Mitogen-activated protein kinase (MAPK) in cardiac tissues

Multi-Omics Analysis Reveals the Role of Sigma-1 Receptor in a Takotsubo-like Cardiomyopathy Model

Takotsubo syndrome (TTS) is a stress-induced cardiomyopathy that presents with sudden onset of chest pain and dyspneic and cardiac dysfunction as a result of extreme physical or emotional stress. The sigma-1 receptor (Sigmar1) is a ligand-dependent molecular chaperone that is postulated to be involved in various processes related to cardiovascular disease. However, the role of Sigmar1 in TTS remains unresolved. In this study, we established a mouse model of TTS using wild-type and Sigmar1 knockout mice to investigate the involvement of Sigmar1 in TTS development. Our results revealed that Sigmar1 knockout exacerbated cardiac dysfunction, with a noticeable decrease in ejection fraction (EF) and fractional shortening (FS) compared to the wild-type model. In terms of the gut microbiome, we observed regulation of Firmicutes and Bacteroidetes ratios; suppression of probiotic Lactobacillus growth; and a rise in pathogenic bacterial species, such as Colidextribacter. Metabolomic and transcriptomic analyses further suggested that Sigmar1 plays a role in regulating tryptophan metabolism and several signaling pathways, including MAPK, HIF-1, calcium signaling, and apoptosis pathways, which may be crucial in TTS pathogenesis. These findings offer valuable insight into the function of Sigmar1 in TTS, and this receptor may represent a promising therapeutic target for TTS.

Lamin A/C Cardiomyopathies: Current Understanding and Novel Treatment Strategies

OPINION STATEMENT

Dilated cardiomyopathy (DCM) is the third leading cause of heart failure in the USA. A major gene associated with DCM with cardiac conduction system disease is lamin A/C (LMNA) gene. Lamins are type V filaments that serve a variety of roles, including nuclear structure support, DNA repair, cell signaling pathway mediation, and chromatin organization. In 1999, LMNA was found responsible for Emery-Dreifuss muscular dystrophy (EDMD) and, since then, has been found in association with a wide spectrum of diseases termed laminopathies, including LMNA cardiomyopathy. Patients with LMNA mutations have a poor prognosis and a higher risk for sudden cardiac death, along with other cardiac effects like dysrhythmias, development of congestive heart failure, and potential need of a pacemaker or ICD. As of now, there is no specific treatment for laminopathies, including LMNA cardiomyopathy, because the mechanism of LMNA mutations in humans is still unclear. This review discusses LMNA mutations and how they relate to DCM, the necessity for further investigation to better understand LMNA mutations, and potential treatment options ranging from clinical and therapeutic to cellular and molecular techniques.

Dihydroartemisinin transiently activates the JNK/SAPK signaling pathway in endothelial cells

Artemisinin and its derivatives are well-known anti-malaria drugs and in the early stages of research for cancer treatment. Dihydroartemisinin (DHA), a more water-soluble derivative of artemisinin, has demonstrated strong anti-angiogenic activity. The purpose of the present study was to investigate the underlying molecular mechanisms of the effect of DHA on angiogenesis. Human umbilical vein endothelial cells (HUVECs) treated with DHA were examined for apoptosis and activation of the c-Jun N-terminal kinase (JNK) signaling pathway, one of the major mitogen-activated protein kinase cascades. It was observed that 20 µM DHA induces transient activation of JNK in HUVECs. DHA also elevates the expression of cyclooxygenase-2 and matrix metalloproteinase-13, which is abolished by treatment with the JNK inhibitor SP600125. Although DHA persistently increases inhibitor of κB-α protein and thus inhibits nuclear factor-κB signaling, it does not affect apoptosis or caspase 3/9 activities in HUVECs. The present study provides key information for understanding the effects of DHA on endothelial cells, which is required for investigating its potential for clinic application as a chemotherapeutic agent.

Differential ERK1/2 Signaling and Hypertrophic Response to Endothelin-1 in Cardiomyocytes from SHR and Wistar-Kyoto Rats: A Potential Target for Combination Therapy of Hypertension

Extracellular signal regulated kinase½ (ERK1/2) signaling is critical to endothelin-1 (ET-1)-induced cardiomyocyte hypertrophy. This study was to investigate ERK1/2 signaling and hypertrophic response to ET-1 stimulation in cardiomyocytes (CMs) from spontaneous hypertensive rats (SHR) and normotensive Wistar-Kyoto rats (WKY). Primary neonatal SHR and WKY CMs were exposed to ET-1 for up to 24 hrs. Minimal basal ERK1/2 phosphorylation was present in WKY CMs, while a significant baseline ERK1/2 phosphorylation was observed in SHR CMs. ET-1 induced a time- and dose-dependent increase in ERK1/2 phosphorylation in both SHR and WKY CMs. However, ET-1-induced ERK1/2 activation occurred much earlier with significantly higher peak phosphorylation level, and stayed elevated for longer duration in SHR CMs than that in WKY CMs. ET-1-induced hypertrophic response was more prominent in SHR CMs than that in WKY CMs as reflected by increased cell surface area, intracellular actin density, and protein synthesis. Pre-treatment with ERK1/2 phosphorylation inhibitor PD98059 completely prevented ET-1-induced ERK1/2 phosphorylation and increases in cell surface area and protein synthesis in SHR and WKY CMs. The specific PI3 kinase inhibitor LY294002 blocked ET-1-induced Akt and ERK1/2 phosphorylation, and protein synthesis in CMs. These data indicated that ERK1/2 signaling was differentially enhanced in CMs, and was associated with increased cardiac hypertrophic response to ET-1 in SHR. ET-1-induced ERK1/2 activation and cardiac hypertrophy appeared to be mediated via PI3 kinase/Akt signaling in SHR and WKY. The differential ERK1/2 activation in SHR CMs by ET-1 might represent a potential target for combination therapy of hypertension.

