The Endoplasmic Reticulum Chaperone GRP78/BiP Modulates Prion Propagation in vitro and in vivo

The dance of proteostasis and metabolism: Unveiling the caloristatic controlling switch

The heat shock response (HSR) is an ancient and evolutionarily conserved mechanism designed to restore cellular homeostasis following proteotoxic challenges. However, it has become increasingly evident that disruptions in energy metabolism also trigger the HSR. This interplay between proteostasis and energy regulation is rooted in the fundamental need for ATP to fuel protein synthesis and repair, making the HSR an essential component of cellular energy management. Recent findings suggest that the origins of proteostasis-defending systems can be traced back over 3.6 billion years, aligning with the emergence of sugar kinases that optimized glycolysis around 3.594 billion years ago. This evolutionary connection is underscored by the spatial similarities between the nucleotide-binding domain of HSP70, the key player in protein chaperone machinery, and hexokinases. The HSR serves as a hub that integrates energy metabolism and resolution of inflammation, further highlighting its role in maintaining cellular homeostasis. Notably, 5'-adenosine monophosphate-activated protein kinase emerges as a central regulator, promoting the HSR during predominantly proteotoxic stress while suppressing it in response to predominantly metabolic stress. The complex relationship between 5'-adenosine monophosphate-activated protein kinase and the HSR is finely tuned, with paradoxical effects observed under different stress conditions. This delicate equilibrium, known as caloristasis, ensures that cellular homeostasis is maintained despite shifting environmental and intracellular conditions. Understanding the caloristatic controlling switch at the heart of this interplay is crucial. It offers insights into a wide range of conditions, including glycemic control, obesity, type 2 diabetes, cardiovascular and neurodegenerative diseases, reproductive abnormalities, and the optimization of exercise routines. These findings highlight the profound interconnectedness of proteostasis and energy metabolism in cellular function and adaptation.

Bacteriophage-encoded chaperonins stimulate prion protein fibrillation in an ATP-dependent manner

The pathogenesis of the various prion diseases is based on the conformational conversion of the prion protein from its physiological cellular form to the insoluble scrapie isoform. Several chaperones, including the Hsp60 family of group I chaperonins, are known to contribute to this transformation, but data on their effects are scarce and conflicting. In this work, two GroEL-like phage chaperonins, the single-ring OBP and the double-ring EL, were found to stimulate monomeric prion protein fibrillation in an ATP-dependent manner. The resulting fibrils were characterised by thioflavin T fluorescence, electron microscopy, proteinase K digestion assay and other methods. In the presence of ATP, chaperonins were found to promote the conversion of prion protein monomers into short amyloid fibrils with their further aggregation into less toxic large clusters. Fibrils generated with the assistance of phage chaperonins differ in morphology and properties from those formed spontaneously from monomeric prion in the presence of denaturants at acidic pH.

Arginine regulates HSPA5/BiP translation through ribosome pausing in triple-negative breast cancer cells

BACKGROUND

Triple-negative breast cancer (TNBC) is an aggressive subtype of breast cancer with a high mortality rate due to a lack of therapeutic targets. Many TNBC cells are reliant on extracellular arginine for survival and express high levels of binding immunoglobin protein (BiP), a marker of metastasis and endoplasmic reticulum (ER) stress response.

METHODS

In this study, the effect of arginine shortage on BiP expression in the TNBC cell line MDA-MB-231 was evaluated. Two stable cell lines were generated in MDA-MB-231 cells: the first expressed wild-type BiP, and the second expressed a mutated BiP free of the two arginine pause-site codons, CCU and CGU, termed G-BiP.

RESULTS

The results showed that arginine shortage induced a non-canonical ER stress response by inhibiting BiP translation via ribosome pausing. Overexpression of G-BiP in MDA-MB-231 cells promoted cell resistance to arginine shortage compared to cells overexpressing wild-type BiP. Additionally, limiting arginine led to decreased levels of the spliced XBP1 in the G-BiP overexpressing cells, potentially contributing to their improved survival compared to the parental WT BiP overexpressing cells.

CONCLUSION

In conclusion, these findings suggest that the downregulation of BiP disrupts proteostasis during arginine shortage-induced non-canonical ER stress and plays a key role in cell growth inhibition, indicating BiP as a target of codon-specific ribosome pausing upon arginine shortage.

Effect of temperature and nucleotide on the binding of BiP chaperone to a protein substrate

BiP (immunoglobulin heavy-chain binding protein) is a Hsp70 monomeric ATPase motor that plays broad and crucial roles in maintaining proteostasis inside the cell. Structurally, BiP is formed by two domains, a nucleotide-binding domain (NBD) with ATPase activity connected by a flexible hydrophobic linker to the substrate-binding domain. While the ATPase and substrate binding activities of BiP are allosterically coupled, the latter is also dependent on nucleotide binding. Recent structural studies have provided new insights into BiP's allostery; however, the influence of temperature on the coupling between substrate and nucleotide binding to BiP remains unexplored. Here, we study BiP's binding to its substrate at the single molecule level using thermo-regulated optical tweezers which allows us to mechanically unfold the client protein and explore the effect of temperature and different nucleotides on BiP binding. Our results confirm that the affinity of BiP for its protein substrate relies on nucleotide binding, by mainly regulating the binding kinetics between BiP and its substrate. Interestingly, our findings also showed that the apparent affinity of BiP for its protein substrate in the presence of nucleotides remains invariable over a wide range of temperatures, suggesting that BiP may interact with its client proteins with similar affinities even when the temperature is not optimal. Thus, BiP could play a role as a "thermal buffer" in proteostasis.

Deregulation of mTORC1-TFEB axis in human iPSC model of GBA1-associated Parkinson's disease

Mutations in the GBA1 gene are the single most frequent genetic risk factor for Parkinson's disease (PD). Neurodegenerative changes in GBA1-associated PD have been linked to the defective lysosomal clearance of autophagic substrates and aggregate-prone proteins. To elucidate novel mechanisms contributing to proteinopathy in PD, we investigated the effect of GBA1 mutations on the transcription factor EB (TFEB), the master regulator of the autophagy-lysosomal pathway (ALP). Using PD patients' induced-pluripotent stem cells (iPSCs), we examined TFEB activity and regulation of the ALP in dopaminergic neuronal cultures generated from iPSC lines harboring heterozygous GBA1 mutations and the CRISPR/Cas9-corrected isogenic controls. Our data showed a significant decrease in TFEB transcriptional activity and attenuated expression of many genes in the CLEAR network in GBA1 mutant neurons, but not in the isogenic gene-corrected cells. In PD neurons, we also detected increased activity of the mammalian target of rapamycin complex1 (mTORC1), the main upstream negative regulator of TFEB. Increased mTORC1 activity resulted in excess TFEB phosphorylation and decreased nuclear translocation. Pharmacological mTOR inhibition restored TFEB activity, decreased ER stress and reduced α-synuclein accumulation, indicating improvement of neuronal protiostasis. Moreover, treatment with the lipid substrate reducing compound Genz-123346, decreased mTORC1 activity and increased TFEB expression in the mutant neurons, suggesting that mTORC1-TFEB alterations are linked to the lipid substrate accumulation. Our study unveils a new mechanism contributing to PD susceptibility by GBA1 mutations in which deregulation of the mTORC1-TFEB axis mediates ALP dysfunction and subsequent proteinopathy. It also indicates that pharmacological restoration of TFEB activity could be a promising therapeutic approach in GBA1-associated neurodegeneration.

Melatonin Can Modulate Neurodegenerative Diseases by Regulating Endoplasmic Reticulum Stress

As people age, their risks of developing degenerative diseases such as cancer, diabetes, Parkinson's Disease (PD), Alzheimer's Disease (AD), rheumatoid arthritis, and osteoporosis are generally increasing. Millions of people worldwide suffer from these diseases as they age. In most countries, neurodegenerative diseases are generally recognized as the number one cause afflicting the elderly. Endoplasmic reticulum (ER) stress has been suggested to be associated with some human neurological diseases, such as PD and AD. Melatonin, a neuroendocrine hormone mainly synthesized in the pineal gland, is involved in pleiotropically biological functions, including the control of the circadian rhythm, immune enhancement, and antioxidant, anti-aging, and anti-tumor effects. Although there are many papers on the prevention or suppression of diseases by melatonin, there are very few papers about the effects of melatonin on ER stress in neurons and neurodegenerative diseases. This paper aims to summarize and present the effects of melatonin reported so far, focusing on its effects on neurons and neurodegenerative diseases related to ER stress. Studies have shown that the primary target molecule of ER stress for melatonin is CHOP, and PERK and GRP78/BiP are the secondary target molecules. Therefore, melatonin is crucial in protecting neurons and treating neurodegeneration against ER stress.

