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

  1. Ageing Res Rev. 2021 Jul 31. pii: S1568-1637(21)00164-1. [Epub ahead of print]70 101417
      One evident hallmark of Alzheimer's disease (AD) is the irregular accumulation of proteins due to changes in proteostasis involving endoplasmic reticulum (ER) stress. To alleviate ER stress and reinstate proteostasis, cells undergo an integrated signaling cascade called the unfolded protein response (UPR) that reduces the number of misfolded proteins and inhibits abnormal protein accumulation. Aging is associated with changes in the expression of ER chaperones and folding enzymes, leading to the impairment of proteostasis, and accumulation of misfolded proteins. The disrupted initiation of UPR prevents the elimination of unfolded proteins, leading to ER stress. In AD, the accumulation of misfolded proteins caused by sustained cellular stress leads to neurodegeneration and neuronal death. Current research has revealed that ER stress can trigger an inflammatory response through diverse transducers of UPR. Although the involvement of a neuroinflammatory component in AD has been documented for decades, whether it is a contributing factor or part of the neurodegenerative events is so far unknown. Besides, a feedback loop occurs between neuroinflammation and ER stress, which is strongly associated with neurodegenerative processes in AD. In this review, we focus on the current research on ER stress and UPR in cellular aging and neuroinflammatory processes, leading to memory impairment and synapse dysfunction in AD.
    Keywords:  Aging; Alzheimer’s disease; ER stress; Endoplasmic reticulum; Neuroinflammation; Unfolded protein response
  2. Biomedicines. 2021 Jul 08. pii: 791. [Epub ahead of print]9(7):
      The spliced form of X-box binding protein 1 (XBP1s) is an active transcription factor that plays a vital role in the unfolded protein response (UPR). Under endoplasmic reticulum (ER) stress, unspliced Xbp1 mRNA is cleaved by the activated stress sensor IRE1α and converted to the mature form encoding spliced XBP1 (XBP1s). Translated XBP1s migrates to the nucleus and regulates the transcriptional programs of UPR target genes encoding ER molecular chaperones, folding enzymes, and ER-associated protein degradation (ERAD) components to decrease ER stress. Moreover, studies have shown that XBP1s regulates the transcription of diverse genes that are involved in lipid and glucose metabolism and immune responses. Therefore, XBP1s has been considered an important therapeutic target in studying various diseases, including cancer, diabetes, and autoimmune and inflammatory diseases. XBP1s is involved in several unique mechanisms to regulate the transcription of different target genes by interacting with other proteins to modulate their activity. Although recent studies discovered numerous target genes of XBP1s via genome-wide analyses, how XBP1s regulates their transcription remains unclear. This review discusses the roles of XBP1s in target genes transcriptional regulation. More in-depth knowledge of XBP1s target genes and transcriptional regulatory mechanisms in the future will help develop new therapeutic targets for each disease.
    Keywords:  ATF6; ER stress; IRE1; RIDD; UPR; XBP1s; unfolded protein response
  3. Int J Mol Sci. 2021 Jul 29. pii: 8146. [Epub ahead of print]22(15):
      Neurodegenerative diseases are an ever-increasing problem for the rapidly aging population. Despite this, our understanding of how these neurodegenerative diseases develop and progress, is in most cases, rudimentary. Protein kinase RNA (PKR)-like ER kinase (PERK) comprises one of three unfolded protein response pathways in which cells attempt to manage cellular stress. However, because of its role in the cellular stress response and the far-reaching implications of this pathway, error within the PERK pathway has been shown to lead to a variety of pathologies. Genetic and clinical studies show a correlation between failure of the PERK pathway in neural cells and the development of neurodegeneration, but the wide array of methodology of these studies is presenting conflicting narratives about the role of PERK in these affected systems. Because of the connection between PERK and pathology, PERK has become a high value target of study for understanding neurodegenerative diseases and potentially how to treat them. Here, we present a review of the literature indexed in PubMed of the PERK pathway and some of the complexities involved in investigating the protein's role in the development of neurodegenerative diseases as well as how it may act as a target for therapeutics.
    Keywords:  PERK; endoplasmic reticulum stress; neurodegeneration; tauopathy; therapy; unfolded protein response
  4. PLoS Genet. 2021 Aug 05. 17(8): e1009734
      The heat shock response (HSR) is a highly conserved cellular process that promotes survival during stress. A hallmark of the HSR is the rapid induction of heat shock proteins (HSPs), such as HSP-70, by transcriptional activation. Once the stress is alleviated, HSPs return to near basal levels through incompletely understood mechanisms. Here, we show that the microRNA pathway acts during heat shock recovery in Caenorhabditis elegans. Depletion of the miRNA Argonaute, Argonaute Like Gene 1 (ALG-1), after an episode of heat shock resulted in decreased survival and perdurance of high hsp-70 levels. We present evidence that regulation of hsp-70 is dependent on miR-85 and sequences in the hsp-70 3'UTR that contain target sites for this miRNA. Regulation of hsp-70 by the miRNA pathway was found to be particularly important during recovery from HS, as animals that lacked miR-85 or its target sites in the hsp-70 3'UTR overexpressed HSP-70 and exhibited reduced viability. In summary, our findings show that down-regulation of hsp-70 by miR-85 after HS promotes survival, highlighting a previously unappreciated role for the miRNA pathway during recovery from stress.
  5. Cell Death Dis. 2021 Aug 05. 12(8): 770
      Rare monogenic disorders often share molecular etiologies involved in the pathogenesis of common diseases. Congenital disorders of glycosylation (CDG) and deglycosylation (CDDG) are rare pediatric disorders with symptoms that range from mild to life threatening. A biological mechanism shared among CDG and CDDG as well as more common neurodegenerative diseases such as Alzheimer's disease and amyotrophic lateral sclerosis, is endoplasmic reticulum (ER) stress. We developed isogenic human cellular models of two types of CDG and the only known CDDG to discover drugs that can alleviate ER stress. Systematic phenotyping confirmed ER stress and identified elevated autophagy among other phenotypes in each model. We screened 1049 compounds and scored their ability to correct aberrant morphology in each model using an agnostic cell-painting assay based on >300 cellular features. This primary screen identified multiple compounds able to correct morphological phenotypes. Independent validation shows they also correct cellular phenotypes and alleviate each of the ER stress markers identified in each model. Many of the active compounds are associated with microtubule dynamics, which points to new therapeutic opportunities for both rare and more common disorders presenting with ER stress, such as Alzheimer's disease and amyotrophic lateral sclerosis.
