bims-proarb Biomed News
on Proteostasis in aging and regenerative biology
Issue of 2021‒08‒29
twenty-five papers selected by
Rich Giadone
Harvard University

  1. Sci Rep. 2021 Aug 24. 11(1): 17139
      In human cells under stress conditions, misfolded polypeptides can form potentially cytotoxic insoluble aggregates. To eliminate aggregates, the HSP70 chaperone machinery extracts and resolubilizes polypeptides for triage to refolding or degradation. Yeast and bacterial chaperones of the small heat-shock protein (sHSP) family can bind substrates at early stages of misfolding, during the aggregation process. The co-aggregated sHSPs then facilitate downstream disaggregation by HSP70. Because it is unknown whether a human sHSP has this activity, we investigated the disaggregation role of human HSPB1. HSPB1 co-aggregated with unfolded protein substrates, firefly luciferase and mammalian lactate dehydrogenase. The co-aggregates formed with HSPB1 were smaller and more regularly shaped than those formed in its absence. Importantly, co-aggregation promoted the efficient disaggregation and refolding of the substrates, led by HSP70. HSPB1 itself was also extracted during disaggregation, and its homo-oligomerization ability was not required. Therefore, we propose that a human sHSP is an integral part of the chaperone network for protein disaggregation.
  2. J Theor Biol. 2021 Aug 23. pii: S0022-5193(21)00296-4. [Epub ahead of print] 110877
      One of the most important questions in cell biology is how cell fate is determined when exposed to extreme stresses such as heat shock. It has been long understood that organisms exposed to high temperature stresses typically protect themselves with a heat shock response (HSR), where accumulation of denatured or unfolded proteins triggers the synthesis of heat shock proteins (HSPs) through the heat shock transcription factor, e.g., heat shock factor 1 (HSF1). In this study, a dynamical model validated with experiments is presented to analyse the role of HSF1 SUMOylation in response to heat shock. Key features of this model are inclusion of heat shock response and SUMOylation of HSF1, and HSP synthesis at molecular level, describing the dynamical evolution of the key variables involved in the regulation of HSPs. The model has been employed to predict the SUMOylation levels of HSF1 with different external temperature stimuli. The results show that the SUMOylated HSF1 levels agree closely with the experimental findings. This demonstrates the validity of this nonlinear dynamic model for the important role of SUMOylation in response to heat shock.
    Keywords:  SUMOylation; heat shock proteins (HSP); heat shock response (HSR); heat shock transcription factor (HSF); mathematical modelling; post‐translational modification (PTM)
  3. Front Mol Neurosci. 2021 ;14 661993
      Exposure to early-life stress (ELS) can persistently modify neuronal circuits and functions, and contribute to the expression of misfolded and aggregated proteins that are hallmarks of several neurodegenerative diseases. The healthy brain is able to clear dysfunctional proteins through the ubiquitin-proteasome system (UPS) and the autophagy-lysosomal pathway (ALP). Accumulating evidence indicates that impairment of these pathways contributes to enhanced protein aggregation and neurodegeneration. While stress is a known precipitant of neurological decline, few specific mechanistic links underlying this relationship have been identified. We hypothesized that neonatal maternal separation (MatSep), a well-established model of ELS, has the ability to alter the levels of UPS and ALP components in the brain, and thus has the potential to disrupt proteostasis. The expression of proteostasis-associated protein markers was evaluated by immunoblotting in the hippocampus and cortex of adult Wistar rats that were previously subjected to MatSep. We observed multiple sex- and MatSep-specific changes in the expression of proteins in the ALP, mitophagy, and UPS pathways, particularly in the hippocampus of adult animals. In contrast, MatSep had limited influence on proteostasis marker expression in the cortex of adult animals. Our results indicate that MatSep can selectively modify the intracellular protein degradation machinery in ways that may impact the development and progression of neurodegenerative disease.
    Keywords:  aging; autophagy; early life adversity; mitophagy; proteasome; sex differences; stress
  4. J Mol Biol. 2021 Aug 24. pii: S0022-2836(21)00448-4. [Epub ahead of print] 167215
      Protein aggregation is a feature of numerous neurodegenerative diseases. However, regulated, often reversible formation of protein aggregates, also known as condensates, helps control a wide range of cellular activities including stress response, gene expression, memory, cell development and differentiation. This review presents examples of aggregates found in biological systems, how they are used, and cellular strategies that control aggregation and disaggregation. We include features of the aggregating proteins themselves, environmental factors, co-aggregates, post-translational modifications and well-known aggregation-directed activities that influence their formation, material state, stability and dissolution. We highlight the emerging roles of biomolecular condensates in early animal development, and disaggregation processing proteins that have recently been shown to play key roles in gametogenesis and embryogenesis.
