The potential role of MLC phosphatase and MAPK signalling in the pathogenesis of vascular dysfunction in heart failure

Signaling pathways and targeted therapy for myocardial infarction

Although the treatment of myocardial infarction (MI) has improved considerably, it is still a worldwide disease with high morbidity and high mortality. Whilst there is still a long way to go for discovering ideal treatments, therapeutic strategies committed to cardioprotection and cardiac repair following cardiac ischemia are emerging. Evidence of pathological characteristics in MI illustrates cell signaling pathways that participate in the survival, proliferation, apoptosis, autophagy of cardiomyocytes, endothelial cells, fibroblasts, monocytes, and stem cells. These signaling pathways include the key players in inflammation response, e.g., NLRP3/caspase-1 and TLR4/MyD88/NF-κB; the crucial mediators in oxidative stress and apoptosis, for instance, Notch, Hippo/YAP, RhoA/ROCK, Nrf2/HO-1, and Sonic hedgehog; the controller of myocardial fibrosis such as TGF-β/SMADs and Wnt/β-catenin; and the main regulator of angiogenesis, PI3K/Akt, MAPK, JAK/STAT, Sonic hedgehog, etc. Since signaling pathways play an important role in administering the process of MI, aiming at targeting these aberrant signaling pathways and improving the pathological manifestations in MI is indispensable and promising. Hence, drug therapy, gene therapy, protein therapy, cell therapy, and exosome therapy have been emerging and are known as novel therapies. In this review, we summarize the therapeutic strategies for MI by regulating these associated pathways, which contribute to inhibiting cardiomyocytes death, attenuating inflammation, enhancing angiogenesis, etc. so as to repair and re-functionalize damaged hearts.

The antihypertensive effect of MK on spontaneously hypertensive rats through the AMPK/Akt/eNOS/NO and ERK1/2/Cx43 signaling pathways

We investigated the antihypertensive effects of maximakinin (MK) on spontaneously hypertensive rats (SHRs). The effects of MK on arterial blood pressure in SHRs were observed, and flow cytometry and 4,5-diaminofluorescein-2 staining were used to examine MK-induced nitric oxide (NO) release in human umbilical vein endothelial cells (HUVECs). Western blotting was used to analyze the effects of MK on the expression of AMP-activated protein kinase (AMPK), Akt, Connexin 43, ERK1/2, p38, and p-eNOS in HUVECs. The results showed that MK induced a more significant antihypertensive effect on SHRs than bradykinin (BK). MK induced significant increases in endothelial nitric oxide synthase (eNOS) phosphorylation and NO release in HUVECs. MK also significantly increased the phosphorylation of Akt and AMPK in HUVECs. The AMPK inhibitor compound C blocked the effect of MK on the generation of NO. MK induced the phosphorylation of ERK1/2, p38, and Connexin 43. The expression of p-Connexin 43 was significantly decreased in the presence of the ERK1/2 inhibitor U0126 but not the p38 inhibitor SB203580. The effects of MK on the phosphorylation of AMPK and ERK1/2 were significantly decreased by the BK B₂ receptor inhibitor HOE-140. In summary, MK can significantly reduce blood pressure in SHRs. The antihypertensive effect might be mediated through the activation of the BK B₂ receptor, while the downstream AMPK/PI3K/Akt/eNOS/NO and ERK1/2/Connexin 43 signaling pathways play additional roles.

