Bacterial heat shock proteins directly induce cytokine mRNA and interleukin-1 secretion in macrophage cultures

DnaJ-induced miRNA-146a negatively regulates the expression of IL-8 in macrophages

As a member of the damage-associated molecular patterns, heat shock proteins (HSPs) are widely recognized for their role in initiating innate immune responses. These highly conserved proteins are expressed ubiquitously in both prokaryotes and eukaryotes. In this study, our aim was to investigate how DnaJ, a HSP40 homolog derived from Pseudomonas aeruginosa (P. aeruginosa), influences the regulation of IL-8 expression in macrophages. Treatment with DnaJ served as a stimulus, inducing a more robust expression of IL-8 compared to other HSP homologs, including DnaK, GroEL, and HtpG. This effect was achieved through the activation of the NF-κB signaling pathway. Interestingly, DnaJ treatment also significantly increased the expression of microRNA-146a (miR-146a), which appears to play a role in modulating the expression of innate defense genes. As a consequence, pre-treatment with DnaJ led to a reduction in the extent of IL-8 induction in response to P. aeruginosa treatment. Notably, this reduction was counteracted by transfection of a miR-146a inhibitor, highlighting the involvement of miR-146a in P. aeruginosa-mediated induction of IL-8 expression. Therefore, this study uncovers the role of DnaJ in triggering the expression of miR-146a, which, in turn, modulates the excessive expression of IL-8 induced by P. aeruginosa infection.

Mycobacterial Heat Shock Proteins in Sarcoidosis and Tuberculosis

Pathological similarities between sarcoidosis (SA) and tuberculosis (TB) suggest the role of mycobacterial antigens in the etiopathogenesis of SA. The Dubaniewicz group revealed that not whole mycobacteria, but Mtb-HSP70, Mtb-HSP 65, and Mtb-HSP16 were detected in the lymph nodes, sera, and precipitated immune complexes in patients with SA and TB. In SA, the Mtb-HSP16 concentration was higher than that of Mtb-HSP70 and that of Mtb-HSP65, whereas in TB, the Mtb-HSP16 level was increased vs. Mtb-HSP70. A high Mtb-HSP16 level, induced by low dose-dependent nitrate/nitrite (NOx), may develop a mycobacterial or propionibacterial genetic dormancy program in SA. In contrast to TB, increased peroxynitrite concentration in supernatants of peripheral blood mononuclear cell cultures treated with Mtb-HSP may explain the low level of NOx detected in SA. In contrast to TB, monocytes in SA were resistant to Mtb-HSP-induced apoptosis, and CD4+T cell apoptosis was increased. Mtb-HSP-induced apoptosis of CD8+T cells was reduced in all tested groups. In Mtb-HSP-stimulated T cells, lower CD8+γδ+IL-4+T cell frequency with increased TNF-α,IL-6,IL-10 and decreased INF-γ,IL-2,IL-4 production were present in SA, as opposed to an increased presence of CD4+γδ+TCR cells with increased TNF-α,IL-6 levels in TB, vs. controls. Mtb-HSP modulating the level of co-stimulatory molecules, regulatory cells, apoptosis, clonal deletion, epitope spread, polyclonal activation and molecular mimicry between human and microbial HSPs may also participate in the induction of autoimmunity, considered in SA. In conclusion, in different genetically predisposed hosts, the same antigens, e.g., Mtb-HSP, may induce the development of TB or SA, including an autoimmune response in sarcoidosis.

DnaJ-induced TLR7 mediates an increase in interferons through the TLR4-engaged AKT/NF-κB and JNK signaling pathways in macrophages

Toll-like receptor 7 (TLR7) signaling plays pivotal roles in innate immunity by sensing viral single-stranded RNA thereby triggering inflammatory signaling cascades and eliciting protective antiviral responses. In this study, we found that TLR7 expression is highly induced in response to Pseudomonas aeruginosa (P. aeruginosa) infection in a dose- and time-dependent manner. P. aeruginosa-derived DnaJ, a homolog of HSP40, was identified as a related inducing agent for TLR7 expression, and expression of DnaJ was stimulated when host cells were infected with P. aeruginosa. Interestingly, DnaJ was not involved in mediating an increase in the expression levels of TLR3 and TLR8, other well-known antiviral receptors. The induction of TLR7 in response to DnaJ was mediated by the activation of the AKT (Thr308 and Ser473)/NF-κB and p38/JNK MAPKs signaling pathways, consequently transmitting related signals for the expression of interferons (IFNs). Of note, these antiviral responses were regulated, at least in part, by TLR4, which senses the presence of DnaJ and then promotes downstream activation of the AKT (Ser473)/NF-κB and JNK signaling cascades. Taken together, these results suggest that P. aeruginosa-derived DnaJ is sufficient to promote an increase in TLR7 expression in the TLR4-engaged AKT/NF-κB and JNK signaling pathways, thereby promoting an increased antiviral response through the elevated expression of IFNs.

Negative regulation of interleukin 1β expression in response to DnaK from Pseudomonas aeruginosa via the PI3K/PDK1/FoxO1 pathways

Interleukin (IL)-1β is crucial for a wide range of inflammatory responses. Previously, we reported that IL-1β is produced in response to Pseudomonas aeruginosa-derived DnaK via NF-κB and JNK pathways; however, the signaling pathways that counter the process to maintain IL-1β homeostasis are unknown. Here, we show that DnaK-mediated expression of IL1β is increased markedly in macrophages upon blockade of PI3K/PDK1. This was verified by measuring released IL-1β protein. The negative effect of PI3K on IL-1β production was dependent on suppression of both NF-κB and JNK activation. Intriguingly, PDK1 (an underlying mediator of PI3K) acted as an upstream regulator for the activation of NF-κB, but downregulated JNK activation. Furthermore, production of IL-1β and activation of JNK were triggered by inhibition of phosphorylated FoxO1; phosphorylation of FoxO1 was controlled by PDK1 signaling in response to DnaK. Thus, IL-1β production is modulated by P. aeruginosa-derived DnaK via cross-talk between JNK and PI3K/PDK1/FoxO1 pathways.

Regulation of Antimicrobial Pathways by Endogenous Heat Shock Proteins in Gastrointestinal Disorders

Heat shock proteins (HSPs) are essential mediators of cellular homeostasis by maintaining protein functionality and stability, and activating appropriate immune cells. HSP activity is influenced by a variety of factors including diet, microbial stimuli, environment and host immunity. The overexpression and down-regulation of HSPs is associated with various disease phenotypes, including the inflammatory bowel diseases (IBD) such as Crohn’s disease (CD). While the precise etiology of CD remains unclear, many of the putative triggers also influence HSP activity. The development of different CD phenotypes therefore may be a result of the disease-modifying behavior of the environmentally-regulated HSPs. Understanding the role of bacterial and endogenous HSPs in host homeostasis and disease will help elucidate the complex interplay of factors. Furthermore, discerning the function of HSPs in CD may lead to therapeutic developments that better reflect and respond to the gut environment.

Heat shock proteins and cardiovascular disease

The development of stress drives a host of biological responses that include the overproduction of a family of proteins named heat shock proteins (HSPs), because they were initially studied after heat exposure. HSPs are evolutionarily preserved proteins with a high degree of interspecies homology. HSPs are intracellular proteins that also have extracellular expression. The primary role of HSPs is to protect cell function by preventing irreversible protein damage and facilitating molecular traffic through intracellular pathways. However, in addition to their chaperone role, HSPs are immunodominant molecules that stimulate natural as well as disease-related immune reactivity. The latter may be a consequence of molecular mimicry, generating cross-reactivity between human HSPs and the HSPs of infectious agents. Autoimmune reactivity driven by HSPs could also be the result of enhancement of the immune response to peptides generated during cellular injury and of their role in the delivery of peptides to the major histocompatibility complex in antigen-presenting cells. In humans, HSPs have been found to participate in the pathogenesis of a large number of diseases. This review is focused on the role of HSPs in atherosclerosis and essential hypertension.

