bims-proarb Biomed News
on Proteostasis in aging and regenerative biology
Issue of 2021‒08‒15
thirty-four papers selected by
Rich Giadone
Harvard University

  1. Cell Stem Cell. 2021 Aug 06. pii: S1934-5909(21)00294-0. [Epub ahead of print]
      Maintaining proteostasis is key to resisting stress and promoting healthy aging. Proteostasis is necessary to preserve stem cell function, but little is known about the mechanisms that regulate proteostasis during stress in stem cells, and whether disruptions of proteostasis contribute to stem cell aging is largely unexplored. We determined that ex-vivo-cultured mouse and human hematopoietic stem cells (HSCs) rapidly increase protein synthesis. This challenge to HSC proteostasis was associated with nuclear accumulation of Hsf1, and deletion of Hsf1 impaired HSC maintenance ex vivo. Strikingly, supplementing cultures with small molecules that enhance Hsf1 activation partially suppressed protein synthesis, rebalanced proteostasis, and supported retention of HSC serial reconstituting activity. Although Hsf1 was dispensable for young adult HSCs in vivo, Hsf1 deficiency increased protein synthesis and impaired the reconstituting activity of middle-aged HSCs. Hsf1 thus promotes proteostasis and the regenerative activity of HSCs in response to culture stress and aging.
    Keywords:  Hsf1; aging; heat shock response; hematopoiesis; hematopoietic stem cell; protein synthesis; proteostasis; stem cell; stress; translation
  2. J Cell Sci. 2022 Mar 01. pii: jcs258325. [Epub ahead of print]135(5):
      When the temperature is increased, the heat-shock response is activated to protect the cellular environment. The transcriptomics and proteomics of this process are intensively studied, while information about how the cell responds structurally to heat stress is mostly lacking. Here, Saccharomyces cerevisiae were subjected to a mild continuous heat shock (38°C) and intermittently cryo-immobilised for electron microscopy. Through measuring changes in all distinguishable organelle numbers, sizes and morphologies in over 2100 electron micrographs, a major restructuring of the internal architecture of the cell during the progressive heat shock was revealed. The cell grew larger but most organelles within it expanded even more, shrinking the volume of the cytoplasm. Organelles responded to heat shock at different times, both in terms of size and number, and adaptations of the morphology of some organelles (such as the vacuole) were observed. Multivesicular bodies grew by almost 70%, indicating a previously unknown involvement in the heat-shock response. A previously undescribed electron-translucent structure accumulated close to the plasma membrane. This all-encompassing approach provides a detailed chronological progression of organelle adaptation throughout the cellular heat-stress response.
    Keywords:  Budding yeast; Electron microscopy; Heat shock; Organelles; Ultrastructure
  3. Neural Regen Res. 2022 Mar;17(3): 512-515
      Stress response is a cellular widespread mechanism encoded by a common protein program composed by multiple cellular factors that converge in a defense reaction to protect the cell against damage. Among many mechanisms described, heat shock proteins were proposed as universally conserved protective factors in the stress core proteome, coping with different stress stimuli through its canonical role in protein homeostasis. However, emerging evidences reveal non-canonical roles of heat shock proteins relevant for physiological and pathological conditions. Here, we review the implications of inducible heat shock proteins in the central nervous system physiology. In particular, we discuss the relevance of heat shock proteins in the maintenance of synapses, as a balanced protective mechanism in central nervous system development, pathological conditions and aging.
    Keywords:  aging; central nervous system; chaperones; environment; neuroprotection; pathology; stress; synapses
  4. Autophagy. 2021 Aug 12. 1-2
      Temperature variations induce stressful conditions that challenge the ability of organisms to maintain cell homeostasis. The intensity and duration of heat stress affect cell response very differently, ranging from a beneficial effect - hormesis - to necrotic cell death. There is a strong interplay between the cell response to heat shock and macroautophagy/autophagy, which is induced to cope with stress. Using Caenorhabditis elegans, we developed a new paradigm to study adaptation to acute non-lethal heat-stress (aHS) during development. We found that aHS results in transient fragmentation of mitochondria, decreased cellular respiration, and delayed development. Moreover, an active autophagy flux associated with mitophagy events is triggered in many tissues, enables the rebuilding of the mitochondrial network and modulates the adaptive plasticity of the development, showing that the autophagic response is protective for C. elegans. Using genetic and cellular approaches, we showed that mitochondria are a major site for autophagosome biogenesis in the epidermis, under both standard and heat-stress conditions. We determined that DRP-1 (Dynamin-Related Protein 1) involved in mitochondrial fission, is an important player for the autophagy process and the adaptation to aHS. Our study suggests that DRP-1 is involved in coordinating mitochondrial fission and autophagosome biogenesis during stress.
    Keywords:  Autophagy; C. elegans; DRP-1; development plasticity; heat shock; mitochondria
  5. Curr Mol Pharmacol. 2021 Aug 06.
      Skeletal muscles are considered the largest reservoirs of the protein pool in the body and are critical for the maintenances of body homeostasis. Skeletal muscle atrophy is supported by various physiopathological conditions that lead to loss of muscle mass and contractile capacity of the skeletal muscle. Lysosomal mediated autophagy and ubiquitin-proteasomal system (UPS) concede the major intracellular systems of muscle protein degradation that result in the loss of mass and strength. Both systems recognize ubiquitination as a signal of degradation through different mechanisms, a sign of dynamic interplay between systems. Hence, growing shreds of evidence suggest the interdependency of autophagy and UPS in the progression of skeletal muscle atrophy under various pathological conditions. Therefore, understanding the molecular dynamics as well associated factors responsible for their interdependency is a necessity for the new therapeutic insights to counteract the muscle loss. Based on current literature, the present review summarizes the factors interplay in between the autophagy and UPS in favor of enhanced proteolysis of skeletal muscle and how they affect the anabolic signaling pathways under various conditions of skeletal muscle atrophy.
