Plasma membranes as heat stress sensors: from lipid-controlled molecular switches to therapeutic applications

Delineating the Rules for Structural Adaptation of Membrane-Associated Proteins to Evolutionary Changes in Membrane Lipidome

Membrane function is fundamental to life. Each species explores membrane lipid diversity within a genetically predefined range of possibilities. How membrane lipid composition in turn defines the functional space available for evolution of membrane-centered processes remains largely unknown. We address this fundamental question using related fission yeasts Schizosaccharomyces pombe and Schizosaccharomyces japonicus. We show that, unlike S. pombe that generates membranes where both glycerophospholipid acyl tails are predominantly 16-18 carbons long, S. japonicus synthesizes unusual "asymmetrical" glycerophospholipids where the tails differ in length by 6-8 carbons. This results in stiffer bilayers with distinct lipid packing properties. Retroengineered S. pombe synthesizing the S.-japonicus-type phospholipids exhibits unfolded protein response and downregulates secretion. Importantly, our protein sequence comparisons and domain swap experiments support the hypothesis that transmembrane helices co-evolve with membranes, suggesting that, on the evolutionary scale, changes in membrane lipid composition may necessitate extensive adaptation of the membrane-associated proteome.

Alcohol protects the CNS by activating HSF1 and inducing the heat shock proteins

Although alcohol abuse and dependence have profound negative health consequences, emerging evidence suggests that exposure to low/moderate concentrations of ethanol protects multiple organs and systems. In the CNS, moderate drinking decreases the risk of dementia and Alzheimer's disease. This neuroprotection correlates with an increased expression of the heat shock proteins (HSPs). Multiple epidemiological studies revealed an inverse association between ethanol intoxication and traumatic brain injury mortality. In this case, ethanol-induced HSPs limit the inflammatory immune response diminishing cell death and improving the neurobehavioural outcome. Ethanol also protects the brain against ischemic injuries via the HSPs. In our laboratory, we demonstrated that ethanol increased the expression of several HSP genes in neurons and astrocytes by activating the transcription factor, heat shock factor 1 (HSF1). HSF1 induces HSPs that target misfolded proteins for refolding or degradation, increasing the survival chances of the cells. These data indicate that ethanol neuroprotection is mediated by the activation HSF1 and the induction of HSPs.

Heat-Shock Proteins in Neuroinflammation

The heat-shock response, one of the main pro-survival mechanisms of a living organism, has evolved as the biochemical response of cells to cope with heat stress. The most well-characterized aspect of the heat-shock response is the accumulation of a conserved set of proteins termed heat-shock proteins (HSPs). HSPs are key players in protein homeostasis acting as chaperones by aiding the folding and assembly of nascent proteins and protecting against protein aggregation. HSPs have been associated with neurological diseases in the context of their chaperone activity, as they were found to suppress the aggregation of misfolded toxic proteins. In recent times, HSPs have proven to have functions apart from the classical molecular chaperoning in that they play a role in a wider scale of neurological disorders by modulating neuronal survival, inflammation, and disease-specific signaling processes. HSPs are gaining importance based on their ability to fine-tune inflammation and act as immune modulators in various bodily fluids. However, their effect on neuroinflammation processes is not yet fully understood. In this review, we summarize the role of neuroinflammation in acute and chronic pathological conditions affecting the brain. Moreover, we seek to explore the existing literature on HSP-mediated inflammatory function within the central nervous system and compare the function of these proteins when they are localized intracellularly compared to being present in the extracellular milieu.

Understanding the liver under heat stress with statistical learning: an integrated metabolomics and transcriptomics computational approach

BACKGROUND

We present results from a computational analysis developed to integrate transcriptome and metabolomic data in order to explore the heat stress response in the liver of the modern broiler chicken. Heat stress is a significant cause of productivity loss in the poultry industry, both in terms of increased livestock morbidity and its negative influence on average feed efficiency. This study focuses on the liver because it is an important regulator of metabolism, controlling many of the physiological processes impacted by prolonged heat stress. Using statistical learning methods, we identify genes and metabolites that may regulate the heat stress response in the liver and adaptations required to acclimate to prolonged heat stress.

RESULTS

We describe how disparate systems such as sugar, lipid and amino acid metabolism, are coordinated during the heat stress response.

CONCLUSIONS

Our findings provide more detailed context for genomic studies and generates hypotheses about dietary interventions that can mitigate the negative influence of heat stress on the poultry industry.

Stress-related hormones affect carbohydrate metabolism in Drosophila females

A highly conservative insulin signaling pathway, stable work of which is indicated by carbohydrates metabolism, is also known to play an important role in the control of stress resistance. Here we demonstrate that exposure to heat stress leads to a rise in the levels of trehalose and glucose in females of Drosophila melanogaster, but does not affect the expression level of the trehalase (Treh) gene. We have shown that the rise in juvenile hormone (JH) and dopamine decreases levels of both carbohydrates under the normal conditions but brings them to values close to normal following the stress exposure. The data obtained suggest that (a) dopamine and JH involved in the neuroendocrine stress reaction in D. melanogaster also take part in the regulation of carbohydrates metabolism, tending to normalize it after stress; (b) the regulation of trehalose content under stress does not occur at the level of transcription of the degrading enzyme.

Feeling the Heat: Searching for Plant Thermosensors

To draw the complete picture of plant thermal signaling, it is important to find the missing links between the temperature cue, the actual sensing, and the subsequent response. In this context, several plant thermosensors have been proposed. Here, we compare these with thermosensors in various other organisms, put them in the context of thermosensing in plants, and suggest a set of criteria to which a thermosensor must adhere. Finally, we propose that more emphasis should be given to structural analysis of DNA, RNA, and proteins in light of the activity of potential thermosensors.

