Regulation of contractility by Hsp27 and Hic-5 in rat mesenteric small arteries

Vascular mechanotransduction

This review aims to survey the current state of mechanotransduction in vascular smooth muscle cells (VSMCs) and endothelial cells (ECs), including their sensing of mechanical stimuli and transduction of mechanical signals that result in the acute functional modulation and longer-term transcriptomic and epigenetic regulation of blood vessels. The mechanosensors discussed include ion channels, plasma membrane-associated structures and receptors, and junction proteins. The mechanosignaling pathways presented include the cytoskeleton, integrins, extracellular matrix, and intracellular signaling molecules. These are followed by discussions on mechanical regulation of transcriptome and epigenetics, relevance of mechanotransduction to health and disease, and interactions between VSMCs and ECs. Throughout this review, we offer suggestions for specific topics that require further understanding. In the closing section on conclusions and perspectives, we summarize what is known and point out the need to treat the vasculature as a system, including not only VSMCs and ECs but also the extracellular matrix and other types of cells such as resident macrophages and pericytes, so that we can fully understand the physiology and pathophysiology of the blood vessel as a whole, thus enhancing the comprehension, diagnosis, treatment, and prevention of vascular diseases.

Phosphorylation of the small heat shock protein HspB1 regulates cytoskeletal recruitment and cell motility

The small heat shock protein HspB1, also known as Hsp25/27, is a ubiquitously expressed molecular chaperone that responds to mechanical cues. Uniaxial cyclic stretch activates the p38 mitogen-activated protein kinase (MAPK) signaling cascade and increases the phosphorylation of HspB1. Similar to the mechanosensitive cytoskeletal regulator zyxin, phospho-HspB1 is recruited to features of the stretch-stimulated actin cytoskeleton. To evaluate the role of HspB1 and its phosphoregulation in modulating cell function, we utilized CRISPR/Cas9-edited HspB1-null cells and determined they were altered in behaviors such as actin cytoskeletal remodeling, cell spreading, and cell motility. In our model system, expression of WT HspB1, but not nonphosphorylatable HspB1, rescued certain characteristics of the HspB1-null cells including the enhanced cell motility of HspB1-null cells and the deficient actin reinforcement of stretch-stimulated HspB1-null cells. The recruitment of HspB1 to high-tension structures in geometrically constrained cells, such as actin comet tails emanating from focal adhesions, also required a phosphorylatable HspB1. We show that mechanical signals activate posttranslational regulation of the molecular chaperone, HspB1, and are required for normal cell behaviors including actin cytoskeletal remodeling, cell spreading, and cell migration.

Neflamapimod induces vasodilation in resistance mesenteric arteries by inhibiting p38 MAPKα and downstream Hsp27 phosphorylation

Neflamapimod, a selective inhibitor of p38 mitogen activated protein kinase alpha (MAPKα), is under clinical investigation for its efficacy in Alzheimer's disease (AD) and dementia with Lewy Bodies (DLB). Here, we investigated if neflamapimod-mediated acute inhibition of p38 MAPKα could induce vasodilation in resistance-size rat mesenteric arteries. Our pressure myography data demonstrated that neflamapimod produced a dose-dependent vasodilation in mesenteric arteries. Our Western blotting data revealed that acute neflamapimod treatment significantly reduced the phosphorylation of p38 MAPKα and its downstream target heat-shock protein 27 (Hsp27) involved in cytoskeletal reorganization and smooth muscle contraction. Likewise, non-selective inhibition of p38 MAPK by SB203580 attenuated p38 MAPKα and Hsp27 phosphorylation, and induced vasodilation. Endothelium denudation or pharmacological inhibition of endothelium-derived vasodilators such as nitric oxide (NO) and prostacyclin (PGI₂) had no effect on such vasodilation. Neflamapimod-evoked vasorelaxation remained unaltered by the inhibition of smooth muscle cell K⁺ channels. Altogether, our data for the first time demonstrates that in resistance mesenteric arteries, neflamapimod inhibits p38 MAPKα and phosphorylation of its downstream actin-associated protein Hsp27, leading to vasodilation. This novel finding may be clinically significant and is likely to improve systemic blood pressure and cognitive deficits in AD and DLB patients for which neflamapimod is being investigated.

