Expression of heat shock protein 60 in human proximal tubule cells exposed to heat, sodium arsenite and CdCl(2)

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.

The Roles of Heat Shock Protein-60 and 70 and Inflammation in Obesity-Related Kidney Disease

Introduction

The exact mechanisms of obesity-related kidney disease (ORKD) are not fully known. Heat shock proteins (HSPs) may play a role in ORKD mechanisms because of their role in cell apoptosis, cytoprotection, and inflammatory processes. We aimed to determine the role of circulating serum HSP-60 and HSP-70 levels as a biomarker for ORKD.

Materials and methods

This study included 40 ORKD patients, 40 obese age-matched and sex-matched controls with similar body mass index (BMI), and 40 healthy controls. Their serum biochemical and hemogram parameters as well as HSP-60 and HSP-70 levels were evaluated and compared. Their neutrophil-to-lymphocyte ratio (NLR) and C-reactive protein levels were assessed to define inflammation. 

Results

The patients had significantly higher HSP-60 levels than the obese and healthy controls (537.58 ± 170.35, 430.80 ± 110.61, and 371.85 ± 76.34, respectively; p<0.00). The results revealed that the 24-hour urinary protein levels had a positive correlation (r= 0.544), whereas the glomerular filtration rate had a negative correlation (r = 0.38) with the serum HSP-60 level. According to the regression analysis performed on the HSP-60 and 24-hour urinary protein excretion levels, an increase in the HSP-60 level significantly increased the 24-hour urinary protein excretion rate (r=0.15; p<0.005). The HSP-60 levels were correlated with inflammatory markers

Conclusion

The serum HSP-60 levels increased in patients with ORKD. This increase was correlated with 24-hour urinary protein excretion. Increased circulating levels of HSP-60 may play a role in the initiation and/or progression of renal damage and inflammation. HSP-60 is a potential biomarker for ORKD. However, additional information and studies are required to further elucidate this finding.

Heat stress-induced renal damage in poultry and the protective effects of HSP60 and HSP47

The present study investigates the effects of heat stress on the kidney in broilers, based on previous findings which showed that heat stress caused cardiac damage in broilers. Further, the possible renoprotective role of aspirin and the heat shock proteins HSP60 and HSP47 was also investigated. The enzyme levels of urea and uric acid, which are indicators of renal damage, and lactate dehydrogenase, an indicator of oxidative damage, were measured in chickens that were only exposed to heat stress, chickens that were pretreated with aspirin before heat stress, and chickens that were only treated with aspirin. Further, histological examination of renal tissue from the three groups was also performed. Finally, expression of HSP60 and HSP47 was also examined. In the heat stress group, the enzyme measurements were indicative of renal dysfunction and oxidative damage, and the histological findings were indicative of renal ischemia and damage. Aspirin seemed to have a protective effect against the renal damage caused by the stress, based on the enzyme measurements and histopathological findings in the aspirin-treated group. The findings also indicate that aspirin may induce HSP60 and HSP47 expression in renal cells. Finally, the expression patterns of HSP60 and HSP47 indicated that they may play a renoprotective role, as their expression was higher in the aspirin-treated groups. In conclusion, the present findings show that heat stress causes renal damage in poultry and that aspirin may play a protective role against this damage via pathways that involve HSP60 and HSP47.

Effect of hemin, baicalein and heme oxygenase-1 (HO-1) enzyme activity inhibitors on Cd-induced accumulation of HO-1, HSPs and aggresome-like structures in Xenopus kidney epithelial cells

Cadmium is a highly toxic environmental pollutant that can cause many adverse effects including cancer, neurological disease and kidney damage. Aquatic amphibians are particularly susceptible to this toxicant as it was shown to cause developmental abnormalities and genotoxic effects. In mammalian cells, the accumulation of heme oxygenase-1 (HO-1), which catalyzes the breakdown of heme into CO, free iron and biliverdin, was reported to protect cells against potentially lethal concentrations of CdCl₂. In the present study, CdCl₂ treatment of A6 kidney epithelial cells, derived from the frog, Xenopus laevis, induced the accumulation of HO-1, heat shock protein 70 (HSP70) and HSP30 as well as an increase in the production of aggregated protein and aggresome-like structures. Treatment of cells with inhibitors of HO-1 enzyme activity, tin protoporphyrin (SnPP) and zinc protoporphyrin (ZnPP), enhanced CdCl₂-induced actin cytoskeletal disorganization and the accumulation of HO-1, HSP70, aggregated protein and aggresome-like structures. Treatment of cells with hemin and baicalein, which were previously shown to provide cytoprotection against various stresses, induced HO-1 accumulation in a concentration-dependent manner. Also, treatment of cells with hemin and baicalein suppressed CdCl₂-induced actin dysregulation and the accumulation of aggregated protein and aggresome-like structures. This cytoprotective effect was inhibited by SnPP. These results suggest that HO-1-mediated protection against CdCl₂ toxicity includes the maintenance of actin cytoskeletal and microtubular structure and the suppression of aggregated protein and aggresome-like structures.

