Tissue angiotensin II during progression or ventricular hypertrophy to heart failure in hypertensive rats; differential effects on PKC epsilon and PKC beta

An Update on Protein Kinases as Therapeutic Targets-Part I: Protein Kinase C Activation and Its Role in Cancer and Cardiovascular Diseases

Protein kinases are one of the most significant drug targets in the human proteome, historically harnessed for the treatment of cancer, cardiovascular disease, and a growing number of other conditions, including autoimmune and inflammatory processes. Since the approval of the first kinase inhibitors in the late 1990s and early 2000s, the field has grown exponentially, comprising 98 approved therapeutics to date, 37 of which were approved between 2016 and 2021. While many of these small-molecule protein kinase inhibitors that interact orthosterically with the protein kinase ATP binding pocket have been massively successful for oncological indications, their poor selectively for protein kinase isozymes have limited them due to toxicities in their application to other disease spaces. Thus, recent attention has turned to the use of alternative allosteric binding mechanisms and improved drug platforms such as modified peptides to design protein kinase modulators with enhanced selectivity and other pharmacological properties. Herein we review the role of different protein kinase C (PKC) isoforms in cancer and cardiovascular disease, with particular attention to PKC-family inhibitors. We discuss translational examples and carefully consider the advantages and limitations of each compound (Part I). We also discuss the recent advances in the field of protein kinase modulators, leverage molecular docking to model inhibitor-kinase interactions, and propose mechanisms of action that will aid in the design of next-generation protein kinase modulators (Part II).

Studies to Elucidate the Mechanism of Cardio Protective and Hypotensive Activities of Anogeissus acuminata (Roxb. ex DC.) in Rodents

Anogeissus acuminata (Roxb. ex DC.) is a folkloric medicinal plant in Asia; including Pakistan; used as a traditional remedy for cardiovascular disorders. This study was planned to establish a pharmacological basis for the trivial uses of Anogeissus acuminata in certain medical conditions related to cardiovascular systems and to explore the underlying mechanisms. Mechanistic studies suggested that crude extract of Anogeissus acuminata (Aa.Cr) produced in vitro cardio-relaxant and vasorelaxant effects in isolated paired atria and aorta coupled with in vivo decrease in blood pressure by invasive method; using pressure and force transducers connected to Power Lab Data Acquisition System. Moreover; Aa.Cr showed positive effects in left ventricular hypertrophy in Sprague Dawley rats observed hemodynamically by a decrease in cardiac cell size and fibrosis; along with absence of inflammatory cells; coupled with reduced levels of angiotensin converting enzyme (ACE) and renin concentration along with increased concentrations of nitric oxide (NO) and cyclic guanosine monophosphate (cGMP). In Acute Myocardial Infarction (AMI) model; creatine kinase (CK), creatine kinase-MB (CK-MB) and lactic acid dehydrogenase (LDH levels) were found to be decreased; along with decreased necrosis; edema and recruitment of inflammatory cells histologically. In vivo and ex vivo studies of Anogeissus acuminata provided evidence of vasorelaxant; hypotensive and cardioprotective properties facilitated through blockage of voltage-gated Ca⁺⁺ ion channel; validating its use in cardiovascular diseases.

Responses of PKCε to cardiac overloads on myocardial sympathetic innervation and NET expression

Protein kinase C (PKC) is a key mediator of many diverse physiological and pathological responses. PKC activation play an important regulatory role of cardiac function. The present study was performed to investigate whether there were differential activations of the PKCε and how the activation coupled with norepinephrine transporter (NET) surface expression, sympathetic innervation pattern and extracellular matrix remodeling in different cardiac hemodynamic overloads induced by abdominal aortic constriction or aortocaval fistula. At 8weeks after the operations, heart failure were induced, accompanied with myocardial hypertrophy, which was more pronounced in pressure overload (POL) than that of volume overload (VOL) rats, left ventricular dysfunction and increased plasma norepinephrine (NE). In POL rats there was an increase in myocardial collagen deposition, in contrast, the amount decreased in VOL as compared with the sham rats. POL remarkably upregulated PKCε membrane-cytosol ratio and downregulated NET membrane fraction, whereas, in VOL induced opposite changes. Accompanied with the PKCε activation, nerve sprouting, evidenced by myocardial GAP43 protein increased, and different nerve phenotypes were found, in POL tyrosine hydroxylase (TH) positive nerve density increased with NET and choline acetyltransferase (ChAT) immunoreactivity density decreased, in contrast, in VOL NET and ChAT increased, TH did not change. The overloads did not induce alteration of NET mRNA expression, but resulted in different myocardial β₁-AR mRNA expression, in POL β₁-AR mRNAwas significantly downregulated, while in VOL rats unaltered. Conclusion, the present results suggested that the different cardiac hemodynamic overload could differentially activate a common signaling, PKCε intermediate and thereby generate biological diversity.

PRKCE gene encoding protein kinase C-epsilon-Dual roles at sarcomeres and mitochondria in cardiomyocytes

Protein kinase C-epsilon (PKCε) is an isoform of a large PKC family of enzymes that has a variety of functions in different cell types. Here we discuss two major roles of PKCε in cardiac muscle cells; specifically, its role in regulating cardiac muscle contraction via targeting the sarcomeric proteins, as well as modulating cardiac cell energy production and metabolism by targeting cardiac mitochondria. The importance of PKCε action is described within the context of intracellular localization, as substrate selectivity and specificity is achieved through spatiotemporal targeting of PKCε. Accordingly, the role of PKCε in regulating myocardial function in physiological and pathological states has been documented in both cardioprotection and cardiac hypertrophy.

Regulation of mitochondrial functions by protein phosphorylation and dephosphorylation

The mitochondria are double membrane-bound organelles found in most eukaryotic cells. They generate most of the cell’s energy supply of adenosine triphosphate (ATP). Protein phosphorylation and dephosphorylation are critical mechanisms in the regulation of cell signaling networks and are essential for almost all the cellular functions. For many decades, mitochondria were considered autonomous organelles merely functioning to generate energy for cells to survive and proliferate, and were thought to be independent of the cellular signaling networks. Consequently, phosphorylation and dephosphorylation processes of mitochondrial kinases and phosphatases were largely neglected. However, evidence accumulated in recent years on mitochondria-localized kinases/phosphatases has changed this longstanding view. Mitochondria are increasingly recognized as a hub for cell signaling, and many kinases and phosphatases have been reported to localize in mitochondria and play important functions. However, the strength of the evidence on mitochondrial localization and the activities of the reported kinases and phosphatases vary greatly, and the detailed mechanisms on how these kinases/phosphatases translocate to mitochondria, their subsequent function, and the physiological and pathological implications of their localization are still poorly understood. Here, we provide an updated perspective on the recent advancement in this area, with an emphasis on the implications of mitochondrial kinases/phosphatases in cancer and several other diseases.

Reduction in Na(+) current by angiotensin II is mediated by PKCα in mouse and human-induced pluripotent stem cell-derived cardiomyocytes

BACKGROUND

Ventricular arrhythmias and sudden cardiac deaths are among the leading causes of mortality in patients with heart failure, and the underlying mechanisms remain incompletely understood. Chronic elevation of angiotensin II (ANGII) is known to be one of the main contributors to heart failure.

OBJECTIVE

We tested whether ANGII can alter ventricular conduction and Na(+) current using transgenic mice with cardiomyocyte-restricted overexpression of ANGII type 1 receptor (AT1R).

METHODS

We used surface electrocardiograms along with current- and voltage-clamp techniques to characterize the electrophysiological properties of AT1R mice while the underlying regulatory mechanisms were explored using reverse transcription/quantitative polymerase chain reaction, Western blots, and immunofluorescence techniques.

RESULTS

Electrophysiological data indicated that chronic AT1R activation in ventricular myocytes caused a 60% reduction in Na(+) current density that slowed the maximal velocity of the action potential upstroke, leading to a prolongation of the QRS complex. These changes occur independently of cardiac hypertrophy, suggesting a direct role for ANGII/AT1R in slowing ventricular conduction. Western blots demonstrated a selective increase in sarcolemmal protein kinase Cα (PKCα) in AT1R mice, indicating PKCα activation. Furthermore, immunofluorescence analysis showed reorganization of PKCα expression to sarcolemma and colocalization with NaV1.5 in AT1R myocytes. The involvement of PKCα in regulating Na(+) current was subsequently demonstrated in human-induced pluripotent stem cell-derived cardiomyocytes where ANGII treatment reduced Na(+) current density. Concomitant treatment with αV5-3, a PKCα translocation inhibitor peptide, blocked the ANGII effect.

CONCLUSION

Overall, this study suggests that in mouse and human cardiomyocytes, PKCα is an important mediator of the ANGII-induced reduction in Na(+) current and may contribute to ventricular arrhythmias.

