A. Graham Pockley

Heat shock proteins as regulators of the immune response

Until recently, heat shock proteins (also known as heat stress proteins) have mostly been regarded as intracellular molecules that mediate a range of essential housekeeping and cytoprotective functions. However, interest in their role as intercellular signalling molecules has been fuelled by the observations that these molecules can be released and are present in the extracellular environment under physiological conditions. They can elicit cytokine production by, and adhesion molecule expression of, a range of cell types, and they can deliver maturation signals and peptides to antigen presenting cells through receptor-mediated interactions. These functions suggest that heat shock proteins could be immunoregulatory agents with potent and widely-applicable therapeutic uses. Furthermore, the induction of self heat shock protein immune reactivity can attenuate autoimmunity and delay transplant rejection, and heat shock proteins derived from tumours and pathogens can elicit specific, protective immunity. This review will focus on this rapidly evolving area of heat shock protein biology.

Caught with their PAMPs down? The extracellular signalling actions of molecular chaperones are not due to microbial contaminants

In recent years, it has been hypothesised that a new signalling system may exist in vertebrates in which secreted molecular chaperones form a dynamic continuum between the cellular stress response and corresponding homeostatic physiological mechanisms. This hypothesis seems to be supported by the finding that many molecular chaperones are released from cells and act as extracellular signals for a range of cells. However, this nascent field of biological research seems to suffer from an excessive criticism that the biological activities of molecular chaperones are due to undefined components of the microbial expression hosts used to generate recombinant versions of these proteins. In this article, a number of the proponents of the cell signalling actions of molecular chaperones take this criticism head-on. They show that sufficient evidence exists to support fully the hypothesis that molecular chaperones have cell–cell signalling actions that are likely to be part of the homeostatic mechanism of the vertebrate.

Heat shock proteins in health and disease: therapeutic targets or therapeutic agents?

For many years, heat shock or stress proteins have been regarded as intracellular molecules that have a range of housekeeping and cytoprotective functions, only being released into the extracellular environment in pathological situations such as necrotic cell death. However, evidence is now accumulating to indicate that, under certain circumstances, these proteins can be released from cells in the absence of cellular necrosis, and that extracellular heat shock proteins have a range of immunoregulatory activities. The capacity of heat shock proteins to induce pro-inflammatory responses, together with the phylogenetic similarity between prokaryotic and eukaryotic heat shock proteins, has led to the proposition that these proteins provide a link between infection and autoimmune disease. Indeed, both elevated levels of antibodies to heat shock proteins and an enhanced immune reactivity to heat shock proteins have been noted in a variety of pathogenic disease states. However, further evaluation of heat shock protein reactivity in autoimmune disease and after transplantation has shown that, rather than promoting disease, reactivity to self-heat shock proteins can downregulate the disease process. It might be that self-reactivity to heat shock proteins is a physiological response that regulates the development and progression of pro-inflammatory immunity to these ubiquitously expressed molecules. The evolving evidence that heat shock proteins are present in the extracellular environment, that reactivity to heat shock proteins does not necessarily reflect adverse, pro-inflammatory responses and that the promotion of reactivity to self-heat shock proteins can downregulate pathogenic processes all suggest a potential role for heat shock proteins as therapeutic agents, rather than as therapeutic targets.

Molecular chaperones and protein‐folding catalysts as intercellular signaling regulators in immunity and inflammation

This review critically examines the hypothesis that molecular chaperones and protein‐folding catalysts from prokaryotes and eukaryotes can be secreted by cells and function as intercellular signals, principally but not exclusively, for leukocytes. A growing number of molecular chaperones have been reported to function as ligands for selected receptors and/or receptors for specific ligands. Molecular chaperones initially appeared to act primarily as stimulatory signals for leukocytes and thus, were seen as proinflammatory mediators. However, evidence is now emerging that molecular chaperones can have anti‐inflammatory actions or, depending on the protein and concentration, anti‐ and proinflammatory functions. Recasting the original hypothesis, we propose that molecular chaperones and protein‐folding catalysts are “moonlighting” proteins that function as homeostatic immune regulators but may also under certain circumstances, contribute to tissue pathology. One of the key issues in the field of molecular chaperone biology relates to the role of microbial contaminants in their signaling activity; this too will be evaluated critically. The most fascinating aspect of molecular chaperones probably relates to evidence for their therapeutic potential in human disease, and ongoing studies are evaluating this potential in a range of clinical settings.

Heat Shock Proteins, Anti-heat Shock Protein Reactivity And Allograft Rejection

Heat shock proteins are families of highly conserved immunodominant molecules, reactivity to which has been implicated in the pathogenesis of a number of autoimmune and vascular disease states. However, heat shock proteins are cytoprotective, and in clinical and experimental arthritis, anti-heat shock protein reactivity can down modulate immune responses via a self-Hsp reactive, Th2-type mechanism. Despite a number of studies associating heat shock protein expression and anti-heat shock protein reactivity with allograft rejection, the balance between protective and damaging effects and the precise influence of these responses on graft outcome is unclear. This article reviews current knowledge surrounding heat shock proteins, autoimmunity, and allograft rejection and presents a perspective on the potential influence of these proteins and the stress response on allograft outcome.

Elevated heat shock protein 60 levels are associated with higher risk of coronary heart disease in Chinese.

