bims-proned Biomed News
on Proteostasis in neurodegeneration
Issue of 2024‒01‒07
twenty papers selected by
Verena Kohler, Umeå University

  1. ACS Chem Neurosci. 2024 Jan 02.
      Progressive loss of dopaminergic (DA) neurons in the substantia nigra pars compacta, hypothalamus, and thalamus is a hallmark of Parkinson's disease. Neuronal death is linked to the abrupt aggregation of α-synuclein (α-Syn), a small membrane protein that regulates cell vesicle trafficking. α-Syn aggregation rate, as well as the secondary structure and toxicity of α-Syn fibrils, could be uniquely altered by lipids. However, molecular mechanisms that determine such a remarkable difference in the toxicity of α-Syn fibrils formed in the presence of lipids remain unclear. In this study, we used a set of molecular assays to determine the molecular mechanism by which α-Syn fibrils formed in the presence of phosphatidylcholine (PC), cardiolipin (CL), and cholesterol (Cho) exert cell toxicity. We found that rat dopaminergic cells exposed to α-Syn fibrils formed in the presence of different lipids exert drastically different magnitudes and dynamics of unfolded protein response (UPR) in the endoplasmic reticulum (ER) and mitochondria (MT). Specifically, α-Syn:CL were found to cause the strongest, whereas α-Syn fibrils formed in the absence of lipids had the lowest magnitude of the UPR cell response. We also found the opposite dynamics of the ER- and MT-UPR responses in rat dopaminergic cells exposed to protein aggregates. These results could suggest that facing severe ER stress, dopaminergic cells suppress MT-UPR response, enabling the maximal ATP production to restore their normal physiological function. These findings help to better understand complex mechanisms of cell toxicity of amyloid aggregates and ultimately find neuroprotective drug candidates that will be able to suppress the spread of Parkinson's disease.
    Keywords:  cardiolipin; cholesterol; mitochondria; phosphatidylcholine; unfolded protein response; α-synuclein
  2. Biophys J. 2024 Jan 04. pii: S0006-3495(24)00001-8. [Epub ahead of print]
      Phosphorylated TAR DNA-binding protein of 43 kDa (TDP-43) is present within the aggregates of several age-related neurodegenerative disorders, such as amyotrophic lateral sclerosis (ALS), frontotemporal lobar degeneration (FTLD) and Alzheimer's disease, to the point that the presence of phosphorylated TDP-43 is considered a hallmark of some of these diseases. The majority of known TDP-43 phosphorylation sites detected in ALS/FTLD patients is located in the low complexity domain (LCD), the same domain that has been shown to be critical for TDP-43 liquid-liquid phase separation (LLPS). However, the effect of these LCD phosphorylation sites on TDP-43 LLPS has been largely unexplored, and any work that has been done has largely focused on sites near the C-terminal end of the LCD. Here, we used a phosphomimetic approach to explore the impact of phosphorylation at residues S332 and S333, sites located within the transiently α-helical region of TDP-43 that have been observed to be phosphorylated in disease, on protein LLPS. Our turbidimetry and fluorescence microscopy data demonstrate that these phosphomimetic substitutions greatly suppress LLPS, and solution NMR data strongly suggest that this effect is at least in part due to the loss of α-helical propensity of the phosphomimetic protein variant. We also show that the S332D and S333D substitutions slow TDP-43 LCD droplet aging and fibrillation of the protein. Overall, these findings provide a biophysical basis for understanding the effect of phosphorylation within the transiently α-helical region of TDP-43 LCD on protein LLPS and fibrillation, suggesting that phosphorylation at residues 332 and 333 is not necessarily directly related to the pathogenic process.
    Keywords:  TAR DNA-binding protein of 43 kDa (TDP-43); amyotrophic lateral sclerosis (ALS) (Lou Gehrig disease); intrinsically-disordered protein; liquid-liquid phase separation; neurodegenerative diseases; protein aggregation; protein phosphorylation
  3. Neurosci Lett. 2023 Dec 27. pii: S0304-3940(23)00569-4. [Epub ahead of print] 137610
      BACKGROUND: Protein misfolding and inclusion body aggregation caused by α-Syn mutations in the brain often cause neurodegeneration and cognitive impairment, among which the A53T point mutation is more common. Inhibition of adenosine A2A receptor (A2AR) can alleviate the pathological symptoms of brain dysfunction caused by A53T-α-Syn protofibrils, but the mechanism of action is still unclear.AIM: This studies aimed to investigate the potential therapeutic role of the A2AR inhibitor KW6002 in a mouse model of brain synucleinopathy.
