Heat shock protein 60 is released in immune-mediated glomerulonephritis and aggravates disease: in vivo evidence for an immunologic danger signal

A longitudinal assessment of heat exposure and biomarkers of kidney function on heat shock protein 70 and antibodies among agricultural workers

BACKGROUND

Exposure to extreme heat impacts millions of people worldwide and outdoor workers are among the populations most affected by hot temperatures. Heat stress induces several biological responses in humans, including the production of heat shock proteins (HSP) and antibodies against HSP (anti-HSP) which may play a central role in the body's cellular response to a hot environment.

OBJECTIVE

This longitudinal study investigated the impact of elevated temperatures and humidity on the presence of HSP70 and anti-HSP70 and examined relationships with markers of kidney function in an at-risk workforce under conditions of extreme heat and exertion in Guatemala.

METHODS

We collected ambient temperature and relative humidity data as well as biomarkers and clinical data from 40 sugarcane workers at the start and the end of a 6-month harvest. We used generalized mixed-effects models to estimate temperature effects on HSP70 and anti-HSP70 levels. In addition, we examined trends between HSP70 and anti-HSP70 levels and markers of kidney function across the harvest.

RESULTS

At the end of the harvest, temperatures were higher, and workers had, on average, higher levels of HSP70 and anti-HSP70 compared to the beginning of the season. We observed significant increasing trends with temperature indices, heat index, and HSP70 levels. Maximum temperature was associated with HSP70 increments after controlling for age, systolic and diastolic blood pressure (β: 0.21, 95% Confidence Interval: 0.09, 0.33). Kidney function decline across the harvest was associated with both higher levels of anti-HSP70 levels at the end of the harvest as well as greater increases in anti-HSP70 levels across the harvest.

CONCLUSIONS

These results suggest that workplace heat exposure may increase the production of HSP70 and anti-HSP70 levels and that there may be a relationship between increasing anti-HSP70 antibodies and the development of renal injury. HSP70 holds promise as a biomarker of heat stress in exposed populations.

Heat Shock Response and Heat Shock Proteins: Current Understanding and Future Opportunities in Human Diseases

The heat shock response is an evolutionarily conserved mechanism that protects cells or organisms from the harmful effects of various stressors such as heat, chemicals toxins, UV radiation, and oxidizing agents. The heat shock response triggers the expression of a specific set of genes and proteins known as heat shock genes/proteins or molecular chaperones, including HSP100, HSP90, HSP70, HSP60, and small HSPs. Heat shock proteins (HSPs) play a crucial role in thermotolerance and aiding in protecting cells from harmful insults of stressors. HSPs are involved in essential cellular functions such as protein folding, eliminating misfolded proteins, apoptosis, and modulating cell signaling. The stress response to various environmental insults has been extensively studied in organisms from prokaryotes to higher organisms. The responses of organisms to various environmental stressors rely on the intensity and threshold of the stress stimuli, which vary among organisms and cellular contexts. Studies on heat shock proteins have primarily focused on HSP70, HSP90, HSP60, small HSPs, and ubiquitin, along with their applications in human biology. The current review highlighted a comprehensive mechanism of heat shock response and explores the function of heat shock proteins in stress management, as well as their potential as therapeutic agents and diagnostic markers for various diseases.

A longitudinal assessment of heat exposure and biomarkers of kidney function on heat shock protein 70 and antibodies among agricultural workers

Background

Exposure to extreme heat impacts millions of people worldwide and outdoor workers are among the populations most affected by high temperatures. Heat stress induces several biological responses in humans, including the production of heat shock proteins (HSP) and antibodies against HSP (anti-HSP) which may play a central role in the body's cellular response to a hot environment.

Objective

This longitudinal study investigated the impact of high temperatures and humidity on the presence of HSP70 and anti-HSP70 and examined relationships with markers of kidney function in an at-risk workforce under conditions of extreme heat and exertion in Guatemala.

Methods

We collected ambient temperature and relative humidity data as well as biomarkers and clinical data from 40 sugarcane workers at the start and the end of a 6-month harvest. We used generalized mixed-effects models to estimate temperature effects on HSP70 and anti-HSP70 levels. In addition, we examined trends between HSP70 and anti-HSP70 levels and markers of kidney function across the harvest.

Results

At the end of the harvest, temperatures were higher, and workers had, on average, higher levels of HSP70 and anti-HSP70 compared to the beginning of the season. We observed significant increasing trends with temperature indices and HSP70 levels. Maximum temperature was associated with HSP70 increments after controlling for age, systolic and diastolic blood pressure (β: 0.21, 95% Confidence Interval: 0.09, 0.33). Kidney function decline across the harvest was associated with both higher levels of anti-HSP70 levels at the end of the harvest as well as greater increases in anti-HSP70 levels across the harvest.

Conclusions

These results suggest that workplace heat exposure may increase the production of HSP70 and anti-HSP70 levels and that there may be a relationship between increasing anti-HSP70 antibodies and the development of renal injury. HSP70 holds promise as a biomarker of heat stress in exposed populations.

Peroxiredoxin 1 aggravates acute kidney injury by promoting inflammation through Mincle/Syk/NF-κB signaling

Damage-associated molecular patterns (DAMPs) are a cause of acute kidney injury (AKI). Our knowledge of these DAMPs remains incomplete. Here, we report serum peroxiredoxin 1 (Prdx1) as a novel DAMP for AKI. Lipopolysaccharide (LPS) and kidney ischemia/reperfusion injury instigated AKI with concurrent increases in serum Prdx1 and reductions of Prdx1 expression in kidney tubular epithelial cells. Genetic knockout of Prdx1 or use of a Prdx1-neutralizing antibody protected mice from AKI and this protection was impaired by introduction of recombinant Prdx1 (rPrdx1). Mechanistically, lipopolysaccharide increased serum and kidney proinflammatory cytokines, macrophage infiltration, and the content of M1 macrophages. All these events were suppressed in Prdx1-/- mice and renewed upon introduction of rPrdx1. In primary peritoneal macrophages, rPrdx1 induced M1 polarization, activated macrophage-inducible C-type lectin (Mincle) signaling, and enhanced proinflammatory cytokine production. Prdx1 interacted with Mincle to initiate acute kidney inflammation. Of note, rPrdx1 upregulated Mincle and the spleen tyrosine kinase Syk system in the primary peritoneal macrophages, while knockdown of Mincle abolished the increase in activated Syk. Additionally, rPrdx1 treatment enhanced the downstream events of Syk, including transcription factor NF-κB signaling pathways. Furthermore, serum Prdx1 was found to be increased in patients with AKI; the increase of which was associated with kidney function decline and inflammatory biomarkers in patient serum. Thus, kidney-derived serum Prdx1 contributes to AKI at least in part by activating Mincle signaling and downstream pathways.