Role of thioredoxin-1 in ischemic preconditioning, postconditioning and aged ischemic hearts

Thioredoxin is one of the most important cellular antioxidant systems known to date, and is responsible of maintaining the reduced state of the intracellular space. Trx-1 is a small cytosolic protein whose transcription is induced by stress. Therefore it is possible that this antioxidant plays a protective role against the oxidative stress caused by an increase of reactive oxygen species concentration, as occurs during the reperfusion after an ischemic episode. However, in addition to its antioxidant properties, it is able to activate other cytoplasmic and nuclear mediators that confer cardioprotection. It is remarkable that Trx-1 also participates in myocardial protection mechanisms such as ischemic preconditioning and postconditioning, activating proteins related to cellular survival. In this sense, it has been shown that Trx-1 inhibition abolished the preconditioning cardioprotective effect, evidenced through apoptosis and infarct size. Furthermore, ischemic postconditioning preserves Trx-1 content at reperfusion, after ischemia. However, comorbidities such as aging can modify this powerful cellular defense leading to decrease cardioprotection. Even ischemic preconditioning and postconditioning protocols performed in aged animal models failed to decrease infarct size. Therefore, the lack of success of antioxidants therapies to treat ischemic heart disease could be solved, at least in part, avoiding the damage of Trx system.

Involvement of RBP4 in hyperinsulinism-induced vascular smooth muscle cell proliferation

Retinol-binding protein 4 (RBP4) is a newly discovered adipocytokine related to insulin resistance (IR). Hyperinsulinemia and IR are the major risk factors for cardiovascular diseases (CVD). The role of RBP4 in CVD has not yet been determined. The present study was designed to analyze the correlation of RBP4 and CVD risk factors and to evaluate the role of RBP4 in proliferation of vascular smooth muscle cells during hyperinsulinemia and the underlying mechanisms. Plasma RBP4 concentration, IR-related indexes, and cardiovascular risk factors were measured from blood samples of hyperinsulinemic rats (HIns) and control SD rats (Cons). The vascular morphology and the expression of ERK1/2, p-ERK1/2 in arterial tissues of rats were assessed. Different concentrations of RBP4 (1, 4 μg/ml) were used as intervention factor during insulin-induced aortic smooth muscle cells (RASMCs) proliferation. The expression of cell growth signaling pathways was assessed to identify the active pathway during this proliferation. Specifically, ERK1/2 inhibitor PD98059 and JAK2 inhibitor AG490 were used to detect it. RBP4 expression was higher in HIns compared with Cons (p < 0.01). Plasma RBP4 concentrations were positively correlated with TG (r = 0.490), hsCRP (r = 0.565), media thickness (r = 0.890), and p-ERK1/2 protein (r = 0.746) (p < 0.05 each). In cultured RASMCs, RBP4 enhanced insulin-induced proliferation of cells and expression of p-ERK1/2 and p-JAK2. Blockade of ERK1/2 signaling pathway inhibited RBP4-induced proliferation of RASMCs, while suppressing JAK2 remains unchanged. These results suggest that plasma RBP4 concentrations were associated with CVD. In addition, RBP4 increases the proliferation of VSMCs induced by hyperinsulinism via activation of MAPK signaling pathway.

Dihydroartemisinin inhibits vascular endothelial growth factor-induced endothelial cell migration by a p38 mitogen-activated protein kinase-independent pathway

Dihydroartemisinin (DHA), a semi-synthetic derivative of artemisinin, has been demonstrated to possess a strong antiangiogenic activity. However, the molecular mechanisms underlying this effect remain unclear. Endothelial cell (EC) migration is an essential component of angiogenesis, and the p38 mitogen-activated protein kinase (MAPK) signaling pathway plays a key role in the regulation of migration induced by vascular endothelial growth factor (VEGF). The aim of the present study was to investigate the effects of DHA on EC migration and the p38 MAPK signaling pathway. Human umbilical vein ECs (HUVECs) were treated with DHA and VEGF-induced migration was analyzed. The activation of p38 MAPK was detected by western blot analysis, and the migration assays were performed with a p38-specific inhibitor, SB203850. It was revealed that 20 μM DHA significantly reduced EC migration in the transwell migration assay, wound healing assay and electrical cell-substrate impedance sensing real-time analysis. However, DHA did not affect p38 MAPK phosphorylation or expression. In the absence or presence of SB203850, DHA induced a similar proportional reduction of EC migration in the three migration assays. Therefore, the present study demonstrated that DHA inhibits VEGF-induced EC migration via a p38 MAPK-independent pathway.

Retinol binding protein 4 promotes hyperinsulinism‑induced proliferation of rat aortic smooth muscle cells

Recent studies have suggested that retinol binding protein 4 (RBP4), an adipocytokine related to insulin resistance (IR), may play an important role in the development of atherosclerosis and cardiovascular diseases (CVD). Abnormal proliferation and migration of vascular smooth muscle cells (VSMCs) is one of the most common causes of atherosclerosis. Hyperinsulinism promotes proliferation of VSMCs through the MAPK pathway. However, whether RBP4 is involved in insulin-induced proliferation of VSMCs leading to atherosclerosis remains unclear. In the present study, we evaluated the role of RBP4 and the potential relevance of signaling pathways in this process. Different concentrations of RBP4 (1 and 4 μg/ml) were added to rat aortic smooth muscle cells (RASMCs) during insulin-induced proliferation. The levels of cell growth signaling pathway proteins ERK1/2, p-ERK1/2, JAK2, p-JAK2, STAT3 and p-STAT3 were assessed by western blotting in order to identify the pathway(s) that are activated during insulin-induced proliferation. The specific inhibitors of ERK1/2 (PD98059) and JAK2 (AG490) were used to confirm our findings. Insulin induced proliferation of RASMCs in a concentration- and time-dependent manner, and increased the expression of ERK1/2, p-ERK1/2, JAK2, p-JAK2, STAT3 and p-STAT3 in a time-dependent manner. RBP4 enhanced insulin-induced proliferation of RASMCs and expression of p-ERK1/2 and p-JAK2. RBP4-induced proliferation of RASMCs was reduced by the ERK1/2 inhibitor, while it was unaffected by the JAK2 inhibitor. These results suggest that RBP4 mediates VSMC proliferation induced by insulin via activation of the MAPK pathway, and highlight RBP4 as a modulator of atherosclerosis in hyperinsulinemia, therby enhancing our understanding on a number of unexpected aspects of CVD.

