PKC-alpha regulates cardiac contractility and propensity toward heart failure

Cardiac RKIP induces a beneficial β-adrenoceptor-dependent positive inotropy

In heart failure therapy, it is generally assumed that attempts to produce a long-term increase in cardiac contractile force are almost always accompanied by structural and functional damage. Here we show that modest overexpression of the Raf kinase inhibitor protein (RKIP), encoded by Pebp1 in mice, produces a well-tolerated, persistent increase in cardiac contractility that is mediated by the β1-adrenoceptor (β1AR). This result is unexpected, as β1AR activation, a major driver of cardiac contractility, usually has long-term adverse effects. RKIP overexpression achieves this tolerance via simultaneous activation of the β2AR subtype. Analogously, RKIP deficiency exaggerates pressure overload-induced cardiac failure. We find that RKIP expression is upregulated in mouse and human heart failure, indicative of an adaptive role for RKIP. Pebp1 gene transfer in a mouse model of heart failure has beneficial effects, suggesting a new therapeutic strategy for heart failure therapy.

Gene expression profiling of CD133-positive cells in coronary artery disease

Gene expression profiles of CD133-positive cells from patients with coronary artery disease (CAD) were analyzed to identify key genes associated with cardiac therapy. Furthermore, the effect of exercise on gene expression was also investigated. Gene expression data set (accession number: GSE18608) was downloaded from the Gene Expression Omnibus, including blood samples from four healthy subjects (H), and from 10 patients with coronary artery disease at baseline (B) and after 3 months (3M) of exercise. Differential analysis was performed for H vs. B and H vs. 3M using limma package of R. Two‑way cluster analysis was performed using the expression levels of the differentially expressed genes (DEGs) by package pheatmap of R. Functional enrichment analysis was applied on the DEGs using the Database for Annotation, Visualization and Integrated Discovery. Relevant small molecules were predicted using the Connectivity map database (cMap). A total of 131 and 71 DEGs were identified in patients with CAD prior to and following 3 months of exercise. The two groups of DEGs were compared and 44 genes overlapped. In cluster analysis with the expression levels of the common DEGs, patients with CAD could be well separated from the healthy controls. Functional enrichment analysis showed that response to peptide hormone stimulus and anti‑apoptosis pathways were significantly enriched in the common DEGs. A total of 12 relevant small molecules were revealed by cMap based upon the expression levels of common DEGs, such as 5252917 and MG‑262. Three months of exercise in part normalized the gene expression in CAD patients. The genes not altered by exercise may be the targets of small molecules, such as 5252917 and MG-262.

The Effect of PKCα on the Light Response of Rod Bipolar Cells in the Mouse Retina

PURPOSE

Protein kinase C α (PKCα) is abundantly expressed in rod bipolar cells (RBCs) in the retina, yet the physiological function of PKCα in these cells is not well understood. To elucidate the role of PKCα in visual processing in the eye, we examined the effect of genetic deletion of PKCα on the ERG and on RBC light responses in the mouse.

METHODS

Immunofluorescent labeling was performed on wild-type (WT), TRPM1 knockout, and PKCα knockout (PKC-KO) retina. Scotopic and photopic ERGs were recorded from WT and PKC-KO mice. Light responses of RBCs were measured using whole-cell recordings in retinal slices from WT and PKC-KO mice.

RESULTS

Protein kinase C alpha expression in RBCs is correlated with the activity state of the cell. Rod bipolar cells dendrites are a major site of PKCα phosphorylation. Electroretinogram recordings indicated that loss of PKCα affects the scotopic b-wave, including a larger peak amplitude, longer implicit time, and broader width of the b-wave. There were no differences in the ERG a- or c-wave between PKCα KO and WT mice, indicating no measurable effect of PKCα in photoreceptors or the RPE. The photopic ERG was unaffected consistent with the lack of detectable PKCα in cone bipolar cells. Whole-cell recordings from RBCs in PKC-KO retinal slices revealed that, compared with WT, RBC light responses in the PKC-KO retina are delayed and of longer duration.

CONCLUSIONS

Protein kinase C alpha plays an important modulatory role in RBCs, regulating both the peak amplitude and temporal properties of the RBC light response in the rod visual pathway.

Protein kinase Cα inhibits myocardin-induced cardiomyocyte hypertrophy through the promotion of myocardin phosphorylation

Myocardin plays a key role in the development of cardiac hypertrophy. However, the upstream signals that control the stability and transactivity of myocardin remain to be fully understood. The expression of protein kinase Cα (PKCα) also induces cardiac hypertrophy. An essential downstream molecule of PKCα, extracellular signal-regulated kinase 1/2, was reported to negatively regulate the activities of myocardin. But, the effect of cooperation between PKCα and myocardin and the potential molecular mechanism by which PKCα regulates myocardin-mediated cardiac hypertrophy are unclear. In this study, a luciferase assay was performed using H9C2 cells transfected with expression plasmids for PKCα and myocardin. Surprisingly, the results showed that PKCα inhibited the transcriptional activity of myocardin. PKCα inhibited myocardin-induced cardiomyocyte hypertrophy, demonstrated by the decrease in cell surface area and fetal gene expression, in cardiomyocyte cells overexpressing PKCα and myocardin. The potential mechanism underlying the inhibition effect of PKCα on the function of myocardin is further explored. PKCα directly promoted the basal phosphorylation of endogenous myocardin at serine and threonine residues. In myocardin-overexpressing cardiomyocyte cells, PKCα induced the excessive phosphorylation of myocardin, resulting in the degradation of myocardin and a transcriptional suppression of hypertrophic genes. These results demonstrated that PKCα inhibits myocardin-induced cardiomyocyte hypertrophy through the promotion of myocardin phosphorylation.

Dynamics and Membrane Interactions of Protein Kinase C

Protein kinase C (PKC) is a family of Ser/Thr kinases that regulate a multitude of cellular processes through participation in the phosphoinositide signaling pathway. Significant research efforts have been directed at understanding the structure, function, and regulatory modes of the enzyme since its discovery and identification as the first receptor for tumor-promoting phorbol esters. The activation of PKC involves a transition from the cytosolic autoinhibited latent form to the membrane-associated active form. The membrane recruitment step is accompanied by the conformational rearrangement of the enzyme, which relieves autoinhibitory interactions and thereby allows PKC to phosphorylate its targets. The multidomain structure and intrinsic flexibility of PKC present remarkable challenges and opportunities for the biophysical and structural biology studies of this class of enzymes and their interactions with membranes, the major focus of this Current Topic. I will highlight the recent advances in the field, outline the current challenges, and identify areas where biophysics and structural biology approaches can provide insight into the isoenzyme-specific regulation of PKC activity.

AZT-induced mitochondrial toxicity: an epigenetic paradigm for dysregulation of gene expression through mitochondrial oxidative stress

Mitochondrial dysfunction causes oxidative stress and cardiomyopathy. Oxidative stress also is a side effect of dideoxynucleoside antiretrovirals (NRTI) and is observed in NRTI-induced cardiomyopathy. We show here that treatment with the NRTI AZT {1-[(2R,4S,5S)-4-azido-5-(hydroxymethyl)oxolan-2-yl]-5-methylpyrimidine-2,4-dione} modulates cardiac gene expression epigenetically through production of mitochondrially derived reactive oxygen species. Transgenic mice with ubiquitous expression of mitochondrially targeted catalase (MCAT) and C57Bl/6 wild-type mice littermates (WT) were administered AZT (0.22 mg/day po, 35 days), and cardiac DNA and mRNA were isolated. In AZT-treated WT, 95 cardiac genes were differentially expressed compared with vehicle-treated WTs. When MCAT mice were treated with AZT, each of those 95 genes reverted toward the expression of vehicle-treated WTs. In AZT-treated WT hearts, Mthfr [5,10-methylenetetrahydrofolate reductase; a critical enzyme in synthesis of methionine cycle intermediates including S-adenosylmethionine (SAM)], was overexpressed. Steady-state abundance of SAM in cardiac extracts from AZT-treated MCAT mice increased 60% above that of vehicle-treated MCAT. No such change occurred in WT. AZT caused hypermethylation (47%) and hypomethylation (53%) of differentially methylated DNA regions in WT cardiac DNA. AZT-treated MCAT heart DNA exhibited greater hypermethylation (91%) and less hypomethylation (9%) compared with vehicle-treated MCAT controls. The gene encoding protein kinase C-α displayed multifocal epigenetic regulation caused by oxidative stress. Results show that mitochondrially derived oxidative stress in the heart hinders cardiac DNA methylation, alters steady-state abundance of SAM, alters cardiac gene expression, and promotes characteristic pathophysiological changes of cardiomyopathy. This mechanism for NRTI toxicity offers insight into long-term side effects from these commonly used antiviral agents.