A peptide derived from HSP60 reduces proinflammatory cytokines and soluble mediators: a therapeutic approach to inflammation

Cytokines are secretion proteins that mediate and regulate immunity and inflammation. They are crucial in the progress of acute inflammatory diseases and autoimmunity. In fact, the inhibition of proinflammatory cytokines has been widely tested in the treatment of rheumatoid arthritis (RA). Some of these inhibitors have been used in the treatment of COVID-19 patients to improve survival rates. However, controlling the extent of inflammation with cytokine inhibitors is still a challenge because these molecules are redundant and pleiotropic. Here we review a novel therapeutic approach based on the use of the HSP60-derived Altered Peptide Ligand (APL) designed for RA and repositioned for the treatment of COVID-19 patients with hyperinflammation. HSP60 is a molecular chaperone found in all cells. It is involved in a wide diversity of cellular events including protein folding and trafficking. HSP60 concentration increases during cellular stress, for example inflammation. This protein has a dual role in immunity. Some HSP60-derived soluble epitopes induce inflammation, while others are immunoregulatory. Our HSP60-derived APL decreases the concentration of cytokines and induces the increase of FOXP3+ regulatory T cells (Treg) in various experimental systems. Furthermore, it decreases several cytokines and soluble mediators that are raised in RA, as well as decreases the excessive inflammatory response induced by SARS-CoV-2. This approach can be extended to other inflammatory diseases.

Macrophages in the kidney in health, injury and repair

Macrophages are a key component of the renal mononuclear phagocyte system, playing a major role in defense against infection, renal injury and repair. Yolk sac macrophage precursors seed the early embryonic kidney and are important for renal development. Later, renal macrophages are derived from hematopoietic stem cells and in adult life, there is a significant contribution from circulating monocytes, which is enhanced in response to infection or injury. Macrophages are highly plastic and can alter their phenotype in response to cues from parenchymal renal cells. Danger-associated molecules released from injured kidney cells may activate macrophages toward a pro-inflammatory phenotype, mediating further recruitment of inflammatory cells, exacerbating renal injury and activating renal fibroblasts to promote scarring. In acute kidney injury, once the injury stimulus has abated, macrophages may adopt a more reparative phenotype, dampening the immune response and promoting repair of renal tissue. However, in chronic kidney disease ongoing activation of pro-inflammatory monocytes and persistence of reparative macrophages leads to glomerulosclerosis and tubulointerstitial fibrosis, the hallmarks of end-stage kidney disease. Several strategies to inhibit the recruitment, activation and secretory products of pro-inflammatory macrophages have proven beneficial in pre-clinical models and are now undergoing clinical trials in patients with kidney disease. In addition, macrophages may be utilized in cell therapy as a "Trojan Horse" to deliver targeted therapies to the kidney. Single-cell RNA sequencing has identified a previously unappreciated spectrum of macrophage phenotypes, which may be selectively present in injury or repair, and ongoing functional analyses of these subsets may identify more specific targets for therapeutic intervention.

Immunosenescence: an unexplored role in glomerulonephritis

Immunosenescence is a natural ageing phenomenon with alterations in innate and especially adaptive immunity and contributes to reduced antimicrobial defence and chronic low‐grade inflammation. This is mostly reflected by an increase in organ‐directed and/or circulating reactive and cytolytic terminally differentiated T cells that have lost their expression of the costimulatory receptor CD28. Apart from being induced by a genetic predisposition, ageing or viral infections (particularly cytomegalovirus infection), immunosenescence is accelerated in many inflammatory diseases and uraemia. This translates into an enhancement of vascular inflammation and cardiovascular disease varying from endothelial dysfunction to plaque rupture. Emerging data point to a mechanistic role of CD28^null T cells in glomerulonephritis, where they initiate and propagate local inflammation in concordance with dendritic cells and macrophages. They are suitably equipped to escape immunological dampening by the absence of homing to lymph nodes, anti‐apoptotic properties and resistance to suppression by regulatory T cells. Early accumulation of senescent CD28^null T cells precedes glomerular or vascular injury, and targeting these cells could open avenues for early treatment interventions that aim at abrogating a detrimental vicious cycle.

Patients with Proliferative Lupus Nephritis Have Autoantibodies That React to Moesin and Demonstrate Increased Glomerular Moesin Expression

Kidney involvement in systemic lupus erythematosus (SLE)—termed lupus nephritis (LN)—is a severe manifestation of SLE that can lead to end-stage kidney disease (ESKD). LN is characterized by immune complex deposition and inflammation in the glomerulus. We tested the hypothesis that autoantibodies targeting podocyte and glomerular cell proteins contribute to the development of immune complex formation in LN. We used Western blotting with SLE sera from patients with and without LN to identify target antigens in human glomerular and cultured human-derived podocyte membrane proteins. Using liquid chromatography-tandem mass spectrometry (LC-MS/MS), we identified the proteins in the gel regions corresponding to reactive bands observed with sera from LN patients. We identified 102 proteins that were present in both the podocyte and glomerular samples. We identified 10 high-probability candidates, including moesin, using bioinformatic analysis. Confirmation of moesin as a target antigen was conducted using immunohistochemical analysis (IHC) of kidney biopsy tissue and enzyme-linked immunosorbent assay (ELISA) to detect circulating antibodies. By IHC, biopsies from patients with proliferative lupus nephritis (PLN, class III/IV) demonstrated significantly increased glomerular expression of moesin (p < 0.01). By ELISA, patients with proliferative LN demonstrated significantly increased antibodies against moesin (p < 0.01). This suggests that moesin is a target glomerular antigen in lupus nephritis.

Intense immunostaining of heat shock protein 70 within renal interstitium associates with long-term renal survival in an ANCA-associated vasculitis cohort

In anti-neutrophilic cytoplasmic antibody (ANCA)-associated vasculitis (AAV) genetic predisposition, ANCA autoantibodies, neutrophil extracellular traps (NETs), complement activation, and toll-like receptor signaling are implicated in AAV pathogenesis. Heat shock proteins (HSPs), a highly conserved group of small-sized molecular chaperones, take part in protein folding during cellular stress. Although HSPs were initially observed intracellularly, it has been shown that they can be secreted in the extracellular space and modulate the immune response in various autoimmune diseases including AAV. The scope of the present study is to investigate the role of heat shock protein 60 (HSP60) and 70 (HSP70) in the long renal effects in an ANCA vasculitis cohort. In this cohort of ANCA-associated vasculitis, 29 patients were followed up over 20 years. At diagnosis, immunohistochemistry was performed for HSP60 and HSP70 within the various nephron compartments. Higher renal HSP60 expression was associated with increased interstitial inflammatory infiltrates at diagnosis, while HSP70 expression was associated with a greater extent of interstitial fibrosis at diagnosis. Notably, intense tissue expression of HSP70 at the time of biopsy was associated with a worsened kidney survival. Renal HSP70 expression was associated with poor renal outcomes during long-term follow-up. This finding may indicate a role of HSPs in renal disease progression in ANCA vasculitis. Further validating studies are needed to verify a causative association between HSP70 expression and renal outcomes in ANCA-associated vasculitis.

DAMPening sterile inflammation of the kidney

Renal ischemia reperfusion injury (IRI) is a serious cause of acute kidney injury (AKI). Danger-associated-molecular pattern molecules (DAMPs) are thought to promote IRI by initiating immune cell infiltration and driving disease progression, but the underlying pathophysiological mechanisms are mainly unclear. Poluzzi et al. demonstrate that soluble biglycan is a bimodal DAMP that both recruits proinflammatory macrophages and initiates resolution of inflammation and tissue remodeling in IRI, identifying a potential therapeutic target.

