bims-minimp Biomed News
on Mitochondria, innate immunity, proteostasis
Issue of 2021‒08‒22
twenty-nine papers selected by
Hanna Salmonowicz
International Institute of Molecular Mechanisms and Machines of the Polish Academy of Sciences

  1. Commun Biol. 2021 Aug 16. 4(1): 974
      Human ATP-dependent Lon protease (LONP1) forms homohexameric, ring-shaped complexes. Depletion of LONP1 causes aggregation of a broad range of proteins in the mitochondrial matrix and decreases the levels of their soluble forms. The ATP hydrolysis activity, but not protease activity, of LONP1 is critical for its chaperone-like anti-aggregation activity. LONP1 forms a complex with the import machinery and an incoming protein, and protein aggregation is linked with matrix protein import. LONP1 also contributes to the degradation of imported, aberrant, unprocessed proteins using its protease activity. Taken together, our results show that LONP1 functions as a gatekeeper for specific proteins imported into the mitochondrial matrix.
  2. Sci Rep. 2021 Aug 20. 11(1): 17003
      Several studies reported that mitochondrial stress induces cytosolic proteostasis in yeast and C. elegans. Notably, inhibition of mitochondrial translation with doxcycyline decreases the toxicity of β-amyloid aggregates, in a C. elegans. However, how mitochondrial stress activates cytosolic proteostasis remains unclear. Further whether doxycycline has this effect in mammals and in disease relevant tissues also remains unclear. We show here that doxycycline treatment in mice drastically reduces the accumulation of proteins destined for degradation by the proteasome in a CNS region-specific manner. This effect is associated with the activation of the ERα axis of the mitochondrial unfolded protein response (UPRmt), in both males and females. However, sexually dimorphic mechanisms of proteasome activation were observed. Doxycycline also activates the proteasome in fission yeast, where ERα is not expressed. Rather, the ancient ERα-coactivator Mms19 regulates this response in yeast. Our results suggest that the UPRmt initiates a conserved mitochondria-to-cytosol stress signal, resulting in proteasome activation, and that this signal has adapted during evolution, in a sex and tissue specific-manner. Therefore, while our results support the use of doxycycline in the prevention of proteopathic diseases, they also indicate that sex is an important variable to consider in the design of future clinical trials using doxycycline.
  3. EMBO Rep. 2021 Aug 19. e53790
      Zellweger spectrum disorder (ZSD) is the most severe peroxisomal biogenesis disorder (PBD). Why ZSD patients not only loose functional peroxisomes but also present with severe mitochondrial dysfunction was a long-standing mystery. In this issue, Nuebel et al (2021) identified that loss of peroxisomes leads to re-routing of peroxisomal proteins to mitochondria, thereby impairing mitochondrial structure and function. The findings provide the first molecular understanding of the mitochondrial-peroxisomal link in ZSD.
  4. Cell Death Dis. 2021 Aug 16. 12(9): 794
      Cellular therapy exerts profound therapeutic potential for curing a broad spectrum of diseases. Adult stem cells reside within a specified dynamic niche in vivo, which is essential for continuous tissue homeostatic maintenance through balancing self-renewal with lineage selection. Meanwhile, adult stem cells may be multipotent or unipotent, and are present in both quiescent and actively dividing states in vivo of the mammalians, which may switch to each other state in response to biophysical cues through mitochondria-mediated mechanisms, such as alterations in mitochondrial respiration and metabolism. In general, stem cells facilitate tissue repair after tissue-specific homing through various mechanisms, including immunomodulation of local microenvironment, differentiation into functional cells, cell "empowerment" via paracrine secretion, immunoregulation, and intercellular mitochondrial transfer. Interestingly, cell-source-specific features have been reported between different tissue-derived adult stem cells with distinct functional properties due to the different microenvironments in vivo, as well as differential functional properties in different tissue-derived stem cell-derived extracellular vehicles, mitochondrial metabolism, and mitochondrial transfer capacity. Here, we summarized the current understanding on roles of mitochondrial dynamics during stem cell homeostasis and aging, and lineage-specific differentiation. Also, we proposed potential unique mitochondrial molecular signature features between different source-derived stem cells and potential associations between stem cell aging and mitochondria-endoplasmic reticulum (ER) communication, as well as potential novel strategies for anti-aging intervention and healthy aging.