    Keywords:  ABCF gene family; Amyloid; RuvBL gene family; biomolecular condensate; chaperone
  5. Stem Cell Reports. 2021 Aug 07. pii: S2213-6711(21)00383-0. [Epub ahead of print]
      The ε4 allele of APOE-encoding apolipoprotein (ApoE) is one of the strongest genetic risk factors for Alzheimer's disease (AD). One of the overarching questions is whether and how this astrocyte-enriched risk factor initiates AD-associated pathology in neurons such as amyloid-β (Aβ) accumulation. Here, we generate neurons and astrocytes from isogenic human induced pluripotent stem cells (hiPSCs) carrying either APOE ε3 or APOE ε4 allele and investigate the effect of astrocytic ApoE4 on neuronal Aβ production. Secretory factors in conditioned media from ApoE4 astrocytes significantly increased amyloid precursor protein (APP) levels and Aβ secretion in neurons. We further found that increased cholesterol secretion from ApoE4 astrocytes was necessary and sufficient to induce the formation of lipid rafts that potentially provide a physical platform for APP localization and facilitate its processing. Our study reveals the contribution of ApoE4 astrocytes to amyloidosis in neurons by expanding lipid rafts and facilitating Aβ production through an oversupply of cholesterol.
    Keywords:  Alzheimer's disease; apolipoprotein E; cholesterol; human induced pluripotent stem cells; lipid rafts
  6. Autophagy. 2021 Aug 25. 1-2
      Abnormalities of the neuronal endolysosome and macroautophagy/autophagy system are an early and prominent feature of Alzheimer disease (AD). SORL1 is notable as a gene in which mutations are causal for a rare, autosomal dominant form of AD, and also variants that increase the risk of developing the common form of late-onset AD. In our recent study, we used patient-derived stem cells and CRISPR engineering to study the effects of SORL1 mutations on the endolysosome and autophagy system in human forebrain neurons. SORL1 mutations causal for monogenic AD are typically truncating mutations, and we found, using stem cells generated from an individual with dementia due to a heterozygous SORL1 truncation mutation, that this class of mutation results in SORL1 haploinsufficiency. Reducing SORL1 protein by half results in disrupted endosomal trafficking in patient-derived neurons, which we confirmed by studying the endolysosomal system in isogenic CRISPR-engineered SORL1 heterozygous null neurons. We also found that SORL1 homozygous null neurons develop more severe phenotypes, with endosome abnormalities, lysosome dysfunction and defects in the degradative phase of autophagy. Endolysosome and autophagy defects in SORL1 mutant neurons are dependent on APP, a key AD gene, as they are rescued by extracellular antisense oligonucleotides that reduce APP protein.
    Keywords:  Alzheimer’s disease; autophagy; endosome; live-cell imaging; lysosome
  7. Science. 2021 Aug 27. 373(6558): 998-1004
      In eukaryotic cells, half of all proteins function as subunits within multiprotein complexes. Imbalanced synthesis of subunits leads to unassembled intermediates that must be degraded to minimize cellular toxicity. Here, we found that excess PSMC5, a subunit of the proteasome base, was targeted for degradation by the HERC1 ubiquitin ligase in mammalian cells. HERC1 identified unassembled PSMC5 by its cognate assembly chaperone PAAF1. Because PAAF1 only dissociates after assembly, HERC1 could also engage later assembly intermediates such as the PSMC4-PSMC5-PAAF1 complex. A missense mutant of HERC1 that causes neurodegeneration in mice was impaired in the recognition and ubiquitination of the PSMC5-PAAF1 complex. Thus, proteasome assembly factors can serve as adaptors for ubiquitin ligases to facilitate elimination of unassembled intermediates and maintain protein homeostasis.
