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

Protein kinase C: A potential therapeutic target for endothelial dysfunction in diabetes

Protein kinase C (PKC) is a family of serine/threonine protein kinases that play an important role in many organs and systems and whose activation contributes significantly to endothelial dysfunction in diabetes. The increase in diacylglycerol (DAG) under high glucose conditions mediates PKC activation and synthesis, which stimulates oxidative stress and inflammation, resulting in impaired endothelial cell function. This article reviews the contribution of PKC to the development of diabetes-related endothelial dysfunction and summarizes the drugs that inhibit PKC activation, with the aim of exploring therapeutic modalities that may alleviate endothelial dysfunction in diabetic patients.

Deoxyelephantopin-a novel PPARγ agonist regresses pressure overload-induced cardiac fibrosis via IL-6/STAT-3 pathway in crosstalk with PKCδ

Pathological cardiac hypertrophy is associated with ventricular fibrosis leading to heart failure. The use of thiazolidinediones as Peroxisome Proliferator-Activated Receptor-gamma (PPARγ)-modulating anti-hypertrophic therapeutics has been restricted due to major side-effects. The present study aims to evaluate the anti-fibrotic potential of a novel PPARγ agonist, deoxyelephantopin (DEP) in cardiac hypertrophy. AngiotensinII treatment in vitro and renal artery ligation in vivo was performed to mimic pressure overload-induced cardiac hypertrophy. Myocardial fibrosis was evaluated by Masson's trichrome staining and hydroxyproline assay. Our results showed that DEP treatment significantly improves the echocardiographic parameters by ameliorating ventricular fibrosis without any bystander damage to other major organs. Following molecular docking, all atomistic molecular dynamics simulation, reverse transcription-polymerase chain reaction and immunoblot analyses, we established DEP as a PPARγ agonist stably interacting with the ligand-binding domain of PPARγ. DEP specifically downregulated the Signal Transducer and Activator of Transcription (STAT)-3-mediated collagen gene expression in a PPARγ-dependent manner, as confirmed by PPARγ silencing and site-directed mutagenesis of DEP-interacting PPARγ residues. Although DEP impaired STAT-3 activation, it did not have any effect on the upstream Interleukin (IL)-6 level implying possible crosstalk of the IL-6/STAT-3 axis with other signaling mediators. Mechanistically, DEP increased the binding of PPARγ with Protein Kinase C-delta (PKCδ) which impeded the membrane translocation and activation of PKCδ, downregulating STAT-3 phosphorylation and resultant fibrosis. This study, therefore, for the first time demonstrates DEP as a novel cardioprotective PPARγ agonist. The therapeutic potential of DEP as an anti-fibrotic remedy can be exploited against hypertrophic heart failure in the future.

Exercise-induced signaling pathways to counteracting cardiac apoptotic processes

Cardiovascular diseases are the most common cause of death in the world. One of the major causes of cardiac death is excessive apoptosis. However, multiple pathways through moderate exercise can reduce myocardial apoptosis. After moderate exercise, the expression of anti-apoptotic proteins such as IGF-1, IGF-1R, p-PI3K, p-Akt, ERK-1/2, SIRT3, PGC-1α, and Bcl-2 increases in the heart. While apoptotic proteins such as PTEN, PHLPP-1, GSK-3, JNK, P38MAPK, and FOXO are reduced in the heart. Exercise-induced mechanical stress activates the β and α5 integrins and subsequently, focal adhesion kinase phosphorylation activates the Akt/mTORC1 and ERK-1/2 pathways, leading to an anti-apoptotic response. One of the reasons for the decrease in exercise-induced apoptosis is the decrease in Fas-ligand protein, Fas-death receptor, TNF-α receptor, Fas-associated death domain (FADD), caspase-8, and caspase-3. In addition, after exercise mitochondrial-dependent apoptotic factors such as Bid, t-Bid, Bad, p-Bad, Bak, cytochrome c, and caspase-9 are reduced. These changes lead to a reduction in oxidative damage, a reduction in infarct size, a reduction in cardiac apoptosis, and an increase in myocardial function. After exercising in the heart, the levels of RhoA, ROCK1, Rac1, and ROCK2 decrease, while the levels of PKCε, PKCδ, and PKCɑ are activated to regulate calcium and prevent mPTP perforation. Exercise has an anti-apoptotic effect on heart failure by increasing the PKA-Akt-eNOS and FSTL1-USP10-Notch1 pathways, reducing the negative effects of CaMKIIδ, and increasing the calcineurin/NFAT pathway. Exercise plays a protective role in the heart by increasing HSP20, HSP27, HSP40, HSP70, HSP72, and HSP90 along with increasing JAK2 and STAT3 phosphorylation. However, research on exercise and factors such as Pim-1, Notch, and FAK in cardiac apoptosis is scarce, so further research is needed. Future research is recommended to discover more anti-apoptotic pathways. It is also recommended to study the synergistic effect of exercise with gene therapy, dietary supplements, and cell therapy for future research.

