Antihypertensive drug guanabenz is active in vivo against both yeast and mammalian prions

Chemical Chaperones to Inhibit Endoplasmic Reticulum Stress: Implications in Diseases

The endoplasmic reticulum (ER) is responsible for structural transformation or folding of de novo proteins for transport to the Golgi. When the folding capacity of the ER is exceeded or excessive accumulation of misfolded proteins occurs, the ER enters a stressed condition (ER stress) and unfolded protein responses (UPR) are triggered in order to rescue cells from the stress. Recovery of ER proceeds toward either survival or cell apoptosis. ER stress is implicated in many pathologies, such as diabetes, cardiovascular diseases, inflammatory diseases, neurodegeneration, and lysosomal storage diseases. As a survival or adaptation mechanism, chaperone molecules are upregulated to manage ER stress. Chemical versions of chaperone have been developed in search of drug candidates for ER stress-related diseases. In this review, synthetic or semi-synthetic chemical chaperones are categorized according to potential therapeutic area and listed along with their chemical structure and activity. Although only a few chemical chaperones have been approved as pharmaceutical drugs, a dramatic increase in literatures over the recent decades indicates enormous amount of efforts paid by many researchers. The efforts warrant clearer understanding of ER stress and the related diseases and consequently will offer a promising drug discovery platform with chaperone activity.

Prion therapeutics: Lessons from the past

Prion diseases are a group of incurable zoonotic neurodegenerative diseases (NDDs) in humans and other animals caused by the prion proteins. The abnormal folding and aggregation of the soluble cellular prion proteins (PrPC) into scrapie isoform (PrPSc) in the Central nervous system (CNS) resulted in brain damage and other neurological symptoms. Different therapeutic approaches, including stalling PrPC to PrPSc conversion, increasing PrPSc removal, and PrPC stabilization, for which a spectrum of compounds, ranging from organic compounds to antibodies, have been explored. Additionally, a non-PrP targeted drug strategy using serpin inhibitors has been discussed. Despite numerous scaffolds being screened for anti-prion activity in vitro, only a few were effective in vivo and unfortunately, almost none of them proved effective in the clinical studies, most likely due to toxicity and lack of permeability. Recently, encouraging results from a prion-protein monoclonal antibody, PRN100, were presented in the first human trial on CJD patients, which gives a hope for better future for the discovery of other new molecules to treat prion diseases. In this comprehensive review, we have re-visited the history and discussed various classes of anti-prion agents, their structure, mode of action, and toxicity. Understanding pathogenesis would be vital for developing future treatments for prion diseases. Based on the outcomes of existing therapies, new anti-prion agents could be identified/synthesized/designed with reduced toxicity and increased bioavailability, which could probably be effective in treating prion diseases.

Recent advances in cellular models for discovering prion disease therapeutics

INTRODUCTION

Prion diseases are a group of rare and lethal rapidly progressive neurodegenerative diseases arising due to conversion of the physiological cellular prion protein into its pathological counterparts, denoted as "prions". These agents are resistant to inactivation by standard decontamination procedures and can be transmitted between individuals, consequently driving the irreversible brain damage typical of the diseases.

AREAS COVERED

Since its infancy, prion research has mainly depended on animal models for untangling the pathogenesis of the disease as well as for the drug development studies. With the advent of prion-infected cell lines, relevant animal models have been complemented by a variety of cell-based models presenting a much faster, ethically acceptable alternative.

EXPERT OPINION

To date, there are still either no effective prophylactic regimens or therapies for human prion diseases. Therefore, there is an urgent need for more relevant cellular models that best approximate in vivo models. Each cellular model presented and discussed in detail in this review has its own benefits and limitations. Once embarking in a drug screening campaign for the identification of molecules that could interfere with prion conversion and replication, one should carefully consider the ideal cellular model.

Guanabenz ameliorates disease in vanishing white matter mice in contrast to sephin1

OBJECTIVE

Vanishing white matter (VWM) is a leukodystrophy, characterized by stress-sensitive neurological deterioration and premature death. It is currently without curative treatment. It is caused by bi-allelic pathogenic variants in the genes encoding eukaryotic initiation factor 2B (eIF2B). eIF2B is essential for the regulation of the integrated stress response (ISR), a physiological response to cellular stress. Preclinical studies on VWM mouse models revealed that deregulated ISR is key in the pathophysiology of VWM and an effective treatment target. Guanabenz, an α2-adrenergic agonist, attenuates the ISR and has beneficial effects on VWM neuropathology. The current study aimed at elucidating guanabenz's disease-modifying potential and mechanism of action in VWM mice. Sephin1, an ISR-modulating guanabenz analog without α2-adrenergic agonistic properties, was included to separate effects on the ISR from α2-adrenergic effects.

METHODS

Wild-type and VWM mice were subjected to placebo, guanabenz or sephin1 treatments. Effects on clinical signs, neuropathology, and ISR deregulation were determined. Guanabenz's and sephin1's ISR-modifying effects were tested in cultured cells that expressed or lacked the α2-adrenergic receptor.

RESULTS

Guanabenz improved clinical signs, neuropathological hallmarks, and ISR regulation in VWM mice, but sephin1 did not. Guanabenz's effects on the ISR in VWM mice were not replicated in cell cultures and the contribution of α2-adrenergic effects on the deregulated ISR could therefore not be assessed.

INTERPRETATION

Guanabenz proved itself as a viable treatment option for VWM. The exact mechanism through which guanabenz exerts its ameliorating impact on VWM requires further studies. Sephin1 is not simply a guanabenz replacement without α2-adrenergic effects.

Guanabenz mitigates the neuropathological alterations and cell death in Alzheimer's disease

Alzheimer's disease (AD) pathology is characterized by cognitive impairment, increased acetylcholinesterase (AChE) activity, and impaired neuronal communication. Clinically, AChE inhibitors are being used to treat AD patients; however, these remain unable to prevent the disease progression. Therefore, further development of new therapeutic molecules is required having broad spectrum effects on AD-related various neurodegenerative events. Since repurposing is a quick mode to search the therapeutic molecules; henceforth, this study was conducted to evaluate the anti-Alzheimer activity of drug guanabenz which is already in use for the management of high blood pressure in clinics. The study was performed employing both cellular and rat models of AD along with donepezil as reference drug. Guanabenz treatment in both the experimental models showed significant protection against AD-specific behavioral and pathological indicators like AChE activity, tau phosphorylation, amyloid precursor protein, and memory retention. In conjunction, guanabenz also attenuated the AD-related oxidative stress, impaired mitochondrial functionality (MMP, cytochrome-c translocation, ATP level, and mitochondrial complex I activity), endoplasmic reticulum stress (GRP78, GADD153, cleaved caspase-12), neuronal apoptosis (Bcl-2, Bax, cleaved caspase-3), and DNA fragmentation. In conclusion, findings suggested the panoptic protective effect of guanabenz on disease-related multiple degenerative markers and signaling. Furthermore, clinical trial may shed light and expedite the availability of new therapeutic anti-Alzheimer's molecule for the wellbeing of AD patients.

