Myosin light chain kinase inhibitor ML7 improves vascular endothelial dysfunction via tight junction regulation in a rabbit model of atherosclerosis

Protease-activated receptor 2 drives migration in a colon cancer cell line but not in noncancerous human epithelial cells

The inflamed mucosa contains a complex assortment of proteases that may participate in wound healing or the development of inflammation-associated colon cancer. We sought to determine the role of protease-activated receptor 2 (PAR2) in epithelial wound healing in both untransformed and transformed colonic epithelial cells. Monolayers of primary epithelial cells derived from organoids cultivated from patient colonic biopsies and of the T84 colon cancer cell line were grown to confluence, wounded in the presence of a selective PAR2-activating peptide, and healing was visualized by live cell microscopy. Inhibitors of various signaling molecules were used to assess the relevant pathways responsible for wound healing. Activation of PAR2 induced an enhanced wound-healing response in T84 cells but not primary cells. The PAR2-enhanced wound-healing response was associated with the development of lamellipodia in cells at the wound edge, consistent with sheet migration. The response to PAR2 activation in T84 cells was completely dependent on Src kinase activity and partially dependent on Rac1 activity. The Src-associated signaling molecules, focal adhesion kinase, and epidermal growth factor receptor, which typically mediate wound-healing responses, were not involved in the PAR2 response. Experiments repeated in the presence of the inflammatory cytokines TNF and IFNγ revealed a synergistically enhanced PAR2 wound-healing response in T84s but not primary cells. The epithelial response to proteases may be different between primary and cancer cells and is accentuated in the presence of inflammatory cytokines. Our findings have implications for understanding epithelial restitution in the context of inflammatory bowel disease (IBD) and inflammation-associated colon cancer.NEW & NOTEWORTHY Protease-activated receptor 2 enhances wound healing in the T84 colon cancer cell line, but not in primary cells derived from patient biopsies, an effect that is synergistically enhanced in the presence of the inflammatory cytokines TNF and IFNγ.

Studying the Geroprotective Properties of YAP/TAZ Signaling Inhibitors on Drosophila melanogaster Model

The transcriptional coactivators Yes-associated protein (YAP) and transcriptional coactivator with PDZ-binding motif (TAZ) are the main downstream effectors of the evolutionarily conserved Hippo signaling pathway. YAP/TAZ are implicated in the transcriptional regulation of target genes that are involved in a wide range of key biological processes affecting tissue homeostasis and play dual roles in the aging process, depending on the cellular and tissue context. The aim of the present study was to investigate whether pharmacological inhibitors of Yap/Taz increase the lifespan of Drosophila melanogaster. Real-time qRT-PCR was performed to measure the changes in the expression of Yki (Yorkie, the Drosophila homolog of YAP/TAZ) target genes. We have revealed a lifespan-increasing effect of YAP/TAZ inhibitors that was mostly associated with decreased expression levels of the wg and E2f1 genes. However, further analysis is required to understand the link between the YAP/TAZ pathway and aging.

Comparison of Rheological Properties of Healthy versus Dupuytren Fibroblasts When Treated with a Cell Contraction Inhibitor by Atomic Force Microscope

Mechanical properties of healthy and Dupuytren fibroblasts were investigated by atomic force microscopy (AFM). In addition to standard force curves, rheological properties were assessed using an oscillatory testing methodology, in which the frequency was swept from 1 Hz to 1 kHz, and data were analyzed using the structural damping model. Dupuytren fibroblasts showed larger apparent Young's modulus values than healthy ones, which is in agreement with previous results. Moreover, cell mechanics were compared before and after ML-7 treatment, which is a myosin light chain kinase inhibitor (MLCK) that reduces myosin activity and hence cell contraction. We employed two different concentrations of ML-7 inhibitor and could observe distinct cell reactions. At 1 µM, healthy and scar fibroblasts did not show measurable changes in stiffness, but Dupuytren fibroblasts displayed a softening and recovery after some time. When increasing ML-7 concentration (3 µM), the majority of cells reacted, Dupuytren fibroblasts were the most susceptible, not being able to recover from the drug and dying. These results suggested that ML-7 is a potent inhibitor for MLCK and that myosin II is essential for cytoskeleton stabilization and cell survival.

Intestinal Flora-Derived Kynurenic Acid Protects Against Intestinal Damage Caused by Candida albicans Infection via Activation of Aryl Hydrocarbon Receptor

Colonization of the intestinal tract by Candida albicans (C. albicans) can lead to invasive candidiasis. Therefore, a functional intestinal epithelial barrier is critical for protecting against invasive C. albicans infections. We collected fecal samples from patients with Candida albicans bloodstream infection and healthy people. Through intestinal flora 16sRNA sequencing and intestinal metabolomic analysis, we found that C. albicans infection resulted in a significant decrease in the expression of the metabolite kynurenic acid (KynA). We used a repeated C. albicans intestinal infection mouse model, established following intake of 3% dextran sulfate sodium salt (DSS) for 9 days, and found that KynA, a tryptophan metabolite, inhibited inflammation, promoted expression of intestinal tight junction proteins, and protected from intestinal barrier damage caused by invasive Candida infections. We also demonstrated that KynA activated aryl hydrocarbon receptor (AHR) repressor in vivo and in vitro. Using Caco-2 cells co-cultured with C. albicans, we showed that KynA activated AHR, inhibited the myosin light chain kinase-phospho-myosin light chain (MLCK-pMLC) signaling pathway, and promoted tristetraprolin (TTP) expression to alleviate intestinal inflammation. Our findings suggest that the metabolite KynA which is differently expressed in patients with C. albicans infection and has a protective effect on the intestinal epithelium, via activating AHR, could be explored to provide new potential therapeutic strategies for invasive C. albicans infections.

