Protein kinase Cα as a heart failure therapeutic target

The role of serine/threonine protein kinases in cardiovascular disease and potential therapeutic methods

Protein phosphorylation is an important link in a variety of signaling pathways, and most of the important life processes in cells involve protein phosphorylation. Based on the amino acid residues of phosphorylated proteins, protein kinases can be categorized into the following families: serine/threonine protein kinases, tyrosine-specific protein kinases, histidine-specific protein kinases, tryptophan kinases, and aspartate/glutamyl protein kinases. Of all the protein kinases, most are serine/threonine kinases, where serine/threonine protein kinases are protein kinases that catalyze the phosphorylation of serine or threonine residues on target proteins using ATP as a phosphate donor. The current socially accepted classification of serine/threonine kinases is to divide them into seven major groups: protein kinase A, G, C (AGC), CMGC, Calmodulin-dependent protein kinase (CAMK), Casein kinase (CK1), STE, Tyrosine kinase (TKL) and others. After decades of research, a preliminary understanding of the specific classification and respective functions of serine/threonine kinases has entered a new period of exploration. In this paper, we review the literature of the previous years and introduce the specific signaling pathways and related therapeutic modalities played by each of the small protein kinases in the serine/threonine protein kinase family, respectively, in some common cardiovascular system diseases such as heart failure, myocardial infarction, ischemia-reperfusion injury, and diabetic cardiomyopathy. To a certain extent, the current research results, including molecular mechanisms and therapeutic methods, are fully summarized and a systematic report is made for the prevention and treatment of cardiovascular diseases in the future.

Cardioprotective Strategies After Ischemia-Reperfusion Injury

Acute myocardial infarction (AMI) is associated with high morbidity and mortality worldwide. Although early reperfusion is the most effective strategy to salvage ischemic myocardium, reperfusion injury can develop with the restoration of blood flow. Therefore, it is important to identify protection mechanisms and strategies for the heart after myocardial infarction. Recent studies have shown that multiple intracellular molecules and signaling pathways are involved in cardioprotection. Meanwhile, device-based cardioprotective modalities such as cardiac left ventricular unloading, hypothermia, coronary sinus intervention, supersaturated oxygen (SSO2), and remote ischemic conditioning (RIC) have become important areas of research. Herein, we review the molecular mechanisms of cardioprotection and cardioprotective modalities after ischemia-reperfusion injury (IRI) to identify potential approaches to reduce mortality and improve prognosis in patients with AMI.

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).

Potential implications of protein kinase Cα in pathophysiological conditions and therapeutic interventions

PKCα is a molecule with many functions that play an important role in cell survival and death to maintain cellular homeostasis. Alteration in the normal functioning of PKCα is responsible for the complicated etiology of many pathologies, including cancer, cardiovascular diseases, kidney complications, neurodegenerative diseases, diabetics, and many others. Several studies have been carried out over the years on this kinase's function, and regulation in normal physiology and pathological conditions. A lot of data with antithetical results have therefore accumulated over time to create a complex framework of physiological implications connected to the PKCα function that needs comprehensive elucidation. In light of this information, we critically analyze the multiple roles played by PKCα in basic cellular processes and their molecular mechanism during various pathological conditions. This review further discusses the current approaches to manipulating PKCα signaling amplitude in the patient's favour and proposed PKCα as a therapeutic target to reverse pathological states.

Extracellular Histone-Induced Protein Kinase C Alpha Activation and Troponin Phosphorylation Is a Potential Mechanism of Cardiac Contractility Depression in Sepsis

Reduction in cardiac contractility is common in severe sepsis. However, the pathological mechanism is still not fully understood. Recently it has been found that circulating histones released after extensive immune cell death play important roles in multiple organ injury and disfunction, particularly in cardiomyocyte injury and contractility reduction. How extracellular histones cause cardiac contractility depression is still not fully clear. In this work, using cultured cardiomyocytes and a histone infusion mouse model, we demonstrate that clinically relevant histone concentrations cause significant increases in intracellular calcium concentrations with subsequent activation and enriched localization of calcium-dependent protein kinase C (PKC) α and βII into the myofilament fraction of cardiomyocytes in vitro and in vivo. Furthermore, histones induced dose-dependent phosphorylation of cardiac troponin I (cTnI) at the PKC-regulated phosphorylation residues (S43 and T144) in cultured cardiomyocytes, which was also confirmed in murine cardiomyocytes following intravenous histone injection. Specific inhibitors against PKCα and PKCβII revealed that histone-induced cTnI phosphorylation was mainly mediated by PKCα activation, but not PKCβII. Blocking PKCα also significantly abrogated histone-induced deterioration in peak shortening, duration and the velocity of shortening, and re-lengthening of cardiomyocyte contractility. These in vitro and in vivo findings collectively indicate a potential mechanism of histone-induced cardiomyocyte dysfunction driven by PKCα activation with subsequent enhanced phosphorylation of cTnI. These findings also indicate a potential mechanism of clinical cardiac dysfunction in sepsis and other critical illnesses with high levels of circulating histones, which holds the potential translational benefit to these patients by targeting circulating histones and downstream pathways.

Calcium-Signalling in Human Glaucoma Lamina Cribrosa Myofibroblasts

Glaucoma is one of the most common causes of treatable visual impairment in the developed world, affecting approximately 64 million people worldwide, some of whom will be bilaterally blind from irreversible optic nerve damage. The optic nerve head is a key site of damage in glaucoma where there is fibrosis of the connective tissue in the lamina cribrosa (LC) extracellular matrix. As a ubiquitous second messenger, calcium (Ca²⁺) can interact with various cellular proteins to regulate multiple physiological processes and contribute to a wide range of diseases, including cancer, fibrosis, and glaucoma. Our research has shown evidence of oxidative stress, mitochondrial dysfunction, an elevated expression of Ca²⁺ entry channels, Ca²⁺-dependent pumps and exchangers, and an abnormal rise in cytosolic Ca²⁺ in human glaucomatous LC fibroblast cells. We have evidence that this increase is dependent on Ca²⁺ entry channels located in the plasma membrane, and its release is from internal stores in the endoplasmic reticulum (ER), as well as from the mitochondria. Here, we summarize some of the molecular Ca²⁺-dependent mechanisms related to this abnormal Ca²⁺-signalling in human glaucoma LC cells, with a view toward identifying potential therapeutic targets for ongoing optic neuropathy.

Activation of PKC results in improved contractile effects and Ca cycling by inhibition of PP2A-B56α

Protein phosphatase 2A (PP2A) represents a heterotrimer that is responsible for the dephosphorylation of important regulatory myocardial proteins. The present study was aimed to test whether the phosphorylation of PP2A-B56α at Ser⁴¹ by PKC is involved in the regulation of myocyte Ca²⁺ cycling and contraction. For this purpose, heart preparations of wild-type (WT) and transgenic mice overexpressing the non-phosphorylatable S41A mutant form (TG) were stimulated by administration of the direct PKC activator phorbol 12-myristate 13-acetate (PMA), and functional effects were studied. PKC activation was accompanied by the inhibition of PP2A activity in WT cardiomyocytes, whereas this effect was absent in TG. Consistently, the increase in the sarcomere length shortening and the peak amplitude of Ca²⁺ transients after PMA administration in WT cardiomyocytes was attenuated in TG. However, the co-stimulation with 1 µM isoprenaline was able to offset these functional deficits. Moreover, TG hearts did not show an increase in the phosphorylation of the myosin-binding protein C after administration of PMA but was detected in corresponding WT. PMA modulated voltage-dependent activation of the L-type Ca²⁺ channel (LTCC) differently in the two genotypes, shifting V_1/2a by +1.5 mV in TG and by 2.4 mV in WT. In the presence of PMA, I_CaL inactivation remained unchanged in TG, whereas it was slower in corresponding WT. Our data suggest that PKC-activated enhancement of myocyte contraction and intracellular Ca²⁺ signaling is mediated by phosphorylation of B56α at Ser⁴¹, leading to a decrease in PP2A activity.