Caveolin-3 Overexpression Attenuates Cardiac Hypertrophy via Inhibition of T-type Ca2+ Current Modulated by Protein Kinase Cα in Cardiomyocytes

Pathological cardiac hypertrophy is characterized by subcellular remodeling of the ventricular myocyte with a reduction in the scaffolding protein caveolin-3 (Cav-3), altered Ca(2+) cycling, increased protein kinase C expression, and hyperactivation of calcineurin/nuclear factor of activated T cell (NFAT) signaling. However, the precise role of Cav-3 in the regulation of local Ca(2+) signaling in pathological cardiac hypertrophy is unclear. We used cardiac-specific Cav-3-overexpressing mice and in vivo and in vitro cardiac hypertrophy models to determine the essential requirement for Cav-3 expression in protection against pharmacologically and pressure overload-induced cardiac hypertrophy. Transverse aortic constriction and angiotensin-II (Ang-II) infusion in wild type (WT) mice resulted in cardiac hypertrophy characterized by significant reduction in fractional shortening, ejection fraction, and a reduced expression of Cav-3. In addition, association of PKCα and angiotensin-II receptor, type 1, with Cav-3 was disrupted in the hypertrophic ventricular myocytes. Whole cell patch clamp analysis demonstrated increased expression of T-type Ca(2+) current (ICa, T) in hypertrophic ventricular myocytes. In contrast, the Cav-3-overexpressing mice demonstrated protection from transverse aortic constriction or Ang-II-induced pathological hypertrophy with inhibition of ICa, T and intact Cav-3-associated macromolecular signaling complexes. siRNA-mediated knockdown of Cav-3 in the neonatal cardiomyocytes resulted in enhanced Ang-II stimulation of ICa, T mediated by PKCα, which caused nuclear translocation of NFAT. Overexpression of Cav-3 in neonatal myocytes prevented a PKCα-mediated increase in ICa, T and nuclear translocation of NFAT. In conclusion, we show that stable Cav-3 expression is essential for protecting the signaling mechanisms in pharmacologically and pressure overload-induced cardiac hypertrophy.

Beneficial effects of angiotensin-(1-7) against deoxycorticosterone acetate-induced diastolic dysfunction occur independently of changes in blood pressure

Mineralocorticoids have been implicated in the pathogenesis of diastolic heart failure. On the contrary, angiotensin (Ang)-(1-7) has emerged as a potential strategy for treatment of cardiac dysfunction induced by excessive mineralocorticoid receptor activation. A critical question about the cardioprotective effect of Ang-(1-7) in hypertensive models is its dependence on blood pressure (BP) reduction. Here, we addressed this question by investigating the mechanisms involved in Ang-(1-7) cardioprotection against mineralocorticoid receptor activation. Sprague-Dawley (SD) and transgenic (TG) rats that overexpress an Ang-(1-7) producing fusion protein (TG(A1-7)3292) were treated with deoxycorticosterone acetate (DOCA) for 6 weeks. After treatment, SD rats became hypertensive and developed ventricular hypertrophy. These parameters were attenuated in TG-DOCA. SD-DOCA rats developed diastolic dysfunction which was associated at the cellular level with reduced Ca(2+) transient. Oppositely, TG-DOCA myocytes presented enhanced Ca(2+) transient. Moreover, higher extracellular signal-regulated kinase phosphorylation, type 1 phosphatase, and protein kinase Cα levels were found in SD-DOCA cells. In vivo, pressor effects of DOCA can contribute to the diastolic dysfunction, raising the question of whether protection in TG was a consequence of reduced BP. To address this issue, BP in SD-DOCA was kept at TG-DOCA level by giving hydralazine or by reducing the DOCA amount given to rats (Low-DOCA). Under similar BP, diastolic dysfunction and molecular changes were still evident in DOCA-hydralazine and SD-low-DOCA, but not in TG-DOCA. In conclusion, Ang-(1-7) protective signaling against DOCA-induced diastolic dysfunction occurs independently of BP attenuation and is mediated by the activation of pathways involved in Ca(2+) handling, hypertrophy, and survival.

Systems Pharmacology Dissecting Holistic Medicine for Treatment of Complex Diseases: An Example Using Cardiocerebrovascular Diseases Treated by TCM

Holistic medicine is an interdisciplinary field of study that integrates all types of biological information (protein, small molecules, tissues, organs, external environmental signals, etc.) to lead to predictive and actionable models for health care and disease treatment. Despite the global and integrative character of this discipline, a comprehensive picture of holistic medicine for the treatment of complex diseases is still lacking. In this study, we develop a novel systems pharmacology approach to dissect holistic medicine in treating cardiocerebrovascular diseases (CCDs) by TCM (traditional Chinese medicine). Firstly, by applying the TCM active ingredients screened out by a systems-ADME process, we explored and experimentalized the signed drug-target interactions for revealing the pharmacological actions of drugs at a molecule level. Then, at a/an tissue/organ level, the drug therapeutic mechanisms were further investigated by a target-organ location method. Finally, a translational integrating pathway approach was applied to extract the diseases-therapeutic modules for understanding the complex disease and its therapy at systems level. For the first time, the feature of the drug-target-pathway-organ-cooperations for treatment of multiple organ diseases in holistic medicine was revealed, facilitating the development of novel treatment paradigm for complex diseases in the future.

Circulating Pneumolysin Is a Potent Inducer of Cardiac Injury during Pneumococcal Infection

Streptococcus pneumoniae accounts for more deaths worldwide than any other single pathogen through diverse disease manifestations including pneumonia, sepsis and meningitis. Life-threatening acute cardiac complications are more common in pneumococcal infection compared to other bacterial infections. Distinctively, these arise despite effective antibiotic therapy. Here, we describe a novel mechanism of myocardial injury, which is triggered and sustained by circulating pneumolysin (PLY). Using a mouse model of invasive pneumococcal disease (IPD), we demonstrate that wild type PLY-expressing pneumococci but not PLY-deficient mutants induced elevation of circulating cardiac troponins (cTns), well-recognized biomarkers of cardiac injury. Furthermore, elevated cTn levels linearly correlated with pneumococcal blood counts (r=0.688, p=0.001) and levels were significantly higher in non-surviving than in surviving mice. These cTn levels were significantly reduced by administration of PLY-sequestering liposomes. Intravenous injection of purified PLY, but not a non-pore forming mutant (PdB), induced substantial increase in cardiac troponins to suggest that the pore-forming activity of circulating PLY is essential for myocardial injury in vivo. Purified PLY and PLY-expressing pneumococci also caused myocardial inflammatory changes but apoptosis was not detected. Exposure of cultured cardiomyocytes to PLY-expressing pneumococci caused dose-dependent cardiomyocyte contractile dysfunction and death, which was exacerbated by further PLY release following antibiotic treatment. We found that high PLY doses induced extensive cardiomyocyte lysis, but more interestingly, sub-lytic PLY concentrations triggered profound calcium influx and overload with subsequent membrane depolarization and progressive reduction in intracellular calcium transient amplitude, a key determinant of contractile force. This was coupled to activation of signalling pathways commonly associated with cardiac dysfunction in clinical and experimental sepsis and ultimately resulted in depressed cardiomyocyte contractile performance along with rhythm disturbance. Our study proposes a detailed molecular mechanism of pneumococcal toxin-induced cardiac injury and highlights the major translational potential of targeting circulating PLY to protect against cardiac complications during pneumococcal infections.

