Membrane-lipid therapy in operation: the HSP co-inducer BGP-15 activates stress signal transduction pathways by remodeling plasma membrane rafts

Membrane-localized magnetic hyperthermia promotes intracellular delivery of cell-impermeant probes

In this work, we report the disruptive use of membrane-localized magnetic hyperthermia to promote the internalization of cell-impermeant probes. Under an alternating magnetic field, magnetic nanoparticles (MNPs) immobilized on the cell membrane via bioorthogonal click chemistry act as nanoheaters and lead to the thermal disruption of the plasma membrane, which can be used for internalization of different types of molecules, such as small fluorescent probes and nucleic acids. Noteworthily, no cell death, oxidative stress and alterations of the cell cycle are detected after the thermal stimulus, although cells are able to sense and respond to the thermal stimulus through the expression of different types of heat shock proteins (HSPs). Finally, we demonstrate the utility of this approach for the transfection of cells with a small interference RNA (siRNA), revealing a similar efficacy to a standard transfection method based on the use of cationic lipid-based reagents (such as Lipofectamine), but with lower cell toxicity. These results open the possibility of developing new procedures for "opening and closing" cellular membranes with minimal disturbance of cellular integrity. This on-demand modification of cell membrane permeability could allow the direct intracellular delivery of biologically relevant (bio)molecules, drugs and nanomaterials, thus overcoming traditional endocytosis pathways and avoiding endosomal entrapment.

The Clinical Validation of Modulated Electro-Hyperthermia (mEHT)

The mEHT method uses tissues' thermal and bioelectromagnetic heterogeneity for the selective mechanisms. The success of the therapy for advanced, relapsed, and metastatic aggressive tumors can only be demonstrated by measuring survival time and quality of life (QoL). The complication is that mEHT-treated patients cannot be curatively treated any longer with "gold standards", where the permanent progression of the disease, the refractory, relapsing situation, the organ failure, the worsening of blood counts, etc., block them. Collecting a cohort of these patients is frequently impossible. Only an intent-to-treat (ITT) patient group was available. Due to the above limitations, many studies have single-arm data collection. The Phase III trial of advanced cervix tumors subgrouping of HIV-negative and -positive patients showed the stable efficacy of mEHT in all patients' subgroups. The single-arm represents lower-level evidence, which can be improved by comparing the survival data of various studies from different institutes. The Kaplan-Meier probability comparison had no significant differences, so pooled data were compared to other methods. Following this approach, we demonstrate the feasibility and superiority of mEHT in the cases of glioblastoma multiform, pancreas carcinomas, lung tumors, and colorectal tumors.

Crosstalk between Lipid Rafts and Aging: New Frontiers for Delaying Aging

With the rapid aging in the global population, delay of aging has become a hot research topic. Lipid rafts (LRs) are microdomains in the plasma membrane that contain sphingolipids and cholesterol. Emerging evidence indicates an interesting interplay between LRs and aging. LRs and their components are altered with aging. Further, the aging process is strongly influenced by LRs. In recent years, LRs and their component signaling molecules have been recognized to affect aging by interfering with its hallmarks. Therefore, targeting LRs is a promising strategy to delay aging.

Quantitative Comparison of HSF1 Activators

The heat shock response (HSR) pathway is a highly conserved rescue mechanism, which protects the cells from harmful insults disturbing the cellular protein homeostasis via expression of chaperones. Furthermore, it was demonstrated to play crucial roles in various diseases like neurodegeneration and cancer. For neurodegenerative diseases, an overexpression of chaperones is a potential therapeutic approach to clear the cells from non-functional protein aggregates. Therefore, activators of the HSR pathway and its master regulator HSF1 are under close observation. There are numerous HSR activators published in the literature using different model systems, experimental designs, and readout assays. The aim of this work was to provide a quantitative comparison of a broad range of published activators using a newly developed HSF responsive dual-luciferase cell line. Contrary to natural target genes, which are regulated by multiple input pathways, the artificial reporter exclusively reacts to HSF activity. In addition, the results were compared to endogenous heat shock protein expression. As a result, great differences in the intensity of pathway activation were observed. In addition, a parallel viability assessment revealed high variability in the specificity of the drugs. Furthermore, the differences seen compared to published data indicate that some activators exhibit tissue-specific differences leading to interesting assumptions about the regulation of HSF1.

Mycobacterial Membranes as Actionable Targets for Lipid-Centric Therapy in Tuberculosis

Infectious diseases remain significant health concerns worldwide, and resistance is particularly common in patients with tuberculosis caused by Mycobacterium tuberculosis. The development of anti-infectives with novel modes of action may help overcome resistance. In this regard, membrane-active agents, which modulate membrane components essential for the survival of pathogens, present attractive antimicrobial agents. Key advantages of membrane-active compounds include their ability to target slow-growing or dormant bacteria and their favorable pharmacokinetics. Here, we comprehensively review recent advances in the development of membrane-active chemotypes that target mycobacterial membranes and discuss clinically relevant membrane-active antibacterial agents that have shown promise in counteracting bacterial infections. We discuss the relationship between the membrane properties and the synthetic requirements within the chemical scaffold, as well as the limitations of current membrane-active chemotypes. This review will lay the chemical groundwork for the development of membrane-active antituberculosis agents and will foster the discovery of more effective antitubercular agents.

