-3 days) Sprague-Dawley rats were exposed to endothelin-1 (ET-1, 10 nM) in the presence or absence of various treatments. The results demonstrate that CAL affected both AMPKalpha and GSK-3beta phosphorylation in a time-dependent manner. In cultured cardiomyocytes, ET-1 increased phosphorylation of AMPKalpha(1)/alpha(2)(Ser485/Ser491) and GSK-3beta(Ser9) by 80% (P<0.05) and 225% (P<0.05) respectively, both of which were significantly blunted by the NHE-1 inhibitor AVE-4890 (5 microM). ET-1-induced phosphorylation of GSK-3beta(Ser9) was attenuated by inhibitors of phosphatidylinositol 3-kinase (LY294002), Akt (Akt inhibitor VIII), ERK1/2 (PD98059) and by the AMPK agonist 5-aminoimidazole-4-carboxamide-1-beta-D-ribofuranoside (AICAR). Prevention of GSK-3beta(Ser9) phosphorylation was also accompanied by suppression of ET-1-induced increases in cell surface area, ANP and alpha-skeletal actin gene expression. Co-immunoprecipitation studies revealed that GSK-3beta interacts with components of the mPTP, voltage-dependent anion channel (VDAC) and adenine nucleotide translocase. Furthermore, ET-1 reduced phosphorylation of VDAC, which was associated with both mPTP opening and mitochondrial membrane depolarization. These effects were mimicked by the GSK-3beta inhibitor SB216763, thus showing that modulation of mPTP formation is GSK-3beta-dependent. In conclusion, anti-hypertrophic effect of NHE-1 inhibition can be mediated through activation of GSK-3beta which in turn induces inhibition of mPTP opening due to VDAC phosphorylation.

Role of P2X purinergic receptors in the rescue of ischemic heart failure

Evidence is accumulating to support the presence of P2X purinergic receptors in the heart. However, the biological role of this receptor remains to be defined. The objectives here were to determine the role of cardiac P2X receptors in modulating the progression of post-myocardial infarction ischemic heart failure and to investigate the underlying mechanism. The P2X4 receptor (P2X4R) is an important subunit of native cardiac P2X receptors, and the cardiac-specific transgenic overexpression of P2X4R (Tg) was developed as a model. Left anterior descending artery ligation resulted in similar infarct size between Tg and wild-type (WT) mice (P > 0.1). However, Tg mice showed an enhanced cardiac contractile performance at 7 days, 1 mo, and 2 mo after infarction and an increased survival at 1 and 2 mo after infarction (P < 0.01). The enhanced intact heart function was manifested by a greater global left ventricular developed pressure and rate of contraction of left ventricular pressure in vitro and by a significantly increased fractional shortening and systolic thickening in the noninfarcted region in vivo (P < 0.05). The salutary effects on the ischemic heart failure phenotype were seen in both sexes and were not the result of any difference in infarct size in Tg versus WT hearts. An enhanced contractile function of the noninfarcted area in the Tg heart was likely an important rescuing mechanism. The cardiac P2X receptor is a novel target to treat post-myocardial infarction ischemic heart failure.

Chronic inhibition of the Na+/H+ - exchanger causes regression of hypertrophy, heart failure, and ionic and electrophysiological remodelling

BACKGROUND AND PURPOSE

Increased activity of the Na+/H+ -exchanger (NHE-1) in heart failure underlies raised [Na+]i causing disturbances of calcium handling. Inhibition of NHE-1, initiated at the onset of pressure/volume overload, prevents development of hypertrophy, heart failure and remodelling. We hypothesized that chronic inhibition of NHE-1, initiated at a later stage, would induce regression of hypertrophy, heart failure, and ionic and electrophysiological remodelling.

EXPERIMENTAL APPROACH

Development of heart failure in rabbits was monitored electrocardiographically and echocardiographically, after one or three months. Cardiac myocytes were also isolated. One group of animals were treated with cariporide (inhibitor of NHE-1) in the diet after one month. Cytoplasmic calcium, sodium and action potentials were measured with fluorescent markers and sarcoplasmic reticulum calcium content by rapid cooling. Calcium after-transients were elicited after rapid pacing. Sodium channel current (INa) was measured using patch-clamp techniques.

KEY RESULTS

Hypertrophy and heart failure developed after one month and progressed during the next two months. After one month, dietary treatment with cariporide was initiated. Two months of treatment reduced hypertrophy and heart failure, duration of action potential QT-interval and QRS, and restored sodium and calcium handling and the incidence of calcium after-transients. In cardiac myocytes, parameters of INa were not changed by cariporide.