Short and long term gene expression variation and networking in human proximal tubule cells when exposed to cadmium

Cadmium (Cd²⁺) is a known nephrotoxin causing tubular necrosis during acute exposure and potentially contributing to renal failure in chronic long-term exposure. To investigate changes in global gene expression elicited by cadmium, an in-vitro exposure system was developed from cultures of human renal epithelial cells derived from cortical tissue obtained from nephrectomies. These cultures exhibit many of the qualities of proximal tubule cells. Using these cells, a study was performed to determine the cadmium-induced global gene expression changes after short-term (1 day, 9, 27, and 45 μM) and long-term cadmium exposure (13 days, 4.5, 9, and 27 μM). These studies revealed fundamental differences in the types of genes expressed during each of these time points. The obtained data was further analyzed using regression to identify cadmium toxicity responsive genes. Regression analysis showed 403 genes were induced and 522 genes were repressed by Cd²⁺ within 1 day, and 366 and 517 genes were induced and repressed, respectively, after 13 days. We developed a gene set enrichment analysis method to identify the cadmium induced pathways that are unique in comparison to traditional approaches. The perturbation of global gene expression by various Cd²⁺ concentrations and multiple time points enabled us to study the transcriptional dynamics and gene interaction using a mutual information-based network model. The most prominent network module consisted of INHBA, KIF20A, DNAJA4, AKAP12, ZFAND2A, AKR1B10, SCL7A11, and AKR1C1.

Microarray analysis of gene expression patterns in human proximal tubule cells over a short and long time course of cadmium exposure

Numerous studies showed that renal proximal tubules cells are the cell type critically affected by chronic exposure to cadmium (Cd(2+)). The aim of the present study was to apply global gene expression technology and a human renal epithelial cell culture model (HPT) to determine whether time of exposure to Cd(2+) exerts a major influence on the resulting pattern of global gene expression. HPT cells were exposed to Cd(2+) for a short, 1-d, period of exposure (9, 27, and 45 μM) versus a longer, 13-d, period (4.5, 9, and 27 μM), with the hypothesis being that the stress response of the cells would be more active during the short time of exposure. The results showed that the differential expression of genes was very extensive for HPT cells exposed to Cd(2+) for 1 d, with more than 1848 genes displaying alterations compared to control and with the major categories of genes being involved in stress responses; cell death; checkpoint arrest, DNA repair, and the cell cycle; inflammatory responses; and cell adhesion, motion and differentiation. In contrast, HPT cells exposed to Cd(2+) for 13 d showed 923 genes to be differentially expressed, with a marked reduction in the number of differentially expressed stress response genes and a significant increase in the number of genes involved in development and differentiation. There were 387 differentially expressed genes common to both times of exposure. Data suggest that unless one is actively seeking to study the acute stress response, global gene expression technology should not be applied within an early time course of toxicant exposure.

Effects of cadmium on cellular protein and glutathione synthesis and expression of stress proteins in eastern oysters, Crassostrea virginica Gmelin

