Mechanisms of nitric oxide interplay with Rho GTPase family members in modulation of actin membrane dynamics in pericytes and fibroblasts

Mechanobiology of portal hypertension

The interplay between mechanical stimuli and cellular mechanobiology orchestrates the physiology of tissues and organs in a dynamic balance characterized by constant remodelling and adaptative processes. Environmental mechanical properties can be interpreted as a complex set of information and instructions that cells read continuously, and to which they respond. In cirrhosis, chronic inflammation and injury drive liver cells dysfunction, leading to excessive extracellular matrix deposition, sinusoidal pseudocapillarization, vascular occlusion and parenchymal extinction. These pathological events result in marked remodelling of the liver microarchitecture, which is cause and result of abnormal environmental mechanical forces, triggering and sustaining the long-standing and progressive process of liver fibrosis. Multiple mechanical forces such as strain, shear stress, and hydrostatic pressure can converge at different stages of the disease until reaching a point of no return where the fibrosis is considered non-reversible. Thereafter, reciprocal communication between cells and their niches becomes the driving force for disease progression. Accumulating evidence supports the idea that, rather than being a passive consequence of fibrosis and portal hypertension (PH), mechanical force-mediated pathways could themselves represent strategic targets for novel therapeutic approaches. In this manuscript, we aim to provide a comprehensive review of the mechanobiology of PH, by furnishing an introduction on the most important mechanisms, integrating these concepts into a discussion on the pathogenesis of PH, and exploring potential therapeutic strategies.

Establishment of fibroblast and myofibroblast phenotypes for use in in vitro co-culture models

Fibroblasts function to secrete and modify components of the extracellular matrix. During wound healing, fibroblasts migrate to the site of injury and differentiate into contractile myofibroblasts; this differentiation is characterised by an increased contractile capacity. Fully differentiated myofibroblasts can be distinguished from fibroblasts via the higher expression of α-smooth muscle actin as well as a denser cytoskeleton. Impaired wound healing has been characterised by a lack of myofibroblasts; as a result, tissue does not fully regain its strength and function. Under pathological conditions, this may be associated with the effect that a pro-inflammatory microenvironment has on fibroblast and skeletal muscle progenitor cell migration and differentiation. Given their distinct roles in tissue maintenance and repair, the communication between fibroblasts versus myofibroblasts with other cellular mediators of repair is likely to influence cell behaviour and the outcome of wound repair. An in vitro test model is required to investigate this intercellular influence, but the establishment of such a model is hampered by the difficulty in retaining the dedifferentiated fibroblastic phenotype under regular serum-containing cell culture conditions. We present a model that supports the establishment and retention in culture of fibroblast and myofibroblast phenotypes for use in a simple, inexpensive, yet relevant in vitro 2D assay. This model is then applied in a co-culture setting to determine whether the presence of myoblasts affects the ability of fibroblasts versus myofibroblasts to close an in vitro wound. Our results emphasize the importance of considering the impact of paracrine communication between all cells during wound healing.

Cytoskeletal Arrest: An Anoxia Tolerance Mechanism

Polymerization of actin filaments and microtubules constitutes a ubiquitous demand for cellular adenosine-5′-triphosphate (ATP) and guanosine-5′-triphosphate (GTP). In anoxia-tolerant animals, ATP consumption is minimized during overwintering conditions, but little is known about the role of cell structure in anoxia tolerance. Studies of overwintering mammals have revealed that microtubule stability in neurites is reduced at low temperature, resulting in withdrawal of neurites and reduced abundance of excitatory synapses. Literature for turtles is consistent with a similar downregulation of peripheral cytoskeletal activity in brain and liver during anoxic overwintering. Downregulation of actin dynamics, as well as modification to microtubule organization, may play vital roles in facilitating anoxia tolerance. Mitochondrial calcium release occurs during anoxia in turtle neurons, and subsequent activation of calcium-binding proteins likely regulates cytoskeletal stability. Production of reactive oxygen species (ROS) formation can lead to catastrophic cytoskeletal damage during overwintering and ROS production can be regulated by the dynamics of mitochondrial interconnectivity. Therefore, suppression of ROS formation is likely an important aspect of cytoskeletal arrest. Furthermore, gasotransmitters can regulate ROS levels, as well as cytoskeletal contractility and rearrangement. In this review we will explore the energetic costs of cytoskeletal activity, the cellular mechanisms regulating it, and the potential for cytoskeletal arrest being an important mechanism permitting long-term anoxia survival in anoxia-tolerant species, such as the western painted turtle and goldfish.

Comparative proteome analyses highlight several exercise-like responses of mouse sciatic nerve after IP injection of irisin

Many beneficial effects of exercise on the nervous system are mediated by hormone (growth factor)/receptor signaling. Considering the accumulating evidence on the similarity of some beneficial effects, irisin can be a proposed effector of exercise; however, the mechanism underlying these effects remains largely unknown. More evidence on the mechanism of action might reveal its potential as a treatment strategy to substitute exercise recovery protocols for nerve injuries in physically disabled patients. To evaluate the underlying mechanism of irisin involvement in nerve adaptation and exerting beneficial effects, we studied the proteome profile alteration of mouse sciatic nerve after irisin administration. We also compared it with two 8-week protocols of resistance exercise and endurance exercise. The results indicate that irisin contributes to the regulation of nerve metabolism via overexpression of Ckm and ATP5j2 proteins. Irisin administration may improve sciatic nerve function by maintaining the architecture, enhancing axonal transport, and promoting synapse plasticity through increased structural and regulatory proteins and NO production. We also showed that irisin has the potential to induce neurotrophic support on the sciatic nerve by maintaining cell redox homeostasis, and responses to oxidative stress via the upregulation of disulfide-isomerase and superoxide dismutase enzymes. Comparing with exercise groups, these effects are somewhat exercise-like responses. These data suggest that irisin can be a promising therapeutic candidate for specific targeting of defects in peripheral neuropathies and nerve injuries as an alternative for physical therapy.

Implications of microgravity-induced cell signaling alterations upon cancer cell growth, invasiveness, metastatic potential, and control by host immunity

The human endeavor to venture beyond the orbit of Earth is challenged by both continuous space radiation and microgravity-induced immune dysfunction. If cancers were to develop in astronauts, it is unclear how these abnormal cells would grow and progress in the microgravity environment. It is unknown if the astronaut's immune response would be able to control or eradicate cancer. A better molecular understanding of how the mechanical force of gravity affects the cell as well as the aggressiveness of cancers and the functionality of host immunity is needed. This review will summarize findings related to microgravity-mediated alterations in the cell cytoskeleton, cell-cell, and cell-extracellular matrix interactions including cadherins, immunoglobulin superfamily of adhesion molecules, selectins, and integrins and related cell signaling. The effects of spaceflight and simulated microgravity on cell viability, cancer cell growth, invasiveness, angiogenesis, metastasis as well as immune cell functions and the subsequent signaling pathways involved will be discussed. Microgravity-induced alterations in function and signaling of the major anti-cancer immune populations will be examined including natural killer cells, dendritic cells, CD4⁺ T cells, and CD8⁺ T cells. Further studies regarding the molecular events impacted by microgravity in both cancer and immune cells will greatly increase the development of therapies to restrict tumor growth and enhance cancer-specific responses for both astronauts and patients on Earth.

Sodium nitroprusside prevents the detrimental effects of glucose on the neurovascular unit and behaviour in zebrafish

Diabetes is associated with dysfunction of the neurovascular unit, although the mechanisms of this are incompletely understood and currently no treatment exists to prevent these negative effects. We previously found that the nitric oxide (NO) donor sodium nitroprusside (SNP) prevents the detrimental effect of glucose on neurovascular coupling in zebrafish. We therefore sought to establish the wider effects of glucose exposure on both the neurovascular unit and on behaviour in zebrafish, and the ability of SNP to prevent these. We incubated 4-days post-fertilisation (dpf) zebrafish embryos in 20 mM glucose or mannitol for 5 days until 9 dpf, with or without 0.1 mM SNP co-treatment for 24 h (8-9 dpf), and quantified vascular NO reactivity, vascular mural cell number, expression of a klf2a reporter, glial fibrillary acidic protein (GFAP) and transient receptor potential cation channel subfamily V member 4 (TRPV4), as well as spontaneous neuronal activation at 9 dpf, all in the optic tectum. We also assessed the effect on light/dark preference and locomotory characteristics during free-swimming studies. We find that glucose exposure significantly reduced NO reactivity, klf2a reporter expression, vascular mural cell number and TRPV4 expression, while significantly increasing spontaneous neuronal activation and GFAP expression (all in the optic tectum). Furthermore, when we examined larval behaviour, we found that glucose exposure significantly altered light/dark preference and high and low speed locomotion while in light. Co-treatment with SNP reversed all these molecular and behavioural effects of glucose exposure. Our findings comprehensively describe the negative effects of glucose exposure on the vascular anatomy, molecular phenotype and function of the optic tectum, and on whole-organism behaviour. We also show that SNP or other NO donors may represent a therapeutic strategy to ameliorate the complications of diabetes on the neurovascular unit.This article has an associated First Person interview with the first author of the paper.