    METHODS: A53T-α-Syn fibre precursor cell nuclear protein was injected into the bilateral prefrontal cortex of mice to establish a synucleinopathy animal model, and the A2AR inhibitor KW6002 (5 mg/kg) was injected intraperitoneally to intervene.
    RESULT: The intracerebral injection of A53T-α-Syn protofibrils triggers the formation of inclusion bodies in the brain, leading to astrocyte activation, an increased number of apoptotic cells, and suppression of autophagic flux. The administration of KW6002 significantly reversed these phenomena. In vitro experiments revealed that A53T-α-Syn protofibrils inhibited HT-22 autophagy in mouse hippocampal neuronal cells, whereas KW6002 increased cellular autophagic flux, upregulated the expression of LAMP2A and Hsc70 proteins and inhibited the expression of SQSTM1 protein. The present study suggests that KW6002 reduces the level of α-Syn phosphorylation by inhibiting A2AR protein, at the same time, enhances the autophagic flux of neuronal cells, resulting in the degradation of A53T-α-Syn protofibrils and thus reducing the neuronal toxicity and apoptosis induced by A53T-α-Syn protofibrils.
    CONCLUSION: KW6002 has a significant protective effect on neuronal injury induced by A53T-α-Syn.
    Keywords:  Adenosine A2A receptor; Autophagic flux; Autophagosome; Folding protein degradation; HT-22 cells
  4. Nihon Yakurigaku Zasshi. 2024 ;159(1): 2-5
      The advent of a super-aged society poses urgent challenges in overcoming age-related neurological disorders and extending a healthy lifespan. Neurodegenerative diseases such as Alzheimer's disease, dementia with Lewy bodies, and Parkinson's disease are characterized by the accumulation of pathogenic proteins in the brain, leading to the formation of intracellular aggregates known as pathological hallmarks. In the early stages of protein accumulation, before the onset of clinical symptoms such as cognitive impairment or motor dysfunction, brain inflammation begins to occur. Subsequently, neuronal death progresses, and clinical symptoms manifest as dementia or Parkinson's disease. Therefore, there is a need for early prediction of neurodegeneration and the development of disease-modifying drugs for pre-symptomatic prevention. To address this issue, we have focused on enhancing the degradation of amyloid-β protein by targeting Ca2+/calmodulin-dependent kinase II (CaMKII)/proteasome system and on suppressing the propagation and uptake mechanisms of α-synuclein by targeting fatty acid-binding proteins (FABPs) coupled with the long isoform of dopamine D2 (D2L) receptor. Additionally, our analysis of FABP knockout mice has revealed an increased expression of FABPs in the neurodegenerative process, suggesting their involvement in mitochondrial dysfunction and neuronal death. Based on these findings, this article highlights the physiological significance of FABP family proteins in neurodegeneration and discusses the analysis of plasma biomarkers for predicting neurodegenerative disorders and the discriminatory methods for distinguishing between Alzheimer's disease, dementia with Lewy bodies, and Parkinson's disease. Furthermore, we explore the potential of ultra-early prediction of neurodegenerative disorders.