Hemin-Induced Endothelial Dysfunction and Endothelial to Mesenchymal Transition in the Pathogenesis of Pulmonary Hypertension Due to Chronic Hemolysis

Pulmonary hypertension in sickle cell disease is an independent predictor of mortality, yet the pathogenesis of pulmonary vascular disease in chronic hemolytic disorders remains incompletely understood and treatment options are limited primarily to supportive care. The release of extracellular hemoglobin has been implicated in the development of pulmonary hypertension, and in this study we explored the direct effects of hemin, the oxidized moiety of heme, on the pulmonary artery endothelium. We found that low dose hemin exposure leads to significantly increased endothelial cell proliferation, migration, and cytokine release as markers of endothelial dysfunction. Protein expression changes in our pulmonary artery endothelial cells showed upregulation of mesenchymal markers after hemin treatment in conjunction with a decrease in endothelial markers. Endothelial to mesenchymal transition (EndoMT) resulting from hemin exposure was further confirmed by showing upregulation of the transcription factors SNAI1 and SLUG, known to regulate EndoMT. Lastly, given the endothelial dysfunction and phenotypic transition observed, the endothelial cytoskeleton was considered a potential novel target. Inhibiting myosin light chain kinase, to prevent phosphorylation of myosin light chain and cytoskeletal contraction, attenuated hemin-induced endothelial hyper-proliferation, migration, and cytokine release. The findings in this study implicate hemin as a key inducer of endothelial dysfunction through EndoMT, which may play an important role in pulmonary vascular remodeling during the development of pulmonary hypertension in chronic hemolytic states.

IP3 receptor orchestrates maladaptive vascular responses in heart failure

Patients with heart failure (HF) have augmented vascular tone, which increases cardiac workload, impairing ventricular output and promoting further myocardial dysfunction. The molecular mechanisms underlying the maladaptive vascular responses observed in HF are not fully understood. Vascular smooth muscle cells (VSMCs) control vasoconstriction via a Ca²⁺-dependent process, in which the type 1 inositol 1,4,5-trisphosphate receptor (IP3R1) on the sarcoplasmic reticulum (SR) plays a major role. To dissect the mechanistic contribution of intracellular Ca²⁺ release to the increased vascular tone observed in HF, we analyzed the remodeling of IP3R1 in aortic tissues from patients with HF and from controls. VSMC IP3R1 channels from patients with HF and HF mice were hyperphosphorylated by both serine and tyrosine kinases. VSMCs isolated from IP3R1^VSMC–/– mice exhibited blunted Ca²⁺ responses to angiotensin II (ATII) and norepinephrine compared with control VSMCs. IP3R1^VSMC–/– mice displayed significantly reduced responses to ATII, both in vivo and ex vivo. HF IP3R^1VSMC–/– mice developed significantly less afterload compared with HF IP3R1^fl/fl mice and exhibited significantly attenuated progression toward decompensated HF and reduced interstitial fibrosis. Ca²⁺-dependent phosphorylation of the MLC by MLCK activated VSMC contraction. MLC phosphorylation was markedly increased in VSMCs from patients with HF and HF mice but reduced in VSMCs from HF IP3R1^VSMC–/– mice and HF WT mice treated with ML-7. Taken together, our data indicate that VSMC IP3R1 is a major effector of increased vascular tone, which contributes to increased cardiac afterload and decompensation in HF.

A Novel Tigecycline Adjuvant ML-7 Reverses the Susceptibility of Tigecycline-Resistant Klebsiella pneumoniae

The increasing incidence of tigecycline resistance undoubtedly constitutes a serious threat to global public health. The combination therapies had become the indispensable strategy against this threat. Herein, 11 clinical tigecycline-resistant Klebsiella pneumoniae which mainly has mutations in ramR, acrR, or macB were collected for tigecycline adjuvant screening. Interestingly, ML-7 hydrochloride (ML-7) dramatically potentiated tigecycline activity. We further picked up five analogs of ML-7 and evaluated their synergistic activities with tigecycline by using checkerboard assay. The results revealed that ML-7 showed certain synergy with tigecycline, while other analogs exerted attenuated synergistic effects among tigecycline-resistant isolates. Thus, ML-7 was selected for further investigation. The results from growth curves showed that ML-7 combined with tigecycline could completely inhibit the growth of bacteria, and the time-kill analysis revealed that the combination exhibited synergistic bactericidal activities for tigecycline-resistant isolates during 24 h. The ethidium bromide (EtBr) efflux assay demonstrated that ML-7 could inhibit the functions of efflux pump. Besides, ML-7 disrupted the proton motive force (PMF) via increasing ΔpH, which in turn lead to the inhibition of the functions of efflux pump, reduction of intracellular ATP levels, as well as accumulation of ROS. All of which promoted the death of bacteria. And further transcriptomic analysis revealed that genes related to the mechanism of ML-7 mainly enriched in ABC transporters. Taken together, these results revealed the potential of ML-7 as a novel tigecycline adjuvant to circumvent tigecycline-resistant Klebsiella pneumoniae.