Depressor effect of chymase inhibitor in mice with high salt-induced moderate hypertension

The aim of the present study was to determine whether long-term high salt intake in the drinking water induces hypertension in wild-type (WT) mice and whether a chymase inhibitor or other antihypertensive drugs could reverse the increase of blood pressure. Eight-week-old male WT mice were supplied with drinking water containing 2% salt for 12 wk (high-salt group) or high-salt drinking water plus an oral chymase inhibitor (TPC-806) at four different doses (25, 50, 75, or 100 mg/kg), captopril (75 mg/kg), losartan (100 mg/kg), hydrochlorothiazide (3 mg/kg), eplerenone (200 mg/kg), or amlodipine (6 mg/kg). Control groups were given normal water with or without the chymase inhibitor. Blood pressure and heart rate gradually showed a significant increase in the high-salt group, whereas a dose-dependent depressor effect of the chymase inhibitor was observed. There was also partial improvement of hypertension in the losartan- and eplerenone-treated groups but not in the captopril-, hydrochlorothiazide-, and amlodipine-treated groups. A high salt load significantly increased chymase-dependent ANG II-forming activity in the alimentary tract. In addition, the relative contribution of chymase to ANG II formation, but not actual average activity, showed a significant increase in skin and skeletal muscle, whereas angiotensin-converting enzyme-dependent ANG II-forming activity and its relative contribution were reduced by high salt intake. Plasma and urinary renin-angiotensin system components were significantly increased in the high-salt group but were significantly suppressed in the chymase inhibitor-treated group. In conclusion, 2% salt water drinking for 12 wk caused moderate hypertension and activated the renin-angiotensin system in WT mice. A chymase inhibitor suppressed both the elevation of blood pressure and heart rate, indicating a definite involvement of chymase in salt-sensitive hypertension.

Cyclic mechanical strain of myocytes modifies CapZβ1 post translationally via PKCε

The heart is exquisitely sensitive to mechanical stimuli and adapts to increased demands for work by enlarging the cardiomyocytes. In order to determine links between mechano-transduction mechanisms and hypertrophy, neonatal rat ventricular myocytes (NRVM) were subjected to physiologic strain for analysis of the dynamics of the actin capping protein, CapZ, and its post-translational modifications (PTM). CapZ binding rates were assessed after strain by fluorescence recovery after photobleaching (FRAP) of green fluorescent protein (GFP) expressed by a GFP-CapZβ1 adenovirus. To assess the role of the protein kinase C epsilon isoform (PKCε), rest or cyclic strain were combined with specific PKCε activation by constitutively active PKCε, or by inhibition with dominant negative PKCε (dnPKCε) expression. Significant increases of CapZ FRAP kinetics with strain were blunted by dnPKCε, suggesting that PKCε is involved in mechano-transduction signaling. Similar combinations of strain and PKC regulation in NRVMs were studied by PTM profiles of CapZβ1 using quantitative two-dimensional gel electrophoresis. The significantly increased charge on CapZ seen with mechanical strain was reversed by the addition of dnPKCε. Potential clinical relevance was confirmed in vivo by PTMs of CapZ in the failing heart of one-year old transgenic mice over-expressing PKCε. Furthermore, with strain there was significant PKCε translocation to the Z-disc and co-localization with CapZβ1 or α-actinin, which was quantified on confocal images. A hypothetical model is presented proposing that one destination of the mechanotransduction signaling pathways might be for PTMs of CapZ thereby regulating actin capping and filament assembly.

PARP-inhibitor treatment prevents hypertension induced cardiac remodeling by favorable modulation of heat shock proteins, Akt-1/GSK-3β and several PKC isoforms

Spontaneously hypertensive rat (SHR) is a suitable model for studies of the complications of hypertension. It is known that activation of poly(ADP-ribose) polymerase enzyme (PARP) plays an important role in the development of postinfarction as well as long-term hypertension induced heart failure. In this study, we examined whether PARP-inhibitor (L-2286) treatment could prevent the development of hypertensive cardiopathy in SHRs. 6-week-old SHR animals were treated with L-2286 (SHR-L group) or placebo (SHR-C group) for 24 weeks. Wistar-Kyoto rats were used as aged-matched, normotensive controls (WKY group). Echocardiography was performed, brain-derived natriuretic peptide (BNP) activity and blood pressure were determined at the end of the study. We detected the extent of fibrotic areas. The amount of heat-shock proteins (Hsps) and the phosphorylation state of Akt-1(Ser473), glycogen synthase kinase (GSK)-3β(Ser9), forkhead transcription factor (FKHR)(Ser256), mitogen activated protein kinases (MAPKs), and protein kinase C (PKC) isoenzymes were monitored. The elevated blood pressure in SHRs was not influenced by PARP-inhibitor treatment. Systolic left ventricular function and BNP activity did not differ among the three groups. L-2286 treatment decreased the marked left ventricular (LV) hypertrophy which was developed in SHRs. Interstitial collagen deposition was also decreased by L-2286 treatment. The phosphorylation of extracellular signal-regulated kinase (ERK)1/2(Thr183-Tyr185), Akt-1(Ser473), GSK-3β(Ser9), FKHR(Ser256), and PKC ε(Ser729) and the level of Hsp90 were increased, while the activity of PKC α/βII(Thr638/641), ζ/λ(410/403) were mitigated by L-2286 administration. We could detect signs of LV hypertrophy without congestive heart failure in SHR groups. This alteration was prevented by PARP inhibition. Our results suggest that PARP-inhibitor treatment has protective effect already in the early stage of hypertensive myocardial remodeling.

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.

Phosphoprotein abundance changes in hypertensive cardiac remodeling

There is over-whelming evidence that protein phosphorylations regulate cardiac function and remodeling. A wide variety of protein kinases, e.g., phosphoinositide 3-kinase (PI3K), Akt, GSK-3, TGFβ, and PKA, MAPKs, PKC, Erks, and Jaks, as well as phosphatases, e.g., phosphatase I (PP1) and calcineurin, control cardiomyocyte growth and contractility. In the present work, we used global phosphoprotein profiling to identify phosphorylated proteins associated with pressure overload (PO) cardiac hypertrophy and heart failure. Phosphoproteins from hypertrophic and systolic failing hearts from male hypertensive Dahl salt-sensitive rats, trans-aortic banded (TAC), and spontaneously hypertensive heart failure (SHHF) rats were analyzed. Profiling was performed by 2-dimensional difference in gel electrophoresis (2D-DIGE) on phospho-enriched proteins. A total of 25 common phosphoproteins with differences in abundance in (1) the 3 hypertrophic and/or (2) the 2 systolic failure heart models were identified (CI>99%) by matrix assisted laser desorption ionization mass spectrometry (MALDI-MS) and Mascot analysis. Among these were (1) myofilament proteins, including alpha-tropomyosin and myosin regulatory light chain 2, cap Z interacting protein (cap ZIP), and tubulin β5; (2) mitochondrial proteins, including pyruvate dehydrogenase α, branch chain ketoacid dehydrogenase E1, and mitochondrial creatine kinase; (3) phosphatases, including protein phosphatase 2A and protein phosphatase 1 regulatory subunit; and (4) other proteins including proteosome subunits α type 3 and β type 7, and eukaryotic translation initiation factor 1A (eIF1A). The results include previously described and novel phosphoproteins in cardiac hypertrophy and systolic failure.

Protein quality control disruption by PKCβII in heart failure; rescue by the selective PKCβII inhibitor, βIIV5-3

Myocardial remodeling and heart failure (HF) are common sequelae of many forms of cardiovascular disease and a leading cause of mortality worldwide. Accumulation of damaged cardiac proteins in heart failure has been described. However, how protein quality control (PQC) is regulated and its contribution to HF development are not known. Here, we describe a novel role for activated protein kinase C isoform βII (PKCβII) in disrupting PQC. We show that active PKCβII directly phosphorylated the proteasome and inhibited proteasomal activity in vitro and in cultured neonatal cardiomyocytes. Importantly, inhibition of PKCβII, using a selective PKCβII peptide inhibitor (βIIV5-3), improved proteasomal activity and conferred protection in cultured neonatal cardiomyocytes. We also show that sustained inhibition of PKCβII increased proteasomal activity, decreased accumulation of damaged and misfolded proteins and increased animal survival in two rat models of HF. Interestingly, βIIV5-3-mediated protection was blunted by sustained proteasomal inhibition in HF. Finally, increased cardiac PKCβII activity and accumulation of misfolded proteins associated with decreased proteasomal function were found also in remodeled and failing human hearts, indicating a potential clinical relevance of our findings. Together, our data highlights PKCβII as a novel inhibitor of proteasomal function. PQC disruption by increased PKCβII activity in vivo appears to contribute to the pathophysiology of heart failure, suggesting that PKCβII inhibition may benefit patients with heart failure. (218 words).

