bims-proned 2024-02-18 papers

bims-proned

Biomed News

on Proteostasis in neurodegeneration

Issue of 2024‒02‒18
nineteen papers selected by
Verena Kohler, Umeå University

Protein-protein interactions regulating α-synuclein pathology.
Efficient inhibition of amyloid fibrillation and cytotoxicity of α-synuclein and human insulin using biosynthesized silver nanoparticles decorated by green tea polyphenols.
In vitro modulation of mTOR and mGlur5 influence α-synuclein accumulation.
Enzymatic and synthetic regulation of polypeptide folding.
Cathepsin L prevents the accumulation of alpha-synuclein fibrils in the cell.
Abnormal protein post-translational modifications induces aggregation and abnormal deposition of protein, mediating neurodegenerative diseases.
O-GlcNAc forces an α-synuclein amyloid strain with notably diminished seeding and pathology.
Molecular insights into aggrephagy: Their cellular functions in the context of neurodegenerative diseases.
The contribution of β-amyloid, Tau and α-synuclein to blood-brain barrier damage in neurodegenerative disorders.
Discovery of Effective Dual PROTAC Degraders for Neurodegenerative Disease-Associated Aggregates.
Tryptanthrin Analogs Substoichiometrically Inhibit Seeded and Unseeded Tau4RD Aggregation.
The effects of biological crowders on fibrillization, structure, diffusion, and conformational dynamics of α-synuclein.
Relationships between protein degradation, cellular senescence, and organismal aging.
Reduced progranulin increases tau and α-synuclein inclusions and alters mouse tauopathy phenotypes via glucocerebrosidase.
Proteostatic remodeling of small heat shock chaperones - crystallins by Ran-binding protein 2 and the peptidyl-prolyl cis-trans isomerase and chaperone activities of its cyclophilin domain.
Molecular Insights into the Inhibition and Disaggregation Effects of EGCG on Aβ40 and Aβ42 Cofibrillation.
Biochemical approaches to assess the impact of post-translational modifications on pathogenic tau conformations using recombinant protein.
The coherence between PSMC6 and α-ring in the 26S proteasome is associated with Alzheimer's disease.
Stochastic Optical Reconstruction Microscopy Imaging of Multiple System Atrophy Inclusions Suggests Stepwise α-Synuclein Aggregation.

Trends Neurosci. 2024 Feb 13. pii: S0166-2236(24)00014-6. [Epub ahead of print]

Protein-protein interactions regulating α-synuclein pathology.

Jiannan Wang, Lijun Dai, Sichun Chen, Zhaohui Zhang, Xin Fang, Zhentao Zhang.

  Parkinson's disease (PD) is a neurodegenerative disease characterized by the degeneration of dopaminergic neurons in the substantia nigra pars compacta (SNpc) and the formation of Lewy bodies (LBs). The main proteinaceous component of LBs is aggregated α-synuclein (α-syn). However, the mechanisms underlying α-syn aggregation are not yet fully understood. Converging lines of evidence indicate that, under certain pathological conditions, various proteins can interact with α-syn and regulate its aggregation. Understanding these protein-protein interactions is crucial for unraveling the molecular mechanisms contributing to PD pathogenesis. In this review we provide an overview of the current knowledge on protein-protein interactions that regulate α-syn aggregation. Additionally, we briefly summarize the methods used to investigate the influence of protein-protein interactions on α-syn aggregation and propagation.

Keywords:  Lewy body; Parkinson’s disease; aggregation; cross-seeding; microbial proteins; strain

DOI:  https://doi.org/10.1016/j.tins.2024.01.002
Sci Rep. 2024 Feb 16. 14(1): 3907

Efficient inhibition of amyloid fibrillation and cytotoxicity of α-synuclein and human insulin using biosynthesized silver nanoparticles decorated by green tea polyphenols.

Behnaz Mirzaei-Behbahani, Ali Akbar Meratan, Beitollah Moosakhani, Mahya Mohammad-Zaheri, Zahra Mousavi-Jarrahi, Nasser Nikfarjam, Mohammad Bagher Shahsavani, Ali Akbar Saboury.