Cadmium (Cd) is an important toxicant in estuarine and coastal environments that can strongly affect energy balance of aquatic organisms by increasing the organism's basal energy demand and reducing its aerobic capacity. Mechanisms of cadmium-induced increase in basal metabolic costs are not well understood and may involve elevated detoxification costs due to the synthesis of cellular protective proteins and glutathione. We studied the short-term effects of cadmium exposure (4 h) on protein and glutathione (GSH) synthesis and expression of stress proteins (heat shock proteins HSP60, HSP70 and HSP90) and metallothioneins in isolated gill and hepatopancreas cells of the eastern oyster, Crassostrea virginica. Our study showed that exposure to cadmium resulted in a dose-dependent increase in the rate of protein synthesis in oyster cells, which reached 150% of the control at the highest tested Cd level (2000 micromol l(-1)). GSH synthesis was significantly inhibited by the highest Cd concentrations, especially in hepatopancreas, which resulted in a slight but significant decrease in the total GSH concentrations. Elevated protein synthesis was associated with the increased expression of metallothioneins and heat shock proteins. Interestingly, stress protein response differed considerably between gill and hepatopancreas cells. In hepatopancreas, expression of metallothionein mRNA (measured by real-time PCR) increased 2-8-fold in response to Cd exposure, whereas no significant increase in metallothionein expression was found in Cd-exposed gill cells. By contrast, HSP60 and HSP70 protein levels increased significantly in Cd-exposed gill cells (by 1.5-2-fold) but not in hepatopancreas. No change in HSP90 expression was detected in response to Cd exposure in oyster cells. These data indicate that metallothionein expression may provide sufficient protection against Cd-induced damage to intracellular proteins in hepatopancreas, alleviating the need for overexpression of molecular chaperones. By contrast, Cd detoxification mechanisms such as inducible metallothioneins and GSH appear to be insufficient to fully prevent protein damage in gill cells, thus necessitating induction of HSPs as a secondary line of cellular defense. Therefore, gills are likely to be among the most Cd-sensitive tissues in oysters, which may have important implications for impaired oxygen uptake contributing to energy misbalance and reduced aerobic scope in Cd-exposed oysters.

Molecular cloning and characterization of Cpn60 in the free-living nematode Plectus acuminatus

Heat shock proteins (Hsps) have provoked interest not only because of their involvement in human diseases but also for their potential as biomarkers of environmental pollution. Whereas the former interest is covered by numerous reports, the latter is an exciting new field of research. We report the isolation of the full-length cpn60 messenger ribonucleic acid (mRNA) and partial genomic deoxyribonucleic acid from the free-living, environmental sentinel nematode Plectus acuminatus, a species used in classical ecotoxicity tests. Although the primary sequence displays high identity scores to other nematodes and human Cpn60 (75% and 70%, respectively), the intron-exon structure differs markedly. Furthermore, although mRNA levels remained constant after exposure to ZnCl2 (0-330 microM) under laboratory conditions, protein levels increased significantly in a dose-dependent manner. In conclusion, this first account of molecular genetic similarities and differences of Cpn60 in a neglected nematode taxon provides a valuable insight into its potential uses in gene-based ecotoxicological risk assessment exercises.

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

Heat shock proteins (Hsp) are ubiquitous intracellular proteins that can be released in various forms of cellular stress. Some Hsp, such as Hsp60, have been shown to stimulate directly T cell-mediated immune responses in vitro. Here, it is demonstrated that Hsp60 is released from the kidneys and excreted into the urine of mice with nephrotoxic nephritis (NTN), a model of rapidly progressive glomerulonephritis. For examining the functional relevance of Hsp60 release, this protein was injected into mice with subnephritogenic NTN, in which only transient proteinuria and minimal organ damage occur that do not progress to terminal kidney failure. Injection of Hsp60 strikingly aggravated disease, as evidenced by global glomerular necrosis, tubulointerstitial damage, and complete anuria after 10 to 12 d. This effect was mediated neither by endotoxin contaminations of Hsp60 nor by autologous antibodies. It was strictly T cell dependent but not associated with a systemic Th1/Th2 shift. Thus, Hsp60 is an endogenous mediator stimulating immune effector mechanisms that contribute to the progression of NTN. These findings demonstrate in vivo that Hsp60 fulfills criteria of immunologic danger signals and suggest that such signals may be involved in immune-mediated kidney disease.

