bims-proned 2024-12-29 papers

bims-proned

Biomed News

on Proteostasis in neurodegeneration

Issue of 2024–12–29
twenty-two papers selected by
Verena Kohler, Umeå University

Neuronal constitutive endolysosomal perforations enable α-synuclein aggregation by internalized PFFs.
Synaptic sabotage: How Tau and α-Synuclein undermine synaptic health.
N-acetylation of α-synuclein enhances synaptic vesicle clustering mediated by α-synuclein and lysophosphatidylcholine.
Non-enzymatic posttranslational protein modifications in protein aggregation and neurodegenerative diseases.
Impairment of lipid homeostasis causes lysosomal accumulation of endogenous protein aggregates through ESCRT disruption.
Inhibition of Phosphorylated Alpha-Synuclein Aggregation by Synthetic Protein Mimetics and Foldamers.
Protein Citrullination in Amyotrophic Lateral Sclerosis and Other Neurodegenerative Diseases.
Cellular Uptake of Tau Aggregates Triggers Disulfide Bond Formation in Four-Repeat Tau Monomers.
OTUD5 Protects Dopaminergic Neurons by Promoting the Degradation of α-Synuclein in Parkinson's Disease Model.
Antibody-mediated clearance of an ER-resident aggregate that causes glaucoma.
Tetrahydrofolic acid accelerates amyloid fibrillization, decreases cytotoxic oligomers and suppresses their toxicity.
Hydroxycinnamic acids mediated modulation of α-Synuclein fibrillation: Biophysical insights.
Biochemical analysis to study wild-type and polyglutamine-expanded ATXN3 species.
Chaperone Proteins: The Rising Players in Muscle Atrophy.
Overexpression of α-synuclein in PDF neurons alters sleep-wake pattern by regulating lipid metabolism in Drosophila.
Ultrasensitive Protein Aggregate Quantification Assays for Neurodegenerative Diseases on the Simoa Platform.
N-terminus α-synuclein detection reveals new and more diverse aggregate morphologies in multiple system atrophy and Parkinson's disease.
Globular-shaped Aβ oligomers have diverse mechanisms for promoting Aβ aggregations with the facilitation of fibril elongation.
Computational Tools and Methods for the Study of Systemic Amyloidosis at the Clinical and Molecular Level.
Cannabidiol induces autophagy via CB1 receptor and reduces α-synuclein cytosolic levels.
Decreased Hsp90 activity protects against TDP-43 neurotoxicity in a C. elegans model of amyotrophic lateral sclerosis.
BCKDK loss impairs mitochondrial Complex I activity and drives alpha-synuclein aggregation in models of Parkinson's disease.

J Cell Biol. 2025 Feb 03. pii: e202401136. [Epub ahead of print]224(2):

Neuronal constitutive endolysosomal perforations enable α-synuclein aggregation by internalized PFFs.

Anwesha Sanyal, Gustavo Scanavachi, Elliott Somerville, Anand Saminathan, Athul Nair, Ricardo F Bango Da Cunha Correia, Beren Aylan, Ewa Sitarska, Athanasios Oikonomou, Nikos S Hatzakis, Tom Kirchhausen.

Endocytosis, required for the uptake of receptors and their ligands, can also introduce pathological aggregates such as α-synuclein (α-syn) in Parkinson's Disease. We show here the unexpected presence of intrinsically perforated endolysosomes in neurons, suggesting involvement in the genesis of toxic α-syn aggregates induced by internalized preformed fibrils (PFFs). Aggregation of endogenous α-syn in late endosomes and lysosomes of human iPSC-derived neurons (iNs), seeded by internalized α-syn PFFs, caused the death of the iNs but not of the parental iPSCs and non-neuronal cells. Live-cell imaging of iNs showed constitutive perforations in ∼5% of their endolysosomes. These perforations, identified by 3D electron microscopy in iNs and CA1 pyramidal neurons and absent in non-neuronal cells, may facilitate cytosolic access of endogenous α-syn to PFFs in the lumen of endolysosomes, triggering aggregation. Inhibiting the PIKfyve phosphoinositol kinase reduced α-syn aggregation and associated iN death, even with ongoing PFF endolysosomal entry, suggesting that maintaining endolysosomal integrity might afford a therapeutic strategy to counteract synucleinopathies.

DOI: https://doi.org/10.1083/jcb.202401136
J Cell Biol. 2025 Feb 03. pii: e202409104. [Epub ahead of print]224(2):

Synaptic sabotage: How Tau and α-Synuclein undermine synaptic health.

Valerie Uytterhoeven, Patrik Verstreken, Eliana Nachman.

Synaptic dysfunction is one of the earliest cellular defects observed in Alzheimer's disease (AD) and Parkinson's disease (PD), occurring before widespread protein aggregation, neuronal loss, and cognitive decline. While the field has focused on the aggregation of Tau and α-Synuclein (α-Syn), emerging evidence suggests that these proteins may drive presynaptic pathology even before their aggregation. Therefore, understanding the mechanisms by which Tau and α-Syn affect presynaptic terminals offers an opportunity for developing innovative therapeutics aimed at preserving synapses and potentially halting neurodegeneration. This review focuses on the molecular defects that converge on presynaptic dysfunction caused by Tau and α-Syn. Both proteins have physiological roles in synapses. However, during disease, they acquire abnormal functions due to aberrant interactions and mislocalization. We provide an overview of current research on different essential presynaptic pathways influenced by Tau and α-Syn. Finally, we highlight promising therapeutic targets aimed at maintaining synaptic function in both tauopathies and synucleinopathies.