PKCβII inhibition attenuates myocardial infarction induced heart failure and is associated with a reduction of fibrosis and pro-inflammatory responses

Protein kinase C βII (PKCβII) levels increase in the myocardium of patients with end-stage heart failure (HF). Also targeted overexpression of PKCβII in the myocardium of mice leads to dilated cardiomyopathy associated with inflammation, fibrosis and myocardial dysfunction. These reports suggest a deleterious role of PKCβII in HF development. Using a post-myocardial infarction (MI) model of HF in rats, we determined the benefit of chronic inhibition of PKCβII on the progression of HF over a period of 6 weeks after the onset of symptoms and the cellular basis for these effects. Four weeks after MI, rats with HF signs that were treated for 6 weeks with the PKCβII selective inhibitor (βIIV5-3 conjugated to TAT(47-57) carrier peptide) (3 mg/kg/day) showed improved fractional shortening (from 21% to 35%) compared to control (TAT(47-57) carrier peptide alone). Formalin-fixed mid-ventricle tissue sections stained with picrosirius red, haematoxylin and eosin and toluidine blue dyes exhibited a 150% decrease in collagen deposition, a two-fold decrease in inflammation and a 30% reduction in mast cell degranulation, respectively, in rat hearts treated with the selective PKCβII inhibitor. Further, a 90% decrease in active TGFβ1 and a significant reduction in SMAD2/3 phosphorylation indicated that the selective inhibition of PKCβII attenuates cardiac remodelling mediated by the TGF-SMAD signalling pathway. Therefore, sustained selective inhibition of PKCβII in a post-MI HF rat model improves cardiac function and is associated with inhibition of pathological myocardial remodelling.

Regulation of cardiac excitability by protein kinase C isozymes

Cardiac excitability and electrical activity are determined by the sum of individual ion channels, gap junctions and exchanger activities. Electrophysiological remodeling during heart disease involves changes in membrane properties of cardiomyocytes and is related to higher prevalence of arrhythmia-associated morbidity and mortality. Pharmacological and genetic manipulation of cardiac cells as well as animal models of cardiovascular diseases are used to identity changes in electrophysiological properties and the molecular mechanisms associated with the disease. Protein kinase C (PKC) and several other kinases play a pivotal role in cardiac electrophysiological remodeling. Therefore, identifying specific therapies that regulate these kinases is the main focus of current research. PKC, a family of serine/threonine kinases, has been implicated as potential signaling nodes associated with biochemical and biophysical stress in cardiovascular diseases. In this review, we describe the role of PKC isozymes that are involved in cardiac excitability and discuss both genetic and pharmacological tools that were used, their attributes and limitations. Selective and effective pharmacological interventions to normalize cardiac electrical activities and correct cardiac arrhythmias will be of great clinical benefit.

βIIPKC and εPKC isozymes as potential pharmacological targets in cardiac hypertrophy and heart failure

Cardiac hypertrophy is a complex adaptive response to mechanical and neurohumoral stimuli and under continual stressor, it contributes to maladaptive responses, heart failure and death. Protein kinase C (PKC) and several other kinases play a role in the maladaptative cardiac responses, including cardiomyocyte hypertrophy, myocardial fibrosis and inflammation. Identifying specific therapies that regulate these kinases is a major focus of current research. PKC, a family of serine/threonine kinases, has emerged as potential mediators of hypertrophic stimuli associated with neurohumoral hyperactivity in heart failure. In this review, we describe the role of PKC isozymes that is involved in cardiac hypertrophy and heart failure. This article is part of a special issue entitled "Key Signaling Molecules in Hypertrophy and Heart Failure".

Doxercalciferol, a pro-hormone of vitamin D, prevents the development of cardiac hypertrophy in rats

BACKGROUND

Activated vitamin D analog, paricalcitol, has been shown to attenuate the development of cardiac hypertrophy in Dahl salt sensitive (DSS) rats. To determine whether an antihypertrophic effect is class specific, we tested if doxercalciferol (a pro-hormone vitamin D2 analog) could also attenuate the development of cardiac hypertrophy in DSS rats.

METHODS AND RESULTS

Male DSS rats were fed a high salt (HS) diet for 6 weeks beginning at 6 weeks of age. Doxercalciferol was administered intraperitoneally at 150 ng, 3 times per week (Monday, Wednesday, Friday) for 6 weeks. Pathological and echocardiographic findings demonstrated that rats on HS diet with doxercalciferol administration had significant decrease in cardiac hypertrophy and improved cardiac function compared to the HS + vehicle. In addition, there was a significant decrease in plasma brain natriuretic peptide (BNP) level and tissue atrial natriuretic factor (ANF) mRNA level with doxercalciferol treatment. Doxercalciferol also significantly reduced the level of protein kinase C-α (PKCα) suggesting that PKC-mediated cardiac hypertrophy may be associated with vitamin D deficiency.

CONCLUSIONS

Administration of doxercalciferol attenuated the development of HS diet induced cardiac hypertrophy and cardiac dysfunction in DSS rats.

Pharmacological inhibition of βIIPKC is cardioprotective in late-stage hypertrophy

We previously found that in the hearts of hypertensive Dahl salt-sensitive rats, βIIPKC levels increase during the transition from compensated cardiac hypertrophy to cardiac dysfunction. Here we showed that a six-week treatment of these hypertensive rats with a βIIPKC-specific inhibitor, βIIV5-3, prolonged their survival by at least 6weeks, suppressed myocardial fibrosis and inflammation, and delayed the transition from compensated hypertrophy to cardiac dysfunction. In addition, changes in the levels of the Ca(2+)-handling proteins, SERCA2 and the Na(+)/Ca(2+) exchanger, as well as troponin I phosphorylation, seen in the control-treated hypertensive rats were not observed in the βΙΙPKC-treated rats, suggesting that βΙΙPKC contributes to the regulation of calcium levels in the myocardium. In contrast, treatment with the selective inhibitor of βIPKC, an alternative spliced form of βIIPKC, had no beneficial effects in these rats. We also found that βIIV5-3, but not βIV5-3, improved calcium handling in isolated rat cardiomyocytes and enhanced contractility in isolated rat hearts. In conclusion, our data using an in vivo model of cardiac dysfunction (late-phase hypertrophy), suggest that βIIPKC contributes to the pathology associated with heart failure and thus an inhibitor of βIIPKC may be a potential treatment for this disease.

Angiotensin receptor blockade improves the net balance of cardiac Ca(2+) handling-related proteins in sympathetic hyperactivity-induced heart failure

AIMS

The clinical benefits of angiotensin II type 1 (AT1) receptor blockers (ARB) in heart failure (HF) include cardiac anti-remodeling and improved ventricular function. However, the cellular mechanisms underlying the benefits of ARB on ventricular function need to be better clarified. In the present manuscript, we evaluated the effects of AT1 receptor blockade on the net balance of Ca(2+) handling proteins in hearts of mice lacking α(2A) and α(2C) adrenoceptors (α(2A)/α(2C)ARKO), which develop sympathetic hyperactivity (SH) induced-HF.

MAIN METHODS

A cohort of male wild-type (WT) and congenic α(2A)/α(2C)ARKO mice in a C57BL6/J genetic background (5-7mo of age) was randomly assigned to receive either placebo or ARB (Losartan, 10mg/kg for 8wks). Ventricular function (VF) was assessed by echocardiography, and cardiac myocyte width and ventricular fibrosis by a computer-assisted morphometric system. Sarcoplasmic reticulum Ca(2+) ATPase (SERCA2), phospholamban (PLN), phospho-Ser(16)-PLN, phospho-Thr(17)-PLN, phosphatase 1 (PP1), Na(+)-Ca(2+) exchanger (NCX), Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) and phospho-Thr(286)-CaMKII were analyzed by Western blot.

KEY FINDINGS

α(2A)/α(2C)ARKO mice displayed ventricular dysfunction, cardiomyocyte hypertrophy and cardiac fibrosis paralleled by decreased SERCA2 and increased phospho-Thr(17)-PLN, CaMKII, phospho-Thr(286)-CaMKII and NCX levels. ARB induced anti-cardiac remodeling effect and improved VF in α(2A)/α(2C)ARKO associated with increased SERCA2 and phospho-Ser(16)-PLN levels, and SERCA2:NCX ratio. Additionally, ARB decreased phospho-Thr(17)-PLN levels as well as reestablished NCX, CaMKII and phospho-Thr(286)-CaMKII toward WT levels.

SIGNIFICANCE

Altogether, these data provide new insights on intracellular Ca(2+) regulatory mechanisms underlying improved ventricular function by ARB therapy in HF.