    Keywords:  Skeletal muscle atrophy; autophagosome-lysosome system; mitophagy; myostatin and ubiquitination; ubiquitin-proteasomal system
  6. Immunol Rev. 2021 Aug 08.
      The high rate of antibody production places considerable metabolic and folding stress on plasma cells (PC). Not surprisingly, they rely on the unfolded protein response (UPR), a universal signaling, and transcriptional network that monitors the health of the secretory pathway and mounts cellular responses to stress. Typically, the UPR utilizes three distinct stress sensors in the ER membrane, each regulating a subset of targets to re-establish homeostasis. PC use a specialized UPR scheme-they preemptively trigger the UPR via developmental signals and suppress two of the sensors, PERK and ATF6, relying on IRE1 alone. The specialized PC UPR program is tuned to the specific needs at every stage of development-from early biogenesis of secretory apparatus, to massive immunoglobulin expression later. Furthermore, the UPR in PC integrates with other pathways essential in a highly secretory cell-mTOR pathway that ensures efficient synthesis, autophagosomes that recycle components of the synthetic machinery, and apoptotic signaling that controls cell fate in the face of excessive folding stress. This specialized PC program is not shared with other secretory cells, for reasons yet to be defined. In this review, we give a perspective into how and why PC need such a unique UPR program.
    Keywords:  anticipatory unfolded protein response; autophagy; expansion of secretory apparatus; inactivation of sensors
  7. Elife. 2021 Aug 09. pii: e69601. [Epub ahead of print]10
      The microtubule-associated protein, tau, is the major subunit of neurofibrillary tangles associated with neurodegenerative conditions, such as Alzheimer's disease. In the cell, however, tau aggregation can be prevented by a class of proteins known as molecular chaperones. While numerous chaperones are known to interact with tau, though, little is known regarding the mechanisms by which these prevent tau aggregation. Here, we describe the effects of ATP-independent Hsp40 chaperones, DNAJA2 and DNAJB1, on tau amyloid-fiber formation, and compare these to the small heat-shock protein HSPB1. We find that the chaperones play complementary roles, with each preventing tau aggregation differently and interacting with distinct sets of tau species. Whereas HSPB1 only binds tau monomers, DNAJB1 and DNAJA2 recognize aggregation-prone conformers and even mature fibers. In addition, we find that both Hsp40s bind tau seeds and fibers via their C-terminal domain II (CTDII), with DNAJA2 being further capable of recognizing tau monomers by a second, distinct site in CTDI. These results lay out the mechanisms by which the diverse members of the Hsp40 family counteract the formation and propagation of toxic tau aggregates, and highlight the fact that chaperones from different families/classes play distinct, yet complementary roles in preventing pathological protein aggregation.
    Keywords:  molecular biophysics; structural biology
  8. Neural Regen Res. 2022 Mar;17(3): 508-511
      Parkinson's disease, the second most prevalent neurodegenerative disorder worldwide, is characterized by a progressive loss of dopaminergic neurons in substantia nigra pars compacta, causing motor symptoms. This disorder's main hallmark is the formation of intraneuronal protein inclusions, named Lewy bodies and neurites. The major component of these arrangements is α-synuclein, an intrinsically disordered and soluble protein that, in pathological conditions, can form toxic and cell-to-cell transmissible amyloid structures. Preventing α-synuclein aggregation has attracted significant effort in the search for a disease-modifying therapy for Parkinson's disease. Small molecules like SynuClean-D, epigallocatechin gallate, trodusquemine, or anle138b exemplify this therapeutic potential. Here, we describe a subset of compounds containing a single aromatic ring, like dopamine, ZPDm, gallic acid, or entacapone, which act as molecular chaperones against α-synuclein aggregation. The simplicity of their structures contrasts with the complexity of the aggregation process, yet the block efficiently α-synuclein assembly into amyloid fibrils, in many cases, redirecting the reaction towards the formation of non-toxic off-pathway oligomers. Moreover, some of these compounds can disentangle mature α-synuclein amyloid fibrils. Their simple structures allow structure-activity relationship analysis to elucidate the role of different functional groups in the inhibition of α-synuclein aggregation and fibril dismantling, making them informative lead scaffolds for the rational development of efficient drugs.
    Keywords:  Parkinson’s disease; amyloid; aromatic rings; dopamine; inhibition; neurodegeneration; oligomers; protein aggregation; α-synuclein