  Green tea polyphenols (GTPs), particularly epigallocatechin-3-gallate, stand out among natural small molecules screened for their ability to target protein aggregates due to their potent anti-amyloidogenic and neuroprotective activities against various disease-related peptides and proteins. However, the clinical applications of GTPs in amyloid-related diseases have been greatly limited by drawbacks such as poor chemical stability and low bioavailability. To address these limitations, this study utilized an Iranian green tea polyphenolic extract as a reducing agent to neutralize silver ions and facilitate the formation of silver nanoparticle capped by GTPs (GTPs-capped AgNPs). The results obtained from this study demonstrate that GTPs-capped AgNPs are more effective than free GTPs at inhibiting amyloid fibrillation and reducing cytotoxicity induced by amyloid fibrils of human insulin and α-synuclein (α-syn). This improved efficacy is attributed to the increased surface/volume ratio of GTPs-capped AgNPs, which can enhance their binding affinity to amyloidogenic species and boosts their antioxidant activity. The mechanism by which GTPs-capped AgNPs inhibit amyloid fibrillation appears to vary depending on the target protein. For structured protein human insulin, GTPs-capped AgNPs hinder fibrillation by constraining the protein in its native-like state. In contrast, GTPs-capped AgNPs modulate fibrillation of intrinsically disordered proteins like α-syn by redirecting the aggregation pathway towards the formation of non-toxic off-pathway oligomers or amorphous aggregates. These findings highlight polyphenol-functionalized nanoparticles as a promising strategy for targeting protein aggregates associated with neurodegenerative diseases.

Keywords:  Amyloid fibril; Cytotoxicity; GTPs; GTPs-capped AgNPs; Human insulin; α-Synuclein

DOI:  https://doi.org/10.1038/s41598-024-54464-4
Mol Brain. 2024 Feb 15. 17(1): 9

In vitro modulation of mTOR and mGlur5 influence α-synuclein accumulation.

Viktoria Xing, Kyle Biggar, Stephen S G Ferguson, Shawn Hayley.

  One of the main hallmarks of Parkinson's disease (PD) is abnormal alpha-synuclein (α-syn) aggregation which forms the main component of intracellular Lewy body inclusions. This short report used preformed α-syn fibrils, as well as an A53T mutant α-syn adenovirus to mimic conditions of pathological protein aggregation in dopaminergic human derived SH-SY5Y neural cells. Since there is evidence that the mTOR pathway and glutamatergic signaling each influence protein aggregation, we also assessed the impact of the mTOR inhibitor, rapamycin and the mGluR5 allosteric modulator, CTEP. We found that both rapamycin and CTEP induced a significant reduction of α-syn fibrils in SH-SY5Y cells and this effect was associated with a reduction in mTOR signaling and enhancement in autophagic pathway factors. These data support the possibility that CTEP (or rapamycin) might be a useful pharmacological approach to target abnormal α-syn accumulation by promoting intracellular degradation or enhanced clearance.

Keywords:  In vitro; Parkinson’s disease; mGluR5; mTOR; α-synuclein

DOI:  https://doi.org/10.1186/s13041-023-01074-2
Chem Sci. 2024 Feb 14. 15(7): 2282-2299

Enzymatic and synthetic regulation of polypeptide folding.

Takahiro Muraoka, Masaki Okumura, Tomohide Saio.

Proper folding is essential for the biological functions of all proteins. The folding process is intrinsically error-prone, and the misfolding of a polypeptide chain can cause the formation of toxic aggregates related to pathological outcomes such as neurodegenerative disease and diabetes. Chaperones and some enzymes are involved in the cellular proteostasis systems that assist polypeptide folding to diminish the risk of aggregation. Elucidating the molecular mechanisms of chaperones and related enzymes is important for understanding proteostasis systems and protein misfolding- and aggregation-related pathophysiology. Furthermore, mechanistic studies of chaperones and related enzymes provide important clues to designing chemical mimics, or chemical chaperones, that are potentially useful for recovering proteostasis activities as therapeutic approaches for treating and preventing protein misfolding-related diseases. In this Perspective, we provide a comprehensive overview of the latest understanding of the folding-promotion mechanisms by chaperones and oxidoreductases and recent progress in the development of chemical mimics that possess activities comparable to enzymes, followed by a discussion of future directions.