  6. FEBS Lett. 2021 Aug 06.
      Maintenance of the proteome (proteostasis) is essential for cellular homeostasis and prevents cytotoxic stress responses that arise from protein misfolding. However, little is known about how different types of misfolded proteins impact homeostasis, especially when protein degradation pathways are compromised. We examined the effects of misfolded protein expression on yeast growth by characterizing a suite of substrates possessing the same aggregation-prone domain but engaging different quality control pathways. We discovered that treatment with a proteasome inhibitor was more toxic in yeast expressing misfolded membrane proteins, and this growth defect was mirrored in yeast lacking a proteasome-specific transcription factor, Rpn4p. These results highlight weaknesses in the proteostasis network's ability to handle the stress arising from an accumulation of misfolded membrane proteins.
  7. Front Pharmacol. 2021 ;12 640758
      Alzheimer's disease (AD) is tightly related to endoplasmic reticulum stress (ER stress), which aggravates two dominant pathological manifestations of AD: senile plaques and neurofibrillary tangles. Berberine is widely applied in the clinical treatment of many diseases and is reported to have anti-AD effects. In the present study, berberine was shown to ameliorate ER stress and cognitive impairment in APP/PS1 mice. We found ER stress plays a role as a central hub for signal transduction, which was evidenced by the hyperactivation of glycogen synthase kinase 3β (GSK3β) to phosphorylate tau and the activation of PRKR-like endoplasmic reticulum kinase (PERK) subsequently to phosphorylate eukaryotic translation initiation factor-2 α (eIF2α). Also, eIF2α has regulated the expression of beta-site APP cleaving enzyme-1 (BACE1), which cleaves APP into pro-oligomerized amyloid beta 42 (Aβ42), the main component of senile plaques, proven by using siRNA targeting at eIF2α. Mechanically, berberine can reduce GSK3β activity, contributing to the downregulation of tau phosphorylation. Berberine also suppressed Aβ42 production via inhibiting the PERK/eIF2α/BACE1 signaling pathway. Taken together, these findings indicated that berberine had the potential to ameliorate two major pathological manifestations of AD mainly by suppressing ER stress. Our work provided knowledge on the pharmacological intervention of AD and the possible targets for future drug development.
    Keywords:  Alzheimer’s disease; Aβ42 production; berberine; endoplasmic reticulum stress; tau hyperphosphorylation
  8. Biomedicines. 2021 Jul 17. pii: 833. [Epub ahead of print]9(7):
      Mounting evidence shows a link between mitochondrial dysfunction and neurodegenerative disorders, including Alzheimer Disease. Increased oxidative stress, defective mitodynamics, and impaired oxidative phosphorylation leading to decreased ATP production, can determine synaptic dysfunction, apoptosis, and neurodegeneration. Furthermore, mitochondrial proteostasis and the protease-mediated quality control system, carrying out degradation of potentially toxic peptides and misfolded or damaged proteins inside mitochondria, are emerging as potential pathogenetic mechanisms. The enzyme pitrilysin metallopeptidase 1 (PITRM1) is a key player in these processes; it is responsible for degrading mitochondrial targeting sequences that are cleaved off from the imported precursor proteins and for digesting a mitochondrial fraction of amyloid beta (Aβ). In this review, we present current evidence obtained from patients with PITRM1 mutations, as well as the different cellular and animal models of PITRM1 deficiency, which points toward PITRM1 as a possible driving factor of several neurodegenerative conditions. Finally, we point out the prospect of new diagnostic and therapeutic approaches.
    Keywords:  Alzheimer Disease; PITRM1; mitochondrial dysfunction; mitochondrial protein quality control; mitochondrial proteostasis; neurodegeneration; neurodegenerative dementia; neurodegenerative diseases; pitrilysin metallopeptidase 1; protein aggregation; spinocerebellar ataxia
  9. Front Aging Neurosci. 2021 ;13 698601
      Mitochondrial autophagy is an early defense and protection process that selectively clears dysfunctional or excessive mitochondria through a distinctive mechanism to maintain intracellular homeostasis. Mitochondrial dysfunction during cerebral stroke involves metabolic disbalance, oxidative stress, apoptosis, endoplasmic reticulum stress, and abnormal mitochondrial autophagy. This article reviews the research progress on the mechanism of mitochondrial autophagy in ischemic stroke to provide a theoretical basis for further research on mitochondrial autophagy and the treatment of ischemic stroke.
    Keywords:  FUNDC1; NIX/BNIP3; PINK1/Parkin; cerebral stroke; mitochondrial autophagy
  10. Int J Biol Macromol. 2021 Aug 03. pii: S0141-8130(21)01565-8. [Epub ahead of print]
      Winter cold is one of the major environmental stresses for ectotherm species. Chilo suppressalis, a notorious lepidopteran pest of rice, has a wide geographic region that includes temperate zones with severe environmental conditions. Although C. suppressalis exhibits remarkable cold tolerance, its cold-adaptation mechanisms remain unclear. Here, we used bioinformatics approaches to evaluate transcript levels of genes comprising the C. suppressalis heat shock protein (HSP)/co-chaperone network in response to cold-induced stress. Using all such genes identified in the C. suppressalis genome, we experimentally examined the corresponding transcript levels under cold-acclimation or intermittent cold-shock stresses in diapause and non-diapausing larvae. In total, we identified 19 HSPs and 8 HSP co-chaperones in the C. suppressalis genome. Nine (hsp90, hsp75, hsp70, hsp40, small hsp, activator of 90 kDa heat shock protein ATPase-like, heat shock factor, heat shock factor binding protein 1-like and HSPB1-associated protein 1) were highly cold-inducible and likely comprise the principal cold-response HSP/co-chaperone network in C. suppressalis. We also found that transcriptional regulation of the HSP/co-chaperone networks response differs between cold-acclimation and short-term cold-shock. Moreover, activation of the HSP/co-chaperone network depends on the diapause state of overwintering larvae and cold acclimation may further increase larval cold tolerance. These results provide key new insights in the cold-adaptation mechanisms in C. suppressalis.