The Unfolded Protein Responses in Health, Aging, and Neurodegeneration: Recent Advances and Future Considerations

Aging and age-related neurodegeneration are both associated with the accumulation of unfolded and abnormally folded proteins, highlighting the importance of protein homeostasis (termed proteostasis) in maintaining organismal health. To this end, two cellular compartments with essential protein folding functions, the endoplasmic reticulum (ER) and the mitochondria, are equipped with unique protein stress responses, known as the ER unfolded protein response (UPR^ER) and the mitochondrial UPR (UPR^mt), respectively. These organellar UPRs play roles in shaping the cellular responses to proteostatic stress that occurs in aging and age-related neurodegeneration. The loss of adaptive UPR^ER and UPR^mt signaling potency with age contributes to a feed-forward cycle of increasing protein stress and cellular dysfunction. Likewise, UPR^ER and UPR^mt signaling is often altered in age-related neurodegenerative diseases; however, whether these changes counteract or contribute to the disease pathology appears to be context dependent. Intriguingly, altering organellar UPR signaling in animal models can reduce the pathological consequences of aging and neurodegeneration which has prompted clinical investigations of UPR signaling modulators as therapeutics. Here, we review the physiology of both the UPR^ER and the UPR^mt, discuss how UPR^ER and UPR^mt signaling changes in the context of aging and neurodegeneration, and highlight therapeutic strategies targeting the UPR^ER and UPR^mt that may improve human health.

Therapeutic strategies for identifying small molecules against prion diseases

Prion diseases are fatal neurodegenerative disorders, for which there are no effective therapeutic and diagnostic agents. The main pathological hallmark has been identified as conformational changes of the cellular isoform prion protein (PrP^C) to a misfolded isoform of the prion protein (PrP^Sc). Targeting PrP^C and its conversion to PrP^Sc is still the central dogma in prion drug discovery, particularly in in silico and in vitro screening endeavors, leading to the identification of many small molecules with therapeutic potential. Nonetheless, multiple pathological targets are critically involved in the intricate pathogenesis of prion diseases. In this context, multi-target-directed ligands (MTDLs) emerge as valuable therapeutic approach for their potential to effectively counteract the complex etiopathogenesis by simultaneously modulating multiple targets. In addition, diagnosis occurs late in the disease process, and consequently a successful therapeutic intervention cannot be provided. In this respect, small molecule theranostics, which combine imaging and therapeutic properties, showed tremendous potential to cure and diagnose in vivo prion diseases. Herein, we review the major advances in prion drug discovery, from anti-prion small molecules identified by means of in silico and in vitro screening approaches to two rational strategies, namely MTDLs and theranostics, that have led to the identification of novel compounds with an expanded anti-prion profile.

Protein synthesis modulation as a therapeutic approach for amyotrophic lateral sclerosis and frontotemporal dementia

Protein synthesis is essential for cells to perform life metabolic processes. Pathological alterations of protein content can lead to particular diseases. Cells have an intrinsic array of mechanisms and pathways that are activated when protein misfolding, accumulation, aggregation or mislocalization occur. Some of them (like the unfolded protein response) represent complex interactions between endoplasmic reticulum sensors and elongation factors that tend to increase expression of chaperone proteins and/or repress translation in order to restore protein homeostasis (also known as proteostasis). This is even more important in neurons, as they are very susceptible to harmful effects associated with protein overload and proteostatic mechanisms are less effective with age. Several neurodegenerative pathologies such as Alzheimer's, Parkinson's, and Huntington's diseases, amyotrophic lateral sclerosis and frontotemporal dementia exhibit a particular molecular signature of distinct, unbalanced protein overload. In amyotrophic lateral sclerosis and frontotemporal dementia, the majority of cases present intracellular inclusions of ubiquitinated transactive response DNA-binding protein of 43 kDa (TDP-43). TDP-43 is an RNA binding protein that participates in RNA metabolism, among other functions. Dysregulation of TDP-43 (e.g. aggregation and mislocalization) can dramatically affect neurons, and this has been linked to disease development. Expression of amyotrophic lateral sclerosis/frontotemporal dementia TDP-43-related mutations in cellular and animal models has been shown to recapitulate key features of the amyotrophic lateral sclerosis/frontotemporal dementia disease spectrum. These variants can be causative of degeneration onset and progression. Most neurodegenerative diseases (including amyotrophic lateral sclerosis and frontotemporal dementia) have no cure at the moment; however, modulating translation has recently emerged as an attractive approach that can be performed at several steps (i.e. regulating activation of initiation and elongation factors, inhibiting unfolded protein response activation or inducing chaperone expression and activity). This review focuses on the features of protein imbalance in neurodegenerative disorders and the relevance of developing therapeutical compounds aiming at restoring proteostasis. We strive to highlight the importance of research on drugs that, not only restore protein imbalance without compromising translational activity of cells, but are also as safe as possible for the patients.

Pharmacological targeting of endoplasmic reticulum stress in disease

The accumulation of misfolded proteins in the endoplasmic reticulum (ER) leads to ER stress, resulting in activation of the unfolded protein response (UPR) that aims to restore protein homeostasis. However, the UPR also plays an important pathological role in many diseases, including metabolic disorders, cancer and neurological disorders. Over the last decade, significant effort has been invested in targeting signalling proteins involved in the UPR and an array of drug-like molecules is now available. However, these molecules have limitations, the understanding of which is crucial for their development into therapies. Here, we critically review the existing ER stress and UPR-directed drug-like molecules, highlighting both their value and their limitations.

LC-MS/MS determination of guanabenz E/Z isomers and its application to in vitro and in vivo DMPK profiling studies

Endoplasmic reticulum (ER) stress underlies a variety of disorders involving inflammation, such as diabetes, neurodegenerative diseases. Guanabenz acetate (Wytensin®, GA), a clinically approved antihypertensive drug, efficiently counteracts ER stress. The entirety of clinically used GA is the E-isomer, while the Z-isomer is known to lack significant hypotensive properties. We recently discovered that the Z-isomer retains anti-ER stress activity. Coupled with its lack of sedative effects, (Z)-GA is well positioned as a potential therapeutic for a host of ER stress-related disorders. We set forth to characterize the metabolism and pharmacokinetics (DMPK) of (Z)-GA in vitro and in vivo. Toward this end, a reliable and sensitive LC-MS/MS method for simultaneous determination of the (E)- and (Z)-guanabenz was developed. Chromatographic separation of the isomers was achieved on a C18 reverse phase column with a gradient elution. Tandem mass spectrometric detection was conducted using an AB Sciex 5500 QTrap mass spectrometer with positive electrospray ionization. Full validation of the method was performed in mouse plasma with a simple and low plasma volume protein precipitation procedure. The method demonstrated good linearity, reproducibility, and accuracy over a range of 0.5-1000 nM with minimal matrix effect and excellent extraction efficiency. In addition, the developed method was successfully applied to DMPK studies of the GA isomers in vitro and in vivo. Results of these studies revealed for the first time that the DMPK profile of (Z)-guanabenz is distinct from that of (E)-guanabenz, with higher apparent volume of distribution (V_d) and clearance, presumably due to lower plasma protein binding.

