HSP70 Enhances Macrophage Phagocytosis by Interaction With Lipid Raft-Associated TLR-7 and Upregulating p38 MAPK and PI3K Pathways

Extracellular Heat Shock Protein 70 Increases the Glucocorticoid Receptor and Dual-Specificity Phosphatase 1 via Toll-like Receptor 4 and Attenuates Inflammation in Airway Epithelial Cells

Heat shock protein 70 (HSP70) regulates the ligand binding of the glucocorticoid receptor (GR). In asthma patients, heat treatment increased both the GR expression and secretion of extracellular HSP70 (eHSP70) by bronchial epithelial cells (EC). The objective of this study was to assess the effects of eHSP70 on GR expression and the GR-dependent regulation of immune response in human bronchial ECs. Cells were treated with either eHSP70 or transfected with an expression vector for intracellular HSP70 (iHSP70). Ribonucleic acid (RNA) and protein levels were detected by reverse transcriptase-polymerase chain reaction (RT-PCR), Western blotting, and immunofluorescence. Interleukin (IL-6 and IL-8) secretion was determined by enzyme linked immunosorbent assay (ELISA). The overexpression of iHSP70 decreased, while eHSP70 increased GR expression. In addition, eHSP70 increased the expression of the GR target dual-specificity phosphatase 1 (DUSP-1). In doing so, eHSP70 reduced the tumor growth factor (TGF)-β1-dependent activation of extracellular signal-regulated kinase (Erk)-1/2 and cyclic AMP response element binding protein (CREB) and the secretion of IL-6 and IL-8. Blocking the GR or Toll-like receptor 4 (TLR4) counteracted all eHSP70-induced effects. This study demonstrates a novel anti-inflammatory effect of eHSP70 by the signaling cascade of TLR4-GR-DUSP1, which inhibits TGF-β1-activated pro-inflammatory ERK1/2-CREB signaling and cytokine secretion. The findings suggest that eHSP70 might present a novel non-steroidal therapeutic strategy to control airway inflammation in asthma.

Colorectal cancer-derived extracellular vesicles containing HSP70 enhance macrophage phagocytosis by up-regulating MARCO expression

In recent years, we have realized that extracellular vesicles (EVs) play a critical role in regulating the intercellular communication between tumor and immune cells in the tumor microenvironment (TME). Tumor-derived extracellular vesicles (TDEVs) profoundly affect the functional changes of tumor-associated macrophages (TAMs) and promote their M2 polarization. Meanwhile, macrophages have a strong phagocytic ability in phagocytosing apoptotic cells. Especially in the course of chemotherapy or radiotherapy, TAMs can phagocytose and remove apoptotic tumor cells, showing anti-inflammatory and pro-tumor effects. However, the underlying mechanisms by which TDEVs regulate macrophage phagocytosis of apoptotic tumor cells have not been fully elucidated. In this study, we focused on the effect of colorectal cancer-derived extracellular vesicles (CRC-EVs) on macrophages. We demonstrated that CRC-EVs enhanced macrophage phagocytosis of apoptotic CRC cells. We then determined that heat shock protein 70 (HSP70) carried in CRC-EVs was responsible for this effect by using mass spectrometry-based proteomic analysis and the CRISPR-Cas9 system. Through transcriptome sequencing of macrophages, we found that the enhanced phagocytosis of macrophages was mainly due to the up-regulation of the macrophage receptor with collagenous structure (MARCO). In addition, we confirmed that the up-regulation of MARCO was mediated by the AKT-STAT3 signaling pathway. Taken together, this study revealed a novel EVs-mediated macrophage phagocytosis mechanism involved in the clearance of apoptotic tumor cells in TME. Targeting TDEVs may have potential therapeutic applications in tumor treatment.

Immunogenic Cell Death Activates the Tumor Immune Microenvironment to Boost the Immunotherapy Efficiency

Tumor immunotherapy is only effective in a fraction of patients due to a low response rate and severe side effects, and these challenges of immunotherapy in clinics can be addressed through induction of immunogenic cell death (ICD). ICD is elicited from many antitumor therapies to release danger associated molecular patterns (DAMPs) and tumor-associated antigens to facilitate maturation of dendritic cells (DCs) and infiltration of cytotoxic T lymphocytes (CTLs). The process can reverse the tumor immunosuppressive microenvironment to improve the sensitivity of immunotherapy. Nanostructure-based drug delivery systems (NDDSs) are explored to induce ICD by incorporating therapeutic molecules for chemotherapy, photosensitizers (PSs) for photodynamic therapy (PDT), photothermal conversion agents for photothermal therapy (PTT), and radiosensitizers for radiotherapy (RT). These NDDSs can release loaded agents at a right dose in the right place at the right time, resulting in greater effectiveness and lower toxicity. Immunotherapeutic agents can also be combined with these NDDSs to achieve the synergic antitumor effect in a multi-modality therapeutic approach. In this review, NDDSs are harnessed to load multiple agents to induce ICD by chemotherapy, PDT, PTT, and RT in combination of immunotherapy to promote the therapeutic effect and reduce side effects associated with cancer treatment.

circ_0000045 promotes proliferation, migration, and invasion of head and neck squamous cell carcinomas via regulating HSP70 and MAPK pathway

Objective

Head and neck squamous cell carcinoma (HNSCC) is one severe malignancy driven by complex cellular and signaling mechanisms. However, the roles of circular RNAs (circRNAs) in HNSCC’s development remains poorly understood. Therefore, this study investigated the functions of differentially expressed circRNAs in regulating HNSCC cell functions.

Methods

Differentially expressed circRNAs were characterized through RNA sequencing in HNSCC tissues. CircRNA’s identity was then confirmed using RT-PCR and Sanger’s sequencing. Next, expression levels of circRNA and mRNA were detected by qRT-PCR, after which protein abundances were measured by Western blotting. Subsequently, the proliferation, migration, and invasion of HNSCC cells was assessed by MTS, wound healing, and Transwell system, respectively, followed by identification of circRNA-binding proteins in HNSCC cells by circRNA pull-down, coupled with mass spectrometry.

Results

Great alterations in circRNA profiles were detected in HNSCC tissues, including the elevated expression of circ_0000045. As observed, silencing of circ_0000045 effectively repressed the proliferation, migration, and invasion of HNSCC cell lines (FaDu and SCC-9). Contrarily, circ_0000045’s overexpression promoted the proliferation, migration, and invasion in FaDu and SCC-9 cells. Results also showed that circ_0000045 was associated with multiple RNA-binding proteins in HNSCC cells, such as HSP70. Moreover, circ_0000045 knockdown enhanced HSP70 expression and inhibited JNK2 and P38’s expression in HNSCC cells, which were oppositely regulated by circ_0000045’s overexpression.

Conclusion

The high expression of circ_0000045; therefore, promoted cell proliferation, migration, and invasion during HNSCC’s development through regulating HSP70 protein and mitogen-activated protein kinase signaling.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12885-022-09880-y.