Molecular and cellular mechanisms of cadmium carcinogenesis

Cadmium is a heavy metal, which is widely used in industry, affecting human health through occupational and environmental exposure. In mammals, it exerts multiple toxic effects and has been classified as a human carcinogen by the International Agency for Research on Cancer. Cadmium affects cell proliferation, differentiation, apoptosis and other cellular activities. Cd2+ does not catalyze Fenton-type reactions because it does not accept or donate electrons under physiological conditions, and it is only weakly genotoxic. Hence, indirect mechanisms are implicated in the carcinogenicity of cadmium. In this review multiple mechanisms are discussed, such as modulation of gene expression and signal transduction, interference with enzymes of the cellular antioxidant system and generation of reactive oxygen species (ROS), inhibition of DNA repair and DNA methylation, role in apoptosis and disruption of E-cadherin-mediated cell-cell adhesion. Cadmium affects both gene transcription and translation. The major mechanisms of gene induction by cadmium known so far are modulation of cellular signal transduction pathways by enhancement of protein phosphorylation and activation of transcription and translation factors. Cadmium interferes with antioxidant defense mechanisms and stimulates the production of reactive oxygen species, which may act as signaling molecules in the induction of gene expression and apoptosis. The inhibition of DNA repair processes by cadmium represents a mechanism by which cadmium enhances the genotoxicity of other agents and may contribute to the tumor initiation by this metal. The disruption of E-cadherin-mediated cell-cell adhesion by cadmium probably further stimulates the development of tumors. It becomes clear that there exist multiple mechanisms which contribute to the carcinogenicity of cadmium, although the relative weights of these contributions are difficult to estimate.

Hsp27, Hsp70, and metallothionein in MDCK and LLC-PK1 renal epithelial cells: effects of prolonged exposure to cadmium

Cadmium is a widely distributed industrial and environmental toxin. The principal target organ of chronic sublethal cadmium exposure is the kidney. In renal epithelial cells, acute high-dose cadmium exposure induces differential expression of proteins, including heat shock proteins. However, few studies have examined heat shock protein expression in cells after prolonged exposure to cadmium at sublethal concentrations. Here, we assayed total cell protein, neutral red uptake, cell death, and levels of metallothionein and heat shock proteins Hsp27 and inducible Hsp70 in cultures of MDCK and LLC-PK1 renal epithelial cells treated with cadmium for 3 days. Treatment with cadmium at concentrations equal to or greater than 10 microM (LLC-PK1) or 25 microM (MDCK) reduced measures of cell vitality and induced cell death. However, a concentration-dependent increase in Hsp27 was detected in both cell types treated with as little as 5 microM cadmium. Accumulation of Hsp70 was correlated only with cadmium treatment at concentrations also causing cell death. Metallothionein was maximally detected in cells treated with cadmium at concentrations that did not reduce cell vitality, and further increases were not detected at greater concentrations. These results reveal that heat shock proteins accumulate in renal epithelial cells during prolonged cadmium exposure, that cadmium induces differential expression of heat shock protein in epithelial cells, and that protein expression patterns in epithelial cells are specific to the cadmium concentration and degree of cellular injury. A potential role for Hsp27 in the cellular response to sublethal cadmium-induced injury is also implicated by our results.

Upregulation of stress response mRNAs in COS-7 cells exposed to cadmium

Exposure of cells to cadmium (Cd) is known to stimulate the expression of various types of genes. These changes in gene expression are presumed to be related to the cellular response to Cd toxicity. To better understand the mechanisms related to Cd toxicity, suppression subtractive hybridization was carried out on COS-7 cells (African green monkey kidney cells) and the gene expression induced by Cd exposure was investigated. Heat shock protein (hsp) 10, 40, 60, 70, 89alpha and metallothionein II (MTII) mRNAs were found to be induced by Cd. This is the first report to describe the Cd-inducibility of hsp10, 40 and 89alpha mRNAs. Semi-quantitative reverse-transcription polymerase chain reaction showed the diverse expression patterns of these genes, depending on Cd concentration and exposure time. A marked elevation of hsp70 mRNA and induction of mRNA for the co-chaperone, hsp40, were detected. A relatively low level of hsp10 and hsp60 mRNAs was induced, with only a 2-fold increase within 24 h. Hsp89alpha mRNA was induced shortly after Cd exposure. These various induction patterns suggest that hsps play different roles in the cell against Cd toxicity.

