Spatial compartmentalization of tumor necrosis factor (TNF) receptor 1-dependent signaling pathways in human airway smooth muscle cells. Lipid rafts are essential for TNF-alpha-mediated activation of RhoA but dispensable for the activation of the NF-kappaB and MAPK pathways

Alteration of cholesterol content and oxygen level in intestinal organoids after infection with Staphylococcus aureus

The pathogenicity elicited by Staphylococcus (S.) aureus, one of the best-studied bacteria, in the intestine is not well understood. Recently, we demonstrated that S. aureus infection induces alterations in membrane composition that are associated with concomitant impairment of intestinal function. Here, we used two organoid models, induced pluripotent stem cell (iPSC)-derived intestinal organoids and colonic intestinal stem cell-derived intestinal organoids (colonoids), to examine how sterol metabolism and oxygen levels change in response to S. aureus infection. HPLC quantification showed differences in lipid homeostasis between infected and uninfected cells, characterized by a remarkable decrease in total cellular cholesterol. As the altered sterol metabolism is often due to oxidative stress response, we next examined intracellular and extracellular oxygen levels. Three different approaches to oxygen measurement were applied: (1) cell-penetrating nanoparticles to quantify intracellular oxygen content, (2) sensor plates to quantify extracellular oxygen content in the medium, and (3) a sensor foil system for oxygen distribution in organoid cultures. The data revealed significant intracellular and extracellular oxygen drop after infection in both intestinal organoid models as well as in Caco-2 cells, which even 48 h after elimination of extracellular bacteria, did not return to preinfection oxygen levels. In summary, we show alterations in sterol metabolism and intra- and extracellular hypoxia as a result of S. aureus infection. These results will help understand the cellular stress responses during sustained bacterial infections in the intestinal epithelium.

TRAIL and its receptors in cardiac diseases

Cardiovascular disease is a leading cause of death worldwide. Loss of cardiomyocytes that occurs during many types of damage to the heart such as ischemic injury and stress caused by pressure overload, diminishes cardiac function due to their limited regenerative capacity and promotes remodeling, which further damages the heart. Cardiomyocyte death occurs through two primary mechanisms, necrosis and apoptosis. Apoptosis is a highly regulated form of cell death that can occur through intrinsic (mitochondrial) or extrinsic (receptor mediated) pathways. Extrinsic apoptosis occurs through a subset of Tumor Necrosis Receptor (TNF) family receptors termed "Death Receptors." While some ligands for death receptors have been extensively studied in the heart, such as TNF-α, others have been virtually unstudied. One poorly characterized cardiac TNF related ligand is TNF-Related Apoptosis Inducing Ligand (TRAIL). TRAIL binds to two apoptosis-inducing receptors, Death Receptor (DR) 4 and DR5. There are also three decoy TRAIL receptors, Decoy Receptor (DcR) 1, DcR2 and osteoprotegerin (OPG). While TRAIL has been extensively studied in the cancer field due to its ability to selectively induce apoptosis in transformed cell types, emerging clinical evidence points towards a role for TRAIL and its receptors in cardiac pathology. This article will highlight our current understanding of TRAIL and its receptors in normal and pathological conditions in the heart.

Ameliorative Effect of Tocotrienols on Perimenopausal-Associated Osteoporosis-A Review

Osteoporosis, or bone loss, is a disease that affects many women globally. As life expectancy increases, the risk of osteoporosis in women also increases, too, and this will create a burden on the healthcare and economic sectors of a country. Osteoporosis was once thought to be a disease that would occur only after menopause. However, many studies have shown that osteoporosis may develop even in the perimenopausal stage. Due to the erratic levels of estrogen and progesterone during the perimenopausal stage, studies suggest that women are exposed to the risk of developing osteoporosis even at this stage. The erratic hormonal changes result in the production of proinflammatory mediators and cause oxidative stress, which leads to the progressive loss of bone-building activities. Tocotrienols, members of vitamin E, have many health-promoting properties. Due to their powerful anti-oxidative and anti-inflammatory properties, tocotrienols have shown positive anti-osteoporotic properties in post-menopausal studies. Hence, we propose here that tocotrienols could also possibly alleviate perimenopausal osteoporosis by discussing in this review the connection between inflammatory mediators produced during perimenopause and the risk of osteoporosis. Tocotrienols could potentially be an anti-osteoporotic agent, but due to their low bioavailability, they have not been as effective as they could be. Several approaches have been evaluated to overcome this issue, as presented in this review. As the anti-osteoporotic effects of tocotrienols were mostly studied in post-menopausal models, we hope that this review could pave the way for more research to be done to evaluate their effect on peri-menopausal models so as to reduce the risk of osteoporosis from an earlier stage.

Hypolipidemic and reduced nitrergic effects of p-hydroxycinnamic diesters extracted from Copernicia prunifera in mice challenged by a high-fat diet

Dyslipidemia is a chronic non-transmissible condition that has increased due to an unhealthy lifestyle. Statins have been used as the standard treatment to control hyperlipidemia. However, side effects and high costs may be associated with its prolonged treatment, so plants derivatives have been an attractive therapy to overcome these problems. Among the compounds extracted from plants, the p-hydroxycinnamic diesters (HCE), present in carnauba wax (CW), have been found with good pharmacological properties. Therefore, this study aimed to evaluate the potential anti-hypercholesterolemic and possible toxicological effects of HCE in C57BL/6J mice under a high-fat (HF) diet. Male C57BL/6J mice were fed during 60 days under the HF diet and therefore were either treated with HCE (200 and 400 mg/kg) or simvastatin (20 mg/kg) or received saline (controls) by gavage for 30 days under the same diet. HCE treatment was able to reduce serum total cholesterol and LDL levels. Besides, this compound increased liver X receptor (LXR) and but not significantly affected IL-1β and TNF-α liver mRNA transcription activity. In conclusion, HCE treatment was found safe and may attenuate the deleterious effects of dyslipidemia due to chronic feeding with western diets.

Regulation of Death Receptor Signaling by S-Palmitoylation and Detergent-Resistant Membrane Micro Domains-Greasing the Gears of Extrinsic Cell Death Induction, Survival, and Inflammation

Death-receptor-mediated signaling results in either cell death or survival. Such opposite signaling cascades emanate from receptor-associated signaling complexes, which are often formed in different subcellular locations. The proteins involved are frequently post-translationally modified (PTM) by ubiquitination, phosphorylation, or glycosylation to allow proper spatio-temporal regulation/recruitment of these signaling complexes in a defined cellular compartment. During the last couple of years, increasing attention has been paid to the reversible cysteine-centered PTM S-palmitoylation. This PTM regulates the hydrophobicity of soluble and membrane proteins and modulates protein:protein interaction and their interaction with distinct membrane micro-domains (i.e., lipid rafts). We conclude with which functional and mechanistic roles for S-palmitoylation as well as different forms of membrane micro-domains in death-receptor-mediated signal transduction were unraveled in the last two decades.

Defining raft domains in the plasma membrane

Many plasma membrane (PM) functions depend on the cholesterol concentration in the PM in strikingly nonlinear, cooperative ways: fully functional in the presence of physiological cholesterol levels (35~45 mol%), and nonfunctional below 25 mol% cholesterol; namely, still in the presence of high concentrations of cholesterol. This suggests the involvement of cholesterol-based complexes/domains formed cooperatively. In this review, by examining the results obtained by using fluorescent lipid analogs and avoiding the trap of circular logic, often found in the raft literature, we point out the fundamental similarities of liquid-ordered (Lo)-phase domains in giant unilamellar vesicles, Lo-phase-like domains formed at lower temperatures in giant PM vesicles, and detergent-resistant membranes: these domains are formed by cooperative interactions of cholesterol, saturated acyl chains, and unsaturated acyl chains, in the presence of >25 mol% cholesterol. The literature contains evidence, indicating that the domains formed by the same basic cooperative molecular interactions exist and play essential roles in signal transduction in the PM. Therefore, as a working definition, we propose that raft domains in the PM are liquid-like molecular complexes/domains formed by cooperative interactions of cholesterol with saturated acyl chains as well as unsaturated acyl chains, due to saturated acyl chains' weak multiple accommodating interactions with cholesterol and cholesterol's low miscibility with unsaturated acyl chains and TM proteins. Molecules move within raft domains and exchange with those in the bulk PM. We provide a logically established collection of fluorescent lipid probes that preferentially partition into raft and non-raft domains, as defined here, in the PM.

Location, location, location: A compartmentalized view of TNF-induced necroptotic signaling

Necroptosis is a lytic, proinflammatory cell death pathway, which has been implicated in host defense and, when dysregulated, the pathology of many human diseases. The central mediators of this pathway are the receptor-interacting serine/threonine protein kinases RIPK1 and RIPK3 and the terminal executioner, the pseudokinase mixed lineage kinase domain-like (MLKL). Here, we review the chronology of signaling along the RIPK1-RIPK3-MLKL axis and highlight how the subcellular compartmentalization of signaling events controls the initiation and execution of necroptosis. We propose that a network of modulators surrounds the necroptotic signaling core and that this network, rather than acting universally, tunes necroptosis in a context-, cell type-, and species-dependent manner. Such a high degree of mechanistic flexibility is likely an important property that helps necroptosis operate as a robust, emergency form of cell death.