The focal adhesion protein β-parvin controls cardiomyocyte shape and sarcomere assembly in response to mechanical load

Physiological and pathological cardiac stress induced by exercise and hypertension, respectively, increase the hemodynamic load for the heart and trigger specific hypertrophic signals in cardiomyocytes leading to adaptive or maladaptive cardiac hypertrophy responses involving a mechanosensitive remodeling of the contractile cytoskeleton. Integrins sense load and have been implicated in cardiac hypertrophy, but how they discriminate between the two types of cardiac stress and translate mechanical loads into specific cytoskeletal signaling pathways is not clear. Here, we report that the focal adhesion protein β-parvin is highly expressed in cardiomyocytes and facilitates the formation of cell protrusions, the serial assembly of newly synthesized sarcomeres, and the hypertrophic growth of neonatal rat ventricular cardiomyocytes (NRVCs) in vitro. In addition, physiological mechanical loading of NRVCs by either the application of cyclic, uni-axial stretch, or culture on physiologically stiff substrates promotes NRVC elongation in a β-parvin-dependent manner, which is achieved by binding of β-parvin to α/β-PIX, which in turn activates Rac1. Importantly, loss-of-function studies in mice also revealed that β-parvin is essential for the exercise-induced cardiac hypertrophy response in vivo. Our results identify β-parvin as a novel mechano-responsive signaling hub in hypertrophic cardiomyocytes that drives cell elongation in response to physiological mechanical loads.

Aqueous extract of Solanum nigrum attenuates Angiotensin-II induced cardiac hypertrophy and improves cardiac function by repressing protein kinase C-ζ to restore HSF2 deSUMOlyation and Mel-18-IGF-IIR signaling suppression

ETHNOPHARMACOLOGICAL RELEVANCE

Solanum nigrum, commonly known as Makoi or black shade has been traditionally used in Asian countries and other regions of world to treat liver disorders, diarrhoea, inflammatory conditions, chronic skin ailments (psoriasis and ringworm), fever, hydrophobia, painful periods, eye diseases, etc. It has been observed that S. nigrum contains substances, like steroidal saponins, total alkaloid, steroid alkaloid, and glycoprotein, which show anti-tumor activity. However; there is no scientific evidence of the efficacy of S. nigrum in the treatment of cardiac hypertrophy.

AIM

To investigate the ability of S. nigrum to attenuate Angiotensin II - induced cardiac hypertrophy and improve cardiac function through the suppression of protein kinase PKC-ζ and Mel-18-IGF-IIR signaling leading to the restoration of HSF2 desumolyation.

MATERIALS AND METHODS

Cardiomyoblast cells (H9c2) were challenged with 100 nM Angiotensin-II (AngII) for 24 h and were then treated with different concentration of S.nigrum or Calphostin C for 24 h. The hypertrophic effect in cardiomyoblast cells were determined by immunofluorescence staining and the modulations in hypertrophic protein marker along with Protein Kinase C-ζ, MEL18, HSF2, and Insulin like growth factor II (IGFIIR), markers were analyzed by western blotting. In vivo experiments were performed using 12 week old male Wistar Kyoto rats (WKY) and Spontaneously hypertensive rats (SHR) separated into five groups. [1]Control WKY, [2] WKY -100 mg/kg of S.nigrum treatment, [3] SHR, [4] SHR-100 mg/kg of S.nigrum treatment, [5] SHR-300 mg/kg of S.nigrum treatment. S. nigrum was administered intraperitoneally for 8 week time interval.