Phosphorylation of MYL12 by Myosin Light Chain Kinase Regulates Cellular Shape Changes in Cochlear Hair Cells

The organ of Corti is an auditory organ located in the cochlea, comprising hair cells (HCs) and other supporting cells. Cellular shape changes of HCs are important for the development of auditory epithelia and hearing function. It was previously observed that HCs and inner sulcus cells (ISCs) demonstrate cellular shape changes similar to the apical constriction of the neural epithelia. Apical constriction is induced via actomyosin cable contraction in the apical junctional complex and necessary for the physiological function of the epithelium. Actomyosin cable contraction is mainly regulated by myosin regulatory light chain (MRLC) phosphorylation by myosin light chain kinase (MLCK). However, MRLC and MLCK isoforms expressed in HCs and ISCs are unknown. Hence, we investigated the expression patterns and roles of MRLCs and MLCKs in HCs. Droplet digital PCR revealed that HCs expressed MYL12A/B and MYL9, which are non-muscle MRLC and smooth muscle MLCK (smMLCK), respectively. Immunofluorescence staining throughout the organ of Corti demonstrated that only MYL12 was expressed in the apical portion of HCs, whereas MYL12 and MYL9 were expressed on ISCs. In addition, purified MYL12B was phosphorylated by smMLCK in vitro, and the harvested HCs contained phosphorylated MYL12. Furthermore, accompanied by the expansion of the cell area of outer HCs, MYL12 phosphorylation was reduced by ML-7, which is an inhibitor of smMLCK. In conclusion, MYL12 phosphorylation by smMLCK contributed to the apical constriction-like cellular shape change of HCs possibly relating to the development of auditory epithelia and hearing function.

Baicalin Protects Vascular Tight Junctions in Piglets During Glaesserella parasuis Infection

Glaesserella parasuis (G. parasuis) can cause Glässer's disease and severely affect swine industry worldwide. This study is an attempt to address the issue of the capability of G. parasuis to damage the vascular barrier and the effects of baicalin on vascular tight junctions (TJ) in order to investigate the interactions between the pathogen and the porcine vascular endothelium. Piglets were challenged with G. parasuis and treated with or without baicalin. The expressions of vascular TJ genes were examined using RT-PCR. The distribution patterns of TJ proteins were detected by immunofluorescence. The involved signaling pathways were determined by Western blot assays on related proteins. G. parasuis can downregulate TJ expression and disrupt the distribution of TJ proteins. Baicalin can alleviate the downregulation of vascular TJ mRNA, maintain the distribution, and prevent the abnormalities of TJ. These results provide ample evidence that baicalin has the capacity to protect vascular TJ damaged by G. parasuis through inhibiting PKC and MLCK/MLC pathway activation. As a result, baicalin is a promising candidate for application as a natural agent for the prevention and control of G. parasuis infection.

Microelectromechanical System Measurement of Platelet Contraction: Direct Interrogation of Myosin Light Chain Phosphorylation

Myosin Light Chain (MLC) regulates platelet contraction through its phosphorylation by Myosin Light Chain Kinase (MLCK) or dephosphorylation by Myosin Light Chain Phosphatase (MLCP). The correlation between platelet contraction force and levels of MLC phosphorylation is unknown. We investigate the relationship between platelet contraction force and MLC phosphorylation using a novel microelectromechanical (MEMS) based clot contraction sensor (CCS). The MLCK and MLCP pair were interrogated by inhibitors and activators of platelet function. The CCS was fabricated from silicon using photolithography techniques and force was validated over a range of deflection for different chip spring constants. The force of platelet contraction measured by the clot contraction sensor (CCS) was compared to the degree of MLC phosphorylation by Western Blotting (WB) and ELISA. Stimulators of MLC phosphorylation produced higher contraction force, higher phosphorylated MLC signal in ELISA and higher intensity bands in WB. Inhibitors of MLC phosphorylation produced the opposite. Contraction force is linearly related to levels of phosphorylated MLC. Direct measurements of clot contractile force are possible using a MEMS sensor platform and correlate linearly with the degree of MLC phosphorylation during coagulation. Measured force represents the mechanical output of the actin/myosin motor in platelets regulated by myosin light chain phosphorylation.