Involvement of Stat3 phosphorylation in mild heat shock-induced thermotolerance

Thermotolerance is a phenomenon in which cells become resistant to stress by prior exposure to heat shock, and its development is associated with the induction of heat shock proteins (Hsps), including Hsp70. We previously showed that the expression of Hsp70 is regulated by the cytokine signaling transcription factor Stat3, but the role of Stat3 in thermotolerance is not known. In this study, we examined the possible involvement of Stat3 in the acquisition of thermotolerance. We found that severe heat shock-induced morphological changes and decreases in cell viability, which were suppressed by exposure to non-lethal mild heat shock prior to severe heat shock. This thermotolerance development was accompanied by Stat3 phosphorylation and the induction of Hsps such as Hsp105, Hsp70, and Hsp27. Stat3 phosphorylation and Hsp induction were inhibited by AG490, an inhibitor of JAK tyrosine kinase. Consistent with this, we found that mild heat shock-induced thermotolerance was partially suppressed by AG490 or knockdown of Hsp105. We also found that the Stat3 inhibitor Stattic suppresses the acquisition of thermotolerance by inhibiting the mild heat shock-induced Stat3 phosphorylation and Hsp105 expression. These results suggest that the mild heat shock-dependent stimulation of the JAK-Stat signaling pathway contributes to the development of thermotolerance via the induction of Hsps including Hsp105. This signaling pathway may be a useful target for hyperthermia cancer therapy.

Hsp70 interactions with membrane lipids regulate cellular functions in health and disease

Beyond guarding the cellular proteome the major stress inducible heat shock protein Hsp70 has been shown to interact with lipids. Non-cytosolic Hsp70 stabilizes membranes during stress challenges and, in pathophysiological states, facilitates endocytosis, counteracts apoptotic mechanisms, sustains survival pathways or represents a signal that can be recognized by the immune system. Disease-coupled lipid-associated functions of Hsp70 may be targeted via distinct subcellular localizations of Hsp70 itself or its specific interacting lipids. With a special focus on interacting lipids, here we discuss localization-dependent roles of the membrane-bound Hsp70 in the context of its therapeutic potential, particularly in cancer and neurodegenerative diseases.

Exposure to a Nonionic Surfactant Induces a Response Akin to Heat-Shock Apoptosis in Intestinal Epithelial Cells: Implications for Excipients Safety

Amphipathic, nonionic, surfactants are widely used in pharmaceutical, food, and agricultural industry to enhance product features; as pharmaceutical excipients, they are also aimed at increasing cell membrane permeability and consequently improving oral drugs absorption. Here, we report on the concentration- and time-dependent succession of events occurring throughout and subsequent exposure of Caco-2 epithelium to a "typical" nonionic surfactant (Kolliphor HS15) to provide a molecular explanation for nonionic surfactant cytotoxicity. The study shows that the conditions of surfactant exposure, which increase plasma membrane fluidity and permeability, produced rapid (within 5 min) redox and mitochondrial effects. Apoptosis was triggered early during exposure (within 10 min) and relied upon an initial mitochondrial membrane hyperpolarization (5-10 min) as a crucial step, leading to its subsequent depolarization and caspase-3/7 activation (60 min). The apoptotic pathway appears to be triggered prior to substantial surfactant-induced membrane damage (observed ≥60 min). We hence propose that the cellular response to the model nonionic surfactant is triggered via surfactant-induced increase in plasma membrane fluidity, a phenomenon akin to the stress response to membrane fluidization induced by heat shock, and consequent apoptosis. Therefore, the fluidization effect that confers surfactants the ability to enhance drug permeability may also be intrinsically linked to the propagation of their cytotoxicity. The reported observations have important implications for the safety of a multitude of nonionic surfactants used in drug delivery formulations and to other permeability enhancing compounds with similar plasma membrane fluidizing mechanisms.

Corticoids modulate liposome membrane fluidity and permeability depending on membrane composition and experimental protocol design

Given that literature data may give inconsistent results on the effect of a drug on lipid membrane properties, this work aims to investigate the impact of the liposome composition and experimental protocol design on glucocorticoids (GRs: cortisol, cortisone, fludrocortisone acetate, methylprednisolone, prednisolone and prednisone)-modulating membrane fluidity and permeability. GRs-loaded liposomes consisting of dipalmitoylphosphatidylcholine (DPPC) and cholesterol (CHOL) were prepared by reverse phase evaporation technique (REV) at DPPC:CHOL:GR molar ratios of 100:100:2.5, and 100:100:10. The formulations were characterized for their size and homogeneity, encapsulation efficiency and loading rates of GRs, incorporation rates and loading rates of DPPC and CHOL. Changes in DPPC membrane fluidity (CHOL% 0, 10, 20, 30 and 100) after exposure to methylprednisolone were monitored by using 5- and 16-doxyl stearic acids (DSA) as spin probes. For permeability studies, the above-mentioned GRs-loaded liposomes and the preformed liposomes exposed to GRs (2.5 mol%) were compared for the leakage of an encapsulated fluorescent dye, sulforhodamine B (SRB), at 37 °C in buffer (pH 7.5) containing NaCl. The SRB release kinetics were analyzed by the Higuchi model for two release phases (from 0 to 10 h, and from 10 to 48 h). All formulations exhibited a monodispersed size distribution of liposomes with a mean particle value close to 0.4 μm, also the DPPC and CHOL were highly incorporated (>95%). High loading rate values of DPPC and CHOL were also obtained. Except for fludrocortisone acetate (51%) and prednisolone (77%), high loading rate values of GRs were obtained (>81%). Fluidity and permeability studies showed that the GR concentration, CHOL content, experimental protocol design including the period of incubation represent critical parameters to be considered in analyzing the effect of drugs on the membrane properties.

