bims-nenemi 2021-09-19 papers

bims-nenemi

Biomed News

on Neuroinflammation, neurodegeneration and mitochondria

Issue of 2021–09–19
twenty-one papers selected by
Marco Tigano, Thomas Jefferson University

Mitochondrial Nucleic Acid as a Driver of Pathogenic Type I Interferon Induction in Mendelian Disease.
A role for mitochondrial DNA in cellular proteostasis.
Decreased Mitochondrial Membrane Potential Activates the Mitochondrial Unfolded Protein Response.
Adenosine-to-inosine editing of endogenous Z-form RNA by the deaminase ADAR1 prevents spontaneous MAVS-dependent type I interferon responses.
Mutations in the adenosine deaminase ADAR1 that prevent endogenous Z-RNA binding induce Aicardi-Goutières-syndrome-like encephalopathy.
Negative Regulation of RNF90 on RNA Virus-Triggered Antiviral Immune Responses Targeting MAVS.
The molecular mechanism of RIG-I activation and signaling.
Histone demethylase LSD1 promotes RIG-I poly-ubiquitination and anti-viral gene expression.
Autophagy-competent mitochondrial translation elongation factor TUFM inhibits caspase-8-mediated apoptosis.
Mitochondria: endosymbiont bacteria DNA sequence as a target against cancer.
Apoptotic stress induces Bax-dependent, caspase-independent redistribution of LINC complex nesprins.
Extensive alternative splicing triggered by mitonuclear mismatch in naturally introgressed Rhinolophus bats.
Activation of mTORC1 and c-Jun by Prohibitin1 loss in Schwann cells may link mitochondrial dysfunction to demyelination.
Mitochondrial reactive oxygen species trigger metformin-dependent antitumor immunity via activation of Nrf2/mTORC1/p62 axis in tumor-infiltrating CD8T lymphocytes.
Alzheimer's disease-causing presenilin-1 mutations have deleterious effects on mitochondrial function.
Riboflavin transporter SLC52A1, a target of p53, suppresses cellular senescence by activating mitochondrial complex II.
Activation of Hippo signaling pathway mediates mitochondria dysfunction and dilated cardiomyopathy in mice.
MKP-1 Overexpression Reduces Postischemic Myocardial Damage through Attenuation of ER Stress and Mitochondrial Damage.
HDAC6: A Key Link Between Mitochondria and Development of Peripheral Neuropathy.
Saikosaponin-A induces apoptosis of cervical cancer through mitochondria- and endoplasmic reticulum stress-dependent pathway in vitro and in vivo: involvement of PI3K/AKT signaling pathway.
Targeted epigenetic induction of mitochondrial biogenesis enhances antitumor immunity in mouse model.

Front Immunol. 2021 ;12 729763

Mitochondrial Nucleic Acid as a Driver of Pathogenic Type I Interferon Induction in Mendelian Disease.

Alice Lepelley, Timothy Wai, Yanick J Crow.

  The immune response to viral infection involves the recognition of pathogen-derived nucleic acids by intracellular sensors, leading to type I interferon (IFN), and downstream IFN-stimulated gene, induction. Ineffective discrimination of self from non-self nucleic acid can lead to autoinflammation, a phenomenon implicated in an increasing number of disease states, and well highlighted by the group of rare genetic disorders referred to as the type I interferonopathies. To understand the pathogenesis of these monogenic disorders, and polyfactorial diseases associated with pathogenic IFN upregulation, such as systemic lupus erythematosus and dermatomyositis, it is important to define the self-derived nucleic acid species responsible for such abnormal IFN induction. Recently, attention has focused on mitochondria as a novel source of immunogenic self nucleic acid. Best appreciated for their function in oxidative phosphorylation, metabolism and apoptosis, mitochondria are double membrane-bound organelles that represent vestigial bacteria in the cytosol of eukaryotic cells, containing their own DNA and RNA enclosed within the inner mitochondrial membrane. There is increasing recognition that a loss of mitochondrial integrity and compartmentalization can allow the release of mitochondrial nucleic acid into the cytosol, leading to IFN induction. Here, we provide recent insights into the potential of mitochondrial-derived DNA and RNA to drive IFN production in Mendelian disease. Specifically, we summarize current understanding of how nucleic acids are detected as foreign when released into the cytosol, and then consider the findings implicating mitochondrial nucleic acid in type I interferonopathy disease states. Finally, we discuss the potential for IFN-driven pathology in primary mitochondrial disorders.

Keywords:  autoinflammation; innate immunity; mitochondria; mitochondrial disease; mtDNA; mtRNA; type I interferon; type I interferonopathy

DOI:  https://doi.org/10.3389/fimmu.2021.729763
Nat Rev Genet. 2021 Sep 13.

A role for mitochondrial DNA in cellular proteostasis.

Caroline Barranco.

DOI: https://doi.org/10.1038/s41576-021-00418-9
MicroPubl Biol. 2021 ;2021

Decreased Mitochondrial Membrane Potential Activates the Mitochondrial Unfolded Protein Response.

Brandon J Berry, Tyrone O Nieves, Andrew P Wojtovich.