Tumor-stroma biomechanical crosstalk: a perspective on the role of caveolin-1 in tumor progression

Tumor stiffening is a hallmark of malignancy that actively drives tumor progression and aggressiveness. Recent research has shed light onto several molecular underpinnings of this biomechanical process, which has a reciprocal crosstalk between tumor cells, stromal fibroblasts, and extracellular matrix remodeling at its core. This dynamic communication shapes the tumor microenvironment; significantly determines disease features including therapeutic resistance, relapse, or metastasis; and potentially holds the key for novel antitumor strategies. Caveolae and their components emerge as integrators of different aspects of cell function, mechanotransduction, and ECM-cell interaction. Here, we review our current knowledge on the several pivotal roles of the essential caveolar component caveolin-1 in this multidirectional biomechanical crosstalk and highlight standing questions in the field.

Clathrin- and dynamin-dependent endocytosis limits canonical NF-κB signaling triggered by lymphotoxin β receptor

Background

Lymphotoxin β receptor (LTβR) is a member of tumor necrosis factor receptor (TNFR) superfamily which regulates the immune response. At the cellular level, upon ligand binding, the receptor activates the pro-inflammatory NF-κB and AP-1 pathways. Yet, the intracellular distribution of LTβR, the routes of its endocytosis and their connection to the signaling activation are not characterized. Here, we investigated the contribution of LTβR internalization to its signaling potential.

Methods

Intracellular localization of LTβR in unstimulated and stimulated cells was analyzed by confocal microscopy. Endocytosis impairment was achieved through siRNA- or CRISPR/Cas9-mediated depletion, or chemical inhibition of proteins regulating endocytic routes. The activation of LTβR-induced signaling was examined. The levels of effector proteins of the canonical and non-canonical branches of the NF-κB pathway, and the phosphorylation of JNK, Akt, ERK1/2, STAT1 and STAT3 involved in diverse signaling cascades, were measured by Western blotting. A transcriptional response to LTβR stimulation was assessed by qRT-PCR analysis.

Results

We demonstrated that LTβR was predominantly present on endocytic vesicles and the Golgi apparatus. The ligand-bound pool of the receptor localized to endosomes and was trafficked towards lysosomes for degradation. Depletion of regulators of different endocytic routes (clathrin-mediated, dynamin-dependent or clathrin-independent) resulted in the impairment of LTβR internalization, indicating that this receptor uses multiple entry pathways. Cells deprived of clathrin and dynamins exhibited enhanced activation of canonical NF-κB signaling represented by increased degradation of IκBα inhibitor and elevated expression of LTβR target genes. We also demonstrated that clathrin and dynamin deficiency reduced to some extent LTβR-triggered activation of the non-canonical branch of the NF-κB pathway.

Conclusions

Our work shows that the impairment of clathrin- and dynamin-dependent internalization amplifies a cellular response to LTβR stimulation. We postulate that receptor internalization restricts responsiveness of the cell to subthreshold stimuli.

Selective Blockade of TNFR1 Improves Clinical Disease and Bronchoconstriction in Experimental RSV Infection

Respiratory syncytial virus (RSV) is the leading cause of bronchiolitis in infants and young children. Although some clinical studies have speculated that tumor necrosis factor (TNF)-α is a major contributor of RSV-mediated airway disease, experimental evidence remains unclear or conflicting. TNF-α initiates inflammation and cell death through two distinct receptors: TNF-receptor (TNFR)1 and TNFR2. Here we delineate the function of TNF-α by short-lasting blockade of either receptor in an experimental BALB/c mouse model of RSV infection. We demonstrate that antibody-mediated blockade of TNFR1, but not TNFR2, results in significantly improved clinical disease and bronchoconstriction as well as significant reductions of several inflammatory cytokines and chemokines, including IL-1α, IL-1β, IL-6, Ccl3, Ccl4, and Ccl5. Additionally, TNFR1 blockade was found to significantly reduce neutrophil number and activation status, consistent with the concomitant reduction of pro-neutrophilic chemokines Cxcl1 and Cxcl2. Similar protective activity was also observed when a single-dose of TNFR1 blockade was administered to mice following RSV inoculation, although this treatment resulted in improved alveolar macrophage survival rather than reduced neutrophil activation. Importantly, short-lasting blockade of TNFR1 did not affect RSV peak replication in the lung. This study suggests a potential therapeutic approach for RSV bronchiolitis based on selective blockade of TNFR1.

Role of Tumor Necrosis Factor-α in vascular hyporeactivity following endotoxic shock and its mechanism

BACKGROUND

Vascular hyporeactivity plays an important role in organ dysfunction induced by endotoxic shock. Given that cytokine, such as TNF-α, plays an important role in endotoxic shock, the aim of the present study is to investigate the role of Tumor Necrosis Factor (TNF)-α in vascular hyporeactivity following endotoxic shock and the mechanisms.

METHODS

Lipopolysaccharide (LPS) (1 mg/kg) injection was used for replicating the endotoxic shock model in the rabbit. The changes in the level of TNF-α in plasma in the rabbits model and the contractile response of superior mesenteric arteries (SMA) to norepinephrine (NE) and Ca were observed. The mechanisms in TNF-α-induced vascular hyporeactivity were further explored.

RESULTS

The levels of TNF-α in plasma were gradually increased after 1 hour of LPS administration and reached the peak at 6 hours. The contractile responses of SMA to NE were decreased at 1 hour of LPS and lowest at 6 hour. TNF-α (200 ng/mL) incubation decreased contractile response of SMA to NE significantly. Further studies found that calcium desensitization participated in the occurrence of TNF-α-induced vascular hyporeactivity, the changes were consistent with the changes of vascular reactivity, calcium sensitivities were decreased significantly at 1 hour, 2 hours, 4 hours, and 6 hours after LPS injection. TNF-α (200 ng/mL) incubation could significantly reduce the contractile response of SMA to Ca. The activity of Rho-kinase and the changes of myosin light chain 20 (MLC20) phosphorylation level were significantly decreased at 6 hours following LPS administration, and TNF-α (200 ng/mL) incubation led to a decrease of Rho-kinase and MLC20 phosphorylation. Arginine vasopressin significantly antagonized TNF-α (200 ng/mL)-induced the decrease of the vascular reactivity and calcium sensitivity.

CONCLUSION

TNF-α is involved in vascular hyporeactivity after endotoxic shock. Calcium desensitization plays an important role in TNF-α-induced vascular hyporeactivity after endotoxic shock. Rho-kinase/MLC20 phosphorylation pathway takes part in the regulation of calcium desensitization and vascular hyporeactivity induced by TNF-α. Arginine vasopressin is beneficial to endotoxic shock in TNF-α-induced vascular hyporeactivity.

Structural Similarity with Cholesterol Reveals Crucial Insights into Mechanisms Sustaining the Immunomodulatory Activity of the Mycotoxin Alternariol

The proliferation of molds in domestic environments can lead to uncontrolled continuous exposure to mycotoxins. Even if not immediately symptomatic, this may result in chronic effects, such as, for instance, immunosuppression or allergenic promotion. Alternariol (AOH) is one of the most abundant mycotoxins produced by Alternaria alternata fungi, proliferating among others in fridges, as well as in humid walls. AOH was previously reported to have immunomodulatory potential. However, molecular mechanisms sustaining this effect remained elusive. In differentiated THP-1 macrophages, AOH hardly altered the secretion of pro-inflammatory mediators when co-incubated with lipopolysaccharide (LPS), opening up the possibility that the immunosuppressive potential of the toxin could be related to an alteration of a downstream pro-inflammatory signaling cascade. Intriguingly, the mycotoxin affected the membrane fluidity in macrophages and it synergistically reacted with the cholesterol binding agent MβCD. In silico modelling revealed the potential of the mycotoxin to intercalate in cholesterol-rich membrane domains, like caveolae, and immunofluorescence showed the modified interplay of caveolin-1 with Toll-like Receptor (TLR) 4. In conclusion, we identified the structural similarity with cholesterol as one of the key determinants of the immunomodulatory potential of AOH.