A self-organized actomyosin drives multiple intercellular junction disruption and directly promotes neutrophil recruitment in lipopolysaccharide-induced acute lung injury

Acute lung injury (ALI), with the hallmarks of vascular integrity disruption and neutrophil recruitment, is associated with high morbidity and mortality. Enhanced actomyosin assembly contributes to endothelial cell contact dysfunction. However, the roles and mechanisms of actomyosin assembly in ALI are not totally clear. We investigated the dynamic alterations and roles of actomyosin in ALI in vivo and in vitro models induced by LPS. Pulmonary levels of E-cadherin, vascular endothelial-cadherin, occludin, myosin phosphatase target subunit 1, and thymosin β4 were decreased, and the number and activity of neutrophils and the levels of actomyosin, p-ρ-associated protein kinase, p-myosin light-chain kinase, and profilin1 were increased within 3 d after LPS administration, and then, those alterations were recovered within the next 4 d, which was consistent with the alterations of lung histology, vascular permeability, edema, and serum levels of IL-6 and TNF-α. Direct or indirect inhibition of increased F-actin or myosin assembly ameliorated the reduction of intercellular junction molecules, the activation and migration of neutrophils, and the degree of lung injury. Moreover, neutrophil activation further promoted actomyosin assembly and aggravated lung injury. Conclusively, the enhancement of self-organized actomyosin contributes to alveolar-capillary barrier disruption and neutrophil recruitment in inflammatory response, which is a potential therapeutic target for ALI.-Chen, B., Yang, Z., Yang, C., Qin, W., Gu, J., Hu, C., Chen, A., Ning, J., Yi, B., Lu, K. A self-organized actomyosin drives multiple intercellular junction disruption and directly promotes neutrophil recruitment in lipopolysaccharide-induced acute lung injury.

Revisiting the Role of TRP, Orai, and ASIC Channels in the Pulmonary Arterial Response to Hypoxia

The pulmonary arteries are exquisitely responsive to oxygen changes. They rapidly and proportionally contract as arterial PO₂ decrease, and they relax as arterial PO₂ is re-established. The hypoxic pulmonary vasoconstriction (HPV) is intrinsic since it does not require neural or endocrine factors, as evidenced in isolated vessels. On the other hand, pulmonary arteries also respond to sustained hypoxia with structural and functional remodeling, involving growth of smooth muscle medial layer and later recruitment of adventitial fibroblasts, secreted mitogens from endothelium and changes in the response to vasoconstrictor and vasodilator stimuli. Hypoxic pulmonary arterial vasoconstriction and remodeling are relevant biological responses both under physiological and pathological conditions, to explain matching between ventilation and perfusion, fetal to neonatal transition of pulmonary circulation and pulmonary artery over-constriction and thickening in pulmonary hypertension. Store operated channels (SOC) and receptor operated channels (ROC) are plasma membrane cationic channels that mediate calcium influx in response to depletion of internal calcium stores or receptor activation, respectively. They are involved in both HPV and pathological remodeling since their pharmacological blockade or genetic suppression of several of the Stim, Orai, TRP, or ASIC proteins in SOC or ROC complexes attenuate the calcium increase, the tension development, the pulmonary artery smooth muscle proliferation, and pulmonary arterial hypertension. In this Mini Review, we discussed the evidence obtained in in vivo animal models, at the level of isolated organ or cells of pulmonary arteries, and we identified and discussed the questions for future research needed to validate these signaling complexes as targets against pulmonary hypertension.

Brain natriuretic peptide protects against hyperresponsiveness of human asthmatic airway smooth muscle via an epithelial cell-dependent mechanism