Effect of Lycium barbarum polysaccharides on cell signal transduction pathways

Lycium barbarum polysaccharide (LBP), is a major active ingredient Lycium barbarum (LB), which exhibits several beneficial effects through NF-κB, PI3K-Akt-mTOR, p38-MAPK, Wnt-β-catenin, PI3K-Akt-GSK-3β, and MyD88 signal pathway, including anti-oxidation, and anti-aging, hypolipidemic and hypoglycemic, radiation, anti-tumor, and neuroprotection. Today, many researching papers are published on the LBP in physiology and pathology; however, the review of the LBP taking part in the signal transduction pathway in physiology and pathology is rear searched. Therefore, this research topic is a collection of reviews and original research articles that focus on the methods of the LBP extraction and its effects on the signal transduction pathway. The aim of this study is to provide theoretical evidence for in-depth analysis of the mechanisms of LBP in clinical clinical research studies.

Establishment of Host-Algal Endosymbioses: Genetic Response to Symbiont Versus Prey in a Sponge Host

The freshwater sponge Ephydatia muelleri and its Chlorella-like algal partner is an emerging model for studying animal: algal endosymbiosis. The sponge host is a tractable laboratory organism, and the symbiotic algae are easily cultured. We took advantage of these traits to interrogate questions about mechanisms that govern the establishment of durable intracellular partnerships between hosts and symbionts in facultative symbioses. We modified a classical experimental approach to discern the phagocytotic mechanisms that might be co-opted to permit persistent infections, and identified genes differentially expressed in sponges early in the establishment of endosymbiosis. We exposed algal-free E. muelleri to live native algal symbionts and potential food items (bacteria and native heat-killed algae), and performed RNA-Seq to compare patterns of gene expression among treatments. We found a relatively small but interesting suite of genes that are differentially expressed in the host exposed to live algal symbionts, and a larger number of genes triggered by host exposure to heat-killed algae. The upregulated genes in sponges exposed to live algal symbionts were mostly involved in endocytosis, ion transport, metabolic processes, vesicle-mediated transport, and oxidation–reduction. One of the host genes, an ATP-Binding Cassette transporter that is downregulated in response to live algal symbionts, was further evaluated for its possible role in the establishment of the symbiosis. We discuss the gene expression profiles associated with host responses to living algal cells in the context of conditions necessary for long-term residency within host cells by phototrophic symbionts as well as the genetic responses to sponge phagocytosis and immune-driven pathways.

HSP70 inhibition suppressed glioma cell viability during hypoxia/reoxygenation by inhibiting the ERK1/2 and PI3K/AKT signaling pathways

Heat shock protein 70 (HSP70) can regulate astrocyte viability under hypoxic and ischemic conditions. However, the protective mechanism involved is not completely clear. This study aimed to investigate whether HSP70 protects U87 glioma cells against hypoxic damage via the extracellular signal-regulated kinases 1/2 (ERK1/2) and phosphoinositide 3-kinase/protein kinase B (PI3K/AKT) signaling pathways. Lentivirus-mediated HSP70-siRNA was used for HSP70 silencing. U87 glioma cells with lentiviral infection were exposed to hypoxia for 4, 8, 12, and 24 h, respectively, followed by a 24-h reoxygenation treatment. A Cell-Counting Kit-8 was then used to evaluate the viability of the U87 glioma cells. Reverse transcription quantitative polymerase chain reaction (RT-qPCR) and western blotting were performed to determine the mRNA and protein levels, respectively. The expression of HSP70, p-ERK1/2, p-AKT, and U87 cell viability were increased after 8 h of hypoxia/24 h of reoxygenation (P < 0.01). However, HSP70 silencing significantly decreased the U87 cell viability after the hypoxia/reoxygenation treatment (P < 0.01). The protein expressions of p-ERK1/2 and p-AKT also decreased in HSP70-silenced U87 cells (P < 0.01). In conclusion, HSP70 inhibition suppressed the viability of U87 glioma cells during hypoxia/reoxygenation (at least partially) by inhibiting the ERK1/2 and PI3K/AKT signaling pathways. This study may help to understand the molecular mechanisms underlying the progression and development of cerebral hypoxia-ischemia.

The Dual Role of Myeloperoxidase in Immune Response

The heme protein myeloperoxidase (MPO) is a major constituent of neutrophils. As a key mediator of the innate immune system, neutrophils are rapidly recruited to inflammatory sites, where they recognize, phagocytose, and inactivate foreign microorganisms. In the newly formed phagosomes, MPO is involved in the creation and maintenance of an alkaline milieu, which is optimal in combatting microbes. Myeloperoxidase is also a key component in neutrophil extracellular traps. These helpful properties are contrasted by the release of MPO and other neutrophil constituents from necrotic cells or as a result of frustrated phagocytosis. Although MPO is inactivated by the plasma protein ceruloplasmin, it can interact with negatively charged components of serum and the extracellular matrix. In cardiovascular diseases and many other disease scenarios, active MPO and MPO-modified targets are present in atherosclerotic lesions and other disease-specific locations. This implies an involvement of neutrophils, MPO, and other neutrophil products in pathogenesis mechanisms. This review critically reflects on the beneficial and harmful functions of MPO against the background of immune response.

Molecular Chaperones: Molecular Assembly Line Brings Metabolism and Immunity in Shape

Molecular chaperones are a set of conserved proteins that have evolved to assist the folding of many newly synthesized proteins by preventing their misfolding under conditions such as elevated temperatures, hypoxia, acidosis and nutrient deprivation. Molecular chaperones belong to the heat shock protein (HSP) family. They have been identified as important participants in immune functions including antigen presentation, immunostimulation and immunomodulation, and play crucial roles in metabolic rewiring and epigenetic circuits. Growing evidence has accumulated to indicate that metabolic pathways and their metabolites influence the function of immune cells and can alter transcriptional activity through epigenetic modification of (de)methylation and (de)acetylation. However, whether molecular chaperones can regulate metabolic programs to influence immune activity is still largely unclear. In this review, we discuss the available data on the biological function of molecular chaperones to immune responses during inflammation, with a specific focus on the interplay between molecular chaperones and metabolic pathways that drive immune cell fate and function.

The Evolution of Dendritic Cell Immunotherapy against HIV-1 Infection: Improvements and Outlook

Dendritic cells (DC) are key phagocytic cells that play crucial roles in both the innate and adaptive immune responses against the human immunodeficiency virus type 1 (HIV-1). By processing and presenting pathogen-derived antigens, dendritic cells initiate a directed response against infected cells. They activate the adaptive immune system upon recognition of pathogen-associated molecular patterns (PAMPs) on infected cells. During the course of HIV-1 infection, a successful adaptive (cytotoxic CD8⁺ T-cell) response is necessary for preventing the progression and spread of infection in a variety of cells. Dendritic cells have thus been recognized as a valuable tool in the development of immunotherapeutic approaches and vaccines effective against HIV-1. The advancements in dendritic cell vaccines in cancers have paved the way for applications of this form of immunotherapy to HIV-1 infection. Clinical trials with patients infected with HIV-1 who are well-suppressed by antiretroviral therapy (ART) were recently performed to assess the efficacy of DC vaccines, with the goal of mounting an HIV-1 antigen-specific T-cell response, ideally to clear infection and eliminate the need for long-term ART. This review summarizes and compares methods and efficacies of a number of DC vaccine trials utilizing autologous dendritic cells loaded with HIV-1 antigens. The potential for advancement and novel strategies of improving efficacy of this type of immunotherapy is also discussed.