DOI: https://doi.org/10.1039/d3sc05781j
Genes Cells. 2024 Feb 17.

Cathepsin L prevents the accumulation of alpha-synuclein fibrils in the cell.

Ayumi Matsuki, Yoshihisa Watanabe, Sho Hashimoto, Atsushi Hoshino, Satoaki Matoba.

  The deposition of α-synuclein (α-Syn) fibrils in neuronal cells has been implicated as a causative factor in Parkinson's disease (PD) and dementia with Lewy Bodies (DLB). α-Syn can be degraded by autophagy, proteasome, and chaperone-mediated autophagy, and previous studies have suggested the potency of certain cathepsins, lysosomal proteases, for α-Syn degradation. However, no studies have comprehensively evaluated all cathepsins. Here, we evaluated the efficacy of all 15 cathepsins using a cell model of α-Syn fibril propagation and found that overexpression of cathepsin L (CTSL) was the most effective in preventing the accumulation of α-Syn aggregates. CTSL-mediated degradation of α-Syn aggregates was dependent on the autophagy machinery, and CTSL itself promoted autophagy flux. Interestingly, CTSL was effective in autophagic degradation of wild-type (WT) α-Syn, but not in the case of A53T and E46K missense mutations, which are causative for familial PD. These results suggest that CTSL is a potential therapeutic strategy for sporadic PD pathology in WT α-Syn.

Keywords:  autophagy flux; cathepsin L; degradation; α-Synuclein

DOI:  https://doi.org/10.1111/gtc.13099
Cell Biosci. 2024 Feb 12. 14(1): 22

Abnormal protein post-translational modifications induces aggregation and abnormal deposition of protein, mediating neurodegenerative diseases.

Wei Li, Hong-Lian Li, Jian-Zhi Wang, Rong Liu, Xiaochuan Wang.

  Protein post-translational modifications (PPTMs) refer to a series of chemical modifications that occur after the synthesis of protein. Proteins undergo different modifications such as phosphorylation, acetylation, ubiquitination, and so on. These modifications can alter the protein's structure, function, and interaction, thereby regulating its biological activity. In neurodegenerative diseases, several proteins undergo abnormal post-translational modifications, which leads to aggregation and abnormal deposition of protein, thus resulting in neuronal death and related diseases. For example, the main pathological features of Alzheimer's disease are the aggregation of beta-amyloid protein and abnormal phosphorylation of tau protein. The abnormal ubiquitination and loss of α-synuclein are related to the onset of Parkinson's disease. Other neurodegenerative diseases such as Huntington's disease, amyotrophic lateral sclerosis, and so on are also connected with abnormal PPTMs. Therefore, studying the abnormal PPTMs in neurodegenerative diseases is critical for understanding the mechanism of these diseases and the development of significant therapeutic strategies. This work reviews the implications of PPTMs in neurodegenerative diseases and discusses the relevant therapeutic strategies.

Keywords:  Neurodegenerative diseases; Protein post-translational modifications (PPTMs); Treatment strategy

DOI:  https://doi.org/10.1186/s13578-023-01189-y
Nat Chem Biol. 2024 Feb 12.

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

Aaron T Balana, Anne-Laure Mahul-Mellier, Binh A Nguyen, Mian Horvath, Afraah Javed, Eldon R Hard, Yllza Jasiqi, Preeti Singh, Shumaila Afrin, Rose Pedretti, Virender Singh, Virginia M-Y Lee, Kelvin C Luk, Lorena Saelices, Hilal A Lashuel, Matthew R Pratt.

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.

DOI: https://doi.org/10.1038/s41589-024-01551-2
J Mol Biol. 2024 Feb 13. pii: S0022-2836(24)00065-2. [Epub ahead of print] 168493

Molecular insights into aggrephagy: Their cellular functions in the context of neurodegenerative diseases.

Valentín Cóppola Segovia, Fulvio Reggiori.