  5. Curr Opin Microbiol. 2021 Aug 16. pii: S1369-5274(21)00101-6. [Epub ahead of print]63 189-194
      Invading microbes occupy the host cytosol and take up nutrients on which host organelles are also dependent. Thus, host organelles are poised to interact with intracellular microbes. Despite the essential role of host mitochondria in cellular metabolic homeostasis and in mediating cellular responses to microbial infection, we know little of how these organelles interact with intracellular pathogens, and how such interactions affect disease pathogenesis. Here, we give an overview of the different classes of physical and metabolic interactions reported to occur between mitochondria and eukaryotic pathogens. Investigating the underlying molecular mechanisms and functions of such interactions will reveal novel aspects of infection biology.
  6. Biomed Pharmacother. 2021 Aug 16. pii: S0753-3322(21)00824-6. [Epub ahead of print]142 112041
      Senescence is a crucial player in several metabolic disorders and chronic inflammatory diseases. Recent data prove the involvement of hepatocyte senescence in the development of NAFLD (non-alcoholic fatty liver disease). As the main energy and ROS (reactive oxygen species) producing organelle, mitochondria play the central role in accelerated senescence and diseases development. In this review, we focus on the role of regulation of mitochondrial Ca2+ homeostasis, NAD+/NADH ratio, UPRmt (mitochondrial unfolded protein response), phospholipids and fatty acid oxidation in hepatic senescence, lifespan and NAFLD disease susceptibility. Additionally, the involvement of mitochondrial and nuclear mutations in lifespan-modulation and NAFLD development is discussed. While nuclear and mitochondria DNA mutations and SNPs (single nucleotide polymorphisms) can be used as effective diagnostic markers and targets for treatments, advanced age should be considered as an independent risk factor for NAFLD development.
    Keywords:  DNA damage response; Hepatic senescence; Mitochondrial dysfunction; NAFLD; ROS; UPR(mt)
  7. Cell Calcium. 2021 Aug 05. pii: S0143-4160(21)00107-X. [Epub ahead of print]98 102453
      Mitochondria-endoplasmic reticulum (ER) contact sites (MERCS) are morpho-functional units, formed at the loci of close apposition of the ER-forming endomembrane and outer mitochondrial membrane (OMM). These sites contribute to fundamental cellular processes including lipid biosynthesis, autophagy, apoptosis, ER-stress and calcium (Ca2+) signalling. At MERCS, Ca2+ ions are transferred from the ER directly to mitochondria through a core protein complex composed of inositol-1,4,5 trisphosphate receptor (InsP3R), voltage-gated anion channel 1 (VDAC1), mitochondrial calcium uniporter (MCU) and adaptor protein glucose-regulated protein 75 (Grp75); this complex is regulated by several associated proteins. Deregulation of ER-mitochondria Ca2+ transfer contributes to pathogenesis of neurodegenerative and other diseases. The efficacy of Ca2+ transfer between ER and mitochondria depends on the protein composition of MERCS, which controls ER-mitochondria interaction regulating, for example, the transversal distance between ER membrane and OMM and the extension of the longitudinal interface between ER and mitochondria. These parameters are altered in neurodegeneration. Here we overview the ER and mitochondrial Ca2+ homeostasis, the composition of ER-mitochondrial Ca2+ transfer machinery and alterations of the ER-mitochondria Ca2+ transfer in three major neurodegenerative diseases: motor neurone diseases, Parkinson disease and Alzheimer's disease.
    Keywords:  Alzheimer's disease; Amyotrophic lateral sclerosis; Endoplasmic reticulum; Mitochondria; Mitochondria-ER contact sites; Motor neurone disease; Parkinson's disease
  8. Ageing Res Rev. 2021 Aug 12. pii: S1568-1637(21)00169-0. [Epub ahead of print] 101422
      During aging the immune system (IS) undergoes remarkable changes that collectively are known as immunosenescence. It is a multifactorial and dynamic phenomenon that affects both natural and acquired immunity and plays a critical role in most chronic diseases in older people. For a long time, immunosenescence has been considered detrimental because it may lead to a low-grade, sterile chronic inflammation we proposed to call "inflammaging" and a progressive reduction in the ability to trigger effective antibody and cellular responses against infections and vaccinations. Recently, many scientists revised this negative meaning because it can be considered an essential adaptation/remodeling resulting from the lifelong immunological biography of single individuals from an evolutionary perspective. Inflammaging can be considered an adaptive process because it can trigger an anti-inflammatory response to counteract the age-related pro-inflammatory environment. Centenarians represent a valuable model to study the beneficial changes occurring in the IS with age. These extraordinary individuals reached the extreme limits of human life by slowing down the aging process and, in most cases, delaying, avoiding or surviving the major age-associated diseases. They indeed show a complex and heterogeneous phenotype determined by an improved ability to adapt and remodel in response to harmful stimuli. This review aims to point out the intimate relationship between immunosenescence and inflammaging and how these processes impact unsuccessful aging rather than longevity. We also describe the gut microbiota age-related changes as one of the significant triggers of inflammaging and the sex/gender differences in the immune system of the elderly, contributing to the sex/gender disparity in terms of epidemiology, pathophysiology, symptoms and severity of age-related diseases. Finally, we discuss how these phenomena could influence the susceptibility to COVID-19 infection.