Mitochondria are ATP-producing organelles that also signal throughout the cell. Mitochondrial protein homeostasis is regulated through membrane potential-dependent protein import and quality control signaling. The mitochondrial unfolded protein response (UPRmt) is a specific program that responds to imbalances in nuclear and mitochondrial gene expression. Mounting evidence suggests that the electrochemical gradient that powers mitochondrial function, the mitochondrial membrane potential (Δψm), is a core regulator of the UPRmt. Here we tested this notion directly by pharmacologically dissipating Δψm and monitoring UPRmt activation. We found that chemical dissipation of Δψm using FCCP indeed activated UPRmt dose-dependently in C. elegans assayed by the HSP-60::GFP reporter strain.

DOI: https://doi.org/10.17912/micropub.biology.000445
Immunity. 2021 Sep 14. pii: S1074-7613(21)00343-5. [Epub ahead of print]54(9): 1961-1975.e5

Adenosine-to-inosine editing of endogenous Z-form RNA by the deaminase ADAR1 prevents spontaneous MAVS-dependent type I interferon responses.

Qiannan Tang, Rachel E Rigby, George R Young, Astrid Korning Hvidt, Tanja Davis, Tiong Kit Tan, Anne Bridgeman, Alain R Townsend, George Kassiotis, Jan Rehwinkel.

  Nucleic acids are powerful triggers of innate immunity and can adopt the Z-conformation, an unusual left-handed double helix. Here, we studied the biological function(s) of Z-RNA recognition by the adenosine deaminase ADAR1, mutations in which cause Aicardi-Goutières syndrome. Adar1mZα/mZα mice, bearing two point mutations in the Z-nucleic acid binding (Zα) domain that abolish Z-RNA binding, displayed spontaneous induction of type I interferons (IFNs) in multiple organs, including in the lung, where both stromal and hematopoietic cells showed IFN-stimulated gene (ISG) induction. Lung neutrophils expressed ISGs induced by the transcription factor IRF3, indicating an initiating role for neutrophils in this IFN response. The IFN response in Adar1mZα/mZα mice required the adaptor MAVS, implicating cytosolic RNA sensing. Adenosine-to-inosine changes were enriched in transposable elements and revealed a specific requirement of ADAR1's Zα domain in editing of a subset of RNAs. Thus, endogenous RNAs in Z-conformation have immunostimulatory potential curtailed by ADAR1, with relevance to autoinflammatory disease in humans.

Keywords:  ADAR1; Aicardi–Goutières syndrome; MAVS; MDA5; RNA editing; Z-RNA; Zα domain; influenza A virus; interferon; neutrophil

DOI:  https://doi.org/10.1016/j.immuni.2021.08.011
Immunity. 2021 Sep 14. pii: S1074-7613(21)00356-3. [Epub ahead of print]54(9): 1976-1988.e7

Mutations in the adenosine deaminase ADAR1 that prevent endogenous Z-RNA binding induce Aicardi-Goutières-syndrome-like encephalopathy.

Taisuke Nakahama, Yuki Kato, Toshiharu Shibuya, Maal Inoue, Jung In Kim, Tuangtong Vongpipatana, Hiroyuki Todo, Yanfang Xing, Yukio Kawahara.

  Mutations in the adenosine-to-inosine RNA-editing enzyme ADAR1 p150, including point mutations in the Z-RNA recognition domain Zα, are associated with Aicardi-Goutières syndrome (AGS). Here, we examined the in vivo relevance of ADAR1 binding of Z-RNA. Mutation of W197 in Zα, which abolished Z-RNA binding, reduced RNA editing. Adar1W197A/W197A mice displayed severe growth retardation after birth, broad expression of interferon-stimulated genes (ISGs), and abnormal development of multiple organs. Notably, malformation of the brain was accompanied by white matter vacuolation and gliosis, reminiscent of AGS-associated encephalopathy. Concurrent deletion of the double-stranded RNA sensor MDA5 ameliorated these abnormalities. ADAR1 (W197A) expression increased in a feedback manner downstream of type I interferons, resulting in increased RNA editing at a subset of, but not all, ADAR1 target sites. This increased expression did not ameliorate inflammation in Adar1W197A/W197A mice. Thus, editing of select endogenous RNAs by ADAR1 is essential for preventing inappropriate MDA5-mediated inflammation, with relevance to the pathogenesis of AGS.

Keywords:  ADAR1; AGS; ISG; MDA5; RNA editing; Z-RNA; encephalopathy; hematopoiesis; inosine

DOI:  https://doi.org/10.1016/j.immuni.2021.08.022
Front Immunol. 2021 ;12 730483

Negative Regulation of RNF90 on RNA Virus-Triggered Antiviral Immune Responses Targeting MAVS.

Bo Yang, Ge Zhang, Xiao Qin, Yulu Huang, Xiaowen Ren, Jingliang Sun, Shujun Ma, Yanzi Liu, Di Song, Yue Liu, Yuhan Cui, Hui Wang, Jie Wang.