The atypical 'b' splice variant of phospholipase Cβ1 promotes cardiac contractile dysfunction

The activity of the early signaling enzyme, phospholipase Cβ1b (PLCβ1b), is selectively elevated in diseased myocardium and activity increases with disease progression. We aimed to establish the contribution of heightened PLCβ1b activity to cardiac pathology. PLCβ1b, the alternative splice variant, PLCβ1a, and a blank virus were expressed in mouse hearts using adeno-associated viral vectors (rAAV6-FLAG-PLCβ1b, rAAV6-FLAG-PLCβ1a, or rAAV6-blank) delivered intravenously (IV). Following viral delivery, FLAG-PLCβ1b was expressed in all of the chambers of the mouse heart and was localized to the sarcolemma. Heightened PLCβ1b expression caused a rapid loss of contractility, 4-6 weeks, that was fully reversed, within 5 days, by inhibition of protein kinase Cα (PKCα). PLCβ1a did not localize to the sarcolemma and did not affect contractile function. Expression of PLCβ1b, but not PLCβ1a, caused downstream dephosphorylation of phospholamban and depletion of the Ca(2+) stores of the sarcoplasmic reticulum. We conclude that heightened PLCβ1b activity observed in diseased myocardium contributes to pathology by PKCα-mediated contractile dysfunction. PLCβ1b is a cardiac-specific signaling system, and thus provides a potential therapeutic target for the development of well-tolerated inotropic agents for use in failing myocardium.

Combined cardiomyocyte PKCδ and PKCε gene deletion uncovers their central role in restraining developmental and reactive heart growth

Cell growth is orchestrated by changes in gene expression that respond to developmental and environmental cues. Among the signaling pathways that direct growth are enzymes of the protein kinase C (PKC) family, which are ubiquitous proteins belonging to three distinct subclasses: conventional PKCs, novel PKCs, and atypical PKCs. Functional overlap makes determining the physiological actions of different PKC isoforms difficult. We showed that two novel PKC isoforms, PKCδ and PKCε, redundantly govern stress-reactive and developmental heart growth by modulating the expression of cardiac genes central to stress-activated protein kinase and periostin signaling. Mice with combined postnatal cardiomyocyte-specific genetic ablation of PKCδ and germline deletion of PKCε (DCKO) had normally sized hearts, but their hearts had transcriptional changes typical of pathological hypertrophy. Cardiac hypertrophy and dysfunction induced by hemodynamic overloading were greater in DCKO mice than in mice with a single deletion of either PKCδ or PKCε. Furthermore, gene expression analysis of the hearts of DCKO mice revealed transcriptional derepression of the genes encoding the kinase ERK (extracellular signal-regulated kinase) and periostin. Mice with combined embryonic ablation of PKCδ and PKCε showed enhanced growth and cardiomyocyte hyperplasia that induced pathological ventricular stiffening and early lethality, phenotypes absent in mice with a single deletion of PKCδ or PKCε. Our results indicate that novel PKCs provide retrograde feedback inhibition of growth signaling pathways central to cardiac development and stress adaptation. These growth-suppressing effects of novel PKCs have implications for therapeutic inhibition of PKCs in cancer, heart, and other diseases.

mTORC2 regulates cardiac response to stress by inhibiting MST1

The mTOR and Hippo pathways have recently emerged as the major signaling transduction cascades regulating organ size and cellular homeostasis. However, direct crosstalk between two pathways is yet to be determined. Here, we demonstrate that mTORC2 is a direct negative regulator of the MST1 kinase, a key component of the Hippo pathway. mTORC2 phosphorylates MST1 at serine 438 in the SARAH domain, thereby reducing its homodimerization and activity. We found that Rictor/mTORC2 preserves cardiac structure and function by restraining the activity of MST1 kinase. Cardiac-specific mTORC2 disruption through Rictor deletion leads to a marked activation of MST1 that, in turn, promotes cardiac dysfunction and dilation, impairing cardiac growth and adaptation in response to pressure overload. In conclusion, our study demonstrates the existence of a direct crosstalk between mTORC2 and MST1 that is critical for cardiac cell survival and growth.

Activation of protein kinase C-α and Src kinase increases urea transporter A1 α-2, 6 sialylation

The urea transporter A1 (UT-A1) is a glycosylated protein with two glycoforms: 117 and 97 kD. In diabetes, the increased abundance of the heavily glycosylated 117-kD UT-A1 corresponds to an increase of kidney tubule urea permeability. We previously reported that diabetes not only causes an increase of UT-A1 protein abundance but also, results in UT-A1 glycan changes, including an increase of sialic acid content. Because activation of the diacylglycerol (DAG)-protein kinase C (PKC) pathway is elevated in diabetes and PKC-α regulates UT-A1 urea transport activity, we explored the role of PKC in UT-A1 glycan sialylation. We found that activation of PKC specifically promotes UT-A1 glycan sialylation in both UT-A1-MDCK cells and rat kidney inner medullary collecting duct suspensions, and inhibition of PKC activity blocks high glucose-induced UT-A1 sialylation. Overexpression of PKC-α promoted UT-A1 sialylation and membrane surface expression. Conversely, PKC-α-deficient mice had significantly less sialylated UT-A1 compared with wild-type mice. Furthermore, the effect of PKC-α-induced UT-A1 sialylation was mainly mediated by Src kinase but not Raf-1 kinase. Functionally, increased UT-A1 sialylation corresponded with enhanced urea transport activity. Thus, our results reveal a novel mechanism by which PKC regulates UT-A1 function by increasing glycan sialylation through Src kinase pathways, which may have an important role in preventing the osmotic diuresis caused by glucosuria under diabetic conditions.

Myocardial stiffness in patients with heart failure and a preserved ejection fraction: contributions of collagen and titin

BACKGROUND

The purpose of this study was to determine whether patients with heart failure and a preserved ejection fraction (HFpEF) have an increase in passive myocardial stiffness and the extent to which discovered changes depend on changes in extracellular matrix fibrillar collagen and cardiomyocyte titin.

METHODS AND RESULTS

Seventy patients undergoing coronary artery bypass grafting underwent an echocardiogram, plasma biomarker determination, and intraoperative left ventricular epicardial anterior wall biopsy. Patients were divided into 3 groups: referent control (n=17, no hypertension or diabetes mellitus), hypertension (HTN) without (-) HFpEF (n=31), and HTN with (+) HFpEF (n=22). One or more of the following studies were performed on the biopsies: passive stiffness measurements to determine total, collagen-dependent and titin-dependent stiffness (differential extraction assay), collagen assays (biochemistry or histology), or titin isoform and phosphorylation assays. In comparison with controls, patients with HTN(-)HFpEF had no change in left ventricular end-diastolic pressure, myocardial passive stiffness, collagen, or titin phosphorylation but had an increase in biomarkers of inflammation (C-reactive protein, soluble ST2, tissue inhibitor of metalloproteinase 1). In comparison with both control and HTN(-)HFpEF, patients with HTN(+)HFpEF had increased left ventricular end-diastolic pressure, left atrial volume, N-terminal propeptide of brain natriuretic peptide, total, collagen-dependent, and titin-dependent stiffness, insoluble collagen, increased titin phosphorylation on PEVK S11878(S26), reduced phosphorylation on N2B S4185(S469), and increased biomarkers of inflammation.

CONCLUSIONS

Hypertension in the absence of HFpEF did not alter passive myocardial stiffness. Patients with HTN(+)HFpEF had a significant increase in passive myocardial stiffness; collagen-dependent and titin-dependent stiffness were increased. These data suggest that the development of HFpEF depends on changes in both collagen and titin homeostasis.

