Endothelin-1 and fibroblast growth factors stimulate the mitogen-activated protein kinase signaling cascade in cardiac myocytes. The potential role of the cascade in the integration of two signaling pathways leading to myocyte hypertrophy

MAPKs signaling is obligatory for male reproductive function in a development-specific manner

Mitogen-activated protein kinases (MAPKs) represent widely expressed and evolutionarily conserved proteins crucial for governing signaling pathways and playing essential roles in mammalian male reproductive processes. These proteins facilitate the transmission of signals through phosphorylation cascades, regulating diverse intracellular functions encompassing germ cell development in testis, physiological maturation of spermatozoa within the epididymis, and motility regulation at ejaculation in the female reproductive tract. The conservation of these mechanisms appears prevalent across species, including humans, mice, and, to a limited extent, livestock species such as bovines. In Sertoli cells (SCs), MAPK signaling not only regulates the proliferation of immature SCs but also determines the appropriate number of SCs in the testes at puberty, thereby maintaining male fertility by ensuring the capacity for sperm cell production. In germ cells, MAPKs play a crucial role in dynamically regulating testicular cell-cell junctions, supporting germ cell proliferation and differentiation. Throughout spermatogenesis, MAPK signaling ensures the appropriate Sertoli-to-germ cell ratio by regulating apoptosis, controlling the metabolism of developing germ cells, and facilitating the maturation of spermatozoa within the cauda epididymis. During ejaculation in the female reproductive tract, MAPKs regulate two pivotal events-capacitation and the acrosome reaction essential for maintaining the fertility potential of sperm cells. Any disruptions in MAPK pathway signaling possibly may disturb the testicular microenvironment homeostasis, sperm physiology in the male body before ejaculation and in the female reproductive tract during fertilization, ultimately compromising male fertility. Despite decades of research, the physiological function of MAPK pathways in male reproductive health remains inadequately understood. The current review attempts to combine recent findings to elucidate the impact of MAPK signaling on male fertility and proposes future directions to enhance our understanding of male reproductive functions.

Cooperative Binding of ETS2 and NFAT Links Erk1/2 and Calcineurin Signaling in the Pathogenesis of Cardiac Hypertrophy

Supplemental Digital Content is available in the text.

Cardiac hypertrophy is an independent risk factor for heart failure, a leading cause of morbidity and mortality globally. The calcineurin/NFAT (nuclear factor of activated T cells) pathway and the MAPK (mitogen-activated protein kinase)/Erk (extracellular signal-regulated kinase) pathway contribute to the pathogenesis of cardiac hypertrophy as an interdependent network of signaling cascades. How these pathways interact remains unclear and few direct targets responsible for the prohypertrophic role of NFAT have been described.

Regulatory role of endogenous and exogenous fibroblast growth factor 1 in the cardiovascular system and related diseases

Fibroblast growth factor 1 (FGF1) has a critical regulatory role in the development of the cardiovascular system (CVS) and is strongly associated with the progression or treatment of cardiovascular diseases (CVDs). However, the regulatory mechanisms of FGF1 in CVS and CVDs have not yet been fully elucidated. Therefore, this review article summarized the existing literature reports on the role of FGF1 in CVS under physiological and pathological conditions. First, the expression and physiological functions of endogenous FGF1 is fully demonstrated. Then, we analyzed the role of exogenous FGF1 in normal CVS and related pathological processes. Specifically, the potential signaling pathways might be mediated by FGF1 in CVDs treatment is discussed in detail. In addition, the barriers and feasible solutions for the application of FGF1 are further analyzed. Finally, we highlight therapeutic considerations of FGF1 for CVDs in the future. Thus, this article may be as a reference to provide some ideas for the follow-up research.

4-Methylumbelliferone Attenuates Macrophage Invasion and Myocardial Remodeling in Pressure-Overloaded Mouse Hearts

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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.

TAK733 attenuates adrenergic receptor-mediated cardiomyocyte hypertrophy via inhibiting ErkThr188 phosphorylation

BACKGROUND

Cardiac hypertrophy is an important risk factor for heart failure. The MEK-ERK axis has been reported as a major regulator in controlling cardiac hypertrophy. TAK733 is a potent and selective MEK inhibitor that suppresses cell growth in a broad range of cell lines.

OBJECTIVE

Therefore, we aimed to investigate the anti-hypertrophic effect of TAK733 in cardiomyocytes.

METHODS

Cardiomyocyte hypertrophy was induced with norepinephrine (NE) or phenylepinephrine (PE) using H9c2 cells. To confirm the cardiomyocyte hypertrophy, cell size and protein synthesis were measured and hypertrophy-related gene expression was estimated by reverse transcription polymerase chain reaction. To identify the signaling pathway involved, immunoblot analysis were performed.

RESULTS

We observed that NE activated MEK-ERK signaling and increased ANP and BNP expression, resulting in cardiomyocyte hypertrophy. TAK733 significantly reduced cardiomyocyte hypertrophy by regulating NE-induced ERK1/2 and ERKThr188 activation, hypertrophy marker expression, and cardiomyocyte hypertrophy through depression of MEK activity. In addition, we examined that PE-induced cardiomyocyte hypertrophy was also attenuated by TAK733.

CONCLUSIONS

Here, we report that TAK733 suppressed NE- or PE-induced cardiomyocyte hypertrophy by repressing a crucial component of cardiac hypertrophy-related pathways. These results suggest that TAK733 may be a useful therapeutics for cardiac hypertrophy and warrants further in vivo studies.

The slow force response to stretch: Controversy and contradictions

When exposed to an abrupt stretch, cardiac muscle exhibits biphasic active force enhancement. The initial, instantaneous, force enhancement is well explained by the Frank-Starling mechanism. However, the cellular mechanisms associated with the second, slower phase remain contentious. This review explores hypotheses regarding this "slow force response" with the intention of clarifying some apparent contradictions in the literature. The review is partitioned into three sections. The first section considers pathways that modify the intracellular calcium handling to address the role of the sarcoplasmic reticulum in the mechanism underlying the slow force response. The second section focuses on extracellular calcium fluxes and explores the identity and contribution of the stretch-activated, non-specific, cation channels as well as signalling cascades associated with G-protein coupled receptors. The final section introduces promising candidates for the mechanosensor(s) responsible for detecting the stretch perturbation.

The Biological Role of Nestin(+)-Cells in Physiological and Pathological Cardiovascular Remodeling

The intermediate filament protein nestin was identified in diverse populations of cells implicated in cardiovascular remodeling. Cardiac resident neural progenitor/stem cells constitutively express nestin and following an ischemic insult migrate to the infarct region and participate in angiogenesis and neurogenesis. A modest number of normal adult ventricular fibroblasts express nestin and the intermediate filament protein is upregulated during the progression of reparative and reactive fibrosis. Nestin depletion attenuates cell cycle re-entry suggesting that increased expression of the intermediate filament protein in ventricular fibroblasts may represent an activated phenotype accelerating the biological impact during fibrosis. Nestin immunoreactivity is absent in normal adult rodent ventricular cardiomyocytes. Following ischemic damage, the intermediate filament protein is induced in a modest population of pre-existing adult ventricular cardiomyocytes bordering the peri-infarct/infarct region and nestin⁽⁺⁾-ventricular cardiomyocytes were identified in the infarcted human heart. The appearance of nestin⁽⁺⁾-ventricular cardiomyocytes post-myocardial infarction (MI) recapitulates an embryonic phenotype and depletion of the intermediate filament protein inhibits cell cycle re-entry. Recruitment of the serine/threonine kinase p38 MAPK secondary to an overt inflammatory response after an ischemic insult may represent a seminal event limiting the appearance of nestin⁽⁺⁾-ventricular cardiomyocytes and concomitantly suppressing cell cycle re-entry. Endothelial and vascular smooth muscle cells (VSMCs) express nestin and upregulation of the intermediate filament protein may directly contribute to vascular remodeling. This review will highlight the biological role of nestin⁽⁺⁾-cells during physiological and pathological remodeling of the heart and vasculature and discuss the phenotypic advantage attributed to the intermediate filament protein.