    Keywords:  Aging; COVID-19; Centenarians; Immunosenescence; Inflammaging; Innate immunity; Longevity
  9. Nature. 2021 Aug 18.
      Protein quality control systems are crucial for cellular function and organismal health. At present, most known protein quality control systems are multicomponent machineries that operate via ATP-regulated interactions with non-native proteins to prevent aggregation and promote folding1, and few systems that can broadly enable protein folding by a different mechanism have been identified. Moreover, proteins that contain the extensively charged poly-Asp/Glu (polyD/E) region are common in eukaryotic proteomes2, but their biochemical activities remain undefined. Here we show that DAXX, a polyD/E protein that has been implicated in diverse cellular processes3-10, possesses several protein-folding activities. DAXX prevents aggregation, solubilizes pre-existing aggregates and unfolds misfolded species of model substrates and neurodegeneration-associated proteins. Notably, DAXX effectively prevents and reverses aggregation of its in vivo-validated client proteins, the tumour suppressor p53 and its principal antagonist MDM2. DAXX can also restore native conformation and function to tumour-associated, aggregation-prone p53 mutants, reducing their oncogenic properties. These DAXX activities are ATP-independent and instead rely on the polyD/E region. Other polyD/E proteins, including ANP32A and SET, can also function as stand-alone, ATP-independent molecular chaperones, disaggregases and unfoldases. Thus, polyD/E proteins probably constitute a multifunctional protein quality control system that operates via a distinctive mechanism.
  10. FEBS J. 2021 Aug 17.
      Accumulation of mutations such as deletions in mitochondrial DNA is associated with ageing, cancer and human genetic disorders. These deletions are often flanked by GC-skewed sequence motifs that can potentially fold into secondary non-B DNA conformations. G-quadruplexes are emerging as key initiators of mitochondrial genomic instability. In this issue, Dahal et al provide an in silico analysis of sequence motifs that can fold into altered DNA structures in mitochondrial genomic regions that contain frequent deletions. They show the formation of five G-quadruplexes near such frequent breakpoints using biochemical and biophysical approaches in vitro and more importantly inside mammalian cells. Comment on:
    Keywords:  G4; Non-B DNA; genomic instability; mitochondrial DNA deletions
  11. Proc Natl Acad Sci U S A. 2021 Aug 24. pii: e2101674118. [Epub ahead of print]118(34):
      The inability of adult mammalian cardiomyocytes to proliferate underpins the development of heart failure following myocardial injury. Although the newborn mammalian heart can spontaneously regenerate for a short period of time after birth, this ability is lost within the first week after birth in mice, partly due to increased mitochondrial reactive oxygen species (ROS) production which results in oxidative DNA damage and activation of DNA damage response. This increase in ROS levels coincides with a postnatal switch from anaerobic glycolysis to fatty acid (FA) oxidation by cardiac mitochondria. However, to date, a direct link between mitochondrial substrate utilization and oxidative DNA damage is lacking. Here, we generated ROS-sensitive fluorescent sensors targeted to different subnuclear compartments (chromatin, heterochromatin, telomeres, and nuclear lamin) in neonatal rat ventricular cardiomyocytes, which allowed us to determine the spatial localization of ROS in cardiomyocyte nuclei upon manipulation of mitochondrial respiration. Our results demonstrate that FA utilization by the mitochondria induces a significant increase in ROS detection at the chromatin level compared to other nuclear compartments. These results indicate that mitochondrial metabolic perturbations directly alter the nuclear redox status and that the chromatin appears to be particularly sensitive to the prooxidant effect of FA utilization by the mitochondria.
