The small heat shock protein Hsp27 binds α-synuclein fibrils, preventing elongation and cytotoxicity

Single-molecule observations of human small heat shock proteins in complex with aggregation-prone client proteins

Small heat shock proteins (sHsps) are molecular chaperones that act to prevent the aberrant aggregation of misfolded proteins. Whilst it is suggested that sHsps prevent aggregation by binding to misfolded client proteins, the dynamic and heterogeneous nature of sHsps has hindered attempts to establish the mechanistic details of how sHsp-client protein complexes form. Single-molecule approaches have emerged as a powerful tool to investigate dynamic and heterogeneous interactions such as those that can occur between sHsps and their client proteins. Here, we use total internal reflection fluorescence microscopy to observe and characterise the complexes formed between model aggregation-prone client proteins (firefly luciferase, rhodanese and chloride intracellular channel 1 protein), and the human sHsps αB-crystallin (αB-c; HSPB5) and Hsp27 (HSPB1). We show that small (monomeric or dimeric) forms of both αB-c and Hsp27 bind to misfolded or oligomeric forms of the client proteins at early stages of aggregation, resulting in the formation of soluble sHsp-client complexes. Stoichiometric analysis of these complexes revealed that additional αB-c subunits accumulate onto pre-existing sHsp-client complexes to form larger species - this does not occur to the same extent for Hsp27. Instead, Hsp27-client interactions tend to be more transient than those of αB-c. Elucidating these mechanisms of sHsp function is crucial to our understanding of how these molecular chaperones act to inhibit protein aggregation and maintain cellular proteostasis.

Structural Context Modulates the Conformational Ensemble of the Intrinsically Disordered Amino Terminus of α-Synuclein

Regions of intrinsic disorder play crucial roles in biological systems, yet they often elude characterization by conventional biophysical techniques. To capture conformational distributions across different time scales, we employed a freezing approach coupled with solid-state NMR analysis. Using segmentally isotopically labeled α-synuclein (α-syn), we investigated the conformational ensembles of the six alanines, three glycines, and a single site (L8) in the disordered amino terminus under three distinct conditions: in 8 M urea, as a frozen monomer in buffer, and within the disordered regions flanking the amyloid core. The experimental spectra varied significantly among these conditions and deviated from those of a statistical coil. In 8 M urea, monomeric α-syn exhibited the most restricted conformational sampling, rarely accessing chemical shifts characteristic of α-helices or β-strands. In buffer, monomeric α-syn showed a broader conformational sampling, favoring α-helical conformations and, to a lesser extent, random coil states. Notably, amino acids in the disordered regions flanking the amyloid core demonstrated the most extensive conformational sampling, with broad peaks encompassing the entire range of possible chemical shifts and a marked increase in highly extended β-strand conformations. Collectively, this work demonstrates that intrinsically disordered regions exhibit distinct conformational ensembles, which are influenced not only by the chemical environment but also by the conformations of adjacent protein sequences. The differences in the conformational ensembles of the disordered amino terminus may explain why the monomer and the amyloid form of α-syn interact with different biomolecules inside cells.

Characterization and chemoproteomic profiling of protein O-GlcNAcylation in SOD1-G93A mouse model

BACKGROUND

Amyotrophic lateral sclerosis (ALS) is a devastating motor neuron disease. Protein O-linked β-N-acetylglucosamine (O-GlcNAc) modification has been found to affect the processing of several important proteins implicated in ALS. However, the overall level and cellular localization of O-GlcNAc during ALS progression are incompletely understood, and large-scale profiling of O-GlcNAcylation sites in this context remains unexplored.

METHODS

By using immunostaining analysis and chemoenzymatic labeling-based quantitative chemoproteomics, we assayed O-GlcNAcylation dynamics of lumbar spinal cords from SOD-G93A mice and their non-transgenic (NTG) littermates, the most widely used animal model for studying ALS pathogenesis.

RESULTS

We discovered that the global O-GlcNAcylation was significantly reduced at the disease end stage. Correlatively, a great increase of OGA was observed. Immunohistochemistry and immunofluorescence analysis showed a higher proportion of O-GlcNAc-positive neurons in the NTG group, while O-GlcNAc colocalization with astrocytes/microglia was elevated in SOD1-G93A mice. Moreover, we reported the identification of 568 high-confidence O-GlcNAc sites from end-stage SOD1-G93A and NTG mice. Of the 568 sites, 226-many of which occurred on neuronal function and structure-related proteins-were found to be dynamically regulated.

CONCLUSION

These data provide a valuable resource for dissecting the functional role of O-GlcNAcylation in ALS and shed light on promising therapeutic avenues for ALS. The chemoenzymatic labeling-based chemoproteomic approach is applicable for probing O-GlcNAc dynamics in various pathological processes.

Small Heat Shock Proteins: Protein Aggregation Amelioration and Neuro- and Age-Protective Roles

Protein misfolding, aggregation, and aberrant aggregate accumulation play a central role in neurodegenerative disease progression. The proteotoxic factors also govern the aging process to a large extent. Molecular chaperones modulate proteostasis and thereby impact aberrant-protein-induced proteotoxicity. These chaperones have a diverse functional spectrum, including nascent protein folding, misfolded protein sequestration, refolding, or degradation. Small heat shock proteins (sHsps) possess an ATP-independent chaperone-like activity that prevents protein aggregation by keeping target proteins in a folding-competent state to be refolded by ATP-dependent chaperones. Due to their near-universal upregulation and presence in sites of proteotoxic stress like diseased brains, sHsps were considered pathological. However, gene knockdown and overexpression studies have established their protective functions. This review provides an updated overview of the sHsp role in protein aggregation amelioration and highlights evidence for sHsp modulation of neurodegenerative disease-related protein aggregation and aging.

Factors Affecting Pathological Amyloid Protein Transformation: From Post-Translational Modifications to Chaperones

The review discusses the influence of various factors (e.g., post-translational modifications and chaperones) on the pathological transformation of amyloidogenic proteins involved in the onset and development of neurodegenerative diseases (Alzheimer's and Parkinson's diseases) and spongiform encephalopathies of various origin with special focus on the role of α-synuclein, prion protein, and, to a lesser extent, beta-amyloid peptide. The factors investigated by the authors of this review are discussed in more detail, including posttranslational modifications (glycation and S-nitrosylation), cinnamic acid derivatives and dendrimers, and chaperonins (eukaryotic, bacterial, and phage). A special section is devoted to the role of the gastrointestinal microbiota in the pathogenesis of amyloid neurodegenerative diseases, in particular, its involvement in the transformation of infectious prions and possibly other proteins capable of prion-like transmission of amyloidogenic diseases.

Exploring heat shock proteins as therapeutic targets for Parkinson's disease

Parkinson's disease (PD) is characterized by the accumulation of misfolded α-synuclein (α-syn). Promoting the degradation of misfolded proteins has been shown to be an effective approach to alleviate PD. This review highlights the roles of specific heat shock proteins (HSPs) in modulating α-syn aggregation and neuronal survival. HSP27 prevents glycosylation-induced α-syn aggregation, disrupts copper ion interactions, inhibits mitochondrial apoptosis, and prevents dopaminergic neuronal cell death. HSP70 alleviates dopaminergic neuronal damage by promoting mitophagy and preventing neuronal apoptosis. HSC70 plays a critical role in chaperone-mediated autophagy and facilitates lysosomal degradation. GRP78 mitigates abnormal protein aggregation. The HSP70-HSP40-HSP110 system is capable of degrading α-syn amyloid fibers. Inhibition of HSP90 expression protects neurons. Further research should prioritize developing regulators of HSPs as treatments for PD. While HSPs offer promise in PD management, their complex roles necessitate cautious therapeutic development to harness their potential. Understanding the specific roles of different HSPs will be essential to developing effective therapies for α-syn clearance.