Identification of a Common Different Gene Expression Signature in Ischemic Cardiomyopathy

The molecular mechanisms underlying the development of ischemic cardiomyopathy (ICM) remain poorly understood. Gene expression profiling is helpful to discover the molecular changes taking place in ICM. The aim of this study was to identify the genes that are significantly changed during the development of heart failure caused by ICM. The differentially expressed genes (DEGs) were identified from 162 control samples and 227 ICM patients. PANTHER was used to perform gene ontology (GO), and Reactome for pathway enrichment analysis. A protein–protein interaction network was established using STRING and Cytoscape. A further validation was performed by real-time polymerase chain reaction (RT-PCR). A total of 255 common DEGs was found. Gene ontology, pathway enrichment, and protein–protein interaction analysis showed that nucleic acid-binding proteins, enzymes, and transcription factors accounted for a great part of the DEGs, while immune system signaling and cytokine signaling displayed the most significant changes. Furthermore, seven hub genes and nine transcription factors were identified. Interestingly, the top five upregulated DEGs were located on chromosome Y, and four of the top five downregulated DEGs were involved in immune and inflammation signaling. Further, the top DEGs were validated by RT-PCR in human samples. Our study explored the possible molecular mechanisms of heart failure caused by ischemic heart disease.

Protein phosphatase 5 regulates titin phosphorylation and function at a sarcomere-associated mechanosensor complex in cardiomyocytes

Serine/threonine protein phosphatase 5 (PP5) is ubiquitously expressed in eukaryotic cells; however, its function in cardiomyocytes is unknown. Under basal conditions, PP5 is autoinhibited, but enzymatic activity rises upon binding of specific factors, such as the chaperone Hsp90. Here we show that PP5 binds and dephosphorylates the elastic N2B-unique sequence (N2Bus) of titin in cardiomyocytes. Using various binding and phosphorylation tests, cell-culture manipulation, and transgenic mouse hearts, we demonstrate that PP5 associates with N2Bus in vitro and in sarcomeres and is antagonistic to several protein kinases, which phosphorylate N2Bus and lower titin-based passive tension. PP5 is pathologically elevated and likely contributes to hypo-phosphorylation of N2Bus in failing human hearts. Furthermore, Hsp90-activated PP5 interacts with components of a sarcomeric, N2Bus-associated, mechanosensor complex, and blocks mitogen-activated protein-kinase signaling in this complex. Our work establishes PP5 as a compartmentalized, well-controlled phosphatase in cardiomyocytes, which regulates titin properties and kinase signaling at the myofilaments.

Protein phosphatase 5 (PP5) is expressed in many cell types but its role in cardiomyocytes is unknown. Here the authors show that PP5 binds and dephosphorylates elastic titin in cardiac sarcomeres, and that PP5 is increased in heart failure, reducing cardiomyocyte compliance.

Peri-interventional endothelin-A receptor blockade improves long-term outcome in patients with ST-elevation acute myocardial infarction

Endothelin (ET)-1 is a pro-fibrotic vasoconstrictive peptide causing microvascular dysfunction and cardiac remodelling after acute ST-elevation myocardial infarction (STEMI). It acts via two distinct receptors, ET-A and ET-B, and is involved in inflammation and atherogenesis. Patients with posterior-wall STEMI were randomly assigned to intravenous BQ-123 at 400 nmol/minute (min) or placebo over 60 min, starting immediately prior to primary percutaneous coronary intervention (n=54). Peripheral blood samples were drawn at baseline as well as after 24 hours and 30 days. Myeloperoxidase (MPO), as a marker of neutrophil activation and matrix metalloproteinase 9 (MMP-9), a marker of extracellular matrix degradation were measured in plasma. Clinical follow-up was conducted by an investigator blinded to treatment allocation over three years. During the median follow-up period of 3.6 years (interquartile range [IQR] 3.3–4.1) we observed a longer event-free survival in patients randomised to receive BQ-123 compared with patients randomised to placebo (mean 4.5 years (95% confidence interval: 3.9–5) versus mean 3 years (2.2–3.7), p=0.031). Patients randomised to ET-A receptor blockade demonstrated a greater reduction of MPO levels from baseline to 24 hours compared to placebo-treated patients (-177 ng/ml (IQR 103–274) vs –108 ng/ml (74–147), p=0.006). In addition, a pronounced drop in MMP-9 levels (-568 ng/ml (44–1157) vs –117 ng/ml (57–561), p=0.018) was observed. There was no significant difference in amino-terminal propetide of pro-collagen type III levels. In conclusion, short-term administration of BQ-123 leads to a reduction in MPO, as well as MMP-9 plasma levels and to a longer event-free survival in patients with STEMI.

ClinicalTrials.gov Identifier: NCT00502528

Cardiac actions of fibroblast growth factor 23

Fibroblast growth factors (FGF) are mitogenic signal mediators that induce cell proliferation and survival. Although cardiac myocytes are post-mitotic, they have been shown to be able to respond to local and circulating FGFs. While precise molecular mechanisms are not well characterized, some FGF family members have been shown to induce cardiac remodeling under physiologic conditions by mediating hypertrophic growth in cardiac myocytes and by promoting angiogenesis, both events leading to increased cardiac function and output. This FGF-mediated physiologic scenario might transition into a pathologic situation involving cardiac cell death, fibrosis and inflammation, and eventually cardiac dysfunction and heart failure. As discussed here, cardiac actions of FGFs - with the majority of studies focusing on FGF2, FGF21 and FGF23 - and their specific FGF receptors (FGFR) and precise target cell types within the heart, are currently under experimental investigation. Especially cardiac effects of endocrine FGFs entered center stage over the past five years, as they might provide communication routes that couple metabolic mechanisms, such as bone-regulated phosphate homeostasis, or metabolic stress, such as hyperphosphatemia associated with kidney injury, with changes in cardiac structure and function. In this context, it has been shown that elevated serum FGF23 can directly tackle cardiac myocytes via FGFR4 thereby contributing to cardiac hypertrophy in models of chronic kidney disease, also called uremic cardiomyopathy. Precise characterization of FGFs and their origin and regulation of expression, and even more importantly, the identification of the FGFR isoforms that mediate their cardiac actions should help to develop novel pharmacological interventions for heart failure, such as FGFR4 inhibition to tackle uremic cardiomyopathy.