Expression and purification of the N-terminal regulatory domain of Protein Kinase C for biophysical studies

We report the protocol for heterologous expression and purification of the N-terminal regulatory region of two Protein Kinase C (PKC)(1) isozymes, one conventional and one novel. Previous studies of these domains relied almost exclusively on the fusion constructs with high-molecular-weight solubility fusion partners such as GST and MBP. We developed experimental procedures that enabled us to overcome challenges associated with the amphiphilic character of the regulatory domain and generate sufficient quantities of fusion partner-free proteins for biophysical work. The key features of the protocol are the identity of the cleavable fusion partner, expression conditions, growth medium additives, introduction of mutation/solubility tags, and incorporation of osmolytes. The protein yields are sufficient for cost-effective production of isotopically enriched proteins for NMR work and biophysical studies in general. Our work opens up an avenue for the structural studies of these challenging proteins with high amphiphilic character.

Can lercanidipine improve renal function in patients with atherosclerotic renal artery stenosis undergoing renal artery intervention?

OBJECTIVE

To investigate the renal-protective effect of lercanidipine in patients undergoing renal artery intervention.

METHODS

A prospective, single-center, cohort study was conducted and patients, 30-75 years of age, with atherosclerotic renal artery stenosis were consecutively enrolled between September 2011 and October 2012. Lercanidipine (10-20 mg/day) was regularly taken after the intervention. Follow up visits were performed at 3 and 6 months after the intervention. Serum creatinine, clinical blood pressure, 24 hour ambulatory blood pressure, pulse wave velocity, and 24 hour urine protein were assessed. Adverse events were recorded.

RESULTS

In total, 55 patients (mean age 63.5 ± 8.9 years) were enrolled and 52 completed the study. Renal function, estimated glomerular filtration rate (eGFR) and 24 hour urine protein at 3 months after the intervention were not statistically different compared with the baseline. At 6 months after the intervention eGFR significantly increased versus baseline (78 ± 23 ml/min/1.73 m(2) vs 71 ± 21 ml/min/1.73 m(2), p = 0.021); 24 hour urine protein decreased significantly (0.02 g [IQR, 0.01-0.1] vs 0.03 g [IQR, 0.01-0.28], p = 0.042). Blood pressure control improved at 3 months and 6 months after the intervention. The need for antihypertensive drugs decreased; clinical systolic blood pressure, diastolic blood pressure and 24 hour average systolic blood pressure and diastolic blood pressure decreased. The pulse wave velocity decreased after 3 and 6 months. At the end of follow-up, none of the following adverse events occurred: death, dialysis, myocardial infarction or stroke. Mild lower extremity edema occurred in only one patient. No other side effects occurred.

CONCLUSIONS

This study showed that lercanidipine can improve renal function in patients undergoing renal artery intervention.

Impaired IKs channel activation by Ca(2+)-dependent PKC shows correlation with emotion/arousal-triggered events in LQT1

BACKGROUND

The most common inherited cardiac arrhythmia, LQT1, is due to IKs potassium channel mutations and is linked to high risk of adrenergic-triggered cardiac events. We recently showed that although exercise-triggered events are very well treated by ß-blockers for these patients, acute arousal-triggered event rate were not significantly reduced after beta-blocker treatment, suggesting that the mechanisms underlying arousal-triggered arrhythmias may be different from those during exercise. IKs is strongly regulated by β-adrenergic receptor (β-AR) signaling, but little is known about the role of α1-AR-mediated regulation.

METHODS AND RESULTS

Here we show, using a combination of cellular electrophysiology and computational modeling, that IKs phosphorylation and α1-AR regulation via activation of calcium-dependent PKC isoforms (cPKC) may be a key mechanism to control channel voltage-dependent activation and consequently action potential duration (APD) in response to adrenergic-stimulus. We show that simulated mutation-specific combined adrenergic effects (β+α) on APD were strongly correlated to acute stress-triggered cardiac event rate for patients while β-AR effects alone were not.

CONCLUSION

We were able to show that calcium-dependent PKC signaling is key to normal QT shortening during acute arousal and when impaired, correlates with increased rate of sudden arousal-triggered cardiac events. Our study suggests that the acute α1-AR-cPKC regulation of IKs is important for QT shortening in "fight-or-flight" response and is linked to decreased risk of sudden emotion/arousal-triggered cardiac events in LQT1 patients.

Alpha-1-adrenergic receptors in heart failure: the adaptive arm of the cardiac response to chronic catecholamine stimulation

Alpha-1-adrenergic receptors (ARs) are G protein-coupled receptors activated by catecholamines. The alpha-1A and alpha-1B subtypes are expressed in mouse and human myocardium, whereas the alpha-1D protein is found only in coronary arteries. There are far fewer alpha-1-ARs than beta-ARs in the nonfailing heart, but their abundance is maintained or increased in the setting of heart failure, which is characterized by pronounced chronic elevation of catecholamines and beta-AR dysfunction. Decades of evidence from gain and loss-of-function studies in isolated cardiac myocytes and numerous animal models demonstrate important adaptive functions for cardiac alpha-1-ARs to include physiological hypertrophy, positive inotropy, ischemic preconditioning, and protection from cell death. Clinical trial data indicate that blocking alpha-1-ARs is associated with incident heart failure in patients with hypertension. Collectively, these findings suggest that alpha-1-AR activation might mitigate the well-recognized toxic effects of beta-ARs in the hyperadrenergic setting of chronic heart failure. Thus, exogenous cardioselective activation of alpha-1-ARs might represent a novel and viable approach to the treatment of heart failure.

Nuclear localization of a1A-adrenergic receptors is required for signaling in cardiac myocytes: an “inside-out” a1-AR signaling pathway

Background

Recent studies indicate that α1‐adrenergic receptors (α1‐ARs) are cardioprotective by preventing cardiac myocyte death and augmenting contractility in heart failure. Although G‐protein‐coupled receptors are assumed to localize to and signal at the plasma membrane, we previously demonstrated that endogenous α1‐ARs localize to the nuclei in adult cardiac myocytes. However, the functional consequence of this nuclear localization remains unclear. Here, we attempted to reconcile nuclear localization of α1‐ARs with their physiologic function by examining α1‐AR‐induced contractility in adult cardiac myocytes.

Methods and Results

By measuring shortening in unloaded, cultured adult cardiac myocytes, we found that the α1A‐subtype regulated contractility through phosphorylation of cardiac troponin I (cTnI) at the protein kinase C (PKC) site, threonine 144. Reconstitution of an α1A‐subtype nuclear localization mutant in cardiac myocytes lacking α1‐ARs failed to rescue nuclear α1A‐mediated phosphorylation of cTnI and myocyte contractility. Leptomycin B, the nuclear export inhibitor, also blocked α1A‐mediated phosphorylation of cTnI. These data indicate that α1‐AR signaling originates in the nucleus. Consistent with these observations, we localized the α1A‐subtype to the inner nuclear membrane, identified PKCα, δ, and ε in the nucleus, and found that α1‐ARs activate PKCδ in nuclei isolated from adult cardiac myocytes. Finally, we found that a PKCδ nuclear localization mutant blunted α1‐induced phosphorylation of cTnI.

Conclusions

Together, our data identify a novel, “inside‐out” nuclear α1A‐subtype/PKCδ/cTnI‐signaling pathway that regulates contractile function in adult cardiac myocytes. Importantly, these data help resolve the discrepancy between nuclear localization of α1‐ARs and α1‐AR‐mediated physiologic function.

Defects in T-tubular electrical activity underlie local alterations of calcium release in heart failure

Action potentials (APs), via the transverse axial tubular system (TATS), synchronously trigger uniform Ca(2+) release throughout the cardiomyocyte. In heart failure (HF), TATS structural remodeling occurs, leading to asynchronous Ca(2+) release across the myocyte and contributing to contractile dysfunction. In cardiomyocytes from failing rat hearts, we previously documented the presence of TATS elements which failed to propagate AP and displayed spontaneous electrical activity; the consequence for Ca(2+) release remained, however, unsolved. Here, we develop an imaging method to simultaneously assess TATS electrical activity and local Ca(2+) release. In HF cardiomyocytes, sites where T-tubules fail to conduct AP show a slower and reduced local Ca(2+) transient compared with regions with electrically coupled elements. It is concluded that TATS electrical remodeling is a major determinant of altered kinetics, amplitude, and homogeneity of Ca(2+) release in HF. Moreover, spontaneous depolarization events occurring in failing T-tubules can trigger local Ca(2+) release, resulting in Ca(2+) sparks. The occurrence of tubule-driven depolarizations and Ca(2+) sparks may contribute to the arrhythmic burden in heart failure.

