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Rockfield SM, Turnis ME, Rodriguez-Enriquez R, Bathina M, Ng SK, Kurtz N, Becerra Mora N, Pelletier S, Robinson CG, Vogel P, Opferman JT. Genetic ablation of Immt induces a lethal disruption of the MICOS complex. Life Sci Alliance 2024; 7:e202302329. [PMID: 38467404 PMCID: PMC10927357 DOI: 10.26508/lsa.202302329] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2023] [Revised: 02/29/2024] [Accepted: 03/01/2024] [Indexed: 03/13/2024] Open
Abstract
The mitochondrial contact site and cristae organizing system (MICOS) is important for crista junction formation and for maintaining inner mitochondrial membrane architecture. A key component of the MICOS complex is MIC60, which has been well studied in yeast and cell culture models. However, only one recent study has demonstrated the embryonic lethality of losing Immt (the gene encoding MIC60) expression. Tamoxifen-inducible ROSA-CreERT2-mediated deletion of Immt in adult mice disrupted the MICOS complex, increased mitochondria size, altered cristae morphology, and was lethal within 12 d. Pathologically, these mice displayed defective intestinal muscle function (paralytic ileus) culminating in dehydration. We also identified bone marrow (BM) hypocellularity in Immt-deleted mice, although BM transplants from wild-type mice did not improve survival. Altogether, this inducible mouse model demonstrates the importance of MIC60 in vivo, in both hematopoietic and non-hematopoietic tissues, and provides a valuable resource for future mechanistic investigations into the MICOS complex.
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Affiliation(s)
- Stephanie M Rockfield
- https://ror.org/02r3e0967 Department of Cell and Molecular Biology, St. Jude Children's Research Hospital, Memphis, TN, USA
| | - Meghan E Turnis
- https://ror.org/02r3e0967 Department of Cell and Molecular Biology, St. Jude Children's Research Hospital, Memphis, TN, USA
| | - Ricardo Rodriguez-Enriquez
- https://ror.org/02r3e0967 Department of Cell and Molecular Biology, St. Jude Children's Research Hospital, Memphis, TN, USA
| | - Madhavi Bathina
- https://ror.org/02r3e0967 Department of Cell and Molecular Biology, St. Jude Children's Research Hospital, Memphis, TN, USA
| | - Seng Kah Ng
- https://ror.org/02r3e0967 Department of Cell and Molecular Biology, St. Jude Children's Research Hospital, Memphis, TN, USA
| | - Nathan Kurtz
- https://ror.org/02r3e0967 Electron Microscopy, Department of Cellular Imaging Shared Resources, St. Jude Children's Research Hospital, Memphis, TN, USA
| | - Nathalie Becerra Mora
- https://ror.org/02r3e0967 Electron Microscopy, Department of Cellular Imaging Shared Resources, St. Jude Children's Research Hospital, Memphis, TN, USA
| | - Stephane Pelletier
- https://ror.org/02r3e0967 Transgenic Core Facility, Department of Immunology, St. Jude Children's Research Hospital, Memphis, TN, USA
| | - Camenzind G Robinson
- https://ror.org/02r3e0967 Electron Microscopy, Department of Cellular Imaging Shared Resources, St. Jude Children's Research Hospital, Memphis, TN, USA
| | - Peter Vogel
- https://ror.org/02r3e0967 Comparative Pathology Core, Pathology Department, St. Jude Children's Research Hospital, Memphis, TN, USA
| | - Joseph T Opferman
- https://ror.org/02r3e0967 Department of Cell and Molecular Biology, St. Jude Children's Research Hospital, Memphis, TN, USA
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Newman LE, Weiser Novak S, Rojas GR, Tadepalle N, Schiavon CR, Grotjahn DA, Towers CG, Tremblay MÈ, Donnelly MP, Ghosh S, Medina M, Rocha S, Rodriguez-Enriquez R, Chevez JA, Lemersal I, Manor U, Shadel GS. Mitochondrial DNA replication stress triggers a pro-inflammatory endosomal pathway of nucleoid disposal. Nat Cell Biol 2024; 26:194-206. [PMID: 38332353 PMCID: PMC11026068 DOI: 10.1038/s41556-023-01343-1] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2023] [Accepted: 12/20/2023] [Indexed: 02/10/2024]
Abstract
Mitochondrial DNA (mtDNA) encodes essential subunits of the oxidative phosphorylation system, but is also a major damage-associated molecular pattern (DAMP) that engages innate immune sensors when released into the cytoplasm, outside of cells or into circulation. As a DAMP, mtDNA not only contributes to anti-viral resistance, but also causes pathogenic inflammation in many disease contexts. Cells experiencing mtDNA stress caused by depletion of the mtDNA-packaging protein, transcription factor A, mitochondrial (TFAM) or during herpes simplex virus-1 infection exhibit elongated mitochondria, enlargement of nucleoids (mtDNA-protein complexes) and activation of cGAS-STING innate immune signalling via mtDNA released into the cytoplasm. However, the relationship among aberrant mitochondria and nucleoid dynamics, mtDNA release and cGAS-STING activation remains unclear. Here we show that, under a variety of mtDNA replication stress conditions and during herpes simplex virus-1 infection, enlarged nucleoids that remain bound to TFAM exit mitochondria. Enlarged nucleoids arise from mtDNA experiencing replication stress, which causes nucleoid clustering via a block in mitochondrial fission at a stage when endoplasmic reticulum actin polymerization would normally commence, defining a fission checkpoint that ensures mtDNA has completed replication and is competent for segregation into daughter mitochondria. Chronic engagement of this checkpoint results in enlarged nucleoids trafficking into early and then late endosomes for disposal. Endosomal rupture during transit through this endosomal pathway ultimately causes mtDNA-mediated cGAS-STING activation. Thus, we propose that replication-incompetent nucleoids are selectively eliminated by an adaptive mitochondria-endosomal quality control pathway that is prone to innate immune system activation, which might represent a therapeutic target to prevent mtDNA-mediated inflammation during viral infection and other pathogenic states.
