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      Mitochondrial ROS promote mitochondrial dysfunction and inflammation in ischemic acute kidney injury by disrupting TFAM-mediated mtDNA maintenance

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          Abstract

          Aims: Ischemia-reperfusion injury (IRI)-induced acute kidney injury (IRI-AKI) is characterized by elevated levels of reactive oxygen species (ROS), mitochondrial dysfunction, and inflammation, but the potential link among these features remains unclear. In this study, we aimed to investigate the specific role of mitochondrial ROS (mtROS) in initiating mitochondrial DNA (mtDNA) damage and inflammation during IRI-AKI.

          Methods: The changes in renal function, mitochondrial function, and inflammation in IRI-AKI mice with or without mtROS inhibition were analyzed in vivo. The impact of mtROS on TFAM (mitochondrial transcription factor A), Lon protease, mtDNA, mitochondrial respiration, and cytokine release was analyzed in renal tubular cells in vitro. The effects of TFAM knockdown on mtDNA, mitochondrial function, and cytokine release were also analyzed in vitro. Finally, changes in TFAM and mtDNA nucleoids were measured in kidney samples from IRI-AKI mice and patients.

          Results: Decreasing mtROS levels attenuated renal dysfunction, mitochondrial damage, and inflammation in IRI-AKI mice. Decreasing mtROS levels also reversed the decrease in TFAM levels and mtDNA copy number that occurs in HK2 cells under oxidative stress. mtROS reduced the abundance of mitochondrial TFAM in HK2 cells by suppressing its transcription and promoting Lon-mediated TFAM degradation. Silencing of TFAM abolished the Mito-Tempo (MT)-induced rescue of mitochondrial function and cytokine release in HK2 cells under oxidative stress. Loss of TFAM and mtDNA damage were found in kidneys from IRI-AKI mice and AKI patients.

          Conclusion: mtROS can promote renal injury by suppressing TFAM-mediated mtDNA maintenance, resulting in decreased mitochondrial energy metabolism and increased cytokine release. TFAM defects may be a promising target for renal repair after IRI-AKI.

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          Most cited references58

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          Mitochondrial reactive oxygen species (ROS) and ROS-induced ROS release.

          Byproducts of normal mitochondrial metabolism and homeostasis include the buildup of potentially damaging levels of reactive oxygen species (ROS), Ca(2+), etc., which must be normalized. Evidence suggests that brief mitochondrial permeability transition pore (mPTP) openings play an important physiological role maintaining healthy mitochondria homeostasis. Adaptive and maladaptive responses to redox stress may involve mitochondrial channels such as mPTP and inner membrane anion channel (IMAC). Their activation causes intra- and intermitochondrial redox-environment changes leading to ROS release. This regenerative cycle of mitochondrial ROS formation and release was named ROS-induced ROS release (RIRR). Brief, reversible mPTP opening-associated ROS release apparently constitutes an adaptive housekeeping function by the timely release from mitochondria of accumulated potentially toxic levels of ROS (and Ca(2+)). At higher ROS levels, longer mPTP openings may release a ROS burst leading to destruction of mitochondria, and if propagated from mitochondrion to mitochondrion, of the cell itself. The destructive function of RIRR may serve a physiological role by removal of unwanted cells or damaged mitochondria, or cause the pathological elimination of vital and essential mitochondria and cells. The adaptive release of sufficient ROS into the vicinity of mitochondria may also activate local pools of redox-sensitive enzymes involved in protective signaling pathways that limit ischemic damage to mitochondria and cells in that area. Maladaptive mPTP- or IMAC-related RIRR may also be playing a role in aging. Because the mechanism of mitochondrial RIRR highlights the central role of mitochondria-formed ROS, we discuss all of the known ROS-producing sites (shown in vitro) and their relevance to the mitochondrial ROS production in vivo. Copyright © 2014 the American Physiological Society.
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            Mitochondrial DNA Stress Primes the Antiviral Innate Immune Response