Putative role of natural products as Protein Kinase C modulator in different disease conditions

INTRODUCTION

Protein kinase C (PKC) is a promising drug target for various therapeutic areas. Natural products derived from plants, animals, microorganisms, and marine organisms have been used by humans as medicine from prehistoric times. Recently, several compounds derived from plants have been found to modulate PKC activities through competitive binding with ATP binding site, and other allosteric regions of PKC. As a result fresh race has been started in academia and pharmaceutical companies to develop an effective naturally derived small-molecule inhibitor to target PKC activities. Herein, in this review, we have discussed several natural products and their derivatives, which are reported to have an impact on PKC signaling cascade.

METHODS

All information presented in this review article regarding the regulation of PKC by natural products has been acquired by a systematic search of various electronic databases, including ScienceDirect, Scopus, Google Scholar, Web of science, ResearchGate, and PubMed. The keywords PKC, natural products, curcumin, rottlerin, quercetin, ellagic acid, epigallocatechin-3 gallate, ingenol 3 angelate, resveratrol, protocatechuic acid, tannic acid, PKC modulators from marine organism, bryostatin, staurosporine, midostaurin, sangivamycin, and other relevant key words were explored.

RESULTS

The natural products and their derivatives including curcumin, rottlerin, quercetin, ellagic acid, epigallocatechin-3 gallate, ingenol 3 angelate, resveratrol, bryostatin, staurosporine, and midostaurin play a major role in the management of PKC activity during various disease progression.

CONCLUSION

Based on the comprehensive literature survey, it could be concluded that various natural products can regulate PKC activity during disease progression. However, extensive research is needed to circumvent the challenge of isoform specific regulation of PKC by natural products.

Upregulation of COX-2 and PGE2 Induced by TNF-α Mediated Through TNFR1/MitoROS/PKCα/P38 MAPK, JNK1/2/FoxO1 Cascade in Human Cardiac Fibroblasts

Purpose

Tumor necrosis factor-α (TNF-α) has been shown to exert as a pathogenic factor in cardiac fibrosis and heart failure which were associated with the up-regulation of cyclooxygenase (COX)-2/prostaglandin E₂ (PGE₂) axis. However, whether TNF-α-induced COX-2/PGE₂ upregulation mediated through ROS-dependent cascade remains elusive in human cardiac fibroblasts (HCFs). This study aims to address the underlying mechanisms of TNF-α-induced COX-2/PGE₂ expression.

Methods

Here, we used TNF receptor neutralizing antibody (TNFR nAb), pharmacologic inhibitors, and siRNAs to dissect the involvement of signaling components examined by Western blot and ELISA in TNF-α-mediated responses in HCFs. MitoSOX Red was used to measure mitoROS generation. Isolation of subcellular fractions was performed to determine membrane translocation of PKCα. Promoter luciferase assay and chromatin immunoprecipitation (ChIP) assay were used to determine the role of transcription factor.

Results

We found that TNF-α time- and concentration-dependently upregulated COX-2 protein and mRNA expression as well as PGE₂ synthesis which was attenuated by TNFR1 nAb, the inhibitor of mitochondrial ROS scavenger (MitoTEMPO), protein kinase C [(PKC)α, Gö6976], p38 MAPK [p38 inhibitor VIII, (p38i VIII)], JNK1/2 (SP600125), or forkhead box protein O1 [(FoxO1), AS1842856], and transfection with their respective siRNAs in HCFs. TNF-α-stimulated PKCα phosphorylation was inhibited by TNFR1 nAb, MitoTEMPO, or Gö6976. TNF-α stimulated phosphorylation of p38 MAPK and JNK1/2 was attenuated by TNFR1 nAb, MitoTEMPO, Gö6976, and their inhibitors p38i VIII and SP600125. Moreover, TNF-α-triggered FoxO1 phosphorylation was abolished by AS1842856, TNFR1 nAb, and its upstream inhibitors MitoTEMPO, Gö6976, p38i VIII, and SP600125. Phosphorylation of FoxO1 could enhance its interaction with the COX-2 promoter element revealed by ChIP assay, which was attenuated by AS1842856.

Conclusion

Our results suggested that TNF-α-induced COX-2/PGE₂ upregulation is mediated through TNFR1-dependent MitoROS/PKCα/p38 MAPK and JNK1/2 cascade to activate FoxO1 binding with the COX-2 promoter in HCFs.

Kinase inhibitors allosterically disrupt a regulatory interaction to enhance PKCα membrane translocation

The eukaryotic kinase domain has multiple intrinsically disordered regions whose conformation dictates kinase activity. Small molecule kinase inhibitors (SMKIs) rely on disrupting the active conformations of these disordered regions to inactivate the kinase. While SMKIs are selected for their ability to cause this disruption, the allosteric effects of conformational changes in disordered regions is limited by a lack of dynamic information provided by traditional structural techniques. In this study, we integrated multiscale molecular dynamics simulations with FRET sensors to characterize a novel allosteric mechanism that is selectively triggered by SMKI binding to the protein kinase Cα domain. The indole maleimide inhibitors BimI and sotrastaurin were found to displace the Gly-rich loop (G-loop) that normally shields the ATP-binding site. Displacement of the G-loop interferes with a newly identified, structurally conserved binding pocket for the C1a domain on the N lobe of the kinase domain. This binding pocket, in conjunction with the N-terminal regulatory sequence, masks a diacylglycerol (DAG) binding site on the C1a domain. SMKI-mediated displacement of the G-loop released C1a and exposed the DAG binding site, enhancing protein kinase Cα translocation both to synthetic lipid bilayers and to live cell membranes in the presence of DAG. Inhibitor chemotype determined the extent of the observed allosteric effects on the kinase domain and correlated with the extent of membrane recruitment. Our findings demonstrate the allosteric effects of SMKIs beyond the confines of kinase catalytic conformation and provide an integrated computational-experimental paradigm to investigate parallel mechanisms in other kinases.

MBNL1 regulates isoproterenol-induced myocardial remodelling in vitro and in vivo

Myocardial remodelling is a common phenomenon in cardiovascular diseases, which threaten human health and the quality of life. Due to the lack of effective early diagnosis and treatment methods, the molecular mechanism of myocardial remodelling should be explored in depth. In this study, we observed the high expression of MBNL1 in cardiac tissue and peripheral blood of an isoproterenol (ISO)-induced cardiac hypertrophy mouse model. MBNL1 promoted ISO-induced cardiac hypertrophy and fibrosis by stabilizing Myocardin mRNA in vivo and in vitro. Meanwhile, an increase in MBNL1 may induce the apoptosis of cardiomyocytes treated with ISO via TNF-α signalling. Interestingly, MBNL1 can be activated by p300 in cardiomyocytes treated with ISO. At last, Myocardin can reverse activate the expression of MBNL1. These results suggest that MBNL1 may be a potential target for the early diagnosis and clinical treatment of myocardial remodelling.