Puerarin attenuates cerebral damage by improving cerebral microcirculation in spontaneously hypertensive rats

Puerariae Lobatae Radix (Gegen in Chinese) is the dried root of Pueraria lobata, a semiwoody, perennial, and leguminous vine native to China. Puerarin is one of the effective components of isoflavones isolated from the root of Pueraria lobata. Previous studies showed that extracts derived from the root of Pueraria lobata possessed antihypertensive effect. Our study is to investigate whether puerarin contributes to prevention of stroke by improving cerebral microcirculation in rats. Materials and Methods. Video microscopy and laser Doppler perfusion imaging on the pia mater were used to measure the diameter of microvessel and blood perfusion in 12-week old spontaneously hypertensive rats (SHRs) and age-matched normotensive WKY rats. Histological alterations were observed by hematoxylin and eosin staining, and microvessel density in cerebral tissue was measured by immunohistochemical analysis with anti-Factor VIII antibody. Cell proliferation was detected by [(3)H]-TdR incorporation, and activities of p42/44 mitogen activated protein kinases (p42/44 MAPKs) were detected by western blot analysis in cultured cerebral microvascular endothelial cells (MECs). Results. Intravenous injection of puerarin relaxed arterioles and increased the blood flow perfusion in the pia mater in SHRs. Puerarin treatment for 14 days reduced the blood pressure to a normal level in SHRs (P < 0.05) and increased the arteriole diameter in the pia mater significantly as compared with vehicle treatment. Arteriole remodeling, edema, and ischemia in cerebral tissue were attenuated in puerarin-treated SHRs. Microvessel density in cerebral tissue was greater with puerarin than with vehicle treatment. Puerarin-treated MECs showed greater proliferation and p42/44 MAPKs activities than vehicle treatment. Conclusions. Puerarin possesses effects of antihypertension and stroke prevention by improved microcirculation in SHRs, which results from the increase in cerebral blood perfusion both by arteriole relaxation and p42/44 MAPKs-mediated angiogenesis.

Caveolin and caveolae in age associated cardiovascular disease

It is estimated that the elderly (> 65 years of age) will increase from 13%−14% to 25% by 2035. If this trend continues, > 50% of the United States population and more than two billion people worldwide will be “aged” in the next 50 years. Aged individuals face formidable challenges to their health, as aging is associated with a myriad of diseases. Cardiovascular disease is the leading cause of morbidity and mortality in the United States with > 50% of mortality attributed to coronary artery disease and > 80% of these deaths occurring in those age 65 and older. Therefore, age is an important predictor of cardiovascular disease. The efficiency of youth is built upon cellular signaling scaffolds that provide tight and coordinated signaling. Lipid rafts are one such scaffold of which caveolae are a subset. In this review, we consider the importance of caveolae in common cardiovascular diseases of the aged and as potential therapeutic targets. We specifically address the role of caveolin in heart failure, myocardial ischemia, and pulmonary hypertension.

Gene expression profiling of the proliferative effect of periplocin on mouse cardiac microvascular endothelial cells

OBJECTIVE

Periplocin is an active digitalis-like component from Cortex Periplocae, which has been widely used in the treatment of heart diseases in China for many years. According to the recommendations on the cardiovascular effect of periplocin from in vivo experiments, subsequent in vitro experiments are greatly needed for the global assessment of periplocin. The objective of this study is to investigate the cell proliferation effect and the mechanism of periplocin on endothelial cells.

METHODS

The proliferative activity of periplocin (0.4, 2, 10, 50, 250 micromol/L; 6, 12, 24, 48, 72 h) was investigated by a comparison with the well-reported cardiac glycoside, ouabain, on mouse cardiac microvascular endothelial cells (CMEC). 3-(4,5-dimethylthiazolyl)-2,5-diphenyltetrazolium bromide (MTT), lactate dehydrogenase (LDH) and 5-bromo-2-deoxyuridine (BrdU) assays were used to evaluate cell proliferation and viability. Subsequently, cDNA microarray experiments were performed on periplocin- (50 micromol/L) and ouabain- (50 micromol/L) treated cells, and data was analyzed by ArrayTrack software.

RESULTS

Periplocin could increase cell viability to a level lower than ouabain in the MTT analysis, but decrease LDH release simultaneously. The BrdU incorporation assay showed an increase in cell proliferation with 2-50 micromol/L periplocin. Genes related to protein serine/threonine kinase were the most significantly enriched in the 160 genes identified in periplocin versus the control. In the 165 genes regulated by periplocin versus ouabain, GTP-binding was the most altered term.

CONCLUSIONS

The results demonstrated the proliferation action of periplocin on CMEC. Meanwhile, its lower cytotoxicity compared to ouabain provides a new insight into the treatment of heart failure.

Molecular mechanisms of early brain injury after subarachnoid hemorrhage

OBJECTIVES

Increasing body of experimental and clinical data indicates that early brain injury after initial bleeding largely contributes to unfavorable outcome after subarachnoid hemorrhage (SAH). This review presents molecular mechanisms underlying brain injury at its early stages after SAH.

METHODS

PubMed was searched using term 'subarachnoid hemorrhage' and key words referring to molecular and cellular pathomechanisms of SAH-induced early brain injury.

RESULTS

The authors reviewed intracranial phenomena and molecular agents that contribute to the early development of pathological sequelae of SAH in cerebral and vascular tissues, including cerebral ischemia and its interactions with injurious blood components, blood-brain barrier disruption, brain edema and apoptosis.

DISCUSSION

It is believed that detailed knowledge of molecular signaling pathways after SAH will serve to improve therapeutic interventions. The most promising approach is the protection of neurovascular unit including anti-apoptosis therapy.