Ageing causes an aortic contractile dysfunction phenotype by targeting the expression of members of the extracellular signal-regulated kinase pathway

The extracellular signal-regulated kinase (ERK) pathway is a well-known regulator of vascular smooth muscle cell proliferation, but it also serves as a regulator of caldesmon, which negatively regulates vascular contractility. This study examined whether aortic contractile function requires ERK activation and if this activation is regulated by ageing. Biomechanical experiments revealed that contractile responses to the alpha1-adrenergic agonist phenylephrine are attenuated specifically in aged mice, which is associated with downregulation of ERK phosphorylation. ERK inhibition attenuates phenylephrine-induced contractility, indicating that the contractile tone is at least partially ERK-dependent. To explore the mechanisms of this age-related downregulation of ERK phosphorylation, we transfected microRNAs, miR-34a and miR-137 we have previously shown to increase with ageing and demonstrated that in A7r5 cells, both miRs downregulate the expression of Src and paxillin, known regulators of ERK signalling, as well as ERK phosphorylation. Further studies in aortic tissues transfected with miRs show that miR-34a but not miR-137 has a negative effect on mRNA levels of Src and paxillin. Furthermore, ERK phosphorylation is decreased in aortic tissue treated with the Src inhibitor PP2. Increases in miR-34a and miR-137 with ageing downregulate the expression of Src and paxillin, leading to impaired ERK signalling and aortic contractile dysfunction.

MAPKs Are Highly Abundant but Do Not Contribute to α1-Adrenergic Contraction of Rat Saphenous Arteries in the Early Postnatal Period

Previously, the abundance of p42/44 and p38 MAPK proteins had been shown to be higher in arteries of 1- to 2-week-old compared to 2- to 3-month-old rats. However, the role of MAPKs in vascular tone regulation in early ontogenesis remains largely unexplored. We tested the hypothesis that the contribution of p42/44 and p38 MAPKs to the contraction of peripheral arteries is higher in the early postnatal period compared to adulthood. Saphenous arteries of 1- to 2-week-old and 2- to 3-month-old rats were studied using wire myography and western blotting. The α₁-adrenoceptor agonist methoxamine did not increase the phosphorylation level of p38 MAPK in either 1- to 2-week-old or 2- to 3-month-old rats. Accordingly, inhibition of p38 MAPK did not affect arterial contraction to methoxamine in either age group. Methoxamine increased the phosphorylation level of p42/44 MAPKs in arteries of 2- to 3-month-old and of p44 MAPK in 1- to 2-week-old rats. Inhibition of p42/44 MAPKs reduced methoxamine-induced contractions in arteries of 2- to 3-month-old, but not 1- to 2-week-old rats. Thus, despite a high abundance in arterial tissue, p38 and p42/44 MAPKs do not regulate contraction of the saphenous artery in the early postnatal period. However, p42/44 MAPK activity contributes to arterial contractions in adult rats.

Cluster analyses of the TCGA and a TMA dataset using the coexpression of HSP27 and CRYAB improves alignment with clinical-pathological parameters of breast cancer and suggests different epichaperome influences for each sHSP

Our cluster analysis of the Cancer Genome Atlas for co-expression of HSP27 and CRYAB in breast cancer patients identified three patient groups based on their expression level combination (high HSP27 + low CRYAB; low HSP27 + high CRYAB; similar HSP27 + CRYAB). Our analyses also suggest that there is a statistically significant inverse relationship between HSP27 and CRYAB and known clinicopathological markers in breast cancer. Screening an unbiased 248 breast cancer patient tissue microarray (TMA) for the protein expression of HSP27 and phosphorylated HSP27 (HSP27-82pS) with CRYAB also identified three patient groups based on HSP27 and CRYAB expression levels. TMA24 also had recorded clinical-pathological parameters, such as ER and PR receptor status, patient survival, and TP53 mutation status. High HSP27 protein levels were significant with ER and PR expression. HSP27-82pS associated with the best patient survival (Log Rank test). High CRYAB expression in combination with wild-type TP53 was significant for patient survival, but a different patient outcome was observed when mutant TP53 was combined with high CRYAB expression. Our data suggest that HSP27 and CRYAB have different epichaperome influences in breast cancer, but more importantly evidence the value of a cluster analysis that considers their coexpression. Our approach can deliver convergence for archival datasets as well as those from recent treatment and patient cohorts and can align HSP27 and CRYAB expression to important clinical-pathological features of breast cancer.

