Thermotolerance in mammalian cells. Protein denaturation and aggregation, and stress proteins

Novel pressure- and temperature-controlled flexible ureteroscope system with a suction ureteral access sheath: a multicenter retrospective feasibility study

PURPOSE

The purpose of this study was to assess the feasibility of a pressure-controlled and temperature-controlled flexible ureteroscope system (PT Scope™) during flexible ureteroscopy.

MATERIALS AND METHODS

We developed the PT Scope™, a novel ureteroscope system with capabilities for monitoring and controlling intrarenal pressure and temperature to maintain them within set parameters. Data were retrospectively collected from 48 consecutive patients diagnosed with upper urinary tract stones who underwent flexible ureteroscopic lithotripsy using the PT Scope™ across five centers in China. Analyses focused on 24-h postoperative stone-free rates, intrarenal pressure and temperature measurements, and other procedural data.

RESULTS

Among the 48 patients treated with the PT Scope™ system, a significant stone-free rate of 89.6% was achieved within 24 h postoperation, without any instances of intraoperative complications such as perforation or mucosal hemorrhage. Only two patients reported mild postoperative pain and were managed with NSAIDs, and there were no cases of postoperative fever or sepsis. The average maximum intrarenal pressure and temperature were recorded at 30.2 ± 4.20 mmHg and 36.6 ± 4.27 °C, respectively. Notably, during lithotripsy, both the pressure and temperature were maintained below 30 mmHg and 43 °C for 99% of the procedure duration, respectively.

CONCLUSION

This preliminary investigation indicates that the PT Scope™ is a safe and effective tool for the treatment of upper urinary tract stones, offering the benefit of regulating intrarenal pressure and temperature within predetermined limits. These findings support the feasibility of the system for clinical application.

An In Vivo Assessment of a Novel Temperature Control Flexible Ureteroscope System for Monitoring and Controlling Intrarenal Temperature During Flexible Ureteroscopy

OBJECTIVE

To evaluate the efficacy of a novel temperature control flexible ureteroscope system in the precise monitoring and control of intrarenal temperature (IRT) during ureteroscopy.

METHODS

We developed a novel temperature control flexible ureteroscope system (PT-Scope), including a temperature-monitoring ureteroscope and a irrigation-suction platform for temperature regulation. A porcine thermometry model was established to observe temperature changes under varying holmium laser powers (10, 20, 30 W) and irrigation rates (0, 20, 50 mL/min), utilizing percutaneous nephrostomy thermometry and PT-Scope measurements, with subsequent evaluation of temperature variations at different distances from the laser fiber tip. A porcine kidney stone model was established while porcine was randomly assigned to two groups: In the temperature control group, PT-Scope was connected to the irrigation-suction platform with temperature regulation, while in the nontemperature control group without temperature regulation. Comparative analysis was performed to evaluate differences in IRT between the two groups.

RESULTS

Across various laser powers and irrigation rates, the temperature measurement capability of the PT-Scope was precise, demonstrating consistency with percutaneous nephrostomy temperature measurements. The temperature obtained from the PT-Scope reflect the temperature approximately 0.05 cm away from the fiber tip, whereas temperatures close to fiber tip were significantly higher. The peak temperature of the temperature control group vs nontemperature control group were 31.70 ± 2.609°C and 44.37 ± 3.318 °C, respectively (P < 0.01). The mean temperature of the temperature control group vs nontemperature control group was 27.40 ± 2.107 °C vs 35.9 ± 1.921 °C (P < 0.01).

CONCLUSION

PT-Scope has demonstrated the capability to precisely monitor and control IRT within a safe threshold.

Ultrasmall Bi/Cu Coordination Polymer Combined with Glucose Oxidase for Tumor Enhanced Chemodynamic Therapy by Starvation and Photothermal Treatment

Multi-modal combination therapy for tumor is expected to have superior therapeutic effect compared with monotherapy. In this study, a super-small bismuth/copper-gallic acid coordination polymer nanoparticle (BCN) protected by polyvinylpyrrolidone is designed, which is co-encapsulated with glucose oxidase (GOX) by phospholipid to obtain nanoprobe BCGN@L. It shows that BCN has an average size of 1.8 ± 0.7 nm, and photothermal conversion of BCGN@L is 31.35% for photothermal imaging and photothermal therapy (PTT). During the treatment process of 4T1 tumor-bearing nude mice, GOX catalyzes glucose in the tumor to generate gluconic acid and hydrogen peroxide (H2 O2 ), which reacts with copper ions (Cu2+ ) to produce toxic hydroxyl radicals (•OH) for chemodynamic therapy (CDT) and new fresh oxygen (O2 ) to supply to GOX for further catalysis, preventing tumor hypoxia. These reactions increase glucose depletion for starvation therapy , decrease heat shock protein expression, and enhance tumor sensitivity to low-temperature PTT. The in vitro and in vivo results demonstrate that the combination of CDT with other treatments produces excellent tumor growth inhibition. Blood biochemistry and histology analysis suggests that the nanoprobe has negligible toxicity. All the positive results reveal that the nanoprobe can be a promising approach for incorporation into multi-modal anticancer therapy.

Similar adaptative mechanism but divergent demographic history of four sympatric desert rodents in Eurasian inland

Phenotypes associated with metabolism and water retention are thought to be key to the adaptation of desert species. However, knowledge on the genetic changes and selective regimes on the similar and divergent ways to desert adaptation in sympatric and phylogenetically close desert organisms remains limited. Here, we generate a chromosome level genome assembly for Northern three-toed jerboa (Dipus sagitta) and three other high-quality genome assemblies for Siberian jerboa (Orientallactaga sibirica), Midday jird (Meriones meridianus), and Desert hamster (Phodopus roborovskii). Genomic analyses unveil that desert adaptation of the four species mainly result from similar metabolic pathways, such as arachidonic acid metabolism, thermogenesis, oxidative phosphorylation, insulin related pathway, DNA repair and protein synthesis and degradation. However, the specific evolved genes in the same adaptative molecular pathway often differ in the four species. We also reveal similar niche selection but different demographic histories and sensitivity to climate changes, which may be related to the diversified genomic adaptative features. In addition, our study suggests that nocturnal rodents have evolved some specific adaptative mechanism to desert environments compared to large desert animals. Our genomic resources will provide an important foundation for further research on desert genetic adaptations.

Evaluation of the Heat Shock Protein 90 Inhibitor Ganetespib as a Sensitizer to Hyperthermia-Based Cancer Treatments

Simple Summary

Hyperthermia boosts the effects of radio- and chemotherapy regimens, but its clinical potential is hindered by the ability of (cancer) cells to activate a protective mechanism known as the heat stress response. Strategies that inhibit its activation or functions have the potential, therefore, to improve the overall efficacy of hyperthermia-based treatments. In this study, we evaluated the efficacy of the HSP90 inhibitor ganetespib in promoting the effects of radiotherapy or cisplatin combined with hyperthermia in vitro and in a cervix cancer mouse model.