Intra-Cellular Calcium Signaling Pathways (PKC, RAS/RAF/MAPK, PI3K) in Lamina Cribrosa Cells in Glaucoma

The lamina cribrosa (LC) is a key site of fibrotic damage in glaucomatous optic neuropathy and the precise mechanisms of LC change remain unclear. Elevated Ca²⁺ is a major driver of fibrosis, and therefore intracellular Ca²⁺ signaling pathways are relevant glaucoma-related mechanisms that need to be studied. Protein kinase C (PKC), mitogen-activated MAPK kinases (p38 and p42/44-MAPK), and the PI3K/mTOR axis are key Ca²⁺ signal transducers in fibrosis and we therefore investigated their expression and activity in normal and glaucoma cultured LC cells. We show, using Western immune-blotting, that hyposmotic-induced cellular swelling activates PKCα, p42/p44, and p38 MAPKs, the activity is transient and biphasic as it peaks between 2 min and 10 min. The expression and activity of PKCα, p38 and p42/p44-MAPKs are significantly (p < 0.05) increased in glaucoma LC cells at basal level, and at different time-points after hyposmotic stretch. We also found elevated mRNA expression of mRNA expression of PI3K, IP3R, mTOR, and CaMKII in glaucoma LC cells. This study has identified abnormalities in multiple calcium signaling pathways (PKCα, MAPK, PI3K) in glaucoma LC cells, which might have significant functional and therapeutic implications in optic nerve head (ONH) fibrosis and cupping in glaucoma.

Dynamic regulation of NADPH oxidase 5 by intracellular heme levels and cellular chaperones

NADPH oxidase 5 (NOX5) is a transmembrane signaling enzyme that produces superoxide in response to elevated cytosolic calcium. In addition to its association with numerous human diseases, NOX5 has recently been discovered to play crucial roles in the immune response and cardiovascular system. Details of NOX5 maturation, and specifically its response to changes in intracellular heme levels have remained unclear. Here we establish an experimental system in mammalian cells that allows us to probe the influence of heme availability on ROS production by NOX5. We identified a mode of dynamic regulatory control over NOX5 activity through modulation of its heme saturation and oligomeric state by intracellular heme levels and Hsp90 binding. This regulatory mechanism allows for fine-tuning and reversible modulation of NOX5 activity in response to stimuli.

Association of Regulatory Genetic Variants for Protein Kinase Cα with Mortality and Drug Efficacy in Patients with Heart Failure

PURPOSE

Protein kinase C alpha (gene: PRKCA) is a key regulator of cardiac contractility. Two genetic variants have recently been discovered to regulate PRKCA expression in failing human heart tissue (rs9909004 [T → C] and rs9303504 [C → G]). The association of those variants with clinical outcomes in patients with heart failure (HF), and their interaction with HF drug efficacy, is unknown.

METHODS

Patients with HF in a prospective registry starting in 2007 were genotyped by whole genome array (n = 951). The primary outcome was all-cause mortality. Cox proportional hazards models adjusted for established clinical risk factors and genomic ancestry tested the independent association of rs9909004 or rs9303504 and the variant interactions with cornerstone HF pharmacotherapies (beta-blockers or angiotensin-converting enzyme inhibitors/angiotensin receptor blockers) in additive genetic models.

RESULTS

The minor allele of rs9909004, but not of rs9303504, was independently associated with a decreased risk for all-cause mortality: adjusted HR = 0.81 (95% CI = 0.67-0.98), p = 0.032. The variants did not significantly interact with mortality benefit associated with cornerstone HF pharmacotherapies (p > 0.1 for all).

CONCLUSIONS

A recently discovered cardiac-specific regulatory variant for PRKCA (rs9909004) was independently associated with a decreased risk for all-cause mortality in patients with HF. The variant did not interact with mortality benefit associated with cornerstone HF pharmacotherapies.

Protein kinase Cα deletion causes hypotension and decreased vascular contractility

AIM

Protein kinase Cα (PKCα) is a critical regulator of multiple cell signaling pathways including gene transcription, posttranslation modifications and activation/inhibition of many signaling kinases. In regards to the control of blood pressure, PKCα causes increased vascular smooth muscle contractility, while reducing cardiac contractility. In addition, PKCα has been shown to modulate nephron ion transport. However, the role of PKCα in modulating mean arterial pressure (MAP) has not been investigated. In this study, we used a whole animal PKCα knock out (PKC KO) to test the hypothesis that global PKCα deficiency would reduce MAP, by a reduction in vascular contractility.

METHODS

Radiotelemetry measurements of ambulatory blood pressure (day/night) were obtained for 18 h/day during both normal chow and high-salt (4%) diet feedings. PKCα mice had a reduced MAP, as compared with control, which was not normalized with high-salt diet (14 days). Metabolic cage studies were performed to determine urinary sodium excretion.

RESULTS

PKC KO mice had a significantly lower diastolic, systolic and MAP as compared with control. No significant differences in urinary sodium excretion were observed between the PKC KO and control mice, whether fed normal chow or high-salt diet. Western blot analysis showed a compensatory increase in renal sodium chloride cotransporter expression. Both aorta and mesenteric vessels were removed for vascular reactivity studies. Aorta and mesenteric arteries from PKC KO mice had a reduced receptor-independent relaxation response, as compared with vessels from control. Vessels from PKC KO mice exhibited a decrease in maximal contraction, compared with controls.

CONCLUSION

Together, these data suggest that global deletion of PKCα results in reduced MAP due to decreased vascular contractility.

Protein Kinase C: Targets to Regenerate Brain Injuries?

Acute or chronic injury to the central nervous system (CNS), causes neuronal death and irreversible cognitive deficits or sensory-motor alteration. Despite the capacity of the adult CNS to generate new neurons from neural stem cells (NSC), neuronal replacement following an injury is a restricted process, which does not naturally result in functional regeneration. Therefore, potentiating endogenous neurogenesis is one of the strategies that are currently being under study to regenerate damaged brain tissue. The insignificant neurogenesis that occurs in CNS injuries is a consequence of the gliogenic/non-neurogenic environment that inflammatory signaling molecules create within the injured area. The modification of the extracellular signals to generate a neurogenic environment would facilitate neuronal replacement. However, in order to generate this environment, it is necessary to unearth which molecules promote or impair neurogenesis to introduce the first and/or eliminate the latter. Specific isozymes of the protein kinase C (PKC) family differentially contribute to generate a gliogenic or neurogenic environment in injuries by regulating the ADAM17 mediated release of growth factor receptor ligands. Recent reports describe several non-tumorigenic diterpenes isolated from plants of the Euphorbia genus, which specifically modulate the activity of PKC isozymes promoting neurogenesis. Diterpenes with 12-deoxyphorbol or lathyrane skeleton, increase NPC proliferation in neurogenic niches in the adult mouse brain in a PKCβ dependent manner exerting their effects on transit amplifying cells, whereas PKC inhibition in injuries promotes neurogenesis. Thus, compounds that balance PKC activity in injuries might be of use in the development of new drugs and therapeutic strategies to regenerate brain injuries.