NADPH oxidase in the vasculature: Expression, regulation and signalling pathways; role in normal cardiovascular physiology and its dysregulation in hypertension

The last 20-25 years have seen an explosion of interest in the role of NADPH oxidase (NOX) in cardiovascular function and disease. In vascular smooth muscle and endothelium, NOX generates reactive oxygen species (ROS) that act as second messengers, contributing to the control of normal vascular function. NOX activity is altered in response to a variety of stimuli, including G-protein coupled receptor agonists, growth-factors, perfusion pressure, flow and hypoxia. NOX-derived ROS are involved in smooth muscle constriction, endothelium-dependent relaxation and smooth muscle growth, proliferation and migration, thus contributing to the fine-tuning of blood flow, arterial wall thickness and vascular resistance. Through reversible oxidative modification of target proteins, ROS regulate the activity of protein tyrosine phosphatases, kinases, G proteins, ion channels, cytoskeletal proteins and transcription factors. There is now considerable, but somewhat contradictory evidence that NOX contributes to the pathogenesis of hypertension through oxidative stress. Specific NOX isoforms have been implicated in endothelial dysfunction, hyper-contractility and vascular remodelling in various animal models of hypertension, pulmonary hypertension and pulmonary arterial hypertension, but also have potential protective effects, particularly NOX4. This review explores the multiplicity of NOX function in the healthy vasculature and the evidence for and against targeting NOX for antihypertensive therapy.

Alleviation of murine osteoarthritis by deletion of the focal adhesion mechanosensitive adapter, Hic-5

Excessive mechanical stress is a major cause of knee osteoarthritis. However, the mechanism by which the mechanical stress begets osteoarthritis development remains elusive. Hydrogen peroxide-inducible clone-5 (Hic-5; TGFβ1i1), a TGF-β inducible focal adhesion adaptor, has previously been reported as a mediator of mechanotransduction. In this study, we analyzed the in vivo function of Hic-5 in development of osteoarthritis, and found that mice lacking Hic-5 showed a significant reduction in development of osteoarthritis in the knee. Furthermore, we found reduced expression of catabolic genes, such as metalloproteinase-13 and a disintegrin and metalloproteinase with thrombospondin type 1 motif 5 in osteoarthritic lesions in mice lacking Hic-5. During osteoarthritis development, Hic-5 is detected in chondrocytes of articular cartilage. To investigate the role of Hic-5 in chondrocytes, we isolated chondrocytes from articular cartilage of wild type and Hic-5-deficient mice. In these primary cultured chondrocytes, Hic-5 deficiency resulted in suppression of catabolic gene expression induced by osteoarthritis-related cytokines such as tumor necrosis factor α and interleukin 1β. Furthermore, Hic-5 deficiency in chondrocytes suppressed catabolic gene expression induced by mechanical stress. Revealing the regulation of chondrocyte catabolism by Hic-5 contributes to understanding the pathophysiology of osteoarthritis induced by mechanical stress.

Focal adhesion kinase family is involved in matrix contraction by transdifferentiated Müller cells

Transdifferentiated Müller cells that adopt a fibroblastic/myofibroblastic phenotype have been identified in epiretinal membranes (ERMs) in several ocular disorders, and have been implicated to play a role in the formation and/or the contraction of ERMs. We have previously demonstrated that dasatinib, a dual inhibitor of Src-family kinases and Abl kinase, can prevent matrix contraction by transdifferentiated Müller cells. In this study, we examined molecules involved in matrix contraction downstream of primary dasatinib targets. Tyrosine phosphorylation of focal adhesion kinase (FAK) family members FAK and PYK2 was significantly reduced by dasatinib, and select inhibitors for these kinases PF431396, which inhibits both FAK and PYK2, and PF573228, which only inhibits FAK and not PYK2, significantly reduced matrix contraction by transdifferentiated Müller cells. Dasatinib and PF431396 significantly reduced phosphorylation of Hic-5, a protein implicated to play a role in focal adhesions and cell signaling. Our data shows that FAK family members are involved in matrix contraction by transdifferentiated Müller cells, and also implicates that Hic-5 is situated downstream of the FAK family within the signaling pathway.

