Heat shock protein 90 inhibitors prolong survival, attenuate inflammation, and reduce lung injury in murine sepsis

Harvesting, identification and barrier function of human lung microvascular endothelial cells

Endothelial barrier dysfunction is an important contributor to the pathogenesis of acute lung injury (ALI) and acute respiratory distress syndrome (ARDS). Even though approaches that target the prevention and repair of endothelial barrier dysfunction are clearly needed, our understanding of the molecular regulation of pulmonary microvascular endothelial permeability remains incomplete. Cultured pulmonary microvascular endothelial cells represent an attractive paradigm for the study of barrier function. Here, we describe a method for the harvest, identification and culture of human lung microvascular endothelial cells (HLMVEC). HLMVEC thus obtained, grow as a monolayer, exhibit contact inhibition and have the typical cobblestone appearance. They express endothelial proteins, such as von Willebrand factor and endothelial nitric oxide synthase and take up an acetylated LDL. Furthermore, HLMVEC respond predictably and with superior sensitivity to the barrier disruptive effects of Gram positive and Gram negative bacterial products, thrombin, vascular endothelial growth factor and microtubule disrupting agents. These HLMVEC present an in-house-derived alternative to commercially available human cells for the study of mechanisms contributing to ALI and ARDS.

Tripterine prevents endothelial barrier dysfunction by inhibiting endogenous peroxynitrite formation

BACKGROUND AND PURPOSE

Tripterine is an inhibitor of heat shock protein 90 and an active component of Tripterygium wilfordii Hook F., which is used in traditional Chinese medicine to treat inflammatory diseases such as rheumatoid arthritis. We hypothesized that tripterine inhibits endogenous peroxynitrite formation and thereby prevents endothelial barrier dysfunction.

EXPERIMENTAL APPROACH

Effects of tripterine were investigated on endothelial barrier function, inducible nitric oxide synthase (iNOS) expression, nicotinamide adenine dinucleotide phasphate (NADPH) oxidase activity, 3-nitrotyrosine formation, protein phosphatase type 2A (PP2A) activity, activation of extracellular-regulated kinase (ERK), c-Jun terminal kinase (JNK) and Janus kinase (Jak2), and degradation of IkappaB in microvascular endothelial cells exposed to pro-inflammatory stimulus [lipopolysaccharide (LPS) + interferon gamma (IFNgamma)] and on vascular permeability in air pouches of mice injected with LPS + IFNgamma.

KEY RESULTS

LPS + IFNgamma caused an increase in monolayer permeability, induction of iNOS and NADPH oxidase type 1 (Nox1) proteins, formation of superoxide, nitric oxide and 3-nitrotyrosine, and increase in PP2A activity in endothelial cells. These effects of LPS + IFNgamma were diminished by tripterine (50-200 nM). Further, LPS + IFNgamma-induced expression of iNOS and Nox1 was attenuated by the mitogen-activated protein kinase kinase 1/2 (MEK1/2) inhibitor PD98059, the JNK inhibitor SP600125, the Jak2 inhibitor AG490 and the NFkappaB inhibitor MG132, but not by the p38 mitogen-activated protein kinase inhibitor SB203580. LPS + IFNgamma stimulated phosphorylation of ERK, JNK and Jak2, and degradation of IkappaB, but only Jak2 phosphorylation was sensitive to tripterine (50-200 nM). Further, tripterine diminished the increased vascular permeability in inflamed air pouches.

CONCLUSION AND IMPLICATIONS

Our results indicate that, by preventing Jak2-dependent induction of iNOS and Nox1, tripterine inhibits peroxynitrite precursor synthesis, attenuates the increased activity of PP2A and consequently protects endothelial barrier function.

Celastrol binds to ERK and inhibits FcepsilonRI signaling to exert an anti-allergic effect