  5. NPJ Parkinsons Dis. 2024 Jan 02. 10(1): 2
      Highly specialized microtubules in neurons are crucial to both health and disease of the nervous system, and their properties are strictly regulated by different post-translational modifications, including α-Tubulin acetylation. An imbalance in the levels of acetylated α-Tubulin has been reported in experimental models of Parkinson's disease (PD) whereas pharmacological or genetic modulation that leads to increased acetylated α-Tubulin successfully rescues axonal transport defects and inhibits α-Synuclein aggregation. However, the role of acetylation of α-Tubulin in the human nervous system is largely unknown as most studies are based on in vitro evidence. To capture the complexity of the pathological processes in vivo, we analysed post-mortem human brain of PD patients and control subjects. In the brain of PD patients at Braak stage 6, we found a redistribution of acetylated α-Tubulin, which accumulates in the neuronal cell bodies in subcortical structures but not in the cerebral cortex, and decreases in the axonal compartment, both in putamen bundles of fibres and in sudomotor fibres. High-resolution and 3D reconstruction analysis linked acetylated α-Tubulin redistribution to α-Synuclein oligomerization and to phosphorylated Ser 129 α-Synuclein, leading us to propose a model for Lewy body (LB) formation. Finally, in post-mortem human brain, we observed threadlike structures, resembling tunnelling nanotubes that contain α-Synuclein oligomers and are associated with acetylated α-Tubulin enriched neurons. In conclusion, we support the role of acetylated α-Tubulin in PD pathogenesis and LB formation.
  6. J Integr Neurosci. 2023 Oct 23. 22(6): 145
      Fluctuations in mechanical force vectors within living cells can substantially influence the behavior and functions of proteins. Tau protein can spontaneously be raptured and entangled in refolding under picoNewton compressive forces that are biologically available in a living cell: a hidden aggregation pathway due to stress and crowding. Our findings were achieved through a customized modification of atomic force microscopy (AFM) for single-molecule manipulation. This previously hidden phenomenon of proteins rupturing collectively while subsequently and spontaneously refolding into a complex entangled conformation, distinct from the Tau protein's folded or unfolded states, could potentially explain the early-event initiation of the aggregation of the Tau protein seen in various neurodegenerative diseases. This article introduces our recent discovery of the missing Tau protein property that is of significant relevance to the Tau protein and neurodegenerative disease research and medical treatment, aiming to stimulate the collective observation and a new perspective on the Tau aggregation mechanism and disease mechanism studies.
    Keywords:  Tau protein; aggregation; mechanical force; neuronal degenerate diseases
  7. bioRxiv. 2023 Dec 14. pii: 2023.12.13.571598. [Epub ahead of print]
      The microtubule-associated protein tau is implicated in neurodegenerative diseases characterized by amyloid formation. Mutations associated with frontotemporal dementia increase tau aggregation propensity and disrupt its endogenous microtubule-binding activity. The structural relationship between aggregation propensity and biological activity remains unclear. We employed a multi-disciplinary approach, including computational modeling, NMR, cross-linking mass spectrometry, and cell models to design tau sequences that stabilize its structural ensemble. Our findings reveal that substitutions near the conserved 'PGGG' beta-turn motif can modulate local conformation, more stably engaging in interactions with the 306 VQIVYK 311 amyloid motif to decrease aggregation in vitro and in cells. Designed tau sequences maintain microtubule binding and explain why 3R isoforms of tau exhibit reduced pathogenesis over 4R isoforms. We propose a simple mechanism to reduce the formation of pathogenic species while preserving biological function, offering insights for therapeutic strategies aimed at reducing protein misfolding in neurodegenerative diseases.
  8. Res Sq. 2023 Dec 11. pii: [Epub ahead of print]
      Proteostasis is maintained through regulated protein synthesis and degradation and chaperone-assisted protein folding. However, this is challenging in neuronal projections because of their polarized morphology and constant synaptic proteome remodeling. Using high-resolution fluorescence microscopy, we discovered that neurons localize a subset of chaperone mRNAs to their dendrites and use microtubule-based transport to increase this asymmetric localization following proteotoxic stress. The most abundant dendritic chaperone mRNA encodes a constitutive heat shock protein 70 family member (HSPA8). Proteotoxic stress also enhanced HSPA8 mRNA translation efficiency in dendrites. Stress-mediated HSPA8 mRNA localization to the dendrites was impaired by depleting fused in sarcoma-an amyotrophic lateral sclerosis-related protein-in cultured mouse motor neurons and expressing a pathogenic variant of heterogenous nuclear ribonucleoprotein A2/B1 in neurons derived from human induced pluripotent stem cells. These results reveal a crucial and unexpected neuronal stress response in which RNA-binding proteins increase the dendritic localization of HSPA8 mRNA to maintain proteostasis and prevent neurodegeneration.
