bims-minimp 2021-08-01 papers

on Mitochondria, innate immunity, proteostasis

Issue of 2021–08–01
nineteen papers selected by
Hanna Salmonowicz, International Institute of Molecular Mechanisms and Machines of the Polish Academy of Sciences

Super-resolution microscopy reveals the arrangement of inner membrane protein complexes in mammalian mitochondria.
Loss of mitochondrial transcription factor A in neural stem cells leads to immature brain development and triggers the activation of the integral stress response in vivo.
Accessing Mitochondrial Protein Import in Living Cells by Protein Microinjection.
TFAM-deficient mouse skin fibroblasts: an ex vivo model of mitochondrial dysfunction.
A new functional role of mitochondria-anchored protein ligase in peroxisome morphology in mammalian cells.
Loss of the mitochondrial phosphate carrier SLC25A3 induces remodeling of the cardiac mitochondrial protein acylome.
miR-1 coordinately regulates lysosomal v-ATPase and biogenesis to impact proteotoxicity and muscle function during aging.
Move it to lose it: Mitocytosis expels damaged mitochondria.
Anterograde regulation of mitochondrial genes and FGF21 signaling by hepatic LSD1.
MDVs to the rescue: How autophagy-deficient cancer cells adapt to defective mitophagy.
Nrf2 deficiency decreases NADPH from impaired IDH shuttle and pentose phosphate pathway in retinal pigmented epithelial cells to magnify oxidative stress-induced mitochondrial dysfunction.
Maintaining proteostasis under mechanical stress.
A Novel NAD Signaling Mechanism in Axon Degeneration and its Relationship to Innate Immunity.
Nampt affects mitochondrial function in aged oocytes by mediating the downstream effector FoxO3a.
GAS6 ameliorates advanced age-associated meiotic defects in mouse oocytes by modulating mitochondrial function.
All cells are created equal in the sight of autophagy: selective autophagy maintains homeostasis in senescent cells.
Genomic instability induced by radiation-mimicking chemicals is not associated with persistent mitochondrial degeneration.
Establishment, maintenance, and recall of inflammatory memory.
Eribulin activates the cGAS-STING pathway via the cytoplasmic accumulation of mtDNA.

J Cell Sci. 2021 07 01. pii: jcs252197. [Epub ahead of print]134(13):

Super-resolution microscopy reveals the arrangement of inner membrane protein complexes in mammalian mitochondria.

Catherine S Palmer, Jieqiong Lou, Betty Kouskousis, Elvis Pandzic, Alexander J Anderson, Yilin Kang, Elizabeth Hinde, Diana Stojanovski.

  The mitochondrial inner membrane is a protein-rich environment containing large multimeric complexes, including complexes of the mitochondrial electron transport chain, mitochondrial translocases and quality control machineries. Although the inner membrane is highly proteinaceous, with 40-60% of all mitochondrial proteins localised to this compartment, little is known about the spatial distribution and organisation of complexes in this environment. We set out to survey the arrangement of inner membrane complexes using stochastic optical reconstruction microscopy (STORM). We reveal that subunits of the TIM23 complex, TIM23 and TIM44 (also known as TIMM23 and TIMM44, respectively), and the complex IV subunit COXIV, form organised clusters and show properties distinct from the outer membrane protein TOM20 (also known as TOMM20). Density based cluster analysis indicated a bimodal distribution of TIM44 that is distinct from TIM23, suggesting distinct TIM23 subcomplexes. COXIV is arranged in larger clusters that are disrupted upon disruption of complex IV assembly. Thus, STORM super-resolution microscopy is a powerful tool for examining the nanoscale distribution of mitochondrial inner membrane complexes, providing a 'visual' approach for obtaining pivotal information on how mitochondrial complexes exist in a cellular context.

Keywords:  COXIV; Mitochondria; Mitochondrial complexes; Nanoscopy; Protein import; STORM; TIM23

DOI:  https://doi.org/10.1242/jcs.252197
PLoS One. 2021 ;16(7): e0255355

Loss of mitochondrial transcription factor A in neural stem cells leads to immature brain development and triggers the activation of the integral stress response in vivo.

Rintaro Kuroda, Kaoru Tominaga, Katsumi Kasashima, Kenji Kuroiwa, Eiji Sakashita, Hiroko Hayakawa, Tom Kouki, Nobuhiko Ohno, Kensuke Kawai, Hitoshi Endo.