DOI: https://doi.org/10.1083/jcb.202409104
Elife. 2024 Dec 27. pii: RP97228. [Epub ahead of print]13

N-acetylation of α-synuclein enhances synaptic vesicle clustering mediated by α-synuclein and lysophosphatidylcholine.

Chuchu Wang, Chunyu Zhao, Hu Xiao, Jiali Qiang, Zhenying Liu, Jinge Gu, Shengnan Zhang, Dan Li, Yaoyang Zhang, Jacqueline Burré, Jiajia Diao, Cong Liu.

  Previously, we reported that α-synuclein (α-syn) clusters synaptic vesicles (SV) Diao et al., 2013, and neutral phospholipid lysophosphatidylcholine (LPC) can mediate this clustering Lai et al., 2023. Meanwhile, post-translational modifications (PTMs) of α-syn such as acetylation and phosphorylation play important yet distinct roles in regulating α-syn conformation, membrane binding, and amyloid aggregation. However, how PTMs regulate α-syn function in presynaptic terminals remains unclear. Here, based on our previous findings, we further demonstrate that N-terminal acetylation, which occurs under physiological conditions and is irreversible in mammalian cells, significantly enhances the functional activity of α-syn in clustering SVs. Mechanistic studies reveal that this enhancement is caused by the N-acetylation-promoted insertion of α-syn's N-terminus and increased intermolecular interactions on the LPC-containing membrane. N-acetylation in our work is shown to fine-tune the interaction between α-syn and LPC, mediating α-syn's role in synaptic vesicle clustering.

Keywords:  alpha-synuclein; lysophosphatidylcholine; membrane binding; molecular biophysics; mouse; structural biology; synaptic vesicle

DOI:  https://doi.org/10.7554/eLife.97228
RSC Chem Biol. 2024 Dec 19.

Non-enzymatic posttranslational protein modifications in protein aggregation and neurodegenerative diseases.

Tim Baldensperger, Miriam Preissler, Christian F W Becker.

Highly reactive metabolic intermediates and other small molecules frequently react with amino acid side chains, leading to non-enzymatic posttranslational modifications (nPTMs) of proteins. The abundance of these modifications increases under high metabolic activity or stress conditions and can dramatically impact protein structure and function. Although protein quality control mechanisms typically mitigate the effects of these impaired proteins, in long-lived and degradation-resistant proteins, nPTMs accumulate. In some cases, such as cataract development and diabetes, clear links between nPTMs, aging, and disease progression have been established. In neurodegenerative diseases such as Alzheimer's and Parkinson's disease, a key question is whether accumulation of nPTMs is a cause or consequence of protein aggregation. This review focuses on major nPTMs found on proteins with central roles in neurodegenerative diseases such as α-synuclein, β-amyloid, and tau. We summarize current knowledge on the formation of these modifications and discuss their potential impact on disease onset and progression. Additionally, we examine what is known to date about how nPTMs impair cellular detoxification, repair, and degradation systems. Finally, we critically discuss the available methodologies to systematically investigate nPTMs at the molecular level and outline suitable approaches to study their effects on protein aggregation. We aim to foster more research into the role of nPTMs in neurodegeneration by adapting methodologies that have proven successful in studying enzymatic posttranslational modifications. Specifically, we advocate for site-specific incorporation of these modifications into target proteins using advanced chemical and molecular biology techniques.

DOI: https://doi.org/10.1039/d4cb00221k
Elife. 2024 Dec 23. pii: RP86194. [Epub ahead of print]12

Impairment of lipid homeostasis causes lysosomal accumulation of endogenous protein aggregates through ESCRT disruption.

John Yong, Jacqueline E Villalta, Ngoc Vu, Matthew A Kukurugya, Niclas Olsson, Magdalena Preciado López, Julia R Lazzari-Dean, Kayley Hake, Fiona E McAllister, Bryson D Bennett, Calvin H Jan.

  Protein aggregation increases during aging and is a pathological hallmark of many age-related diseases. Protein homeostasis (proteostasis) depends on a core network of factors directly influencing protein production, folding, trafficking, and degradation. Cellular proteostasis also depends on the overall composition of the proteome and numerous environmental variables. Modulating this cellular proteostasis state can influence the stability of multiple endogenous proteins, yet the factors contributing to this state remain incompletely characterized. Here, we performed genome-wide CRISPRi screens to elucidate the modulators of proteostasis state in mammalian cells, using a fluorescent dye to monitor endogenous protein aggregation. These screens identified known components of the proteostasis network and uncovered a novel link between protein and lipid homeostasis. Increasing lipid uptake and/or disrupting lipid metabolism promotes the accumulation of sphingomyelins and cholesterol esters and drives the formation of detergent-insoluble protein aggregates at the lysosome. Proteome profiling of lysosomes revealed ESCRT accumulation, suggesting disruption of ESCRT disassembly, lysosomal membrane repair, and microautophagy. Lipid dysregulation leads to lysosomal membrane permeabilization but does not otherwise impact fundamental aspects of lysosomal and proteasomal functions. Together, these results demonstrate that lipid dysregulation disrupts ESCRT function and impairs proteostasis.