  The antiviral innate immunity is the first line of host defense against viral infection. Mitochondrial antiviral signaling protein (MAVS, also named Cardif/IPS-1/VISA) is a critical protein in RNA virus-induced antiviral signaling pathways. Our previous research suggested that E3 ubiquitin-protein ligases RING-finger protein (RNF90) negatively regulate cellular antiviral responses by targeting STING for degradation, though its role in RNA virus infection remains unknown. This study demonstrated that RNF90 negatively regulated RNA virus-triggered antiviral innate immune responses in RNF90-silenced PMA-THP1 cells, RNF90-deficient cells (including HaCaTs, MEFs, and BMDMs), and RNF90-deficient mice. However, RNF90 regulated RNA virus-triggered antiviral innate immune responses independent of STING. RNF90 promoted K48-linked ubiquitination of MAVS and its proteasome-dependent degradation, leading to the inhibition of innate immune responses. Altogether, our findings suggested a novel function and mechanism of RNF90 in antiviral innate immunity.

Keywords:  MAVS; RNF90; antiviral innate immune responses; degradation; signaling pathway; ubiquitination

DOI:  https://doi.org/10.3389/fimmu.2021.730483
Immunol Rev. 2021 Sep 12.

The molecular mechanism of RIG-I activation and signaling.

Daniel Thoresen, Wenshuai Wang, Drew Galls, Rong Guo, Ling Xu, Anna Marie Pyle.

  RIG-I is our first line of defense against RNA viruses, serving as a pattern recognition receptor that identifies molecular features common among dsRNA and ssRNA viral pathogens. RIG-I is maintained in an inactive conformation as it samples the cellular space for pathogenic RNAs. Upon encounter with the triphosphorylated terminus of blunt-ended viral RNA duplexes, the receptor changes conformation and releases a pair of signaling domains (CARDs) that are selectively modified and interact with an adapter protein (MAVS), thereby triggering a signaling cascade that stimulates transcription of interferons. Here, we describe the structural determinants for specific RIG-I activation by viral RNA, and we describe the strategies by which RIG-I remains inactivated in the presence of host RNAs. From the initial RNA triggering event to the final stages of interferon expression, we describe the experimental evidence underpinning our working knowledge of RIG-I signaling. We draw parallels with behavior of related proteins MDA5 and LGP2, describing evolutionary implications of their collective surveillance of the cell. We conclude by describing the cell biology and immunological investigations that will be needed to accurately describe the role of RIG-I in innate immunity and to provide the necessary foundation for pharmacological manipulation of this important receptor.

Keywords:  RLR; anti-viral response; innate immunity; interferon; pattern recognition receptor

DOI:  https://doi.org/10.1111/imr.13022
PLoS Pathog. 2021 Sep;17(9): e1009918

Histone demethylase LSD1 promotes RIG-I poly-ubiquitination and anti-viral gene expression.

Qi-Xin Hu, Hui-Yi Wang, Lu Jiang, Chen-Yu Wang, Lin-Gao Ju, Yuan Zhu, Bo Zhong, Min Wu, Zhen Wang, Lian-Yun Li.

Under RNA virus infection, retinoic acid-inducible gene I (RIG-I) in host cells recognizes viral RNA and activates the expression of type I IFN. To investigate the roles of protein methyltransferases and demethylases in RIG-I antiviral signaling pathway, we screened all the known related enzymes with a siRNA library and identified LSD1 as a positive regulator for RIG-I signaling. Exogenous expression of LSD1 enhances RIG-I signaling activated by virus stimulation, whereas its deficiency restricts it. LSD1 interacts with RIG-I, promotes its K63-linked polyubiquitination and interaction with VISA/MAVS. Interestingly, LSD1 exerts its function in antiviral response not dependent on its demethylase activity but through enhancing the interaction between RIG-I with E3 ligases, especially TRIM25. Furthermore, we provide in vivo evidence that LSD1 increases antiviral gene expression and inhibits viral replication. Taken together, our findings demonstrate that LSD1 is a positive regulator of signaling pathway triggered by RNA-virus through mediating RIG-I polyubiquitination.

DOI: https://doi.org/10.1371/journal.ppat.1009918
Cell Death Differ. 2021 Sep 12.

Autophagy-competent mitochondrial translation elongation factor TUFM inhibits caspase-8-mediated apoptosis.

Chang-Yong Choi, Mai Tram Vo, John Nicholas, Young Bong Choi.

Mitochondria support multiple cell functions, but an accumulation of dysfunctional or excessive mitochondria is detrimental to cells. We previously demonstrated that a defect in the autophagic removal of mitochondria, termed mitophagy, leads to the acceleration of apoptosis induced by herpesvirus productive infection. However, the exact molecular mechanisms underlying activation of mitophagy and regulation of apoptosis remain poorly understood despite the identification of various mitophagy-associated proteins. Here, we report that the mitochondrial translation elongation factor Tu, a mitophagy-associated protein encoded by the TUFM gene, locates in part on the outer membrane of mitochondria (OMM) where it acts as an inhibitor of altered mitochondria-induced apoptosis through its autophagic function. Inducible depletion of TUFM potentiated caspase-8-mediated apoptosis in virus-infected cells with accumulation of altered mitochondria. In addition, TUFM depletion promoted caspase-8 activation induced by treatment with TNF-related apoptosis-inducing ligand in cancer cells, potentially via dysregulation of mitochondrial dynamics and mitophagy. Importantly, we revealed the existence of and structural requirements for autophagy-competent TUFM on the OMM; the GxxxG motif within the N-terminal mitochondrial targeting sequences of TUFM was required for self-dimerization and mitophagy. Furthermore, we found that autophagy-competent TUFM was subject to ubiquitin-proteasome-mediated degradation but stabilized upon mitophagy or autophagy activation. Moreover, overexpression of autophagy-competent TUFM could inhibit caspase-8 activation. These studies extend our knowledge of mitophagy regulation of apoptosis and could provide a novel strategic basis for targeted therapy of cancer and viral diseases.