    Keywords:  Chilo suppressalis; Cold adaptation; Gene network; HSP co-chaperone; Heat shock protein
  11. Cells. 2021 Jul 05. pii: 1694. [Epub ahead of print]10(7):
      Emerging evidence indicates that cellular senescence could be a critical inducing factor for aging-associated neurodegenerative disorders. However, the involvement of cellular senescence remains unclear in Parkinson's disease (PD). To determine this, we assessed the effects of α-synuclein preformed fibrils (α-syn PFF) or 1-methyl-4-phenylpyridinium (MPP+) on changes in cellular senescence markers, employing α-syn PFF treated-dopaminergic N27 cells, primary cortical neurons, astrocytes and microglia and α-syn PFF-injected mouse brain tissues, as well as human PD patient brains. Our results demonstrate that α-syn PFF-induced toxicity reduces the levels of Lamin B1 and HMGB1, both established markers of cellular senescence, in correlation with an increase in the levels of p21, a cell cycle-arrester and senescence marker, in both reactive astrocytes and microglia in mouse brains. Using Western blot and immunohistochemistry, we found these cellular senescence markers in reactive astrocytes as indicated by enlarged cell bodies within GFAP-positive cells and Iba1-positive activated microglia in α-syn PFF injected mouse brains. These results indicate that PFF-induced pathology could lead to astrocyte and/or microglia senescence in PD brains, which may contribute to neuropathology in this model. Targeting senescent cells using senolytics could therefore constitute a viable therapeutic option for the treatment of PD.
    Keywords:  HMGB1; Lamin B1; SATB1; alpha-synuclein preformed fibrils; cellular senescence; microglia activation; p21; reactive astrocytes
  12. Cell Mol Neurobiol. 2021 Aug 04.
      Neurons are susceptible to different cellular stresses and this vulnerability has been implicated in the pathogenesis of Huntington's disease (HD). Accumulating evidence suggest that acute or chronic stress, depending on its duration and severity, can cause irreversible cellular damages to HD neurons, which contributes to neurodegeneration. In contrast, how normal and HD neurons respond during the resolution of a cellular stress remain less explored. In this study, we challenged normal and HD cells with a low-level acute ER stress and examined the molecular and cellular responses after stress removal. Using both striatal cell lines and primary neurons, we first showed the temporal activation of p-eIF2α-ATF4-GADD34 pathway in response to the acute ER stress and during recovery between normal and HD cells. HD cells were more vulnerable to cell death during stress recovery and were associated with increased number of apoptotic/necrotic cells and decreased cell proliferation. This is also supported by the Gene Ontology analysis from the RNA-seq data which indicated that "apoptosis-related Biological Processes" were more enriched in HD cells during stress recovery. We further showed that HD cells were defective in restoring global protein synthesis during stress recovery and promoting protein synthesis by an integrated stress response inhibitor, ISRIB, could attenuate cell death in HD cells. Together, these data suggest that normal and HD cells undergo distinct mechanisms of transcriptional reprogramming, leading to different cell fate decisions during the stress recovery.
    Keywords:  ER stress; Huntington’s disease; Protein synthesis; Stress recovery; UPR
  13. Cell Death Discov. 2021 Aug 05. 7(1): 203
      Dual topologies of proteins at the ER membrane are known for a variety of proteins allowing the same protein to exert different functions according to the topology adopted. A dual topology of the co-chaperone ERdj4, which resides in the endoplasmic reticulum (ER), was proposed recently, a thesis that we found to align all published data and existing controversies into one whole picture. The aim of this review is to reassess all primary data available in the literature on ER-resident Hsp40 co-chaperones with respect to their topology. After careful and critical analyses of all experimental data published so far, we identified, next to ERdj4, two other co-chaperones, ERdj3 and ERdj6, that also display features of a dual topology at the ER membrane. We assume that during cellular stress subpools of some ER-resident J protein can alter their topology so that these proteins can exert different functions in order to adapt to cellular stress.
  14. Symmetry (Basel). 2021 Mar;pii: 455. [Epub ahead of print]13(3):
      Homochirality of DNA and prevalent chirality of free and protein-bound amino acids in a living organism represents the challenge for modern biochemistry and neuroscience. The idea of an association between age-related disease, neurodegeneration, and racemization originated from the studies of fossils and cataract disease. Under the pressure of new results, this concept has a broader significance linking protein folding, aggregation, and disfunction to an organism's cognitive and behavioral functions. The integrity of cognitive function is provided by a delicate balance between the evolutionarily imposed molecular homo-chirality and the epigenetic/developmental impact of spontaneous and enzymatic racemization. The chirality of amino acids is the crucial player in the modulation the structure and function of proteins, lipids, and DNA. The collapse of homochirality by racemization is the result of the conformational phase transition. The racemization of protein-bound amino acids (spontaneous and enzymatic) occurs through thermal activation over the energy barrier or by the tunnel transfer effect under the energy barrier. The phase transition is achieved through the intermediate state, where the chirality of alpha carbon vanished. From a thermodynamic consideration, the system in the homo-chiral (single enantiomeric) state is characterized by a decreased level of entropy. The oscillating protein chirality is suggesting its distinct significance in the neurotransmission and flow of perceptual information, adaptive associative learning, and cognitive laterality. The common pathological hallmarks of neurodegenerative disorders include protein misfolding, aging, and the deposition of protease-resistant protein aggregates. Each of the landmarks is influenced by racemization. The brain region, cell type, and age-dependent racemization critically influence the functions of many intracellular, membrane-bound, and extracellular proteins including amyloid precursor protein (APP), TAU, PrP, Huntingtin, α-synuclein, myelin basic protein (MBP), and collagen. The amyloid cascade hypothesis in Alzheimer's disease (AD) coexists with the failure of amyloid beta (Aβ) targeting drug therapy. According to our view, racemization should be considered as a critical factor of protein conformation with the potential for inducing order, disorder, misfolding, aggregation, toxicity, and malfunctions.