Keywords:  CRISPR; ESCRT; aggregation; cell biology; human; lipid dysregulation; lysosome; proteostasis

DOI:  https://doi.org/10.7554/eLife.86194
ACS Chem Neurosci. 2024 Dec 24.

Inhibition of Phosphorylated Alpha-Synuclein Aggregation by Synthetic Protein Mimetics and Foldamers.

Emily G Oldani, Nicholas H Stillman, Ryan A Dohoney, Charles Zuwu Baysah, Sunil Kumar.

  The formation of Lewy bodies (LB) is a pathological hallmark for synucleinopathies, which is an umbrella term for many diseases, including Parkinson's disease, Lewy body dementia, and multiple system atrophy. One of the main components of LB is the aggregates of phosphorylated modification of α-Synuclein at residue 129 (αS-129), a neuronal protein expressed in the dopaminergic neurons in the brain. There are equivocal results about the role of αS-129, suggesting its involvement in both potentiating pathology and a functional role to rescue pathology. Regardless, a potential therapeutic strategy for LB-based pathologies could be the identification of inhibitors of both αS and αS-129 aggregation. However, to the best of our knowledge, there are no reports of ligands that can potently inhibit the aggregation of αS-129. Our group has recently identified potent antagonists of αS aggregation based on the oligopyridylamide (synthetic protein mimetics) and oligoquinoline (foldamers) scaffolds. Both ligands were potent antagonists of αS aggregation-mediated disease phenotypes in various PD models. Here, we tested both ligands against αS-129 aggregation and the coaggregation of αS and αS-129 (αS/αS-129). Both ligands were potent antagonists of αS-129 aggregation and coaggregation of αS/αS-129 in biophysical and cellular models of PD. Both ligands rescued cell toxicity mediated by the coaggregation of αS/αS-129. To the best of our knowledge, these are the first ligands that potently inhibit the major component of LB. This finding will aid in the development of therapeutic insights into aggregation-related synucleinopathies.

Keywords:  Lewy bodies; alpha-synuclein; oligopyridylamides; oligoquinolines; phosphorylated S129; protein mimetics

DOI:  https://doi.org/10.1021/acschemneuro.4c00546
J Exp Neurol. 2024 ;5(4): 183-191

Protein Citrullination in Amyotrophic Lateral Sclerosis and Other Neurodegenerative Diseases.

Issa O Yusuf, Webb Camille, Paul R Thompson, Zuoshang Xu.

  Protein citrullination (PC) is a posttranslational modification (PTM) that converts a peptidyl arginine into a peptidyl citrulline. Aberrant PC is a hallmark of neurodegenerative diseases, including amyotrophic lateral sclerosis (ALS), Alzheimer's disease, Parkinson's disease, prion disease, and multiple sclerosis. Common among these diseases is a dramatic increase of PC in reactive astrocytes. Some citrullinated proteins have been identified. The most prominent are astrocytic cytoskeletal proteins such as GFAP and vimentin, and myelin protein MBP. Recent investigation in ALS has revealed new changes, including a decreased PC in neurons and an association of PC with myelin protein aggregates. These findings suggest that PC contributes to protein aggregation, neuronal dysfunction, neuroinflammation, and axonal degeneration. However, how PC impact neurodegeneration remains to be understood. Further studies are needed to understand a range of questions, from how PC modulates individual protein functions to its impact on diseases. Because of the PC's robust changes in neurodegenerative diseases, there are also prospects that this PTM may be harnessed as biomarkers, and modulation of this PTM may be an avenue for therapy. In this review, we summarize the current understanding of PC in ALS and other neurodegenerative diseases, the investigative methods for PC, and PC's potential as a biomarker and a therapeutic target.

Keywords:  Alzheimer’s disease; Neurodegenerative disease; Parkinson’s disease

DOI:  https://doi.org/10.33696/neurol.5.101
ACS Chem Neurosci. 2024 Dec 23.

Cellular Uptake of Tau Aggregates Triggers Disulfide Bond Formation in Four-Repeat Tau Monomers.

Brad J Krzesinski, Tyler J Holub, Zachariah Y Gabani, Martin Margittai.

  Oxidative stress is an important driver of aging and has been linked to numerous neurodegenerative disorders, including Alzheimer's disease. A key pathological hallmark of Alzheimer's are filamentous inclusions made of the microtubule associated protein Tau. Based on alternative splicing, Tau protein can feature either three or four microtubule binding repeats. Distinctively, three-repeat Tau contains a single cysteine; four-repeat Tau contains two. Although there is evidence that the cysteines in pathological Tau filaments exist in the reduced form, very little is known about the alternative disulfide-bonded state. It is unclear whether it can exist nontransiently in the reducing environment of the cytosol. Such knowledge, however, is important as different redox states of Tau could modulate aggregation. To address this question, we transfected HEK293 cells expressing the P301S variant of four-repeat Tau with fibril seeds composed of compact, disulfide-bonded Tau monomers. In vitro, these fibrils are observed to recruit only compact Tau, but not Tau in which the cysteines are reduced or replaced by alanines or serines. In line with this characteristic, the fibrils dissociate when treated with a reducing agent. When offered to HEK293 cells, variant Tau protein is recruited to the seeds forming intracellular fibrils with the same seeding properties as the in vitro counterparts. Markedly, the proteins in these fibrils have a compact, disulfide-bonded configuration and dissociate upon reduction. These findings reveal that uptake of exogeneous fibril seeds triggers oxidation of Tau monomers, modulating intracellular aggregation.

