Transient Heat Shock Research Articles

Atmospheric plasma sprayed W coating/Detonation sprayed W-steel composite coating/steel substrate-based coating system for the tokamak first wall

To study the manufacturing method of the tungsten armored first wall of tokamak devices, the W-316 L steel (W-SS) composite coatings were fabricated on 316 L steel substrates by detonation spraying (DS) as the interlayer of pure tungsten coatings manufactured by atmospheric plasma spraying (APS). The main characteristics and performance under transient heat shocks of the APS W/DS W-SS /substrate-based three-layer coating system were studied and compared with the APS W/substrate-based coating system. The results showed the porosity of the DS W-SS was about 1.9% with most of the pores smaller than 70 nm. In contrast, the porosity of the APS W reached about 8.6% and most of the pores were up to hundreds of nanometers. The bonding strength tests proved that both the adhesions of APS W to DS W-SS and DS W-SS to the substrate were much higher (almost 1.5 times) than the adhesion of APS W to the substrates. The three-layer specimens performed much better than the APS W/substrate specimens during the transient heat shock tests as expected. Besides, a special microstructure variation occurred on the three-layer specimens before its damage under the tests which was considered helpful to prolong its life-span under high heat flux. In a conclusion, the DS W-SS interlayer improved the service performance of the APS W/substrate-based coating significantly and demonstrates its potential for application in current tokamak experimental devices.

β-II tubulin isotype directs stiffness and differentiation of neuroblastoma SH-SY5Y cells.

β-tubulin isotypes regulate the structure and bundling of microtubule (MT) lattice, its dynamics, and resulting functions. They exhibit differential tissue expression, varying due to physical and biochemical cues. In this work, we investigated the effect of transient heat shock at 42°C on the nuclear and cytoplasmic stiffness of SH-SY5Y neuroblastoma cells through atomic force microscopy. Moreover, the variations in the expression of β-tubulin isotypes as a heat shock response were also monitored. The heat-exposed cells endured a recovery at 37°C for 24h and they manifested an increase of cytoplasmic stiffness by 130 ± 25% with respect to untreated controls. The expression of β-II tubulin isotype in heat-recovered cells is augmented by 51 ± 5% whereas the levels of total tubulin and β-III tubulin isotype remain unaltered. Upon depletion of β-II tubulin isotype using shRNA, the increase in cytoplasmic stiffness was dampened. However, it remained unaffected upon depletion with β-III tubulin isotype shRNA. This features the role of the β-II tubulin isotype in regulating cellular stiffness. In addition, neuroblastoma SH-SY5Y cells undergo differentiation by initiating neuritogenesis and prior evidence suggests the indispensable role of β-II tubulin isotype in this process. The heat-recovered cells which expressed higher levels of β-II tubulin isotype expedited the differentiation process in 3-day which was around 5-day for control cells, however, upon depletion of β-II tubulin isotype, the cells almost lost their differentiation potential. Altogether, this work highlights the role of β-II tubulin isotype as a biomarker for cellular stiffness.

Lack of peroxisomal catalase affects heat shock response in Caenorhabditis elegans.

Exact mechanisms of heat shock-induced lifespan extension, although documented across species, are still not well understood. Here, we show that fully functional peroxisomes, specifically peroxisomal catalase, are needed for the activation of canonical heat shock response and heat-induced hormesis in Caenorhabditis elegans Although during heat shock, the HSP-70 chaperone is strongly up-regulated in the WT and in the absence of peroxisomal catalase (ctl-2(ua90)II), the small heat shock proteins display modestly increased expression in the mutant. Nuclear foci formation of HSF-1 is reduced in the ctl-2(ua90)II mutant. In addition, heat-induced lifespan extension, observed in the WT, is absent in the ctl-2(ua90)II strain. Activation of the antioxidant response and pentose phosphate pathway are the most prominent changes observed during heat shock in the WT worm but not in the ctl-2(ua90)II mutant. Involvement of peroxisomes in the cell-wide cellular response to transient heat shock reported here gives new insight into the role of organelle communication in the organism's stress response.