A novel inhibitory effect of oxazol-5-one compounds on ROCKII signaling in human coronary artery vascular smooth muscle cells

The selectivity of (4Z)-2-(4-chloro-3-nitrophenyl)-4-(pyridin-3-ylmethylidene)-1,3-oxazol-5-one (DI) for zipper-interacting protein kinase (ZIPK) was previously described by in silico computational modeling, screening a large panel of kinases, and determining the inhibition efficacy. Our assessment of DI revealed another target, the Rho-associated coiled-coil-containing protein kinase 2 (ROCKII). In vitro studies showed DI to be a competitive inhibitor of ROCKII (Ki, 132 nM with respect to ATP). This finding was supported by in silico molecular surface docking of DI with the ROCKII ATP-binding pocket. Time course analysis of myosin regulatory light chain (LC20) phosphorylation catalyzed by ROCKII in vitro revealed a significant decrease upon treatment with DI. ROCKII signaling was investigated in situ in human coronary artery vascular smooth muscle cells (CASMCs). ROCKII down-regulation using siRNA revealed several potential substrates involved in smooth muscle contraction (e.g., LC20, Par-4, MYPT1) and actin cytoskeletal dynamics (cofilin). The application of DI to CASMCs attenuated LC20, Par-4, LIMK, and cofilin phosphorylations. Notably, cofilin phosphorylation was not significantly decreased with a novel ZIPK selective inhibitor (HS-38). In addition, CASMCs treated with DI underwent cytoskeletal changes that were associated with diminution of cofilin phosphorylation. We conclude that DI is not selective for ZIPK and is a potent inhibitor of ROCKII.

MicroRNA-203 mimics age-related aortic smooth muscle dysfunction of cytoskeletal pathways

Increased aortic stiffness is a biomarker for subsequent adverse cardiovascular events. We have previously reported that vascular smooth muscle Src-dependent cytoskeletal remodelling, which contributes to aortic plasticity, is impaired with ageing. Here, we use a multi-scale approach to determine the molecular mechanisms behind defective Src-dependent signalling in an aged C57BL/6 male mouse model. Increased aortic stiffness, as measured in vivo by pulse wave velocity, was found to have a comparable time course to that in humans. Bioinformatic analyses predicted several miRs to regulate Src-dependent cytoskeletal remodelling. qRT-PCR was used to determine the relative levels of predicted miRs in aortas and, notably, the expression of miR-203 increased almost twofold in aged aorta. Increased miR-203 expression was associated with a decrease in both mRNA and protein expression of Src, caveolin-1 and paxillin in aged aorta. Probing with phospho-specific antibodies confirmed that overexpression of miR-203 significantly attenuated Src and extracellular signal regulated kinase (ERK) signalling, which we have previously found to regulate vascular smooth muscle stiffness. In addition, transfection of miR-203 into aortic tissue from young mice increased phenylephrine-induced aortic stiffness ex vivo, mimicking the aged phenotype. Upstream of miR-203, we found that DNA methyltransferases (DNMT) 1, 3a, and 3b are also significantly decreased in the aged mouse aorta and that DNMT inhibition significantly increases miR-203 expression. Thus, the age-induced increase in miR-203 may be caused by epigenetic promoter hypomethylation in the aorta. These findings indicate that miR-203 promotes a re-programming of Src/ERK signalling pathways in vascular smooth muscle, impairing the regulation of stiffness in aged aorta.

The role of mechanotransduction on vascular smooth muscle myocytes' [corrected] cytoskeleton and contractile function

Smooth muscle (SM) exhibits a highly organized structural hierarchy that extends over multiple spatial scales to perform a wide range of functions at the cellular, tissue, and organ levels. Early efforts primarily focused on understanding vascular SM (VSM) function through biochemical signaling. However, accumulating evidence suggests that mechanotransduction, the process through which cells convert mechanical stimuli into biochemical cues, is requisite for regulating contractility. Cytoskeletal proteins that comprise the extracellular, intercellular, and intracellular domains are mechanosensitive and can remodel their structure and function in response to external mechanical cues. Pathological stimuli such as malignant hypertension can act through the same mechanotransductive pathways to induce maladaptive remodeling, leading to changes in cellular shape and loss of contractile function. In both health and disease, the cytoskeletal architecture integrates the mechanical stimuli and mediates structural and functional remodeling in the VSM.

Non-receptor tyrosine kinases and the actin cytoskeleton in contractile vascular smooth muscle

The contractility of vascular smooth muscle cells within the walls of arteries is regulated by mechanical stresses and vasoactive signals. Transduction of these diverse stimuli into a cellular response occurs through many different mechanisms, one being reorganisation of the actin cytoskeleton. In addition to a structural role in maintaining cellular architecture it is now clear that the actin cytoskeleton of contractile vascular smooth muscle cells is a dynamic structure reacting to changes in the cellular environment. Equally clear is that disrupting the cytoskeleton or interfering with its rearrangement, has profound effects on artery contractility. The actin cytoskeleton associates with dense plaques, also called focal adhesions, at the plasma membrane of smooth muscle cells. Vasoconstrictors and mechanical stress induce remodelling of the focal adhesions, concomitant with cytoskeletal reorganisation. Recent work has shown that non-receptor tyrosine kinases and tyrosine phosphorylation of focal adhesion proteins such as paxillin and Hic-5 are important for actin cytoskeleton and focal adhesion remodelling and contraction.