Genetic Reduction in Left Ventricular Protein Kinase C-α and Adverse Ventricular Remodeling in Human Subjects

BACKGROUND

Inhibition of PKC-α (protein kinase C-α) enhances contractility and cardioprotection in animal models, but effects in humans are unknown. Genotypes at rs9912468 strongly associate with PRKCA expression in the left ventricle, enabling genetic approaches to measure effects of reduced PKC-α in human populations.

METHODS AND RESULTS

We analyzed the cis expression quantitative trait locus for PRKCA marked by rs9912468 using 313 left ventricular specimens from European Ancestry patients. The forward strand minor allele (G) at rs9912468 is associated with reduced PKC-α transcript abundance (1.7-fold reduction in minor allele homozygotes, P=1×10^-41). This association was cardiac specific in expression quantitative trait locus data sets that span 16 human tissues. Cardiac epigenomic data revealed a predicted enhancer in complete (R²=1.0) linkage disequilibrium with rs9912468 within intron 2 of PRKCA. We cloned this region and used reporter constructs to verify cardiac-specific enhancer activity in vitro in cardiac and noncardiac cells and in vivo in zebrafish. The PRKCA enhancer contains 2 common genetic variants and 4 haplotypes; the haplotype correlated with the rs9912468 PKC-α-lowering allele (G) showed lowest activity. In contrast to previous reports in animal models, the PKC-α-lowering allele is associated with adverse left ventricular remodeling (higher mass, larger diastolic dimension), reduced fractional shortening, and higher risk of dilated cardiomyopathy in human populations.

CONCLUSIONS

These findings support PKC-α as a regulator of the human heart but suggest that PKC-α inhibition may adversely affect the left ventricle depending on timing and duration. Pharmacological studies in human subjects are required to discern potential benefits and harms of PKC-α inhibitors as an approach to treat heart disease.

Sensitization of the Angiotensin II AT1 Receptor Contributes to RKIP-Induced Symptoms of Heart Failure

Inhibition of the G-protein-coupled receptor kinase 2 (GRK2) is an emerging treatment approach for heart failure. Therefore, cardio-protective mechanisms induced by GRK2 inhibition are under investigation. We compared two different GRK2 inhibitors, i.e., (i) the dual-specific GRK2 and raf kinase inhibitor protein, RKIP, and (ii) the dominant-negative GRK2-K220R mutant. We found that RKIP induced a strong sensitization of Gq/11-dependent, heart failure-promoting angiotensin II AT1 receptor signaling. The AT1-sensitizing function of RKIP was mediated by the RKIP-GRK2 interaction because the RKIP-S153V mutant, which does not interact with GRK2, had no effect on AT1-stimulated signaling. In contrast, GRK2-K220R significantly inhibited the AT1-stimulated signal. The in vivo relevance of these major differences between two different approaches of GRK2 inhibition was analyzed by generation of transgenic mice with myocardium-specific expression of RKIP and GRK2-K220R. Our results showed that a moderately increased cardiac protein level of RKIP was sufficient to induce major symptoms of heart failure in aged, 8-months-old RKIP-transgenic mice in two different genetic backgrounds. In contrast, GRK2-K220R protected against chronic pressure overload-induced cardiac dysfunction. The AT1 receptor contributed to RKIP-induced heart failure because treatment with the AT1 receptor antagonist, losartan, retarded symptoms of heart failure in RKIP-transgenic mice. Thus, sensitization of the heart failure-promoting AT1 receptor by the RKIP-GRK2 interaction contributes to heart failure whereas dominant-negative GRK2-K220R is cardioprotective. Because RKIP is up-regulated on cardiac biopsy specimens of heart failure patients, the deduced heart failure-promoting mechanism of RKIP could also be relevant for the human disease.

Mutant Muscle LIM Protein C58G causes cardiomyopathy through protein depletion

Cysteine and glycine rich protein 3 (CSRP3) encodes Muscle LIM Protein (MLP), a well-established disease gene for Hypertrophic Cardiomyopathy (HCM). MLP, in contrast to the proteins encoded by the other recognised HCM disease genes, is non-sarcomeric, and has important signalling functions in cardiomyocytes. To gain insight into the disease mechanisms involved, we generated a knock-in mouse (KI) model, carrying the well documented HCM-causing CSRP3 mutation C58G.

In vivo phenotyping of homozygous KI/KI mice revealed a robust cardiomyopathy phenotype with diastolic and systolic left ventricular dysfunction, which was supported by increased heart weight measurements. Transcriptome analysis by RNA-seq identified activation of pro-fibrotic signalling, induction of the fetal gene programme and activation of markers of hypertrophic signalling in these hearts. Further ex vivo analyses validated the activation of these pathways at transcript and protein level. Intriguingly, the abundance of MLP decreased in KI/KI mice by 80% and in KI/+ mice by 50%. Protein depletion was also observed in cellular studies for two further HCM-causing CSRP3 mutations (L44P and S54R/E55G). We show that MLP depletion is caused by proteasome action. Moreover, MLP C58G interacts with Bag3 and results in a proteotoxic response in the homozygous knock-in mice, as shown by induction of Bag3 and associated heat shock proteins.

In conclusion, the newly generated mouse model provides insights into the underlying disease mechanisms of cardiomyopathy caused by mutations in the non-sarcomeric protein MLP. Furthermore, our cellular experiments suggest that protein depletion and proteasomal overload also play a role in other HCM-causing CSPR3 mutations that we investigated, indicating that reduced levels of functional MLP may be a common mechanism for HCM-causing CSPR3 mutations.

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We present a mouse model for non-sarcomeric hypertrophic cardiomyopathy (HCM).

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Homozygous Muscle LIM Protein (MLP) C58G mice have systolic and diastolic dysfunction.

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MLP C58G is depleted via proteasomal pathways.

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Protein depletion is also a hallmark of further HCM causing MLP mutations.

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MLP C58G interacts with Bag3 and causes a proteotoxic response.

Astragalosides increase the cardiac diastolic function and regulate the "Calcium sensing receptor-protein kinase C-protein phosphatase 1" pathway in rats with heart failure

This study was designed to investigate the effects of astragalosides on cardiac diastolic function, and an emphasis was placed on the variation of the upstream molecular regulators of phospholamban. Chronic heart failure (CHF) rats were induced by ligaturing the left anterior coronary artery, and rats in the therapeutic groups were treated with either a 50 mg/kg dose of captopril, 10 mg/kg dose of astragalosides or 20 mg/kg dose of astragalosides. Four weeks after treatment, the ratio of the early and atrial peak filling velocities (E/A) and maximal slope diastolic pressure decrement (-dp/dt) both decreased in CHF rats (by 30.3% and 25.5%, respectively) and significantly increased in 20 mg/kg astragalosides and captopril-treated rats. The protein phosphatase-1 activity was lower in the 20 mg/kg astragalosides group than in the CHF group (0.22 vs 0.44, P < 0.01), and the inhibitor-1 levels in the astragalosides and captopril-treated groups were increased. Chronic heart failure increased expression of protein kinase C-α and calcium-sensing receptor, and these changes were attenuated by astragalosides therapy. Astragalosides restored the diastolic dysfunction of chronic heart failure rats, possibly by downregulation of calcium-sensing receptor and protein kinase C-α, which in turn augmented inhibitor-1 expression, reduced protein phosphatase-1 activity and increased phospholamban phosphorylation.