Abstract

Hyperthermia is being used as a radio- and chemotherapy sensitizer for a growing range of tumor subtypes in the clinic. Its potential is limited, however, by the ability of cancer cells to activate a protective mechanism known as the heat stress response (HSR). The HSR is marked by the rapid overexpression of molecular chaperones, and recent advances in drug development make their inhibition an attractive option to improve the efficacy of hyperthermia-based therapies. Our previous in vitro work showed that a single, short co-treatment with a HSR (HSP90) inhibitor ganetespib prolongs and potentiates the effects of hyperthermia on DNA repair, enhances hyperthermic sensitization to radio- and chemotherapeutic agents, and reduces thermotolerance. In the current study, we first validated these results using an extended panel of cell lines and more robust methodology. Next, we examined the effects of hyperthermia and ganetespib on global proteome changes. Finally, we evaluated the potential of ganetespib to boost the efficacy of thermo-chemotherapy and thermo-radiotherapy in a xenograft murine model of cervix cancer. Our results revealed new insights into the effects of HSR inhibition on cellular responses to heat and show that ganetespib could be employed to increase the efficacy of hyperthermia when combined with radiation.

Nanomaterial-mediated low-temperature photothermal therapy via heat shock protein inhibition

With the continuous development of nanobiotechnology in recent years, combining photothermal materials with nanotechnology for tumor photothermal therapy (PTT) has drawn many attentions nanomedicine research. Although nanomaterial-mediated PTT is more specific and targeted than traditional treatment modalities, hyperthermia can also damage normal cells. Therefore, researchers have proposed the concept of low-temperature PTT, in which the expression of heat shock proteins (HSPs) is inhibited. In this article, the research strategies proposed in recent years based on the inhibition of HSPs expression to achieve low-temperature PTT was reviewed. Folowing this, the synthesis, properties, and applications of these nanomaterials were introduced. In addition, we also summarized the problems of nanomaterial-mediated low-temperature PTT at this stage and provided an outlook on future research directions.

Integrity and wound healing of rainbow trout intestinal epithelial cell sheets at hypo-, normo-, and hyper-thermic temperatures

How temperature influences fish physiological systems, such as the intestinal barrier, is important for understanding and alleviating the impact of global warming on fish and aquaculture. Monolayers of the rainbow trout cell line, RTgutGC, with or without linear 500 μm wide gaps (wounds) were the in vitro models used to study the integrity and healing of intestinal epithelial sheets at different temperatures. Cultures at hypothermic (4 °C) or hyperthermic (≥ 26 °C) temperatures were compared to normothermic control cultures (18-22 °C). Monolayers remained intact for at least a week at temperatures from 4 to 28 °C, but had lost their integrity after 3 h at 32 °C as the cells pulled away from one another and from the plastic surface. F-actin appeared as prominent stress fibers in cells at 28 °C and as blobs in cells at 32 °C. At normothermia and at 26 °C, cells migrated as sheets into the gaps and closed (healed) the gaps within 5-6 days. By contrast, wounds took 14 days to heal at 4 °C. At 28 °C some cells migrated into the gap in the first few days but mainly as single cells rather than collectively and wounds never healed. When monolayers with wounds were challenged at 32 °C for 3 h and returned to 18-22 °C, cells lost their shape and actin organization and over the next 6 days detached and died. When monolayers were subjected to 26 °C for 24 h and challenged at 32 °C for 3 h prior to being placed at 18-22 °C, cell shape and actin cytoskeleton were maintained, and wounds were healed over 6 days. Thus, intestinal epithelial cells become thermostabilized for shape, cytoskeleton and migration by a prior heat exposure.

Interfering with Tumor Hypoxia for Radiotherapy Optimization

Hypoxia in solid tumors is an important predictor of treatment resistance and poor clinical outcome. The significance of hypoxia in the development of resistance to radiotherapy has been recognized for decades and the search for hypoxia-targeting, radiosensitizing agents continues. This review summarizes the main hypoxia-related processes relevant for radiotherapy on the subcellular, cellular and tissue level and discusses the significance of hypoxia in radiation oncology, especially with regard to the current shift towards hypofractionated treatment regimens. Furthermore, we discuss the strategies to interfere with hypoxia for radiotherapy optimization, and we highlight novel insights into the molecular pathways involved in hypoxia that might be utilized to increase the efficacy of radiotherapy.

Trehalose Inhibits the Heat-Induced Formation of the Amyloid-Like Structure of Soluble Proteins Isolated from Human Cataract Lens

The age-dependent loss of solubility and aggregation of crystallins constitute the pathological hallmarks of cataract. Several biochemical and biophysical factors are responsible for the reduction of crystallins' solubility and formation of irreversible protein aggregates, which display amyloid-like characteristics. The present study reports the heat-induced aggregation of soluble proteins isolated from human cataract lenses and the formation of amyloid-like structures. Exposure of protein at 55 °C for 4 h resulted in extensive (≈ 60%) protein aggregation. The heat-induced protein aggregates displayed substantial (≈ 20 nm) redshift in the wavelength of maximum absorption (λ_max) of Congo red (CR) and increase in Thioflavin T (ThT) fluorescence emission intensity, indicating the presence of amyloid-like structures in the heat-induced protein aggregates. Subsequently, the addition of trehalose resulted in substantial inhibition of heat-induced aggregation and the formation of amyloid-like structure. The ability of trehalose to inhibit the heat-induced aggregation was found to be linearly dependent upon its concentration used. The optimum effect was observed in the presence of 30-40% (w/v) trehalose where the aggregated was found to be reduced from 60 to 30%. The present study demonstrated the ability to trehalose to inhibit the protein aggregation and interfere with the formation of amyloid-like structures.

Temperature training improves transcriptional homeostasis after heat shock in juvenile Atlantic sturgeon (Acipenser oxyrinchus)

Exposure to high temperatures can lead to thermotolerance in fish, which is hypothesized to potentially improve post-release survival in species under restocking programs, like Atlantic sturgeon. The aim of this study was to determine whether Atlantic sturgeon juveniles exposed to a 4-week temperature treatment respond differently to a subsequent heat shock than juveniles exposed to heat shock for the first time (naive fish). Response to heat shock was assessed by mapping the liver transcriptome. In total, 838 unique contigs were differentially expressed between the trained and the control group (592 downregulated, 261 upregulated, and 15 down- or upregulated, depending on the condition), corresponding to genes involved in the response to heat, tissue damage, proteolysis, and metabolism. Temperature-trained fish showed 2-4-fold fewer dysregulated contigs than naive fish, indicating their ability to maintain and recover homeostasis faster. During heat shock, hspc1 was upregulated in both experimental groups, while hspa1 and dnaja4 were exclusively upregulated in the control. Overall, compensatory mechanisms were observed in addition to the heat shock response. Only two genes, fgg and apnl, were upregulated at nearly all timepoints in both groups. Peptidases were more strongly downregulated in control fish, which also showed a reduction in lipid metabolism during recovery. Keratins, pck1, gadd45ga, and gadd45gb were differentially expressed between trained and control fish, and due to their roles in tissue protection and ER stress reduction, they might be responsible for the maintenance of the transcriptional homeostasis observed in trained fish.