Impact of endothelial nitric oxide synthase polymorphisms on urothelial cell carcinoma development

OBJECTIVES

Urothelial cell carcinoma (UCC), a major malignancy of the genitourinary tract, is induced through carcinogenic etiological factors. Endothelial nitric oxide synthase (eNOS) is one of the major isoforms of nitric oxide synthase and is involved in various pathophysiologic and physiologic processes. In this study, eNOS single-nucleotide polymorphisms were investigated to evaluate UCC susceptibility and clinicopathological characteristics.

MATERIALS AND METHODS

Two single-nucleotide polymorphisms of eNOS in 431 patients with UCC and 862 controls without cancer were analyzed using real-time polymerase chain reaction.

RESULTS

The results showed that 272 men with UCC having eNOS 894 G > T rs1799983 "GT + TT" variants had a high risk of developing a large tumor (T1-T4, P = 0.038). Furthermore, a correlation was observed between the expressions of eNOS and invasive tumor, metastasis and poor survival in urothelial carcinoma in The Cancer Genome Atlas data set.

CONCLUSION

Our results indicated that male patients with UCC carrying eNOS 894 G > T rs1799983 "GT + TT" genetic variants have a high risk of developing a large tumor, and eNOS polymorphisms may serve as a marker or therapeutic target in UCC treatment.

Biology of portal hypertension

Portal hypertension develops as a result of increased intrahepatic vascular resistance often caused by chronic liver disease that leads to structural distortion by fibrosis, microvascular thrombosis, dysfunction of liver sinusoidal endothelial cells (LSECs), and hepatic stellate cell (HSC) activation. While the basic mechanisms of LSEC and HSC dysregulation have been extensively studied, the role of microvascular thrombosis and platelet function in the pathogenesis of portal hypertension remains to be clearly characterized. As a secondary event, portal hypertension results in splanchnic and systemic arterial vasodilation, leading to the development of a hyperdynamic circulatory syndrome and subsequently to clinically devastating complications including gastroesophageal varices and variceal hemorrhage, hepatic encephalopathy from the formation of portosystemic shunts, ascites, and renal failure due to the hepatorenal syndrome. This review article discusses: (1) mechanisms of sinusoidal portal hypertension, focusing on HSC and LSEC biology, pathological angiogenesis, and the role of microvascular thrombosis and platelets, (2) the mesenteric vasculature in portal hypertension, and (3) future directions for vascular biology research in portal hypertension.

MeHg affects the activation of FAK, Src, Rac1 and Cdc42, critical proteins for cell movement in PDGF-stimulated SH-SY5Y neuroblastoma cells

Methylmercury (MeHg) is an environmental neurotoxicant that inhibits neuronal migration. This process requires several cyclic steps involving the formation of membrane protrusions (lamellipodia and filopodia) and focal adhesion turnover. FAK and Src are critical proteins that regulate both processes. The FAK-Src complex promotes the activation of Rac1 and Cdc42, two GTPases involved in the remodeling of the actin cytoskeletal network. Here, we studied the effect of MeHg (1, 10, 100, 500 and 1000nM) on cell migration, the formation of cell protrusions, focal adhesion location and the activation of FAK, Src, Rac1 and Cdc42 using the SH-SY5Y neuroblastoma cell line stimulated with PDGF-BB (PDGF). The data show that MeHg (1-500nM) inhibited PDGF-stimulated cell migration. In PDGF-stimulated cells, MeHg (100-1000nM) decreased protrusions and increased the size of the p-FAK^Y397 clusters. MeHg also inhibited PDGF-induced FAK and Src activation and, at 100nM, MeHg inhibited the activation of Rac1 and Cdc42. Altogether, the findings show that low concentrations of MeHg inhibit SH-SY5Y cell migration by disrupting the activation and disassembly of FAK. This negatively affects the activation of Src, Rac1 and Cdc42, all of which are critical proteins for the regulation of cell movement. These effects could be related to the MeHg-mediated inhibition of PDGF-induced formation of lamellipodia and filopodia, focal adhesion disassembly and PDGF-induced movement.

Proteinase-activated receptor 2 (PAR2) in hepatic stellate cells - evidence for a role in hepatocellular carcinoma growth in vivo

BACKGROUND

Previous studies have established that proteinase-activated receptor 2 (PAR2) promotes migration and invasion of hepatocellular carcinoma (HCC) cells, suggesting a role in HCC progression. Here, we assessed the impact of PAR2 in HCC stromal cells on HCC growth using LX-2 hepatic stellate cells (HSCs) and Hep3B cells as model.

METHODS

PAR2 expression and function in LX-2 cells was analysed by RT-PCR, confocal immunofluorescence, electron microscopy, and [Ca(2+)]i measurements, respectively. The impact of LX-2-expressed PAR2 on tumour growth in vivo was monitored using HCC xenotransplantation experiments in SCID mice, in which HCC-like tumours were induced by coinjection of LX-2 cells and Hep3B cells. To characterise the effects of PAR2 activation in LX-2 cells, various signalling pathways were analysed by immunoblotting and proteome profiler arrays.

RESULTS

Following verification of functional PAR2 expression in LX-2 cells, in vivo studies showed that these cells promoted tumour growth and angiogenesis of HCC xenografts in mice. These effects were significantly reduced when F2RL1 (encoding PAR2) was downregulated by RNA interference (RNAi). In vitro studies confirmed these results demonstrating RNAi mediated inhibition of PAR2 attenuated Smad2/3 activation in response to TGF-β1 stimulation in LX-2 cells and blocked the pro-mitotic effect of LX-2 derived conditioned medium on Hep3B cells. Furthermore, PAR2 stimulation with trypsin or a PAR2-selective activating peptide (PAR2-AP) led to activation of different intracellular signalling pathways, an increased secretion of pro-angiogenic and pro-mitotic factors and proteinases, and an enhanced migration rate across a collagen-coated membrane barrier. Silencing F2RL1 by RNAi or pharmacological inhibition of Src, hepatocyte growth factor receptor (Met), platelet-derived growth factor receptor (PDGFR), p42/p44 mitogen activated protein kinase (MAPK) or matrix-metalloproteinases (MMPs) blocked PAR2-AP-induced migration.

CONCLUSION

PAR2 in HSCs plays a crucial role in promoting HCC growth presumably by mediating migration and secretion of pro-angiogenic and pro-mitotic factors. Therefore, PAR2 in stromal HSCs may have relevance as a therapeutic target of HCC.

MiR-29a Assists in Preventing the Activation of Human Stellate Cells and Promotes Recovery From Liver Fibrosis in Mice

The microRNA-29 (miR-29) family is known to suppress the activation of hepatic stellate cells (HSCs) and reversibly control liver fibrosis; however, the mechanism of how miR-29a controls liver fibrosis remains largely unknown. This study was conducted to clarify the mechanism of anti-fibrotic effect of miR-29a and to explore if miR-29a is a promising candidate for nucleic acid medicine against liver fibrosis. Two liver fibrosis murine models (carbon tetrachloride or thioacetamide) were used. MiR-29a mixed with atelocollagen was systemically administered. Hepatic fibrosis was evaluated by histological analysis and the expression levels of fibrosis-related genes. We observed that miR-29a treatment dramatically accelerated the reversion of liver fibrosis in vivo. Additionally, miR-29a regulated the mRNA expression of collagen type I alpha 1 (COL1A1) and platelet-derived growth factor C (PDGFC). We also noted that miR-29a significantly suppressed COL1A1 mRNA expression and cell viability and significantly increased caspase-9 activity (P < 0.05) in LX-2 cells. Pretreatment of miR-29a inhibited activation of LX-2 cell by transforming growth factor beta treatment. MiR-29a exhibited anti-fibrotic effect without cell toxicity in vivo and directly suppressed the expression of PDGF-related genes as well as COL1A1 and induced apoptosis of LX-2 cells. MiR-29a is a promising nucleic acid inhibitor to target liver fibrosis.