Lipids in Pathophysiology and Development of the Membrane Lipid Therapy: New Bioactive Lipids

Membranes are mainly composed of a lipid bilayer and proteins, constituting a checkpoint for the entry and passage of signals and other molecules. Their composition can be modulated by diet, pathophysiological processes, and nutritional/pharmaceutical interventions. In addition to their use as an energy source, lipids have important structural and functional roles, e.g., fatty acyl moieties in phospholipids have distinct impacts on human health depending on their saturation, carbon length, and isometry. These and other membrane lipids have quite specific effects on the lipid bilayer structure, which regulates the interaction with signaling proteins. Alterations to lipids have been associated with important diseases, and, consequently, normalization of these alterations or regulatory interventions that control membrane lipid composition have therapeutic potential. This approach, termed membrane lipid therapy or membrane lipid replacement, has emerged as a novel technology platform for nutraceutical interventions and drug discovery. Several clinical trials and therapeutic products have validated this technology based on the understanding of membrane structure and function. The present review analyzes the molecular basis of this innovative approach, describing how membrane lipid composition and structure affects protein-lipid interactions, cell signaling, disease, and therapy (e.g., fatigue and cardiovascular, neurodegenerative, tumor, infectious diseases).

The Paradoxical Effect of PARP Inhibitor BGP-15 on Irinotecan-Induced Cachexia and Skeletal Muscle Dysfunction

Simple Summary

Both cancer and the chemotherapy used to treat it are drivers of cachexia, a life-threatening body-wasting condition which complicates cancer treatment. Poly-(ADP-ribose) polymerase (PARP) inhibitors are currently being investigated as a treatment against cancer. Here, we present paradoxical evidence that they might also be useful for mitigating the skeletal muscle specific side-effects of anti-cancer chemotherapy or exacerbate them. BGP-15 is a small molecule PARP inhibitor which protected against irinotecan (IRI)-induced cachexia and loss of skeletal muscle mass and dysfunction in our study. However, peculiarly, BGP-15 adjuvant therapy reduced protein synthesis rates and the expression of key cytoskeletal proteins associated with the dystrophin-associated protein complex and increased matrix metalloproteinase activity, while it increased the propensity for fast-twitch muscles to tear during fatiguing contraction. Our data suggest that both IRI and BGP-15 cause structural remodeling involving proteins associated with the contractile apparatus, cytoskeleton and/or the extracellular matrix which may be only transient and ultimately beneficial or may paradoxically onset a muscular dystrophy phenotype and be detrimental if more permanent.

Abstract

Chemotherapy-induced muscle wasting and dysfunction is a contributing factor to cachexia alongside cancer and increases the risk of morbidity and mortality. Here, we investigate the effects of the chemotherapeutic agent irinotecan (IRI) on skeletal muscle mass and function and whether BGP-15 (a poly-(ADP-ribose) polymerase-1 (PARP-1) inhibitor and heat shock protein co-inducer) adjuvant therapy could protect against IRI-induced skeletal myopathy. Healthy 6-week-old male Balb/C mice (n = 24; 8/group) were treated with six intraperitoneal injections of either vehicle, IRI (30 mg/kg) or BGP-15 adjuvant therapy (IRI+BGP; 15 mg/kg) over two weeks. IRI reduced lean and tibialis anterior mass, which were attenuated by IRI+BGP treatment. Remarkably, IRI reduced muscle protein synthesis, while IRI+BGP reduced protein synthesis further. These changes occurred in the absence of a change in crude markers of mammalian/mechanistic target of rapamycin (mTOR) Complex 1 (mTORC1) signaling and protein degradation. Interestingly, the cytoskeletal protein dystrophin was reduced in both IRI- and IRI+BGP-treated mice, while IRI+BGP treatment also decreased β-dystroglycan, suggesting significant remodeling of the cytoskeleton. IRI reduced absolute force production of the soleus and extensor digitorum longus (EDL) muscles, while IRI+BGP rescued absolute force production of the soleus and strongly trended to rescue force output of the EDL (p = 0.06), which was associated with improvements in mass. During the fatiguing stimulation, IRI+BGP-treated EDL muscles were somewhat susceptible to rupture at the musculotendinous junction, likely due to BGP-15’s capacity to maintain the rate of force development within a weakened environment characterized by significant structural remodeling. Our paradoxical data highlight that BGP-15 has some therapeutic advantage by attenuating IRI-induced skeletal myopathy; however, its effects on the remodeling of the cytoskeleton and extracellular matrix, which appear to make fast-twitch muscles more prone to tearing during contraction, could suggest the induction of muscular dystrophy and, thus, require further characterization.

Bioglass could increase cell membrane fluidity with ion products to develop its bioactivity

OBJECTIVES

Silicate bioactive glass (BG) has been widely demonstrated to stimulate both of the hard and soft tissue regeneration, in which ion products released from BG play important roles. However, the mechanism by which ion products act on cells on cells is unclear.

MATERIALS AND METHODS

Human umbilical vein endothelial cells and human bone marrow stromal cells were used in this study. Fluorescence recovery after photobleaching and generalized polarization was used to characterize changes in cell membrane fluidity. Migration, differentiation and apoptosis experiments were carried out. RNA and protein chip were detected. The signal cascade is simulated to evaluate the effect of increased cell membrane fluidity on signal transduction.

RESULTS

We have demonstrated that ion products released from BG could effectively enhance cell membrane fluidity in a direct and physical way, and Si ions may play a major role. Bioactivities of BG ion products on cells, such as migration and differentiation, were regulated by membrane fluidity. Furthermore, we have proved that BG ion products could promote apoptosis of injured cells based on our conclusion that BG ion products increased membrane fluidity.

CONCLUSIONS

This study proved that BG ion products could develop its bioactivity on cells by directly enhancing cell membrane fluidity and subsequently affected cell behaviours, which may provide an explanation for the general bioactivities of silicate material.