Heat shock response regulates stimulus-specificity and sensitivity of the pro-inflammatory NF-κB signalling

BACKGROUND

Ability to adapt to temperature changes trough the Heat Shock Response (HSR) pathways is one of the most fundamental and clinically relevant cellular response systems. Heat Shock (HS) affects the signalling and gene expression responses of the Nuclear Factor κB (NF-κB) transcription factor, a critical regulator of proliferation and inflammation, however, our quantitative understanding of how cells sense and adapt to temperature changes is limited.

METHODS

We used live-cell time-lapse microscopy and mathematical modelling to understand the signalling of the NF-κB system in the human MCF7 breast adenocarcinoma cells in response to pro-inflammatory Interleukin 1β (IL1β) and Tumour Necrosis Factor α (TNFα) cytokines, following exposure to a 37-43 °C range of physiological and clinical temperatures.

RESULTS

We show that exposure to 43 °C 1 h HS inhibits the immediate NF-κB signalling response to TNFα and IL1β stimulation although uptake of cytokines is not impaired. Within 4 h after HS treatment IL1β-induced NF-κB responses return to normal levels, but the recovery of the TNFα-induced responses is still affected. Using siRNA knock-down of Heat Shock Factor 1 (HSF1) we show that this stimulus-specificity is conferred via the Inhibitory κB kinase (IKK) signalosome where HSF1-dependent feedback regulates TNFα, but not IL1β-mediated IKK recovery post HS. Furthermore, we demonstrate that through the temperature-dependent denaturation and recovery of IKK, TNFα and IL1β-mediated signalling exhibit different temperature sensitivity and adaptation to repeated HS when exposed to a 37-43 °C temperature range. Specifically, IL1β-mediated NF-κB responses are more robust to temperature changes in comparison to those induced by TNFα treatment.

CONCLUSIONS

We demonstrate that the kinetics of the NF-κB system following temperature stress is cytokine specific and exhibit differential adaptation to temperature changes. We propose that this differential temperature sensitivity is mediated via the IKK signalosome, which acts as a bona fide temperature sensor trough the HSR cross-talk. This novel quantitative understanding of NF-κB and HSR interactions is fundamentally important for the potential optimization of therapeutic hyperthermia protocols. Video Abstract.

YB-1 recruitment to stress granules in zebrafish cells reveals a differential adaptive response to stress

The survival of cells exposed to adverse environmental conditions entails various alterations in cellular function including major changes in the transcriptome as well as a radical reprogramming of protein translation. While in mammals this process has been extensively studied, stress responses in non-mammalian vertebrates remain poorly understood. One of the key cellular responses to many different types of stressors is the transient generation of structures called stress granules (SGs). These represent cytoplasmic foci where untranslated mRNAs are sorted or processed for re-initiation, degradation, or packaging into mRNPs. Here, using the evolutionarily conserved Y-box binding protein 1 (YB-1) and G3BP1 as markers, we have studied the formation of stress granules in zebrafish (D. rerio) in response to different environmental stressors. We show that following heat shock, zebrafish cells, like mammalian cells, form stress granules which contain both YB-1 and G3BP1 proteins. Moreover, zfYB-1 knockdown compromises cell viability, as well as recruitment of G3BP1 into SGs, under heat shock conditions highlighting the essential role played by YB-1 in SG assembly and cell survival. However, zebrafish PAC2 cells do not assemble YB-1-positive stress granules upon oxidative stress induced by arsenite, copper or hydrogen peroxide treatment. This contrasts with the situation in human cells where SG formation is robustly induced by exposure to oxidative stressors. Thus, our findings point to fundamental differences in the mechanisms whereby mammalian and zebrafish cells respond to oxidative stress.

Hyperthermia: The Optimal Treatment to Overcome Radiation Resistant Hypoxia

Regions of low oxygenation (hypoxia) are a characteristic feature of solid tumors, and cells existing in these regions are a major factor influencing radiation resistance as well as playing a significant role in malignant progression. Consequently, numerous pre-clinical and clinical attempts have been made to try and overcome this hypoxia. These approaches involve improving oxygen availability, radio-sensitizing or killing the hypoxic cells, or utilizing high LET (linear energy transfer) radiation leading to a lower OER (oxygen enhancement ratio). Interestingly, hyperthermia (heat treatments of 39⁻45 °C) induces many of these effects. Specifically, it increases blood flow thereby improving tissue oxygenation, radio-sensitizes via DNA repair inhibition, and can kill cells either directly or indirectly by causing vascular damage. Combining hyperthermia with low LET radiation can even result in anti-tumor effects equivalent to those seen with high LET. The various mechanisms depend on the time and sequence between radiation and hyperthermia, the heating temperature, and the time of heating. We will discuss the role these factors play in influencing the interaction between hyperthermia and radiation, and summarize the randomized clinical trials showing a benefit of such a combination as well as suggest the potential future clinical application of this combination.

Mathematical Models of Cell Response Following Heating

The cells of the cardiovascular system can experience temperature excesses of a few degrees during a diseased state or of tens of degrees during a thermal therapy treatment. These raised temperatures may be acute or of long duration. The multiple cell lines that compose each tissue then react, in approximate order of increasing thermal insult, by expressing heat shock proteins, undergoing apoptosis, or suffering necrosis. Mathematical models of the response of cells could aid in planning and designing thermal therapies. The multi-factor nature of the cell response makes it challenging to develop such models. The models most used clinically are mathematically simple and based on the response of representative tissues. The model that might provide the most fundamental understanding of the biochemical response of cells requires many parameters, some of which are difficult to measure. None of the semi-empirical models that provide improved prediction of cell fate have been widely accepted to plan therapies. There remain great opportunities for developing mathematical models cell response.

Protein Disaggregation in Multicellular Organisms

Protein aggregates are formed in cells with profoundly perturbed proteostasis, where the generation of misfolded proteins exceeds the cellular refolding and degradative capacity. They are a hallmark of protein conformational disorders and aged and/or environmentally stressed cells. Protein aggregation is a reversible process in vivo, which counteracts proteotoxicities derived from aggregate persistence, but the chaperone machineries involved in protein disaggregation in Metazoa were uncovered only recently. Here we highlight recent advances in the mechanistic understanding of the major protein disaggregation machinery mediated by the Hsp70 chaperone system and discuss emerging alternative disaggregation activities in multicellular organisms.