The role of celastrol, a triterpene extracted from the Chinese "Thunder of God Vine," in allergic inflammation was investigated. Celastrol decreased the secretion of beta-hexosaminidase, decreased the release of histamine, decreased the expression of Th2 cytokines and decreased calcium influx and cell adhesion in antigen-stimulated RBL2H3 cells. Exposure to celastrol decreased the phosphorylation of extracellular regulated kinase (ERK) and the ERK kinase activity was decreased in RBL2H3 cells. A molecular dynamics simulation showed binding of celastrol to a large pocket in ERK2, which serves as the ATP-binding site. Exposure to celastrol inhibited the interaction between immunoglobulin Fc epsilon receptor I (FcepsilonRIgamma) and ERK and inhibited interaction between FcepsilonRIgamma and protein kinase C delta (PKCdelta). Antigen stimulation induced an interaction between Rac1 and ERK as well as an interaction between Rac1 and PKCdelta. Inhibition of ERK decreased Rac1 activity and inhibition of Rac1 decreased ERK activity in antigen-stimulated RBL2H3 cells. Celastrol regulated the expression of epithelial-mesenchymal transition (EMT)-related proteins through inhibition of PKCalpha, PKCdelta, and Rac1 in antigen-stimulated RBL2H3 cells. Exposure to celatrol inhibited PKCdelta activity in antigen-stimulated RBL2H3 cells. Celastrol exerted a negative effect on FcepsilonRIbeta signaling by inhibiting the interaction between heat shock protein 90 (hsp90) and proteins, such as, FcepsilonRIbeta, Akt and PKCalpha. Celastrol exerted a negative effect on in vivo atopic dermatitis induced by 2, 4-dinitrofluorobenzene (DNFB), which requires ERK. Celastrol also showed an inhibitory effect on skin inflammation induced by phorbol myristate acetate (PMA) in Balb/c mice. In summary, celastrol binds to ERK and inhibits FcepsilonRI signaling to exert an anti-inflammatory effect.

The minor salivary gland proteome in Sjögren's syndrome

OBJECTIVE

To identify the global protein expression (the proteome) in the minor salivary glands from primary Sjögren's syndrome (pSS) patients and non-SS controls.

MATERIALS AND METHODS

Minor labial salivary glands were obtained from six pSS patients and from six age-matched non-SS controls, lysed in SDS buffer and pooled into two groups, respectively. The lysates were analysed by liquid chromatography electrospray ionization combined with tandem mass spectrometry. Also, the proteins were separated by two-dimensional polyacrylamide gel electrophoresis and protein spots were subjected to mass spectrometry.

RESULTS

Heat shock proteins, mucins, carbonic anhydrases, enolase, vimentin and cyclophilin B were among the proteins identified. The differences in the proteomes of minor salivary glands from pSS patients and non-SS controls were mainly related to ribosomal proteins, immunity and stress. Alpha-defensin-1 and calmodulin were among six proteins exclusively identified in pSS patients.

CONCLUSION

We have identified several minor salivary gland proteins that may have implications for clarifying the SS pathophysiology. This experiment adds to the knowledge of proteins produced in salivary glands in health and disease, and may form the basis of further studies on biomarkers of prognostic and diagnostic value.

Regulators of endothelial and epithelial barrier integrity and function in acute lung injury

Permeability edema is a life-threatening complication accompanying acute lung injury (ALI), severe pneumonia and the acute respiratory distress syndrome (ARDS), which can be associated with a reduced alveolar liquid clearance (ALC) capacity, a disruption of the alveolar epithelial barrier, and an increased capillary endothelial permeability. Bacterial and viral infections can directly promote pulmonary endothelial hyperpermeability and indirectly decrease the function and/or expression of ion transporters regulating ALC in type II alveolar epithelial cells, by means of inducing a strong inflammatory and oxidative stress response in the infected lungs. Apart from ventilation strategies, no standard treatment exists for permeability edema, making the search for novel regulators of endothelial and epithelial hyperpermeability and dysfunction important. Here, we present an overview of recently identified substances that inhibit and/or reverse endothelial barrier disruption and permeability or alveolar epithelial dysfunction: (1) zinc chelators, which were shown to attenuate the effects of oxidative stress on the pulmonary endothelium; (2) peroxisome proliferator activated receptor (PPAR) ligands, which have been shown to exert anti-inflammatory effects, by decreasing the expression of pro-inflammatory genes; (3) extracellular ATP, produced during inflammation, which induces a rapid and dose-dependent increase in transendothelial electrical resistance (TER) across pulmonary endothelial cells; (4) the lectin-like domain of TNF, which is spatially distinct from the receptor binding sites and which protects from hydrostatic and permeability edema and (5) Hsp90 inhibitors, which prevent and repair toxin-induced hyperpermeability. Unraveling the mechanism of action of these agents could contribute to the development of novel therapeutic strategies to combat permeability edema.

Endothelial nitric oxide (NO) and its pathophysiologic regulation

Nitric oxide (NO) is a gaseous lipophilic free radical generated by three distinct isoforms of nitric oxide synthases (NOS), type 1 or neuronal (nNOS), type 2 or inducible (iNOS) and type 3 or endothelial NOS (eNOS). Expression of eNOS is altered in many types of cardiovascular disease, such as atherosclerosis, diabetes and hypertension. The ubiquitous chaperone heat shock protein 90 (hsp90) associates with NOS and is important for its proper folding and function. Current studies point toward a therapeutic potential by modulating hsp90-NOS association in various vascular diseases. Here we review the transcriptional regulation of endothelial NOS and factors affecting eNOS activity and function, as well as the important vascular pathologies associated with altered NOS function, focusing on the regulatory role of hsp90 and other factors in NO-associated pathogenesis of these diseases.