Targeting metabolic syndrome with phytochemicals: Focus on the role of molecular chaperones and hormesis in drug discovery

Adaptive cellular stress response confers stress tolerance against inflammatory and metabolic disorders. In response to metabolic stress, the key mediator of cellular adaptation and tolerance is a class of molecules called the molecular chaperones (MCs). MCs are highly conserved molecules that play critical role in maintaining protein stability and functionality. Hormesis in this context is a unique adaptation mechanism where a low dose of a stressor (which is toxic at high dose) confers a stress-resistant adaptive cellular phenotype. Hormesis can be observed at different level of biological organization at various measurable endpoints. The MCs are believed to play a key role in adaptation during hormesis. Several phytochemicals are known for their hormetic response and are called phytochemical hormetins. The role of phytochemical-mediated hormesis on the adaptive cellular processes is proposed as a potential therapeutic approach to target inflammation associated with metabolic syndrome. However, the screening of phytochemical hormetins would require a paradigm shift in the methods currently used in drug discovery.

Andersen-Tawil Syndrome Is Associated With Impaired PIP2 Regulation of the Potassium Channel Kir2.1

Andersen-Tawil syndrome (ATS) type-1 is associated with loss-of-function mutations in KCNJ2 gene. KCNJ2 encodes the tetrameric inward-rectifier potassium channel Kir2.1, important to the resting phase of the cardiac action potential. Kir-channels' activity requires interaction with the agonist phosphatidylinositol-4,5-bisphosphate (PIP₂). Two mutations were identified in ATS patients, V77E in the cytosolic N-terminal "slide helix" and M307V in the C-terminal cytoplasmic gate structure "G-loop." Current recordings in Kir2.1-expressing HEK cells showed that each of the two mutations caused Kir2.1 loss-of-function. Biotinylation and immunostaining showed that protein expression and trafficking of Kir2.1 to the plasma membrane were not affected by the mutations. To test the functional effect of the mutants in a heterozygote set, Kir2.1 dimers were prepared. Each dimer was composed of two Kir2.1 subunits joined with a flexible linker (i.e. WT-WT, WT dimer; WT-V77E and WT-M307V, mutant dimer). A tetrameric assembly of Kir2.1 is expected to include two dimers. The protein expression and the current density of WT dimer were equally reduced to ~25% of the WT monomer. Measurements from HEK cells and Xenopus oocytes showed that the expression of either WT-V77E or WT-M307V yielded currents of only about 20% compared to the WT dimer, supporting a dominant-negative effect of the mutants. Kir2.1 sensitivity to PIP₂ was examined by activating the PIP₂ specific voltage-sensitive phosphatase (VSP) that induced PIP₂ depletion during current recordings, in HEK cells and Xenopus oocytes. PIP₂ depletion induced a stronger and faster decay in Kir2.1 mutant dimers current compared to the WT dimer. BGP-15, a drug that has been demonstrated to have an anti-arrhythmic effect in mice, stabilized the Kir2.1 current amplitude following VSP-induced PIP₂ depletion in cells expressing WT or mutant dimers. This study underlines the implication of mutations in cytoplasmic regions of Kir2.1. A newly developed calibrated VSP activation protocol enabled a quantitative assessment of changes in PIP₂ regulation caused by the mutations. The results suggest an impaired function and a dominant-negative effect of the Kir2.1 variants that involve an impaired regulation by PIP₂. This study also demonstrates that BGP-15 may be beneficial in restoring impaired Kir2.1 function and possibly in treating ATS symptoms.

Negative Inotropic Effect of BGP-15 on the Human Right Atrial Myocardium

Cardiovascular morbidity and mortality carry great socioeconomic burden worldwide that mandates the development of new, efficacious therapeutic agents with limited adverse effects. O-(3-piperidino-2-hydroxy-1-propyl) nicotinic acid amidoxime (BGP-15) is a known, well-tolerable drug candidate that exerts beneficial effects in several disease models. As BGP-15 has a significant structural similarity with propranolol, it arose that BGP-15 might also have a direct effect on the heart. Thus, in the present work, we investigated the effect of BGP-15 and propranolol on the contractility of isolated, paced, human right atrial samples (obtained from patients undergone open-heart surgery), with or without previous isoproterenol (ISO) stimulation (evoking an indirect or direct effect, respectively). We found that both BGP-15 and propranolol exerted direct as well as indirect negative inotropic effects on the atrial myocardium, reaching similar maximal response. However, BGP-15 had considerably smaller potency than propranolol regarding both types of negative inotropy. In addition, BGP-15, in contrast to propranolol, had a significantly greater indirect negative inotropic effect on samples exhibiting strong response to ISO. Moreover, the indirect negative inotropic effect of BGP-15 was significantly greater on samples derived from diabetic patients than on samples obtained from non-diabetic ones. Our results suggest that the enhanced ISO sensitivity is associated with the diabetic state, and BGP-15 exerts greater negative inotropic effect on the human atrial myocardium in both conditions (as compared to the atrial tissue that is not ISO oversensitive and/or diabetic). Additionally, the negative inotropic effects of BGP-15 and propranolol seem to be mediated by in part different molecular pathways in the atrial myocardium.

Pharmacological Overview of the BGP-15 Chemical Agent as a New Drug Candidate for the Treatment of Symptoms of Metabolic Syndrome

BGP-15 is a new insulin sensitizer drug candidate, which was developed by Hungarian researchers. In recent years, numerous research groups have studied its beneficial effects. It is effective in the treatment of insulin resistance and it has protective effects in Duchenne muscular dystrophy, diastolic dysfunction, tachycardia, heart failure, and atrial fibrillation, and it can alleviate cardiotoxicity. BGP-15 exhibits chemoprotective properties in different cytostatic therapies, and has also proven to be photoprotective. It can additionally have advantageous effects in mitochondrial-stress-related diseases. Although the precise mechanism of the effect is still unknown to us, we know that the molecule is a PARP inhibitor, chaperone co-inducer, reduces ROS production, and is able to remodel the organization of cholesterol-rich membrane domains. In the following review, our aim was to summarize the investigated molecular mechanisms and pharmacological effects of this potential API. The main objective was to present the wide pharmacological potentials of this chemical agent.