MR imaging of caveolin gene-specific alterations in right ventricular wall thickness

Caveolin-1 and caveolin-3 are expressed in the mammalian heart. Mice deficient in caveolin 1 or 3 exhibit cardiac abnormalities including left ventricular hypertrophy and reduced fractional shortening. Cardiac imaging technologies such as transthoracic echocardiography and cardiac-gated magnetic resonance imaging (MRI) are effective tools for the study of left ventricular morphology and function in mice; however, there has not been widespread use of these technologies in studies of right ventricular morphology. In particular, right ventricular wall thickness has been difficult to assess using cardiac imaging technologies. We report here the use of centerline analysis of cardiac-gated MR images to more accurately determine right ventricular wall thickness in the mouse heart. Right ventricular wall thickness was evaluated in Cav-1 null, Cav-3 null and Cav-1/3 null mice, as well as wild-type control mice. Using this technique, we find that caveolin null mice exhibit significant thickening of the right ventricular wall as compared with age-matched wild-type controls. Interestingly, right ventricular wall thickening is greatest in the Cav-1/3 null mice. Furthermore, significant right ventricular wall thickening is also seen in the Cav-1 null mice. Histological analyses revealed right ventricular hypertrophy consistent with the imaging results. These studies demonstrate the utility of MRI in determining right ventricular wall thickness and underscore the severity of the right ventricular hypertrophy in caveolin null mice.

Renoprotective effect of benazepril on diabetic nephropathy mediated by P42/44MAPK

The effects of benazepril on P42/44MAPK, angiotensin II expression in renal tissue and renal pathological change of the experimental diabetic rats were assessed and the possible mechanism of benazepril's renoprotective effect was explored. Adult male Wistar rats, 11-12 weeks age, weighing initially 160 to 200 g were randomly allocated into 2 groups: control group (A, n = 6) and experimental group (n = 12). Diabetic rats in experimental group were rendered diabetic by intraperitoneal injection of Streptozotocin (60 mg/kg body weight), and randomly subdivided into B group (diabetic control) and C group (diabetic rats treated with benazepril, 6 mg/kg every day). Studies were performed 8 weeks after induction of diabetes. Twenty-four h urine of every rat was collected to detect urine creatinine. Serum glucose concentration and serum creatinine were determined by collecting blood samples from the inferior vena cava. Body and kidney weight were recorded. Creatinine clearance (Ccr) and ratio of kidney weight to body weight were calculated. Plasma and renal tissue angiotensin II concentration was assayed by radioimmunoassay (RIA). The phospo-p44/42MAPK protein expression was detected by Western-blot. The results showed that benazepril had no significant effect on the blood glucose level in diabetic rats in two experimental groups. Ccr and ratio of kidney weight to body weight were increased in group B (P < 0.01) as compared with normal rats at the end of the 8th week. At the end of the 8th week, Ccr in group C was lower than that in group B (P < 0.01). The ratio of kidney weight to body weight in group C was lower than that in group B at the 8th week. There were glomeruli hypertrophy and slight or moderate mesangium proliferation in diabetic rats, while there was fragmentally proliferative mesangium in group C at the end of the 8th week. Renal tissue angiotensin II concentration was significantly increased in group B, while benazepril could significantly decrease the concentration of angiotensin II in renal tissue. The expression of the phospo-p44/42MAPK protein in group B was increased as compared with group A, while it was decreased in group C as compared with group B. P42/ 44MAPK pathway participated in the pathogenesis of diabetic nephropathy. Benazepril can eliminate high filtration of glomeruli, decrease proteinuria, and eliminate renal hypertrophy as well as renal destruction. Renoprotective effect of benazepril in diabetic rats may be partly related to the inhibition of angiotensin II -P42/44MAPK pathway.

Signaling pathways for early brain injury after subarachnoid hemorrhage

Few studies have examined the signaling pathways that contribute to early brain injury after subarachnoid hemorrhage (SAH). Using a rat SAH model, the authors explored the role of vascular endothelial growth factor (VEGF) and mitogen-activation protein kinase (MAPK) in early brain injury. Male Sprague-Dawley rats (n = 172) weighing 300 to 350 g were used for the experimental SAH model, which was induced by puncturing the bifurcation of the left anterior cerebral and middle cerebral arteries. The blood-brain barrier (BBB), brain edema, intracranial pressure, and mortality were evaluated at 24 hours after SAH. The phosphorylation of VEGF and different MAPK subgroups (ERK1/2, p38, and JNK) were examined in both the cortex and the major cerebral arteries. Experimental SAH increased intracranial pressure, BBB permeability, and brain edema and produced high mortality. SAH induced phosphorylation of VEGF and MAPKs in the cerebral arteries and, to a lesser degree, in the cortex. PP1, an Src-family kinase inhibitor, reduced BBB permeability, brain edema, and mortality and decreased the phosphorylation of VEGF and MAPKs. The authors conclude that VEGF contributes to early brain injury after SAH by enhancing the activation of the MAPK pathways, and that the inhibition of these pathways might offer new treatment strategies for SAH.

Contribution of Src tyrosine kinase to cerebral vasospasm after subarachnoid hemorrhage

OBJECT

Mitogen-activated protein kinase (MAPK) has been implicated in cerebral vasospasm after subarachnoid hemorrhage (SAH). This study was conducted to investigate whether Src tyrosine kinase, an upstream regulator of MAPK, is involved in cerebral vasospasm.

METHODS

An established canine double-hemorrhage model was used. Twenty-four dogs were divided into four groups: control, vehicle-treated, Src inhibitor PP2-treated, and Src inhibitor damnacanthal-treated groups. Vehicle (dimethyl sulfoxide), PP2, or damnacanthal was injected daily into the cisterna magna of 18 dogs at 3 to 6 days after induction of SAH. Angiography was performed on Day 0 (the day on which the first blood injection was administered to induce SAH) and on Day 7. Western blot analysis of Src and MAPK activation in basilar arteries (BAs) collected on Day 7 post-SAH was performed. Severe vasospasm was observed in the BAs of vehicle-treated dogs. Mild vasospasm was observed in all dogs treated with Src inhibitors. Phosphorylated Src and MAPK were increased after SAH and activation of these kinases in the BAs was abolished by PP2 and damnacanthal.