Synergistic Multi-Pronged Interactions Mediate the Effective Inhibition of Alpha-Synuclein Aggregation by the Chaperone HtrA1

The misfolding, aggregation, and the seeded spread of alpha synuclein (α-Syn) aggregates are linked to the pathogenesis of various neurodegenerative diseases, including Parkinson's disease (PD). Understanding the mechanisms by which chaperone proteins prevent the production and seeding of α-Syn aggregates is crucial for developing effective therapeutic leads for tackling neurodegenerative diseases. We show that a catalytically inactive variant of the chaperone HtrA1 (HtrA1*) effectively inhibits both α-Syn monomer aggregation and templated fibril seeding, and demonstrate that this inhibition is mediated by synergistic interactions between its PDZ and Protease domains and α-Syn. Using biomolecular NMR, AFM and Rosetta-based computational analyses, we propose that the PDZ domain interacts with the C-terminal end of the monomer and the intrinsically disordered C-terminal domain of the α-Syn fibril. Furthermore, in agreement with sequence specificity calculations, the Protease domain cleaves in the aggregation-prone NAC domain at site T92/A93 in the monomer. Thus, through multi-pronged interactions and multi-site recognition of α-Syn, HtrA1* can effectively intervene at different stages along the α-Syn aggregation pathway, making it a robust inhibitor of α-Syn aggregation and templated seeding. Our studies illustrate, at high resolution, the crucial role of HtrA1 interactions with both the intrinsically disordered α-Syn monomers and with the dynamic flanking regions around the fibril core for inhibition of aggregation. This inhibition mechanism of the HtrA1 chaperone may provide a natural mechanistic blueprint for highly effective therapeutic agents against protein aggregation.

Significance Statement

PD and other synucleinopathies are marked by misfolding and aggregation of α-Syn, forming higher-order species that propagate aggregation in a prion-like manner. Understanding how chaperone proteins inhibit α-Syn aggregation and spread is essential for therapeutic development against neurodegeneration. Through an integrative approach of solution-based NMR, AFM, aggregation kinetics, and computational analysis, we reveal how a catalytically inactive variant of the chaperone HtrA1 effectively disrupts aggregation pathways. We find that the inactive Protease and PDZ domains of HtrA1 synergistically bind to key intrinsically disordered sites on both α-Syn monomers and fibrils, thereby effectively inhibiting both aggregation and templated seeding. Our work provides a natural and unique blueprint for designing inhibitors to prevent the formation and seeding of aggregates in neurodegenerative diseases.

Opportunities for Therapeutic Modulation of O-GlcNAc

O-Linked β-N-acetylglucosamine (O-GlcNAc) is an essential, dynamic monosaccharide post-translational modification (PTM) found on serine and threonine residues of thousands of nucleocytoplasmic proteins. The installation and removal of O-GlcNAc is controlled by a single pair of enzymes, O-GlcNAc transferase (OGT) and O-GlcNAcase (OGA), respectively. Since its discovery four decades ago, O-GlcNAc has been found on diverse classes of proteins, playing important functional roles in many cellular processes. Dysregulation of O-GlcNAc homeostasis has been implicated in the pathogenesis of disease, including neurodegeneration, X-linked intellectual disability (XLID), cancer, diabetes, and immunological disorders. These foundational studies of O-GlcNAc in disease biology have motivated efforts to target O-GlcNAc therapeutically, with multiple clinical candidates under evaluation. In this review, we describe the characterization and biochemistry of OGT and OGA, cellular O-GlcNAc regulation, development of OGT and OGA inhibitors, O-GlcNAc in pathophysiology, clinical progress of O-GlcNAc modulators, and emerging opportunities for targeting O-GlcNAc. This comprehensive resource should motivate further study into O-GlcNAc function and inspire strategies for therapeutic modulation of O-GlcNAc.

The inhibitory action of the chaperone BRICHOS against the α-Synuclein secondary nucleation pathway

The complex kinetics of disease-related amyloid aggregation of proteins such as α-Synuclein (α-Syn) in Parkinson's disease and Aβ42 in Alzheimer's disease include primary nucleation, amyloid fibril elongation and secondary nucleation. The latter can be a key accelerator of the aggregation process. It has been demonstrated that the chaperone domain BRICHOS can interfere with the secondary nucleation process of Aβ42. Here, we explore the mechanism of secondary nucleation inhibition of the BRICHOS domain of the lung surfactant protein (proSP-C) against α-Syn aggregation and amyloid formation. We determine the 3D NMR structure of an inactive trimer of proSP-C BRICHOS and its active monomer using a designed mutant. Furthermore, the interaction between the proSP-C BRICHOS chaperone and a substrate peptide has been studied. NMR-based interaction studies of proSP-C BRICHOS with α-Syn fibrils show that proSP-C BRICHOS binds to the C-terminal flexible fuzzy coat of the fibrils, which is the secondary nucleation site on the fibrils. Super-resolution fluorescence microscopy demonstrates that proSP-C BRICHOS runs along the fibrillar axis diffusion-dependently sweeping off monomeric α-Syn from the fibrils. The observed mechanism explains how a weakly binding chaperone can inhibit the α-Syn secondary nucleation pathway via avidity where a single proSP-C BRICHOS molecule is sufficient against up to ~7-40 α-Syn molecules embedded within the fibrils.

Structural context modulates the conformational ensemble of the intrinsically disordered amino terminus of α-synuclein

Regions of intrinsic disorder play crucial roles in biological systems, yet they often elude characterization by conventional biophysical techniques. To capture conformational distributions across different timescales, we employed a freezing approach coupled with solid-state NMR analysis. Using segmentally isotopically labeled α-synuclein (α-syn), we investigated the conformational preferences of the six alanines, three glycines, and a single site (L8) in the disordered amino terminus under three distinct conditions: in 8 M urea, as a frozen monomer in buffer, and within the disordered regions flanking the amyloid core. The experimental spectra varied significantly among these conditions and deviated from those of a statistical coil. In 8 M urea, monomeric α-syn exhibited the most restricted conformational sampling, rarely accessing chemical shifts characteristic of α-helices or β-strands. In buffer, monomeric α-syn showed broader conformational sampling, favoring α-helical conformations and, to a lesser extent, random coil states. Notably, amino acids in the disordered regions flanking the amyloid core demonstrated the most extensive conformational sampling, with broad peaks encompassing the entire range of possible chemical shifts and a marked preference for highly extended β-strand conformations. Collectively, this work demonstrates that intrinsically disordered regions exhibit distinct conformational preferences, which are influenced not only by the chemical environment but also by the conformations of adjacent protein sequences. The differences in the conformational ensembles of the disordered amino terminus may explain why the monomer and the amyloid form of α-syn interact with different biomolecules inside cells.

HSPB6: A lipid-dependent molecular chaperone inhibits α-synuclein aggregation

The process of protein misfolding and aggregation is associated with various cytotoxic effects. Understanding how this phenomenon is regulated by the protein homeostasis system, however, is difficult, since it takes place through a complex non-linear network of coupled microscopic steps, including primary nucleation, fibril elongation, and secondary nucleation, which depend on environmental factors. To address this problem, we studied how the aggregation of α-synuclein, a protein associated with Parkinson's disease, is modulated by molecular chaperones and lipid membranes. We focused on small heat shock proteins (sHSPs/HSPBs), which interact with proteins and lipids and are upregulated during aging, a major risk factor for protein misfolding diseases. HSPBs act on different microscopic steps to prevent α-synuclein aggregation, with HSPB6 showing a lipid-dependent chaperone activity. Our findings provide an example of how HSPBs diversified their mechanisms of action to reach an efficient regulation of protein misfolding and aggregation within the complex cellular environment.

In cell NMR reveals cells selectively amplify and structurally remodel amyloid fibrils

Amyloid forms of α-synuclein adopt different conformations depending on environmental conditions. Advances in structural biology have accelerated fibril characterization. However, it remains unclear which conformations predominate in biological settings because current methods typically not only require isolating fibrils from their native environments, but they also do not provide insight about flexible regions. To address this, we characterized α-syn amyloid seeds and used sensitivity enhanced nuclear magnetic resonance to investigate the amyloid fibrils resulting from seeded amyloid propagation in different settings. We found that the amyloid fold and conformational preferences of flexible regions are faithfully propagated in vitro and in cellular lysates. However, seeded propagation of amyloids inside cells led to the minority conformation in the seeding population becoming predominant and more ordered, and altered the conformational preferences of flexible regions. The examination of the entire ensemble of protein conformations in biological settings that is made possible with this approach may advance our understanding of protein misfolding disorders and facilitate structure-based drug design efforts.

Aberrant protein aggregation in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a fatal disease. As its pathological mechanisms are not well understood, there are no efficient therapeutics for it at present. While it is highly heterogenous both etiologically and clinically, it has a common salient hallmark, i.e., aberrant protein aggregation (APA). The upstream pathogenesis and the downstream effects of APA in ALS are sophisticated and the investigation of this pathology would be of consequence for understanding ALS. In this paper, the pathomechanism of APA in ALS and the candidate treatment strategies for it are discussed.