Keywords:  Alzheimer’s disease; Tau protein; aggregation; amyloid; conformation; disulfide; fibril; redox switch; seeding barrier; thiol

DOI:  https://doi.org/10.1021/acschemneuro.4c00607
Adv Sci (Weinh). 2024 Dec 25. e2406700

OTUD5 Protects Dopaminergic Neurons by Promoting the Degradation of α-Synuclein in Parkinson's Disease Model.

Xiaomeng Song, Tengfei Liu, Lu Yu, Qiuran Ji, Xin Guo, Runzhe Zong, Yiquan Li, Gan Huang, Qidi Xue, Qingyi Fu, Bingyu Liu, Yi Zheng, Lin Chen, Chengjiang Gao, Huiqing Liu.

  Defective clearance and accumulation of α-synuclein (α-Syn) is the key pathogenic factor in Parkinson's disease (PD). Recent studies emphasize the importance of E3 ligases in regulating the degradation of α-Syn. However, the molecular mechanisms by which deubiquitinases regulate α-Syn degradation are scarcely studied. In this study, it is found that the protein levels of α-Syn are negatively regulated by ovarian tumor protease deubiquitinase 5 (OTUD5) which protects dopaminergic (DA) neurons in the PD model. Mechanistically, OTUD5 promotes K63-linked polyubiquitination of α-Syn independent of its deubiquitinating enzyme activity and mediates its endolysosomal degradation by recruiting the E3 ligase neural precursor cell expressed developmentally downregulated 4 (NEDD4). Furthermore, OTUD5 conditional knockout in DA neurons results in more severe α-Syn related pathology and dyskinesia after injection of α-Syn preformed fibrils (PFF). Overall, the data unveil a novel mechanism to regulate the degradation of α-Syn and provide a new therapeutic strategy to alleviate DA neurodegeneration.

Keywords:  deubiquitinase; endolysosomal pathway; nedd4; otud5; parkinson's disease; α‐synuclein

DOI:  https://doi.org/10.1002/advs.202406700
PNAS Nexus. 2025 Jan;4(1): pgae556

Antibody-mediated clearance of an ER-resident aggregate that causes glaucoma.

Minh Thu Ma, Ahlam N Qerqez, Kamisha R Hill, Laura R Azouz, Hannah A Youngblood, Shannon E Hill, Yemo Ku, Donna M Peters, Jennifer A Maynard, Raquel L Lieberman.

  Recombinant antibodies are a promising class of therapeutics to treat protein misfolding associated with neurodegenerative diseases, and several antibodies that inhibit aggregation are approved or in clinical trials to treat Alzheimer's disease. Here, we developed antibodies targeting the aggregation-prone β-propeller olfactomedin (OLF) domain of myocilin, variants of which comprise the strongest genetic link to glaucoma and cause early onset vision loss for several million individuals worldwide. Mutant myocilin aggregates intracellularly in the endoplasmic reticulum (ER). Subsequent ER stress causes cytotoxicity that hastens dysregulation of intraocular pressure, the primary risk factor for most forms of glaucoma. Our antibody discovery campaign yielded two recombinant antibodies: anti-OLF1 recognizes a linear epitope, while anti-OLF2 is selective for natively folded OLF and inhibits aggregation in vitro. By binding OLF, these antibodies engage autophagy/lysosomal degradation to promote degradation of two pathogenic mutant myocilins. This work demonstrates the potential for therapeutic antibodies to disrupt ER-localized protein aggregates by altering the fate of folding intermediates. This approach could be translated as a precision medicine to treat myocilin-associated glaucoma with in situ antibody expression. More generally, the study supports the approach of enhancing lysosomal degradation to treat proteostasis decline in glaucoma and other diseases.

Keywords:  autophagy; molecular recognition; myocilin; protein misfolding; proteostasis

DOI:  https://doi.org/10.1093/pnasnexus/pgae556
Int J Biol Macromol. 2024 Dec 19. pii: S0141-8130(24)09852-0. [Epub ahead of print]290 139041

Tetrahydrofolic acid accelerates amyloid fibrillization, decreases cytotoxic oligomers and suppresses their toxicity.

Wenqian Wang, Xinming Wu, Qingfu Zhang, Tong Zhang, Luying Jiang, Lili Qu, Fuping Lu, Fufeng Liu.

  Soluble cytotoxic oligomers produced during the fibrillation of both α-synuclein (αS) and amyloid-β protein (Aβ) are key pathogenic factors in Parkinson's disease (PD) and Alzheimer's disease (AD). Reducing toxic oligomers by regulating the aggregation process of αS and Aβ is an important strategy for the treatment of PD and AD. Herein, tetrahydrofolic acid (THF) is found to accelerate amyloid fibrillization, decreases cytotoxic oligomers and suppresses their toxicity. Thioflavin T and atomic force microscopy assays results showed that THF was able to accelerate the formation of dense fibrils from αS and Aβ in a dose-dependent manner. Strikingly, this was accompanied by a reduction in the abundance of toxic oligomers, and these results were confirmed by DB. Meanwhile, MTT and FDA/PI assays demonstrated that THF-induced accelerated fibril formation was accompanied by a reduction in αS- and Aβ-induced cytotoxicity. In addition, the lifespan of genetically modified αS and Aβ expressing C. elegans was extended by feeding THF, although plaque deposits of αS and Aβ increased. These findings suggest that THF enhances the conversion of αS and Aβ oligomers into less toxic fibrils and is a potential therapeutic agent for PD and AD.