Application of 2D coupled algorithms to thermally induced dynamics of temperature-dependent nanocomposite cylindrical panels under transient heat shock

The current investigation examines the thermal wave motion in a functionally graded cylindrical panel with carbon nanotubes exposed to rapid surface heating. The equivalent temperature-dependent material properties of the nanocomposite media are achieved by employing a modified homogenization technique. Due to the time-dependent nature of the applied heat function, the heat conduction equation is calculated transiently. Furthermore, due to the temperature dependency of the properties, the heat conduction equation is nonlinear and is solved by the combined finite-difference and Picard methods. The Crank–Nicolson time solving scheme is utilized to determine the temperature profile of each composite system point across time. The first-order shear deformation and Donnell strain theories regulate the system’s motion equations. The combined 2D generalized differential quadrature and Newmark procedures are implemented to numerically simulate the composite structure’s physical variables. Following verification, the effects of composite media parameters and panel characteristics on the shell reaction subjected to thermal shock are examined.

Tetrodotoxin prevents heat-shock induced granule cell dispersion in hippocampal slice cultures

Granule cell dispersion (GCD) has been associated as a pathological feature of temporal lobe epilepsy (TLE). Early-life epileptiform activity such as febrile seizures has been proposed to have a causal link to developing chronic TLE. During postnatal development, the hippocampus may be particularly vulnerable to hyperexcitability-induced insults since neuronal migration and differentiation are still ongoing in the hippocampus. Further, the extracellular matrix (ECM), here in particular the protein reelin, has been implicated in the pathophysiology of GCD. Thus, loss of reelin-expressing cells, Cajal-Retzius cells and subsets of interneurons, may be related to GCD. To study the possible role of febrile seizures, we previously induced GCD in vitro by subjecting hippocampal slice cultures to a transient heat-shock, which was not accompanied by loss of Cajal-Retzius cells. In order to examine the mechanisms involved in heat-shock induced GCD, the present study aimed to determine whether such dispersion could be prevented by blocking cellular electrical activity. Here we show that the extent of heat-shock induced GCD could be significantly reduced by treatment with the sodium channel blocker tetrodotoxin (TTX), suggesting that electrical activity is an important factor involved in heat-shock induced GCD.

Preliminary studies on detonation sprayed W/W-steel composite coating materials on steel substrates for the first wall of blanket

The mismatch of the thermo-mechanical properties of tungsten and steel would lead to large thermal stress between detonation sprayed (DS) tungsten coatings and steel substrates. DS W-steel composite coatings were prepared on 316 L stainless steel (SS) substrates as the interlayer of DS-W coatings to solve this issue. The DS-W coatings manufactured on 316 L SS substrates without interlayers were used for comparing. The surface and cross-section morphologies showed the composite coating material was dense steel lamellas-stacked structure in which tungsten particles dispersed homogeneously. The EDS and XRD results showed the composite coating was consisted of three different textures: W, SS and W-SS compound alloy. But the tungsten content in the coating was lower than the expected 50 vol% due to the low deposition efficiency of the tungsten powders. The Vickers hardness of the composite coating was 577– 647 HV which was between that of the DS-W and the SS substrate. The bonding strengths of the DS W/W-SS/SS substrate three-layer coating samples and the DS-W/SS substrate coating samples were about 61.33 MPa and 52.45 MPa, respectively. Besides, the three-layer samples had better performance under the transient heat shock tests than that of the DS-W/SS substrate samples. All these results proved the addition of the DS W-SS composite interlayers improved the overall properties of the DS-W/SS substrate system. The relatively low tungsten content in the composite coatings should be optimized to further improve the performance of the three-layer coating system in the following.

