Glucose metabolism in Neurospora is altered by heat shock and by disruption of HSP30

Differential Roles of Three α-Crystallin Domain-Containing sHsps of Beauveria bassiana in Asexual Development, Multiple Stress Tolerance and Virulence

Small heat shock proteins (sHsps) containing conserved α-crystallin domain play important roles in many cellular processes, but little is known about the functions of sHsps in filamentous entomopathogens. Here, three sHsps of Hsp20, Hsp30a, and Hsp30b were characterized in Beauveria bassiana, a filamentous fungal insect pathogen that serves as the main source of wide-spectrum fungal insecticides. The results demonstrated that these three genes are interrelated at the transcriptional level under normal and heat-shocked conditions. Meanwhile, all the deletion mutants showed significant but differential changes in cell wall integrity, antioxidant activity, hyphal tolerance to carbendazim fungicide, conidial tolerance to 45 °C wet heat and virulence. However, only Δhsp30b showed growth defects on rich and minimal media at 25 °C and Δhsp30a displayed the reduction in conidiophores and conidia. Moreover, the single deletion of hsp30a and hsp30b caused the decreases in hyphal growth at 34 °C and conidial tolerance to UV-B irradiation. Our findings provide a global insight into vital roles of hsp20, hsp30a, and hsp30b in asexual development, environmental adaptation, and fungal virulence of B. bassiana.

Toward the discovery of biological functions associated with the mechanosensor Mtl1p of Saccharomyces cerevisiae via integrative multi-OMICs analysis

Functional analysis of the Mtl1 protein in Saccharomyces cerevisiae has revealed that this transmembrane sensor endows yeast cells with resistance to oxidative stress through a signaling mechanism called the cell wall integrity pathway (CWI). We observed upregulation of multiple heat shock proteins (HSPs), proteins associated with the formation of stress granules, and the phosphatase subunit of trehalose 6-phosphate synthase which suggests that mtl1Δ strains undergo intrinsic activation of a non-lethal heat stress response. Furthermore, quantitative global proteomic analysis conducted on TMT-labeled proteins combined with metabolome analysis revealed that mtl1Δ strains exhibit decreased levels of metabolites of carboxylic acid metabolism, decreased expression of anabolic enzymes and increased expression of catabolic enzymes involved in the metabolism of amino acids, with enhanced expression of mitochondrial respirasome proteins. These observations support the idea that Mtl1 protein controls the suppression of a non-lethal heat stress response under normal conditions while it plays an important role in metabolic regulatory mechanisms linked to TORC1 signaling that are required to maintain cellular homeostasis and optimal mitochondrial function.

Ammonia exposure induced abnormal expression of cytokines and heat shock proteins via glucose metabolism disorders in chicken neutrophils

Ammonia (NH₃) is a highly irritant, alkaline gas. Atmospheric emission of NH₃ was recognized as an environmental challenge. As a global issue, the NH₃ emission survey with spatially detailed information demonstrated that the sources of atmospheric NH₃ include agriculture (livestock wastes, fertilizers) and some industrial activities. As an environmental pollution, excessive NH₃ exposure can induce many bird dysfunction. Neutrophils respond to multiple invading pathogens through different mechanisms. In order to investigate the effect of NH₃ exposure on broilers' neutrophil, 1-day-old broilers were treated with/without NH₃ for 28 days. We extracted neutrophils from peripheral blood of chicken with/without NH₃ exposure and subsequently stimulated with PMA. Changes of cytokines and inflammatory bodies, heat shock proteins (HSPs), and glucose metabolism of neutrophil were examined in both cases. We not only explored that the index associated with inflammation changed due to NH₃ exposure but also observed the status of neutrophils which was treated with PMA stimulation. After NH₃ exposure, IL-1β and IL-6 were significantly increased on broilers neutrophil. Inflammatory-related factors (NLRP3, ASC, and caspase-1) were significantly elevated. The mRNA expression of HSP70 and HSP90 was increased significantly. All glucose metabolism indicators were reduced. In summary, we concluded that NH₃ enhanced inflammation and disrupted glucose metabolism, and increased the expression of HSPs and inflammatory factors. In addition, the sensitivity of neutrophils to exogenous stimuli was diminished. This information can not only be used to evaluate the damage of NH₃-spiked neutrophils to chickens, but also provide clues for human health pathophysiology caused by excess NH₃, providing valuable information for NH₃ risk management.