Current Approaches for Combination Therapy of Cancer: The Role of Immunogenic Cell Death

Cell death resistance is a key feature of tumor cells. One of the main anticancer therapies is increasing the susceptibility of cells to death. Cancer cells have developed a capability of tumor immune escape. Hence, restoring the immunogenicity of cancer cells can be suggested as an effective approach against cancer. Accumulating evidence proposes that several anticancer agents provoke the release of danger-associated molecular patterns (DAMPs) that are determinants of immunogenicity and stimulate immunogenic cell death (ICD). It has been suggested that ICD inducers are two different types according to their various activities. Here, we review the well-characterized DAMPs and focus on the different types of ICD inducers and recent combination therapies that can augment the immunogenicity of cancer cells.

Cyclophosphamide Enhances Cancer Antibody Immunotherapy in the Resistant Bone Marrow Niche by Modulating Macrophage FcγR Expression

Therapy-resistant microenvironments represent a major barrier toward effective elimination of disseminated cancer. Many hematologic and solid tumors are resistant to therapeutic antibodies in the bone marrow (BM), but not in the periphery (e.g., spleen). We previously showed that cyclophosphamide (CTX) sensitizes the BM niche to antibody therapeutics. Here, we show that (i) BM resistance was induced not only by the tumor but also by the intrinsic BM microenvironment; (ii) CTX treatment overcame both intrinsic and extrinsic resistance mechanisms by augmenting macrophage activation and phagocytosis, including significant upregulation of activating Fcγ receptors (FcγRIII and FcγRIV) and downregulation of the inhibitory receptor, FcγRIIB; and (iii) CTX synergized with cetuximab (anti-EGFR) and trastuzumab (anti-Her2) in eliminating metastatic breast cancer in the BM of humanized mice. These findings provide insights into the mechanisms by which CTX synergizes with antibody therapeutics in resistant niche-specific organs and its applicability in treating BM-resident tumors.

Allicin Inhibited Staphylococcus aureus -Induced Mastitis by Reducing Lipid Raft Stability via LxRα in Mice

Mastitis, inflammation of the mammary gland, occurs in both humans and animals. Staphylococcus aureus is the most common infectious bacterial pathogen associated with mastitis. We investigated the effects of allicin on S. aureus-induced mastitis in mice. Pathological histology revealed that allicin inhibited S. aureus-induced pathological damage and myeloperoxidase activity in mammary tissues. Enzyme-linked immunosorbent assays demonstrated that allicin reduced the production of IL-1β and TNF-α as well as inhibited the NF-κB and mitogen-activated protein kinase pathway by reducing phosphorylation of p65, IκBα, p38, JNK, and ERK. Western blotting revealed that allicin reduced TLR2 and TLR6 expression in mammary tissues and cells but not in HEK293 cells. The lipid raft content was reduced by allicin, which inhibited signaling downstream of TLR2 and TLR6. Liver X receptor α (LXRα) luciferase reporter assays and LXRα interference experiments showed that allicin improved the LXRα activity and adenosine 5'-triphosphate-binding cassette G and A1 (ABCG and ABCA1) expression, thereby reducing the cholesterol level, lipid raft formation, and downstream TLR2 and TLR6 pathway activity. These results demonstrated that allicin exerted anti-inflammatory effects against S. aureus mastitis by improving the LXRα activity and reducing lipid raft formation.

Extracellular heat shock proteins in neurodegenerative diseases: New perspectives

One pathological hallmark of neurodegenerative diseases and CNS trauma is accumulation of insoluble, hydrophobic molecules and protein aggregations found both within and outside cells. These may be the consequences of an inadequate or overburdened cellular response to stresses resulting from potentially toxic changes in extra- and intracellular environments. The upregulated expression of heat shock proteins (HSPs) is one example of a highly conserved cellular response to both internal and external stress. Intracellularly these proteins act as chaperones, playing vital roles in the folding of nascent polypeptides, the translocation of proteins between subcellular locations, and the disaggregation of misfolded or aggregated proteins in an attempt to maintain cellular proteostasis during both homeostatic and stressful conditions. While the predominant study of the HSPs has focused on their intracellular chaperone functions, it remains unclear if all neuronal populations can mount a complete stress response. Alternately, it is now well established that some members of this family of proteins can be secreted by nearby, non-neuronal cells to act in the extracellular environment. This review addresses the current literature detailing the use of exogenous and extracellular HSPs in the treatment of cellular and animal models of neurodegenerative disease. These findings offer a new measure of therapeutic potential to the HSPs, but obstacles must be overcome before they can be efficiently used in a clinical setting.

Overexpressed Hsp70 alleviated formaldehyde-induced apoptosis partly via PI3K/Akt signaling pathway in human bronchial epithelial cells

Formaldehyde (FA) is a ubiquitous environmental pollutant, which can induce apoptosis in lung cell and is related to the pathogenesis of asthma, pneumonia, and chronic obstructive pulmonary disease. Heat shock protein 70 (Hsp70) is an ATP-dependent molecular chaperone and exhibits an anti-apoptosis ability in a variety of cells. Previous studies reported that the expression of Hsp70 was induced when organisms were exposed to FA. Whether Hsp70 plays a role in the FA-induced apoptosis and the involved cell signaling pathway remain largely unknown. In this study, human bronchial epithelial cells with overexpressed Hsp70 and the control were exposed to different concentrations of FA (0, 40, 80, and 160 μmol/L) for 24 hours. Apoptosis and the expression levels of PI3K, Akt, p-Akt, MEK, p-MEK, and GLI2 were detected by Annexin-APC/7AAD double-labeled flow cytometry and western blot. The results showed that overexpression of Hsp70 decreased the apoptosis induced by FA and alleviated the decline of PI3k and p-Akt significantly. Inhibitor (LY 294002, a specific inhibitor of PI3K-Akt) test result indicated that PI3K-Akt signaling pathway was involved in the inhibition of FA-induced apoptosis by Hsp70 overexpression and also active in the maintenance of GLI2 level. However, it also suggested that other signaling pathways activated by overexpressed Hsp70 participated in this process, which was needed to be elucidated in further research.

Antibiotics induce polarization of pleural macrophages to M2-like phenotype in patients with tuberculous pleuritis

Pleural macrophages play critical roles in pathogenesis of tuberculous pleuritis, but very little is known about their response to anti-tuberculosis antibiotics treatment. Here, we examined whether and how pleural macrophages change in phenotype, transcription and function following antibiotics treatment in patients with tuberculous pleuritis. Results show pro-inflammatory cytokines were down-regulated significantly post antibiotic treatment in the pleural effusions and pleural macrophages up-regulated markers characteristic of M2 macrophages such as CD163 and CD206. Differential expression analysis of transcriptomes from four paired samples before and after treatment identified 230 treatment-specific responsive genes in pleural macrophages. Functional analysis identified interferon-related pathway to be the most responsive genes and further confirmed macrophage polarization to M2-like phenotype. We further demonstrate that expression of a significant fraction of responsive genes was modulated directly by antibiotics in pleural macrophages in vitro. Our results conclude that pleural macrophages polarize from M1-like to M2-like phenotype within a mean of 3.5 days post antibiotics treatment, which is dependent on both pleural cytokine environment and direct modulatory effects of antibiotics. The treatment-specific genes could be used to study the roles of pleural macrophages in the pathogenesis of tuberculous pleuritis and to monitor the response to antibiotics treatment.