  8. Biol Pharm Bull. 2021 Aug 25.
      Microglial activation and neuroinflammation induced by amyloid β (Aβ) play pivotal roles in Alzheimer's disease (AD) pathogenesis. Astragaloside IV (AS-IV) is one of the major active compounds of the traditional Chinese medicine Astmgali Radix. It has been reported that AS-IV could protect against Aβ-induced neuroinflammation and cognitive impairment, but the underlying mechanisms need to be further clarified. In this study, the therapeutic effects of AS-IV were investigated in an oligomeric Aβ (oAβ) induced AD mice model. The effects of AS-IV on microglial activation, neuronal damage and NADPH oxidase expression were further studied. Different doses of AS-IV were administered intragastrically once a day after intracerebroventricularly oAβ injection. Results of behavioral experiments including novel object recognition (NOR) test and Morris water maze (MWM) test revealed that AS-IV administration could significantly ameliorate oAβ-induced cognitive impairment in a dose dependent manner. ELISA results showed that increased levels of ROS, TNF-α, IL-1β and IL-6 in hippocampal tissues induced by oAβ injection were remarkably inhibited after AS-IV treatment. OAβ induced microglial activation and neuronal damage was significantly suppressed in AS-IV-treated mice brain, observed in immunohistochemistry results. Furthermore, oAβ upregulated protein expression of NADPH oxidase subunits gp91phox, p47phox, p22phox and p67phox were remarkably reduced by AS-IV in western blotting assay. These results revealed that AS-IV could ameliorate oAβ-induced cognitive impairment, neuroinflammation and neuronal damage, which were possibly mediated by inhibition of microglial activation and down-regulation of NADPH oxidase protein expression. Our findings provide new insights of AS-IV for the treatment of neuroinflammation related diseases such as AD.
    Keywords:  Alzheimer's disease; Astragaloside IV; NADPH oxidase; cognitive impairment; microglial activation; neuroinflammation
  9. FEBS Open Bio. 2021 Aug 27.
      Cell senescence is closely related to autophagy. In this article, we identified a natural nucleoside analogue, cordycepin, that has the ability to significantly improve lysosomal function, enhance the activity of the lysosomal representative protease cathepsin B (CTSB), and promote the expression of the functional protein lysosomal-associated membrane protein 2 (LAMP2) on the lysosomal membrane. Cordycepin then restores the damaged autophagy level of aging cells by activating the classic AMPK and mTOR-p70S6K signaling pathways, thus inhibiting cell senescence in an H2 O2 -induced stress-induced premature senescence (SIPS) cell model. This study provides new theoretical support for the further development of cordycepin and clinical antiaging drugs to inhibit cell senescence and suggests that the regulatory mechanisms of lysosomes in senescent cells should be considered when treating age-related diseases.
    Keywords:  AMPK signaling pathways; autophagy; cell senescence; cordycepin; lysosomal function; lysosomal protease
  10. Oxid Med Cell Longev. 2021 ;2021 6682336
      Brain aging is characterized by dysfunctional autophagy and cellular senescence, among other features. While autophagy can either promote or suppress cellular senescence in proliferating cells, in postmitotic cells, such as neurons, autophagy impairment promotes cellular senescence. CRM1 (exportin-1/XPO1) exports hundreds of nuclear proteins into the cytoplasm, including the transcription factors TFEB (the main inducer of autophagy and lysosomal biogenesis genes) and STAT3, another autophagy modulator. It appears that CRM1 is a modulator of aging-associated senescence and autophagy, because pharmacological inhibition of CRM1 improved autophagic degradation in flies, by increasing nuclear TFEB levels, and because enhanced CRM1 activity is mechanistically linked to senescence in fibroblasts from Hutchinson-Gilford progeria syndrome patients and old healthy individuals; furthermore, the exogenous overexpression of CRM1 induced senescence in normal fibroblasts. In this work, we tested the hypothesis that impaired autophagic flux during brain aging occurs due to CRM1 accumulation in the brain. We found that CRM1 levels and activity increased in the hippocampus and cortex during physiological aging, which resulted in a decrease of nuclear TFEB and STAT3. Consistent with an autophagic flux impairment, we observed accumulation of the autophagic receptor p62/SQSTM1 in neurons of old mice, which correlated with increased neuronal senescence. Using an in vitro model of neuronal senescence, we demonstrate that CRM1 inhibition improved autophagy flux and reduced SA-β-gal activity by restoring TFEB nuclear localization. Collectively, our data suggest that enhanced CRM1-mediated export of proteins during brain aging perturbs neuronal homeostasis, contributing to autophagy impairment, and neuronal senescence.