    Keywords:  D-amino acids; adaptive associative learning; aggregation; association; brain information processing; cognitive functions; cognitive laterality; intrinsically disordered proteins; misfolding; neurodegeneration; non-equilibrium phase transitions; post translational modification; protein folding; protein folding energy landscape; racemization
  15. Mol Biol Rep. 2021 Aug 02.
      BACKGROUND: The current study was set to assess the effect of heat stress exposure on oxidative stress, apoptosis, and endoplasmic reticulum stress markers in the cerebellum of male mice.METHODS: Fifty male C57BL/6 mice were assigned to five groups of (I) control, (II) heat stress (HS)7, (III) HS14, (IV) HS21, and (V) HS42 groups. Animals in the control group were not exposed to HS. Mice in the II-V groups were exposed to HS once a day over 7, 14, 21, and 42 days, respectively. Cerebellar reactive oxygen species (ROS) levels, expression of heat shock protein (HSP)70 and caspase 3 as well as endoplasmic reticulum stress-related proteins (PERK, p-PERK, CHOP, and Full-length ATF-6) expression were determined on the 7th, 14th, 21st, and 42nd days.
    RESULTS: ROS levels and HSP70 expression increased following HS on the 14th, 21st, and 42nd days and the 7th, and 14th days with a peak level of expression on the 14th day following HS. HSP70 levels decreased afterward on the 21st and 42nd days compared with the control group. Besides, exposure to HS for 14, 21, and 42 days resulted in a significant increase in the CHOP and p-PERK levels in the cerebellum compared with the control group. Heat exposure also increased protein expression of cleaved caspase 3 and active ATF-6/Full-length ATF-6 on the 21st and 42nd days in the cerebellum compared with the control animals.
    CONCLUSION: These findings indicated that chronic HS augmented oxidative stress, endoplasmic reticulum stress, and apoptosis pathways in the cerebellum of mice.
    Keywords:  Apoptosis; Cerebellum; Endoplasmic reticulum stress; Heat shock protein (HSP)70; Heat stress; Oxidative stress
  16. Cells. 2021 Jul 15. pii: 1789. [Epub ahead of print]10(7):
      Amyotrophic lateral sclerosis (ALS) is a devastating neurodegenerative disease for which there is currently no cure. Progress in the characterization of other neurodegenerative mechanisms has shifted the spotlight onto an intracellular structure called mitochondria-endoplasmic reticulum (ER) contacts (MERCs) whose ER portion can be biochemically isolated as mitochondria-associated membranes (MAMs). Within the central nervous system (CNS), these structures control the metabolic output of mitochondria and keep sources of oxidative stress in check via autophagy. The most relevant MERC controllers in the ALS pathogenesis are vesicle-associated membrane protein-associated protein B (VAPB), a mitochondria-ER tether, and the ubiquitin-specific chaperone valosin containing protein (VCP). These two systems cooperate to maintain mitochondrial energy output and prevent oxidative stress. In ALS, mutant VAPB and VCP take a central position in the pathology through MERC dysfunction that ultimately alters or compromises mitochondrial bioenergetics. Intriguingly, both proteins are targets themselves of other ALS mutant proteins, including C9orf72, FUS, or TDP-43. Thus, a new picture emerges, where different triggers cause MERC dysfunction in ALS, subsequently leading to well-known pathological changes including endoplasmic reticulum (ER) stress, inflammation, and motor neuron death.
    Keywords:  amyotrophic lateral sclerosis (ALS); mitochondria-associated membranes (MAMs); mitochondria-endoplasmic reticulum contacts (MERCs)
  17. Front Cell Neurosci. 2021 ;15 695479
      Amyloid-β (Aβ) is the predominant pathologic protein in Alzheimer's disease (AD). The production and deposition of Aβ are important factors affecting AD progression and prognosis. The deposition of neurotoxic Aβ contributes to damage of the blood-brain barrier. However, the BBB is also crucial in maintaining the normal metabolism of Aβ, and dysfunction of the BBB aggravates Aβ deposition. This review characterizes Aβ deposition and BBB damage in AD, summarizes their interactions, and details their respective mechanisms.
    Keywords:  Alzheimer’s disease; P-glycoprotein; amyloid-β; blood–brain barrier; low-density lipoprotein receptor-related protein 1; receptor for advanced glycation end products
  18. Metab Brain Dis. 2021 Aug 04.
      A protein's structure is determined by its amino acid sequence and post-translational modifications, and provides the basis for its physiological functions. Across all organisms, roughly a third of the proteome comprises proteins that contain highly unstructured or intrinsically disordered regions. Proteins comprising or containing extensive unstructured regions are referred to as intrinsically disordered proteins (IDPs). IDPs are believed to participate in complex physiological processes through refolding of IDP regions, dependent on their binding to a diverse array of potential protein partners. They thus play critical roles in the assembly and function of protein complexes. Recent advances in experimental and computational analyses predicted multiple interacting partners for the disordered regions of proteins, implying critical roles in signal transduction and regulation of biological processes. Numerous disordered proteins are sequestered into aggregates in neurodegenerative diseases such as Alzheimer's disease (AD) where they are enriched even in serum, making them good candidates for serum biomarkers to enable early detection of AD.
    Keywords:  Aggregate proteome; Biomarker; Intrinsically disordered proteins; Neurodegneration; Protein aggregation
  19. Adv Sci (Weinh). 2021 Aug 02. e2101462
      Alzheimer's disease (AD) is a progressive neurodegenerative disease with no cure. Huge efforts have been made to develop anti-AD drugs in the past decades. However, all drug development programs for disease-modifying therapies have failed. Possible reasons for the high failure rate include incomplete understanding of complex pathophysiology of AD, especially sporadic AD (sAD), and species difference between humans and animal models used in preclinical studies. In this study, sAD is modeled using human induced pluripotent stem cell (hiPSC)-derived 3D brain organoids. Because the blood-brain barrier (BBB) leakage is a well-known risk factor for AD, brain organoids are exposed to human serum to mimic the serum exposure consequence of BBB breakdown in AD patient brains. The serum-exposed brain organoids are able to recapitulate AD-like pathologies, including increased amyloid beta (Aβ) aggregates and phosphorylated microtubule-associated tau protein (p-Tau) level, synaptic loss, and impaired neural network. Serum exposure increases Aβ and p-Tau levels through inducing beta-secretase 1 (BACE) and glycogen synthase kinase-3 alpha / beta (GSK3α/β) levels, respectively. In addition, single-cell transcriptomic analysis of brain organoids reveals that serum exposure reduced synaptic function in both neurons and astrocytes and induced immune response in astrocytes. The human brain organoid-based sAD model established in this study can provide a powerful platform for both mechanistic study and therapeutic development in the future.