Paraquat-induced inflammatory response of microglia through HSP60/TLR4 signaling

Previous studies showed that paraquat (PQ) caused the apoptosis of dopaminergic neurons by inducing the generation of oxygen radical. The purpose of this study is to explore PQ-induced microglial inflammatory response and its underlying molecular mechanisms. The murine microglia BV2 cell line was used. After stimulation with PQ and lipopolysaccharides (positive control), the concentrations of tumor necrosis factor-α (TNF-α), interleukin 1β (IL-1β), and interleukin 6 (IL-6) in the culture supernatant and mRNA expression of TNF-α and IL-1β were determined by ELISA and quantitative real-time Polymerase Chain Reaction (PCR), respectively. The protein expression of heat shock protein 60 (HSP60) and toll-like receptor 4 (TLR4), along with the mRNA expression of transcription factors of nuclear factor κB-p65 (NF-κB-p65) and activated protein 1 (AP1, c-fos, and c-jun dimer) were evaluated with western blot and quantitative real-time PCR, respectively. The results showed that PQ activated microglia, which was characterized by increasing the generation and upregulated mRNA expression of pro-inflammatory cytokines, TNF-α, IL-1β, and IL-6. In addition, PQ significantly enhanced the expressions of HSP60 and TLR4 proteins in BV2 cells, as well as NF-κB-p65, c-fos, and c-jun mRNA. These findings suggest that PQ can activate microglia and enhance the expression and secretion of pro-inflammatory cytokines in a HSP60/TLR4 signaling, leading to the inflammatory response.

Immunohistochemistry of Human Hsp60 in Health and Disease: From Autoimmunity to Cancer

Hsp60 (also called Cpn60) is a chaperonin with essential functions for cell physiology and survival. Additionally, its involvement in the pathogenesis of a variety of diseases (e.g., some autoimmune disorders and cancer) is becoming evident with new research. For example, the distribution and levels of Hsp60 in cells and tissues have been found altered in many pathologic conditions, and the significance of these alterations is being investigated in a number of laboratories. The aim of this ongoing research is to determine the meaning of these Hsp60 alterations with regard to pathogenetic mechanisms, diagnosis, classification of lesions, and assessing prognosis and response to treatment.Hsp60 occurs in the mitochondria, i.e., its typical residence according to classic knowledge, and also in other locales, such as the cytosol, the cell membrane, the intercellular space, and biological fluids (e.g., blood and cerebrospinal fluid). Detection and quantitative determinations in all these locations are becoming essential components of laboratory pathology in clinics and research. Consequently, immunohistochemistry targeting Hsp60 is also becoming essential for pathologists and researchers interested in disorders involving this chaperonin.In this chapter, we summarize some recent discoveries on the participation of Hsp60 in the pathogenesis of human diseases, and describe in detail how to perform immunohistochemical reactions for detecting the chaperonin, determining its location, and measuring its quantitative levels.

The Increased Expression of Toll-Like Receptor 4 in Renal and Skin Lesions in Lupus Erythematosus

Toll-like receptor 4 (TLR-4), a bacterial lipopolysaccharide sensor, is an innate immunity essential modulator. It is expressed on both immune and non-immune cells and may contribute to the cutaneous and renal manifestations during lupus erythematosus (LE). Our purpose is to evaluate TLR-4 expression and analyzing its role in lupus nephritis (LN) and chronic cutaneous lupus erythematosus (CLE) pathogenesis. TLR-4 immunohistochemical staining was performed on 30 LN renal biopsies compared with 11 healthy renal tissues and 30 skin biopsies from CLE patients compared with 15 normal individuals. CLE patients' biopsies showed a strong and diffuse TLR-4 expression throughout the epidermis and labeled inflammatory infiltrate and glands in the dermis whereas controls' skin expressed weakly TLR-4 only in the epidermis basal layer. LN glomeruli and tubules showed an increased and more intense TLR-4 expression compared with normal controls where TLR-4 expression was weak and rarely detected in glomeruli, diffuse and weak in tubules. A significant difference in TLR-4 expression between LN classes, both in glomeruli and tubules, was observed. These data confirm an up-regulation of TLR-4 expression in the affected tissues of CLE and LN patients and highlight the critical role of TLR-4 in the pathogenesis of cutaneous and renal disorders in LE.

Heat shock proteins and kidney disease: perspectives of HSP therapy

Heat shock proteins (HSPs) mediate a diverse range of cellular functions, prominently including folding and regulatory processes of cellular repair. A major property of these remarkable proteins, dependent on intracellular or extracellular location, is their capacity for immunoregulation that optimizes immune activity while avoiding hyperactivated inflammation. In this review, recent investigations are described, which examine roles of HSPs in protection of kidney tissue from various traumatic influences and demonstrate their potential for clinical management of nephritic disease. The HSP70 class is particularly attractive in this respect due to its multiple protective effects. The review also summarizes current understanding of HSP bioactivity in the pathophysiology of various kidney diseases, including acute kidney injury, diabetic nephropathy, chronic glomerulonephritis, and lupus nephritis-along with other promising strategies for their remediation, such as DNA vaccination.

Heat shock proteins in the kidney

Heat shock proteins (Hsps) are essential to cell survival through their function as protein chaperones. The role they play in kidney health and disease is varied. Hsp induction may be either beneficial or detrimental to the kidney, depending on the specific Hsp, type of cell, and context. This review addresses the role of Hsps in the kidney, including during development, as osmoprotectants, and in various kidney disease models. Heat shock transcription factor, activated by a stress on renal cells, induces Hsp elaboration and separately regulates immune responses that can contribute to renal injury. Induced Hsps in the intracellular compartment are mostly beneficial in the kidney by stabilizing and restoring cell architecture and function through acting as protein chaperones. Intracellular Hsps also inhibit apoptosis and facilitate cell proliferation, preserving renal tubule viability after acute injury, but enhancing progression of cystic kidney disease and malignancy. Induced Hsps in the extracellular compartment, either circulating or located on outer cell membranes, are mainly detrimental through enhancing inflammation pathways to injury. Correctly harnessing these stress proteins promises the opportunity to alter the course of acute and chronic kidney disease.

Increased extracellular heat shock protein 90α in severe sepsis and SIRS associated with multiple organ failure and related to acute inflammatory-metabolic stress response in children

Mammalian heat-shock-protein (HSP) 90α rapidly responses to environmental insults. We examined the hypothesis that not only serum HSP72 but also HSP90α is increased in the systemic inflammatory response syndrome (SIRS), severe-sepsis (SS), and/or sepsis (S) compared to healthy children (H); we assessed HSP90α relation to (a) multiple organ system failure (MOSF) and (b) inflammatory-metabolic response and severity of illness.A total of 65 children with S, SS, or SIRS and 25 H were included. ELISA was used to evaluate extracellular HSP90α and HSP72, chemiluminescence interleukins (ILs), flow-cytometry neutrophil-CD64 (nCD64)-expression.HSP90α, along with HSP72, were dramatically increased among MOSF patients. Patients in septic groups and SIRS had elevated HSP90α compared to H (P < 0.01). HSP90α was independently related to predicted death rate and severity of illness; positively to HSP72, nCD64, ILs, length of stay, days on ventilator, and fever; negatively to HDL and LDL (P < 0.05). The HSP72 was increased in SS/S and related negatively to HDL and LDL (P < 0.05).Serum HSP90α is markedly elevated in children with severe sepsis and is associated with MOSF. Better than the HSP72, also increased in SS, SIRS, and MOSF, HSP90α is related to the inflammatory stress, fever, outcome endpoints, and predicted mortality and inversely related to the low-LDL/low-HDL stress metabolic pattern.