Protective Effects of Baicalin on Peritoneal Tight Junctions in Piglets Challenged with Glaesserella parasuis

Glaesserella parasuis (G. parasuis) causes inflammation and damage to piglets. Whether polyserositis caused by G. parasuis is due to tight junctions damage and the protective effect of baicalin on it have not been examined. Therefore, this study aims to investigate the effects of baicalin on peritoneal tight junctions of piglets challenged with G. parasuis and its underlying molecular mechanisms. Piglets were challenged with G. parasuis and treated with or without baicalin. RT-PCR was performed to examine the expression of peritoneal tight junctions genes. Immunofluorescence was carried out to detect the distribution patterns of tight junctions proteins. Western blot assays were carried out to determine the involved signaling pathways. Our data showed that G. parasuis infection can down-regulate the tight junctions expression and disrupt the distribution of tight junctions proteins. Baicalin can alleviate the down-regulation of tight junctions mRNA in peritoneum, prevent the abnormalities and maintain the continuous organization of tight junctions. Our results provide novel evidence to support that baicalin has the capacity to protect peritoneal tight junctions from G. parasuis-induced inflammation. The protective mechanisms of baicalin could be associated with inhibition of the activation of PKC and MLCK/MLC signaling pathway. Taken together, these data demonstrated that baicalin is a promising natural agent for the prevention and treatment of G. parasuis infection.

Alternative pathways control actomyosin contractility in epitheliomuscle cells during morphogenesis and body contraction

In adult Hydra, epitheliomuscle cells form the monolayered ecto- and endodermal epithelia. Their basal myonemes function as a longitudinal and circular muscle, respectively. Based on the observation that a Rho/Rock pathway, controlling the cell shape changes during detachment of Hydra buds, is not involved in body movement, at least two actomyosin compartments must exist in these cells: a basal one for body movement and a cortical one for cell shape changes. We therefore analyzed the regional and subcellular localization of the Ser19-phosphorylated myosin regulatory light chain (pMLC20). Along the body column, pMLC20 was detected strongly in the basal myonemes and weakly in the apical cell compartments of ectodermal epitheliomuscle cells. In cells of the bud base undergoing morphogenesis, pMLC20 was localized to intracellular stress fibers as well as to the apical and additionally to the lateral cortical compartment. Pharmacological inhibition revealed that pMLC20 is induced in these compartments by at least two independent pathways. In myonemes, MLC is phosphorylated mainly by myosin light chain kinase (MLCK). In contrast, the cortical apical and lateral MLC phosphorylation in constricting ectodermal cells of the bud base is stimulated via the Rho/ROCK pathway.

Myosin light chain kinase inhibitor ML7 improves vascular endothelial dysfunction and permeability via the mitogen-activated protein kinase pathway in a rabbit model of atherosclerosis

Endothelial dysfunction (ED) and hyperpermeability are considered as the initiating steps in early atherosclerosis. Phosphorylation of myosin light chain (MLC) is key to cause vascular hyperpermeability via endothelial cell contraction. However, it is unclear whether MLC phosphorylation can also regulate the balance between contraction and relaxation of endothelial cells, thereby affecting endothelium-dependent diastolic function and leading to ED. The present study investigated relationships between ED and MLC phosphorylation and underlying mechanisms. Twenty-four male New Zealand white rabbits were randomly divided into three groups: control, AS, and ML7 (MLCK inhibitor) groups, and fed with normal diet, high-fat diet (HFD), and HFD plus oral ML7 (1 mg/kg daily) respectively. HFD-fed rabbits showed typical atheromatous lesions and endothelial hyperpermeability, and these lesions could be partly reversed following ML7 therapy. Western blotting revealed significant increased expression of myosin light chain kinase (MLCK) and phosphorylation of MLC, JNK, and ERK in the arterial wall of rabbits in the AS group compared with those of the control group (p < 0.05), whereas the ML7 group showed markedly decreased levels of these proteins compared with the AS group (p <  0.05). The endothelium-dependent relaxation rate was significantly reduced both in vitro and in vivo in AS group, and was improved using ML7 therapy. Taken together, these results indicate that MLCK expression and subsequent MLC phosphorylation increase vascular endothelial permeability and endothelium-dependent diastolic dysfunction by promoting endothelial cell contraction, which may be initiated by the activation of the MAP/ERK (MEK) and MAP/JNK (MEK) pathways.

Calcium in Vascular Smooth Muscle Cell Elasticity and Adhesion: Novel Insights Into the Mechanism of Action

Vascular smooth muscle cells (VSMCs) are the predominant cell type in the arterial wall. These cells play a critical role in maintaining vascular homeostasis including vasoconstriction and vasodilatation through active contraction and relaxation. Dysregulation of VSMC function alters the response of blood vessels to mechanical stress, contributing to the pathogenesis of vascular diseases, particularly atherosclerosis and hypertension. The stiffness of VSMCs is a major regulator of vascular function. Previous studies suggest that intracellular Ca2+ controls the stiffness of VSMCs by a mechanism involving myosin contractile apparatus. More recent studies highlight important functions of cytoskeletal α-smooth muscle actin (α-SMA), α5β1 integrin, and integrin-mediated cell-extracellular matrix (ECM) interactions in Ca2+-dependent regulation of VSMC stiffness and adhesion to the ECM, providing novel insights into the mechanism of calcium action.