Tissue-specific landscape of protein aggregation and quality control in an aging vertebrate

Protein aggregation is a hallmark of age-related neurodegeneration. Yet, aggregation during normal aging and in tissues other than the brain is poorly understood. Here, we leverage the African turquoise killifish to systematically profile protein aggregates in seven tissues of an aging vertebrate. Age-dependent aggregation is strikingly tissue specific and not simply driven by protein expression differences. Experimental interrogation in killifish and yeast, combined with machine learning, indicates that this specificity is linked to protein-autonomous biophysical features and tissue-selective alterations in protein quality control. Co-aggregation of protein quality control machinery during aging may further reduce proteostasis capacity, exacerbating aggregate burden. A segmental progeria model with accelerated aging in specific tissues exhibits selectively increased aggregation in these same tissues. Intriguingly, many age-related protein aggregates arise in wild-type proteins that, when mutated, drive human diseases. Our data chart a comprehensive landscape of protein aggregation during vertebrate aging and identify strong, tissue-specific associations with dysfunction and disease.

Modulation of Alzheimer's Disease Aβ40 Fibril Polymorphism by the Small Heat Shock Protein αB-Crystallin

Deposition of amyloid plaques in the brains of Alzheimer's disease (AD) patients is a hallmark of the disease. AD plaques consist primarily of the beta-amyloid (Aβ) peptide but can contain other factors such as lipids, proteoglycans, and chaperones. So far, it is unclear how the cellular environment modulates fibril polymorphism and how differences in fibril structure affect cell viability. The small heat-shock protein (sHSP) alpha-B-Crystallin (αBC) is abundant in brains of AD patients, and colocalizes with Aβ amyloid plaques. Using solid-state NMR spectroscopy, we show that the Aβ40 fibril seed structure is not replicated in the presence of the sHSP. αBC prevents the generation of a compact fibril structure and leads to the formation of a new polymorph with a dynamic N-terminus. We find that the N-terminal fuzzy coat and the stability of the C-terminal residues in the Aβ40 fibril core affect the chemical and thermodynamic stability of the fibrils and influence their seeding capacity. We believe that our results yield a better understanding of how sHSP, such as αBC, that are part of the cellular environment, can affect fibril structures related to cell degeneration in amyloid diseases.

2-Butoxytetrahydrofuran, Isolated from Holothuria scabra, Attenuates Aggregative and Oxidative Properties of α-Synuclein and Alleviates Its Toxicity in a Transgenic Caenorhabditis elegans Model of Parkinson's Disease

Aggregative α-synuclein and incurring oxidative stress are pivotal cascading events, leading to dopaminergic (DAergic) neuronal loss and contributing to clinical manifestations of Parkinson's disease (PD). Our previous study demonstrated that 2-butoxytetrahydrofuran (2-BTHF), isolated from Holothuria scabra (H. scabra), could inhibit amyloid-β aggregation and its ensuing toxicity, which leads to Alzheimer's disease. In the present study, we found that 2-BTHF also attenuated the aggregative and oxidative activities of α-synuclein and lessened its toxicity in a transgenic Caenorhabditis elegans (C. elegans) PD model. Such worms treated with 100 μM of 2-BTHF showed substantial reductions in α-synuclein accumulation and DAergic neurodegeneration. Mechanistically, 2-BTHF, at this concentration, significantly decreased aggregation of monomeric α-synuclein and restored locomotion and dopamine-dependent behaviors. Molecular docking exhibited potential bindings of 2-BTHF to HSF-1 and DAF-16 transcription factors. Additionally, 2-BTHF significantly increased the mRNA transcripts of genes encoding proteins involved in proteostasis, including the molecular chaperones hsp-16.2 and hsp-16.49, the ubiquitination/SUMOylation-related ubc-9 gene, and the autophagy-related genes atg-7 and lgg-1. Transcriptomic profiling revealed an additional mechanism of 2-BTHF in α-synuclein-expressing worms, which showed upregulation of PPAR signaling cascades that mediated fatty acid metabolism. 2-BTHF significantly restored lipid deposition, upregulated the fat-7 gene, and enhanced gcs-1-mediated glutathione synthesis in the C. elegans PD model. Taken together, this study demonstrated that 2-BTHF could abrogate aggregative and oxidative properties of α-synuclein and attenuate its toxicity, thus providing a possible therapeutic application for the treatment of α-synuclein-induced PD.

O-GlcNAc forces an α-synuclein amyloid strain with notably diminished seeding and pathology

Amyloid-forming proteins such α-synuclein and tau, which are implicated in Alzheimer's and Parkinson's disease, can form different fibril structures or strains with distinct toxic properties, seeding activities and pathology. Understanding the determinants contributing to the formation of different amyloid features could open new avenues for developing disease-specific diagnostics and therapies. Here we report that O-GlcNAc modification of α-synuclein monomers results in the formation of amyloid fibril with distinct core structure, as revealed by cryogenic electron microscopy, and diminished seeding activity in seeding-based neuronal and rodent models of Parkinson's disease. Although the mechanisms underpinning the seeding neutralization activity of the O-GlcNAc-modified fibrils remain unclear, our in vitro mechanistic studies indicate that heat shock proteins interactions with O-GlcNAc fibril inhibit their seeding activity, suggesting that the O-GlcNAc modification may alter the interactome of the α-synuclein fibrils in ways that lead to reduce seeding activity in vivo. Our results show that posttranslational modifications, such as O-GlcNAc modification, of α-synuclein are key determinants of α-synuclein amyloid strains and pathogenicity.

Fibrillar Alpha-Synuclein Alters the Intracellular Chaperone Levels within Hours of Its Internalization

Parkinson's disease (PD) is the second most prevalent neurodegenerative disorder worldwide. According to the Braak hypothesis, the disease spreads along specific neuroanatomical pathways. Studies indicate that fibrillar alpha-synuclein (F-αSyn) can propagate from cell-to-cell by following intercellular connections, leading to the selective death of certain cell groups like substantia nigra dopaminergic neurons and advancing the pathology. Internalized F-αSyn can be eliminated by lysosomes, proteasomes, or chaperones before it replicates inside the cell. Research has shown that F-αSyn can somehow escape from endosomes, lysosomes, and proteasomes and replicate itself. However, the impact of chaperones on intracellular levels during the initial hours of their internalization remains unknown. The present study investigates the effect of F-αSyn on chaperone levels within the first 6 and 12 h after internalization. Our findings showed that within the first 6 h, Hsc70 and Hsp90 levels were increased, while within 12 h, F-αSyn leads to a decrease or suppression of numerous intracellular chaperone levels. Exploring the pathological effects of PD on cells will contribute to identifying more targets for therapeutic interventions.

Reactive astrocytes secrete the chaperone HSPB1 to mediate neuroprotection

Molecular chaperones are protective in neurodegenerative diseases by preventing protein misfolding and aggregation, such as extracellular amyloid plaques and intracellular tau neurofibrillary tangles in Alzheimer's disease (AD). In addition, AD is characterized by an increase in astrocyte reactivity. The chaperone HSPB1 has been proposed as a marker for reactive astrocytes; however, its astrocytic functions in neurodegeneration remain to be elucidated. Here, we identify that HSPB1 is secreted from astrocytes to exert non-cell-autonomous protective functions. We show that in human AD brain, HSPB1 levels increase in astrocytes that cluster around amyloid plaques, as well as in the adjacent extracellular space. Moreover, in conditions that mimic an inflammatory reactive response, astrocytes increase HSPB1 secretion. Concomitantly, astrocytes and neurons can uptake astrocyte-secreted HSPB1, which is accompanied by an attenuation of the inflammatory response in reactive astrocytes and reduced pathological tau inclusions. Our findings highlight a protective mechanism in disease conditions that encompasses the secretion of a chaperone typically regarded as intracellular.

Sensitized Emission Imaging Allows Nanoscale Surface Polarity Mapping of α-Synuclein Amyloid Fibrils

When misfolded, α-Synuclein (α-Syn), a natively disordered protein, aggregates to form amyloid fibrils responsible for the neurodegeneration observed in Parkinson's disease. Structural studies revealed distinct molecular packing of α-Syn in different fibril polymorphs and variations of interprotofilament connections in the fibrillar architecture. Fibril polymorphs have been hypothesized to exhibit diverse surface polarities depending on the folding state of the protein during aggregation; however, the spatial variation of surface polarity in amyloid fibrils remains unexplored. To map the local polarity (or hydrophobicity) along α-Syn fibrils, we visualized the spectral characteristics of two dyes with distinct polarities-hydrophilic Thioflavin T (ThT) and hydrophobic Nile red (NR)─when both are bound to α-Syn fibrils. Dual-channel fluorescence imaging reveals uneven partitioning of ThT and NR along individual fibrils, implying that relatively more polar/hydrophobic patches are spread over a few hundred nanometers. Remarkably, spectrally resolved sensitized emission imaging of α-Syn fibrils provides unambiguous evidence of energy transfer from ThT to NR, implying that dyes of dissimilar polarity are in close proximity. Furthermore, spatially resolved fluorescence spectroscopy of the solvatochromic probe NR allowed us to quantitatively map the range and variation of the polarity parameter ET30 along individual fibrils. Our results suggest the existence of interlaced polar and nonpolar nanoscale domains throughout the fibrils; however, the relative populations of these patches vary considerably over larger length scales likely due to heterogeneous packing of α-Syn during fibrilization and dissimilar exposed polarities of polymorphic segments. The employed method may provide a foundation for imaging modalities of other similar structurally unresolved systems with diverse hydrophobic-hydrophilic topology.