Thalidomide Improves the Intestinal Mucosal Injury and Suppresses Mesenteric Angiogenesis and Vasodilatation by Down-Regulating Inflammasomes-Related Cascades in Cirrhotic Rats

Background and Aims

By blocking TNFα-related effects, thalidomide not only inhibits hepatic fibrogenesis but improves peripheral vasodilatation and portal hypertension in cirrhotic rats. Nonetheless, the investigation of thalidomide's effects on splanchnic and collateral microcirculation has been limited. Our study explored the roles of intestinal and mesenteric TNFα along with inflammasome-related pathway in relation to cirrhosis and the splanchnic/collateral microcirculation.

Methods

Using in vivo and in vitro approaches, mechanisms of the effects of thalidomide on intestinal and mesenteric inflammatory, vasodilatory and angiogenic cascades-related abnormalities were explored in cirrhotic rats that had received 1-month thalidomide (C-T) treatment.

Results

In cirrhotic rats, high tumor necrosis factor (TNF)α, vascular endothelial growth factor (VEGF) and nitric oxide (NO)x levels were associated with the NOD-like receptors protein 3 (NLRP3), IL-1β and caspase-1 inflammasome over-expression in splenorenal shunt and mesenteric tissues. The thalidomide-related inhibition of mesenteric and splenorenal shunt inflammasome expression was accompanied by a significantly decreased intestinal mucosal injury and inflammasome immunohistochemical staining expression. Suppression of various angiogenic cascades, namely VEGF-NOS-NO, was paralleled by a decrease in mesenteric angiogenesis as detected by CD31 immunofluorescence staining and by reduced portosystemic shunting (PSS) in C-T rats. The down-regulation of the mesenteric and collateral vasodilatory VEGF-NOS-NO cascades resulted in a correction of vasoconstrictive hypo-responsiveness and in an attenuation of vasodilatory hyper-responsiveness when analyzed by in situ perfusion of the superior mesenteric arterial (SMA) and portosystemic collaterals. There was also a decrease in SMA blood flow and an increase in SMA resistance in the C-T rats. Additionally, acute incubation with thalidomide abolished TNFα-augmented VEGF-mediated migration of and tube formation of human umbilical vein endothelial cells, which was accompanied by corresponding changes in inflammatory and angiogenic substances release.

Conclusions

The suppression of inflammasome over-expression by chronic thalidomide treatment ameliorates inflammatory, angiogenic and vasodilatory cascades-related pathogenic changes in the splanchnic and collateral microcirculation of cirrhotic rats. Thalidomide seems to be a promising agent that might bring about beneficial changes to the disarrangements of peripheral, hepatic, splanchnic and collateral systems in cirrhosis.

Leukocytes: The Double-Edged Sword in Fibrosis

Skin tissue scar formation and fibrosis are often characterized by the increased production and deposition of extracellular matrix components, accompanied by the accumulation of a vast number of myofibroblasts. Scaring is strongly associated with inflammation and wound healing to regain tissue integrity in response to skin tissue injury. However, increased and uncontrolled inflammation, repetitive injury, and individual predisposition might lead to fibrosis, a severe disorder resulting in the formation of dense and stiff tissue that loses the physical properties and physiological functions of normal tissue. Fibrosis is an extremely complicated and multistage process in which bone marrow-derived leukocytes act as both pro- and antifibrotic agents, and therefore, few, if any, effective therapies are available for the most severe and lethal forms of fibrosis. Herein, we discuss the current knowledge on the multidimensional impact of leukocytes on the induction of fibrosis, focusing on skin fibrosis.

L-Plastin S-glutathionylation promotes reduced binding to β-actin and affects neutrophil functions

Posttranslational modifications (PTMs) of cytoskeleton proteins due to oxidative stress associated with several pathological conditions often lead to alterations in cell function. The current study evaluates the effect of nitric oxide (DETA-NO)-induced oxidative stress-related S-glutathionylation of cytoskeleton proteins in human PMNs. By using in vitro and genetic approaches, we showed that S-glutathionylation of L-plastin (LPL) and β-actin promotes reduced chemotaxis, polarization, bactericidal activity, and phagocytosis. We identified Cys-206, Cys-283, and Cys-460as S-thiolated residues in the β-actin-binding domain of LPL, where cys-460 had the maximum score. Site-directed mutagenesis of LPL Cys-460 further confirmed the role in the redox regulation of LPL. S-Thiolation diminished binding as well as the bundling activity of LPL. The presence of S-thiolated LPL was detected in neutrophils from both diabetic patients and db/db mice with impaired PMN functions. Thus, enhanced nitroxidative stress may results in LPL S-glutathionylation leading to impaired chemotaxis, polarization, and bactericidal activity of human PMNs, providing a mechanistic basis for their impaired functions in diabetes mellitus.

Adiponectin attenuates liver fibrosis by inducing nitric oxide production of hepatic stellate cells

Adiponectin protects against liver fibrosis, but the mechanisms have not been fully elucidated. Here, we showed that adiponectin upregulated inducible nitric oxide synthase (iNOS) messenger RNA (mRNA) and protein expression in hepatic non-parenchymal cells, particularly in hepatic stellate cells (HSCs), and increased nitric oxide (NO2-/NO3-) concentration in HSC-conditioned medium. Adiponectin attenuated HSC proliferation and migration but promoted apoptosis in a NO-dependent manner. More advanced liver fibrosis with decreased iNOS/NO levels was observed in adiponectin knockout mice comparing to wide-type mice when administered with CCI4 while NO donor supplementation rescued the phenotype. Further experiments demonstrated that adiponectin-induced iNOS/NO system activation is mediated through adipoR2-AMPK-JNK/Erk1/2-NF-κB signaling. These data suggest that adiponectin inhibits HSC function, further limiting the development of liver fibrosis at least in part through adiponectin-induced NO release. Therefore, adiponectin-mediated NO signaling may be a novel target for the treatment of liver fibrosis.

KEY MESSAGES

• Adiponectin activates HSC iNOS/NO and SEC eNOS/NO systems. • Adiponectin inhibits HSC proliferation and migration but promotes its apoptosis. • Adiponectin inhibits CCL4-induced liver fibrosis by modulation of liver iNOS/NO. • Adiponectin stimulates HSC iNOS/NO via adipoR2-AMPK-JNK/ErK1/2-NF-κB pathway.

Sodium Ferulate Reduces Portal Pressure Through Inhibition of RhoA/Rho-Kinase and Activation of Endothelial Nitric Oxide Synthase in Cirrhotic Rats

BACKGROUND AND AIMS

Recent studies have demonstrated that increased RhoA/Rho-kinase activity and reduced nitric oxide activity have the necessary machinery to induce cirrhosis. However, it is unclear whether this regulates the functions of hepatic stellate cells (HSCs). In this study, we used sodium ferulate (SF) in a cirrhotic rat model and examined its roles in regulating RhoA activation in HSCs and the subsequent effects on contraction of HSCs.

METHODS

Bile duct ligation method was used to induce cirrhosis in rats. Intrahepatic resistance was investigated in in situ perfused livers. Hepatic RhoA, Rho-kinase and eNOS expressions were studied by RT-PCR and Western blot. RhoA pull-down assay and collagen gel contraction assay of HSCs were performed by incubation with SF in the absence or presence of GGPP.

RESULTS

We showed that in cirrhotic liver, SF can efficiently affect RhoA activation via lowering the synthesis of GGPP in HSCs. These actions effectively reduced basal intrahepatic resistance in cirrhotic rats. Our study further suggested that SF effectively decreased Rho-kinase activity and increased activity of eNOS at both the mRNA and protein levels. SF treatment of HSCs reduced RhoA GTP without affecting the total RhoA protein level, and GGPP had the ability to block SF-induced protein expression. Furthermore, SF inhibited the contraction of activated HSCs and this inhibition was efficiently reversed by addition of GGPP.

CONCLUSIONS

SF inhibits hepatic RhoA/Rho-kinase signaling and activates the NO/PKG pathway in cirrhotic rats. This may serve as a mechanism for reducing the contraction of activated HSCs upon SF treatment.