MicroRNA-92a promotes vascular smooth muscle cell proliferation and migration through the ROCK/MLCK signalling pathway

To identify the interaction between known regulators of atherosclerosis, microRNA-92a (miR-92a), Rho-associated coiled-coil-forming kinase (ROCK) and myosin light chain kinase (MLCK), we examined their expressions during proliferation and migration of platelet-derived growth factor-BB (PDGF-BB)-regulated vascular smooth muscle cells (VSMCs), both in vivo and in vitro. During the formation of atherosclerosis plaque in mice, a parallel increase in expression levels of MLCK and miR-92a was observed while miR-92a expression was reduced in ML-7 (an inhibitor of MLCK) treated mice and in MLCK-deficient VSMCs. In vitro results indicated that both MLCK and miR-92a shared the same signalling pathway. Transfection of miR-92a mimic partially restored the effect of MLCK's deficiency and antagonized the effect of Y27632 (an inhibitor of ROCK) on the down-regulation of VSMCs activities. ML-7 increased the expression of Kruppel-like factor 4 (KLF4, a target of miR-92a), and siRNA-KLF4 increased VSMCs' activity level. Consistently, inhibition of either MLCK or ROCK enhanced the KLF4 expression. Moreover, we observed that ROCK/MLCK up-regulated miR-92a expression in VSMCs through signal transducer and activator of transcription 3 (STAT3) activation. In conclusion, the activation of ROCK/STAT3 and/or MLCK/STAT3 may up-regulate miR-92a expression, which subsequently inhibits KLF4 expression and promotes PDGF-BB-mediated proliferation and migration of VSMCs. This new downstream node in the ROCK/MLCK signalling pathway may offer a potential intervention target for treatment of atherosclerosis.

Glucagon-like peptide-1 attenuates endothelial barrier injury in diabetes via cAMP/PKA mediated down-regulation of MLC phosphorylation

OBJECTIVE

Glucagon-like peptide-1 (GLP-1) showed protective effects on endothelium-dependent dilatation. Since endothelial barrier dysfunction also plays a pivotal role in atherosclerosis, this study was designed to investigate the effects of GLP-1 on endothelial barrier function in diabetic aortic endothelium and explore the underlying mechanism.

METHODS

For in vivo studies, diabetic rats were established and subjected to 12- and 24-week treatment of exenatide. The morphological changes of aortic endothelium were observed with transmission electron microscope. A permeability assay of aortic endothelium was performed using the surface biotinylation technique. Protein expression was detected by immunohistochemical analysis and Western blots. For in vitro studies, human umbilical vein endothelial cells (HUVECs) were cultured in medium enriched with advanced glycation end products (AGEs) or AGEs plus GLP-1 and other reagents. The integrity of endothelium was evaluated by endothelial monolayer permeability assay and transendothelial resistance. The in vitro expressions of relevant proteins in signaling pathways were also detected by immunofluorescence and Western blots.

RESULTS

In vivo, the enhanced aortic endothelial permeability in diabetic aortas were attenuated by exenatide treatment. Additionally, myosin light chain (MLC) phosphorylation, related to actomyosin contractility, and activation of its upstream targets in diabetic aorta were inhibited after administration of exenatide. In vitro, the endothelial monolayer permeability and the assembly of stress fibers were reduced by GLP-1 intervention under diabetic condition. Meanwhile, AGE-induced MLC phosphorylation mediating ECs contractility was inhibited by GLP-1. Furthermore, GLP-1 down-regulated the upstream targets of MLC phosphorylation, including RAGE, Rho/ROCK and MAPK signaling pathways. Intriguingly, the effects of GLP-1 elicited on ECs contractility and barrier function in diabetes were blunted by inhibition of GLP-1R, cAMP or PKA and stimulation of Rho/ROCK and MAPK signaling pathways.

CONCLUSION

The findings of this study suggest that the stabilizing effect of GLP-1 on the endothelial barrier and contraction of AGE-treated ECs is caused by GLP-1R/cAMP/PKA activation and the subsequent inactivation of RAGE/Rho/ROCK as well as MAPK signaling pathways.

Involvement of inhibitor kappa B kinase 2 (IKK2) in the regulation of vascular tone

Inhibitor kappa B kinase 2 (IKK2) plays an essential role in the activation of nuclear factor kappa B (NF-kB). Recently, it has been suggested that IKK2 acts as a myosin light chain kinase (MLCK) and contributes to vasoconstriction in mouse aorta. However, the underlying mechanisms are still unknown. Therefore, we investigated whether IKK2 acts as a MLCK or regulates the activity of myosin light chain phosphatase (MLCP). Pressure myograph was used to measure vascular tone in rat mesenteric arteries. Immunofluorescence staining was performed to identify phosphorylation levels of MLC (ser19), MYPT1 (thr853 and thr696) and CPI-17 (thr38). SC-514 (IKK2 inhibitor, 50 μM) induced relaxation in the mesenteric arteries pre-contracted with 70 mM high K⁺ solution or U-46619 (thromboxane analog, 5 μM). The relaxation induced by SC-514 was increased in the arteries pre-contracted with U-46619 compared to arteries pre-contracted with 70 mM high K⁺ solution. U-46619-induced contraction was decreased by treatment of SC-514 in the presence of MLCK inhibitor, ML-7 (10 μM). In the absence of intracellular Ca²⁺, U-46619 still induced contraction, which was decreased by treatment of SC-514. Furthermore, phosphorylation levels of MLC (ser19) and MYPT1 (thr853) were decreased by treatment of SC-514. IKK2 is involved in the vascular contraction through regulation of MLCP activity by phosphorylating MYPT1 at thr853 in rat mesenteric arteries. These findings suggest IKK2 could be a new pharmacological target for specific therapies of various vascular diseases.