  9. J Mol Med (Berl). 2024 Jan 02.
      The pathological aggregation and misfolding of tau and amyloid-β play a key role in Alzheimer's disease (AD). However, the underlying pathological mechanisms remain unclear. Emerging evidences indicate that liquid-liquid phase separation (LLPS) has great impacts on regulating human health and diseases, especially neurodegenerative diseases. A series of studies have revealed the significance of LLPS in AD. In this review, we summarize the latest progress of LLPS in AD, focusing on the impact of metal ions, small-molecule inhibitors, and proteinaceous partners on tau LLPS and aggregation, as well as toxic oligomerization, the role of LLPS on amyloid-β (Aβ) aggregation, and the cross-interactions between amyloidogenic proteins in AD. Eventually, the fundamental methods and techniques used in LLPS study are introduced. We expect to present readers a deeper understanding of the relationship between LLPS and AD.
    Keywords:  Alzheimer’s disease; Amyloidogenic proteins; Liquid–liquid phase separation; Tau
  10. Proc Natl Acad Sci U S A. 2024 Jan 09. 121(2): e2309700120
      α-, β-, and γ-Synuclein are intrinsically disordered proteins implicated in physiological processes in the nervous system of vertebrates. α-synuclein (αSyn) is the amyloidogenic protein associated with Parkinson's disease and certain other neurodegenerative disorders. Intensive research has focused on the mechanisms that cause αSyn to form amyloid structures, identifying its NAC region as being necessary and sufficient for amyloid assembly. Recent work has shown that a 7-residue sequence (P1) is necessary for αSyn amyloid formation. Although γ-synuclein (γSyn) is 55% identical in sequence to αSyn and its pathological deposits are also observed in association with neurodegenerative conditions, γSyn is resilient to amyloid formation in vitro. Here, we report a rare single nucleotide polymorphism (SNP) in the SNCG gene encoding γSyn, found in two patients with amyotrophic lateral sclerosis (ALS). The SNP results in the substitution of Met38 with Ile in the P1 region of the protein. These individuals also had a second, common and nonpathological, SNP in SNCG resulting in the substitution of Glu110 with Val. In vitro studies demonstrate that the Ile38 variant accelerates amyloid fibril assembly. Contrastingly, Val110 retards fibril assembly and mitigates the effect of Ile38. Substitution of residue 38 with Leu had little effect, while Val retards, and Ala increases the rate of amyloid formation. Ile38 γSyn also results in the formation of γSyn-containing inclusions in cells. The results show how a single point substitution can enhance amyloid formation of γSyn and highlight the P1 region in driving amyloid formation in another synuclein family member.
    Keywords:  ALS; aggregation; amyloid; oligomers; γ-synuclein
  11. J Integr Neurosci. 2023 Nov 23. 22(6): 166
      BACKGROUND: Synucleinopathies, which are major pathological features of Parkinson's disease (PD), are characterized by misfolded aggregates of α-synuclein in the peripheral and central nervous system. Icariin (ICA) is the main active component of Epimedium flavonoids. Our previous study found that ICA decreases α-synuclein expression in APPV717I transgenic mice.METHODS: The aim of the present study was to examine the potential applications and mechanisms of ICA in PD using A53T α-synuclein transgenic (A53T Tg) mice. After 3 months of intragastric ICA administration, rotarod and pole tests were used to assess behavioral changes in A53T Tg mice at 8 and 13 months of age. SH-SY5Y cells over-expressing wild-type α-synuclein were used to further examine the pharmacological effect and underlying mechanism of ICA. Western blotting and immunocytochemistry were used to detect the expression levels of α-synuclein and its related proteins.
    RESULTS: ICA significantly improved the impaired motor function and coordination in A53T Tg mice. It also decreased the expression, Ser129 phosphorylation, and aggregation of α-synuclein in SH-SY5Y cells transfected with α-synuclein and the striatum of A53T Tg mice. Moreover, ICA increased the expression of parkin, which is associated with the ubiquitin-proteasome system (UPS), and decreased the level of polo-like kinase 2 (PLK2), an enzyme that phosphorylates α-synuclein.
    CONCLUSIONS: ICA alleviated motor impairments in A53T mice, an effect which may be associated with the decreased phosphorylation and aggregation of α-synuclein through PLK2 and parkin regulation.