  Protein homeostasis or proteostasis is an equilibrium of biosynthetic production, folding and transport of proteins, and their timely and efficient degradation. Proteostasis is guaranteed by a network of protein quality control systems aimed at maintaining the proteome functional and avoiding accumulation of potentially cytotoxic proteins. Terminal unfolded and dysfunctional proteins can be directly turned over by the ubiquitin-proteasome system (UPS) or first amassed into aggregates prior to degradation. Aggregates can also be disposed into lysosomes by a selective type of autophagy known as aggrephagy, which relies on a set of so-called selective autophagy receptors (SARs) and adaptor proteins. Failure in eliminating aggregates, also due to defects in aggrephagy, can have devastating effects as underscored by several neurodegenerative diseases or proteinopathies, which are characterized by the accumulation of aggregates mostly formed by a specific disease-associated, aggregate-prone protein depending on the clinical pathology. Despite its medical relevance, however, the process of aggrephagy is far from being understood. Here we review the findings that have helped in assigning a possible function to specific SARs and adaptor proteins in aggrephagy in the context of proteinopathies, and also highlight the interplay between aggrephagy and the pathogenesis of proteinopathies.

Keywords:  Aggregate; Aggrephagy; Alzheimer’s disease; Autophagy; Huntington’s disease; Neurodegenerative diseases; Parkinson’s disease; Selective autophagy receptors; amyotrophic lateral sclerosis; frontotemporal lobar degeneration; proteinopathies

DOI:  https://doi.org/10.1016/j.jmb.2024.168493
Acta Neuropathol. 2024 Feb 12. 147(1): 39

The contribution of β-amyloid, Tau and α-synuclein to blood-brain barrier damage in neurodegenerative disorders.

Ying-Chieh Wu, Tizibt Ashine Bogale, Jari Koistinaho, Marina Pizzi, Taisia Rolova, Arianna Bellucci.

  Central nervous system (CNS) accumulation of fibrillary deposits made of Amyloid β (Aβ), hyperphosphorylated Tau or α-synuclein (α-syn), present either alone or in the form of mixed pathology, characterizes the most common neurodegenerative diseases (NDDs) as well as the aging brain. Compelling evidence supports that acute neurological disorders, such as traumatic brain injury (TBI) and stroke, are also accompanied by increased deposition of toxic Aβ, Tau and α-syn species. While the contribution of these pathological proteins to neurodegeneration has been experimentally ascertained, the cellular and molecular mechanisms driving Aβ, Tau and α-syn-related brain damage remain to be fully clarified. In the last few years, studies have shown that Aβ, Tau and α-syn may contribute to neurodegeneration also by inducing and/or promoting blood-brain barrier (BBB) disruption. These pathological proteins can affect BBB integrity either directly by affecting key BBB components such as pericytes and endothelial cells (ECs) or indirectly, by promoting brain macrophages activation and dysfunction. Here, we summarize and critically discuss key findings showing how Aβ, Tau and α-syn can contribute to BBB damage in most common NDDs, TBI and stroke. We also highlight the need for a deeper characterization of the role of these pathological proteins in the activation and dysfunction of brain macrophages, pericytes and ECs to improve diagnosis and treatment of acute and chronic neurological disorders.

Keywords:  Amyloid β; Brain macrophages; Endothelial cells; Pericytes; Tau; α-synuclein

DOI:  https://doi.org/10.1007/s00401-024-02696-z
J Med Chem. 2024 Feb 14.

Discovery of Effective Dual PROTAC Degraders for Neurodegenerative Disease-Associated Aggregates.

Wentao Zhu, Wenqian Zhang, Jian Chen, Yichen Tong, Fang Xu, Jiyan Pang.

The aggregation of specific proteins is a histopathological hallmark in various neurodegenerative diseases (NDs), among which Alpha-synuclein (α-Syn) and tau have received increased attention. The targeted protein degradation (TPD) strategy has been studied in the treatment of NDs, but multitarget bifunctional molecules have been ignored. Herein, a series of effective dual PROTAC degraders were developed, which could degrade α-Syn aggregates and total tau simultaneously. The degradation effects were evaluated in vitro, and the results showed that T3 could significantly knockdown α-Syn aggregates and total tau in the degradation efficiency with DC50 of 1.57 ± 0.55 and 4.09 ± 0.90 μM, respectively. Further mechanistic exploration showed that the degradation effect was mediated by the ubiquitin-proteasome system (UPS). Additionally, the therapeutic efficacy of T3 was confirmed in an MPTP-induced PD mouse model. Our results suggest that these dual PROTACs may provide a potential therapeutic strategy for NDs.