Cardiokines as Modulators of Stress-Induced Cardiac Disorders

Almost 30 years ago, the protein, atrial natriuretic peptide, was identified as a heart-secreted hormone that provides a peripheral signal from the myocardium that communicates to the rest of the organism to modify blood pressure and volume under conditions of heart failure. Since then, additional peripheral factors secreted by the heart, termed cardiokines, have been identified and shown to coordinate this interorgan cross talk. In addition to this interorgan communication, cardiokines also act in an autocrine/paracrine manner to play a role in intercellular communication within the myocardium. This review focuses on the roles of newly emerging cardiokines that are mainly increased in stress-induced cardiac diseases. The potential of these cardiokines as clinical biomarkers for diagnosis and prognosis of cardiac disorders is also discussed.

The fibrosis-cell death axis in heart failure

Cardiac stress can induce morphological, structural and functional changes of the heart, referred to as cardiac remodeling. Myocardial infarction or sustained overload as a result of pathological causes such as hypertension or valve insufficiency may result in progressive remodeling and finally lead to heart failure (HF). Whereas pathological and physiological (exercise, pregnancy) overload both stimulate cardiomyocyte growth (hypertrophy), only pathological remodeling is characterized by increased deposition of extracellular matrix proteins, termed fibrosis, and loss of cardiomyocytes by necrosis, apoptosis and/or phagocytosis. HF is strongly associated with age, and cardiomyocyte loss and fibrosis are typical signs of the aging heart. Fibrosis results in stiffening of the heart, conductivity problems and reduced oxygen diffusion, and is associated with diminished ventricular function and arrhythmias. As a consequence, the workload of cardiomyocytes in the fibrotic heart is further augmented, whereas the physiological environment is becoming less favorable. This causes additional cardiomyocyte death and replacement of lost cardiomyocytes by fibrotic material, generating a vicious cycle of further decline of cardiac function. Breaking this fibrosis-cell death axis could halt further pathological and age-related cardiac regression and potentially reverse remodeling. In this review, we will describe the interaction between cardiac fibrosis, cardiomyocyte hypertrophy and cell death, and discuss potential strategies for tackling progressive cardiac remodeling and HF.

Role of the endothelin system in sexual dimorphism in cardiovascular and renal diseases

Epidemiological studies of blood pressure in men and women and in experimental animal models point to substantial sex differences in the occurrence of arterial hypertension as well as in the various manifestations of arterial hypertension, including myocardial infarction, stroke, retinopathy, chronic kidney failure, as well as hypertension-associated diseases (e.g. diabetes mellitus). Increasing evidence demonstrates that the endothelin (ET) system is a major player in the genesis of sex differences in cardiovascular and renal physiology and diseases. Sex differences in the ET system have been described in the vasculature, heart and kidney of humans and experimental animals. In the current review, we briefly describe the role of the ET system in the cardiovascular and renal systems. We also update information on sex differences at different levels of the ET system including synthesis, circulating and tissue levels, receptors, signaling pathways, ET actions, and responses to antagonists in different organs that contribute to blood pressure regulation. Knowledge of the mechanisms underlying sex differences in arterial hypertension can impact therapeutic strategies. Sex-targeted and/or sex-tailored approaches may improve treatment of cardiovascular and renal diseases.

Cardiac nonmyocytes in the hub of cardiac hypertrophy

Cardiac hypertrophy is characterized by complex multicellular alterations, such as cardiomyocyte growth, angiogenesis, fibrosis, and inflammation. The heart consists of myocytes and nonmyocytes, such as fibroblasts, vascular cells, and blood cells, and these cells communicate with each other directly or indirectly via a variety of autocrine or paracrine mediators. Accumulating evidence has suggested that nonmyocytes actively participate in the development of cardiac hypertrophy. In this review, recent progress in our understanding of the importance of nonmyocytes as a hub for induction of cardiac hypertrophy is summarized with an emphasis of the contribution of noncontact communication mediated by diffusible factors between cardiomyocytes and nonmyocytes in the heart.

Hierarchical paracrine interaction of breast cancer associated fibroblasts with cancer cells via hMAPK-microRNAs to drive ER-negative breast cancer phenotype

Multiple juxtacrine and paracrine interactions occur between cancer cells and non-cancer cells of the tumor microenvironment (TME) that direct tumor progression. Cancer Associated Fibroblasts (CAFs) are an integral component of the TME, and the majority of breast tumor stroma is comprised of CAFs. Heterotypic interactions between cancer cells and non-cancer cells of the TME occur via soluble agents, including cytokines, hormones, growth factors, and secreted microRNAs. We previously identified a microRNA signature indicative of hyperactive MAPK signaling (hMAPK-miRNA signature) that significantly associated with reduced recurrence-free and overall survival. Here we report that the hMAPK-miRNA signature associates with a high metric of stromal cell infiltrate, and we investigate the role of microRNAs, particularly hMAPK-microRNAs, secreted by CAFs on estrogen receptor (ER) expression in breast cancer cells. ER-positive MCF-7/ltE2- cells were treated with conditioned media (CM) from CAFs derived from breast cancers of different PAM50 subtypes (CAFBAS, CAFHER2, and CAFLA). CAF CM isolated specifically from ER-negative primary breast tumors led to ER repression in vitro. Nanoparticle tracking analysis and transmission electron microscopy confirmed the presence of CAF-secreted exosomes in CM and the uptake of these exosomes by the ER+ MCF-7/ltE2- cells. Differentially expressed microRNAs in CAF CM as well as in MCF-7/ltE2- cells treated with this CM were identified. Knockdown of miR-221/222 in CAFBAS resulted in knockdown of miR221/222 levels in the conditioned media and the CM from CAFBAS; miR221/222 knockdown rescued ER repression in ER-positive cell lines treated with CAFBAS-CM. Collectively, our results demonstrate that CAF-secreted microRNAs are directly involved in ER-repression, and may contribute to the MAPK-induced ER repression in breast cancer cells.

The role of SUMO-1 in cardiac oxidative stress and hypertrophy

AIMS

Small ubiquitin-like modifier type 1 (SUMO-1) has been shown to play a critical role in the dysfunction of the cardiac isoform of sarcoplasmic reticulum calcium ATPase (SERCA2a) pump in the setting of heart failure. In cardiac hypertrophy, the role of SUMO-1 has not been defined and our study's goals were to examine the effects of modulating SUMO-1 on the hypertrophic response both in vitro and in vivo and to examine whether oxidative stress (during cardiac hypertrophy) is abrogated by SUMO-1 gene transfer.

RESULTS

In mice undergoing transverse aortic constriction (TAC), SUMO-1 levels increased slightly during the compensated stage of hypertrophy and then dropped sharply during the transition to heart failure. In isolated cardiomyocytes, SUMO-1 gene transfer inhibited the hypertrophic response in the presence of phenylephrine. Adeno-associated vector type 9 (AAV9) gene transfer of SUMO-1 prevented the heart from undergoing hypertrophy after TAC and prevented the development of left ventricular dysfunction. Furthermore, SUMO-1 gene transfer blocked the negative effects of H2O2 on SERCA2a activity in cardiac myocytes, while in vivo indices of oxidative stress were decreased by SUMO-1 in cardiac hypertrophy and heart failure.

INNOVATION AND CONCLUSION

The results of this study indicate that post-translational modifications of SERCA2a caused by the toxic environment of the hypertrophied and failing myocardium can be prevented by SUMO-1. Antioxid. Redox Signal. 21, 1986-2001.