Highly Specific Modulators of Protein Kinase C Localization: Applications to Heart Failure

Heart failure (HF) in which the blood supply does not match the body's needs, affects 10% of the population over 65 years old. The protein kinase C (PKC) family of kinases has a key role in normal and disease states. Here we discuss the role of PKC in HF and focus on the use of specific PKC regulators to identify the mechanism leading to this Pathology and potential leads for therapeutics.

Mammalian target of rapamycin is a critical regulator of cardiac hypertrophy in spontaneously hypertensive rats

Evidence exists that protein kinase C and the mammalian target of rapamycin are important regulators of cardiac hypertrophy. We examined the contribution of these signaling kinases to cardiac growth in spontaneously hypertensive rats (SHRs). Systolic blood pressure was increased (P<0.001) at 10 weeks in SHRs versus Wistar-Kyoto controls (162+/-3 versus 128+/-1 mm Hg) and was further elevated (P<0.001) at 17 weeks in SHRs (184+/-7 mm Hg). Heart:body weight ratio was not different between groups at 10 weeks but was 22% greater (P<0.01) in SHRs versus Wistar-Kyoto controls at 17 weeks. At 10 weeks, activation of Akt and S6 ribosomal protein was greater (P<0.01) in SHRs but returned to normal by 17 weeks. In contrast, SHRs had protein kinase C activation only at 17 weeks. To determine whether mammalian target of rapamycin regulates the initial development of hypertrophy, rats were treated with rapamycin (2 mg/kg per day IP) or saline vehicle from 13 to 16 weeks of age. Rapamycin inhibited cardiac mammalian target of rapamycin in SHRs, as evidenced by reductions (P<0.001) in phosphorylation of S6 ribosomal protein and eukaryotic translation initiation factor-4E binding protein 1. Rapamycin treatment also reduced (P<0.001) heart weight and hypertrophy by 47% and 53%, respectively, in SHRs in spite of increased (P<0.001) systolic blood pressure versus untreated SHRs (213+/-8 versus 189+/-6 mm Hg). Atrial natriuretic peptide, brain natriuretic peptide, and cardiac function were unchanged between SHRs treated with rapamycin or vehicle. These data show that mammalian target of rapamycin is required for the development of cardiac hypertrophy evoked by rising blood pressure in SHRs.

Neural cell adhesion molecule is a cardioprotective factor up-regulated by metabolic stress

Screening for cell surface proteins up-regulated under stress conditions may lead to the identification of new therapeutic targets. To search for genes whose expression was enhanced by treatment with oligomycin, a mitochondrial-F(0)F(1) ATP synthase inhibitor, signal sequence trapping was performed in H9C2 rat cardiac myoblasts. One of the genes identified was that for neural cell adhesion molecule (NCAM, CD56), a major regulator of development, cell survival, migration, and neurite outgrowth in the nervous system. Immunohistochemical analyses in a mouse myocardial infarction model revealed that NCAM was strongly expressed in residual cardiac myocytes in the infarcted region. Increased expression of NCAM was also found during the remodeling period in a rat model of hypertension-induced heart failure. Lentivirus-mediated knockdown of NCAM decreased the cell growth and survival following oligomycin treatment in H9C2 cells. In primary rat neonatal cardiac myocytes, NCAM was also found to be up-regulated and played a protective role following oligomycin treatment. Analyses of downstream signaling revealed that knockdown of NCAM significantly decreased the basal AKT phosphorylation level. In contrast, NCAM mimetic peptide P2d activated AKT and significantly reduced oligomycin-induced cardiomyocyte death, which was abolished by treatment with the PI3K inhibitor LY-294002 as well as overexpression of the dominant-negative AKT mutant. These findings demonstrate that NCAM is a cardioprotective factor up-regulated under metabolic stress in cardiomyocytes and augmentation of this signal improved survival.

Protein kinase C in heart failure: a therapeutic target?

Heart failure (HF) afflicts about 5 million people and causes 300,000 deaths a year in the United States alone. An integral part of the pathogenesis of HF is cardiac remodelling, and the signalling events that regulate it are a subject of intense research. Cardiac remodelling is the sum of responses of the heart to causes of HF, such as ischaemia, myocardial infarction, volume and pressure overload, infection, inflammation, and mechanical injury. These responses, including cardiomyocyte hypertrophy, myocardial fibrosis, and inflammation, involve numerous cellular and structural changes and ultimately result in a progressive decline in cardiac performance. Pharmacological and genetic manipulation of cultured heart cells and animal models of HF and the analysis of cardiac samples from patients with HF are all used to identify the molecular and cellular mechanisms leading to the disease. Protein kinase C (PKC) isozymes, a family of serine-threonine protein kinase enzymes, were found to regulate a number of cardiac responses, including those associated with HF. In this review, we describe the PKC isozymes that play critical roles in specific aspects of cardiac remodelling and dysfunction in HF.

Angiotensin II-dependent hypertension increases Na transport-related oxygen consumption by the thick ascending limb

Renal medullary superoxide (O(2)(-)) increases in angiotensin (Ang) II-dependent hypertension. O(2)(-) increases thick ascending limb Na transport, but the effect of Ang II-dependent hypertension on the thick ascending limb is unknown. We hypothesized that Ang II-dependent hypertension increases thick ascending limb NaCl transport because of enhanced O(2)(-) production and increased protein kinase C (PKC) alpha activity. We measured the effect of Ang II-dependent hypertension on furosemide-sensitive oxygen consumption (a measure of Na transport), O(2)(-) production, and PKCalpha translocation (a measure of PKCalpha activity) in thick ascending limb suspensions. Ang II-dependent hypertension increased furosemide-sensitive oxygen consumption (26.2+/-1.0% versus 36.6+/-1.2% of total oxygen consumption; P<0.01). O(2)(-) was also increased (1.1+/-0.2 versus 3.2+/-0.5 nmol of O(2)(-)/min per milligram of protein; P<0.03) in thick ascending limbs. Unilateral renal infusion of Tempol decreased O(2)(-) (2.4+/-0.4 versus 1.2+/-0.2 nmol of O(2)(-)/min per milligram of protein; P<0.04) and furosemide-sensitive oxygen consumption (32.8+/-1.3% versus 24.0+/-2.1% of total oxygen consumption; P<0.01) in hypertensive rats. Tempol did not affect O(2)(-) or furosemide-sensitive oxygen consumption in normotensive controls and did not alter systolic blood pressure. Ang II-dependent hypertension increased PKCalpha translocation (5.7+/-0.3 versus 13.8+/-1.4 AU per milligram of protein; P<0.01). Unilateral renal infusion of Tempol reduced PKCalpha translocation (5.0+/-0.9 versus 10.4+/-2.6 AU per milligram of protein; P<0.04) in hypertensive rats. Unilateral renal infusion of the PKCalpha inhibitor Gö6976 reduced furosemide-sensitive oxygen consumption (37.4+/-1.5% versus 25.1+/-1.0% of total oxygen consumption; P<0.01) in hypertensive rats. We conclude that Ang II-dependent hypertension enhances thick ascending limb Na transport-related oxygen consumption by increasing O(2)(-) and PKCalpha activity.

Up-regulation of endothelin type B receptors in the human internal mammary artery in culture is dependent on protein kinase C and mitogen-activated kinase signaling pathways

Background

Up-regulation of vascular endothelin type B (ET_B) receptors is implicated in the pathogenesis of cardiovascular disease. Culture of intact arteries has been shown to induce similar receptor alterations and has therefore been suggested as a suitable method for, ex vivo, in detail delineation of the regulation of endothelin receptors. We hypothesize that mitogen-activated kinases (MAPK) and protein kinase C (PKC) are involved in the regulation of endothelin ET_B receptors in human internal mammary arteries.

Methods

Human internal mammary arteries were obtained during coronary artery bypass graft surgery and were studied before and after 24 hours of organ culture, using in vitro pharmacology, real time PCR and Western blot techniques. Sarafotoxin 6c and endothelin-1 were used to examine the endothelin ET_A and ET_B receptor effects, respectively. The involvement of PKC and MAPK in the endothelin receptor regulation was examined by culture in the presence of antagonists.

Results

The endohtelin-1-induced contraction (after endothelin ET_B receptor desensitization) and the endothelin ET_A receptor mRNA expression levels were not altered by culture. The sarafotoxin 6c contraction, endothelin ET_B receptor protein and mRNA expression levels were increased after organ culture. This increase was antagonized by; (1) PKC inhibitors (10 μM bisindolylmaleimide I and 10 μM Ro-32-0432), and (2) inhibitors of the p38, extracellular signal related kinases 1 and 2 (ERK1/2) and C-jun terminal kinase (JNK) MAPK pathways (10 μM SB203580, 10 μM PD98059 and 10 μM SP600125, respectively).