DOI: https://doi.org/10.1021/acs.jmedchem.3c01719
bioRxiv. 2024 Feb 03. pii: 2024.02.02.578649. [Epub ahead of print]

Tryptanthrin Analogs Substoichiometrically Inhibit Seeded and Unseeded Tau4RD Aggregation.

Ellie I James, David W Baggett, Edcon Chang, Joel Schachter, Thomas Nixey, Karoline Choi, Miklos Guttman, Abhinav Nath.

Microtubule-associated protein tau is an intrinsically disordered protein (IDP) that forms characteristic fibrillar aggregates in several diseases, the most well-known of which is Alzheimer's disease (AD). Despite keen interest in disrupting or inhibiting tau aggregation to treat AD and related dementias, there are currently no FDA-approved tau-targeting drugs. This is due, in part, to the fact that tau and other IDPs do not exhibit a single well-defined conformation but instead populate a fluctuating conformational ensemble that precludes finding a stable "druggable" pocket. Despite this challenge, we previously reported the discovery of two novel families of tau ligands, including a class of aggregation inhibitors, identified through a protocol that combines molecular dynamics, structural analysis, and machine learning. Here we extend our exploration of tau druggability with the identification of tryptanthrin and its analogs as potent, substoichiometric aggregation inhibitors, with the best compounds showing potencies in the low nanomolar range even at a ∼100-fold molar excess of tau4RD. Moreover, conservative changes in small molecule structure can have large impacts on inhibitory potency, demonstrating that similar structure-activity relationship (SAR) principles as used for traditional drug development also apply to tau and potentially to other IDPs.

DOI: https://doi.org/10.1101/2024.02.02.578649
Protein Sci. 2024 Mar;33(3): e4894

The effects of biological crowders on fibrillization, structure, diffusion, and conformational dynamics of α-synuclein.

Sina Heravi, Jude Vincent Dobbin Power, Anand Yethiraj, Valerie Booth.

  α-synuclein is an intrinsically disordered protein (IDP) whose aggregation in presynaptic neuronal cells is a pathological hallmark of Lewy body formation and Parkinson's disease. This aggregation process is likely affected by the crowded macromolecular cellular environment. In this study, α-synuclein was studied in the presence of both a synthetic crowder, Ficoll70, and a biological crowder composed of lysed cells that better mimics the biocomplexity of the cellular environment. 15 N-1 H HSQC NMR results show similar α-synuclein chemical shifts in non-crowded and all crowded conditions implying that it remains similarly unstructured in all conditions. Nevertheless, both HSQC NMR and fluorescence measurements indicate that, only in the cell lysate, α-synuclein forms aggregates over a timescale of 48 h. 15 N-edited diffusion measurements indicate that all crowders slow down the α-synuclein's diffusivity. Interestingly, at high concentrations, α-synuclein diffuses faster in cell lysate than in Ficoll70, possibly due to additional soft (e.g., electrostatic or hydrophobic) interactions. 15 N-edited relaxation measurements show that some residues are more mobile in cell lysate than in Ficoll70; the rates that are most different are predominantly in hydrophobic residues. We thus examined cell lysates with reduced hydrophobicity and found slower dynamics (higher relaxation rates) in several α-synuclein residues. Taken together, these experiments suggest that while cell lysate does not substantially affect α-synuclein structure (HSQC spectra), it does affect chain dynamics and translational diffusion, and strongly affects aggregation over a timescale of days, in a manner that is different from either no crowder or an artificial crowder: soft hydrophobic interactions are implicated.

Keywords:  NMR; intrinsically disordered protein; macromolecular crowding; relaxation; translational diffusion; α-synuclein

DOI:  https://doi.org/10.1002/pro.4894
J Biochem. 2024 Feb 13. pii: mvae016. [Epub ahead of print]

Relationships between protein degradation, cellular senescence, and organismal aging.

Jun Hamazaki, Shigeo Murata.