Cytoskeletal reorganization evoked by Rho-associated kinase- and protein kinase C-catalyzed phosphorylation of cofilin and heat shock protein 27, respectively, contributes to myogenic constriction of rat cerebral arteries

Our understanding of the molecular events contributing to myogenic control of diameter in cerebral resistance arteries in response to changes in intravascular pressure, a fundamental mechanism regulating blood flow to the brain, is incomplete. Myosin light chain kinase and phosphatase activities are known to be increased and decreased, respectively, to augment phosphorylation of the 20-kDa regulatory light chain subunits (LC20) of myosin II, which permits cross-bridge cycling and force development. Here, we assessed the contribution of dynamic reorganization of the actin cytoskeleton and thin filament regulation to the myogenic response and serotonin-evoked constriction of pressurized rat middle cerebral arteries. Arterial diameter and the levels of phosphorylated LC(20), calponin, caldesmon, cofilin, and HSP27, as well as G-actin content, were determined. A decline in G-actin content was observed following pressurization from 10 mm Hg to between 40 and 120 mm Hg and in three conditions in which myogenic or agonist-evoked constriction occurred in the absence of a detectable change in LC20 phosphorylation. No changes in thin filament protein phosphorylation were evident. Pressurization reduced G-actin content and elevated the levels of cofilin and HSP27 phosphorylation. Inhibitors of Rho-associated kinase and PKC prevented the decline in G-actin; reduced cofilin and HSP27 phosphoprotein content, respectively; and blocked the myogenic response. Furthermore, phosphorylation modulators of HSP27 and cofilin induced significant changes in arterial diameter and G-actin content of myogenically active arteries. Taken together, our findings suggest that dynamic reorganization of the cytoskeleton involving increased actin polymerization in response to Rho-associated kinase and PKC signaling contributes significantly to force generation in myogenic constriction of cerebral resistance arteries.

Negative regulation of NADPH oxidase 4 by hydrogen peroxide-inducible clone 5 (Hic-5) protein

Hydrogen peroxide-inducible clone 5 (Hic-5) is a focal adhesion adaptor protein induced by the profibrotic cytokine TGF-β1. We have demonstrated previously that TGF-β1 induces myofibroblast differentiation and lung fibrosis by activation of the reactive oxygen species-generating enzyme NADPH oxidase 4 (Nox4). Here we investigated a potential role for Hic-5 in regulating Nox4, myofibroblast differentiation, and senescence. In normal human diploid fibroblasts, TGF-β1 induces Hic-5 expression in a delayed manner relative to the induction of Nox4 and myofibroblast differentiation. Hic-5 silencing induced constitutive Nox4 expression and enhanced TGF-β1-inducible Nox4 levels. The induction of constitutive Nox4 protein in Hic-5-silenced cells was independent of transcription and translation and controlled by the ubiquitin-proteasomal system. Hic-5 associates with the ubiquitin ligase Cbl-c and the ubiquitin-binding protein heat shock protein 27 (HSP27). The interaction of these proteins is required for the ubiquitination of Nox4 and for maintaining low basal levels of this reactive oxygen species-generating enzyme. Our model suggests that TGF-β1-induced Hic-5 functions as a negative feedback mechanism to limit myofibroblast differentiation and senescence by promoting the ubiquitin-proteasomal system-mediated degradation of Nox4. Together, these studies indicate that endogenous Hic-5 suppresses senescence and profibrotic activities of myofibroblasts by down-regulating Nox4 protein expression. Additionally, these are the first studies, to our knowledge, to demonstrate posttranslational regulation of Nox4.