In Silico Analysis of Differential Gene Expression in Three Common Rat Models of Diastolic Dysfunction

Standard therapies for heart failure with preserved ejection fraction (HFpEF) have been unsuccessful, demonstrating that the contribution of the underlying diastolic dysfunction pathophysiology differs from that of systolic dysfunction in heart failure and currently is far from being understood. Complicating the investigation of HFpEF is the contribution of several comorbidities. Here, we selected three established rat models of diastolic dysfunction defined by three major risk factors associated with HFpEF and researched their commonalities and differences. The top differentially expressed genes in the left ventricle of Dahl salt sensitive (Dahl/SS), spontaneous hypertensive heart failure (SHHF), and diabetes 1 induced HFpEF models were derived from published data in Gene Expression Omnibus and used for a comprehensive interpretation of the underlying pathophysiological context of each model. The diversity of the underlying transcriptomic of the heart of each model is clearly observed by the different panel of top regulated genes: the diabetic model has 20 genes in common with the Dahl/SS and 15 with the SHHF models. Advanced analytics performed in Ingenuity Pathway Analysis (IPA^®) revealed that Dahl/SS heart tissue transcripts triggered by upstream regulators lead to dilated cardiomyopathy, hypertrophy of heart, arrhythmia, and failure of heart. In the heart of SHHF, a total of 26 genes were closely linked to cardiovascular disease including cardiotoxicity, pericarditis, ST-elevated myocardial infarction, and dilated cardiomyopathy. IPA Upstream Regulator analyses revealed that protection of cardiomyocytes is hampered by inhibition of the ERBB2 plasma membrane-bound receptor tyrosine kinases. Cardioprotective markers such as natriuretic peptide A (NPPA), heat shock 27 kDa protein 1 (HSPB1), and angiogenin (ANG) were upregulated in the diabetes 1 induced model; however, the model showed a different underlying mechanism with a majority of the regulated genes involved in metabolic disorders. In conclusion, our findings suggest that multiple mechanisms may contribute to diastolic dysfunction and HFpEF, and thus drug therapies may need to be guided more by phenotypic characteristics of the cardiac remodeling events than by the underlying molecular processes.

Protein Kinase C Inhibition With Ruboxistaurin Increases Contractility and Reduces Heart Size in a Swine Model of Heart Failure With Reduced Ejection Fraction

Inotropic support is often required to stabilize the hemodynamics of patients with acute decompensated heart failure; while efficacious, it has a history of leading to lethal arrhythmias and/or exacerbating contractile and energetic insufficiencies. Novel therapeutics that can improve contractility independent of beta-adrenergic and protein kinase A-regulated signaling, should be therapeutically beneficial. This study demonstrates that acute protein kinase C-α/β inhibition, with ruboxistaurin at 3 months' post-myocardial infarction, significantly increases contractility and reduces the end-diastolic/end-systolic volumes, documenting beneficial remodeling. These data suggest that ruboxistaurin represents a potential novel therapeutic for heart failure patients, as a moderate inotrope or therapeutic, which leads to beneficial ventricular remodeling.

Research advances in kinase enzymes and inhibitors for cardiovascular disease treatment

The targeting of protein kinases has great future potential for the design of new drugs against cardiovascular diseases (CVDs). Enormous efforts have been made toward achieving this aim. Unfortunately, kinase inhibitors designed to treat CVDs have suffered from numerous limitations such as poor selectivity, bad permeability and toxicity. So, where are we now in terms of discovering effective kinase targeting drugs to treat CVDs? Various drug design techniques have been approached for this purpose since the discovery of the inhibitory activity of Staurosporine against protein kinase C in 1986. This review aims to provide context for the status of several emerging classes of direct kinase modulators to treat CVDs and discuss challenges that are preventing scientists from finding new kinase drugs to treat heart disease.

Protein kinase C isozyme expression in right ventricular hypertrophy induced by pulmonary hypertension in chronically hypoxic rats

In chronic hypoxia, pulmonary hypertension (PH) induces right ventricular hypertrophy (RVH). Evidence indicates that protein kinase C (PKC) serves a crucial role in hypoxia-induced RVH. The present study investigated PKC isoform-specific expression and its involvement in RVH. Rats were exposed to normobaric hypoxia for a number of days to induce PH. PKC isoform-specific membrane translocation and protein expression in the myocardium were evaluated by western blotting and immunostaining. A total of six isoforms of conventional PKC (cPKC; α, βI and βII) and of novel PKC (nPKC; δ, ε and η), were detected in the rat myocardium. Hypoxic exposure (1–21 days) induced PH with RVH and vascular remodeling. nPKCδ membrane translocation at 3–7 days and cPKCβI expression at 1–21 days in the RV following hypoxic exposure were significantly decreased as compared with the normoxia control group. Membrane translocation of cPKCβII at 14–21 days and of nPKCη at 7–21 days in the left ventricle following hypoxic exposure was significantly increased when compared with the control. The results of the present study suggested that the alterations in membrane translocation, and nPKCδ and cPKCβI expression, are associated with RVH following PH, and the upregulation of cPKCβII membrane translocation is involved in left-sided heart failure.

Protein kinase C mechanisms that contribute to cardiac remodelling

Protein phosphorylation is a highly-regulated and reversible process that is precisely controlled by the actions of protein kinases and protein phosphatases. Factors that tip the balance of protein phosphorylation lead to changes in a wide range of cellular responses, including cell proliferation, differentiation and survival. The protein kinase C (PKC) family of serine/threonine kinases sits at nodal points in many signal transduction pathways; PKC enzymes have been the focus of considerable attention since they contribute to both normal physiological responses as well as maladaptive pathological responses that drive a wide range of clinical disorders. This review provides a background on the mechanisms that regulate individual PKC isoenzymes followed by a discussion of recent insights into their role in the pathogenesis of diseases such as cancer. We then provide an overview on the role of individual PKC isoenzymes in the regulation of cardiac contractility and pathophysiological growth responses, with a focus on the PKC-dependent mechanisms that regulate pump function and/or contribute to the pathogenesis of heart failure.

Effect of α7 nicotinic acetylcholine receptor activation on cardiac fibroblasts: a mechanism underlying RV fibrosis associated with cigarette smoke exposure

Right ventricular (RV) dysfunction is associated with numerous smoking-related illnesses, including chronic obstructive pulmonary disease (COPD), in which it is present even in the absence of pulmonary hypertension. It is unknown whether exposure to cigarette smoke (CS) has direct effects on RV function and cardiac fibroblast (CF) proliferation or collagen synthesis. In this study, we evaluated cardiac function and fibrosis in mice exposed to CS and determined mechanisms of smoke-induced changes in CF signaling and fibrosis. AKR mice were exposed to CS for 6 wk followed by echocardiography and evaluation of cardiac hypertrophy, collagen content, and pulmonary muscularization. Proliferation and collagen content were evaluated in primary isolated rat CFs exposed to CS extract (CSE) or nicotine. Markers of cell proliferation, fibrosis, and proliferative signaling were determined by immunoblot or Sircol collagen assay. Mice exposed to CS had significantly decreased RV function, as determined by tricuspid annular plane systolic excursion. There were no changes in left ventricular parameters. RV collagen content was significantly elevated, but there was no change in RV hypertrophy or pulmonary vascular muscularization. CSE directly increased CF proliferation and collagen content in CF. Nicotine alone reproduced these effects. CSE and nicotine-induced fibroblast proliferation and collagen content were mediated through α7 nicotinic acetylcholine receptors and were dependent on PKC-α, PKC-δ, and reduced p38-MAPK phosphorylation. CS and nicotine have direct effects on CFs to induce proliferation and fibrosis, which may negatively affect right heart function.