Chaperonomics in leptospirosis

INTRODUCTION

Knowledge of the function of molecular chaperones is required for a better understanding of cellular proteostasis. Nevertheless, such information is currently dispersed as most of previous studies investigated chaperones on a single-angle basis. Recently, a new subdiscipline of chaperonology, namely 'chaperonomics' (defined as 'systematic analysis of chaperone genes, transcripts, proteins, or their interaction networks using omics technologies'), has been emerging to better understand biological, physiological, and pathological roles of chaperones. Areas covered: This review provides broad overviews of bacterial chaperones, heat shock proteins (HSPs), and leptospirosis, and then focuses on recent progress of chaperonomics applied to define roles of HSPs in various pathogenic and saprophytic leptospiral species and serovars. Expert commentary: Comprehensive analysis of leptospiral chaperones/HSPs using a chaperonomics approach holds great promise for better understanding of functional roles of chaperones/HSPs in bacterial survival and disease pathogenesis. Moreover, this new approach may also lead to further development of chaperones/HSPs-based diagnostics and/or vaccine discovery for leptospirosis.

HSP60 critically regulates endogenous IL-1β production in activated microglia by stimulating NLRP3 inflammasome pathway

Background

Interleukin-1β (IL-1β) is one of the most important cytokine secreted by activated microglia as it orchestrates the vicious cycle of inflammation by inducing the expression of various other pro-inflammatory cytokines along with its own production. Microglia-mediated IL-1β production is a tightly regulated mechanism which involves the activation of nucleotide-binding oligomerization domain leucine-rich repeat and pyrin domain-containing 3 (NLRP3) inflammasome pathway. Our previous study suggests the critical role of heat shock protein 60 (HSP60) in IL-1β-induced inflammation in microglia through TLR4-p38 MAPK axis. However, whether HSP60 regulates endogenous IL-1β production is not known. Therefore, to probe the underlying mechanism, we elucidate the role of HSP60 in endogenous IL-1β production.

Methods

We used in vitro (N9 murine microglial cells) and in vivo (BALB/c mouse) models for our study. HSP60 overexpression and knockdown experiment was done to elucidate the role of HSP60 in endogenous IL-1β production by microglia. Western blotting and quantitative real-time PCR was performed using N9 cells and BALB/c mice brain, to analyze various proteins and transcript levels. Reactive oxygen species levels and mitochondrial membrane depolarization in N9 cells were analyzed by flow cytometry. We also performed caspase-1 activity assay and enzyme-linked immunosorbent assay to assess caspase-1 activity and IL-1β production, respectively.

Results

HSP60 induces the phosphorylation and nuclear localization of NF-κB both in vitro and in vivo. It also induces perturbation in mitochondrial membrane potential and enhances reactive oxygen species (ROS) generation in microglia. HSP60 further activates NLRP3 inflammasome by elevating NLRP3 expression both at RNA and protein levels. Furthermore, HSP60 enhances caspase-1 activity and increases IL-1β secretion by microglia. Knockdown of HSP60 reduces the IL-1β-induced production of IL-1β both in vitro and in vivo. Also, we have shown for the first time that knockdown of HSP60 leads to decreased IL-1β production during Japanese encephalitis virus (JEV) infection, which eventually leads to decreased inflammation and increased survival of JEV-infected mice.

Conclusion

HSP60 mediates microglial IL-1β production by regulating NLRP3 inflammasome pathway and reduction of HSP60 leads to reduction of inflammation in JEV infection.

Electronic supplementary material

The online version of this article (10.1186/s12974-018-1214-5) contains supplementary material, which is available to authorized users.

Mycobacterium tuberculosis GrpE, A Heat-Shock Stress Responsive Chaperone, Promotes Th1-Biased T Cell Immune Response via TLR4-Mediated Activation of Dendritic Cells

Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis, is an extremely successful pathogen with multifactorial ability to control the host immune response. Insights into the Mtb factors modulating host response are required for the discovery of novel vaccine antigen targets as well as a better understanding of dynamic interactions between the bacterial factors and host cells. Here, we exploited the functional role of Mtb GrpE, a cofactor of heat-shock protein 70 (HSP70), in promoting naïve CD4⁺/CD8⁺T cell differentiation toward Th1-type T-cell immunity through interaction with dendritic cells (DCs). GrpE functionally induced DC maturation by up-regulating the expression of cell surface molecules (CD80, CD86, and MHC class I and II) and production of several pro-inflammatory cytokines (TNF-α, IL-1β, IL-6, and IL-12p70) in DCs. These effects of GrpE in DC activation were initiated upon binding to Toll-like receptor 4 (TLR4) followed by activation of downstream MyD88-, TRIF-, MAPK-, and NF-κB-dependent signaling pathways. GrpE-activated DCs displayed an excellent capacity to effectively polarize naïve CD4⁺ and CD8⁺ T cells toward Th1-type T-cell immunity with the dose-dependent secretion of IFN-γ and IL-2 together with increased levels of CXCR3 expression. Notably, GrpE-stimulated DCs induced the proliferation of GrpE-specific Th1-type effector/memory CD4⁺/CD8⁺CD44^highCD62L^low T cells from the spleen of Mtb-infected mice in a TLR4-dependent manner. Collectively, these results demonstrate that GrpE is a novel immune activator that interacts with DCs, in particular, via TLR4, to generate Th1-biased memory T cells in an antigen-specific manner. GrpE may contribute to the enhanced understanding of host-pathogen interactions as well as providing a rational basis for the discovery of new potential targets to develop an effective tuberculosis vaccine.

The evaluation of immunogenic impact of selected bacterial, recombinant Hsp60 antigens in DBA/2J mice

Heat Shock Proteins (HSP) are highly conserved proteins that are widely spread throughout all organisms. They function in the cytoplasm as chaperones; however, they could be expressed on the cell surface. It has been shown that Hsp60 obtained from gram-negative bacteria are able to stimulate cells of the acquired and innate immune system. The aim of this study was the evaluation of the immunogenic properties of recombinant Hsp60 proteins derived from four common pathogenic bacteria: Escherichia coli, Histophilus somni, Pasteurella multocida and Salmonella Enteritidis. The analysis of the humoral immune response in DBA/2J mice hyperimmunized with selected rHsp60 revealed high levels of IgG rHsp60-antibody with the predominance of the IgG₁ subclass, in the reaction with both homologous and heterologous antigens. The presence of IgG_2a and IgG_2b was also observed; however, no antibodies of subclass IgG₃ were detected. The comparison of plasma IgG antibody reactivity of mice immunized with two different doses of rHsp60 (10/20 μg) showed that the lower dose was sufficient to induce a strong humoral response. The reactivity of the IgG rHsp60-antibody with whole bacterial cells showed a significantly higher reaction with H. somni compared with other pathogens. It was demonstrated that the addition of all rHsp60 with polymyxin B to the culture medium stimulated splenocytes isolated from hyperimmunized mice to release IL-1β and IL-6. As a strong stimulator of the immune system, bacterial-origin Hsp60 seems to be an interesting potential component of subunit vaccines aimed at the development of protection for animals during infections caused by gram-negative bacteria.