  Aging is a major risk factor for many diseases. Recent studies have shown that age-related disruption of proteostasis leads to the accumulation of abnormal proteins and that dysfunction of the two major intracellular proteolytic pathways, the ubiquitin-proteasome pathway, and the autophagy-lysosome pathway, is largely responsible for this process. Conversely, it has been shown that activation of these proteolytic pathways may contribute to lifespan extension and suppression of pathological conditions, making it a promising intervention for anti-aging. This review provides an overview of the important role of intracellular protein degradation in aging and summarizes how the disruption of proteostasis is involved in age-related diseases.

Keywords:  aging; autophagy; proteasome; proteostasis; senescence

DOI:  https://doi.org/10.1093/jb/mvae016
Nat Commun. 2024 Feb 16. 15(1): 1434

Reduced progranulin increases tau and α-synuclein inclusions and alters mouse tauopathy phenotypes via glucocerebrosidase.

Hideyuki Takahashi, Sanaea Bhagwagar, Sarah H Nies, Hongping Ye, Xianlin Han, Marius T Chiasseu, Guilin Wang, Ian R Mackenzie, Stephen M Strittmatter.

Comorbid proteinopathies are observed in many neurodegenerative disorders including Alzheimer's disease (AD), increase with age, and influence clinical outcomes, yet the mechanisms remain ill-defined. Here, we show that reduction of progranulin (PGRN), a lysosomal protein associated with TDP-43 proteinopathy, also increases tau inclusions, causes concomitant accumulation of α-synuclein and worsens mortality and disinhibited behaviors in tauopathy mice. The increased inclusions paradoxically protect against spatial memory deficit and hippocampal neurodegeneration. PGRN reduction in male tauopathy attenuates activity of β-glucocerebrosidase (GCase), a protein previously associated with synucleinopathy, while increasing glucosylceramide (GlcCer)-positive tau inclusions. In neuronal culture, GCase inhibition enhances tau aggregation induced by AD-tau. Furthermore, purified GlcCer directly promotes tau aggregation in vitro. Neurofibrillary tangles in human tauopathies are also GlcCer-immunoreactive. Thus, in addition to TDP-43, PGRN regulates tau- and synucleinopathies via GCase and GlcCer. A lysosomal PGRN-GCase pathway may be a common therapeutic target for age-related comorbid proteinopathies.

DOI: https://doi.org/10.1038/s41467-024-45692-3
bioRxiv. 2024 Jan 30. pii: 2024.01.26.577462. [Epub ahead of print]

Proteostatic remodeling of small heat shock chaperones - crystallins by Ran-binding protein 2 and the peptidyl-prolyl cis-trans isomerase and chaperone activities of its cyclophilin domain.

Hemangi Patil, Kyoung-In Cho, Paulo A Ferreira.

Disturbances in phase transitions and intracellular partitions of nucleocytoplasmic shuttling substrates promote protein aggregation - a hallmark of neurodegenerative diseases. The modular Ran-binding protein 2 (Ranbp2) is a cytosolic molecular hub for rate-limiting steps of disassembly and phase transitions of Ran-GTP-bound protein ensembles exiting nuclear pores. Chaperones also play central roles in phase transitions and proteostasis by suppressing protein aggregation. Ranbp2 haploinsufficiency promotes the age-dependent neuroprotection of the chorioretina against photo-oxidative stress by proteostatic regulations of Ranbp2 substrates and by countering the build-up of poly-ubiquitylated substrates. Further, the peptidyl-prolyl cis-trans isomerase (PPIase) and chaperone activities of the cyclophilin domain (CY) of Ranbp2 modulate the proteostasis of selective neuroprotective substrates, such as hnRNPA2B1, STAT3, HDAC4 or L/M-opsin, while promoting a decline of ubiquitylated substrates. However, links between CY PPIase activity on client substrates and its effect(s) on ubiquitylated substrates are unclear. Here, proteomics of genetically modified mice with deficits of Ranbp2 uncovered the regulation of the small heat shock chaperones - crystallins by Ranbp2 in the chorioretina. Loss of CY PPIase of Ranbp2 up-regulates αA-crystallin proteostasis, which is repressed in non-lenticular tissues. Conversely, the αA-crystallin's substrates, γ-crystallins, are down-regulated by impairment of CY's C-terminal chaperone activity. These CY-dependent effects cause the age-dependent decline of ubiquitylated substrates without overt chorioretinal morphological changes. A model emerges whereby the Ranbp2 CY-dependent remodeling of crystallins' proteostasis subdues molecular aging and preordains chorioretinal neuroprotection by augmenting the chaperone buffering capacity and the decline of ubiquitylated substrates against proteostatic impairments. Further, CY's moonlighting activity holds pan -therapeutic potential against neurodegeneration.