Cytokines in immunogenic cell death: Applications for cancer immunotherapy

Despite advances in treatments like chemotherapy and radiotherapy, metastatic cancer remains a leading cause of death for cancer patients. While many chemotherapeutic agents can efficiently eliminate cancer cells, long-term protection against cancer is not achieved and many patients experience cancer recurrence. Mobilizing and stimulating the immune system against tumor cells is one of the most effective ways to protect against cancers that recur and/or metastasize. Activated tumor specific cytotoxic T lymphocytes (CTLs) can seek out and destroy metastatic tumor cells and reduce tumor lesions. Natural Killer (NK) cells are a front-line defense against drug-resistant tumors and can provide tumoricidal activity to enhance tumor immune surveillance. Cytokines like IFN-γ or TNF play a crucial role in creating an immunogenic microenvironment and therefore are key players in the fight against metastatic cancer. To this end, a group of anthracyclines or treatments like photodynamic therapy (PDT) exert their effects on cancer cells in a manner that activates the immune system. This process, known as immunogenic cell death (ICD), is characterized by the release of membrane-bound and soluble factors that boost the function of immune cells. This review will explore different types of ICD inducers, some in clinical trials, to demonstrate that optimizing the cytokine response brought about by treatments with ICD-inducing agents is central to promoting anti-cancer immunity that provides long-lasting protection against disease recurrence and metastasis.

Effect of stress on heat shock protein levels, immune response and survival to fungal infection of Mamestra brassicae larvae

Although the utilisation of fungal biological control agents to kill insect pests is desirable, it is known that the outcome of infection may be influenced by a number of criteria, including whether or not the target insect is stressed. In the current work, topical treatment of larvae of the lepidopteran pest, Mamestra brassicae, with conidia of Beauveria bassiana, followed by a heat stress (HS; 37°C for 1h) 48h later, resulted in a similar level of larval survival to that occurring for no heat stress (No-HS), fungus-treated larvae. By contrast, when the HS was applied 24h after fungal treatment, larval survival was significantly increased, indicating that the HS is protecting the larvae from B. bassiana. Similarly, exposure of larvae to a HS provided protection against Metarhizium brunneum (V275) at 48h (but not 24h) after fungal treatment. To elucidate the mechanism(s) that might contribute to HS-induced increases in larval survival against fungal infection, the effects of a HS on key cellular and humoral immune responses and on the level of selected heat shock proteins (HSP) were assessed. When larvae were kept under control (No HS) conditions, there was no significant difference in the haemocyte number per ml of haemolymph over a 24h period. However, exposure of larvae to a HS, significantly increased the haemocyte density immediately after (t=0h) and 4h after HS compared to the No HS controls, whilst it returned to control levels at t=24h. In addition, in vitro assays indicated that haemocytes harvested from larvae immediately after (0h) and 4h (but not 24h) after a HS exhibited higher rates of phagocytosis of FITC-labelled B. bassiana conidia compared to haemocytes harvested from non-HS larvae. Interestingly, the HS did not appear to increase anti-fungal activity in larval plasma. Western blot analysis using antibodies which cross react with Drosophila melanogaster HSP, resulted in a relatively strong signal for HSP 70 and HSP 90 from extracts of 50,000 and 100,000haemocytes, respectively, harvested from No-HS larvae. By contrast, for HSP 60, a lysate derived from 200,000haemocytes resulted in a relatively weak signal. When larvae were exposed to a HS, the level of all three HSP increased compared to the No HS control 4h and 16h after the HS. However, 24h after treatment, any heat stress-mediated increase in HSP levels was minimal and not consistently detected. Similar results were obtained when HSP 90, 70, and 60 levels were assessed in fat body harvested from heat stressed and non-heat stressed larvae. With regard to HSP 27, no signal was obtained even when a lysate from 200,000haemocytes or three times the amount of fat body were processed, suggesting that the anti-HSP 27 antibody utilised does not cross-react with the M. brassicae HSP. The results suggest that a HS-mediated increase in haemocyte density and phagocytic activity, together with an upregulation of HSP 90 and 70, may contribute to increasing the survival of M. brassicae larvae treated with B. bassiana and M. brunneum (V275).

Extracellular HSPs: The Complicated Roles of Extracellular HSPs in Immunity

Extracellular heat-shock proteins (HSPs) interact with the immune system in a very complex manner. Many such HSPs exert powerful effects on the immune response, playing both stimulatory and regulatory roles. However, the influence of the HSPs on immunity appears to be positive or negative in nature – rarely neutral. Thus, the HSPs can act as dominant antigens and can comprise key components of antitumor vaccines. They can also function as powerful immunoregulatory agents and, as such, are employed to treat inflammatory diseases or to extend the lifespan of tissue transplants. Small modifications in the cellular milieu have been shown to flip the allegiances of HSPs from immunoregulatory agents toward a potent inflammatory alignment. These mutable properties of HSPs may be related to the ability of these proteins to interact with multiple receptors often with mutually confounding properties in immune cells. Therefore, understanding the complex immune properties of HSPs may help us to harness their potential in treatment of a range of conditions.

Association between Toll-like receptor 7 Gln11Leu single-nucleotide polymorphism and basal cell carcinoma

Non-melanoma skin cancers (NMSC) are the most common form of human skin cancer. The majority of NMSC are basal cell carcinoma (BCC) and squamous cell carcinoma (SCC) with a BCC:SCC incidence ratio of 4:1 in immunocompetent patients. Toll-like receptors (TLRs) are transmembrane glycoproteins that recognize pathogen-associated molecular patterns and damage-associated molecular patterns, against which they activate the innate immune response and initiate the adaptive immune response. Genetic variations of these receptors can alter the immune system and are involved in evolution and susceptibility of various diseases, including cancer. Imiquimod, an agonist of TLR7, is applied topically in the treatment of premalignant and malignant skin disorders, in particular BCC. The high efficacy of this TLR7 agonist toward BCC supports a possible role of this receptor in the induction of BCC and, consequently, polymorphisms of this receptor could be responsible for a greater or lesser susceptibility to BCC. The aim of the present study was to evaluate whether the presence of the functional TLR7 rs179008/Gln11Leu promoter polymorphism conferred an increased susceptibility to BCC. A case-control study with 177 BCC cases and 158 controls was performed to highlight the possible association between this polymorphism and the susceptibility to BCC. As the TLR7 gene is localized on chromosome X, the allelic frequency of this polymorphism was analyzed separately in males and females. The analysis of the distribution of frequencies of wild-type TLR7 and variant TLR7 carrying the single-nucleotide polymorphism (SNP) rs179008 in patients with BCC and healthy subjects did not reveal any statistically significant difference between cases and controls. This study does not suggest the involvement of the SNP rs179008 of TLR7 in the susceptibility to BCC, but cannot exclude a role for TLR7 in BCC carcinogenesis considering the high efficacy of the TLR7 agonist, imiquimod, in the treatment of this neoplastic disorder.