Role and mechanism of the Hsp70 molecular chaperone machines in bacterial pathogens

Heat shock proteins are highly conserved, stress-inducible, ubiquitous proteins that maintain homeostasis in both eukaryotes and prokaryotes. Hsp70 proteins belong to the heat shock protein family and enhance bacterial survival in hostile environments. Hsp70, known as DnaK in prokaryotes, supports numerous processes such as the assembly and disassembly of protein complexes, the refolding of misfolded and clustered proteins, membrane translocation and the regulation of regulatory proteins. The chaperone-based activity of Hsp70 depends on dynamic interactions between its two domains, known as the ATPase domain and the substrate-binding domain. It also depends on interactions between these domains and other co-chaperone molecules such as the Hsp40 protein family member DnaJ and nucleotide exchange factors. DnaJ is the primary chaperone that interacts with nascent polypeptide chains and functions to prevent their premature release from the ribosome and misfolding before it is targeted by DnaK. Adhesion of bacteria to host cells is mediated by both host and bacterial Hsp70. Following infection of the host, bacterial Hsp70 (DnaK) is in a position to initiate bacterial survival processes and trigger an immune response by the host. Any mutations in the dnaK gene have been shown to decrease the viability of bacteria inside the host. This review will give insights into the structure and mechanism of Hsp70 and its role in regulating the protein activity that contributes to pathogenesis.

Importance of the C-terminal histidine residues of Helicobacter pylori GroES for Toll-like receptor 4 binding and interleukin-8 cytokine production

Helicobacter pylori infection is associated with the development of gastric and duodenal ulcers as well as gastric cancer. GroES of H. pylori (HpGroES) was previously identified as a gastric cancer-associated virulence factor. Our group showed that HpGroES induces interleukin-8 (IL-8) cytokine release via a Toll-like receptor 4 (TLR4)-dependent mechanism and domain B of the protein is crucial for interactions with TLR4. In the present study, we investigated the importance of the histidine residues in domain B. To this end, a series of point mutants were expressed in Escherichia coli, and the corresponding proteins purified. Interestingly, H96, H104 and H115 were not essential, whereas H100, H102, H108, H113 and H118 were crucial for IL-8 production and TLR4 interactions in KATO-III cells. These residues were involved in nickel binding. Four of five residues, H102, H108, H113 and H118 induced certain conformation changes in extended domain B structure, which is essential for interactions with TLR4 and consequent IL-8 production. We conclude that interactions of nickel ions with histidine residues in domain B help to maintain the conformation of the C-terminal region to conserve the integrity of the HpGroES structure and modulate IL-8 release.

Heat shock proteins (HSPs) in the homeostasis of regulatory T cells (Tregs)

Heat shock proteins (HSPs) belong to the family of conservative polypeptides with a high homology of the primary structure. The uniqueness of this family lies in their ability to interact with a large number of different proteins and provide protection from cellular and environmental stress factors as molecular chaperones to keep protein homeostasis. While intracellular HSPs play a mainly protective role, extracellular or membrane-bound HSPs mediate immunological functions and immunomodulatory activity. In immune system are subsets of cells including regulatory T cells (Tregs) with suppressive functions. HSPs are implicated in the function of innate and adaptive immune systems, stimulate T lymphocyte proliferation and immunomodulatory functions, increase the effectiveness of cross-presentation of antigens, and induce the secretion of cytokines. HSPs are also important in the induction, proliferation, suppressive function, and cytokine production of Tregs, which are a subset of CD4+ T cells maintaining peripheral tolerance. Together HSPs and Tregs are potential tools for future clinical interventions in autoimmune disease.

Review: Pathogen-associated molecular pattern contamination as putative endogenous ligands of Toll-like receptors

Extensive work in recent years has suggested that a number of endogenous molecules, their derivatives or degradation products may be potent activators of the innate immune system capable of inducing pro-inflammatory cytokine production by the monocyte—macrophage system and the activation and maturation of dendritic cells. The cytokine-like effects of these endogenous molecules are mediated via Toll-like receptor (TLR) signal transduction pathways in a manner similar to pathogen-associated molecular patterns (PAMPs). However, recent evidence suggests that the reported cytokine effects of some of these putative endogenous ligands are in fact due to contaminating PAMPs. The reasons for the failure to recognize PAMP contaminants being responsible for the putative TLR ligands of these endogenous molecules include: (i) failure to use highly purified preparations free of PAMP contamination; (ii) failure to recognize the heat sensitivity of lipopolysaccharide (LPS); and (iii) failure to consider contaminant(s) other than LPS. Strategies are proposed to avoid future designation of PAMP contamination as putative endogenous ligands of TLRs.

INSURMOUNTABLE HEAT: THE EVOLUTION AND PERSISTENCE OF DEFENSIVE HYPERTHERMIA

Fever, the rise in body temperature set point in response to infection or injury, is a highly conserved trait among vertebrates, and documented in many arthropods. Fever is known to reduce illness duration and mortality. These observations present an evolutionary puzzle: why has fever continued to be an effective response to fast-evolving pathogenic microbes across diverse phyla, and probably over countless millions of years? Framing fever as part of a more general thermal manipulation strategy that we term defensive hyperthermia, we hypothesize that the solution lies in the independent contributions to pathogen fitness played by virulence and infectivity. A host organism deploying defensive hyperthermia alters the ecological environment of an invading pathogen. To the extent that the pathogen evolves to be able to function effectively at elevated temperatures, it disadvantages itself at infecting the next (thermonormative) host, becoming more likely to be thwarted by that host's immune system and outcompeted by wild ecotype conspecifics (a genetically distinct strain adapted to specific environmental conditions) that, although more vulnerable to elevated temperatures, operate more effectively at the host's normal temperature. We evaluate this hypothesis in light of existing evidence concerning pathogen thermal specialization, and discuss theoretical and translational implications of this model.

IL12, IL10, IFNγ and TNFα Expression in Human Primary Monocytes Stimulated with Bacterial Heat Shock GroEL (Hsp64) Protein

Actinobacillus (Aggregatibacter) actinomycetemicomitans (Aa) is a bacterium that lives in the oral cavity and plays an important role in periodontal diseases. The effect of A.actinomycetemcomitans's heat shock family protein GroEL on host or immune cells including monocytes is quite limited. In this study, the recombinant A.actinomycetemcomitans's GroEL protein (rAaGroEL) was used as an antigen and its effects on monocytes of peripheral blood mononuclear cells (PBMCs) was investigated. To do that, PBMCs were stimulated with rAaGroEL protein at different time points (16h to 96h) and the cytokines of CD14+ monocytes were detected with intracellular cytokine staining by Flow cytometry. Data showed that AaGroEL protein has an antigenic effect on human primary monocytes. AaGroEL protein responsive CD14 monocytes stimulates the expression of IL12, IL10, IFNγ and TNFα cytokines with different kinetics and expression profile. Therefore, A. actinomycetemcomitans's heat shock GroEL protein can modulate innate and adaptive immune responses and contribute to an inflammatory diseases pathology.

Analysis of Protein Composition and Bioactivity of Neoponera villosa Venom (Hymenoptera: Formicidae)

Ants cause a series of accidents involving humans. Such accidents generate different reactions in the body, ranging from a mild irritation at the bite site to anaphylactic shock, and these reactions depend on the mechanism of action of the venom. The study of animal venom is a science known as venomics. Through venomics, the composition of the venom of several ant species has already been characterized and their biological activities described. Thus, the aim of this study was to evaluate the protein composition and biological activities (hemolytic and immunostimulatory) of the venom of Neoponera villosa (N. villosa), an ant widely distributed in South America. The protein composition was evaluated by proteomic techniques, such as two-dimensional electrophoresis. To assess the biological activity, hemolysis assay was carried out and cytokines were quantified after exposure of macrophages to the venom. The venom of N. villosa has a profile composed of 145 proteins, including structural and metabolic components (e.g., tubulin and ATPase), allergenic and immunomodulatory proteins (arginine kinase and heat shock proteins (HSPs)), protective proteins of venom (superoxide dismutase (SOD) and catalase) and tissue degradation proteins (hyaluronidase and phospholipase A2). The venom was able to induce hemolysis in human erythrocytes and also induced release of both pro-inflammatory cytokines, as the anti-inflammatory cytokine release by murine macrophages. These results allow better understanding of the composition and complexity of N. villosa venom in the human body, as well as the possible mechanisms of action after the bite.