  9. Am J Physiol Cell Physiol. 2021 08 11.
      Defined as the dysfunction and/or cell death caused by toxic lipids accumulation in hepatocytes, hepatic lipotoxicity plays a pathological role in non-alcoholic fatty liver disease. The cellular and molecular mechanisms underlying lipotoxicity remain to be elucidated. In this study, using AML12 cells, a non-transformed murine hepatocyte cell line, exposed to palmitate (a 16-C saturated fatty acid) as an experimental model, we investigated the role and mechanisms of nicotinamide N-methyltransferase (NNMT), a methyltransferase catalyzing nicotinamide methylation and degradation, in hepatic lipotoxicity. We initially identified activating transcription factor 4 (ATF4) as a major transcription factor for hepatic NNMT expression. Here, we demonstrated that palmitate upregulates NNMT expression via activating ATF4 in a mechanistic target of rapamycin complex 1 (mTORC1)-dependent mechanism in that mTORC1 inhibition by both Torin1 and rapamycin attenuated ATF4 activation and NNMT upregulation. We further demonstrated that the mTORC1-dependent ATF4 activation is an integral signaling event of unfolded protein response (UPR) as both ATF4 activation and NNMT upregulation by tunicamycin, a well-documented endoplasmic reticulum (ER) stress inducer, are blunted when hepatocytes were pretreated with Torin1. Importantly, our data uncovered that NNMT upregulation contributes to palmitate-induced hepatotoxicity as NNMT inhibition, via either pharmacological (NNMT inhibitors) or genetic approach (siRNA transfection), provided protection against palmitate lipotoxicity. Our further mechanistic exploration identified protein kinase A (PKA) activation to contribute, at least, partially to the protective effect of NNMT inhibition against lipotoxicity. Collectively, our data demonstrated that NNMT upregulation by the mTORC1-ATF4 pathway activation contributes to the development of lipotoxicity in hepatocytes.
    Keywords:  ATF4; Lipotoxicity; NNMT; Palmitate; mTORC1
  10. Sci Rep. 2021 Aug 11. 11(1): 16356
      Retinitis Pigmentosa (RP) is a blinding disease that arises from loss of rods and subsequently cones. The P23H rhodopsin knock-in (P23H-KI) mouse develops retinal degeneration that mirrors RP phenotype in patients carrying the orthologous variant. Previously, we found that the P23H rhodopsin protein was degraded in P23H-KI retinas, and the Unfolded Protein Response (UPR) promoted P23H rhodopsin degradation in heterologous cells in vitro. Here, we investigated the role of a UPR regulator gene, activating transcription factor 6 (Atf6), in rhodopsin protein homeostasis in heterozygous P23H rhodopsin (Rho+/P23H) mice. Significantly increased rhodopsin protein levels were found in Atf6-/-Rho+/P23H retinas compared to Atf6+/-Rho+/P23H retinas at early ages (~ P12), while rhodopsin mRNA levels were not different. The IRE1 pathway of the UPR was hyper-activated in young Atf6-/-Rho+/P23H retinas, and photoreceptor layer thickness was unchanged at this early age in Rho+/P23H mice lacking Atf6. By contrast, older Atf6-/-Rho+/P23H mice developed significantly increased retinal degeneration in comparison to Atf6+/-Rho+/P23H mice in all retinal layers, accompanied by reduced rhodopsin protein levels. Our findings demonstrate that Atf6 is required for efficient clearance of rhodopsin protein in rod photoreceptors expressing P23H rhodopsin, and that loss of Atf6 ultimately accelerates retinal degeneration in P23H-KI mice.
  11. World J Stem Cells. 2021 Jul 26. 13(7): 737-752
      The mitochondrial unfolded protein response (UPRmt) is an evolutionarily conserved adaptive mechanism for improving cell survival under mitochondrial stress. Under physiological and pathological conditions, the UPRmt is the key to maintaining intracellular homeostasis and proteostasis. Important roles of the UPRmt have been demonstrated in a variety of cell types and in cell development, metabolism, and immune processes. UPRmt dysfunction leads to a variety of pathologies, including cancer, inflammation, neurodegenerative disease, metabolic disease, and immune disease. Stem cells have a special ability to self-renew and differentiate into a variety of somatic cells and have been shown to exist in a variety of tissues. These cells are involved in development, tissue renewal, and some disease processes. Although the roles and regulatory mechanisms of the UPRmt in somatic cells have been widely reported, the roles of the UPRmt in stem cells are not fully understood. The roles and functions of the UPRmt depend on stem cell type. Therefore, this paper summarizes the potential significance of the UPRmt in embryonic stem cells, tissue stem cells, tumor stem cells, and induced pluripotent stem cells. The purpose of this review is to provide new insights into stem cell differentiation and tumor pathogenesis.
    Keywords:  Cancer; Mammals; Mitochondrial unfolded protein response; Stem cells
  12. Biochem J. 2021 Aug 13. 478(15): 2953-2975
      The Unfolded Protein response is an adaptive pathway triggered upon alteration of endoplasmic reticulum (ER) homeostasis. It is transduced by three major ER stress sensors, among which the Inositol Requiring Enzyme 1 (IRE1) is the most evolutionarily conserved. IRE1 is an ER-resident type I transmembrane protein exhibiting an ER luminal domain that senses the protein folding status and a catalytic kinase and RNase cytosolic domain. In recent years, IRE1 has emerged as a relevant therapeutic target in various diseases including degenerative, inflammatory and metabolic pathologies and cancer. As such several drugs altering IRE1 activity were developed that target either catalytic activity and showed some efficacy in preclinical pathological mouse models. In this review, we describe the different drugs identified to target IRE1 activity as well as their mode of action from a structural perspective, thereby identifying common and different modes of action. Based on this information we discuss on how new IRE1-targeting drugs could be developed that outperform the currently available molecules.