Brain natriuretic peptide (BNP) relaxes airways by activating natriuretic peptide receptor-A and elevating cyclic guanosine monophosphate. BNP is more effective in passively sensitized human bronchi compared with control airways. The molecular and cellular patterns involved in this signaling are unknown. The aim of this study was to investigate the influence of BNP on airway smooth muscle (ASM) cells obtained from donors with asthma and healthy donors and to identify the mechanisms involved in BNP-mediated relaxation. The contractile response of ASM cells was microscopically assessed in vitro in the presence of 1 μM BNP or with supernatant from human bronchial epithelial (BEAS-2B) cells pretreated with 1 μM BNP. We investigated the role of muscarinic M2 receptors and inducible nitric oxide synthase (iNOS), quantified the release of acetylcholine and nitric oxide (NO), and assessed the gene/protein expression of iNOS and myosin phosphatase target subunit 1 (MYPT1). Supernatant from BEAS-2B cells treated with BNP reduced the hyperreactivity of asthmatic ASM cells by shifting the potency of histamine by 1.19-fold but had no effect in healthy ASM cells. BNP was not effective directly on ASM cells. Blocking muscarinic M2-receptors and iNOS abolished the protective role of supernatant from BEAS-2B treated with BNP. BNP stimulated the release of acetylcholine (210.7 ± 11.1%) from BEAS-2B cells that in turn increased MYPT1 and iNOS gene/protein expression and enhanced NO levels in asthmatic ASM supernatant (35.0 ± 13.0%). This study provides evidence that BNP protects against bronchial hyperresponsiveness via an interaction between respiratory epithelium and ASM in subjects with asthma.

Isoproterenol induces vascular oxidative stress and endothelial dysfunction via a Giα-coupled β2-adrenoceptor signaling pathway

OBJECTIVE

Sustained β-adrenergic stimulation is a hallmark of sympathetic hyperactivity in cardiovascular diseases. It is associated with oxidative stress and altered vasoconstrictor tone. This study investigated the β-adrenoceptor subtype and the signaling pathways implicated in the vascular effects of β-adrenoceptor overactivation.

METHODS AND RESULTS

Mice lacking the β1- or β2-adrenoceptor subtype (β1KO, β2KO) and wild-type (WT) were treated with isoproterenol (ISO, 15 μg.g(-1) x day(-1), 7 days). ISO significantly enhanced the maximal vasoconstrictor response (Emax) of the aorta to phenylephrine in WT (+34%) and β1KO mice (+35%) but not in β2KO mice. The nitric oxide synthase (NOS) inhibitor L-NAME abolished the differences in phenylephrine response between the groups, suggesting that ISO impaired basal NO availability in the aorta of WT and β1KO mice. Superoxide dismutase (SOD), pertussis toxin (PTx) or PD 98,059 (p-ERK 1/2 inhibitor) incubation reversed the hypercontractility of aortic rings from ISO-treated WT mice; aortic contraction of ISO-treated β2KO mice was not altered. Immunoblotting revealed increased aortic expression of Giα-3 protein (+50%) and phosphorylated ERK1/2 (+90%) and decreased eNOS dimer/monomer ratio in ISO-treated WT mice. ISO enhanced the fluorescence response to dihydroethidium (+100%) in aortas from WT mice, indicating oxidative stress that was normalized by SOD, PTx and L-NAME. The ISO effects were abolished in β2KO mice.

CONCLUSIONS

The β2-adrenoceptor/Giα signaling pathway is implicated in the enhanced vasoconstrictor response and eNOS uncoupling-mediated oxidative stress due to ISO treatment. Thus, long-term β2-AR activation might results in endothelial dysfunction.

Myosin phosphatase isoforms and related transcripts in the pig coronary circulation and effects of exercise and chronic occlusion

Myosin phosphatase (MP) is a key target of signaling pathways that regulate smooth muscle tone and blood flow. Alternative splicing of MP targeting subunit (MYPT1) exon 24 (E24) generates isoforms with variable presence of a C-terminal leucine zipper (LZ) required for activation of MP by NO/cGMP. Here we examined the expression of MP and associated genes in a disease model in the coronary circulation. Female Yucatan miniature swine remained sedentary or were exercise-trained beginning eight weeks after placement of an ameroid constrictor around the left circumflex (LCX) artery. Fourteen weeks later epicardial arteries (~1mm) and resistance arterioles (~125 μm) were harvested and assayed for gene expression. MYPT1 isoforms were distinct in the epicardial arteries (E24-/LZ+) and resistance arterioles (E24+/LZ-) and unchanged by exercise training or coronary occlusion. MYPT1, CPI-17 and PDE5 mRNA levels were not different between arteries and arterioles while Kir2.1 and eNOS were 6.6-fold and 3.9-fold higher in the arterioles. There were no significant changes in transcript abundance in epicardial arteries of the collateralized (LCX) vs. non-occluded left anterior descending (LAD) territories, or in exercise-trained vs. sedentary pigs. There was a significant 1.2 fold increase in CPI-17 in collateral-dependent arterioles, independent of exercise, and a significant 1.7 fold increase in PDE5 in arterioles from exercise-trained pigs, independent of occlusion. We conclude that differences in MYPT1 E24 (LZ) isoforms, eNOS, and Kir2.1 distinguish epicardial arteries and resistance coronary arterioles. Up-regulation of coronary arteriolar PDE5 by exercise and CPI-17 by chronic occlusion could contribute to altered vasomotor responses and requires further study.