Nitric oxide enhances keratinocyte cell migration by regulating Rho GTPase via cGMP-PKG signalling

Objective

Nitric oxide (NO) has been shown to improve wound healing, but the mechanism underlying this function is not well defined. Here, we explored the effect of NO on the migration of a human keratinocyte cell line (HaCaT) and its possible mechanism.

Methods

The effects of NO on HaCaT cells in the presence of different concentrations of the NO donor sodium nitroprusside (SNP) were evaluated in a cell migration assay. Subsequently, the cytoskeleton reorganization of cultured HaCaT cells stained with rhodamine-phalloidin was observed with a confocal laser scanning microscope. The mRNA expression and active proteins of CDC42, Rac1 and RhoA in the cultured cells were determined via RT-PCR and pull-down assays, respectively. Furthermore, the roles of various inhibitors or agonists specific to cGMP, PKG and CDC42, Rac1, RhoA in the effects of NO on HaCaT cell migration, F-actin stress fibre formation, and Rho GTPase expression were observed.

Results

It was also found HaCaT cell migration was increased by SNP in a dose-dependent manner, and the other two NO donors either spermine NONOate or SNAP had almost the same effects on HaCat cell migrations. The formation of F-actin stress fibres in SNP-treated HaCaT cells was increased. The mRNA expression and the active proteins of CDC42, Rac1 and RhoA were found to be upregulated after SNP treatment. Similar effects were observed after the cells were treated with a cGMP or PKG agonist. Additionally, the SNP-mediated upregulation of the mRNA expression and the active proteins of CDC42, Rac1 and RhoA were inhibited by the addition of an inhibitor of cGMP or PKG. Moreover, the SNP-mediated promoting effects of migration and cytoskeleton reorganization were inhibited by treatment with inhibitors of cGMP, PKG, CDC42, Rac1 and RhoA respectively.

Conclusion

Our data indicated that the stimulatory effects of NO on cell migration of HaCaT cells are mediated by the cGMP signalling pathway via the upregulation of Rho-GTPase expression, which might promote cytoskeleton reorganization.

Hepatic stellate cells and extracellular matrix in hepatocellular carcinoma: more complicated than ever

Hepatocellular carcinoma (HCC) is the fifth most common cancer worldwide and the third leading cause of cancer death. Recent epidemiological data indicate that the mortality rate of HCC will double over the next decades in the USA and Europe. Liver cancer progresses in a large percentage of cases during the clinical course of chronic fibro-inflammatory liver diseases leading to cirrhosis. Therefore, HCC development is regarded as the result of different environmental risk factors each involving different genetic, epigenetic- and chromosomal alterations and gene mutations. During tumour progression, the malignant hepatocytes and the activated hepatic stellate cells are accompanied by cancer-associated fibroblasts, myofibroblasts and immune cells generally called tumour stromal cells. This new and dynamic milieu further enhances the responsiveness of tumour cells towards soluble mediators secreted by tumour stromal cells, thus directly affecting the malignant hepatocytes. This results in altered molecular pathways with cell proliferation as the most important mechanism of liver cancer progression. Given this contextual complexity, it is of utmost importance to characterize the molecular pathogenesis of HCC, and to identify the dominant pathways/drivers and aberrant signalling pathways. This will allow an effective therapy for HCC that should combine strategies affecting both cancer and the tumour stromal cells. This review provides an overview of the recent challenges and issues regarding hepatic stellate cells, extracellular matrix dynamics, liver fibrosis/cirrhosis and therapy, tumour microenvironment and HCC.

In vitro anti-proliferative and anti-angiogenic activities of thalidomide dithiocarbamate analogs

Inhibition of angiogenesis is currently perceived as a promising strategy in the treatment of cancer. The anti-angiogenicity of thalidomide has inspired a second wave of research on this teratogenic drug. The present study aimed to investigate the anti-proliferative and anti-angiogenic activities of two thalidomide dithiocarbamate analogs by studying their anti-proliferative effects on human umbilical vein endothelial cells (HUVECs) and MDA-MB-231 human breast cancer cell lines. Their action on the expression levels of IL-6, IL-8, TNF-α, VEGF165, and MMP-2 was also assessed. Furthermore, their effect on angiogenesis was evaluated through wound healing, migration, tube formation, and nitric oxide (NO) assays. Results illustrated that the proliferation of HUVECs and MDA-MB-231 cells was not significantly affected by thalidomide at 6.25-100μM. Thalidomide failed to block angiogenesis at similar concentrations. By contrast, thalidomide dithiocarbamate analogs exhibited significant anti-proliferative action on HUVECs and MDA-MB-231 cells without causing cytotoxicity and also showed powerful anti-angiogenicity in wound healing, migration, tube formation, and NO assays. Thalidomide analogs 1 and 2 demonstrated more potent activity to suppress expression levels of IL-6, IL-8, TNF-α, VEGF165, and MMP-2 than thalidomide. Analog 1 consistently, showed the highest potency and efficacy in all the assays. Taken together, our results support further development and evaluation of novel thalidomide analogs as anti-tumor and anti-angiogenic agents.

Everolimus is a potent inhibitor of activated hepatic stellate cell functions in vitro and in vivo, while demonstrating anti-angiogenic activities

The present study demonstrates the therapeutic potential of everolimus for the treatment of hepatocellular carcinomas in the fibrotic liver by inhibiting hepatic stellate cell activation and angiogenesis.

Hepatic stellate cells and metastatic liver neoplasms

Hepatic stellate cells (HSCs) were first described in the 19th century as a type of multi-functional mesenchymal cells. They are considered as the component of liver microenvironment because of their capacity to differentiate into myofibroblasts which are highly proliferative and have collagen secretion capacity. This paper reviews the interactions between tumor cells and HSCs in liver microenvironment and discusses mechanisms by which tumor-derived factors activate HSCs, and in turn, activated HSC promotes metastatic tumor growth. The interactions between tumor cells and HSCs in liver microenvironment can be regarded as an "amplification loop". The activation of HSCs is a complex process that is regulated by multiple pathways, such as the transforming growth factor-β and platelet-derived growth factor signaling pathways. HSCs provide a possible therapeutic target for liver metastases to effectively increase the survival of patients.

Nitric oxide protects endothelium from cadmium mediated leakiness

Cadmium targets the vascular endothelium causing endothelial dysfunction and leakiness of endothelial barrier. Nitric oxide plays a major role in mediating endothelial functions including angiogenesis, migration and permeability. The present study investigates the nitric oxide effects on cadmium induced endothelial leakiness. Results of ex vivo and in vitro permeability assays showed that even a sub-lethal dose of cadmium chloride (1 µM) was sufficient to induce leakiness of endothelial cells. Cadmium drastically altered the actin polymerisation pattern and membrane tension of these cells compared to controls. Addition of nitric oxide donor Spermine NONOate (SP) significantly blunted cadmium-mediated effects and recover endothelial cells integrity. Cadmium-induced cytoskeletal rearrangements and membrane leakiness are associated with the low nitric oxide availability and high reactive oxygen species generation. In brief, we show the protective role of nitric oxide against cadmium-mediated endothelial leakiness.

Study of the cellular mechanism of Sunitinib mediated inactivation of activated hepatic stellate cells and its implications in angiogenesis

The development of hepatocellular carcinomas from malignant hepatocytes is frequently associated with intra- and peritumoral accumulation of connective tissue arising from activated hepatic stellate cells (HSC). Inhibition of receptor tyrosine kinase (RTK) signaling showed promise in the treatment of hepatocellular carcinoma. However, there is a lack of knowledge about the effects of RTK inhibitors on the tumor supportive cells. We performed in vitro experiments to study whether Sunitinib, a platelet-derived growth factor (PDGF) and vascular endothelial growth factor (VEGF) RTKs' inhibitor, could block both activated HSC functions and angiogenesis and thus prevent the progression of cirrhotic liver to hepatocellular carcinoma. In immortalized human activated HSC LX-2, treatment with Sunitinib 100 nM blocked collagen synthesis by 47%, as assessed by Sirius Red staining, attenuated HSC contraction by 65%, and reduced cell migration by 28% as evaluated using a Boyden's chamber, without affecting cell viability, measured by Trypan blue staining, and apoptosis, measured by propidium iodide (PI) incorporation assay. Our data revealed that Sunitinib treatment blocked the transdifferentiation of primary human HSC (hHSC) to activated myofibroblast-like cells by 65% without affecting hHSC apoptosis and migration. In in vitro angiogenic assays, Sunitinib 100 nM reduced endothelial cells (EC) ring formation by 46% and tube formation by 68%, and decreased vascular sprouting in aorta ring assay and angiogenesis in vascular bed of chick embryo. In conclusion, the present study demonstrates that the RTK inhibitor Sunitinib blocks the activation of HSC and angiogenesis suggesting its potential as a drug candidate in pathological conditions like liver fibrosis and hepatocellular carcinoma.