The anticonvulsive Phenhydan® suppresses extrinsic cell death

Different forms of regulated cell death-like apoptosis and necroptosis contribute to the pathophysiology of clinical conditions including ischemia-reperfusion injury, myocardial infarction, sepsis, and multiple sclerosis. In particular, the kinase activity of the receptor-interacting serine/threonine protein kinase 1 (RIPK1) is crucial for cell fate in inflammation and cell death. However, despite its involvement in pathological conditions, no pharmacologic inhibitor of RIPK1-mediated cell death is currently in clinical use. Herein, we screened a collection of clinical compounds to assess their ability to modulate RIPK1-mediated cell death. Our small-scale screen identified the anti-epilepsy drug Phenhydan® as a potent inhibitor of death receptor-induced necroptosis and apoptosis. Accordingly, Phenhydan® blocked activation of necrosome formation/activation as well as death receptor-induced NF-κB signaling by influencing the membrane function of cells, such as lipid raft formation, thus exerting an inhibitory effect on pathophysiologic cell death processes. By targeting death receptor signaling, the already FDA-approved Phenhydan® may provide new therapeutic strategies for inflammation-driven diseases caused by aberrant cell death.

Palmitoylation is required for TNF-R1 signaling

BACKGROUND

Binding of tumor necrosis factor (TNF) to TNF-receptor 1 (TNF-R1) can induce either cell survival or cell death. The selection between these diametrically opposed effects depends on the subcellular location of TNF-R1: plasma membrane retention leads to survival, while endocytosis leads to cell death. How the respective TNF-R1 associated signaling complexes are recruited to the distinct subcellular location is not known. Here, we identify palmitoylation of TNF-R1 as a molecular mechanism to achieve signal diversification.

METHODS

Human monocytic U937 cells were analyzed. Palmitoylated proteins were enriched by acyl resin assisted capture (AcylRAC) and analyzed by western blot and mass spectrometry. Palmitoylation of TNF-R1 was validated by metabolic labeling. TNF induced depalmitoylation and involvement of APT2 was analyzed by enzyme activity assays, pharmacological inhibition and shRNA mediated knock-down. TNF-R1 palmitoylation site analysis was done by mutated TNF-R1 expression in TNF-R1 knock-out cells. Apoptosis (nuclear DNA fragmentation, caspase 3 assays), NF-κB activation and TNF-R1 internalization were used as biological readouts.

RESULTS

We identify dynamic S-palmitoylation as a new mechanism that controls selective TNF signaling. TNF-R1 itself is constitutively palmitoylated and depalmitoylated upon ligand binding. We identified the palmitoyl thioesterase APT2 to be involved in TNF-R1 depalmitoylation and TNF induced NF-κB activation. Mutation of the putative palmitoylation site C248 interferes with TNF-R1 localization to the plasma membrane and thus, proper signal transduction.

CONCLUSIONS

Our results introduce palmitoylation as a new layer of dynamic regulation of TNF-R1 induced signal transduction at a very early step of the TNF induced signaling cascade. Understanding the underlying mechanism may allow novel therapeutic options for disease treatment in future.

TNFR1 membrane reorganization promotes distinct modes of TNFα signaling

Signaling by the ubiquitously expressed tumor necrosis factor receptor 1 (TNFR1) after ligand binding plays an essential role in determining whether cells exhibit survival or death. TNFR1 forms distinct signaling complexes that initiate gene expression programs downstream of the transcriptional regulators NFκB and AP-1 and promote different functional outcomes, such as inflammation, apoptosis, and necroptosis. Here, we investigated the ways in which TNFR1 was organized at the plasma membrane at the nanoscale level to elicit different signaling outcomes. We confirmed that TNFR1 forms preassembled clusters at the plasma membrane of adherent cells in the absence of ligand. After trimeric TNFα binding, TNFR1 clusters underwent a conformational change, which promoted lateral mobility, their association with the kinase MEKK1, and activation of the JNK/p38/NFκB pathway. These phenotypes required a minimum of two TNFR1-TNFα contact sites; fewer binding sites resulted in activation of NFκB but not JNK and p38. These data suggest that distinct modes of TNFR1 signaling depend on nanoscale changes in receptor organization.

Cholesterol modulates the signaling of chemosensory bitter taste receptor T2R14 in human airway cells

Bitter taste receptors (T2Rs) are a group of 25 chemosensory receptors expressed at significant levels in the human airways. In human airways, bitter taste receptor 14 (T2R14)-mediated physiological response in ameliorating obstructive airway disorders is an active area of investigation. Therefore, understanding various factors regulating the structure and function of T2R14 will be beneficial. We hypothesize that membrane lipids like cholesterol play a regulatory role in T2R14 signaling in airway cells. We confirmed the expression and signaling of T2R14 in primary human airway smooth muscle (HASM) cells and the human airway epithelial cell line (NuLi-1) using immunoblot analysis and intracellular calcium concentration mobilization experiments, respectively. Next, T2R14 signaling was examined in membrane cholesterol-altered environments by methyl-β-cyclodextrin or cholesterol oxidase treatments. In the cells analyzed, cholesterol depletion affected the agonist-induced T2R14 signaling, and cholesterol replenishment rescued its efficacy. An alternative approach for cholesterol depletion (with cholesterol oxidase pretreatment) also negatively affected the agonist potency at T2R14 in HASM cells. To understand the molecular mechanism of interaction between cholesterol and T2R14, we used site-directed mutagenesis coupled with functional assays and examined the role of putative cholesterol-binding motifs (CRAC and CARC) in T2R14. Functional characterization of wild-type and mutant T2R14 receptors suggests that amino acid residues K110, F236, and L239 are crucial in T2R14-cholesterol functional interaction. In conclusion, our results show that cholesterol influences the T2R14 signaling efficacy by forming direct interactions with the receptor and consequently plays a regulatory role in T2R14-mediated signaling in human airway cells.

Studying the TRAF2 binding to model membranes: The role of subunits dissociation

The ability of a C-terminal truncated form of TRAF2 to bind synthetic vesicles has been quantitatively studied by steady-state fluorescence energy transfer from the protein to large unilamellar vesicles (LUVs) prepared with different lipid mixtures. The dissociation constants, the free energy of binding, and the average number of phospholipids interacting with truncated TRAF2 have been evaluated from the corresponding binding curves. The results indicate that the protein strongly interacts with the lipid bilayer, preferentially in the monomeric state. These findings have been discussed in terms of their possible role in the activity of TRAF2 in vivo.

Dysregulated expression of microRNAs and mRNAs in pulmonary artery remodeling in ascites syndrome in broiler chickens

Ascites syndrome (AS), also known as pulmonary artery hypertension, remains a challenging disease that severely affects both humans and broiler chickens. Pulmonary artery remodeling presents a key step in the development of AS. In this study, we obtained pulmonary artery tissues from broilers with and without AS to perform miRNA sequencing analysis, miRNA-mRNA association analysis and pathological examinations. 29 significantly differentially expressed miRNAs were found both in known and novel miRNAs with 18 up-regulated and 11 down-regulated miRNAs. Their predicted potential targets were involved in a wide range of functional clusters as indicated via GO (Gene Ontology) and KEGG (Kyoto Encyclopedia of Genes and Genomes) analyses. The upregulation of miR-155, miR-23b-3p, miR-146b-5p and miR-146b-3p were found closely associated with the pathogenesis of pulmonary artery remodeling in AS progression. The association analysis for the miRNAs-mRNAs showed that these 29 significantly differentially expressed miRNAs regulate 162 differentially expressed target genes. Among them, 20 miRNAs correlated with 18 predicted target genes that appear to be involved in pulmonary artery remodeling, mainly in three broad physiological processes: the hypoxia sensing response (HIF1α, NHE1, STAT5 and STAT3), endothelial permeability dysfunction (CD44, TRAF2, CDK2AP1, LZTFL1, JAZF1, PEBP1, LRP1B, RPS14 and THBS2) and inflammation (MEOX2, STAT5, STAT3, IRF8, MAP3K8, IL-1BETA and TNFRSF1B). Pathological pulmonary artery remodeling in the AS broilers was consistently observed in the present study. Taken together, the current analysis further illuminates the molecular mechanism of pulmonary artery remodeling underlying AS progression.

New insight into the interaction of TRAF2 C-terminal domain with lipid raft microdomains

In this study we provide the first evidence of the interaction of a truncated-TRAF2 with lipid raft microdomains. We have analyzed this interaction by measuring the diffusion coefficient of the protein in large and giant unilamellar vesicles (LUVs and GUVs, respectively) obtained both from synthetic lipid mixtures and from natural extracts. Steady-state fluorescence measurements performed with synthetic vesicles indicate that this truncated form of TRAF2 displays a tighter binding to raft-like LUVs with respect to the control (POPC-containing LUVs), and that this process depends on the protein oligomeric state. Generalized Polarization measurements and spectral phasor analysis revealed that truncated-TRAF2 affects the membrane fluidity, especially when vesicles are heated up at physiological temperature. The addition of nanomolar concentration of TRAF2 in GUVs also seems to exert a mechanical action, as demonstrated by the formation of intraluminal vesicles, a process in which ganglioside GM1 plays a crucial role.