CONCLUSIONS

The tyrosine kinase Src is an important upstream regulator of MAPK, and inhibition of Src might offer a new therapy in the management of cerebral vasospasm.

Caveolin-1 null mice develop cardiac hypertrophy with hyperactivation of p42/44 MAP kinase in cardiac fibroblasts

Recently, development of a caveolin-1-deficient (Cav-1 null) mouse model has allowed the detailed analysis of caveolin-1's function in the context of a whole animal. Interestingly, we now report that the hearts of Cav-1 null mice are markedly abnormal, despite the fact that caveolin-1 is not expressed in cardiac myocytes. However, caveolin-1 is abundantly expressed in the nonmyocytic cells of the heart, i.e., cardiac fibroblasts and endothelia. Quantitative imaging studies of Cav-1 null hearts demonstrate a significantly enlarged right ventricular cavity and a thickened left ventricular wall with decreased systolic function. Histological analysis reveals myocyte hypertrophy with interstitial/perivascular fibrosis. Because caveolin-1 is thought to act as a negative regulator of the p42/44 MAP kinase cascade, we performed Western blot analysis with phospho-specific antibodies that only recognize activated ERK1/2. As predicted, the p42/44 MAP kinase cascade is hyperactivated in Cav-1 null heart tissue (i.e., interstitial fibrotic lesions) and isolated cardiac fibroblasts. In addition, endothelial and inducible nitric oxide synthase levels are dramatically upregulated. Thus loss of caveolin-1 expression drives p42/44 MAP kinase activation and cardiac hypertrophy.

Aldosterone stimulates proliferation of cardiac fibroblasts by activating Ki-RasA and MAPK1/2 signaling

Aldosterone plays a pathological role in cardiac fibrosis by directly affecting cardiac fibroblasts. Understanding of the cellular mechanisms of aldosterone action in cardiac fibroblasts, however, is rudimentary. One possibility is that aldosterone promotes proliferation of cardiac fibroblasts by activating specific cellular signaling cascades. The current study tests whether aldosterone stimulates proliferation of isolated adult rat cardiac myofibroblasts (RCF) by activating Kirsten Ras (Ki-RasA) and its effector, the MAPK1/2 cascade. Aldosterone (10 nM) significantly increased RCF proliferation. This action was sensitive to the mineralocorticoid receptor (MR) antagonist spironolactone. Expression of MR in RCF and the whole rat heart was confirmed by immunoblotting. Aldosterone significantly increased absolute and active (GTP bound) Ki-RasA levels in RCF. Aldosterone, in addition, significantly increased phospho-c-Raf and phospho-MAPK1/2. The effects of aldosterone on Ki-RasA and phospho-c-Raf proteins were inhibited by spironolactone but not RU-486, suggesting that aldosterone acts via MR. Inhibitors of MEK1/2 and c-Raf prevented aldosterone-induced activation of MAPK1/2 and proliferation. These results show that aldosterone directly increases RCF proliferation through MR-dependent activation of Ki-RasA and its effector, the MAPK1/2 cascade. Activation of cardiac fibroblasts through such a cascade may play a role in the pathological actions exerted by aldosterone on the heart.

Calreticulin inhibits the MEK1,2-ERK1,2 pathway in alpha 1-adrenergic receptor/Gh-stimulated hypertrophy of neonatal rat cardiomyocytes

In cardiac myocytes, stimulation of alpha(1)-adrenoceptor (AR) leads to a hypertrophic phenotype. The G(h) protein (transglutaminase II, TGII) is tissue type transglutaminase and transmits the alpha(1B)-adrenoceptor signal with GTPase activity. Recently, it has been shown that the calreticulin (CRT) down-regulates both GTP binding and transglutaminase activities of TGII. To elucidate whether G(h) mediates norepinephrine-stimulated intracellular signal transductions leading to activation of extracellular signal-regulated kinases (ERKs) and neonatal rat cardiomyocyte hypertrophy, we examined the effects of G(h) on the activation of ERKs and inhibitory effects of CRT on alpha(1)-adrenoceptor/G(h) signaling. In neonatal rat cardiomyocytes, norepinephrine-induced ERKs activation was inhibited by an alpha(1)-adrenoceptor blocker (prazosin), but not by an beta-adrenoceptor blocker (propranolol). Overexpression of the G(h) protein stimulated norepinephrine-induced ERKs activation, which was inhibited by alpha-adrenoceptor blocker (prazosin). Co-overexpression of G(h) and CRT abolished norepinephrine-induced ERKs activation. Taken together, norepinephrine induces hypertrophy in neonatal rat cardiomyocytes through alpha(1)-AR stimulation and G(h) is partly involved in norepinephrine-induced MEK1,2/ERKs activation. Activation of G(h)-mediated MEK1,2/ERKs was completely inhibited by CRT.

Urotensin II induces hypertrophic responses in cultured cardiomyocytes from neonatal rats

Urotensin II (UII), a cyclic neuropeptide, functions not only in the central nervous system but also in non-neural systems including cardiovascular systems. In the present study we examined whether UII regulates hypertrophy in cardiomyocytes. The exposure of cultured cardiomyocytes from neonatal rats to UII dose-dependently activated extracellular signal-regulated kinases (ERKs), important molecules in the development of cardiac hypertrophy. ERK activation by UII at 100 nM peaked at 8 min after stimulation. UII markedly induced expression of specific genes encoding atrial natriuretic peptide and brain natriuretic peptide, and significantly increased amino acid incorporation into proteins. Incubation of cardiomyocytes with UII increased cell size and myofibril organisation. UII, then, might participate in cardiomyocyte hypertrophy.