Exosomes, endogenous retroviruses and toll-like receptors: pregnancy recognition in ewes

Conceptus–endometrial communication during the peri-implantation period of pregnancy ensures establishment of pregnancy. We hypothesized that this dialog involves exosomes, ovine endogenous jaagsiekte retroviruses (enJSRV) and toll-like receptors (TLR) which regulate the secretion of interferon tau (IFNT), the pregnancy recognition signal in ruminants. First, exosomes isolated from uterine flushings from cyclic and pregnant ewes were analyzed for exosomal content and uterine expression of heat shock protein 70 (HSC70). Then, conceptus trophectoderm cells (oTr1) treated with different doses of exosomes were analyzed for the expression of genes involved in TLR-mediated cell signaling. The results revealed that exosomes contain mRNAs for enJSRV-ENV,HSC70, interleukins, and interferon (IFN)-regulatory factors. Exosomal content of enJSRV-ENVmRNA and protein decreased from days 10 and 12 to day 16 of gestation, and uterine expression of HSC70 increased in pregnant ewes compared with cyclic ewes. The oTr1 cells proliferated and secreted IFNT in a dose-dependent manner in response to exosomes from cyclic ewes. The expression ofCD14,CD68,IRAK1,TRAF6,IRF6,andIRF7mRNAs that are key to TLR-mediated expression of type 1 IFNs was significantly influenced by day of pregnancy. This study demonstrated that exosomes are liberated into the uterine lumen during the estrous cycle and early pregnancy; however, in pregnant ewes, exosomes stimulate trophectoderm cells to proliferate and secrete IFNT coordinately with regulation of TLR-mediated cell signaling. These results support our hypothesis that free and/or exosomal enJSRV act on the trophectoderm via TLR to induce the secretion of IFNT in a manner similar to that for innate immune responses of macrophages and plasmacytoid dendritic cells to viral pathogens.

Sequence-dependent internalization of aggregating peptides

Recently, a number of aggregation disease polypeptides have been shown to spread from cell to cell, thereby displaying prionoid behavior. Studying aggregate internalization, however, is often hampered by the complex kinetics of the aggregation process, resulting in the concomitant uptake of aggregates of different sizes by competing mechanisms, which makes it difficult to isolate pathway-specific responses to aggregates. We designed synthetic aggregating peptides bearing different aggregation propensities with the aim of producing modes of uptake that are sufficiently distinct to differentially analyze the cellular response to internalization. We found that small acidic aggregates (≤500 nm in diameter) were taken up by nonspecific endocytosis as part of the fluid phase and traveled through the endosomal compartment to lysosomes. By contrast, bigger basic aggregates (>1 μm) were taken up through a mechanism dependent on cytoskeletal reorganization and membrane remodeling with the morphological hallmarks of phagocytosis. Importantly, the properties of these aggregates determined not only the mechanism of internalization but also the involvement of the proteostatic machinery (the assembly of interconnected networks that control the biogenesis, folding, trafficking, and degradation of proteins) in the process; whereas the internalization of small acidic aggregates is HSF1-independent, the uptake of larger basic aggregates was HSF1-dependent, requiring Hsp70. Our results show that the biophysical properties of aggregates determine both their mechanism of internalization and proteostatic response. It remains to be seen whether these differences in cellular response contribute to the particular role of specific aggregated proteins in disease.

Heat-shock response increases lung injury caused by Pseudomonas aeruginosa via an interleukin-10-dependent mechanism in mice

BACKGROUND

The heat-shock response (HSR) protects from insults, such as ischemia-reperfusion injury, by inhibiting signaling pathways activated by sterile inflammation. However, the mechanisms by which the HSR activation would modulate lung damage and host response to a bacterial lung infection remain unknown.

METHODS

HSR was activated with whole-body hyperthermia or by intraperitoneal geldanamycin in mice that had their lungs instilled with Pseudomonas aeruginosa 24 h later (at least six mice per experimental group). Four hours after instillation, lung endothelial and epithelial permeability, bacterial counts, protein levels in bronchoalveolar lavage fluid, and lung myeloperoxidase activity were measured. Mortality rate 24 h after P. aeruginosa instillation was recorded. The HSR effect on the release of interleukin-10 and killing of P. aeruginosa bacteria by a mouse alveolar macrophage cell line and on neutrophil phagocytosis was also examined.

RESULTS

HSR activation worsened lung endothelial (42%) and epithelial permeability (50%) to protein, decreased lung bacterial clearance (71%), and increased mortality (50%) associated with P. aeruginosa pneumonia, an effect that was not observed in heat-shock protein-72-null mice. HSR-mediated decrease in neutrophil phagocytosis (69%) and bacterial killing (38%) by macrophages was interleukin-10 dependent, a mechanism confirmed by increased lung bacterial clearance and decreased mortality (70%) caused by P. aeruginosa pneumonia in heat-shocked interleukin-10-null mice.

CONCLUSIONS

Prior HSR activation worsens lung injury associated with P. aeruginosa pneumonia in mice via heat-shock protein-72- and interleukin-10-dependent mechanisms. These results provide a novel mechanism for the immunosuppression observed after severe trauma that is known to activate HSR in humans.

Heat shock protein-27 attenuates foam cell formation and atherogenesis by down-regulating scavenger receptor-A expression via NF-κB signaling

Previously, we showed an inverse correlation between HSP27 serum levels and experimental atherogenesis in ApoE(-/-) mice that over-express HSP27 and speculated that the apparent binding of HSP27 to scavenger receptor-A (SR-A) was of mechanistic importance in attenuating foam cell formation. However, the nature and importance of the interplay between HSP27 and SR-A in atheroprotection remained unclear. Treatment of THP-1 macrophages with recombinant HSP27 (rHSP27) inhibited acLDL binding (-34%; p<0.005) and uptake (-38%, p<0.05). rHSP27 reduced SR-A mRNA (-39%, p=0.02), total protein (-56%, p=0.01) and cell surface (-53%, p<0.001) expression. The reduction in SR-A expression by rHSP27 was associated with a 4-fold increase in nuclear factor-kappa B (NF-κB) signaling (p<0.001 versus control), while an inhibitor of NF-κB signaling, BAY11-7082, attenuated the negative effects of rHSP27 on both SR-A expression and lipid uptake. To determine if SR-A is required for HSP27 mediated atheroprotection in vivo, ApoE(-/-) and ApoE(-/-) SR-A(-/-) mice fed with a high fat diet were treated for 3weeks with rHSP25. Compared to controls, rHSP25 therapy reduced aortic en face and aortic sinus atherosclerotic lesion size in ApoE(-/-) mice by 39% and 36% (p<0.05), respectively, but not in ApoE(-/-)SR-A(-/-) mice. In conclusion, rHSP27 diminishes SR-A expression, resulting in attenuated foam cell formation in vitro. Regulation of SR-A by HSP27 may involve the participation of NF-κB signaling. Lastly, SR-A is required for HSP27-mediated atheroprotection in vivo.