    Keywords:  ER stress; IRE1; structure activity relationship (SAR); structure-based drug design (SBDD); unfolded protein response
  13. Sci Rep. 2021 Aug 13. 11(1): 16492
      Heat shock transcription factors (HSFs) are central elements in the regulatory network that controls plant heat stress response. They are involved in multiple transcriptional regulatory pathways and play important roles in heat stress signaling and responses to a variety of other stresses. We identified 41 members of the HSF gene family in moso bamboo, which were distributed non-uniformly across its 19 chromosomes. Phylogenetic analysis showed that the moso bamboo HSF genes could be divided into three major subfamilies; HSFs from the same subfamily shared relatively conserved gene structures and sequences and encoded similar amino acids. All HSF genes contained HSF signature domains. Subcellular localization prediction indicated that about 80% of the HSF proteins were located in the nucleus, consistent with the results of GO enrichment analysis. A large number of stress response-associated cis-regulatory elements were identified in the HSF upstream promoter sequences. Synteny analysis indicated that the HSFs in the moso bamboo genome had greater collinearity with those of rice and maize than with those of Arabidopsis and pepper. Numerous segmental duplicates were found in the moso bamboo HSF gene family. Transcriptome data indicated that the expression of a number of PeHsfs differed in response to exogenous gibberellin (GA) and naphthalene acetic acid (NAA). A number of HSF genes were highly expressed in the panicles and in young shoots, suggesting that they may have functions in reproductive growth and the early development of rapidly-growing shoots. This study provides fundamental information on members of the bamboo HSF gene family and lays a foundation for further study of their biological functions in the regulation of plant responses to adversity.
  14. Brain. 2021 Aug 11. pii: awab249. [Epub ahead of print]
      Agents that raise cGMP by activating Protein Kinase G increase 26S proteasome activities, protein ubiquitination, and degradation of misfolded proteins. Therefore, they may be useful in treating neurodegenerative and other diseases caused by an accumulation of misfolded proteins. Mutations in myelin protein zero (MPZ) cause the peripheral neuropathy Charcot Marie Tooth 1B (CMT1B). In peripheral nerves of a mouse model of CMT1B, where the mutant MPZS63del is expressed, proteasome activities are reduced, mutant MPZS63del and polyubiquitinated proteins accumulate, and the Unfolded Protein Response (p-eif2 α) is induced. In HEK293 cells, raising cGMP stimulated ubiquitination and degradation of MPZS63del, but not of MPZWT. Treating S63del mice with the phosphodiesterase 5 inhibitor, sildenafil, to raise cGMP increased proteasome activity in sciatic nerves and reduced the levels of polyubiquitinated proteins, the proteasome reporter ubG76V-GFP, and p-elF2α. Furthermore, sildenafil treatment reduced the number of amyelinated axons, and increased myelin thickness and nerve conduction velocity in sciatic nerves. Thus, agents that raise cGMP, including ones widely used in medicine, may be useful therapies for CMT1B and other proteotoxic diseases.
    Keywords:  Charcot Marie Tooth; cGMP; proteasome; protein degradation; proteostasis
  15. Mol Biol Cell. 2021 Aug 11. mbcE21050254
      Basically all mammalian tissues are constantly exposed to a variety of environmental mechanical signals. Depending on the signal strength, mechanics intervenes in a multitude of cellular processes and is thus capable to induce simple cellular adaptations but also complex differentiation processes and even apoptosis. The underlying recognition typically depends on mechanosensitive proteins, which most often sense the mechanical signal for the induction of a cellular signaling cascade by changing their protein conformation. However, the fate of mechanosensors after mechanical stress application is still poorly understood and it remains unclear whether protein degradation pathways affect the mechanosensitivity of cells. Here, we show that cyclic stretch induces autophagosome formation in a time-dependent manner. Formation depends on the cochaperone BAG3 and thus likely involves BAG3-mediated chaperone-assisted selective autophagy. Furthermore, we demonstrate that strain-induced cell reorientation is clearly delayed upon inhibition of autophagy, suggesting a bidirectional crosstalk between mechanotransduction and autophagic degradation. The strength of the observed delay depends on stable adhesion structures and stress fiber formation in a RhoA-dependent manner.
  16. Front Cell Dev Biol. 2021 ;9 722821
    Keywords:  autophagy; differentiation; lysosomes; reprogramming; stem cells
  17. Neurochem Int. 2021 Aug 10. pii: S0197-0186(21)00202-3. [Epub ahead of print] 105156
      Notch1 not only plays a key role in the development of the nervous system but also modulates synaptic plasticity and memory. However, the role of Notch1 in the brain of diabetes is still unclear. We hypothesize that Notch1 is involved in type I diabetes-induced cognitive dysfunction. In this study, adult male C57BL/6J mice carrying a heterozygous null mutation in the Notch1 gene (Notch1+/-) and wild-type littermate controls were used in this experiment. They were subjected to streptozocin (55 mg/kg, i.p.) for consecutive five days. After 12 weeks, the cognitive function of all mice was detected by novel object recognition (NOR) test and electrophysiological recording. Our results demonstrated that the levels of Notch1 mRNA and Notch1 receptor were increased in the hippocampus of the wild-type diabetic mice at 12 weeks. It suggested that the Notch1 signal pathway was activated. Compared with the wild-type diabetic mice, the discrimination index and the long-term potentiation was further decreased in the Notch1+/- diabetic group, the impairment of neuronal ultrastructure was exacerbated in the hippocampus of the Notch1+/- diabetic mice, and the number of synapses and autophagic vacuoles were significantly reduced in the Notch1+/- diabetic group. Moreover, some postsynaptic associated protein expressions were down-regulated, as well as the Beclin1 expression and the ratio of LC3II/LC3I were reduced in the hippocampus of the Notch1+/- diabetic mice. Interestingly, the phosphorylation of mTOR, Akt, and ERK1/2 were all inhibited in the Notch1+/- diabetic group. Taken together, these results suggest that Notch1 deficiency deteriorates the synaptic plasticity and inhibits the activation of autophagy partly via the mTOR-independent signal pathway in the hippocampus of type I diabetic mice.