    Keywords:  brain organoids; disease modeling; induced pluripotent stem cells; serum exposure; sporadic Alzheimer's disease
  20. ACS Chem Neurosci. 2021 Aug 02.
      The IRE1/XBP1 signaling pathway is the most conserved component of the endoplasmic reticulum unfolded protein response (UPRER). Activating this branch to correct defects in ER proteostasis is regarded as a promising anti-Parkinson's disease (PD) strategy. P-53 is a marine-derived xyloketal B analog which exhibited potential neuroprotective activities in previous research studies; however, the molecular mechanism underneath its protective effect remains unknown. Herein, a transcriptomic approach was introduced to explore the protective mechanism of P-53. RNA microarray profiling was conducted based on an MPP+-induced C. elegans PD model, and bioinformatics analyses including GO enrichment and PPI network analysis were subsequently performed. In particular, the recovery of the impaired UPRER was highlighted as a main physiological change caused by P-53, and a cluster of genes including abu and hsp family genes which are involved in the IRE1/XBP1 branch of the UPRER were identified as the key genes related to its neuroprotective effect. The transcription levels of these key genes were validated by RT-qPCR assays. Further results showed that P-53 enhanced the phosphorylation of IRE1, the splicing of xbp-1 mRNA, and the translation of XBP1S and boosted the expression level of the downstream targets of the IRE1/XBP1 signaling pathway. Moreover, it was also demonstrated that P-53 accelerated the scavenging of misfolded α-synuclein and attenuated the correlative mitochondrial dysfunction. Finally, the protective effect of P-53 against MPP+-induced dopaminergic neuronal loss was assessed. Taken together, these results revealed that P-53 plays its neuroprotective role through regulating of the IRE1/XBP1 signaling pathway and laid the foundation for its further development as an ER proteostasis-regulating agent.
    Keywords:  IRE1/XBP1 signaling pathway; Parkinson’s disease (PD); Xyloketals; endoplasmic reticulum unfolded protein response (UPRER); transcriptomic profiling
  21. J Cell Sci. 2021 Aug 05. pii: jcs.258685. [Epub ahead of print]
      The phase separation of the non-membrane bound Sec bodies occurs in Drosophila S2 cells by coalescence of components of the ER exit sites under the stress of amino-acid starvation. Here we address which signaling pathways cause Sec body formation and find that two pathways are critical. The first is the activation of the salt inducible kinases (SIK) by Na+ stress, that when it is strong is sufficient. The second is activation of IRE1 and PERK downstream of ER stress induced by absence of amino- acids, which needs to be combined with moderate salt stress to induce Sec body formation. SIK and IRE1/PERK activation appear to potentiate each other through the stimulation of the unfolded protein response, a key parameter in Sec body formation. This work pioneers the role of SIK in phase transition and re-enforces the role of IRE1 and PERK as a metabolic sensor for the level of circulating amino-acids and salt.
    Keywords:  Amino-acid starvation; Drosophila S2 cells; Phase separation; Salt stress; Sec body; Unfolded Protein Response
  22. Biomedicines. 2021 Jul 10. pii: 801. [Epub ahead of print]9(7):
      Alzheimer's disease (AD) is the most common type of dementia, contributing to 60-80% of cases. It is a neurodegenerative disease that usually starts symptomless in the first two to three decades and then propagates into a long-term, irreversible disease, resulting in the progressive loss of memory, reasoning, abstraction and language capabilities. It is a complex disease, involving a large number of entangled players, and there is no effective treatment to cure it or alter its progressive course. Therefore, a thorough understanding of the disease pathology and an early diagnosis are both necessary. AD has two significant pathological hallmarks: extracellular senile plaques composed of amyloid β-peptide (Aβ) and intracellular neurofibrillary tangles composed of hyperphosphorylated tau protein, and the aggregation of Aβ, which starts in earlier stages, is usually claimed to be the primary cause of AD. Secretases that cleave Aβ precursor protein (APP) and produce neurotoxic Aβ reside in distinct organelles of the cell, and current concepts suggest that APP moves between distinct intracellular compartments. Obviously, APP transport and processing are intimately related processes that cannot be dissociated from each other, and, thus, how and where APP is transported determines its processing fate. In this review, we summarize critical mechanisms underlying neuronal APP transport, which we divide into separate parts: (1) secretory pathways and (2) endocytic and autophagic pathways. We also include two lipoprotein receptors that play essential roles in APP transport: sorting-related receptor with A-type repeats and sortilin. Moreover, we consider here some major disruptions in the neuronal transport of APP that contribute to AD physiology and pathology. Lastly, we discuss current methods and technical difficulties in the studies of APP transport.