Overexpression of endoglin modulates TGF-β1-signalling pathways in a novel immortalized mouse hepatic stellate cell line

Hepatic stellate cells (HSCs) play a major role in the pathogenesis of liver fibrosis. Working on primary HSCs requires difficult isolation procedures; therefore we have generated and here characterize a mouse hepatic stellate cell line expressing GFP under control of the collagen 1(I) promoter/enhancer. These cells are responsive to pro-fibrogenic stimuIi, such as PDGF or TGF-β1, and are able to activate intracellular signalling pathways including Smads and MAP kinases. Nevertheless, due to the basal level of activation, TGF-β1 did not significantly induce GFP expression contrasting the TGF-β1 regulated endogenous collagen I expression. We could demonstrate that the accessory TGF-β-receptor endoglin, which is endogenously expressed at very low levels, has a differential effect on signalling of these cells when transiently overexpressed. In the presence of endoglin activation of Smad1/5/8 was drastically enhanced. Moreover, the phosphorylation of ERK1/2 was increased, and the expression of vimentin, α-smooth muscle actin and connective tissue growth factor was upregulated. Endoglin induced a slight increase in expression of the inhibitor of differentiation-2 while the amount of endogenous collagen type I was reduced. Therefore, this profibrogenic cell line with hepatic stellate cell origin is not only a promising novel experimental tool, which can be used in vivo for cell tracing experiments. Furthermore it allows investigating the impact of various regulatory proteins (e.g. endoglin) on profibrogenic signal transduction, differentiation and hepatic stellate cell biology.

Echovirus 30 induced neuronal cell death through TRIO-RhoA signaling activation

BACKGROUND

Echovirus 30 (Echo30) is one of the most frequently identified human enteroviruses (EVs) causing aseptic meningitis and encephalitis. However the mechanism underlying the pathogenesis of Echo30 infection with significant clinical outcomes is not completely understood. The aim of this investigation is to illustrate molecular pathologic alteration in neuronal cells induced by Echo30 infection using clinical isolate from young patient with neurologic involvement.

METHODOLOGY/PRINCIPAL FINDINGS

To characterize the neuronal cellular response to Echo30 infection, we performed a proteomic analysis based on two-dimensional gel electrophoresis (2-DE) and MALDI-TOF/TOF Mass Spectrophotometric (MS) analysis. We identified significant alteration of several protein expression levels in Echo30-infected SK-N-SH cells. Among these proteins, we focused on an outstanding up-regulation of Triple functional domain (TRIO) in Echo30-infected SK-N-SH cells. Generally, TRIO acts as a key component in the regulation of axon guidance and cell migration. In this study, we determined that TRIO plays a role in the novel pathways in Echo30 induced neuronal cell death.

CONCLUSIONS/SIGNIFICANCE

Our finding shows that TRIO plays a critical role in neuronal cell death by Echo30 infection. Echo30 infection activates TRIO-guanine nucleotide exchange factor (GEF) domains (GEFD2) and RhoA signaling in turn. These results suggest that Echo30 infection induced neuronal cell death by activation of the TRIO-RhoA signaling. We expect the regulation of TRIO-RhoA signaling may represent a new therapeutic approach in treating aseptic meningitis and encephalitis induced by Echo30.

Nitric oxide augments mesenchymal stem cell ability to repair liver fibrosis

Background

Liver fibrosis is a major health problem worldwide and poses a serious obstacle for cell based therapies. Mesenchymal stem cells (MSCs) are multipotent and important candidate cells for future clinical applications however success of MSC therapy depends upon their homing and survival in recipient organs. This study was designed to improve the repair potential of MSCs by transplanting them in sodium nitroprusside (SNP) pretreated mice with CCl₄ induced liver fibrosis.

Methods

SNP 100 mM, a nitric oxide (NO) donor, was administered twice a week for 4 weeks to CCl₄-injured mice. MSCs were isolated from C57BL/6 wild type mice and transplanted in the left lateral lobe of the liver in experimental animals. After 4 weeks, animals were sacrificed and liver improvement was analyzed. Analysis of fibrosis by qRT-PCR and sirius red staining, homing, bilirubin and alkaline phosphatase (ALP) serum levels between different treatment groups were compared to control.

Results

Liver histology demonstrated enhanced MSCs homing in SNP-MSCs group compared to MSCs group. The gene expression of fibrotic markers; αSMA, collagen 1α1, TIMP, NFκB and iNOS was down regulated while cytokeratin 18, albumin and eNOS was up-regulated in SNP-MSCs group. Combine treatment sequentially reduced fibrosis in SNP-MSCs treated liver compared to the other treatment groups. These results were also comparable with reduced serum levels of bilirubin and ALP observed in SNP-MSCs treated group.

Conclusion

This study demonstrated that NO effectively augments MSC ability to repair liver fibrosis induced by CCl₄ in mice and therefore is a better treatment regimen to reduce liver fibrosis.

Hepatic stellate cells: partners in crime for liver metastases?

Hepatic stellate cells (HSCs) were recently postulated as a component of the prometastatic liver microenvironment, because they can transdifferentiate into highly proliferative and motile myofibroblasts that are implicated in the desmoplastic reaction and metastatic growth. This review focuses on bidirectional interactions between tumor cells and HSCs in the liver microenvironment and discusses mechanisms whereby tumor-derived factors activate HSCs, and in turn, activated HSCs promote metastatic growth. Bidirectional interactions between tumors and HSCs may function as an "amplification loop" to further enhance metastatic growth in the liver. The activation of HSCs is a complex process regulated by multiple factors such as transforming growth factor-β and platelet-derived growth factor signaling pathways, which may present as therapeutic targets in the prevention and treatment of liver metastases.

CONCLUSION

HSCs may present a new therapeutic target in the treatment of liver metastases. Targeting HSCs and/or myofibroblasts with transforming growth factor-β or platelet-derived growth factor antagonists in coordination with chemotherapy, radiotherapy, or surgery may prove to be effective at reducing liver metastases and increasing the survival benefit of patients by targeting both tumor cells and the tumor microenvironment.

Protein kinase G signaling disrupts Rac1-dependent focal adhesion assembly in liver specific pericytes

Nitric oxide (NO) regulates the function of perivascular cells (pericytes), including hepatic stellate cells (HSC), mainly by activating cGMP and cGMP-dependent kinase (PKG) via NO/cGMP paracrine signaling. Although PKG is implicated in integrin-mediated cell adhesion to extracellular matrix, whether or how PKG signaling regulates the assembly of focal adhesion complexes (FA) and migration of HSC is not known. With the help of complementary molecular and cell biological approaches, we demonstrate here that activation of PKG signaling in HSC inhibits vascular tubulogenesis, migration/chemotaxis, and assembly of mature FA plaques, as assessed by vascular tubulogenesis assays and immunofluorescence localization of FA markers such as vinculin and vasodilator-stimulated phosphoprotein (VASP). To determine whether PKG inhibits FA assembly by phosphorylation of VASP at Ser-157, Ser-239, and Thr-278, we mutated these putative phosphorylation sites to alanine (VASP3A, phosphoresistant mutant) or aspartic acid (VASP3D, phosphomimetic), respectively. Data generated from these two mutants suggest that the effect of PKG on FA is independent of these three phosphorylation sites. In contrast, activation of PKG inhibits the activity of small GTPase Rac1 and its association with the effector protein IQGAP1. Moreover, PKG activation inhibits the formation of a trimeric protein complex containing Rac1, IQGAP1, and VASP. Finally, we found that expression of a constitutively active Rac1 mutant abolishes the inhibitory effects of PKG on FA formation. In summary, our data suggest that activation of PKG signaling in pericytes inhibits FA formation by inhibiting Rac1.