Mitochondrial dysfunction is significantly associated with neurological deficits and age-related neurological diseases. While mitochondria are dynamically regulated and properly maintained during neurogenesis, the manner in which mitochondrial activities are controlled and contribute to these processes is not fully understood. Mitochondrial transcription factor A (TFAM) contributes to mitochondrial function by maintaining mitochondrial DNA (mtDNA). To clarify how mitochondrial dysfunction affects neurogenesis, we induced mitochondrial dysfunction specifically in murine neural stem cells (NSCs) by inactivating Tfam. Tfam inactivation in NSCs resulted in mitochondrial dysfunction by reducing respiratory chain activities and causing a severe deficit in neural differentiation and maturation both in vivo and in vitro. Brain tissue from Tfam-deficient mice exhibited neuronal cell death primarily at layer V and microglia were activated prior to cell death. Cultured Tfam-deficient NSCs showed a reduction in reactive oxygen species produced by the mitochondria. Tfam inactivation during neurogenesis resulted in the accumulation of ATF4 and activation of target gene expression. Therefore, we propose that the integrated stress response (ISR) induced by mitochondrial dysfunction in neurogenesis is activated to protect the progression of neurodegenerative diseases.

DOI: https://doi.org/10.1371/journal.pone.0255355
Front Cell Dev Biol. 2021 ;9 698658

Accessing Mitochondrial Protein Import in Living Cells by Protein Microinjection.

Andrey Bogorodskiy, Ivan Okhrimenko, Ivan Maslov, Nina Maliar, Dmitrii Burkatovskii, Florian von Ameln, Alexey Schulga, Philipp Jakobs, Joachim Altschmied, Judith Haendeler, Alexandros Katranidis, Ivan Sorokin, Alexey Mishin, Valentin Gordeliy, Georg Büldt, Wolfgang Voos, Thomas Gensch, Valentin Borshchevskiy.

  Mitochondrial protein biogenesis relies almost exclusively on the expression of nuclear-encoded polypeptides. The current model postulates that most of these proteins have to be delivered to their final mitochondrial destination after their synthesis in the cytoplasm. However, the knowledge of this process remains limited due to the absence of proper experimental real-time approaches to study mitochondria in their native cellular environment. We developed a gentle microinjection procedure for fluorescent reporter proteins allowing a direct non-invasive study of protein transport in living cells. As a proof of principle, we visualized potential-dependent protein import into mitochondria inside intact cells in real-time. We validated that our approach does not distort mitochondrial morphology and preserves the endogenous expression system as well as mitochondrial protein translocation machinery. We observed that a release of nascent polypeptides chains from actively translating cellular ribosomes by puromycin strongly increased the import rate of the microinjected pre-protein. This suggests that a substantial amount of mitochondrial translocase complexes was involved in co-translational protein import of endogenously expressed pre-proteins. Our protein microinjection method opens new possibilities to study the role of mitochondrial protein import in cell models of various pathological conditions as well as aging processes.

Keywords:  GFP; SNAP-tag; fluorescence microscopy; microinjection; mitochondria; mitochondrial protein import

DOI:  https://doi.org/10.3389/fcell.2021.698658
Dis Model Mech. 2021 Jul 27. pii: dmm.048995. [Epub ahead of print]

TFAM-deficient mouse skin fibroblasts: an ex vivo model of mitochondrial dysfunction.

Manuel J Del Rey, Carolina Meroño, Cristina Municio, Alicia Usategui, María Mittelbrunn, Inés García-Consuegra, Gabriel Criado, José L Pablos.