Bacterial infection elicits heat shock protein 72 release from pleural mesothelial cells

Heat shock protein 70 (HSP70) has been implicated in infection-related processes and has been found in body fluids during infection. This study aimed to determine whether pleural mesothelial cells release HSP70 in response to bacterial infection in vitro and in mouse models of serosal infection. In addition, the in vitro cytokine effects of the HSP70 isoform, Hsp72, on mesothelial cells were examined. Further, Hsp72 was measured in human pleural effusions and levels compared between non-infectious and infectious patients to determine the diagnostic accuracy of pleural fluid Hsp72 compared to traditional pleural fluid parameters. We showed that mesothelial release of Hsp72 was significantly raised when cells were treated with live and heat-killed Streptococcus pneumoniae. In mice, intraperitoneal injection of S. pneumoniae stimulated a 2-fold increase in Hsp72 levels in peritoneal lavage (p<0.01). Extracellular Hsp72 did not induce or inhibit mediator release from cultured mesothelial cells. Hsp72 levels were significantly higher in effusions of infectious origin compared to non-infectious effusions (p<0.05). The data establish that pleural mesothelial cells can release Hsp72 in response to bacterial infection and levels are raised in infectious pleural effusions. The biological role of HSP70 in pleural infection warrants exploration.

Endocytosis of gene delivery vectors: from clathrin-dependent to lipid raft-mediated endocytosis

The ideal nonviral vector delivers its nucleic acid cargo to a specific intracellular target. Vectors enter cells mainly through endocytosis and are distributed to various intracellular organelles. Recent advances in microscopy, lipidomics, and proteomics confirm that the cell membrane is composed of clusters of lipids, organized in the form of lipid raft domains, together with non-raft domains that comprise a generally disordered lipid milieu. The binding of a nonviral vector to either region can determine the pathway for its endocytic uptake and subsequent intracellular itinerary. Given this model of the cell membrane structure, endocytic pathways should be reclassified in relation to lipid rafts. In this review, we attempt to assess the currently recognized endocytic pathways in mammalian cells. The endocytic pathways are classified in relation to the membrane regions that make up the primary endocytic vesicles. This review covers the well-recognized clathrin-mediated endocytosis (CME), phagocytosis, and macropinocytosis in addition to the less addressed pathways that take place in lipid rafts. These include caveolae-mediated, flotillin-dependent, GTPase regulator associated with focal adhesion kinase-1 (GRAF1)-dependent, adenosine diphosphate-ribosylation factor 6 (Arf6)-dependent, and RhoA-dependent endocytic pathways. We summarize the regulators associated with each uptake pathway and methods for interfering with these regulators are discussed. The fate of endocytic vesicles resulting from each endocytic uptake pathway is highlighted.

Myeloid cell-specific serine palmitoyltransferase subunit 2 haploinsufficiency reduces murine atherosclerosis

Serine palmitoyltransferase (SPT) is the first and rate-limiting enzyme of the de novo biosynthetic pathway of sphingomyelin (SM). Both SPT and SM have been implicated in the pathogenesis of atherosclerosis, the development of which is driven by macrophages; however, the role of SPT in macrophage-mediated atherogenesis is unknown. To address this issue, we have analyzed macrophage inflammatory responses and reverse cholesterol transport, 2 key mediators of atherogenesis, in SPT subunit 2-haploinsufficient (Sptlc2(+/-)) macrophages. We found that Sptlc2(+/-) macrophages have significantly lower SM levels in plasma membrane and lipid rafts. This reduction not only impaired inflammatory responses triggered by TLR4 and its downstream NF-κB and MAPK pathways, but also enhanced reverse cholesterol transport mediated by ABC transporters. LDL receptor-deficient (Ldlr(-/-)) mice transplanted with Sptlc2(+/-) bone marrow cells exhibited significantly fewer atherosclerotic lesions after high-fat and high-cholesterol diet feeding. Additionally, Ldlr(-/-) mice with myeloid cell-specific Sptlc2 haploinsufficiency exhibited significantly less atherosclerosis than controls. These findings suggest that SPT could be a novel therapeutic target in atherosclerosis.

Sphingomyelin and its role in cellular signaling

Sphingolipid de novo biosynthesis is related with metabolic diseases. However, the mechanism is still not quite clear. Sphingolipids are ubiquitous and critical components of biological membranes. Their biosynthesis starts with soluble precursors in the endoplasmic reticulum and culminates in the Golgi complex and plasma membrane. The interaction of sphingomyelin, cholesterol, and glycosphingolipid drives the formation of plasma membrane rafts. Lipid rafts have been shown to be involved in cell -signaling, lipid and protein sorting, and membrane trafficking. It is well known that toll-like receptors, class A and B scavenger receptors, and insulin receptor are located in lipid rafts. Sphingomyelin is also a reservoir for other sphingolipids. So, sphingomyelin has important impact in cell -signaling through its structural role in lipid rafts or its catabolic inter-mediators, such as ceramide and glycoceramide. In this chapter, we will discuss both aspects.

Sphingolipid metabolism and atherosclerosis

Atherosclerosis is the major cause of mortality in the developed countries. Although presently known risk factors have some predictive value for the disease, a major part of the variability in this process remains unexplained. It is extremely important to find new approaches for better understanding of the disease and for treating it. Exploration of the sphingolipid metabolism is one of these approaches. Sphingolipids are a large class of lipids with structural and signaling functions. Recent researches indicated that these lipids play important roles in the development of atherosclerosis. In this chapter, we summarized the major findings in the field.

Impact of sphingomyelin synthase 1 deficiency on sphingolipid metabolism and atherosclerosis in mice

OBJECTIVE

Sphingomyelin synthase (SMS) catalyzes the conversion of ceramide to sphingomyelin and sits at the crossroads of sphingolipid biosynthesis. SMS has 2 isoforms: SMS1 and SMS2. Although they have the same SMS activity, they are different enzymes with distinguishable subcellular localizations and cell expression patterns. It is conceivable that these differences could yield different consequences, in terms of sphingolipid metabolism and its related atherogenesis.

METHODS AND RESULTS

We created Sms1 gene knockout mice and found that Sms1 deficiency significantly decreased plasma, liver, and macrophage sphingomyelin (59%, 45%, and 54%, respectively), but only had a marginal effect on ceramide levels. Surprisingly, we found that Sms1 deficiency dramatically increased glucosylceramide and GM3 levels in plasma, liver, and macrophages (4- to 12-fold), whereas Sms2 deficiency had no such effect. We evaluated the total SMS activity in tissues and found that Sms1 deficiency causes 77% reduction in SMS activity in macrophages, indicating SMS1 is the major SMS in macrophages. Moreover, Sms1-deficient macrophages have a significantly higher glucosylceramide synthase activity. We also found that Sms1 deficiency significantly attenuated toll-like 4 receptor-mediated nuclear factor-κB and mitogen-activated protein kinase activation after lipopolysaccharide treatment. To evaluate atherogenicity, we transplanted Sms1 knockout mouse bone marrow into low-density lipoprotein receptor knockout mice (Sms1(-/-)→Ldlr(-/-)). After 3 months on a western diet, these animals showed a significant decrease of atherosclerotic lesions in the root and the entire aorta (35% and 44%, P<0.01, respectively) and macrophage content in lesions (51%, P<0.05), compared with wild-type→Ldlr(-/-) mice.