Cardiac-targeting magnetic lipoplex delivery of SH-IGF1R plasmid attenuate norepinephrine-induced cardiac hypertrophy in murine heart

Recent studies have demonstrated a number of molecular mechanisms contributing to the initiation of cardiac hypertrophy response to pressure overload. IGF1R (insulin-like growth factor-1 receptor), an important oncogene, is overexpressed in hypertrophic heart and mediates the hypertrophic pathology process. In this study, we applied with liposomal magnetofection that potentiated gene transfection by applying an external magnetic field to enhance its transfection efficiency. Liposomal magnetofection provided high efficiency in transgene expression in vivo. In vivo, IGF1R-specific-shRNA (small-hairpin RNA) by magnetofection inhibited IGF1R protein expression by 72.2 ± 6.8, 80.7 ± 9.6 and 84.5 ± 5.6%, at 24, 48 and 72 h, respectively, after pGFPshIGF1R injection, indicating that liposomal magnetofection is a promising method that allows the targeting of gene therapy for heart failure. Furthermore, we found that the treated animals (liposomal magnetofection with shIGF1R) showed reduced septal and posterior wall thickness, reduced HW:BWs (heart weight-to-body weights) compared with controls. Moreover, we also found that liposomal magnetofection-based shIGF1R transfection decreased the expression level of p-ERK (phosphorylated extracellular-signal-regulated kinase)1/2, p-AKT1 (phosphorylated protein kinase B1) compared with untreated hearts. These results suggested that liposomal magnetofection-mediated IGF1R-specific-shRNA may be a promising method, and suppression the IGF1R expression inhibited norepinephrine-induced cardiac hypertrophic process via inhibiting PI3K (phosphoinositide 3-kinase)/AKT pathway.

Regulatory RNAs and paracrine networks in the heart

Cardiac hypertrophy and fibrosis are two closely related adaptive response mechanisms of the myocardium to mechanical, metabolic, and genetic stress that finally contribute to the development of heart failure (HF). This relation is based on a dynamic interplay between many cell types including cardiomyocytes and fibroblasts during disease progression. Both cell types secrete a variety of growth factors, cytokines, and hormones that influence hypertrophic cardiomyocyte growth and fibrotic fibroblast activation in a paracrine and autocrine manner. It has become evident that, aside proteinous signals, microRNAs (miRNAs) and possible other RNA species such as long non-coding RNAs are potential players in such a cell-to-cell communication. By directly acting as paracrine signals or by modulating downstream intercellular signalling mediators, miRNAs can act as moderators of the intercellular crosstalk. These small regulators can potentially be secreted in a 'mircrine' fashion, so that miRNAs can be assumed as the message itself. This review will summarize the recent findings about the paracrine crosstalk between cardiac fibroblasts and cardiomyocytes and addresses how miRNAs may be involved in this interplay. It also highlights therapeutic strategies targeting factors of pathological communication for the treatment of HF.

Endothelin-1 induces connective tissue growth factor expression in human lung fibroblasts by ETAR-dependent JNK/AP-1 pathway

Endothelin-1 (ET-1) acts as a key mediator of vasoconstriction and tissue repair. Overproduction of connective tissue growth factor (CTGF) underlies the development of lung fibrosis. ET-1 induces expression of matrix-associated genes in lung fibroblasts, however, little is known about the signaling pathway of CTGF expression caused by ET-1. In this study, we found that ET-1 caused concentration- and time-dependently increases in CTGF expression in human embryonic lung fibroblast cell line (WI-38). ET-1-induced CTGF expression was inhibited by BQ123 (ETAR antagonist), but not BQ788 (ETBR antagonist). Moreover, ET-1-induced CTGF expression was significantly reduced by JNK inhibitor (SP600125), the dominant-negative mutants of JNK1/2 (JNK1/2 DN), and AP-1 inhibitor (curcumin). ET-1 induced phosphorylations of JNK and c-Jun in time-dependent manners. AP-1 luciferase activity was concentration-dependently increased by ET-1, and this effect was attenuated by SP600125. We also found that ET-1-induced CTGF expression was most controlled by the AP-1 binding region of CTGF promoter. ET-1-indiced CTGF luciferase activity was predominately controlled by the sequence -747 to -408 bp upstream of the transcription start site on the human CTGF promoter. Furthermore, ET-1 caused the formation of AP-1-specific DNA-protein complex and the recruitment of c-Jun to the CTGF promoter. Moreover, we found that ET-1 induced α-smooth muscle actin (α-SMA) expression, which was inhibited by BQ123, SP600125, curcumin, and anti-CTGF antibody. These results suggest that ET-1 stimulates expressions of CTGF and α-SMA through ETAR/JNK/AP-1 signaling pathway, and CTGF is required for ET-1-induced α-SMA expression in human lung fibroblasts.

Fibroblast-mediated pathways in cardiac hypertrophy

Under normal physiological conditions, cardiac fibroblasts are the primary producers of extracellular matrix and supply a mechanical scaffold for efficacious heart contractions induced by cardiomyocytes. In the hypertrophic heart, cardiac fibroblasts provide a pivotal contribution to cardiac remodeling. Many growth factors and extracellular matrix components secreted by cardiac fibroblasts induce and modify cardiomyocyte hypertrophy. Recent evidence revealed that cardiomyocyte-cardiac fibroblast communications are complex and multifactorial. Many growth factors and molecules contribute to cardiac hypertrophy via different roles that include induction of hypertrophy and the feedback hypertrophic response, fine-tuning of adaptive hypertrophy, limitation of left ventricular dilation, and modification of interstitial changes. This review focuses on recent work and topics and provides a mechanistic insight into cardiomyocyte-cardiac fibroblast communication in cardiac hypertrophy. This article is part of a Special Issue entitled "Myocyte-Fibroblast Signalling in Myocardium ".

The role of the paracrine/autocrine mediator endothelin-1 in regulation of cardiac contractility and growth

Endothelin-1 (ET-1) is a critical autocrine and paracrine regulator of cardiac physiology and pathology. Produced locally within the myocardium in response to diverse mechanical and neurohormonal stimuli, ET-1 acutely modulates cardiac contractility. During pathological cardiovascular conditions such as ischaemia, left ventricular hypertrophy and heart failure, myocyte expression and activity of the entire ET-1 system is enhanced, allowing the peptide to both initiate and maintain maladaptive cellular responses. Both the acute and chronic effects of ET-1 are dependent on the activation of intracellular signalling pathways, regulated by the inositol-trisphosphate and diacylglycerol produced upon activation of the ET(A) receptor. Subsequent stimulation of protein kinases C and D, calmodulin-dependent kinase II, calcineurin and MAPKs modifies the systolic calcium transient, myofibril function and the activity of transcription factors that coordinate cellular remodelling. The precise nature of the cellular response to ET-1 is governed by the timing, localization and context of such signals, allowing the peptide to regulate both cardiomyocyte physiology and instigate disease.

LINKED ARTICLES

This article is part of a themed section on Endothelin. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2013.168.issue-1.