Structure specific neuro-toxicity of α-synuclein oligomer

Parkinson's disease (PD) is linked to α-synuclein (aS) aggregation and deposition of amyloid in the substantia nigra region of the brain tissues. In the current investigation we produced two distinct classes of aS oligomer of differed protein conformation, stability and compared their toxic nature to cultured neuronal cells. Lyophilized oligomer (LO) was produced in storage of aS at-20 °C for 7 days and it was enriched with loosely hold molten globule like structure with residues having preferences for α-helical conformational space. The size of the oligomer was 4-5.5 nm under AFM. This kind of oligomer exhibited potential toxicity towards neuronal cell lines and did not transform into compact β-sheet rich amyloid fiber even after incubation at 37 °C for several days. Formation of another type of oligomer was often observed in the lag phase of aS fibrillation that often occurred at an elevated temperature (37 °C). This kind of heat induced oligomer (IO) was more hydrophobic and relatively less toxic to neuronal cells compared to lyophilized oligomer (LO). Importantly, initiation of hydrophobic zipping of aS caused the transformation of IO into thermodynamically stable β-sheet rich amyloid fibril. On the other hand, the presence of molten globule like conformation in LO, rendered greater toxicity to cultured neuronal cells.

Upregulation of Hsp27 via further inhibition of histone H2A ubiquitination confers protection against myocardial ischemia/reperfusion injury by promoting glycolysis and enhancing mitochondrial function

Research suggests that ischemic glycolysis improves myocardial tolerance to anoxia and low-flow ischemia. The rate of glycolysis during ischemia reflects the severity of the injury caused by ischemia and subsequent functional recovery following reperfusion. Histone H2AK119 ubiquitination (H2Aub) is a common modification that is primarily associated with gene silencing. Recent studies have demonstrated that H2Aub contributes to the development of cardiovascular diseases. However, the underlying mechanism remains unclear. This study identified Hsp27 (heat shock protein 27) as a H2Aub binding protein and explored its involvement in mediating glycolysis and mitochondrial function. Functional studies revealed that inhibition of PRC1 (polycomb repressive complex 1) decreased H2Aub occupancy and promoted Hsp27 expression through inhibiting ubiquitination. Additionally, it increased glycolysis by activating the NF-κB/PFKFB3 signaling pathway during myocardial ischemia. Furthermore, Hsp27 reduced mitochondrial ROS production by chaperoning COQ9, and suppressed ferroptosis during reperfusion. A delivery system was developed based on PCL-PEG-MAL (PPM)-PCM-SH (CWLSEAGPVVTVRALRGTGSW) to deliver PRT4165 (PRT), a potent inhibitor of PRC1, to damaged myocardium, resulting in decreased H2Aub. These findings revealed a novel epigenetic mechanism connecting glycolysis and ferroptosis in protecting the myocardium against ischemia/reperfusion injury.

Linking Heat Shock Protein 70 and Parkin in Parkinson's Disease

Parkinson's disease (PD) is a neurodegenerative disease that affects millions of elderly people worldwide and is characterized by the progressive loss of dopaminergic neurons in the substantia nigra pars compacta (SNpc). The precise mechanisms underlying the pathogenesis of PD are still not fully understood, but it is well accepted that the misfolding, aggregation, and abnormal degradation of proteins are the key causative factors of PD. Heat shock protein 70 (Hsp70) is a molecular chaperone that participates in the degradation of misfolded and aggregated proteins in living cells and organisms. Parkin, an E3 ubiquitin ligase, participates in the degradation of proteins via the proteasome pathway. Recent studies have indicated that both Hsp70 and Parkin play pivotal roles in PD pathogenesis. In this review, we focus on discussing how dysregulation of Hsp70 and Parkin leads to PD pathogenesis, the interaction between Hsp70 and Parkin in the context of PD and their therapeutic applications in PD.

Modulating Stress Proteins in Response to Therapeutic Interventions for Parkinson's Disease

Parkinson's disease (PD) is a neurodegenerative illness characterized by the degeneration of dopaminergic neurons in the substantia nigra, resulting in motor symptoms and without debilitating motors. A hallmark of this condition is the accumulation of misfolded proteins, a phenomenon that drives disease progression. In this regard, heat shock proteins (HSPs) play a central role in the cellular response to stress, shielding cells from damage induced by protein aggregates and oxidative stress. As a result, researchers have become increasingly interested in modulating these proteins through pharmacological and non-pharmacological therapeutic interventions. This review aims to provide an overview of the preclinical experiments performed over the last decade in this research field. Specifically, it focuses on preclinical studies that center on the modulation of stress proteins for the treatment potential of PD. The findings display promise in targeting HSPs to ameliorate PD outcomes. Despite the complexity of HSPs and their co-chaperones, proteins such as HSP70, HSP27, HSP90, and glucose-regulated protein-78 (GRP78) may be efficacious in slowing or preventing disease progression. Nevertheless, clinical validation is essential to confirm the safety and effectiveness of these preclinical approaches.

TXNL1 has dual functions as a redox active thioredoxin-like protein as well as an ATP- and redox-independent chaperone

TXNL1 (also named TRP32, for thioredoxin related protein of 32 kDa) is a cytosolic thioredoxin-fold protein expressed in all cell types and conserved from yeast to mammals, but with yet poorly known function. Here, we expressed and purified human TXNL1 together with several Cys-to-Ser variants, characterizing their enzymatic properties. TXNL1 could reduce disulfides in insulin, cystine and glutathione disulfide (GSSG) in reactions coupled to thioredoxin reductase (TXNRD1, TrxR1) using NADPH, similarly to thioredoxin (TXN, Trx1), but with lower catalytic efficacy due to at least one order of magnitude higher Km of TrxR1 for TXNL1 compared to Trx1. However, in sharp contrast to Trx1, we found that TXNL1 also had efficient chaperone activity that did not require ATP. TXNL1 made non-covalent complexes with reduced insulin, thereby keeping it in solution, and TXNL1 provided chaperone function towards whole cell lysate proteins by preventing their aggregation during heating. The chaperone activities of TXNL1 did not require its redox activity or any dithiol-disulfide exchange reactions, as revealed using Cys-to-Ser substituted variants, as well as a maintained chaperone activity of TXNL1 also in the absence of TrxR1 and NADPH. These results reveal that TXNL1 has dual functions, supporting TrxR1-driven redox activities in disulfide reduction reactions, as well as being an ATP-independent chaperone that does not require involvement of its redox activity.

Integrating single-nucleus sequence profiling to reveal the transcriptional dynamics of Alzheimer's disease, Parkinson's disease, and multiple sclerosis

BACKGROUND

Alzheimer's disease (AD), Parkinson's disease (PD), and multiple sclerosis (MS) are three nervous system diseases that partially overlap clinically and genetically. However, bulk RNA-sequencing did not accurately detect the core pathogenic molecules in them. The availability of high-quality single cell RNA-sequencing data of post-mortem brain collections permits the generation of a large-scale gene expression in different cells in human brain, focusing on the molecular features and relationships between diseases and genes. We integrated single-nucleus RNA-sequencing (snRNA-seq) datasets of human brains with AD, PD, and MS to identify transcriptomic commonalities and distinctions among them.

METHODS

The snRNA-seq datasets were downloaded from Gene Expression Omnibus (GEO) database. The Seurat package was used for snRNA-seq data processing. The uniform manifold approximation and projection (UMAP) were utilized for cluster identification. The FindMarker function in Seurat was used to identify the differently expressed genes. Functional enrichment analysis was carried out using the Gene Set Enrichment Analysis (GSEA) and Gene ontology (GO). The protein-protein interaction (PPI) analysis of differentially expressed genes (DEGs) was analyzed using STRING database ( http://string-db.org ). SCENIC analysis was performed using utilizing pySCENIC (v0.10.0) based on the hg19-tss-centered-10 kb-10species databases. The analysis of potential therapeutic drugs was analyzed on Connectivity Map ( https://clue.io ).