    Keywords:  metabolism; mitochondria; reactive oxygen species
  12. iScience. 2021 Aug 20. 24(8): 102895
      The mitochondrial uniporter is a Ca2+-selective ion-conducting channel in the inner mitochondrial membrane that is involved in various cellular processes. The components of this uniporter, including the pore-forming membrane subunit MCU and the modulatory subunits MCUb, EMRE, MICU1, and MICU2, have been identified in recent years. Previously, extensive studies revealed various aspects of uniporter activities and proposed multiple regulatory models of mitochondrial Ca2+ uptake. Recently, the individual auxiliary components of the uniporter and its holocomplex have been structurally characterized, providing the first insight into the component structures and their spatial relationship within the context of the uniporter. Here, we review recent uniporter structural studies in an attempt to establish an architectural framework, elucidating the mechanism that governs mitochondrial Ca2+ uptake and regulation, and to address some apparent controversies. This information could facilitate further characterization of mitochondrial Ca2+ permeation and a better understanding of uniporter-related disease conditions.
    Keywords:  Ion; Membranes; Molecular biology
  13. Redox Biol. 2021 Jun 10. pii: S2213-2317(21)00197-X. [Epub ahead of print]46 102038
      Due to the high redox activity of the mitochondrion, this organelle can suffer oxidative stress. To manage energy demands while minimizing redox stress, mitochondrial homeostasis is maintained by the dynamic processes of mitochondrial biogenesis, mitochondrial network dynamics (fusion/fission), and mitochondrial clearance by mitophagy. Friedreich's ataxia (FA) is a mitochondrial disease resulting in a fatal hypertrophic cardiomyopathy due to the deficiency of the mitochondrial protein, frataxin. Our previous studies identified defective mitochondrial iron metabolism and oxidative stress potentiating cardiac pathology in FA. However, how these factors alter mitochondrial homeostasis remains uncharacterized in FA cardiomyopathy. This investigation examined the muscle creatine kinase conditional frataxin knockout mouse, which closely mimics FA cardiomyopathy, to dissect the mechanisms of dysfunctional mitochondrial homeostasis. Dysfunction of key mitochondrial homeostatic mechanisms were elucidated in the knockout hearts relative to wild-type littermates, namely: (1) mitochondrial proliferation with condensed cristae; (2) impaired NAD+ metabolism due to perturbations in Sirt1 activity and NAD+ salvage; (3) increased mitochondrial biogenesis, fusion and fission; and (4) mitochondrial accumulation of Pink1/Parkin with increased autophagic/mitophagic flux. Immunohistochemistry of FA patients' heart confirmed significantly enhanced expression of markers of mitochondrial biogenesis, fusion/fission and autophagy. These novel findings demonstrate cardiac frataxin-deficiency results in significant changes to metabolic mechanisms critical for mitochondrial homeostasis. This mechanistic dissection provides critical insight, offering the potential for maintaining mitochondrial homeostasis in FA and potentially other cardio-degenerative diseases by implementing innovative treatments targeting mitochondrial homeostasis and NAD+ metabolism.
    Keywords:  Cardiomyopathy; Iron; Iron loading; Mitochondria; Mitochondrial homeostasis
  14. EMBO Rep. 2021 Aug 17. e52445
      In eukaryotic cells, proteins are targeted to their final subcellular locations with precise timing. A key underlying mechanism is the active transport of cognate mRNAs, which in many systems can be linked intimately to membrane trafficking. A prominent example is the long-distance endosomal transport of mRNAs and their local translation. Here, we describe current highlights of fundamental mechanisms of the underlying transport process as well as of biological functions ranging from endosperm development in plants to fungal pathogenicity and neuronal processes. Translation of endosome-associated mRNAs often occurs at the cytoplasmic surface of endosomes, a process that is needed for membrane-assisted formation of heteromeric protein complexes and for accurate subcellular targeting of proteins. Importantly, endosome-coupled translation of mRNAs encoding mitochondrial proteins, for example, seems to be particularly important for efficient organelle import and for regulating subcellular mitochondrial activity. In essence, these findings reveal a new mechanism of loading newly synthesised proteins onto endocytic membranes enabling intimate crosstalk between organelles. The novel link between endosomes and mitochondria adds an inspiring new level of complexity to trafficking and organelle biology.