The GroEL protein of Porphyromonas gingivalis regulates atherogenic phenomena in endothelial cells mediated by upregulating toll-like receptor 4 expression

Porphyromonas gingivalis (P. gingivalis) is a bacterial species that causes periodontitis. GroEL from P. gingivalis may possess biological activity and may be involved in the destruction of periodontal tissues. However, it is unclear whether P. gingivalis GroEL enhances the appearance of atherogenic phenomena in endothelial cells and vessels. Here, we constructed recombinant GroEL from P. gingivalis to investigate its effects in human coronary artery endothelial cells (HCAECs) in vitro and on aortas of high-cholesterol (HC)-fed B57BL/6 and B57BL/6-Tlr4(lps-del) mice in vivo. The results showed that GroEL impaired tube-formation capacity under non-cytotoxic conditions in HCAECs. GroEL increased THP-1 cell/HCAEC adhesion by increasing the expression of intracellular adhesion molecule (ICAM)-1 and vascular adhesion molecule (VCAM)-1 in endothelial cells. Additionally, GroEL increased DiI-oxidized low density lipoprotein (oxLDL) uptake, which may be mediated by elevated lectin-like oxLDL receptor (LOX)-1 but not scavenger receptor expressed by endothelial cells (SREC) and scavenger receptor class B1 (SR-B1) expression. Furthermore, GroEL interacts with toll-like receptor 4 (TLR4) and plays a causal role in atherogenesis in HCAECs. Human antigen R (HuR), an RNA-binding protein with a high affinity for the 3' untranslated region (3'UTR) of TLR4 mRNA, contributes to the up-regulation of TLR4 induced by GroEL in HCAECs. In a GroEL animal administration study, GroEL elevated ICAM-1, VCAM-1, LOX-1 and TLR4 expression in the aortas of HC diet-fed wild C57BL/6 but not C57BL/6-Tlr4(lps-del) mice. Taken together, our findings suggest that P. gingivalis GroEL may contribute to cardiovascular disorders by affecting TLR4 expression.

Cryptococcal heat shock protein 70 homolog Ssa1 contributes to pulmonary expansion of Cryptococcus neoformans during the afferent phase of the immune response by promoting macrophage M2 polarization

Numerous virulence factors expressed by Cryptococcus neoformans modulate host defenses by promoting nonprotective Th2-biased adaptive immune responses. Prior studies demonstrate that the heat shock protein 70 homolog, Ssa1, significantly contributes to serotype D C. neoformans virulence through the induction of laccase, a Th2-skewing and CNS tropic factor. In the present study, we sought to determine whether Ssa1 modulates host defenses in mice infected with a highly virulent serotype A strain of C. neoformans (H99). To investigate this, we assessed pulmonary fungal growth, CNS dissemination, and survival in mice infected with either H99, an SSA1-deleted H99 strain (Δssa1), and a complement strain with restored SSA1 expression (Δssa1::SSA1). Mice infected with the Δssa1 strain displayed substantial reductions in lung fungal burden during the innate phase (days 3 and 7) of the host response, whereas less pronounced reductions were observed during the adaptive phase (day 14) and mouse survival increased only by 5 d. Surprisingly, laccase activity assays revealed that Δssa1 was not laccase deficient, demonstrating that H99 does not require Ssa1 for laccase expression, which explains the CNS tropism we still observed in the Ssa1-deficient strain. Lastly, our immunophenotyping studies showed that Ssa1 directly promotes early M2 skewing of lung mononuclear phagocytes during the innate phase, but not the adaptive phase, of the immune response. We conclude that Ssa1's virulence mechanism in H99 is distinct and laccase-independent. Ssa1 directly interferes with early macrophage polarization, limiting innate control of C. neoformans, but ultimately has no effect on cryptococcal control by adaptive immunity.

Extracellular matrix-associated proteins form an integral and dynamic system during Pseudomonas aeruginosa biofilm development

Though the essential role of extracellular matrix in biofilm development has been extensively documented, the function of matrix-associated proteins is elusive. Determining the dynamics of matrix-associated proteins would be a useful way to reveal their functions in biofilm development. Therefore, we applied iTRAQ-based quantitative proteomics to evaluate matrix-associated proteins isolated from different phases of Pseudomonas aeruginosa ATCC27853 biofilms. Among the identified 389 proteins, 54 changed their abundance significantly. The increased abundance of stress resistance and nutrient metabolism-related proteins over the period of biofilm development was consistent with the hypothesis that biofilm matrix forms micro-environments in which cells are optimally organized to resist stress and use available nutrients. Secreted proteins, including novel putative effectors of the type III secretion system were identified, suggesting that the dynamics of pathogenesis-related proteins in the matrix are associated with biofilm development. Interestingly, there was a good correlation between the abundance changes of matrix-associated proteins and their expression. Further analysis revealed complex interactions among these modulated proteins, and the mutation of selected proteins attenuated biofilm development. Collectively, this work presents the first dynamic picture of matrix-associated proteins during biofilm development, and provides evidences that the matrix-associated proteins may form an integral and well regulated system that contributes to stress resistance, nutrient acquisition, pathogenesis and the stability of the biofilm.

Autophagy protects monocytes from Wolbachia heat shock protein 60-induced apoptosis and senescence

Monocyte dysfunction by filarial antigens has been a major mechanism underlying immune evasion following hyporesponsiveness during patent lymphatic filariasis. Recent studies have initiated a paradigm shift to comprehend the immunological interactions of Wolbachia and its antigens in inflammation, apoptosis, lymphocyte anergy, etc. Here we showed that recombinant Wolbachia heat shock protein 60 (rWmhsp60) interacts with TLR-4 and induces apoptosis in monocytes of endemic normal but not in chronic patients. Higher levels of reactive oxygen species (ROS) induced after TLR-4 stimulation resulted in loss of mitochondrial membrane potential and caspase cascade activation, which are the plausible reason for apoptosis. Furthermore, release in ROS owing to TLR-4 signaling resulted in the activation of NF-κB p65 nuclear translocation which leads to inflammation and apoptosis via TNF receptor pathway following the increase in IL-6 and TNF-α level. Here for the first time, we report that in addition to apoptosis, rWmhsp60 antigen in filarial pathogenesis also induces molecular senescence in monocytes. Targeting TLR-4, therefore, presents a promising candidate for treating rWmhsp60-induced apoptosis and senescence. Strikingly, induction of autophagy by rapamycin detains TLR-4 in late endosomes and subverts TLR-4-rWmhsp60 interaction, thus protecting TLR-4–mediated apoptosis and senescence. Furthermore, rapamycin-induced monocytes were unresponsive to rWmhsp60, and activated lymphocytes following PHA stimulation. This study demonstrates that autophagy mediates the degradation of TLR-4 signaling and protects monocytes from rWmhsp60 induced apoptosis and senescence.