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.

Therapeutic Benefits from Nanoparticles: The Potential Significance of Nanoscience in Retinal Degenerative Diseases

Several nanotechnology podiums have gained remarkable attention in the area of medical sciences, including diagnostics and treatment. In the past decade, engineered multifunctional nanoparticles have served as drug and gene carriers. The most important aspect of translating nanoparticles from the bench to bedside is safety. These nanoparticles should not elicit any immune response and should not be toxic to humans or the environment. Lipid-based nanoparticles have been shown to be the least toxic for in vivo applications, and significant progress has been made in gene and drug delivery employing lipid-based nanoassemblies. Several excellent reviews and reports discuss the general use and application of lipid-based nanoparticles; our review focuses on the application of lipid-based nanoparticles for the treatment of ocular diseases, and recent advances in and updates on their use.

Mitochondrial regulation of [Ca2+]i oscillations during cell cycle resumption of the second meiosis of oocyte

Oocyte is arrested at metaphase of the second meiosis until fertilization switching on [Ca²⁺]i oscillations. Oocyte activation inefficiency is the most challenging problem for failed fertilization and embryonic development. Mitochondrial function and intracellular [Ca²⁺]i oscillations are two critical factors for the oocyte's developmental potential. We aimed to understand the possible correlation between mitochondrial function and [Ca²⁺]i oscillations in oocytes. To this end, mitochondrial uncoupler CCCP which damages mitochondrial function and two small molecule mitochondrial agonists, L-carnitine (LC) and BGP-15, were used to examine the regulation of [Ca²⁺]i by mitochondrial functions. With increasing CCCP concentrations, [Ca²⁺]i oscillations were gradually diminished and high concentrations of CCCP led to oocyte death. LC enhanced mitochondrial membrane potential and [Ca²⁺]i oscillations and even improved the damage induced by CCCP, however, BGP-15 had no beneficial effect on oocyte activation. We have found that mitochondrial function plays a vital role in the generation of [Ca²⁺]i oscillations in oocytes, and thus mitochondria may interact with the ER to generate [Ca²⁺]i oscillations during oocyte activation. Improvement of mitochondrial functions with small molecules can be expected to improve oocyte activation and embryonic development in infertile patients without invasive micromanipulation.

BGP-15 improves contractile function of regenerating soleus muscle

This study investigated the effect of the heat shock protein inducer O-[3-piperidino-2-hydroxy-1-propyl]-nicotinic amidoxime (BGP-15) on the morphology and contractile function of regenerating soleus muscles from mice. Cryolesioned soleus muscles from young mice treated daily with BGP-15 (15 mg/Kg) were evaluated on post-cryolesion day 10. At this time point, there was a significant decrease in the cross-sectional area of regenerating myofibers, maximal force, specific tetanic force, and fatigue resistance of regenerating soleus muscles. BGP-15 did not reverse the decrease in myofiber cross-sectional area but effectively prevented the reduction in tetanic force and fatigue resistance of regenerating muscles. In addition, BGP-15 treatment increased the expression of embryonic myosin heavy chain (e-MyHC), MyHC-II and MyHC-I in regenerating muscles. Although BGP-15 did not alter voltage dependent anion-selective channel 2 (VDAC2) expression in cryolesioned muscles, it was able to increase inducible 70-kDa heat shock protein (HSP70) expression. Our results suggest that BGP-15 improves strength recovery in regenerating soleus muscles by accelerating the re-expression of adult MyHC-II and MyHC-I isoforms and HSP70 induction. The beneficial effects of BGP-15 on the contractile function of regenerating muscles reinforce the potential of this molecule to be used as a therapeutic agent.

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.

The chaperone co-inducer BGP-15 alleviates ventilation-induced diaphragm dysfunction

Ventilation-induced diaphragm dysfunction (VIDD) is a marked decline in diaphragm function in response to mechanical ventilation, which has negative consequences for individual patients' quality of life and for the health care system, but specific treatment strategies are still lacking. We used an experimental intensive care unit (ICU) model, allowing time-resolved studies of diaphragm structure and function in response to long-term mechanical ventilation and the effects of a pharmacological intervention (the chaperone co-inducer BGP-15). The marked loss of diaphragm muscle fiber function in response to mechanical ventilation was caused by posttranslational modifications (PTMs) of myosin. In a rat model, 10 days of BGP-15 treatment greatly improved diaphragm muscle fiber function (by about 100%), although it did not reverse diaphragm atrophy. The treatment also provided protection from myosin PTMs associated with HSP72 induction and PARP-1 inhibition, resulting in improvement of mitochondrial function and content. Thus, BGP-15 may offer an intervention strategy for reducing VIDD in mechanically ventilated ICU patients.

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.

Chaperone co-inducer BGP-15 inhibits histone deacetylases and enhances the heat shock response through increased chromatin accessibility

Defects in cellular protein homeostasis are associated with many severe and prevalent pathological conditions such as neurodegenerative diseases, muscle dystrophies, and metabolic disorders. One way to counteract these defects is to improve the protein homeostasis capacity through induction of the heat shock response. Despite numerous attempts to develop strategies for chemical activation of the heat shock response by heat shock transcription factor 1 (HSF1), the underlying mechanisms of drug candidates' mode of action are poorly understood. To lower the threshold for the heat shock response activation, we used the chaperone co-inducer BGP-15 that was previously shown to have beneficial effects on several proteinopathic disease models. We found that BGP-15 treatment combined with heat stress caused a substantial increase in HSF1-dependent heat shock protein 70 (HSPA1A/B) expression already at a febrile range of temperatures. Moreover, BGP-15 alone inhibited the activity of histone deacetylases (HDACs), thereby increasing chromatin accessibility at multiple genomic loci including the stress-inducible HSPA1A. Intriguingly, treatment with well-known potent HDAC inhibitors trichostatin A and valproic acid enhanced the heat shock response and improved cytoprotection. These results present a new pharmacological strategy for restoring protein homeostasis by inhibiting HDACs, increasing chromatin accessibility, and lowering the threshold for heat shock response activation.