    Keywords:  Autophagy; Cognitive function; Diabetes mellitus; Hippocampus; Notch1
  18. Front Neurosci. 2021 ;15 700729
      Increased blood-brain barrier (BBB) permeability and extensive neuronal changes have been described earlier in both healthy and pathological aging like apolipoprotein B-100 (APOB-100) and amyloid precursor protein (APP)-presenilin-1 (PSEN1) transgenic mouse models. APOB-100 hypertriglyceridemic model is a useful tool to study the link between cerebrovascular pathology and neurodegeneration, while APP-PSEN1 humanized mouse is a model of Alzheimer's disease. The aim of the current study was to characterize the inflammatory changes in the brain with healthy aging and in neurodegeneration. Also, the cerebro-morphological and cognitive alterations have been investigated. The nose-to-brain delivery of a P-glycoprotein substrate model drug (quinidine) was monitored in the disease models and compared with the age-matched controls. Our results revealed an inflammatory balance shift in both the healthy aged and neurodegenerative models. In normal aging monocyte chemoattractant protein-1, stem cell factor and Rantes were highly upregulated indicating a stimulated leukocyte status. In APOB-100 mice, vascular endothelial growth factor (VEGF), platelet-derived growth factor (PDGF-BB), and interleukin-17A (IL-17A) were induced (vascular reaction), while in APP-PSEN1 mice resistin, IL-17A and GM-CSF were mostly upregulated. The nasal drug absorption was similar in the brain and blood indicating the molecular bypass of the BBB. The learning and memory tests showed no difference in the cognitive performance of healthy aged and young animals. Based on these results, it can be concluded that various markers of chronic inflammation are present in healthy aged and diseased animals. In APOB-100 mice, a cerebro-ventricular dilation can also be observed. For development of proper anti-aging and neuroprotective compounds, further studies focusing on the above inflammatory targets are suggested.
    Keywords:  APOB-100 mice; APP-PSEN1 mice; Alzheimer’s disease; aging; cytokines; in vivo microdialysis; magnetic resonance imaging; nose-to-brain delivery
  19. Stem Cell Res Ther. 2021 Aug 11. 12(1): 452
      Mitophagy is a specific autophagic phenomenon in which damaged or redundant mitochondria are selectively cleared by autophagic lysosomes. A decrease in mitophagy can accelerate the aging process. Mitophagy is related to health and longevity and is the key to protecting stem cells from metabolic stress damage. Mitophagy decreases the metabolic level of stem cells by clearing active mitochondria, so mitophagy is becoming increasingly necessary to maintain the regenerative capacity of old stem cells. Stem cell senescence is the core problem of tissue aging, and tissue aging occurs not only in stem cells but also in transport amplifying cell chambers and the stem cell environment. The loss of the autophagic ability of stem cells can cause the accumulation of mitochondria and the activation of the metabolic state as well as damage the self-renewal ability and regeneration potential of stem cells. However, the claim remains controversial. Mitophagy is an important survival strategy against nutrient deficiency and starvation, and mitochondrial function and integrity may affect the viability, proliferation and differentiation potential, and longevity of normal stem cells. Mitophagy can affect the health and longevity of the human body, so the number of studies in this field has increased, but the mechanism by which mitophagy participates in stem cell development is still not fully understood. This review describes the potential significance of mitophagy in stem cell developmental processes, such as self-renewal, differentiation and aging. Through this work, we discovered the role and mechanism of mitophagy in different types of stem cells, identified novel targets for killing cancer stem cells and curing cancer, and provided new insights for future research in this field.
    Keywords:  Autophagy; Cancer stem cells; Mitochondria; Mitophagy; Stem cells
  20. Breed Sci. 2021 Apr;71(2): 184-192
      Heat stress during grain filling has been documented to decrease wheat grain yield and quality in arid regions worldwide. We studied the effect of heat stress on wheat flour quality in heat tolerant cultivars to define the effects of heat stress on flour quality and to identify germplasm combining traits for heat tolerance and good flour quality. We studied the kernel phenotypic traits, the expression of seed storage proteins (SSPs), and the resulting flour quality under heat and normal conditions. Under heat stress, all cultivars yielded narrow-shaped seeds, and increased protein contents as compared to the control plants grown under normal conditions. The specific sedimentation values used to estimate the gluten quality varied between cultivars. We identified cultivars that could maintain good flour quality under heat stress conditions: 'Imam', which possessed the Glu-D1d allele responsible for the suitable bread-making; 'Bohaine', which displayed high expression level of SSPs; and 'Condor', which possessed slight variations in the ratio of each SSP under heat stress conditions. Combining the desirable traits from these cultivars could yield a wheat cultivar with heat tolerance and good flour quality.
    Keywords:  Triticum aestivum L.; heat stress; kernel traits; seed storage protein; wheat flour quality
  21. Stem Cell Rev Rep. 2021 Aug 10.
      This review captures recent advances in biological and translational research on stem cells. In particular, we discuss new discoveries and concepts regarding stem cell treatment of aging-related disorders. A myriad of stem cell sources exists, from hematopoietic to mesenchymal and neural cell lineages. We examine current applications of exogenous adult bone marrow-derived stem cells as an effective and safe transplantable cell source, as well as the use of electrical stimulation to promote endogenous neurogenesis for Parkinson's disease. We also explore the potential of transplanting exogenous umbilical cord blood cells and mobilizing host resident stem cells in vascular dementia and aging. In addition, we assess the ability of small molecules to recruit resident stem cells in Alzheimer's disease. Finally, we evaluate mechanisms of action recently implicated in stem cell therapy, such as the role of long non-coding RNAs, G-protein coupled receptor 5, and NeuroD1. Our goal is to provide a synopsis of recent milestones regarding the application of stem cells in aging.