Effect of Diabetes Mellitus and Its Control on Myocardial Contractile Function in Rats

AIM: This work was done to study the effect of both types of diabetes mellitus (DM) on myocardial contractility in rats. Also, we investigated the role of treatment of DM with insulin and rosiglitazone (used as treatment for type 1 and type 2 DM respectively) in improvement of myocardial dysfunction in diabetic rats.METHODS: The study included 50 male Wistar albino rats, divided into 5 groups: control (group I), streptozotocin induced type 1 DM (group II), fructose induced type 2 DM (group III), insulin treated type 1 diabetic rats (group IV) and rosiglitazone treated type 2 diabetic rats (group V). At the end of the study, retro-orbital blood samples were withdrawn and blood glucose, plasma triglyceride (TG), total cholesterol (TC) and thyroid hormones levels were measured. Rats were then anesthetized and their hearts were excised and connected to Langendorff apparatus to perform mechanical cardiac performance tests including heart rate (HR), left ventricular developed pressure (LVDP) and maximum rate of pressure rise (+dp/dt).RESULTS: Data of the study showed that relative to control group, there was significant increase in blood glucose, plasma TG and TC levels while, thyroid hormones and myocardial performance parameters showed significant decrease in both type 1 and type 2 diabetic rats. Treatment of type 1 diabetic rats with insulin and type 2 with rosiglitazone resulted in significant decrease in blood glucose, plasma TG and TC levels associated with significant improvement in thyroid hormones and myocardial performance parameters. The results also showed that insulin treatment of type 1 was more effective in ameliorating all parameters than treatment of type 2 by rosiglitazone.CONCLUSION: We concluded that the induction of both types of diabetes resulted in decreased myocardial performance parameters. The  treatment of type 1 and type 2 diabetes by insulin and oral rosiglitazone respectively improved to a great extent the altered metabolism and  mechanical myocardial parameters, with more improving effect of  insulin in type 1 than rosiglitazone in type 2 DM.

Cardiomyocyte-specific loss of diacylglycerol acyltransferase 1 (DGAT1) reproduces the abnormalities in lipids found in severe heart failure

Diacylglycerol acyltransferase 1 (DGAT1) catalyzes the final step in triglyceride synthesis, the conversion of diacylglycerol (DAG) to triglyceride. Dgat1(-/-) mice exhibit a number of beneficial metabolic effects including reduced obesity and improved insulin sensitivity and no known cardiac dysfunction. In contrast, failing human hearts have severely reduced DGAT1 expression associated with accumulation of DAGs and ceramides. To test whether DGAT1 loss alone affects heart function, we created cardiomyocyte-specific DGAT1 knock-out (hDgat1(-/-)) mice. hDgat1(-/-) mouse hearts had 95% increased DAG and 85% increased ceramides compared with floxed controls. 50% of these mice died by 9 months of age. The heart failure marker brain natriuretic peptide increased 5-fold in hDgat1(-/-) hearts, and fractional shortening (FS) was reduced. This was associated with increased expression of peroxisome proliferator-activated receptor α and cluster of differentiation 36. We crossed hDgat1(-/-) mice with previously described enterocyte-specific Dgat1 knock-out mice (hiDgat1(-/-)). This corrected the early mortality, improved FS, and reduced cardiac ceramide and DAG content. Treatment of hDgat1(-/-) mice with the glucagon-like peptide 1 receptor agonist exenatide also improved FS and reduced heart DAG and ceramide content. Increased fatty acid uptake into hDgat1(-/-) hearts was normalized by exenatide. Reduced activation of protein kinase Cα (PKCα), which is increased by DAG and ceramides, paralleled the reductions in these lipids. Our mouse studies show that loss of DGAT1 reproduces the lipid abnormalities seen in severe human heart failure.

Aliskiren ameliorates pressure overload-induced heart hypertrophy and fibrosis in mice

AIM

Aliskiren (ALK) is a renin inhibitor that has been used in the treatment of hypertension. The aim of this study was to determine whether ALK could ameliorate pressure overload-induced heart hypertrophy and fibrosis, and to elucidate the mechanisms of action.

METHODS

Transverse aortic constriction (TAC) was performed in mice to induce heart pressure overload. ALK (150 mg·kg(-1)·d(-1), po), the autophagy inhibitor 3-methyladenine (10 mg·kg(-1) per week, ip) or the PKCβI inhibitor LY333531 (1 mg·kg(-1)·d-(1), po) was administered to the mice for 4 weeks. Heart hypertrophy, fibrosis and function were evaluated based on echocardiography, histological and biochemical measurements. Mechanically stretched cardiomyocytes of rats were used for in vitro experiments. The levels of signaling proteins were measured using Western blotting, while the expression of the relevant genes was analyzed using real-time QRT-PCR.

RESULTS

TAC induced marked heart hypertrophy and fibrosis, accompanied by high levels of Ang II in plasma and heart, and by PKCβI/α and ERK1/2 phosphorylation in heart. Meanwhile, TAC induced autophagic responses in heart, i.e. increases in autophagic structures, expression of Atg5 and Atg16 L1 mRNAs and LC3-II and Beclin-1 proteins. These pathological alterations in TAC-mice were significantly ameliorated or blocked by ALK administration. In TAC-mice, 3-methyladenine administration also ameliorated heart hypertrophy, fibrosis and dysfunction, while LY333531 administration inhibited ERK phosphorylation and autophagy in heart. In mechanically stretched cardiomyocytes, CGP53353 (a PKCβI inhibitor) prevented ERK phosphorylation and autophagic responses, while U0126 (an ERK inhibitor) blocked autophagic responses.

CONCLUSION

ALK ameliorates heart hypertrophy, fibrosis and dysfunction in the mouse model in setting of chronic pressure overload, via suppressing Ang II-PKCβI-ERK1/2-regulated autophagy.

Protein kinase Cα (PKCα) regulates bone architecture and osteoblast activity

Bones' strength is achieved and maintained through adaptation to load bearing. The role of the protein kinase PKCα in this process has not been previously reported. However, we observed a phenotype in the long bones of Prkca^−/− female but not male mice, in which bone tissue progressively invades the medullary cavity in the mid-diaphysis. This bone deposition progresses with age and is prevented by disuse but unaffected by ovariectomy. Castration of male Prkca^−/− but not WT mice results in the formation of small amounts of intramedullary bone. Osteoblast differentiation markers and Wnt target gene expression were up-regulated in osteoblast-like cells derived from cortical bone of female Prkca^−/− mice compared with WT. Additionally, although osteoblastic cells derived from WT proliferate following exposure to estradiol or mechanical strain, those from Prkca^−/− mice do not. Female Prkca^−/− mice develop splenomegaly and reduced marrow GBA1 expression reminiscent of Gaucher disease, in which PKC involvement has been suggested previously. From these data, we infer that in female mice, PKCα normally serves to prevent endosteal bone formation stimulated by load bearing. This phenotype appears to be suppressed by testicular hormones in male Prkca^−/− mice. Within osteoblastic cells, PKCα enhances proliferation and suppresses differentiation, and this regulation involves the Wnt pathway. These findings implicate PKCα as a target gene for therapeutic approaches in low bone mass conditions.