Parthenosporophytes of the brown alga Ectocarpus siliculosus exhibit sex-dependent differences in thermotolerance as well as fatty acid and sterol composition

In the filamentous brown alga Ectocarpus siliculosus, male and female sex is expressed during the haploid parthenosporophyte phase of the life cycle. Here, we found that male parthenosporophytes displayed thermotolerance whereas female specimens displayed severely reduced viability at 25 °C and 28 °C. Profiling of polyunsaturated fatty acids showed that n-3 and n-6 were the predominant species in male and female parthenosporophytes, respectively, and that the n-3/n-6 fatty acid ratio was not affected by a temperature change. Both male and female parthenosporophytes contained the sterols fucosterol, cholesterol, and ergosterol, but these were present at higher levels at 10-25 °C in female specimens than in males. Thus, these fatty acids and sterols would be expected to make the membranes more rigid in the female compared to the male, which is opposite to the paradigm that increased rigidity confers thermotolerance. Our results suggest that the sex-dependent thermotolerance in E. siliculosus parthenosporophytes is not explained by the relationship between membrane fluidity and differences in fatty acids and sterol compositions.

Nitric oxide-heat shock protein axis in menopausal hot flushes: neglected metabolic issues of chronic inflammatory diseases associated with deranged heat shock response

BACKGROUND

Although some unequivocal underlying mechanisms of menopausal hot flushes have been demonstrated in animal models, the paucity of similar approaches in humans impedes further mechanistic outcomes. Human studies might show some as yet unexpected physiological mechanisms of metabolic adaptation that permeate the phase of decreased oestrogen levels in both symptomatic and asymptomatic women. This is particularly relevant because both the severity and time span of hot flushes are associated with increased risk of chronic inflammatory disease. On the other hand, oestrogen induces the expression of heat shock proteins of the 70 kDa family (HSP70), which are anti-inflammatory and cytoprotective protein chaperones, whose expression is modulated by different types of physiologically stressful situations, including heat stress and exercise. Therefore, lower HSP70 expression secondary to oestrogen deficiency increases cardiovascular risk and predisposes the patient to senescence-associated secretory phenotype (SASP) that culminates in chronic inflammatory diseases, such as obesities, type 2 diabetes, neuromuscular and neurodegenerative diseases.

OBJECTIVE AND RATIONALE

This review focuses on HSP70 and its accompanying heat shock response (HSR), which is an anti-inflammatory and antisenescent pathway whose intracellular triggering is also oestrogen-dependent via nitric oxide (NO) production. The main goal of the manuscript was to show that the vasomotor symptoms that accompany hot flushes may be a disguised clue for important neuroendocrine alterations linking oestrogen deficiency to the anti-inflammatory HSR.

SEARCH METHODS

Results from our own group and recent evidence on hypothalamic control of central temperature guided a search on PubMed and Google Scholar websites.

OUTCOMES

Oestrogen elicits rapid production of the vasodilatory gas NO, a powerful activator of HSP70 expression. Whence, part of the protective effects of oestrogen over cardiovascular and neuroendocrine systems is tied to its capacity of inducing the NO-elicited HSR. The hypothalamic areas involved in thermoregulation (infundibular nucleus in humans and arcuate nucleus in other mammals) and whose neurons are known to have their function altered after long-term oestrogen ablation, particularly kisspeptin-neurokinin B-dynorphin neurons, (KNDy) are the same that drive neuroprotective expression of HSP70 and, in many cases, this response is via NO even in the absence of oestrogen. From thence, it is not illogical that hot flushes might be related to an evolutionary adaptation to re-equip the NO-HSP70 axis during the downfall of circulating oestrogen.

WIDER IMPLICATIONS

Understanding of HSR could shed light on yet uncovered mechanisms of menopause-associated diseases as well as on possible manipulation of HSR in menopausal women through physiological, pharmacological, nutraceutical and prebiotic interventions. Moreover, decreased HSR indices (that can be clinically determined with ease) in perimenopause could be of prognostic value in predicting the moment and appropriateness of starting a HRT.

Dihydropyridine Derivatives Modulate Heat Shock Responses and have a Neuroprotective Effect in a Transgenic Mouse Model of Alzheimer's Disease

Heat shock proteins (Hsps) have chaperone activity and play a pivotal role in the homeostasis of proteins by preventing misfolding, by clearing aggregated and damaged proteins from cells, and by maintaining proteins in an active state. Alzheimer’s disease (AD) is thought to be caused by amyloid-β peptide that triggers tau hyperphosphorylation, which is neurotoxic. Although proteostasis capacity declines with age and facilitates the manifestation of neurodegenerative diseases such as AD, the upregulation of chaperones improves prognosis. Our research goal is to identify potent Hsp co-inducers that enhance protein homeostasis for the treatment of AD, especially 1,4-dihydropyridine derivatives optimized for their ability to modulate cellular stress responses. Based on favorable toxicological data and Hsp co-inducing activity, LA1011 was selected for the in vivo analysis of its neuroprotective effect in the APPxPS1 mouse model of AD. Here, we report that 6 months of LA1011 administration effectively improved the spatial learning and memory functions in wild type mice and eliminated neurodegeneration in double mutant mice. Furthermore, Hsp co-inducer therapy preserves the number of neurons, increases dendritic spine density, and reduces tau pathology and amyloid plaque formation in transgenic AD mice. In conclusion, the Hsp co-inducer LA1011 is neuroprotective and therefore is a potential pharmaceutical candidate for the therapy of neurodegenerative diseases, particularly AD.

Heat Shock Proteins and Autophagy Pathways in Neuroprotection: from Molecular Bases to Pharmacological Interventions

Neurodegenerative diseases (NDDs) such as Alzheimer's disease, Parkinson's disease and Huntington's disease (HD), amyotrophic lateral sclerosis, and prion diseases are all characterized by the accumulation of protein aggregates (amyloids) into inclusions and/or plaques. The ubiquitous presence of amyloids in NDDs suggests the involvement of disturbed protein homeostasis (proteostasis) in the underlying pathomechanisms. This review summarizes specific mechanisms that maintain proteostasis, including molecular chaperons, the ubiquitin-proteasome system (UPS), endoplasmic reticulum associated degradation (ERAD), and different autophagic pathways (chaperon mediated-, micro-, and macro-autophagy). The role of heat shock proteins (Hsps) in cellular quality control and degradation of pathogenic proteins is reviewed. Finally, putative therapeutic strategies for efficient removal of cytotoxic proteins from neurons and design of new therapeutic targets against the progression of NDDs are discussed.