Conclusion

In conclusion, PKC and MAPK seem to be involved in the up-regulation of endothelin ET_B receptor expression in human internal mammary arteries. Inhibiting these intracellular signal transduction pathways may provide a future therapeutic target for hindering the development of vascular endothelin ET_B receptor changes in cardiovascular disease.

Mast cells and epsilonPKC: a role in cardiac remodeling in hypertension-induced heart failure

Heart failure (HF) is a chronic syndrome in which pathological cardiac remodeling is an integral part of the disease and mast cell (MC) degranulation-derived mediators have been suggested to play a role in its progression. Protein kinase C (PKC) signaling is a key event in the signal transduction pathway of MC degranulation. We recently found that inhibition of epsilonPKC slows down the progression of hypertension-induced HF in salt-sensitive Dahl rats fed a high-salt diet. We therefore determined whether epsilonPKC inhibition affects MC degranulation in this model. Six week-old male Dahl rats were fed with a high-salt diet to induce systemic hypertension, which resulted in concentric left ventricular hypertrophy at the age of 11 weeks, followed by myocardial dilatation and HF at the age of 17 weeks. We administered epsilonV1-2, an epsilonPKC-selective inhibitor peptide (3 mg/kg/day), deltaV1-1, a deltaPKC-selective inhibitor peptide (3 mg/kg/day), TAT (negative control; at equimolar concentration; 1.6 mg/kg/day) or olmesartan (angiotensin receptor blocker [ARB] as a positive control; 3 mg/kg/day) between 11 weeks and 17 weeks. Treatment with epsilonV1-2 attenuated cardiac MC degranulation without affecting MC density, myocardial fibrosis, microvessel patency, vascular thickening and cardiac inflammation in comparison to TAT- or deltaV1-1-treatment. Treatment with ARB also attenuated MC degranulation and cardiac remodeling, but to a lesser extent when compared to epsilonV1-2. Finally, epsilonV1-2 treatment inhibited MC degranulation in isolated peritoneal MCs. Together, our data suggest that epsilonPKC inhibition attenuates pathological remodeling in hypertension-induced HF, at least in part, by preventing cardiac MC degranulation.

Alteration of gene expression during progression of hypertension-induced cardiac dysfunction in rats

Hypertension induced by high-salt diet in Dahl salt-sensitive rats leads to compensatory cardiac hypertrophy by approximately 11 wk, cardiac dysfunction at approximately 17 wk, and death from cardiac dysfunction at approximately 21 wk. It is unclear what molecular hallmarks distinguish the compensatory hypertrophy from the decompensated cardiac dysfunction phase. Here we compared the gene expression in rat cardiac tissue from the compensatory hypertrophic phase (11 wk, n = 6) with the cardiac dysfunction phase (17 wk, n = 6) and with age-matched normotensive controls. Messenger RNA levels of 93 genes, selected based on predicted association with cardiac dysfunction, were measured by quantitative real-time PCR. In the hypertrophic phase, the expression of three genes, atrial natriuretic peptide (ANP; P = 0.0089), brain natriuretic peptide (P = 0.0012), and endothelin-1 precursor (P = 0.028), significantly increased, whereas there was decreased expression of 24 other genes including SOD2 (P = 0.0148), sarco(endo)plasmic reticulum Ca(2+)-ATPase 2a (P = 0.0002), and ryanodine receptor 2 (P = 0.0319). In the subsequent heart cardiac dysfunction phase, the expression of an additional 20 genes including inducible nitric oxide synthase (NOS; P = 0.0135), angiotensin I-converting enzyme (P = 0.0082), and IL-1beta (P < 0.0001) increased, whereas the expression of seven genes decreased compared with those of age-matched controls. Furthermore, the expression of 22 genes, including prepro-endothelin-1, ANP, angiotensin I-converting enzyme, beta(1)-adrenergic receptor, SOD2, and endothelial NOS, significantly changed in the cardiac dysfunction phase compared with the compensatory hypertrophic phase. Finally, principal component analysis successfully segregated animals with decompensatory cardiac dysfunction from controls, as well as from animals at the compensated hypertrophy phase, suggesting that we have identified molecular markers for each stage of the disease.

Sustained pharmacological inhibition of deltaPKC protects against hypertensive encephalopathy through prevention of blood-brain barrier breakdown in rats

Hypertensive encephalopathy is a potentially fatal condition associated with cerebral edema and the breakdown of the blood-brain barrier (BBB). The molecular pathways leading to this condition, however, are unknown. We determined the role of deltaPKC, which is thought to regulate microvascular permeability, in the development of hypertensive encephalopathy using deltaV1-1 - a selective peptide inhibitor of deltaPKC. As a model of hypertensive encephalopathy, Dahl salt-sensitive rats were fed an 8% high-salt diet from 6 weeks of age and then were infused s.c. with saline, control TAT peptide, or deltaV1-1 using osmotic minipumps. The mortality rate and the behavioral symptoms of hypertensive encephalopathy decreased significantly in the deltaV1-1-treated group relative to the control-treated group, and BBB permeability was reduced by more than 60%. Treatment with deltaV1-1 was also associated with decreased deltaPKC accumulation in capillary endothelial cells and in the endfeet of capillary astrocytes, which suggests decreased microvasculature disruption. Treatment with deltaV1-1 prevented hypertension-induced tight junction disruption associated with BBB breakdown, which suggests that deltaPKC may specifically act to dysregulate tight junction components. Together, these results suggest that deltaPKC plays a role in the development of hypertension-induced encephalopathy and may be a therapeutic target for the prevention of BBB disruption.

Pharmacological inhibition of epsilon-protein kinase C attenuates cardiac fibrosis and dysfunction in hypertension-induced heart failure

Studies on genetically manipulated mice suggest a role for epsilon-protein kinase C (epsilonPKC) in cardiac hypertrophy and in heart failure. The potential clinical relevance of these findings was tested here using a pharmacological inhibitor of epsilonPKC activity during the progression to heart failure in hypertensive Dahl rats. Dahl rats, fed an 8% high-salt diet from the age of 6 weeks, exhibited compensatory cardiac hypertrophy by 11 weeks, followed by heart failure at approximately 17 weeks and death by the age of approximately 20 weeks (123+/-3 days). Sustained treatment between weeks 11 and 17 with the selective epsilonPKC inhibitor epsilonV1-2 or with an angiotensin II receptor blocker olmesartan prolonged animal survival by approximately 5 weeks (epsilonV1-2: 154+/-7 days; olmesartan: 149+/-5 days). These treatments resulted in improved fractional shortening (epsilonV1-2: 58+/-2%; olmesartan: 53+/-2%; saline: 41+/-6%) and decreased cardiac parenchymal fibrosis when measured at 17 weeks without lowering blood pressure at any time during the treatment. Combined treatment with epsilonV1-2, together with olmesartan, prolonged animal survival by 5 weeks (37 days) relative to olmesartan alone (from 160+/-5 to 197+/-14 days, respectively) and by approximately 11 weeks (74 days) on average relative to saline-treated animals, suggesting that the pathway inhibited by epsilonPKC inhibition is not identical to the olmesartan-induced effect. These data suggest that an epsilonPKC-selective inhibitor such as epsilonV1-2 may have a potential in augmenting current therapeutic strategies for the treatment of heart failure in humans.

PKC isozymes in chronic cardiac disease: possible therapeutic targets?

Cardiovascular disease is the leading cause of death in the United States. Therefore, identifying therapeutic targets is a major focus of current research. Protein kinase C (PKC), a family of serine/threonine kinases, has been identified as playing a role in many of the pathologies of heart disease. However, the lack of specific PKC regulators and the ubiquitous expression and normal physiological functions of the 11 PKC isozymes has made drug development a challenge. Here we discuss the validity of therapeutically targeting PKC, an intracellular signaling enzyme. We describe PKC structure, function, and distribution in the healthy and diseased heart, as well as the development of rationally designed isozyme-selective regulators of PKC functions. The review focuses on the roles of specific PKC isozymes in atherosclerosis, fibrosis, and cardiac hypertrophy, and examines principles of pharmacology as they pertain to regulators of signaling cascades associated with these diseases.

Evolution of Left Atrial Systolic and Diastolic Functions in Different Stages of Hypertension: Distinct Effects of Blood Pressure Control

BACKGROUND

To evaluate the left atrial (LA) volume, and LA systolic (contractile) and diastolic (expansion) functions in different stages of hypertension with or without atrial fibrillation (AF), as well as the effects of good blood pressure control.

METHODS

A prospective observational study. Individuals including 22 normotensive controls, 23 patients with mild hypertension, 20 with severe hypertension, and 17 with hypertension and paroxysmal AF were recruited for paired echocardiography studies at baseline and 6 months after control of hypertension.