Anti-prion Drugs Targeting the Protein Folding Activity of the Ribosome Reduce PABPN1 Aggregation

Prion diseases are caused by the propagation of PrPSc, the pathological conformation of the PrPC prion protein. The molecular mechanisms underlying PrPSc propagation are still unsolved and no therapeutic solution is currently available. We thus sought to identify new anti-prion molecules and found that flunarizine inhibited PrPSc propagation in cell culture and significantly prolonged survival of prion-infected mice. Using an in silico therapeutic repositioning approach based on similarities with flunarizine chemical structure, we tested azelastine, duloxetine, ebastine, loperamide and metixene and showed that they all have an anti-prion activity. Like flunarizine, these marketed drugs reduced PrPSc propagation in cell culture and in mouse cerebellum organotypic slice culture, and inhibited the protein folding activity of the ribosome (PFAR). Strikingly, some of these drugs were also able to alleviate phenotypes due to PABPN1 nuclear aggregation in cell and Drosophila models of oculopharyngeal muscular dystrophy (OPMD). These data emphasize the therapeutic potential of anti-PFAR drugs for neurodegenerative and neuromuscular proteinopathies.

Saccharomyces cerevisiae in neuroscience: how unicellular organism helps to better understand prion protein?

The baker’s yeast Saccharomyces (S.) cerevisiae is a single-celled eukaryotic model organism widely used in research on life sciences. Being a unicellular organism, S. cerevisiae has some evident limitations in application to neuroscience. However, yeast prions are extensively studied and they are known to share some hallmarks with mammalian prion protein or other amyloidogenic proteins found in the pathogenesis of Alzheimer’s, Parkinson’s, or Huntington’s diseases. Therefore, the yeast S. cerevisiae has been widely used for basic research on aggregation properties of proteins in cellulo and on their propagation. Recently, a yeast-based study revealed that some regions of mammalian prion protein and amyloid β_1–42 are capable of induction and propagation of yeast prions. It is one of the examples showing that evolutionarily distant organisms share common mechanisms underlying the structural conversion of prion proteins making yeast cells a useful system for studying mammalian prion protein. S. cerevisiae has also been used to design novel screening systems for anti-prion compounds from chemical libraries. Yeast-based assays are cheap in maintenance and safe for the researcher, making them a very good choice to perform preliminary screening before further characterization in systems engaging mammalian cells infected with prions. In this review, not only classical red/white colony assay but also yeast-based screening assays developed during last year are discussed. Computational analysis and research carried out using yeast prions force us to expect that prions are widely present in nature. Indeed, the last few years brought us several examples indicating that the mammalian prion protein is no more peculiar protein – it seems that a better understanding of prion proteins nature-wide may aid us with the treatment of prion diseases and other amyloid-related medical conditions.

Anti-prion and α-Synuclein Aggregation Inhibitory Sterols from the Sponge Lamellodysidea cf. chlorea

In a study aimed at identifying new anti-prion compounds we screened a library of 500 Australian marine invertebrate derived extracts using a yeast-based anti-prion assay. This resulted in an extract from the subtropical sponge Lamellodysidea cf. chlorea showing potent anti-prion activity. The bioassay-guided investigation of the sponge extract led to the isolation of three new bioactive polyoxygenated steroids, lamellosterols A-C (1-3). These sterols were all isolated in low yield, and their structures elucidated by extensive NMR and MS data analysis. Lamellosterols A-C displayed potent anti-prion activity against the [PSI⁺] yeast prion (EC₅₀s of 12.7, 13.8, and 9.8 μM, respectively). Lamellosterol A (1) was further shown to bind to the Parkinson's disease implicated amyloid protein, α-synuclein, and to significantly inhibit its aggregation. Our findings indicate that these polyoxygenated sterol sulfates may be useful compounds to study mechanisms associated with neurodegenerative diseases.

Small Molecules with Anti-Prion Activity

Prion pathologies are fatal neurodegenerative diseases caused by the misfolding of the physiological Prion Protein (PrP^C) into a β-structure-rich isoform called PrP^Sc. To date, there is no available cure for prion diseases and just a few clinical trials have been carried out. The initial approach in the search of anti-prion agents had PrP^Sc as a target, but the existence of different prion strains arising from alternative conformations of PrP^Sc, limited the efficacy of the ligands to a straindependent ability. That has shifted research to PrP^C ligands, which either act as chaperones, by stabilizing the native conformation, or inhibit its interaction with PrP^Sc. The role of transition-metal mediated oxidation processes in prion misfolding has also been investigated. Another promising approach is the indirect action via other cellular targets, like membrane domains or the Protein- Folding Activity of Ribosomes (PFAR). Also, new prion-specific high throughput screening techniques have been developed. However, so far no substance has been found to be able to extend satisfactorily survival time in animal models of prion diseases. This review describes the main features of the Structure-Activity Relationship (SAR) of the various chemical classes of anti-prion agents.

Ribosomal RNA Modulates Aggregation of the Podospora Prion Protein HET-s

The role of the nucleic acids in prion aggregation/disaggregation is becoming more and more evident. Here, using HET-s prion from fungi Podospora anserina (P. anserina) as a model system, we studied the role of RNA, particularly of different domains of the ribosomal RNA (rRNA), in its aggregation process. Our results using Rayleigh light scattering, Thioflavin T (ThT) binding, transmission electron microscopy (TEM) and cross-seeding assay show that rRNA, in particular the domain V of the major rRNA from the large subunit of the ribosome, substantially prevents insoluble amyloid and amorphous aggregation of the HET-s prion in a concentration-dependent manner. Instead, it facilitates the formation of the soluble oligomeric “seeds”, which are capable of promoting de novo HET-s aggregation. The sites of interactions of the HET-s prion protein on domain V rRNA were identified by primer extension analysis followed by UV-crosslinking, which overlap with the sites previously identified for the protein-folding activity of the ribosome (PFAR). This study clarifies a missing link between the rRNA-based PFAR and the mode of propagation of the fungal prions.