The endothelium in acute lung injury/acute respiratory distress syndrome

PURPOSE OF REVIEW

Since pulmonary edema from increased endothelial permeability is the hallmark of acute lung injury, a frequently encountered entity in critical care medicine, the study of endothelial responses in this setting is crucial to the development of effective endothelial-targeted treatments.

RECENT FINDINGS

From the enormous amount of research in the field of endothelial pathophysiology, we have focused on work delineating endothelial alterations elicited by noxious stimuli implicated in acute lung injury. The bulk of the material covered deals with molecular and cellular aspects of the pathogenesis, reflecting current trends in the published literature. We initially discuss pathways of endothelial dysfunction in acute lung injury and then cover the mechanisms of endothelial protection. Several experimental treatments in animal models are presented, which aid in the understanding of the disease pathogenesis and provide evidence for potentially useful therapies.

SUMMARY

Mechanistic studies have delivered several interventions, which are effective in preventing and treating experimental acute lung injury and have thus provided objectives for translational studies. Some of these modalities may evolve into clinically useful tools in the treatment of this devastating illness.

Heat shock protein 90 inhibitors protect and restore pulmonary endothelial barrier function

Heat shock protein 90 (hsp90) inhibitors inactivate and/or degrade various client proteins, including many involved in inflammation. Increased vascular permeability is a hallmark of acute lung injury (ALI) and acute respiratory distress syndrome (ARDS). Thus, we tested the hypothesis that hsp90 inhibitors may prevent and/or restore endothelial cell (EC) permeability after injury. Exposure of confluent bovine pulmonary arterial endothelial cell (BPAEC) monolayer to TGF-beta1, thrombin, bacterial lipopolysaccharide (LPS), or vascular endothelial growth factor (VEGF) increased BPAEC permeability, as revealed by decreased transendothelial electrical resistance (TER). Treatment of injured endothelium with hsp90 inhibitors completely restored TER of BPAEC. Similarly, preincubation of BPAEC with hsp90 inhibitors prevented the decline in TER induced by the exposure to thrombin, LPS, VEGF, or TGF-beta1. In addition, hsp90 inhibitors restored the EC barrier function after PMA or nocodazole-induced hyperpermeability. These effects of the hsp90 inhibitors were associated with the restoration of TGF-beta1- or nocodazole-induced decrease in VE-cadherin and beta-catenin expression at EC junctions. The protective effect of hsp90 inhibitors on TGF-beta1-induced hyperpermeability was critically dependent upon preservation of F-actin cytoskeleton and was associated with the inhibition of agonist-induced myosin light chain (MLC) and myosin phosphatase target subunit 1 (MYPT1) phosphorylation, F-actin stress fibers formation, microtubule disassembly, increase in hsp27 phosphorylation, and association of hsp90 with hsp27, but independent of p38MAPK activity. We conclude that hsp90 inhibitors exert barrier protective effects on BPAEC, at least in part, via inhibition of hsp27-mediated, agonist-induced cytoskeletal rearrangement, and therefore may have useful therapeutic value in ALI, ARDS, and other pulmonary inflammatory disease.

Serum antibodies to Porphyromonas gingivalis chaperone HtpG predict health in periodontitis susceptible patients

Background

Chaperones are ubiquitous conserved proteins critical in stabilization of new proteins, repair/removal of defective proteins and immunodominant antigens in innate and adaptive immunity. Periodontal disease is a chronic inflammatory infection associated with infection by Porphyromonas gingivalis that culminates in the destruction of the supporting structures of the teeth. We previously reported studies of serum antibodies reactive with the human chaperone Hsp90 in gingivitis, a reversible form of gingival disease confined to the oral soft tissues. In those studies, antibodies were at their highest levels in subjects with the best oral health. We hypothesized that antibodies to the HSP90 homologue of P. gingivalis (HtpG) might be associated with protection/resistance against destructive periodontitis.