Lactobacillus reuteri LR1 Improved Expression of Genes of Tight Junction Proteins via the MLCK Pathway in IPEC-1 Cells during Infection with Enterotoxigenic Escherichia coli K88

Intestinal epithelial barrier damage disrupts immune homeostasis and leads to many intestinal disorders. Lactobacillus reuteri strains have probiotic functions in their modulation of the microbiota and immune system in intestines. In this study, the effects of L. reuteri LR1, a new strain isolated from the feces of weaning piglets, on intestinal epithelial barrier damage in IPEC-1 cells caused by challenge with enterotoxigenic Escherichia coli (ETEC) K88 were examined. It was found that L. reuteri LR1, in large part, offset the ETEC K88-induced increase in permeability of IPEC-1 cell monolayers and decreased the adhesion and invasion of the coliform in IPEC-1 cells. In addition, L. reuteri LR1 increased transcript abundance and protein contents of tight junction (TJ) proteins zonula occluden-1 (ZO-1) and occludin in ETEC K88-infected IPEC-1 cells, whereas it had no effects on claudin-1 and F-actin expression. Using colloidal gold immunoelectron microscopy, these effects of L. reuteri LR1 on ZO-1 and occludin content in IPEC-1 cells were confirmed. By using ML-7, a selective inhibitor of myosin light-chain kinase (MLCK), the beneficial effect of L. reuteri LR1 on contents of ZO-1 and occludin was shown to be dependent on the MLCK pathway. In conclusion, L. reuteri LR1 had beneficial effects on epithelial barrier function consistent with increasing ZO-1 and occludin expression via a MLCK-dependent manner in IPEC-1 cells during challenge with ETEC K88.

ML-7 attenuates airway inflammation and remodeling via inhibiting the secretion of Th2 cytokines in mice model of asthma

Previous studies have indicated that smooth muscle myosin light chain kinase (MLCK) has a prominent role in the regulation of smooth muscle contraction, which tends to be upregulated in asthma. In recent years, numerous studies have reported that MLCK is intimately connected with the immunoregulatory mechanism of T cells. The imbalance of T helper type 1 cells (Th1)/Th2 constitutes the immune-associated pathological basis of chronic asthma. Th2-associated cytokines, including interleukin-4, −5, −13, −25 and −33, are involved in airway inflammation, hyperresponsiveness and remodeling, which leads to a progressive decline in lung function. The purpose of the present study was to verify whether inhibition of bronchial MLCK attenuated the expression Th2-associated cytokines in asthmatic mice, including the above-mentioned ones. Female BALB/c mice were used to establish an ovalbumin (OVA)-induced model of asthma, of which one group was treated with the MLCK inhibitor (5-iodonaphthalene-1-sulfonyl) homopiperazine (ML-7). The inhibitor of MLCK, ML-7 attenuated airway inflammation and remodeling by reducing inflammatory cell infiltration and the secretion of Th2 cytokines in mice model of asthma, which may represent a promising therapeutic strategy for asthma.

Monocytic cell junction proteins serve important roles in atherosclerosis via the endoglin pathway

The formation of atherosclerosis is recognized to be caused by multiple factors including pathogenesis in monocytes during inflammation. The current study provided evidence that monocytic junctions were significantly altered in patients with atherosclerosis, which suggested an association between cell junctions and atherosclerosis. Claudin‑1, occludin‑1 and ZO‑1 were significantly enhanced in atherosclerosis, indicating that the tight junction pathway was activated during the pathogenesis of atherosclerosis. In addition, the gene expression of 5 connexin members involved in the gap junction pathway were quantified, indicating that connexin 43 and 46 were significantly up‑regulated in atherosclerosis. Furthermore, inflammatory factors including endoglin and SMAD were observed, suggesting that immune regulative factors were down‑regulated in this pathway. Silicon‑based analysis additionally identified that connexins and tight junctions were altered in association with monocytic inflammation regulations, endoglin pathway. The results imply that reduced expression of the immune regulation pathway in monocytes is correlated with the generation of gap junctions and tight junctions which serve important roles in atherosclerosis.