Infective larvae of Anisakis simplex (Nematoda) accumulate trehalose and glycogen in response to starvation and temperature stress

Anisakis simplex L3 larvae infect fish and other seafood species such as squid or octopi; therefore, humans consuming raw or undercooked fish may become accidental hosts for this parasite. These larvae are induced to enter hypometabolism by cold temperatures. It is assumed that sugars (in particular trehalose and glycogen) are instrumental for survival under environmental stress conditions. To elucidate the mechanisms of environmental stress response in A. simplex, we observed the effects of starvation and temperature on trehalose and glycogen content, the activity of enzymes metabolizing those sugars, and the relative expression of genes of trehalose and glycogen metabolic pathways. The L3 of A. simplex synthesize trehalose both in low (0°C) and high temperatures (45°C). The highest content of glycogen was observed at 45°C at 36 h of incubation. On the second day of incubation, tissue content of trehalose depended on the activity of the enzymes: TPS was more active at 45°C, and TPP was more active at 0°C. The changes in TPP activity were consistent with the transcript level changes of the TPP gene, and the trehalose level, while glycogen synthesis correlates with the expression of glycogen synthase gene at 45°C; this suggests that the synthesis of trehalose is more essential. These results show that trehalose plays a key role in providing energy during the thermotolerance and starvation processes through the molecular and biochemical regulation of trehalose and glycogen metabolism.

Summary: Carbohydrate metabolism in L3 of A. simplex is affected by temperature shock and by starvation. The metabolic shift from glycogen to trehalose suggests that blocking or silencing the trehalose synthesis pathway could be a limiting factor for Anisakis life and development.

The Influence of Post-Exercise Cold-Water Immersion on Adaptive Responses to Exercise: A Review of the Literature

Post-exercise cold-water immersion (CWI) is used extensively in exercise training as a means to minimise fatigue and expedite recovery between sessions. However, debate exists around its merit in long-term training regimens. While an improvement in recovery following a single session of exercise may improve subsequent training quality and stimulus, reports have emerged suggesting CWI may attenuate long-term adaptations to exercise training. Recent developments in the understanding of the molecular mechanisms governing the adaptive response to exercise in human skeletal muscle have provided potential mechanistic insight into the effects of CWI on training adaptations. Preliminary evidence suggests that CWI may blunt resistance signalling pathways following a single exercise session, as well as attenuate key long-term resistance training adaptations such as strength and muscle mass. Conversely, CWI may augment endurance signalling pathways and the expression of genes key to mitochondrial biogenesis following a single endurance exercise session, but have little to no effect on the content of proteins key to mitochondrial biogenesis following long-term endurance training. This review explores current evidence regarding the underlying molecular mechanisms by which CWI may alter cellular signalling and the long-term adaptive response to exercise in human skeletal muscle.

Glucose Starvation Alters Heat Shock Response, Leading to Death of Wild Type Cells and Survival of MAP Kinase Signaling Mutant

A moderate heat shock induces Neurospora crassa to synthesize large quantities of heat shock proteins that are protective against higher, otherwise lethal temperatures. However, wild type cells do not survive when carbohydrate deprivation is added to heat shock. In contrast, a mutant strain defective in a stress-activated protein kinase does survive the combined stresses. In order to understand the basis for this difference in survival, we have determined the relative levels of detected proteins in the mutant and wild type strain during dual stress, and we have identified gene transcripts in both strains whose quantities change in response to heat shock or dual stress. These data and supportive experimental evidence point to reasons for survival of the mutant strain. By using alternative respiratory mechanisms, these cells experience less of the oxidative stress that proves damaging to wild type cells. Of central importance, mutant cells recycle limited resources during dual stress by undergoing autophagy, a process that we find utilized by both wild type and mutant cells during heat shock. Evidence points to inappropriate activation of TORC1, the central metabolic regulator, in wild type cells during dual stress, based upon behavior of an additional signaling mutant and inhibitor studies.