CONCLUSIONS

Sms1 deficiency decreases sphingomyelin, but dramatically increases the levels of glycosphingolipids. Atherosclerosis in Sms1(-/-)→Ldlr(-/-) mice is significantly decreased.

Heat shock proteins: conditional mediators of inflammation in tumor immunity

Heat shock protein (HSP)-based anticancer vaccines have undergone successful preclinical testing and are now entering clinical trial. Questions still remain, however regarding the immunological properties of HSPs. It is now accepted that many of the HSPs participate in tumor immunity, at least in part by chaperoning tumor antigenic peptides, introducing them into antigen presenting cells such as dendritic cells (DC) that display the antigens on MHC class I molecules on the cell surface and stimulate cytotoxic lymphocytes (CTL). However, in order for activated CD8+ T cells to function as effective CTL and kill tumor cells, additional signals must be induced to obtain a sturdy CTL response. These include the expression of co-stimulatory molecules on the DC surface and inflammatory events that can induce immunogenic cytokine cascades. That such events occur is indicated by the ability of Hsp70 vaccines to induce antitumor immunity and overcome tolerance to tumor antigens such as mucin1. Secondary activation of CTL can be induced by inflammatory signaling through Toll-like receptors and/or by interaction of antigen-activated T helper cells with the APC. We will discuss the role of the inflammatory properties of HSPs in tumor immunity and the potential role of HSPs in activating T helper cells and DC licensing.

Involvement of extracellular Hsp72 in wear particle-mediated osteolysis

Wear particle-mediated osteolysis is one of the major problems affecting long-term survival of orthopaedic prostheses, frequently progressing to failure of fixation and revision surgery. Upon challenging with wear particles, macrophages and various other types of cells release soluble factors that stimulate the resorptive activity of osteoclasts and impair the function and activity of osteoblasts. Extracellular Hsp72 has been reported to activate macrophages and up-regulate pro-inflammatory cytokine production, although its role in osteolysis has not been established yet. The purpose of our study was to evaluate the involvement of this protein in the inflammatory response to wear particles that leads to periprosthetic osteolysis. To this end, we used interfacial tissues and blood samples from patients undergoing revision surgery due to aseptic loosening of cementless acetabular cups. Confocal microscopy indicated that Hsp72 co-localises with CD14(+) cells of interfacial tissues. Levels of Hsp72 in the culture media from periprosthetic membranes cultured ex vivo decreased along culture time and Hsp72 levels in sera from patients were lower and under the assay detection limit compared with those from age-matched control subjects. This suggests that interfacial tissues are not actively producing the protein but likely recruit it from peripheral circulation. Incubation of human macrophages with titanium (Ti) particles decreased the release of Hsp72 into culture media. Treatment with recombinant human Hsp72 enhanced considerably IL-6 levels in culture media which were not modified after macrophage co-stimulation with Ti particles, while pre-incubation with Hsp72 increased the Ti particle-induced TNF-α and IL-1β production. Altogether, these data indicate that extracellular Hsp72 amplifies the inflammatory response to wear debris by interacting with resident macrophages in periprosthetic tissues.

Heat shock proteins and cancer vaccines: developments in the past decade and chaperoning in the decade to come

Molecular chaperone-peptide complexes extracted from tumors (heat shock protein [HSP] vaccines) have been intensively studied in the preceding two decades, proving to be safe and effective in treating a number of malignant diseases. They offer personalized therapy and target a cross-section of antigens expressed in patients' tumors. Future advances may rely on understanding the molecular underpinnings of this approach to immunotherapy. One property common to HSP vaccines is the ability to stimulate antigen uptake by scavenger receptors on the antigen-presenting cell surface and trigger T-lymphocyte activation. HSPs can also induce signaling through Toll-Like receptors in a range of immune cells and this may mediate the effectiveness of vaccines.

Pediatric Sepsis - Part V: Extracellular Heat Shock Proteins: Alarmins for the Host Immune System

Heat shock proteins (HSPs) are molecular chaperones that facilitate the proper folding and assembly of nascent polypeptides and assist in the refolding and stabilization of damaged polypeptides. Through these largely intracellular functions, the HSPs maintain homeostasis and assure cell survival. However, a growing body of literature suggests that HSPs have important effects in the extracellular environment as well. Extracellular HSPs are released from damaged or stressed cells and appear to act as local "danger signals" that activate stress response programs in surrounding cells. Importantly, extracellular HSPs have been shown to activate the host innate and adaptive immune response. With this in mind, extracellular HSPs are commonly included in a growing list of a family of proteins known as danger-associated molecular patterns (DAMPs) or alarmins, which trigger an immune response to tissue injury, such as may occur with trauma, ischemia-reperfusion injury, oxidative stress, etc. Extracellular HSPs, including Hsp72 (HSPA), Hsp27 (HSPB1), Hsp90 (HSPC), Hsp60 (HSPD), and Chaperonin/Hsp10 (HSPE) are especially attractrive candidates for DAMPs or alarmins which may be particularly relevant in the pathophysiology of the sepsis syndrome.

Exosomal membrane molecules are potent immune response modulators

Exosomes are endosome-derived vesicles (40-100 nm) formed during the formation of multi-vesicular bodies (MVBs). Occasionally, the MVBs fuse with the plasma membrane releasing their intra-luminal vesicles into the extracellular media, which are then known as exosomes. Different cell types such as B-cells, dendritic cells, platelets, reticulocytes and macrophages can release exosomes and current research in this area is more focused towards exosomes released by antigen-presenting cells. Exosomes have recently been shown to be immunomodulatory and the mechanism of immune response initiation by them is beginning to emerge. Besides molecules present inside the lumen of exosomes, it has been suggested that certain exosomal membrane molecules can interact with their surface receptors on the target cells thereby inducing an immunomodulatory response. In this review, Hsp70 and galectin-5, two immunogenic molecules present on exosomal membrane, are discussed in detail for initiating this response.

Heat shock protein 90 mediates efficient antigen cross presentation through the scavenger receptor expressed by endothelial cells-I

Ag cross presentation is an important mechanism for CD8(+) T cell activation by APCs. We have investigated mechanisms involved in heat shock protein 90 (Hsp90) chaperone-mediated cross presentation of OVA-derived Ags. Hsp90-OVA peptide complexes bound to scavenger receptor expressed by endothelial cells (SREC-I) on the surface of APCs. SREC-I then mediated internalization of Hsp90-OVA polypeptide complexes through a Cdc42-regulated, dynamin-independent endocytic pathway known as the GPI-anchored protein-enriched early endosomal compartment to recycling endosomes. Peptides that did not require processing could then be loaded directly onto MHC class I in endosomes, whereas longer peptides underwent endosomal and cytosomal processing by aminopeptidases and proteases. Cross presentation of Hsp90-chaperoned peptides through this pathway to CD8(+) T cells was highly efficient compared with processing of free polypeptides. In addition, Hsp90 also activated c-Src kinase associated with SREC-I, an activity that we determined to be required for effective cross presentation. Extracellular Hsp90 can thus convey antigenic peptides through an efficient endocytosis pathway in APCs and facilitate cross presentation in a highly regulated manner.