[Budding yeast, a model and a tool… also for biomedical research]

Yeast has been used for thousands of years as a leavening agent and for alcoholic fermentation, but it is only in 1857 that Louis Pasteur described the microorganism at the basis of these two tremendously important economic activities. From there, yeast strains could be selected and modified on a rational basis to optimize these uses, thereby also allowing the development of yeast as a popular eukaryotic model system. This model led to a cornucopia of seminal discoveries in cell biology. For about two decades yeast has also been used as a model and a tool for therapeutic research, from the production of therapeutics and the development of diagnostic tools to the identification of new therapeutic targets, drug candidates and chemical probes. These diverse chemobiological applications of yeast are presented and discussed in the present review article.

Potential benefit of manipulating protein quality control systems in neurodegenerative diseases

The deposition of proteins of abnormal conformation is one of the major hallmarks of the common neurodegenerative diseases including Alzheimer's, Parkinson's, amyotrophic lateral sclerosis, frontotemporal dementia, and prion diseases. Protein quality control systems have evolved to protect cells and organisms against the harmful consequences of abnormally folded proteins that are constantly produced in small amounts. Mutations in rare inherited forms of neurodegenerative diseases have provided compelling evidence that failure of protein quality control systems can drive neurodegeneration. With extensive knowledge of these systems, and the notion that protein quality control may decline with age, many laboratories are now focussing on manipulating these evolutionarily optimized defence mechanisms to reduce the protein misfolding burden for therapeutic benefit.

Pharmacological modulation of the ER stress response ameliorates oculopharyngeal muscular dystrophy

Oculopharyngeal muscular dystrophy (OPMD) is a rare late onset genetic disease leading to ptosis, dysphagia and proximal limb muscles at later stages. A short abnormal (GCN) triplet expansion in the polyA-binding protein nuclear 1 (PABPN1) gene leads to PABPN1-containing aggregates in the muscles of OPMD patients. Here we demonstrate that treating mice with guanabenz acetate (GA), an FDA-approved antihypertensive drug, reduces the size and number of nuclear aggregates, improves muscle force, protects myofibers from the pathology-derived turnover and decreases fibrosis. GA targets various cell processes, including the unfolded protein response (UPR), which acts to attenuate endoplasmic reticulum (ER) stress. We demonstrate that GA increases both the phosphorylation of the eukaryotic translation initiation factor 2α subunit and the splicing of Xbp1, key components of the UPR. Altogether these data show that modulation of protein folding regulation is beneficial for OPMD and promote the further development of GA or its derivatives for treatment of OPMD in humans. Furthermore, they support the recent evidences that treating ER stress could be therapeutically relevant in other more common proteinopathies.

Sephin1 Reduces Prion Infection in Prion-Infected Cells and Animal Model

Prion diseases are fatal infectious neurodegenerative disorders in human and animals caused by misfolding of the cellular prion protein (PrP^C) into the infectious isoform PrP^Sc. These diseases have the potential to transmit within or between species, and no cure is available to date. Targeting the unfolded protein response (UPR) as an anti-prion therapeutic approach has been widely reported for prion diseases. Here, we describe the anti-prion effect of the chemical compound Sephin1 which has been shown to protect in mouse models of protein misfolding diseases including amyotrophic lateral sclerosis (ALS) and multiple sclerosis (MS) by selectively inhibiting the stress-induced regulatory subunit of protein phosphatase 1, thus prolonging eIF2α phosphorylation. We show here that Sephin1 dose and time dependently reduced PrP^Sc in different neuronal cell lines which were persistently infected with various prion strains. In addition, prion seeding activity was reduced in Sephin1-treated cells. Importantly, we found that Sephin1 significantly overcame the endoplasmic reticulum (ER) stress induced in treated cells, as measured by lower expression of stress-induced aberrant prion protein. In a mouse model of prion infection, intraperitoneal treatment with Sephin1 significantly prolonged survival of prion-infected mice. When combining Sephin1 with the neuroprotective drug metformin, the survival of prion-infected mice was also prolonged. These results suggest that Sephin1 could be a potential anti-prion drug selectively targeting one component of the UPR pathway.

Identifying Anti-prion Chemical Compounds Using a Newly Established Yeast High-Throughput Screening System

Prion-like protein aggregation underlies the pathology of a group of fatal neurodegenerative diseases in humans, including Alzheimer's disease (AD), Parkinson's disease, amyotrophic lateral sclerosis, and transmissible spongiform encephalopathy. At present, few high-throughput screening (HTS) systems are available for anti-prion small-molecule identification. Here we describe an innovative phenotypic HTS system in yeast that allows for efficient identification of chemical compounds that eliminate the yeast prion [SWI⁺]. We show that some identified anti-[SWI⁺] compounds can destabilize other non-[SWI⁺] prions, and their antagonizing effects can be prion- and/or variant specific. Intriguingly, among the identified hits are several previously identified anti-PrP^Sc compounds and a couple of US Food and Drug Administration-approved drugs for AD treatment, validating the efficacy of this HTS system. Moreover, a few hits can reduce proteotoxicity induced by expression of several pathogenic mammalian proteins. Thus, we have established a useful HTS system for identifying compounds that can potentially antagonize prionization and human proteinopathies.

Anti-prion drug screening system in Saccharomyces cerevisiae based on an artificial [LEU2+] prion

Proteinaceous infectious particles causing mammalian transmissible spongiform encephalopathies or prions are being extensively studied. However due to their hazardous nature, the initial screening of potential anti-prion drugs is often made in a yeast-based screening system utilizing a well-characterized [PSI⁺] prion (amyloid formed by the translation termination factor Sup35p). In the [PSI⁺] prion screening system (white/red colony assay), the prion phenotype yields white colonies while addition of an anti-prion drug will yield red colonies. However, this system has some limitations. It is difficult to quantify the effectiveness of the anti-prion compound, the diffusion of the studied compound may affect the result, and the deficiency of glutathione in cells may prevent the formation of red pigment in cured cells. Therefore, alternative yeast prion screening systems are still needed. This article aims to present an alternative yeast-based system to evaluate anti-prion activity of chemical compounds. The method that was used is based on an artificial [LEU2⁺] prion created by fusing Leu2p with the prion-forming domain of Sup35p in Saccharomyces cerevisiae. Phenotypic analysis and semi-denaturating detergent agarose gel electrophoresis (SDD-AGE) confirmed the presence of the artificial [LEU2⁺] prion in yeast cells. This screening system verified the anti-prion activity of 3 drugs that were found to have been active in the white/red colony assay, while one compound (6-chlorotacrine) that was active in the white/red colony assay was found to be inactive in the [LEU2⁺] system. This new system also appears to be more sensitive than the white/red colony assay.