Absence of PKC-alpha attenuates lithium-induced nephrogenic diabetes insipidus

Lithium, an effective antipsychotic, induces nephrogenic diabetes insipidus (NDI) in ∼40% of patients. The decreased capacity to concentrate urine is likely due to lithium acutely disrupting the cAMP pathway and chronically reducing urea transporter (UT-A1) and water channel (AQP2) expression in the inner medulla. Targeting an alternative signaling pathway, such as PKC-mediated signaling, may be an effective method of treating lithium-induced polyuria. PKC-alpha null mice (PKCα KO) and strain-matched wild type (WT) controls were treated with lithium for 0, 3 or 5 days. WT mice had increased urine output and lowered urine osmolality after 3 and 5 days of treatment whereas PKCα KO mice had no change in urine output or concentration. Western blot analysis revealed that AQP2 expression in medullary tissues was lowered after 3 and 5 days in WT mice; however, AQP2 was unchanged in PKCα KO. Similar results were observed with UT-A1 expression. Animals were also treated with lithium for 6 weeks. Lithium-treated WT mice had 19-fold increased urine output whereas treated PKCα KO animals had a 4-fold increase in output. AQP2 and UT-A1 expression was lowered in 6 week lithium-treated WT animals whereas in treated PKCα KO mice, AQP2 was only reduced by 2-fold and UT-A1 expression was unaffected. Urinary sodium, potassium and calcium were elevated in lithium-fed WT but not in lithium-fed PKCα KO mice. Our data show that ablation of PKCα preserves AQP2 and UT-A1 protein expression and localization in lithium-induced NDI, and prevents the development of the severe polyuria associated with lithium therapy.

Genetic association study of QT interval highlights role for calcium signaling pathways in myocardial repolarization

The QT interval, an electrocardiographic measure reflecting myocardial repolarization, is a heritable trait. QT prolongation is a risk factor for ventricular arrhythmias and sudden cardiac death (SCD) and could indicate the presence of the potentially lethal Mendelian Long QT Syndrome (LQTS). Using a genome-wide association and replication study in up to 100,000 individuals we identified 35 common variant QT interval loci, that collectively explain ∼8-10% of QT variation and highlight the importance of calcium regulation in myocardial repolarization. Rare variant analysis of 6 novel QT loci in 298 unrelated LQTS probands identified coding variants not found in controls but of uncertain causality and therefore requiring validation. Several newly identified loci encode for proteins that physically interact with other recognized repolarization proteins. Our integration of common variant association, expression and orthogonal protein-protein interaction screens provides new insights into cardiac electrophysiology and identifies novel candidate genes for ventricular arrhythmias, LQTS,and SCD.

RhoA/ROCK signaling and pleiotropic α1A-adrenergic receptor regulation of cardiac contractility

Aims

To determine the mechanisms by which the α_1A-adrenergic receptor (AR) regulates cardiac contractility.

Background

We reported previously that transgenic mice with cardiac-restricted α_1A-AR overexpression (α_1A-TG) exhibit enhanced contractility but not hypertrophy, despite evidence implicating this Gα_q/11-coupled receptor in hypertrophy.

Methods

Contractility, calcium (Ca²⁺) kinetics and sensitivity, and contractile proteins were examined in cardiomyocytes, isolated hearts and skinned fibers from α_1A-TG mice (170-fold overexpression) and their non-TG littermates (NTL) before and after α_1A-AR agonist stimulation and blockade, angiotensin II (AngII), and Rho kinase (ROCK) inhibition.

Results

Hypercontractility without hypertrophy with α_1A-AR overexpression is shown to result from increased intracellular Ca²⁺ release in response to agonist, augmenting the systolic amplitude of the intracellular Ca²⁺ concentration [Ca²⁺]_i transient without changing resting [Ca²⁺]_i. In the absence of agonist, however, α_1A-AR overexpression reduced contractility despite unchanged [Ca²⁺]_i. This hypocontractility is not due to heterologous desensitization: the contractile response to AngII, acting via its Gα_q/11-coupled receptor, was unaltered. Rather, the hypocontractility is a pleiotropic signaling effect of the α_1A-AR in the absence of agonist, inhibiting RhoA/ROCK activity, resulting in hypophosphorylation of both myosin phosphatase targeting subunit 1 (MYPT1) and cardiac myosin light chain 2 (cMLC2), reducing the Ca²⁺ sensitivity of the contractile machinery: all these effects were rapidly reversed by selective α_1A-AR blockade. Critically, ROCK inhibition in normal hearts of NTLs without α_1A-AR overexpression caused hypophosphorylation of both MYPT1 and cMLC2, and rapidly reduced basal contractility.

Conclusions

We report for the first time pleiotropic α_1A-AR signaling and the physiological role of RhoA/ROCK signaling in maintaining contractility in the normal heart.

PDE5 inhibitor efficacy is estrogen dependent in female heart disease

Inhibition of cGMP-specific phosphodiesterase 5 (PDE5) ameliorates pathological cardiac remodeling and has been gaining attention as a potential therapy for heart failure. Despite promising results in males, the efficacy of the PDE5 inhibitor sildenafil in female cardiac pathologies has not been determined and might be affected by estrogen levels, given the hormone's involvement in cGMP synthesis. Here, we determined that the heart-protective effect of sildenafil in female mice depends on the presence of estrogen via a mechanism that involves myocyte eNOS-dependent cGMP synthesis and the cGMP-dependent protein kinase Iα (PKGIα). Sildenafil treatment failed to exert antiremodeling properties in female pathological hearts from Gαq-overexpressing or pressure-overloaded mice after ovary removal; however, estrogen replacement restored the effectiveness of sildenafil in these animals. In females, sildenafil-elicited myocardial PKG activity required estrogen, which stimulated tonic cardiomyocyte cGMP synthesis via an eNOS/soluble guanylate cyclase pathway. In contrast, eNOS activation, cGMP synthesis, and sildenafil efficacy were not estrogen dependent in male hearts. Estrogen and sildenafil had no impact on pressure-overloaded hearts from animals expressing dysfunctional PKGIα, indicating that PKGIα mediates antiremodeling effects. These results support the importance of sex differences in the use of PDE5 inhibitors for treating heart disease and the critical role of estrogen status when these agents are used in females.

Simultaneous loss of phospholipase Cδ1 and phospholipase Cδ3 causes cardiomyocyte apoptosis and cardiomyopathy

Phospholipase C (PLC) is a key enzyme in phosphoinositide turnover. Among 13 PLC isozymes, PLCδ1 and PLCδ3 share high sequence homology and similar tissue distribution, and are expected to have functional redundancy in many tissues. We previously reported that the simultaneous loss of PLCδ1 and PLCδ3 caused embryonic lethality because of excessive apoptosis and impaired vascularization of the placenta. Prenatal death of PLCδ1/PLCδ3 double-knockout mice hampered our investigation of the roles of these genes in adult animals. Here, we generated PLCδ1/PLCδ3 double-knockout mice that expressed PLCδ1 in extra-embryonic tissues (cDKO mice) to escape embryonic lethality. The cDKO mice were born at the expected Mendelian ratio, which indicated that the simultaneous loss of PLCδ1 and PLCδ3 in the embryo proper did not impair embryonic development. However, half of the cDKO mice died prematurely. In addition, the surviving cDKO mice spontaneously showed cardiac abnormalities, such as increased heart weight/tibial length ratios, impaired cardiac function, cardiac fibrosis, dilation, and hypertrophy. Predating these abnormalities, excessive apoptosis of their cardiomyocytes was observed. In addition, siRNA-mediated simultaneous silencing of PLCδ1 and PLCδ3 increased apoptosis in differentiated-H9c2 cardiomyoblasts. Activation of Akt and protein kinase C (PKC) θ was impaired in the hearts of the cDKO mice. siRNA-mediated simultaneous silencing of PLCδ1 and PLCδ3 also decreased activated Akt and PKCθ in differentiated-H9c2 cardiomyoblasts. These results indicate that PLCδ1 and PLCδ3 are required for cardiomyocyte survival and normal cardiac function.

Myostatin regulates energy homeostasis in the heart and prevents heart failure

RATIONALE

Myostatin is a major negative regulator of skeletal muscle mass and initiates multiple metabolic changes, including enhanced insulin sensitivity. However, the function of myostatin in the heart is barely understood, although it is upregulated in the myocardium under several pathological conditions.

OBJECTIVE

Here, we aimed to decipher the role of myostatin and myostatin-dependent signaling pathways for cardiac function and cardiac metabolism in adult mice. To avoid potential counterregulatory mechanisms occurring in constitutive and germ-line-based myostatin mutants, we generated a mouse model that allows myostatin inactivation in adult cardiomyocytes.