    Keywords:  Alzheimer’s disease; amyloid precursor protein; amyloid β-peptide neuronal transport; sortilin; sorting-related receptor with A-type repeats
  23. Tissue Cell. 2021 Jul 22. pii: S0040-8166(21)00112-9. [Epub ahead of print]72 101596
      The role of autophagy in the transplantation of induced pluripotent stem cells (iPSCs)-derived neural stem cells (NSCs) to treat spinal cord injury (SCI) and neurogenic bladder was investigated in this study. NSCs derived from human iPSCs were identified by and immunofluorescence assay. To clarify the role of autophagy, iPSCs were treated with either an autophagy inducer (rapamycin), or an autophagy inhibitor (chloroquine). Cell Counting kit-8 (CCK-8), western blot and flow cytometry were used to detect the effect of autophagy on the viability and differentiation of iPSCs. Sixty Wistar rats were selected to establish the SCI model and treated with iPSCs-derived NSCs transplantation. The effect of autophagy on the bladder function of rats with different treatments was evaluated by Basso, Beattie, and Bresnahan (BBB) score, bladder function score, bladder weight measurement, Hematoxylin & Eosin (H&E) staining, and Masson staining. The results of in vitro experiment showed that rapamycin enhanced the cell activity of iPSCs, increased the number of nestin positive cells, up-regulated Beclin-1 and LC3BI/II expressions, and down-regulated p62 expression. And the results of in vivo experiment showed that rapamycin improved exercise ability and bladder function, partially restored bladder weight, and significantly reduced bladder tissue damage in SCI rats. However, chloroquine showed the opposite results. The differentiation of iPSCs into NSCs could be promoted by induced autophagy, while neurogenic bladder of SCI was restored by autophagy activation.
    Keywords:  Autophagy; Induced pluripotent stem cells; Neural stem cells; Neurogenic bladder; Spinal cord injury
  24. Int J Mol Sci. 2021 Jul 28. pii: 8077. [Epub ahead of print]22(15):
      Since their discovery, heat shock proteins (HSPs) have been identified in all domains of life, which demonstrates their importance and conserved functional role in maintaining protein homeostasis. Mitochondria possess several members of the major HSP sub-families that perform essential tasks for keeping the organelle in a fully functional and healthy state. In humans, the mitochondrial HSP70 chaperone system comprises a central molecular chaperone, mtHSP70 or mortalin (HSPA9), which is actively involved in stabilizing and importing nuclear gene products and in refolding mitochondrial precursor proteins, and three co-chaperones (HSP70-escort protein 1-HEP1, tumorous imaginal disc protein 1-TID-1, and Gro-P like protein E-GRPE), which regulate and accelerate its protein folding functions. In this review, we summarize the roles of mitochondrial molecular chaperones with particular focus on the human mtHsp70 and its co-chaperones, whose deregulated expression, mutations, and post-translational modifications are often considered to be the main cause of neurological disorders, genetic diseases, and malignant growth.
    Keywords:  GRPE; HEP1; TID-1; cancer; mitochondrial chaperones; mortalin; mtHSP70; neurodegenerative disorders; post-translational modification; protein quality control
  25. Brain Struct Funct. 2021 Aug 06.
      The decreased efficiency of autophagic processing in the central nervous system during aging may be a contributing factor in neurodegenerative diseases. BAG3 (Bcl2 associated athanogene 3) is a major member of the BAG family of co-molecular chaperones that mediate selective macroautophagy. Therefore, we analyzed the expression and distribution of BAG3 in the brain at postnatal 0 day (P0), P15, 1-, 2-, 9-, 12-, and 18 month-old C57BL/6 mice, thus covering almost all ages. Except for a significant steep drop in mRNA and protein levels in the cortex and hippocampus soon after birth, there were minimal differences in the expression and distribution of BAG3 among P15, M1, M2, M9, and M12 mice; however, at 18 months, BAG3 expression was significantly higher. Immunohistochemical analyses showed that BAG3 is mainly located in the neuronal cytoplasm and processes in C57BL/6 the cerebral cortex and hippocampus from P0 to M18 postnatal development. These findings indicate that BAG3 might be stable in young and middle-aged mice, but unstable in aged mice.
    Keywords:  BAG3; NeuN; α-Tubulin
  26. J Parkinsons Dis. 2021 Jul 26.
      BACKGROUND: α-synuclein (α-syn) aggregation contributes to the progression of multiple neurodegenerative diseases. We recently found that the isoform b of the co-chaperone DNAJB6 is a strong suppressor of a-syn aggregation in vivo and in vitro. However, nothing is known about the role of the endogenous isoform b of DNAJB6 (DNAJB6b) in health and disease, due to lack of specific antibodies.OBJECTIVE: Here we generated a novel anti-DNAJB6b antibody to analyze the localization and expression this isoform in cells, in tissue and in clinical material.
    METHODS: To address this we used immunocytochemistry, immunohistochemistry, as well as a novel quantitative DNAJB6 specific ELISA method.
    RESULTS: The endogenous protein is mainly expressed in the cytoplasm and in neurites in vitro, where it is found more in dendrites than in axons. We further verified in vivo that DNAJB6b is expressed in the dopaminergic neurons of the substantia nigra pars compacta (SNpc), which is a neuronal subpopulation highly sensitive to α-syn aggregation, that degenerate to a large extend in patients with Parkinson's disease (PD) and multiple system atrophy (MSA). When we analyzed the expression levels of DNAJB6b in brain material from PD and MSA patients, we found a downregulation of DNAJB6b by use of ELISA based quantification. Interestingly, this was also true when analyzing tissue from patients with progressive supranuclear palsy, a taupathic atypical parkinsonian disorder. However, the total level of DNAJB6 was upregulated in these three diseases, which may indicate an upregulation of the other major isoform of DNAJB6, DNAJB6a.
    CONCLUSION: This study shows that DNAJB6b is downregulated in several different neurodegenerative diseases, which makes it an interesting target to further investigate in relation to amyloid protein aggregation and disease progression.