Diversity of the protein kinase C gene family Implications for cardiovascular disease

All eukaryotic cells are capable of responding to a changing intracellular environment and to extracellular stimuli. These functional responses are highly regulated by diverse means; one of the most common mechanisms of regulation requires the covalent phosphorylation of intracellular proteins, which when phosphorylated, mediate many functional events. The general class of enzymes that catalyzes the phosphorylation of effectors (substrates), the protein kinases, may be divided into two broad categories, depending on whether they phosphorylate serine and threonine residues or tyrosine residues. Evidence has accumulated that implicates abnormal activation of protein kinase C (PKC), which is one family of serine-threonine protein kinases, in cells and tissues from patients or models of cardiovascular disease. In this review, we present the molecular and biochemical basis for the diversity of the PKC family, and briefly summarize the evidence that PKC is implicated in cardiovascular pathology and the potential therapeutic implications and approaches.

Endothelin-1-dependent signaling pathways in the myocardium

Endothelin-1 (ET-1) is a locally acting vasoactive peptide that also has profound effects on the contractile properties and growth of the cardiac myocyte. Binding of ET-1 to its transmembrane heptahelical receptors activates G proteins of the G(q) and G(i) classes. Activation of G(q) stimulates hydrolysis of phosphatidylinositol-4,5-bisphosphate, and the diacylglycerol thus formed stimulates protein kinase C. Subsequently, the protein kinase Raf is activated and this leads to activation of the extracellular signal-regulated protein kinase (ERK) subfamily of mitogen-activated protein kinases. Activation of G(i) counteracts β-adrenoceptor-mediated increases in cAMP concentrations. We have attempted to rationalize the established physiological consequences of ET-1 agonism in the cardiac myocyte (that is, on contraction and growth) in terms of activation of these signaling pathways.

Physiological regulation of cardiac contractility by endogenous reactive oxygen species

Increased production of reactive oxygen species (ROS) has been linked to the pathogenesis of congestive heart failure. However, emerging evidence suggests the involvement of ROS in the regulation of various physiological cellular processes in the myocardium. In this review, we summarize the latest findings regarding the role of ROS in the acute regulation of cardiac contractility. We discuss ROS-dependent modulation of the inotropic responses to G protein-coupled receptor agonists (e.g. β-adrenergic receptor agonists and endothelin-1), the potential cellular sources of ROS (e.g. NAD(P)H oxidases and mitochondria) and the proposed end-targets and signalling pathways by which ROS affect contractility. Accumulating new data supports the fundamental role of endogenously generated ROS to regulate cardiac function under physiological conditions.

Endothelin and endothelin receptors in the renal and cardiovascular systems

Endothelin-1 (ET-1) is a multifunctional hormone which regulates the physiology of the cardiovascular and renal systems. ET-1 modulates cardiac contractility, systemic and renal vascular resistance, salt and water renal reabsorption, and glomerular function. ET-1 is responsible for a variety of cellular events: contraction, proliferation, apoptosis, etc. These effects take place after the activation of the two endothelin receptors ET(A) and ET(B), which are present - among others - on cardiomyocytes, fibroblasts, smooth muscle and endothelial cells, glomerular and tubular cells of the kidney. The complex and numerous intracellular pathways, which can be contradictory in term of functional response depending on the receptor type, cell type and physiological situation, are described in this review. Many diseases share an enhanced ET-1 expression as part of the pathophysiology. However, the use of endothelin blockers is currently restricted to pulmonary arterial hypertension, and more recently to digital ulcer. The complexity of the endothelin system does not facilitate the translation of the molecular knowledge to clinical applications. Endothelin antagonists can prevent disease development but secondary undesirable effects limit their usage. Nevertheless, the increasing understanding of the effects of ET-1 on the cardiac and renal physiology maintains the endothelin system as a promising therapeutic target.

Insulin-like growth factor-1 preconditioning accentuates intrinsic survival mechanism in stem cells to resist ischemic injury by orchestrating protein kinase cα-erk1/2 activation

AIMS

To test our hypothesis that the intrinsic molecular mechanism in stem cells for adaptation to ischemia is accentuated by preconditioning with insulin-like growth factor (IGF-1).

RESULTS

Bone marrow Sca-1(+) cells were exposed to oxygen and glucose deprivation (OGD) for up to 12 h. Erk1/2 was activated in Sca-1(+) cells under OGD which was blocked by MEK inhibitor (PD98059) and resulted in accelerated cell death. Moreover, elevated intracellular calcium with concomitant activation of protein kinase C (PKC) was observed under OGD. Pretreatment with nifedipine or dantrolene reduced cellular calcium, abrogated PKC and Erk1/2 activation, and increased cytotoxicity. Treatment with phorbol 12-myristate 13-acetate (PMA) for 30 min (short-term) activated Erk1/2, whereas 12 h (long-term) PMA treatment abrogated PKCα, reduced Erk1/2 activation and significantly increased cell death under OGD. These results were confirmed by loss-of-function studies using PKCα and Erk1/2 specific small interfering RNA. Gain-of-function studies with PKCα plasmid transfection improved cell survival under OGD. Preconditioning with 100 nM IGF-1 accentuated the intrinsic mechanism of resistance of the cells to ischemia via Erk1/2 activation and improved their survival under OGD as well as post-transplantation in an experimentally infarcted heart.

INNOVATION

Strategies to target intrinsic survival mechanism in stem cells by growth factor preconditioning to enhance their survival via activation of PKCα and Erk1/2 are innovative.

CONCLUSIONS

Intracellular calcium elevation under OGD activated PKCα and Erk1/2 as a part of the intrinsic prosurvival mechanism that was accentuated during preconditioning with IGF-1 to protect Sca-1(+) cells from ischemic injury.

PPARα activation inhibits endothelin-1-induced cardiomyocyte hypertrophy by prevention of NFATc4 binding to GATA-4

Peroxisome proliferator-activated receptor alpha (PPARα) has been implicated in the pathogenesis of cardiac hypertrophy, although its mechanism of action remains largely unknown. To determine the effect of PPARα activation on endothelin-1 (ET-1)-induced cardiomyocyte hypertrophy and explore its molecular mechanisms, we evaluated the interaction of PPARα with nuclear factor of activated T-cells c4 (NFATc4) in nuclei of cardiomyocytes from neonatal rats in primary culture. In ET-1-stimulated cardiomyocytes, data from electrophoretic mobility-shift assays (EMSA) and co-immunoprecipitation (co-IP) revealed that fenofibrate (Fen), a PPARα activator, in a concentration-dependent manner, enhanced the association of NFATc4 with PPARα and decreased its interaction with GATA-4, in promoter complexes involved in activation of the rat brain natriuretic peptide (rBNP) gene. Effects of PPARα overexpression were similar to those of its activation by Fen. PPARα depletion by small interfering RNA abolished inhibitory effects of Fen on NFATc4 binding to GATA-4 and the rBNP DNA. Quantitative RT-PCR and confocal microscopy confirmed inhibitory effects of PPARα activation on elevation of rBNP mRNA levels and ET-1-induced cardiomyocyte hypertrophy. Our results suggest that activated PPARα can compete with GATA-4 binding to NFATc4, thereby decreasing transactivation of NFATc4, and interfering with ET-1 induced cardiomyocyte hypertrophy.