RESULTS

The gene regulatory network analysis identified several hub genes regulated in AD, PD, and MS, in which HSPB1 and HSPA1A were key molecules. These upregulated HSP family genes interact with ribosome genes in AD and MS, and with immunomodulatory genes in PD. We further identified several transcriptional regulators (SPI1, CEBPA, TFE3, GRHPR, and TP53) of the hub genes, which has important implications for uncovering the molecular crosstalk among AD, PD, and MS. Arctigenin was identified as a potential therapeutic drug for AD, PD, and MS.

CONCLUSIONS

Together, the integrated snRNA-seq data and findings have significant implications for unraveling the shared and unique molecular crosstalk among AD, PD, and MS. HSPB1 and HSPA1A as promising targets involved in the pathological mechanisms of neurodegenerative diseases. Additionally, the identification of arctigenin as a potential therapeutic drug for AD, PD, and MS further highlights its potential in treating these neurological disorders. These discoveries lay the groundwork for future research and interventions to enhance our understanding and treatment of AD, PD, and MS.

Coumarin-chalcone hybrid LM-021 and indole derivative NC009-1 targeting inflammation and oxidative stress to protect BE(2)-M17 cells against α-synuclein toxicity

Parkinson's disease (PD) is featured mainly by the loss of dopaminergic neurons and the presence of α-synuclein-containing aggregates in the substantia nigra of brain. The α-synuclein fibrils and aggregates lead to increased oxidative stress and neural toxicity in PD. Chronic inflammation mediated by microglia is one of the hallmarks of PD pathophysiology. In this report, we showed that coumarin-chalcone hybrid LM-021 and indole derivative NC009-1 reduced the expression of major histocompatibility complex-II, NLR family pyrin domain containing (NLRP) 3, caspase-1, inducible nitric oxide synthase, interleukin (IL)-1β, IL-6, and tumor necrosis factor (TNF)-α in α-synuclein-activated mouse BV-2 microglia. Release of pro-inflammatory mediators including nitric oxide, IL-1β, IL-6 and TNF-α was also mitigated. In BE(2)-M17 cells expressing A53T α-synuclein aggregates, LM-021 and NC009-1 reduced α-synuclein aggregation, neuroinflammation, oxidative stress and apoptosis, and promoted neurite outgrowth. These protective effects were mediated by downregulating NLRP1, IL-1β and IL-6, and their downstream pathways including nuclear factor (NF)-κB inhibitor alpha (IκBα)/NF-κB P65 subunit (P65), c-Jun N-terminal kinase (JNK)/proto-oncogene c-Jun (JUN), mitogen-activated protein kinase 14 (P38)/signal transducer and activator of transcription (STAT) 1, and Janus kinase 2 (JAK2)/STAT3. The study results indicate LM-021 and NC009-1 as potential new drug candidates for PD.

Neurodegenerative Proteinopathies Induced by Environmental Pollutants: Heat Shock Proteins and Proteasome as Promising Therapeutic Tools

Environmental pollutants' (EPs) amount and diversity have increased in recent years due to anthropogenic activity. Several neurodegenerative diseases (NDs) are theorized to be related to EPs, as their incidence has increased in a similar way to human EPs exposure and they reproduce the main ND hallmarks. EPs induce several neurotoxic effects, including accumulation and gradual deposition of misfolded toxic proteins, producing neuronal malfunction and cell death. Cells possess different mechanisms to eliminate these toxic proteins, including heat shock proteins (HSPs) and the proteasome system. The accumulation and deleterious effects of toxic proteins are induced through HSPs and disruption of proteasome proteins' homeostatic function by exposure to EPs. A therapeutic approach has been proposed to reduce accumulation of toxic proteins through treatment with recombinant HSPs/proteasome or the use of compounds that increase their expression or activity. Our aim is to review the current literature on NDs related to EP exposure and their relationship with the disruption of the proteasome system and HSPs, as well as to discuss the toxic effects of dysfunction of HSPs and proteasome and the contradictory effects described in the literature. Lastly, we cover the therapeutic use of developed drugs and recombinant proteasome/HSPs to eliminate toxic proteins and prevent/treat EP-induced neurodegeneration.

Single point mutations at the S129 residue of α-synuclein and their effect on structure, aggregation, and neurotoxicity

Parkinson's disease is an age-related neurological disorder, and the pathology of the disease is linked to different types of aggregates of α-synuclein or alpha-synuclein (aS), which is an intrinsically disordered protein. The C-terminal domain (residues 96-140) of the protein is highly fluctuating and possesses random/disordered coil conformation. Thus, the region plays a significant role in the protein's solubility and stability by an interaction with other parts of the protein. In the current investigation, we examined the structure and aggregation behavior of two artificial single point mutations at a C-terminal residue at position 129 that represent a serine residue in the wild-type human aS (wt aS). Circular Dichroism (CD) and Raman spectroscopy were performed to analyse the secondary structure of the mutated proteins and compare it to the wt aS. Thioflavin T assay and atomic force microscopy imaging helped in understanding the aggregation kinetics and type of aggregates formed. Finally, the cytotoxicity assay gave an idea about the toxicity of the aggregates formed at different stages of incubation due to mutations. Compared to wt aS, the mutants S129A and S129W imparted structural stability and showed enhanced propensity toward the α-helical secondary structure. CD analysis showed proclivity of the mutant proteins toward α-helical conformation. The enhancement of α-helical propensity lengthened the lag phase of fibril formation. The growth rate of β-sheet-rich fibrillation was also reduced. Cytotoxicity tests on SH-SY5Y neuronal cell lines established that the S129A and S129W mutants and their aggregates were potentially less toxic than wt aS. The average survivability rate was ∼40% for cells treated with oligomers (presumably formed after 24 h of incubation of the freshly prepared monomeric protein solution) produced from wt aS and ∼80% for cells treated with oligomers obtained from mutant proteins. The relative structural stability with α-helical propensity of the mutants could be a plausible reason for their slow rate of oligomerization and fibrillation, and this was also the possible reason for reduced toxicity to neuronal cells.

Kisspeptin-10 Mitigates α-Synuclein-Mediated Mitochondrial Apoptosis in SH-SY5Y-Derived Neurons via a Kisspeptin Receptor-Independent Manner

The hypothalamic neurohormone kisspeptin-10 (KP-10) was inherently implicated in cholinergic pathologies when aberrant fluctuations of expression patterns and receptor densities were discerned in neurodegenerative micromilieus. That said, despite variable degrees of functional redundancy, KP-10, which is biologically governed by its cognate G-protein-coupled receptor, GPR54, attenuated the progressive demise of α-synuclein (α-syn)-rich cholinergic-like neurons. Under explicitly modeled environments, in silico algorithms further rationalized the surface complementarities between KP-10 and α-syn when KP-10 was unambiguously accommodated in the C-terminal binding pockets of α-syn. Indeed, the neuroprotective relevance of KP-10's binding mechanisms can be insinuated in the amelioration of α-syn-mediated neurotoxicity; yet it is obscure whether these extenuative circumstances are contingent upon prior GPR54 activation. Herein, choline acetyltransferase (ChAT)-positive SH-SY5Y neurons were engineered ad hoc to transiently overexpress human wild-type or E46K mutant α-syn while the mitigation of α-syn-induced neuronal death was ascertained via flow cytometric and immunocytochemical quantification. Recapitulating the specificity observed on cell viability, exogenously administered KP-10 (0.1 µM) substantially suppressed wild-type and E46K mutant α-syn-mediated apoptosis and mitochondrial depolarization in cholinergic differentiated neurons. In particular, co-administrations with a GPR54 antagonist, kisspeptin-234 (KP-234), failed to abrogate the robust neuroprotection elicited by KP-10, thereby signifying a GPR54 dispensable mechanism of action. Consistent with these observations, KP-10 treatment further diminished α-syn and ChAT immunoreactivity in neurons overexpressing wild-type and E46K mutant α-syn. Overall, these findings lend additional credence to the previous notion that KP-10's binding zone may harness efficacious moieties of neuroprotective intent.