Keywords:  Acceleration of aggregation; Amyloid-β; Reduce cytotoxicity; Tetrahydrofolic acid; α-Synuclein

DOI:  https://doi.org/10.1016/j.ijbiomac.2024.139041
Biochem Biophys Res Commun. 2024 Dec 15. pii: S0006-291X(24)01731-5. [Epub ahead of print]744 151195

Hydroxycinnamic acids mediated modulation of α-Synuclein fibrillation: Biophysical insights.

Tinku, Sinjan Choudhary.

  The fibrillation of α-synuclein (α-Syn) is considered a major contributor to Parkinson's disease (PD). Recent therapeutic measures have focused on inhibiting the fibrillation of α-Syn using various small molecules. We report here the effects of two different hydroxycinnamic acids; chlorogenic acid and sinapic acid on α-Syn fibrillation and have also discussed the mechanistic insights into their mode of modulation. The fluorescence spectroscopy shows that the two hydroxycinnamic acids bind with α-Syn with moderate affinity. Molecular docking studies provide a detailed insights into binding at the residue level and isothermal titration calorimetry reveals specific interactions, like hydrogen bonding, hydrophobic interactions, and van der Waals forces involved in the binding process. Fibrillation kinetics and transmission microscopic studies demonstrated that both chlorogenic acid and sinapic acid attenuate α-Syn fibrillation in a concentration dependent manner. Circular dichroism spectroscopy shows that these compounds bind with α-Syn and delay its structural transition in β-sheet containing fibrillar structures. Both the compounds are also effective even if added after the onset of fibrillation and the fibrillar species formed in the presence of these acids are unable to induce secondary nucleation in monomeric α-Syn. Such kind of structural and mechanistic insights are extremely crucial for designing therapeutic intervention in PD and other neurodegenerative diseases.

Keywords:  Fluorescence spectroscopy; Inhibition; Isothermal titration calorimetry; Protein fibrillation; α-synuclein

DOI:  https://doi.org/10.1016/j.bbrc.2024.151195
PLoS One. 2024 ;19(12): e0315868

Biochemical analysis to study wild-type and polyglutamine-expanded ATXN3 species.

Grégoire Quinet, María Cristina Paz-Cabrera, Raimundo Freire.

Spinocerebellar ataxia type 3 (SCA3) is a cureless neurodegenerative disease recognized as the most prevalent form of dominantly inherited ataxia worldwide. The main hallmark of SCA3 is the expansion of a polyglutamine tract located in the C-terminal of Ataxin-3 (or ATXN3) protein, that triggers the mis-localization and toxic aggregation of ATXN3 in neuronal cells. The propensity of wild type and polyglutamine-expanded ATXN3 proteins to aggregate has been extensively studied over the last decades. In vitro studies with mass spectrometry techniques revealed a time-dependent aggregation of polyglutamine-expanded ATXN3 that occurs in several steps, leading to fibrils formation, a high status of aggregation. For in vivo experiments though, the techniques commonly used to demonstrate aggregation of polyglutamine proteins, such as filter trap assays, SDS-PAGE and SDS-AGE, are unable to unequivocally show all the stages of aggregation of wild type and polyglutamine-expanded ATXN3 proteins. Here we describe a systematic and detailed analysis of different known techniques to detect the various forms of both wild type and pathologic ATXN3 aggregates, and we discuss the power and limitation of each strategy.

DOI: https://doi.org/10.1371/journal.pone.0315868
J Cachexia Sarcopenia Muscle. 2024 Dec 20.

Chaperone Proteins: The Rising Players in Muscle Atrophy.

Davide Acquarone, Alessandro Bertero, Mara Brancaccio, Matteo Sorge.

  Despite significant progress in understanding the molecular aetiology of muscle atrophy, there is still a great need for new targets and drugs capable of counteracting muscle wasting. The role of an impaired proteostasis as the underlying causal mechanism of muscle atrophy is a well-established concept. From the earliest work on muscle atrophy and the identification of the first atrogenes, the hyper-activation of the proteolytic systems, such as autophagy and the ubiquitin proteasome system, has been recognized as the major driver of atrophy. However, the role of other key regulators of proteostasis, the chaperone proteins, has been largely overlooked. Chaperone proteins play a pivotal role in protein folding and in preventing the aggregation of misfolded proteins. Indeed, some chaperones, such as αB-crystallin and Hsp25, are involved in compensatory responses aimed at counteracting protein aggregation during sarcopenia. Chaperones also regulate different intracellular signalling pathways crucial for atrogene expression and the control of protein catabolism, such as the AKT and NF-kB pathways, which are regulated by Hsp70 and Hsp90. Furthermore, the downregulation of certain chaperones causes severe muscle wasting per se and experimental strategies aimed at preventing this downregulation have shown promising results in mitigating or reversing muscle atrophy. This highlights the therapeutic potential of targeting chaperones and confirms their crucial anti-atrophic functions. In this review, we summarize the most relevant data showing the modulation and the causative role of chaperone proteins in different types of skeletal muscle atrophies.