Comprehensive proteomic profiling of early antral follicles from sheep

The present study evaluates the proteome of early antral follicles from Ovis aries. Fifty follicles were collected from ovaries of adult ewes and extracted proteins were trypsin-digested, desalted and analyzed by LC-MS/MS. Genes were screened for potential modulation by miRNAs and protein data, subjected to functional enrichment analysis. Label-free mass spectrometry allowed the identification of 2503 follicle proteins, confirming vimentin, actin, lamin, heat shock proteins and histones as the most abundant ones. In silico analyses indicated that miRNAs modulate the expression of genes coding proteins of the sheep follicles involved in cell cycle, cell differentiation, aging, apoptosis, cell death, adipocyte differentiation, cell division. The most important biological processes associated with the follicle proteins were innate immune response, translation, adaptive immune response and protein folding, while molecular functions linked to the proteome of sheep antral follicles related to metal ion binding, ATP binding, oxygen binding, RNA binding and GTP binding, among others. Upload of 2503 Uniport accession codes through DAVID platform matched 1274 genes, associated with translation, metabolic process, proteolysis involved in cellular protein catabolic process, zona pellucida receptor complex and others. KEEG pathways analysis indicated genes correlated with ovine follicular development, with major pathways listed as carbon metabolism, biosynthesis of amino acids, glutathione metabolism, oxidative phosphorylation, fatty acid degradation and oocyte meiosis. This represents a comprehensive atlas of proteins expressed in sheep early antral follicles and will contribute to future identification of biomarkers for follicular development and oocyte maturation.

Endoplasmic reticulum stress and ubiquitin-proteasome system impairment in natural scrapie

Chronic accumulation of misfolded proteins such as PrP^Sc can alter the endoplasmic reticulum homeostasis triggering the unfolded protein response (UPR). In this pathogenic event, the molecular chaperones play an important role. Several reports in humans and animals have suggested that neurodegeneration is related to endoplasmic reticulum stress in diseases caused by the accumulation of misfolded proteins. In this study, we investigated the expression of three endoplasmic reticulum stress markers: PERK (protein kinase R-like endoplasmic reticulum kinase), BiP (binding immunoglobulin protein), and PDI (Protein Disulfide Isomerase). In addition, we evaluated the accumulation of ubiquitin as a marker for protein degradation mediated by the proteasome. These proteins were studied in brain tissues of sheep affected by scrapie in clinical and preclinical stages of the disease. Results were compared with those observed in healthy controls. Scrapie-infected sheep showed significant higher levels of PERK, BiP/Grp78 and PDI than healthy animals. As we observed before in models of spontaneous prion disease, PDI was the most altered ER stress marker between scrapie-infected and healthy sheep. Significantly increased intraneuronal and neuropil ubiquitinated deposits were observed in certain brain areas in scrapie-affected animals compared to controls. Our results suggest that the neuropathological and neuroinflammatory phenomena that develop in prion diseases cause endoplasmic reticulum stress in brain cells triggering the UPR. In addition, the significantly higher accumulation of ubiquitin aggregates in scrapie-affected animals suggests an impairment of the ubiquitin-proteasome system in natural scrapie. Therefore, these proteins may contribute as biomarkers and/or therapeutic targets for prion diseases.

Agr2-associated ER stress promotes adherent-invasive E. coli dysbiosis and triggers CD103+ dendritic cell IL-23-dependent ileocolitis

Endoplasmic reticulum (ER) stress is associated with Crohn's disease (CD), but its impact on host-microbe interaction in disease pathogenesis is not well defined. Functional deficiency in the protein disulfide isomerase anterior gradient 2 (AGR2) has been linked with CD and leads to epithelial cell ER stress and ileocolitis in mice and humans. Here, we show that ileal expression of AGR2 correlates with mucosal Enterobactericeae abundance in human inflammatory bowel disease (IBD) and that Agr2 deletion leads to ER-stress-dependent expansion of mucosal-associated adherent-invasive Escherichia coli (AIEC), which drives Th17 cell ileocolitis in mice. Mechanistically, our data reveal that AIEC-induced epithelial cell ER stress triggers CD103⁺ dendritic cell production of interleukin-23 (IL-23) and that IL-23R is required for ileocolitis in Agr2^-/- mice. Overall, these data reveal a specific and reciprocal interaction of the expansion of the CD pathobiont AIEC with ER-stress-associated ileocolitis and highlight a distinct cellular mechanism for IL-23-dependent ileocolitis.

AR12 increases BAG3 expression which is essential for Tau and APP degradation via LC3-associated phagocytosis and macroautophagy

We defined the mechanisms by which the chaperone ATPase inhibitor AR12 and the multi-kinase inhibitor neratinib interacted to reduce expression of Tau and amyloid-precursor protein (APP) in microglia and neuronal cells. AR12 and neratinib interacted to increase the phosphorylation of eIF2A S51 and the expression of BAG3, Beclin1 and ATG5, and in parallel, enhanced autophagosome formation and autophagic flux. Knock down of BAG3, Beclin1 or ATG5 abolished autophagosome formation and significantly reduced degradation of p62, LAMP2, Tau, APP, and GRP78 (total and plasma membrane). Knock down of Rubicon, a key component of LC3-associated phagocytosis (LAP), significantly reduced autophagosome formation but not autophagic flux and prevented degradation of Tau, APP, and cell surface GRP78, but not ER-localized GRP78. Knock down of Beclin1, ATG5 or Rubicon or over-expression of GRP78 prevented the significant increase in eIF2A phosphorylation. Knock down of eIF2A prevented the increase in BAG3 expression and significantly reduced autophagosome formation, autophagic flux, and it prevented Tau and APP degradation. We conclude that AR12 has the potential to reduce Tau and APP levels in neurons and microglia via the actions of LAP, endoplasmic reticulum stress signaling and macroautophagy. We hypothesize that the initial inactivation of GRP78 catalytic function by AR12 facilitates an initial increase in eIF2A phosphorylation which in turn is essential for greater levels of eIF2A phosphorylation, greater levels of BAG3 and macroautophagy and eventually leading to significant amounts of APP/Tau degradation.

Proteostasis unbalance in prion diseases: Mechanisms of neurodegeneration and therapeutic targets

Transmissible spongiform encephalopathies (TSEs), or prion diseases, are progressive neurodegenerative disorders of the central nervous system that affect humans and animals as sporadic, inherited, and infectious forms. Similarly to Alzheimer's disease and other neurodegenerative disorders, any attempt to reduce TSEs' lethality or increase the life expectancy of affected individuals has been unsuccessful. Typically, the onset of symptoms anticipates the fatal outcome of less than 1 year, although it is believed to be the consequence of a decades-long process of neuronal death. The duration of the symptoms-free period represents by itself a major obstacle to carry out effective neuroprotective therapies. Prions, the infectious entities of TSEs, are composed of a protease-resistant protein named prion protein scrapie (PrP^Sc) from the prototypical TSE form that afflicts ovines. PrP^Sc misfolding from its physiological counterpart, cellular prion protein (PrP^C), is the unifying pathogenic trait of all TSEs. PrP^Sc is resistant to intracellular turnover and undergoes amyloid-like fibrillation passing through the formation of soluble dimers and oligomers, which are likely the effective neurotoxic entities. The failure of PrP^Sc removal is a key pathogenic event that defines TSEs as proteopathies, likewise other neurodegenerative disorders, including Alzheimer's, Parkinson's, and Huntington's disease, characterized by alteration of proteostasis. Under physiological conditions, protein quality control, led by the ubiquitin-proteasome system, and macroautophagy clears cytoplasm from improperly folded, redundant, or aggregation-prone proteins. There is evidence that both of these crucial homeostatic pathways are impaired during the development of TSEs, although it is still unclear whether proteostasis alteration facilitates prion protein misfolding or, rather, PrP^Sc protease resistance hampers cytoplasmic protein quality control. This review is aimed to critically analyze the most recent advancements in the cause-effect correlation between PrP^C misfolding and proteostasis alterations and to discuss the possibility that pharmacological restoring of ubiquitin-proteasomal competence and stimulation of autophagy could reduce the intracellular burden of PrP^Sc and ameliorate the severity of prion-associated neurodegeneration.