Stimulation of multiple MAPK pathways by mechanical overload in the perfused amphibian heart

The mitogen-activated protein kinase (MAPK) signal transduction pathway activated by mechanical stress was investigated in the isolated perfused amphibian (Rana ridibunda) heart. High perfusion pressure induced the rapid (30 s) and prolonged (30 min) phosphorylation of a p43-extracellular regulated kinase, a response almost completely inhibited by 25 microM PD-98059. c-Jun NH2-terminal kinase (JNK) was also phosphorylated with maximal values attained at 15 min and remained elevated over 30 min. In-gel kinase assays verified that phosphorylated JNKs are active, phosphorylating the transcription factor c-Jun. Furthermore, pressure overload rapidly stimulated the p38-MAPK phosphorylation (30 s), a transient process (5 min) abolished by 1 microM SB-203580. In-gel kinase assays revealed that with phosphorylation, active p38-MAPKs phosphorylate their substrate MAP kinase-activated protein kinase 2. Biochemical analysis along with immunohistochemical studies showed that with activation, the three MAPK subfamily members examined are localized not only in the cytoplasm but in the nucleus as well. Present results therefore demonstrate for the first time in an amphibian species the involvement of multiple MAPK pathways in the mechanical overload-induced adaptive responses of the heart as well as their possible physiological roles.

Oscillation in the activities of MEK/ERK1/2 during cardiopulmonary bypass in pigs

BACKGROUND

Because cardiopulmonary bypass (CPB) is associated with edema and vasoreactive dysfunction and ERK1/2 pathway is involved in vascular contractility and permeability, a time course study was performed to monitor MEK/ERK1/2/Elk-1 activities during CPB.

METHODS

Pigs were subjected to normothermic CPB for 90 minutes followed by post-CPB perfusion for 180 minutes. Atrial myocardium was sampled before CPB, 5 minutes after CPB onset, 5 minutes after weaning from CPB, and at the end of post-CPB. Skeletal muscle and mesenteric vessels samples were harvested before CPB, 5 minutes after CPB institution, and every 30 minutes thereafter to the end of post-CPB. Samples were analyzed by immunoblotting and immunofluorescence microscopy with the use of specific antibodies against active (phosphorylated) forms of ERK1/2, MEK1/2, and Elk-1.

RESULTS

Pigs that were subjected to CPB showed an increase in phospho-ERK1/2 after 30 minutes of CPB, followed by a decrease after 90 minutes. Another phosphorylation peak was observed 30 to 60 minutes of post-CPB, followed by a decrease to below baseline at the end of reperfusion. MEK1/2 and Elk-1 activation profiles paralleled ERK1/2 activity peaks. Control samples showed no significant increase above basal levels.

CONCLUSIONS

Activation of MEK/ERK1/2/Elk-1 pathways closely follows major CPB surgical manipulations (institution and termination) and could be related to morbidity during and after CPB.

Growth hormone signalling and apoptosis in neonatal rat cardiomyocytes

Growth hormone (GH) has been reported to be useful to treat heart failure. To elucidate whether GH has direct beneficial effects on the heart, we examined effects of GH on oxidative stress-induced apoptosis in cardiac myocytes. TUNEL staining and DNA ladder analysis revealed that hydrogen peroxide (H2O2)-induced apoptosis of cardiomyocytes was significantly suppressed by the pretreatment with GH. GH strongly activated extracellular signal-regulated kinases (ERKs) in cardiac myocytes and the cardioprotective effect of GH was abolished by inhibition of ERKs. Overexpression of dominant negative mutant Ras suppressed GH-stimulated ERK activation. Overexpression of Csk that inactivates Src family tyrosine kinases also inhibited ERK activation evoked by GH. A broad-spectrum inhibitor of protein tyrosine kinases (PTKs), genistein, strongly suppressed GH-induced ERK activation and the cardioprotective effect of GH against apoptotic cell death. GH induced tyrosine phosphorylation of EGF receptor and JAK2 in cardiac myocytes, and an EGF receptor inhibitor tyrphostin AG1478 and a JAK2 inhibitor tyrphostin B42 completely inhibited GH-induced ERK activation. Tyrphostin B42 also suppressed the phosphorylation of EGF receptor stimulated by GH. These findings suggest that GH has a direct protective effect on cardiac myocytes against apoptosis and that the effect of GH is attributed at least in part to the activation of ERKs through Ras and PTKs including JAK2, Src, and EGF receptor tyrosine kinase.

Activation of multiple MAPK pathways (ERKs, JNKs, p38-MAPK) by diverse stimuli in the amphibian heart

We investigated the expression and activation of three MAPK subfamilies in the isolated perfused amphibian heart. ERK was detected as a 43 kDa band; p38-MAPK was detected as a band corresponding to 38 kDa and JNKs were detected as two bands corresponding to 46 and 52 kDa, respectively. PMA induced the activation of the ERK pathway as assessed by determining the phosphorylation state of ERK and the upstream component MEK1/2. PD98059 abolished this activation. p38-MAPK was phosphorylated by sorbitol (almost 12-fold, maximal within 10-15 min) and JNKs were phosphorylated and activated by sorbitol or anoxia/reoxygenation (approximately 4- and 2.5-fold, respectively). SB203580 completely blocked the activation of p38-MAPK by sorbitol. These results indicate that the MAPK pathways activated by phorbol esters, hyperosmotic stress or anoxia/ reoxygenation in the amphibian heart may have an important role in this experimental system.