Keywords:  cachexia; chaperone proteins; heat shock proteins; muscle atrophy; proteostasis; sarcopenia

DOI:  https://doi.org/10.1002/jcsm.13659
Sleep. 2024 Dec 21. pii: zsae297. [Epub ahead of print]

Overexpression of α-synuclein in PDF neurons alters sleep-wake pattern by regulating lipid metabolism in Drosophila.

Dong Xia, Ying Chen, Xiang Fu, Hui-Yi Liu, Mu-Yan Sun, Fen Wang, Yong Zhang, Chun-Feng Liu, Jun-Yi Liu.

  Parkinson's disease (PD) is a complex neurodegenerative disorder, characterized by the aggregation of α-synuclein (α-syn). Current research increasingly indicates the prevalence of sleep-wake disorders in early-stage PD, although the underlying pathogenic mechanisms remain unclear. In this study, transgenic Drosophila models were utilized to observe excessive daytime sleepiness and impaired anticipation in flies overexpressing α-syn in pan-neurons and circadian clock neurons. Additionally, deficits in projection of Pigment Dispersing Factor (PDF) neuron terminals, which are involved in Drosophila sleep and circadian rhythm, were identified. An imbalance in lipid metabolism homeostasis was detected in the brains of α-syn overexpressing mutants. Ultimately, the inhibition of Sterol Regulatory Element-Binding Protein (SREBP) activity led to an improvement in the reduced daytime sleep duration phenotype. Our results suggest that lipid pathways play a role in sleep-wake disorders triggered by α-syn mutation and aggregation, thereby providing valuable insights into potential therapeutic avenues for disrupted sleep patterns associated with PD.

Keywords:  Parkinson’s disease; Pigment Dispersing Factor neuron; lipid metabolism; sleep-wake pattern; α-synuclein

DOI:  https://doi.org/10.1093/sleep/zsae297
Anal Chem. 2024 Dec 24.

Ultrasensitive Protein Aggregate Quantification Assays for Neurodegenerative Diseases on the Simoa Platform.

Dorothea Böken, Zengjie Xia, Jeff Y L Lam, Emre Fertan, Yunzhao Wu, Elizabeth A English, Juraj Konc, Florence Layburn, Gonçalo J L Bernardes, Henrik Zetterberg, Matthew R Cheetham, David Klenerman.

Nanoscale aggregates play a key role in the pathogenesis of neurodegenerative disorders such as Alzheimer's and Parkinson's disease. However, quantifying these aggregates in complex biological samples, such as biofluids and postmortem brain tissue, has been challenging due to their low concentration and small size, necessitating the development of methods with high sensitivity and specificity. Here, we have developed ultrasensitive assays utilizing the Quanterix Simoa platform to detect α-synuclein, β-amyloid and tau aggregates, including those with common posttranslational modifications such as truncation of α-synuclein and AT8 phosphorylation of tau aggregates. All assays had a detection limit in the low pM range. As a part of this work, we developed silica-nanoparticle calibrators, allowing for the quantification of all aggregates. These assays were validated for aggregate and target specificity through denaturation and cross-reactivity experiments. We then applied these assays to brain homogenate samples from Alzheimer's disease and control samples, demonstrating their applicability to postmortem tissue. Lastly, we explored the potential of these assays for blood-based diagnostics by detecting aggregates in serum samples from early Alzheimer's disease patients.

DOI: https://doi.org/10.1021/acs.analchem.4c04188
Transl Neurodegener. 2024 Dec 27. 13(1): 67

N-terminus α-synuclein detection reveals new and more diverse aggregate morphologies in multiple system atrophy and Parkinson's disease.

James A Wiseman, YuHong Fu, Richard L M Faull, Clinton P Turner, Maurice A Curtis, Glenda M Halliday, Birger V Dieriks.

   BACKGROUND: Parkinson's disease (PD) and multiple system atrophy (MSA) are classified as α-synucleinopathies and are primarily differentiated by their clinical phenotypes. Delineating these diseases based on their specific α-synuclein (α-Syn) proteoform pathologies is crucial for accurate antemortem biomarker diagnosis. Newly identified α-Syn pathologies in PD raise questions about whether MSA exhibits a similar diversity. This prompted the need for a comparative study focusing on α-Syn epitope-specific immunoreactivities in both diseases, which could clarify the extent of pathological overlap and diversity, and guide more accurate biomarker development.
METHODS: We utilised a multiplex immunohistochemical approach to detect multiple structural domains of α-Syn proteoforms across multiple regions prone to pathological accumulation in MSA (n = 10) and PD (n = 10). Comparison of epitope-specific α-Syn proteoforms was performed in the MSA medulla, inferior olivary nucleus, substantia nigra, hippocampus, and cerebellum, and in the PD olfactory bulb, medulla, substantia nigra, hippocampus, and entorhinal cortex.
RESULTS: N-terminus and C-terminus antibodies detected significantly more α-Syn pathology in MSA than antibodies for phosphorylated (pS129) α-Syn, which are classically used to detect α-Syn. Importantly, C-terminus immunolabelling is more pronounced in MSA compared to PD. Meanwhile, N-terminus immunolabelling consistently detected the highest percentage of α-Syn across pathologically burdened regions of both diseases, which could be of biological significance. As expected, oligodendroglial involvement distinguished MSA from PD, but in contrast to PD, no substantial astrocytic or microglial α-Syn accumulation in MSA occurred. These data confirm glial-specific changes between these diseases when immunolabelling the N-terminus epitope. In comparison, N-terminus neuronal α-Syn was present in PD and MSA, with most MSA neurons lacking pS129 α-Syn proteoforms. This explains why characterisation of neuronal MSA pathologies is lacking and challenges the reliance on pS129 antibodies for the accurate quantification of α-Syn pathological load across α-synucleinopathies.
CONCLUSIONS: These findings underscore the necessity of utilising a multiplex approach to detect α-Syn, most importantly including the N-terminus, to capture the entire spectrum of α-Syn proteoforms in α-synucleinopathies. The data provide novel insights toward the biological differentiation of these α-synucleinopathies and pave the way for more refined antemortem diagnostic methods to facilitate early identification and intervention of these neurodegenerative diseases.