Changes in the plasma membrane in metabolic disease: impact of the membrane environment on G protein-coupled receptor structure and function

Drug development targeting GPCRs often utilizes model heterologous cell expression systems, reflecting an implicit assumption that the membrane environment has little functional impact on these receptors or on their responsiveness to drugs. However, much recent data have illustrated that membrane components can have an important functional impact on intrinsic membrane proteins. This review is directed toward gaining a better understanding of the structure of the plasma membrane in health and disease, and how this organelle can influence GPCR structure, function and regulation. It is important to recognize that the membrane provides a potential mode of lateral allosteric regulation of GPCRs and can affect the effectiveness of drugs and their biological responses in various disease states, which can even vary among individuals across the population. The type 1 cholecystokinin receptor is reviewed as an exemplar of a class A GPCR that is affected in this way by changes in the plasma membrane.

LINKED ARTICLES

This article is part of a themed section on Molecular Pharmacology of GPCRs. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v175.21/issuetoc.

Hyperthermia and associated changes in membrane fluidity potentiate P2X7 activation to promote tumor cell death

Extracellular ATP (eATP) accumulation within the tumor microenvironment (TME) has the potential to activate purinergic signaling. The eATP evoked signaling effects bolster antitumor immune responses while exerting direct cytotoxicity on tumor cells and vascular endothelial cells, mediated at least in part through P2X7 receptors. Approaches to augment purinergic signaling in TME e.g. by ectonucleotidase CD39 blockade, and/or boosting P2X7 functional responses, might be used as immunomodulatory therapies in cancer treatment. In this study, we delineated the translatable strategy of hyperthermia to demonstrate impacts on P2X7 responsiveness to eATP. Hyperthermia (40°C) was noted to enhance eATP-mediated cytotoxicity on MCA38 colon cancer cells. Increased membrane fluidity induced by hyperthermia boosted P2X7 functionality, potentiating pore opening and modulating downstream AKT/PRAS40/mTOR signaling events. When combined with cisplatin or mitomycin C, hyperthermia and eATP together markedly potentiate cancer cell death. Our data indicate that clinically tolerable hyperthermia with modulated P2X7-purinergic signaling will boost efficacy of conventional cancer treatments.

Discovery of Novel Insulin Sensitizers: Promising Approaches and Targets

Insulin resistance is the undisputed root cause of type 2 diabetes mellitus (T2DM). There is currently an unmet demand for safe and effective insulin sensitizers, owing to the restricted prescription or removal from market of certain approved insulin sensitizers, such as thiazolidinediones (TZDs), because of safety concerns. Effective insulin sensitizers without TZD-like side effects will therefore be invaluable to diabetic patients. The specific focus on peroxisome proliferator-activated receptor γ- (PPARγ-) based agents in the past decades may have impeded the search for novel and safer insulin sensitizers. This review discusses possible directions and promising strategies for future research and development of novel insulin sensitizers and describes the potential targets of these agents. Direct PPARγ agonists, selective PPARγ modulators (sPPARγMs), PPARγ-sparing compounds (including ligands of the mitochondrial target of TZDs), agents that target the downstream effectors of PPARγ, along with agents, such as heat shock protein (HSP) inducers, 5'-adenosine monophosphate-activated protein kinase (AMPK) activators, 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1) selective inhibitors, biguanides, and chloroquines, which may be safer than traditional TZDs, have been described. This minireview thus aims to provide fresh perspectives for the development of a new generation of safe insulin sensitizers.

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.

Lipids in infectious diseases - The case of AIDS and tuberculosis

Lipids play a central role in many infectious diseases. AIDS (Acquired Immune Deficiency Syndrome) and tuberculosis are two of the deadliest infectious diseases to have struck mankind. The pathogens responsible for these diseases, Human Immunodeficiency Virus-1 and Mycobacterium tuberculosis, rely on lipids and on lipid membrane properties to gain access to their host cells, to persist in them and ultimately to egress from their hosts. In this Review, we discuss the life cycles of these pathogens and the roles played by lipids and membranes. We then give an overview of therapies that target lipid metabolism, modulate host membrane properties or implement lipid-based drug delivery systems. This article is part of a Special Issue entitled: Membrane Lipid Therapy: Drugs Targeting Biomembranes edited by Pablo V. Escribá.

BGP-15 prevents the death of neurons in a mouse model of familial dysautonomia

Hereditary sensory and autonomic neuropathy type III, or familial dysautonomia [FD; Online Mendelian Inheritance in Man (OMIM) 223900], affects the development and long-term viability of neurons in the peripheral nervous system (PNS) and retina. FD is caused by a point mutation in the gene IKBKAP/ELP1 that results in a tissue-specific reduction of the IKAP/ELP1 protein, a subunit of the Elongator complex. Hallmarks of the disease include vasomotor and cardiovascular instability and diminished pain and temperature sensation caused by reductions in sensory and autonomic neurons. It has been suggested but not demonstrated that mitochondrial function may be abnormal in FD. We previously generated an Ikbkap/Elp1 conditional-knockout mouse model that recapitulates the selective death of sensory (dorsal root ganglia) and autonomic neurons observed in FD. We now show that in these mice neuronal mitochondria have abnormal membrane potentials, produce elevated levels of reactive oxygen species, are fragmented, and do not aggregate normally at axonal branch points. The small hydroxylamine compound BGP-15 improved mitochondrial function, protecting neurons from dying in vitro and in vivo, and promoted cardiac innervation in vivo. Given that impairment of mitochondrial function is a common pathological component of neurodegenerative diseases such as amyotrophic lateral sclerosis and Alzheimer's, Parkinson's, and Huntington's diseases, our findings identify a therapeutic approach that may have efficacy in multiple degenerative conditions.