HSP60 plays a regulatory role in IL-1β-induced microglial inflammation via TLR4-p38 MAPK axis

Background

IL-1β, also known as “the master regulator of inflammation”, is a potent pro-inflammatory cytokine secreted by activated microglia in response to pathogenic invasions or neurodegeneration. It initiates a vicious cycle of inflammation and orchestrates various molecular mechanisms involved in neuroinflammation. The role of IL-1β has been extensively studied in neurodegenerative disorders; however, molecular mechanisms underlying inflammation induced by IL-1β are still poorly understood. The objective of our study is the comprehensive identification of molecular circuitry involved in IL-1β-induced inflammation in microglia through protein profiling.

Methods

To achieve our aim, we performed the proteomic analysis of N9 microglial cells with and without IL-1β treatment at different time points. Expression of HSP60 in response to IL-1β administration was checked by quantitative real-time PCR, immunoblotting, and immunofluorescence. Interaction of HSP60 with TLR4 was determined by co-immunoprecipitation. Inhibition of TLR4 was done using TLR4 inhibitor to reveal its effect on IL-1β-induced inflammation. Further, effect of HSP60 knockdown and overexpression were assessed on the inflammation in microglia. Specific MAPK inhibitors were used to reveal the downstream MAPK exclusively involved in HSP60-induced inflammation in microglia.

Results

Total 21 proteins were found to be differentially expressed in response to IL-1β treatment in N9 microglial cells. In silico analysis of these proteins revealed unfolded protein response as one of the most significant molecular functions, and HSP60 turned out to be a key hub molecule. IL-1β induced the expression as well as secretion of HSP60 in extracellular milieu during inflammation of N9 cells. Secreted HSP60 binds to TLR4 and inhibition of TLR4 suppressed IL-1β-induced inflammation to a significant extent. Our knockdown and overexpression studies demonstrated that HSP60 increases the phosphorylation of ERK, JNK, and p38 MAPKs in N9 cells during inflammation. Specific inhibition of p38 by inhibitors suppressed HSP60-induced inflammation, thus pointed towards the major role of p38 MAPK rather than ERK1/2 and JNK in HSP60-induced inflammation. Furthermore, silencing of upstream modulator of p38, i.e., MEK3/6 also reduced HSP60-induced inflammation.

Conclusions

IL-1β induces expression of HSP60 in N9 microglial cells that further augments inflammation via TLR4-p38 MAPK axis.

Electronic supplementary material

The online version of this article (doi:10.1186/s12974-016-0486-x) contains supplementary material, which is available to authorized users.

Autoantibodies targeting glomerular annexin A2 identify patients with proliferative lupus nephritis

PURPOSE

Patients with systemic lupus erythematosus (SLE) frequently develop lupus nephritis (LN), a complication frequently leading to end stage kidney disease. Immune complex deposition in the glomerulus is central to the development of LN. Using a targeted proteomic approach, we tested the hypothesis that autoantibodies targeting glomerular antigens contribute to the development of LN.

EXPERIMENTAL DESIGN

Human podocyte and glomerular proteins were separated by SDS-PAGE and immunoblotted with sera from SLE patients with and without LN. The regions of those gels corresponding to reactive bands observed with sera from LN patients were analyzed using LC-MS/MS.

RESULTS

LN reactive bands were seen at approximately 50 kDa in podocyte extracts and between 36 and 50 kDa in glomerular extracts. Those bands were analyzed by LC-MS/MS and 102 overlapping proteins were identified. Bioinformatic analysis determined that 36 of those proteins were membrane associated, including a protein previously suggested to contribute to glomerulonephritis and LN, annexin A2. By ELISA, patients with proliferative LN demonstrated significantly increased antibodies against annexin A2.

CONCLUSION AND CLINICAL RELEVANCE

Proteomic approaches identified multiple candidate antigens for autoantibodies in patients with LN. Serum antibodies against annexin A2 were significantly elevated in subjects with proliferative LN, validating those antibodies as potential biomarkers.

Circulating Mitochondrial DAMPs Are Not Effective Inducers of Proteinuria and Kidney Injury in Rodents

Mitochondria in eukaryotic cells are derived from bacteria in evolution. Like bacteria, mitochondria contain DNA with unmethylated CpG motifs and formyl peptides, both of which have recently been shown to be damage associated molecular patterns (DAMPs) and induce immune response and cell injury. Based on the facts that circulating mitochondrial DAMPs (mtDAMPs) are increased in the patients of trauma or burn injury who also have proteinuria, that mtDAMPs can activate immune cells which in turn secrete glomerular permeability factors, that renal intrinsic cells express a variety of DAMP receptors, and that mtDAMPs can directly increase endothelial cell permeability in vitro, we hypothesized that mtDAMPs may be novel circulating factors inducing proteinuria and kidney injury. We tested this hypothesis by directly injecting mtDAMPs into rodents and examining urinary protein and kidney histology. We prepared mtDAMP samples, including mitochondrial DNA (mtDNA) and mitochondrial debris (MTD), from rodent liver. In mice, injection of mtDNA for 20 μg/ml initial concentration in circulation (much higher than the clinical range), did not cause any renal manifestations. However, an increased dose leading to 45 μg/ml initial concentration in circulation resulted in a transient, slight increase in urinary albumin. In rats, MTD injection resulting in 450 μg/ml initial concentration of MTD protein in circulation, which was much higher than the clinical range, caused mild, transient proteinuria and lung lesions. Multiple injections of such large amount of either mtDNA or MTD into rodents on 3 consecutive days also failed in inducing proteinuria and kidney injury. In summary, clinical levels of circulating mtDAMPs do not induce proteinuria and clinically irrelevant high levels of mtDAMPs cause only a transient and slight increase in urinary protein in rodents, suggesting that circulating mtDAMPs may not be responsible for the proteinuria and kidney injury in patients with trauma, burn injury, and other diseases.

The role of necrotic cell death in the pathogenesis of immune mediated nephropathies

Necrosis, an inflammatory form of cell death, has been considered to be an accidental death and/or cell death due to injury. However, the literature in the last decade has established that necrosis is a regulated form of cell death, and that inhibition of specific molecular pathways leading to necrosis can block it and reduce inflammation. Since necrotic lesions are observed in several immune mediated human pathologies, in this review we will discuss the impact that this form of programmed cellular demise has in the pathology of immune mediated nephropathies.

Heat shock protein 60: an endogenous inducer of dopaminergic cell death in Parkinson disease

BACKGROUND

Increasing evidence suggests that inflammation associated with microglial cell activation in the substantia nigra (SN) of patients with Parkinson disease (PD) is not only a consequence of neuronal degeneration, but may actively sustain dopaminergic (DA) cell loss over time. We aimed to study whether the intracellular chaperone heat shock protein 60 (Hsp60) could serve as a signal of CNS injury for activation of microglial cells.