Interaction of Hsp90 with phospholipid model membranes

Heat shock protein 90 (Hsp90) is an essential molecular chaperone with versatile functions in cell homeostatic control under both normal and stress conditions. Hsp90 has been found to be expressed on the cell surface, but the mechanism of Hsp90 association to the membrane remains obscure. In this study, the direct interaction of Hsp90 and phospholipid vesicles was characterized, and the role of Hsp90 on membrane physical state was explored. Using surface plasmon resonance (SPR), we observed a strong interaction between Hsp90 and different compositions of lipid. Hsp90 had a preference to bind with more unsaturated phospholipid species and the affinity was higher with negatively charged lipids than zwitterionic lipids. Increasing the mole fraction of cholesterol in the phospholipid led to a decrease of binding affinity to Hsp90. Circular dichroism (CD) spectroscopy of Hsp90 in PC membranes showed more α-helix structure than in aqueous buffer. The differential scanning calorimeter (DSC) and fluorescence polarization results showed Hsp90 could affect the transition temperature and fluidity of the bilayer. We postulate from these results that the association between Hsp90 and membranes may involve both electrostatic and hydrophobic force, and constitute a possible mechanism that modulates membrane lipid order during thermal fluctuations.

Mild heat induces a distinct "eustress" response in Chinese Hamster Ovary cells but does not induce heat shock protein synthesis

The current research on cellular heat stress management focuses on the roles of heat shock proteins (HSPs) and the proteostasis network under severe stress conditions. The mild, fever-type stress and the maintenance of membrane homeostasis are less well understood. Herein, we characterized the acute effect of mild, fever-range heat shock on membrane organization, and HSP synthesis and localization in two mammalian cell lines, to delineate the role of membranes in the sensing and adaptation to heat. A multidisciplinary approach combining ultrasensitive fluorescence microscopy and lipidomics revealed the molecular details of novel cellular “eustress”, when cells adapt to mild heat by maintaining membrane homeostasis, activating lipid remodeling, and redistributing chaperone proteins. Notably, this leads to acquired thermotolerance in the complete absence of the induction of HSPs. At higher temperatures, additional defense mechanisms are activated, including elevated expression of molecular chaperones, contributing to an extended stress memory and acquired thermotolerance.

Cellular Response to ELF-MF and Heat: Evidence for a Common Involvement of Heat Shock Proteins?

It has been shown that magnetic fields in the extremely low frequency range (ELF-MF) can act as a stressor in various in vivo or in vitro systems, at flux density levels below those inducing excitation of nerve and muscle cells, which are setting the limits used by most generally accepted exposure guidelines, such as the ones published by the International Commission on Non-Ionizing Radiation Protection. In response to a variety of physiological and environmental factors, including heat, cells activate an ancient signaling pathway leading to the transient expression of heat shock proteins (HSPs), which exhibit sophisticated protection mechanisms. A number of studies suggest that also ELF-MF exposure can activate the cellular stress response and cause increased HSPs expression, both on the mRNA and the protein levels. In this review, we provide some of the presently available data on cellular responses, especially regarding HSP expression, due to single and combined exposure to ELF-MF and heat, with the aim to compare the induced effects and to detect possible common modes of action. Some evidence suggest that MF and heat can act as costressors inducing a kind of thermotolerance in cell cultures and in organisms. The MF exposure might produce a potentiated or synergistic biological response such as an increase in HSPs expression, in combination with a well-defined stress, and in turn exert beneficial effects during certain circumstances.

Phospholipase Dδ negatively regulates plant thermotolerance by destabilizing cortical microtubules in Arabidopsis

The pattern of cortical microtubule arrays plays an important role in plant growth and adaptation in response to hormonal and environmental changes. Cortical microtubules are connected with the plasma membrane (PM); however, how the membrane affects cortical microtubule organization is not well understood. Here, we showed that phospholipase Dδ (PLDδ) was associated with the PM and co-localized with microtubules in cells. In vitro analysis revealed that PLDδ bound to microtubules, resulting in microtubule disorganization. Site-specific mutations that decreased PLDδ enzymatic activity impaired its effects on destabilizing microtubule organization. Heat shock transiently activated PLDδ, without any change of its PM localization, triggering microtubule dissociation from PM and depolymerization and seedling death in Arabidopsis, but these effects were alleviated in pldδ knockout mutants. Complementation of pldδ with wild-type PLDδ, but not mutated PLDδ, restored the phenotypes of microtubules and seedling survival to those of wild-type Arabidopsis. Thus, we conclude that the PM-associated PLDδ negatively regulates plant thermotolerance via destabilizing cortical microtubules, in an activity-dependent manner, rather than its subcellular translocation.

Heat-induced inflammation and its role in esophageal cancer

Esophageal cancer, the sixth most common cause of death from cancer worldwide, consists of different histological types and displays various patterns of incidence. Esophageal adenocarcinoma and esophageal squamous cell carcinoma are the most prevalent types. As epidemiological studies report that ingesting hot substances is one major risk factor for squamous cell carcinoma, evaluating the effect of this external stress on esophagus cells seems desirable. This specific kind of stress brings about cellular changes and stabilizes them by affecting different cellular features such as genetic stability, membrane integrity and the regulation of signaling pathways. It also causes tissue injury by affecting the extracellular matrix and cell viability. Thus, one of the main consequences of thermal injury is the activation of the immune system, which can result in chronic inflammation. The genetic alteration that has occurred during thermal injury and the consequent reduction in the function of repair systems is further strengthened by chronic inflammation, thereby increasing the probability that mutated cell lines may appear. The molecules that present in this circumstance, such as heat shock proteins, cytokines, chemokines and other inflammatory factors, affect intercellular signaling pathways, including nuclear factor kappa-light-chain-enhancer of activated B cells, signal transducer activator of transcription-3 and hypoxia-inducible factor 1α in supporting the survival and emergence of mutant phenotypes and the consequent malignant progression in altered cell lines. This investigation of these effective factors and their probable role in the tumorigenic path may improve current understanding.