Applications of chitin and its derivatives in biological medicine

Chitin and its derivatives-as a potential resource as well as multiple functional substrates-have generated attractive interest in various fields such as biomedical, pharmaceutical, food and environmental industries, since the first isolation of chitin in 1811. Moreover, chitosan and its chitooligosaccharides (COS) are degraded products of chitin through enzymatic and acidic hydrolysis processes; and COS, in particular, is well suited for potential biological application, due to the biocompatibility and nontoxic nature of chitosan. In this review, we investigate the current bioactivities of chitin derivatives, which are all correlated with their biomedical properties. Several new and cutting edge insights here may provide a molecular basis for the mechanism of chitin, and hence may aid its use for medical and pharmaceutical applications.

[Pathophysiology of portal hypertension, what's new?]

Portal hypertension (PHT) is associated with changes in the intrahepatic, systemic and portosystemic collateral circulations. Alteration in vasoreactivity (vasodilation and vasoconstriction) plays a central role in the pathogenesis of PHT by contributing to increased intrahepatic resistance, hyperdynamic circulation and the expansion of the collateral circulation. PHT is also importantly characterized by changes in vascular structure; termed vascular remodeling, which is an adaptive response of the vessel wall that occurs in response to chronic changes in the environment such as shear stress. Angiogenesis, the sprouting of new blood vessels, also occurs in PHT, especially in the expansion of the portosystemic collateral circulation. These complementary processes of vasoreactivity, vascular remodeling and angiogenesis represent important targets in the research for the treatment of portal hypertension.

Inhibition of VEGF- and NO-dependent angiogenesis does not impair liver regeneration

Angiogenesis occurs through a convergence of diverse signaling mechanisms with prominent pathways that include autocrine effects of endothelial nitric oxide (NO) synthase (eNOS)-derived NO and vascular endothelial growth factor (VEGF). However, the redundant and distinct roles of NO and VEGF in angiogenesis remain incompletely defined. Here, we use the partial hepatectomy model in mice genetically deficient in eNOS to ascertain the influence of eNOS-derived NO on the angiogenesis that accompanies liver regeneration. While sinusoidal endothelial cell (SEC) eNOS promotes angiogenesis in vitro, surprisingly the absence of eNOS did not influence the angiogenesis that occurs after partial hepatectomy in vivo. While this observation could not be attributed to induction of alternate NOS isoforms, it was associated with induction of VEGF signaling as evidenced by enhanced levels of VEGF ligand in regenerating livers from mice genetically deficient in eNOS. However, surprisingly, mice that were genetically heterozygous for deficiency in the VEGF receptor, fetal liver kinase-1, also maintained unimpaired capacity for liver regeneration. In summary, inhibition of VEGF- and NO-dependent angiogenesis does not impair liver regeneration, indicating signaling redundancies that allow liver regeneration to continue in the absence of this canonical vascular pathway.

Focal adhesion assembly in myofibroblasts fosters a microenvironment that promotes tumor growth

Cells within the tumor microenvironment influence tumor growth through multiple mechanisms. Pericytes such as hepatic stellate cells are an important cell within the tumor microenvironment; their transformation into highly motile myofibroblasts leads to angiogenesis, stromal cell recruitment, matrix deposition, and ensuing tumor growth. Thus, a better understanding of mechanisms that regulate motility of pericytes is required. Focal adhesions (FAs) form a physical link between the extracellular environment and the actin cytoskeleton, a requisite step for cell motility. FAs contain a collection of proteins including the Ena/VASP family member, vasodilator-stimulated phosphoprotein (VASP); however, a role for VASP in FA development has been elusive. Using a comprehensive siRNA knockdown approach and a variety of VASP mutants coupled with complementary cell imaging methodologies, we demonstrate a requirement of VASP for optimal development of FAs and cell spreading in LX2 liver myofibroblasts, which express high levels of endogenous VASP. Rac1, a binding partner of VASP, acts in tandem with VASP to regulate FAs. In vivo, perturbation of Ena/VASP function in tumor myofibroblast precursor cells significantly reduces pericyte recruitment to tumor vasculature, myofibroblastic transformation, tumor angiogenesis, and tumor growth, providing in vivo pathobiologic relevance to these findings. Taken together, our results identify Ena/VASP as a significant modifier of tumor growth through regulation of FA dynamics and ensuing pericyte/myofibroblast function within the tumor microenvironment.

Fabrication and characterization of an inorganic gold and silica nanoparticle mediated drug delivery system for nitric oxide

Nitric oxide (NO) plays an important role in inhibiting the development of hepatic fibrosis and its ensuing complication of portal hypertension by inhibiting human hepatic stellate cell (HSC) activation. Here we have developed a gold nanoparticle and silica nanoparticle mediated drug delivery system containing NO donors, which could be used for potential therapeutic application in chronic liver disease. The gold nanoconjugates were characterized using several physico-chemical techniques such as UV-visible spectroscopy and transmission electron microscopy. Silica nanoconjugates were synthesized and characterized as reported previously. NO released from gold and silica nanoconjugates was quantified under physiological conditions (pH = 7.4 at 37 degrees C) for a substantial period of time. HSC proliferation and the vascular tube formation ability, manifestations of their activation, were significantly attenuated by the NO released from these nanoconjugates. This study indicates that gold and silica nanoparticle mediated drug delivery systems for introducing NO could be used as a strategy for the treatment of hepatic fibrosis or chronic liver diseases, by limiting HSC activation.

Neuropilin-1 promotes cirrhosis of the rodent and human liver by enhancing PDGF/TGF-beta signaling in hepatic stellate cells

PDGF-dependent hepatic stellate cell (HSC) recruitment is an essential step in liver fibrosis and the sinusoidal vascular changes that accompany this process. However, the mechanisms that regulate PDGF signaling remain incompletely defined. Here, we found that in two rat models of liver fibrosis, the axonal guidance molecule neuropilin-1 (NRP-1) was upregulated in activated HSCs, which exhibit the highly motile myofibroblast phenotype. Additionally, NRP-1 colocalized with PDGF-receptor beta (PDGFRbeta) in HSCs both in the injury models and in human and rat HSC cell lines. In human HSCs, siRNA-mediated knockdown of NRP-1 attenuated PDGF-induced chemotaxis, while NRP-1 overexpression increased cell motility and TGF-beta-dependent collagen production. Similarly, mouse HSCs genetically modified to lack NRP-1 displayed reduced motility in response to PDGF treatment. Immunoprecipitation and biochemical binding studies revealed that NRP-1 increased PDGF binding affinity for PDGFRbeta-expressing cells and promoted downstream signaling. An NRP-1 neutralizing Ab ameliorated recruitment of HSCs, blocked liver fibrosis in a rat model of liver injury, and also attenuated VEGF responses in cultured liver endothelial cells. In addition, NRP-1 overexpression was observed in human specimens of liver cirrhosis caused by both hepatitis C and steatohepatitis. These studies reveal a role for NRP-1 as a modulator of multiple growth factor targets that regulate liver fibrosis and the vascular changes that accompany it and may have broad implications for liver cirrhosis and myofibroblast biology in a variety of other organ systems and disease conditions.

Simulated microgravity perturbs actin polymerization to promote nitric oxide-associated migration in human immortalized Eahy926 cells

Microgravity causes endothelium dysfunctions and vascular endothelium remodeling in astronauts returning from space flight. Cardiovascular deconditioning occurs as a consequence of an adaptive response to microgravity partially due to the effects exerted at cellular level. Directional migration of endothelial cell which are central in maintaining the structural integrity of vascular walls is regulated by chemotactic, haptotactic, and mechanotactic stimuli which are essential for vasculogenesis. We explored the migration property of transformed endothelial cells (EC) exposed to 2-h microgravity, simulated using a three-dimensional clinostat constructed based on blueprint published by the Fokker Space, Netherlands. Migration of EC was measured using the scrap wound healing in the presence or absence of actin polymerization inhibitor-cytochalasin D (CD) in Eahy926 cell lines. Simulated microgravity increased cellular migration by 25% while CD-blocked microgravity induced cellular migration. The key migratory structures of cells, filopodia and lamellipodia, formed by EC were more in simulated microgravity compared to gravity. Parallel experiments with phalloidin and diaminorhodamine-4M (DAR-4M) showed that simulated microgravity caused actin rearrangements that lead to 25% increase in nitric oxide production. Further nitric oxide measurements showed a higher nitric oxide production which was not abrogated by phosphoinositol 3 kinase inhibitor (Wortmanin). Bradykinin, an inducer of nitric oxide, prompted two folds higher nitric oxide production along with simulated microgravity in a synergistic manner. We suggest that limited exposure to simulated microgravity increases Eahy926 cell migration by modulating actin and releasing nitric oxide.