Anti-prion Butenolides and Diphenylpropanones from the Australian Ascidian Polycarpa procera

A library of 500 Australian marine invertebrate extracts was screened for anti-prion activity using a yeast-based assay, and this resulted in an extract from the ascidian Polycarpa procera showing potent activity. Purification of this extract led to the isolation of six new butenolide metabolites, the procerolides 1-4 and two related diphenylpropanones, the procerones 5 and 6, as the bioactive components. The structures of 1-6 were elucidated from the analysis of 1D/2D NMR and MS data, and their absolute configurations determined from comparison of experimental and computed ECD data. Compounds 1-6 were tested for anti-prion activity in a yeast-based assay, and 1 and 5 displayed potent bioactivity (EC₅₀ of 23 and 29 μM, respectively) comparable to the potently active anti-prion compound guanabenz. The procerolides and procerones are the first anti-prion compounds to be reported from ascidians, indicating that ascidians may be an untapped source of new lead anti-prion compounds.

Sneaking Out for Happy Hour: Yeast-Based Approaches to Explore and Modulate Immune Response and Immune Evasion

Many pathogens (virus, bacteria, fungi, or parasites) have developed a wide variety of mechanisms to evade their host immune system. The budding yeast Saccharomyces cerevisiae has successfully been used to decipher some of these immune evasion strategies. This includes the cis-acting mechanism that limits the expression of the oncogenic Epstein–Barr virus (EBV)-encoded EBNA1 and thus of antigenic peptides derived from this essential but highly antigenic viral protein. Studies based on budding yeast have also revealed the molecular bases of epigenetic switching or recombination underlying the silencing of all except one members of extended families of genes that encode closely related and highly antigenic surface proteins. This mechanism is exploited by several parasites (that include pathogens such as Plasmodium, Trypanosoma, Candida, or Pneumocystis) to alternate their surface antigens, thereby evading the immune system. Yeast can itself be a pathogen, and pathogenic fungi such as Candida albicans, which is phylogenetically very close to S. cerevisiae, have developed stealthiness strategies that include changes in their cell wall composition, or epitope-masking, to control production or exposure of highly antigenic but essential polysaccharides in their cell wall. Finally, due to the high antigenicity of its cell wall, yeast has been opportunistically exploited to create adjuvants and vectors for vaccination.

PromISR-6, a Guanabenz Analogue, Improves Cellular Survival in an Experimental Model of Huntington's Disease

Guanabenz (GBZ), an α₂-adrenergic agonist, demonstrated off-target effects that restored protein homeostasis and ameliorated pathobiology in experimental models of neurodegenerative disease. However, GBZ did not directly activate the integrated stress response (ISR), and its proposed mode of action remains controversial. Utilizing an iterative in silico screen of over 10,000 GBZ analogues, we analyzed 432 representative compounds for cytotoxicity in Wild-type, PPP1R15A-/-, and PPP1R15B-/- mouse embryonic fibroblasts. Nine compounds clustering into three functional groups were studied in detail using cell biological and biochemical assays. Our studies demonstrated that PromISR-6 is a potent GBZ analogue that selectively activated ISR, eliciting sustained eIF2α phosphorylation. ISRIB, an ISR inhibitor, counteracted PromISR-6-mediated translational inhibition and reduction in intracellular mutant Huntingtin aggregates. Reduced protein synthesis combined with PromISR-6-stimulated autophagic clearance made PromISR-6 the most efficacious GBZ analogue to reduce Huntingtin aggregates and promote survival in a cellular model of Huntington's disease.

The antibiotic robenidine exhibits guanabenz-like cytoprotective properties by a mechanism independent of protein phosphatase PP1:PPP1R15A

The aminoguanidine compound robenidine is widely used as an antibiotic for the control of coccidiosis, a protozoal infection in poultry and rabbits. Interestingly, robenidine is structurally similar to guanabenz (analogs), which are currently undergoing clinical trials as cytoprotective agents for the management of neurodegenerative diseases. Here we show that robenidine and guanabenz protect cells from a tunicamycin-induced unfolded protein response to a similar degree. Both compounds also reduced the tumor necrosis factor α-induced activation of NF-κB. The cytoprotective effects of guanabenz (analogs) have been explained previously by their ability to maintain eIF2α phosphorylation by allosterically inhibiting protein phosphatase PP1:PPP1R15A. However, using a novel split-luciferase-based protein-protein interaction assay, we demonstrate here that neither robenidine nor guanabenz disrupt the interaction between PPP1R15A and either PP1 or eIF2α in intact cells. Moreover, both drugs also inhibited the unfolded protein response in cells that expressed a nonphosphorylatable mutant (S51A) of eIF2α. Our results identify robenidine as a PP1:PPP1R15A-independent cytoprotective compound that holds potential for the management of protein misfolding-associated diseases.

Azines: synthesis, structure, electronic structure and their applications

Azines (2,3-diaza-1,3-butadienes): structure, electronic structure, tautomerism, and their applications in organic synthesis, medicinal chemistry and materials chemistry.

Yeast-based screening of natural product extracts results in the identification of prion inhibitors from a marine sponge

One of the major medical challenges of the twenty-first century is the treatment of incurable and fatal neurodegenerative disorders caused by misfolded prion proteins. Since the discovery of these diseases a number of studies have been conducted to identify small molecules for their treatment, however to date no curative treatment is available. These studies can be highly expensive and time consuming, but more recent experimental approaches indicate a significant application for yeast prions in these studies. We therefore used yeast prions to optimize previous high-throughput methods for the cheaper, easier and more rapid screening of natural extracts. Through this approach we aimed to identify natural yeast-prion inhibitors that could be useful in the development of novel treatment strategies for neurodegenerative disorders. We screened 500 marine invertebrate extracts from temperate waters in Australia allowing the identification of yeast-prion inhibiting extracts. Through the bioassay-driven chemical investigation of an active Suberites sponge extract, a group of bromotyrosine derivatives were identified as potent yeast-prion inhibitors. This study outlines the importance of natural products and yeast prions as a first-stage screen for the identification of new chemically diverse and bioactive compounds.

Autophagy stimulation as a promising approach in treatment of neurodegenerative diseases

Autophagy is a process of degradation of macromolecules in the cytoplasm, particularly proteins of a long half-life, as well as whole organelles, in eukaryotic cells. Lysosomes play crucial roles during this degradation. Autophagy is a phylogenetically old, and evolutionarily conserved phenomenon which occurs in all eukaryotic cells. It can be found in yeast Saccharomyces cerevisiae, insect Drosophila melanogaster, and mammals, including humans. Its high importance for cell physiology has been recognized, and in fact, dysfunctions causing impaired autophagy are associated with many severe disorders, including cancer and metabolic brain diseases. The types and molecular mechanisms of autophagy have been reviewed recently by others, and in this paper they will be summarized only briefly. Regulatory networks controlling the autophagy process are usually described as negative regulations. In contrast, here, we focus on different ways by which autophagy can be stimulated. In fact, activation of this process by different factors or processes can be considered as a therapeutic strategy in metabolic neurodegenerative diseases. These aspects are reviewed and discussed in this article.