Silk Fibroin-Alginate-Hydroxyapatite Composite Particles in Bone Tissue Engineering Applications In Vivo

The aim of this study was to evaluate the in vivo bone regeneration capability of alginate (AL), AL/hydroxyapatite (HA), and AL/HA/silk fibroin (SF) composites. Forty Sprague Dawley rats were used for the animal experiments. Central calvarial bone (diameter: 8.0 mm) defects were grafted with AL, AL/HA, or AL/HA/SF. New bone formation was evaluated by histomorphometric analysis. To demonstrate the immunocompatibility of each group, the level of tumor necrosis factor (TNF)-α expression was studied by immunohistochemistry (IHC) and quantitative reverse transcription polymerase chain reaction (qRT-PCR) at eight weeks post implantation. Additionally, osteogenic markers, such as fibroblast growth factor (FGF)-23, osteoprotegerin (OPG), and Runt-related transcription factor (Runx2) were evaluated by qPCR or IHC at eight weeks post implantation. The AL/HA/SF group showed significantly higher new bone formation than did the control group (p = 0.044) and the AL group (p = 0.035) at four weeks post implantation. Additionally, the AL/HA/SF group showed lower relative TNF-α mRNA levels and higher FGF-23 mRNA levels than the other groups did at eight weeks post implantation. IHC results demonstrated that the AL/HA/SF group had lower TNF-α expression and higher OPG and Runx2 expression at eight weeks post implantation. Additionally, no evidence of the inflammatory reaction or giant cell formation was observed around the residual graft material. We concluded that the AL/HA/SF composite could be effective as a scaffold for bone tissue engineering.

Sphingosylphosphorylcholine inhibits macrophage adhesion to vascular smooth muscle cells

Inflammation in de-endothelialised arteries contributes to the development of cardiovascular diseases. The process that initiates this inflammatory response is the adhesion of monocytes/macrophages to exposed vascular smooth muscle cells, typically stimulated by cytokines such as tumour necrosis factor-α (TNF). The aim of this study was to determine the effect of the sphingolipid sphingosylphosphorylcholine (SPC) on the interaction of monocytes/macrophages with vascular smooth muscle cells. Rat aortic smooth muscle cells and rat bone marrow-derived macrophages were co-cultured using an in vitro assay following incubation with sphingolipids to assess inter-cellular adhesion. We reveal that SPC inhibits the TNF-induced adhesion of macrophages to smooth muscle cells. This anti-adhesive effect was the result of SPC-induced changes to the smooth muscle cells (but not the macrophages) and was mediated, at least partly, via the sphingosine 1-phosphate receptor subtype 2. Lipid raft domains were also required. Although SPC did not alter expression or membrane distribution of the adhesion proteins intercellular adhesion molecule-1 and vascular cellular adhesion protein-1 in smooth muscle cells, SPC preincubation inhibited the TNF-induced increase in inducible nitric oxide synthase (NOS2) resulting in a subsequent decrease in nitric oxide production. Inhibiting NOS2 activation in smooth muscle cells led to a decrease in the adhesion of macrophages to smooth muscle cells. This study has therefore delineated a novel pathway which can inhibit the interaction between macrophages and vascular smooth muscle cells via SPC-induced repression of NOS2 expression. This mechanism could represent a potential drug target in vascular disease.

Clinical perspectives of TRAIL: insights into central nervous system disorders

The TNF-related apoptosis inducing ligand TRAIL is a member of the TNF superfamily that has been firstly studied and evaluated for its anti-cancer activity, and the insights into its biology have already led to the identification of several TRAIL-based anticancer strategies with strong clinical therapeutic potentials. Nonetheless, the TRAIL system is far more complex and it can lead to a wider range of biological effects other than the ability of inducing apoptosis in cancer cells. By virtue of the different receptors and the different signalling pathways involved, TRAIL plays indeed a role in the regulation of different processes of the innate and adaptive immune system and this feature makes it an intriguing molecule under consideration in the development/progression/treatment of several immunological disorders. In this context, central nervous system represents a peculiar anatomic site where, despite its "status" of immune-privileged site, both innate and adaptive inflammatory responses occur and are involved in several pathological conditions. A number of studies have evaluated the role of TRAIL and of TRAIL-related pathways as pro-inflammatory or protective stimuli, depending on the specific pathological condition, confirming a twofold nature of this molecule. In this light, the aim of this review is to summarize the main preclinical evidences of the potential/involvement of TRAIL molecule and TRAIL pathways for the treatment of central nervous system disorders and the key suggestions coming from their assessment in preclinical models as proof of concept for future clinical studies.

Roles and Clinical Applications of OPG and TRAIL as Biomarkers in Cardiovascular Disease

Cardiovascular diseases (CVD) remain the major cause of death and premature disability in Western societies. Assessing the risk of CVD is an important aspect in clinical decision-making. Among the growing number of molecules that are studied for their potential utility as CVD biomarkers, a lot of attention has been focused on osteoprotegerin (OPG) and its ligands, which are receptor activator of nuclear factor κB ligand (RANKL) and TNF-related apoptosis-inducing ligand. Based on the existing literature and on our experience in this field, here we review what the possible roles of OPG and TRAIL in CVD are and their potential utility as CVD biomarkers.

The Tm7sf2 Gene Deficiency Protects Mice against Endotoxin-Induced Acute Kidney Injury

Cholesterol is essential for diverse cellular functions and cellular and whole-body cholesterol homeostasis is highly controlled. Cholesterol can also influence cellular susceptibility to injury. The connection between cholesterol metabolism and inflammation is exemplified by the Tm7sf2 gene, the absence of which reveals an essential role in cholesterol biosynthesis under stress conditions but also results in an inflammatory phenotype, i.e. NF-κB activation and TNFα up-regulation. Here, by using Tm7sf2^+/+and Tm7sf2^−/− mice, we investigated whether the Tm7sf2 gene, through its role in cholesterol biosynthesis under stress conditions, is involved in the renal failure induced by the administration of LPS. We found that the loss of Tm7sf2 gene results in significantly reduced blood urea nitrogen levels accompanied by decreased renal inflammatory response and neutral lipid accumulation. The increased expression of fatty acids catabolic enzymes reduces the need of the renal autophagy, a known crucial nutrient-sensing pathway in lipid metabolism. Moreover, we observed that the Tm7sf2 insufficiency is responsible for the inhibition of the NF-κB signalling thus dampening the inflammatory response and leading to a reduced renal damage. These results suggest a pivotal role for Tm7sf2 in renal inflammatory and lipotoxic response under endotoxemic conditions.

Simvastatin reduces burn injury-induced splenic apoptosis via downregulation of the TNF-α/NF-κB pathway

OBJECTIVE

Recent studies have suggested that epidermal burn injuries are associated with inflammation and immune dysfunction. Simvastatin has been shown to possess potent anti-inflammatory properties. Thus, we hypothesized that simvastatin protects against burn-induced apoptosis in the spleen via its anti-inflammatory activity.

METHODS

Wild-type, tumor necrosis factor alpha knockout (TNF-α KO) and NF-κB KO mice were subjected to full-thickness burn injury or sham treatment. The mice then were treated with or without simvastatin, and the spleen was harvested to measure the extent of apoptosis. Expression levels of TNF-α and NF-κB were also determined in spleen tissue and serum.

RESULTS

Burn injury induced significant splenic apoptosis and systemic cytokine production. Simvastatin protected the spleen from apoptosis, reduced cytokine production in the serum, and increased the survival rate. Simvastatin decreased burn-induced TNF-α and NF-κB expression in the spleen and serum. TNF-α and NF-κB KO mice demonstrated lower levels of apoptosis in spleen in response to burn injury. Simvastatin did not further decrease burn-caused apoptosis and mortality in either strain of KO mice.

CONCLUSIONS

Simvastatin reduces burn-induced splenic apoptosis via downregulation of the TNF-α/NF-κB pathway.

Antigen-induced airway hyperresponsiveness and obstruction is related to caveolin-1 expression in airway smooth muscle in a guinea pig asthma model

BACKGROUND

Caveolin-1 is a fundamental signalling scaffold protein involved in contraction; however, the role of caveolin-1 in airway responsiveness remains unclear. We evaluated the relationship between caveolin-1 expression in airway smooth muscle (ASM) and antigen-induced airway responsiveness and obstruction in a guinea pig asthma model.

METHODS

Airway obstruction in sensitised guinea pigs, induced by antigenic (ovalbumin) challenges administered every 10 days, was measured. Antigen-induced responsiveness to histamine and the expression of caveolin-1 and cavin 1, 2 and 3 were evaluated at the third ovalbumin challenge. The control group received saline solution instead of ovalbumin.