A comparison of 60, 70, and 90 kDa stress protein expression in normal rat NRK-52 and human HK-2 kidney cell lines following in vitro exposure to arsenite and cadmium alone or in combination

Arsenite and cadmium are two potent nephrotoxicants and common Superfund site elements. These elements are included among the stress protein inducers, but information regarding relationships between toxicity produced by combinations of these agents to the stress protein response is lacking. In this study, the immortalized cell lines normal rat kidney NRK-52E and human kidney HK-2 were exposed in vitro to arsenite (As(3+)), cadmium (Cd(2+)), or to equimolar As(3+) plus Cd(2+) mixture combinations for 3 and 5 h over a concentration range of 0.1-100 microM. After a 12-h recovery period, cultured cells were then evaluated for expression of the 60, 70, and 90 kDa major stress protein families. Results indicated that expression of stress proteins varied depending on the species of kidney cells exposed, the exposure concentrations, and the length of exposure to each element on an individual basis and for combined mixtures. For the HK-2 kidney cell line, increased levels of the 70 kDa stress protein was observed for single and combined element exposures whereas there was no change or a decrease of stress proteins 60 and 90 kDa. Increased 70 kDa expression was observed for 10-microM doses of single elements and for a lower dose of 1 microM of the As plus Cd mixture at 3- and 5-h exposures. NRK-52 kidney cells exposed to equivalent doses of As(3+) and Cd(2+) alone or in combination showed increased levels of all stress proteins 60, 70, and 90 kDa. This increase was seen for 10 microM of the As plus Cd mixture at 3 h whereas for single element exposures, increased stress protein levels were generally observed for the 100-microM doses. At 5 h- exposure, 60 and 90 kDa levels increased for 10 microM of Cd(2+) and 60 kDa levels increased for 1 microM of As(3+). However, exposures to 10 microM of the As plus Cd mixture decreased 60 kDa protein expression to control levels at 5 h. For both kidney cell lines, there was a decrease in the stress protein expression levels for all three stress protein families for 100-microM doses of the mixture combination for 3- and 5-h exposures. These data indicate a dose- and combination-related correlation between depression of the stress protein response and the onset of overt cellular toxicity and/or cell death. The threshold for these changes was cell line specific.

Transient induction of metallothionein isoform 3 (MT-3), c-fos, c-jun and c-myc in human proximal tubule cells exposed to cadmium

Cadmium (Cd(+2)) has been shown to transiently increase the expression of mRNA for the third isoform of the metallothionein (MT-3) gene family in cultured human proximal tubule (HPT) cells. The goal of the present study was to further define the expression of MT-3 in mortal (HPT) and immortal (HK-2) cultures of HPT cells when exposed to lethal and sub-lethal concentrations of Cd(+2) under both acute and chronic time periods of exposure. Expression of MT-3 mRNA and protein was determined in cultured HPT cells and HK-2 cells using reverse-transcription-polymerase chain reaction (RT-PCR) and immuno-blotting, and expression of c-fos, c-jun and c-myc mRNA by RT-PCR. The results confirmed that exposure of the HPT cells to Cd(+2) induced a transient increase in MT-3 mRNA and extended the induction to include a subsequent transient increase in the level of the MT-3 protein. The induction of MT-3 was rapid and returned to control values within 48 h of exposure despite the continued presence of lethal and sublethal concentrations of Cd(+2). It was also demonstrated that the pattern of expression of MT-3 mRNA was similar to that of the early response genes, c-fos, c-jun and c-myc. It was shown that the HK-2 cells did not express MT-3 when exposed to Cd(+2), but had similar expression of the c-fos, c-jun and c-myc genes. The results demonstrate that MT-3 expression is metal responsive in HPT cells.

Stress proteins induced by arsenic

The elevated expression of stress proteins is considered to be a universal response to adverse conditions, representing a potential mechanism of cellular defense against disease and a potential target for novel therapeutics. Exposure to arsenicals either in vitro or in vivo in a variety of model systems has been shown to cause the induction of a number of the major stress protein families such as heat shock proteins (Hsp). Among them are members with low molecular weight, such as metallotionein and ubiquitin, as well as ones with masses of 27, 32, 60, 70, 90, and 110 kDa. In most of the cases, the induction of stress proteins depends on the capacity of the arsenical to reach the target, its valence, and the type of exposure, arsenite being the biggest inducer of most Hsp in several organs and systems. Hsp induction is a rapid dose-dependent response (1-8 h) to the acute exposure to arsenite. Thus, the stress response appears to be useful to monitor the sublethal toxicity resulting from a single exposure to arsenite. The present paper offers a critical review of the capacity of arsenicals to modulate the expression and/or accumulation of stress proteins. The physiological consequences of the arsenic-induced stress and its usefulness in monitoring effects resulting from arsenic exposure in humans and other organisms are discussed.