Uncovering temporospatial sensitive TBI targeting strategies via in vivo phage display

The heterogeneous pathophysiology of traumatic brain injury (TBI) is a barrier to advancing diagnostics and therapeutics, including targeted drug delivery. We used a unique discovery pipeline to identify novel targeting motifs that recognize specific temporal phases of TBI pathology. This pipeline combined in vivo biopanning with domain antibody (dAb) phage display, next-generation sequencing analysis, and peptide synthesis. We identified targeting motifs based on the complementarity-determining region 3 structure of dAbs for acute (1 day post-injury) and subacute (7 days post-injury) post-injury time points in a preclinical TBI model (controlled cortical impact). Bioreactivity and temporal sensitivity of the targeting motifs were validated via immunohistochemistry. Immunoprecipitation-mass spectrometry indicated that the acute TBI targeting motif recognized targets associated with metabolic and mitochondrial dysfunction, whereas the subacute TBI motif was largely associated with neurodegenerative processes. This pipeline successfully discovered temporally specific TBI targeting motif/epitope pairs that will serve as the foundation for the next-generation targeted TBI therapeutics and diagnostics.

Butyrylcholinesterase in SH-SY5Y human neuroblastoma cells

Cultured SH-SY5Y human neuroblastoma cells are used in neurotoxicity assays. These cells express markers of the cholinergic and dopaminergic systems. Acetylcholinesterase (AChE) activity has been reported in these cells. Neurotoxic organophosphate compounds that inhibit AChE, also inhibit butyrylcholinesterase (BChE). We confirmed the presence of AChE in the cell lysate by activity assays, Western blot, and liquid chromatography-tandem mass spectrometry (LC-MS/MS) of immunopurified AChE. A nondenaturing gel stained for AChE activity identified the catalytically active AChE in SH-SY5Y cells as the unstable monomer. We also identified immature BChE in the cell lysate. The concentration of active BChE protein was similar to that of active AChE protein. The rate of substrate hydrolysis by AChE was 10-fold higher than substrate hydrolysis by BChE. The higher rate was due to the 10-fold higher specific activity of AChE over BChE (5000 units/mg for AChE; 500 units/mg for BChE). Neither cholinesterase was secreted. Tryptic peptides of immunopurified AChE and BChE were identified by LC-MS/MS on an Orbitrap Lumos Fusion mass spectrometer. The unfolded protein chaperone, binding immunoglobulin protein BiP/GRP78, was identified in the mass spectral data from all cholinesterase samples, suggesting that BiP was co-extracted with cholinesterase. This suggests that the cytoplasmic cholinesterases are immature forms of AChE and BChE that bind to BiP. It was concluded that SH-SY5Y cells express active AChE and active BChE, but the proteins do not mature to glycosylated tetramers.

Clearance of variant Creutzfeldt-Jakob disease prions in vivo by the Hsp70 disaggregase system

The metazoan Hsp70 disaggregase protects neurons from proteotoxicity that arises from the accumulation of misfolded protein aggregates. Hsp70 and its co-chaperones disassemble and extract polypeptides from protein aggregates for refolding or degradation. The effectiveness of the chaperone system decreases with age and leads to accumulation rather than removal of neurotoxic protein aggregates. Therapeutic enhancement of the Hsp70 protein disassembly machinery is proposed to counter late-onset protein misfolding neurodegenerative disease that may arise. In the context of prion disease, it is not known whether stimulation of protein aggregate disassembly paradoxically leads to enhanced formation of seeding competent species of disease-specific proteins and acceleration of neurodegenerative disease. Here we have tested the hypothesis that modulation of Hsp70 disaggregase activity perturbs mammalian prion-induced neurotoxicity and prion seeding activity. To do so we used prion protein (PrP) transgenic Drosophila that authentically replicate mammalian prions. RNASeq identified that Hsp70, DnaJ-1 and Hsp110 gene expression was downregulated in prion-exposed PrP Drosophila. We demonstrated that RNAi knockdown of Hsp110 or DnaJ-1 gene expression in variant Creutzfeldt–Jakob disease prion-exposed human PrP Drosophila enhanced neurotoxicity, whereas overexpression mitigated toxicity. Strikingly, prion seeding activity in variant Creutzfeldt–Jakob disease prion-exposed human PrP Drosophila was ablated or reduced by Hsp110 or DnaJ-1 overexpression, respectively. Similar effects were seen in scrapie prion-exposed ovine PrP Drosophila with modified Hsp110 or DnaJ-1 gene expression. These unique observations show that the metazoan Hsp70 disaggregase facilitates the clearance of mammalian prions and that its enhanced activity is a potential therapeutic strategy for human prion disease.

Endoplasmic Reticulum Stress of Gut Enterocyte and Intestinal Diseases

The endoplasmic reticulum, a vast reticular membranous network from the nuclear envelope to the plasma membrane responsible for the synthesis, maturation, and trafficking of a wide range of proteins, is considerably sensitive to changes in its luminal homeostasis. The loss of ER luminal homeostasis leads to abnormalities referred to as endoplasmic reticulum (ER) stress. Thus, the cell activates an adaptive response known as the unfolded protein response (UPR), a mechanism to stabilize ER homeostasis under severe environmental conditions. ER stress has recently been postulated as a disease research breakthrough due to its significant role in multiple vital cellular functions. This has caused numerous reports that ER stress-induced cell dysfunction has been implicated as an essential contributor to the occurrence and development of many diseases, resulting in them targeting the relief of ER stress. This review aims to outline the multiple molecular mechanisms of ER stress that can elucidate ER as an expansive, membrane-enclosed organelle playing a crucial role in numerous cellular functions with evident changes of several cells encountering ER stress. Alongside, we mainly focused on the therapeutic potential of ER stress inhibition in gastrointestinal diseases such as inflammatory bowel disease (IBD) and colorectal cancer. To conclude, we reviewed advanced research and highlighted future treatment strategies of ER stress-associated conditions.

A Feasible Alternative Strategy Targeting Furin Disrupts SARS-CoV-2 Infection Cycle

The COVID-19 causing coronavirus (SARS-CoV-2) remains a public health threat worldwide. SARS-CoV-2 enters human lung cells via its spike glycoprotein binding to angiotensin-converting enzyme 2 (ACE2). Notably, the cleavage of the spike by the host cell protease furin in virus-producing cells is critical for subsequent spike-driven entry into lung cells. Thus, effective targeted therapies blocking the spike cleavage and activation in viral producing cells may provide an alternate strategy to break the viral transmission cycle and to overcome disease pathology. Here we engineered and described an antibody-based targeted strategy, which directly competes with the furin mediated proteolytic activation of the spike in virus-producing cells. The described approach involves engineering competitive furin substrate residues in the IgG1 Fc-extended flexible linker domain of SARS-CoV-2 spike targeting antibodies. Considering the site of spike furin cleavage and SARS-CoV-2 egress remains uncertain, the experimental strategy pursued here revealed novel mechanistic insights into proteolytic processing of the spike protein, which suggest that processing does not occur in the constitutive secretory pathway. Furthermore, our results show blockade of furin-mediated cleavage of the spike protein for membrane fusion activation and virus host-cell entry function. These findings provide an alternate insight of targeting applicability to SARS-CoV-2 and the future coronaviridae family members, exploiting the host protease system to gain cellular entry and subsequent chain of infections. IMPORTANCE Since its emergence in December 2019, COVID-19 has remained a global economic and health threat. Although RNA and DNA vector-based vaccines induced antibody response and immunological memory have proven highly effective against hospitalization and mortality, their long-term efficacy remains unknown against continuously evolving SARS-CoV-2 variants. As host cell-enriched furin-mediated cleavage of SARS-CoV-2 spike protein is critical for viral entry and chain of the infection cycle, the solution described here of an antibody Fc-conjugated furin competing peptide is significant. In a scenario where spike mutational drifts do not interfere with the Fc-conjugated antibody's epitope, the proposed furin competing strategy confers a broad-spectrum targeting design to impede the production of efficiently transmissible SARS-CoV-2 viral particles. In addition, the proposed approach is plug-and-play against other potentially deadly viruses that exploit secretory pathway independent host protease machinery to gain cellular entry and subsequent transmissions to host cells.

Cell surface expression of GRP78 and CXCR4 is associated with childhood high-risk acute lymphoblastic leukemia at diagnostics

Acute lymphocytic leukemia is the most common type of cancer in pediatric individuals. Glucose regulated protein (GRP78) is an endoplasmic reticulum chaperone that facilitates the folding and assembly of proteins and regulates the unfolded protein response pathway. GRP78 has a role in survival of cancer and metastasis and cell-surface associated GRP78 (sGRP78) is expressed on cancer cells but not in normal cells. Here, we explored the presence of sGRP78 in pediatric B-ALL at diagnosis and investigated the correlation with bona fide markers of leukemia. By using a combination of flow cytometry and high multidimensional analysis, we found a distinctive cluster containing high levels of sGRP78, CD10, CD19, and CXCR4 in bone marrow samples obtained from High-risk leukemia patients, which was absent in the compartment of Standard-risk leukemia. We confirmed that sGRP78+CXCR4+ blood-derived cells were more frequent in High-risk leukemia patients. Finally, we analyzed the dissemination capacity of sGRP78 leukemia cells in a model of xenotransplantation. sGRP78+ cells emigrated to the bone marrow and lymph nodes, maintaining the expression of CXCR4. Testing the presence of sGRP78 and CXCR4 together with conventional markers may help to achieve a better categorization of High and Standard-risk pediatric leukemia at diagnosis.