Keywords:  Epitope-specific; Lewy body diseases; Multiple system atrophy; Multiplex; N-terminus; Parkinson’s disease; Truncational variants; α-Synuclein

DOI:  https://doi.org/10.1186/s40035-024-00456-3
Neurobiol Dis. 2024 Dec 22. pii: S0969-9961(24)00377-2. [Epub ahead of print] 106775

Globular-shaped Aβ oligomers have diverse mechanisms for promoting Aβ aggregations with the facilitation of fibril elongation.

Hiroto Nakano, Sadao Hikishima, Makoto Mori, Jota Minamikawa, Daiki Muramatsu, Yasuhiro Sakashita, Tokuhei Ikeda, Moeko Noguchi-Shinohara, David B Teplow, Kenjiro Ono.

  The accumulation of amyloid β-proteins (Aβ) in the extracellular space, forming insoluble plaques, is a primary pathological process underlying Alzheimer's disease (AD). Among the various Aβ species that appear during Aβ aggregation, Aβ oligomers are considered the most neurotoxic form. However, the precise mechanisms of their molecular functions within the Aβ aggregation cascade have not been clarified so far. This research aimed to uncover the structural and functional characteristics of globular-shaped Aβ oligomers (gAβO) under in vitro conditions. We performed thioflavin T (ThT) assays on low-molecular-weight (LMW) Aβ42, testing different concentrations of Aβ42 mature fibril (MF) seeds and gAβO. Fibril formation was continuously observed using high-speed atomic force microscopy (HS-AFM) in LMW Aβ42 with different sample conditions. Conformational changes of Aβ42 aggregates in the presence of gAβO was also evaluated using circular dichroism spectroscopy. The results of the ThT analysis and HS-AFM observation indicated that gAβO promoted fibril formation of LMW Aβ42 while gAβO itself did not form fibrous aggregates, indicating that gAβO would have a catalytic effects on LMW Aβ42 aggregation. We also showed that the molecular interaction of gAβO was altered by the presence and amount of MF seeds in the reaction buffers, indicating that complex interactions would exist among different Aβ species. The results of our present research demonstrated that gAβO would have significant roles to accelerate Aβ aggregation in AD pathogenesis. 225 < 250 words.

Keywords:  Alzheimer's disease; Aβ; Globular-shaped Aβ oligomer; High-molecular-weight Aβ oligomer; High-speed atomic force microscopy

DOI:  https://doi.org/10.1016/j.nbd.2024.106775
Methods Mol Biol. 2025 ;2884 369-387

Computational Tools and Methods for the Study of Systemic Amyloidosis at the Clinical and Molecular Level.

Dario Di Silvestre, Francesca Brambilla, Giampaolo Merlini, Pierluigi Mauri.

  Amyloidosis diseases are characterized by protein misfolding, which forms insoluble beta-sheet fibrils progressively deposited in tissues. Deposition in the form of amyloid aggregates can occur in various organs, damaging their structure and function. The hallmark of amyloidosis is aberrant interactions leading to protein aggregation and proteotoxicity. Accordingly, amyloidosis-related samples represent a valuable source of information to generate new knowledge useful for diagnostic, prognostic, and therapeutic purposes. In this scenario, we outline the path to apply computational methods and strategies based on the combination of proteomics and systems biology approaches. In addition to algorithms useful for subtyping amyloid deposits or assessing proteome recovery after drug treatment, our chapter provides workflows based on protein-protein interaction and protein co-expression network models. In particular, the main steps to reconstruct and analyze them at both functional and topological levels are described. Our chapter aims to provide tools and instructions to identify and monitor prognostic, diagnostic, and therapeutic markers and to shed light on the processes, pathways, and functions affected by amyloidogenic proteins.

Keywords:  Amyloidosis; Diagnosis; Hubs; PPI; Protein co-expression; Proteome recovery; Proteomics

DOI:  https://doi.org/10.1007/978-1-0716-4298-6_22
Brain Res. 2024 Dec 20. pii: S0006-8993(24)00669-3. [Epub ahead of print]1850 149414

Cannabidiol induces autophagy via CB1 receptor and reduces α-synuclein cytosolic levels.

Adolfo G Erustes, Vanessa C Abílio, Claudia Bincoletto, Mauro Piacentini, Gustavo J S Pereira, Soraya S Smaili.