RESULTS

After the first challenge, antigen exposure induced a transient airway obstruction and airway hyperresponsiveness, high levels of IL-4 and IL-5 in lung and airway globet cells proliferation at the third antigenic challenge. Caveolin-1 mRNA levels in total lung decreased in the experimental group compared with controls. Flow cytometric analysis of ASM from the experimental group showed a high number of cells expressing caveolin-1 compared with controls. This increase was confirmed by western blot. Airway obstruction and hyperresponsiveness correlated with the degree of increased caveolin-1 expression in ASM cells (P < 0.05; r = 0.69 and -0.52, respectively). The expression of cavins 1, 2 and 3 in ASM also increased in the experimental group compared to controls. Immunohistochemical findings reveal that differences in ASM caveolin-1 were not evident between groups. Nevertheless, a marked decrease in caveolin-1 and caspase 3 was observed in the pulmonary vascular smooth muscle of asthma model compared with controls. Histological analysis did not reveal differences in smooth muscles mass or subepithelial fibrosis levels in airways between groups. However, an enlargement of smooth muscle mass was observed in the pulmonary microvessels of experimental animals. This enlargement did not induce changes in pulmonary or systemic arterial pressures.

CONCLUSIONS

Our data suggest that caveolin-1 expression in ASM has a crucial role in the development of antigen-induced airway obstruction and hyperresponsiveness in a guinea pig asthma model. In addition, the asthma model in guinea pigs appears to induce a contractile smooth muscle phenotype in the airways and a proliferative smooth muscle phenotype in pulmonary vessels.

TRAIL modulates the immune system and protects against the development of diabetes

TRAIL or tumor necrosis factor (TNF) related apoptosis-inducing ligand is a member of the TNF superfamily of proteins, whose best characterized function is the induction of apoptosis in tumor, infected, or transformed cells through activation of specific receptors. In nontransformed cells, however, the actions of TRAIL are less well characterized. Recent studies suggest that TRAIL may be implicated in the development and progression of diabetes. Here we review TRAIL biological actions, its effects on the immune system, and how and to what extent it has been shown to protect against diabetes.

Dual regulation of tumor necrosis factor-α on myosin light chain phosphorylation in vascular smooth muscle

We previously demonstrated that inhibitor κB kinase 2 (IKK2) is a myosin light chain kinase (MLCK). In the present study, we assess whether the prototypical activator of IKK2 tumor necrosis factor-α (TNF-α) regulates the MLCK activity of IKK2 and thus MLC phosphorylation in vascular smooth muscle cells (VSMCs). Kinase activity assay revealed that TNF-α downregulated the MLCK activity of IKK2 in human VSMCs (HVSMCs). However, Western blot analysis did not demonstrate a significant effect of TNF-α on MLC phosphorylation in HVSMCs, and myograph analysis did not reveal a significant effect of TNF-α on the contraction of the aorta from Sprague-Dawley rats and C57Bl/6j mice, suggesting a dual regulation of MLC phosphorylation by TNF-α. Confirming this notion, TNF-α significantly increased MLC phosphorylation in IKK2(-/-) but not wild-type cells. Furthermore, our results show that TNF-α increased GTP-bound RhoA and MLC phosphatase subunit MYPT1 phosphorylation and markedly reduced MLC phosphorylation in the presence of Rho-kinase inhibitor Y-27632, suggesting that downregulation of MLCK activity of IKK2 by TNF-α is antagonized by simultaneous RhoA/Rho-kinase activation. These results indicate that TNF-α dually regulates MLC phosphorylation through both IKK2 and RhoA/Rho-kinase pathways.

TRAF2 facilitates vaccinia virus replication by promoting rapid virus entry

Tumor necrosis factor receptor (TNFR)-associated factor 2 (TRAF2) is a pivotal intracellular mediator of signaling pathways downstream of TNFR1 and -2 with known pro- and antiviral effects. We investigated its role in the replication of the prototype poxvirus vaccinia virus (VACV). Loss of TRAF2 expression, either through small interfering RNA treatment of HeLa cells or through genetic knockout in murine embryonic fibroblasts (MEFs), led to significant reductions in VACV growth following low-multiplicity infection. In single-cycle infections, there was delayed production of both early and late VACV proteins as well as accelerated virus-induced alterations to cell morphology, indicating that TRAF2 influences early stages of virus replication. Consistent with an early role, uncoating assays showed normal virus attachment but delayed virus entry in the absence of TRAF2. Although alterations to c-Jun N-terminal kinase (JNK) signaling were apparent in VACV-infected TRAF2^−/− MEFs, treatment of wild-type cells with a JNK inhibitor did not affect virus entry. Instead, treatment with an inhibitor of endosomal acidification greatly reduced virus entry into TRAF2^−/− MEFs, suggesting that VACV is reliant on the endosomal route of entry in the absence of TRAF2. Thus, TRAF2 is a proviral factor for VACV that plays a role in promoting efficient viral entry, most likely via the plasma membrane.

IMPORTANCE Tumor necrosis factor receptor-associated factors (TRAFs) are key facilitators of intracellular signaling with roles in innate and adaptive immunity and stress responses. We have discovered that TRAF2 is a proviral factor in vaccinia virus replication in both HeLa cells and mouse embryonic fibroblasts and that its influence is exercised through promotion of efficient virus entry.

ROCK1 translocates from non-caveolar to caveolar regions upon KCl stimulation in airway smooth muscle

Airway smooth muscle (ASM) membrane depolarization through KCl opens L-type voltage dependent Ca2+ channels (Ca(v)1.2); its opening was considered the cause of KCl contraction. This substance is used to bypass intracellular second messenger pathways. It is now clear that KCl also activates RhoA/Rho kinase (ROCK) pathway. ROCK isoforms are characterized as ROCK1 and ROCK2. Because ROCK1 seems the most abundant isotype in lung, we studied its participation in KCl stimulated bovine ASM. With methyl-beta-cyclodextrin (MbetaCD) we disrupted caveolae, a membrane compartment considered as the RhoA/ROCK assembly site, and found that KCl contraction was reduced to the same extent (~26%) as Y-27632 (ROCK inhibitor) treated tissues. We confirmed that KCl induces ROCK activation and this effect was annulled by Y-27632 or MbetaCD. In isolated plasmalemma, ROCK1 was localized in non-caveolar membrane fractions in Western blots from control tissues, but it transferred to caveolae in samples from tissues stimulated with KCl. Ca(v)1.2 was found at the non-caveolar membrane fractions in control and MbetaCD treated tissues. In MbetaCD treated tissues stimulated with KCl, contraction was abolished by nifedipine; only the response to Ca(v)1.2 opening remained as the ROCK component disappeared. Our results show that, in ASM, the KCl contraction involves the translocation of ROCK1 from non-caveolar to caveolar regions and that the proper physiological response depends on this translocation.

The role of caveolae in the pathophysiology of lung diseases

Caveolae are flask-shaped plasma membrane invaginations formed by constitutive caveolin proteins and regulatory cavin proteins. Caveolae harbor a range of signaling components such as receptors, ion channels and regulatory molecules. There is now increasing evidence that caveolins and cavins play an important role in a variety of diseases. However, the mechanisms by which these caveolar proteins affect lung health and disease are still under investigation, with emerging data suggesting complex roles in disease pathophysiology. This review summarizes the current state of understanding of how caveolar proteins contribute to lung structure and function and how their altered expression and/or function can influence lung diseases.

Inflammation, caveolae and CD38-mediated calcium regulation in human airway smooth muscle

The pro-inflammatory cytokine tumor necrosis factor-alpha (TNFα) increases expression of CD38 (a membrane-associated bifunctional enzyme regulating cyclic ADP ribose), and enhances agonist-induced intracellular Ca(2+) ([Ca(2+)]i) responses in human airway smooth muscle (ASM). We previously demonstrated that caveolae and their constituent protein caveolin-1 are important for ASM [Ca(2+)]i regulation, which is further enhanced by TNFα. Whether caveolae and CD38 are functionally linked in mediating TNFα effects is unknown. In this regard, whether the related cavin proteins (cavin-1 and -3) that maintain structure and function of caveolae play a role is also not known. In the present study, we hypothesized that TNFα effects on CD38 expression and function in human ASM involve caveolae. Caveolar fractions from isolated human ASM cells expressed CD38 and its expression was upregulated by exposure to 20ng/ml TNFα (48h). ASM cells expressed cavin-1 and cavin-3, which were also upregulated by TNFα. Knockdown of caveolin-1, cavin-1 or cavin-3 (using siRNA) all significantly reduced CD38 expression and ADP-ribosyl cyclase activity in the presence or absence of TNFα. Furthermore, caveolin-1, cavin-1 and cavin-3 siRNAs reduced [Ca(2+)]i responses to histamine under control conditions, and blunted the enhanced [Ca(2+)]i responses in TNFα-exposed cells. These data demonstrate that CD38 is expressed within caveolae and its function is linked to the caveolar regulatory proteins caveolin-1, cavin-1 and -3. The link between caveolae and CD38 is further enhanced during airway inflammation demonstrating the important role of caveolae in regulation of [Ca(2+)]i and contractility in the airway.