Transcriptomic Adaptation of Legionella pneumophila to Transient Heat Shock

A natural inhabitant of freshwater microbial ecology, Legionella pneumophila is an opportunistically pathogenic bacteria that has found a niche in hot water distribution systems (HWDS) where it challenges hospitals with the spread of nosocomial infection. Superheat-and-flush is a high-temperature pasteurization which can be temporarily effective, but systems often test positive for contamination soon after pasteurization. Because of the centrality of pasteurization in HWDS sanitation schemes, an understanding of the L. pneumophila intrinsic heat shock response may help improve the strategies used to counter its proliferation and ability to trigger nosocomial outbreaks. We tested a group of strains to assess differences in heat shock tolerance between clinical, laboratory, and environmental strains of different origin. The transcriptome of a model Philadelphia-1 L. pneumophila strain in response to heat shock was determined using microarray as an exploratory analysis of the heat shock response: 401 genes were induced, including genes involved in determining protein fate and ribosome biosynthesis while 43 genes were downregulated. Mutants of 3 individual genes were tested to find their direct effects on heat shock tolerance. Deletions of dksA or rpoS, genes involved in the regulation of life cycle switching and important for surviving long-term nutrient deprivation in freshwater lowered heat shock tolerance, suggesting an overlap in the pathways required to tolerate these stressors. Surprisingly, the deletion of htpG, the 90-kilodalton heat shock protein, was found to increase the ability to survive under transient heat shock. Taken altogether, our results show that L. pneumophila exhibits most components of the conserved bacterial heat shock response. Based on this exploratory transcriptomic study, we have provided data that can act as a platform for the research of L. pneumophila's survival to pasteurization in hot water systems.

Preliminary studies on the main characteristics and transient heat shock performances of detonation sprayed tungsten coatings on 316 L steel substrates

Detonation spraying (DS) method was used to deposit tungsten coatings on 316 L steel substrates for the potential usage of the first wall of blanket in nuclear fusion devices. The main characteristics and anti-transient heat shock performances of the DS-W coatings were studied and compared with that of the atmospheric plasma sprayed tungsten (APS-W) coatings. The results showed that the DS-W coating had a very dense structure with its porosity of about 0.97%. The oxygen content of the DS-W coating that roughly detected with an energy dispersive spectrometer was much lower than that of the APS-W coating and the initial tungsten powders. It was considered that this result should be due to the unexpectedly introduced W2C during the DS process. These W2C would act as deoxidation agent and decrease the oxygen content in the coating. The microhardness of the DS-W coatings was much higher than that of the APS-W coatings and the pure tungsten bulk. It was analyzed that the dense structure, the reinforcement by W2C and the fine-grained strengthening effect during the DS process were responsible for this result. Furthermore, the DS-W/steel specimens exhibited excellent bonding strength and transient heat shock resistance. After having been tested under 3.5 MJ/m2 of transient heat loads, the DS-W/steel sample was still on a good status without obvious damages. Besides, it was believed that the overall performance of the DS-W coatings should be further improved through appropriate post-processing methods. As a conclusion, the DS-W coating demonstrated outstanding properties and its great potential for the application in plasma-facing materials.

A Genomic Catalog of Stress Response Genes in Anaerobic Fungi for Applications in Bioproduction.

Anaerobic fungi are a potential biotechnology platform to produce biomass-degrading enzymes. Unlike model fungi such as yeasts, stress responses that are relevant during bioprocessing have not yet been established for anaerobic fungi. In this work, we characterize both the heat shock and unfolded protein responses of four strains of anaerobic fungi (Anaeromyces robustus, Caecomyces churrovis, Neocallimastix californiae, and Piromyces finnis). The inositol-requiring 1 (Ire1) stress sensor, which typically initiates the fungal UPR, was conserved in all four genomes. However, these genomes also encode putative transmembrane kinases with catalytic domains that are similar to the metazoan stress-sensing enzyme PKR-like endoplasmic reticulum kinase (PERK), although whether they function in the UPR of anaerobic fungi remains unclear. Furthermore, we characterized the global transcriptional responses of Anaeromyces robustus and Neocallimastix californiae to a transient heat shock. Both fungi exhibited the hallmarks of ER stress, including upregulation of genes with functions in protein folding, ER-associated degradation, and intracellular protein trafficking. Relative to other fungi, the genomes of Neocallimastigomycetes contained the greatest gene percentage of HSP20 and HSP70 chaperones, which may serve to stabilize their asparagine-rich genomes. Taken together, these results delineate the unique stress response of anaerobic fungi, which is an important step toward their development as a biotechnology platform to produce enzymes and valuable biomolecules.