Integrin activation and focal complex formation in cardiac hypertrophy

Cardiac hypertrophy is characterized by both remodeling of the extracellular matrix (ECM) and hypertrophic growth of the cardiocytes. Here we show increased expression and cytoskeletal association of the ECM proteins fibronectin and vitronectin in pressure-overloaded feline myocardium. These changes are accompanied by cytoskeletal binding and phosphorylation of focal adhesion kinase (FAK) at Tyr-397 and Tyr-925, c-Src at Tyr-416, recruitment of the adapter proteins p130(Cas), Shc, and Nck, and activation of the extracellular-regulated kinases ERK1/2. A synthetic peptide containing the Arg-Gly-Asp (RGD) motif of fibronectin and vitronectin was used to stimulate adult feline cardiomyocytes cultured on laminin or within a type-I collagen matrix. Whereas cardiocytes under both conditions showed RGD-stimulated ERK1/2 activation, only collagen-embedded cells exhibited cytoskeletal assembly of FAK, c-Src, Nck, and Shc. In RGD-stimulated collagen-embedded cells, FAK was phosphorylated only at Tyr-397 and c-Src association occurred without Tyr-416 phosphorylation and p130(Cas) association. Therefore, c-Src activation is not required for its cytoskeletal binding but may be important for additional phosphorylation of FAK. Overall, our study suggests that multiple signaling pathways originate in pressure-overloaded heart following integrin engagement with ECM proteins, including focal complex formation and ERK1/2 activation, and many of these pathways can be activated in cardiomyocytes via RGD-stimulated integrin activation.

Angiotensin II-induced cardiac hypertrophy is associated with different mitogen-activated protein kinase activation in normotensive and hypertensive mice

OBJECTIVE

In addition to its haemodynamic effects, angiotensin II (AngII) is thought to contribute to the development of cardiac hypertrophy via its growth factor properties. The activation of mitogen-activated protein kinases (MAPK) is crucial for stimulating cardiac growth. Therefore, the present study aimed to determine whether the trophic effects of AngII and the AngII-induced haemodynamic load were associated with specific cardiac MAPK pathways during the development of hypertrophy. Methods The activation of the extracellular-signal-regulated kinase (ERK), the c-jun N-terminal kinase (JNK) and the p38 kinase was followed in the heart of normotensive and hypertensive transgenic mice with AngII-mediated cardiac hypertrophy. Secondly, we used physiological models of AngII-dependent and AngII-independent renovascular hypertension to study the activation of cardiac MAPK pathways during the development of hypertrophy.

RESULTS

In normotensive transgenic animals with AngII-induced cardiac hypertrophy, p38 activation is associated with the development of hypertrophy while ERK and JNK are modestly stimulated. In hypertensive transgenic mice, further activation of ERK and JNK is observed. Moreover, in the AngII-independent model of renovascular hypertension and cardiac hypertrophy, p38 is not activated while ERK and JNK are strongly stimulated. In contrast, in the AngII-dependent model, all three kinases are stimulated.

CONCLUSIONS

These data suggest that p38 activation is preferentially associated with the direct effects of AngII on cardiac cells, whereas stimulation of ERK and JNK occurs in association with AngII-induced mechanical stress.

Cardiac swelling-induced chloride current is enhanced by endothelin

Endothelins (ETs) are a family of peptide hormones that act on G protein-coupled ET(A) and ET(B) receptors. ETs exert inotropic and chronotropic actions in the heart. Myocardial ischemia is associated with increased plasma levels of ET and cell swelling. We examined the effect of ETs on dog atrial swelling-induced chloride current (I(Cl,swell)). Whole-cell patch clamp was used; 10 nM ET-1 or ET-2 increased I(Cl,swell) by approximately twofold. ET-2 had no effect if I(Cl,swell) activation was prevented by hypertonic superfusate. Outward ET-2-induced current was blocked by 150 microM DIDS more effectively than inward current. Overnight pretreatment with phorbol 12-myristate 13-acetate (1.6 microM), pertussis toxin (100 ng/ml), or dialysis of the cell with 300 microM 2'-deoxyadenosine 3'-monophosphate, a P-site inhibitor of adenylyl cyclase, did not diminish the effect of ET-2. The effect of ET-2 was blocked by an ET(A1)- (BQ123), but not an ET(B)-selective (BQ788) antagonist. ET-2-induced currents were inhibited approximately 70% by PD 98059 (30 microM), a selective MAPK kinase (MEK) blocker. PD 98059 did not affect basal whole cell current or I(Cl,swell) before exposure to ET-2. The data suggest that MEK activity is not required for activation of atrial I(Cl,swell) but that ET-2 stimulates I(Cl,swell) by a MEK-dependent pathway.

Neuropeptide Y (NPY) potentiates phenylephrine-induced mitogen-activated protein kinase activation in primary cardiomyocytes via NPY Y5 receptors

Neuropeptide Y (NPY) has been shown to participate in the cardiovascular response mediated by the sympathetic system. In this report, we investigate the growth factor properties of NPY on cardiac myocytes. Mitogen-activated protein kinases (MAPK) are key signaling molecules in the transduction of trophic signals. Therefore, the role of NPY in inducing MAPK activation was studied in mouse neonatal cardiomyocytes. Exposure of neonatal cardiomyocytes to either NPY, phenylephrine, or angiotensin II induces a rapid phosphorylation of the extracellular responsive kinase, the c-jun N-terminal kinase, and the p38 kinase as well as an activation of protein kinase C (PKC). Moreover, NPY potentiates phenylephrine-induced MAPK and PKC stimulation. In contrast, NPY has no synergistic effect on angiotensin II-stimulated MAPK phosphorylation or PKC activity. NPY effects are pertussis toxin-sensitive and calcium-independent and are mediated by NPY Y5 receptors. Taken together, these results suggest that NPY, via G(i) protein-coupled NPY Y5 receptors, could participate in the development of cardiac hypertrophy during chronic sympathetic stimulation by potentiating alpha-adrenergic signals.

Phenotype dictates the growth response of vascular smooth muscle cells to pulse pressure in vitro

The objective of this study was to determine the effect of phenotype on pulse pressure-induced signaling and growth of vascular smooth muscle cells in vitro. Using a perfused transcapillary culture system, cells were exposed to increases in pulsatile flow and hence pulse pressure and maintained for 72 h before cells were harvested. Cell proliferation was determined by cell number, DNA synthesis, and proliferating cell nuclear antigen expression. Mitogen-activated protein kinase (MAPK) levels were determined by immunoblot and kinase activity by phosphorylation of myelin basic protein. Cell phenotype was determined by immunoblot and immunocytofluorescence using antisera specific for the differentiation markers alpha-actin, myosin, calponin, osteopontin, and phospholamban. In cells that highly expressed these differentiation markers, there was a significant increase in cell growth in response to chronic increases in pulse pressure without a significant change in MAPK activity in these cells. In contrast, in cells that weakly expressed SMC differentiation markers, there was a significant decrease in cell growth concomitant with a significant decrease in MAPK signaling in these cells. We conclude that SMC phenotype dictates the growth response of SMC to mechanical force in vitro.