DOI: https://doi.org/10.1038/s41418-021-00868-y
Cancer Sci. 2021 Sep 17.

Mitochondria: endosymbiont bacteria DNA sequence as a target against cancer.

Hiroki Nagase, Takayoshi Watanabe, Nobuko Koshikawa, Seigi Yamamoto, Keizo Takenaga, Jason Lin.

  As the energy factory for the cell, the mitochondrion, through its role of adenosine triphosphate production by oxidative phosphorylation, can be regarded as the guardian of well-regulated cellular metabolism; the integrity of mitochondrial functions, however, is particularly vulnerable in cancer due to the lack of superstructures such as histone and lamina folds to protect the mitochondrial genome from unintended exposure, which consequently elevates risks of mutation. In cancer, mechanisms responsible for enforcing quality control surveillance for identifying and eliminating defective mitochondria is often poorly regulated, and certain uneliminated mitochondrial DNA (mtDNA) mutations and polymorphisms can be advantageous for the proliferation, progression and metastasis of tumor cells. Such pathogenic mtDNA aberrations are likely to increase and occasionally be homoplasmic in cancer cells and, intriguingly, in normal cells in the proximity of tumor microenvironments (TME) as well. Distinct characteristics of these abnormalities in mtDNA may provide a new path for cancer therapy. Here we discuss a promising novel therapeutic strategy, utilizing the sequence-specific properties of pyrrole-imidazole polyamide-triphenylphosphonium conjugates, against cancer for clearing abnormal mtDNA by reactivating mitochondrial quality control surveillance.

Keywords:  Age-related disorder; Anti-cancer therapy; Apoptosis; Autophagy; BCL family; Exocytosis; Mitochondria; Mitochondrial disease; Mitochondrial quality control (MQC); Mitophagy; Mutation; Polymorphism; Pyrrole-imidazole polyamide; Reactive oxygen species (ROS); Senescence; Triphenylphosphonium (TPP); mtDNA

DOI:  https://doi.org/10.1111/cas.15143
Cell Death Discov. 2020 Sep 18. 6(1): 90

Apoptotic stress induces Bax-dependent, caspase-independent redistribution of LINC complex nesprins.

Liora Lindenboim, Dan Grozki, Ayelet R Amsalem-Zafran, Aida Peña-Blanco, Gregg G Gundersen, Christoph Borner, Didier Hodzic, Ana J Garcia-Sáez, Howard J Worman, Reuven Stein.

The canonical function of Bcl-2 family proteins is to regulate mitochondrial membrane integrity. In response to apoptotic signals the multi-domain pro-apoptotic proteins Bax and Bak are activated and perforate the mitochondrial outer membrane by a mechanism which is inhibited by their interaction with pro-survival members of the family. However, other studies have shown that Bax and Bak may have additional, non-canonical functions, which include stress-induced nuclear envelope rupture and discharge of nuclear proteins into the cytosol. We show here that the apoptotic stimuli cisplatin and staurosporine induce a Bax/Bak-dependent degradation and subcellular redistribution of nesprin-1 and nesprin-2 but not nesprin-3, of the linker of nucleoskeleton and cytoskeleton (LINC) complex. The degradation and redistribution were caspase-independent and did not occur in Bax/Bak double knockout (DKO) mouse embryo fibroblasts (MEFs). Re-expression of Bax in Bax/Bak DKO MEFs restored stress-induced redistribution of nesprin-2 by a mechanism which requires Bax membrane localization and integrity of the α helices 5/6, and the Bcl-2 homology 3 (BH3) domain. We found that nesprin-2 interacts with Bax in close proximity to perinuclear mitochondria in mouse and human cells. This interaction requires the mitochondrial targeting and N-terminal region but not the BH3 domain of Bax. Our results identify nesprin-2 as a Bax binding partner and also a new function of Bax in impairing the integrity of the LINC complex.

DOI: https://doi.org/10.1038/s41420-020-00327-6
Ecol Evol. 2021 Sep;11(17): 12003-12010

Extensive alternative splicing triggered by mitonuclear mismatch in naturally introgressed Rhinolophus bats.

Wenli Chen, Xiuguang Mao.