Caveolin-1 knockout mice exhibit airway hyperreactivity

Caveolae are flask-shaped plasma membrane invaginations expressing the scaffolding caveolin proteins. Although caveolins have been found in endothelium and epithelium (where they regulate nitric oxide synthase activity), their role in smooth muscle is still under investigation. We and others have previously shown that caveolae of human airway smooth muscle (ASM), which express caveolin-1, contain Ca(2+) and force regulatory proteins and are involved in mediating the effects of inflammatory cytokines such as TNF-α on intracellular Ca(2+) concentration responses to agonist. Accordingly, we tested the hypothesis that in vivo, absence of caveolin-1 leads to reduced airway hyperresponsiveness, using a knockout (KO) (Cav1 KO) mouse and an ovalbumin-sensitized/challenged (OVA) model of allergic airway hyperresponsiveness. Surprisingly, airway responsiveness to methacholine, tested by use of a FlexiVent system, was increased in Cav1 KO control (CTL) as well as KO OVA mice, which could not be explained by a blunted immune response to OVA. In ASM of wild-type (WT) OVA mice, expression of caveolin-1, the caveolar adapter proteins cavins 1-3, and caveolae-associated Ca(2+) and force regulatory proteins such as Orai1 and RhoA were all increased, effects absent in Cav1 KO CTL and OVA mice. However, as with WT OVA, both CTL and OVA Cav1 KO airways showed signs of enhanced remodeling, with high expression of proliferation markers and increased collagen. Separately, epithelial cells from airways of all three groups displayed lower endothelial but higher inducible nitric oxide synthase and arginase expression. Arginase activity was also increased in these three groups, and the inhibitor nor-NOHA (N-omega-nor-l-arginine) enhanced sensitivity of isolated tracheal rings to ACh, especially in Cav1 KO mice. On the basis of these data disproving our original hypothesis, we conclude that caveolin-1 has complex effects on ASM vs. epithelium, resulting in airway hyperreactivity in vivo mediated by altered airway remodeling and bronchodilation.

Caveolins and lung function

The primary function of the mammalian lung is to facilitate diffusion of oxygen to venous blood and to ventilate carbon dioxide produced by catabolic reactions within cells. However, it is also responsible for a variety of other important functions, including host defense and production of vasoactive agents to regulate not only systemic blood pressure, but also water, electrolyte and acid-base balance. Caveolin-1 is highly expressed in the majority of cell types in the lung, including epithelial, endothelial, smooth muscle, connective tissue cells, and alveolar macrophages. Deletion of caveolin-1 in these cells results in major functional aberrations, suggesting that caveolin-1 may be crucial to lung homeostasis and development. Furthermore, generation of mutant mice that under-express caveolin-1 results in severe functional distortion with phenotypes covering practically the entire spectrum of known lung diseases, including pulmonary hypertension, fibrosis, increased endothelial permeability, and immune defects. In this Chapter, we outline the current state of knowledge regarding caveolin-1-dependent regulation of pulmonary cell functions and discuss recent research findings on the role of caveolin-1 in various pulmonary disease states, including obstructive and fibrotic pulmonary vascular and inflammatory diseases.

The tumor necrosis factor receptor stalk regions define responsiveness to soluble versus membrane-bound ligand

The family of tumor necrosis factor receptors (TNFRs) and their ligands form a regulatory signaling network that controls immune responses. Various members of this receptor family respond differently to the soluble and membrane-bound forms of their respective ligands. However, the determining factors and underlying molecular mechanisms of this diversity are not yet understood. Using an established system of chimeric TNFRs and novel ligand variants mimicking the bioactivity of membrane-bound TNF (mTNF), we demonstrate that the membrane-proximal extracellular stalk regions of TNFR1 and TNFR2 are crucial in controlling responsiveness to soluble TNF (sTNF). We show that the stalk region of TNFR2, in contrast to the corresponding part of TNFR1, efficiently inhibits both the receptor's enrichment/clustering in particular cell membrane regions and ligand-independent homotypic receptor preassembly, thereby preventing sTNF-induced, but not mTNF-induced, signaling. Thus, the stalk regions of the two TNFRs not only have implications for additional TNFR family members, but also provide potential targets for therapeutic intervention.

Caveolae and propofol effects on airway smooth muscle

BACKGROUND

The i.v. anaesthetic propofol produces bronchodilatation. Airway relaxation involves reduced intracellular Ca(2+) ([Ca(2+)](i)) in airway smooth muscle (ASM) and lipid rafts (caveolae), and constitutional caveolin proteins regulate [Ca(2+)](i). We postulated that propofol-induced bronchodilatation involves caveolar disruption.

METHODS

Caveolar fractions of human ASM cells were tested for propofol content. [Ca(2+)](i) responses of ASM cells loaded with fura-2 were performed in the presence of 10 µM histamine with and without clinically relevant concentrations of propofol (10 and 30 μM and intralipid control). Effects on sarcoplasmic reticulum (SR) Ca(2+) release were evaluated in zero extracellular Ca(2+) using the blockers Xestospongin C and ryanodine. Store-operated Ca(2+) entry (SOCE) after SR depletion was evaluated using established techniques. The role of caveolin-1 in the effect of propofol was tested using small interference RNA (siRNA) suppression. Changes in intracellular signalling cascades relevant to [Ca(2+)](i) and force regulation were also evaluated.

RESULTS

Propofol was present in ASM caveolar fractions in substantial concentrations. Exposure to 10 or 30 µM propofol form decreased [Ca(2+)](i) peak (but not plateau) responses to histamine by ~40%, an effect persistent in zero extracellular Ca(2+). Propofol effects were absent in caveolin-1 siRNA-transfected cells. Inhibition of ryanodine receptors prevented propofol effects on [Ca(2+)](i), while propofol blunted [Ca(2+)](i) responses to caffeine. Propofol reduced SOCE, an effect also prevented by caveolin-1 siRNA. Propofol effects were associated with decreased caveolin-1 expression and extracellular signal-regulated kinase phosphorylation.

CONCLUSIONS

These novel data suggest a role for caveolae (specifically caveolin-1) in propofol-induced bronchodilatation. Due to its lipid nature, propofol may transiently disrupt caveolar regulation, thus altering ASM [Ca(2+)](i).

Acidic sphingomyelinase induced by electrophiles promotes proinflammatory cytokine production in human bladder carcinoma ECV-304 cells

Electrophiles in environmental pollutants or cigarette smoke are high risk factors for various diseases caused by cell injuries such as apoptosis and inflammation. Here we show that electrophilic compounds such as diethyl malate (DEM), methyl mercury and cigarette smoke extracts significantly enhanced the expression of acidic sphingomyelinase (ASMase). ASMase activity and the amount of ceramide of DEM-treated cells were approximately 6 times and 4 times higher than these of non-treated cells, respectively. Moreover, we found that DEM pretreatment enhanced the production of IL-6 induced by TNF-α. Knockdown of ASMase attenuated the enhancement of TNF-α-dependent IL-6 production. On the other hand, enhancement of TNF-α-induced IL-6 production was observed in ASMase-overexpressing cells without DEM. Fractionation of the lipid raft revealed that the TNF receptor 1 (TNFR1) was migrated into the lipid raft in DEM-treated cells or ASMase-overexpressing cells. The TNF-α-induced IL-6 expression required the clustering of TNFR1 since IL-6 expression were decreased by the destruction of the lipid raft with filipin. These results demonstrated a new role for ASMase in the acceleration of the production of TNF-induced IL-6 as a pro-inflammatory cytokine and indicated that electrophiles could potentiate inflammation response by up-regulating of ASMase expression following formation of lipid rafts.

Sphingosine-1-phosphate-induced release of TIMP-2 from vascular smooth muscle cells inhibits angiogenesis

Following myocardial infarction, angiogenesis occurs as a result of thrombus formation, which permits reperfusion of damaged myocardium. Sphingosine 1-phosphate (S1P) is a naturally occurring lipid mediator released from platelets and is found in high concentrations at sites of thrombosis. S1P might therefore be involved in regulating angiogenesis following myocardial infarction and might influence reperfusion. The aims of this study were to determine the effects of S1P in human coronary arterial cell angiogenesis and delineate the subsequent mechanisms. An in vitro model of angiogenesis was developed using a co-culture of human coronary artery endothelial cells, human coronary smooth muscle cells and human fibroblasts. In this model, S1P inhibited angiogenesis and this was dependent on the presence of smooth muscle cells. The mechanism of the inhibitory effect was through S1P-induced release of a soluble mediator from smooth muscle cells. This mediator was identified as tissue inhibitor of metalloproteinase-2 (TIMP-2). Release of TIMP-2 was dependent on S1P-induced activation of Rho kinase and directly contributed to incomplete formation of endothelial cell adherens junctions. This was observed as a diffuse localisation of VE-cadherin, leading to decreased tubulogenesis. A similar inhibitory response to S1P was demonstrated in an ex vivo human arterial model of angiogenesis. In summary, S1P-induced inhibition of angiogenesis in human artery endothelial cells is mediated by TIMP-2 from vascular smooth muscle cells. This reduces the integrity of intercellular junctions between nascent endothelial cells. S1P might therefore inhibit the angiogenic response following myocardial infarction.