Pravastatin slows the progression of heart failure by inhibiting the c-Jun N-terminal kinase-mediated intrinsic apoptotic signaling pathway

Tumor necrosis factor‑α (TNF-α) and c‑Jun N‑terminal kinases (JNKs) are known to be associated with apoptosis and are important in cardiac remodeling. It remains to be determined whether statins inhibit cardiac remodeling through interfering with TNF‑α‑JNK‑related signaling pathways. This study was designed to investigate the effect of pravastatin on the progression of hypertrophy to heart failure in transverse aortic constriction (TAC) and the associations with TNF‑α‑JNK signaling. Either pravastatin (5 or 20 mg/kg/day) or vehicle was orally administered to male C57BL/6J mice with TAC. Cardiac remodeling and left ventricular hemodynamics, as well as JNK-dependent apoptotic signals were analyzed 4 weeks following TAC. Neonatal rat cardiomyocytes were cultured to investigate the effect of pravastatin on TNF‑α‑induced JNK‑related apoptotic signals. Notably, pravastatin reduced the heart/body weight and lung/body weight ratios. In addition, a decrease of left ventricular (LV) echocardiographic dimensions, an increase of LV fractional shortening and diastolic index, a reduction of JNK activity, caspase‑12 and Bax were observed in the pravastatin‑treated groups. The TNF‑α‑induced phosphorylation of JNK and upregulation of caspase‑12 and Bax in cultured cardiomyocytes was inhibited by pravastatin. These results indicated that pravastatin attenuates cardiac remodeling by inhibiting JNK‑dependent pro‑apoptotic signaling.

Proteomics screen to reveal molecular changes mediated by C722G missense mutation in CHRM2 gene

Previously, we reported a missense mutation (C722G) in the M2-muscarinic acetylcholine receptor (CHRM2) gene associated with familial dilated cardiomyopathy. However, the exact molecular mechanisms by the related protein changes of CHRM2-C722G mutation induced are still unclear. CHRM2 and CHRM2-C722G lentiviral vector was infected to CHO cells. Proteomic analysis by label-free shotgun strategy and the STRING 9.0 software were performed. A total of 102 proteins with at least 2-fold change in the CHRM2-C722G group were identified, 42 proteins were up-regulated, whereas 57 were down-regulated. These altered proteins belong to three broad functional categories: (i) metabolic (e.g. Cytosolic acyl coenzyme A thioester hydrolase, Malate dehydrogenase); (ii) cytoskeletal (e.g. Actin-related protein, Myosin light polypeptide 6 and Alpha-actinin-1) and (iii) stress response (e.g. heat shock protein 70, Ras-related protein Rab-10). Interestingly, the marked differences in the expression of selected eight proteins (change >4.0-fold), were connected with many proteins related to apoptosis and immune/inflammatory response such as: FOS, BAX, MYC, TP53 and IL6. This novel study demonstrated for the first time a full-scale screening of the proteomics research by CHRM2-C722G mutation and profiled 102 changed proteins, of which, eight might be critical in cardiac dysfunction for future mapping.