    Keywords:  PLK2; icariin; motor impairment; parkin; synucleinopathy; α-synuclein
  12. Brain Res. 2023 Dec 29. pii: S0006-8993(23)00513-9. [Epub ahead of print]1826 148742
      The Endoplasmic reticulum (ER), a critical cellular organelle, maintains cellular homeostasis by regulating calcium levels and orchestrating essential functions such as protein synthesis, folding, and lipid production. A pivotal aspect of ER function is its role in protein quality control. When misfolded proteins accumulate within the ER due to factors like protein folding chaperone dysfunction, toxicity, oxidative stress, or inflammation, it triggers the Unfolded protein response (UPR). The UPR involves the activation of chaperones like calnexin, calreticulin, glucose-regulating protein 78 (GRP78), and Glucose-regulating protein 94 (GRP94), along with oxidoreductases like protein disulphide isomerases (PDIs). Cells employ the Endoplasmic reticulum-associated degradation (ERAD) mechanism to counteract protein misfolding. ERAD disruption causes the detachment of GRP78 from transmembrane proteins, initiating a cascade involving Inositol-requiring kinase/endoribonuclease 1 (IRE1), Activating transcription factor 6 (ATF6), and Protein kinase RNA-like endoplasmic reticulum kinase (PERK) pathways. The accumulation and deposition of misfolded proteins within the cell are hallmarks of numerous neurodegenerative diseases. These aberrant proteins disrupt normal neuronal signalling and contribute to impaired cellular homeostasis, including oxidative stress and compromised protein degradation pathways. In essence, ER stress is defined as the cellular response to the accumulation of misfolded proteins in the endoplasmic reticulum, encompassing a series of signalling pathways and molecular events that aim to restore cellular homeostasis. This comprehensive review explores ER stress and its profound implications for the pathogenesis and progression of neurodegenerative diseases.
    Keywords:  Calcium homeostasis; ER stress; Misfolded proteins; Neurodegeneration; Unfolded protein response
  13. NPJ Parkinsons Dis. 2024 Jan 02. 10(1): 1
      In Parkinson's disease (PD), and other α-synucleinopathies, α-synuclein (α-Syn) aggregates form a myriad of conformational and truncational variants. Most antibodies used to detect and quantify α-Syn in the human brain target epitopes within the C-terminus (residues 96-140) of the 140 amino acid protein and may fail to capture the diversity of α-Syn variants present in PD. We sought to investigate the heterogeneity of α-Syn conformations and aggregation states in the PD human brain by labelling with multiple antibodies that detect epitopes along the entire length of α-Syn. We used multiplex immunohistochemistry to simultaneously immunolabel tissue sections with antibodies mapping the three structural domains of α-Syn. Discrete epitope-specific immunoreactivities were visualised and quantified in the olfactory bulb, medulla, substantia nigra, hippocampus, entorhinal cortex, middle temporal gyrus, and middle frontal gyrus of ten PD cases, and the middle temporal gyrus of 23 PD, and 24 neurologically normal cases. Distinct Lewy neurite and Lewy body aggregate morphologies were detected across all interrogated regions/cases. Lewy neurites were the most prominent in the olfactory bulb and hippocampus, while the substantia nigra, medulla and cortical regions showed a mixture of Lewy neurites and Lewy bodies. Importantly, unique N-terminus immunoreactivity revealed previously uncharacterised populations of (1) perinuclear, (2) glial (microglial and astrocytic), and (3) neuronal lysosomal α-Syn aggregates. These epitope-specific N-terminus immunoreactive aggregate populations were susceptible to proteolysis via time-dependent proteinase K digestion, suggesting a less stable oligomeric aggregation state. Our identification of unique N-terminus immunoreactive α-Syn aggregates adds to the emerging paradigm that α-Syn pathology is more abundant and complex in human brains with PD than previously realised. Our findings highlight that labelling multiple regions of the α-Syn protein is necessary to investigate the full spectrum of α-Syn pathology and prompt further investigation into the functional role of these N-terminus polymorphs.