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.

BGP-15 Protects against Oxidative Stress- or Lipopolysaccharide-Induced Mitochondrial Destabilization and Reduces Mitochondrial Production of Reactive Oxygen Species

Reactive oxygen species (ROS) play a critical role in the progression of mitochondria-related diseases. A novel insulin sensitizer drug candidate, BGP-15, has been shown to have protective effects in several oxidative stress-related diseases in animal and human studies. In this study, we investigated whether the protective effects of BGP-15 are predominantly via preserving mitochondrial integrity and reducing mitochondrial ROS production. BGP-15 was found to accumulate in the mitochondria, protect against ROS-induced mitochondrial depolarization and attenuate ROS-induced mitochondrial ROS production in a cell culture model, and also reduced ROS production predominantly at the complex I-III system in isolated mitochondria. At physiologically relevant concentrations, BGP-15 protected against hydrogen peroxide-induced cell death by reducing both apoptosis and necrosis. Additionally, it attenuated bacterial lipopolysaccharide (LPS)-induced collapse of mitochondrial membrane potential and ROS production in LPS-sensitive U-251 glioma cells, suggesting that BGP-15 may have a protective role in inflammatory diseases. However, BGP-15 did not have any antioxidant effects as shown by in vitro chemical and cell culture systems. These data suggest that BGP-15 could be a novel mitochondrial drug candidate for the prevention of ROS-related and inflammatory disease progression.

BGP-15 Improves Aspects of the Dystrophic Pathology in mdx and dko Mice with Differing Efficacies in Heart and Skeletal Muscle

Duchenne muscular dystrophy is a severe and progressive striated muscle wasting disorder that leads to premature death from respiratory and/or cardiac failure. We have previously shown that treatment of young dystrophic mdx and dystrophin/utrophin null (dko) mice with BGP-15, a coinducer of heat shock protein 72, ameliorated the dystrophic pathology. We therefore tested the hypothesis that later-stage BGP-15 treatment would similarly benefit older mdx and dko mice when the dystrophic pathology was already well established. Later stage treatment of mdx or dko mice with BGP-15 did not improve maximal force of tibialis anterior (TA) muscles (in situ) or diaphragm muscle strips (in vitro). However, collagen deposition (fibrosis) was reduced in TA muscles of BGP-15-treated dko mice but unchanged in TA muscles of treated mdx mice and diaphragm of treated mdx and dko mice. We also examined whether BGP-15 treatment could ameliorate aspects of the cardiac pathology, and in young dko mice it reduced collagen deposition and improved both membrane integrity and systolic function. These results confirm BGP-15's ability to improve aspects of the dystrophic pathology but with differing efficacies in heart and skeletal muscles at different stages of the disease progression. These findings support a role for BGP-15 among a suite of pharmacological therapies for Duchenne muscular dystrophy and related disorders.

Targeting Heat Shock Proteins Mitigates Ventilator Induced Diaphragm Muscle Dysfunction in an Age-Dependent Manner

Intensive care unit (ICU) patients are often overtly subjected to mechanical ventilation and immobilization, which leads to impaired limb and respiratory muscle function. The latter, termed ventilator-induced diaphragm dysfunction (VIDD) has recently been related to compromised heat shock protein (Hsp) activation. The administration of a pharmacological drug BGP-15 acting as a Hsp chaperone co-inducer has been found to partially alleviate VIDD in young rats. Considering that the mean age in the ICU is increasing, we aimed to explore whether the beneficial functional effects are also present in old rats. For that, we exposed young (7–8 months) and old (28–32 months) rats to 5-day controlled mechanical ventilation and immobilization with or without systemic BGP-15 administration. We then dissected diaphragm muscles, membrane–permeabilized bundles and evaluated the contractile function at single fiber level. Results confirmed that administration of BGP-15 restored the force-generating capacity of isolated muscle cells from young rats in conjunction with an increased expression of Hsp72. On the other hand, our results highlighted that old rats did not positively respond to the BGP-15 treatment. Therefore, it is of crucial importance to comprehend in more depth the effect of VIDD on diaphragm function and ascertain any further age-related differences.

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.

Involvement of small heat shock proteins, trehalose, and lipids in the thermal stress management in Schizosaccharomyces pombe

Changes in the levels of three structurally and functionally different important thermoprotectant molecules, namely small heat shock proteins (sHsps), trehalose, and lipids, have been investigated upon heat shock in Schizosaccharomyces pombe. Both α-crystallin-type sHsps (Hsp15.8 and Hsp16) were induced after prolonged high-temperature treatment but with different kinetic profiles. The shsp null mutants display a weak, but significant, heat sensitivity indicating their importance in the thermal stress management. The heat induction of sHsps is different in wild type and in highly heat-sensitive trehalose-deficient (tps1Δ) cells; however, trehalose level did not show significant alteration in shsp mutants. The altered timing of trehalose accumulation and induction of sHsps suggest that the disaccharide might provide protection at the early stage of the heat stress while elevated amount of sHsps are required at the later phase. The cellular lipid compositions of two different temperature-adapted wild-type S. pombe cells are also altered according to the rule of homeoviscous adaptation, indicating their crucial role in adapting to the environmental temperature changes. Both Hsp15.8 and Hsp16 are able to bind to different lipids isolated from S. pombe, whose interaction might provide a powerful protection against heat-induced damages of the membranes. Our data suggest that all the three investigated thermoprotectant macromolecules play a pivotal role during the thermal stress management in the fission yeast.