Stereospecific effects of ginsenoside 20-Rg3 inhibits TGF-β1-induced epithelial-mesenchymal transition and suppresses lung cancer migration, invasion and anoikis resistance

The epithelial-mesenchymal transition (EMT) is a pivotal cellular process during which epithelial polarized cells become motile mesenchymal-appearing cells, which, in turn, promotes the metastatic potential of cancer. Ginseng is a perennial plant belonging to the genus Panax that exhibits a wide range of pharmacological and physiological activities. Ginsenosides 20-Rg3, which is the active component of ginseng, has various medical effects, such as anti-tumorigenic, anti-angiogenesis, and anti-fatiguing activities. In addition, ginsenosides 20(S)-Rg3 and 20(R)-Rg3 are epimers, and this epimerization is produced by steaming. However, the possible role of 20(S)-Rg3 and 20(R)-Rg3 in the EMT is unclear. We investigated the effect of 20(S)-Rg3 and 20(R)-Rg3 on the EMT. Transforming growth factor-beta 1 (TGF-β1) induces the EMT to promote lung adenocarcinoma migration, invasion, and anoikis resistance. To understand the repressive role of 20(S)-Rg3 and 20(R)-Rg3 in lung cancer migration, invasion, and anoikis resistance, we investigated the potential use of 20(S)-Rg3 and 20(R)-Rg3 as inhibitors of TGF-β1-induced EMT development in A549 lung cancer cells in vitro. Here, we show that 20(R)-Rg3, but not 20(S)-Rg3, markedly increased expression of the epithelial marker E-cadherin and repressed Snail upregulation and expression of the mesenchymal marker vimentin during initiation of the TGF-β1-induced EMT. 20(R)-Rg3 also inhibited the TGF-β1-induced increase in cell migration, invasion, and anoikis resistance of A549 lung cancer cells. Additionally, 20(R)-Rg3 markedly inhibited TGF-β1-regulated matrix metalloproteinase-2 and activation of Smad2 and p38 mitogen activated protein kinase. Taken together, our findings provide new evidence that 20(R)-Rg3 suppresses lung cancer migration, invasion, and anoikis resistance in vitro by inhibiting the TGF-β1-induced EMT.

Curcumin inhibits TGF-β1-induced MMP-9 and invasion through ERK and Smad signaling in breast cancer MDA- MB-231 cells

OBJECTIVE

To evaluate the effects of curcumin on matrixmetalloproteinase-9 (MMP-9) and invasion ability induced by transforming growth factor-β1 (TGF-β1) in MDA-MB-231 cells and potential mechanisms.

METHODS

Human breast cancer MDA- MB-231 cells were used with the CCK-8 assay to measure the cytotoxicity of curcumin. After treatment with 10 ng/ml TGF-β1, with or without curcumin (≤10 μM), cell invasion was checked by transwell chamber. The effects of curcumin on TGF-β1-stimulated MMP-9 and phosphorylation of Smad2, extracellular-regulated kinase (ERK), and p38 mitogen activated protein kinases (p38MAPK) were examined by Western blotting. Supernatant liquid were collected to analyze the activity of MMP-9 via zymography. Following treatment with PD98059, a specific inhibitor of ERK, and SB203580, a specific inhibitor of p38MAPK, Western blotting and zymography were employed to examine MMP-9 expression and activity, respectively.

RESULTS

Low dose curcumin (≤10 μM) did not show any obvious toxicity to the cells, while 0~10 μmol/L caused a concentration-dependent reduction in cell invasion provoked by TGF-β1. Curcumin also markedly inhibited TGF-β1-regulated MMP-9 and activation of Smad2, ERK1/2 and p38 in a dose- and time-dependent manner. Additionally, PD98059, but not SB203580, showed a similar pattern of inhibition of MMP-9 expression.

CONCLUSION

Curcumin inhibited TGF-β1-stimulated MMP-9 and the invasive phenotype in MDA-MB-231 cells, possibly associated with TGF-β/Smad and TGF-β/ERK signaling.

The role of actin filament dynamics in the myogenic response of cerebral resistance arteries

The myogenic response has a critical role in regulation of blood flow to the brain. Increased intraluminal pressure elicits vasoconstriction, whereas decreased intraluminal pressure induces vasodilatation, thereby maintaining flow constant over the normal physiologic blood pressure range. Improved understanding of the molecular mechanisms underlying the myogenic response is crucial to identify deficiencies with pathologic consequences, such as cerebral vasospasm, hypertension, and stroke, and to identify potential therapeutic targets. Three mechanisms have been suggested to be involved in the myogenic response: (1) membrane depolarization, which induces Ca(2+) entry, activation of myosin light chain kinase, phosphorylation of the myosin regulatory light chains (LC(20)), increased actomyosin MgATPase activity, cross-bridge cycling, and vasoconstriction; (2) activation of the RhoA/Rho-associated kinase (ROCK) pathway, leading to inhibition of myosin light chain phosphatase by phosphorylation of MYPT1, the myosin targeting regulatory subunit of the phosphatase, and increased LC(20) phosphorylation; and (3) activation of the ROCK and protein kinase C pathways, leading to actin polymerization and the formation of enhanced connections between the actin cytoskeleton, plasma membrane, and extracellular matrix to augment force transmission. This review describes these three mechanisms, emphasizing recent developments regarding the importance of dynamic actin polymerization in the myogenic response of the cerebral vasculature.