    Keywords:  Aging-related disorders; Regenerative medicine; Stem cells; Transplantation
  22. J Alzheimers Dis Rep. 2021 ;5(1): 479-495
      Background: Current understanding of amyloid-β protein (Aβ) aggregation and toxicity provides an extensive list of drugs for treating Alzheimer's disease (AD); however, one of the most promising strategies for its treatment has been tri-peptides.Objective: The aim of this study is to examine those tri-peptides, such as Arg-Arg-Try (RRY), which have the potential of Aβ1-42 aggregating inhibition and Aβ clearance.
    Methods: In the present study, in silico, in vitro, and in vivo studies were integrated for screening tri-peptides binding to Aβ, then evaluating its inhibition of aggregation of Aβ, and finally its rescuing cognitive deficit.
    Results: In the in silico simulations, molecular docking and molecular dynamics determined that seven top-ranking tri-peptides could bind to Aβ1-42 and form stable complexes. Circular dichroism, ThT assay, and transmission electron microscope indicated the seven tri-peptides might inhibit the aggregation of Aβ1-42 in vitro. In the in vivo studies, Morris water maze, ELISA, and Diolistic staining were used, and data showed that RRY was capable of rescuing the Aβ1-42-induced cognitive deficit, reducing the Aβ1-42 load and increasing the dendritic spines in the transgenic mouse model.
    Conclusion: Such converging outcomes from three consecutive studies lead us to conclude that RRY is a preferred inhibitor of Aβ1-42 aggregation and treatment for Aβ-induced cognitive deficit.
    Keywords:  APP/PS1 transgenic mice; Alzheimer’s disease; amyloid-β ; high throughput screening; small peptide
  23. Annu Rev Microbiol. 2021 Aug 10.
      Heat shock protein 90 (Hsp90) is a molecular chaperone that folds and remodels proteins, thereby regulating the activity of numerous substrate proteins. Hsp90 is widely conserved across species and is essential in all eukaryotes and in some bacteria under stress conditions. To facilitate protein remodeling, bacterial Hsp90 collaborates with the Hsp70 molecular chaperone and its cochaperones. In contrast, the mechanism of protein remodeling performed by eukaryotic Hsp90 is more complex, involving more than 20 Hsp90 cochaperones in addition to Hsp70 and its cochaperones. In this review, we focus on recent progress toward understanding the basic mechanisms of bacterial Hsp90-mediated protein remodeling and the collaboration between Hsp90 and Hsp70. We describe the universally conserved structure and conformational dynamics of these chaperones and their interactions with one another and with client proteins. The physiological roles of Hsp90 in Escherichia coli and other bacteria are also discussed. We anticipate that the information gained from exploring the mechanism of the bacterial chaperone system will provide a framework for understanding the more complex eukaryotic Hsp90 system. Expected final online publication date for the Annual Review of Microbiology, Volume 75 is October 2021. Please see for revised estimates.
  24. Proc Natl Acad Sci U S A. 2021 Aug 17. pii: e2025578118. [Epub ahead of print]118(33):
      Cellular function depends on the correct folding of proteins inside the cell. Heat-shock proteins 70 (Hsp70s), being among the first molecular chaperones binding to nascently translated proteins, aid in protein folding and transport. They undergo large, coordinated intra- and interdomain structural rearrangements mediated by allosteric interactions. Here, we applied a three-color single-molecule Förster resonance energy transfer (FRET) combined with three-color photon distribution analysis to compare the conformational cycle of the Hsp70 chaperones DnaK, Ssc1, and BiP. By capturing three distances simultaneously, we can identify coordinated structural changes during the functional cycle. Besides the known conformations of the Hsp70s with docked domains and open lid and undocked domains with closed lid, we observed additional intermediate conformations and distance broadening, suggesting flexibility of the Hsp70s in adopting the states in a coordinated fashion. Interestingly, the difference of this distance broadening varied between DnaK, Ssc1, and BiP. Study of their conformational cycle in the presence of substrate peptide and nucleotide exchange factors strengthened the observation of additional conformational intermediates, with BiP showing coordinated changes more clearly compared to DnaK and Ssc1. Additionally, DnaK and BiP were found to differ in their selectivity for nucleotide analogs, suggesting variability in the recognition mechanism of their nucleotide-binding domains for the different nucleotides. By using three-color FRET, we overcome the limitations of the usual single-distance approach in single-molecule FRET, allowing us to characterize the conformational space of proteins in higher detail.
    Keywords:  conformational dynamics; coordinated motion; heat-shock proteins; single-molecule Förster resonance energy transfer; three-color photon distribution analysis
  25. Aging (Albany NY). 2021 Aug 12. 13(undefined):
      The physiological function of amyloid precursor protein (APP) in the control of endothelial function during aging is unclear. Aortas of young (4-6 months old) and aged (23-26 months old) wild-type (WT) and endothelium-specific APP-deficient (eAPP-/-) mice were used to study aging-induced changes in vascular phenotype. Unexpectedly, aging significantly increased protein expression of APP in aortas of WT mice but not in aortas of eAPP-/- mice thereby demonstrating selective upregulation APP expression in vascular endothelium of aged aortas. Most notably, endothelial dysfunction (impairment of endothelium-dependent relaxations) induced by aging was significantly exacerbated in aged eAPP-/- mice aortas as compared to age-matched WT mice. Consistent with this observations, endothelial nitric oxide synthase (eNOS) protein expression was significantly decreased in aged eAPP-/- mice as compared to age matched WT mice. In addition, protein expression of cyclooxygenase 2 and release of prostaglandins were significantly increased in both aged WT and eAPP-/- mice. Notably, treatment with cyclooxygenase inhibitor, indomethacin, normalized endothelium-dependent relaxations in aged WT mice, but not in aged eAPP-/- mice. In aggregate, our findings support the concept that aging-induced upregulation of APP in vascular endothelium is an adaptive response designed to protect and preserve expression and function of eNOS.