Artificial Lipid Membranes: Past, Present, and Future

The multifaceted role of biological membranes prompted early the development of artificial lipid-based models with a primary view of reconstituting the natural functions in vitro so as to study and exploit chemoreception for sensor engineering. Over the years, a fair amount of knowledge on the artificial lipid membranes, as both, suspended or supported lipid films and liposomes, has been disseminated and has helped to diversify and expand initial scopes. Artificial lipid membranes can be constructed by several methods, stabilized by various means, functionalized in a variety of ways, experimented upon intensively, and broadly utilized in sensor development, drug testing, drug discovery or as molecular tools and research probes for elucidating the mechanics and the mechanisms of biological membranes. This paper reviews the state-of-the-art, discusses the diversity of applications, and presents future perspectives. The newly-introduced field of artificial cells further broadens the applicability of artificial membranes in studying the evolution of life.

Membrane-lipid therapy: A historical perspective of membrane-targeted therapies - From lipid bilayer structure to the pathophysiological regulation of cells

Our current understanding of membrane lipid composition, structure and functions has led to the investigation of their role in cell signaling, both in healthy and pathological cells. As a consequence, therapies based on the regulation of membrane lipid composition and structure have been recently developed. This novel field, known as Membrane Lipid Therapy, is growing and evolving rapidly, providing treatments that are now in use or that are being studied for their application to oncological disorders, Alzheimer's disease, spinal cord injury, stroke, diabetes, obesity, and neuropathic pain. This field has arisen from relevant discoveries on the behavior of membranes in recent decades, and it paves the way to adopt new approaches in modern pharmacology and nutrition. This innovative area will promote further investigation into membranes and the development of new therapies with molecules that target the cell membrane. Due to the prominent roles of membranes in the cells' physiology and the paucity of therapeutic approaches based on the regulation of the lipids they contain, it is expected that membrane lipid therapy will provide new treatments for numerous pathologies. The first on-purpose rationally designed molecule in this field, minerval, is currently being tested in clinical trials and it is expected to enter the market around 2020. However, it seems feasible that during the next few decades other membrane regulators will also be marketed for the treatment of human pathologies. This article is part of a Special Issue entitled: Membrane Lipid Therapy: Drugs Targeting Biomembranes edited by Pablo V. Escribá.

WITHDRAWN: Membrane-lipid therapy: A historical perspective of membrane-targeted therapies-From lipid bilayer structure to the pathophysiological regulation of cells

The Publisher regrets that this article is an accidental duplication of an article that has already been published, http://dx.doi.org/10.1016/j.bbamem.2017.05.017. The duplicate article has therefore been withdrawn. The full Elsevier Policy on Article Withdrawal can be found at https://www.elsevier.com/about/our-business/policies/article-withdrawal.

Metabolic crosstalk between membrane and storage lipids facilitates heat stress management in Schizosaccharomyces pombe

Cell membranes actively participate in stress sensing and signalling. Here we present the first in-depth lipidomic analysis to characterize alterations in the fission yeast Schizosaccharomyces pombe in response to mild heat stress (HS). The lipidome was assessed by a simple one-step methanolic extraction. Genetic manipulations that altered triglyceride (TG) content in the absence or presence of HS gave rise to distinct lipidomic fingerprints for S. pombe. Cells unable to produce TG demonstrated long-lasting growth arrest and enhanced signalling lipid generation. Our results reveal that metabolic crosstalk between membrane and storage lipids facilitates homeostatic maintenance of the membrane physical/chemical state that resists negative effects on cell growth and viability in response to HS. We propose a novel stress adaptation mechanism in which heat-induced TG synthesis contributes to membrane rigidization by accommodating unsaturated fatty acids of structural lipids, enabling their replacement by newly synthesized saturated fatty acids.

Acute exercise boosts cell proliferation and the heat shock response in lymphocytes: correlation with cytokine production and extracellular-to-intracellular HSP70 ratio

Exercise stimulates immune responses, but the appropriate "doses" for such achievements are unsettled. Conversely, in metabolic tissues, exercise improves the heat shock (HS) response, a universal cytoprotective response to proteostasis challenges that are centred on the expression of the 70-kDa family of intracellular heat shock proteins (iHSP70), which are anti-inflammatory. Concurrently, exercise triggers the export of HSP70 towards the extracellular milieu (eHSP70), where they work as pro-inflammatory cytokines. As the HS response is severely compromised in chronic degenerative diseases of inflammatory nature, we wondered whether acute exercise bouts of different intensities could alter the HS response of lymphocytes from secondary lymphoid organs and whether this would be related to immunoinflammatory responses. Adult male Wistar rats swam for 20 min at low, moderate, high or strenuous intensities as per an overload in tail base. Controls remained at rest under the same conditions. Afterwards, mesenteric lymph node lymphocytes were assessed for the potency of the HS response (42 °C for 2 h), NF-κB binding activity, mitogen-stimulated proliferation and cytokine production. Exercise stimulated cell proliferation in an "inverted-U" fashion peaking at moderate load, which was paralleled by suppression of NF-κB activation and nuclear location, and followed by enhanced HS response in relation to non-exercised animals. Comparative levels of eHSP70 to iHSP70 (H-index) matched IL-2/IL-10 ratios. We conclude that exercise, in a workload-dependent way, stimulates immunoinflammatory performance of lymphocytes of tissues far from the circulation and this is associated with H-index of stress response, which is useful to assess training status and immunosurveillance balance.