Effect of PKC inhibitor on experimental autoimmune myocarditis in Lewis rats

Myocarditis is a major cause of sudden, unexpected death in young people. However, it is still one of the most challenging diseases to treat in cardiology. In the present study, we showed that both expression level and activity of PKC-α were up-regulated in the rat heart of experimental autoimmune myocarditis (EAM). Intraperitoneal administration of PKC inhibitor (Ro-32-0432) at the end of the most severe inflammation period of EAM still significantly reduced the EAM induced expression of failure biomarkers. Furthermore, Ro-32-0432 reduced the ratio of Bax/Bcl-2 and suppressed the expression of cleaved caspase-3, both of which were increased in the heart of the EAM rats, suggesting an anti-apoptotic role of Ro-32-0432. Besides, Ro-32-0432 suppressed EAM-induced cardiac fibrosis and release of pro-inflammatory cytokines IL-1β and IL-17. These results suggest that inhibition of PKC may serve as a potential therapeutic strategy for the treatment of myocarditis.

Ginsenoside Rb1 improves cardiac function and remodeling in heart failure

We investigated the effect of ginsenoside Rb1 on cardiac function and remodeling in heart failure (HF). Four weeks after HF induction, the rats were administrated with ginsenoside Rb1 (35 and 70 mg/kg) and losartan (4.5 mg/kg) for 8 weeks. Losartan was used as a positive control. Cardiac function was assessed by measuring hemodynamic parameters. Histological changes were analyzed by HE and Masson’s trichrome staining. Cardiac hypertrophy, fibrosis, mitochondrial membrane potential and glucose transporter type 4 (GLUT4) levels were evaluated. In the present study, high dose of (H−) ginsenoside Rb1 decreased heart rate, improved cardiac function and alleviated histological changes induced by HF. H-ginsenoside Rb1 attenuated cardiac hypertrophy and myocardial fibrosis by decreasing left ventricular (LV) weight/heart weight ratio and cardiomyocyte cross-sectional area and reducing the levels of atrial natriuretic factor (ANF), β-myosin heavy chain (β-MHC), periostin, collagen I, Angiotensin II (Ang II), Angiotensin converting enzyme (ACE) and Ang II type 1 (AT1) receptor. Moreover, H-ginsenoside Rb1 decreased mitochondrial membrane potential and enhanced the translocation of GLUT4 to plasma membrane. The TGF-β1/Smad and ERK signaling pathways were inhibited and the Akt pathway was activated. These findings suggest that ginsenoside Rb1 might restore cardiac/mitochondrial function, increase glucose uptake and protect against cardiac remodeling via the TGF-β1/Smad, ERK and Akt signaling pathways.

Sub-cellular localization specific SUMOylation in the heart

Although the majority of SUMO substrates are localized in the nucleus, SUMOylation is not limited to nuclear proteins and can be also detected in extra-nuclear proteins. In this review, we will highlight and discuss how SUMOylation in different cellular compartments regulate biological processes. First, we will discuss the key role of SUMOylation of proteins in the extra-nuclear compartment in cardiomyocytes, which is overwhelmingly cardio-protective. On the other hand, SUMOylation of nuclear proteins is generally detrimental to the cardiac function mainly because of the trans-repressive nature of SUMOylation on many transcription factors. We will also discuss the potential role of SUMOylation in epigenetic regulation. In this review, we will propose a new concept that shuttling of SUMO proteases between the nuclear and extra-nuclear compartments without changing their enzymatic activity regulates the extent of SUMOylation in these compartments and determines the response and fate of cardiomyocytes after cardiac insults. Approaches focused specifically to inhibit this shuttling in cardiomyocytes will be necessary to understand the whole picture of SUMOylation and its pathophysiological consequences in the heart, especially after cardiac insults. This article is part of a Special Issue entitled: Genetic and epigenetic control of heart failure - edited by Jun Ren & Megan Yingmei Zhang.

Doxazosin Stimulates Galectin-3 Expression and Collagen Synthesis in HL-1 Cardiomyocytes Independent of Protein Kinase C Pathway

Doxazosin, a drug commonly prescribed for hypertension and prostate disease, increases heart failure risk. However, the underlying mechanism remains unclear. Galectin-3 is an important mediator that plays a pathogenic role in cardiac hypertrophy and heart failure. In the present study, we investigated whether doxazosin could stimulate galectin-3 expression and collagen synthesis in cultured HL-1 cardiomyocytes. We found that doxazosin dose-dependently induced galectin-3 protein expression, with a statistically significant increase in expression with a dose as low as 0.01 μM. Doxazosin upregulated collagen I and α-smooth muscle actin (α-SMA) protein levels and also induced apoptotic protein caspase-3 in HL-1 cardiomyocytes. Although we previously reported that activation of protein kinase C (PKC) stimulates galectin-3 expression, blocking the PKC pathway with the PKC inhibitor chelerythrine did not prevent doxazosin-induced galectin-3 and collagen expression. Consistently, doxazosin treatment did not alter total and phosphorylated PKC. These results suggest that doxazosin-stimulated galectin-3 is independent of PKC pathway. To determine if the α1-adrenergic pathway is involved, we pretreated the cells with the irreversible α-adrenergic receptor blocker phenoxybenzamine and found that doxazosin-stimulated galectin-3 and collagen expression was similar to controls, suggesting that doxazosin acts independently of α1-adrenergic receptor blockade. Collectively, we show a novel effect of doxazosin on cardiomycytes by stimulating heart fibrosis factor galectin-3 expression. The mechanism of action of doxazosin is not mediated through either activation of the PKC pathway or antagonism of α1-adrenergic receptors.

Curcumin Inhibits Protein Kinase Cα Activity by Binding to Its C1 Domain

Curcumin is a polyphenolic nutraceutical that acts on multiple biological targets, including protein kinase C (PKC). PKC is a family of serine/threonine kinases central to intracellular signal transduction. We have recently shown that curcumin selectively inhibits PKCα, but not PKCε, in CHO-K1 cells [Pany, S. (2016) Biochemistry 55, 2135-2143]. To understand which domain(s) of PKCα is responsible for curcumin binding and inhibitory activity, we made several domain-swapped mutants in which the C1 (combination of C1A and C1B) and C2 domains are swapped between PKCα and PKCε. Phorbol ester-induced membrane translocation studies using confocal microscopy and immunoblotting revealed that curcumin inhibited phorbol ester-induced membrane translocation of PKCε mutants, in which the εC1 domain was replaced with αC1, but not the PKCα mutant in which αC1 was replaced with the εC1 domain, suggesting that αC1 is a determinant for curcumin's inhibitory effect. In addition, curcumin inhibited membrane translocation of PKCε mutants, in which the εC1A and εC1B domains were replaced with the αC1A and αC1B domains, respectively, indicating the role of both αC1A and αC1B domains in curcumin's inhibitory effects. Phorbol 13-acetate inhibited the binding of curcumin to αC1A and αC1B with IC₅₀ values of 6.27 and 4.47 μM, respectively. Molecular docking and molecular dynamics studies also supported the higher affinity of curcumin for αC1B than for αC1A. The C2 domain-swapped mutants were inactive in phorbol ester-induced membrane translocation. These results indicate that curcumin binds to the C1 domain of PKCα and highlight the importance of this domain in achieving PKC isoform selectivity.