SIGNIFICANCE

It was a full-scale screening of the proteomics research by CHRM2-C722G mutation. These proteins might serve as valuable biomarkers that could predict the presence of a precursor field. These proteins might serve to further explore the pathophysiological mechanisms in familial DCM patients with C176W mutation.

Altered reactivity of tertiary mesenteric arteries following acute myocardial ischemia

BACKGROUND

It is unknown if cardiac ischemia has any deleterious effect on the contractile properties of nonischemic, peripheral vascular beds. Thus, the objective of the present study was to determine whether acute myocardial ischemia results in peripheral vascular dysfunction.

METHODS AND RESULTS

This study characterized force maintenance and the sensitivity to acetylcholine (ACh)-mediated smooth muscle (SM) relaxation of tertiary (3rd) mesenteric arteries from Sprague-Dawley rats following 30 min of myocardial ischemia. Both the phosphorylation of nonmuscle (NM) light chain (LC) and SM-LCs as well as the expression of myosin phosphatase targeting subunit 1 (MYPT1) were also determined. Our data demonstrate that acute myocardial ischemia resulted in vascular dysfunction of 3rd mesenteric vessels, characterized by decreases in force maintenance, ACh- and cGMP-mediated SM relaxation, the phosphorylation of NM-LCs and SM-LCs, and MYPT1 expression. Ischemia was also associated with an increase in protein polyubiquitination, suggesting that during ischemia MYPT1 is targeted for degradation or proteolysis.

CONCLUSION

Acute myocardial ischemia produces peripheral vascular dysfunction; the changes in LC phosphorylation and MYPT1 expression result in a decrease in both tone and the sensitivity to NO-mediated SM relaxation of the peripheral vasculature.

Dietary genistein enhances phosphorylation of regulatory myosin light chain in the myocardium of ovariectomized mice

There is evidence that isoflavones, such as genistein, can directly or indirectly improve lipid profile and lower blood pressure and hence exert cardiovascular protection. It is further believed, that genistein attenuates vascular contraction and thus vascular tone and blood pressure through altering the phosphorylation of the regulatory myosin light chain (MLC) probably via the myosin light chain kinase (MLCK) or the RhoA pathway. However, the direct role of genistein in the myocardium is poorly reviewed. In this study, we investigated the impact of genistein on the cardiac proteome in ovariectomized female mice using a 2DE-MS approach. Dietary genistein intake considerably changed the abundance of several cytoskeletal and contractile proteins and enhanced the phosphorylation of MLC. The MLC phosphorylation was mediated through increased abundance of MLCK and inhibition of myosin light chain phosphatase latest known to be inversely regulated by RhoA. Contrary to others, in our model genistein did neither inhibit the cardiac MLCK, nor the cardiac RhoA pathway in vivo.

Hypoxia modulates the expression of leucine zipper-positive MYPT1 and its interaction with protein kinase G and Rho kinases in pulmonary arterial smooth muscle cells

We have shown previously that acute hypoxia downregulates protein kinase G (PKG) expression and activity in ovine fetal pulmonary vessels and pulmonary arterial smooth muscle cells (SMC). Here, we report that acute hypoxia also reduces the expression of leucinezipper-positive MYPT1 (LZ⁺MYPT1), a subunit of myosin light chain (MLC) phosphatase, in ovine fetal pulmonary arterial SMC. We found that in hypoxia, there is greater interaction between LZ⁺ MYPT1 and RhoA and Rho kinase 1 (ROCK1)/Rho kinase 2 (ROCK2) and decreased interaction between LZ⁺ MYPT1 and PKG, resulting in increased MLC₂₀ phosphorylation, a higher pMLC₂₀/MLC₂₀ ratio and SMC contraction. In normoxic SMC PKG overexpression, LZ⁺ MYPT1 expression is upregulated while PKG knockdown had an opposite effect. LZ⁺ MYPT1 overexpression enhanced the interaction between PKG and LZ⁺ MYPT1. Overexpression of a mutant LZ^- MYPT1 isoform in SMC mimicked the effects of acute hypoxia and decreased pMLC₂₀/MLC₂₀ ratio. Collectively, our data suggest that hypoxia downregulates LZ⁺ MYPT1 expression by suppressing PKG levels, reduces the interaction of LZ⁺ MYPT1 with PKG and promotes LZ⁺ MYPT1 interaction with RhoA or ROCK1/ROCK2, thereby promoting pulmonary arterial SMC contraction.