Heat shock proteins and exercise adaptations. Our knowledge thus far and the road still ahead

By its very nature, exercise exerts a challenge to the body's cellular homeostatic mechanisms. This homeostatic challenge affects not only the contracting skeletal muscle but also a number of other organs and results over time in exercise-induced adaptations. Thus it is no surprise that heat shock proteins (HSPs), a group of ancient and highly conserved cytoprotective proteins critical in the maintenance of protein and cellular homeostasis, have been implicated in exercise/activity-induced adaptations. It has become evident that HSPs such as HSP72 are induced or activated with acute exercise or after chronic exercise training regimens. These observations have given scientists an insight into the protective mechanisms of these proteins and provided an opportunity to exploit their protective role to improve health and physical performance. Although our knowledge in this area of physiology has improved dramatically, many questions still remain unanswered. Further understanding of the role of HSPs in exercise physiology may prove beneficial for therapeutic targeting in diseased patient cohorts, exercise prescription for disease prevention, and training strategies for elite athletes.

Hsp70 plays an important role in high-fat diet induced gestational hyperglycemia in mice

Gestational diabetes mellitus (GDM) has emerged as an epidemic disease during the last decade, affecting about 2 to 5% pregnant women. Even among women who have gestational hyperglycemia may also be positively related to adverse outcomes as GDM. Since heat shock protein (Hsp) 70 has been reported to be associated with diabetes and insulin resistance and its expression was reported to be negatively regulated by the membrane-permeable Hsp70 inhibitor MAL3-101 while positively regulated by the Hsp70 activator BGP-15, we investigated whether Hsp70 played a role in a gestational hyperglycemia mouse model. Mice were divided into non-pregnant and pregnant groups, and each comprised three subgroups: control, high-fat diet (HFD) + MAL3-101, and HFD + BGP-15. We examined the serum levels of triglycerides, total cholesterol, glucose, and insulin, as well as conducted thermal detection of brown adipose tissue (BAT). The role of Hsp70 in BAT apoptosis was also investigated by terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay and caspase-3 staining. Higher serum level of Hsp70 was associated with increased bodyweight gain after pregnancy in mice fed HFD. Circulating Hsp70 was elevated in control pregnant mice compared to control non-pregnant mice. BGP-induced serum Hsp70 expression reduced triglycerides, total cholesterol, glucose, and insulin levels in the serum. Additionally, thermal detection of BAT, TUNEL, and caspase-3 staining revealed relationship correlation between Hsp70 and BAT functions. Hsp70 level is associated with hyperglycemia during pregnancy. Our results support the role of Hsp70 in facilitating BAT activities and protecting BAT cells from apoptosis via caspase-3 pathway.

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.

Chaperoning to the metabolic party: The emerging therapeutic role of heat-shock proteins in obesity and type 2 diabetes

Background

From their initial, accidental discovery 50 years ago, the highly conserved Heat Shock Proteins (HSPs) continue to exhibit fundamental roles in the protection of cell integrity. Meanwhile, in the midst of an obesity epidemic, research demonstrates a key involvement of low grade inflammation, and mitochondrial dysfunction amongst other mechanisms, in the pathology of insulin resistance and type 2 diabetes mellitus (T2DM). In particular, tumor necrosis factor alpha (TNFα), endoplasmic reticulum (ER) and oxidative stress all appear to be associated with obesity and stimulate inflammatory kinases such as c jun amino terminal kinase (JNK), inhibitor of NF-κβ kinase (IKK) and protein kinase C (PKC) which in turn, inhibit insulin signaling. Mitochondrial dysfunction in skeletal muscle has also been proposed to be prominent in the pathogenesis of T2DM either by reducing the ability to oxidize fatty acids, leading to the accumulation of deleterious lipid species in peripheral tissues such as skeletal muscle and liver, or by altering the cellular redox state. Since HSPs act as molecular chaperones and demonstrate crucial protective functions in stressed cells, we and others have postulated that the manipulation of HSP expression in metabolically relevant tissues represents a therapeutic avenue for obesity-induced insulin resistance.

Scope of Review

This review summarizes the literature from both animal and human studies, that has examined how HSPs, particularly the inducible HSP, Heat Shock Protein 72 (Hsp72) alters glucose homeostasis and the possible approaches to modulating Hsp72 expression. A summation of the role of chemical chaperones in metabolic disorders is also included.

Major Conclusions

Targeted manipulation of Hsp72 or use of chemical chaperiones may have clinical utility in treating metabolic disorders such as insulin resistance and T2DM.

Therapeutic inducers of the HSP70/HSP110 protect mice against traumatic brain injury

Traumatic brain injury (TBI) induces severe harm and disability in many accident victims and combat-related activities. The heat-shock proteins Hsp70/Hsp110 protect cells against death and ischemic damage. In this study, we used mice deficient in Hsp110 or Hsp70 to examine their potential requirement following TBI. Data indicate that loss of Hsp110 or Hsp70 increases brain injury and death of neurons. One of the mechanisms underlying the increased cell death observed in the absence of Hsp110 and Hsp70 following TBI is the increased expression of reactive oxygen species-induced p53 target genes Pig1, Pig8, and Pig12. To examine whether drugs that increase the levels of Hsp70/Hsp110 can protect cells against TBI, we subjected mice to TBI and administered Celastrol or BGP-15. In contrast to Hsp110- or Hsp70i-deficient mice that were not protected following TBI and Celastrol treatment, there was a significant improvement of wild-type mice following administration of these drugs during the first week following TBI. In addition, assessment of neurological injury shows significant improvement in contextual and cued fear conditioning tests and beam balance in wild-type mice that were treated with Celastrol or BGP-15 following TBI compared to TBI-treated mice. These studies indicate a significant role of Hsp70/Hsp110 in neuronal survival following TBI and the beneficial effects of Hsp70/Hsp110 inducers toward reducing the pathological consequences of TBI. Our data indicate that loss of Hsp110 or Hsp70 in mice increases brain injury following TBI. (a) One of the mechanisms underlying the increased cell death observed in the absence of these Hsps following TBI is the increased expression of ROS-induced p53 target genes known as Pigs. In addition, (b) using drugs (Celastrol or BGP-15) to increase Hsp70/Hsp110 levels protect cells against TBI, suggesting the beneficial effects of Hsp70/Hsp110 inducers to reduce the pathological consequences of TBI.