  11. Cell Biol Toxicol. 2021 Aug 27.
      Autophagy is a conserved intracellular catabolic pathway that removes cytoplasmic components to contribute to neuronal homeostasis. Accumulating evidence has increasingly shown that the induction of autophagy improves neuronal health and extends longevity in several animal models. Therefore, there is a great interest in the identification of effective autophagy enhancers with potential nutraceutical or pharmaceutical properties to ameliorate age-related diseases, such as neurodegenerative disorders, and/or promote longevity. Queen bee acid (QBA, 10-hydroxy-2-decenoic acid) is the major fatty acid component of, and is found exclusively in, royal jelly, which has beneficial properties for human health. It is reported that QBA has antitumor, anti-inflammatory, and antibacterial activities and promotes neurogenesis and neuronal health; however, the mechanism by which QBA exerts these effects has not been fully elucidated. The present study investigated the role of the autophagic process in the protective effect of QBA. We found that QBA is a novel autophagy inducer that triggers autophagy in various neuronal cell lines and mouse and fly models. The beclin-1 (BECN1) and mTOR pathways participate in the regulation of QBA-induced autophagy. Moreover, our results showed that QBA stimulates sirtuin 1 (SIRT1), which promotes autophagy by the deacetylation of critical ATG proteins. Finally, QBA-mediated autophagy promotes neuroprotection in Parkinson's disease in vitro and in a mouse model and extends the lifespan of Drosophila melanogaster. This study provides detailed evidences showing that autophagy induction plays a critical role in the beneficial health effects of QBA.
    Keywords:  Autophagy; Longevity; Neurodegeneration; Parkinson’s disease; QBA; SIRT1
  12. Diabetologia. 2021 Aug 27.
      AIMS/HYPOTHESIS: We studied the effects of heterozygous human INS gene mutations on insulin secretion, endoplasmic reticulum (ER) stress and other mechanisms in both MIN6 and human induced pluripotent stem cells (hiPSC)-derived beta-like cells, as well as the effects of prolonged overexpression of mutant human INS in MIN6 cells.METHODS: We modelled the structure of mutant C109Y and G32V proinsulin computationally to examine the in silico effects. We then overexpressed either wild-type (WT), mutant (C109Y or G32V), or both WT and mutant human preproinsulin in MIN6 cells, both transiently and stably over several weeks. We measured the levels of human and rodent insulin secreted, and examined the transcript and protein levels of several ER stress and apoptotic markers. We also reprogrammed human donor fibroblasts heterozygous for the C109Y mutation into hiPSCs and differentiated these into pancreatic beta-like cells, which were subjected to single-cell RNA-sequencing and transcript and protein analyses for ER stress and apoptotic markers.
    RESULTS: The computational modelling studies, and short-term and long-term expression studies in beta cells, revealed the presence of ER stress, organelle changes and insulin processing defects, resulting in a decreased amount of insulin secreted but not the ability to secrete insulin. By 9 weeks of expression of mutant human INS, dominant-negative effects of mutant INS were evident and beta cell insulin secretory capacity declined. INS+/C109Y patient-derived beta-like cells and single-cell RNA-sequencing analyses then revealed compensatory upregulation in genes involved in insulin secretion, processing and inflammatory response.
    CONCLUSIONS/INTERPRETATION: The results provide deeper insights into the mechanisms of beta cell failure during INS mutation-mediated diabetes disease progression. Decreasing spliced X-box binding protein 1 (sXBP1) or inflammatory response could be avenues to restore the function of the remaining WT INS allele.