Methodology/Principal Findings

ELISA assays using cloned HtpG and peptide antigens confirmed gingivitis subjects colonized with P. gingivalis had higher serum levels of anti-HtpG and, concomitantly, lower levels of attachment loss. Additionally, serum antibody levels to P. gingivalis HtpG protein were higher in healthy subjects compared to patients with either chronic or aggressive periodontitis. We found a negative association between tooth attachment loss and anti-P. gingivalis HtpG (p = 0.043) but not anti-Fusobacterium nucleatum (an oral opportunistic commensal) HtpG levels. Furthermore, response to periodontal therapy was more successful in subjects having higher levels of anti-P. gingivalis HtpG before treatment (p = 0.018). There was no similar relationship to anti-F. nucleatum HtpG levels. Similar results were obtained when these experiments were repeated with a synthetic peptide of a region of P. gingivalis HtpG.

Conclusions/Significance

Our results suggest: 1) anti-P. gingivalis HtpG antibodies are protective and therefore predict health periodontitis-susceptable patients; 2) may augment the host defence to periodontitis and 3) a unique peptide of P. gingivalis HtpG offers significant potential as an effective diagnostic target and vaccine candidate. These results are compatible with a novel immune control mechanism unrelated to direct binding of bacteria.

Heat shock protein 90 inhibitors attenuate LPS-induced endothelial hyperpermeability

Endothelial hyperperme ability leading to vascular leak is an important consequence of sepsis and sepsis-induced lung injury. We previously reported that heat shock protein (hsp) 90 inhibitor pretreatment improved pulmonary barrier dysfunction in a murine model of sepsis-induced lung injury. We now examine the effects of hsp90 inhibitors on LPS-mediated endothelial hyperpermeability, as reflected in changes in transendothelial electrical resistance (TER) of bovine pulmonary arterial endothelial cells (BPAEC). Vehicle-pretreated cells exposed to endotoxin exhibited a concentration-dependent decrease in TER, activation of pp60(Src), phosphorylation of the focal adhesion protein paxillin, and reduced expression of the adherens junction proteins, vascular endothelial (VE)-cadherin and beta-catenin. Pretreatment with the hsp90 inhibitor, radicicol, prevented the decrease in TER, maintained VE-cadherin and beta-catenin expression, and inhibited activation of pp60(Src) and phosphorylation of paxillin. Similarly, when BPAEC hyperpermeability was induced by endotoxin-activated neutrophils, pretreatment of neutrophils and/or endothelial cells with radicicol protected against the activated neutrophil-induced decrease in TER. Increased paxillin phosphorylation and decreased expression of beta-catenin and VE-cadherin were also observed in mouse lungs 12 h after intraperitoneal endotoxin and attenuated in mice pretreated with radicicol. These results suggest that hsp90 plays an important role in sepsis-associated endothelial barrier dysfunction.

Regulation of muscle growth by pathogen-associated molecules

Skeletal muscle demonstrates great plasticity in response to environmental and hormonal factors including pathogen-associated molecules, inflammatory cytokines, and growth factors. These signals impinge on muscle by forcing individual muscle fibers to either grow or atrophy. We recently demonstrated that skeletal muscle cells express multiple Toll-like receptors (TLR) that recognize bacterial cell wall components, such as lipopolysaccharide (LPS). Exposure of myocytes to LPS and other TLR ligands initiates an inflammatory response culminating in the autocrine production of cytokines and NO by NO synthase (NOS)2. The TLR signal through protein kinases that phosphorylate and promote the degradation of an inhibitory protein that normally retains the transcription factor, nuclear factor kappaB (NFkappaB), in the cytoplasm. Phosphorylation and degradation of the inhibitor of NFkappaB allows for translocation of NFkappaB to the nucleus and activation of inflammatory genes. Overexpression of a constitutively active inhibitor of NFkappaB kinase in skeletal muscle causes severe wasting, and we found that inhibitors of either the phosphorylation of IkappaB or its proteolytic degradation prevent TLR ligand-induced expression of cytokines and NOS2. The combination of LPS and interferon gamma dramatically enhances the magnitude and duration of LPS-stimulated NOS2 expression and reduces protein translation. Lipopolysaccharide and interferon gamma also downregulates signaling from the mammalian target of rapamycin, a kinase that directs changes in cell size. Inhibitors of NOS block the fall in muscle cell protein synthesis and restore translational signaling, indicating that activation of the NOS2-NO pathway is responsible for the observed decrease in muscle protein synthesis. Our work provides a molecular explanation for reduced muscle growth during infection. Muscle is largely self-sufficient because it expresses receptors, signaling pathways, and effectors to regulate its own size. Prolonged activation of NFkappaB and NOS2 have emerged as detrimental facets of the immune response in muscle. The interplay between inflammatory components and growth factor signaling clearly places muscle at the interface between growth and immunity.