Myosin Light Chain Kinase: A Potential Target for Treatment of Inflammatory Diseases

Myosin light chain kinase (MLCK) induces contraction of the perijunctional apical actomyosin ring in response to phosphorylation of the myosin light chain. Abnormal expression of MLCK has been observed in respiratory diseases, pancreatitis, cardiovascular diseases, cancer, and inflammatory bowel disease. The signaling pathways involved in MLCK activation and triggering of endothelial barrier dysfunction are discussed in this review. The pharmacological effects of regulating MLCK expression by inhibitors such as ML-9, ML-7, microbial products, naturally occurring products, and microRNAs are also discussed. The influence of MLCK in inflammatory diseases starts with endothelial barrier dysfunction. The effectiveness of anti-MLCK treatment may depend on alleviation of that primary pathological mechanism. This review summarizes evidence for the potential benefits of anti-MLCK agents in the treatment of inflammatory disease and the importance of avoiding treatment-related side effects, as MLCK is widely expressed in many different tissues.

Tongxinluo Reverses the Hypoxia-suppressed Claudin-9 in Cardiac Microvascular Endothelial Cells

Background:

Claudin-5, claudin-9, and claudin-11 are expressed in endothelial cells to constitute tight junctions, and their deficiency may lead to hyperpermeability, which is the initiating process and pathological basis of cardiovascular disease. Although tongxinluo (TXL) has satisfactory antianginal effects, whether and how it modulates claudin-5, claudin-9, and claudin-11 in hypoxia-stimulated human cardiac microvascular endothelial cells (HCMECs) have not been reported.

Methods:

In this study, HCMECs were stimulated with CoCl₂ to mimic hypoxia and treated with TXL. First, the messenger RNA (mRNA) expression of claudin-5, claudin-9, and claudin-11 was confirmed. Then, the protein content and distribution of claudin-9, as well as cell morphological changes were evaluated after TXL treatment. Furthermore, the distribution and content histone H3K9 acetylation (H3K9ac) in the claudin-9 gene promoter, which guarantees transcriptional activation, were examined to explore the underlying mechanism, by which TXL up-regulates claudin-9 in hypoxia-stimulated HCMECs.

Results:

We found that hypoxia-suppressed claudin-9 gene expression in HCMECs (F = 7.244; P = 0.011) and the hypoxia-suppressed claudin-9 could be reversed by TXL (F = 61.911; P = 0.000), which was verified by its protein content changes (F = 29.142; P = 0.000). Moreover, high-dose TXL promoted the cytomembrane localization of claudin-9 in hypoxia-stimulated HCMECs, with attenuation of cell injury. Furthermore, high-dose TXL elevated the hypoxia-inhibited H3K9ac in the claudin-9 gene promoter (F = 37.766; P = 0.000), activating claudin-9 transcription.

Conclusions:

The results manifested that TXL reversed the hypoxia-suppressed claudin-9 by elevating H3K9ac in its gene promoter, playing protective roles in HCMECs.

High glucose decreases claudins-5 and -11 in cardiac microvascular endothelial cells: Antagonistic effects of tongxinluo

Purpose/aim of the study: Claudins-5, -9, and -11 are tight-junction proteins that are mainly expressed in endothelial cells. Their deficiency may lead to cell barrier dysfunction, which is considered as the initiating process and pathological basis of cardiovascular disease in diabetes. We investigated whether high glucose (HG) affects claudins-5, -9, and -11 in human cardiac microvascular endothelial cells (HCMECs), and examined the effects of the traditional Chinese medication tongxinluo (TXL) on these tight junction proteins.

MATERIALS AND METHODS

HCMECs were exposed to HG with and without TXL treatment, and then mRNA and protein levels of claudins-5, -9, and -11 were examined. The distribution of claudins-5 and -11 was also investigated. Histone H3K9 acetylation (H3K9ac) in claudin-5 and claudin-11 gene promoters, which functions in transactivation, was measured.

RESULTS

We found that HG suppressed claudins-5 and -11 gene expression in HCMECs, and TXL reversed the HG-mediated inhibition of claudins-5 and -11 mRNA and protein expressions. Treatment with high-dose of TXL promoted cell membrane localization of claudins-5 and -11 in HG-stimulated HCMECs. Furthermore, high-dose of TXL blocked the inhibition of H3K9ac in claudin-5 and claudin-11 gene promoters caused by exposure to HG, thus activating gene transcription.

CONCLUSIONS

Our results show that HG suppressed claudins-5 and -11 in HCMECs, and TXL could reverse the HG-induced suppression of claudins-5 and -11 by increasing H3K9ac in their respective gene promoters.

Regulation of pulmonary endothelial barrier function by kinases

The pulmonary endothelium is the target of continuous physiological and pathological stimuli that affect its crucial barrier function. The regulation, defense, and repair of endothelial barrier function require complex biochemical processes. This review examines the role of endothelial phosphorylating enzymes, kinases, a class with profound, interdigitating influences on endothelial permeability and lung function.

Phosphorylated Myosin Light Chain 2 (p-MLC2) as a Molecular Marker of Antemortem Coronary Artery Spasm

Background

It is not uncommon that only mild coronary artery stenosis is grossly revealed after a system autopsy. While coronary artery spasm (CAS) is the suspected mechanism of these deaths, no specific biomarker has been identified to suggest antemortem CAS.