Transient Low-Temperature Effects on Propidium Iodide Uptake in Lance Array Nanoinjected HeLa Cells

Understanding environmental factors relative to transfection protocols is key for improving genetic engineering outcomes. In the following work, the effects of temperature on a nonviral transfection procedure previously described as lance array nanoinjection are examined in context of molecular delivery of propidium iodide (PI), a cell membrane impermeable nucleic acid dye, to HeLa 229 cells. For treatment samples, variables include varying the temperature of the injection solution (3C and 23C) and the magnitude of the pulsed voltage used during lance insertion into the cells (+5 V and +7 V). Results indicate that PI is delivered at levels significantly higher for samples injected at 3C as opposed to 23C at four different postinjection intervals (t = 0, 3, 6, 9 mins; p-value ≤ 0.005), reaching a maximum value of 8.3 times the positive control for 3 C/7 V pulsed samples. Suggested in this work is that between 3 and 6 mins postinjection, a large number of induced pores from the injection event close. While residual levels of PI still continue to enter the treatment samples after 6 mins, it occurs at decreased levels, suggesting from a physiological perspective that many lance array nanoinjection (LAN) induced pores have closed, some are still present.

Effects of mild cold shock (25°C) followed by warming up at 37°C on the cellular stress response

Temperature variations in cells, tissues and organs may occur in a number of circumstances. We report here that reducing temperature of cells in culture to 25°C for 5 days followed by a rewarming to 37°C affects cell biology and induces a cellular stress response. Cell proliferation was almost arrested during mild hypothermia and not restored upon returning to 37°C. The expression of cold shock genes, CIRBP and RBM3, was increased at 25°C and returned to basal level upon rewarming while that of heat shock protein HSP70 was inversely regulated. An activation of pro-apoptotic pathways was evidenced by FACS analysis and increased Bax/Bcl2 and BclX(S/L) ratios. Concomitant increased expression of the autophagosome-associated protein LC3II and AKT phosphorylation suggested a simultaneous activation of autophagy and pro-survival pathways. However, a large proportion of cells were dying 24 hours after rewarming. The occurrence of DNA damage was evidenced by the increased phosphorylation of p53 and H2AX, a hallmark of DNA breaks. The latter process, as well as apoptosis, was strongly reduced by the radical oxygen species (ROS) scavenger, N-acetylcysteine, indicating a causal relationship between ROS, DNA damage and cell death during mild cold shock and rewarming. These data bring new insights into the potential deleterious effects of mild hypothermia and rewarming used in various research and therapeutical fields.

Use of 1H nuclear magnetic resonance to measure intracellular metabolite levels during growth and asexual sporulation in Neurospora crassa

Conidiation is an asexual sporulation pathway that is a response to adverse conditions and is the main mode of dispersal utilized by filamentous fungal pathogens for reestablishment in a more favorable environment. Heterotrimeric G proteins (consisting of α, β, and γ subunits) have been shown to regulate conidiation in diverse fungi. Previous work has demonstrated that all three of the Gα subunits in the filamentous fungus Neurospora crassa affect the accumulation of mass on poor carbon sources and that loss of gna-3 leads to the most dramatic effects on conidiation. In this study, we used (1)H nuclear magnetic resonance (NMR) to profile the metabolome of N. crassa in extracts isolated from vegetative hyphae and conidia from cultures grown under conditions of high or low sucrose. We compared wild-type and Δgna-3 strains to determine whether lack of gna-3 causes a significant difference in the global metabolite profile. The results demonstrate that the global metabolome of wild-type hyphae is influenced by carbon availability. The metabolome of the Δgna-3 strain cultured on both high and low sucrose is similar to that of the wild type grown on high sucrose, suggesting an overall defect in nutrient sensing in the mutant. However, analysis of individual metabolites revealed differences in wild-type and Δgna-3 strains cultured under conditions of low and high sucrose.

Isolation and expression of heat shock protein 30 gene from Penicillium marneffei

Penicillium marneffei is a dimorphic fungus that can cause disseminated mycosis, especially in AIDS patients. The role of heat shock proteins and stress response-related proteins in P. marneffei remains unknown. In this study, we isolated a cDNA encoding for heat shock protein 30 (Hsp30) of P. marneffei using an antibody screening method. The DNA sequence and deduced amino acid sequence analysis showed high homology to other fungal hsp30 genes. Expression of P. marneffei hsp30 in response to temperature increase was determined by Northern blot analysis. A high level of hsp30 transcript was detected in yeast cells grown at 37 degrees C, whereas a very low or undetectable transcript level was observed in mycelial cells at 25 degrees C. A recombinant Hsp30 protein was produced and tested preliminarily for its immunoreactivity with sera from P. marneffei-infected AIDS patients using Western blot analysis. The positive immunoblot result, with some serum samples, confirmed the antigenic property of the Hsp30. Collectively, the high response of hsp30 to temperature increase could indicate it may play a role in heat stress response and cell adaptation. This is the first report showing that this small heat shock protein could elicit the human immune response.