Membrane chaperoning by members of the PspA/IM30 protein family

PspA, IM30 (Vipp1) and LiaH, which all belong to the PspA/IM30 protein family, form high molecular weight oligomeric structures. For all proteins membrane binding and protection of the membrane structure and integrity has been shown or postulated. Here we discuss the possible membrane chaperoning activity of PspA, IM30 and LiaH and propose that larger oligomeric structures bind to stressed membrane regions, followed by oligomer disassembly and membrane stabilization by protein monomers or smaller/different oligomeric scaffolds.

Metabolomics revealed diurnal heat stress and zinc supplementation-induced changes in amino acid, lipid, and microbial metabolism

Heat stress (HS) dramatically disrupts the events in energy and nutrient metabolism, many of which requires zinc (Zn) as a cofactor. In this study, metabolic effects of HS and Zn supplementation were evaluated by examining growth performance, blood chemistry, and metabolomes of crossbred gilts fed with ZnNeg (no Zn supplementation), ZnIO (120 ppm ZnSO₄), or ZnAA (60 ppm ZnSO₄ + 60 ppm zinc amino acid complex) diets under diurnal HS or thermal‐neutral (TN) condition. The results showed that growth performance was reduced by HS but not by Zn supplementation. Among measured serum biochemicals, HS was found to increase creatinine but decrease blood urea nitrogen (BUN) level. Metabolomic analysis indicated that HS greatly affected diverse metabolites associated with amino acid, lipid, and microbial metabolism, including urea cycle metabolites, essential amino acids, phospholipids, medium‐chain dicarboxylic acids, fatty acid amides, and secondary bile acids. More importantly, many changes in these metabolite markers were correlated with both acute and adaptive responses to HS. Relative to HS‐induced metabolic effects, Zn supplementation‐associated effects were much more limited. A prominent observation was that ZnIO diet, potentially through its influences on microbial metabolism, yielded different responses to HS compared with two other diets, which included higher levels of short‐chain fatty acids (SCFAs) in cecal fluid and higher levels of lysine in the liver and feces. Overall, comprehensive metabolomic analysis identified novel metabolite markers associated with HS and Zn supplementation, which could guide further investigation on the mechanisms of these metabolic effects.

The central role of heat shock factor 1 in synaptic fidelity and memory consolidation

Networks of neuronal synapses are the fundamental basis for making and retaining memory. Reduced synapse number and quality correlates with loss of memory in dementia. Heat shock factor 1 (HSF1), the major transcription factor regulating expression of heat shock genes, plays a central role in proteostasis, in establishing and sustaining synaptic fidelity and function, and in memory consolidation. Support for this thesis is based on these observations: (1) heat shock induces improvements in synapse integrity and memory consolidation; (2) synaptic depolarization activates HSF1; (3) activation of HSF1 alone (independent of the canonical heat shock response) augments formation of essential synaptic elements-neuroligands, vesicle transport, synaptic scaffolding proteins, lipid rafts, synaptic spines, and axodendritic synapses; (4) HSF1 coalesces and activates memory receptors in the post-synaptic dendritic spine; (5) huntingtin or α-synuclein accumulation lowers HSF1 while HSF1 lowers huntingtin and α-synuclein aggregation-a potential vicious cycle; and (6) HSF1 agonists (including physical activity) can improve cognitive function in dementia models. Thus, via direct gene expression of synaptic elements, production of HSPs that assure high protein fidelity, and activation of other neuroprotective signaling pathways, HSF1 agonists could provide breakthrough therapy for dementia-associated disease.

The Role of the Membrane-Initiated Heat Shock Response in Cancer

The heat shock response (HSR) is a cellular response to diverse environmental and physiological stressors resulting in the induction of genes encoding molecular chaperones, proteases, and other proteins that are essential for protection and recovery from cellular damage. Since different perturbations cause accumulation of misfolded proteins, cells frequently encounter fluctuations in the environment which alter proteostasis. Since tumor cells use their natural adaptive mechanism of coping with stress and misfolded proteins, in recent years, the proteostasis network became a promising target for anti-tumor therapy. The membrane is the first to be affected by heat shock and therefore may be the first one to sense heat shock. The membrane also connects between the extracellular and the intracellular signals. Hence, there is a “cross talk” between the HSR and the membranes since heat shock can induce changes in the fluidity of membranes, leading to membrane lipid remodeling that occurs in several diseases such as cancer. During the last decade, a new possible therapy has emerged in which an external molecule is used that could induce membrane lipid re-organization. Since at the moment there are very few substances that regulate the HSR effectively, an alternative way has been searched to modulate chaperone activities through the plasma membrane. Recently, we suggested that the use of the membrane Transient Receptor Potential Vanilloid-1 (TRPV1) modulators regulated the HSR in cancer cells. However, the primary targets of the signal transduction pathway are yet un-known. This review provides an overview of the current literature regarding the role of HSR in membrane remodeling in cancer since a deep understanding of the membrane biology in cancer and the membrane heat sensing pathway is essential to design novel efficient therapies.

Improving efficacy of hyperthermia in oncology by exploiting biological mechanisms

It has long been established that hyperthermia increases the therapeutic benefit of radiation and chemotherapy in cancer treatment. During the last few years there have been substantial technical improvements in the sources used to apply and measure heat, which greatly increases enthusiasm for the clinical use of hyperthermia. These advances are converging with a better understanding of the physiological and molecular effects of hyperthermia. Therefore, we are now at a juncture where the parameters that will influence the efficacy of hyperthermia in cancer treatment can be optimised in a more systematic and rational manner. In addition, the novel insights in hyperthermia's many biological effects on tumour cells will ultimately result in new treatment regimes. For example, the molecular effects of hyperthermia on the essential cellular process of DNA repair suggest novel combination therapies, with DNA damage response targeting drugs that should now be clinically explored. Here, we provide an overview of recent studies on the various macroscopic and microscopic biological effects of hyperthermia. We indicate the significance of these effects on current treatments and suggest how they will help design novel future treatments.