Molecular characterization of Hsf1 as a master regulator of heat shock response in the thermotolerant methylotrophic yeast Ogataea parapolymorpha.

Ogataea parapolymorpha (Hansenula polymorpha DL-1) is a thermotolerant methylotrophic yeast with biotechnological applications. Here, O. parapolymorpha genes whose expression is induced in response to heat shock were identified by transcriptome analysis and shown to possess heat shock elements (HSEs) in their promoters. The function of O. parapolymorpha HSF1 encoding a putative heat shock transcription factor 1 (OpHsf1) was characterized in the context of heat stress response. Despite exhibiting low sequence identity (26%) to its Saccharomyces cerevisiae homolog, OpHsf1 harbors conserved domains including a DNA binding domain (DBD), domains involved in trimerization (TRI), transcriptional activation (AR1, AR2), transcriptional repression (CE2), and a C-terminal modulator (CTM) domain. OpHSF1 could complement the temperature sensitive (Ts) phenotype of a S. cerevisiae hsf1 mutant. An O. parapolymorpha strain with an H221R mutation in the DBD domain of OpHsf1 exhibited significantly retarded growth and a Ts phenotype. Intriguingly, the expression of heat-shock-protein-coding genes harboring HSEs was significantly decreased in the H221R mutant strain, even under non-stress conditions, indicating the importance of the DBD for the basal growth of O. parapolymorpha. Notably, even though the deletion of C-terminal domains (ΔCE2, ΔAR2, ΔCTM) of OpHsf1 destroyed complementation of the growth defect of the S. cerevisiae hsf1 strain, the C-terminal domains were shown to be dispensable in O. parapolymorpha. Overexpression of OpHsf1 in S. cerevisiae increased resistance to transient heat shock, supporting the idea that OpHsf1 could be useful in the development of heat-shock-resistant yeast host strains.

Indirect Detection of Ligand Binding by Thermal Melt Analysis.

A thermal shift assay (TSA) involves measuring the effect of a compound on the thermal stability of a protein as an indirect measure of ligand binding. In this chapter, we provide a protocol for a conventional TSA with recombinant/purified proteins using differential scanning fluorimetry (DSF), followed by a protocol for a Cellular Thermal Shift Assay (CETSA®), which measures the soluble cellular protein remaining after a transient heat shock of live cells to detect intracellular ligand binding.

Role of TRP channels and HSPs in thermal stress response in the aphid parasitoid Aphelinus asychis (Hymenoptera: Aphelinidae)

Aphelinus asychis is an important aphid endoparasitoid. Under field and greenhouse conditions, high temperature is one of the factors limiting the application of A. asychis for biological pest control. To explore the potential role of transient receptor potential (TRP) channels and heat shock proteins (HSPs) in this process, we identified 11 genes encoding TRP channels and nine genes encoding HSPs. Three proteins (AasyTRPA5, AasyPyrexia, AasyPainless) that belong to transient receptor potential ankyrin (TRPA) subfamily and nine HSPs are involved in the response to high temperature. We also investigated the survival of A. asychis and the response of the identified TRP channels and HSPs to high temperature. The results showed that the maximum temperature that allowed A. asychis survival was approximately 41°C; females had higher survival rates than that of the males at 40 and 41°C. Short-term heat-shock resulted in increased expression of Aasyshsp in males, and Aasyhsp40, Aasyhsp68, Aasyhsp70-4, Aasyhsp70-5 and Aasyhsp90 were upregulated and then downregulated, whereas Aasyhsp70-3 was upregulated at 41°C. Moreover, Aasyhsp40 and Aasyhsp90 showed higher expression levels in females, while Aasyshsp and Aasyhsp70-3 presented opposite expression patterns. At temperature above 35°C, expression of AasyPyrexia in females was significant higher than that in males, whereas AasyPainless and AasyTRPA5 presented higher expression in males at 40 and 41°C, respectively. Altogether, these results indicate that protection against thermal stress in A. asychis is coordinated by TRP channels and HSPs. These findings provide a basis for understanding the potential mechanism of A. asychis in response to high temperatures.