  Mitochondrial function needs strong interactions of mitochondrial and nuclear (mitonuclear) genomes, which can be disrupted by mitonuclear mismatch due to mitochondrial DNA (mtDNA) introgression between two formerly isolated populations or taxa. This mitonuclear disruption may cause severe cellular stress in mismatched individuals. Gene expression changes and alternative splicing (AS) are two important transcriptional regulations to respond to environmental or cellular stresses. We previously identified a naturally introgressed population in the intermediate horseshoe bat (Rhinolophus affinis). Individuals from this population belong to R. a. himalayanus and share almost identical nuclear genetic background; however, some of them had mtDNA from another subspecies (R. a. macrurus). With this unique natural system, we examined gene expression changes in six tissues between five mitonuclear mismatched and five matched individuals. A small number of differentially expressed genes (DEGs) were identified, and functional enrichment analysis revealed that most DEGs were related to immune response although some may be involved in response to oxidative stress. In contrast, we identified extensive AS events and alternatively spliced genes (ASGs) between mismatched and matched individuals. Functional enrichment analysis revealed that multiple ASGs were directly or indirectly associated with energy production in mitochondria which is vital for survival of organism. To our knowledge, this is the first study to examine the role of AS in responding to cellular stress caused by mitonuclear mismatch in natural populations. Our results suggest that AS may play a more important role than gene expression regulation in responding to severe environmental or cellular stresses.

Keywords:  gene expression; horseshoe bats; introgressive hybridization; mitonuclear interaction; transcriptome

DOI:  https://doi.org/10.1002/ece3.7966
Elife. 2021 Sep 14. pii: e66278. [Epub ahead of print]10

Activation of mTORC1 and c-Jun by Prohibitin1 loss in Schwann cells may link mitochondrial dysfunction to demyelination.

Gustavo Della Flora Nunes, Emma R Wilson, Edward Hurley, Bin He, Bert W O'Malley, Yannick Poitelon, Lawrence Wrabetz, M Laura Feltri.

  Schwann cell (SC) mitochondria are quickly emerging as an important regulator of myelin maintenance in the peripheral nervous system (PNS). However, the mechanisms underlying demyelination in the context of mitochondrial dysfunction in the PNS are incompletely understood. We recently showed that conditional ablation of the mitochondrial protein Prohibitin 1 (PHB1) in SCs causes a severe and fast progressing demyelinating peripheral neuropathy in mice, but the mechanism that causes failure of myelin maintenance remained unknown. Here, we report that mTORC1 and c-Jun are continuously activated in the absence of Phb1, likely as part of the SC response to mitochondrial damage. Moreover, we demonstrate that these pathways are involved in the demyelination process, and that inhibition of mTORC1 using rapamycin partially rescues the demyelinating pathology. Therefore, we propose that mTORC1 and c-Jun may play a critical role as executioners of demyelination in the context of perturbations to SC mitochondria.

Keywords:  mouse; neuroscience

DOI:  https://doi.org/10.7554/eLife.66278
J Immunother Cancer. 2021 Sep;pii: e002954. [Epub ahead of print]9(9):

Mitochondrial reactive oxygen species trigger metformin-dependent antitumor immunity via activation of Nrf2/mTORC1/p62 axis in tumor-infiltrating CD8T lymphocytes.

Mikako Nishida, Nahoko Yamashita, Taisaku Ogawa, Keita Koseki, Eiji Warabi, Tomoyuki Ohue, Masaaki Komatsu, Hirokazu Matsushita, Kazuhiro Kakimi, Eiryo Kawakami, Katsuyuki Shiroguchi, Heiichiro Udono.

   BACKGROUND: Metformin (Met) is the first-line treatment for type 2 diabetes mellitus and plays an effective role in treating various diseases, such as cardiovascular disease, neurodegenerative disease, cancer, and aging. However, the underlying mechanism of Met-dependent antitumor immunity remains to be elucidated.
METHODS: MitoTEMPO, a scavenger of mitochondrial superoxide, abolished the antitumor effect of Met, but not antiprogrammed cell death (PD-1) antibody (Ab) treatment. Consequently, we studied the mechanism of the Met-induced antitumor effect. Expressions of glucose transporter (Glut)-1, mitochondrial reactive oxygen species (mtROS), interferon (IFN)-γ, Ki67, autophagy markers, activation markers for NF-E2-related factor 2 (Nrf2), and mammalian target of rapamaycin complex 1 (mTORC1) in CD8+ tumor-infiltrating T lymphocytes (CD8TILs) were examined by flow cytometry analysis. In addition, conditional knockout mice for Nrf2 and p62 were used to detect these markers, together with the monitoring of in vivo tumor growth. RNA sequencing was performed for CD8TILs and tumor cells. Melanoma cells containing an IFN-γ receptor (IFNγR) cytoplasmic domain deletion mutant was overexpressed and used for characterization of the metabolic profile of those tumor cells using a Seahorse Flux Analyzer.
RESULTS: Met administration elevates mtROS and cell surface Glut-1, resulting in the production of IFN-γ in CD8TILs. mtROS activates Nrf2 in a glycolysis-dependent manner, inducing activation of autophagy, glutaminolysis, mTORC1, and p62/SQSTM1. mTORC1-dependent phosphorylation of p62 at serine 351 (p-p62(S351)) is also involved in activation of Nrf2. Conditional deletion of Nrf2 in CD8TILs abrogates mTORC1 activation and antitumor immunity by Met. In synergy with the effect of anti-PD-1 Ab, Met boosts CD8TIL proliferation and IFN-γ secretion, resulting in decreased glycolysis and oxidative phosphorylation in tumor cells. Consequently, Glut-1 is elevated in CD8TILs, together with the expansion of activated dendritic cells. Moreover, tumor cells lacking in IFNγR signaling abolish IFN-γ production and proliferation of CD8TILs.
CONCLUSIONS: We found that Met stimulates production of mtROS, which triggers Glut-1 elevation and Nrf2 activation in CD8TILs. Nrf2 activates mTORC1, whereas mTORC1 activates Nrf2 in a p-p62(S351)-dependent manner, thus creating a feedback loop that ensures CD8TILs' proliferation. In combination with anti-PD-1 Ab, Met stimulates robust proliferation of CD8TILs and IFN-γ secretion, resulting in an IFN-γ-dependent reprogramming of the tumor microenvironment.