O-GlcNAc modification forces the formation of an α-Synuclein amyloid-strain with notably diminished seeding activity and pathology

The process of amyloid fibril formation remains one of the primary targets for developing diagnostics and treatments for several neurodegenerative diseases (NDDs). Amyloid-forming proteins such α-Synuclein and Tau, which are implicated in the pathogenesis of Alzheimer's and Parkinson's disease, can form different types of fibril structure, or strains, that exhibit distinct structures, toxic properties, seeding activities, and pathology spreading patterns in the brain. Therefore, understanding the molecular and structural determinants contributing to the formation of different amyloid strains or their distinct features could open new avenues for developing disease-specific diagnostics and therapies. In this work, we report that O-GlcNAc modification of α-Synuclein monomers results in the formation of amyloid fibril with distinct core structure, as revealed by Cryo-EM, and diminished seeding activity in seeding-based neuronal and rodent models of Parkinson's disease. Although the mechanisms underpinning the seeding neutralization activity of the O-GlcNAc modified fibrils remain unclear, our in vitro mechanistic studies indicate that heat shock proteins interactions with O-GlcNAc fibril inhibit their seeding activity, suggesting that the O-GlcNAc modification may alter the interactome of the α-Synuclein fibrils in ways that lead to reduce seeding activity in vivo. Our results show that post-translational modifications, such as O-GlcNAc modification, of α-Synuclein are key determinants of α-Synuclein amyloid strains and pathogenicity. These findings have significant implications for how we investigate and target amyloids in the brain and could possibly explain the lack of correlation between amyloid burden and neurodegeneration or cognitive decline in some subtypes of NDDs.

Untangling the complexity of heat shock protein 27 in cancer and metastasis

Heat shock protein 27 is a type of molecular chaperone whose expression gets up-regulated due to reaction towards different stressful triggers including anticancer treatments. It is known to be a major player of resistance development in cancer cells, whereby cells are sheltered against the therapeutics that normally activate apoptosis. Heat shock protein 27 (HSP27) is one of the highly expressed proteins during various cellular insults and is a strong tumor survival factor. HSP27 influences various cellular pathways associated with cancer cell survival and growth such as apoptosis, autophagy, metastasis, angiogenesis, epithelial to mesenchymal transition, etc. HSP27 is molecular machinery which prevents the clumping of numerous substrates or client proteins which get mutated in cancer. It has been reported in several studies that targeting HSP27 is difficult because of its dynamic structure and absence of an ATP-binding site. Here, in this review, we have summarized different modulators of HSP27 and their mechanism of action as well. Effect of deregulated HSP27 in various cancer models, limitations of targeting HSP27, resistance against the conventional drugs generated due to the overexpression of HSP27, and measures to counteract this effect have also been discussed here in detail.

Chemical Biology Approaches to Understanding Neuronal O-GlcNAcylation

O-linked β-N-acetylglucosamine (O-GlcNAc) is a ubiquitous post-translational modification in mammals, decorating thousands of intracellular proteins. O-GlcNAc cycling is an essential regulator of myriad aspects of cell physiology and is dysregulated in numerous human diseases. Notably, O-GlcNAcylation is abundant in the brain and numerous studies have linked aberrant O-GlcNAc signaling to various neurological conditions. However, the complexity of the nervous system and the dynamic nature of protein O-GlcNAcylation have presented challenges for studying of neuronal O-GlcNAcylation. In this context, chemical approaches have been a particularly valuable complement to conventional cellular, biochemical, and genetic methods to understand O-GlcNAc signaling and to develop future therapeutics. Here we review selected recent examples of how chemical tools have empowered efforts to understand and rationally manipulate O-GlcNAcylation in mammalian neurobiology.

Contribution of Extracellular Vesicles and Molecular Chaperones in Age-Related Neurodegenerative Disorders of the CNS

Many neurodegenerative disorders are characterized by the abnormal aggregation of misfolded proteins that form amyloid deposits which possess prion-like behavior such as self-replication, intercellular transmission, and consequent induction of native forms of the same protein in surrounding cells. The distribution of the accumulated proteins and their correlated toxicity seem to be involved in the progression of nervous system degeneration. Molecular chaperones are known to maintain proteostasis, contribute to protein refolding to protect their function, and eliminate fatally misfolded proteins, prohibiting harmful effects. However, chaperone network efficiency declines during aging, prompting the onset and the development of neurological disorders. Extracellular vesicles (EVs) are tiny membranous structures produced by a wide range of cells under physiological and pathological conditions, suggesting their significant role in fundamental processes particularly in cellular communication. They modulate the behavior of nearby and distant cells through their biological cargo. In the pathological context, EVs transport disease-causing entities, including prions, α-syn, and tau, helping to spread damage to non-affected areas and accelerating the progression of neurodegeneration. However, EVs are considered effective for delivering therapeutic factors to the nervous system, since they are capable of crossing the blood-brain barrier (BBB) and are involved in the transportation of a variety of cellular entities. Here, we review the neurodegeneration process caused mainly by the inefficiency of chaperone systems as well as EV performance in neuropathies, their potential as diagnostic biomarkers and a promising EV-based therapeutic approach.

Potential application of heat shock proteins as therapeutic targets in Parkinson's disease

Parkinson's disease (PD) is a common chronic neurodegenerative disease, and the heat shock proteins (HSPs) are proved to be of great value for PD. In addition, HSPs can maintain protein homeostasis, degrade and inhibit protein aggregation by properly folding and activating intracellular proteins in PD. This study mainly summarizes the important roles of HSPs in PD and explores their feasibility as targets. We introduced the structural and functional characteristics of HSPs and the physiological functions of HSPs in PD. HSPs can protect neurons from damage by degrading aggregates with three mechanisms, including the aggregation and removing α-Synuclein (α-Syn) aggregates, promotion the autophagy of abnormal proteins, and inhibition the apoptosis of degenerated neurons. This study underscores the importance of HSPs as targets in PD and helps to expand new mechanisms in PD treatment strategies.

Molecular and Cellular Interactions in Pathogenesis of Sporadic Parkinson Disease

An increasing number of the population all around the world suffer from age-associated neurodegenerative diseases including Parkinson’s disease (PD). This disorder presents different signs of genetic, epigenetic and environmental origin, and molecular, cellular and intracellular dysfunction. At the molecular level, α-synuclein (αSyn) was identified as the principal molecule constituting the Lewy bodies (LB). The gut microbiota participates in the pathogenesis of PD and may contribute to the loss of dopaminergic neurons through mitochondrial dysfunction. The most important pathogenetic link is an imbalance of Ca²⁺ ions, which is associated with redox imbalance in the cells and increased generation of reactive oxygen species (ROS). In this review, genetic, epigenetic and environmental factors that cause these disorders and their cause-and-effect relationships are considered. As a constituent of environmental factors, the example of organophosphates (OPs) is also reviewed. The role of endothelial damage in the pathogenesis of PD is discussed, and a ‘triple hit hypothesis’ is proposed as a modification of Braak’s dual hit one. In the absence of effective therapies for neurodegenerative diseases, more and more evidence is emerging about the positive impact of nutritional structure and healthy lifestyle on the state of blood vessels and the risk of developing these diseases.

Immunohistochemical Demonstration of the pGlu79 α-Synuclein Fragment in Alzheimer’s Disease and Its Tg2576 Mouse Model

The deposition of β-amyloid peptides and of α-synuclein proteins is a neuropathological hallmark in the brains of Alzheimer’s disease (AD) and Parkinson’s disease (PD) subjects, respectively. However, there is accumulative evidence that both proteins are not exclusive for their clinical entity but instead co-exist and interact with each other. Here, we investigated the presence of a newly identified, pyroglutamate79-modified α-synuclein variant (pGlu79-aSyn)—along with the enzyme matrix metalloproteinase-3 (MMP-3) and glutaminyl cyclase (QC) implicated in its formation—in AD and in the transgenic Tg2576 AD mouse model. In the human brain, pGlu79-aSyn was detected in cortical pyramidal neurons, with more distinct labeling in AD compared to control brain tissue. Using immunohistochemical double and triple labelings and confocal laser scanning microscopy, we demonstrate an association of pGlu79-aSyn, MMP-3 and QC with β-amyloid plaques. In addition, pGlu79-aSyn and QC were present in amyloid plaque-associated reactive astrocytes that were also immunoreactive for the chaperone heat shock protein 27 (HSP27). Our data are consistent for the transgenic mouse model and the human clinical condition. We conclude that pGlu79-aSyn can be generated extracellularly or within reactive astrocytes, accumulates in proximity to β-amyloid plaques and induces an astrocytic protein unfolding mechanism involving HSP27.