RESULTS

With increasing severity of hypertension, left ventricular (LV) diastolic function deteriorated with decreasing LV septal E'/A' and increasing E/E' ratios. LA expansion index was reduced in parallel. LA expansion index was correlated positively with LV E'/A' (r = 0.43, p = 0.022) and inversely with LV E/E' (r = 0.49, p = 0.009). Significant improvement of LV diastolic function and LA expansion index preceded the reduction of LA volume after blood pressure control. In patients with paroxysmal AF, LA volume reduction was more evident in patients receiving angiotensin-converting enzyme inhibitors or angiotensin II type 1 receptor blockers.

CONCLUSIONS

With progressive LV diastolic dysfunction in hypertension, there was a corresponding deterioration in LA diastolic function. Effective blood pressure control for 6 months improved LA diastolic function.

Altered PKC expression and phosphorylation in response to the nature, direction, and magnitude of mechanical stretch

Protein kinase C (PKC) isozymes have been shown to play a role in mechanotransduction in a variety of cell types. We sought to identify the PKC isozymes involved in transducing mechanical (cyclic vs. static), direction and intensity of stretch by examining changes in protein expression and phosphorylation. We used a 3-dimensional culture system with aligned neonatal rat cardiac myocytes on silastic membranes. Myocytes were subjected to either cyclic stretch at 5 cycles/min or static stretch for a period of 24 h at intensities of 0%, 2.5%, 5%, or 10% of full membrane length. Stretch was applied in perpendicular or parallel directions to myocyte alignment. PKC delta was most sensitive to stretch applied perpendicular to myocyte alignment regardless of the nature of stretch, while phospho PKC delta T505 increased in response to static-perpendicular stretch. PKC epsilon expression was altered by cyclic stretch but not static stretch, while phospho PKC epsilon S719 remained unchanged. PKC alpha expression was not altered by stretch; however, phospho PKC alpha S657 increased in a dose-dependent manner following cyclic-perpendicular stretch. Our results indicate that changes in PKC expression and phosphorylation state may be a mechanism for cardiac myocytes to discriminate between the nature, direction, and intensity of mechanical stretch.

PKCepsilon increases phosphorylation of the cardiac myosin binding protein C at serine 302 both in vitro and in vivo

Cardiac myosin binding protein C (cMyBPC) phosphorylation is essential for normal cardiac function. Although PKC was reported to phosphorylate cMyBPC in vitro, the relevant PKC isoforms and functions of PKC-mediated cMyBPC phosphorylation are unknown. We recently reported that a transgenic mouse model with cardiac-specific overexpression of PKCepsilon (PKCepsilon TG) displayed enhanced sarcomeric protein phosphorylation and dilated cardiomyopathy. In the present study, we have investigated cMyBPC phosphorylation in PKCepsilon TG mice. Western blotting and two-dimensional gel electrophoresis demonstrated a significant increase in cMyBPC serine (Ser) phosphorylation in 12-month-old TG mice compared to wild type (WT). In vitro PKCepsilon treatment of myofibrils increased the level of cMyBPC Ser phosphorylation in WT mice to that in TG mice, whereas treatment of TG myofibrils with PKCepsilon showed only a minimal increase in cMyBPC Ser phosphorylation. Three peptide motifs of cMyBPC were identified as the potential PKCepsilon consensus sites including a 100% matched motif at Ser302 and two nearly matched motifs at Ser811 and Ser1203. We treated synthetic peptides corresponding to the sequences of these three motifs with PKCepsilon and determined phosphorylation by mass spectrometry and ELISA assay. PKCepsilon induced phosphorylation at the Ser302 site but not at the Ser811 or Ser1203 sites. A S302A point mutation in the Ser302 peptide abolished the PKCepsilon-dependent phosphorylation. Taken together, our data show that the Ser302 on mouse cMyBPC is a likely PKCepsilon phosphorylation site both in vivo and in vitro and may contribute to the dilated cardiomyopathy associated with increased PKCepsilon activity.

DeltaPKC mediates microcerebrovascular dysfunction in acute ischemia and in chronic hypertensive stress in vivo

Maintaining cerebrovascular function is a priority for reducing damage following acute ischemic events such as stroke, and under chronic stress in diseases such as hypertension. Ischemic episodes lead to endothelial cell damage, deleterious inflammatory responses, and altered neuronal and astrocyte regulation of vascular function. These, in turn, can lead to impaired cerebral blood flow and compromised blood-brain barrier function, promoting microvascular collapse, edema, hemorrhagic transformation, and worsened neurological recovery. Multiple studies demonstrate that protein kinase C (PKC), a widely expressed serine/threonine kinase, is involved in mediating arterial tone and microvascular function. However, there is no clear understanding about the role of individual PKC isozymes. We show that intraperitoneal injection of deltaV1-1-TAT(47-57) (0.2 mg/kg in 1 mL), an isozyme-specific peptide inhibitor of deltaPKC, improved microvascular pathology, increased the number of patent microvessels by 92% compared to control-treated animals, and increased cerebral blood flow by 26% following acute focal ischemia induced by middle cerebral artery occlusion in normotensive rats. In addition, acute delivery of deltaV1-1-TAT(47-57) in hypertensive Dahl rats increased cerebral blood flow by 12%, and sustained delivery deltaV1-1-TAT(47-57) (5 uL/h, 1 mM), reduced infarct size by 25% following an acute stroke induced by MCA occlusion for 90 min. Together, these findings demonstrate that deltaPKC is an important therapeutic target for protection of microvascular structure and function under both acute and chronic conditions of cerebrovascular stress.

Peptides Derived from the C2 Domain of Protein Kinase Cϵ (ϵPKC) Modulate ϵPKC Activity and Identify Potential Protein-Protein Interaction Surfaces

Peptides derived from protein kinase C (PKC) modulate its activity by interfering with critical protein-protein interactions within PKC and between PKC and PKC-binding proteins (Souroujon, M. C., and Mochly-Rosen, D. (1998) Nat. Biotechnol. 16, 919-924). We previously demonstrated that the C2 domain of PKC plays a critical role in these interactions. By focusing on epsilonPKC and using a rational approach, we then identified one C2-derived peptide that acts as an isozyme-selective activator and another that acts as a selective inhibitor of epsilonPKC. These peptides were used to identify the role of epsilonPKC in protection from cardiac and brain ischemic damage, in prevention of complications from diabetes, in reducing pain, and in protecting transplanted hearts. The efficacy of these two peptides led us to search for additional C2-derived peptides with PKC-modulating activities. Here we report on the activity of a series of 5-9-residue peptides that are derived from regions that span the length of the C2 domain of epsilonPKC. These peptides were tested for their effect on PKC activity in cells in vivo and in an ex vivo model of acute ischemic heart disease. Most of the peptides acted as activators of PKC, and a few peptides acted as inhibitors. PKC-dependent myristoylated alanine-rich C kinase substrate phosphorylation in epsilonPKC knock-out cells revealed that only a subset of the peptides were selective for epsilonPKC over other PKC isozymes. These epsilonPKC-selective peptides were also protective of the myocardium from ischemic injury, an epsilonPKC-dependent function (Liu, G. S., Cohen, M. V., Mochly-Rosen, D., and Downey, J. M. (1999) J. Mol. Cell. Cardiol. 31, 1937-1948), and caused selective translocation of epsilonPKC over other isozymes when injected systemically into mice. Examination of the structure of the C2 domain from epsilonPKC revealed that peptides with similar activities clustered into discrete regions within the domain. We propose that these regions represent surfaces of protein-protein interactions within epsilonPKC and/or between epsilonPKC and other partner proteins; some of these interactions are unique to epsilonPKC, and others are common to other PKC isozymes.

RBCK1, a protein kinase CbetaI (PKCbetaI)-interacting protein, regulates PKCbeta-dependent function

RBCK1 (RBCC protein interacting with PKC 1) has originally been identified as a protein kinase CbetaI (PKCbetaI)-binding partner by a two-hybrid screen and as one of the gene transcripts that increases during adult cardiac hypertrophy. To address whether RBCK1 and PKCbetaI functions are interconnected, we used cultured neonatal myocytes where we previously found that the activity of PKCbetaI is required for an increase in cell size, also called hypertrophy. In this study, we showed that acute treatment of cardiac myocytes with phenylephrine, a prohypertrophic stimulant, transiently increased the association of RBCK1 with PKCbetaI within 1 min. A prolonged phenylephrine treatment also resulted in an increase of the interaction of the two proteins. Endogenous RBCK1 protein levels increased upon phenylephrine-induced hypertrophy. Further, adenovirus-based RBCK1 overexpression in the absence of phenylephrine increased cardiac cell size. This RBCK1-mediated hypertrophy required PKCbeta activity, since the increase in cell size was inhibited when the RBCK1-expressing cells were treated with PKCbeta-selective antagonists, supporting our previous observation that both PKCbetaI and PKCbetaII are required for hypertrophy. Unexpectedly, RBCK1-induced increased cell size was inhibited by phenylephrine. This effect correlated with a decrease in the level of both PKCbeta isoforms. Most importantly, RNA interference for RBCK1 significantly inhibited the increase in cell size of cardiac myocytes following phenylephrine treatment. Our results suggest that RBCK1 binds PKCbetaI and is a key regulator of PKCbetaI function in cells and that, together with PKCbetaII, the three proteins are essential for developmental hypertrophy of cardiac myocytes.