RESULTS

Western blotting results indicate that S. nigrum significantly attenuates AngII induced cardiac hypertrophy. Furthermore, actin staining confirmed the ability of S. nigrum to ameliorate AngII induced cardiac hypertrophy. Moreover, S. nigrum administration suppressed the hypertrophic signaling mediators like Protein Kinase C-ζ, Mel-18, and IGFIIR in a dose-dependent manner and HSF2 activation (restore deSUMOlyation) that leads to downregulation of IGF-IIR expression. Additionally in vivo experiments demonstrate the reduced heart sizes of S. nigrum treated SHRs rats when compared to control WKY rats.

CONCLUSION

Collectively, the data reveals the cardioprotective effect of S. nigrum inhibiting PKC-ζ with alleviated IGF IIR level in the heart that profoundly remits cardiac hypertrophy for hypertension-induced heart failure.

A CRISPR/Cas9 zebrafish lamin A/C mutant model of muscular laminopathy

BACKGROUND

Lamin A/C gene (LMNA) mutations frequently cause cardiac and/or skeletal muscle diseases called striated muscle laminopathies. We created a zebrafish muscular laminopathy model using CRISPR/Cas9 technology to target the zebrafish lmna gene.

RESULTS

Heterozygous and homozygous lmna mutants present skeletal muscle damage at 1 day post-fertilization (dpf), and mobility impairment at 4 to 7 dpf. Cardiac structure and function analyses between 1 and 7 dpf show mild and transient defects in the lmna mutants compared to wild type (WT). Quantitative RT-PCR analysis of genes implicated in striated muscle laminopathies show a decrease in jun and nfκb2 expression in 7 dpf homozygous lmna mutants compared to WT. Homozygous lmna mutants have a 1.26-fold protein increase in activated Erk 1/2, kinases associated with striated muscle laminopathies, compared to WT at 7 dpf. Activated Protein Kinase C alpha (Pkc α), a kinase that interacts with lamin A/C and Erk 1/2, is also upregulated in 7 dpf homozygous lmna mutants compared to WT.

CONCLUSIONS

This study presents an animal model of skeletal muscle laminopathy where heterozygous and homozygous lmna mutants exhibit prominent skeletal muscle abnormalities during the first week of development. Furthermore, this is the first animal model that potentially implicates Pkc α in muscular laminopathies.

Pharmacological Protein Kinase C Modulators Reveal a Pro-hypertrophic Role for Novel Protein Kinase C Isoforms in Human Induced Pluripotent Stem Cell-Derived Cardiomyocytes

Background: Hypertrophy of cardiomyocytes (CMs) is initially a compensatory mechanism to cardiac overload, but when prolonged, it leads to maladaptive myocardial remodeling, impairing cardiac function and causing heart failure. A key signaling molecule involved in cardiac hypertrophy is protein kinase C (PKC). However, the role of different PKC isoforms in mediating the hypertrophic response remains controversial. Both classical (cPKC) and novel (nPKC) isoforms have been suggested to play a critical role in rodents, whereas the role of PKC in hypertrophy of human CMs remains to be determined. Here, we aimed to investigate the effects of two different types of PKC activators, the isophthalate derivative HMI-1b11 and bryostatin-1, on CM hypertrophy and to elucidate the role of cPKCs and nPKCs in endothelin-1 (ET-1)-induced hypertrophy in vitro.