Roles of specific lipid species in the cell and their molecular mechanism

Thousands of different molecular species of lipids are present within a single cell, being involved in modulating the basic processes of life. The vast number of different lipid species can be organized into a number of different lipid classes, which may be defined as a group of lipids with a common chemical structure, such as the headgroup, apart from the nature of the hydrocarbon chains. Each lipid class has unique biological roles. In some cases, a relatively small change in the headgroup chemical structure can result in a drastic change in function. Such phenomena are well documented, and largely understood in terms of specific interactions with proteins. In contrast, there are observations that the entire structural specificity of a lipid molecule, including the hydrocarbon chains, is required for biological activity through specific interactions with membrane proteins. Understanding of these phenomena represents a fundamental change in our thinking of the functions of lipids in biology. There are an increasing number of diverse examples of roles for specific lipids in cellular processes including: Signal transduction; trafficking; morphological changes; cell division. We are gaining knowledge and understanding of the underlying molecular mechanisms. They are of growing importance in both basic and applied sciences.

Stress signaling: serotonin spreads systemic stress

Cells respond to elevated temperatures through a well-characterized heat-shock response that enables short-term survival, long-term adaptation and mitigation of macromolecular damage. New work reveals a cell non-autonomous layer of stress-response regulation between neurons and the gonad involving serotonin.

Membrane lipid therapy: Modulation of the cell membrane composition and structure as a molecular base for drug discovery and new disease treatment

Nowadays we understand cell membranes not as a simple double lipid layer but as a collection of complex and dynamic protein-lipid structures and microdomains that serve as functional platforms for interacting signaling lipids and proteins. Membrane lipids and lipid structures participate directly as messengers or regulators of signal transduction. In addition, protein-lipid interactions participate in the localization of signaling protein partners to specific membrane microdomains. Thus, lipid alterations change cell signaling that are associated with a variety of diseases including cancer, obesity, neurodegenerative disorders, cardiovascular pathologies, etc. This article reviews the newly emerging field of membrane lipid therapy which involves the pharmacological regulation of membrane lipid composition and structure for the treatment of diseases. Membrane lipid therapy proposes the use of new molecules specifically designed to modify membrane lipid structures and microdomains as pharmaceutical disease-modifying agents by reversing the malfunction or altering the expression of disease-specific protein or lipid signal cascades. Here, we provide an in-depth analysis of this emerging field, especially its molecular bases and its relevance to the development of innovative therapeutic approaches.

TRP channels interaction with lipids and its implications in disease

Transient receptor potential (TRP) proteins are a family of ion channels central for sensory signaling. These receptors and, in particular, those involved in thermal sensing are also involved in pain signaling. Noteworthy, thermosensory receptors are polymodal ion channels that respond to both physical and chemical stimuli, thus integrating different environmental clues. In addition, their activity is modulated by algesic agents and lipidergic substances that are primarily released in pathological states. Lipids and lipid-like molecules have been found that can directly activate some thermosensory channels or modulate their activity by either potentiating or inhibiting it. To date, more than 50 endogenous lipids that can regulate TRP channel activity in sensory neurons have been described, thus representing the majority of known endogenous TRP channel modulators. Lipid modulators of TRP channels comprise lipids from a variety of metabolic pathways, including metabolites of the cyclooxygenase, lipoxygenase and cytochrome-P450 pathways, phospholipids and lysophospholipids. Therefore, TRP-channels are able to integrate and interpret incoming signals from the different metabolic lipid pathways. Taken together, the large number of lipids that can activate, sensitize or inhibit neuronal TRP-channels highlights the pivotal role of these molecules in sensory biology as well as in pain transduction and perception. This article is part of a Special Issue entitled: Lipid-protein interactions. Guest Editors: Amitabha Chattopadhyay and Jean-Marie Ruysschaert.

An artificial HSE promoter for efficient and selective detection of heat shock pathway activity

Detection of cellular stress is of major importance for the survival of cells. During evolution, a network of stress pathways developed, with the heat shock (HS) response playing a major role. The key transcription factor mediating HS signalling activity in mammalian cells is the HS factor HSF1. When activated it binds to the heat shock elements (HSE) in the promoters of target genes like heat shock protein (HSP) genes. They are induced by HSF1 but in addition they integrate multiple signals from different stress pathways. Here, we developed an artificial promoter consisting only of HSEs and therefore selectively reacting to HSF-mediated pathway activation. The promoter is highly inducible but has an extreme low basal level. Direct comparison with the HSPA1A promoter activity indicates that heat-dependent expression can be fully recapitulated by isolated HSEs in human cells. Using this sensitive reporter, we measured the HS response for different temperatures and exposure times. In particular, long heat induction times of 1 or 2 h were compared with short heat durations down to 1 min, conditions typical for burn injuries. We found similar responses to both long and short heat durations but at completely different temperatures. Exposure times of 2 h result in pathway activation at 41 to 44 °C, whereas heat pulses of 1 min lead to a maximum HS response between 47 and 50 °C. The results suggest that the HS response is initiated by a combination of temperature and exposure time but not by a certain threshold temperature.