Generalized thermoelastic diffusion problems with fractional order strain

The studies of the coupling of thermodiffusion and mechanical deformation in solids have aroused great interests with miniaturization of the micro/nano-electromechanical devices and wide application of ultrafast heating technologies. In such situation, it is commonly accompanied with high heat/diffusion flux and thermal/diffusion induced stress accordingly. So far, although there have been many developments and extensions of research and theorizing within the generalized thermoelastic diffusion problems, these theoretical formulations are only applicable when the strain rate is assumed to be relatively small, but this is questionable under ultrafast heating condition. The present work aims to investigate generalized thermoelastic diffusion problems with fractional order strain within the extended thermodynamic framework. For numerical evaluation, the analytical model of a sandwich structure with ideal interfacial conditions is investigated whilst its bounding surfaces are subjected to symmetrical transient heat and chemical potential shock loads. From numerical results, the effects of the fractional order parameters and material characteristic parameters of each layer on structural transient thermo-elasto-diffusive responses are also analyzed and discussed, which is expected to provide a comprehensive understanding on thermoelastic diffusive coupling and optimal design of sandwich structures under extreme fast heating condition.

Transient window of resilience during early development minimizes teratogenic effects of heat in zebrafish embryos.

Background: Transient heat shock during early development is an established experimental paradigm for doubling the genome of the zebrafish zygote, which has practical applications in expedited identification of recessive mutations in genetic screens. Despite the simplicity of the strategy and the genetic tractability of zebrafish, heat shock has not been used for genome doubling since the proof‐of‐principle experiments done in the 1980s. This is because of poor survival of embryos that ensue from transient heat shocks and gross developmental abnormalities in the few survivors, which is incompatible with phenotype driven screens. Results: We show that heat shocks during early zebrafish development uncouple the second cycle of DNA and centrosome duplication. Interestingly, the developmental time of the heat shock that triggers the dissociation between DNA and centrosome duplication cycles significantly affect the potential of embryos to survive and attain normal morphology. The potential to develop normally after a heat shock alters in a developmental time span of 2 min in zebrafish embryos, a phenomenon that has not been reported in any species. Conclusions: The existence of heat resilient developmental windows and reduced heat teratogenicity during these windows could be an effective step forward in practical application of transient heat for experimental manipulation of ploidy in zebrafish. More broadly, heat resilience before zygotic genome activation suggests that metazoan embryos may possess innate protective features against heat beyond the canonical heat shock response. Developmental Dynamics 247:992–1004, 2018. © 2018 Wiley Periodicals, Inc.

Distinct Proteome Remodeling of Industrial Saccharomyces cerevisiae in Response to Prolonged Thermal Stress or Transient Heat Shock.