APP deficiency and HTRA2 modulates PrPc proteostasis in human cancer cells

Cellular protein homeostasis (proteostasis) requires an accurate balance between protein biosynthesis, folding, and degradation, and its instability is causally related to human diseases and cancers. Here, we created numerous engineered cancer cell lines targeting APP (amyloid ß precursor protein) and/or PRNP (cellular prion) genes and we showed that APP knocking-down impaired PRNP mRNA level and vice versa, suggesting a link between their gene regulation. PRNP^KD, APP^KD and PRNP^KD/APP^KD HeLa cells encountered major difficulties to grow in a 3D tissue-like environment. Unexpectedly, we found a cytoplasmic accumulation of the PrP^c protein without PRNP gene up regulation, in both APP^KD and APP^KO HeLa cells. Interestingly, APP and/or PRNP gene ablation enhanced the chaperone/serine protease HTRA2 gene expression, which is a protein processing quality factor involved in Alzheimer's disease. Importantly, HTRA2 gene silencing decreased PRNP mRNA level and lowered PrP^c protein amounts, and conversely, HTRA2 overexpression increased PRNP gene regulation and enhanced membrane-anchored and cytoplasmic PrP^c fractions. PrP^c, APP and HTRA2 destabilized membrane-associated CD24 protein, suggesting changes in the lipid raft structure. Our data show for the first time that APP and the dual chaperone/serine protease HTRA2 protein could modulate PrP^c proteostasis hampering cancer cell behavior.

Hemophilia A Gene Therapy: Current and Next-Generation Approaches

INTRODUCTION

: Hemophilia comprises a group of X-linked hemorrhagic disorders that result from a deficiency of coagulation factors. The disorder affects mainly males and leads to chronic pain, joint deformity, reduced mobility, and increased mortality. Current therapies require frequent administration of replacement clotting factors, but the emergence of alloantibodies (inhibitors) diminishes their efficacy. New therapies are being developed to produce the deficient clotting factors and prevent the emergence of inhibitors.

AREAS COVERED

: This article provides an update on the characteristics and disease pathophysiology of hemophilia A, as well as current treatments, with a special focus on ongoing clinical trials related to gene replacement therapies.

EXPERT OPINION

: Gene replacement therapies provide safe, durable, and stable transgene expression while avoiding the challenges of clotting factor replacement therapies in patients with hemophilia. Improving the specificity of the viral construct and decreasing the therapeutic dose are critical toward minimizing cellular stress, induction of the unfolded protein response, and the resulting loss of protein production in liver cells. Next-generation gene therapies incorporating chimeric DNA sequences in the transgene can increase clotting factor synthesis and secretion, and advance the efficacy, safety, and durability of gene replacement therapy for hemophilia A as well as other blood clotting disorders.

1, 8-cineole protects against ISO-induced heart failure by inhibiting oxidative stress and ER stress in vitro and in vivo

Sugemule-3 is widely adopted in clinical practice to manage cardio-cerebral diseases. 1, 8-cineole is the main ingredient of Sugemule-3, however, the underlying cellular mechanisms for its protective effect are poorly understood. 1, 8-cineole improved the survival of H9C2 cardiomyocytes during isoproterenol (ISO) injury and reduced ISO-induced apoptosis. Compared to the ISO group, 1, 8-cineole highly attenuated the generation of ISO-induced reactive oxygen species (ROS), the depolarization of △ψm, suppression of the Bax/Bcl-2 ratio, and p-caspase 3 expression, in vitro. Furthermore, 1, 8-cineole treatment in H9C2 cardiomyocytes lowered the expressions of 78-kDa glucose-regulated protein (GRP78), p-protein kinase-like ER kinase (PERK), activation of transcription factor (ATF) 4, and ER stress effector protein C/EBP and homologous protein (CHOP). These findings implied that 1, 8-cineole contribute to cardioprotection via the GRP78/CHOP pathways. Using animal models, 1, 8-cineole was revealed to markedly alleviate ISO-induced heart injury, and reduce cardiac hypertrophy, formation of the cytoplasmic vacuole, loss of myofiber, and fibrosis by inhibiting oxidative stress and ER stress. 1, 8-cineole reduces apoptosis by inhibiting signaling pathways related to oxidative stress and ER stress. These findings implicate 1, 8-cineole as a potential therapeutic target for cardiac hypertrophy-related heart diseases, including heart failure.

Bbc3 Loss Enhances Survival and Protein Clearance in Neurons Exposed to the Organophosphate Pesticide Chlorpyrifos

Exposure to environmental toxicants can increase the risk of developing age-related neurodegenerative disorders. Exposure to the widely used organophosphate pesticide chlorpyrifos (CPF) is associated with increased risk of developing Alzheimer's disease and Parkinson's disease, but the cellular mechanisms underlying CPF toxicity in neurons are not completely understood. We evaluated CPF toxicity in mouse primary cortical neuronal cultures, using RNA-sequencing to identify cellular pathways modulated by CPF. CPF exposure altered the expression of genes associated with intrinsic apoptosis, significantly elevating expression of the pro-apoptotic mediator Bbc3/Puma. Bbc3 loss attenuated CPF driven neurotoxicity, induction of other intrinsic apoptosis regulatory genes including Trp53 and Pmaip1 (encoding the NOXA protein), and cleavage of apoptosis executors caspase 3 and poly (ADP-ribose) polymerase (PARP). CPF exposure was associated with enhanced expression of endoplasmic reticulum stress-related genes and proteins and the accumulation of high molecular weight protein species in primary neuronal cultures. No evidence of alterations in the ubiquitin-proteosome system were observed, however, autophagy-related proteins were upregulated in CPF-treated Bbc3-/- neuronal cultures compared with identically exposed WT cultures. Elevated autophagy-related protein expression in Bbc3-/- neuronal cultures was associated with a reduction in CPF-induced high molecular weight alpha-synuclein and tau immunoreactive protein aggregates. Studies indicate that Bbc3-/- neuronal cultures enhance the endoplasmic reticulum stress response and upregulate protein clearance mechanisms as a component of resistance to CPF-mediated toxicity.

Role of vaspin in porcine ovary: effect on signaling pathways and steroid synthesis via GRP78 receptor and protein kinase A†

Vaspin, visceral-adipose-tissue-derived serine protease inhibitor, is involved in the development of obesity, insulin resistance, inflammation, and energy metabolism. Our previous study showed vaspin expression and its regulation in the ovary; however, the role of this adipokine in ovarian cells has never been studied. Here, we studied the in vitro effect of vaspin on various kinase-signaling pathways: mitogen-activated kinase (MAP3/1), serine/threonine kinase (AKT), signal transducer and activator of transcription 3 (STAT3) protein kinase AMP (PRKAA1), protein kinase A (PKA), and on expression of nuclear factor kappa B (NFKB2) as well as on steroid synthesis by porcine ovarian cells. By using western blot, we found that vaspin (1 ng/ml), in a time-dependent manner, increased phosphorylation of MAP3/1, AKT, STAT3, PRKAA1, and PKA, while it decreased the expression of NFKB2. We observed that vaspin, in a dose-dependent manner, increased the basal steroid hormone secretion (progesterone and estradiol), mRNA and protein expression of steroid enzymes using real-time PCR and western blot, respectively, and the mRNA of gonadotropins (FSHR, LHCGR) and steroids (PGR, ESR2) receptors. The stimulatory effect of vaspin on basal steroidogenesis was reversed when ovarian cells were cultured in the presence of a PKA pharmacological inhibitor (KT5720) and when GRP78 receptor was knocked down (siRNA). However, in the presence of insulin-like growth factor type 1 and gonadotropins, vaspin reduced steroidogenesis. Thus, vaspin, by activation of various signaling pathways and stimulation of basal steroid production via GRP78 receptor and PKA, could be a new regulator of porcine ovarian function.