    Keywords:  RNA transport; endosomes; local translation; microtubules; mitochondria; organelle
  15. Mol Cell Biol. 2021 Aug 16. MCB0023321
      Mitochondrial oxidative phosphorylation (OXPHOS) enzymes are made up of dual genetic origin. Mechanisms regulating the expression of nuclear-encoded OXPHOS subunits in response to metabolic cues (glucose vs. glycerol), is significantly understood while regulation of mitochondrially encoded OXPHOS subunits is poorly defined. Here, we show that IRC3 a DEAD/H box helicase, previously implicated in mitochondrial DNA maintenance, is central to integrating metabolic cues with mitochondrial translation. Irc3 associates with mitochondrial small ribosomal subunit in cells consistent with its role in regulating translation elongation based on Arg8m reporter system. IRC3 deleted cells retained mitochondrial DNA despite growth defect on glycerol plates. Glucose grown Δirc3ρ+ and irc3 temperature-sensitive cells at 370C have reduced translation rates from majority of mRNAs. In contrast, when galactose was the carbon source, reduction in mitochondrial translation was observed predominantly from Cox1 mRNA in Δirc3ρ+ but no defect was observed in irc3 temperature-sensitive cells, at 370C. In support, of a model whereby IRC3 responds to metabolic cues to regulate mitochondrial translation, suppressors of Δirc3 isolated for restoration of growth on glycerol media restore mitochondrial protein synthesis differentially in presence of glucose vs. glycerol.
  16. EMBO J. 2021 Aug 19. e107260
      The cellular protein quality control machinery is important for preventing protein misfolding and aggregation. Declining protein homeostasis (proteostasis) is believed to play a crucial role in age-related neurodegenerative disorders. However, how neuronal proteostasis capacity changes in different diseases is not yet sufficiently understood, and progress in this area has been hampered by the lack of tools to monitor proteostasis in mammalian models. Here, we have developed reporter mice for in vivo analysis of neuronal proteostasis. The mice express EGFP-fused firefly luciferase (Fluc-EGFP), a conformationally unstable protein that requires chaperones for proper folding, and that reacts to proteotoxic stress by formation of intracellular Fluc-EGFP foci and by reduced luciferase activity. Using these mice, we provide evidence for proteostasis decline in the aging brain. Moreover, we find a marked reaction of the Fluc-EGFP sensor in a mouse model of tauopathy, but not in mouse models of Huntington's disease. Mechanistic investigations in primary neuronal cultures demonstrate that different types of protein aggregates have distinct effects on the cellular protein quality control. Thus, Fluc-EGFP reporter mice enable new insights into proteostasis alterations in different diseases.
    Keywords:  Huntington’s disease; nuclear and cytoplasmic aggregates; protein homeostasis; reporter mouse; tauopathy
  17. Front Cell Dev Biol. 2021 ;9 688523
      Mitochondria are the main hubs for cellular energy production. Metabolites produced in mitochondria not only feed many important biosynthesis pathways but also function as signaling molecules. Mitochondrial biosynthesis requires collaboration of both nuclear and mitochondrial gene expression systems. In addition, mitochondria have to quickly respond to changes inside and outside the cells and have their own functional states reported to the nucleus and other cellular compartments. The underlying molecular mechanisms of these complex regulations have not been well understood. Recent evidence indicates that in addition to small molecules, non-coding RNAs may contribute to the communication between mitochondria and other cellular compartments and may even serve as signals. In this review, we summarize the current knowledge about mitochondrial non-coding RNAs (including nucleus-encoded non-coding RNAs that are imported into mitochondria and mitochondrion-encoded non-coding RNAs that are exported), their trafficking and their functions in co-regulation of mitochondrial and other cellular processes.
    Keywords:  PNPASE; mitochondria; non-coding RNAs; nucleus; retrograde signaling; trafficking
  18. Commun Biol. 2021 Aug 19. 4(1): 989
      Mouse models of genetic mitochondrial disorders are generally used to understand specific molecular defects and their biochemical consequences, but rarely to map compensatory changes allowing survival. Here we took advantage of the extraordinary mitochondrial resilience of hepatic Lrpprc knockout mice to explore this question using native proteomics profiling and lipidomics. In these mice, low levels of the mtRNA binding protein LRPPRC induce a global mitochondrial translation defect and a severe reduction (>80%) in the assembly and activity of the electron transport chain (ETC) complex IV (CIV). Yet, animals show no signs of overt liver failure and capacity of the ETC is preserved. Beyond stimulation of mitochondrial biogenesis, results show that the abundance of mitoribosomes per unit of mitochondria is increased and proteostatic mechanisms are induced in presence of low LRPPRC levels to preserve a balance in the availability of mitochondrial- vs nuclear-encoded ETC subunits. At the level of individual organelles, a stabilization of residual CIV in supercomplexes (SCs) is observed, pointing to a role of these supramolecular arrangements in preserving ETC function. While the SC assembly factor COX7A2L could not contribute to the stabilization of CIV, important changes in membrane glycerophospholipid (GPL), most notably an increase in SC-stabilizing cardiolipins species (CLs), were observed along with an increased abundance of other supramolecular assemblies known to be stabilized by, and/or participate in CL metabolism. Together these data reveal a complex in vivo network of molecular adjustments involved in preserving mitochondrial integrity in energy consuming organs facing OXPHOS defects, which could be therapeutically exploited.