  Mitochondrial dysfunction in different cell types is associated to several pathological processes and potentially contributes to chronic inflammatory and ageing-related diseases. Mitochondrial Transcription Factor A (TFAM) plays a critical role in maintaining mtDNA integrity and function. Taking advantage of the Tfamfl/fl UBC-Cre/ERT2+/+ mice, we sought to develop a cellular in vitro system to investigate the role of mitochondrial dysfunction in the stromal cell component. We describe an inducible model of mitochondrial dysfunction by stable depletion of TFAM in primary mouse skin fibroblast (SK-FB) after 4-hydroxytamoxifen (4-OHT) administration. Tfam gene deletion caused a sustained reduction of Tfam and mtDNA-encoded mRNA expression in Cre(+) cultured for low (LP) and high passages (HP). Ultimately, Tfam knockout translated into a loss of TFAM protein. TFAM depletion led to a substantial reduction of the mitochondrial respiratory chain (MRC) complexes that was exacerbated in HP SK-FB cultures. The assembly pattern showed that the respiratory complexes fail to reach the respirasome in 4-OHT Cre(+) SK-FB. Functionally, we determined the mitochondrial function and the glycolytic activity by mito-stress and glycolysis-stress test respectively. These analysis showed that mitochondrial dysfunction was developed after long-term 4-OHT treatment in HP Cre(+) SK-FB and was compensated by an increase in the glycolytic capacity. Finally, expression analysis revealed that 4-OHT-treated HP Cre(+) SK-FB showed a senescent and pro-inflammatory phenotype. In conclusion, we have generated and validated the first ex vivo model of fibroblast mitochondrial dysfunction that results in a pro-inflammatory phenotype applicable to explore this process in other cell types in a variety of pathological conditions.

Keywords:  Cellular senescence; Fibroblasts; Inflammation; Mitochondrial dysfunction; TFAM

DOI:  https://doi.org/10.1242/dmm.048995
J Cell Biochem. 2021 Jul 28.

A new functional role of mitochondria-anchored protein ligase in peroxisome morphology in mammalian cells.

Abhishek Mohanty, Rodolfo Zunino, Vincent Soubannier, Shilpa Dilipkumar.

  Mitochondria and peroxisomes are metabolically interconnected and functionally active subcellular organelles. These two dynamic organelles, share a number of common biochemical functions such as β-oxidation of fatty acids and detoxification of peroxides. The biogenesis and morphology of both these organelles in the mammalian cells is controlled by common transcription factors like PGC1α, and by a common fission machinery comprising of fission proteins like DRP1, Mff, and hFis1, respectively. In addition, the outer membrane mitochondria-anchored protein ligase (MAPL), the first mitochondrial SUMO E3 ligase with a RING-finger domain, also regulates mitochondrial morphology inducing mitochondrial fragmentation upon its overexpression. This fragmentation is dependent on both the RING domain of MAPL and the presence of the mitochondrial fission GTPase dynamin-related protein-1 (DRP1). Earlier studies have demonstrated that mitochondrial-derived vesicles are formed independently of the known mitochondrial fission GTPase, DRP1 are enriched for MAPL and are targeted to peroxisomes. The current study shows that MAPL regulates morphology of peroxisomes in a cell-type specific manner. Fascinatingly, the peroxisome elongation caused either due to silencing of DRP1 or by addition of polyunsaturated fatty acid, docosahexaenoic acid was blocked by overexpressing MAPL in mammalian cell lines. Furthermore, the transfection and colocalisation studies of MAPL with peroxisome membrane marker, PMP70, in different cell lines clearly revealed a cell-type specificity of transport of MAPL to peroxisomes. Previous work has placed the Vps35 (retromer component) as vital for delivery of MAPL to peroxisomes, placing the retromer as critical for the formation of MAPL-positive mitochondrial-derived vesicles. The results of polyethylene glycol-based cell-cell fusion assay signified that the enrichment of MAPL in peroxisomes is through vesicles and a retromer dependent phenomenon. Thus, a novel function for MAPL in peroxisomes is established to regulate peroxisome elongation and morphology under growth conditions and thus possibly modulate peroxisome fission.

Keywords:  Vps35; mitochondrial anchored protein ligase; mitochondrial-derived vesicles; peroxisome fission; retromer complex; vesicular transport

DOI:  https://doi.org/10.1002/jcb.30114
Am J Physiol Cell Physiol. 2021 07 28.

Loss of the mitochondrial phosphate carrier SLC25A3 induces remodeling of the cardiac mitochondrial protein acylome.

Jessica N Peoples, Nasab Ghazal, Duc M Duong, Katherine R Hardin, Janet R Manning, Nicholas T Seyfried, Victor Faundez, Jennifer Q Kwong.