Effect of bacteriophage-encoded chaperonins on amyloid transformation of α-synuclein

Controversial information about the role of chaperonins in the amyloid transformation of proteins and, in particular, α-synuclein, requires a more detailed study of the observed effects due to the structure and functional state of various chaperonins. In this work, two types of phage chaperonins, the double-ring EL and the single-ring OBP, were shown to stimulate α-synuclein fibrillation in an ATP-dependent manner. Chaperonin morphology does not affect the stimulation of α-synuclein amyloid transformation. However, the ATP-dependent effect of single- and double-ring chaperonins on this process differs, which can lead to different morphology of resulting fibrils. Fibril formation seems to proceed without substrate encapsulation in the internal cavity of chaperonin, because of the structural features of phage chaperonins and their ability to function without co-chaperonins. In the absence of ATP, both chaperonins, on the contrary, completely prevent α-synuclein amyloid transformation, which provides the possibility of their use as anti-amyloid agents, in the form of incomplete molecules or mutants with suppressed ATPase activity.

The Monomeric α-Crystallin Domain of the Small Heat-shock Proteins αB-crystallin and Hsp27 Binds Amyloid Fibril Ends

Small heat-shock proteins (sHSPs) are ubiquitously expressed molecular chaperones present in all kingdoms of life that inhibit protein misfolding and aggregation. Despite their importance in proteostasis, the structure-function relationships of sHSPs remain elusive. Human sHSPs are characterised by a central, highly conserved α-crystallin domain (ACD) and variable-length N- and C-terminal regions. The ACD forms antiparallel homodimers via an extended β-strand, creating a shared β-sheet at the dimer interface. The N- and C-terminal regions mediate formation of higher order oligomers that are thought to act as storage forms for chaperone-active dimers. We investigated the interactions of the ACD of two human sHSPs, αB-crystallin (αB-C) and Hsp27, with apolipoprotein C-II amyloid fibrils using analytical ultracentrifugation and nuclear magnetic resonance spectroscopy. The ACD was found to interact transiently with amyloid fibrils to inhibit fibril elongation and naturally occurring fibril end-to-end joining. This interaction was sensitive to the concentration of fibril ends indicating a 'fibril-capping' interaction. Furthermore, resonances arising from the ACD monomer were attenuated to a greater extent than those of the ACD dimer in the presence of fibrils, suggesting that the monomer may bind fibrils. This hypothesis was supported by mutagenesis studies in which disulfide cross-linked ACD dimers formed by both αB-C and Hsp27 were less effective at inhibiting amyloid fibril elongation and fibril end-to-end joining than ACD constructs lacking disulfide cross-linking. Our results indicate that sHSP monomers inhibit amyloid fibril elongation, highlighting the importance of the dynamic oligomeric nature of sHSPs for client binding.

Kisspeptin-10 Rescues Cholinergic Differentiated SHSY-5Y Cells from α-Synuclein-Induced Toxicity In Vitro

The neuropathological substrate of dementia with Lewy bodies (DLB) is defined by the inextricable cross-seeding accretion of amyloid-β (Aβ) and α-synuclein (α-syn)-laden deposits in cholinergic neurons. The recent revelation that neuropeptide kisspeptin-10 (KP-10) is able to mitigate Aβ toxicity via an extracellular binding mechanism may provide a new horizon for innovative drug design endeavors. Considering the sequence similarities between α-syn’s non-amyloid-β component (NAC) and Aβ’s C-terminus, we hypothesized that KP-10 would enhance cholinergic neuronal resistance against α-syn’s deleterious consequences through preferential binding. Here, human cholinergic SH-SY5Y cells were transiently transformed to upsurge the mRNA expression of α-syn while α-syn-mediated cholinergic toxicity was quantified utilizing a standardized viability-based assay. Remarkably, the E46K mutant α-syn displayed elevated α-syn mRNA levels, which subsequently induced more cellular toxicity compared with the wild-type α-syn in choline acetyltransferase (ChAT)-positive cholinergic neurons. Treatment with a high concentration of KP-10 (10 µM) further decreased cholinergic cell viability, while low concentrations of KP-10 (0.01–1 µM) substantially suppressed wild-type and E46K mutant α-syn-mediated toxicity. Correlating with the in vitro observations are approximations from in silico algorithms, which inferred that KP-10 binds favorably to the C-terminal residues of wild-type and E46K mutant α-syn with CDOCKER energy scores of −118.049 kcal/mol and −114.869 kcal/mol, respectively. Over the course of 50 ns simulation time, explicit-solvent molecular dynamics conjointly revealed that the docked complexes were relatively stable despite small-scale fluctuations upon assembly. Taken together, our findings insinuate that KP-10 may serve as a novel therapeutic scaffold with far-reaching implications for the conceptualization of α-syn-based treatments.

Insights Into the Role of Heat Shock Protein 27 in the Development of Neurodegeneration

Small heat shock protein 27 is a critically important chaperone, that plays a key role in several essential and varied physiological processes. These include thermotolerance, apoptosis, cytoskeletal dynamics, cell differentiation, protein folding, among others. Despite its relatively small size and intrinsically disordered termini, it forms large and polydisperse oligomers that are in equilibrium with dimers. This equilibrium is driven by transient interactions between the N-terminal region, the α-crystallin domain, and the C-terminal region. The continuous redistribution of binding partners results in a conformationally dynamic protein that allows it to adapt to different functions where substrate capture is required. However, the intrinsic disorder of the amino and carboxy terminal regions and subsequent conformational variability has made structural investigations challenging. Because heat shock protein 27 is critical for so many key cellular functions, it is not surprising that it also has been linked to human disease. Charcot-Marie-Tooth and distal hereditary motor neuropathy are examples of neurodegenerative disorders that arise from single point mutations in heat shock protein 27. The development of possible treatments, however, depends on our understanding of its normal function at the molecular level so we might be able to understand how mutations manifest as disease. This review will summarize recent reports describing investigations into the structurally elusive regions of Hsp27. Recent insights begin to provide the required context to explain the relationship between a mutation and the resulting loss or gain of function that leads to Charcot-Marie Tooth disease and distal hereditary motor neuropathy.

Regulation by Different Types of Chaperones of Amyloid Transformation of Proteins Involved in the Development of Neurodegenerative Diseases

The review highlights various aspects of the influence of chaperones on amyloid proteins associated with the development of neurodegenerative diseases and includes studies conducted in our laboratory. Different sections of the article are devoted to the role of chaperones in the pathological transformation of alpha-synuclein and the prion protein. Information about the interaction of the chaperonins GroE and TRiC as well as polymer-based artificial chaperones with amyloidogenic proteins is summarized. Particular attention is paid to the effect of blocking chaperones by misfolded and amyloidogenic proteins. It was noted that the accumulation of functionally inactive chaperones blocked by misfolded proteins might cause the formation of amyloid aggregates and prevent the disassembly of fibrillar structures. Moreover, the blocking of chaperones by various forms of amyloid proteins might lead to pathological changes in the vital activity of cells due to the impaired folding of newly synthesized proteins and their subsequent processing. The final section of the article discusses both the little data on the role of gut microbiota in the propagation of synucleinopathies and prion diseases and the possible involvement of the bacterial chaperone GroE in these processes.

Rapid screening of high expressing Escherichia coli colonies using a novel dicistronic-autoinducible system

Background

Identification of high-expressing colonies is one of the main concerns in the upstream process of recombinant protein development. The common method to screen high-producing colonies is SDS-PAGE, a laborious and time-consuming process, which is based on a random and qualitative way. The current study describes the design and development of a rapid screening system composed of a dicistronic expression system containing a reporter (enhanced green fluorescent protein, eGFP), protein model (staphylokinase, SAK), and a self-inducible system containing heat shock protein 27 (Hsp27).

Results

Dicistronic-autoinducible system expressed eGFP and SAK successfully in 5-ml and 1-L culture volumes. High expressing colonies were identified during 6 h via fluorescent signals. In addition, the biological activity of the protein model was confirmed semi-quantitatively and quantitatively through radial caseinolytic and chromogenic methods, respectively. There was a direct correlation between eGFP fluorescent intensity and SAK activity. The correlation and linearity of expression between the two genes were respectively confirmed with Pearson correlation and linear regression. Additionally, the precision, limit of detection (LOD), and limit of quantification (LOQ) were determined. The expression of eGFP and SAK was stable during four freeze–thaw cycles. In addition, the developed protocol showed that the transformants can be inoculated directly to the culture, saving time and reducing the error-prone step of colony picking.