Keywords:  adaptive immunity; cd8-positive T-lymphocytes; immunomodulation; lymphocytes; tumor microenvironment; tumor-infiltrating

DOI:  https://doi.org/10.1136/jitc-2021-002954
Theranostics. 2021 ;11(18): 8855-8873

Alzheimer's disease-causing presenilin-1 mutations have deleterious effects on mitochondrial function.

Jihoon Han, Heejin Park, Chinmoyee Maharana, A-Ryeong Gwon, Jinsu Park, Seung Hyun Baek, Han-Gyu Bae, Yoonsuk Cho, Hark Kyun Kim, Jae Hoon Sul, Jeongmi Lee, Eunae Kim, Junsik Kim, Yongeun Cho, Sunyoung Park, Leon F Palomera, Thiruma V Arumugam, Mark P Mattson, Dong-Gyu Jo.

  Mitochondrial dysfunction and oxidative stress are frequently observed in the early stages of Alzheimer's disease (AD). Studies have shown that presenilin-1 (PS1), the catalytic subunit of γ-secretase whose mutation is linked to familial AD (FAD), localizes to the mitochondrial membrane and regulates its homeostasis. Thus, we investigated how five PS1 mutations (A431E, E280A, H163R, M146V, and Δexon9) observed in FAD affect mitochondrial functions. Methods: We used H4 glioblastoma cell lines genetically engineered to inducibly express either the wild-type PS1 or one of the five PS1 mutants in order to examine mitochondrial morphology, dynamics, membrane potential, ATP production, mitochondria-associated endoplasmic reticulum (ER) membranes (MAMs), oxidative stress, and bioenergetics. Furthermore, we used brains of PS1M146V knock-in mice, 3xTg-AD mice, and human AD patients in order to investigate the role of PS1 in regulating MAMs formation. Results: Each PS1 mutant exhibited slightly different mitochondrial dysfunction. Δexon9 mutant induced mitochondrial fragmentation while A431E, E280A, H163R, and M146V mutants increased MAMs formation. A431E, E280A, M146V, and Δexon9 mutants also induced mitochondrial ROS production. A431E mutant impaired both complex I and peroxidase activity while M146V mutant only impaired peroxidase activity. All PS1 mutants compromised mitochondrial membrane potential and cellular ATP levels were reduced by A431E, M146V, and Δexon9 mutants. Through comparative profiling of hippocampal gene expression in PS1M146V knock-in mice, we found that PS1M146V upregulates Atlastin 2 (ATL2) expression level, which increases ER-mitochondria contacts. Down-regulation of ATL2 after PS1 mutant induction rescued abnormally elevated ER-mitochondria interactions back to the normal level. Moreover, ATL2 expression levels were significantly elevated in the brains of 3xTg-AD mice and AD patients. Conclusions: Overall, our findings suggest that each of the five FAD-linked PS1 mutations has a deleterious effect on mitochondrial functions in a variety of ways. The adverse effects of PS1 mutations on mitochondria may contribute to MAMs formation and oxidative stress resulting in an accelerated age of disease onset in people harboring mutant PS1.

Keywords:  ATL2; Alzheimer's disease; MAMs; Mitochondria; Presenilin-1

DOI:  https://doi.org/10.7150/thno.59776
Mol Biol Cell. 2021 Sep 15. mbcE21050262

Riboflavin transporter SLC52A1, a target of p53, suppresses cellular senescence by activating mitochondrial complex II.

Taiki Nagano, Yuto Awai, Shione Kuwaba, Taiichi Osumi, Kentaro Mio, Tetsushi Iwasaki, Shinji Kamada.

Cellular senescence is a state of permanent proliferative arrest induced by a variety of stresses, such as DNA damage. The transcriptional activity of p53 has been known to be essential for senescence induction. It remains unknown, however, whether among the downstream genes of p53, there is a gene that has anti-senescence function. Our recent studies have indicated that the expression of SLC52A1 (also known as GPR172B/RFVT1), a riboflavin transporter, is upregulated specifically in senescent cells depending on p53, but the relationship between senescence and SLC52A1 or riboflavin has not been described. Here, we examined the role of SLC52A1 in senescence. We found that knockdown of SLC52A1 promoted senescence phenotypes induced by DNA damage in tumor and normal cells. The senescence suppressive-action of SLC52A1 was dependent on its riboflavin transport activity. Furthermore, elevation of intracellular riboflavin led to activation of mitochondrial membrane potential (MMP) mediated by the mitochondrial electron transport chain complex II. Finally, the SLC52A1-dependent activation of MMP inhibited the AMPK-p53 pathway, a central mediator of mitochondria dysfunction-related senescence. These results suggest that SLC52A1 contributes to suppress senescence through the uptake of riboflavin and acts downstream of p53 as a negative feedback mechanism to limit aberrant senescence induction.