To gain a deep understanding of yeast-cell response to heat stress, multiple laboratory strains have been intensively studied via genome-wide expression analysis for the mechanistic dissection of classical heat-shock response (HSR). However, robust industrial strains of Saccharomyces cerevisiae have hardly been explored in global analysis for elucidation of the mechanism of thermotolerant response (TR) during fermentation. Herein, we employed data-independent acquisition and sequential window acquisition of all theoretical mass spectra based proteomic workflows to characterize proteome remodeling of an industrial strain, ScY01, responding to prolonged thermal stress or transient heat shock. By comparing the proteomic signatures of ScY01 in TR versus HSR as well as the HSR of the industrial strain versus a laboratory strain, our study revealed disparate response mechanisms of ScY01 during thermotolerant growth or under heat shock. In addition, through proteomics data-mining for decoding transcription factor interaction networks followed by validation experiments, we uncovered the functions of two novel transcription factors, Mig1 and Srb2, in enhancing the thermotolerance of the industrial strain. This study has demonstrated that accurate and high-throughput quantitative proteomics not only provides new insights into the molecular basis for complex microbial phenotypes but also pinpoints upstream regulators that can be targeted for improving the desired traits of industrial microorganisms.

Effects of Mild and Low Temperature Incubation on Heat Tolerance in <i>Bombyx mori</i> Embryos

Object: For ectothermic insects, thermal tolerance is one of the most essential properties for survival in ambient environments. However, the molecular mechanisms involved in thermal tolerance in the silkworm, <i>Bombyx mori</i> L. (Lepidoptera: Bombycidae) have not been fully elucidated. The present study investigated mechanisms that provide heat tolerance in embryos of <i>Bombyx mori</i>. Materials and Methods: Eggs of the bivoltine silkworm strain p50 were exposed to different temperatures, to determine the lethal threshold temperature and to assess the effects of mild and low temperature incubation on tolerance to heat shock and on embryonic protein profiles. Protein levels were measured by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE). Results: When eggs were exposed to transient heat shock for one hour, the lethal threshold temperature was between 47.0°C and 48.0°C. However, exposure to 40.0°C for four hours, substantially elevated tolerance to the threshold heat shock and simultaneously increased levels of 70 and 27 kDa proteins in eggs, whereas exposure to 35.0°C did not. Exposure to 10.0°C for four hours lowered heat tolerance and did not alter the expression of 70 and 27 kDa proteins. Conclusion: The present findings indicated that hardening silkworm eggs at mild temperatures increases heat tolerance in embryos. To our knowledge this is the first observation of heat hardening in silkworm embryos. These putative heat-shock proteins of 70 and 27 kDa might be involved in the effect of mild temperature hardening on heat tolerance. Cold stress might deprive embryos of energy reserves available for protection against heat damage. Protective mechanisms against heat and cold stress are probably different in this species. Further studies of the molecular mechanisms of heat tolerance should provide insight into the development of novel, high-yield silkworm strains in tropical environments.

Hsp90 induces increased genomic instability toward DNA-damaging agents by tuning down RAD53 transcription.

It is well documented that elevated body temperature causes tumors to regress upon radiotherapy. However, how hyperthermia induces DNA damage sensitivity is not clear. We show that a transient heat shock and particularly the concomitant induction of Hsp90 lead to increased genomic instability under DNA-damaging conditions. Using Saccharomyces cerevisiae as a model eukaryote, we demonstrate that elevated levels of Hsp90 attenuate efficient DNA damage signaling and dictate preferential use of the potentially mutagenic double-strand break repair pathway. We show that under normal physiological conditions, Hsp90 negatively regulates RAD53 transcription to suppress DNA damage checkpoint activation. However, under DNA damaging conditions, RAD53 is derepressed, and the increased level of Rad53p triggers an efficient DNA damage response. A higher abundance of Hsp90 causes increased transcriptional repression on RAD53 in a dose-dependent manner, which could not be fully derepressed even in the presence of DNA damage. Accordingly, cells behave like a rad53 loss-of-function mutant and show reduced NHEJ efficiency, with a drastic failure to up-regulate RAD51 expression and manifestly faster accumulation of CLN1 and CLN2 in DNA-damaged G1, cells leading to premature release from checkpoint arrest. We further demonstrate that Rad53 overexpression is able to rescue all of the aforementioned deleterious effects caused by Hsp90 overproduction.