  Mitochondria are recognized as signaling organelles because, under stress, mitochondria can trigger various signaling pathways to coordinate the cell's response. The specific pathway(s) engaged by mitochondria in response to mitochondrial energy defects in vivo and in high-energy tissues like the heart are not fully understood. Here, we investigated cardiac pathways activated in response to mitochondrial energy dysfunction by studying mice with cardiomyocyte-specific loss of the mitochondrial phosphate carrier (SLC25A3), an established model that develops cardiomyopathy as a result of defective mitochondrial ATP synthesis. Mitochondrial energy dysfunction induced a striking pattern of acylome remodeling, with significantly increased post-translational acetylation and malonylation. Mass spectrometry-based proteomics further revealed that energy dysfunction-induced remodeling of the acetylome and malonylome preferentially impacts mitochondrial proteins. Acetylation and malonylation modified a highly interconnected interactome of mitochondrial proteins, and both modifications were present on the enzyme isocitrate dehydrogenase 2 (IDH2). Intriguingly, IDH2 activity was enhanced in SLC25A3-deleted mitochondria, and further study of IDH2 sites targeted by both acetylation and malonylation revealed that these modifications can have site-specific and distinct functional effects. Finally, we uncovered a novel crosstalk between the two modifications, whereby mitochondrial energy dysfunction-induced acetylation of sirtuin 5 (SIRT5), inhibited its function. Because SIRT5 is a mitochondrial deacylase with demalonylase activity, this finding suggests that acetylation can modulate the malonylome. Together, our results position acylations as an arm of the mitochondrial response to energy dysfunction and suggest a mechanism by which focal disruption to the energy production machinery can have an expanded impact on global mitochondrial function.

Keywords:  acetylation; acylations; energy; heart; mitochondria

DOI:  https://doi.org/10.1152/ajpcell.00156.2021
Elife. 2021 Jul 27. pii: e66768. [Epub ahead of print]10

miR-1 coordinately regulates lysosomal v-ATPase and biogenesis to impact proteotoxicity and muscle function during aging.

Isabelle Schiffer, Birgit Gerisch, Kazuto Kawamura, Raymond Laboy, Jennifer Hewitt, Martin Sebastian Denzel, Marcelo A Mori, Siva Vanapalli, Yidong Shen, Orsolya Symmons, Adam Antebi.

  Muscle function relies on the precise architecture of dynamic contractile elements, which must be fine-tuned to maintain motility throughout life. Muscle is also plastic, and remodeled in response to stress, growth, neural and metabolic inputs. The conserved muscle-enriched microRNA, miR-1, regulates distinct aspects of muscle development, but whether it plays a role during aging is unknown. Here we investigated Caenorhabditis elegans miR-1 in muscle function in response to proteostatic stress. mir-1 deletion improved mid-life muscle motility, pharyngeal pumping, and organismal longevity upon polyQ35 proteotoxic challenge. We identified multiple vacuolar ATPase subunits as subject to miR-1 control, and the regulatory subunit vha-13/ATP6V1A as a direct target downregulated via its 3'UTR to mediate miR-1 physiology. miR-1 further regulates nuclear localization of lysosomal biogenesis factor HLH-30/TFEB and lysosomal acidification. Our studies reveal that miR-1 coordinately regulates lysosomal v-ATPase and biogenesis to impact muscle function and health during aging.

Keywords:  C. elegans; genetics; genomics; lysosomal v-ATPase; miR-1; polyglutamine; proteostasis; vha-13

DOI:  https://doi.org/10.7554/eLife.66768
Dev Cell. 2021 Jul 26. pii: S1534-5807(21)00546-3. [Epub ahead of print]56(14): 2014-2015

Move it to lose it: Mitocytosis expels damaged mitochondria.

Chahat Mehra, Lena Pernas.

Mechanisms by which cells remove damaged mitochondria extracellularly are unclear. Recent work by Jiao and colleagues in Cell shows that migrating cells expel dysfunctional mitochondria in membrane-bound structures called migrasomes to maintain mitochondrial homeostasis.

DOI: https://doi.org/10.1016/j.devcel.2021.07.001
JCI Insight. 2021 Jul 27. pii: 147692. [Epub ahead of print]

Anterograde regulation of mitochondrial genes and FGF21 signaling by hepatic LSD1.

Yang Cao, Lingyi Tang, Kang Du, Kitt Paraiso, Qiushi Sun, Zhengxia Liu, Xiaolong Ye, Yuan Fang, Fang Yuan, Yu-Han Chen, Yumay Chen, Xiaorong Wang, Clinton Yu, Ira L Blitz, Ping H Wang, Lan Huang, Haibo Cheng, Xiang Lu, Ken Wy Cho, Marcus Seldin, Zhuyuan Fang, Qin Yang.