The MC159 protein from the molluscum contagiosum poxvirus inhibits NF-κB activation by interacting with the IκB kinase complex

Molluscum contagiosum virus (MCV) causes persistent neoplasms in healthy and immunocompromised people. Its ability to persist likely is due to its arsenal of viral immunoevasion proteins. For example, the MCV MC159 protein inhibits TNF-R1-induced NF-κB activation and apoptosis. The MC159 protein is a viral FLIP and, as such, possesses two tandem death effector domains (DEDs). We show in this article that, in human embryonic kidney 293 T cells, the expression of wild-type MC159 or a mutant MC159 protein containing the first DED (MC159 A) inhibited TNF-induced NF-κB, or NF-κB activated by PMA or MyD88 overexpression, whereas a mutant protein lacking the first DED (MC159 B) did not. We hypothesized that the MC159 protein targeted the IκB kinase (IKK) complex to inhibit these diverse signaling events. Indeed, the MC159 protein, but not MC159 B, coimmunoprecipitated with IKKγ. MC159 coimmunoprecipitated with IKKγ when using mouse embryonic fibroblasts that lack either IKKα or IKKβ, suggesting that the MC159 protein interacted directly with IKKγ. MC159-IKKγ coimmunoprecipitations were detected during infection of cells with either MCV isolated from human lesions or with a recombinant MC159-expressing vaccinia virus. MC159 also interacts with TRAF2, a signaling molecule involved in NF-κB activation. However, mutational analysis of MC159 failed to reveal a correlation between MC159-TRAF2 interactions and MC159's inhibitory function. We propose that MC159-IKK interactions, but not MC159-TRAF2 interactions, are responsible for inhibiting NF-κB activation.

Caveolin-1 regulation of store-operated Ca(2+) influx in human airway smooth muscle

Caveolae, plasma membrane invaginations with constitutive caveolin proteins, harbour proteins involved in intracellular calcium ([Ca(2+)](i)) regulation. In human airway smooth muscle (ASM), store-operated Ca(2+) entry (SOCE) is a key component of [Ca(2+)](i) regulation, and contributes to increased [Ca(2+)](i) in inflammation. SOCE involves proteins Orai1 and stromal interaction molecule (STIM)1. We investigated the link between caveolae, SOCE and inflammation in ASM. [Ca(2+)](i) was measured in human ASM cells using fura-2. Small interference RNA (siRNA) or overexpression vectors were used to alter expression of caveolin-1 (Cav-1), Orai1 or STIM1. Tumour necrosis factor (TNF)-α was used as a representative pro-inflammatory cytokine. TNF-α increased SOCE following sarcoplasmic reticulum Ca(2+) depletion, and increased whole-cell and caveolar Orai1 (but only intracellular STIM1). Cav-1 siRNA decreased caveolar and whole-cell Orai1 (but not STIM1) expression, and blunted SOCE, even in the presence of TNF-α. STIM1 overexpression substantially enhanced SOCE: an effect only partially reversed by Cav-1 siRNA. In contrast, Orai1 siRNA substantially blunted SOCE even in the presence of TNF-α. Cav-1 overexpression significantly increased Orai1 expression and SOCE, especially in the presence of TNF-α. These results demonstrate that caveolar expression and regulation of proteins such as Orai1 are important for [Ca(2+)](i) regulation in human ASM cells and its modulation during inflammation.

Caveolins and lung function

The primary function of the mammalian lung is to facilitate diffusion of oxygen to venous blood and to ventilate carbon dioxide produced by catabolic reactions within cells. However, it is also responsible for a variety of other important functions, including host defense and production of vasoactive agents to regulate not only systemic blood pressure, but also water, electrolyte and acid-base balance. Caveolin-1 is highly expressed in the majority of cell types in the lung, including epithelial, endothelial, smooth muscle, connective tissue cells, and alveolar macrophages. Deletion of caveolin-1 in these cells results in major functional aberrations, suggesting that caveolin-1 may be crucial to lung homeostasis and development. Furthermore, generation of mutant mice that under-express caveolin-1 results in severe functional distortion with phenotypes covering practically the entire spectrum of known lung diseases, including pulmonary hypertension, fibrosis, increased endothelial permeability, and immune defects. In this Chapter, we outline the current state of knowledge regarding caveolin-1-dependent regulation of pulmonary cell functions and discuss recent research findings on the role of caveolin-1 in various pulmonary disease states, including obstructive and fibrotic pulmonary vascular and inflammatory diseases.

Receptor activator of NF-κB ligand-dependent expression of caveolin-1 in osteoclast precursors, and high dependency of osteoclastogenesis on exogenous lipoprotein

Although extensive studies have done much to clarify the molecular mechanisms of osteoclastogenesis during the last ten years, there may still be unknown molecules associated with osteoclast differentiation. Thus, we used fluorescent differential display to screen for genes whose expression is induced by receptor activator of NF-κB ligand (RANKL), a crucial molecule for osteoclast formation. We identified caveolin-1 (Cav-1) as a RANKL-induced gene. Cav-1 is a major structural protein of caveolae and lipid rafts, cholesterol-enriched microdomains in the plasma membrane (PM). The RANKL-induced Cav-1 was immediately conveyed to lipid rafts. Conversely, expression of flotillin-1 (Flot-1), another scaffolding protein of lipid rafts, was reduced during osteoclastogenesis, indicating conversion of Flot-1-predominant rafts into Cav-1-enriched rafts. However, in vitro osteoclastogenesis of precursor cells from Cav-1-null mice was comparable to that of wild-type mice, while Cav-2 expression in the knockout osteoclasts was maintained. Conversely, Cav-2 gene silencing in Cav-1-null osteoclast precursors using siRNA for Cav-2 increased osteoclast formation, suggesting that the Cav-1/Cav-2 complex may act as a negative regulator for osteoclastogenesis. On the other hand, destruction of lipid rafts by removal of cholesterol from the PM by methyl-ß-cyclodextrin (MCD) treatment caused disordered signal transductions for osteoclastogenesis, such as hyperactivation of Erk1/2 and insensitivity of Akt to RANKL stimulus. The abnormal signaling was reproduced by deleting exogenous lipoproteins from the culture medium, which also resulted in reduced osteoclast formation. In addition, the deletion caused delayed expression of nuclear factor of activated T cells c1 (NFATc1), and depressed its activation in the cytosol and inhibited its translocation into nuclei. Simultaneously, the deletion reduced the level of FcRγ, a trigger protein for initiating the calcium signaling needed to activate NFATc1, and decreased Cav-1 in lipid rafts. These findings indicate that the molecular mechanisms of osteoclastogenesis are highly dependent on extracellular lipoprotein and the integrity of lipid rafts, and suggest possible involvement of cholesterol.

Caveolin-1 in cytokine-induced enhancement of intracellular Ca(2+) in human airway smooth muscle

Diseases such as asthma are characterized by airway hyperresponsiveness. Enhanced airway smooth muscle (ASM) intracellular Ca(2+) ([Ca(2+)](i)) response to agonist stimulation leading to increased airway constriction has been suggested to contribute to airway hyperresponsiveness. Caveolae are flask-shaped plasma membrane invaginations that express the scaffolding protein caveolin and contain multiple proteins important in [Ca(2+)](i) signaling (e.g., agonist receptors, ion channels). We recently demonstrated that caveolae and caveolin-1 are important in [Ca(2+)](i) regulation in human ASM. Proinflammatory cytokines such as tumor necrosis factor (TNF)-α and interleukin (IL)-13 modulate [Ca(2+)](i) in ASM. We hypothesized that cytokine upregulation of caveolar signaling in ASM contributes to enhanced agonist-induced [Ca(2+)](i) in inflammation. Enzymatically dissociated human ASM cells were exposed to medium (control), 20 ng/ml TNF-α, or 50 ng/ml IL-13 for 24 h. Caveolae-enriched membrane fractions displayed substantial increase in caveolin-1 and -2 expressions by TNF-α and IL-13. Transfection with caveolin-1-mRed DNA substantially accelerated and increased plasma membrane caveolin-1 expression by TNF-α and to a lesser extent by IL-13. Caveolin-1 enhancement was inhibited by nuclear factor-κB and mitogen-activated protein kinase inhibitors. In fura 2-loaded ASM cells, [Ca(2+)](i) responses to 1 μM ACh, 10 μM histamine, or 10 nM bradykinin were all exaggerated by TNF-α as well as IL-13 exposure. However, disruption of caveolae using caveolin-1 suppression via small-interfering RNA resulted in significant blunting of agonist-induced [Ca(2+)](i) responses of vehicle and TNF-α-exposed cells. These functional data were correlated to the presence of TNFR(1) receptor (but not the IL-4/IL-13 receptor) within caveolae. Overall, these results indicate that caveolin-1 plays an important role in airway inflammation by modulating the effect of specific cytokines on [Ca(2+)](i).