Ephrin B2/EphB4 pathway in hepatic stellate cells stimulates Erk-dependent VEGF production and sinusoidal endothelial cell recruitment

Chemotaxis signals between hepatic stellate cells (HSC) and sinusoidal endothelial cells (SEC) maintain hepatic vascular homeostasis and integrity and also regulate changes in sinusoidal structure in response to liver injury. Our prior studies have demonstrated that the bidirectional chemotactic signaling molecules EphrinB2 and EphB4 are expressed in HSC. The aim of our present study was to explore whether and how the EphrinB2/EphB4 system in HSC could promote SEC recruitment, which is essential for sinusoidal structure and remodeling. Stimulation of human HSC (hHSC) with chimeric agonists (2 microg/ml) of either EphrinB2 or EphB4 (EphrinB2 Fc or EphB4 Fc, respectively) significantly increased VEGF mRNA levels in hHSC as assessed by quantitative PCR, with respective small interfering RNAs for EphrinB2 and EphB4 inhibiting this increase (P < 0.05, n = 3). EphrinB2 agonist-induced increase in VEGF mRNA levels in hHSC was associated with increased phosphorylation of Erk and was significantly blocked by U0126 (20 microM), an inhibitor of MEK, which is a kinase upstream from Erk (P < 0.05, n = 3). The EphB4 agonist also significantly increased human VEGF promoter activity (P < 0.05, n = 3) as assessed by promoter reporter luciferase assay in transfected LX2-HSC. This was associated with upregulation of the vasculoprotective transcription factor, Kruppel-like factor 2 (KLF2). In Boyden chamber assays, conditioned media from hHSC stimulated with agonists of EphrinB2 or EphB4 increased SEC chemotaxis in a VEGF-dependent manner, compared with control groups that included basal media with agonists of EphrinB2, EphB4, or HSC-conditioned media from HSC in absence of agonist stimulation (P < 0.05, n = 3). EphB4 expression was detected in situ within liver sinusoidal vessels of rats after carbon tetrachloride-induced liver injury. In summary, activation of the EphrinB2/EphB4 signaling pathway in HSC promotes chemotaxis of SEC through a pathway that involves Erk, KLF2, and VEGF. These studies identify EphrinB2 or EphB4 as a key intermediary that links HSC signal transduction pathways with angiogenesis and sinusoidal remodeling.

Chaperonin containing T-complex polypeptide subunit eta (CCT-eta) is a specific regulator of fibroblast motility and contractility

Integumentary wounds in mammalian fetuses heal without scar; this scarless wound healing is intrinsic to fetal tissues and is notable for absence of the contraction seen in postnatal (adult) wounds. The precise molecular signals determining the scarless phenotype remain unclear. We have previously reported that the eta subunit of the chaperonin containing T-complex polypeptide (CCT-eta) is specifically reduced in healing fetal wounds in a rabbit model. In this study, we examine the role of CCT-eta in fibroblast motility and contractility, properties essential to wound healing and scar formation. We demonstrate that CCT-eta (but not CCT-beta) is underexpressed in fetal fibroblasts compared to adult fibroblasts. An in vitro wound healing assay demonstrated that adult fibroblasts showed increased cell migration in response to epidermal growth factor (EGF) and platelet derived growth factor (PDGF) stimulation, whereas fetal fibroblasts were unresponsive. Downregulation of CCT-eta in adult fibroblasts with short inhibitory RNA (siRNA) reduced cellular motility, both basal and growth factor-induced; in contrast, siRNA against CCT-beta had no such effect. Adult fibroblasts were more inherently contractile than fetal fibroblasts by cellular traction force microscopy; this contractility was increased by treatment with EGF and PDGF. CCT-eta siRNA inhibited the PDGF-induction of adult fibroblast contractility, whereas CCT-beta siRNA had no such effect. In each of these instances, the effect of downregulating CCT-eta was to modulate the behavior of adult fibroblasts so as to more closely approximate the characteristics of fetal fibroblasts. We next examined the effect of CCT-eta modulation on alpha-smooth muscle actin (alpha-SMA) expression, a gene product well known to play a critical role in adult wound healing. Fetal fibroblasts were found to constitutively express less alpha-SMA than adult cells. Reduction of CCT-eta with siRNA had minimal effect on cellular beta-actin but markedly decreased alpha-SMA; in contrast, reduction of CCT-beta had minimal effect on either actin isoform. Direct inhibition of alpha-SMA with siRNA reduced both basal and growth factor-induced fibroblast motility. These results indicate that CCT-eta is a specific regulator of fibroblast motility and contractility and may be a key determinant of the scarless wound healing phenotype by means of its specific regulation of alpha-SMA expression.

Adenosine inhibits chemotaxis and induces hepatocyte-specific genes in bone marrow mesenchymal stem cells

Bone marrow-derived mesenchymal stem cells (MSCs) have therapeutic potential in liver injury, but the signals responsible for MSC localization to sites of injury and initiation of differentiation are not known. Adenosine concentration is increased at sites of cellular injury and inflammation, and adenosine is known to signal a variety of cellular changes. We hypothesized that local elevations in the concentration of adenosine at sites of tissue injury regulate MSC homing and differentiation. Here we demonstrate that adenosine does not induce MSC chemotaxis but dramatically inhibits MSC chemotaxis in response to the chemoattractant hepatocyte growth factor (HGF). Inhibition of HGF-induced chemotaxis by adenosine requires the A2a receptor and is mediated via up-regulation of the cyclic adenosine monophosphate (AMP)/protein kinase A pathway. This results in inhibition of cytosolic calcium signaling and down-regulation of HGF-induced Rac1. Because of the important role of Rac1 in the formation of actin stress fibers, we examined the effect of adenosine on stress fiber formation and found that adenosine inhibits HGF-induced stress fiber formation. In addition, we found that adenosine induces the expression of some key endodermal and hepatocyte-specific genes in mouse and human MSCs in vitro.

CONCLUSION

We propose that the inhibition of MSC chemotaxis at sites of high adenosine concentration results in localization of MSCs to areas of cellular injury and death in the liver. We speculate that adenosine might initiate the process of differentiation of MSCs into hepatocyte-like cells.

TIMP-2 modulates VEGFR-2 phosphorylation and enhances phosphodiesterase activity in endothelial cells

In this study, we examine the effects of tissue inhibitor of metalloproteinases-2 (TIMP-2) on the phosphorylation status of specific phosphotyrosine residues on the vascular endothelial cell growth factor receptor-2 (VEGFR-2) cytoplasmic tail and examine the effects on associated downstream signaling pathways. To focus on metalloproteinase-independent mechanisms, we used the TIMP-2 analog known as Ala+TIMP-2 that is deficient in matrix metalloproteinase-inhibitory activity. Our experiments are designed to compare the effects of VEGF-A stimulation with or without Ala+TIMP-2 pretreatment, as well as basal responses in human microvascular endothelial cells. Our results show that Ala+TIMP-2 selectively alters the phosphorylation pattern of VEGFR-2 after VEGF-A stimulation and disrupts the downstream activation of PLC-gamma, Ca(+2) flux, Akt, and eNOS, as well as decreasing cGMP levels. Moreover, we observed an Ala+TIMP-2-induced reduction in cGMP levels typically elevated by exogenous NO donors implicating Ala+TIMP-2 in the direct activation of an isobutylmethylxanthine (IBMX)-sensitive cGMP phosphodiesterase activity. TIMP-2 suppression of endothelial mitogenesis and angiogenesis involves at least two mechanisms, one mediated by protein tyrosine phosphatase inhibition of VEGFR-2 activation as well as downstream signaling and a second mechanism involving direct activation of an IBMX-sensitive phosphodiesterase activity.

Antifibrotic effects of ZK14, a novel nitric oxide-donating biphenyldicarboxylate derivative, on rat HSC-T6 cells and CCl4-induced hepatic fibrosis

AIM

To study the pharmacologic effect of ZK(14), a novel nitric oxide-donating biphenyldicarboxylate (DDB) derivative, on HSC-T6 cells and on CCl(4)-induced hepatic fibrosis.