FGF23 induces left ventricular hypertrophy

Chronic kidney disease (CKD) is a public health epidemic that increases risk of death due to cardiovascular disease. Left ventricular hypertrophy (LVH) is an important mechanism of cardiovascular disease in individuals with CKD. Elevated levels of FGF23 have been linked to greater risks of LVH and mortality in patients with CKD, but whether these risks represent causal effects of FGF23 is unknown. Here, we report that elevated FGF23 levels are independently associated with LVH in a large, racially diverse CKD cohort. FGF23 caused pathological hypertrophy of isolated rat cardiomyocytes via FGF receptor-dependent activation of the calcineurin-NFAT signaling pathway, but this effect was independent of klotho, the coreceptor for FGF23 in the kidney and parathyroid glands. Intramyocardial or intravenous injection of FGF23 in wild-type mice resulted in LVH, and klotho-deficient mice demonstrated elevated FGF23 levels and LVH. In an established animal model of CKD, treatment with an FGF-receptor blocker attenuated LVH, although no change in blood pressure was observed. These results unveil a klotho-independent, causal role for FGF23 in the pathogenesis of LVH and suggest that chronically elevated FGF23 levels contribute directly to high rates of LVH and mortality in individuals with CKD.

Electroacupuncture at PC6 (Neiguan) Improves Extracellular Signal-Regulated Kinase Signaling Pathways Through the Regulation of Neuroendocrine Cytokines in Myocardial Hypertrophic Rats

Electroacupuncture (EA) therapy has been widely accepted as a useful therapeutic technique with low or no risk in the clinical prevention of cardiac hypertrophy. However, the signaling transduction mechanism underlying this effect remains unclear. The current study investigates the effects of EA on the signaling pathways of myocardial hypertrophy (MH) in rats. Up to 40 3-month-old Sprague-Dawley (SD) rats were randomly divided into normal, model, PC6 (Neiguan), and LI4 (Hegu) groups, with ten rats in each group. All the rats except for the normal group received 3 mg/kg·d of isoprinosine hydrochloride (ISO) injection into the back skin. The rats in the PC6 and LI4 groups received EA for 14 days. On the 15th day, electrocardiograms were recorded, and the ultrastructure of the myocardial cells was observed. The myocardial hypertrophy indices (MHIs), electrocardiograph (ECG), ultrastructure observation, levels of plasma angiotensin II (Ang II) and endothelin (ET), as well as protein expression of extracellular signal-regulated kinase (ERK), and phosphorylation extracellular signal regulating kinase (p-ERK) in the left ventricular myocardial tissue were measured. The results indicated that EA can improve cardiac function in MH rats by modulating upstream neuroendocrine cytokines that regulate the ERK signaling pathways.

Mitogen-activated protein kinase in endothelin-1-induced cardiac differentiation of mouse embryonic stem cells

Endothelin-1(ET-1) is a potent vasoconstrictor involved in the development of cardiovascular diseases and is an important regulator of heart development. However, the role of ET-1 in cardiac differentiation of mouse embryonic stem cells (mESCs) and the underlying molecular mechanisms remain poorly understood. In the present study, we showed that ET-1 significantly up-regulated gene expression of the cardiac specific transcriptional factors Nkx2.5, GATA4, and conduction system specific marker CX40, with no affect on the gene expression of α-MHC and β-MHC in cardiac differentiation of mESCs. The percentage of beating embryoid bodies (EB) and the Troponin T (TnT) positive area in total EBs was unchanged following ET-1 treatment, while the percentage of spindle cells that stained positively with TnT was increased in the presence of ET-1. Further investigation indicated that the percentage of beating EBs and the TnT positive area were decreased by the extracellular signal-related kinases (ERK)-1/2 inhibitor U0126 and the p38 inhibitor SB203580, but not by the Jun amino-terminal kinases (JNK) inhibitor SP600125. Inhibition of ERK1/2, p38, and JNK pathways also blocked the up-regulation of Nkx2.5 and GATA4 by ET-1, however only inhibition of the ERK1/2 pathway had negatively effects on the increase in CX40 expression in response to ET-1. ET-1 induced an increase in the percentage of spindle cells was also inhibited by U0126. Our results suggest that ET-1 plays a significant role in the cardiac differentiation of mESCs, especially in those cells committed to the conduction system, with the ERK1/2 pathway playing a critical role in this process.

Regulation of blood pressure and salt homeostasis by endothelin

Endothelin (ET) peptides and their receptors are intimately involved in the physiological control of systemic blood pressure and body Na homeostasis, exerting these effects through alterations in a host of circulating and local factors. Hormonal systems affected by ET include natriuretic peptides, aldosterone, catecholamines, and angiotensin. ET also directly regulates cardiac output, central and peripheral nervous system activity, renal Na and water excretion, systemic vascular resistance, and venous capacitance. ET regulation of these systems is often complex, sometimes involving opposing actions depending on which receptor isoform is activated, which cells are affected, and what other prevailing factors exist. A detailed understanding of this system is important; disordered regulation of the ET system is strongly associated with hypertension and dysregulated extracellular fluid volume homeostasis. In addition, ET receptor antagonists are being increasingly used for the treatment of a variety of diseases; while demonstrating benefit, these agents also have adverse effects on fluid retention that may substantially limit their clinical utility. This review provides a detailed analysis of how the ET system is involved in the control of blood pressure and Na homeostasis, focusing primarily on physiological regulation with some discussion of the role of the ET system in hypertension.

Role of reactive oxygen species in the regulation of cardiac contractility

Increased production of reactive oxygen species (ROS) has been linked to the pathogenesis of contractile dysfunction in heart failure. However, it is unclear whether ROS can regulate physiological cellular processes in the myocardium. Here, we characterized the role of endogenous ROS production in the acute regulation of cardiac contractility in the intact rat heart. In isolated perfused rat hearts, endothelin-1 (ET-1, 1nmol/L) stimulated ROS formation in the left ventricle, which was prevented by the antioxidant N-acetylcysteine and the NAD(P)H oxidase inhibitor apocynin. N-acetylcysteine, the superoxide dismutase mimetic MnTMPyP, and apocynin significantly attenuated ET-1-mediated inotropic effect, which was accompanied by inhibition of extracellular signal regulated kinase 1/2 (ERK1/2) phosphorylation. Moreover, the mitochondrial K(ATP) channel blocker 5-HD, and the mitochondrial large conductance calcium activated potassium channel blocker paxilline, but not the sarcolemmal K(ATP) channel blocker HMR 1098 attenuated the inotropic response to ET-1. However, ET-1-induced ROS generation was not abolished by inhibiting mitochondrial K(ATP) channel opening. In contrast to ET-1 stimulation, the positive inotropic effect of β(1)-adrenergic receptor agonist dobutamine (250nmol/L) was significantly augmented by N-acetylcysteine and apocynin. Moreover, dobutamine-induced phospholamban phosphorylation was markedly enhanced by apocynin. In conclusion, NAD(P)H oxidase-derived ROS play a physiological role in the acute regulation of cardiac contractility in the intact rat heart. Our results reveal that ET-1-induced increase in cardiac contractility is partially dependent on enhanced ROS generation, which in turn, activates the ERK1/2 pathway. On the other hand, β-adrenergic receptor-induced positive inotropic effect and phospholamban phosphorylation is enhanced by NAD(P)H oxidase inhibition.