  Mitochondrial biogenesis and function are controlled by anterograde regulatory pathways involving more than one thousand nuclear-encoded proteins. Transcriptional networks controlling the nuclear-encoded mitochondrial genes remain to be fully elucidated. Here we show that histone demethylase LSD1 knockout from adult mouse liver (LSD1-LKO) reduces the expression of one-third of all nuclear-encoded mitochondrial genes and decreases mitochondrial biogenesis and function. LSD1-modulated histone methylation epigenetically regulates nuclear-encoded mitochondrial genes. Furthermore, LSD1 regulates gene expression and protein methylation of nicotinamide mononucleotide adenylyltransferase 1 (NMNAT1), which controls the final step of NAD+ synthesis and limits NAD+ availability in nucleus. Lsd1 knockout reduces NAD+-dependent SIRT1 and SIRT7 deacetylase activity, leading to hyperacetylation and hypofunctioning of GABPβ and PGC-1α, the major transcriptional factor/cofactor for nuclear-encoded mitochondrial genes. Despite the reduced mitochondrial function in liver, LSD1-LKO mice are protected from diet-induced hepatic steatosis and glucose intolerance, partially due to induction of hepatokine FGF21. Thus, LSD1 orchestrates a core regulatory network involving epigenetic modifications and NAD+ synthesis to control mitochondrial function and hepatokine production.

Keywords:  Diabetes; Endocrinology; Obesity

DOI:  https://doi.org/10.1172/jci.insight.147692
Dev Cell. 2021 Jul 26. pii: S1534-5807(21)00529-3. [Epub ahead of print]56(14): 2010-2012

MDVs to the rescue: How autophagy-deficient cancer cells adapt to defective mitophagy.

Laura Poillet-Perez, Eileen White.

Cancers are dependent on mitochondria, the powerhouse of the cell, and autophagy, the mechanism to preserve mitochondrial quality and function. In this issue of Developmental Cell, Towers et al. identify mitochondria-derived vesicles (MDVs) as a new adaptive mechanism enabling cancer cells to compensate for autophagy loss and to maintain mitochondrial function.

DOI: https://doi.org/10.1016/j.devcel.2021.06.022
Aging Cell. 2021 Jul 27. e13444

Nrf2 deficiency decreases NADPH from impaired IDH shuttle and pentose phosphate pathway in retinal pigmented epithelial cells to magnify oxidative stress-induced mitochondrial dysfunction.

Marisol Cano, Sayantan Datta, Lei Wang, Tongyun Liu, Miguel Flores-Bellver, Mira Sachdeva, Debasish Sinha, James T Handa.

  The nuclear factor-erythroid 2-related factor-2 (Nrf2), a major antioxidant transcription factor, is decreased in several age-related diseases including age-related macular degeneration (AMD), the most common cause of blindness among the elderly in western society. Since Nrf2's mito-protective response is understudied, we investigated its antioxidant response on mitochondria. Control and Nrf2-deficient retinal pigmented epithelial (RPE) cells were compared after treating with cigarette smoke extract (CSE). Mitochondrial antioxidant abundance and reactive oxygen species (ROS) were quantified. Mitochondrial function was assessed by TMRM assay, NADPH, electron transport chain activity, and Seahorse. Results were corroborated in Nrf2-/- mice and relevance to AMD was provided by immunohistochemistry of human globes. CSE induced mitochondrial ROS to impair mitochondrial function. H2 O2 increase in particular, was magnified by Nrf2 deficiency, and corresponded with exaggerated mitochondrial dysfunction. While Nrf2 did not affect mitochondrial antioxidant abundance, oxidized PRX3 was magnified by Nrf2 deficiency due to decreased NADPH from decreased expression of IDH2 and pentose phosphate pathway (PPP) genes. With severe CSE stress, intrinsic apoptosis was activated to increase cell death. PPP component TALDO1 immunolabeling was decreased in dysmorphic RPE of human AMD globes. Despite limited regulation of mitochondrial antioxidant expression, Nrf2 influences PPP and IDH shuttle activity that indirectly supplies NADPH for the TRX2 system. These results provide insight into how Nrf2 deficiency impacts the mitochondrial antioxidant response, and its role in AMD pathobiology.

Keywords:  aging; mitochondria; oxidative stress; reactive oxygen species

DOI:  https://doi.org/10.1111/acel.13444
EMBO Rep. 2021 Jul 26. e52507

Maintaining proteostasis under mechanical stress.