METHODS

Hsp60 mRNA expression in the mesencephalon and the striatum of C57/BL6 mice treated with MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) and the Hsp60/TH mRNA ratios in the SN of PD patients and aged-matched subjects were measured. To further investigate a possible link between the neuronal Hsp60 response and PD-related cellular stress, Hsp60 immunoblot analysis and quantification in cell lysates from SH-SY5Y after treatment with 100 μM MPP+ (1-methyl-4-phenylpyridinium) at different time points (6, 12, 24 and 48 hours) compared to control cells were performed. Additional MTT and LDH assay were used. We next addressed the question as to whether Hsp60 influences the survival of TH+ neurons in mesencephalic neuron-glia cultures treated either with MPP+ (1 μM), hHsp60 (10 μg/ml) or a combination of both. Finally, we measured IL-1β, IL-6, TNF-α and NO-release by ELISA in primary microglial cell cultures following treatment with different hHsp60 preparations. Control cultures were exposed to LPS.

RESULTS

In the mesencephalon and striatum of mice treated with MPTP and also in the SN of PD patients, we found that Hsp60 mRNA was up-regulated. MPP+, the active metabolite of MPTP, also caused an increased expression and release of Hsp60 in the human dopaminergic cell line SH-SY5Y. Interestingly, in addition to being toxic to DA neurons in primary mesencephalic cultures, exogenous Hsp60 aggravated the effects of MPP+. Yet, although we demonstrated that Hsp60 specifically binds to microglial cells, it failed to stimulate the production of pro-inflammatory cytokines or NO by these cells.

CONCLUSIONS

Overall, our data suggest that Hsp60 is likely to participate in DA cell death in PD but via a mechanism unrelated to cytokine release.

Role of Toll-like receptors in diabetic nephropathy

Diabetic nephropathy is the leading cause of kidney failure and its increasing prevalence and incidence has imposed global socio-economic stress on healthcare systems worldwide. Although historically considered a metabolic disorder, recent studies have established that inflammatory responses are central to the pathogenesis of diabetic nephropathy. TLRs (Toll-like receptors) are a family of pattern recognition receptors responsible for the initiation of inflammatory and immune responses. The regulation of TLR2 and TLR4 have been implicated in the pathogenesis of various kidney diseases, and emerging evidence shows their involvement in the perpetuation of inflammation in the diabetic kidney. The present review focuses on the relative contributions of TLR2 and TLR4 in recognizing endogenous ligands relevant to diabetic nephropathy and their subsequent activation of NF-κB (nuclear factor κB), which results in the synthesis and secretion of pro-inflammatory cytokines and chemokines. Moreover, we discuss the pro-inflammatory signalling pathways of TLR2 and TLR4, in which their interruption or blockade may prove to be important therapeutic targets, potentially translated into clinical treatments for diabetic nephropathy. Currently, inhibitors to TLR2 and TLR4 are undergoing clinical trials in various inflammatory models of disease, but none in patients with diabetic nephropathy. Given the existing literature, there is a fundamental necessity to undertake trials in patients with diabetic nephropathy with a focus on renal end points.

Heat shock protein 72 expressing stress in sepsis: unbridgeable gap between animal and human studies--a hypothetical "comparative" study

Heat shock protein 72 (Hsp72) exhibits a protective role during times of increased risk of pathogenic challenge and/or tissue damage. The aim of the study was to ascertain Hsp72 protective effect differences between animal and human studies in sepsis using a hypothetical “comparative study” model. Forty-one in vivo (56.1%), in vitro (17.1%), or combined (26.8%) animal and 14 in vivo (2) or in vitro (12) human Hsp72 studies (P < 0.0001) were enrolled in the analysis. Of the 14 human studies, 50% showed a protective Hsp72 effect compared to 95.8% protection shown in septic animal studies (P < 0.0001). Only human studies reported Hsp72-associated mortality (21.4%) or infection (7.1%) or reported results (14.3%) to be nonprotective (P < 0.001). In animal models, any Hsp72 induction method tried increased intracellular Hsp72 (100%), compared to 57.1% of human studies (P < 0.02), reduced proinflammatory cytokines (28/29), and enhanced survival (18/18). Animal studies show a clear Hsp72 protective effect in sepsis. Human studies are inconclusive, showing either protection or a possible relation to mortality and infections. This might be due to the fact that using evermore purified target cell populations in animal models, a lot of clinical information regarding the net response that occurs in sepsis is missing.

Keratin 18 and heat-shock protein in chronic kidney disease

Chronic kidney disease (CKD) is an affliction associated with increased systemic stress and cell death. We will review the role of keratin 18 (K-18) and caspase-cleaved CK-18 (ccK-18) as markers for increased apoptosis and necrosis during renal failure progression. The importance of preventative expression of heat-shock proteins (HSPs) in response to cell stress will also be discussed. The frequent development of CKD leads to serious complications. The potential of use of K-18 and HSP as early biomarkers of renal failure will be reviewed. Also, the role of these proteins with respect to dialysis regimes and in acute ischemic kidney injury following renal transplantation will be discussed.

Targeted expression of a pan-caspase inhibitor in tubular epithelium attenuates interstitial inflammation and fibrogenesis in nephritic but not nephrotic mice

The caspase family of enzymes participates in apoptotic and proinflammatory reactions in any cell. Here we studied the role of caspase activation in the tubular epithelium of diseased kidneys using mice transgenic for the baculovirus pan-caspase inhibitor p35 gene held in a nonexpressed state (control mice) but target-expressed in the renal proximal tubule cells when crossed with mice expressing Cre recombinase under the control of the γ-glutamyltransferase promoter. Proinflammatory and profibrogenic parameters such as the number of monocytes and fibroblasts in the kidneys were significantly increased at 28 days in the control mice, but not in the renal tubule-targeted mice expressing p35 in a nephrotoxic serum nephritis model of disease. These cellular changes paralleled the number of apoptotic tubular cells and protein levels of active caspase-3 in the kidneys at 7 and 28 days of both the control and proximal tubule-targeted mice. Surprisingly, all of these parameters were not significantly affected at 7 and 28 days by targeted p35 expression in tubular epithelium when compared with nontargeted control mice in a model of adriamycin nephrosis. Thus, our study shows the critical role of caspase activation in the tubular epithelium in apoptosis along with proinflammatory and profibrogenic processes in nephrotoxic serum nephritis but not adriamycin nephrosis.

Vaccination with Strongyloides ratti heat shock protein 60 increases susceptibility to challenge infection by induction of Th1 response

The control of strongyloidiasis affecting approximately 100 million people - caused by the gastrointestinal nematode Strongyloides stercoralis - is still based on anti-helminthic treatment. In the current study we analysed the immune response to Strongyloides ratti heat shock protein 60 (srHSP60) as a possible vaccine candidate in the murine system. We show that srHSP60 is a target of both, humoral and cellular response in S. ratti-infected mice. Strikingly, vaccination with srHSP60 without adjuvant or with CFA induced a S. ratti-specific Th1 response in vivo that did not confer protection but slightly increased larval output during challenge infection. Using in vitro T cell stimulation assays we provide further evidence that srHSP60 skewed activated T cells towards a Th1 response that interfered with efficient clearance of S. ratti infection. Vaccination with alum-precipitated srHSP60, in contrast, overruled the Th1-inducing activity intrinsic to srHSP60, induced a Th2 response, and conferred partial protection against a challenge infection. As srHSP60 is actively secreted by S. ratti during all life stages, our findings strongly suggest that srHSP60 induced polarization towards a Th1 response reflects a mechanism of immune evasion by this pathogenic nematode.