    Keywords:  aging; amyloid precursor protein; endothelial nitric oxide synthase; endothelium; prostaglandins
  26. Nutrients. 2021 Jul 03. pii: 2298. [Epub ahead of print]13(7):
      Endoplasmic reticulum stress (ERS) and autophagy pathways are implicated in disuse muscle atrophy. The effects of high eicosapentaenoic (EPA) or high docosahexaenoic (DHA) fish oils on soleus muscle ERS and autophagy markers were investigated in a rat hindlimb suspension (HS) atrophy model. Adult Wistar male rats received daily by gavage supplementation (0.3 mL per 100 g b.w.) of mineral oil or high EPA or high DHA fish oils (FOs) for two weeks. Afterward, the rats were subjected to HS and the respective treatments concomitantly for an additional two-week period. After four weeks, we evaluated ERS and autophagy markers in the soleus muscle. Results were analyzed using two-way analysis of variance (ANOVA) and Bonferroni post hoc test. Gastrocnemius muscle ω-6/ω-3 fatty acids (FAs) ratio was decreased by both FOs indicating the tissue incorporation of omega-3 fatty acids. HS altered (p < 0.05) the protein content (decreasing total p38 and BiP and increasing p-JNK2/total JNK2 ratio, and caspase 3) and gene expressions (decreasing BiP and increasing IRE1 and PERK) of ERS and autophagy (decreasing Beclin and increasing LC3 and ATG14) markers in soleus. Both FOs attenuated (p < 0.05) the increase in PERK and ATG14 expressions induced by HS. Thus, both FOs could potentially attenuate ERS and autophagy in skeletal muscles undergoing atrophy.
    Keywords:  docosahexaenoic acid; eicosapentanoic acid; hindlimb suspension; skeletal muscle atrophy; unfolded protein response; ω-3 fatty acids
  27. Proc Natl Acad Sci U S A. 2021 Aug 17. pii: e2102191118. [Epub ahead of print]118(33):
      Alzheimer's disease (AD) is characterized by the presence of amyloid β (Aβ) plaques, tau tangles, inflammation, and loss of cognitive function. Genetic variation in a cholesterol transport protein, apolipoprotein E (apoE), is the most common genetic risk factor for sporadic AD. In vitro evidence suggests that apoE links to Aβ production through nanoscale lipid compartments (lipid clusters), but its regulation in vivo is unclear. Here, we use superresolution imaging in the mouse brain to show that apoE utilizes astrocyte-derived cholesterol to specifically traffic neuronal amyloid precursor protein (APP) in and out of lipid clusters, where it interacts with β- and γ-secretases to generate Aβ-peptide. We find that the targeted deletion of astrocyte cholesterol synthesis robustly reduces amyloid and tau burden in a mouse model of AD. Treatment with cholesterol-free apoE or knockdown of cholesterol synthesis in astrocytes decreases cholesterol levels in cultured neurons and causes APP to traffic out of lipid clusters, where it interacts with α-secretase and gives rise to soluble APP-α (sAPP-α), a neuronal protective product of APP. Changes in cellular cholesterol have no effect on α-, β-, and γ-secretase trafficking, suggesting that the ratio of Aβ to sAPP-α is regulated by the trafficking of the substrate, not the enzymes. We conclude that cholesterol is kept low in neurons, which inhibits Aβ accumulation and enables the astrocyte regulation of Aβ accumulation by cholesterol signaling.
    Keywords:  Alzheimer’s; apoE; cholesterol; lipids; neurodegeneration
  28. Neural Regen Res. 2022 Mar;17(3): 503-507
      The expanded lifespan of people, while a positive advance, has also amplified the prevalence of age-related disorders, which include mild cognitive impairment, dementia, and Alzheimer's disease. Therefore, competent therapies that could improve the healthspan of people have great significance. Some of the dietary and pharmacological approaches that augment the lifespan could also preserve improved cognitive function in old age. Metformin, a drug widely used for treating diabetes, is one such candidate that could alleviate age-related cognitive dysfunction. However, the possible use of metformin to alleviate age-related cognitive dysfunction has met with conflicting results in human and animal studies. While most clinical studies have suggested the promise of metformin to maintain better cognitive function and reduce the risk for developing dementia and Alzheimer's disease in aged diabetic people, its efficacy in the nondiabetic population is still unclear. Moreover, a previous animal model study implied that metformin could adversely affect cognitive function in the aged. However, a recent animal study using multiple behavioral tests has reported that metformin treatment in late middle age improved cognitive function in old age. The study also revealed that cognition-enhancing effects of metformin in aged animals were associated with the activation of the energy regulator adenosine monophosphate-activated protein kinase, diminished neuroinflammation, inhibition of the mammalian target of rapamycin signaling, and augmented autophagy in the hippocampus. The proficiency of metformin to facilitate these favorable modifications in the aged hippocampus likely underlies its positive effect on cognitive function. Nonetheless, additional studies probing the outcomes of different doses and durations of metformin treatment at specific windows in the middle and old age across sex in nondiabetic and non-obese prototypes are required to substantiate the promise of metformin to maintain better cognitive function in old age.