Direct Endoplasmic Reticulum Targeting by the Selective Alkylphospholipid Analog and Antitumor Ether Lipid Edelfosine as a Therapeutic Approach in Pancreatic Cancer

Pancreatic ductal adenocarcinoma (PDAC), the most common malignancy of the pancreas, shows a dismal and grim overall prognosis and survival rate, which have remained virtually unchanged for over half a century. PDAC is the most lethal of all cancers, with the highest mortality-to-incidence ratio. PDAC responds poorly to current therapies and remains an incurable malignancy. Therefore, novel therapeutic targets and drugs are urgently needed for pancreatic cancer treatment. Selective induction of apoptosis in cancer cells is an appealing approach in cancer therapy. Apoptotic cell death is highly regulated by different signaling routes that involve a variety of subcellular organelles. Endoplasmic reticulum (ER) stress acts as a double-edged sword at the interface of cell survival and death. Pancreatic cells exhibit high hormone and enzyme secretory functions, and thereby show a highly developed ER. Thus, pancreatic cancer cells display a prominent ER. Solid tumors have to cope with adverse situations in which hypoxia, lack of certain nutrients, and the action of certain antitumor agents lead to a complex interplay and crosstalk between ER stress and autophagy-the latter acting as an adaptive survival response. ER stress also mediates cell death induced by a number of anticancer drugs and experimental conditions, highlighting the pivotal role of ER stress in modulating cell fate. The alkylphospholipid analog prototype edelfosine is selectively taken up by tumor cells, accumulates in the ER of a number of human solid tumor cells-including pancreatic cancer cells-and promotes apoptosis through a persistent ER-stress-mediated mechanism both in vitro and in vivo. Here, we discuss and propose that direct ER targeting may be a promising approach in the therapy of pancreatic cancer, opening up a new avenue for the treatment of this currently incurable and deadly cancer. Furthermore, because autophagy acts as a cytoprotective response to ER stress, potentiation of the triggering of a persistent ER response by combination therapy, together with the use of autophagy blockers, could improve the current gloomy expectations for finding a cure for this type of cancer.

Role of Polyphenols on Gut Microbiota and the Ubiquitin-Proteasome System in Neurodegenerative Diseases

Today, neurodegenerative diseases have become a remarkable public health challenge due to their direct relation with aging. Accordingly, understanding the molecular and cellular mechanisms occurring in the pathogenesis of them is essential. Both protein aggregations as a result of the ubiquitin-proteasome system (UPS) inefficiency and gut microbiota alternation are the main pathogenic hallmarks. Polyphenols upregulating this system may decrease the developing rate of neurodegenerative diseases. Most of the dietary intake of polyphenols is converted into other microbial metabolites, which have completely different biological properties from the original polyphenols and should be thoroughly investigated. Herein, several prevalent neurodegenerative diseases are pinpointed to explain the role of gut microbiota alternations and the role of molecular changes, especially UPS down-regulation in their pathogenesis. Some of the most important polyphenols found in our diet are explained along with their microbial metabolites in the body.

Targeting the Mild-Hypoxia Driving Force for Metabolic and Muscle Transcriptional Reprogramming of Gilthead Sea Bream (Sparus aurata) Juveniles

Simple Summary

Reduced oxygen availability generates a number of adaptive features across all the animal kingdom, and the goal of this study was targeting the mild-hypoxia driving force for metabolic and muscle transcriptional reprogramming of gilthead sea bream juveniles. Attention was focused on blood metabolic and muscle transcriptomic landmarks before and after exhaustive exercise. Our results after mild-hypoxia conditioning highlighted an increased contribution of lipid metabolism to whole energy supply to preserve the aerobic energy production, a better swimming performance regardless of changes in feed intake, as well as reduced protein turnover and improved anaerobic fitness with the restoration of normoxia.

Abstract

On-growing juveniles of gilthead sea bream were acclimated for 45 days to mild-hypoxia (M-HYP, 40–60% O₂ saturation), whereas normoxic fish (85–90% O₂ saturation) constituted two different groups, depending on if they were fed to visual satiety (control fish) or pair-fed to M-HYP fish. Following the hypoxia conditioning period, all fish were maintained in normoxia and continued to be fed until visual satiation for 3 weeks. The time course of hypoxia-induced changes was assessed by changes in blood metabolic landmarks and muscle transcriptomics before and after exhaustive exercise in a swim tunnel respirometer. In M-HYP fish, our results highlighted a higher contribution of aerobic metabolism to whole energy supply, shifting towards a higher anaerobic fitness following normoxia restoration. Despite these changes in substrate preference, M-HYP fish shared a persistent improvement in swimming performance with a higher critical speed at exercise exhaustion. The machinery of muscle contraction and protein synthesis and breakdown was also largely altered by mild-hypoxia conditioning, contributing this metabolic re-adjustment to the positive regulation of locomotion and to the catch-up growth response during the normoxia recovery period. Altogether, these results reinforce the presence of large phenotypic plasticity in gilthead sea bream, and highlights mild-hypoxia as a promising prophylactic measure to prepare these fish for predictable stressful events.

The Potential Role of Small-Molecule PERK Inhibitor LDN-0060609 in Primary Open-Angle Glaucoma Treatment

Primary open-angle glaucoma (POAG) constitutes the most common type of glaucoma. Emerging evidence suggests that Endoplasmic Reticulum (ER) stress and the protein kinase RNA-like endoplasmic reticulum kinase (PERK)-mediated Unfolded Protein Response (UPR) signaling pathway play a key role in POAG pathogenesis. Thus, the main aim of the study was to evaluate the effectiveness of the PERK inhibitor LDN-0060609 in cellular model of glaucoma using primary human trabecular meshwork (HTM) cells. To evaluate the level of the ER stress marker proteins, Western blotting and TaqMan gene expression assay were used. The cytotoxicity was measured by XTT, LDH assays and Giemsa staining, whereas genotoxicity via comet assay. Changes in cell morphology were assessed by phase-contrast microscopy. Analysis of apoptosis was performed by caspase-3 assay and flow cytometry (FC), whereas cell cycle progression by FC. The results obtained have demonstrated that LDN-0060609 triggered a significant decrease of ER stress marker proteins within HTM cells with induced ER stress conditions. Moreover, LDN-0060609 effectively increased viability, reduced DNA damage, increased proliferation, restored normal morphology, reduced apoptosis and restored normal cell cycle distribution of HTM cells with induced ER stress conditions. Thereby, PERK inhibitors, such as LDN-0060609, may provide an innovative, ground-breaking treatment strategy against POAG.

Functional genomics screen identifies proteostasis targets that modulate prion protein (PrP) stability

Prion protein (PrP) adopts either a helical conformation (PrPC) or an alternative, beta sheet-rich, misfolded conformation (PrPSc). The PrPSc form has the ability to "infect" PrPC and force it into the misfolded state. Accumulation of PrPSc is associated with a number of lethal neurodegenerative disorders, including Creutzfeldt-Jacob disease (CJD). Knockout of PrPC protects cells and animals from PrPSc infection; thus, there is interest in identifying factors that regulate PrPC stability, with the therapeutic goal of reducing PrPC levels and limiting infection by PrPSc. Here, we assembled a short-hairpin RNA (shRNA) library composed of 25+ shRNA sequences for each of 133 protein homeostasis (aka proteostasis) factors, such as molecular chaperones and co-chaperones. This Proteostasis shRNA Library was used to identify regulators of PrPC stability in HEK293 Hu129M cells. Strikingly, the screen identified a number of Hsp70 family members and their co-chaperones as putative targets. Indeed, a chemical pan-inhibitor of Hsp70s reduced PrPC levels and limited conversion to PrPSc in N2a cells. These results implicate specific proteostasis sub-networks, especially the Hsp70 system, as potential new targets for the treatment of CJD. More broadly, the Proteostasis shRNA Library might be a useful tool for asking which proteostasis factors are important for a given protein.

Possible mechanisms of the PERK pathway on neuronal apoptosis in a rat model of surgical brain injury

Protein kinase R-like endoplasmic reticulum kinase (PERK) is an important transmembrane protein in the endoplasmic reticulum (ER). PERK signaling has a critical function in neuronal apoptosis. This work aimed to assess PERK signaling for its function in surgical brain injury (SBI) and to explore the underlying mechanisms. Totally 120 male Sprague Dawley (SD) rats were assessed in an SBI model. The effects of the PERK inhibitor GSK2606414 were examined by Western-blot, immunofluorescent staining, TUNEL staining, fluoro-jade C (FJC) staining and neurological assays in rats with SBI. In this study, p-PERK and p-eIF2α protein amounts were increased upon SBI establishment, peaking at 24 h. Meanwhile, administration of GSK2606414 reversed these effects and prevented neuronal apoptosis. The PERK pathway has a significant function in neuronal apoptosis, and its suppression after SBI promotes the alleviation of brain injury. This suggests that targeting the PERK signaling pathway may represent an efficient therapeutic option for improving prognosis in SBI patients.