Fosinopril and Carvedilol Reverse Hypertrophy and Change the Levels of Protein Kinase Cɛ and Components of its Signaling Complex

OBJECTIVE

To demonstrate the alterations of Protein Kinase C epsilon (PKC epsilon) and components of its signaling complexes after treatment with fosinopril and carvedilol and analyze potential molecular mechanisms of the two drugs for cardiac hypertrophy and heart failure.

METHODS

Pressure-overload cardiac hypertrophy (POH) was developed in 8-week-old male Sprague Dawley rats by abdominal aortic banding. The rats were divided into three groups at the age of 20 weeks: POH without failure group, reversed POH with drugs group, and POH with failure group on high diet. Western Blot analysis, co-immunoprecipitation and proteomic analysis were performed in ventricular tissues of rat hearts.

RESULTS

Increased PKC epsilon was found during POH. PKC epsilon decreased during transition from POH to heart failure (HF). However, increased PKC epsilon inclined to recover to normal levels after treatment with both drugs. There were differential proteins in PKC epsilon complexes during the different stages of POH. The two significant PKC epsilon-binding proteins, MAD1 and Lyn A, were only present in PKC epsilon complex during reversing POH with drugs.

CONCLUSION

Chronic administration of carvedilol and fosinopril could reverse the development of POH and delay the appearance of HF, partly by regulating PKC epsilon level and its signaling complex. MAD1 and Lyn A may be important proteins participating in the reversing process.

Down-regulation of cardiac apelin system in hypertrophied and failing hearts: Possible role of angiotensin II-angiotensin type 1 receptor system

Cardiac apelin has recently been suggested to contribute to the pathophysiology of heart failure (HF) in humans. In animal experiments, its infusion acutely improved systolic as well as diastolic LV function. Although its deficit could critically determine the cardiac dysfunction, its regulatory mechanism is unknown. Accordingly, we investigated the role and regulation of the cardiac apelin system in the diseased heart using Dahl salt-sensitive rats, which show a distinctive transition from compensatory LV hypertrophy (LVH) to HF. In the compensatory LVH stage, apelin and its receptor APJ mRNA showed no change compared with control animals, while these were markedly down-regulated in the HF stage (72% and 57% decrease, respectively). The rats were chronically treated with telmisartan (angiotensin type 1 receptor blocker [ARB], 5 mg/kg/day, n=9), ONO-4817 (matrix metalloproteinase [MMP] inhibitor, 200 mg/kg/day, n=9), bisoprolol (beta blocker, 3 mg/kg/day, n=6) or vehicle (0.5%CMC, n=9) from the LVH stage. Although the functional improvements were similar among the three treated groups 6 weeks after treatment, restoration of cardiac apelin and APJ expression was observed only in the ARB group. Furthermore, in angiotensin II-infused rats, cardiac apelin mRNA was decreased after 24 h of treatment and its restoration was achieved by treatment with ARB. These results indicate that the cardiac apelin system is markedly down-regulated in experimental HF and may be regulated by the angiotensin II-angiotensin type 1 receptor system directly. Inhibition of the renin-angiotensin system may have beneficial effects, at least in part, through restoration of the cardiac apelin system in the treatment of HF.

Contribution of reactive oxygen species to the pathogenesis of left ventricular failure in Dahl salt-sensitive hypertensive rats: effects of angiotensin II blockade

OBJECTIVE

We investigated the contribution of reduced nicotinamide-adenine dinucleotide phosphate (NADPH) oxidase-dependent reactive oxygen species (ROS) generation to the pathogenesis of diastolic heart failure (DHF) in Dahl salt-sensitive (DS) hypertensive rats, with the aim of testing our hypothesis that the cardioprotective effects of angiotensin II (Ang II) blockade are provided by the suppression of this pathway.

METHODS

DS rats were maintained on high (H: 8.0% NaCl) or low (L: 0.3% NaCl) salt diets from age 7 to 17 weeks. DS/H rats were also treated with candesartan cilexetil (10 mg/kg per day, orally) or a superoxide dismutase mimetic, tempol (3 mmol/l in drinking water) from age 7 to 17 weeks.

RESULTS

DS/H rats represented hypertension, left ventricular (LV) relaxation abnormality and myocardial stiffening with preserved systolic heart function. As compared with DS/L rats, DS/H rats showed higher levels of transforming growth factor-beta (TGF-beta), connective tissue growth factor (CTGF), p22phox and gp91phox mRNA expression, NADPH oxidase activity and thiobarbituric acid-reactive substance (TBARS) contents in LV tissues. Gene expression of uncoupling protein-2 (UCP-2), an inner mitochondrial membrane proton transporter, was also 2.8 +/- 0.5-fold higher. In DS/H rats, treatment with candesartan did not alter blood pressure, but resulted in a marked improvement of the hemodynamic deterioration; these therapeutic effects were accompanied by decreases in myocardial NADPH oxidase activity, TBARS contents and the expression of TGF-beta, CTGF, p22phox, gp91phox and UCP-2. Similar therapeutic effects were provided by treatment with tempol in DS/H rats.

CONCLUSIONS

Our data suggest that NADPH oxidase-mediated ROS production contributes to the pathogenesis of DHF in DS hypertensive rats, and that the cardioprotective effects of AngII blockade are, at least partially, mediated through the suppression of this pathway.

Controversies in ventricular remodelling

Ventricular remodelling describes structural changes in the left ventricle in response to chronic alterations in loading conditions, with three major patterns: concentric remodelling, when a pressure load leads to growth in cardiomyocyte thickness; eccentric hypertrophy, when a volume load produces myocyte lengthening; and myocardial infarction, an amalgam of patterns in which stretched and dilated infarcted tissue increases left-ventricular volume with a combined volume and pressure load on non-infarcted areas. Whether left-ventricular hypertrophy is adaptive or maladaptive is controversial, as suggested by patterns of signalling pathways, transgenic models, and clinical findings in aortic stenosis. The transition from apparently compensated hypertrophy to the failing heart indicates a changing balance between metalloproteinases and their inhibitors, effects of reactive oxygen species, and death-promoting and profibrotic neurohumoral responses. These processes are evasive therapeutic targets. Here, we discuss potential novel therapies for these disorders, including: sildenafil, an unexpected option for anti-transition therapy; surgery for increased sphericity caused by chronic volume overload of mitral regurgitation; an antifibrotic peptide to inhibit the fibrogenic effects of transforming growth factor beta; mechanical intervention in advanced heart failure; and stem-cell therapy.

Protein kinase C isoforms as specific targets for modulation of vascular smooth muscle function in hypertension

Vascular contraction is an important determinant of the peripheral vascular resistance and blood pressure. The mechanisms underlying vascular smooth muscle (VSM) contraction and the pathological changes that occur in hypertension have been the subject of numerous studies and interpretations. Activation of VSM by vasoconstrictor stimuli at the cell surface causes an increase in [Ca(2+)](i), Ca(2+)-dependent activation of myosin light chain (MLC) kinase, MLC phosphorylation, actin-myosin interaction and VSM contraction. Additional signaling pathways involving Rho-kinase and protein kinase C (PKC) may increase the myofilament force sensitivity to [Ca(2+)](i) and MLC phosphorylation, and thereby maintain vascular contraction. PKC is a particularly intriguing protein kinase as it comprises a family of Ca(2+)-dependent and Ca(2+)-independent isoforms, which have different tissue and subcellular distribution, and undergo differential translocation during cell activation. PKC translocation to the cell surface may trigger a cascade of protein kinases, such as mitogen-activated protein kinase (MAPK) and MAPK kinase (MEK) that ultimately interact with the contractile myofilaments and cause VSM contraction. Also, PKC translocation to the nucleus may promote VSM growth and proliferation. Increased PKC expression and activity have been identified in several forms of hypertension. The subcellular location of PKC may determine the state of VSM activity, and may be useful in the diagnosis/prognosis of hypertension. Vascular PKC isoforms may represent specific targets for modulation of VSM hyperactivity, and isoform-specific PKC inhibitors may be useful in treatment of Ca(2+) antagonist-resistant forms of hypertension.