The overproduction of Synechocystis sp. PCC 6803 heat-shock protein (Sll0170) protects Escherichia coli against high-temperature stress

The most important role of molecular chaperones, especially under extreme temperature, is in handling with the impact of such stress on proteins and avoiding loss of their native conformation. Molecular chaperones play roles in the folding, transport, synthesis and quality control of other proteins under extreme temperature. The genome of the cyanobacterium Synechocystis PCC 6803 includes three dnaK genes (encoding heat-shock protein 70, Hsp70). The role of the second Hsp70 protein (Sll0170; DnaK2) in the acquisition of thermotolerance in Escherichia coli cells was investigated. Escherichia coli strain BL21 (DE3) was transformed with an expression vector (pTYB21) carrying the coding sequence of the Sll0170 gene under the control of the lac promoter. The recombinant cells which showed inducible expression of DnaK2 were observed to have improved viability compared to the wild-type strain upon transfer from 37 °C to 52 °C for up to 2, 4 and 6 min. Moreover, the growth of the wild-type cell culture decreased to 64% of that of the recombinant cell culture, following a transient (15 min) heat shock at 45 °C after which the culture was subsequently transferred back to 37 °C. Interestingly, the recombinant E. coli cells showed significantly faster culture growth than the wild-type cells at 37 °C.

Heat stress-induced Cup9-dependent transcriptional regulation of SIR2.

The epigenetic writer Sir2 maintains the heterochromatin state of chromosome in three chromosomal regions, namely, the silent mating type loci, telomeres, and the ribosomal DNA (rDNA). In this study, we demonstrated the mechanism by which Sir2 is regulated under heat stress. Our study reveals that a transient heat shock causes a drastic reduction in the SIR2 transcript which results in sustained failure to initiate silencing for as long as 90 generations. Hsp82 overexpression, which is the usual outcome of heat shock treatment, leads to a similar downregulation of SIR2 transcription. Using a series of genetic experiments, we have established that heat shock or Hsp82 overexpression causes upregulation of CUP9 that, in turn, represses SIR2 transcription by binding to its upstream activator sequence. We have mapped the cis regulatory element of SIR2. Our study shows that the deletion of cup9 causes reversal of the Hsp82 overexpression phenotype and upregulation of SIR2 expression in heat-induced Hsp82-overexpressing cells. On the other hand, we found that Cup9 overexpression represses SIR2 transcription and leads to a failure in the establishment of heterochromatin. The results of our study highlight the mechanism by which environmental factors amend the epigenetic configuration of chromatin.

Hsp90 chaperones PPARγ and regulates differentiation and survival of 3T3-L1 adipocytes

Adipose tissue dysregulation has a major role in various human diseases. The peroxisome proliferator-activated receptor-γ (PPARγ) is a key regulator of adipocyte differentiation and function, as well as a target of insulin-sensitizing drugs. The Hsp90 chaperone stabilizes a diverse set of signaling 'client' proteins, thereby regulates various biological processes. Here we report a novel role for Hsp90 in controlling PPARγ stability and cellular differentiation. Specifically, we show that the Hsp90 inhibitors geldanamycin and novobiocin efficiently impede the differentiation of murine 3T3-L1 preadipocytes. Geldanamycin at higher concentrations also inhibits the survival of both developing and mature adipocytes, respectively. Further, Hsp90 inhibition disrupts an Hsp90-PPARγ complex, leads to the destabilization and proteasomal degradation of PPARγ, and inhibits the expression of PPARγ target genes, identifying PPARγ as an Hsp90 client. A similar destabilization of PPARγ and a halt of adipogenesis also occur in response to protein denaturing stresses caused by a single transient heat-shock or proteasome inhibition. Recovery from stress restores PPARγ stability and adipocyte differentiation. Thus, our findings reveal Hsp90 as a critical stress-responsive regulator of adipocyte biology and offer a potential therapeutic target in obesity and the metabolic syndrome.