    Keywords:  Beta cell; ER stress; Insulin; Insulin secretion; Mutation; Pancreas; Stem cells; iPS cells
  13. Proteomes. 2021 Aug 02. pii: 36. [Epub ahead of print]9(3):
      We recently discovered three distinct pathophysiological subtypes in Alzheimer's disease (AD) using cerebrospinal fluid (CSF) proteomics: one with neuronal hyperplasticity, a second with innate immune system activation, and a third subtype with blood-brain barrier dysfunction. It remains unclear whether AD proteomic subtype profiles are a consequence of amyloid aggregation, or might exist upstream from aggregated amyloid. We studied this question in 127 older individuals with intact cognition and normal AD biomarkers in two independent cohorts (EMIF-AD MBD and ADNI). We clustered 705 proteins measured in CSF that were previously related to AD. We identified in these cognitively intact individuals without AD pathology three subtypes: two subtypes were seen in both cohorts (n = 49 with neuronal hyperplasticity and n = 44 with blood-brain barrier dysfunction), and one only in ADNI (n = 12 with innate immune activation). The proteins specific for these subtypes strongly overlapped with AD subtype protein profiles (overlap coefficients 92%-71%). Longitudinal p181-tau and amyloid β 1-42 (Aβ42) CSF analysis showed that in the hyperplasticity subtype p181-tau increased (β = 2.6 pg/mL per year, p = 0.01) and Aβ42 decreased over time (β = -4.4 pg/mL per year, p = 0.03), in the innate immune activation subtype p181-tau increased (β = 3.1 pg/mL per year, p = 0.01) while in the blood-brain barrier dysfunction subtype Aβ42 decreased (β = -3.7 pg/mL per year, p = 0.009). These findings suggest that AD proteomic subtypes might already manifest in cognitively normal individuals and may predispose for AD before amyloid has reached abnormal levels.
    Keywords:  Alzheimer’s disease; amyloid beta; cerebrospinal fluid proteomics; cognitive functioning; risk factors; tau
  14. PLoS One. 2021 ;16(8): e0256640
      Bag-1 is a multifunctional protein that regulates Hsp70 chaperone activity, apoptosis, and proliferation. The three major Bag-1 isoforms have different subcellular localizations and partly non-overlapping functions. To identify the detailed interaction network of each isoform, we utilized mass spectrometry-based proteomics and found that interactomes of Bag-1 isoforms contained many common proteins, with variations in their abundances. Bag-1 interactomes were enriched with proteins involved in protein processing and degradation pathways. Novel interaction partners included VCP/p97; a transitional ER ATPase, Rad23B; a shuttling factor for ubiquitinated proteins, proteasome components, and ER-resident proteins, suggesting a role for Bag-1 also in ER-associated protein degradation (ERAD). Bag-1 pull-down from cells and tissues from breast cancer patients validated these interactions and showed cancer-related prominence. Using in silico predictions we detected hotspot residues of Bag-1. Mutations of these residues caused loss of binding to protein quality control elements and impaired proteasomal activity in MCF-7 cells. Following CD147 glycosylation pattern, we showed that Bag-1 downregulated VCP/p97-dependent ERAD. Overall, our data extends the interaction map of Bag-1, and broadens its role in protein homeostasis. Targeting the interaction surfaces revealed in this study might be an effective strategy in the treatment of cancer.
  15. Mol Neurodegener. 2021 Aug 23. 16(1): 57
      Microtubule-associated protein tau is abnormally aggregated in neuronal and glial cells in a range of neurodegenerative diseases that are collectively referred to as tauopathies. Multiple studies have suggested that pathological tau species may act as a seed that promotes aggregation of endogenous tau in naïve cells and contributes to propagation of tau pathology. While they share pathological tau aggregation as a common feature, tauopathies are distinct from one another with respect to predominant tau isoforms that accumulate and the selective vulnerability of brain regions and cell types that have tau inclusions. For instance, primary tauopathies present with glial tau pathology, while it is mostly neuronal in Alzheimer's disease (AD). Also, morphologies of tau inclusions can greatly vary even within the same cell type, suggesting distinct mechanisms or distinct tau conformers in each tauopathy. Neuropathological heterogeneity across tauopathies challenges our understanding of pathophysiology behind tau seeding and aggregation, as well as our efforts to develop effective therapeutic strategies for AD and other tauopathies. In this review, we describe diverse neuropathological features of tau inclusions in neurodegenerative tauopathies and discuss what has been learned from experimental studies with mouse models, advanced transcriptomics, and cryo-electron microscopy (cryo-EM) on the biology underlying cell type-specific tau pathology.