    Keywords:  Alpha-synuclein; DNAJB6; clinical samples; neurodegeneration; synucleinopathy
  27. Mol Cell Proteomics. 2021 Jul 28. pii: S1535-9476(21)00097-9. [Epub ahead of print] 100125
      Various pathologies result from disruptions to or stress of endoplasmic reticulum (ER) homeostasis, such as Parkinson's disease and most neurodegenerative illnesses, diabetes, pulmonary fibrosis, viral infections and cancers. A critical process in maintaining ER homeostasis is the selection of misfolded proteins by the ER quality-control system (ERQC) for destruction via ER-associated degradation (ERAD). One key protein proposed to act during the first steps of misfolded glycoprotein degradation is the ER degradation-enhancing α-mannosidase-like protein 2 (EDEM2). Therefore, characterization of the EDEM2 associated proteome is of great interest. We took advantage of using melanoma cells overexpressing EDEM2 as a cancer model system, to start documenting at the deglycoproteome level (N-glycosites identification) the emerging link between ER homeostasis and cancer progression. The dataset created for identifying the EDEM2 glyco-clients carrying high mannose/hybrid N-glycans provides a comprehensive N-glycosites analysis mapping over 1000 N-glycosites on more than 600 melanoma glycoproteins. To identify EDEM2-associated proteins we used affinity-proteomics and proteome-wide analysis of sucrose density fractionation in an integrative workflow. Using intensity and spectral count-based quantification, we identify seven new EDEM2 partners, all of which are involved in ERQC and ERAD. Moreover, we defined novel endogenous candidates for EDEM2-dependent ERAD by combining deglycoproteomics, SILAC-based proteomics, and biochemical methods. These included tumor antigens and several ER-transiting endogenous melanoma proteins, including ITGA1 and PCDH2, the expression of which was negatively correlated with that of EDEM2. Tumor antigens are key in the antigen presentation process, whilst ITGA1 and PCDH2 are involved in melanoma metastasis and invasion. EDEM2 could therefore have a regulatory role in melanoma through the modulation of these glycoproteins degradation and trafficking. The data presented herein suggest that EDEM2 is involved in ER homeostasis to a greater extent than previously suggested.
    Keywords:  EDEM2; ER quality control; ERAD; glycoproteomics; mass spectrometry; melanoma; proteomics; pulse-SILAC
  28. Cells. 2021 Jul 16. pii: 1802. [Epub ahead of print]10(7):
      Alzheimer's disease (AD) is the most common type of dementia in the elderly population. The disease is characterized by progressive memory loss, cerebral atrophy, extensive neuronal loss, synaptic alterations, brain inflammation, extracellular accumulation of amyloid-β (Aβ) plaques, and intracellular accumulation of hyper-phosphorylated tau (p-tau) protein. Many recent clinical trials have failed to show therapeutic benefit, likely because at the time in which patients exhibit clinical symptoms the brain is irreversibly damaged. In recent years, induced pluripotent stem cells (iPSCs) have been suggested as a promising cell therapy to recover brain functionality in neurodegenerative diseases such as AD. To evaluate the potential benefits of iPSCs on AD progression, we stereotaxically injected mouse iPSC-derived neural precursors (iPSC-NPCs) into the hippocampus of aged triple transgenic (3xTg-AD) mice harboring extensive pathological abnormalities typical of AD. Interestingly, iPSC-NPCs transplanted mice showed improved memory, synaptic plasticity, and reduced AD brain pathology, including a reduction of amyloid and tangles deposits. Our findings suggest that iPSC-NPCs might be a useful therapy that could produce benefit at the advanced clinical and pathological stages of AD.
    Keywords:  Alzheimer’s disease; amyloid-beta; clinical symptoms; inflammation; stem cells; tau; therapy
  29. EMBO Rep. 2021 Aug 02. e52289
      Degradation of the endoplasmic reticulum (ER) via selective autophagy (ER-phagy) is vital for cellular homeostasis. We identify FAM134A/RETREG2 and FAM134C/RETREG3 as ER-phagy receptors, which predominantly exist in an inactive state under basal conditions. Upon autophagy induction and ER stress signal, they can induce significant ER fragmentation and subsequent lysosomal degradation. FAM134A, FAM134B/RETREG1, and FAM134C are essential for maintaining ER morphology in a LC3-interacting region (LIR)-dependent manner. Overexpression of any FAM134 paralogue has the capacity to significantly augment the general ER-phagy flux upon starvation or ER-stress. Global proteomic analysis of FAM134 overexpressing and knockout cell lines reveals several protein clusters that are distinctly regulated by each of the FAM134 paralogues as well as a cluster of commonly regulated ER-resident proteins. Utilizing pro-Collagen I, as a shared ER-phagy substrate, we observe that FAM134A acts in a LIR-independent manner and compensates for the loss of FAM134B and FAM134C, respectively. FAM134C instead is unable to compensate for the loss of its paralogues. Taken together, our data show that FAM134 paralogues contribute to common and unique ER-phagy pathways.
    Keywords:  Collagen; ER stress; ER-phagy; FAM134; autophagy
  30. STAR Protoc. 2021 Sep 17. 2(3): 100674
      Ubiquitin stress-induced NEDDylation leads to the formation of aggresome-like bodies (ALBs) in the perinuclear region of cells. Therefore, imaging analysis is essential for characterizing the biological phenotypes of ALBs. Here, we describe a protocol to monitor ALBs induced by ubiquitin stress using immunocytochemistry and to quantify cells containing ALBs. This optimized protocol details the use of readily available materials and reagents and can be applied to explore diverse molecules involved in stress-induced ALBs. For complete details on the use and execution of this protocol, please refer to Kim et al. (2021).
    Keywords:  Cell Biology; Microscopy; Molecular Biology; Proteomics
  31. Cell Stress Chaperones. 2021 Aug 02.
      Small heat shock proteins (sHSPs) function as molecular chaperones in multiple physiological processes and are active during thermal stress. sHSP expression is controlled by heat shock transcription factor (HSF); however, few studies have been conducted on HSF in agricultural pests. Liriomyza trifolii is an introduced insect pest of horticultural and vegetable crops in China. In this study, the master regulator, HSF1, was cloned and characterized from L. trifolii, and the expression levels of HSF1 and five sHSPs were studied during heat stress. HSF1 expression in L. trifolii generally decreased with rising temperatures, whereas expression of the five sHSPs showed an increasing trend that correlated with elevated temperatures. All five sHSPs and HSF1 showed an upward trend in expression with exposure to 40 ℃ without a recovery period. When a recovery period was incorporated after thermal stress, the expression patterns of HSF1 and sHSPs in L. trifolii exposed to 40 °C was significantly lower than expression with no recovery period. To elucidate potential interactions between HSF1 and sHSPs, double-stranded RNA was synthesized to knock down HSF1 in L. trifolii by RNA interference. The knockdown of HSF1 by RNAi decreased the survival rate and expression of HSP19.5, HSP20.8, and HSP21.3 during high-temperature stress. This study expands our understanding of HSF1-regulated gene expression in L. trifolii exposed to heat stress.