Comparison of anticancer effect of Pleurotus ostreatus extract with doxorubicin hydrochloride alone and plus thermotherapy on erythroleukemia cell line

Background Recent studies have introduced Pleurotus ostreatus (Pleurotaceae) as a herbal medicine for treating different types of cancer. This survey utilizes P. ostreatus and doxorubicin hydrochloride (DOX) alone and then with hyperthermia to investigate the erythroleukemia cell line. This study evaluates and compares the apoptotic and necrotic effects of various treatments on the KG-1 cell line. Methods The proliferation of KG-1 cells was measured by using a tetrazolium salt (MTT)-based colorimetric assay during 96 h after treatment by gradient dilutions of 100 ng/mL to 100 mg/mL of P. ostreatus methanol extract and then the minimum inhibitory concentration (MIC) was determined and was applied in additional experiments. Afterward, the cells were treated using P. ostreatus extract, DOX (6.95 mg/L), and hyperthermia (42 and 44 °C), separately and then applying hyperthermia. Finally, the ratios of apoptosis and necrosis after 24 h incubation were evaluated by using flow cytometry. Results The MIC of the extract was determined (1 mg/mL), which significantly increased the ratio of apoptosis rather than necrosis, whereas the DOX treatment primarily induced necrosis on the KG-1 cells. The anticancer effects of the mushroom extract were significantly increased when it was combined with thermotherapy, which exhibited apoptotic effects at 42 °C but induced necrosis at 44 °C. Conclusions The results suggest that P. ostreatus extract induces apoptosis on KG-1 cells and its anticancer effects are significantly increased in combination with thermotherapy. Therefore, P. ostreatus could be considered as an alternative with anticancer effect for further studies in erythroleukemia patients.

Blood-brain barrier transport and neuroprotective potential of blackberry-digested polyphenols: an in vitro study

PURPOSE

Epidemiological and intervention studies have attempted to link the health effects of a diet rich in fruits and vegetables with the consumption of polyphenols and their impact in neurodegenerative diseases. Studies have shown that polyphenols can cross the intestinal barrier and reach concentrations in the bloodstream able to exert effects in vivo. However, the effective uptake of polyphenols into the brain is still regarded with some reservations. Here we describe a combination of approaches to examine the putative transport of blackberry-digested polyphenols (BDP) across the blood-brain barrier (BBB) and ultimate evaluation of their neuroprotective effects.

METHODS

BDP was obtained by in vitro digestion of blackberry extract and BDP major aglycones (hBDP) were obtained by enzymatic hydrolysis. Chemical characterization and BBB transport of extracts were evaluated by LC-MSⁿ. BBB transport and cytoprotection of both extracts was assessed in HBMEC monolayers. Neuroprotective potential of BDP was assessed in NT2-derived 3D co-cultures of neurons and astrocytes and in primary mouse cerebellar granule cells. BDP-modulated genes were evaluated by microarray analysis.

RESULTS

Components from BDP and hBDP were shown to be transported across the BBB. Physiologically relevant concentrations of both extracts were cytoprotective at endothelial level and BDP was neuroprotective in primary neurons and in an advanced 3D cell model. The major canonical pathways involved in the neuroprotective effect of BDP were unveiled, including mTOR signaling and the unfolded protein response pathway. Genes such as ASNS and ATF5 emerged as novel BDP-modulated targets.

CONCLUSIONS

BBB transport of BDP and hBDP components reinforces the health benefits of a diet rich in polyphenols in neurodegenerative disorders. Our results suggest some novel pathways and genes that may be involved in the neuroprotective mechanism of the BDP polyphenol components.

Overcoming the Heat Endurance of Tumor Cells by Interfering with the Anaerobic Glycolysis Metabolism for Improved Photothermal Therapy

In this study, we developed a general method to decorate plasmonic gold nanorods (GNRs) with a CD44-targeting functional polymer, containing a hyaluronic acid (HA)-targeting moiety and a small molecule Glut1 inhibitor of diclofenac (DC), to obtain GNR/HA-DC. This nanosystem exhibited the superiority of selectively sensitizing tumor cells for photothermal therapy (PTT) by inhibiting anaerobic glycolysis. Upon specifically targeting CD44, sequentially time-dependent DC release could be achieved by the trigger of hyaluronidase (HAase), which abundantly existed in tumor tissues. The released DC depleted the Glut1 level in tumor cells and induced a cascade effect on cellular metabolism by inhibiting glucose uptake, blocking glycolysis, decreasing ATP levels, hampering heat shock protein (HSP) expression, and ultimately leaving malignant cells out from the protection of HSPs to stress (e.g., heat), and then tumor cells were more easy to kill. Owing to the sensitization effect of GNR/HA-DC, CD44 overexpressed tumor cells could be significantly damaged by PTT with an enhanced therapeutic efficiency in vitro and in vivo.

Heat shock proteins as potential targets for protective strategies in neurodegeneration

Protein aggregates are hallmarks of nearly all age-related neurodegenerative diseases, including Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, and several polyglutamine diseases such as Huntington's disease and different forms of spinocerebellar ataxias (SCA; SCA1-3, SCA6, and SCA7). The collapse of cellular protein homoeostasis can be both a cause and a consequence of this protein aggregation. Boosting components of the cellular protein quality control system has been widely investigated as a strategy to counteract protein aggregates or their toxic consequences. Heat shock proteins (HSPs) play a central part in regulating protein quality control and contribute to protein aggregation and disaggregation. Therefore, HSPs are viable targets for the development of drugs aimed at reducing pathogenic protein aggregates that are thought to contribute to the development of so many neurodegenerative disorders.

Metazoan Hsp70-based protein disaggregases: emergence and mechanisms

Proteotoxic stresses and aging cause breakdown of cellular protein homeostasis, allowing misfolded proteins to form aggregates, which dedicated molecular machines have evolved to solubilize. In bacteria, fungi, protozoa and plants protein disaggregation involves an Hsp70•J-protein chaperone system, which loads and activates a powerful AAA+ ATPase (Hsp100) disaggregase onto protein aggregate substrates. Metazoans lack cytosolic and nuclear Hsp100 disaggregases but still eliminate protein aggregates. This longstanding puzzle of protein quality control is now resolved. Robust protein disaggregation activity recently shown for the metazoan Hsp70-based disaggregases relies instead on a crucial cooperation between two J-protein classes and interaction with the Hsp110 co-chaperone. An expanding multiplicity of Hsp70 and J-protein family members in metazoan cells facilitates different configurations of this Hsp70-based disaggregase allowing unprecedented versatility and specificity in protein disaggregation. Here we review the architecture, operation, and adaptability of the emerging metazoan disaggregation system and discuss how this evolved.