Stress-induced cell death is mediated by ceramide synthesis in Neurospora crassa

The combined stresses of moderate heat shock (45 degrees C) and analog-induced glucose deprivation constitute a lethal stress for Neurospora crassa. We found that this cell death requires fatty acid synthesis and the cofactor biotin. In the absence of the cofactor, the stressed cells are particularly sensitive to exogenous ceramide, which is lethal at low concentrations. When we extracted endogenous sphingolipids, we found that unique ceramides were induced (i) by the inhibitory glucose analog 2-deoxyglucose and (ii) by combined heat shock and 2-deoxyglucose. We determined that the former is a 2-deoxyglucose-modified ceramide. By structural analysis, we identified the latter, induced by dual stress, as C(18)(OH)-phytoceramide. We also identified C(24)(OH)-phytoceramide as a constitutive ceramide that continues to be produced during the combined stresses. The unusual C(18)(OH)-phytoceramide is not made by germinating asexual spores subjected to the same heat and carbon stress. Since these spores, unlike growing cells, do not die from the stresses, this suggests a possible connection between synthesis of the dual-stress-induced ceramide and cell death. This connection is supported by the finding that a (dihydro)ceramide synthase inhibitor, australifungin, renders cells resistant to death from these stresses. The OS-2 mitogen-activated protein kinase, homologous to mammalian p38, may be involved in the cell death signaling pathway. Strains lacking OS-2 survived the combined stresses better than the wild type, and phosphorylated OS-2 increased in wild-type cells in response to heat shock and combined heat and carbon stress.

Fungal heat-shock proteins in human disease

Heat-shock proteins (hsps) have been identified as molecular chaperones conserved between microbes and man and grouped by their molecular mass and high degree of amino acid homology. This article reviews the major hsps of Saccharomyces cerevisiae, their interactions with trehalose, the effect of fermentation and the role of the heat-shock factor. Information derived from this model, as well as from Neurospora crassa and Achlya ambisexualis, helps in understanding the importance of hsps in the pathogenic fungi, Candida albicans, Cryptococcus neoformans, Aspergillus spp., Histoplasma capsulatum, Paracoccidioides brasiliensis, Trichophyton rubrum, Phycomyces blakesleeanus, Fusarium oxysporum, Coccidioides immitis and Pneumocystis jiroveci. This has been matched with proteomic and genomic information examining hsp expression in response to noxious stimuli. Fungal hsp90 has been identified as a target for immunotherapy by a genetically recombinant antibody. The concept of combining this antibody fragment with an antifungal drug for treating life-threatening fungal infection and the potential interactions with human and microbial hsp90 and nitric oxide is discussed.

Lessons from the genome sequence of Neurospora crassa: tracing the path from genomic blueprint to multicellular organism

We present an analysis of over 1,100 of the approximately 10,000 predicted proteins encoded by the genome sequence of the filamentous fungus Neurospora crassa. Seven major areas of Neurospora genomics and biology are covered. First, the basic features of the genome, including the automated assembly, gene calls, and global gene analyses are summarized. The second section covers components of the centromere and kinetochore complexes, chromatin assembly and modification, and transcription and translation initiation factors. The third area discusses genome defense mechanisms, including repeat induced point mutation, quelling and meiotic silencing, and DNA repair and recombination. In the fourth section, topics relevant to metabolism and transport include extracellular digestion; membrane transporters; aspects of carbon, sulfur, nitrogen, and lipid metabolism; the mitochondrion and energy metabolism; the proteasome; and protein glycosylation, secretion, and endocytosis. Environmental sensing is the focus of the fifth section with a treatment of two-component systems; GTP-binding proteins; mitogen-activated protein, p21-activated, and germinal center kinases; calcium signaling; protein phosphatases; photobiology; circadian rhythms; and heat shock and stress responses. The sixth area of analysis is growth and development; it encompasses cell wall synthesis, proteins important for hyphal polarity, cytoskeletal components, the cyclin/cyclin-dependent kinase machinery, macroconidiation, meiosis, and the sexual cycle. The seventh section covers topics relevant to animal and plant pathogenesis and human disease. The results demonstrate that a large proportion of Neurospora genes do not have homologues in the yeasts Saccharomyces cerevisiae and Schizosaccharomyces pombe. The group of unshared genes includes potential new targets for antifungals as well as loci implicated in human and plant physiology and disease.