DOI: https://doi.org/10.1091/mbc.E21-05-0262
Theranostics. 2021 ;11(18): 8993-9008

Activation of Hippo signaling pathway mediates mitochondria dysfunction and dilated cardiomyopathy in mice.

Wei Wu, Mark Ziemann, Kevin Huynh, Gang She, Zheng-Da Pang, Yi Zhang, Thy Duong, Helen Kiriazis, Tian-Tian Pu, Ru-Yue Bai, Jing-Jing Li, Yu Zhang, Ming-Xia Chen, Junichi Sadoshima, Xiu-Ling Deng, Peter J Meikle, Xiao-Jun Du.

  Rationale: Mitochondrial dysfunction facilitates heart failure development forming a therapeutic target, but the mechanism involved remains unclear. We studied whether the Hippo signaling pathway mediates mitochondrial abnormalities that results in onset of dilated cardiomyopathy (DCM). Methods: Mice with DCM due to overexpression of Hippo pathway kinase Mst1 were studied. DCM phenotype was evident in adult animals but contractile dysfunction was identified as an early sign of DCM at 3 weeks postnatal. Electron microscopy, multi-omics and biochemical assays were employed. Results: In 3-week and adult DCM mouse hearts, cardiomyocyte mitochondria exhibited overt structural abnormalities, smaller size and greater number. RNA sequencing revealed comprehensive suppression of nuclear-DNA (nDNA) encoded gene-sets involved in mitochondria turnover and all aspects of metabolism. Changes in cardiotranscriptome were confirmed by lower protein levels of multiple mitochondrial proteins in DCM heart of both ages. Mitochondrial DNA-encoded genes were also downregulated; due apparently to repression of nDNA-encoded transcriptional factors. Lipidomics identified remodeling in cardiolipin acyl-chains, increased acylcarnitine content but lower coenzyme Q10 level. Mitochondrial dysfunction was featured by lower ATP content and elevated levels of lactate, branched-chain amino acids and reactive oxidative species. Mechanistically, inhibitory YAP-phosphorylation was enhanced, which was associated with attenuated binding of transcription factor TEAD1. Numerous suppressed mitochondrial genes were identified as YAP-targets. Conclusion: Hippo signaling activation mediates mitochondrial damage by repressing mitochondrial genes, which causally promotes the development of DCM. The Hippo pathway therefore represents a therapeutic target against mitochondrial dysfunction in cardiomyopathy.

Keywords:  Hippo pathway; dilated cardiomyopathy; heart failure; mitochondria; transcriptome analysis

DOI:  https://doi.org/10.7150/thno.62302
Oxid Med Cell Longev. 2021 ;2021 8905578

MKP-1 Overexpression Reduces Postischemic Myocardial Damage through Attenuation of ER Stress and Mitochondrial Damage.

Xiaoling Hou, Lijun Li, Si Chen, Cheng Ge, Mingzhi Shen, Zhenhong Fu.

Mitochondrial dysfunction and endoplasmic reticulum (ER) stress contribute to postischemic myocardial damage, but the upstream regulatory mechanisms have not been identified. In this study, we analyzed the role of mitogen-activated protein kinase (MAPK) phosphatase 1 (MKP-1) in the regulation of mitochondrial function and ER stress in hypoxic cardiomyocytes. Our results show that MKP-1 overexpression sustains viability and reduces hypoxia-induced apoptosis among H9C2 cardiomyocytes. MKP-1 overexpression attenuates ER stress and expression of ER stress genes and improves mitochondrial function in hypoxia-treated H9C2 cells. MKP-1 overexpression also increases ATP production and mitochondrial respiration and attenuates mitochondrial oxidative damage in hypoxic cardiomyocytes. Moreover, our results demonstrate that ERK and JNK are the downstream signaling targets of MKP-1 and that MKP-1 overexpression activates ERK, while it inhibits JNK. Inhibition of ERK reduces the ability of MKP-1 to preserve mitochondrial function and ER homeostasis in hypoxic cardiomyocytes. These results show that MKP-1 plays an essential role in the regulation of mitochondrial function and ER stress in hypoxic H9C2 cardiomyocytes through normalization of the ERK pathway and suggest that MKP-1 may serve as a novel target for the treatment of postischemic myocardial injury.

DOI: https://doi.org/10.1155/2021/8905578
Front Mol Neurosci. 2021 ;14 684714

HDAC6: A Key Link Between Mitochondria and Development of Peripheral Neuropathy.

Krystal English, Michelle Craig Barton.

