bims-mitdyn 2020-08-23 papers

bims-mitdyn

Biomed News

on Mitochondrial dynamics: mechanisms

Issue of 2020–08–23
eight papers selected by
Edmond Chan, Queen’s University, School of Medicine

Coupled transmembrane mechanisms control MCU-mediated mitochondrial Ca2+ uptake.
Klf5 down-regulation induces vascular senescence through eIF5a depletion and mitochondrial fission.
Mitochondrial fatty acid synthesis coordinates oxidative metabolism in mammalian mitochondria.
Mitochondrial dysfunction caused by outer membrane vesicles from Gram-negative bacteria activates intrinsic apoptosis and inflammation.
Proteasomal degradation induced by DPP9-mediated processing competes with mitochondrial protein import.
Solid-phase inclusion as a mechanism for regulating unfolded proteins in the mitochondrial matrix.
The Multiparametric Analysis of Mitochondrial Dynamics in T Cells from Cryopreserved Peripheral Blood Mononuclear Cells (PBMCs).
The mitochondria regulation of stem cell aging.

Proc Natl Acad Sci U S A. 2020 Aug 14. pii: 202005976. [Epub ahead of print]

Coupled transmembrane mechanisms control MCU-mediated mitochondrial Ca2+ uptake.

Horia Vais, Riley Payne, Usha Paudel, Carmen Li, J Kevin Foskett.

  Ca2+ uptake by mitochondria regulates bioenergetics, apoptosis, and Ca2+ signaling. The primary pathway for mitochondrial Ca2+ uptake is the mitochondrial calcium uniporter (MCU), a Ca2+-selective ion channel in the inner mitochondrial membrane. MCU-mediated Ca2+ uptake is driven by the sizable inner-membrane potential generated by the electron-transport chain. Despite the large thermodynamic driving force, mitochondrial Ca2+ uptake is tightly regulated to maintain low matrix [Ca2+] and prevent opening of the permeability transition pore and cell death, while meeting dynamic cellular energy demands. How this is accomplished is controversial. Here we define a regulatory mechanism of MCU-channel activity in which cytoplasmic Ca2+ regulation of intermembrane space-localized MICU1/2 is controlled by Ca2+-regulatory mechanisms localized across the membrane in the mitochondrial matrix. Ca2+ that permeates through the channel pore regulates Ca2+ affinities of coupled inhibitory and activating sensors in the matrix. Ca2+ binding to the inhibitory sensor within the MCU amino terminus closes the channel despite Ca2+ binding to MICU1/2. Conversely, disruption of the interaction of MICU1/2 with the MCU complex disables matrix Ca2+ regulation of channel activity. Our results demonstrate how Ca2+ influx into mitochondria is tuned by coupled Ca2+-regulatory mechanisms on both sides of the inner mitochondrial membrane.

Keywords:  EMRE; MICU1; calcium; electrophysiology; mitochondria

DOI:  https://doi.org/10.1073/pnas.2005976117
PLoS Biol. 2020 Aug 20. 18(8): e3000808

Klf5 down-regulation induces vascular senescence through eIF5a depletion and mitochondrial fission.

Dong Ma, Bin Zheng, He-Liang Liu, Yong-Bo Zhao, Xiao Liu, Xin-Hua Zhang, Qiang Li, Wei-Bo Shi, Toru Suzuki, Jin-Kun Wen.

Although dysregulation of mitochondrial dynamics has been linked to cellular senescence, which contributes to advanced age-related disorders, it is unclear how Krüppel-like factor 5 (Klf5), an essential transcriptional factor of cardiovascular remodeling, mediates the link between mitochondrial dynamics and vascular smooth muscle cell (VSMC) senescence. Here, we show that Klf5 down-regulation in VSMCs is correlated with rupture of abdominal aortic aneurysm (AAA), an age-related vascular disease. Mice lacking Klf5 in VSMCs exacerbate vascular senescence and progression of angiotensin II (Ang II)-induced AAA by facilitating reactive oxygen species (ROS) formation. Klf5 knockdown enhances, while Klf5 overexpression suppresses mitochondrial fission. Mechanistically, Klf5 activates eukaryotic translation initiation factor 5a (eIF5a) transcription through binding to the promoter of eIF5a, which in turn preserves mitochondrial integrity by interacting with mitofusin 1 (Mfn1). Accordingly, decreased expression of eIF5a elicited by Klf5 down-regulation leads to mitochondrial fission and excessive ROS production. Inhibition of mitochondrial fission decreases ROS production and VSMC senescence. Our studies provide a potential therapeutic target for age-related vascular disorders.