    Keywords:  activated microglia; aging; autophagy; cognitive dysfunction; mTOR signaling; memory; metformin; neuroinflammation
  29. J Dairy Sci. 2021 Aug 04. pii: S0022-0302(21)00783-9. [Epub ahead of print]
      Insulin-like growth factor-1 (IGF-1) plays a key role in proliferation and galactopoiesis in mammary epithelial cells (MEC), but its definitive functions on endoplasmic reticulum (ER) during protein synthesis remain unknown. The present study aimed to elucidate the effects of IGF-1 on ER biogenesis in MEC in vitro and examined the expression of ER biogenesis-associated genes in the mammary gland during early lactation. We treated mammary alveolar cells-large T antigen cells (immortalized bovine MEC line established via stable transfection with simian virus-40 large T-antigen) with IGF-1 and examined ER biogenesis using the fluorescence intensity of an ER tracker and quantitative real-time PCR. We found IGF-1 significantly increased ER tracker staining and upregulated mRNA levels of ER biogenesis-related genes, such as CHKA (choline kinase α), PCYT1A (choline-phosphate cytidylyltransferase A), and SURF4 (surfeit locus protein 4). We focused on unfolded protein response to explore molecular mechanisms by which IGF-1 induces ER biogenesis. We found IGF-1 significantly increased mRNA levels of the XBP1 splicing form (XBP1s). Based on western blot analysis, IGF-1 induced the expression of (inositol-requiring kinase 1 α) protein, upstream of XBP1s, and phosphorylated-IRE1α. The inhibition of IRE1 endoribonuclease activity with 4-methylumbelliferone 8-carbaldehyde (4μ8C) significantly suppressed the increase in ER tracker fluorescence and ER biogenesis-related gene expression induced by IGF-1. Also, IGF-1-induced XBP1s and ER biogenesis-associated gene expression was inhibited by rapamycin, an inhibitor of mTORC1 (mammalian target of rapamycin complex 1), indicating that IRE1-XBP1 activation by IGF-1 is mediated by mTORC1. Moreover, to clarify the expression of XBP1s and ER biogenesis-associated genes expression under normal physiological conditions, mammary gland tissue from biopsies of dairy cows during late gestation and lactation were analyzed. In vivo data highlighted the significant increases in the mRNA levels of XBP1s and ER biogenesis-related genes in mammary gland tissue immediately after calving through 6 wk of lactation. The mRNA levels of IGF1R (IGF-1 receptor) in mammary glands increased during 6 wk of lactation. Therefore, the present study indicated for the first time that IGF-1 induces ER biogenesis by activating the IRE1-XBP1 axis under the regulation of mTORC1 in bovine MEC line.
    Keywords:  IGF-1; endoplasmic reticulum biogenesis; mammary epithelial cell; unfolded protein response
  30. Hum Mol Genet. 2021 Aug 10. pii: ddab227. [Epub ahead of print]
      TAR DNA binding protein 43 (TDP-43) is an RNA processing protein central to the pathogenesis of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). Nuclear TDP-43 mislocalises in patients to the cytoplasm, where it forms ubiquitin-positive inclusions in affected neurons and glia. Physiologically, cytoplasmic TDP-43 is associated with stress granules (SGs). Here, we explored TDP-43 cytoplasmic accumulation and stress granule formation following osmotic and oxidative stress. We show that sorbitol drives TDP-43 redistribution to the cytoplasm, while arsenite induces the recruitment of cytoplasmic TDP-43 to TIA-1 positive SGs. We demonstrate that inducing acute oxidative stress after TDP-43 cytoplasmic relocalisation by osmotic shock induces PARP cleavage, which triggers cellular toxicity. Recruitment of cytoplasmic TDP-43 to polyribosomes occurs in an SH-SY5Y cellular stress model and is observed in FTD brain lysate. Moreover, the processing body (P-body) marker DCP1a is detected in TDP-43 granules during recovery from stress. Overall, this study supports a central role for cytoplasmic TDP-43 in controlling protein translation in stressed cells.
    Keywords:  TDP-43FUSALSPolysomesStress Granule (SG)
  31. Expert Rev Neurother. 2021 Aug 09.
      INTRODUCTION: The clinical validation and qualification of biomarkers reflecting the complex pathophysiology of neurodegenerative diseases (NDDs) is a fundamental challenge for current drug discovery, development and next-generation clinical practice. Novel ultrasensitive detection techniques and protein misfolding amplification assays hold the potential to optimize and accelerate this process.AREAS COVERED: Here the authors perform a systematic PubMed-based state-of-the-art review and perspective report on blood-based ultrasensitive detection techniques and protein misfolding amplification assays for biomarkers discovery and development in NDDs.
    EXPERT OPINION: Ultrasensitive assays present innovative solutions for blood-based assessments during the entire Alzheimer's Disease (AD) biological and clinical continuum, for contexts of use (COU) such as prediction, detection, early diagnosis and prognosis of AD. Moreover, cerebrospinal fluid (CSF)-based misfolding amplification assays, show encouraging performance in detecting α-synucleinopathies in prodromal or at-high-risk individuals and may serve as tools for patients' stratification by the presence of α-synuclein (α-syn) pathology. Further clinical research will help overcome current methodological limitations, also through exploring multiple accessible bodily matrices. Eventually, integrative longitudinal studies will support precise definitions for appropriate COU across NDDs.
    Keywords:  Alzheimer’s Disease; Fluid biomarkers; Neurodegenerative diseases; PMCA; Parkinson’s Disease; RT-QuIC; Ultrasensitive techniques