Methods and Results: We used neonatal rat ventricular myocytes (NRVMs) and human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) to study the effects of pharmacological PKC modulators and ET-1. We used quantitative reverse transcription PCR to quantify hypertrophic gene expression and high-content analysis (HCA) to investigate CM morphology. In both cell types, ET-1, PKC activation (bryostatin-1 and HMI-1b11) and inhibition of cPKCs (Gö6976) increased hypertrophic gene expression. In NRVMs, these treatments also induced a hypertrophic phenotype as measured by increased recognition, intensity and area of α-actinin and F-actin fibers. Inhibition of all PKC isoforms with Gö6983 inhibited PKC agonist-induced hypertrophy, but could not fully block ET-1-induced hypertrophy. The mitogen-activated kinase kinase 1/2 inhibitor U0126 inhibited PKC agonist-induced hypertrophy fully and ET-1-induced hypertrophy partially. While ET-1 induced a clear increase in the percentage of pro-B-type natriuretic peptide-positive hiPSC-CMs, none of the phenotypic parameters used in HCA directly correlated with gene expression changes or with phenotypic changes observed in NRVMs.

Conclusion: This work shows similar hypertrophic responses to PKC modulators in NRVMs and hiPSC-CMs. Pharmacological PKC activation induces CM hypertrophy via activation of novel PKC isoforms. This pro-hypertrophic effect of PKC activators should be considered when developing PKC-targeted compounds for e.g. cancer or Alzheimer’s disease. Furthermore, this study provides further evidence on distinct PKC-independent mechanisms of ET-1-induced hypertrophy both in NRVMs and hiPSC-CMs.

Protein Kinase C Alpha Cellular Distribution, Activity, and Proximity with Lamin A/C in Striated Muscle Laminopathies

Striated muscle laminopathies are cardiac and skeletal muscle conditions caused by mutations in the lamin A/C gene (LMNA). LMNA codes for the A-type lamins, which are nuclear intermediate filaments that maintain the nuclear structure and nuclear processes such as gene expression. Protein kinase C alpha (PKC-α) interacts with lamin A/C and with several lamin A/C partners involved in striated muscle laminopathies. To determine PKC-α’s involvement in muscular laminopathies, PKC-α’s localization, activation, and interactions with the A-type lamins were examined in various cell types expressing pathogenic lamin A/C mutations. The results showed aberrant nuclear PKC-α cellular distribution in mutant cells compared to WT. PKC-α activation (phos-PKC-α) was decreased or unchanged in the studied cells expressing LMNA mutations, and the activation of its downstream targets, ERK 1/2, paralleled PKC-α activation alteration. Furthermore, the phos-PKC-α-lamin A/C proximity was altered. Overall, the data showed that PKC-α localization, activation, and proximity with lamin A/C were affected by certain pathogenic LMNA mutations, suggesting PKC-α involvement in striated muscle laminopathies.

Energy Metabolism in Exercise-Induced Physiologic Cardiac Hypertrophy

Physiologic hypertrophy of the heart preserves or enhances systolic function without interstitial fibrosis or cell death. As a unique form of physiological stress, regular exercise training can trigger the adaptation of cardiac muscle to cause physiological hypertrophy, partly due to its ability to improve cardiac metabolism. In heart failure (HF), cardiac dysfunction is closely associated with early initiation of maladaptive metabolic remodeling. A large amount of clinical and experimental evidence shows that metabolic homeostasis plays an important role in exercise training, which is conducive to the treatment and recovery of cardiovascular diseases. Potential mechanistic targets for modulation of cardiac metabolism have become a hot topic at present. Thus, exploring the energy metabolism mechanism in exercise-induced physiologic cardiac hypertrophy may produce new therapeutic targets, which will be helpful to design novel effective strategies. In this review, we summarize the changes of myocardial metabolism (fatty acid metabolism, carbohydrate metabolism, and mitochondrial adaptation), metabolically-related signaling molecules, and probable regulatory mechanism of energy metabolism during exercise-induced physiological cardiac hypertrophy.