METHODS AND RESULTS

Cardiac MRI revealed that genetic inactivation of myostatin signaling in the adult murine heart caused cardiac hypertrophy and heart failure, partially recapitulating effects of the age-dependent decline of the myostatin paralog growth and differentiation factor 11. We found that myostatin represses AMP-activated kinase activation in the heart via transforming growth factor-β-activated kinase 1, thereby preventing a metabolic switch toward glycolysis and glycogen accumulation. Furthermore, myostatin stimulated expression of regulator of G-protein signaling 2, a GTPase-activating protein that restricts Gaq and Gas signaling and thereby protects against cardiac failure. Inhibition of AMP-activated kinase in vivo rescued cardiac hypertrophy and prevented enhanced glycolytic flow and glycogen accumulation after inactivation of myostatin in cardiomyocytes.

CONCLUSIONS

Our results uncover an important role of myostatin in the heart for maintaining cardiac energy homeostasis and preventing cardiac hypertrophy.

Gene therapy for heart disease: molecular targets, vectors and modes of delivery to myocardium

Despite the numerous hurdles that gene therapy has encountered along the way, clinical trials over the last few years are showing promising results in many fields of medicine, including cardiology, where many targets are moving toward clinical development. In this review, the authors discuss the current state of the art in terms of clinical and preclinical development. They also examine vector technology and available vector-delivery strategies.

Epac1-dependent phospholamban phosphorylation mediates the cardiac response to stresses

PKA phosphorylates multiple molecules involved in calcium (Ca2+) handling in cardiac myocytes and is considered to be the predominant regulator of β-adrenergic receptor-mediated enhancement of cardiac contractility; however, recent identification of exchange protein activated by cAMP (EPAC), which is independently activated by cAMP, has challenged this paradigm. Mice lacking Epac1 (Epac1 KO) exhibited decreased cardiac contractility with reduced phospholamban (PLN) phosphorylation at serine-16, the major PKA-mediated phosphorylation site. In Epac1 KO mice, intracellular Ca2+ storage and the magnitude of Ca2+ movement were decreased; however, PKA expression remained unchanged, and activation of PKA with isoproterenol improved cardiac contractility. In contrast, direct activation of EPAC in cardiomyocytes led to increased PLN phosphorylation at serine-16, which was dependent on PLC and PKCε. Importantly, Epac1 deletion protected the heart from various stresses, while Epac2 deletion was not protective. Compared with WT mice, aortic banding induced a similar degree of cardiac hypertrophy in Epac1 KO; however, lack of Epac1 prevented subsequent cardiac dysfunction as a result of decreased cardiac myocyte apoptosis and fibrosis. Similarly, Epac1 KO animals showed resistance to isoproterenol- and aging-induced cardiomyopathy and attenuation of arrhythmogenic activity. These data support Epac1 as an important regulator of PKA-independent PLN phosphorylation and indicate that Epac1 regulates cardiac responsiveness to various stresses.

Apelin increases cardiac contractility via protein kinase Cε- and extracellular signal-regulated kinase-dependent mechanisms

Background

Apelin, the endogenous ligand for the G protein-coupled apelin receptor, is an important regulator of the cardiovascular homoeostasis. We previously demonstrated that apelin is one of the most potent endogenous stimulators of cardiac contractility; however, its underlying signaling mechanisms remain largely elusive. In this study we characterized the contribution of protein kinase C (PKC), extracellular signal-regulated kinase 1/2 (ERK1/2) and myosin light chain kinase (MLCK) to the positive inotropic effect of apelin.

Methods and Results

In isolated perfused rat hearts, apelin increased contractility in association with activation of prosurvival kinases PKC and ERK1/2. Apelin induced a transient increase in the translocation of PKCε, but not PKCα, from the cytosol to the particulate fraction, and a sustained increase in the phosphorylation of ERK1/2 in the left ventricle. Suppression of ERK1/2 activation diminished the apelin-induced increase in contractility. Although pharmacological inhibition of PKC attenuated the inotropic response to apelin, it had no effect on ERK1/2 phosphorylation. Moreover, the apelin-induced positive inotropic effect was significantly decreased by inhibition of MLCK, a kinase that increases myofilament Ca²⁺ sensitivity.

Conclusions

Apelin increases cardiac contractility through parallel and independent activation of PKCε and ERK1/2 signaling in the adult rat heart. Additionally MLCK activation represents a downstream mechanism in apelin signaling. Our data suggest that, in addition to their role in cytoprotection, modest activation of PKCε and ERK1/2 signaling improve contractile function, therefore these pathways represent attractive possible targets in the treatment of heart failure.

Mammalian target of rapamycin signaling in cardiac physiology and disease

The protein kinase mammalian or mechanistic target of rapamycin (mTOR) is an atypical serine/threonine kinase that exerts its main cellular functions by interacting with specific adaptor proteins to form 2 different multiprotein complexes, mTOR complex 1 (mTORC1) and mTOR complex 2 (mTORC2). mTORC1 regulates protein synthesis, cell growth and proliferation, autophagy, cell metabolism, and stress responses, whereas mTORC2 seems to regulate cell survival and polarity. The mTOR pathway plays a key regulatory function in cardiovascular physiology and pathology. However, the majority of information available about mTOR function in the cardiovascular system is related to the role of mTORC1 in the unstressed and stressed heart. mTORC1 is required for embryonic cardiovascular development and for postnatal maintenance of cardiac structure and function. In addition, mTORC1 is necessary for cardiac adaptation to pressure overload and development of compensatory hypertrophy. However, partial and selective pharmacological and genetic inhibition of mTORC1 was shown to extend life span in mammals, reduce pathological hypertrophy and heart failure caused by increased load or genetic cardiomyopathies, reduce myocardial damage after acute and chronic myocardial infarction, and reduce cardiac derangements caused by metabolic disorders. The optimal therapeutic strategy to target mTORC1 and increase cardioprotection is under intense investigation. This article reviews the information available regarding the effects exerted by mTOR signaling in cardiovascular physiology and pathological states.

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

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

Diabetic cardiomyopathy: mechanisms and new treatment strategies targeting antioxidant signaling pathways

Cardiovascular disease is the primary cause of morbidity and mortality among the diabetic population. Both experimental and clinical evidence suggest that diabetic subjects are predisposed to a distinct cardiomyopathy, independent of concomitant macro- and microvascular disorders. 'Diabetic cardiomyopathy' is characterized by early impairments in diastolic function, accompanied by the development of cardiomyocyte hypertrophy, myocardial fibrosis and cardiomyocyte apoptosis. The pathophysiology underlying diabetes-induced cardiac damage is complex and multifactorial, with elevated oxidative stress as a key contributor. We now review the current evidence of molecular disturbances present in the diabetic heart, and their role in the development of diabetes-induced impairments in myocardial function and structure. Our focus incorporates both the contribution of increased reactive oxygen species production and reduced antioxidant defenses to diabetic cardiomyopathy, together with modulation of protein signaling pathways and the emerging role of protein O-GlcNAcylation and miRNA dysregulation in the progression of diabetic heart disease. Lastly, we discuss both conventional and novel therapeutic approaches for the treatment of left ventricular dysfunction in diabetic patients, from inhibition of the renin-angiotensin-aldosterone-system, through recent evidence favoring supplementation of endogenous antioxidants for the treatment of diabetic cardiomyopathy. Novel therapeutic strategies, such as gene therapy targeting the phosphoinositide 3-kinase PI3K(p110α) signaling pathway, and miRNA dysregulation, are also reviewed. Targeting redox stress and protective protein signaling pathways may represent a future strategy for combating the ever-increasing incidence of heart failure in the diabetic population.