  19. Nat Commun. 2021 08 17. 12(1): 4980
      Proximity labeling (PL) with genetically-targeted promiscuous enzymes has emerged as a powerful tool for unbiased proteome discovery. By combining the spatiotemporal specificity of PL with methods for functional protein enrichment, we show that it is possible to map specific protein subclasses within distinct compartments of living cells. In particular, we develop a method to enrich subcompartment-specific RNA binding proteins (RBPs) by combining peroxidase-catalyzed PL with organic-aqueous phase separation of crosslinked protein-RNA complexes ("APEX-PS"). We use APEX-PS to generate datasets of nuclear, nucleolar, and outer mitochondrial membrane (OMM) RBPs, which can be mined for novel functions. For example, we find that the OMM RBP SYNJ2BP retains specific nuclear-encoded mitochondrial mRNAs at the OMM during translation stress, facilitating their local translation and import of protein products into the mitochondrion during stress recovery. Functional PL in general, and APEX-PS in particular, represent versatile approaches for the discovery of proteins with novel function in specific subcellular compartments.
  20. J Biol Chem. 2021 Aug 14. pii: S0021-9258(21)00884-X. [Epub ahead of print] 101081
      The human APOBEC3A (A3A) cytidine deaminase is a powerful DNA mutator enzyme recognized as a major source of somatic mutations in tumor cell genomes. However, there is a discrepancy between APOBEC3A mRNA levels after interferon stimulation in myeloid cells and A3A detection at the protein level. To understand this difference, we investigated the expression of two novel alternative "A3Alt" proteins encoded in the +1-shifted reading frame of the APOBEC3A gene. A3Alt-L and its shorter isoform A3Alt-S appear to be transmembrane proteins targeted to the mitochondrial compartment that induce membrane depolarization and apoptosis. Thus, the APOBEC3A gene represents a new example wherein a single gene encodes two pro-apoptotic proteins, A3A cytidine deaminases that target the genome and A3Alt proteins that target mitochondria.
    Keywords:  A3Alt; APOBEC3A; apoptosis; mitochondria
  21. Biomed Pharmacother. 2021 Aug 12. pii: S0753-3322(21)00822-2. [Epub ahead of print]142 112039
      Mitochondrial potassium channels have been implicated in cytoprotective mechanisms. Activation of the mitochondrial large-conductance Ca2+-regulated potassium (mitoBKCa) channel is important for protecting brain tissue against stroke damage as well as heart tissue against ischemia damage. In this paper, we examine the effect of the natural flavonoid quercetin as an activator of the mitoBKCa channel. Quercetin has a beneficial effect on many processes in the human body and interacts with many receptors and signaling pathways. We found that quercetin acts on mitochondria as a mitoBKCa channel opener. The activation observed with the patch-clamp technique was potent and increased the channel open probability from approximately 0.35 to 0.95 at + 40 mV in the micromolar concentration range. Moreover, quercetin at a concentration of 10 µM protected cells by reducing damage from treatment factors (tumor necrosis factor α and cycloheximide) by 40%, enhancing cellular migration and depolarizing the mitochondrial membrane. Moreover, the presence of quercetin increased the gene expression and protein level of the mitoBKCa β3 regulatory subunit. The observed cytoprotective effects suggested the involvement of BKCa channel activation. Additionally, the newly discovered mitoBKCa activator quercetin elucidates a new mitochondrial pathway that is beneficial for vascular endothelial cells.
    Keywords:  Apoptosis; Cell migration; Cytoprotection; Endothelium; Mitochondria; Mitochondrial membrane potential; Mitochondrial potassium channels; Necrosis; Quercetin
  22. Nat Methods. 2021 Aug 19.
      Mitochondria display complex morphology and movements, which complicates their segmentation and tracking in time-lapse images. Here, we introduce Mitometer, an algorithm for fast, unbiased, and automated segmentation and tracking of mitochondria in live-cell two-dimensional and three-dimensional time-lapse images. Mitometer requires only the pixel size and the time between frames to identify mitochondrial motion and morphology, including fusion and fission events. The segmentation algorithm isolates individual mitochondria via a shape- and size-preserving background removal process. The tracking algorithm links mitochondria via differences in morphological features and displacement, followed by a gap-closing scheme. Using Mitometer, we show that mitochondria of triple-negative breast cancer cells are faster, more directional, and more elongated than those in their receptor-positive counterparts. Furthermore, we show that mitochondrial motility and morphology in breast cancer, but not in normal breast epithelia, correlate with metabolic activity. Mitometer is an unbiased and user-friendly tool that will help resolve fundamental questions regarding mitochondrial form and function.