Interaction of the molecular chaperone DNAJB6 with growing amyloid-beta 42 (Aβ42) aggregates leads to sub-stoichiometric inhibition of amyloid formation

The human molecular chaperone protein DNAJB6 was recently found to inhibit the formation of amyloid fibrils from polyglutamine peptides associated with neurodegenerative disorders such as Huntington disease. We show in the present study that DNAJB6 also inhibits amyloid formation by an even more aggregation-prone peptide (the amyloid-beta peptide, Aβ42, implicated in Alzheimer disease) in a highly efficient manner. By monitoring fibril formation using Thioflavin T fluorescence and far-UV CD spectroscopy, we have found that the aggregation of Aβ42 is retarded by DNAJB6 in a concentration-dependent manner, extending to very low sub-stoichiometric molar ratios of chaperone to peptide. Quantitative kinetic analysis and immunochemistry studies suggest that the high inhibitory efficiency is due to the interactions of the chaperone with aggregated forms of Aβ42 rather than the monomeric form of the peptide. This interaction prevents the growth of such species to longer fibrils and inhibits the formation of new amyloid fibrils through both primary and secondary nucleation. A low dissociation rate of DNAJB6 from Aβ42 aggregates leads to its incorporation into growing fibrils and hence to its gradual depletion from solution with time. When DNAJB6 is eventually depleted, fibril proliferation takes place, but the inhibitory activity can be prolonged by introducing DNAJB6 at regular intervals during the aggregation reaction. These results reveal the highly efficacious mode of action of this molecular chaperone against protein aggregation, and demonstrate that the role of molecular chaperones can involve interactions with multiple aggregated species leading to the inhibition of both principal nucleation pathways through which aggregates are able to form.

Saikosaponin-D attenuates heat stress-induced oxidative damage in LLC-PK1 cells by increasing the expression of anti-oxidant enzymes and HSP72

Heat stress stimulates the production of reactive oxygen species (ROS), which cause oxidative damage in the kidney. This study clarifies the mechanism by which saikosaponin-d (SSd), which is extracted from the roots of Bupleurum falcatum L, protects heat-stressed pig kidney proximal tubular (LLC-PK1) cells against oxidative damage. SSd alone is not cytotoxic at concentrations of 1 or 3 μg/mL as demonstrated by a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. To assess the effects of SSd on heat stress-induced cellular damage, LLC-PK1 cells were pretreated with various concentrations of SSd, heat stressed at 42°C for 1 h, and then returned to 37°C for 9 h. DNA ladder and MTT assays demonstrated that SSd helped to prevent heat stress-induced cellular damage when compared to untreated cells. Additionally, pretreatment with SSd increased the activity of superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx) but decreased the concentration of malondialdehyde (MDA) in a dose-dependent manner when compared to controls. Furthermore, real-time PCR and Western blot analysis demonstrated that SSd significantly increased the expression of copper and zinc superoxide dismutase (SOD-1), CAT, GPx-1 and heat shock protein 72 (HSP72) at both the mRNA and protein levels. In conclusion, these results are the first to demonstrate that SSd ameliorates heat stress-induced oxidative damage by modulating the activity of anti-oxidant enzymes and HSP72 in LLC-PK1 cells.

Grape seed extract supplementation attenuates the heat stress-induced responses of jejunum epithelial cells in Simmental × Qinchuan steers

Grape seed extract (GSE), a rich source of polyphenols, is reported to possess antioxidant, anti-inflammatory and immunomodulatory properties. The objective of the present study was to determine whether GSE could attenuate the heat stress-induced responses of jejunum epithelial cells (JEC) in cattle. The JEC of a steer (Simmental × Qinchuan) were exposed to heat stress for 2 h in the absence (0 μg/ml) or presence (10, 20, 40 and 80 μg/ml) of GSE in the culture medium. When cultured at 40°C, JEC supplemented with GSE exhibited increased glutathione peroxidase activity (P= 0·04), viability (P= 0·004), and mRNA expression of epidermal growth factor (EGF; P= 0·03) and EGF receptor (EGFR; P = 0·01). Under the same conditions, the cells exhibited decreased mRNA expression of IL-8 (P= 0·01) and TNF-α (P= 0·03) and decreased protein concentrations of IL-1β (P= 0·02), Toll-like receptor 4 (TLR4; P= 0·04) and heat shock protein 70 (HSP70; P< 0·001). When cultured at 43°C, JEC supplemented with GSE exhibited increased catalase activity (P= 0·04), viability (P< 0·001), and mRNA expression of EGF (P< 0·001) and EGFR (P< 0·001) and decreased protein concentrations of IL-1β (P< 0·001), TLR4 (P= 0·03) and HSP70 (P< 0·001), as well as mRNA expression of IL-8 (P< 0·001), TLR4 (P= 0·002) and TNF-α (P< 0·001). Temperature × GSE concentration interactions were also observed for the concentrations of IL-1β (P< 0·001), IL-8 (P< 0·001), TNF-α (P= 0·01) and HSP70 (P= 0·04) and viability (P< 0·001) of JEC. The results of the present study indicate that GSE can attenuate the responses of JEC induced by heat stress within a certain range of temperatures.

DNAJB6 is a peptide-binding chaperone which can suppress amyloid fibrillation of polyglutamine peptides at substoichiometric molar ratios

Expanded polyglutamine (polyQ) stretches lead to protein aggregation and severe neurodegenerative diseases. A highly efficient suppressor of polyQ aggregation was identified, the DNAJB6, when molecular chaperones from the HSPH, HSPA, and DNAJ families were screened for huntingtin exon 1 aggregation in cells (Hageman et al. in Mol Cell 37(3):355-369, 2010). Furthermore, also aggregation of polyQ peptides expressed in cells was recently found to be efficiently suppressed by co-expression of DNAJB6 (Gillis et al. in J Biol Chem 288:17225-17237, 2013). These suppression effects can be due to an indirect effect of DNAJB6 on other cellular components or to a direct interaction between DNAJB6 and polyQ peptides that may depend on other cellular components. Here, we have purified the DNAJB6 protein to investigate the suppression mechanism. The purified DNAJB6 protein formed large heterogeneous oligomers, in contrast to the more canonical family member DNAJB1 which is dimeric. Purified DNAJB6 protein, at substoichiometric molar ratios, efficiently suppressed fibrillation of polyQ peptides with 45°Q in a thioflavin T fibrillation. No suppression was obtained with DNAJB1, but with the closest homologue to DNAJB6, DNAJB8. The suppression effect was independent of HSPA1 and ATP. These data, based on purified proteins and controlled fibrillation in vitro, strongly suggest that the fibrillation suppression is due to a direct protein-protein interaction between the polyQ peptides and DNAJB6 and that the DNAJB6 has unique fibrillation suppression properties lacking in DNAJB1. Together, the data obtained in cells and in vitro support the view that DNAJB6 is a peptide-binding chaperone that can interact with polyQ peptides that are incompletely degraded by and released from the proteasome.