            Mitochondrial DNA (mtDNA) is normally present at thousands of copies per cell and is packaged into several hundred higher-order structures termed nucleoids 1 . The abundant mtDNA-binding protein, transcription factor A mitochondrial (TFAM), regulates nucleoid architecture, abundance, and segregation 2 . Complete mtDNA depletion profoundly impairs oxidative phosphorylation (OXPHOS), triggering calcium-dependent stress signaling and adaptive metabolic responses 3 . However, the cellular responses to mtDNA instability, a physiologically relevant stress observed in many human diseases and aging, remain ill-defined 4 . Here we show that moderate mtDNA stress elicited by TFAM deficiency engages cytosolic antiviral signaling to enhance the expression of a subset of interferon-stimulated genes (ISG). Mechanistically, we have found that aberrant mtDNA packaging promotes escape of mtDNA into the cytosol, where it engages the DNA sensor cGAS and promotes STING-IRF3-dependent signaling to elevate ISG expression, potentiate type I interferon responses, and confer broad viral resistance. Furthermore, we demonstrate that herpesviruses induce mtDNA stress, which potentiates antiviral signaling and type I interferon responses during infection. Our results further demonstrate that mitochondria are central participants in innate immunity, identify mtDNA stress as a cell-intrinsic trigger of antiviral signaling, and suggest that cellular monitoring of mtDNA homeostasis cooperates with canonical virus sensing mechanisms to fully license antiviral innate immunity.
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              Oxidized mitochondrial DNA activates the NLRP3 inflammasome during apoptosis.

              We report that in the presence of signal 1 (NF-κB), the NLRP3 inflammasome was activated by mitochondrial apoptotic signaling that licensed production of interleukin-1β (IL-1β). NLRP3 secondary signal activators such as ATP induced mitochondrial dysfunction and apoptosis, resulting in release of oxidized mitochondrial DNA (mtDNA) into the cytosol, where it bound to and activated the NLRP3 inflammasome. The antiapoptotic protein Bcl-2 inversely regulated mitochondrial dysfunction and NLRP3 inflammasome activation. Mitochondrial DNA directly induced NLRP3 inflammasome activation, because macrophages lacking mtDNA had severely attenuated IL-1β production, yet still underwent apoptosis. Both binding of oxidized mtDNA to the NLRP3 inflammasome and IL-1β secretion could be competitively inhibited by the oxidized nucleoside 8-OH-dG. Thus, our data reveal that oxidized mtDNA released during programmed cell death causes activation of the NLRP3 inflammasome. These results provide a missing link between apoptosis and inflammasome activation, via binding of cytosolic oxidized mtDNA to the NLRP3 inflammasome. Copyright © 2012 Elsevier Inc. All rights reserved.
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                Author and article information

                Journal
                Theranostics
                Theranostics
                thno
                Theranostics
                Ivyspring International Publisher (Sydney )
                1838-7640
                2021
                1 January 2021
                : 11
                : 4
                : 1845-1863
                Affiliations
                [1 ]Key Laboratory of Transplant Engineering and Immunology, National Clinical Research Center for Geriatrics, Frontiers Science Center for Disease-related Molecular Network, West China Hospital, Sichuan University, Chengdu, China.
                [2 ]Department of Nephrology, West China Hospital, Sichuan University, Chengdu, China.
                [3 ]Animal Center, West China Hospital, Sichuan University, Chengdu, China.
                Author notes
                ✉ Corresponding author: Jingping Liu, Key Laboratory of Transplant Engineering and Immunology, West China Hospital, Sichuan University, No. 1 Keyuan 4th Road, Gaopeng Ave, Chengdu 610041, China. Tel.: +86-28-85164029; Fax: +86-28-85164030; E-mail: liujingping@ 123456scu.edu.cn .

                #Co-first authors that contributed equally to this work.

                Competing Interests: The authors have declared that no competing interest exists.

                Article
                thnov11p1845
                10.7150/thno.50905
                7778599
                33408785
                3d5add18-7c76-4c51-bc3d-57f062f58163
                © The author(s)

                This is an open access article distributed under the terms of the Creative Commons Attribution License ( https://creativecommons.org/licenses/by/4.0/). See http://ivyspring.com/terms for full terms and conditions.

                History
                : 20 July 2020
                : 11 November 2020
                Categories
                Research Paper

                Molecular medicine
                acute kidney injury,mitochondria,mtdna,ros,tfam
                Molecular medicine
                acute kidney injury, mitochondria, mtdna, ros, tfam

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