Endogenous Mechanisms of Neuroprotection: To Boost or Not to Boost

Postmitotic cells, like neurons, must live through a lifetime. For this reason, organisms/cells have evolved with self-repair mechanisms that allow them to have a long life. The discovery workflow of neuroprotectors during the last years has focused on blocking the pathophysiological mechanisms that lead to neuronal loss in neurodegeneration. Unfortunately, only a few strategies from these studies were able to slow down or prevent neurodegeneration. There is compelling evidence demonstrating that endorsing the self-healing mechanisms that organisms/cells endogenously have, commonly referred to as cellular resilience, can arm neurons and promote their self-healing. Although enhancing these mechanisms has not yet received sufficient attention, these pathways open up new therapeutic avenues to prevent neuronal death and ameliorate neurodegeneration. Here, we highlight the main endogenous mechanisms of protection and describe their role in promoting neuron survival during neurodegeneration.

The Size and Stability of Infectious Prion Aggregates Fluctuate Dynamically during Cellular Uptake and Disaggregation

Prion diseases arise when PrP^Sc, an aggregated, infectious, and insoluble conformer of the normally soluble mammalian prion protein, PrP^C, catalyzes the conversion of PrP^C into more PrP^Sc, which then accumulates in the brain leading to disease. PrP^Sc is the primary, if not sole, component of the infectious prion. Despite the stability and protease insensitivity of PrP^Sc aggregates, they can be degraded after cellular uptake. However, how cells disassemble and degrade PrP^Sc is poorly understood. In this work, we analyzed how the protease sensitivity and size distribution of PrP^Sc aggregates from two different mouse-adapted prion strains, 22L, that can persistently infect cells and 87V, that cannot, changed during cellular uptake. We show that within the first 4 h following uptake large PrP^Sc aggregates from both prion strains become less resistant to digestion by proteinase K (PK) through a mechanism that is dependent upon the acidic environment of endocytic vesicles. We further show that during disassembly, PrP^Sc aggregates from both strains become more resistant to PK digestion through the apparent removal of protease-sensitive PrP^Sc, with PrP^Sc from the 87V strain disassembled more readily than PrP^Sc from the 22L strain. Taken together, our data demonstrate that the sizes and stabilities of PrP^Sc from different prion strains change during cellular uptake and degradation, thereby potentially impacting the ability of prions to infect cells.

Prion-Associated Neurodegeneration Causes Both Endoplasmic Reticulum Stress and Proteasome Impairment in a Murine Model of Spontaneous Disease

Prion diseases are a group of neurodegenerative disorders that can be spontaneous, familial or acquired by infection. The conversion of the prion protein PrP^C to its abnormal and misfolded isoform PrP^Sc is the main event in the pathogenesis of prion diseases of all origins. In spontaneous prion diseases, the mechanisms that trigger the formation of PrP^Sc in the central nervous system remain unknown. Several reports have demonstrated that the accumulation of PrP^Sc can induce endoplasmic reticulum (ER) stress and proteasome impairment from the early stages of the prion disease. Both mechanisms lead to an increment of PrP aggregates in the secretory pathway, which could explain the pathogenesis of spontaneous prion diseases. Here, we investigate the role of ER stress and proteasome impairment during prion disorders in a murine model of spontaneous prion disease (TgVole) co-expressing the Ub^G76V-GFP reporter, which allows measuring the proteasome activity in vivo. Spontaneously prion-affected mice showed a significantly higher accumulation of the PKR-like ER kinase (PERK), the ER chaperone binding immunoglobulin protein (BiP/Grp78), the ER protein disulfide isomerase (PDI) and the Ub^G76V-GFP reporter than age-matched controls in certain brain areas. The upregulation of PERK, BiP, PDI and ubiquitin was detected from the preclinical stage of the disease, indicating that ER stress and proteasome impairment begin at early stages of the spontaneous disease. Strong correlations were found between the deposition of these markers and neuropathological markers of prion disease in both preclinical and clinical mice. Our results suggest that both ER stress and proteasome impairment occur during the pathogenesis of spontaneous prion diseases.

Disruption of Endoplasmic Reticulum Proteostasis in Age-Related Nervous System Disorders

Endoplasmic reticulum (ER) stress is a prominent cellular alteration of diseases impacting the nervous system that are associated to the accumulation of misfolded and aggregated protein species during aging. The unfolded protein response (UPR) is the main pathway mediating adaptation to ER stress, but it can also trigger deleterious cascades of inflammation and cell death leading to cell dysfunction and neurodegeneration. Genetic and pharmacological studies in experimental models shed light into molecular pathways possibly contributing to ER stress and the UPR activation in human neuropathies. Most of experimental models are, however, based on the overexpression of mutant proteins causing familial forms of these diseases or the administration of neurotoxins that induce pathology in young animals. Whether the mechanisms uncovered in these models are relevant for the etiology of the vast majority of age-related sporadic forms of neurodegenerative diseases is an open question. Here, we provide a systematic analysis of the current evidence linking ER stress to human pathology and the main mechanisms elucidated in experimental models. Furthermore, we highlight the recent association of metabolic syndrome to increased risk to undergo neurodegeneration, where ER stress arises as a common denominator in the pathogenic crosstalk between peripheral organs and the nervous system.

Sedum takesimense Protects PC12 Cells against Corticosterone-Induced Neurotoxicity by Inhibiting Neural Apoptosis

Neuronal cell death induced by chronic stress in the central nervous system is a cause of neurological dysfunction. We investigated the neuroprotective potential of a water extract of S. takesimense (WEST) against corticosterone-induced apoptosis in PC12 cells and the possible underlying mechanisms. Cells were pretreated with 50 µg/mL of WEST to evaluate its neuroprotective effect based on endoplasmic reticulum (ER) stress inhibition and mitochondrial function improvement. Pretreatment with WEST prevented corticosterone-induced injury in PC12 cells, resulting in increased cell survival, decreased lactate dehydrogenase (LDH) release, and potent apoptosis inhibition by a reduction in apoptotic nuclei demonstrated by Hoechst 33342 and propidium iodide (PI) double staining, and TUNEL staining. WEST strongly attenuated calcium (Ca²⁺) elevation, inducing the closure of mitochondrial permeability transition pores (mPTPs), which were opened by corticosterone. It also stabilized mitochondrial membrane potential (MMP) loss and inhibited the corticosterone-induced decrease in adenosine triphosphate (ATP) levels. Furthermore, the increased reactive oxygen species (ROS) production induced by corticosterone was prevented in PC12 cells treated with WEST. WEST also downregulated the expression of glucose-regulated protein 78 (GRP78), growth arrest- and DNA damage-inducible gene 153 (GADD153), the pro-apoptotic protein Bcl-2-associated X (Bax), cytochrome c, cysteine-aspartic protease (caspase)-9, and caspase-3, and upregulated the expression of the anti-apoptotic protein B-cell lymphoma 2 (Bcl-2). Thus, WEST exerts a neuroprotective effect by inhibiting the apoptosis pathway in ER stress and the mitochondrial dysfunction induced by corticosterone. These results demonstrate that WEST reduces neuronal damage from the neurotoxicity caused by chronic stress.

Understanding and exploiting interactions between cellular proteostasis pathways and infectious prion proteins for therapeutic benefit

Several neurodegenerative diseases of humans and animals are caused by the misfolded prion protein (PrP^Sc), a self-propagating protein infectious agent that aggregates into oligomeric, fibrillar structures and leads to cell death by incompletely understood mechanisms. Work in multiple biological model systems, from simple baker's yeast to transgenic mouse lines, as well as in vitro studies, has illuminated molecular and cellular modifiers of prion disease. In this review, we focus on intersections between PrP and the proteostasis network, including unfolded protein stress response pathways and roles played by the powerful regulators of protein folding known as protein chaperones. We close with analysis of promising therapeutic avenues for treatment enabled by these studies.

Influence of aging on deterioration of patients with COVID-19

Aging is an important factor affecting the deterioration of patients with coronavirus disease 2019 (COVID-19). The aging and degeneration of various tissues and organs in the elderly lead to impaired organ function. Underlying conditions such as chronic lung disease, cardiovascular disease, and diabetes in aged patients are associated with higher mortality. Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) primarily interacts with the cell surface receptor angiotensin-converting enzyme (ACE) 2 and other accessory proteins such as 78 kDa glucose-regulated protein 78 (GRP78) and CD147. Thus, altered receptor signals in aging and chronic disease play a role in SARS-CoV-2 infection, and are associated with a higher risk of deterioration in different organs. In this review, after a brief introduction to the link between aging and receptors for SARS-CoV-2, we focus on the risk of deterioration in different organs of COVID-19 patients considering aging as the main factor. We further discuss the structural and/or physiological changes in the immune system and organs (lung, heart, kidney, vessels, nerve system), as well as those associated with diabetes, in aging patients, and speculate on the most likely mechanisms underlying the deterioration of COVID-19 patients.