The DNAJB6 and DNAJB8 protein chaperones prevent intracellular aggregation of polyglutamine peptides

Fragments of proteins containing an expanded polyglutamine (polyQ) tract are thought to initiate aggregation and toxicity in at least nine neurodegenerative diseases, including Huntington's disease. Because proteasomes appear unable to digest the polyQ tract, which can initiate intracellular protein aggregation, preventing polyQ peptide aggregation by chaperones should greatly improve polyQ clearance and prevent aggregate formation. Here we expressed polyQ peptides in cells and show that their intracellular aggregation is prevented by DNAJB6 and DNAJB8, members of the DNAJ (Hsp40) chaperone family. In contrast, HSPA/Hsp70 and DNAJB1, also members of the DNAJ chaperone family, did not prevent peptide-initiated aggregation. Intriguingly, DNAJB6 and DNAJB8 also affected the soluble levels of polyQ peptides, indicating that DNAJB6 and DNAJB8 inhibit polyQ peptide aggregation directly. Together with recent data showing that purified DNAJB6 can suppress fibrillation of polyQ peptides far more efficiently than polyQ expanded protein fragments in vitro, we conclude that the mechanism of DNAJB6 and DNAJB8 is suppression of polyQ protein aggregation by directly binding the polyQ tract.

Reassessment of teratogenic risk from antenatal ultrasound

Science has shown that risk of cavitation and hyperthermia following prenatal ultrasound exposure is relatively negligible provided intensity, frequency, duration of exposure, and total numbers of exposures are safely limited. However, noncavitational mechanisms have been poorly studied and occur within what are currently considered “safe” levels of exposure. To date, the teratogenic capacity of noncavitational effectors are largely unknown, although studies have shown that different forms of ultrasound-induced hydraulic forces and pressures can alter membrane fluidity, proliferation, and expression of inflammatory and repair markers. Loose regulations, poor end user training, and unreliable ultrasound equipment may also increase the likelihood of cavitation and hyperthermia during prenatal exposure with prolonged durations and increased intensities. The literature suggests a need for tighter regulations on the use of ultrasound and further studies into its teratogenicity.

Thermotolerance does not reduce the size or remodeling of radiofrequency lesions in the rat myocardium

PURPOSE

Late lesion extension may be involved in the genesis of delayed radiofrequency (RF) effects. Because RF lesion is thermally mediated, we hypothesized that induction of heat shock response (thermotolerance) would modulate lesion healing. We evaluated the effects of thermotolerance on the dimensions and remodeling of RF lesions in a rat model of heart failure.

METHODS

Wistar rats (weight 300 g) subjected to heat stress (n = 22, internal temperature of 42 °C for 10 min) were compared to controls (n = 22, internal temperature of 37 °C for 10 min). After 48 h (peak of HSP70 myocardial concentration), a modified unipolar RF lesion (customized catheter, tip 4.5 mm in diameter; 12 W; 10 s) was created on the left ventricular free wall. Animals were sacrificed 2 h (n = 10 per group) and 4 weeks (n = 12 per group) after ablation for lesion analysis. An echocardiogram was obtained at 4 weeks.

RESULTS

There was no difference between groups regarding the size of acute (controls 27 ± 2 vs. treated 27 ± 3 mm(2)) and chronic lesions (controls 17 ± 1 vs. treated 19 ± 1 mm(2)). Histology of lesions did not differ between groups. The echocardiogram revealed dilation of the cavities and moderate systolic dysfunction without difference between groups. Acute lesion dimensions were similar between control and treated animals over time (ablation undertaken 3, 12, 24, 48, and 72 h after hyperthermia) and also using a conventional ablation catheter (50 °C; 15 W; 10 s).

CONCLUSION

Thermotolerance does not reduce the size or remodeling of RF lesions in the rat myocardium.

The phosphorylation of the heat shock factor as a modulator for the heat shock response

The heat shock response is a well-conserved defence mechanism against the accumulation of misfolded proteins due to prolonged elevated heat. The cell responds to heat shock by raising the levels of heat shock proteins (hsp), which are responsible for chaperoning protein refolding. The synthesis of hsp is highly regulated at the transcription level by specific heat shock (transcription) factors (hsf). One of the regulation mechanisms is the phosphorylation of hsf's. Experimental evidence shows a connection between the hyper-phosphorylation of hsfs and the transactivation of the hsp-encoding genes. In this paper, we incorporate several (de)phosphorylation pathways into an existing well-validated computational model of the heat shock response. We analyze the quantitative control of each of these pathways over the entire process. For each of these pathways we create detailed computational models which we subject to parameter estimation in order to fit them to existing experimental data. In particular, we find conclusive evidence supporting only one of the analyzed pathways. Also, we corroborate our results with a set of computational models of a more reduced size.

Calibrating the photo-thermal response of magneto-fluorescent gold nanoshells

We report the photothermal response and Near Infrared (NIR) imaging sensitivities of magneto-fluorescent silica core gold nanocomplexes designed for molecular image guided thermal therapy of cancer. Approximately 160 nm Silica core gold nanoshells were designed to provide NIR fluorescent and Magnetic Resonance (MR) contrast by incorporating FDA approved dye indocyanine green (ICG) and iron-oxide within an outer silica epilayer. The imaging and therapeutic sensitivity, and the stability of fluorescence contrast for 12 microliters of suspension (containing approximately 7.9 × 10(8) or 1.3 femtoMole nanoshells) buried at depths of 2-8 mm in tissue mimicking scattering media is reported.

Stochastic modelling of the eukaryotic heat shock response

The heat shock response (HSR) is a highly evolutionarily conserved defence mechanism allowing the cell to promptly react to elevated temperature conditions and other forms of stress. It has been subject to intense research for at least two main reasons. First, it is considered a promising candidate for deciphering the engineering principles underlying regulatory networks. Second, heat shock proteins (main actors of the HSR) play crucial role in many fundamental cellular processes. Therefore, profound understanding of the heat shock response would have far-reaching ramifications for the cell biology. Recently, a new deterministic model of the eukaryotic heat shock response has been proposed in the literature. It is very attractive since it consists of only the minimum number of components required by any functional regulatory network, while yet being capable of biological validation. However, it admits small molecule populations of some of the considered metabolites. In this paper a stochastic model corresponding to the deterministic one is constructed and the outcomes of these two models are confronted. The aim with this comparison is to show that, in the case of the heat shock response, the approximation of a discrete system with a continuous model is a reasonable approach. This is not always the truth, especially when the numbers of molecules of the considered species are small. By making the effort of performing and analysing 1000 stochastic simulations, we investigate the range of behaviour the stochastic model is likely to exhibit. We demonstrate that the obtained results agree well with the dynamics displayed by the continuous model, which strengthens the trust in the deterministic description. A proof of the existence and uniqueness of the stationary distribution of the Markov chain underlying the stochastic model is given. Moreover, the obtained view of the stochastic dynamics and the performed comparison to the outcome of the continuous formulation provide more insight into the dynamics of the heat shock response mechanism.