DOI: https://doi.org/10.1101/2024.01.26.577462
J Phys Chem B. 2024 Feb 15.

Molecular Insights into the Inhibition and Disaggregation Effects of EGCG on Aβ40 and Aβ42 Cofibrillation.

Xuhua Li, Yu Zhang, Yuetian Wang, Shengli Zhang, Lei Zhang.

The misfolding and aggregation of amyloid-β (Aβ) peptides play a pivotal role in the pathogenesis of Alzheimer's disease (AD). Aβ40 and Aβ42, the two primary isoforms of Aβ, can not only self-aggregate into homogeneous aggregates but also coaggregate to form mixed fibrils. Epigallocatechin-3-gallate (EGCG), a prominent tea polyphenol, has shown the capability to prevent the self-aggregation of Aβ40 and Aβ42 peptides and disaggregate their homogeneous fibrils. However, its effects on the cofibrillation of Aβ40 and Aβ42 have not yet been explored. Here, we employed molecular dynamic simulations to investigate the effects of EGCG on the coaggregation of Aβ40 and Aβ42, as well as on their mixed fibril. Our findings indicated that EGCG effectively inhibits the codimerization of Aβ40 and Aβ42 primarily by impeding the interchain interaction between the two isoforms. The key binding sites for EGCG on Aβ40 and Aβ42 are the polar residues and aromatic residues, engaging in hydrogen-bond , π-π, and cation-π interactions with EGCG. Additionally, EGCG disaggregates the Aβ40-Aβ42 mixed fibril by reducing its long-range interaction through similar binding sites and interactions as those between EGCG and Aβ40-Aβ42 heterodimers. Our research reveals the comprehensive inhibition and disaggregation effects of EGCG on the cofibrillation of Aβ isoforms, which provides further support for the development of EGCG as an effective antiaggregation agent for AD.

DOI: https://doi.org/10.1021/acs.jpcb.3c07232
Biochem Soc Trans. 2024 Feb 13. pii: BST20230596. [Epub ahead of print]

Biochemical approaches to assess the impact of post-translational modifications on pathogenic tau conformations using recombinant protein.

Mohammed M Alhadidy, Nicholas M Kanaan.

  Tau protein is associated with many neurodegenerative disorders known as tauopathies. Aggregates of tau are thought of as a main contributor to neurodegeneration in these diseases. Increasingly, evidence points to earlier, soluble conformations of abnormally modified monomers and multimeric tau as toxic forms of tau. The biological processes driving tau from physiological species to pathogenic conformations remain poorly understood, but certain avenues are currently under investigation including the functional consequences of various pathological tau changes (e.g. mutations, post-translational modifications (PTMs), and protein-protein interactions). PTMs can regulate several aspects of tau biology such as proteasomal and autophagic clearance, solubility, and aggregation. Moreover, PTMs can contribute to the transition of tau from normal to pathogenic conformations. However, our understating of how PTMs specifically regulate the transition of tau into pathogenic conformations is partly impeded by the relative lack of structured frameworks to assess and quantify these conformations. In this review, we describe a set of approaches that includes several in vitro assays to determine the contribution of PTMs to tau's transition into known pathogenic conformations. The approaches begin with different methods to create recombinant tau proteins carrying specific PTMs followed by validation of the PTMs status. Then, we describe a set of biochemical and biophysical assays that assess the contribution of a given PTM to different tau conformations, including aggregation, oligomerization, exposure of the phosphatase-activating domain, and seeding. Together, these approaches can facilitate the advancement of our understanding of the relationships between PTMs and tau conformations.

Keywords:  aggregation; oligomers; post-translational modifications; protein conformation; recombinant protein; tau

DOI:  https://doi.org/10.1042/BST20230596
Front Mol Neurosci. 2023 ;16 1330853

The coherence between PSMC6 and α-ring in the 26S proteasome is associated with Alzheimer's disease.