Background— Although heat shock protein 60 (Hsp60) is implicated in the pathogenesis of atherosclerosis, its role in coronary heart disease (CHD) is uncertain. This study explored the influence of circulating Hsp60 on CHD in a large case-control study, as well as the impact of acute myocardial infarction on Hsp60 levels in a prospective study. Methods and Results— Plasma Hsp60 and anti-Hsp60 antibody levels were determined by immunoassay. In the case-control study (1003 patients with CHD, 1003 matched control subjects), Hsp60 levels were higher in patients with CHD and were related to CHD (OR comparing extreme quartiles=4.14, P<0.0001). This association remained after adjustment for traditional risk factors (P for trend <0.0001). Individuals having high levels of Hsp60 (greater than the median of 160.24 ng/mL) and anti-Hsp60 antibody (greater than the median of 38.42 U/mL) were at a greater risk of CHD than those with low levels (OR 2.30, P<0.0001). Stronger additive effects (OR 14.04, P<0.0001) were apparent at higher Hsp60 and anti-Hsp60 antibody levels (>1000 ng/mL and greater than the median of 38.42 U/mL, respectively). The simultaneous presence of high Hsp60 and anti-Hsp60 antibody levels, current smoking, hypertension, and diabetes were cumulatively associated with CHD. Individuals who had any 4 or more of these 5 factors had an OR of 38.61 for CHD (P<0.0001) compared with individuals who had none of these factors. For the prospective study, blood was drawn from 20 patients immediately after admission for acute myocardial infarction and 2, 3, and 7 days thereafter. Hsp60 levels were significantly higher on the day of and the day after arrival than 7 days after an acute myocardial infarction (P=0.011 and P=0.026, respectively). Conclusions— Elevated Hsp60 levels are associated with an increased risk for CHD, and Hsp60 and anti-Hsp60 antibody levels combine to increase this risk. In addition, acute myocardial infarction induces Hsp60 release.

The atheroprotective properties of Hsp70: a role for Hsp70-endothelial interactions?

Although heat shock (stress) proteins are typically regarded as being exclusively intracellular molecules, it is now apparent that they can be released from cells in the absence of cellular necrosis. We and others have reported the presence of Hsp60 (HSPD1) and Hsp70 (HSPA1A) in the circulation of normal individuals and our finding that increases in carotid intima-media thicknesses (a measure of atherosclerosis) in subjects with hypertension at a 4-year follow-up are less prevalent in those having high serum Hsp70 (HSPA1A) levels at baseline suggests that circulating Hsp70 (HSPA1A) has atheroprotective effects. Given that circulating Hsp70 (HSPA1A) levels can be in the range which has been shown to elicit a number of biological effects in vitro, and our preliminary findings that Hsp70 (HSPA1A) binds to and is internalised by human endothelial cell populations, we speculate on the mechanisms that might be involved in the apparent atheroprotective properties of this protein.

FK409 inhibits both local and remote organ damage after intestinal ischaemia

In addition to localized tissue injury, intestinal ischaemia–reperfusion (I/R) leads to remote organ damage, in particular to the lungs. Given that nitric oxide (NO) can attenuate I/R‐induced tissue injury in many situations, this study evaluated the effects of the NO donor, FK409, on leukocyte adhesion in the microcirculation of the intestinal villus and also assessed pulmonary tissue damage after intestinal I/R injury. PVG rats were subjected to 30u2009min intestinal ischaemia and a sub‐group of animals received the NO donor FK409 (10u2009mg/kg; i.v.) both 30u2009min prior to ischaemia and 30u2009min post‐reperfusion. The intestinal mucosal surface was visualized via an incision made in an exteriorized ileal segment and leukocyte adhesion in the villous microcirculation was determined by in vivo microscopy. Total and differential leukocyte counts from peripheral blood were evaluated. Lungs were removed at the end for histological assessment. Six out of ten untreated I/R animals failed to survive the 2u2009h reperfusion period, whereas all ten FK409‐treated animals survived. I/R induced a significant increase in villous leukocyte adhesion of untreated I/R animals (p<0.001) and this was significantly decreased by FK409 treatment (p<0.001). The total leukocyte count was significantly decreased in untreated I/R animals (p<0.001) and this primarily resulted from a reduction in circulating neutrophil numbers. This effect was not observed in FK409‐treated animals. Collapsed alveoli, thickened interstitial walls, and a dense neutrophilic infiltrate were apparent in the lungs of untreated I/R animals, whereas lung histology was normal in FK409‐treated animals. In conclusion, FK409 prevented mortality, significantly reduced villous leukocyte adhesion, maintained circulating leukocyte numbers, and prevented pulmonary tissue injury following intestinal I/R. FK409 may therefore be of value in reducing both local and remote tissue damage and improving outcome in situations where intestinal I/R injury is obligatory, such as small bowel transplantation. Copyright

The unfolded protein response and cancer: a brighter future unfolding?

Mammalian cells are bathed in an interstitial fluid that has a tightly regulated composition in healthy states. Interstitial fluid provides cells with all the necessary metabolic substrates (oxygen, glucose, amino acids, etc.), and waste molecules are removed by diffusion gradients that are controlled by local vascular perfusion. The health and normal function of all cells within a body is dependent on the maintenance of this microenvironment. However, many disease states cause fluctuations in this, and in some instances, these might be of sufficient severity to stress and/or be toxic to the cell. Cells have developed a number of responses to enable their survival in a hostile environment. This article discusses one such pathway—the unfolded protein response and its relationship to cancer. The molecular signalling cascade, the mechanism of its activation in cancer and the consequences of its activation for a tumour are discussed, as are clinical studies and potential translational approaches for utilising this pathway for tumour targeting.

Ketotifen abrogates local and systemic consequences of rat intestinal ischemia-reperfusion injury

Background:u2002 Mast cell‐derived vasoactive and pro‐inflammatory mediators, particularly histamine, might contribute to local tissue damage and multiorgan dysfunction induced by intestinal ischemia/reperfusion (I/R). The purpose of the present study was to evaluate the effects of the mast cell stabilizer, ketotifen, on leukocyte adhesion within, and tissue leakage from the mucosal villous microcirculation after intestinal I/R.