  23. Cell. 2021 Aug 19. pii: S0092-8674(21)00939-9. [Epub ahead of print]184(17): 4374-4376
      In this issue of Cell, Evavold et al. (2021) report that mTOR Complex 1 (mTORC1), a metabolic signaling complex, controls reactive oxygen species (ROS) production in mitochondria, which in turn promotes inflammatory cell death mediated by gasdermin D (GSDMD). This provides a new mechanistic connection between metabolic signaling and inflammatory cell death.
  24. Curr Res Physiol. 2021 ;4 163-176
      Folding of the mitochondrial inner membrane (IM) into cristae greatly increases the ATP-generating surface area, S IM, per unit volume but also creates diffusional bottlenecks that could limit reaction rates inside mitochondria. This study explores possible effects of inner membrane folding on mitochondrial ATP output, using a mathematical model for energy metabolism developed by the Jafri group and two- and three-dimensional spatial models for mitochondria, implemented on the Virtual Cell platform. Simulations demonstrate that cristae are micro-compartments functionally distinct from the cytosol. At physiological steady states, standing gradients of ADP form inside cristae that depend on the size and shape of the compartments, and reduce local flux (rate per unit area) of the adenine nucleotide translocase. This causes matrix ADP levels to drop, which in turn reduces the flux of ATP synthase. The adverse effects of membrane folding on reaction fluxes increase with crista length and are greater for lamellar than tubular crista. However, total ATP output per mitochondrion is the product of flux of ATP synthase and S IM which can be two-fold greater for mitochondria with lamellar than tubular cristae, resulting in greater ATP output for the former. The simulations also demonstrate the crucial role played by intracristal kinases (adenylate kinase, creatine kinase) in maintaining the energy advantage of IM folding.
    Keywords:  ATP synthesis; Computational modeling; Cristae; Energy metabolism; Kinases; Mitochondria
  25. Elife. 2021 Aug 20. pii: e69142. [Epub ahead of print]10
      The trafficking of specific protein cohorts to correct subcellular locations at correct times is essential for every signaling and regulatory process in biology. Gene perturbation screens could provide a powerful approach to probe the molecular mechanisms of protein trafficking, but only if protein localization or mislocalization can be tied to a simple and robust phenotype for cell selection, such as cell proliferation or fluorescence-activated cell sorting (FACS). To empower the study of protein trafficking processes with gene perturbation, we developed a genetically-encoded molecular tool named HiLITR. HiLITR converts protein colocalization into proteolytic release of a membrane-anchored transcription factor, which drives the expression of a chosen reporter gene. Using HiLITR in combination with FACS-based CRISPRi screening in human cell lines, we identified genes that influence the trafficking of mitochondrial and ER tail-anchored proteins. We show that loss of the SUMO E1 component SAE1 results in mislocalization and destabilization of many mitochondrial tail-anchored proteins. We also demonstrate a distinct regulatory role for EMC10 in the ER membrane complex, opposing the transmembrane-domain insertion activity of the complex. Through transcriptional integration of complex cellular functions, HiLITR expands the scope of biological processes that can be studied by genetic perturbation screening technologies.
    Keywords:  biochemistry; cell biology; chemical biology; human
  26. Biochem Soc Trans. 2021 Aug 20. pii: BST20210370. [Epub ahead of print]
      Heat shock protein 90 (Hsp90), although one of the most essential intracellular chaperones, can also play key roles in the extracellular milieu. Here, we review the properties of extracellular Hsp90 in cellular homeostasis in the heat shock response (HSR), focusing on cells of the central nervous system. Hsp90 can be secreted by microglia as well as other cell types by non-canonical pathways of secretion. The chaperone may then influence the behavior of distant cells and can for instance protect neuronal cells from the oxidative burst accompanying phagocytosis by microglia of beta-amyloid fibrils. A mechanism involving activation of the transcription factor Nrf2, and induction of the antioxidant response is reported. We review the potential role of extracellular Hsp90, Nrf2 and transcellular chaperone signaling in the non-cell-intrinsic HSR.