The renal mononuclear phagocytic system

The renal mononuclear phagocytic system, conventionally composed of macrophages (Mø) and dendritic cells (DCs), plays a central role in health and disease of the kidney. Overlapping definitions of renal DCs and Mø, stemming from historically separate research tracks and the lack of experimental tools to specifically study the roles of these cells in vivo, have generated confusion and controversy, however, regarding their immunologic function in the kidney. This brief review provides an appraisal of the current state of knowledge of the renal mononuclear phagocytic system interpreted from the perspective of immunologic function. Physical characteristics, ontogeny, and known functions of the main subsets of renal mononuclear phagocytes as they relate to homeostasis, surveillance against injury and infection, and immune-mediated inflammatory injury and repair within the kidney are described. Gaps and inconsistencies in current knowledge are used to create a roadmap of key questions to be answered in future research.

Dangers within: DAMP responses to damage and cell death in kidney disease

The response to exogenous pathogens leads to activation of innate immunity through the release of pathogen-associated molecular patterns (PAMPs) and their binding to pattern recognition receptors. A classic example is septic shock where Toll receptor 4 recognizes PAMPs. Although well accepted, this concept does not explain the activation of innate immunity and inflammation occurs with transplantation, autoimmunity, or trauma. Increasingly recognized is that endogenous molecules released by dying cells (damage-associated molecular patterns; DAMPs) activate cellular receptors leading to downstream inflammation. Thus endogenous danger signals and exogenous PAMPs elicit similar responses through seemingly similar mechanisms. Also emerging is our understanding that normal repair processes benefit from dampening the immune response to these endogenous danger molecules. Here we focus on the role of DAMPs and their putative receptors in the pathogenesis of acute and chronic kidney diseases.

Heat shock proteins in chronic kidney disease

Heat shock proteins (HSP) form a heterogenous, evolutionarily conserved group of molecules with high sequence homology. They mainly act as intracellular chaperones, protecting the protein structure and folding under stress conditions. The extracellular HSP, released in the course of damage or necrosis, play a pivotal role in the innate and adaptive immune responses. They also take part in many pathological processes. The aim of this review is to update the recent developments in the field of HSP in chronic kidney disease (CKD), in regard to three different aspects. The first is the assessment of the role of HSP, either positive or deleterious, in the pathogenesis of CKD and the possibilities to influence its progression. The second is the impact of dialysis, being a potentially modifiable stressor, on HSP and the attempt to assess the value of these proteins as the biocompatibility markers. The last area is that of kidney transplantation and the potential role of HSP in the induction of the immune tolerance in kidney recipients.

The HSP60 immune system network

Heat shock proteins (HSPs) were initially discovered as participants in the cellular response to stress. It is now clear, however, that self and microbial HSPs also play an important role in the control of the immune response. Here, we focus on HSP60 and its interactions with both the innate and adaptive immune system in mammals. We also consider that circulating HSP60 and the quantities and specificities of serum antibodies to HSP60 provide a biomarker to monitor the immune status of the individual. Thus, the dual role of HSP60 as an immune modulator and a biomarker, provides an opportunity to modulate immunity for therapeutic purposes, and to monitor the immune response in health and disease.

Kidney dendritic cells in acute and chronic renal disease

Dendritic cells are not only the master regulators of adaptive immunity, but also participate profoundly in innate immune responses. Much has been learned about their basic immunological functions and their roles in various diseases. Comparatively little is still known about their role in renal disease, despite their obvious potential to affect immune responses in the kidney, and immune responses that are directed against renal components. Kidney dendritic cells form an abundant network in the renal tubulointerstitium and constantly survey the environment for signs of injury or infection, in order to alert the immune system to the need to initiate defensive action. Recent studies have identified a role for dendritic cells in several murine models of acute renal injury and chronic nephritis. Here we summarize the current knowledge on the role of kidney dendritic cells that has been obtained from the study of murine models of renal disease.

T cells and dendritic cells in glomerular disease: the new glomerulotubular feedback loop

A newly described glomerulotubular feedback loop may explain the relationship between glomerular damage, epitope spreading, tubulointerstitial nephritis, proteinuria as a progression factor, and the importance of the local milieu in kidney damage. It also opens the horizons for exciting innovative approaches to therapy of both acute and chronic kidney diseases.

TLR2 plays a role in the activation of human resident renal stem/progenitor cells

In the past few years, adult renal progenitor/stem cells (ARPCs) have been identified in human kidneys, and particularly in Bowman's capsule and proximal tubules. They may play an important role in the kidney regenerative processes and might prospectively be the ideal cell type for the treatment of both acute and chronic renal injury. In this study, microarray analysis identified 6 gene clusters that discriminated normal human glomerular and tubular ARPCs from renal proximal tubular epithelial cells and mesenchymal stem cells. The top-scored pathway in the ARPC gene expression profile contained growth factor receptors and immune system-related genes, including toll-like receptor 2 (TLR2). Stimulation of TLR2 by ligands that mime inflammatory mediators or damage associated molecular pattern molecules induced secretion of elevated amounts of monocyte chemoattractant protein-1 (MCP-1), IL-6, IL-8, and C3 via NF-kappaB activation. TLR2 stimulation also increased the ARPC proliferation rate, suggesting a role for TLR2 in ARPC activation via autocrine signaling. Moreover, TLR2 stimulation improved ARPC differentiation into renal epithelial cells and was responsible of ARPC branching morphogenesis and tubule-like structures formation. For the first time, this study provides a genomic characterization of renal multipotent progenitor cells and shows that TLR2 found on ARPCs might be responsible for their activation in the kidney, orchestrating the activation of crucial signaling networks necessary for renal repair.

The role of Toll-like receptor 2 in inflammation and fibrosis during progressive renal injury

Tissue fibrosis and chronic inflammation are common causes of progressive organ damage, including progressive renal disease, leading to loss of physiological functions. Recently, it was shown that Toll-like receptor 2 (TLR2) is expressed in the kidney and activated by endogenous danger signals. The expression and function of TLR2 during renal fibrosis and chronic inflammation has however not yet been elucidated. Therefore, we studied TLR2 expression in human and murine progressive renal diseases and explored its role by inducing obstructive nephropathy in TLR2^−/− or TLR2^+/+ mice. We found that TLR2 is markedly upregulated on tubular and tubulointerstitial cells in patients with chronic renal injury. In mice with obstructive nephropathy, renal injury was associated with a marked upregulation and change in distribution of TLR2 and upregulation of murine TLR2 danger ligands Gp96, biglycan, and HMGB1. Notably, TLR2 enhanced inflammation as reflected by a significantly reduced influx of neutrophils and production of chemokines and TGF-β in kidneys of TLR2^−/− mice compared with TLR2^+/+ animals. Although, the obstructed kidneys of TLR2^−/− mice had less interstitial myofibroblasts in the later phase of obstructive nephropathy, tubular injury and renal matrix accumulation was similar in both mouse strains. Together, these data demonstrate that TLR2 can initiate renal inflammation during progressive renal injury and that the absence of TLR2 does not affect the development of chronic renal injury and fibrosis.