Molecular Chaperones: A Double-Edged Sword in Neurodegenerative Diseases

Aberrant accumulation of misfolded proteins into amyloid deposits is a hallmark in many age-related neurodegenerative diseases, including Alzheimer’s disease (AD), Parkinson’s disease (PD), Huntington’s disease (HD), and amyotrophic lateral sclerosis (ALS). Pathological inclusions and the associated toxicity appear to spread through the nervous system in a characteristic pattern during the disease. This has been attributed to a prion-like behavior of amyloid-type aggregates, which involves self-replication of the pathological conformation, intercellular transfer, and the subsequent seeding of native forms of the same protein in the neighboring cell. Molecular chaperones play a major role in maintaining cellular proteostasis by assisting the (re)-folding of cellular proteins to ensure their function or by promoting the degradation of terminally misfolded proteins to prevent damage. With increasing age, however, the capacity of this proteostasis network tends to decrease, which enables the manifestation of neurodegenerative diseases. Recently, there has been a plethora of studies investigating how and when chaperones interact with disease-related proteins, which have advanced our understanding of the role of chaperones in protein misfolding diseases. This review article focuses on the steps of prion-like propagation from initial misfolding and self-templated replication to intercellular spreading and discusses the influence that chaperones have on these various steps, highlighting both the positive and adverse consequences chaperone action can have. Understanding how chaperones alleviate and aggravate disease progression is vital for the development of therapeutic strategies to combat these debilitating diseases.

Endoplasmic Reticulum Stress and Unfolded Protein Response in Neurodegenerative Diseases

The endoplasmic reticulum (ER) is an important organelle involved in protein quality control and cellular homeostasis. The accumulation of unfolded proteins leads to an ER stress, followed by an adaptive response via the activation of the unfolded protein response (UPR), PKR-like ER kinase (PERK), inositol-requiring transmembrane kinase/endoribonuclease 1α (IRE1α) and activating transcription factor 6 (ATF6) pathways. However, prolonged cell stress activates apoptosis signaling leading to cell death. Neuronal cells are particularly sensitive to protein misfolding, consequently ER and UPR dysfunctions were found to be involved in many neurodegenerative diseases including Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis and prions diseases, among others characterized by the accumulation and aggregation of misfolded proteins. Pharmacological UPR modulation in affected tissues may contribute to the treatment and prevention of neurodegeneration. The association between ER stress, UPR and neuropathology is well established. In this review, we provide up-to-date evidence of UPR activation in neurodegenerative disorders followed by therapeutic strategies targeting the UPR and ameliorating the toxic effects of protein unfolding and aggregation.

Reciprocal Upshot of Nitric Oxide, Endoplasmic Reticulum Stress, and Ubiquitin Proteasome System in Parkinson's Disease Pathology

Parkinson's disease (PD) pathology involves degeneration of nigrostriatal pathway, postulating symptoms associated with age, environment, and genetic anomalies, including nonlinear disease progression. Hallmark characteristics of PD include dopaminergic neuronal degeneration and death, which may also be exhibited by other neurological diseases, making the diagnosis of the disease intricate at early stage. Such obscure diagnosis of the disease, limited symptomatic improvements with available therapeutics, and their inability to modify the disease status instigate us to appraise the past research and formulate the colligating comprehensive insights. This review is accentuating on the role of nitric oxide, endoplasmic reticulum stress, and their association with the ubiquitin proteasome system (UPS) during PD pathology involving focus on ubiquitin ligases due to their regulatory functions. Meticulous understanding of these major disease-related pathological events and their functional alliance may render novel dimensions for better understanding of disease etiology, related mechanisms, as well as direction toward witnessing of new therapeutic targets for the management of Parkinson's patients.

Sensitivity of allyl isothiocyanate to induce apoptosis via ER stress and the mitochondrial pathway upon ROS production in colorectal adenocarcinoma cells

Allyl isothiocyanate (AITC), a bioactive phytochemical compound that is a constituent of dietary cruciferous vegetables, possesses promising chemopreventive and anticancer effects. However, reports of AITC exerting antitumor effects on apoptosis induction of colorectal cancer (CRC) cells in vitro are not well elucidated. The present study focused on the functional mechanism of the endoplasmic reticulum (ER) stress-based apoptotic machinery induced by AITC in human colorectal cancer HT-29 cells. Our results indicated that AITC decreased cell growth and number, reduced viability, and facilitated morphological changes of apoptotic cell death. DNA analysis by flow cytometry showed G2/M phase arrest, and alterations in the modulated protein levels caused by AITC were detected via western blot analysis. AITC also triggered vital intrinsic apoptotic factors (caspase-9/caspase-3 activity), disrupted mitochondrial membrane potential, and stimulated mitochondrial-related apoptotic molecules (e.g., cytochrome c, apoptotic protease activating factor 1, apoptosis-inducing factor, and endonuclease G). Additionally, AITC prompted induced cytosolic Ca²⁺ release and Ca²⁺-dependent ER stress-related signals, such as calpain 1, activating transcription factor 6α, glucose-regulated proteins 78 and 94, growth arrest- and DNA damage-inducible protein 153 (GADD153), and caspase-4. The level of reactive oxygen species (ROS) production was found to induce the hallmark of ER stress GADD153, proapoptotic marker caspase-3, and calpain activity after AITC treatment. Our findings showed for the first time that AITC induced G2/M phase arrest and apoptotic death via ROS-based ER stress and the intrinsic pathway (mitochondrial-dependent) in HT-29 cells. Overall, AITC may exert an epigenetic effect and is a potential bioactive compound for CRC treatment.

78 kDa Glucose-Regulated Protein Attenuates Protein Aggregation and Monocyte Adhesion Induced by Angiotensin II in Vascular Cells

Investigations of vascular smooth muscle cell (VSMC) phenotypic modulation due to angiotensin II (AngII) stimulation are important for understanding molecular mechanisms contributing to hypertension and associated vascular pathology. AngII induces endoplasmic reticulum (ER) stress in VSMCs, which has been implicated in hypertensive vascular remodeling. Under ER stress, 78 kDa glucose-regulated protein (GRP78) acts as an endogenous chaperone, as well as a master controller of unfolded protein response (UPR) to maintain protein quality control. However, the potential downstream consequences of ER stress induced by AngII on protein quality control and pro-inflammatory phenotype in VSMCs remain elusive. This study aims to identify protein aggregation as evidence of the disruption of protein quality control in VSMCs, and to test the hypothesis that preservation of proteostasis by overexpression of GRP78 can attenuate the AngII-induced pro-inflammatory phenotype in VSMCs. Increases in protein aggregation and enhanced UPR were observed in VSMCs exposed to AngII, which were mitigated by overexpression of GRP78. Moreover, GRP78 overexpression attenuated enhanced monocyte adhesion to VSMCs induced by AngII. Our results thus indicate that the prevention of protein aggregation can potentially mitigate an inflammatory phenotype in VSMCs, which may suggest an alternative therapy for the treatment of AngII-associated vascular disorders.

Pathological Aspects of COVID-19 as a Conformational Disease and the Use of Pharmacological Chaperones as a Potential Therapeutic Strategy

Coronavirus disease 2019 (COVID-19), the seventh human coronavirus infectious disease, was first reported in Wuhan, China, in December 2019, followed by its rapid spread globally (251,059 deaths, on May 5, 2020, by Johns Hopkins University). An early clinical report showed that fever, cough, fatigue, sputum production, and myalgia were initial symptoms, with the development of pneumonia as the disease progressed. Increases in the level of serum liver enzymes, D-dimer, cardiac troponin I, and creatinine have been observed in severely ill patients, indicating that multiple organ failure had occurred in these cases. Lymphopenia and an increase in interleukin-6 (IL-6) were also observed. Although COVID-19 patients are administered glucocorticoid therapy to treat the excessive immune response to severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) infection, the efficacy of this form of therapy is unclear. Viremia is observed in severe cases, suggesting that in addition to type II alveolar epithelial cells, many cell types, such as vascular endothelial cells, cardiomyocytes, renal tubular cells, neuronal cells, and lymphocytes, may be damaged. The improvement of survival rates requires elucidation of the mechanism by which cellular damage occurs during viral infection. Cellular therapy, along with organ support systems such as oxygen therapy, artificial ventilation, extra corporeal membrane oxygenation and dialysis, as well as antiviral therapy, are required. Viral replication in infected host cells may perturb protein folding in the endoplasmic reticulum (ER), causing ER stress. Although an adaptive cellular response, i.e. the unfolded protein response, can compensate for the misfolded protein burden to some extent, continued viral proliferation may induce inflammation and cell death. Therefore, we propose that proteostasis dysfunction may cause conformational disorders in COVID-19. The application of pharmacological chaperone therapy to treat COVID-19 patients is additionally discussed.