Heat shock proteins: in vivo heat treatments reveal adipose tissue depot-specific effects

Heat treatments (HT) and the induction of heat shock proteins (HSPs) improve whole body and skeletal muscle insulin sensitivity while decreasing white adipose tissue (WAT) mass. However, HSPs in WAT have been understudied. The purpose of the present study was to examine patterns of HSP expression in WAT depots, and to examine the effects of a single in vivo HT on WAT metabolism. Male Wistar rats received HT (41°C, 20 min) or sham treatment (37°C), and 24 h later subcutaneous, epididymal, and retroperitoneal WAT depots (SCAT, eWAT, and rpWAT, respectively) were removed for ex vivo experiments and Western blotting. SCAT, eWAT, and rpWAT from a subset of rats were also cultured separately and received a single in vitro HT or sham treatment. HSP72 and HSP25 expression was greatest in more metabolically active WAT depots (i.e., eWAT and rpWAT) compared with the SCAT. Following HT, HSP72 increased in all depots with the greatest induction occurring in the SCAT. In addition, HSP25 increased in the rpWAT and eWAT, while HSP60 increased in the rpWAT only in vivo. Free fatty acid (FFA) release from WAT explants was increased following HT in the rpWAT only, and fatty acid reesterification was decreased in the rpWAT but increased in the SCAT following HT. HT increased insulin responsiveness in eWAT, but not in SCAT or rpWAT. Differences in HSP expression and induction patterns following HT further support the growing body of literature differentiating distinct WAT depots in health and disease.

Insertion of a 59 amino acid peptide in Salmonella Typhimurium membrane results in loss of virulence in mice

We demonstrated previously that expression of a single trans-membrane region of the Δ(12) -desaturase gene of Synechocystis sp. PCC 6803 in Salmonella enterica serovar Typhimurium (Salmonella Typhimurium) altered the membrane physical state of this pathogen, induced a significant change in the pattern of mRNA transcription of major heat shock genes, and inhibited pathogen growth inside murine macrophages. In this study, we demonstrate that injection of the modified Salmonella strain [Stm(pBAD200)] into C57Bl6j mice is safe. Survival of mice was associated with bacterial clearance, an increased number of splenic leukocytes, and high levels of interleukin-12, interferon γ and tumor necrosis factor α in spleens as well as in sera. Furthermore, Stm(pBAD200)-injected mice developed a Salmonella-specific antibody and Th1-like responses. Mice challenged with Stm(pBAD200) are protected from systemic infection with Salmonella wild-type. Similarly, mice infected with Stm(pBAD200) by the oral route survived when challenged with an oral lethal dose of Salmonella wild-type. The avirulent Stm(pBAD200) phenotype is associated with a remarkable change in the expression of the hilC, hilD, hilA, invF and phoP genes, among others, whose products are required for invasion and replication of Salmonella inside phagocytic cells. These data demonstrate the use of trans-membrane peptides to generate attenuated strains, providing a potential novel strategy to develop vaccines for both animal and human use.

The importance of the cellular stress response in the pathogenesis and treatment of type 2 diabetes

Organisms have evolved to survive rigorous environments and are not prepared to thrive in a world of caloric excess and sedentary behavior. A realization that physical exercise (or lack of it) plays a pivotal role in both the pathogenesis and therapy of type 2 diabetes mellitus (t2DM) has led to the provocative concept of therapeutic exercise mimetics. A decade ago, we attempted to simulate the beneficial effects of exercise by treating t2DM patients with 3 weeks of daily hyperthermia, induced by hot tub immersion. The short-term intervention had remarkable success, with a 1 % drop in HbA1, a trend toward weight loss, and improvement in diabetic neuropathic symptoms. An explanation for the beneficial effects of exercise and hyperthermia centers upon their ability to induce the cellular stress response (the heat shock response) and restore cellular homeostasis. Impaired stress response precedes major metabolic defects associated with t2DM and may be a near seminal event in the pathogenesis of the disease, tipping the balance from health into disease. Heat shock protein inducers share metabolic pathways associated with exercise with activation of AMPK, PGC1-a, and sirtuins. Diabetic therapies that induce the stress response, whether via heat, bioactive compounds, or genetic manipulation, improve or prevent all of the morbidities and comorbidities associated with the disease. The agents reduce insulin resistance, inflammatory cytokines, visceral adiposity, and body weight while increasing mitochondrial activity, normalizing membrane structure and lipid composition, and preserving organ function. Therapies restoring the stress response can re-tip the balance from disease into health and address the multifaceted defects associated with the disease.

The heat-shock response co-inducer arimoclomol protects against retinal degeneration in rhodopsin retinitis pigmentosa

Retinitis pigmentosa (RP) is a group of inherited diseases that cause blindness due to the progressive death of rod and cone photoreceptors in the retina. There are currently no effective treatments for RP. Inherited mutations in rhodopsin, the light-sensing protein of rod photoreceptor cells, are the most common cause of autosomal-dominant RP. The majority of mutations in rhodopsin, including the common P23H substitution, lead to protein misfolding, which is a feature in many neurodegenerative disorders. Previous studies have shown that upregulating molecular chaperone expression can delay disease progression in models of neurodegeneration. Here, we have explored the potential of the heat-shock protein co-inducer arimoclomol to ameliorate rhodopsin RP. In a cell model of P23H rod opsin RP, arimoclomol reduced P23H rod opsin aggregation and improved viability of mutant rhodopsin-expressing cells. In P23H rhodopsin transgenic rat models, pharmacological potentiation of the stress response with arimoclomol improved electroretinogram responses and prolonged photoreceptor survival, as assessed by measuring outer nuclear layer thickness in the retina. Furthermore, treated animal retinae showed improved photoreceptor outer segment structure and reduced rhodopsin aggregation compared with vehicle-treated controls. The heat-shock response (HSR) was activated in P23H retinae, and this was enhanced with arimoclomol treatment. Furthermore, the unfolded protein response (UPR), which is induced in P23H transgenic rats, was also enhanced in the retinae of arimoclomol-treated animals, suggesting that arimoclomol can potentiate the UPR as well as the HSR. These data suggest that pharmacological enhancement of cellular stress responses may be a potential treatment for rhodopsin RP and that arimoclomol could benefit diseases where ER stress is a factor.