Src mediates cytokine-stimulated gene expression in airway myocytes through ERK MAPK

The p38 and extracellular signal-regulated kinases (ERK) mitogen-activated protein kinases (MAPK) participate in cytokine-stimulated inflammatory gene expression in airway smooth muscle cells. The following study was undertaken to determine whether Src tyrosine kinases are signaling intermediaries upstream of cytokine-stimulated MAPK activation and gene expression. Treating human airway myocytes with interleukin (IL)-1β, tumor necrosis factor (TNF) α and interferon (IFN) γ caused a rapid 1.8-fold increase in Src family tyrosine kinase activity within 1 minute that remained 2.3 to 2.7 fold above basal conditions for 15 minutes. This activity was blocked by addition of 30 μM PP1, a pyrimidine inhibitor specific for Src family tyrosine kinases, in immune-complex assays to confirm that this stimulus activates Src tyrosine kinase. Addition of PP1 also blocked cytokine-stimulated expression of IL-1β, IL-6 and IL-8, while decreasing phosphorylation of ERK, but not p38 MAPK. Since this inflammatory stimulus may activate additional inflammatory signaling pathways downstream of Src, we tested the effects of PP1 on phosphorylation of signal transducers and activators of transcription (STAT). PP1 had no effect on cytokine-stimulated STAT 1 or STAT 3 phosphorylation. These results demonstrate that Src tyrosine kinases participate in the regulation of IL-1β, IL-6 and IL-8 expression and that these effects of Src are mediated through activation of ERK MAPK and not p38 MAPK or STAT1/STAT3 phosphorylation.

Caveolin-1 and force regulation in porcine airway smooth muscle

Caveolae are specialized membrane microdomains expressing the scaffolding protein caveolin-1. We recently demonstrated the presence of caveolae in human airway smooth muscle (ASM) and the contribution of caveolin-1 to intracellular calcium ([Ca(2+)](i)) regulation. In the present study, we tested the hypothesis that caveolin-1 regulates ASM contractility. We examined the role of caveolins in force regulation of porcine ASM under control conditions as well as TNF-α-induced airway inflammation. In porcine ASM strips, exposure to 10 mM methyl-β-cyclodextrin (CD) or 5 μM of the caveolin-1 specific scaffolding domain inhibitor peptide (CSD) resulted in time-dependent decrease in force responses to 1 μM ACh. Overnight exposure to the cytokine TNF-α (50 ng/ml) accelerated and increased caveolin-1 expression and enhanced force responses to ACh. Suppression of caveolin-1 with small interfering RNA mimicked the effects of CD or CSD. Regarding mechanisms by which caveolae contribute to contractile changes, inhibition of MAP kinase with 10 μM PD98059 did not alter control or TNF-α-induced increases in force responses to ACh. However, inhibiting RhoA with 100 μM fasudil or 10 μM Y27632 resulted in significant decreases in force responses, with lesser effects in TNF-α exposed samples. Furthermore, Ca(2+) sensitivity for force generation was substantially reduced by fasudil or Y27632, an effect even more enhanced in the absence of caveolin-1 signaling. Overall, these results indicate that caveolin-1 is a critical player in enhanced ASM contractility with airway inflammation.

A phospholipase Cγ1-activated pathway regulates transcription in human vascular smooth muscle cells

AIMS

Growth factor-induced repression of smooth muscle (SM) cell marker genes is an integral part of vascular SM (VSM) cell proliferation. This is partly regulated via translocation of extracellular signal-regulated kinase 1/2 (ERK1/2) to the nucleus which activates the transcription factor Elk-1. The mediators involved in ERK1/2 nuclear translocation in VSM cells are unknown. The aim of this study is to examine the mechanisms which regulate growth factor-induced nuclear translocation of ERK1/2 and gene expression in VSM cells.

METHODS AND RESULTS

In cultured human VSM cells, phospholipase C (PLC)γ1 expression was required for platelet-derived growth factor (PDGF)-induced ERK1/2 nuclear translocation, Elk-1 phosphorylation, and subsequent repression of SM α-actin gene expression. The mechanisms of a role for PLCγ1 in ERK1/2 nuclear localization were further examined by investigating interacting proteins. The ERK1/2-binding phosphoprotein, protein enriched in astrocytes-15 (PEA-15), was phosphorylated by PDGF and this phosphorylation required activation of PLCγ1. In cells pre-treated with PEA-15 siRNA, ERK1/2 distribution significantly increased in the nucleus and resulted in decreased SM α-actin expression and increased VSM cell proliferation. Overexpression of PEA-15 increased ERK1/2 localization in the cytoplasm. The regulatory role of PEA-15 phosphorylation was assessed. In VSM cells overexpressing a non-phosphorylatable form of PEA-15, PDGF-induced ERK1/2 nuclear localization was inhibited.

CONCLUSION

These results suggest that PEA-15 phosphorylation by PLCγ1 is required for PDGF-induced ERK1/2 nuclear translocation. This represents an important level of phenotypic control by directly affecting Elk-1-dependent transcription and ultimately SM cell marker protein expression in VSM cells.

Sphingolipids and cardiovascular diseases: lipoprotein metabolism, atherosclerosis and cardiomyopathy

Heart disease is widely believed to develop from two pathological processes. Circulating lipoproteins containing the nondegradable lipid, cholesterol, accumulate within the arterial wall and perhaps are oxidized to more toxic lipids. Both lipid accumulation and vascular reaction to the lipids lead to the gradual thickening of the vascular wall. A second major process that in some circumstances is a primary event is the development of a local inflammatory reaction. This might be a reaction to vessel wall injury that accompanies infections, immune disease, and perhaps diabetes and renal failure. In this chapter, we will focus on the relationship between de novo synthesis of sphingolipids and lipid metabolism, atherosclerosis, and cardiomyopathy.

Amphotericin B membrane action: role for two types of ion channels in eliciting cell survival and lethal effects

The formation of aqueous pores by the polyene antibiotic amphotericin B (AmB) is at the basis of its fungicidal and leishmanicidal action. However, other types of nonlethal and dose-dependent biphasic effects that have been associated with the AmB action in different cells, including a variety of survival responses, are difficult to reconcile with the formation of a unique type of ion channel by the antibiotic. In this respect, there is increasing evidence indicating that AmB forms nonaqueous (cation-selective) channels at concentrations below the threshold at which aqueous pores are formed. The main foci of this review will be (1) to provide a summary of the evidence supporting the formation of cation-selective ion channels and aqueous pores by AmB in lipid membrane models and in the membranes of eukaryotic cells; (2) to discuss the influence of membrane parameters such as thickness fluctuations, the type of sterol present and the existence of sterol-rich specialized lipid raft microdomains in the formation process of such channels; and (3) to develop a cell model that serves as a framework for understanding how the intracellular K(+) and Na(+) concentration changes induced by the cation-selective AmB channels enhance multiple survival response pathways before they are overcome by the more sustained ion fluxes, Ca(2+)-dependent apoptotic events and cell lysis effects that are associated with the formation of AmB aqueous pores.

Rho-kinase mediates TNF-α-induced MCP-1 expression via p38 MAPK signaling pathway in mesangial cells

Macrophage accumulation has been implicated in the pathogenesis of inflammatory glomerular disease. Monocyte chemoattractant protein-1 (MCP-1) plays a central role in recruiting monocytes to the glomeruli. Tumor necrosis factor-α (TNF-α) has been shown to induce MCP-1 expression in mesangial cells, although the precise mechanisms remain unclear. We previously demonstrated that RhoA and its effector, Rho-kinase (Rho-associated coiled-coil containing protein kinase, ROCK), are involved in the pathogenesis of diabetic nephropathy. However, its role in MCP-1 induction by TNF-α has not been elucidated. In the present study, we investigated whether the Rho/Rho-kinase signaling pathway regulates the TNF-α-mediated induction of MCP-1 in mesangial cells. Exposure of mouse mesangial cells (MES-13) to TNF-α resulted in an increase of MCP-1 expression (by RT-PCR) and secretion into the medium (by ELISA). Pull down and Western blot analysis revealed that TNF-α activated RhoA and Rho-kinase. Based on these observations, we speculated that the Rho/Rho-kinase signaling pathway may be involved in MCP-1 induction by TNF-α. In agreement with this concept, Y-27632, a specific Rho-kinase inhibitor, attenuated TNF-α-mediated induction of MCP-1. We demonstrated that Y-27632 inhibited TNF-α-mediated monocyte migration and attenuated TNF-α-mediated p38 MAPK activation. Based on these data we infer that Y-27632 inhibits TNF-α-induced MCP-1 expression, secretion and function through inhibition of Rho-kinase and p38 MAPK activity. Our study suggests that Rho/Rho-kinase is an important therapeutic target of monocyte recruitment and accumulation within the glomerulus in inflammatory renal disease.