Expedition into Taurine Biology: Structural Insights and Therapeutic Perspective of Taurine in Neurodegenerative Diseases

Neurodegenerative diseases (NDs) are characterized by the accumulation of misfolded proteins. The hallmarks of protein aggregation in NDs proceed with impairment in the mitochondrial function, besides causing an enhancement in endoplasmic reticulum (ER) stress, neuroinflammation and synaptic loss. As accumulation of misfolded proteins hampers normal neuronal functions, it triggers ER stress, which leads to the activation of downstream effectors formulating events along the signaling cascade—referred to as unfolded protein response (UPRER) —thereby controlling cellular gene expression. The absence of disease-modifying therapeutic targets in different NDs, and the exponential increase in the number of cases, makes it critical to explore new approaches to treating these devastating diseases. In one such approach, osmolytes (low molecular weight substances), such as taurine have been found to promote protein folding under stress conditions, thereby averting aggregation of the misfolded proteins. Maintaining the structural integrity of the protein, taurine-mediated resumption of protein folding prompts a shift in folding homeostasis more towards functionality than towards aggregation and degradation. Together, taurine enacts protection in NDs by causing misfolded proteins to refold, so as to regain their stability and functionality. The present study provides recent and useful insights into understanding the progression of NDs, besides summarizing the genetics of NDs in correlation with mitochondrial dysfunction, ER stress, neuroinflammation and synaptic loss. It also highlights the structural and functional aspects of taurine in imparting protection against the aggregation/misfolding of proteins, thereby shifting the focus more towards the development of effective therapeutic modules that could avert the development of NDs.

The PERK-Dependent Molecular Mechanisms as a Novel Therapeutic Target for Neurodegenerative Diseases

Higher prevalence of neurodegenerative diseases is strictly connected with progressive aging of the world population. Interestingly, a broad range of age-related, neurodegenerative diseases is characterized by a common pathological mechanism-accumulation of misfolded and unfolded proteins within the cells. Under certain circumstances, such protein aggregates may evoke endoplasmic reticulum (ER) stress conditions and subsequent activation of the unfolded protein response (UPR) signaling pathways via the protein kinase RNA-like endoplasmic reticulum kinase (PERK)-dependent manner. Under mild to moderate ER stress, UPR has a pro-adaptive role. However, severe or long-termed ER stress conditions directly evoke shift of the UPR toward its pro-apoptotic branch, which is considered to be a possible cause of neurodegeneration. To this day, there is no effective cure for Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), or prion disease. Currently available treatment approaches for these diseases are only symptomatic and cannot affect the disease progression. Treatment strategies, currently under detailed research, include inhibition of the PERK-dependent UPR signaling branches. The newest data have reported that the use of small-molecule inhibitors of the PERK-mediated signaling branches may contribute to the development of a novel, ground-breaking therapeutic approach for neurodegeneration. In this review, we critically describe all the aspects associated with such targeted therapy against neurodegenerative proteopathies.

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.

Cell-based HTS identifies a chemical chaperone for preventing ER protein aggregation and proteotoxicity

The endoplasmic reticulum (ER) is responsible for folding secretory and membrane proteins, but disturbed ER proteostasis may lead to protein aggregation and subsequent cellular and clinical pathologies. Chemical chaperones have recently emerged as a potential therapeutic approach for ER stress-related diseases. Here, we identified 2-phenylimidazo[2,1-b]benzothiazole derivatives (IBTs) as chemical chaperones in a cell-based high-throughput screen. Biochemical and chemical biology approaches revealed that IBT21 directly binds to unfolded or misfolded proteins and inhibits protein aggregation. Finally, IBT21 prevented cell death caused by chemically induced ER stress and by a proteotoxin, an aggression-prone prion protein. Taken together, our data show the promise of IBTs as potent chemical chaperones that can ameliorate diseases resulting from protein aggregation under ER stress.

Natural Products as Modulators of the Proteostasis Machinery: Implications in Neurodegenerative Diseases

Proteins play crucial and diverse roles within the cell. To exert their biological function they must fold to acquire an appropriate three-dimensional conformation. Once their function is fulfilled, they need to be properly degraded to hamper any possible damage. Protein homeostasis or proteostasis comprises a complex interconnected network that regulates different steps of the protein quality control, from synthesis and folding, to degradation. Due to the primary role of proteins in cellular function, the integrity of this network is critical to assure functionality and health across lifespan. Proteostasis failure has been reported in the context of aging and neurodegeneration, such as Alzheimer’s and Parkinson’s disease. Therefore, targeting the proteostasis elements emerges as a promising neuroprotective therapeutic approach to prevent or ameliorate the progression of these disorders. A variety of natural products are known to be neuroprotective by protein homeostasis interaction. In this review, we will focus on the current knowledge regarding the use of natural products as modulators of different components of the proteostasis machinery within the framework of age-associated neurodegenerative diseases.

The N-Degron Pathway Mediates ER-phagy

The endoplasmic reticulum (ER) is susceptible to wear-and-tear and proteotoxic stress, necessitating its turnover. Here, we show that the N-degron pathway mediates ER-phagy. This autophagic degradation initiates when the transmembrane E3 ligase TRIM13 (also known as RFP2) is ubiquitinated via the lysine 63 (K63) linkage. K63-ubiquitinated TRIM13 recruits p62 (also known as sequestosome-1), whose complex undergoes oligomerization. The oligomerization is induced when the ZZ domain of p62 is bound by the N-terminal arginine (Nt-Arg) of arginylated substrates. Upon activation by the Nt-Arg, oligomerized TRIM13-p62 complexes are separated along with the ER compartments and targeted to autophagosomes, leading to lysosomal degradation. When protein aggregates accumulate within the ER lumen, degradation-resistant autophagic cargoes are co-segregated by ER membranes for lysosomal degradation. We developed synthetic ligands to the p62 ZZ domain that enhance ER-phagy for ER protein quality control and alleviate ER stresses. Our results elucidate the biochemical mechanisms and pharmaceutical means that regulate ER homeostasis.

Prion disease is accelerated in mice lacking stress-induced heat shock protein 70 (HSP70)

Prion diseases are a group of incurable neurodegenerative disorders that affect humans and animals via infection with proteinaceous particles called prions. Prions are composed of PrP^Sc, a misfolded version of the cellular prion protein (PrP^C). During disease progression, PrP^Sc replicates by interacting with PrP^C and inducing its conversion to PrP^Sc As PrP^Sc accumulates, cellular stress mechanisms are activated to maintain cellular proteostasis, including increased protein chaperone levels. However, the exact roles of several of these chaperones remain unclear. Here, using various methodologies to monitor prion replication (i.e. protein misfolding cyclic amplification and cellular and animal infectivity bioassays), we studied the potential role of the molecular chaperone heat shock protein 70 (HSP70) in prion replication in vitro and in vivo Our results indicated that pharmacological induction of the heat shock response in cells chronically infected with prions significantly decreased PrP^Sc accumulation. We also found that HSP70 alters prion replication in vitro More importantly, prion infection of mice lacking the genes encoding stress-induced HSP70 exhibited accelerated prion disease progression compared with WT mice. In parallel with HSP70 being known to respond to endogenous and exogenous stressors such as heat, infection, toxicants, and ischemia, our results indicate that HSP70 may also play an important role in suppressing or delaying prion disease progression, opening opportunities for therapeutic intervention.

Prions, prionoids and protein misfolding disorders

Prion diseases are progressive, incurable and fatal neurodegenerative conditions. The term 'prion' was first nominated to express the revolutionary concept that a protein could be infectious. We now know that prions consist of PrP^Sc, the pathological aggregated form of the cellular prion protein PrP^C. Over the years, the term has been semantically broadened to describe aggregates irrespective of their infectivity, and the prion concept is now being applied, perhaps overenthusiastically, to all neurodegenerative diseases that involve protein aggregation. Indeed, recent studies suggest that prion diseases (PrDs) and protein misfolding disorders (PMDs) share some common disease mechanisms, which could have implications for potential treatments. Nevertheless, the transmissibility of bona fide prions is unique, and PrDs should be considered as distinct from other PMDs.