    Keywords:  Animal models; Astrocytes; Cryo-EM; MAPT; Microglia; Oligodendroglia; Tau; Tauopathy; Transcriptomics
  16. Sci Rep. 2021 Aug 24. 11(1): 17115
      Heat shock proteins are involved in the response to stress including activation of the immune response. Elevated circulating heat shock proteins are associated with spontaneous preterm birth (SPTB). Intracellular heat shock proteins act as multifunctional molecular chaperones that regulate activity of nuclear hormone receptors. Since SPTB has a significant genetic predisposition, our objective was to identify genetic and transcriptomic evidence of heat shock proteins and nuclear hormone receptors that may affect risk for SPTB. We investigated all 97 genes encoding members of the heat shock protein families and all 49 genes encoding nuclear hormone receptors for their potential role in SPTB susceptibility. We used multiple genetic and genomic datasets including genome-wide association studies (GWASs), whole-exome sequencing (WES), and placental transcriptomics to identify SPTB predisposing factors from the mother, infant, and placenta. There were multiple associations of heat shock protein and nuclear hormone receptor genes with SPTB. Several orthogonal datasets supported roles for SEC63, HSPA1L, SACS, RORA, and AR in susceptibility to SPTB. We propose that suppression of specific heat shock proteins promotes maintenance of pregnancy, whereas activation of specific heat shock protein mediated signaling may disturb maternal-fetal tolerance and promote labor.
  17. Methods Mol Biol. 2021 ;2365 217-244
      We use an in vitro degradation assay with a model substrate to assess proteasomal unfolding ability. Our substrate has an unstructured region that is the site of ubiquitination, followed by an easy-to-unfold domain and a difficult-to-unfold domain. Degradation proceeds through the unstructured and easy-to-unfold domains, but the difficult-to-unfold domain can be degraded completely or, if the proteasome stalls, can be released as a partially degraded fragment. The ratio between these two possible outcomes allows us to quantify the unfolding ability and determine how processively the proteasome degrades its substrates.
    Keywords:  ATP-dependent protease; Proteasome; Protein Degradation; Protein Unfolding; Ubiquitin-proteasome system
  18. Front Immunol. 2021 ;12 705581
      Autophagy is a proposed route of amyloid-β (Aβ) clearance by microglia that is halted in Alzheimer's Disease (AD), though mechanisms underlying this dysfunction remain elusive. Here, primary microglia from adult AD (5xFAD) mice were utilized to demonstrate that 5xFAD microglia fail to degrade Aβ and express low levels of autophagy cargo receptor NBR1. In 5xFAD mouse brains, we show for the first time that AD microglia express elevated levels of microRNA cluster Mirc1/Mir17-92a, which is known to downregulate autophagy proteins. By in situ hybridization in post-mortem AD human tissue sections, we observed that the Mirc1/Mir17-92a cluster member miR-17 is also elevated in human AD microglia, specifically in the vicinity of Aβ deposits, compared to non-disease controls. We show that NBR1 expression is negatively correlated with expression of miR-17 in human AD microglia via immunohistopathologic staining in human AD brain tissue sections. We demonstrate in healthy microglia that autophagy cargo receptor NBR1 is required for Aβ degradation. Inhibiting elevated miR-17 in 5xFAD mouse microglia improves Aβ degradation, autophagy, and NBR1 puncta formation in vitro and improves NBR1 expression in vivo. These findings offer a mechanism behind dysfunctional autophagy in AD microglia which may be useful for therapeutic interventions aiming to improve autophagy function in AD.
    Keywords:  Alzheimer’s disease; Amyloid-β; Mir17-92a; NBR1; autophagy; microRNA; microglia
  19. Adv Exp Med Biol. 2021 ;1288 215-240
      Ubiquitination is one of the most diverse forms of protein post-translational modification that changes the function of the landscape of substrate proteins in response to stimuli, without the need for "de novo" protein synthesis. Ubiquitination is involved in almost all aspects of eukaryotic cell biology, from the best-studied role in promoting the removal of faulty or unnecessary proteins by the way of the ubiquitin proteasome system and autophagy-lysosome pathway to the recruitment of proteins in specific non-proteolytic signaling pathways, as emerged by the more recent discoveries about the protein signature with peculiar types of ubiquitin chains. Spermatogenesis, on its own, is a complex cellular developmental process in which mitosis, meiosis, and cell differentiation coexist so to result in the continuous formation of haploid spermatozoa. Successful spermatogenesis is thus at the same time a mixed result of the precise expression and correct intracellular destination of structural proteins and enzymes, from one hand, and the fine removal by targeted degradation of unfolded or damaged proteins as well as of obsolete, outlived proteins, from the other hand. In this minireview, I will focus on the importance of the ubiquitin system all over the spermatogenic process, discussing both proteolytic and non-proteolytic functions of protein ubiquitination. Alterations in the ubiquitin system have been in fact implicated in pathologies leading to male infertility. Notwithstanding several aspects of the multifaceted world of the ubiquitin system have been clarified, the physiological meaning of the so-called ubiquitin code remains still partially elusive. The studies reviewed in this chapter provide information that could aid the investigators to pursue new promising discoveries in the understanding of human and animal reproductive potential.