Macrophage ABCA1 reduces MyD88-dependent Toll-like receptor trafficking to lipid rafts by reduction of lipid raft cholesterol

We previously showed that macrophages from macrophage-specific ATP-binding cassette transporter A1 (ABCA1) knockout (Abca1(-M/-M)) mice had an enhanced proinflammatory response to the Toll-like receptor (TLR) 4 agonist, lipopolysaccharide (LPS), compared with wild-type (WT) mice. In the present study, we demonstrate a direct association between free cholesterol (FC), lipid raft content, and hyper-responsiveness of macrophages to LPS in WT mice. Abca1(-M/-M) macrophages were also hyper-responsive to specific agonists to TLR2, TLR7, and TLR9, but not TLR3, compared with WT macrophages. We hypothesized that ABCA1 regulates macrophage responsiveness to TLR agonists by modulation of lipid raft cholesterol and TLR mobilization to lipid rafts. We demonstrated that Abca1(-M/-M) vs. WT macrophages contained 23% more FC in isolated lipid rafts. Further, mass spectrometric analysis suggested raft phospholipid composition was unchanged. Although cell surface expression of TLR4 was similar between Abca1(-M/-M) and WT macrophages, significantly more TLR4 was distributed in membrane lipid rafts in Abca1(-M/-M) macrophages. Abca1(-M/-M) macrophages also exhibited increased trafficking of the predominantly intracellular TLR9 into lipid rafts in response to TLR9-specific agonist (CpG). Collectively, our data suggest that macrophage ABCA1 dampens inflammation by reducing MyD88-dependent TLRs trafficking to lipid rafts by selective reduction of FC content in lipid rafts.

Exercise-induced extracellular 72 kDa heat shock protein (Hsp72) stimulates neutrophil phagocytic and fungicidal capacities via TLR-2

This study evaluated the role of toll like receptor 2 (TLR-2) in the interaction of 72 kDa extracellular heat shock protein (Hsp72, a stress-inducible protein) with neutrophils and the participation on TLR-2 in the stimulation of neutrophil phagocytic and fungicidal capacities by post-exercise physiological concentrations of Hsp72. Human peripheral blood neutrophils were incubated with fluorescein isothiocyanate-conjugated Hsp72, and were analyzed by immunofluorescence microscopy and flow cytometry. Both methods revealed an interaction of Hsp72 with neutrophils. In addition, when neutrophils were pre-incubated with an anti-TLR-2 antibody this interaction was clearly decreased. Post-exercise circulating concentration of Hsp72 (8.6 ng/ml) stimulated the phagocytic and fungicidal capacities of neutrophils and this effect could be also blocked using an antibody against TLR-2. Phosphatidylinositol-3-kinase (PI3K), extracellular signal-regulated kinase (ERK) and the nuclear transcription factor kappa beta (NF-kappabeta) were found to be involved in the signaling process, confirming the participation of TLR-2 in the stimulation of neutrophil function by Hsp72. In conclusion, TLR-2 is involved at least in part, in the stimulation of neutrophil phagocytic and fungicidal capacities induced by post-exercise physiological concentrations of Hsp72.

Raft aggregation with specific receptor recruitment is required for microglial phagocytosis of Abeta42

Microglial phagocytosis contributes to the maintenance of brain homeostasis. Mechanisms involved, however, remain unclear. Using Abeta(42) solely as a stimulant, we provide novel insight into regulation of microglial phagocytosis by rafts. We demonstrate the existence of an Abeta(42) threshold level of 250 pg/mL, above which microglial phagocytic function is impaired. Low levels of Abeta(42) facilitate fluorescent bead uptake, whereas phagocytosis is inhibited when Abeta(42) accumulates. We also show that region-specific raft clustering occurs before microglial phagocytosis. Low Abeta(42) levels stimulated this type of raft aggregation, but high Abeta(42) levels inhibited it. Additionally, treatment with high Abeta(42) concentrations caused a redistribution of the raft structural protein flotillin1 from low to higher density fractions along a sucrose gradient. This suggests a loss of raft structural integrity. Certain non-steroidal anti-inflammatory drugs, e.g., the cyclooxygenase 2-specific nonsteroidal anti-inflammatory drugs, celecoxib, raise Abeta(42) levels. We demonstrated that prolonged celecoxib exposure can disrupt rafts in a manner similar to that seen in an elevated Abeta(42) environment: abnormal raft aggregation and Flot1 distribution. This resulted in aberrant receptor recruitment to rafts and impaired receptor-mediated phagocytosis by microglial cells. Specifically, recruitment of the scavenger receptor CD36 to rafts during active phagocytosis was affected. Thus, we propose that maintaining raft integrity is crucial for determining microglial phagocytic outcomes and disease progression.

The HSP72 stress response of monocytes from patients on haemodialysis is impaired

BACKGROUND

Induction of heat shock proteins (HSP), i.e. of the major family member HSP70, is an important cytoprotective-resistance mechanism for monocytes/ macrophages (Mphi). Patients on haemodialysis present with a high infectious morbidity and enhanced carcinoma incidence. Renal insufficiency-related alteration of microbicidal and tumoricidal functions of Mphi, major effectors of the immune system, might promote these diseases.

METHODS

Freshly isolated Mphi from Sprague-Dawley rats 2 weeks after 5/6-nephrectomy and from patients on intermittent haemodialysis (IHD) were stimulated by heat shock (HS) and compared to stimulated Mphi of control rats or healthy volunteers (CTR). Expression of HSP72 (inducible HSP70) was assessed by RT-PCR, and/or flow cytometry. Apoptosis of Mphi was detected by flow cytometry (CD14/annexin V-labelling).

RESULTS

In rat Mphi, baseline HSP72 expression was similar in both groups, but its induction was significantly impaired in renal insufficiency (214 +/- 68% less HSP70-mRNA versus CTR, n = 6). In patients, HSF-1-mRNA and HSP72-mRNA/protein response to HS was significantly lower, but not affected by dialysis session itself. In parallel, apoptosis of Mphi of patients was enhanced (+83 +/- 29% constitutive apoptotic Mphi versus CTR, n = 8), and HS-dependent protection from apoptosis with and without serum depletion (48 h depletion: HS, +275 +/- 37% apoptotic Mphi versus CTR, n = 6; full medium: +166 +/- 62% versus CTR, n = 8, P < 0.05) was inferior.

CONCLUSIONS

Impaired HSP72 stress response of Mphi in patients on haemodialysis might contribute to the observed immune dysfunction and, therefore, to the increased susceptibility to infection and malignancy. Stress impairment is not restricted to uraemia but is already present in a rat model of chronic kidney disease.