  Numerous studies have explored the role of cannabinoids in neurological conditions, chronic pain and neurodegenerative diseases. Restoring autophagy has been proposed as a potential target for the treatment of neurodegenerative diseases. In our study, we used a neuroblastoma cell line that overexpresses wild-type α-synuclein to investigate the effects of cannabidiol on autophagy modulation and reduction in the level of cytosolic α-synuclein. Our results demonstrated that cannabidiol enhances the accumulation of LC3-II- and GFP-LC3-positive vesicles, which indicates an increase in autophagic flux. In addition, cannabidiol-treated cells showed a reduction in cytosolic α-synuclein levels. These effects were inhibited when the cells were treated with a CB1 receptor-selective antagonist, which indicates that the biological effects of cannabidiol are mediated via its interaction with CB1 receptor. Additionally, we also observed that cannabinoid compounds induce autophagy and α-synuclein degradation after they interact with the CB1 receptor. In summary, our data suggest that cannabidiol induces autophagy and reduces cytosolic α-synuclein levels. These biological effects are mediated preferentially through the interaction of cannabidiol with CB1 receptors, and therefore, cannabinoid compounds that act selectively on this receptor could represent a new approach for autophagy modulation and degradation of protein aggregates.

Keywords:  Autophagy; Cannabidiol; Cannabinoid receptors; Cannabis sp.; α-synuclein, Parkinson’s disease

DOI:  https://doi.org/10.1016/j.brainres.2024.149414
PLoS Genet. 2024 Dec 26. 20(12): e1011518

Decreased Hsp90 activity protects against TDP-43 neurotoxicity in a C. elegans model of amyotrophic lateral sclerosis.

Laura Garcia-Toscano, Heather N Currey, Joshua C Hincks, Jade G Stair, Nicolas J Lehrbach, Nicole F Liachko.

Neuronal inclusions of hyperphosphorylated TDP-43 are hallmarks of disease for most patients with amyotrophic lateral sclerosis (ALS). Mutations in TARDBP, the gene coding for TDP-43, can cause some cases of familial inherited ALS (fALS), indicating dysfunction of TDP-43 drives disease. Aggregated, phosphorylated TDP-43 may contribute to disease phenotypes; alternatively, TDP-43 aggregation may be a protective cellular response sequestering toxic protein away from the rest of the cell. The heat shock responsive chaperone Hsp90 has been shown to interact with TDP-43 and stabilize its normal conformation; however, it is not known whether this interaction contributes to neurotoxicity in vivo. Using a C. elegans model of fALS mutant TDP-43 proteinopathy, we find that loss of function of HSP-90 protects against TDP-43 neurotoxicity and subsequent neurodegeneration in adult animals. This protection is accompanied by a decrease in both total and phosphorylated TDP-43 protein. We also find that hsp-90 mutation or inhibition upregulates key stress responsive heat shock pathway gene expression, including hsp-70 and hsp-16.1, and we demonstrate that normal levels of hsp-16.1 are required for hsp-90 mutation effects on TDP-43. We also observe that the neuroprotective effect due to HSP-90 dysfunction does not involve direct regulation of proteasome activity in C. elegans. Our data demonstrate for the first time that Hsp90 chaperone activity contributes to adverse outcomes in TDP-43 proteinopathies in vivo using a whole animal model of ALS.

DOI: https://doi.org/10.1371/journal.pgen.1011518
Acta Neuropathol Commun. 2024 Dec 21. 12(1): 198

BCKDK loss impairs mitochondrial Complex I activity and drives alpha-synuclein aggregation in models of Parkinson's disease.

Aya Jishi, Di Hu, Yutong Shang, Rihua Wang, Steven A Gunzler, Xin Qi.

Mitochondrial dysfunction and α-synuclein (αSyn) aggregation are key contributors to Parkinson's Disease (PD). While genetic and environmental risk factors, including mutations in mitochondrial-associated genes, are implicated in PD, the precise mechanisms linking mitochondrial defects to αSyn pathology remain incompletely understood, hindering the development of effective therapeutic interventions. Here, we identify the loss of branched chain ketoacid dehydrogenase kinase (BCKDK) as a mitochondrial risk factor that exacerbates αSyn pathology by disrupting Complex I function. Our findings reveal a consistent downregulation of BCKDK in dopaminergic (DA) neurons from A53T-αSyn mouse models, PD patient-derived induced pluripotent stem (iPS) cells, and postmortem brain tissues. BCKDK deficiency leads to mitochondrial dysfunction, including reduced membrane potential and increased reactive oxygen species (ROS) production upon administration of a stressor, which in turn promotes αSyn oligomerization. Mechanistically, BCKDK interacts with the NDUFS1 subunit of Complex I to stabilize its function. Loss of BCKDK disrupts this interaction, leading to Complex I destabilization and enhanced αSyn aggregation. Notably, restoring BCKDK expression in neuron-like cells rescues mitochondrial integrity and restores Complex I activity. Similarly, in patient-derived iPS cells differentiated to form dopaminergic neurons, NDUFS1 and phosphorylated aSyn levels are partially restored upon BCKDK expression. These findings establish a mechanistic link between BCKDK deficiency, mitochondrial dysfunction, and αSyn pathology in PD, positioning BCKDK as a potential therapeutic target to mitigate mitochondrial impairment and neurodegeneration in PD.

DOI: https://doi.org/10.1186/s40478-024-01915-8