Guanabenz promotes neuronal survival via enhancement of ATF4 and parkin expression in models of Parkinson disease

Reduced function of parkin appears to be a central pathogenic event in Parkinson disease (PD). Increasing parkin levels enhances survival in models of PD-related neuronal death and is a promising therapeutic objective. Previously, we demonstrated that the transcription factor ATF4 promotes survival in response to PD-mimetic stressors by maintaining parkin levels. ATF4 translation is up-regulated by phosphorylation of the translation initiation factor eIF2α. The small molecule guanabenz enhances eIF2α phosphorylation by blocking the function of GADD34, a regulatory protein that promotes eIF2α dephosphorylation. We tested the hypothesis that guanabenz, by inhibiting GADD34 and consequently increasing eIF2α phosphorylation and elevating ATF4, would improve survival in models of PD by up-regulating parkin. We found that GADD34 is strongly induced by 6-OHDA, and that GADD34 localization is dramatically altered in dopaminergic substantia nigra neurons in PD cases. We further demonstrated that guanabenz attenuates 6-hydroxydopamine (6-OHDA) induced cell death of differentiated PC12 cells and primary ventral midbrain dopaminergic neurons in culture, and of dopaminergic neurons in the substantia nigra of mice. In culture models, guanabenz also increases eIF2α phosphorylation and ATF4 and parkin levels in response to 6-OHDA. Furthermore, if either ATF4 or parkin is silenced, then the protective effect of guanabenz is lost. We also found similar results in a distinct model of neuronal death: primary cultures of cortical neurons treated with the topoisomerase I inhibitor camptothecin, in which guanabenz limited camptothecin-induced neuronal death in an ATF4- and parkin-dependent manner. In summary, our data suggest that guanabenz and other GADD34 inhibitors could be used as therapeutic agents to boost parkin levels and thereby slow neurodegeneration in PD and other neurodegenerative conditions.

Toward Therapy of Human Prion Diseases

Three decades after the discovery of prions as the cause of Creutzfeldt-Jakob disease and other transmissible spongiform encephalopathies, we are still nowhere close to finding an effective therapy. Numerous pharmacological interventions have attempted to target various stages of disease progression, yet none has significantly ameliorated the course of disease. We still lack a mechanistic understanding of how the prions damage the brain, and this situation results in a dearth of validated pharmacological targets. In this review, we discuss the attempts to interfere with the replication of prions and to enhance their clearance. We also trace some of the possibilities to identify novel targets that may arise with increasing insights into prion biology.

Protein misfolding, amyotrophic lateral sclerosis and guanabenz: protocol for a phase II RCT with futility design (ProMISe trial)

INTRODUCTION

Recent studies suggest that endoplasmic reticulum stress may play a critical role in the pathogenesis of amyotrophic lateral sclerosis (ALS) through an altered regulation of the proteostasis, the cellular pathway-balancing protein synthesis and degradation. A key mechanism is thought to be the dephosphorylation of eIF2α, a factor involved in the initiation of protein translation. Guanabenz is an alpha-2-adrenergic receptor agonist safely used in past to treat mild hypertension and is now an orphan drug. A pharmacological action recently discovered is its ability to modulate the synthesis of proteins by the activation of translational factors preventing misfolded protein accumulation and endoplasmic reticulum overload. Guanabenz proved to rescue motoneurons from misfolding protein stress both in in vitro and in vivo ALS models, making it a potential disease-modifying drug in patients. It is conceivable investigating whether its neuroprotective effects based on the inhibition of eIF2α dephosphorylation can change the progression of ALS.

METHODS AND ANALYSES

Protocolised Management In Sepsis is a multicentre, randomised, double-blind, placebo-controlled phase II clinical trial with futility design. We will investigate clinical outcomes, safety, tolerability and biomarkers of neurodegeneration in patients with ALS treated with guanabenz or riluzole alone for 6 months. The primary aim is to test if guanabenz can reduce the proportion of patients progressed to a higher stage of disease at 6 months compared with their baseline stage as measured by the ALS Milano-Torino Staging (ALS-MITOS) system and to the placebo group. Secondary aims are safety, tolerability and change in at least one biomarker of neurodegeneration in the guanabenz arm compared with the placebo group. Findings will provide reliable data on the likelihood that guanabenz can slow the course of ALS in a phase III trial.

ETHICS AND DISSEMINATION

The study protocol was approved by the Ethics Committee of IRCCS 'Carlo Besta Foundation' of Milan (Eudract no. 2014-005367-32 Pre-results) based on the Helsinki declaration.

Bergmann glia translocation: a new disease marker for vanishing white matter identifies therapeutic effects of Guanabenz treatment

AIM

Vanishing White Matter (VWM) is a devastating leucoencephalopathy without effective treatment options. Patients have mutations in the EIF2B1-5 genes, encoding the five subunits of eIF2B, a guanine exchange factor that is an important regulator of protein translation. We recently developed mouse models for VWM that replicate the human disease. To study disease improvement after treatment in these mice, it is essential to have sensitive biomarkers related to disease stage. The Bergmann glia of the cerebellum, an astrocytic subpopulation, translocate into the molecular layer in symptomatic VWM mice and patients. This study looked at the prospects of using Bergmann glia pathology as an objective disease marker for VWM.

METHODS

We defined a new quantitative measurement of Bergmann glia pathology in the cerebellum of VWM mice and patients. To test the sensitivity of this new marker for improvement, VWM mutant mice received long-term treatment with Guanabenz, an FDA-approved anti-hypertensive agent affecting eIF2B activity.

RESULTS

Bergmann glia translocation was significantly higher in symptomatic VWM mice and VWM patients than in controls and worsened over the disease course. Both Bergmann glia pathology and cerebellar myelin pathology improved with Guanabenz treatment in mice, showing that Bergmann glia translocation is a sensitive measurement for improvement.

CONCLUSIONS

Bergmann glia translocation can be used to objectively assess effects of treatment in VWM mice. Future treatment strategies involving compounds regulating eIF2 phosphorylation might benefit VWM patients.

Decoding the selectivity of eIF2α holophosphatases and PPP1R15A inhibitors

The reversible phosphorylation of proteins controls most cellular functions. Protein kinases have been popular drug targets, unlike phosphatases, which remain a drug discovery challenge. Guanabenz and Sephin1 are selective inhibitors of the phosphatase regulatory subunit PPP1R15A (R15A) that prolong the benefit of eIF2α phosphorylation, thereby protecting cells from proteostatic defects. In mice, Sephin1 prevents two neurodegenerative diseases, Charcot-Marie-Tooth 1B (CMT-1B) and SOD1-mediated amyotrophic lateral sclerosis (ALS). However, the molecular basis for R15A inhibition is unknown. Here we reconstituted human recombinant eIF2α holophosphatases, R15A-PP1 and R15B-PP1, whose activity depends on both the catalytic subunit PP1 (protein phosphatase 1) and either R15A or R15B. This system enabled the functional characterization of these holophosphatases and revealed that Guanabenz and Sephin1 induced a selective conformational change in R15A, detected by resistance to limited proteolysis. This altered the recruitment of eIF2α, preventing its dephosphorylation. This work demonstrates that regulatory subunits of phosphatases are valid drug targets and provides the molecular rationale to expand this concept to other phosphatases.