Proteomic analysis of metabolic, cytoskeletal and stress response proteins in human heart failure

Human heart failure is a complex syndrome and a primary cause of morbidity and mortality in the world. However, the molecular pathways involved in the remodelling process are poorly understood. In this study, we performed exhaustive global proteomic surveys of cardiac ventricle isolated from failing and non-failing human hearts, and determined the regulatory pathway to uncover the mechanism underlying heart failure. Two-dimensional gel electrophoresis (2-DE) coupled with tandem mass spectrometry was used to identify differentially expressed proteins in specimens from failing (n = 9) and non-failing (n = 6) human hearts. A total of 25 proteins with at least 1.5-fold change in the failing heart were identified; 15 proteins were up-regulated and 10 proteins were down-regulated. The altered proteins belong to three broad functional categories: (i) metabolic [e.g. NADH dehydrogenase (ubiquinone), dihydrolipoamide dehydrogenase, and the cytochrome c oxidase subunit]; (ii) cytoskeletal (e.g. myosin light chain proteins, troponin I type 3 and transthyretin) and (iii) stress response (e.g. αB-crystallin, HSP27 and HSP20). The marked differences in the expression of selected proteins, including HSP27 and HSP20, were further confirmed by Western blot. Thus, we carried out full-scale screening of the protein changes in human heart failure and profiled proteins that may be critical in cardiac dysfunction for future mapping.

Heterogeneity in relaxation of different sized porcine coronary arteries to nitrovasodilators: role of PKG and MYPT1

The present study was to determine the role of the type I isoform of cGMP-dependent protein kinase (PKG I) and its downstream effector myosin phosphatase target subunit 1 (MYPT1) in the responses of different sized coronary arteries to nitrovasodilators. Relaxations of isolated porcine coronary arteries were determined by isometric tension recording technique. Protein levels of PKG I and its effectors were analyzed by Western blotting. The activities of PKG I and MYPT1 were studied by analyzing phosphorylation of vasodilator-stimulated phosphoprotein (VASP) and MYPT1, respectively. Nitroglycerin, DETA NONOate, and 8-Br-cGMP caused greater relaxations in large than in small coronary arteries. Relaxations were attenuated to a greater extent by Rp-8-Br-PET-cGMPS (a PKG inhibitor) in large vs. small arteries. The expressions of PKG I and MYPT1 in large arteries were more abundant than in small arteries. DETA NONOate stimulated phosphorylation of VASP at Ser239 and inhibited phosphorylation of MYPT1 at Thr853 to a greater extent in large than in small arteries. A suppressed phosphorylation of MYPT1 at Thr853 was caused by 8-Br-cGMP in large but not small arteries, which was inhibited by Rp-8-Br-PET-cGMPS. These results suggest that the greater responsiveness of large coronary arteries to nitrovasodilators result in part from greater activities of PKG I and MYPT1. Dysfunction in nitric oxide signaling is implicated in the vulnerability of large coronary arteries to certain disorders such as atherosclerosis and spasm. Augmentation of PKG I-MYPT1 signaling may be of therapeutic benefit for combating these events.