Catecholamines in cardiac hypertrophy

There has been intense interest in the roles catecholamines may play in compensatory myocardial hypertrophy. This article reviews the following: (1) chronic infusions of catecholamines in experimental animals result in cardiac hypertrophy, but in many of the studies mechanical factors have played a role; (2) experiments using isolated papillary muscles and isolated hearts, stretched isolated myocytes, and denervated hearts in vivo demonstrate that mechanical activity is sufficient to cause increased protein synthesis and cell growth; (3) in neonatal myocyte cell cultures, alpha-adrenergic agonists are powerful stimulants for protein synthesis and cell growth. Beta-adrenergic stimulation of nonmyocyte myocardial cells causes release of a factor that promotes protein synthesis in neonatal myocytes. Either alpha or beta stimulation, probably through different mechanisms, appears to have growth-promoting effects on isolated adult myocytes in culture; (4) alpha stimulation is transduced through the Gq pathway and its activation of phospholipase C, cleavage of phosphatidylinositol (4,5)-bisphosphate, and then further through the ras/raf, mitogen-activated protein (MAP) kinase system; (5) transgenic mice with upregulation of catecholamine-related systems have not clarified the independent role of either the alpha- or beta-adrenergic pathway; and (6) observations in humans suggest that mechanical factors predominate in the development and regression of cardiac hypertrophy. Humoral mechanisms, including catecholamines, may play a role, but their quantitative importance has not been determined. It is hypothesized that catecholamines may play a role in transition from the adaptive to the maladaptive state.

Prostaglandin F2alpha (PGF2alpha) and the isoprostane, 8, 12-iso-isoprostane F2alpha-III, induce cardiomyocyte hypertrophy. Differential activation of downstream signaling pathways

Prostaglandin receptors may be activated by their cognate ligand or by free radical catalyzed isoprostanes, products of arachidonic acid peroxidation. For example, prostaglandin F2alpha (PGF2alpha) causes hypertrophy of neonatal rat ventricular myocytes, via the PGF2alpha receptor (FP). However, the FP may also be activated by the isoprostane, 8,12-iso-iPF2alpha-III (Kunapuli, P., Lawson, J. A., Rokach, J., and FitzGerald, G. A. (1997) J. Biol. Chem. 272, 27147-27154). Both ligands induce myocyte hypertrophy with overlapping potencies. Interestingly, the hypertrophic effects of these two agonists on cardiomyocytes are additive. Furthermore, the preference of these two agonists for activation of intracellular signal transduction pathways differs in several respects. Thus, PGF2alpha and 8,12-iso-iPF2alpha-III stimulate inositol phosphate formation with EC50 values of 50 +/- 12 nM and 3.5 +/- 0.6 microM, respectively. Moreover, PGF2alpha causes a robust activation ( approximately 50-fold) of Erk2, whereas 8,12-iso-iPF2alpha-III has no effect. Similarly, PGF2alpha causes translocation of cytosolic phospholipase A2 and also results in a 7-fold increment in the formation of 6-keto-PGF1alpha, whereas 8,12-iso-iPF2alpha-III exerts no effect on this pathway. On the other hand, both agonists are equally potent in activating JNK1 and c-Jun, whereas neither activates the p38 kinase. Both PGF2alpha and 8,12-iso-iPF2alpha-III activate the p70S6 kinase (p70(S6K)), but not Akt, downstream of phosphatidylinositol-3-kinase (PI3K). However, both wortmannin, a PI3K inhibitor, and rapamycin, an inhibitor of p70(S6K) activity, inhibit 8,12-iso-iPF2alpha-III -induced myocyte hypertrophy, with IC50 values of 60 +/- 12 and 3 +/- 1.7 nM, respectively, whereas neither compound abrogates the PGF2alpha-mediated response. Thus, both PGF2alpha and 8,12-iso-iPF2alpha-III induce myocyte hypertrophy via discrete signaling pathways. Although both agonists signal via the JNK pathway to initiate changes in c-Jun-dependent gene transcription, PGF2alpha preferentially activates the MEK-Erk2- cytosolic phospholipase A2 pathway. In contrast, the PI3K-p70(S6K) pathway appears to be essential for 8,12-iso-iPF2alpha-III-induced myocyte hypertrophy.

Cardiac protein phosphorylation: functional and pathophysiological correlates

Protein phosphorylation acts a pivotal mechanism in regulating the contractile state of the heart by modulating particular levels of autonomic control on cardiac force/length relationships. Early studies of changes in cardiac protein phosphorylation focused on key components of the excitation-coupling process, namely phospholamban of the sarcoplasmic reticulum and myofibrillar troponin I. In more recent years the emphasis has shifted towards the identification of other phosphoproteins, and more importantly, the delineation of the mechanistic and signaling pathways regulating the various known phosphoproteins. In addition to cAMP- and Ca(2+)-calmodulin-dependent kinase processes, these have included regulation by protein kinase C and the ever-emerging family of growth factor-related kinases such as the tyrosine-, mitogen- and stress-activated protein kinases. Similarly, the role of protein dephosphorylation by protein phosphatases has been recognized as integral in modulating normal cardiac cellular function. Recent studies involving a variety of cardiovascular pathologies have demonstrated that changes in the phosphorylation states of key cardiac regulatory proteins may underlie cardiac dysfunction in disease states. The emphasis of this comprehensive review will be on discussing the role of cardiac phosphoproteins in regulating myocardial function and pathophysiology based not only on in vitro data, but more importantly, from ex vivo experiments with corroborative physiological and biochemical evidence.