CONCLUSION AND IMPLICATIONS

In rabbit hearts with hypertrophy and signs of heart failure one month after induction of pressure/volume overload, two months of dietary treatment with the NHE-1 inhibitor cariporide caused regression of hypertrophy, heart failure and ionic and electrophysiological remodelling.

The role of Na dysregulation in cardiac disease and how it impacts electrophysiology

Ca(2+) is well known as the central player in cardiac cell physiology, mediating Ca(2+) activation of myosin ATPase and contraction, the stimulation of Ca(2+)-activated signaling pathways and modulation of mitochondrial energy production. Abnormalities of Ca(2+) handling are a well-studied mechanism of decompensation in heart failure. Less appreciated is the role of cytosolic Na(+) (Na(i) (+)), which can dramatically influence the transfer rates and distribution of Ca(2+) among the intracellular compartments of the myocyte. Since Na(i) (+) can vary widely under different physiological and pathological conditions, and its effects depend on multiple ion gradients and membrane electrical potentials, unraveling the global influence of Na(i) (+) on cell function is complex, requiring an integrative view of cardiomyocyte physiology. Here, we discuss how abnormal Na(i) (+) regulation not only influences the cytosolic Ca(2+) transient and the cellular action potential but also alters mitochondrial Ca(2+) uptake and the balance of energy supply and demand of the cardiomyocyte, which may contribute to oxidative stress and cardiac decompensation. The implications for sudden cardiac death and the potential for novel therapeutic interventions are discussed.

Left ventricular dysfunction and associated cellular injury in rats exposed to chronic intermittent hypoxia

Obstructive sleep apnea (OSA) increases cardiovascular morbidity and mortality. We have reported that chronic intermittent hypoxia (CIH), a direct consequence during OSA, leads to left ventricular (LV) remodeling and dysfunction in rats. The present study is to determine LV myocardial cellular injury that is possibly associated with LV global dysfunction. Fifty-six rats were exposed either to CIH (nadir O(2) 4-5%) or sham (handled normoxic controls, HC), 8 h/day for 6 wk. At the end of the exposure, we studied LV global function by cardiac catheterization, and LV myocardial cellular injury by in vitro analyses. Compared with HC, CIH animals demonstrated elevations in mean arterial pressure and LV end-diastolic pressure, but reductions in cardiac output (CIH 141.3 +/- 33.1 vs. HC 184.4 +/- 21.2 ml x min(-1) x kg(-1), P < 0.01), maximal rate of LV pressure rise in systole (+dP/dt), and maximal rate of LV pressure fall in diastole (-dP/dt). CIH led to significant cell injury in the left myocardium, including elevated LV myocyte size, measured by cell surface area (CIH 3,564 +/- 354 vs. HC 2,628 +/- 242 microm(2), P < 0.05) and cell length (CIH 148 +/- 23 vs. HC 115 +/- 16 microm, P < 0.05), elevated terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL)-stained positive cell number (CIH 98 +/- 45 vs. HC 15 +/- 13, P < 0.01), elevated caspase-3 activity (906 +/- 249 vs. 2,275 +/- 1,169 pmol x min(-1) x mg(-1), P < 0.05), and elevated expression of several remodeling gene markers, including c-fos, atrial natriuretic peptide, beta-myosin heavy chain, and myosin light chain-2. However, there was no difference between groups in sarcomere contractility of isolated LV myocytes, or in LV collagen deposition on trichrome-stained slices. In conclusion, CIH-mediated LV global dysfunction is associated with myocyte hypertrophy and apoptosis at the cellular level.

Excitation-contraction coupling and mitochondrial energetics

Cardiac excitation-contraction (EC) coupling consumes vast amounts of cellular energy, most of which is produced in mitochondria by oxidative phosphorylation. In order to adapt the constantly varying workload of the heart to energy supply, tight coupling mechanisms are essential to maintain cellular pools of ATP, phosphocreatine and NADH. To our current knowledge, the most important regulators of oxidative phosphorylation are ADP, Pi, and Ca2+. However, the kinetics of mitochondrial Ca2+-uptake during EC coupling are currently a matter of intense debate. Recent experimental findings suggest the existence of a mitochondrial Ca2+ microdomain in cardiac myocytes, justified by the close proximity of mitochondria to the sites of cellular Ca2+ release, i. e., the ryanodine receptors of the sarcoplasmic reticulum. Such a Ca2+ microdomain could explain seemingly controversial results on mitochondrial Ca2+ uptake kinetics in isolated mitochondria versus whole cardiac myocytes. Another important consideration is that rapid mitochondrial Ca2+ uptake facilitated by microdomains may shape cytosolic Ca2+ signals in cardiac myocytes and have an impact on energy supply and demand matching. Defects in EC coupling in chronic heart failure may adversely affect mitochondrial Ca2+ uptake and energetics, initiating a vicious cycle of contractile dysfunction and energy depletion. Future therapeutic approaches in the treatment of heart failure could be aimed at interrupting this vicious cycle.