Protein kinase C isozymes in hypertension and hypertrophy: insight from SHHF rat hearts

Chronic hypertension results in cardiac hypertrophy and may lead to congestive heart failure. The protein kinase C (PKC) family has been identified as a signaling component promoting cardiac hypertrophy. We hypothesized that PKC activation may play a role mediating hypertrophy in the spontaneously hypertensive heart failure (SHHF) rat heart. Six-month-old SHHF and normotensive control Wistar Furth (WF) rats were used. Hypertension and cardiac hypertrophy were confirmed in SHHF rats. PKC expression and activation were analyzed by Western blots using isozyme-specific antibodies. Compared to WF, untreated SHHF rats had increased phospho-active alpha (10-fold), delta (4-fold), and epsilon (3-fold) isozyme expression. Furthermore, we analyzed the effect of an angiotensin II type 1 receptor blocker (ARB) and hydralazine (Hy) on PKC regulation in SHHF rat left ventricle (LV). Both the ARB and Hy normalized LV blood pressure, but only the ARB reduced heart mass. Neither treatment affected PKC expression or activity. Our data show differential activation of PKC in the hypertensive, hypertrophic SHHF rat heart. Regression of hypertrophy elicited by an ARB in this model occurred independently of changes in the expression and activity of the PKC isoforms examined.

PKC translocation and ERK1/2 activation in compensated right ventricular hypertrophy secondary to chronic emphysema

Background

Right ventricular hypertrophy (RVH) is an important complication of chronic lung disease. However, the signal transduction pathways involved as well as the physiological changes to the right ventricle have not been investigated. Emphysema was produced in male, Syrian Golden hamsters by intra-tracheal instillation of 250 IU/kg elastase (Emp, n = 17). Saline treated animals served as controls (Con, n = 15).

Results

Nine months later, Emp hamsters had 75% greater lung volume, and evidence of RVH at the gross and myocyte level (RV:tibia length Emp 6.84 ± 1.18 vs. Con 5.14 ± 1.11 mg/mm; myocyte cross sectional area Emp 3737 vs. Con 2695 μm²), but not left ventricular hypertrophy. Serial echocardiographic analysis from baseline to nine months after induction of emphysema revealed increasing right ventricular internal dimension and decreased pulmonary artery acceleration time only in Emp hamsters. There was an increase in translocation of PKC βI and PKC ε from cytosolic to membranous cell fractions in RV of Emp hamsters. Phosphorylation of PKC ε was unchanged. Translocation of PKC α and βII were unchanged. Emp animals had a 22% increase in phospho-ERK 1/2, but no change in levels of total ERK 1/2 compared to Con.

Conclusion

These data suggest that PKC βI, ε and ERK 1/2 may play a role in mediating compensated RVH secondary to emphysema and may have clinical relevance in the pathogenesis of RVH.

Eplerenone Shows Renoprotective Effect by Reducing LOX-1–Mediated Adhesion Molecule, PKCε-MAPK-p90RSK, and Rho-Kinase Pathway

Lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1) may play an important role in atherosclerosis by inducing leukocyte adhesion molecules, such as intercellular and vascular cell adhesion molecule-1 (intercellular adhesion molecule-1 [ICAM-1], vascular cell adhesion molecule-1 [VCAM-1]). We hypothesized that eplerenone, a novel selective aldosterone blocker, produces inhibition of LOX-1–mediated adhesion molecules, suppresses mitogen-activated protein (MAP) kinase and its downstream effector p90 ribosomal S6 kinase (p90RSK) through the protein kinase Cε (PKCε) pathway, and improves endothelial function by inhibition of Rho-kinase in the renal cortex of Dahl salt-sensitive hypertensive (DS) and salt-resistant (DR) rats. Eplerenone (10, 30, and 100 mg/kg per day) was given from the age of 6 weeks to the left ventricular hypertrophy stage (11 weeks) for 5 weeks. At 11 weeks, expression levels of LOX-1, ICAM-1, VCAM-1, and Rho-kinase were higher in DS rats than in DR rats and were decreased by eplerenone. Similarly, upregulated phosphorylation of PKCε, MAP kinase, and p90RSK in DS rats was also inhibited by eplerenone. In contrast, downregulated endothelial nitric oxide synthase mRNA was increased by eplerenone to a similar degree as after treatment with Y-27632, a selective Rho-kinase inhibitor. Eplerenone administration resulted in significant improvement in glomerulosclerosis (eplerenone 10 mg, −61%; 30 mg, −78%; and 100 mg, −84% versus DS; P <0.01, respectively) and urinary protein (10 mg, −78%; 30 mg, −87%; and 100 mg, −88% versus DS; P <0.01, respectively). These results suggest that the renoprotective effects of eplerenone may be partly caused by inhibition of LOX-1–mediated adhesion molecules and PKCε–MAP kinase–p90RSK pathway, and improvement in endothelial function.

Atorvastatin Prevents End-Organ Injury in Salt-Sensitive Hypertension

Statins, inhibitors of cholesterol biosynthesis, are endowed with pleiotropic effects that may contribute to their favorable clinical results. Hypertensive Dahl salt-sensitive (DS) rats have endothelial dysfunction and cardiorenal injury associated with decreased NO bioavailability and increased superoxide (O2-) production linked to a functional upregulation of angiotensin II. We investigated whether atorvastatin (30 mg/kg per day; by gavage) would prevent endothelial nitric oxide (eNOS) downregulation and the increase in O2- in DS rats, thereby reducing end-organ injury. DS rats given a high-salt diet (4% NaCl) for 10 weeks developed hypertension (systolic blood pressure [SBP] 200+/-8 versus 150+/-2 mm Hg in DS rats fed 0.5% NaCl diet [NS]; P<0.05), impaired endothelium-dependent relaxation, functional upregulation of endothelin-1, left ventricular hypertrophy (LVH; 30%), and proteinuria (167%), accompanied by downregulation of aortic eNOS activity (0.7+/-0.2 versus 1.8+/-0.3 nmol/min per gram protein in NS; P<0.05) and increased aortic O2- (2632+/-316 versus 1176+/-112 counts/min per milligram in NS; P<0.05) and plasma 8-F2alpha isoprostanes. Atorvastatin prevented the decrease in eNOS activity (1.5+/-0.3 nmol/min per gram protein) as well as the increase in O2- (1192+/-243 counts/min per milligram) and plasma 8-F2alpha isoprostanes, reduced LVH and proteinuria, and normalized endothelial function and vascular response to endothelin-1, although reduction in SBP was modest (174+/-8 mm Hg). Atorvastatin combined with removal of high salt normalized aortic eNOS activity, SBP, LVH, and proteinuria. These findings strongly suggest that concomitant prevention of vascular eNOS downregulation and inhibition of oxidative stress may contribute to the protection against end-organ injury afforded by this statin in salt-sensitive hypertension.

In salt-sensitive hypertension, increased superoxide production is linked to functional upregulation of angiotensin II

The balance between endothelial nitric oxide (NO) and angiotensin II (Ang II) maintains the homeostasis of the cardiovascular and renal systems. We tested the hypothesis that increased oxidant stress linked to a functional imbalance between NO and Ang II might play a central pathogenetic role in salt-sensitive (SS) hypertension. We studied Dahl SS (DS) rats during the prehypertensive (5 days) and hypertensive (12 weeks) phases of a high-salt (4% NaCl) diet. Control rats received a normal-salt (0.5% NaCl, [NS]) diet. Prehypertensive DS rats (systolic blood pressure [SBP] 138+/-2 mm Hg) manifested a 35% increase (P<0.05) in aortic superoxide (O2-) production without evidence of end-organ damage. Hypertensive DS rats (SBP 214+/-11 mm Hg) had impaired endothelium-dependent relaxation (EDR) and increased aortic O2- production (320%), urinary isoprostane excretion (83%), aortic (20%) and left ventricular (LVH, 21%) hypertrophy, and proteinuria (124%). In prehypertensive DS rats, candesartan (10 mg x kg(-1) x d(-1)) an Ang II type 1 receptor blocker (ARB), normalized O2- production. In hypertensive DS rats, the ARB decreased aortic O2- production by 71% and normalized EDR without affecting SBP (212+/-8 mm Hg), aortic hypertrophy, LVH, or proteinuria. Switching hypertensive DS rats to an NS diet did not affect SBP (208+/-8 mm Hg), LVH, aortic hypertrophy, or proteinuria and had minimal effects on O2- and EDR. Concomitant ARB administration plus a switch to an NS diet normalized SBP (138+/-8 mm Hg) as well as end-organ damage. Dahl salt-resistant rats fed an HS diet for 12 weeks did not show hypertension or increased O2- production. Thus, SS hypertension might represent a specific vascular diathesis linked to functional upregulation of Ang II action (increased O2- synthesis) accompanied by insufficient NO bioavailability, which promotes severe endothelial dysfunction.