Despite knowing the significance of Wolbachia in helminth infections, our understanding of immunity and pathogenesis remains incomplete. Therefore, considering the gravity of the problem, the present study provides evidence that Wolbachia heat shock protein 60 induces apoptosis and senescence through TLR-4. Also, binding of rWmhsp60 to TLR-4 triggered caspase cascade activation following, ROS-mediated mitochondrial potential loss. Moreover, we found that nuclear translocation of NF-κB p65 was predominantly related to TLR-4 expression and resulted in apoptosis- and senescence-mediated inflammation via TNF-α and IL-6. Hence, we hypothesized that modifying TLR-4 expression may provide a plausible target for designing antiparasitic drugs. Here we have shown that induction of autophagy by rapamycin destabilizes TLR-4 expression and protects monocytes from rWmhsp60-induced apoptosis and senescence. In addition, rapamycin-induced monocytes were unresponsive to rWmhsp60 and triggered lymphocyte activation after PHA stimulation. Thus, synergistic usage of rapamycin with existing anti-filarial drugs might reduce the TLR-mediated inflammatory reactions following microfilaricidal treatment.

The GroEL protein of Porphyromonas gingivalis accelerates tumor growth by enhancing endothelial progenitor cell function and neovascularization

Porphyromonas gingivalis is a bacterial species that causes destruction of periodontal tissues. Additionally, previous evidence indicates that GroEL from P. gingivalis may possess biological activities involved in systemic inflammation, especially inflammation involved in the progression of periodontal diseases. The literature has established a relationship between periodontal disease and cancer. However, it is unclear whether P. gingivalis GroEL enhances tumor growth. Here, we investigated the effects of P. gingivalis GroEL on neovasculogenesis in C26 carcinoma cell-carrying BALB/c mice and chick eggs in vivo as well as its effect on human endothelial progenitor cells (EPC) in vitro. We found that GroEL treatment accelerated tumor growth (tumor volume and weight) and increased the mortality rate in C26 cell-carrying BALB/c mice. GroEL promoted neovasculogenesis in chicken embryonic allantois and increased the circulating EPC level in BALB/c mice. Furthermore, GroEL effectively stimulated EPC migration and tube formation and increased E-selectin expression, which is mediated by eNOS production and p38 mitogen-activated protein kinase activation. Additionally, GroEL may enhance resistance against paclitaxel-induced cell cytotoxicity and senescence in EPC. In conclusion, P. gingivalis GroEL may act as a potent virulence factor, contributing to the neovasculogenesis of tumor cells and resulting in accelerated tumor growth.

Porphyromonas gingivalis GroEL induces osteoclastogenesis of periodontal ligament cells and enhances alveolar bone resorption in rats

Porphyromonas gingivalis is a major periodontal pathogen that contains a variety of virulence factors. The antibody titer to P. gingivalis GroEL, a homologue of HSP60, is significantly higher in periodontitis patients than in healthy control subjects, suggesting that P. gingivalis GroEL is a potential stimulator of periodontal disease. However, the specific role of GroEL in periodontal disease remains unclear. Here, we investigated the effect of P. gingivalis GroEL on human periodontal ligament (PDL) cells in vitro, as well as its effect on alveolar bone resorption in rats in vivo. First, we found that stimulation of PDL cells with recombinant GroEL increased the secretion of the bone resorption-associated cytokines interleukin (IL)-6 and IL-8, potentially via NF-κB activation. Furthermore, GroEL could effectively stimulate PDL cell migration, possibly through activation of integrin α1 and α2 mRNA expression as well as cytoskeletal reorganization. Additionally, GroEL may be involved in osteoclastogenesis via receptor activator of nuclear factor κ-B ligand (RANKL) activation and alkaline phosphatase (ALP) mRNA inhibition in PDL cells. Finally, we inoculated GroEL into rat gingiva, and the results of microcomputed tomography (micro-CT) and histomorphometric assays indicated that the administration of GroEL significantly increased inflammation and bone loss. In conclusion, P. gingivalis GroEL may act as a potent virulence factor, contributing to osteoclastogenesis of PDL cells and resulting in periodontal disease with alveolar bone resorption.

Endocytosis of Mycobacterium tuberculosis heat shock protein 60 is required to induce interleukin-10 production in macrophages

Understanding the signaling pathways involved in the regulation of anti-inflammatory and pro-inflammatory responses in tuberculosis is extremely important in tailoring a macrophage innate response to promote anti-tuberculosis immunity in the host. Although the role of toll-like receptors (TLRs) in the regulation of anti-inflammatory and pro-inflammatory responses is known, the detailed molecular mechanisms by which the Mycobacterium tuberculosis bacteria modulate these innate responses are not clearly understood. In this study, we demonstrate that M. tuberculosis heat shock protein 60 (Mtbhsp60, Cpn60.1, and Rv3417c) interacts with both TLR2 and TLR4 receptors, but its interaction with TLR2 leads to clathrin-dependent endocytosis resulting in an increased production of interleukin (IL)-10 and activated p38 MAPK. Blockage of TLR2-mediated endocytosis inhibited IL-10 production but induced production of tumor necrosis factor (TNF)-α and activated ERK1/2. In contrast, upon interaction with TLR4, Mtbhsp60 remained predominantly localized on the cell surface due to poorer endocytosis of the protein that led to decreased IL-10 production and p38 MAPK activation. The Escherichia coli homologue of hsp60 was found to be retained mainly on the macrophage surface upon interaction with either TLR2 or TLR4 that triggered predominantly a pro-inflammatory-type immune response. Our data suggest that cellular localization of Mtbhsp60 upon interaction with TLRs dictates the type of polarization in the innate immune responses in macrophages. This information is likely to help us in tailoring the host protective immune responses against M. tuberculosis.

Innate immune signaling in the pathogenesis of necrotizing enterocolitis

Necrotizing enterocolitis (NEC) is a challenging disease to treat, and caring for patients afflicted by it remains both frustrating and difficult. While NEC may develop quickly and without warning, it may also develop slowly, insidiously, and appear to take the caregiver by surprise. In seeking to understand the molecular and cellular processes that lead to NEC development, we have identified a critical role for the receptor for bacterial lipopolysaccharide (LPS) toll like receptor 4 (TLR4) in the pathogenesis of NEC, as its activation within the intestinal epithelium of the premature infant leads to mucosal injury and reduced epithelial repair. The expression and function of TLR4 were found to be particularly elevated within the intestinal mucosa of the premature as compared with the full-term infant, predisposing to NEC development. Importantly, factors within both the enterocyte itself, such as heat shock protein 70 (Hsp70), and in the extracellular environment, such as amniotic fluid, can curtail the extent of TLR4 signaling and reduce the propensity for NEC development. This review will highlight the critical TLR4-mediated steps that lead to NEC development, with a focus on the proinflammatory responses of TLR4 signaling that have such devastating consequences in the premature host.

Toll-like receptor 4 in experimental kidney transplantation: early mediator of endogenous danger signals

The role of toll-like receptors (TLRs) has been described in the pathogenesis of renal ischemia/reperfusion injury, but data on the expression and function of TLR4 during renal allograft damage are still scarce. We analyzed the expression of TLR4 in an experimental rat model 6 and 28 days after allogeneic kidney transplantation in comparison to control rats and rats after syngeneic transplantation. On day 6, a significant induction in TLR4 expression--restricted to the glomerular compartment--was found in acute rejecting allografts only. TLR4 expression strongly correlated with renal function, and TLR4 induction was accompanied by a significant increase in CC chemokine expression within the graft as well as in urinary CC chemokine excretion. TLR4 induction may be caused by an influx of macrophages as well as TLR4-expressing intrinsic renal cells. Fibrinogen deposition in renal allografts correlated with renal TLR4 expression and may act as a potent stimulator of chemokine release via TLR4 activation. This study provides, for the first time, data about the precise intrarenal localization and TLR4 induction after experimental kidney transplantation. It supports the hypothesis that local TLR4 activation by endogenous ligands may be one pathological link from unspecific primary allograft damage to subsequent chemokine release, infiltration and activation of immune cells leading to deterioration of renal function and induction of renal fibrosis.