Heat-shock responsive genes identified and validated in Atlantic cod (Gadus morhua) liver, head kidney and skeletal muscle using genomic techniques

BACKGROUND

Daily and seasonal changes in temperature are challenges that fish within aquaculture settings cannot completely avoid, and are known to elicit complex organismal and cellular stress responses. We conducted a large-scale gene discovery and transcript expression study in order to better understand the genes that are potentially involved in the physiological and cellular aspects of stress caused by heat-shock. We used suppression subtractive hybridization (SSH) cDNA library construction and characterization to identify transcripts that were dysregulated by heat-shock in liver, skeletal muscle and head kidney of Atlantic cod. These tissues were selected due to their roles in metabolic regulation, locomotion and growth, and immune function, respectively. Fish were exposed for 3 hours to an 8 degrees C elevation in temperature, and then allowed to recover for 24 hours at the original temperature (i.e. 10 degrees C). Tissue samples obtained before heat-shock (BHS), at the cessation of heat-shock (CS), and 3, 12, and 24 hours after the cessation of heat-shock (ACS), were used for reciprocal SSH library construction and quantitative reverse transcription - polymerase chain reaction (QPCR) analysis of gene expression using samples from a group that was transferred but not heat-shocked (CT) as controls.

RESULTS

We sequenced and characterized 4394 ESTs (1524 from liver, 1451 from head kidney and 1419 from skeletal muscle) from three "forward subtracted" libraries (enriched for genes up-regulated by heat-shock) and 1586 from the liver "reverse subtracted" library (enriched for genes down-regulated by heat-shock), for a total of 5980 ESTs. Several cDNAs encoding putative chaperones belonging to the heat-shock protein (HSP) family were found in these libraries, and "protein folding" was among the gene ontology (GO) terms with the highest proportion in the libraries. QPCR analysis of HSP90alpha and HSP70-1 (synonym: HSPA1A) mRNA expression showed significant up-regulation in all three tissues studied. These transcripts were more than 100-fold up-regulated in liver following heat-shock. We also identified HSP47, GRP78 and GRP94-like transcripts, which were significantly up-regulated in all 3 tissues studied. Toll-like receptor 22 (TLR22) transcript, found in the liver reverse SSH library, was shown by QPCR to be significantly down-regulated in the head kidney after heat-shock.

CONCLUSION

Chaperones are an important part of the cellular response to stress, and genes identified in this work may play important roles in resistance to thermal-stress. Moreover, the transcript for one key immune response gene (TLR22) was down-regulated by heat-shock, and this down-regulation may be a component of heat-induced immunosuppression.

Silkworm thermal biology: a review of heat shock response, heat shock proteins and heat acclimation in the domesticated silkworm, Bombyx mori

Heat shock proteins (HSPs) are known to play ecological and evolutionary roles in this postgenomic era. Recent research suggests that HSPs are implicated in cardiovascular biology and disease development, proliferation and regulation of cancer cells, cell death via apoptosis, and several other key cellular functions. These activities have generated great interest amongst cell and molecular biologists, and these biologists are keen to unravel other hitherto unknown potential functions of this group of proteins. Consequently, the biological significance of HSPs has led to cloning and characterization of genes encoding HSPs in many organisms including the silkworm, Bombyx mori L. (Lepidoptera: Bombycidae). However, most of the past investigations in B. mori were confined to expression of HSPs in tissues and cell lines, whereas information on their specific functional roles in biological, physiological, and molecular processes is scarce. Naturally occurring or domesticated polyvoltines (known to be the tropical race) are more resistant to high temperatures and diseases than bi- or univoltines (temperate races). The mechanism of ecological or evolutionary modification of HSPs during the course of domestication of B. mori - particularly in relation to thermotolerance in geographically distinct races/strains - is still unclear. In addition, the heat shock response, thermal acclimation, and hardening have not been studied extensively in B. mori compared to other organisms. Towards this, recent investigations on differential expression of HSPs at various stages of development, considering the concept of the whole organism, open ample scope to evaluate their biological and commercial importance in B. mori which has not been addressed in any of the representative organisms studied so far. Comparatively, heat shock response among different silkworm races/strains of poly-, bi-, and univoltines varies significantly and thermotolerance increases as the larval development proceeds. Hence, this being the first review in this area, an attempt has been made to collate all available information on the heat shock response, HSPs expression, associated genes, amino acid sequences, and acquired/unacquired thermotolerance. The aim is to present this as a valuable resource for addressing the gap in knowledge and understanding evolutionary significance of HSPs between domesticated (B. mori) and non-domesticated insects. It is believed that the information presented here will also help researchers/breeders to design appropriate strategies for developing novel strains for the tropics.

Supraphysiological thermal injury in different human bladder carcinoma cell lines

Depending on the duration of exposure to supraphysiological temperatures, cellular proteins and organelles can suffer from structural alternations and irreversible denaturation, which may induce cell death. The thermotolerance of three human urinary bladder carcinoma cell lines, TSGH-8301, J82 and TCC-SUP (cytological grade 2, 3 and 4, respectively), was investigated in the present study. A home-made heating stage was used to provide a constant temperature for different cell lines of bladder carcinoma. The experimental data showed that the TCC-SUP and TSGH-8301 cells exhibited the lowest and highest thermotolerances, respectively, while J82 cells were intermediate. Moreover, the differences in the thermotolerances for the TSGH-8301 and J82 cells are significant when the supraphysiological temperature is higher than 43 degrees C. As for TSGH-8301 and TCC-SUP cells, the thermotolerances are significantly different for all of the thermal treatments tested. Furthermore, the thermotolerances of J82 and TCC-SUP are significantly different when the cells are exposed to a temperature less than 50 degrees C for longer than 2 min. Overall, the results suggest that the high cytological grade of the cell line of bladder cancer exhibits a low thermotolerance. The kinematic parameters of the activation energy and frequency factor for bladder cancer cell lines with different cytological grades were also quantitatively evaluated in this work.

The heat-induced gamma-H2AX response does not play a role in hyperthermic cell killing

PURPOSE

The goal of this study was to determine whether the heat-induced formation of gamma-H2AX foci is involved in hyperthermic cell killing.

MATERIALS AND METHODS

The heat-induced gamma-H2AX response was determined in cells exhibiting various degrees of heat sensitivity. The panel of cells tested included cells that are transiently thermotolerant, permanently heat resistant, permanently heat sensitive, and permanently resistant to oxidative stress. Cells exposed to non-thermal environmental conditions that lead to protection from, or sensitization to, heat were also tested. The heat sensitivity of cells in which H2AX was knocked out was also ascertained.