The double life of the ribosome: When its protein folding activity supports prion propagation

It is no longer necessary to demonstrate that ribosome is the central machinery of protein synthesis. But it is less known that it is also key player of the protein folding process through another conserved function: the protein folding activity of the ribosome (PFAR). This ribozyme activity, discovered more than 2 decades ago, depends upon the domain V of the large rRNA within the large subunit of the ribosome. Surprisingly, we discovered that anti-prion compounds are also potent PFAR inhibitors, highlighting an unexpected link between PFAR and prion propagation. In this review, we discuss the ancestral origin of PFAR in the light of the ancient RNA world hypothesis. We also consider how this ribosomal activity fits into the landscape of cellular protein chaperones involved in the appearance and propagation of prions and other amyloids in mammals. Finally, we examine how drugs targeting the protein folding activity of the ribosome could be active against mammalian prion and other protein aggregation-based diseases, making PFAR a promising therapeutic target for various human protein misfolding diseases.

Protein Folding Activity of the Ribosome is involved in Yeast Prion Propagation

6AP and GA are potent inhibitors of yeast and mammalian prions and also specific inhibitors of PFAR, the protein-folding activity borne by domain V of the large rRNA of the large subunit of the ribosome. We therefore explored the link between PFAR and yeast prion [PSI(+)] using both PFAR-enriched mutants and site-directed methylation. We demonstrate that PFAR is involved in propagation and de novo formation of [PSI(+)]. PFAR and the yeast heat-shock protein Hsp104 partially compensate each other for [PSI(+)] propagation. Our data also provide insight into new functions for the ribosome in basal thermotolerance and heat-shocked protein refolding. PFAR is thus an evolutionarily conserved cell component implicated in the prion life cycle, and we propose that it could be a potential therapeutic target for human protein misfolding diseases.

Integrated Stress Response Signaling Pathways Induced by Supraphysiological Concentrations of Thyroid Hormone Inhibit Viral Replication

Supraphysiological concentrations (SPCs) of triiodo-L-thyronine (T3) have been used in the treatment of a number of nonviral diseases. However, the signaling mechanisms that regulate the function of T3 at these concentrations and their role in modulating cellular stress pathways and antiviral responses are unknown. Here, we have investigated the effects of SPCs of T3 on integrated stress response (ISR) signaling pathways and the replication of vesicular stomatitis virus (VSV). T3 amplified Poly IC-induced activation of RNA-dependent protein kinase, induced phosphorylation of eIF2α, stress granule (SG) formation, IRE1α phosphorylation, XBP1 splicing, and the expression of stress markers. T3 inhibited VSV replication by modulating SG formation and the expression of stress response markers. ISR activator guanabenz also inhibited VSV replication and amplified T3-induced anti-VSV response. To summarize, we have uncovered novel functions of T3 at SPCs as an activator of ISR signaling pathways and an inhibitor of VSV replication. This study offers a proof of principle of the concept that ISR activating agents like SPC of T3 and guanabenz can be potential antiviral agents.

Translational control by eIF2α in neurons: Beyond the stress response

The translation of mRNAs is a tightly controlled process that responds to multiple signaling pathways. In neurons, this control is also exerted locally due to the differential necessity of proteins in axons and dendrites. The phosphorylation of the alpha subunit of the translation initiation factor 2 (eIF2α) is one of the mechanisms of translational control. The phosphorylation of eIF2α has classically been viewed as a stress response, halting translation initiation. However, in the nervous system this type of regulation has been related to other mechanisms besides stress response, such as behavior, memory consolidation and nervous system development. Additionally, neurodegenerative diseases have a major stress component, thus eIF2α phosphorylation plays a preeminent role and its modulation is currently viewed as a new opportunity for therapeutic interventions. This review consolidates current information regarding eIF2α phosphorylation in neurons and its impact in neurodegenerative diseases. © 2016 Wiley Periodicals, Inc.

The entangled ER-mitochondrial axis as a potential therapeutic strategy in neurodegeneration: A tangled duo unchained

Endoplasmic reticulum (ER) and mitochondrial function have both been shown to be critical events in neurodegenerative diseases. The ER mediates protein folding, maturation, sorting as well acts as calcium storage. The unfolded protein response (UPR) is a stress response of the ER that is activated by the accumulation of misfolded proteins within the ER lumen. Although the molecular mechanisms underlying ER stress-induced apoptosis are not completely understood, increasing evidence suggests that ER and mitochondria cooperate to signal cell death. Similarly, calcium-mediated mitochondrial function and dynamics not only contribute to ATP generation and calcium buffering but are also a linchpin in mediating cell fate. Mitochondria and ER form structural and functional networks (mitochondria-associated ER membranes [MAMs]) essential to maintaining cellular homeostasis and determining cell fate under various pathophysiological conditions. Regulated Ca(2+) transfer from the ER to the mitochondria is important in maintaining control of pro-survival/pro-death pathways. In this review, we summarize the latest therapeutic strategies that target these essential organelles in the context of neurodegenerative diseases.

Surviving protein quality control catastrophes--from cells to organisms

Organisms have evolved mechanisms to cope with and adapt to unexpected challenges and harsh conditions. Unfolded or misfolded proteins represent a threat for cells and organisms, and the deposition of misfolded proteins is a defining feature of many age-related human diseases, including the increasingly prevalent neurodegenerative diseases. These protein misfolding diseases are devastating and currently cannot be cured, but are hopefully not incurable. In fact, the aggregation-prone and potentially harmful proteins at the origins of protein misfolding diseases are expressed throughout life, whereas the diseases are late onset. This reveals that cells and organisms are normally resilient to disease-causing proteins and survive the threat of misfolded proteins up to a point. This Commentary will outline the limits of the cellular resilience to protein misfolding, and discuss the possibility of pushing these limits to help cells and organisms to survive the threat of misfolding proteins and to avoid protein quality control catastrophes.