    Keywords:  Acrosome biogenesis; Autophagy-lysosome pathway; Centrosome inheritance; Meiotic-sex-chromosome inactivation; Mitophagy; USP8; Ubiquitin code; Ubiquitin-proteasome system
  20. Curr Alzheimer Res. 2021 Aug 22.
      BACKGROUND: A role for neutrophils in the pathogenesis of Alzheimer's disease (AD) is emerging. We previously showed that the neutrophil granule proteins cationic antimicrobial protein of 37 kDa (CAP37), cathepsin G (CG), and neutrophil elastase (NE) directly bind the amyloid-beta peptide Aβ1-42, a central player in AD pathogenesis. CAP37, CG, and NE are serine proteases that can cleave Aβ1-42 at different sites and with different catalytic activities.OBJECTIVE: In this study, we compared the effects of these three proteins on Aβ1-42 fibrillation and neurotoxicity.
    METHODS: Using mass spectrometry and in vitro aggregation assay, we found that NE and CG effi- ciently cleave Aβ1-42. This cleavage correlates well with the inhibition of Aβ1-42 aggregation into fi- brils. In contrast, CAP37 did not efficiently cleave Aβ1-42, but was still able to inhibit its fibrillation, most likely through a quenching effect. Inhibition of Aβ1-42 aggregation by NE and CG neutralized its toxicity measured in cultured neurons. In contrast, inhibition of Aβ1-42 aggregation by CAP37 did not inhibit its neurotoxicity.
    RESULTS: We found that a peptide derived from CAP37 could mimic the quenching and inhibition of Aβ1-42 aggregation effects of the full-length protein. Additionally, this peptide was able to inhibit the neurotoxicity of the most toxic Aβ1-42 aggregate, an effect that was not found with the full-length CAP37.
    CONCLUSION: These results shed light on the mechanisms of action of neutrophil granule proteins with regard to inhibition of Aβ1-42 aggregation and neurotoxicity and open up a possible strategy for the discovery of new disease-modifying drugs for AD.
    Keywords:  Alzheimer's disease; amyloid beta; amyloid beta degrading enzyme; bioactive peptide; neurotoxicity; neutrophil
  21. Cells. 2021 Aug 18. pii: 2121. [Epub ahead of print]10(8):
      Neurodegeneration has been predominantly recognized as neuronal breakdown induced by the accumulation of aggregated and/or misfolded proteins and remains a preliminary factor in age-dependent disease. Recently, critical regulating molecular mechanisms and cellular pathways have been shown to induce neurodegeneration long before aggregate accumulation could occur. Although this opens the possibility of identifying biomarkers for early onset diagnosis, many of these pathways vary in their modes of dysfunction while presenting similar clinical phenotypes. With selectivity remaining difficult, it is promising that these neuroprotective pathways are regulated through the ubiquitin-proteasome system (UPS). This essential post-translational modification (PTM) involves the specific attachment of ubiquitin onto a substrate, specifically marking the ubiquitin-tagged protein for its intracellular fate based upon the site of attachment, the ubiquitin chain type built, and isopeptide linkages between different ubiquitin moieties. This review highlights both the direct and indirect impact ubiquitylation has in oxidative stress response and neuroprotection, and how irregularities in these intricate processes lead towards the onset of neurodegenerative disease (NDD).
    Keywords:  CNS; mitochondrial metabolism; neurodegenerative disease; neuroprotection; oxidative stress response; post-translational modifications; redox chemistry; ubiquitin-proteasome system
  22. Pharmaceutics. 2021 Aug 17. pii: 1283. [Epub ahead of print]13(8):
      Heat shock protein 90 (Hsp90) is a chaperone responsible for the maturation of many cancer-related proteins, and is therefore an important target for the design of new anticancer agents. Several Hsp90 N-terminal domain inhibitors have been evaluated in clinical trials, but none have been approved as cancer therapies. This is partly due to induction of the heat shock response, which can be avoided using Hsp90 C-terminal-domain (CTD) inhibition. Several structural features have been shown to be useful in the design of Hsp90 CTD inhibitors, including an aromatic ring, a cationic center and the benzothiazole moiety. This study established a previously unknown link between these structural motifs. Using ligand-based design methodologies and structure-based pharmacophore models, a library of 29 benzothiazole-based Hsp90 CTD inhibitors was prepared, and their antiproliferative activities were evaluated in MCF-7 breast cancer cells. Several showed low-micromolar IC50, with the most potent being compounds 5g and 9i (IC50, 2.8 ± 0.1, 3.9 ± 0.1 μM, respectively). Based on these results, a ligand-based structure-activity relationship model was built, and molecular dynamics simulation was performed to elaborate the binding mode of compound 9i. Moreover, compound 9i showed degradation of Hsp90 client proteins and no induction of the heat shock response.