Jörg Höhfeld, Thomas Benzing, Wilhelm Bloch, Dieter O Fürst, Sebastian Gehlert, Michael Hesse, Bernd Hoffmann, Thorsten Hoppe, Pitter F Huesgen, Maja Köhn, Waldemar Kolanus, Rudolf Merkel, Carien M Niessen, Wojciech Pokrzywa, Markus M Rinschen, Dagmar Wachten, Bettina Warscheid.

  Cell survival, tissue integrity and organismal health depend on the ability to maintain functional protein networks even under conditions that threaten protein integrity. Protection against such stress conditions involves the adaptation of folding and degradation machineries, which help to preserve the protein network by facilitating the refolding or disposal of damaged proteins. In multicellular organisms, cells are permanently exposed to stress resulting from mechanical forces. Yet, for long time mechanical stress was not recognized as a primary stressor that perturbs protein structure and threatens proteome integrity. The identification and characterization of protein folding and degradation systems, which handle force-unfolded proteins, marks a turning point in this regard. It has become apparent that mechanical stress protection operates during cell differentiation, adhesion and migration and is essential for maintaining tissues such as skeletal muscle, heart and kidney as well as the immune system. Here, we provide an overview of recent advances in our understanding of mechanical stress protection.

Keywords:  autophagy; chaperones; mechanobiology; proteostasis; signal transduction

DOI:  https://doi.org/10.15252/embr.202152507
Front Mol Biosci. 2021 ;8 703532

A Novel NAD Signaling Mechanism in Axon Degeneration and its Relationship to Innate Immunity.

Eleanor L Hopkins, Weixi Gu, Bostjan Kobe, Michael P Coleman.

  Axon degeneration represents a pathological feature of many neurodegenerative diseases, including Alzheimer's disease and Parkinson's disease where axons die before the neuronal soma, and axonopathies, such as Charcot-Marie-Tooth disease and hereditary spastic paraplegia. Over the last two decades, it has slowly emerged that a central signaling pathway forms the basis of this process in many circumstances. This is an axonal NAD-related signaling mechanism mainly regulated by the two key proteins with opposing roles: the NAD-synthesizing enzyme NMNAT2, and SARM1, a protein with NADase and related activities. The crosstalk between the axon survival factor NMNAT2 and pro-degenerative factor SARM1 has been extensively characterized and plays an essential role in maintaining the axon integrity. This pathway can be activated in necroptosis and in genetic, toxic or metabolic disorders, physical injury and neuroinflammation, all leading to axon pathology. SARM1 is also known to be involved in regulating innate immunity, potentially linking axon degeneration to the response to pathogens and intercellular signaling. Understanding this NAD-related signaling mechanism enhances our understanding of the process of axon degeneration and enables a path to the development of drugs for a wide range of neurodegenerative diseases.

Keywords:  NAD; NMNAT2; Sarm1; axon degeneration; innate immunity

DOI:  https://doi.org/10.3389/fmolb.2021.703532
J Cell Physiol. 2021 Jul 28.

Nampt affects mitochondrial function in aged oocytes by mediating the downstream effector FoxO3a.

Qingrui Zhuan, Jun Li, Xingzhu Du, Luyao Zhang, Lin Meng, Keren Cheng, Shien Zhu, Yunpeng Hou, Xiangwei Fu.

  Maternal aging can impair the quality and decrease the developmental competence of ovulated oocytes. In this study, compromised germinal vesicle breakdown (GVBD) was found in aged mice oocytes. Furthermore, we observed increased reactive oxygen species (ROS) and mitochondrial Ca2+ levels, along with reduced mitochondrial temperature in aged oocytes. Maternal aging also changed the crotonylation level in oocytes. Forkhead box O3 (FoxO3a), a member of the forkhead protein family involved in the regulation of cell survival and life span reached a peak level in the metaphase II stage. Compared with a younger group, FoxO3a expression increased in aged oocytes. Intracellular localization of FoxO3a changed from the cytoplasm to chromatin in response to aging. The expression of the upstream regulator nicotinamide-phosphoribosyltransferase (Nampt) peaked in the GVBD stage. Moreover, Nampt expression was increased in aged oocytes, and more intense staining of Nampt was found in aged mice ovary. To further study the role of Nampt in mitochondrial function, specific agonist P7C3 and inhibitor FK866 were applied to aged oocytes, and FK866 significantly decreased adenosine triphosphate and mitochondrial membrane potential. In conclusion, mitochondrial dysfunction in aged oocytes was associated with elevated FoxO3a, and suppression of Nampt could further impair mitochondrial function.