    Keywords:  HSF1; Heat stress; Liriomyza trifolii; RNAi; sHSPs
  32. Neuropsychopharmacology. 2021 Aug 02.
      Reduced brain-derived neurotrophic factor (BDNF) and gamma-aminobutyric acid (GABA) neurotransmission co-occur in brain conditions (depression, schizophrenia and age-related disorders) and are associated with symptomatology. Rodent studies show they are causally linked, suggesting the presence of biological pathways mediating this link. Here we first show that reduced BDNF and GABA also co-occur with attenuated autophagy in human depression. Using mice, we then show that reducing Bdnf levels (Bdnf+/-) leads to upregulated sequestosome-1/p62, a key autophagy-associated adaptor protein, whose levels are inversely correlated with autophagic activity. Reduced Bdnf levels also caused reduced surface presentation of α5 subunit-containing GABAA receptor (α5-GABAAR) in prefrontal cortex (PFC) pyramidal neurons. Reducing p62 gene dosage restored α5-GABAAR surface expression and rescued PFC-relevant behavioral deficits of Bdnf+/- mice, including cognitive inflexibility and reduced sensorimotor gating. Increasing p62 levels was sufficient to recreate the molecular and behavioral profiles of Bdnf+/- mice. Collectively, the data reveal a novel mechanism by which deficient BDNF leads to targeted reduced GABAergic signaling through autophagic dysregulation of p62, potentially underlying cognitive impairment across brain conditions.
  33. Int J Biol Macromol. 2021 Jul 29. pii: S0141-8130(21)01609-3. [Epub ahead of print]
      The loss of crystallins solubility with aging and the formation of amyloid-like aggregates is considered the hallmark characteristic of cataract pathology. The present study was carried out to assess the effect of temperature on the soluble lens protein and the formation of protein aggregates with typical amyloid characteristics. The soluble fraction of lens proteins was subjected for heat treatment in the range of 40-60 °C, and the nature of protein aggregates was assessed by using Congo red (CR), thioflavin T (ThT), and 8-anilinonaphthalene-1-sulfonic acid (ANS) binding assays, circular dichroism (CD), Fourier-transform infrared (FT-IR) spectroscopy, and transmission electron microscopy (TEM). The heat-treated protein samples displayed a substantial bathochromic shift (≈15 nm) in the CR's absorption maximum (λmax) and increased ThT and ANS binding. The heat treatment of lens soluble proteins results in the formation of nontoxic, β-sheet rich, non-fibrillar, protein aggregates similar to the structures evident in the insoluble fraction of proteins isolated from the cataractous lens. The data obtained from the present study suggest that the exposure of soluble lens proteins to elevated temperature leads to the formation of non-fibrillar aggregates, establishing the role of amyloid in the heat-induced augmentation of cataracts pathology.
    Keywords:  Amyloids; Cataract; Crystallins; Protein aggregation; Soluble lens protein
  34. Int J Mol Sci. 2021 Jul 30. pii: 8179. [Epub ahead of print]22(15):
      The maintenance of mitochondrial integrity is critical for muscle health. Mitochondria, indeed, play vital roles in a wide range of cellular processes, including energy supply, Ca2+ homeostasis, retrograde signaling, cell death, and many others. All mitochondria-containing cells, including skeletal muscle cells, dispose of several pathways to maintain mitochondrial health, including mitochondrial biogenesis, mitochondrial-derived vesicles, mitochondrial dynamics (fusion and fission process shaping mitochondrial morphology), and mitophagy-the process in charge of the removal of mitochondria though autophagy. The loss of skeletal muscle mass (atrophy) is a major health problem worldwide, especially in older people. Currently, there is no treatment to counteract the progressive decline in skeletal muscle mass and strength that occurs with aging, a process termed sarcopenia. There is increasing data, including our own, suggesting that accumulation of dysfunctional mitochondria contributes to the development of sarcopenia. Impairments in mitochondrial dynamics and mitophagy were recently proposed to contribute to sarcopenia. This review summarizes the current state of knowledge on the role played by mitochondrial dynamics and mitophagy in skeletal muscle health and in the development of sarcopenia. We also highlight recent studies showing that enhancing mitophagy in skeletal muscle is a promising therapeutic target to prevent or even treat skeletal muscle dysfunction in the elderly.
    Keywords:  aging; autophagy; mitochondrial dynamics; mitophagy; sarcopenia; skeletal muscle
  35. Biol Trace Elem Res. 2021 Aug 04.
      Heat stress leads to oxidative stress and induces apoptosis in various cells. Endoplasmic reticulum (ER) stress is an important apoptosis pathway. Manganese (Mn) has been shown to enhance the activity of manganese superoxide dismutase (MnSOD). To explore the potential effect of Mn on ER stress and apoptosis induced by heat stress, we examined crucial factors associated with heat stress, ER stress, and apoptosis in cultured primary chick embryonic myocardial cells that had been pretreated with 20 μM Mn for 24 h and then subjected to 4 h of heat stress. The results showed that Mn decreased (P < 0.05) heat stress-induced reactive oxygen species (ROS) production and exerted antiapoptotic effects by increasing MnSOD enzymatic activity. The heat stress-induced accumulation of intracellular calcium was dramatically reduced (P < 0.05). Mn treatment significantly decreased (P < 0.05) the expression levels of the apoptosis-related gene Bax and ER stress markers glucose-regulated protein 78 (GRP78) and CCAAT/enhancer binding protein homologous protein (CHOP) in primary chick embryonic myocardial cells. Additionally, Mn reduced oxidative stress by activating the nuclear factor E2-related factor 2 (NRF2)/SOD2 signaling pathway. Taken together, our findings indicate that Mn attenuates heat stress-induced apoptosis by inhibiting ROS generation, intracellular calcium accumulation, and the ER stress pathway and activating the NRF2/SOD2 signaling pathway to protect myocardial cells from oxidative stress during chick embryonic development.
    Keywords:  Apoptosis; Endoplasmic reticulum stress; Heat stress; Manganese; MnSOD; Primary chick embryonic myocardial cells