  14. Sci Rep. 2024 01 02. 14(1): 144
      Evidence suggests that beta-amyloid (Aβ)-induced phosphorylation/aggregation of tau protein plays a critical role in the degeneration of neurons and development of Alzheimer's disease (AD), the most common cause of dementia affecting the elderly population. Many studies have pursued a variety of small molecules, including nanoparticles conjugated with drugs to interfere with Aβ and/or tau aggregation/toxicity as an effective strategy for AD treatment. We reported earlier that FDA approved PLGA nanoparticles without any drug can attenuate Aβ aggregation/toxicity in cellular/animal models of AD. In this study, we evaluated the effects of native PLGA on Aβ seed-induced aggregation of tau protein using a variety of biophysical, structural and spectroscopic approaches. Our results show that Aβ1-42 seeds enhanced aggregation of tau protein in the presence and absence of heparin and the effect was attenuated by native PLGA nanoparticles. Interestingly, PLGA inhibited aggregation of both 4R and 3R tau isoforms involved in the formation of neurofibrillary tangles in AD brains. Furthermore, Aβ seed-induced tau aggregation in the presence of arachidonic acid was suppressed by native PLGA. Collectively, our results suggest that native PLGA nanoparticles can inhibit the Aβ seed-induced aggregation of different tau protein isoforms highlighting their therapeutic implication in the treatment of AD.
  15. J Ethnopharmacol. 2023 Dec 27. pii: S0378-8741(23)01498-8. [Epub ahead of print]322 117628
      ETHNOPHARMACOLOGICAL RELEVANCE: Piper longum L., a medicinal and food homologous herb, has a traditional history of use in treating gastrointestinal and neurological disorders. Piperine (PIP) the main alkaloid of P. longum, exists neuroprotective effects on various animal models of Parkinson's disease (PD). Nevertheless, the underlying mechanism, particularly the role of PIP in promoting gut-brain autophagy for α-Synuclein (α-Syn) degradation in PD, remains incompletely understood.AIM OF THE STUDY: To explore the role of PIP in regulating the gut-brain autophagy signaling pathway to reduce α-Syn levels in both the colon and substantia nigra (SN) of PD model rats.
    MATERIALS AND METHODS: Behavioral experiments were conducted to assess the impact of PIP on 6-hydroxydopamine (6-OHDA)-induced PD rats. The intestinal microbiome composition and intestinal metabolites were analyzed by metagenomics and GC-MS/MS. The auto-phagosomes were visualized by transmission electron microscopy. Immunohistochemistry, immunofluorescence, and western blotting were performed to assess the levels of tyrosine hydroxylase (TH), α-Syn, LC3II/LC3I, p62, and the PI3K/AKT/mTOR pathway in both the SN and colon of the rats. The pathway-related inhibitor and agonist were used to verify the autophagy mechanism in the SH-SY5Y cells overexpressing A53T mutant α-Syn (A53T-α-Syn).
    RESULTS: PIP improved autonomic movement and gastrointestinal dysfunctions, reduced α-Syn aggregation and attenuated the loss of dopaminergic neurons in 6-OHDA-induced PD rats. After oral administration of PIP, the radio of LC3II/LC3I increased and the expression of p62 was degraded, as well as the phosphorylation levels of PI3K, AKT and mTOR decreased in the SN and colon of rats. The effect of PIP on reducing A53T-α-Syn through the activation of the PI3K/AKT/mTOR-mediated autophagy pathway was further confirmed in A53T-α-Syn transgenic SH-SY5Y cells. This effect could be inhibited by the autophagy inhibitor bafilomycin A1 and the PI3K agonist 740 Y-P.
    CONCLUSIONS: Our findings suggested that PIP could protect neurons by activating autophagy to degrade α-Syn in the SN and colon, which were related to the suppression of PIP on the activation of PI3K/AKT/mTOR signaling pathway.