Trif is not required for immune complex glomerulonephritis: dying cells activate mesangial cells via Tlr2/Myd88 rather than Tlr3/Trif

Viral RNA or bacterial products can activate glomerular mesangial cells via a subset of Toll-like receptors (Tlr). Because Tlr2-deficient mice were recently found to have attenuated nephrotoxic serum nephritis (NSN), we hypothesized that endogenous Tlr agonists can activate glomerular mesangial cells. Primary mesangial cells from C57BL/6 mice expressed Tlr1-6 and Tlr11 mRNA at considerable levels and produced Il-6 when being exposed to the respective Tlr ligands. Exposure to necrotic cells activated cultured primary mesangial cells to produce Il-6 in a Tlr2/Myd88-dependent manner. Apoptotic cells activated cultured mesangial cells only when being enriched to high numbers. Apoptotic cell-induced Il-6 release was Myd88 dependent, and only purified apoptotic cell RNA induced Trif signaling in mesangial cells. Does Trif signaling contribute to disease activity in glomerulonephritis? To answer this question, we induced autologous NSN by injection of NS raised in rabbits in Trif-mutant and wild-type mice. Lack of Trif did not alter the functional and histomorphological abnormalities of NSN, including the evolution of anti-rabbit IgG and anti-rabbit-specific nephritogenic T cells. We therefore conclude that apoptotic cell RNA is a poor activator of Trif signaling in mesangial cells and that necrotic cells' releases rather activate mesangial cells via the Tlr2/Myd88 signaling pathway.

Calcium signaling in dendritic cells by human or mycobacterial Hsp70 is caused by contamination and is not required for Hsp70-mediated enhancement of cross-presentation

Extracellular heat shock proteins (HSPs) can stimulate antigen-specific immune responses. Using recombinant human (rhu)Hsp70, we previously demonstrated that through complex formation with exogenous antigenic peptides, rhuHsp70 can enhance cross-presentation by antigen-presenting cells (APCs) resulting in stronger T cell stimulation. T cell stimulatory activity has also been described for mycobacterial (myc)Hsp70. MycHsp70-assisted T cell activation has been reported to act through the binding of mycHsp70 to chemokine receptor 5 (CCR5), calcium signaling, phenotypic maturation, and cytokine secretion by dendritic cells (DCs). We report that highly purified rhuHsp70 and mycHsp70 proteins both strongly enhance cross-presentation of exogenous antigens. Augmentation of cross-presentation was seen for different APCs, irrespective of CCR5 expression. Moreover, neither of the purified Hsp70 proteins induced calcium signals in APCs. Instead, calcium signaling activity was found to be caused by contaminating nucleotides present in Hsp70 protein preparations. These results refute the hypothesis that mycHsp70 proteins require CCR5 expression and calcium signaling by APCs for enhanced antigen cross-presentation for T cell stimulation.

Overview of factors contributing to the pathophysiology of progressive renal disease

Some basic premises must be considered when validating hypothesis about progression of renal disease. In an accompanying series of five articles, specific aspects of progression will be reviewed by experts in the field: mechanisms of tissue and matrix remodelling; interstitial fibrosis; the contribution of ischemia and hypoxia; the role and type of the inflammatory infiltrate; and, finally, glomerular sclerosis.

Heat shock protein 60 induces inflammatory mediators in mouse adipocytes

Adipocytes represent an important cellular source of inflammatory mediators. However, the signals for the induction of proinflammatory adipocyte activities are largely unknown. Here, we demonstrate that heat shock protein (Hsp) 60, a potent stimulator of innate immunity, induces the release of the inflammatory mediators interleukin-6, CXCL1 and monocyte chemoattractant protein-1 in a time- and concentration-dependent manner from cells of the adipocyte line 3T3-L1 and from adipocytes of obese mice. These results identify Hsp60 as an important regulator of adipocyte functions which contribute to the development of inflammatory processes as observed in diabetes and diabetes-associated complications.

Use of mizoribine as a rescue drug for steroid-resistant pediatric IgA nephropathy

Recent clinical trials have shown a beneficial effect of mizoribine (Miz), an immunosuppressive drug, in the treatment of new-onset pediatric IgA nephropathy (IgAN). In this study, we evaluated the efficacy of Miz treatment in three children with established steroid-resistant IgAN. The patients had IgAN featuring persistent proteinuria and diffuse mesangial proliferation and had failed to respond to 2 years of treatment with prednisolone. Based upon the second biopsy results, patients were given methylprednisolone (mPSL) pulse therapy that induced a transient reduction in proteinuria, which was reversed when the mPSL dose was tapered. Miz therapy was then instigated in place of pulse mPSL. All three patients showed a substantial reduction in proteinuria and resolution of hematuria within 5 months. A follow-up biopsy in two of the patients showed a substantial reduction in the severity of glomerular lesions and a decrease in the number of activated macrophages. In conclusion, Miz therapy was found to be a safe and effective therapy in three cases of steroid-resistant pediatric IgAN. The ability of Miz to reduce the number of activated macrophages may be an important mechanism by which this drug ameliorated renal disease in these patients.

Renal dendritic cells stimulate IL-10 production and attenuate nephrotoxic nephritis

The role of renal dendritic cells (DCs) in glomerulonephritis is unknown. This question was addressed in nephrotoxic nephritis, a murine model of human necrotizing glomerulonephritis, which is dependent on CD4(+) Th1 cells and macrophages. DCs in nephritic kidneys showed signs of activation, accumulated in the tubulo-interstitium, and infiltrated the periglomerular space surrounding inflamed glomeruli. In ex vivo coculture experiments with antigen-specific CD4(+) T cells, DCs stimulated the secretion of IL-10, which is known to attenuate nephrotoxic nephritis, and the Th1 cytokine IFNgamma. Endogenous renal CD4(+) T cells produced both of these cytokines as well, but those from nephritic mice secreted increased amounts of IL-10. Renal DCs were found to express ICOS-L, an inducer of IL-10. To evaluate the in vivo role of renal DCs in disease, CD11c(+) DCs were depleted on days 4 and 10 after the induction of nephritis by injecting CD11c-DTR/GFP mice with diphtheria toxin. Sparing DCs until day 4 did not affect the autologous phase of nephritis. The number of renal DCs was reduced by 70% to 80%, the number of renal macrophages was unchanged, and periglomerular infiltrates were eliminated. On days 11 to 14, we observed aggravated tubulointerstitial and glomerular damage, reduced creatinine clearance, and increased proteinuria. These findings demonstrate that renal DCs exert a renoprotective effect in nephrotoxic nephritis, possibly by expressing ICOS-L and/or by inducing IL-10 in infiltrating CD4(+) Th1 cells.

Regulation of heat shock protein 70 release in astrocytes: role of signaling kinases

The ability to mount a successful stress response in the face of injury is critical to the long-term viability of individual cells and to the organism in general. The stress response, characterized in part by the upregulation of heat shock proteins, is compromised in several neurodegenerative disorders and in some neuronal populations, including motoneurons (MNs). Because astrocytes have a greater capacity than neurons to survive metabolic stress, and because they are intimately associated with the regulation of neuronal function, it is important to understand their stress response, so that we may to better appreciate the impact of stress on neuronal viability during injury or disease. We show that astrocytes subjected to hyperthermia upregulate Hsp/c70 in addition to intracellular signaling components including activated forms of extracellular-signal-regulated kinase (ERK1/2), Akt, and c-jun N-terminal kinase/stress activated protein kinase (JNK/SAPK). Furthermore, astrocytes release increasing amounts of Hsp/c70 into the extracellular environment following stress, an event that is abrogated when signaling through the ERK1/2 and phosphatidylinositol-3 kinase (PI3K) pathways is compromised and enhanced by inhibition of the JNK pathway. Last, we show that the Hsp/c70 is released from astrocytes in exosomes. Together, these data illustrate the diverse regulation of stress-induced Hsp/c70 release in exosomes, and the way in which the balance of activated signal transduction pathways affects this release. These data highlight how stressful insults can alter the microenvironment of an astrocyte, which may ultimately have implications for the survival of neighboring neurons.