Invasion of eukaryotic cells by Legionella pneumophila: A common strategy for all hosts?

Legionella pneumophila is an environmental micro-organism capable of producing an acute lobar pneumonia, commonly referred to as Legionnaires' disease, in susceptible humans. Legionellae are ubiquitous in aquatic environments, where they survive in biofilms or intracellularly in various protozoans. Susceptible humans become infected by breathing aerosols laden with the bacteria. The target cell for human infection is the alveolar macrophage, in which the bacteria abrogate phagolysosomal fusion. The remarkable ability of L pneumophila to infect a wide range of eukaryotic cells suggests a common strategy that exploits very fundamental cellular processes. The bacteria enter host cells via coiling phagocytosis and quickly subvert organelle trafficking events, leading to formation of a replicative phagosome in which the bacteria multiply. Vegetative growth continues for 8 to 10 h, after which the bacteria develop into a short, highly motile form called the 'mature form'. The mature form exhibits a thickening of the cell wall, stains red with the Gimenez stain, and is between 10 and 100 times more infectious than agar-grown bacteria. Following host cell lysis, the released bacteria infect other host cells, in which the mature form differentiates into a Gimenez-negative vegetative form, and the cycle begins anew. Virulence of L pneumophila is considered to be multifactorial, and there is growing evidence for both stage specific and sequential gene expression. Thus, L pneumophila may be a good model system for dissecting events associated with the host-parasite interactions.

Wolbachia heat shock protein 60 induces pro-inflammatory cytokines and apoptosis in monocytes in vitro

Recombinant Wolbachia heat shock protein 60 (rWmhsp60) induces gene expression of pro-inflammatory cytokines IL-1β, IL-6 and TNF-α in human monocytic cell line THP-1. In addition, it inhibits the phagocytic activity and does not alter the nitric oxide production by differentiated THP-1 macrophages, which corroborates with no significant change in inducible nitric oxide synthase gene expression in rWmhsp60 treated THP-1 monocytes. Further, 24 h stimulation of peripheral blood mononuclear cells from normal individuals by rWmhsp60 reveals that monocytes enter the late apoptotic stage, while lymphocytes do not show apoptosis. Thus these findings suggest that rWmhsp60 may contribute to inflammation mediated monocyte dysfunction in filarial pathogenesis.

Intracellular heat shock protein-70 negatively regulates TLR4 signaling in the newborn intestinal epithelium

Necrotizing enterocolitis (NEC) is the leading cause of gastrointestinal-related mortality in premature infants, and it develops under conditions of exaggerated TLR4 signaling in the newborn intestinal epithelium. Because NEC does not develop spontaneously, despite the presence of seemingly tonic stimulation of intestinal TLR4, we hypothesized that mechanisms must exist to constrain TLR4 signaling that become diminished during NEC pathogenesis and focused on the intracellular stress response protein and chaperone heat shock protein-70 (Hsp70). We demonstrate that the induction of intracellular Hsp70 in enterocytes dramatically reduced TLR4 signaling, as assessed by LPS-induced NF-κB translocation, cytokine expression, and apoptosis. These findings were confirmed in vivo, using mice that either globally lacked Hsp70 or overexpressed Hsp70 within the intestinal epithelium. TLR4 activation itself significantly increased Hsp70 expression in enterocytes, which provided a mechanism of autoinhibition of TLR4 signaling in enterocytes. In seeking to define the mechanisms involved, intracellular Hsp70-mediated inhibition of TLR4 signaling required both its substrate-binding EEVD domain and association with the cochaperone CHIP, resulting in ubiquitination and proteasomal degradation of TLR4. The expression of Hsp70 in the intestinal epithelium was significantly decreased in murine and human NEC compared with healthy controls, suggesting that loss of Hsp70 protection from TLR4 could lead to NEC. In support of this, intestinal Hsp70 overexpression in mice and pharmacologic upregulation of Hsp70 reversed TLR4-induced cytokines and enterocyte apoptosis, as well as prevented and treated experimental NEC. Thus, a novel TLR4 regulatory pathway exists within the newborn gut involving Hsp70 that may be pharmacologically activated to limit NEC severity.

High glucose concentrations alter the biomineralization process in human osteoblastic cells

Diabetes mellitus (DM) may alter bone remodeling, as osteopenia and osteoporosis are among the complications. Moreover, DM increases the risk and severity of chronic inflammatory periodontal disease, in which bone resorption occurs. Broad evidence suggests that chronic inflammation can contribute to the development of DM and its complications. Hyperglycemia is a hallmark of DM that may contribute to sustained inflammation by increasing proinflammatory cytokines, which are known to cause insulin resistance, via toll-like receptor (TLR)-4-mediated mechanisms. However, the mechanisms by which bone-related complications develop in DM are still unknown. Studies done on the effect of high glucose concentrations on osteoblast functions are contradictory because some suggest increases (although others suggest reductions) in the biomineralization process. Therefore, we evaluated the effect of high glucose levels on biomineralization and inflammation markers in a human osteoblastic cell line. Cells were treated with either physiological 5.5 mM or increasing concentrations of glucose up to 24 mM, and we determined the following: i) the quantity and quality of calcium-deposit crystals in culture and ii) the expression of the following: a) proteins associated with the process of biomineralization, b) the receptor activator of nuclear factor kappa-B ligand (RANKL) and osteoprotegerin (OPG), c) cytokines IL1, IL6, IL8, IL10, MCP-1 and TNF alpha, and d) TLR-2, -3, -4 and -9. Our results show that high glucose concentrations (12 mM and particularly 24 mM) alter the biomineralization process in osteoblastic cells and provoke the following: i) a rise in mineralization, ii) an increase in the mRNA expression of RANKL and a decrease of OPG, iii) an increase in the mRNA expression of osteocalcin, bone sialoprotein and the transcription factor Runx2, iv) a diminished quality of the mineral, and v) an increase in the expression of IL1beta, IL6, IL8, MCP-1 and IL10 mRNAs. In addition we found that both high glucose levels and hyperosmotic conditions provoked TLR-2, -3, -4 and -9 overexpression in osteoblastic cells, suggesting that they are susceptible to osmotic stress.

The Legionella pneumophila Chaperonin - An Unusual Multifunctional Protein in Unusual Locations

The Legionella pneumophila chaperonin, high temperature protein B (HtpB), was discovered as a highly immunogenic antigen, only a few years after the identification of L. pneumophila as the causative agent of Legionnaires’ disease. As its counterparts in other bacterial pathogens, HtpB did not initially receive further attention, particularly because research was focused on a few model chaperonins that were used to demonstrate that chaperonins are essential stress proteins, present in all cellular forms of life and involved in helping other proteins to fold. However, chaperonins have recently attracted increasing interest, particularly after several reports confirmed their multifunctional nature and the presence of multiple chaperonin genes in numerous bacterial species. It is now accepted that bacterial chaperonins are capable of playing a variety of protein folding-independent roles. HtpB is clearly a multifunctional chaperonin that according to its location in the bacterial cell, or in the L. pneumophila-infected cell, plays different roles. HtpB exposed on the bacterial cell surface can act as an invasion factor for non-phagocytic cells, whereas the HtpB released in the host cell can act as an effector capable of altering organelle trafficking, the organization of actin microfilaments and cell signaling pathways. The road to discover the multifunctional nature of HtpB has been exciting and here we provide a historical perspective of the key findings linked to such discovery, as well as a summary of the experimental work (old and new) performed in our laboratory. Our current understanding has led us to propose that HtpB is an ancient protein that L. pneumophila uses as a key molecular tool important to the intracellular establishment of this fascinating pathogen.