Keywords:  FoxO3a; Nampt; maternal-aging; mitochondria; oocyte

DOI:  https://doi.org/10.1002/jcp.30532
Aging (Albany NY). 2021 Jul 26. 13(undefined):

GAS6 ameliorates advanced age-associated meiotic defects in mouse oocytes by modulating mitochondrial function.

Kyeoung-Hwa Kim, Eun-Young Kim, Kyung-Ah Lee.

  Previously, we reported that the silencing of growth arrest-specific gene 6 (Gas6) expression in oocytes impairs cytoplasmic maturation by suppressing mitophagy and inducing mitochondrial dysfunction, resulting in fertilization failure. Here, we show that oocyte aging is accompanied by an increase in meiotic defects associated with chromosome misalignment and abnormal spindle organization. Intriguingly, decreased Gas6 mRNA and protein expression were observed in aged oocytes from older females. We further explored the effect of GAS6 on the quality and fertility of aged mouse oocytes using a GAS6 rescue analysis. After treatment with the GAS6 protein, aged oocytes matured normally to the meiosis II (MII) stage. Additionally, maternal age-related meiotic defects were reduced by GAS6 protein microinjection. Restoring GAS6 ameliorated the mitochondrial dysfunction induced by maternal aging. Ultimately, GAS6-rescued MII oocytes exhibited increased ATP levels, reduced ROS levels and elevated glutathione (GSH) levels, collectively indicating improved mitochondrial function in aged oocytes. Thus, the age-associated decrease in oocyte quality was prevented by restoring GAS6. Importantly, GAS6 protein microinjection in aged oocytes also rescued fertility. We conclude that GAS6 improves mitochondrial function to achieve sufficient cytoplasmic maturation and attenuates maternal age-related meiotic errors, thereby efficiently safeguarding oocyte quality and fertility.

Keywords:  Gas6; aged oocyte; fertility; meiotic defect; mitochondria

DOI:  https://doi.org/10.18632/aging.203328
Autophagy. 2021 Jul 27. 1-2

All cells are created equal in the sight of autophagy: selective autophagy maintains homeostasis in senescent cells.

Jaejin Kim, Yeonghyeon Lee, Taerang Jeon, Mi-Sung Kim, Chanhee Kang.

  Macroautophagy/autophagy is a sophisticated quality control program that limits cellular damage and maintains homeostasis, being an essential part of several lifespan-promoting interventions. However, autophagy is also necessary for full establishment of cellular senescence, a causal factor for many age-related diseases and aging. What lies ahead of us to unravel such a paradoxical role of autophagy in senescence is to identify specific targets degraded by autophagy during senescence and determine their importance in the senescence regulatory network. Recently, we developed the "Selective autophagy substrates Identification Platform (SIP)" to advance these goals, providing a rich set of autophagy substrate proteins involved in senescence. Our study demonstrated that selective autophagy coordinates the stress support networks in senescent cells by degrading multiple regulatory components, echoing its homeostatic roles in normal cells. Targeting this type of selective autophagy might provide a unique opportunity to develop non-senescence addiction-based therapeutic strategies for senotherapy by disturbing the homeostatic state of senescent cells.

Keywords:  Autophagy interactome; cellular senescence; inflammation; oxidative stress; proteostasis; regulated protein stability; selective autophagy; stress support networks

DOI:  https://doi.org/10.1080/15548627.2021.1953848
Radiat Environ Biophys. 2021 Jul 30.

Genomic instability induced by radiation-mimicking chemicals is not associated with persistent mitochondrial degeneration.

Luukkonen Jukka, Höytö Anne, Sokka Miiko, Syväoja Juhani, Juutilainen Jukka, Naarala Jonne.

  Ionizing radiation has been shown to cause induced genomic instability (IGI), which is defined as a persistently increased rate of genomic damage in the progeny of the exposed cells. In this study, IGI was investigated by exposing human SH-SY5Y neuroblastoma cells to hydroxyurea and zeocin, two chemicals mimicking different DNA-damaging effects of ionizing radiation. The aim was to explore whether IGI was associated with persistent mitochondrial dysfunction. Changes to mitochondrial function were assessed by analyzing mitochondrial superoxide production, mitochondrial membrane potential, and mitochondrial activity. The formation of micronuclei was used to determine immediate genetic damage and IGI. Measurements were performed either immediately, 8 days, or 15 days following exposure. Both hydroxyurea and zeocin increased mitochondrial superoxide production and affected mitochondrial activity immediately after exposure, and mitochondrial membrane potential was affected by zeocin, but no persistent changes in mitochondrial function were observed. IGI became manifested 15 days after exposure in hydroxyurea-exposed cells. In conclusion, immediate responses in mitochondrial function did not cause persistent dysfunction of mitochondria, and this dysfunction was not required for IGI in human neuroblastoma cells.