Gαq signalling: the new and the old

In the last few years the interactome of Gαq has expanded considerably, contributing to improve our understanding of the cellular and physiological events controlled by this G alpha subunit. The availability of high-resolution crystal structures has led the identification of an effector-binding region within the surface of Gαq that is able to recognise a variety of effector proteins. Consequently, it has been possible to ascribe different Gαq functions to specific cellular players and to identify important processes that are triggered independently of the canonical activation of phospholipase Cβ (PLCβ), the first identified Gαq effector. Novel effectors include p63RhoGEF, that provides a link between G protein-coupled receptors and RhoA activation, phosphatidylinositol 3-kinase (PI3K), implicated in the regulation of the Akt pathway, or the cold-activated TRPM8 channel, which is directly inhibited upon Gαq binding. Recently, the activation of ERK5 MAPK by Gq-coupled receptors has also been described as a novel PLCβ-independent signalling axis that relies upon the interaction between this G protein and two novel effectors (PKCζ and MEK5). Additionally, the association of Gαq with different regulatory proteins can modulate its effector coupling ability and, therefore, its signalling potential. Regulators include accessory proteins that facilitate effector activation or, alternatively, inhibitory proteins that downregulate effector binding or promote signal termination. Moreover, Gαq is known to interact with several components of the cytoskeleton as well as with important organisers of membrane microdomains, which suggests that efficient signalling complexes might be confined to specific subcellular environments. Overall, the complex interaction network of Gαq underlies an ever-expanding functional diversity that puts forward this G alpha subunit as a major player in the control of physiological functions and in the development of different pathological situations.

Somatostatin receptor-2 negatively regulates β-adrenergic receptor mediated Ca(2+) dependent signaling pathways in H9c2 cells

In the present study, we report that somatostatin receptor 2 (SSTR2) plays a crucial role in modulation of β1AR and β2AR mediated signaling pathways that are associated with increased intracellular Ca(2+) and cardiac complications. In H9c2 cells, SSTR2 colocalizes with β1AR or β2AR in receptor specific manner. SSTR2 selective agonist inhibits isoproterenol and formoterol stimulated cAMP formation and PKA phosphorylation in concentration dependent manner. In the presence of SSTR2 agonist, the expression of PKCα and PKCβ was comparable to the basal condition, however SSTR2 agonist inhibits isoproterenol or formoterol induced PKCα and PKCβ expression, respectively. Furthermore, the activation of SSTR2 not only inhibits calcineurin expression and its activity, but also blocks NFAT dephosphorylation and its nuclear translocation. SSTR2 selective agonist abrogates isoproterenol mediated increase in cell size and protein content (an index of hypertrophy). Taken together, the results described here provide direct evidence in support of cardiac protective role of SSTR2 via modulation of Ca(2+) associated signaling pathways attributed to cardiac hypertrophy.

Mouse models of heart failure: cell signaling and cell survival

Heart failure is one of the paramount global causes of morbidity and mortality. Despite this pandemic need, the available clinical counter-measures have not altered substantially in recent decades, most notably in the context of pharmacological interventions. Cell death plays a causal role in heart failure, and its inhibition poses a promising approach that has not been thoroughly explored. In previous approaches to target discovery, clinical failures have reflected a deficiency in mechanistic understanding, and in some instances, failure to systematically translate laboratory findings toward the clinic. Here, we review diverse mouse models of heart failure, with an emphasis on those that identify potential targets for pharmacological inhibition of cell death, and on how their translation into effective therapies might be improved in the future.

Cardiac alpha1-adrenergic receptors: novel aspects of expression, signaling mechanisms, physiologic function, and clinical importance

Adrenergic receptors (AR) are G-protein-coupled receptors (GPCRs) that have a crucial role in cardiac physiology in health and disease. Alpha1-ARs signal through Gαq, and signaling through Gq, for example, by endothelin and angiotensin receptors, is thought to be detrimental to the heart. In contrast, cardiac alpha1-ARs mediate important protective and adaptive functions in the heart, although alpha1-ARs are only a minor fraction of total cardiac ARs. Cardiac alpha1-ARs activate pleiotropic downstream signaling to prevent pathologic remodeling in heart failure. Mechanisms defined in animal and cell models include activation of adaptive hypertrophy, prevention of cardiac myocyte death, augmentation of contractility, and induction of ischemic preconditioning. Surprisingly, at the molecular level, alpha1-ARs localize to and signal at the nucleus in cardiac myocytes, and, unlike most GPCRs, activate "inside-out" signaling to cause cardioprotection. Contrary to past opinion, human cardiac alpha1-AR expression is similar to that in the mouse, where alpha1-AR effects are seen most convincingly in knockout models. Human clinical studies show that alpha1-blockade worsens heart failure in hypertension and does not improve outcomes in heart failure, implying a cardioprotective role for human alpha1-ARs. In summary, these findings identify novel functional and mechanistic aspects of cardiac alpha1-AR function and suggest that activation of cardiac alpha1-AR might be a viable therapeutic strategy in heart failure.

p38α regulates SERCA2a function

cAMP-dependent protein kinase (PKA) regulates the L-type calcium channel, the ryanodine receptor, and phospholamban (PLB) thereby increasing inotropy. Cardiac contractility is also regulated by p38 MAPK, which is a negative regulator of cardiac contractile function. The aim of this study was to identify the mechanism mediating the positive inotropic effect of p38 inhibition. Isolated adult and neonatal cardiomyocytes and perfused rat hearts were utilized to investigate the molecular mechanisms regulated by p38. PLB phosphorylation was enhanced in cardiomyocytes by chemical p38 inhibition, by overexpression of dominant negative p38α and by p38α RNAi, but not with dominant negative p38β. Treatment of cardiomyocytes with dominant negative p38α significantly decreased Ca(2+)-transient decay time indicating enhanced sarco/endoplasmic reticulum Ca(2+)-ATPase function and increased cardiomyocyte contractility. Analysis of signaling mechanisms involved showed that inhibition of p38 decreased the activity of protein phosphatase 2A, which renders protein phosphatase inhibitor-1 phosphorylated and thereby inhibits PP1. In conclusion, inhibition of p38α enhances PLB phosphorylation and diastolic Ca(2+) uptake. Our findings provide evidence for novel mechanism regulating cardiac contractility upon p38 inhibition.

G proteins Gαi1/3 are critical targets for Bordetella pertussis toxin-induced vasoactive amine sensitization

Pertussis toxin (PTX) is an AB5-type exotoxin produced by the bacterium Bordetella pertussis, the causative agent of whooping cough. In vivo intoxication with PTX elicits a variety of immunologic and inflammatory responses, including vasoactive amine sensitization (VAAS) to histamine (HA), serotonin (5-HT), and bradykinin (BDK). Previously, by using a forward genetic approach, we identified the HA H1 receptor (Hrh1/H1R) as the gene in mice that controls differential susceptibility to B. pertussis PTX-induced HA sensitization (Bphs). Here we show, by using inbred strains of mice, F1 hybrids, and segregating populations, that, unlike Bphs, PTX-induced 5-HT sensitivity (Bpss) and BDK sensitivity (Bpbs) are recessive traits and are separately controlled by multiple loci unlinked to 5-HT and BDK receptors, respectively. Furthermore, we found that PTX sensitizes mice to HA independently of Toll-like receptor 4, a purported receptor for PTX, and that the VAAS properties of PTX are not dependent upon endothelial caveolae or endothelial nitric oxide synthase. Finally, by using mice deficient in individual Gαi/o G-protein subunits, we demonstrate that Gαi1 and Gαi3 are the critical in vivo targets of ADP-ribosylation underlying VAAS elicited by PTX exposure.

Cardiac lipotoxicity: molecular pathways and therapeutic implications

Diabetes and obesity are both associated with lipotoxic cardiomyopathy exclusive of coronary artery disease and hypertension. Lipotoxicities have become a public health concern and are responsible for a significant portion of clinical cardiac disease. These abnormalities may be the result of a toxic metabolic shift to more fatty acid and less glucose oxidation with concomitant accumulation of toxic lipids. Lipids can directly alter cellular structures and activate downstream pathways leading to toxicity. Recent data have implicated fatty acids and fatty acyl coenzyme A, diacylglycerol, and ceramide in cellular lipotoxicity, which may be caused by apoptosis, defective insulin signaling, endoplasmic reticulum stress, activation of protein kinase C, MAPK activation, or modulation of PPARs.