Role of rho kinase in the functional and dysfunctional tonic smooth muscles

Tonic smooth muscles play pivotal roles in the pathophysiology of debilitating diseases of the gastrointestinal and cardiovascular systems. Tonic smooth muscles differ from phasic smooth muscles in the ability to spontaneously develop myogenic tone. This ability has been primarily attributed to the local production of specific neurohumoral substances that can work in conjunction with calcium sensitization via signal transduction events associated with the Ras homolog gene family, member A (RhoA)/Rho-associated, coiled-coil containing protein kinase 2 (ROCK II) pathways. In this article, we discuss the molecular pathways involved in the myogenic properties of tonic smooth muscles, particularly the contribution of protein kinase C vs the RhoA/ROCK II pathway in the genesis of basal tone, pathophysiology and novel therapeutic approaches for certain gastrointestinal and cardiovascular diseases. Emerging evidence suggests that manipulation of RhoA/ROCK II activity through inhibitors or silencing of RNA interface techniques could represent a new therapeutic approach for various gastrointestinal and cardiovascular diseases.

The myosin phosphatase targeting protein (MYPT) family: a regulated mechanism for achieving substrate specificity of the catalytic subunit of protein phosphatase type 1δ

The mammalian MYPT family consists of the products of five genes, denoted MYPT1, MYPT2, MBS85, MYPT3 and TIMAP, which function as targeting and regulatory subunits to confer substrate specificity and subcellular localization on the catalytic subunit of type 1δ protein serine/threonine phosphatase (PP1cδ). Family members share several conserved domains, including an RVxF motif for PP1c binding and several ankyrin repeats that mediate protein-protein interactions. MYPT1, MYPT2 and MBS85 contain C-terminal leucine zipper domains involved in dimerization and protein-protein interaction, whereas MYPT3 and TIMAP are targeted to membranes via a C-terminal prenylation site. All family members are regulated by phosphorylation at multiple sites by various protein kinases; for example, Rho-associated kinase phosphorylates MYPT1, MYPT2 and MBS85, resulting in inhibition of phosphatase activity and Ca(2+) sensitization of smooth muscle contraction. A great deal is known about MYPT1, the myosin targeting subunit of myosin light chain phosphatase, in terms of its role in the regulation of smooth muscle contraction and, to a lesser extent, non-muscle motile processes. MYPT2 appears to be the key myosin targeting subunit of myosin light chain phosphatase in cardiac and skeletal muscles. MBS85 most closely resembles MYPT2, but little is known about its physiological function. Little is also known about the physiological role of MYPT3, although it is likely to target myosin light chain phosphatase to membranes and thereby achieve specificity for substrates involved in regulation of the actin cytoskeleton. MYPT3 is regulated by phosphorylation by cAMP-dependent protein kinase. TIMAP appears to target PP1cδ to the plasma membrane of endothelial cells where it serves to dephosphorylate proteins involved in regulation of the actin cytoskeleton and thereby control endothelial barrier function. With such a wide range of regulatory targets, MYPT family members have been implicated in diverse pathological events, including hypertension, Parkinson's disease and cancer.

Protein Kinases as Drug Development Targets for Heart Disease Therapy

Protein kinases are intimately integrated in different signal transduction pathways for the regulation of cardiac function in both health and disease. Protein kinase A (PKA), Ca²⁺-calmodulin-dependent protein kinase (CaMK), protein kinase C (PKC), phosphoinositide 3-kinase (PI3K) and mitogen-activated protein kinase (MAPK) are not only involved in the control of subcellular activities for maintaining cardiac function, but also participate in the development of cardiac dysfunction in cardiac hypertrophy, diabetic cardiomyopathy, myocardial infarction, and heart failure. Although all these kinases serve as signal transducing proteins by phosphorylating different sites in cardiomyocytes, some of their effects are cardioprotective whereas others are detrimental. Such opposing effects of each signal transduction pathway seem to depend upon the duration and intensity of stimulus as well as the type of kinase isoform for each kinase. In view of the fact that most of these kinases are activated in heart disease and their inhibition has been shown to improve cardiac function, it is suggested that these kinases form excellent targets for drug development for therapy of heart disease.