Mycobacterium tuberculosis employs Cpn60.2 as an adhesin that binds CD43 on the macrophage surface

CD43 is a large sialylated glycoprotein found on the surface of haematopoietic cells and has been previously shown to be necessary for efficient macrophage binding and immunological responsiveness to Mycobacterium tuberculosis. Using capsular material from M. tuberculosis and recombinant CD43-Fc, we have employed affinity chromatography to show that Cpn60.2 (Hsp65, GroEL), and to a lesser extent DnaK (Hsp70), bind to CD43. Competitive inhibition using recombinant protein and polyclonal F(ab')(2) antibody-mediated epitope masking studies were used to evaluate M. tuberculosis binding to CD43(+/+) versus CD43(-/-) macrophages. Results showed that Cpn60.2, but not DnaK, acts as a CD43-dependent mycobacterial adhesin for macrophage binding. Assessment of the specific binding between Cpn60.2 and CD43 showed it to be saturable, with a comparatively weak affinity in the low micromolar range. We have also shown that the ability of Cpn60.2 to competitively inhibit M. tuberculosis binding to macrophages is shared by the Escherichia coli homologue, GroEL, but not by the mouse and human Hsp60 homologues. These findings add to a growing field of research that implicates molecular chaperones as having extracellular functions, including bacterial adherence to host cells. Thus, CD43 may act as a Pattern Recognition Receptor (PRR) for bacterial homologues of the 60 kDa molecular chaperone.

Role of heat shock proteins in diseases and their therapeutic potential

Heat shock proteins are ubiquitously expressed intracellular proteins and act as molecular chaperones in processes like protein folding and protein trafficking between different intracellular compartments. They are induced during stress conditions like oxidative stress, nutritional deficiencies and radiation. They are released into extracellular compartment during necrosis. However, recent research findings highlights that, they are not solely present in cytoplasm, but also released into extracellular compartment during normal conditions and even in the absence of necrosis. When present in extracellular compartment, they have been shown to perform various functions like antigen presentation, intercellular signaling and induction of pro-inflammatory cytokines. Heat shock proteins represents as dominant microbial antigens during infection. The phylogenetic similarity between prokaryotic and eukaryotic heat shock proteins has led to proposition that, microbial heat shock proteins can induce self reactivity to host heat shock proteins and result in autoimmune diseases. The self-reactivity of heat shock proteins protects host against disease by controlling induction and release of pro-inflammatory cytokines. However, antibodies to self heat shock proteins haven been implicated in pathogenesis of autoimmune diseases like arthritis and atherosclerosis. Some heat shock proteins are potent inducers of innate and adaptive immunity. They activate dendritic cells and natural killer cells through toll-like receptors, CD14 and CD91. They play an important role in MHC-antigen processing and presentation. These immune effector functions of heat shock proteins are being exploited them as therapeutic agents as well as therapeutic targets for various infectious diseases and cancers.

Immune pathogenesis of asymptomatic chlamydia trachomatis infections in the female genital tract

Chlamydia trachomatis (CT) infections of the female genital tract, although frequently asymptomatic, are a major cause of fallopian-tube occlusion and infertility. Early stage pregnancy loss may also be due to an unsuspected and undetected CT infection. In vitro and in vivo studies have demonstrated that this organism can persist in the female genital tract in a form undetectable by culture. The mechanism of tubal damage as well as the rejection of an embryo may involve an initial immune sensitization to the CT 60 kD heat shock protein (HSP), followed by a reactivation of HSP-sensitized lymphocytes in response to the human HSP and the subsequent release of inflammatory cytokines. The periodic induction of human HSP expression by various microorganisms or by noninfectious mechanisms in the fallopian tubes of women sensitized to the CT HSP may eventually result in tubal scarring and occlusion. Similarly, an immune response to human HSP expression during the early stages of pregnancy may interfere with the immune regulatory mechanisms required for the maintenance of a semiallogeneic embryo.

Multiple moonlighting functions of mycobacterial molecular chaperones

Molecular chaperones and protein folding catalysts are normally thought of as intracellular proteins involved in protein folding quality control. However, in the mycobacteria there is increasing evidence to support the hypothesis that molecular chaperones are also secreted intercellular signalling molecules or can control actions at the cell wall or indeed control the composition of the cell wall. The most recent evidence for protein moonlighting in the mycobacteria is the report that chaperonin 60.2 of Mycobacterium tuberculosis is important in the key event in tuberculosis - the entry of the bacterium into the macrophage. This brief overview highlights the potential importance of the moonlighting functions of molecular chaperones in the biology and pathobiology of the mycobacteria.

Autologous Hsp70 induces antigen specific Th1 immune responses in a murine T-cell lymphoma

Heat Shock protein-70 derived from tumor cells is highly immunogenic and induces specific anti-tumor immune response by directly activating cytotoxic CD8(+) T cells. Additionally, Hsp70 is known to be a strong activator of antigen presenting cells and therefore, up regulates the production of pro-inflammatory cytokines and chemokines. In this study, we have shown the effect of tumor-derived Hsp70 on the induction of delayed type hypersensitivity reaction in a T cell lymphoma bearing mice. The autologous Hsp70 augments contact hypersensitivity and delayed type hypersensitivity responses in mice challenged with allergen in vehicle and antigens respectively. The adoptive transfer of splenocytes derived from Hsp70 immunized mice is able to enhance delayed type hypersensitivity response in antigen challenged normal and DL-bearing host. Furthermore, adoptive transfer of macrophages incubated with autologous Hsp70 also enhances DTH reactivity in mice. The pro-inflammatory cytokines and C-C chemokines are found to be elevated in the DTH footpad extract of antigen challenged normal and DL-bearing mice. Increased production of IFN-gamma and MIP-1alpha+/- suggest that autologous Hsp70 augments the recruitment of antigen specific Th1 cells, which further secretes pro-inflammatory cytokines and C-C chemokines mediating the hypersensitivity reaction upon challenge with antigens.

Ingestion of bacteria overproducing DnaK attenuates Vibrio infection of Artemia franciscana larvae

Feeding of bacterially encapsulated heat shock proteins (Hsps) to invertebrates is a novel way to limit Vibrio infection. As an example, ingestion of Escherichia coli overproducing prokaryotic Hsps significantly improves survival of gnotobiotically cultured Artemia larvae upon challenge with pathogenic Vibrio campbellii. The relationship between Hsp accumulation and enhanced resistance to infection may involve DnaK, the prokaryotic equivalent to Hsp70, a major molecular chaperone in eukaryotic cells. In support of this proposal, heat-stressed bacterial strains LVS 2 (Bacillus sp.), LVS 3 (Aeromonas hydrophila), LVS 8 (Vibrio sp.), GR 8 (Cytophaga sp.), and GR 10 (Roseobacter sp.) were shown in this work to be more effective than nonheated bacteria in protecting gnotobiotic Artemia larvae against V. campbellii challenge. Immunoprobing of Western blots and quantification by enzyme-linked immunosorbent assay revealed that the amount of DnaK in bacteria and their ability to enhance larval resistance to infection by V. campbellii are correlated. Although the function of DnaK is uncertain, it may improve tolerance to V. campbellii via immune stimulation, a possibility of significance from a fundamental perspective and also because it could be applied in aquaculture, a major method of food production.

Trypanosoma carassii hsp70 increases expression of inflammatory cytokines and chemokines in macrophages of the goldfish (Carassius auratus L.)