    Keywords:  Hsp90; allosteric; benzothiazole; cancer; cancer therapy; inhibitor
  23. Int J Mol Sci. 2021 Aug 13. pii: 8697. [Epub ahead of print]22(16):
      Neuroinflammation is involved in the pathogenesis of neurodegenerative diseases such as Alzheimer's disease (AD), and is notably dependent on age. One important inflammatory pathway exerted by innate immune cells of the nervous system in response to danger signals is mediated by inflammasomes (IF) and leads to the generation of potent pro-inflammatory cytokines. The protein "apoptosis-associated speck-like protein containing a caspase recruitment domain" (ASC) modulates IF activation but has also other functions which are crucial in AD. We intended to characterize immunohistochemically ASC and pattern recognition receptors (PRR) of IF in the hippocampus (HP) of the transgenic mouse model Tg2576 (APP), in which amyloid-beta (Aβ) pathology is directly dependent on age. We show in old-aged APP a significant amount of ASC in microglia and astrocytes associated withAβ plaques, in the absence of PRR described by others in glial cells. In addition, APP developed foci with clusters of extracellular ASC granules not spatiallyrelated to Aβ plaques, which density correlated with the advanced age of mice and AD development. Clusters were associated withspecific astrocytes characterized by their enlarged ring-shaped process terminals, ASC content, and frequent perivascular location. Their possible implication in ASC clearance and propagation of inflammation is discussed.
    Keywords:  ASC; Alzheimer’s disease; age; amyloid β plaques; astroglia; hippocampal interneurons; inflammasomes; innate immunity; microglia; neuroinflammation
  24. Life (Basel). 2021 Jul 26. pii: 750. [Epub ahead of print]11(8):
      The processing of the amyloid precursor protein (APP) is a critical event in the formation of amyloid plaques. Platelets contain most of the enzymatic machinery required for APP processing and correlates of intracerebral abnormalities have been demonstrated in platelets of patients with AD. The goal of the present paper was to analyze studies exploring platelet APP metabolism in Alzheimer's disease patients trying to assess potential reliable peripheral biomarkers, to offer new therapeutic solutions and to understand the pathophysiology of the AD. According to the PRISMA guidelines, we performed a systematic review through the PubMed database up to June 2020 with the search terms: "((((((APP) OR Amyloid Precursor Protein) OR AbetaPP) OR Beta Amyloid) OR Amyloid Beta) OR APP-processing) AND platelet". Thirty-two studies were included in this systematic review. The papers included are analytic observational studies, namely twenty-nine cross sectional studies and three longitudinal studies, specifically prospective cohort study. The studies converge in an almost unitary way in affirming that subjects with AD show changes in APP processing compared to healthy age-matched controls. However, the problem of the specificity and sensitivity of these biomarkers is still at issue and would deserve to be deepened in future studies.
    Keywords:  APP processing; Alzheimer’s disease; Aβ amyloid; Aβ cascade; platelet activation
  25. Cells. 2021 Aug 05. pii: 1989. [Epub ahead of print]10(8):
      The selective targeting and disposal of solid protein aggregates are essential for cells to maintain protein homoeostasis. Autophagy receptors including p62, NBR1, Cue5/TOLLIP (CUET), and Tax1-binding protein 1 (TAX1BP1) proteins function in selective autophagy by targeting ubiquitinated aggregates through ubiquitin-binding domains. Here, we summarize previous beliefs and recent findings on selective receptors in aggregate autophagy. Since there are many reviews on selective autophagy receptors, we focus on their oligomerization, which enables receptors to function as pathway determinants and promotes phase separation.
    Keywords:  Cue5; Dsk2; TAX1BP1; autophagy; p62; proteasome; receptors; ubiquitin