    Keywords:  Gut-brain autophagy; PI3K/AKT/mTOR signaling pathway; Parkinson’s disease; Piperine; α-Synuclein
  16. Genes Cells. 2024 Jan 01.
      α-Synuclein (α-Syn)-positive intracellular fibrillar protein deposits, known as Lewy bodies, are thought to be involved in the pathogenesis of Parkinson's disease (PD). Although recent lines of evidence suggested that extracellular α-Syn secreted from pathogenic neurons contributes to the propagation of PD pathology, the precise mechanism of action remains unclear. We have reported that extracellular α-Syn caused sphingosine 1-phosphate (S1P) receptor type 1 (S1PR1) uncoupled from Gi and inhibited downstream G-protein signaling in SH-SY5Y cells, although its patho/physiological role remains to be clarified. Here we show that extracellular α-Syn caused S1P receptor type 3 (S1PR3) uncoupled from G protein in HeLa cells. Further studies indicated that α-Syn treatment reduced cathepsin D activity while enhancing the secretion of immature pro-cathepsin D into cell culture medium, suggesting that lysosomal delivery of cathepsin D was disturbed. Actually, extracellular α-Syn attenuated the retrograde trafficking of insulin-like growth factor-II/mannose 6-phosphate (IGF-II/M6P) receptor, which is under the regulation of S1PR3. These findings shed light on the understanding of dissemination of the PD pathology, that is, the mechanism underlying how extracellular α-Syn secreted from pathogenic cells causes lysosomal dysfunction of the neighboring healthy cells, leading to propagation of the disease.
    Keywords:  Parkinson's disease; cathepsin D; lysosome; mannose 6-phosphate receptor; retrograde trafficking; sphingosine 1-phosphate; α-synuclein
  17. bioRxiv. 2023 Dec 13. pii: 2023.12.12.571303. [Epub ahead of print]
      Ubiquitin-conjugating enzymes (E2s) are key for regulating protein function and turnover via ubiquitination but it remains undetermined which E2s maintain proteostasis during aging. Here, we find that E2s have diverse roles in handling a model aggregation-prone protein (huntingtin-polyQ) in the Drosophila retina: while some E2s mediate aggregate assembly, UBE2D/effete (eff) and other E2s are required for huntingtin-polyQ degradation. UBE2D/eff is key for proteostasis also in skeletal muscle: eff protein levels decline with aging, and muscle-specific eff knockdown causes an accelerated buildup in insoluble poly-ubiquitinated proteins (which progressively accumulate with aging) and shortens lifespan. Transgenic expression of human UBE2D2, homologous to eff, partially rescues the lifespan and proteostasis deficits caused by muscle-specific eff RNAi by re-establishing the physiological levels of eff RNAi -regulated proteins. Interestingly, UBE2D/eff knockdown in young age reproduces many of the proteomic changes that normally occur in old muscles, suggesting that the decrease in UBE2D/eff protein levels that occurs with aging contributes to reshaping the composition of the muscle proteome. Altogether, these findings indicate that UBE2D/eff is a key E2 ubiquitin-conjugating enzyme for maintaining a youthful proteome and for ensuring protein quality control during aging.
  18. J Gerontol A Biol Sci Med Sci. 2024 Jan 04. pii: glad278. [Epub ahead of print]
      Senescent astrocyte accumulation in the brain during normal aging is a driver of age-related neurodegenerative diseases such as Alzheimer's disease (AD). However, the molecular events underlying astrocyte senescence in AD are not fully understood. In this study, we demonstrated that senescent astrocytes display a secretory phenotype known as the senescence-associated secretory phenotype (SASP), which is associated with the upregulation of various proinflammatory factors and the downregulation of neurotrophic growth factors (e.g., NGF and BDNF), resulting in a decrease in astrocyte-mediated neuroprotection and increased risk of neurodegeneration. We found that SerpinA3N is upregulated in senescent primary mouse astrocytes after serial passaging in vitro or by H2O2 treatment. Further exploration of the underlying mechanism revealed that SerpinA3N deficiency protects against senescent astrocyte-induced neurodegeneration by suppressing SASP-related factors and inducing neurotrophic growth factors. Brain tissues from AD model mice possessed increased numbers of senescent astrocytes. Moreover, senescent astrocytes exhibited upregulated SerpinA3N expression in vitro and in vivo, confirming that our cell model recapitulated the in vivo pathology of these neurodegenerative diseases. Altogether, our study reveals a novel molecular strategy to regulate the secretory phenotype of senescent astrocytes and implies that SerpinA3N and its regulatory mechanisms may be potential targets for delaying brain aging and aging-related neurodegenerative diseases.