DOI: https://doi.org/10.1371/journal.pbio.3000808
Elife. 2020 Aug 17. pii: e58041. [Epub ahead of print]9

Mitochondrial fatty acid synthesis coordinates oxidative metabolism in mammalian mitochondria.

Sara M Nowinski, Ashley Solmonson, Scott F Rusin, J Alan Maschek, Claire L Bensard, Sarah Fogarty, Mi-Young Jeong, Sandra Lettlova, Jordan A Berg, Jeffrey T Morgan, Yeyun Ouyang, Bradley C Naylor, Joao A Paulo, Katsuhiko Funai, James E Cox, Steven P Gygi, Dennis R Winge, Ralph J DeBerardinis, Jared Rutter.

  Cells harbor two systems for fatty acid synthesis, one in the cytoplasm (catalyzed by fatty acid synthase, FASN) and one in the mitochondria (mtFAS). In contrast to FASN, mtFAS is poorly characterized, especially in higher eukaryotes, with the major product(s), metabolic roles, and cellular function(s) being essentially unknown. Here we show that hypomorphic mtFAS mutant mouse skeletal myoblast cell lines display a severe loss of electron transport chain (ETC) complexes and exhibit compensatory metabolic activities including reductive carboxylation. This effect on ETC complexes appears to be independent of protein lipoylation, the best characterized function of mtFAS, as mutants lacking lipoylation have an intact ETC. Finally, mtFAS impairment blocks the differentiation of skeletal myoblasts in vitro. Together, these data suggest that ETC activity in mammals is profoundly controlled by mtFAS function, thereby connecting anabolic fatty acid synthesis with the oxidation of carbon fuels.

Keywords:  biochemistry; chemical biology; mouse

DOI:  https://doi.org/10.7554/eLife.58041
Nat Microbiol. 2020 Aug 17.

Mitochondrial dysfunction caused by outer membrane vesicles from Gram-negative bacteria activates intrinsic apoptosis and inflammation.

Pankaj Deo, Seong H Chow, Mei-Ling Han, Mary Speir, Cheng Huang, Ralf B Schittenhelm, Subhash Dhital, Jack Emery, Jian Li, Benjamin T Kile, James E Vince, Kate E Lawlor, Thomas Naderer.

Sensing of microbes activates the innate immune system, depending on functional mitochondria. However, pathogenic bacteria inhibit mitochondrial activity by delivering toxins via outer membrane vesicles (OMVs). How macrophages respond to pathogenic microbes that target mitochondria remains unclear. Here, we show that macrophages exposed to OMVs from Neisseria gonorrhoeae, uropathogenic Escherichia coli and Pseudomonas aeruginosa induce mitochondrial apoptosis and NLRP3 inflammasome activation. OMVs and toxins that cause mitochondrial dysfunction trigger inhibition of host protein synthesis, which depletes the unstable BCL-2 family member MCL-1 and induces BAK-dependent mitochondrial apoptosis. In parallel with caspase-11-mediated pyroptosis, mitochondrial apoptosis and potassium ion efflux activate the NLRP3 inflammasome after OMV exposure in vitro. Importantly, in the in vivo setting, the activation and release of interleukin-1β in response to N. gonorrhoeae OMVs is regulated by mitochondrial apoptosis. Our data highlight how innate immune cells sense infections by monitoring mitochondrial health.

DOI: https://doi.org/10.1038/s41564-020-0773-2
EMBO J. 2020 Aug 20. e103889

Proteasomal degradation induced by DPP9-mediated processing competes with mitochondrial protein import.

Yannik Finger, Markus Habich, Sarah Gerlich, Sophia Urbanczyk, Erik van de Logt, Julian Koch, Laura Schu, Kim Jasmin Lapacz, Muna Ali, Carmelina Petrungaro, Silja Lucia Salscheider, Christian Pichlo, Ulrich Baumann, Dirk Mielenz, Joern Dengjel, Bent Brachvogel, Kay Hofmann, Jan Riemer.

  Plasticity of the proteome is critical to adapt to varying conditions. Control of mitochondrial protein import contributes to this plasticity. Here, we identified a pathway that regulates mitochondrial protein import by regulated N-terminal processing. We demonstrate that dipeptidyl peptidases 8/9 (DPP8/9) mediate the N-terminal processing of adenylate kinase 2 (AK2) en route to mitochondria. We show that AK2 is a substrate of the mitochondrial disulfide relay, thus lacking an N-terminal mitochondrial targeting sequence and undergoing comparatively slow import. DPP9-mediated processing of AK2 induces its rapid proteasomal degradation and prevents cytosolic accumulation of enzymatically active AK2. Besides AK2, we identify more than 100 mitochondrial proteins with putative DPP8/9 recognition sites and demonstrate that DPP8/9 influence the cellular levels of a number of these proteins. Collectively, we provide in this study a conceptual framework on how regulated cytosolic processing controls levels of mitochondrial proteins as well as their dual localization to mitochondria and other compartments.