Cyclic AMP relaxation of rat aortic smooth muscle is mediated in part by decrease of depletion of intracellular Ca(2+) stores and inhibition of capacitative calcium entry

Despite a large number of studies, the mechanism by which 3',5'-cyclic monophosphate (cAMP) induces vasorelaxation is not fully understood. The comparison between results obtained in different vessels or species has often been the source of conflicting reports. In order to shed more light onto this mechanism, we studied the effects of forskolin in phenylephrine-pre-contracted endothelium-denuded rat aorta and measured cAMP levels in rat aortic myocytes by enzyme-immunoassay. Nanomolar forskolin relaxed phenylephrine-induced contractions. This effect was mimicked by dibutyryl-cAMP and was potentiated by rolipram or a p38-mitogen-activated protein kinase (p38-MAPK) inhibitor (SB-203580). Nifedipine and verapamil partially relaxed phenylephrine-induced contractions, while further application of cAMP-elevating agents fully relaxed these contractions. In Ca(2+)-free extracellular solution, forskolin reduced phenylephrine-induced transient contractions and reduced the Ca(2+)-induced contraction after depletion of intracellular stores. Nanomolar concentrations of forskolin increased basal cAMP levels only in the presence of rolipram or phenylephrine, which did not modify intracellular levels of cAMP by themselves. In conclusion, relaxation by cAMP is mediated in part by decrease of depletion of intracellular Ca(2+) stores and inhibition of capacitative calcium entry. This study provides the first evidence that inhibition of PDE4 or p38-MAPK potentiates the vasodilator effect of cAMP-elevating agents in rat aortic myocytes.

A-kinase anchoring proteins that regulate cardiac remodeling

In response to injury or stress, the adult heart undergoes maladaptive changes, collectively defined as pathological cardiac remodeling. Here, we focus on the role of A-kinase anchoring proteins (AKAPs) in 3 main areas associated with cardiac remodeling and the progression of heart failure: excitation-contraction coupling, sarcomeric regulation, and induction of pathological hypertrophy. AKAPs are a diverse family of scaffold proteins that form multiprotein complexes, integrating cAMP signaling with protein kinases, phosphatases, and other effector proteins. Many AKAPs have been characterized in the heart, where they play a critical role in modulating cardiac function.

Redox regulation of protein kinases as a modulator of vascular function

Reactive oxygen species (ROS) are continuously generated in vascular tissues by various oxidoreductase enzymes. They contribute to normal cell signaling, and modulate vascular smooth muscle tone and endothelial permeability in response to physiological agonists and to various cellular stresses and environmental factors, such as hypoxia. While concentrations of ROS are normally tightly controlled by cellular redox buffer systems, if produced in excess they may contribute to vascular disease. Protein kinases are essential components of most cell signaling pathways, including those involving ROS. The functioning of several members of this highly diverse group of enzymes, which include receptor and nonreceptor tyrosine kinases, protein kinase C, mitogen-activated kinases, and Rho-kinase, are modified by ROS, either through direct oxidative modification or indirectly through modification of associated proteins such as tyrosine phosphatases and monomeric G proteins. In this review, we discuss the molecular mechanisms of redox modification of these proteins, the downstream pathways affected, the often complex interaction between major kinase pathways, and feedback to ROS production itself. We also discuss complicating factors such as differential actions of superoxide anion and hydrogen peroxide, questions concerning concentration dependence, and the significance of signaling microdomains.

A-kinase anchoring protein (AKAP)-Lbc anchors a PKN-based signaling complex involved in α1-adrenergic receptor-induced p38 activation

The mitogen-activated protein kinases (MAPKs) pathways are highly organized signaling systems that transduce extracellular signals into a variety of intracellular responses. In this context, it is currently poorly understood how kinases constituting these signaling cascades are assembled and activated in response to receptor stimulation to generate specific cellular responses. Here, we show that AKAP-Lbc, an A-kinase anchoring protein (AKAP) with an intrinsic Rho-specific guanine nucleotide exchange factor activity, is critically involved in the activation of the p38α MAPK downstream of α(1b)-adrenergic receptors (α(1b)-ARs). Our results indicate that AKAP-Lbc can assemble a novel transduction complex containing the RhoA effector PKNα, MLTK, MKK3, and p38α, which integrates signals from α(1b)-ARs to promote RhoA-dependent activation of p38α. In particular, silencing of AKAP-Lbc expression or disrupting the formation of the AKAP-Lbc·p38α signaling complex specifically reduces α(1)-AR-mediated p38α activation without affecting receptor-mediated activation of other MAPK pathways. These findings provide a novel mechanistic hypothesis explaining how assembly of macromolecular complexes can specify MAPK signaling downstream of α(1)-ARs.