Mitochondrial permeability transition pore opening as an endpoint to initiate cell death and as a putative target for cardioprotection

In recent years, mitochondria have been recognized as regulators of cell death via both apoptosis and necrosis in addition to their essential role for cell survival. Cellular dysfunctions induced by intra- or extracellular insults converge on mitochondria and induce a sudden increase in permeability of the inner mitochondrial membrane, the so-called mitochondrial permeability transition. The mitochondrial permeability transition is caused by the opening of permeability transition pores (PTP) in the inner mitochondrial membrane with subsequent loss of ionic homeostasis, matrix swelling and outer membrane rupture. The detailed molecular mechanisms underlying the PTP-induced cellular dysfunction during cardiac pathology such as ischemia/reperfusion or post-infarction remodeling remain to be elucidated. However, a growing body of evidence supports the concept that pharmacological inhibition of the PTP is an effective and promising strategy for the protection of the heart against ischemia/reperfusion injury and for attenuation of the remodeling process which contributes to heart failure. This review summarizes and discusses current data on i) the structure and function of the PTP, ii) possible mechanisms and consequences of PTP opening and iii) the inhibition of PTP opening as a therapeutic approach for treatment of heart disease.

Regulation and Role of the Presynaptic and Myocardial Na+/H+Exchanger NHE1: Effects on the Sympathetic Nervous System in Heart Failure

In acute myocardial ischemia and in chronic heart failure, sympathetic activation with excessive norepinephrine (NE) release from and reduced NE reuptake into sympathetic nerve endings is a prominent cause of arrhythmias and cardiac dysfunction. The Na(+)/H(+) exchanger NHE1 is the predominant isoform in the heart. It contributes to cellular acid-base balance, and electrolyte, and volume homeostasis, and is activated in response to intracellular acidosis and/or activation of guanine nucleotide binding (G) protein-coupled receptors. NHE1 mediates its signaling via protein kinases A (PKA) or C (PKC). In cardiomyocytes, NHE1 is restricted to specialized membrane domains, where it regulates the activity of pH-sensitive proteins and modulates the driving force of the Na(+)/Ca(2+) exchanger. During acute ischemia/reperfusion and in heart failure the activity/amount of NHE1 is increased, leading to intracellular Ca(2+) overload and promoting structural (apoptosis, hypertrophy) and functional (arrhythmias, hypercontraction) myocardial damage. In sympathetic nerve endings, increased NHE1 activity results in the accumulation of axoplasmic Na(+) that diminishes the inward and/or favors the outward transport of NE via the neuronal norepinephrine transporter (NET). The increased NE levels within the nerve-muscle junction facilitate the sustained stimulation of myocardial alpha- and beta-adrenoceptors (ARs), which in turn aggravate the increases in myocardial NHE1 activity and the associated deleterious effects. Furthermore, the responsiveness of the beta-AR declines overtime, which results in further release of NE, initiating a vicious cycle. Accordingly, NHE1 is a potential candidate for targeted intervention to suppress this feedback loop.

Phosphodiesterase 5A Inhibition Induces Na + /H + Exchanger Blockade and Protection Against Myocardial Infarction