How cardiomyocytes sense pathophysiological stresses for cardiac remodeling

In the past decades, the cardiovascular community has laid out the fundamental signaling cascades that become awry in the cardiomyocyte during the process of pathologic cardiac remodeling. These pathways are initiated at the cell membrane and work their way to the nucleus to mediate gene expression. Complexity is multiplied as the cardiomyocyte is subjected to cross talk with other cells as well as a barrage of extracellular stimuli and mechanical stresses. In this review, we summarize the signaling cascades that play key roles in cardiac function and then we proceed to describe emerging concepts of how the cardiomyocyte senses the mechanical and environmental stimuli to transition to the deleterious genetic program that defines pathologic cardiac remodeling. As a highlighting example of these processes, we illustrate the transition from a compensated hypertrophied myocardium to a decompensated failing myocardium, which is clinically manifested as decompensated heart failure.

Selective Modulation of Protein Kinase C α over Protein Kinase C ε by Curcumin and Its Derivatives in CHO-K1 Cells

Members of the protein kinase C (PKC) family of serine/threonine kinases regulate various cellular functions, including cell growth, differentiation, metabolism, and apoptosis. Modulation of isoform-selective activity of PKC by curcumin (1), the active constituent of Curcuma L., is poorly understood, and the literature data are inconsistent and obscure. The effect of curcumin (1) and its analogues, 4-[(2Z,6E)-3-hydroxy-7-(4-hydroxy-3-methoxyphenyl)-5-oxohepta-2,6-dien-1-yl]-2-methoxyphenyl oleate (2), (9Z,12Z)-4-[(2Z,6E)-3-hydroxy-7-(4-hydroxy-3-methoxyphenyl)-5-oxohepta-2,6-dien-1-yl]-2-methoxyphenyl octadeca-9,12-dienoate (3), (9Z,12Z,15Z)-4-[(2Z,6E)-3-hydroxy-7-(4-hydroxy-3-methoxyphenyl)-5-oxohepta-2,6-dien-1-yl]-2-methoxyphenyl octadeca-9,12,15-trienoate (4), and (1E,6E)-1-[4-(hexadecyloxy)-3-methoxyphenyl]-7-(4-hydroxy-3-methoxyphenyl)hepta-1,6-diene-3,5-dione (5), and didemethylcurcumin (6) on the membrane translocation of PKCα, a conventional PKC, and PKCε, a novel PKC, has been studied in CHO-K1 cells, in which these PKC isoforms are endogenously expressed. Translocation of PKC from the cytosol to the membrane was measured using immunoblotting and confocal microscopy. 1 and 6 inhibited the TPA-induced membrane translocation of PKCα but not of PKCε. Modification of the hydroxyl group of curcumin with a long aliphatic chain containing unsaturated double bonds in 2-4 completely abolished this inhibition property. Instead, 2-4 showed significant translocation of PKCα but not of PKCε to the membrane. No membrane translocation was observed with 1, 6, or the analogue 5 having a saturated long chain for either PKCα or PKCε. 1 and 6 inhibited TPA-induced activation of ERK1/2, and 2-4 activated it. ERK1/2 is the downstream readout of PKC. These results show that the hydroxyl group of curcumin is important for PKC activity and the curcumin template can be useful in developing isoform specific PKC modulators for regulating a particular disease state.

Expressing an inhibitor of PLCβ1b sustains contractile function following pressure overload

The activity of phospholipase Cβ1b (PLCβ1b) is selectively elevated in failing myocardium and cardiac expression of PLCβ1b causes contractile dysfunction. PLCβ1b can be selectively inhibited by expressing a peptide inhibitor that prevents sarcolemmal localization. The inhibitory peptide, PLCβ1b-CT was expressed in heart from a mini-gene using adeno-associated virus (rAAV6-PLCβ1b-CT). rAAV6-PLCβ1b-CT, or blank virus, was delivered IV (4×10(9)vg/g body weight) and trans-aortic-constriction (TAC) or sham-operation was performed 8weeks later. Expression of PLCβ1b-CT prevented the loss of contractile function, eliminated lung congestion and improved survival following TAC with either a 'moderate' or 'severe' pressure gradient. Hypertrophy was attenuated but not eliminated. Expression of the PLCβ1b-CT peptide 2-3weeks after TAC reduced contractile dysfunction and lung congestion, without limiting hypertrophy. PLCβ1b inhibition ameliorates pathological responses following acute pressure overload. The targeting of PLCβ1b to the sarcolemma provides the basis for the development of a new class of inotropic agent.

Inhibition of G-protein-coupled Receptor Kinase 2 Prevents the Dysfunctional Cardiac Substrate Metabolism in Fatty Acid Synthase Transgenic Mice

Impairment of myocardial fatty acid substrate metabolism is characteristic of late-stage heart failure and has limited treatment options. Here, we investigated whether inhibition of G-protein-coupled receptor kinase 2 (GRK2) could counteract the disturbed substrate metabolism of late-stage heart failure. The heart failure-like substrate metabolism was reproduced in a novel transgenic model of myocardium-specific expression of fatty acid synthase (FASN), the major palmitate-synthesizing enzyme. The increased fatty acid utilization of FASN transgenic neonatal cardiomyocytes rapidly switched to a heart failure phenotype in an adult-like lipogenic milieu. Similarly, adult FASN transgenic mice developed signs of heart failure. The development of disturbed substrate utilization of FASN transgenic cardiomyocytes and signs of heart failure were retarded by the transgenic expression of GRKInh, a peptide inhibitor of GRK2. Cardioprotective GRK2 inhibition required an intact ERK axis, which blunted the induction of cardiotoxic transcripts, in part by enhanced serine 273 phosphorylation of Pparg (peroxisome proliferator-activated receptor γ). Conversely, the dual-specific GRK2 and ERK cascade inhibitor, RKIP (Raf kinase inhibitor protein), triggered dysfunctional cardiomyocyte energetics and the expression of heart failure-promoting Pparg-regulated genes. Thus, GRK2 inhibition is a novel approach that targets the dysfunctional substrate metabolism of the failing heart.

Regulation of CaMKII signaling in cardiovascular disease

Heart failure (HF) is a major cause of death in the developed countries (Murray and Lopez, 1996; Koitabashi and Kass, 2012). Adverse cardiac remodeling that precedes heart muscle dysfunction is characterized by a myriad of molecular changes affecting the cardiomyocyte. Among these, alterations in protein kinase pathways play often an important mediator role since they link upstream pathologic stress signaling with downstream regulatory programs and thus affect both the structural and functional integrity of the heart muscle. In the context of cardiac disease, a profound understanding for the overriding mechanisms that regulate protein kinase activity (protein-protein interactions, post-translational modifications, or targeting via anchoring proteins) is crucial for the development of specific and effective pharmacological treatment strategies targeting the failing myocardium. In this review, we focus on several mechanisms of upstream regulation of Ca²⁺-calmodulin-dependent protein kinase II that play a relevant pathophysiological role in the development and progression of cardiovascular disease; precise targeting of these mechanisms might therefore represent novel and promising tools for prevention and treatment of HF.