Keywords:  Induced genomic instability; Ionizing radiation mimics; Micronuclei; Mitochondria; Reactive oxygen species

DOI:  https://doi.org/10.1007/s00411-021-00927-5
Cell Stem Cell. 2021 Jul 21. pii: S1934-5909(21)00286-1. [Epub ahead of print]

Establishment, maintenance, and recall of inflammatory memory.

Samantha B Larsen, Christopher J Cowley, Sairaj M Sajjath, Douglas Barrows, Yihao Yang, Thomas S Carroll, Elaine Fuchs.

  Known for nearly a century but through mechanisms that remain elusive, cells retain a memory of inflammation that equips them to react quickly and broadly to diverse secondary stimuli. Using murine epidermal stem cells as a model, we elucidate how cells establish, maintain, and recall inflammatory memory. Specifically, we landscape and functionally interrogate temporal, dynamic changes to chromatin accessibility, histone modifications, and transcription factor binding that occur during inflammation, post-resolution, and in memory recall following injury. We unearth an essential, unifying role for the general stress-responsive transcription factor FOS, which partners with JUN and cooperates with stimulus-specific STAT3 to establish memory; JUN then remains with other homeostatic factors on memory domains, facilitating rapid FOS re-recruitment and gene re-activation upon diverse secondary challenges. Extending our findings, we offer a comprehensive, potentially universal mechanism behind inflammatory memory and less discriminate recall phenomena with profound implications for tissue fitness in health and disease.

Keywords:  AP1 transcription factors; ATAC sequencing; CUT&RUN; ChIP sequencing; FOS; FOS:JUN; STAT3; broadened immune protection; epigenetic memory; histone modifications; inflammation; inflammatory disorders; inflammatory memory; tissue stem cells; trained immunity

DOI:  https://doi.org/10.1016/j.stem.2021.07.001
Mol Pharmacol. 2021 Jul 26. pii: MOLPHARM-AR-2021-000297. [Epub ahead of print]

Eribulin activates the cGAS-STING pathway via the cytoplasmic accumulation of mtDNA.

Charles S Fermaintt, Leila Takahashi-Ruiz, Huiyun Liang, Susan L Mooberry, April L Risinger.

  Microtubule targeting agents (MTAs), including both microtubule stabilizers and destabilizers, are highly effective chemotherapeutic drugs used in the treatment of solid tumors and hematological malignancies. In addition to the shared ability of all MTAs to block cell cycle progression, growing evidence shows that different agents of this class can also have mechanistically distinct effects on non-mitotic microtubule-dependent cellular processes, including cellular signaling and transport. Herein, we test the biological hypothesis that MTAs used in the treatment of triple-negative breast cancer (TNBC) can differentially affect innate immune signaling pathways independent of their antimitotic effects. Our data demonstrate that the microtubule destabilizer eribulin, but not the microtubule stabilizer paclitaxel, induces cGAS-STING-dependent expression of interferon β in both myeloid and TNBC cells. Activation of the cGAS-STING pathway by eribulin was further found to be mediated by the accumulation of cytoplasmic mitochondrial DNA. Together, these findings provide mechanistic insight into how eribulin can induce innate immune signaling independent of its antimitotic or cytotoxic effects. Significance StatementMicrotubule targeted agents are often used in the treatment of breast cancer and, most recently, have been used in combination with immune checkpoint inhibitors to improve their efficacy. While all clinically approved MTAs share an antimitotic mechanism of action, their distinct effects on interphase microtubules can promote differential downstream signaling consequences. We show that the microtubule destabilizer eribulin, but not the microtubule stabilizer paclitaxel, activates the cGAS-STING innate immune signaling pathway through the accumulation of mitochondrial DNA in the cytoplasm.

Keywords:  Anti-cancer agents; Anti-mitotics; Microtubules; breast cancer; cancer; cancer chemotherapy

DOI:  https://doi.org/10.1124/molpharm.121.000297