Acute phosphodiesterase 5A inhibition by sildenafil or EMD360527/5 promoted profound inhibition of the cardiac Na(+)/H(+) exchanger (NHE-1), detected by the almost null intracellular pH recovery from an acute acid load (ammonium prepulse) in isolated papillary muscles from Wistar rats. Inhibition of phosphoglycerate kinase-1 (KT5823) restored normal NHE-1 activity, suggesting a causal link between phosphoglycerate kinase-1 increase and NHE-1 inhibition. We then tested whether the beneficial effects of NHE-1 inhibitors against the deleterious postmyocardial infarction (MI) remodeling can be detected after sildenafil-mediated NHE-1 inhibition. MI was induced by left anterior descending coronary artery ligation in Wistar rats, which were randomized to placebo or sildenafil (100 mg kg(-1) day(-1)) for 6 weeks. Sildenafil significantly increased left ventricular phosphoglycerate kinase-1 activity in the post-MI group without affecting its expression. MI increased heart weight/body weight ratio, left ventricular myocyte cross-sectional area, interstitial fibrosis, and brain natriuretic peptide and NHE-1 expression. Sildenafil blunted these effects. Neither a significant change in infarct size nor a change in arterial or left ventricular systolic pressure was detected after sildenafil. MI decreased fractional shortening and the ratio of the maximum rate of rise of LVP divided by the pressure at the moment such maximum occurs, effects that were prevented by sildenafil. Intracellular pH recovery after an acid load was faster in papillary muscles from post-MI hearts (versus sham), whereas sildenafil significantly inhibited NHE-1 activity in both post-MI and sildenafil-treated sham groups. We conclude that increased phosphoglycerate kinase-1 activity after acute phosphodiesterase 5A inhibition blunts NHE-1 activity and protects the heart against post-MI remodeling and dysfunction.

Normalization of the calcineurin pathway underlies the regression of hypertensive hypertrophy induced by Na+/H+exchanger-1 (NHE-1) inhibitionThis paper is one of a selection of papers published in this Special Issue, entitled The Cellular and Molecular Basis of Cardiovascular Dysfunction, Dhalla 70th Birthday Tribute

Na+/H+exchanger-1 (NHE-1) inhibition induces cardiac hypertrophy regression and (or) prevention in several experimental models, although the intracellular events involved remain unclarified. We aimed to determine whether the calcineurin/NFAT pathway mediates this effect of NHE-1 inhibitors. Spontaneously hypertensive rats (SHR) with cardiac hypertrophy were treated with the NHE-1 inhibitors cariporide and BIIB723 for 30 days. Wistar rats served as normotensive controls. Their hearts were studied by echocardiography, immunoblotting, and real-time RT-PCR. Cytoplasmic Ca2+and calcineurin Aβ expression were measured in cultured neonatal rat ventricular myocytes (NRVM) stimulated with endothelin-1 for 24 h. NHE-1 blockade induced cardiac hypertrophy regression (heart mass/body mass = 3.63 ± 0.07 vs. 3.06 ± 0.05 and 3.02 ± 0.13 for untreated vs. cariporide- and BIIB723-treated SHR, respectively; p < 0.05) and decreased myocardial brain natriuretic peptide, calcineurin Aβ, and nuclear NFAT expressions. Echocardiographic evaluation demonstrated a reduction in left ventricular wall thickness without changes in cavity dimensions or a significant decrease in blood pressure. NHE-1-inhibitor treatment did not affect myocardial stiffness or endocardial shortening, but increased mid-wall shortening, suggesting that a positive inotropic effect develops after hypertrophy regression. Cariporide normalized the increased diastolic Ca2+and calcineurin Aβ expression observed in ET-1-stimulated NRVM. In conclusion, our data suggest that inactivation of calcineurin/NFAT pathway may underlie the regression of cardiac hyper-trophy induced by NHE-1 inhibition.

Structural and functional analysis of the Na+/H+ exchanger

The mammalian NHE (Na+/H+ exchanger) is a ubiquitously expressed integral membrane protein that regulates intracellular pH by removing a proton in exchange for an extracellular sodium ion. Of the nine known isoforms of the mammalian NHEs, the first isoform discovered (NHE1) is the most thoroughly characterized. NHE1 is involved in numerous physiological processes in mammals, including regulation of intracellular pH, cell-volume control, cytoskeletal organization, heart disease and cancer. NHE comprises two domains: an N-terminal membrane domain that functions to transport ions, and a C-terminal cytoplasmic regulatory domain that regulates the activity and mediates cytoskeletal interactions. Although the exact mechanism of transport by NHE1 remains elusive, recent studies have identified amino acid residues that are important for NHE function. In addition, progress has been made regarding the elucidation of the structure of NHEs. Specifically, the structure of a single TM (transmembrane) segment from NHE1 has been solved, and the high-resolution structure of the bacterial Na+/H+ antiporter NhaA has recently been elucidated. In this review we discuss what is known about both functional and structural aspects of NHE1. We relate the known structural data for NHE1 to the NhaA structure, where TM IV of NHE1 shows surprising structural similarity with TM IV of NhaA, despite little primary sequence similarity. Further experiments that will be required to fully understand the mechanism of transport and regulation of the NHE1 protein are discussed.