METHODS

Inhibition of HSC-T6 cell growth by ZK(14) was evaluated by MTT assay. The effect of ZK(14) on the percentage of HSC-T6 cells undergoing apoptosis was measured using Annexin-V/PI double-staining and TUNEL assay. Mitochondrial membrane potential (MMP) and caspase activities were tested. Hepatic fibrosis was induced in Sprague-Dawley rats by intraperitoneal injection with 14% CCl(4). Rats with hepatic fibrosis were randomly divided into four groups: model control, ZK(14) (20 mg/kg), ZK(14) (10 mg/kg) and DDB (5 mg/kg). Levels of aspartate aminotransferase (AST), alanine aminotransferase (ALT), hyaluronic acid (HA), type III collagen (PCIII), and nitric oxide (NO) were assessed, and liver samples were stained with hematoxylin-eosin. The NO level in cells treated with ZK(14) in vitro was also measured.

RESULTS

The effect of ZK(14) on HSC-T6 cell apoptosis was concentration- and time-dependent, with up to 50% of cells becoming apoptotic when exposed to 100 mumol/L ZK(14) for 18 h. ZK(14) treatment resulted in mitochondrial membrane depolarization and activation of caspases 3 and 9. At a dose of 20 mg/kg, ZK(14) significantly decreased serum transaminase (AST, ALT) activities and fibrotic index (HA, PCIII) levels and significantly inhibited fibrogenesis.

CONCLUSION

These data indicate that ZK(14), a novel NO-donating DDB derivative, promotes HSC-T6 apoptosis in vitro through a signaling mechanism involving mitochondria and caspase activation and it inhibits CCl(4)-induced hepatic fibrosis in vivo. The results suggest that ZK(14) has potential therapeutic value in the treatment of hepatic fibrosis.

Thalidomide inhibits lipopolysaccharide-induced nitric oxide production and prevents lipopolysaccharide-mediated lethality in mice

The effect of thalidomide on lipopolysaccharide-induced nitric oxide (NO) production was studied using RAW 264.7 macrophage-like cells. Thalidomide significantly inhibited lipopolysaccharide-induced NO production via reduced expression of an inducible NO synthase. Thalidomide reduced the phosphorylation of the p65 nuclear factor-kappaB subunit, inhibitory kappaB (IkappaB) and IkappaB kinase in lipopolysaccharide-stimulated cells. However, thalidomide did not affect the expression of interferon-beta (IFN-beta) and interferon regulatory factor-1 in response to lipopolysaccharide. Further, thalidomide inhibited the MyD88 augmentation in lipopolysaccharide-stimulated cells, whereas it did not alter the expression of TIR domain-containing adaptor-inducing IFN-beta in the MyD88-independent pathway. Thalidomide significantly inhibited the NO production in response to Pam(3)Cys, CpG DNA and imiquimod as MyD88-dependent Toll-like receptor (TLR) ligands, but not polyI:C as a MyD88-independent TLR ligand. Therefore, thalidomide was suggested to inhibit lipopolysaccharide-induced NO production via downregulation of the MyD88-dependent signal pathway. The anti-inflammatory action of thalidomide might be involved in the prevention of lipopolysaccharide-mediated lethality in mice.

The pericyte: cellular regulator of microvascular blood flow

The vascular system - through its development, response to injury, and remodeling during disease - constitutes one of the key organ systems sustaining normal human physiology; conversely, its dysregulation also underlies multiple pathophysiologic processes. Regulation of vascular endothelial cell function requires the integration of complex signals via multiple cell types, including arterial smooth muscle, capillary and post-capillary pericytes, and other perivascular cells such as glial and immune cells. Here, we focus on the pericyte and its roles in microvascular remodeling, reviewing current concepts in microvascular pathophysiology and offering new insights into the specific roles that pericyte-dependent signaling pathways may play in modulating endothelial growth and microvascular tone during pathologic angiogenesis and essential hypertension.

Adenosine induces loss of actin stress fibers and inhibits contraction in hepatic stellate cells via Rho inhibition

The Rho/ROCK pathway is activated in differentiated hepatic stellate cells (HSCs) and is necessary for assembly of actin stress fibers, contractility, and chemotaxis. Despite the importance of this pathway in HSC biology, physiological inhibitors of the Rho/ROCK pathway in HSCs are not known. We demonstrate that adenosine induces loss of actin stress fibers in the LX-2 cell line and primary HSCs in a manner indistinguishable from Rho/ROCK inhibition. Loss of actin stress fibers occurs via the A2a receptor at adenosine concentrations above 10 muM, which are present during tissue injury. We further demonstrate that loss of actin stress fibers is due to a cyclic adenosine monophosphate, protein kinase A-mediated pathway that results in Rho inhibition. Furthermore, a constitutively active Rho construct can inhibit the ability of adenosine to induce loss of actin stress fibers. Actin stress fibers are required for HSC contraction, and we demonstrate that adenosine inhibits endothelin-1 and lysophosphatidic acid-mediated HSC contraction. We propose that adenosine is a physiological inhibitor of the Rho pathway in HSCs with functional consequences, including loss of HSC contraction.

[The role of activated hepatic stellate cells in liver fibrosis, portal hypertension and cancer angiogenesis]

Although hepatic stellate cells, which are liver specific pericytes, have been recognized within the vasculature of the sinusoid for more than one hundred years, the biology and function of these cells is unclear. Recent studies have highlighted the key role of stellate cells in a number of fundamental processes that include wound healing/fibrosis, vasoregulation, and vascular remodeling/angiogenesis. In the liver, these processes are particularly important in the development of cirrhosis, portal hypertension and cancer. This article highlights the recent advances in our understanding of the biology of hepatic stellate cells and discusses some of the recently-ascribed functions that are relevant to liver fibrosis, portal hypertension and cancer angiogenesis.

Characterization of the CXCR4 signaling in pancreatic cancer cells

CXCL12 and its receptor, CXCR4, are emerging as promising targets for modulating growth, angiogenesis, and metastasis in several human cancers. Indeed, blocking the receptor is sufficient to prevent metastasis and angiogenesis in experimental breast cancer xenografts. Recently, the biological effect of the CXCR4 in pancreatic cancer, one of the most deadly neoplastic diseases, has been reported. However, the molecular mechanism by which CXCR4 contributes to these properties is not completely understood. In this paper, we characterize the signaling pathways activated by CXCR4 in pancreatic cancer. We show that after CXCR4 activation, EGFR becomes tyrosine phosphorylated, and the kinase activity of this receptor, together with the activation of MMPs, Src, and PI3-Kinase, is required for CXCR4-mediated ERK activation. Analysis of this cascade in pancreatic cancer cells revealed that the ERK-mediated pathway regulates genes involved in angiogenesis, such as VEGF, CD44, HIF1alpha, and IL-8. Furthermore, ERK blockage inhibits the migration and tube formation of endothelial cells induced by CXCL12. Considering that inhibitors for several components of this pathway, including CXCR4 itself, are at different stages of clinical trials, this study provides theoretical justification for the clinical testing of these drugs in pancreatic cancer, thus extending the list of potential targets for treating this dismal disease.

Nitric oxide regulates tumor cell cross-talk with stromal cells in the tumor microenvironment of the liver

Tumor progression is regulated through paracrine interactions between tumor cells and stromal cells in the microenvironment, including endothelial cells and myofibroblasts. Nitric oxide (NO) is a key molecule in the regulation of tumor-microenvironment interactions, although its precise role is incompletely defined. By using complementary in vitro and in vivo approaches, we studied the effect of endothelial NO synthase (eNOS)-derived NO on liver tumor growth and metastasis in relation to adjacent stromal myofibroblasts and matrix because liver tumors maintain a rich, vascular stromal network enriched with phenotypically heterogeneous myofibroblasts. Mice with an eNOS deficiency developed liver tumors more frequently in response to carcinogens compared with control animals. In a surgical model of pancreatic cancer liver metastasis, eNOS overexpression in the tumor microenvironment attenuated both the number and size of tumor implants. NO promoted anoikis of tumor cells in vitro and limited their invasive capacity. Because tumor cell anoikis and invasion are both regulated by myofibroblast-derived matrix, we explored the effect of NO on tumor cell protease expression. Both microarray and Western blot analysis revealed eNOS-dependent down-regulation of the matrix protease cathepsin B within tumor cells, and silencing of cathepsin B attenuated tumor cell invasive capacity in a similar manner to that observed with eNOS overexpression. Thus, a NO gradient within the tumor microenvironment influences tumor progression through orchestrated molecular interactions between tumor cells and stroma.