Analysis of interactions between domains of a small heat shock protein, Hsp30 of Neurospora crassa

The alpha-crystallin-related, small heat shock proteins (sHsps), despite their overall variability in sequence, have discrete regions of conserved sequence that are involved in structural organization, as well as nonconserved regions that may perform similar roles in each protein. Recent X-ray diffraction analyses of an archeal and a plant sHsp have revealed both similarities and differences in how they are organized, suggesting that there is variability, particularly in the oligomeric organization of sHsps. As an adjunct to crystallographic analysis of sHsp structure, we employed the yeast 2-hybrid system to detect interactions between peptide regions of the sHsp of Neurospora crassa, Hsp30. We found that the conserved alpha-crystallin domain can be divided into N-terminal and C-terminal subdomains that interact strongly with one another. This interaction likely represents the tertiary contacts of the monomer that were visualized in the crystallographic structures of MjHsp16.5 and wheat Hsp16.9. The conserved sHsp monomeric fold is apparently determined by these regions of conserved sequence. We found that the C-terminal portion of the alpha-crystallin domain also interacts with itself in 2-hybrid assays; however, this interaction requires peptide extension into the semiconserved carboxyl tail. This C-terminal association may represent a principal contact site between dimers that contributes to higher-order assembly, as seen for the crystallized sHsps.

Detection of modifications in the glucose metabolism induced by genetic mutations in Saccharomyces cerevisiae by 13C- and H-NMR spectroscopy

NMR spectroscopy may offer a suitable technique to characterize the glucose metabolism in response to genetic mutations in cells. The effects of various genetic modifications in Saccharomyces cerevisiae yeast were investigated using 13C- and 1H-NMR spectroscopy associated with biochemical techniques. Cells were incubated with [1-13C]glucose in order to study glucose consumption and the formation of various end-products (ethanol, trehalose, glycerol, glutamate and amino acids) as a function of time. Two types of genetic modifications were studied in S. cerevisiae. A genetic modification deleted the N-terminal part of the TFC7 protein which is the smallest subunit (tau55) of the TFIIIC transcription factor. One secondary effect of this mutation was a large deletion of mitochondrial DNA giving the rho-phenotype. The other genetic modification corresponded to the disruption of the HUF gene; the mutated cells were rho+ like the reference strain. Both mutations increase the glycolysis rate and glycerol synthesis and decrease trehalose production. The most modified cells, which contain both TFC7 deletion and HUF gene disruption, utilize glucose in the most extreme manner as in these cells the largest production of the two glycolytic products (ethanol and glycerol) and the smallest trehalose formation occur. The HUF gene disruption serves as a positive modulator of glycolysis and respiration. However, the TFC7 deletion, associated with the phenotype rho-, induces the most damage in the cellular function, dramatically altering the behaviour of the Krebs cycle. The cycle becomes blocked at the level of 2-oxoglutarate, detected by a characteristic pattern of the 13C-NMR glutamate spectra. These NMR spectra corroborate the phenotypic data, the rho-phenotype corresponding to deletions of mitochondria DNA which block all mitochondria protein synthesis and render the cells unable to derive energy from respiration. Moreover, as a consequence of the Krebs cycle blocking, alanine formation is also observed.

Disruption of the gene for Hsp30, an alpha-crystallin-related heat shock protein of Neurospora crassa, causes defects in import of proteins into mitochondria

The gene for Hsp30, the only known alpha-crystallin-related heat shock protein of Neurospora crassa, was disrupted by repeat-induced point mutagenesis, leading to loss of cell survival at high temperature. Hsp30, which is not synthesized at 30 degrees C, associates reversibly with the mitochondria at high temperature (45 degrees C). In this study, we found that import of selected proteins into internal compartments of mitochondria, following their synthesis in the cytosol, was severely impaired at high temperature in a strain mutant in Hsp30. After 70 min of cell incubation at 45 degrees C, most matrix, inner membrane, and intermembrane-space proteins tested were reduced in import by about 50-70% in the mutant, as compared to wild-type cells. In contrast, assembly of selected proteins into the outer mitochondrial membrane was not reduced, except for one component of the preprotein translocase complex of the mitochondrial outer membrane. Three proteins of this complex co-immunoprecipitated with Hsp30 of wild-type cells incubated at 45 degrees C. We propose that Hsp30 interacts with the preprotein translocase of the mitochondrial outer membrane and that it chaperones the activity of one or more components of this translocase complex at high temperature.