Material/Methods

To evaluate the potential of using phosphorylated myosin light chain 2 (p-MLC2) as a diagnostic marker of antemortem CAS, human vascular smooth muscle cells (VSMCs) were cultured and treated with common vasoconstrictors, including prostaglandins F2α (PGF2α), acetylcholine (ACh), and 5-hydroxy tryptamine (5-HT). The p-MLC2 level was examined in the cultured cells using Western blot analysis and in a rat model of spasm provocation tests using immunohistochemistry (IHC). Effects of increased p-MLC2 level on VSMCs contractile activities were assessed in vitro using confocal immunofluorescence assay. Four fatal cases with known antemortem CAS were collected and subject to p-MLC2 detection.

Results

The p-MLC2 was significantly increased in VSMCs after treatments with vasoconstrictors and in the spasm provocation tests. Myofilament was well-organized and densely stained in VSMCs with high p-MLC2 level, but disarrayed in VSMCs with low p-MLC2 level. Three of the 4 autopsied cases showed strongly positive staining of p-MLC2 at the stenosed coronary segment and the adjacent interstitial small arteries. The fourth case was autopsied at the 6th day after death and showed negative-to-mild positive staining of p-MLC2.

Conclusions

p-MLC2 might be a useful marker for diagnosis of antemortem CAS. Autopsy should be performed as soon as possible to collect coronary arteries for detection of p-MLC2.

Non-muscle myosin light chain promotes endothelial progenitor cells senescence and dysfunction in pulmonary hypertensive rats through up-regulation of NADPH oxidase

Non-muscle myosin regulatory light chain (nmMLC20) is reported to exert transcriptional function in regulation of gene expression, and NADPH oxidase (NOX)-derived reactive oxygen species contribute to vascular remodeling of pulmonary artery hypertension (PAH). This study aims to determine if nmMLC20 can promote endothelial progenitor cells (EPCs) senescence and dysfunction through up-regulation of NOX in PAH rats. The rats were exposed to10% hypoxia for 3 weeks to establish a PAH model, which showed an increase in right ventricle systolic pressure, right ventricular and pulmonary vascular remodeling, and the accelerated senescence and impaired functions in EPCs, accompanied by an increase in Rho-kinase (ROCK) and NOX activities, p-nmMLC20 level, NOX expression and H2O2 content; these phenomena were reversed by fasudil, a selective inhibitor of ROCK. Next, normal EPCs were cultured under hypoxia to induce senescence in vitro. Consistent with the in vivo findings, hypoxia increased the senescence and dysfunction of EPCs concomitant with an increase in ROCK and NOX activities, p-nmMLC20 level, NOX expression and H2O2 content; these phenomena were reversed by fasudil. Knockdown of nmMLC20 showed similar results to that of fasudil except no effect on ROCK activity. Based on these observations, we conclude that nmMLC20 could promote the senescence and dysfunctions of EPCs in PAH through up-regulation of NOX in a phosphorylation-dependent manner.

Role of myosin light chain kinase in hypertriglyceridemia-associated acute pancreatitis in rats

AIM: To investigate the role of myosin light chain kinase (MLCK) in hypertriglyceridemia-associated acute pancreatitis (HTGP).

METHODS: Forty-eight male SD rats were randomly divided into two groups to be fed either a high-fat diet (group A) or a normal diet (group B). After being raised for 4 weeks, blood was harvested from the retroorbital venous plexus to measure serum triglyceride (TG) levels. After that, group A was randomly divided into three subgroups: HTG, HTG + AP, and HTG + AP + ML-7; group B were also randomly divided into three subgroups: C, AP, and AP + ML-7. All rats were sacrificed 24 h after the last injection of cerulein. The pancreases were carefully removed for HE staining and transmission electron microscopy to observe the morphological changes, ultrastructure and tight junction (TJ). Blood was obtained from the heart to measure serum amylase levels. The expression and localization of MLCK and p-JNK in the pancreas were assayed by immunohistochemistry.

RESULTS: Compared with group B, serum TG level was significantly increased in group A after being fed a high fat diet (P < 0.01). The pathologic score of the pancreas and serum amylase (AMY) activity were significantly elevated in the HTG + AP group, compared with the AP group (P < 0.05). The ultrastructure of the pancreas in the HTG + AP and AP groups was damaged and the TJ was broadened (most significant in the HTG + AP group). Besides, MLCK and p-JNK were significantly up-regulated in the HTG + AP group compared with those in the AP group (P < 0.05), and there was a positive correlation between the expression of MLCK and p-JNK in the pancreas and the pathologic score of the pancreas (r₁ = 0.795, r₂ = 0.789, P < 0.01). ML-7, an inhibitor of MLCK, significantly ameliorated the pathologic signs of the pancreas, down-regulated AMY level (P < 0.01), improved the TJ and decreased the expression of p-JNK (P < 0.05).

CONCLUSION: MLCK may be associated with the severity of HTGP, and involved in the formation of HTGP by broadening cell-cell TJ and activation of the JNK pathway.