Inhibition of Eukaryotic Initiation Factor 2 Alpha Phosphatase Reduces Tissue Damage and Improves Learning and Memory after Experimental Traumatic Brain Injury

Patients who survive traumatic brain injury (TBI) are often faced with persistent memory deficits. The hippocampus, a structure critical for learning and memory, is vulnerable to TBI and its dysfunction has been linked to memory impairments. Protein kinase RNA-like ER kinase regulates protein synthesis (by phosphorylation of eukaryotic initiation factor 2 alpha [eIF2α]) in response to endoplasmic reticulum (ER) stressors, such as increases in calcium levels, oxidative damage, and energy/glucose depletion, all of which have been implicated in TBI pathophysiology. Exposure of cells to guanabenz has been shown to increase eIF2α phosphorylation and reduce ER stress. Using a rodent model of TBI, we present experimental results that indicate that postinjury administration of 5.0 mg/kg of guanabenz reduced cortical contusion volume and decreased hippocampal cell damage. Moreover, guanabenz treatment attenuated TBI-associated motor, vestibulomotor, recognition memory, and spatial learning and memory dysfunction. Interestingly, when the initiation of treatment was delayed by 24 h, or the dose reduced to 0.5 mg/kg, some of these beneficial effects were still observed. Taken together, these findings further support the involvement of ER stress signaling in TBI pathophysiology and indicate that guanabenz may have translational utility.

Guanabenz (Wytensin™) selectively enhances uptake and efficacy of hydrophobically modified siRNAs

One of the major obstacles to the pharmaceutical success of oligonucleotide therapeutics (ONTs) is efficient delivery from the point of injection to the intracellular setting where functional gene silencing occurs. In particular, a significant fraction of internalized ONTs are nonproductively sequestered in endo-lysosomal compartments. Here, we describe a two-step, robust assay for high-throughput de novo detection of small bioactive molecules that enhance cellular uptake, endosomal escape, and efficacy of ONTs. Using this assay, we screened the LOPAC (Sigma–Aldrich) Library of Pharmacologically Active Compounds and discovered that Guanabenz acetate (Wytensin™), an FDA-approved drug formerly used as an antihypertensive agent, is capable of markedly increasing the cellular internalization and target mRNA silencing of hydrophobically modified siRNAs (hsiRNAs), yielding a ∼100-fold decrease in hsiRNA IC₅₀ (from 132 nM to 2.4 nM). This is one of the first descriptions of a high-throughput small-molecule screen to identify novel chemistries that specifically enhance siRNA intracellular efficacy, and can be applied toward expansion of the chemical diversity of ONTs.

Swa2, the yeast homolog of mammalian auxilin, is specifically required for the propagation of the prion variant [URE3-1]

Yeast prions require a core set of chaperone proteins including Sis1, Hsp70 and Hsp104 to generate new amyloid templates for stable propagation, yet emerging studies indicate that propagation of some prions requires additional chaperone activities, demonstrating chaperone specificity beyond the common amyloid requirements. To comprehensively assess such prion-specific requirements for the propagation of the [URE3] prion variant [URE3-1], we screened 12 yeast cytosolic J-proteins, and here we report a novel role for the J-protein Swa2/Aux1. Swa2 is the sole yeast homolog of the mammalian protein auxilin, which, like Swa2, functions in vesicle-mediated endocytosis by disassembling the structural lattice formed by the protein clathrin. We found that, in addition to Sis1, [URE3-1] is specifically dependent upon Swa2, but not on any of the 11 other J-proteins. Further, we show that [URE3-1] propagation requires both a functional J-domain and the tetratricopeptide repeat (TPR) domain, but surprisingly does not require Swa2-clathrin binding. Because the J-domain of Swa2 can be replaced with the J-domains of other proteins, our data strongly suggest that prion-chaperone specificity arises from the Swa2 TPR domain and supports a model where Swa2 acts through Hsp70, most likely to provide additional access points for Hsp104 to promote prion template generation.

Genome-wide RNA-Seq of Human Motor Neurons Implicates Selective ER Stress Activation in Spinal Muscular Atrophy

Spinal muscular atrophy (SMA) is caused by mutations in the SMN1 gene. Because this gene is expressed ubiquitously, it remains poorly understood why motor neurons (MNs) are one of the most affected cell types. To address this question, we carried out RNA sequencing studies using fixed, antibody-labeled, and purified MNs produced from control and SMA patient-derived induced pluripotent stem cells (iPSCs). We found SMA-specific changes in MNs, including hyper-activation of the ER stress pathway. Functional studies demonstrated that inhibition of ER stress improves MN survival in vitro even in MNs expressing low SMN. In SMA mice, systemic delivery of an ER stress inhibitor that crosses the blood-brain barrier led to the preservation of spinal cord MNs. Therefore, our study implies that selective activation of ER stress underlies MN death in SMA. Moreover, the approach we have taken would be broadly applicable to the study of disease-prone human cells in heterogeneous cultures.

Guanabenz Treatment Accelerates Disease in a Mutant SOD1 Mouse Model of ALS

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease characterized by loss of motor neurons. The mechanisms leading to motor neuron degeneration in ALS are unclear. However, there is evidence for involvement of endoplasmic reticulum (ER) stress and the unfolded protein response (UPR) in ALS, notably in mutant SOD1 mediated models of ALS. Stress induced phosphorylation of the eIF2 alpha subunit by eukaryotic translation initiation factor 2-alpha kinase 3 Perk activates the UPR. Guanabenz is a centrally acting alpha2 adrenergic receptor agonist shown to interact with a regulatory subunit of the protein phosphatase, Pp1/Gadd34, and selectively disrupt the dephosphorylation of the alpha subunit of eukaryotic initiation factor 2 (eif2alpha). Here we demonstrate that guanabenz is protective in fibroblasts expressing G93A mutant SOD1 when they are exposed to tunicamycin mediated ER stress. However, in contrast to other reports, guanabenz treatment accelerated ALS-like disease progression in a strain of mutant SOD1 transgenic ALS mice. This study highlights challenges of pharmacological interventions of cellular stress responses in whole animal models of ALS.

Structural and Functional Analysis of the GADD34:PP1 eIF2α Phosphatase

The attenuation of protein synthesis via the phosphorylation of eIF2α is a major stress response of all eukaryotic cells. The growth-arrest- and DNA-damage-induced transcript 34 (GADD34) bound to the serine/threonine protein phosphatase 1 (PP1) is the necessary eIF2α phosphatase complex that returns mammalian cells to normal protein synthesis following stress. The molecular basis by which GADD34 recruits PP1 and its substrate eIF2α are not fully understood, hindering our understanding of the remarkable selectivity of the GADD34:PP1 phosphatase for eIF2α. Here, we report detailed structural and functional analyses of the GADD34:PP1 holoenzyme and its recruitment of eIF2α. The data highlight independent interactions of PP1 and eIF2α with GADD34, demonstrating that GADD34 functions as a scaffold both in vitro and in cells. This work greatly enhances our molecular understanding of a major cellular eIF2α phosphatase and establishes the foundation for future translational work.