Receptor specific crosstalk and modulation of signaling upon heterodimerization between β1-adrenergic receptor and somatostatin receptor-5

In the present study we describe heterodimerization, trafficking, coupling to adenylyl cyclase and signaling in HEK-293 cells cotransfected with human-somatostatin receptor 5 (hSSTR5) and β(1)-adrenergic receptor (β(1)AR). hSSTR5/β(1)AR exists as heterodimers in basal conditions which was further enhanced upon synergistic activation of both receptors. Activation of either β(1)AR or hSSTR5 displayed dissociation of heterodimerization. In cotransfectants, β(1)AR effect on cAMP was predominant; however, blocking β(1)AR with antagonist resulted in 60% inhibition of forskolin-stimulated cAMP in the presence of hSSTR5 agonists. cAMP/PKA pathway in cotransfected cells was regulated in receptor-specific manner, in contrast, the status of pERK1/2 and pPI3K/AKT was predominantly regulated by hSSTR5. The expression levels of phosphorylated NFAT remained unchanged indicating blockade of calcineurin-mediated dephosphorylation and nuclear translocation of NFAT, the process predominantly regulated by pJNK in SSTR5 dependent manner. Taken together, the functional consequences of results described here might have relevance in the cardiovascular system where SSTR and AR subtypes play important roles.

Monophosphothreonyl extracellular signal-regulated kinases 1 and 2 (ERK1/2) are formed endogenously in intact cardiac myocytes and are enzymically active

ERK1 and ERK2 (ERK1/2) are central to the regulation of cell division, growth and survival. They are activated by phosphorylation of the Thr- and the Tyr- residues in their Thr-Glu-Tyr activation loops. The dogma is that dually-phosphorylated ERK1/2 constitute the principal activities in intact cells. We previously showed that, in neonatal rat cardiac myocytes, endothelin-1 and phorbol 12-myristate 13-acetate (PMA) powerfully and rapidly (maximal at ~ 5 min) activate ERK1/2. Here, we show that dually-phosphorylated ERK1/2 rapidly (< 2 min) appear in the nucleus following stimulation with endothelin-1. We characterized the active ERK1/2 species in myocytes exposed to endothelin-1 or PMA using MonoQ FPLC. Unexpectedly, two peaks of ERK1 and two peaks of ERK2 activity were resolved using in vitro kinase assays. One of each of these represented the dually-phosphorylated species. The other two represented activities for ERK1 or ERK2 which were phosphorylated solely on the Thr- residue. Monophosphothreonyl ERK1/2 represented maximally ~ 30% of total ERK1/2 activity after stimulation with endothelin-1 or PMA, and their k_cat values were estimated to be minimally ~ 30% of the dually-phosphorylated species. Appearance of monophosphothreonyl ERK1/2 was rapid but delayed in comparison with dually-phosphorylated ERK1/2. Of 10 agonists studied, endothelin-1 and PMA were most effective in terms of ERK1/2 activation and in stimulating the appearance of monophosphothreonyl and dually-phosphorylated ERK1/2. Thus, enzymically active monophosphothreonyl ERK1/2 are formed endogenously following activation of the ERK1/2 cascade and we suggest that monophosphothreonyl ERK1/2 arise by protein tyrosine phosphatase-mediated dephosphorylation of dually-phosphorylated ERK1/2.

At the heart of tissue: endothelin system and end-organ damage

ET (endothelin)-1 was first described as a potent vasoconstrictor. Since then, many other deleterious properties mediated via its two receptors, ETA and ETB, have been described, such as inflammation, fibrosis and hyperplasia. These effects, combined with a wide tissue distribution of the ET system, its up-regulation in pathological situations and a local autocrine/paracrine activity due to a high tissue receptor binding, make the tissue ET system a key local player in end-organ damage. Furthermore, ET-1 interacts in tissues with other systems such as the RAAS (renin-angiotensin-aldosterone system) to exert its effects. In numerous genetically modified animal models, non-specific or organ-targeted ET-1 overexpression causes intense organ damage, especially hypertrophy and fibrosis, in the absence of haemodynamic changes, confirming a local activity of the ET system. ET receptor antagonists have been shown to prevent and sometimes reverse these tissue alterations in an organ-specific manner, leading to long-term benefits and an improvement in survival in different animal models. Potential for such benefits going beyond a pure haemodynamic effect have also been suggested by clinical trial results in which ET receptor antagonism decreased the occurrence of new digital ulcers in patients with systemic sclerosis and delayed the time to clinical worsening in patients with PAH (pulmonary arterial hypertension). The tissue ET system allows therapeutic interventions to provide organ selectivity and beneficial effects in diseases associated with tissue inflammation, hypertrophy or fibrosis.

Revisited and revised: is RhoA always a villain in cardiac pathophysiology?

The neonatal rat ventricular myocyte model of hypertrophy has provided tremendous insight with regard to signaling pathways regulating cardiac growth and gene expression. Many mediators thus discovered have been successfully extrapolated to the in vivo setting, as assessed using genetically engineered mice and physiological interventions. Studies in neonatal rat ventricular myocytes demonstrated a role for the small G-protein RhoA and its downstream effector kinase, Rho-associated coiled-coil containing protein kinase (ROCK), in agonist-mediated hypertrophy. Transgenic expression of RhoA in the heart does not phenocopy this response, however, nor does genetic deletion of ROCK prevent hypertrophy. Pharmacologic inhibition of ROCK has effects most consistent with roles for RhoA signaling in the development of heart failure or responses to ischemic damage. Whether signals elicited downstream of RhoA promote cell death or survival and are deleterious or salutary is, however, context and cell-type dependent. The concepts discussed above are reviewed, and the hypothesis that RhoA might protect cardiomyocytes from ischemia and other insults is presented. Novel RhoA targets including phospholipid regulated and regulating enzymes (Akt, PI kinases, phospholipase C, protein kinases C and D) and serum response element-mediated transcriptional responses are considered as possible pathways through which RhoA could affect cardiomyocyte survival.

Involvement of insulin-like growth factor 1 receptor transactivation in endothelin-1-induced signaling in vascular smooth muscle cells

Endothelin-1 (ET-1) is a potent vasoactive peptide that exerts hypertrophic, migratory, and mitogenic effects in vascular smooth muscle cells. ET-1-induced activation of several signaling events has been shown to mediate the cellular effects of ET-1. In the past several years, transactivation of growth factor receptor has gained much recognition in transducing the signaling responses of ET-1. Among various growth factor receptors studied, the involvement of epidermal growth factor receptor transactivation in triggering ET-1-induced responses has been studied in some detail. However, recent studies have implicated insulin-like growth factor 1 receptor transactivation in this process. There are also some suggestions for a role of the Src family of nonreceptor protein tyrosine kinases, such as c-Src, in transducing the signaling responses of vasoactive peptides. In this review, we will examine the contribution of both insulin-like growth factor 1 receptor and c-Src in mediating ET-1-induced signaling responses in vascular smooth muscle cells.