Keywords:  MIA40; adenylate kinase 2; dipeptidyl peptidase 9; mitochondrial protein import; quality control

DOI:  https://doi.org/10.15252/embj.2019103889
Sci Adv. 2020 Aug;6(32): eabc7288

Solid-phase inclusion as a mechanism for regulating unfolded proteins in the mitochondrial matrix.

Linhao Ruan, Joshua T McNamara, Xi Zhang, Alexander Chih-Chieh Chang, Jin Zhu, Yi Dong, Gordon Sun, Amy Peterson, Chan Hyun Na, Rong Li.

Proteostasis declines with age, characterized by the accumulation of unfolded or damaged proteins. Recent studies suggest that proteins constituting pathological inclusions in neurodegenerative diseases also enter and accumulate in mitochondria. How unfolded proteins are managed within mitochondria remains unclear. Here, we found that excessive unfolded proteins in the mitochondrial matrix of yeast cells are consolidated into solid-phase inclusions, which we term deposits of unfolded mitochondrial proteins (DUMP). Formation of DUMP occurs in mitochondria near endoplasmic reticulum-mitochondria contact sites and is regulated by mitochondrial proteins controlling the production of cytidine 5'-diphosphate-diacylglycerol. DUMP formation is age dependent but accelerated by exogenous unfolded proteins. Many enzymes of the tricarboxylic acid cycle were enriched in DUMP. During yeast cell division, DUMP formation is necessary for asymmetric inheritance of damaged mitochondrial proteins between mother and daughter cells. We provide evidence that DUMP-like structures may be induced by excessive unfolded proteins in human cells.

DOI: https://doi.org/10.1126/sciadv.abc7288
Methods Mol Biol. 2020 ;2184 215-224

The Multiparametric Analysis of Mitochondrial Dynamics in T Cells from Cryopreserved Peripheral Blood Mononuclear Cells (PBMCs).

Jesse J R Masson, Matias Ostrowski, Gabriel Duette, Man K S Lee, Andrew J Murphy, Suzanne M Crowe, Clovis S Palmer.

  The analysis of mitochondrial dynamics within immune cells allows us to understand how fundamental metabolism influences immune cell functions, and how dysregulated immunometabolic processes impact biology and disease pathogenesis. For example, during infections, mitochondrial fission and fusion coincide with effector and memory T-cell differentiation, respectively, resulting in metabolic reprogramming. As frozen cells are generally not optimal for immunometabolic analyses, and given the logistic difficulties of analysis on cells within a few hours of blood collection, we have optimized and validated a simple cryopreservation protocol for peripheral blood mononuclear cells, yielding >95% cellular viability, as well as preserved metabolic and immunologic properties. Combining fluorescent dyes with cell surface antibodies, we demonstrate how to analyze mitochondrial density, membrane potential, and reactive oxygen species production in CD4 and CD8 T cells from cryopreserved clinical samples.

Keywords:  CD4 and CD8 T cells; Immunometabolism; Mitochondrial density; Mitochondrial membrane potential; ROS

DOI:  https://doi.org/10.1007/978-1-0716-0802-9_15
Mech Ageing Dev. 2020 Aug 17. pii: S0047-6374(20)30130-5. [Epub ahead of print] 111334

The mitochondria regulation of stem cell aging.

Yong Wan, Toren Finkel.

Mitochondrial dysfunction and stem cell exhaustion are among the nine separate hallmarks of aging. Emerging evidence however suggests that mitochondrial activity can have a profound influence on the self-renewal and function of stem cells, thus mechanistically linking mitochondrial function and stem cell decline. In this review, we discuss how accumulation of mtDNA mutations or alterations in mitochondrial dynamics, turnover, and signaling can modulate age-dependent stem cell function. Finally, we also describe how mitochondrial substrate utilization influences stem and progenitor activity. Together, this growing body of evidence suggests that modulation of mitochondrial activity might provide a strategy to slow or reverse age-dependent stem cell decline, and potentially, slow or reverse human aging.

DOI: https://doi.org/10.1016/j.mad.2020.111334