Effect of epinephrine and insulin resistance on human monocytes obtained from lean and obese healthy participants: a pilot study

We assessed the effect of epinephrine on human monocytes. Monocytes were isolated from 16 healthy obese and 10 lean healthy subjects. Insulin sensitivity was assessed by euglycemic hyperinsulinemic clamp. Obese subjects were subdivided into 2 sub-groups, insulin sensitive (IS) and insulin resistant (IR). Monocyte properties [attachment to laminin 1, migration through laminin 1, oxidized-low density lipoprotein (oxLDL) phagocytosis] were assessed pre- and post-stimulation in vitro with epinephrine. Experiments were repeated after incubation with a Na(+)/H( +) exchanger-1 inhibitor (NHE-1) (cariporide). Epinephrine increased monocyte attachment to laminin in lean and obese IR subjects through involvement of NHE-1, PKC, NO synthase, NADPH oxidase and actin polymerization. In contrast, epinephrine did not affect monocyte migration. Epinephrine increased oxLDL phagocytosis in all groups studied. Incubation with cariporide attenuated oxLDL phagocytosis. Epinephrine induces monocyte dysfunction which may be atherogenic.

Actin cytoskeletal dynamics in smooth muscle: a new paradigm for the regulation of smooth muscle contraction

A growing body of data supports a view of the actin cytoskeleton of smooth muscle cells as a dynamic structure that plays an integral role in regulating the development of mechanical tension and the material properties of smooth muscle tissues. The increase in the proportion of filamentous actin that occurs in response to the stimulation of smooth muscle cells and the essential role of stimulus-induced actin polymerization and cytoskeletal dynamics in the generation of mechanical tension has been convincingly documented in many smooth muscle tissues and cells using a wide variety of experimental approaches. Most of the evidence suggests that the functional role of actin polymerization during contraction is distinct and separately regulated from the actomyosin cross-bridge cycling process. The molecular basis for the regulation of actin polymerization and its physiological roles may vary in diverse types of smooth muscle cells and tissues. However, current evidence supports a model for smooth muscle contraction in which contractile stimulation initiates the assembly of cytoskeletal/extracellular matrix adhesion complex proteins at the membrane, and proteins within this complex orchestrate the polymerization and organization of a submembranous network of actin filaments. This cytoskeletal network may serve to strengthen the membrane for the transmission of force generated by the contractile apparatus to the extracellular matrix, and to enable the adaptation of smooth muscle cells to mechanical stresses. Better understanding of the physiological function of these dynamic cytoskeletal processes in smooth muscle may provide important insights into the physiological regulation of smooth muscle tissues.

Small heat shock proteins in smooth muscle

The small heat shock proteins (HSPs) HSP20, HSP27 and alphaB-crystallin are chaperone proteins that are abundantly expressed in smooth muscles are important modulators of muscle contraction, cell migration and cell survival. This review focuses on factors regulating expression of small HSPs in smooth muscle, signaling pathways that regulate macromolecular structure and the biochemical and cellular functions of small HSPs. Cellular processes regulated by small HSPs include chaperoning denatured proteins, maintaining cellular redox state and modifying filamentous actin polymerization. These processes influence smooth muscle proliferation, cell migration, cell survival, muscle contraction and synthesis of signaling proteins. Understanding functions of small heat shock proteins is relevant to mechanisms of disease in which dysfunctional smooth muscle causes symptoms, or is a target of drug therapy. One example is that secreted HSP27 may be a useful marker of inflammation during atherogenesis. Another is that phosphorylated HSP20 which relaxes smooth muscle may prove to be highly relevant to treatment of hypertension, vasospasm, asthma, premature labor and overactive bladder. Because small HSPs also modulate smooth muscle proliferation and cell migration they may prove to be targets for developing effective, novel treatments of clinical problems arising from remodeling of smooth muscle in vascular, respiratory and urogenital systems.