Jing Xiong, Xinping Pang, Xianghu Song, Lin Yang, Chaoyang Pang.

  Alzheimer's disease (AD) is a heterogeneous age-dependent neurodegenerative disorder. Its hallmarks involve abnormal proteostasis, which triggers proteotoxicity and induces neuronal dysfunction. The 26S proteasome is an ATP-dependent proteolytic nanomachine of the ubiquitin-proteasome system (UPS) and contributes to eliminating these abnormal proteins. This study focused on the relationship between proteasome and AD, the hub genes of proteasome, PSMC6, and 7 genes of α-ring, are selected as targets to study. The following three characteristics were observed: 1. The total number of proteasomes decreased with AD progression because the proteotoxicity damaged the expression of proteasome proteins, as evidenced by the downregulation of hub genes. 2. The existing proteasomes exhibit increased activity and efficiency to counterbalance the decline in total proteasome numbers, as evidenced by enhanced global coordination and reduced systemic disorder of proteasomal subunits as AD advances. 3. The synergy of PSMC6 and α-ring subunits is associated with AD. Synergistic downregulation of PSMC6 and α-ring subunits reflects a high probability of AD risk. Regarding the above discovery, the following hypothesis is proposed: The aggregation of pathogenic proteins intensifies with AD progression, then proteasome becomes more active and facilitates the UPS selectively targets the degradation of abnormal proteins to maintain CNS proteostasis. In this paper, bioinformatics and support vector machine learning methods are applied and combined with multivariate statistical analysis of microarray data. Additionally, the concept of entropy was used to detect the disorder of proteasome system, it was discovered that entropy is down-regulated continually with AD progression against system chaos caused by AD. Another conception of the matrix determinant was used to detect the global coordination of proteasome, it was discovered that the coordination is enhanced to maintain the efficiency of degradation. The features of entropy and determinant suggest that active proteasomes resist the attack caused by AD like defenders, on the one hand, to protect themselves (entropy reduces), and on the other hand, to fight the enemy (determinant reduces). It is noted that these are results from biocomputing and need to be supported by further biological experiments.

Keywords:  Alzheimer’s disease; determinant; entropy; proteasome; support vector machine

DOI:  https://doi.org/10.3389/fnmol.2023.1330853
Mov Disord. 2024 Feb 15.

Stochastic Optical Reconstruction Microscopy Imaging of Multiple System Atrophy Inclusions Suggests Stepwise α-Synuclein Aggregation.

Benoît Vovard, Alexia Bodin, Julien Gouju, Adrien de Guilhem de Lataillade, Pascal Derkinderen, Frédérique Etcharry-Bouyx, Valérie Chauviré, Virginie Guillet-Pichon, Christophe Verny, Franck Letournel, Guy Lenaers, Arnaud Chevrollier, Philippe Codron.

  BACKGROUND: The architecture and composition of glial (GCI) and neuronal (NCI) α-synuclein inclusions observed in multiple system atrophy (MSA) remain to be precisely defined to better understand the disease.METHODS: Here, we used stochastic optical reconstruction microscopy (STORM) to characterize the nanoscale organization of glial (GCI) and neuronal (NCI) α-synuclein inclusions in cryopreserved brain sections from MSA patients.
RESULTS: STORM revealed a dense cross-linked internal structure of α-synuclein in all GCI and NCI. The internal architecture of hyperphosphorylated α-synuclein (p-αSyn) inclusions was similar in glial and neuronal cells, suggesting a common aggregation mechanism. A similar sequence of p-αSyn stepwise intracellular aggregation was defined in oligodendrocytes and neurons, starting from the perinuclear area and growing inside the cells. Consistent with this hypothesis, we found a higher mitochondrial density in GCI and NCI compared to oligodendrocytes and neurons from unaffected donors (P < 0.01), suggesting an active recruitment of the organelles during the aggregation process.
CONCLUSIONS: These first STORM images of GCI and NCI suggest stepwise α-synuclein aggregation in MSA. © 2024 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Keywords:  Parkinson's disease; STORM; dementia with Lewy bodies; multiple system atrophy; α-synuclein

DOI:  https://doi.org/10.1002/mds.29744