Quantitative analysis of ATM phosphorylation in lymphocytes

Since many anticancer therapies target DNA and DNA damage response pathways, biomarkers of DNA damage endpoints may prove valuable in basic and clinical cancer research. Ataxia telangiectasia-mutated (ATM) kinase is the principal regulator of cellular responses to DNA double-strand breaks (DSBs). In humans, ATM autophosphorylation at serine 1981 (p-S1981) is an immediate molecular response to nascent DSBs and ionizing radiation (IR). Here we describe the analytical characteristics and fit-for-purpose validation of a quantitative dual-labeled immunoblot that simultaneously measures p-S1981-ATM and pan-ATM in human peripheral blood mononuclear cells (PBMCs) following ex vivo exposure to 2 Gy IR, facilitating the calculation of %p-ATM. To validate our assay, we isolated PBMCs from 41 volunteers. We report that the median basal level of p-S1981-ATM and pan-ATM was 2.4 and 49.5 ng/10⁷ PBMCs, respectively, resulting in %p-ATM of 4%. Following exposure of PBMCs to 2 Gy IR, p-S1981-ATM levels increased 12-fold to 29.8 ng/10⁷ PBMCs resulting in %p-ATM of 63%. Interestingly, we show that PBMCs from women have a 2.6-fold greater median p-S1981-ATM level following IR exposure than men (44.4 versus 16.9 ng/10⁷ cells; p < 0.01). This results in a significantly greater %p-ATM for women (68% versus 49%; p <  0.01). Our rigorous description of the analytical characteristics and reproducibility of phosphoprotein immunoblotting, along with our finding that the ATM DNA damage response is greater in women, has far reaching implications for biomedical researchers.

PKCα promotes insulin secretion via TRPC1 phosphorylation in INS-1E cells

Protein kinase C (PKC) is a class of phospholipid-dependent serine/threonine kinases that contribute to cell survival, migration, and invasion. Previous studies demonstrated that PKC participates in insulin secretion. However, the role of PKC in glucose-stimulated insulin secretion (GSIS) remains unclear. Herein, we demonstrated that PKC is an important mediator of insulin secretion and revealed a close relationship between PKC activation and insulin secretion in INS-1E cells. Meanwhile, the presence of PKCα was found to induce TRPC1 phosphorylation in INS-1E cells. TRPC1 phosphorylation levels increased by activating PKCα activity. Inhibition of PKCα activity reduced TRPC1 phosphorylation. Finally, we showed that TRPC1 could reverse the decrease in intracellular Ca²⁺ levels and reduced insulin secretion induced by treatment with PKCα inhibitor under high glucose conditions. In conclusion, our findings indicated that TRPC1 and PKCα are involved in promoting insulin secretion and that PKCα promotes insulin secretion via TRPC1 phosphorylation in INS-1E cells.

Sodium ferulate inhibits myocardial hypertrophy induced by abdominal coarctation in rats: Involvement of cardiac PKC and MAPK signaling pathways

Sodium ferulate (SF) is the sodium salt of ferulic acid which is an active ingredient of Radix Angelica Sinensis and Ligusticum chuanxiong hort. Here, we investigated SF inhibition in a rat model of myocardial hypertrophy induced by coarctation of the abdominal aorta. Following coarctation, rats were given SF (20, 40, and 80 mg/kg/day) for 25 consecutive days. We characterized myocardial hypertrophy using myocardial hypertrophic parameters, histopathology, and gene expression of atrial natriuretic factor (ANF) -a gene related to myocardial hypertrophy. We detected the levels of angiotensin II (Ang II) and endothelin-1 (ET-1), protein kinase C beta (PKC-β), Raf-1, extracellular regulated protein kinase 1/2 (ERK1/2), and mitogen-activated protein kinase phosphatase-1 (MKP-1) in myocardium. Notably, coarctation of the abdominal aorta increases myocardial hypertrophic parameters, cardiac myocyte diameter, the concentration of Ang II and ET-1 in myocardium, and gene expression of ANF. SF significantly ameliorates myocardial hypertrophy caused by coarctation of the abdominal aorta; reduces concentrations of Ang II and ET-1; suppresses the overexpression of ANF, PKC-β, Raf-1, and ERK1/2; and increases the expression of MKP-1. These results indicate that SF alleviates myocardial hypertrophy induced by coarctation of the abdominal aorta, and these protective effects could be related to the inhibition of PKC and mitogen-activated protein kinase (MAPK) signaling pathways.

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.

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.