Human heat shock protein 70 enhances tumor antigen presentation through complex formation and intracellular antigen delivery without innate immune signaling

Heat shock proteins (HSPs) have shown promise for the optimization of protein-based vaccines because they can transfer exogenous antigens to dendritic cells and at the same time induce their maturation. Great care must be exercised in interpretating HSP-driven studies, as by-products linked to the recombinant generation of these proteins have been shown to mediate immunological effects. We generated highly purified human recombinant Hsp70 and demonstrated that it strongly enhances the cross-presentation of exogenous antigens resulting in better antigen-specific T cell stimulation. Augmentation of T cell stimulation was a direct function of the degree of complex formation between Hsp70 and peptides and correlated with improved antigen delivery to endosomal compartments. The Hsp70 activity was independent of TAP proteins and was not inhibited by exotoxin A or endosomal acidification. Consequently, Hsp70 enhanced cross-presentation of various antigenic sequences, even when they required different post-uptake processing and trafficking, as exemplified by the tumor antigens tyrosinase and Melan-A/MART-1. Furthermore, Hsp70 enhanced cross-presentation by different antigen-presenting cells (APCs), including dendritic cells and B cells. Importantly, enhanced cross-presentation and antigen-specific T cell activation were observed in the absence of innate signals transmitted by Hsp70. As Hsp70 supports the cross-presentation of different antigens and APCs and is inert to APC function, it may show efficacy in various settings of immune modulation, including induction of antigen-specific immunity or tolerance.

Toll-like receptors: emerging concepts in kidney disease

PURPOSE OF REVIEW

To summarize the recent advances in the role of Toll-like receptors (TLRs) in innate immunity, with a special focus on recent studies addressing the expression and function of TLRs in kidney disease.

RECENT FINDINGS

Pathogen-recognition receptors including TLRs mediate immune activation upon pathogen recognition in different extracellular and intracellular compartments. In contrast to professional antigen-presenting cells, renal cells express a limited pattern of TLR (i.e. express TLR1-TLR6 but lack expression of the endosomal TLR7-TLR9). TLRs on renal cells contribute to the innate immune response in renal infection. Furthermore, recent studies provide experimental evidence for the functional role of TLRs in immune complex disease and autoimmunity. Furthermore, the recognition of endogenous molecules released from injured cells such as biglycan or heat-shock proteins may contribute to acute tubular injury and seem to provide adjuvant activity for renal inflammation. Furthermore, TLR7 and TLR9 are involved in the pathogenesis of lupus nephritis.

SUMMARY

The field of TLR research elucidates the molecular mechanisms of infection-associated kidney diseases but may also further support the concept that innate immunity significantly contributes to the so-called types of nonimmune kidney diseases.

Heat shock response and acute lung injury

All cells respond to stress through the activation of primitive, evolutionarily conserved genetic programs that maintain homeostasis and assure cell survival. Stress adaptation, which is known in the literature by a myriad of terms, including tolerance, desensitization, conditioning, and reprogramming, is a common paradigm found throughout nature, in which a primary exposure of a cell or organism to a stressful stimulus (e.g., heat) results in an adaptive response by which a second exposure to the same stimulus produces a minimal response. More interesting is the phenomenon of cross-tolerance, by which a primary exposure to a stressful stimulus results in an adaptive response whereby the cell or organism is resistant to a subsequent stress that is different from the initial stress (i.e., exposure to heat stress leading to resistance to oxidant stress). The heat shock response is one of the more commonly described examples of stress adaptation and is characterized by the rapid expression of a unique group of proteins collectively known as heat shock proteins (also commonly referred to as stress proteins). The expression of heat shock proteins is well described in both whole lungs and in specific lung cells from a variety of species and in response to a variety of stressors. More importantly, in vitro data, as well as data from various animal models of acute lung injury, demonstrate that heat shock proteins, especially Hsp27, Hsp32, Hsp60, and Hsp70 have an important cytoprotective role during lung inflammation and injury.

Synergistic and differential modulation of immune responses by Hsp60 and lipopolysaccharide

Activation of professional antigen-presenting cells (APC) is a crucial step in the initiation of an efficient immune response. In this study we show that Hsp60 mediates immune stimulation by different mechanisms, dependent and independent of lipopolysaccharide (LPS). We have demonstrated earlier that both, Hsp60 and LPS, increase antigen-specific interferon (IFN) gamma release in T cells. Here we show that in contrast to LPS Hsp60 induces IFNalpha production in professional APC. Neutralization of IFNalpha as well as the absence of functional IFNalphabeta receptor on APC and T cells interfered with Hsp60-mediated IFNgamma secretion in antigen-dependent T cell activation, strongly suggesting that IFNalpha represents one factor contributing to Hsp60-specific immune stimulation. On the other hand, we show that Hsp60 bound to the cell surface of APC colocalizes with the LPS co-receptor CD14 and LPS binding sites. Hsp60 specifically binds bacterial LPS and both molecules synergistically enhanced IL-12p40 production in APC and IFNgamma release in antigen-dependent T cell activation. This effect was Hsp60-specific and dependent on LPS-binding by Hsp60. Furthermore, we show that Hsp60 exclusively binds to macrophages and DC but not to T or B lymphocytes and that both, T cell stimulation by Hsp60 as well as Hsp60/LPS complexes, strictly depends on the presence of professional APC and is not mediated by B cells. Taken together, our data support an extension of the concept of Hsp60 as an endogenous danger signal: besides its function as a classical danger signal indicating unplanned tissue destruction to the innate immune system, in the incident of bacterial infection extracellular Hsp60 may bind LPS and facilitate microbe recognition by lowering the threshold of pathogen-associated molecular pattern (PAMP) detection and enhancing Toll-like receptor (TLR) signaling.

Monocyte-derived DC primed with TLR agonists secrete IL-12p70 in a CD40-dependent manner under hyperthermic conditions

Fever is an evolutionarily conserved mechanism to improve survival during infection. Previous studies have shown that feverlike temperatures directly enhance the function of murine bone marrow-derived dendritic cells (DCs). In the present study, we examined the response of human monocyte-derived DC to 39.5 degrees C hyperthermia. When primed with toll-like receptor agonists or bacterial extract but not proinflammatory cytokines, hyperthermia specifically enhanced secretion of interleukin (IL)-12p70 by DC, without altering the secretion of IL-10, tumor necrosis factor alpha or IL-1beta. These DC induced significantly higher levels of T-cell proliferation and interferon gamma production in assays of antigen presentation and MLR. Endogenous heat-sock protein 70 colocalized with CD40 in DC exposed to hyperthermic conditions. Recombinant CD40-Fc fusion protein blocked the increase in IL-12p70 secretion by DC primed with bacterial extract and hyperthermia. Thus, DC primed with toll-like receptor-agonists respond to hyperthermia with increased IL-12p70 secretion, mediated by heat-shock protein binding and activation of CD40. The data have important applications for clinical immunotherapy and the mechanism of fever.