RESULTS

The protein synthesis independent state of thermotolerance, but not the protein synthesis dependent state of thermotolerance, was found to be involved in the attenuation of the gamma-H2AX response in thermotolerant cells. The initial magnitude of the gamma-H2AX response was found to be the same in all cell lines with altered heat sensitivity. Furthermore, no differences in the resolution of gamma-H2AX foci were found among the cell lines tested. We also found that H2AX knock-out cells were not more heat sensitive.

CONCLUSIONS

We conclude that the heat-induced gamma-H2AX response does not play a role in heat-induced cell killing, thereby adding further evidence that the heat-induced gamma-H2AX foci are not due to DNA double strand breaks.

Alterations in heat-induced radiosensitization accompanied by nuclear structure alterations in Chinese hamster cells

This paper examined heat-induced radiosensitization in two Chinese hamster heat-resistant cell lines, HR-1 and OC-14, that were isolated from the same wild-type HA-1 cell line. It found a reduction of the magnitude of heat-induced radiosensitization after exposure to 43 degrees C in both HR-1 and OC-14 cells and a similar reduction after exposure to 45 degrees C in HR-1 cells, but not in OC-14 cells. The effect of heat exposure on a class of ionizing radiation-induced DNA damage that inhibits the ability of nuclear DNA to undergo super-coiling changes was also studied using the fluorescent halo assay in these three cell lines. Wild type cells exposed to either 43 or 45 degrees C before irradiation had a DNA rewinding ability that was intermediate between control and unheated cells, a phenomenon previously described as a masking effect. This masking effect was significantly reduced in HR-1 cells exposed to either 43 or 45 degrees C or in OC-14 cells exposed to 43 degrees C under conditions that heat-induced radiosensitization was reduced. In contrast, the masking effect was not altered in OC-14 cells exposed to 45 degrees C, conditions under which heat-induced radiosensitization was similar to that observed in wild-type HA-1 cells. These results suggest that a reduction in the masking effect is associated with a reduction of the magnitude of heat-induced radiosensitization in the HR-1 and OC-14 heat-resistant cell lines. The reduction of the masking effect in the cell lines resistant to heat-induced radiosensitization was associated with neither a reduction in the magnitude of the heat-induced increase in total nuclear protein content nor major differences in the protein profiles of the nucleoids isolated from heated cells.

Role of nuclear protein denaturation and aggregation in thermal radiosensitization

Hyperthermia at temperatures above 41 degrees C denatures a set of thermolabile cellular proteins located in all parts of the cell. Non-histone nuclear proteins, including those comprising the nuclear matrix, appear to be particularly thermolabile. Heating isolated nuclear matrices of Chinese hamster lung (CHL) V79 cells to 46 degrees C at 1 degree C/min results in approximately 15% denaturation. Protein unfolding during denaturation exposes buried hydrophobic residues, which increases protein-protein interactions and results in the co-aggregation of denatured thermolabile proteins and native, aggregative-sensitive nuclear proteins. This aggregated protein, the majority of which is native, is insoluble and resistant to extraction during isolation of nuclei and is responsible for the increased protein content, usually expressed as an increased protein:DNA ratio, of nuclei isolated from heated cells. A large fraction of the aggregated protein is found to be associated with the nuclear matrix, distributed throughout the fibre network and nucleolus. Three general consequences of nuclear protein denaturation and aggregation of relevance to cellular damage are: (1) protein (enzyme) inactivation, both direct inactivation of thermolabile proteins and indirect inactivation due to co-aggregation; (2) reduced accessibility and altered physical properties of DNA due to masking by aggregated protein; and (3) protein redistribution into and out of the nucleus. Functional impairment of the nucleus appears to be due to one or a combination of these basic mechanisms.

Protective effects of Hsp70 on the structure and function of SERCA2a expressed in HEK-293 cells during heat stress

Heat shock protein 70 (Hsp70) can physically interact with and prevent thermal inactivation of sarco(endo)plasmic reticulum Ca(2+)-ATPase (SERCA) 1a, the SERCA isoform expressed in adult fast-twitch skeletal muscle. This study examined whether Hsp70 could physically interact with and prevent thermal inactivation of SERCA2a, the SERCA isoform expressed in heart. HEK-293 cells were cotransfected with cDNAs encoding human Hsp70 and rabbit SERCA2a (S2a/Hsp70). Cells cotransfected with SERCA2a cDNA and pMT2 (S2a/pMT2) were used as control. One-half of the cells was heat shocked at 40 degrees C for 1 h (HS), and one-half was maintained at 37 degrees C before harvesting the cells and isolating microsomes. Western blot analysis showed that Hsp70 and SERCA2a were colocalized in the microsomal fraction. The levels of Hsp70 were approximately fivefold higher (P < 0.05) in S2a/Hsp70 compared with S2a/pMT2 and approximately twofold higher (P < 0.05) following HS in all cells. Coimmunoprecipitation demonstrated that Hsp70 directly binds to SERCA2a. Following HS, maximal SERCA2a activity was reduced ( approximately 52%, P < 0.05) in S2a/pMT2 but was increased ( approximately 33%, P < 0.05) in S2a/Hsp70. Thermal inactivation of SERCA2a in S2a/pMT2 was associated with decreased ( approximately 49%, P < 0.05) binding capacity for fluorescein isothiocyanate (FITC) and increased carbonyl ( approximately 42%, P < 0.05) and nitrotyrosine ( approximately 40%, P < 0.05) levels in SERCA2a. By contrast, the HS-induced increase in maximal SERCA2a activity observed in S2a/Hsp70 corresponded with no change (P > 0.05) in FITC-binding capacity and reductions in carbonyl ( approximately 40%, P < 0.05) and nitrotyrosine ( approximately 23%, P < 0.05) levels in SERCA2a compared with S2a/pMT2. These results show that Hsp70 forms a protective interaction with SERCA2a during HS actually reducing oxidation and nitrosylation of SERCA2a thus increasing its maximal activity.

Interaction between Hsp70 and the SR Ca2+pump: a potential mechanism for cytoprotection in heart and skeletal muscle

The overexpression of heat shock protein 70 (Hsp70) provides cytoprotection to cells, making them resistant to otherwise lethal levels of stress. In this review, the role Hsp70 plays in protecting both cardiac and skeletal muscle against the pathophysiological effects of oxidative stress are examined, with a focus on the molecular basis for the cytoprotective effects of Hsp70. The ability of Hsp70 to maintain cell survival undoubtedly involves the regulation of multiple steps within apoptotic pathways, but could also involve the regulation of key upstream mediators of apoptosis (i.e., oxidative stress, Ca2+overload). Hsp70 can stabilize the structure and function of both the skeletal muscle and cardiac Ca2+pump under heat stress conditions. Given that Ca2+overload has long been implicated in cell death, Hsp70 might protect muscle cells by maintaining cellular Ca2+homeostasis, thereby preventing the initiation of apoptosis. The functional interaction between Hsp70 and Ca2+pumps might also promote improvements in muscle contractility after exposure to oxidative stress.