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Affiliation(s)
- Laura E Newman
- Salk Institute for Biological Studies, La Jolla, CA, USA
| | | | - Gladys R Rojas
- Salk Institute for Biological Studies, La Jolla, CA, USA
| | | | | | | | | | | | - Matthew P Donnelly
- Salk Institute for Biological Studies, La Jolla, CA, USA
- Medical Scientist Training Program, University of California, San Diego, La Jolla, CA, USA
- Biomedical Sciences Graduate Program, University of California, San Diego, La Jolla, CA, USA
| | - Sagnika Ghosh
- Salk Institute for Biological Studies, La Jolla, CA, USA
| | | | - Sienna Rocha
- Salk Institute for Biological Studies, La Jolla, CA, USA
| | | | - Joshua A Chevez
- Division of Biological Sciences, University of California, San Diego, La Jolla, CA, USA
| | - Ian Lemersal
- La Jolla Institute for Immunology, La Jolla, CA, USA
| | - Uri Manor
- Salk Institute for Biological Studies, La Jolla, CA, USA.
- Division of Biological Sciences, University of California, San Diego, La Jolla, CA, USA.
- Department of Cell & Developmental Biology, University of California, San Diego, La Jolla, CA, USA.
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Campos Y, Rodriguez-Enriquez R, Palacios G, Van de Vlekkert D, Qiu X, Weesner J, Gomero E, Demmers J, Bertorini T, Opferman JT, Grosveld GC, d'Azzo A. Mitochondrial proteostasis mediated by CRL5 Ozz and Alix maintains skeletal muscle function. bioRxiv 2023:2023.07.11.548601. [PMID: 37503076 PMCID: PMC10369959 DOI: 10.1101/2023.07.11.548601] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 07/29/2023]
Abstract
High energy-demanding tissues, such as skeletal muscle, require mitochondrial proteostasis to function properly. Two quality-control mechanisms, the ubiquitin proteasome system (UPS) and the release of mitochondria-derived vesicles, safeguard mitochondrial proteostasis. However, whether these processes interact is unknown. Here we show that the E3 ligase CRL5 Ozz , a member of the UPS, and its substrate Alix control the mitochondrial concentration of Slc25A4, a solute carrier that is essential for ATP production. The mitochondria in Ozz -/- or Alix -/- skeletal muscle share overt morphologic alterations (they are supernumerary, swollen, and dysmorphic) and have abnormal metabolomic profiles. We found that CRL5 Ozz ubiquitinates Slc25A4 and promotes its proteasomal degradation, while Alix facilitates SLC25A4 loading into exosomes destined for lysosomal destruction. The loss of Ozz or Alix offsets steady-state levels of Slc25A4, which disturbs mitochondrial metabolism and alters muscle fiber composition. These findings reveal hitherto unknown regulatory functions of Ozz and Alix in mitochondrial proteostasis.
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Schellenberg B, Wang P, Keeble JA, Rodriguez-Enriquez R, Walker S, Owens TW, Foster F, Tanianis-Hughes J, Brennan K, Streuli CH, Gilmore AP. Bax exists in a dynamic equilibrium between the cytosol and mitochondria to control apoptotic priming. Mol Cell 2013; 49:959-71. [PMID: 23375500 PMCID: PMC3594749 DOI: 10.1016/j.molcel.2012.12.022] [Citation(s) in RCA: 175] [Impact Index Per Article: 15.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2012] [Revised: 11/02/2012] [Accepted: 12/20/2012] [Indexed: 12/19/2022]
Abstract
The proapoptotic Bcl-2 protein Bax is predominantly found in the cytosol of nonapoptotic cells and is commonly thought to translocate to mitochondria following an apoptotic stimulus. The current model for Bax activation is that BH3 proteins bind to cytosolic Bax, initiating mitochondrial targeting and outer-membrane permeabilization. Here, we challenge this and show that Bax is constitutively targeted to mitochondria but in nonapoptotic cells is constantly translocated back to the cytosol. Using live-cell spinning-disk confocal imaging with a combination of FLIP, FRAP, and photoactivatable GFP-Bax, we demonstrate that disrupting adhesion-dependent survival signals slows the rate of Bax’s dissociation from mitochondria, leading to its accumulation on the outer mitochondrial membrane. The overall accumulation of mitochondrial Bax following loss of survival signaling sensitizes cells to proapoptotic BH3 proteins. Our findings show that Bax is normally in a dynamic equilibrium between cytosol and mitochondria, enabling fluctuations in survival signals to finely adjust apoptotic sensitivity.
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Affiliation(s)
- Barbara Schellenberg
- Wellcome Trust Centre for Cell-Matrix Research, Faculty of Life Sciences, University of Manchester, Manchester, UK
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