We report on the cloning and characterization of Trypanosoma carassii 70 KDa heat shock protein (hsp70). T. carassii hsp70 was secreted/excreted into culture medium in vitro and was recognized by sera from infected fish. Recombinant hsp70 (rhsp70) activated goldfish macrophages and stimulated the production of pro-inflammatory cytokines including interferon gamma (IFNgamma), tumor necrosis factor (TNF)-alpha, interleukin (IL)-1beta, (IL)-12 and chemokines CCL-1 and CXCL-8 (IL-8). T. carassii hsp70-induced cytokine expression was abrogated by pronase treatment of macrophages confirming the existence of receptor(s) on goldfish macrophage surface that recognize parasite molecule. Parasite hsp70 also up-regulated the expression inducible nitric oxide synthase (iNOS) isoforms A and B and induced a strong nitric oxide response of goldfish macrophages.

Heat shock protein 60 causes osteoclastic bone resorption via toll-like receptor-2 in estrogen deficiency

Estrogen deficiency leads to marked increases in osteoclastic bone resorption, but the exact mechanism is unclear. Proteomic analysis was performed on the femur and tibia of ovariectomy (OVX) and sham-operated Sprague-Dawley rats using two-dimensional gel electrophoresis (2-DE) and matrix-assisted laser desorption/ionization-time-of-flight (MALDI-TOF) mass spectrometer (MS). Among the nine proteins differentially expressed between OVX and sham-operated rats, heat shock protein 60 (HSP60) was upregulated by 2.6-fold in the bones of OVX rats, and the plasma concentration of HSP60 was also significantly increased in OVX rats. Estrogen deficiency increases in secretions of interleukin (IL)-1beta and tumor necrosis factor (TNF)-alpha in T cell and osteoclasts (OCs) lineages, IL-1beta and TNF-alpha stimulated the production and secretion of HSP60 from OCs lineages. IL-1 receptor antagonist (ra), TNF-blocking antibody (Ab), and estradiol (E(2)) significantly suppressed the OVX-induced increase in plasma concentrations of HSP60 in mice. HSP60 potentiated OC formation and bone resorption, and pretreatment with HSP60-blocking Ab markedly reduced the potentiation of OC formation and bone resorption by IL-1beta- and TNF-alpha. HSP60 upregulated the expression levels of toll-like receptor (TLR)-2 in bone marrow macrophage (BMMvarphi), and pretreatment with a TLR-2-blocking Ab almost completely inhibited HSP60- or cytokine-induced potentiation of OC formation and/or bone resorption. In conclusion, HSP60 and TLR-2 are novel mediators of estrogen-deficiency-induced bone loss.

Heat shock protein 60, via MyD88 innate signaling, protects B cells from apoptosis, spontaneous and induced

We recently reported that heat shock protein 60 (HSP60) via TLR4 signaling activates B cells and induces them to proliferate and secrete IL-10. We now report that HSP60 inhibits mouse B cell apoptosis, spontaneous or induced by dexamethasone or anti-IgM activation. Unlike HSP60 enhancement of B cell proliferation and IL-10 secretion, TLR4 signaling was not required for the inhibition of apoptosis by HSP60; nevertheless, MyD88 was essential. Inhibition of apoptosis by HSP60 was associated with up-regulation of the antiapoptotic molecules Bcl-2, Bcl-x(L), and survivin, maintenance of the mitochondrial transmembrane potential, and inhibition of caspase-3 activation. Moreover, B cells incubated with HSP60 manifested prolonged survival following transfer into recipient mice. These results extend the varied role of HSP60 in the innate regulation of the adaptive immune response.

Mycobacterium tuberculosis Cpn60.2 and DnaK are located on the bacterial surface, where Cpn60.2 facilitates efficient bacterial association with macrophages

Mycobacterium tuberculosis, the causative agent of tuberculosis, initially contacts host cells with elements of its outer cell wall, or capsule. We have shown that capsular material from the surface of M. tuberculosis competitively inhibits the nonopsonic binding of whole M. tuberculosis bacilli to macrophages in a dose-dependent manner that is not acting through a global inhibition of macrophage binding. We have further demonstrated that isolated M. tuberculosis capsular proteins mediate a major part of this inhibition. Two-dimensional polyacrylamide gel electrophoresis analysis of the capsular proteins showed the presence of a wide variety of protein species, including proportionately high levels of the Cpn60.2 (Hsp65, GroEL2) and DnaK (Hsp70) molecular chaperones. Both of these proteins were subsequently detected on the bacterial surface. To determine whether these molecular chaperones play a role in bacterial binding, recombinant Cpn60.2 and DnaK were tested for their ability to inhibit the association of M. tuberculosis bacilli with macrophages. We found that recombinant Cpn60.2 can inhibit approximately 57% of bacterial association with macrophages, while DnaK was not inhibitory at comparable concentrations. Additionally, when polyclonal F(ab')(2) fragments of anti-Cpn60.2 and anti-DnaK were used to mask the surface presentation of these molecular chaperones, a binding reduction of approximately 34% was seen for anti-Cpn60.2 F(ab')(2), while anti-DnaK F(ab')(2) did not significantly reduce bacterial association with macrophages. Thus, our findings suggest that while M. tuberculosis displays both surface-associated Cpn60.2 and DnaK, only Cpn60.2 demonstrates adhesin functionality with regard to macrophage interaction.

Heat shock proteins and immune system

Heat shock proteins (HSPs) such as HSP 60 (Hsp60), Hsp70, Hsp90, and gp96, have been reported to play important roles in antigen presentation and cross-presentation, activation of macrophages and lymphocytes, and activation and maturation of dendritic cells. HSPs contain peptide-binding domains that bind exposed hydrophobic residues of substrate proteins. As part of their molecular chaperone functions, HSPs bind and deliver chaperoned, antigenic peptides to MHC class I molecules at the cell surface for presentation to lymphocytes. HSPs also bind nonprotein molecules with exposed hydrophobic residues including lipid-based TLR ligands. Recombinant HSP products may be contaminated with pathogen-associated molecules that contain exposed hydrophobic residues such as LPS (a TLR4 ligand), lipoprotein (a TLR2 ligand), and flagellin (a TLR5 ligand). These contaminants appear to be responsible for most, if not all, reported in vitro cytokine effects of HSPs, as highly purified HSPs do not show any cytokine effects. We propose that HSPs are molecular chaperones that bind protein and nonprotein molecules with exposed hydrophobic residues. The reported antigen presentation and cross-presentation and in vitro HSP cytokine functions are a result of molecules bound to or chaperoned by HSPs but not a result of HSPs themselves.

Hsp60D is essential for caspase-mediated induced apoptosis in Drosophila melanogaster

Apart from their roles as chaperones, heat shock proteins are involved in other vital activities including apoptosis with mammalian Hsp60 being ascribed proapoptotic as well as antiapoptotic roles. Using conditional RNAi or overexpression of Hsp60D, a member of the Hsp60 family in Drosophila melanogaster, we show that the downregulation of this protein blocks caspase-dependent induced apoptosis. GMR-Gal4-driven RNAi for Hsp60D in developing eyes dominantly suppressed cell death caused by expression of Reaper, Hid, or Grim (RHG), the key activators of canonical cell death pathway. Likewise, Hsp60D-RNAi rescued cell death induced by GMR-Gal4-directed expression of full-length and activated DRONC. Overexpression of Hsp60D enhanced cell death induced either by directed expression of RHG or DRONC. However, the downregulation of Hsp60D failed to suppress apoptosis caused by unguarded caspases in DIAP1-RNAi flies. Furthermore, in DIAP1-RNAi background, Hsp60D-RNAi also failed to inhibit apoptosis induced by RHG expression. The Hsp60 and DIAP1 show diffuse and distinct granular overlapping distributions in the photoreceptor cells with the bulk of both proteins being outside the mitochondria. Depletion of either of these proteins disrupts the granular distribution of the other. We suggest that in the absence of Hsp60D, DIAP1 is unable to dissociate from effecter and executioner caspases, which thus remain inactive.