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.

Suitable transfection methods for single particle tracing in plant suspension cells

BACKGROUND

A multitude of different imaging systems are already available to image genetically altered RNA species; however, only a few of these techniques are actually suitable to visualize endogenous RNA. One possibility is to use fluorescently-labelled and hybridization-sensitive probes. In order to yield more information about the exact localization and movement of a single RNA molecule, it is necessary to image such probes with highly sensitive microscope setups. More challenges arise if such experiments are conducted in plant cells due to their high autofluorescence and demanding transfection procedures.

RESULTS

Here, we report in planta imaging of single RNA molecules using fluorescently labeled molecular beacons. We tested three different transfection protocols in order to identify optimal conditions for transfection of fluorescent DNA probes and their subsequent detection at the single molecule level.

CONCLUSIONS

We found that an optimized heat shock protocol provided a vastly improved transfection method for small DNA molecules which were used for subsequent single RNA molecule detection in living plant suspension cells.

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.

Rac1 participates in thermally induced alterations of the cytoskeleton, cell morphology and lipid rafts, and regulates the expression of heat shock proteins in B16F10 melanoma cells

Eukaryotic cells exhibit a characteristic response to hyperthermic treatment, involving morphological and cytoskeletal alterations and the induction of heat shock protein synthesis. Small GTPases of the Ras superfamily are known to serve as molecular switches which mediate responses to extracellular stimuli. We addressed here how small GTPase Rac1 integrates signals from heat stress and simultaneously induces various cellular changes in mammalian cells. As evidence that Rac1 is implicated in the heat shock response, we first demonstrated that both mild (41.5°C) and severe (43°C) heat shock induced membrane translocation of Rac1. Following inhibition of the activation or palmitoylation of Rac1, the size of its plasma membrane-bound pool was significantly decreased while the heat shock-induced alterations in the cytoskeleton and cell morphology were prevented. We earlier documented that the size distribution pattern of cholesterol-rich rafts is temperature dependent and hypothesized that this is coupled to the triggering mechanism of stress sensing and signaling. Interestingly, when plasma membrane localization of Rac1 was inhibited, a different and temperature independent average domain size was detected. In addition, inhibition of the activation or palmitoylation of Rac1 resulted in a strongly decreased expression of the genes of major heat shock proteins hsp25 and hsp70 under both mild and severe heat stress conditions.

The effect of hydroxylated fatty acid-containing phospholipids in the remodeling of lipid membranes

The synthetic fatty acid 2-hydroxyoleic acid (2OHOA) is an antitumor drug that regulates membrane lipid composition and structure. An important effect of this drug is the restoration of sphingomyelin (SM) levels in cancer cell membranes, where the SM concentration is lower than in non-tumor cells. It is well known that free fatty acid concentration in cell membranes is lower than 5%, and that fatty acid excess is rapidly incorporated into phospholipids. In a recent work, we have considered the effect of free 2OHOA in model membranes in liquid ordered (Lo) and liquid disordered (Ld) phases, by using all-atom molecular dynamics. This study concerns membranes that are modified upon incorporation of 2OHOA into different phospholipids. 2OHOA-containing phospholipids have a permanent effect on lipid membranes, making a Ld membrane surface more compact and less hydrated, whereas the opposite effect is observed in Lo domains. Moreover, the hydroxyl group of fatty acid chains increases the propensity of Ld model membranes to form hexagonal or other non-lamellar structures. This article is part of a Special Issue entitled: Membrane Structure and Function: Relevance in the Cell's Physiology, Pathology and Therapy.

Differential effect of 2-hydroxyoleic acid enantiomers on protein (sphingomyelin synthase) and lipid (membrane) targets

The complex dual mechanism of action of 2-hydroxyoleic acid (2OHOA), a potent anti-tumor compound used in membrane lipid therapy (MLT), has yet to be fully elucidated. It has been demonstrated that 2OHOA increases the sphingomyelin (SM) cell content via SM synthase (SGMS) activation. Its presence in membranes provokes changes in the membrane lipid structure that induce the translocation of PKC to the membrane and the subsequent overexpression of CDK inhibitor proteins (e.g., p21(Cip1)). In addition, 2OHOA also induces the translocation of Ras to the cytoplasm, provoking the silencing of MAPK and its related pathways. These two differential modes of action are triggered by the interactions of 2OHOA with either lipids or proteins. To investigate the molecular basis of the different interactions of 2OHOA with membrane lipids and proteins, we synthesized the R and S enantiomers of this compound. A molecular dynamics study indicated that both enantiomers interact similarly with lipid bilayers, which was further confirmed by X-ray diffraction studies. By contrast, only the S enantiomer was able to activate SMS in human glioma U118 cells. Moreover, the anti-tumor efficacy of the S enantiomer was greater than that of the R enantiomer, as the former can act through both MLT mechanisms. The present study provides additional information on this novel therapeutic approach and on the magnitude of the therapeutic effects of type-1 and type-2 MLT approaches. This article is part of a Special Issue entitled: Membrane Structure and Function: Relevance in the Cell's Physiology, Pathology and Therapy.