    Keywords:  Nrf2; cytoprotection; extracellular; heat shock proteins
  27. Sci Rep. 2021 Aug 17. 11(1): 16688
      Public health is threatened by climate change and extreme temperature events worldwide. Differences in health predispositions, access to cooling infrastructure and occupation raises an issue of heat-related health inequality in those vulnerable and disadvantaged demographic groups. To address these issues, a comprehensive understanding of the effect of elevated body temperatures on human biological systems and overall health is urgently needed. In this paper we look at the inner workings of the human innate immunity under exposure to heat stress induced through exposure to environment and physical exertion. We couple two experimentally validated computational models: the innate immune system and thermal regulation of the human body. We first study the dynamics of critical indicators of innate immunity as a function of human core temperature. Next, we identify environmental and physical activity regimes that lead to core temperature levels that can potentially compromise the performance of the human innate immunity. Finally, to take into account the response of innate immunity to various intensities of physical activities, we utilise the dynamic core temperatures generated by a thermal regulation model. We compare the dynamics of all key players of the innate immunity for a variety of stresses like running a marathon, doing construction work, and leisure walking at speed of 4 km/h, all in the setting of a hot and humid tropical climate such as present in Singapore. We find that exposure to moderate heat stress leading to core temperatures within the mild febrile range (37, 38][Formula: see text], nudges the innate immune system into activation and improves the efficiency of its response. Overheating corresponding to core temperatures beyond 38[Formula: see text], however, has detrimental effects on the performance of the innate immune system, as it further induces inflammation, which causes a series of reactions that may lead to the non-resolution of the ongoing inflammation. Among the three physical activities considered in our simulated scenarios (marathon, construction work, and walking), marathon induces the highest level of inflammation that challenges the innate immune response with its resolution. Our study advances the current state of research towards understanding the implications of heat exposure for such an essential physiological system as the innate immunity. Although we find that among considered physical activities, a marathon of 2 h and 46 min induces the highest level of inflammation, it must be noted that construction work done on a daily basis under the hot and humid tropical climate, can produce a continuous level of inflammation triggering moieties stretched at a longer timeline beating the negative effects of running a marathon. Our study demonstrates that the performance of the innate immune system can be severely compromised by the exposure to heat stress and physical exertion. This poses significant risks to health especially to those with limited access to cooling infrastructures. This is due in part to having low income, or having to work on outdoor settings, which is the case for construction workers. These risks to public health should be addressed through individual and population-level measures via behavioural adaptation and provision of the cooling infrastructure in outdoor environments.
  28. Pharmacol Biochem Behav. 2021 Aug 13. pii: S0091-3057(21)00153-2. [Epub ahead of print]209 173254
      Evidence suggests the involvement of redox and inflammation fields under conditions of psychological trauma. Factors from immunity, Hypothalamic-Adrenal-Pituitary axis, Kynurenine pathway, Dysglycemia, Glutamatergic systems as well as elements from redox mechanisms participate in a highly complex neurobiological process. Yet, little is known about their interplay. There is evidence suggesting a psychologically traumatic stress induced redox-originated inflammatory activation and vice versa. A holistic approach would suggest a parallel activation of the involved mechanisms with highly tight interdependency. The present report aims at collecting the evidence supporting either directionality of the involved mechanisms, finally suggesting a diagram depicting a synthesis of this interplay.
    Keywords:  Immune system; Inflammation; Oxidative stress; Psychologically traumatic stress; Redox
  29. Spectrochim Acta A Mol Biomol Spectrosc. 2021 Aug 13. pii: S1386-1425(21)00848-9. [Epub ahead of print]264 120271
      Biological microenvironment plays a momentous role in the regulation of various vital activities, and its abnormal changes are often closely related to some diseases. Viscosity, as an indispensable part of microenvironment parameters, has always been one of the research hotspots of investigators. Herein, we constructed a new red-emitting fluorescent probe (HVM) to identify the abnormal situation of mitochondria through viscosity changes in the biological microenvironment. Interestingly, HVM has excellent optical properties such as large stokes shift (160 nm), viscosity sensitivity (195-fold), high photostability, and biochemical properties with low cytotoxicity and excellent biocompatibility. For these reasons, the novel probe could successfully be used to identify the normal and inflammatory models via viscosity changes in biological experiments. Therefore, we provided a convenient synthetic route to obtain viscosity sensor HVM with excellent application properties.
    Keywords:  Fluorescent probe; Inflammation; Mitochondrial; Viscosity