Conclusion

The developed system is applicable for rapid screening of high-expressing colonies in most research laboratories. This system can be investigated for other recombinant proteins expressed in E. coli with a potential capability for automation and use at larger scales.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12934-021-01711-2.

Extracellular vesicle-associated small heat shock proteins as therapeutic agents in neurodegenerative diseases and beyond

Increasing evidence points towards using extracellular vesicles (EVs) as a therapeutic strategy in neurodegenerative diseases such as multiple sclerosis, Parkinson's, and Alzheimer's disease. EVs are nanosized carriers that play an essential role in intercellular communication and cellular homeostasis by transporting an active molecular cargo, including a large variety of proteins. Recent publications demonstrate that small heat shock proteins (HSPBs) exhibit a beneficial role in neurodegenerative diseases. Moreover, it is defined that HSPBs target the autophagy and the apoptosis pathway, playing a prominent role in chaperone activity and cell survival. This review elaborates on the therapeutic potential of EVs and HSPBs, in particular HSPB1 and HSPB8, in neurodegenerative diseases. We conclude that EVs and HSPBs positively influence neuroinflammation, central nervous system (CNS) repair, and protein aggregation in CNS disorders. Moreover, we propose the use of HSPB-loaded EVs as advanced nanocarriers for the future development of neurodegenerative disease therapies.

A novel multi-target strategy to attenuate the progression of Parkinson's disease by diamine hybrid AGE/ALE inhibitor

Instead of a conventional 'one-drug-one-target approach', this article presents a novel multi-target approach with a concept of trapping simultaneously as many detrimental factors as possible involved in the progression of Parkinson's disease. These factors include reactive carbonyl species, reactive oxygen species, Fe^3+/Cu²⁺ and ortho-quinones (o-quinone), in particular. Different from the known multi-target strategies for Parkinson's disease, it is a sort of 'vacuum cleaning' strategy. The new agent consists of reactive carbonyl species scavenging moiety and reactive oxygen species scavenging and metal chelating moiety linked by a spacer. Provided that the capacity of scavenging o-quinones is demonstrated, this type of agent can further broaden its potential therapeutic profile. In order to support this new hypothetical approach, a number of simple in vitro experiments are proposed.

The binding of the small heat-shock protein αB-crystallin to fibrils of α-synuclein is driven by entropic forces

Molecular chaperones are key components of the cellular proteostasis network whose role includes the suppression of the formation and proliferation of pathogenic aggregates associated with neurodegenerative diseases. The molecular principles that allow chaperones to recognize misfolded and aggregated proteins remain, however, incompletely understood. To address this challenge, here we probe the thermodynamics and kinetics of the interactions between chaperones and protein aggregates under native solution conditions using a microfluidic platform. We focus on the binding between amyloid fibrils of α-synuclein, associated with Parkinson's disease, to the small heat-shock protein αB-crystallin, a chaperone widely involved in the cellular stress response. We find that αB-crystallin binds to α-synuclein fibrils with high nanomolar affinity and that the binding is driven by entropy rather than enthalpy. Measurements of the change in heat capacity indicate significant entropic gain originates from the disassembly of the oligomeric chaperones that function as an entropic buffer system. These results shed light on the functional roles of chaperone oligomerization and show that chaperones are stored as inactive complexes which are capable of releasing active subunits to target aberrant misfolded species.

The chaperone HSPB1 prepares protein aggregates for resolubilization by HSP70

In human cells under stress conditions, misfolded polypeptides can form potentially cytotoxic insoluble aggregates. To eliminate aggregates, the HSP70 chaperone machinery extracts and resolubilizes polypeptides for triage to refolding or degradation. Yeast and bacterial chaperones of the small heat-shock protein (sHSP) family can bind substrates at early stages of misfolding, during the aggregation process. The co-aggregated sHSPs then facilitate downstream disaggregation by HSP70. Because it is unknown whether a human sHSP has this activity, we investigated the disaggregation role of human HSPB1. HSPB1 co-aggregated with unfolded protein substrates, firefly luciferase and mammalian lactate dehydrogenase. The co-aggregates formed with HSPB1 were smaller and more regularly shaped than those formed in its absence. Importantly, co-aggregation promoted the efficient disaggregation and refolding of the substrates, led by HSP70. HSPB1 itself was also extracted during disaggregation, and its homo-oligomerization ability was not required. Therefore, we propose that a human sHSP is an integral part of the chaperone network for protein disaggregation.

Illuminating amyloid fibrils: Fluorescence-based single-molecule approaches

The aggregation of proteins into insoluble filamentous amyloid fibrils is a pathological hallmark of neurodegenerative diseases that include Parkinson's disease and Alzheimer's disease. Since the identification of amyloid fibrils and their association with disease, there has been much work to describe the process by which fibrils form and interact with other proteins. However, due to the dynamic nature of fibril formation and the transient and heterogeneous nature of the intermediates produced, it can be challenging to examine these processes using techniques that rely on traditional ensemble-based measurements. Single-molecule approaches overcome these limitations as rare and short-lived species within a population can be individually studied. Fluorescence-based single-molecule methods have proven to be particularly useful for the study of amyloid fibril formation. In this review, we discuss the use of different experimental single-molecule fluorescence microscopy approaches to study amyloid fibrils and their interaction with other proteins, in particular molecular chaperones. We highlight the mechanistic insights these single-molecule techniques have already provided in our understanding of how fibrils form, and comment on their potential future use in studying amyloid fibrils and their intermediates.

Effect of glycolysis and heat shock proteins on hypoxia adaptation of Tibetan sheep at different altitude

Glycolysis and heat shock proteins (HSPs) play an important role in mediating the physiological response to hypoxia. The changes of glycolysis and HSPs with altitude would provide important information regarding ways to prevent hypoxia-related sickness in both animals and humans. In this study, the expression pattern of HIF1A, PDK4, HSP27 and HSP60, indexes activity and content of glucose metabolism were detected in heart, lung, brain, and quadriceps femoris taken from Tibetan sheep (Ovis aries) that were raised at different altitudes (2,500 m, 3,500 m and 4,500 m). The expression of HIF1A and PDK4 was increased with increasing altitude in all of the tissues. The lactate dehydrogenase (LDH) activities and adenosine triphosphate (ATP), nicotinamide adenine dinucleotide (NADH (redox state), NAD⁺), lactic acid (LA), pyruvic acid (PA) contents were all increased with increasing altitude in all of the tissues. The ratio of NADH/NAD⁺ and LA/PA were higher in sheep at an altitude of 4,500 m than of 3,500 m and 2,500 m in all tissues, except for the NADH/NAD⁺ ratio in lung and quadriceps femoris. An increase in the protein and mRNA expression of ATP-independent HSP27 during hypoxia condition was detected. The expression of ATP-dependent HSP60 mRNA and protein was increased in all of the tissues at an altitude of 3,500 m than of 2,500 m, but was decreased at an altitude of 4,500 m. These results suggest that glycolysis and HSPs are upregulated to ensure energy supply and proteostasis during hypoxia, but energy conservation may be prioritized over cytoprotective protein chaperoning in Tibetan sheep tissues during extreme hypoxia.

Mesenchymal stem cell secretome protects against alpha-synuclein-induced neurodegeneration in a Caenorhabditis elegans model of Parkinson's disease

BACKGROUND AIMS

The capacity of the secretome from bone marrow-derived mesenchymal stem cells (BMSCs) to prevent dopaminergic neuron degeneration caused by overexpression of alpha-synuclein (α-syn) was explored using two Caenorhabditis elegans models of Parkinson's disease (PD).

METHODS

First, a more predictive model of PD that overexpresses α-syn in dopamine neurons was subjected to chronic treatment with secretome. This strain displays progressive dopaminergic neurodegeneration that is age-dependent. Following chronic treatment with secretome, the number of intact dopaminergic neurons was determined. Following these initial experiments, a C. elegans strain that overexpresses α-syn in body wall muscle cells was used to determine the impact of hBMSC secretome on α-syn inclusions. Lastly, in silico analysis of the components that constitute the secretome was performed.

RESULTS

The human BMSC (hBMSC) secretome induced a neuroprotective effect, leading to reduced dopaminergic neurodegeneration. Moreover, in animals submitted to chronic treatment with secretome, the number of α-syn inclusions was reduced, indicating that the secretome of MSCs was possibly contributing to the degradation of those structures. In silico analysis identified possible suppressors of α-syn proteotoxicity, including growth factors and players in the neuronal protein quality control mechanisms.

CONCLUSIONS

The present findings indicate that hBMSC secretome has the potential to be used as a disease-modifying strategy in future PD regenerative medicine approaches.