    Keywords:  SerpinA3N; astrocytes senescence; neurodegeneration; senescence-associated secretory phenotype
  19. Mol Biotechnol. 2024 Jan 03.
      Lysine-based post-translational modification (PTM) such as acylation, acetylation, deamination, methylation, SUMOylation, and ubiquitination has proven to be a major regulator of gene expression, chromatin structure, protein stability, protein-protein interaction, protein degradation, and cellular localization. However, besides all the PTMs, ubiquitination stands as the second most common PTM after phosphorylation that is involved in the etiology of neurodegenerative diseases (NDDs) namely, Alzheimer's disease (AD) and Parkinson's disease (PD). NDDs are characterized by the accumulation of misfolded protein aggregates in the brain that lead to disease-related gene mutation and irregular protein homeostasis. The ubiquitin-proteasome system (UPS) is in charge of degrading these misfolded proteins, which involve an interplay of E1, E2, E3, and deubiquitinase enzymes. Impaired UPS has been commonly observed in NDDs and E3 ligases are the key members of the UPS, thus, dysfunction of the same can accelerate the neurodegeneration process. Therefore, the aim of this study is firstly, to find E3 ligases that are common in both AD and PD through data mining. Secondly, to study the impact of mutation on its structure and function. The study deciphered 74 E3 ligases that were common in both AD and PD. Later, 10 hub genes were calculated of which protein-protein interaction, pathway enrichment, lysine site prediction, domain, and motif analysis were performed. The results predicted BRCA1, PML, and TRIM33 as the top three putative lysine-modified E3 ligases involved in AD and PD pathogenesis. However, based on structural characterization, BRCA1 was taken further to study RING domain mutation that inferred K32Y, K32L, K32C, K45V, K45Y, and K45G as potential mutants that alter the structural and functional ability of BRCA1 to interact with Ube2k, E2-conjugating enzyme. The most probable mutant observed after molecular dynamics simulation of 50 ns is K32L. Therefore, our study concludes BRCA1, a potential E3 ligase common in AD and PD, and RING domain mutation at sites K32 and K45 possibly disturbs its interaction with its E2, Ube2k. Graphical representation of all the steps involved to study mutation in the RING domain of BRCA1 which is a common E3 ligase observed in Alzheimer's disease and Parkinson's disease.
    Keywords:  Alzheimer’s disease; BRCA1; Mutation; Neurodegeneration; Parkinson’s disease; RING domain; Ubiquitination
  20. Curr Pharm Biotechnol. 2024 Jan 01.
      Neurodegenerative disease is mainly characterized by the accumulation of misfolded proteins, contributing to mitochondrial impairments, increased production of proinflammatory cytokines and reactive oxygen species, and neuroinflammation resulting in synaptic loss and neuronal loss. These pathophysiological factors are a serious concern in the treatment of neurodegenerative diseases. Based on the symptoms of various neurodegenerative diseases, different treatments are available, but they have serious side effects and fail in clinical trials, too. Therefore, treatments for neurodegenerative diseases are still a challenge at present. Thus, it is important to study an alternative option. Capsaicin is a naturally occurring alkaloid found in capsicum. Besides the TRPV1 receptor activator in nociception, capsaicin showed a protective effect in brain-related disorders. Capsaicin also reduces the aggregation of misfolded proteins, improves mitochondrial function, and decreases ROS generation. Its antioxidant role is due to increased expression of an nrf2-mediated signaling pathway. Nrf2 is a nuclear erythroid 2-related factor, a transcription factor, which has a crucial role in maintaining the normal function of mitochondria and the cellular defense system against oxidative stress. Intriguingly, Nrf2 mediated pathway improved the upregulation of antioxidant genes and inhibition of microglial-induced inflammation, improved mitochondrial resilience and functions, leading to decreased ROS in neurodegenerative conditions, suggesting that Nrf2 activation could be a better therapeutic approach to target pathophysiology of neurodegenerative disease. Therefore, the present review has evaluated the potential role of capsaicin as a pharmacological agent for the treatment and management of various neurodegenerative diseases via the Nrf2-mediated signaling pathway.
    Keywords:  Alzheimer; Capsaicin; Nrf2; Parkinson; neurodegenerative diseases; oxidative stress