  Peripheral neuropathy, which is the result of nerve damage from lesions or disease, continues to be a major health concern due to the common manifestation of neuropathic pain. Most investigations into the development of peripheral neuropathy focus on key players such as voltage-gated ion channels or glutamate receptors. However, emerging evidence points to mitochondrial dysfunction as a major player in the development of peripheral neuropathy and resulting neuropathic pain. Mitochondrial dysfunction in neuropathy includes altered mitochondrial transport, mitochondrial metabolism, as well as mitochondrial dynamics. The mechanisms that lead to mitochondrial dysfunction in peripheral neuropathy are poorly understood, however, the Class IIb histone deacetylase (HDAC6), may play an important role in the process. HDAC6 is a key regulator in multiple mechanisms of mitochondrial dynamics and may contribute to mitochondrial dysregulation in peripheral neuropathy. Accumulating evidence shows that HDAC6 inhibition is strongly associated with alleviating peripheral neuropathy and neuropathic pain, as well as mitochondrial dysfunction, in in vivo and in vitro models of peripheral neuropathy. Thus, HDAC6 inhibitors are being investigated as potential therapies for multiple peripheral neuropathic disorders. Here, we review emerging studies and integrate recent advances in understanding the unique connection between peripheral neuropathy and mitochondrial dysfunction through HDAC6-mediated interactions.

Keywords:  chronic pain; histone deacetylase 6; mitochondria; mitochondrial dysfunction; neuropathic pain; peripheral neuropathy

DOI:  https://doi.org/10.3389/fnmol.2021.684714
Cell Cycle. 2021 Sep 14. 1-12

Saikosaponin-A induces apoptosis of cervical cancer through mitochondria- and endoplasmic reticulum stress-dependent pathway in vitro and in vivo: involvement of PI3K/AKT signaling pathway.

Jikun Du, Daibo Song, Tianshou Cao, Yuanhua Li, Jierong Liu, Baohong Li, Li Li.

  Cervical cancer causes considerable mortality in women worldwide. Saikosaponin-A, a triterpenoid glycoside isolated from Bupleurum falcatum, has been proven to exert anti-cancer property. In this study, we evaluated the possibility of saikosaponin-A on cervical cancer in vitro and in vivo. The results showed that saikosaponin-A induced cell death and altered cellular morphology dose-dependently. Saikosaponin-A significantly induced apoptosis in HeLa cells, confirmed by Hoechst 33,342 staining and flow cytometry. Sequentially, saikosaponin-A triggered the mitochondrial-mediated apoptosis demonstrated by deficiency of MMP, induction of Bax/Bcl-2 ratio, leakage of cytochrome c to cytoplasm, and activation of caspase-3. Moreover, ER stress also participated in the apoptosis induced by saikosaponin-A in HeLa cells as indicated by the upregulation of GPR78, CHOP and caspase-12 expression. Furthermore, HeLa cells showed increased expressions of p-PI3K and p-AKT in response to saikosaponin-A treatment. Additionally, saikosaponin-A could inhibit HeLa tumor growth in nude mice and induce apoptosis, reflected by the induction of TUNEL and the expression of cytochrome c, caspase-3 and CHOP confirmed by immunohistochemistry. These findings at least to a certain extent suggested that saikosaponin-A triggered apoptosis through both mitochondrial pathway and ER stress pathway and inhibiting PI3K/Akt signaling, thereby contributing to against cervical cancer. This work provides a new understanding of saikosaponin-A on therapeutic application in treatment of cancer, which has the potential to be a promising candidate therapeutic agent for cervical cancer patients.

Keywords:  Saikosaponin-a; apoptosis; cervical cancer

DOI:  https://doi.org/10.1080/15384101.2021.1974791
Cell Chem Biol. 2021 Sep 11. pii: S2451-9456(21)00363-9. [Epub ahead of print]

Targeted epigenetic induction of mitochondrial biogenesis enhances antitumor immunity in mouse model.

Madhu Malinee, Ganesh Namasivayam Pandian, Hiroshi Sugiyama.

  Considering the potential of combinatorial therapies in overcoming existing limitations of cancer immunotherapy, there is an increasing need to identify small-molecule modulators of immune cells capable of augmenting the effect of programmed cell death protein 1 (PD-1) blockade, leading to better cancer treatment. Although epigenetic drugs showed potential in combination therapy, the lack of sequence specificity is a major concern. Here, we identify and develop a DNA-based epigenetic activator with tri-arginine vector called EnPGC-1 that can trigger the targeted induction of the peroxisome proliferator-activated receptor-gamma coactivator 1 alpha/beta (PGC-1α/β), a regulator of mitochondrial biogenesis. EnPGC-1 enhances mitochondrial activation, energy metabolism, proliferation of CD8+ T cells in vitro, and, in particular, enhances oxidative phosphorylation, a feature of long-lived memory T cells. Genome-wide gene analysis suggests that EnPGC-1 and not the control compounds can regulate T cell activation as a major biological process. EnPGC-1 also synergizes with PD-1 blockade to enhance antitumor immunity and improved host survival.

Keywords:  PD-1; T-cell activation; cancer immunotherapy; combination therapy; epigenetic activator; mitochondrial biogenesis; oxidative phosphorylation; pyrrole-imidazole polyamide; therapeutic gene modulation

DOI:  https://doi.org/10.1016/j.chembiol.2021.08.001