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.

Plasmonic ruler on field-effect devices for kinase drug discovery applications

Protein kinases are cellular switches that mediate phosphorylation of proteins. Abnormal phosphorylation of proteins is associated with lethal diseases such as cancer. In the pharmaceutical industry, protein kinases have become an important class of drug targets. This study reports a versatile approach for the detection of protein phosphorylation. The change in charge of the myelin basic protein upon phosphorylation by the protein kinase C-alpha (PKC-α) in the presence of adenosine 5'-[γ-thio] triphosphate (ATP-S) was detected on gold metal-insulator-semiconductor (Au-MIS) capacitor structures. Gold nanoparticles (AuNPs) can then be attached to the thio-phosphorylated proteins, forming a Au-film/AuNP plasmonic couple. This was detected by a localized surface plasmon resonance (LSPR) technique alongside MIS capacitance. All reactions were validated using surface plasmon resonance technique and the interaction of AuNPs with the thio-phosphorylated proteins quantified by quartz crystal microbalance. The plasmonic coupling was also visualized by simulations using finite element analysis. The use of this approach in drug discovery applications was demonstrated by evaluating the response in the presence of a known inhibitor of PKC-α kinase. LSPR and MIS on a single platform act as a cross check mechanism for validating kinase activity and make the system robust to test novel inhibitors.

Protein phosphorylation detection using dual-mode field-effect devices and nanoplasmonic sensors

Phosphorylation by kinases is an important post-translational modification of proteins. It is a critical control for the regulation of vital cellular activities, and its dysregulation is implicated in several diseases. A common drug discovery approach involves, therefore, time-consuming screenings of large libraries of candidate compounds to identify novel inhibitors of protein kinases. In this work, we propose a novel method that combines localized surface plasmon resonance (LSPR) and electrolyte insulator semiconductor (EIS)-based proton detection for the rapid identification of novel protein kinase inhibitors. In particular, the selective detection of thiophosphorylated proteins by LSPR is achieved by changing their resonance properties via a pre-binding with gold nanoparticles. In parallel, the EIS field-effect structure allows the real-time electrochemical monitoring of the protein phosphorylation by detecting the release of protons associated with the kinases activity. This innovative combination of both field-effect and nanoplasmonic sensing makes the detection of protein phosphorylation more reliable and effective. As a result, the screening of protein kinase inhibitors becomes more rapid, sensitive, robust and cost-effective.

Alteration in mitochondrial Ca(2+) uptake disrupts insulin signaling in hypertrophic cardiomyocytes

BACKGROUND

Cardiac hypertrophy is characterized by alterations in both cardiac bioenergetics and insulin sensitivity. Insulin promotes glucose uptake by cardiomyocytes and its use as a substrate for glycolysis and mitochondrial oxidation in order to maintain the high cardiac energy demands. Insulin stimulates Ca(2+) release from the endoplasmic reticulum, however, how this translates to changes in mitochondrial metabolism in either healthy or hypertrophic cardiomyocytes is not fully understood.

RESULTS

In the present study we investigated insulin-dependent mitochondrial Ca(2+) signaling in normal and norepinephrine or insulin like growth factor-1-induced hypertrophic cardiomyocytes. Using mitochondrion-selective Ca(2+)-fluorescent probes we showed that insulin increases mitochondrial Ca(2+) levels. This signal was inhibited by the pharmacological blockade of either the inositol 1,4,5-triphosphate receptor or the mitochondrial Ca(2+) uniporter, as well as by siRNA-dependent mitochondrial Ca(2+) uniporter knockdown. Norepinephrine-stimulated cardiomyocytes showed a significant decrease in endoplasmic reticulum-mitochondrial contacts compared to either control or insulin like growth factor-1-stimulated cells. This resulted in a reduction in mitochondrial Ca(2+) uptake, Akt activation, glucose uptake and oxygen consumption in response to insulin. Blocking mitochondrial Ca(2+) uptake was sufficient to mimic the effect of norepinephrine-induced cardiomyocyte hypertrophy on insulin signaling.

CONCLUSIONS

Mitochondrial Ca(2+) uptake is a key event in insulin signaling and metabolism in cardiomyocytes.

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.

Interactions of protein kinase C-α C1A and C1B domains with membranes: a combined computational and experimental study

Protein kinase C-α (PKCα) has been studied widely as a paradigm for conventional PKCs, with two C1 domains (C1A and C1B) being important for the regulation and function of the kinase. However, it is challenging to explore these domains in membrane-bound environments with either simulations or experiments alone. In this work, we have combined modeling, simulations, and experiments to understand the molecular basis of the PKCα C1A and C1B domain interactions with membranes. Our atomistic simulations of the PKCα C1 domains reveal the dynamic interactions of the proteins with anionic lipids, as well as the conserved hydrogen bonds and the distinct nonpolar contacts formed with lipid activators. Corroborating evidence is obtained from additional simulations and experiments in terms of lipid binding and protein diffusion. Overall, our study, for the first time, explains with atomistic detail how the PKCα C1A and C1B domains interact differently with various lipids. On the molecular level, the information provided by our study helps to shed light on PKCα regulation and activation mechanism. The combined computational/experimental approach demonstrated in this work is anticipated to enable further studies to explore the roles of C1 domains in many signaling proteins and to better understand their molecular mechanisms in normal cellular function and disease development.

Differential and conditional activation of PKC-isoforms dictates cardiac adaptation during physiological to pathological hypertrophy

A cardiac hypertrophy is defined as an increase in heart mass which may either be beneficial (physiological hypertrophy) or detrimental (pathological hypertrophy). This study was undertaken to establish the role of different protein kinase-C (PKC) isoforms in the regulation of cardiac adaptation during two types of cardiac hypertrophy. Phosphorylation of specific PKC-isoforms and expression of their downstream proteins were studied during physiological and pathological hypertrophy in 24 week male Balb/c mice (Mus musculus) models, by reverse transcriptase-PCR, western blot analysis and M-mode echocardiography for cardiac function analysis. PKC-δ was significantly induced during pathological hypertrophy while PKC-α was exclusively activated during physiological hypertrophy in our study. PKC-δ activation during pathological hypertrophy resulted in cardiomyocyte apoptosis leading to compromised cardiac function and on the other hand, activation of PKC-α during physiological hypertrophy promoted cardiomyocyte growth but down regulated cellular apoptotic load resulting in improved cardiac function. Reversal in PKC-isoform with induced activation of PKC-δ and simultaneous inhibition of phospho-PKC-α resulted in an efficient myocardium to deteriorate considerably resulting in compromised cardiac function during physiological hypertrophy via augmentation of apoptotic and fibrotic load. This is the first report where PKC-α and -δ have been shown to play crucial role in cardiac adaptation during physiological and pathological hypertrophy respectively thereby rendering compromised cardiac function to an otherwise efficient heart by conditional reversal of their activation.