Role of insulin-like growth factor 1 receptor and c-Src in endothelin-1- and angiotensin II-induced PKB phosphorylation, and hypertrophic and proliferative responses in vascular smooth muscle cellsThis article is one of a selection of papers published in a special issue on Advances in Cardiovascular Research

Endothelin-1 (ET-1) and angiotensin II (Ang II) are vasoactive peptides believed to contribute to the pathogenesis of vascular abnormalities such as hypertension, atherosclerosis, hypertrophy, and restenosis. The concept of transactivation of growth factor receptors, such as epidermal growth factor receptor (EGFR), in triggering vasoactive peptide-induced signaling events has gained much recognition during the past several years. We have demonstrated that insulin-like growth factor type 1 receptor (IGF-1R) plays a role in transducing the effect of H2O2, leading to protein kinase B (PKB) phosphorylation. Since vasoactive peptides elicit their responses through generation of reactive oxygen species, including H2O2, we investigated whether IGF-1R transactivation plays a similar role in ET-1- and Ang II-induced PKB phosphorylation and hypertrophic responses in vascular smooth muscle cells (VSMC). AG1024, a specific inhibitor of IGF-1R protein tyrosine kinase (PTK), attenuated both ET-1- and Ang II-induced PKB phosphorylation in a dose-dependent manner. ET-1 and Ang II treatment also induced the phosphorylation of tyrosine residues in the autophosphorylation sites of IGF-1R, which were blocked by AG1024. In addition, both ET-1 and Ang II evoked tyrosine phosphorylation of c-Src, a nonreceptor PTK, whereas pharmacological inhibition of c-Src PTK activity by PP2, a specific inhibitor of Src-family tyrosine kinase, significantly reduced PKB phosphorylation as well as tyrosine phosphorylation of IGF-1R induced by the 2 vasoactive peptides. Furthermore, protein and DNA synthesis enhanced by ET-1 and Ang II were attenuated by AG1024 and PP2. In conclusion, these data suggest that IGF-1R PTK and c-Src PTK play a critical role in mediating PKB phosphorylation as well as hypertrophic and proliferative responses induced by ET-1 and Ang II in A10 VSMC.

Gq-initiated cardiomyocyte hypertrophy is mediated by phospholipase Cbeta1b

Activation of the heterotrimeric G protein Gq causes cardiomyocyte hypertrophy in vivo and in cell culture models. Hypertrophic responses induced by pressure or volume overload are exacerbated by increased Gq activity and ameliorated by Gq inhibition. Gq activates phospholipase Cbeta (PLCbeta) subtypes, resulting in generation of the intracellular messengers inositol(1,4,5)tris-phosphate [Ins(1,4,5)P(3)] and sn-1,2-diacylglycerol (DAG), which regulate intracellular Ca(2+) and conventional protein kinase C subtypes, respectively. Gq can also signal independently of PLCbeta, and the involvement of either Ins(1,4,5)P(3) or DAG in cardiomyocyte hypertrophy has not been unequivocally established. Overexpression of one splice variant of PLCbeta1, specifically PLCbeta1b, in neonatal rat cardiomyocytes causes increased cell size, elevated protein/DNA ratio, and heightened expression of the hypertrophy-related marker gene, atrial natriuretic peptide. The other splice variant, PLCbeta1a, had no effect. Expression of a 32-aa C-terminal PLCbeta1b peptide, which competes with PLCbeta1b for sarcolemmal association, prevented PLC activation and eliminated hypertrophic responses initiated by Gq or Gq-coupled alpha(1)-adrenergic receptors. In contrast, a PLCbeta1a C-terminal peptide altered neither PLC activity nor cellular hypertrophy. We conclude that hypertrophic responses initiated by Gq are mediated specifically by PLCbeta1b. Preventing PLCbeta1b association with the sarcolemma may provide a useful therapeutic target to limit hypertrophy.

Are transgenic mice the 'alkahest' to understanding myocardial hypertrophy and failure?

Murine transgenesis using cardioselective promoters has become increasingly common in studies of cardiac hypertrophy and heart failure, with expression mediated by pronuclear microinjection being the commonest format. Without wishing to decry their usefulness, in our view, such studies are not necessarily as unambiguous as sometimes portrayed and clarity is not always their consequence. We describe broadly the types of approach undertaken in the heart and point out some of the drawbacks. We provide three arbitrarily-chosen examples where, in spite of a number of often-independent studies, no consensus has yet been achieved. These include glycogen synthase kinase 3, the extracellular signal-regulated kinase pathway and the ryanodine receptor 2. We believe that the transgenic approach should not be viewed in an empyreal light and, depending on the questions asked, we suggest that other experimental systems provide equal (or even more) valuable outcomes.

Antagonism of endothelin-1 inhibits hypoxia-induced apoptosis in cardiomyocytes

Apoptosis is well documented to be a common feature of many pathological processes of the heart. Exogenous endothelin-1 (ET-1) has been shown to be proapoptotic or antiapoptotic, depending on ET-1 concentration, cell type, and the ratio of ETA/ETB receptor subtypes. The role of endogenous ET-1 in cardiomyocyte apoptosis, however, is not clarified. This study observed the effects of the ETA-receptor antagonists BQ610 and BQ123 and the ETB-receptor antagonist BQ788 on hypoxia-induced apoptosis in primary cultured neonatal rat cardiomyocytes. Hypoxic apoptosis was induced by incubating cardiomyocytes in serum-free medium under 3% O2 and 5% CO2 for 24 h and evaluated by TUNEL analysis and flow cytometry. TUNEL analysis showed that the apoptotic cardiomyocytes constituted 24.2% +/- 2.2% of the total cells under hypoxic conditions. Treatment with BQ610 (5 micromol/L) significantly reduced the apoptosis rate to 13.2% +/- 3.7% (data from 4 independent experiments, p < 0.01 vs. hypoxia). Flow cytometry showed that the percentage of apoptotic cells positively stained with annexin V and propidium iodide was 42.76% +/- 4.44% (n = 12) in cultures subjected to hypoxia. BQ123 at 0.04, 0.2, and 1.0 micromol/L dose-dependently reduced the apoptosis rate to 34.00% +/- 10.35% (n = 6, p < 0.05), 30.38% +/- 8.28% (n = 6, p < 0.01), and 22.89% +/- 4.19% (n = 6, p < 0.01), respectively. In contrast, BQ788 did not affect hypoxic apoptosis. These findings suggested that endogenous ET-1 contributed to hypoxia-induced apoptosis in cultured cardiomyocytes, which was mediated by ETA receptors, but not by ETB receptors.

Differential roles of MAPKs and MSK1 signalling pathways in the regulation of c-Jun during phenylephrine-induced cardiac myocyte hypertrophy

Gq-protein-coupled receptor (GqPCR) signalling is associated with the induction of cardiac myocyte hypertrophy, which is characterized by an increase in expression of immediate early genes via activation of pre-existing transcription factors. Here, we explore the role of MSK1 and MAPK signalling pathways in the regulation of the immediate early gene c-jun. The results provide further support for the role of MSK1 in cardiac myocyte hypertrophy and indicate that PE activates distinct signalling mechanisms which culminate with a complex activation of c-jun. ERK1/2 and JNKs are the principal kinases responsible for phosphorylation of c-Jun, whereas c-jun mRNA and protein up-regulation by PE is mediated by multiple signalling pathways that include MSK1, ERK1/2, p38-MAPK and JNKs. These signalling mechanisms seem to be critical to the phenotypic changes of cardiac myocytes in response to hypertrophic stimulation.