bims-midtic 2024-05-05 papers

bims-midtic

Biomed News

on Mitochondrial dynamics and trafficking in cells

Issue of 2024‒05‒05
eighteen papers selected by
Omkar Joshi, Turku Bioscience

A dynamin superfamily-like pseudoenzyme coordinates with MICOS to promote cristae architecture.
Mitochondrial dynamics: updates and perspectives.
SIRT1 regulates mitochondrial fission to alleviate high altitude hypoxia inducedcardiac dysfunction in rats via the PGC-1α-DRP1/FIS1/MFF pathway.
Quantitative Assessment of Mitochondrial Morphology and Electrophysiological Function in the Diabetic Heart.
Socialized mitochondria: mitonuclear crosstalk in stress.
Mitochondrial transfer mediates endothelial cell engraftment through mitophagy.
Mitochondrial dynamics, quality control and mtDNA in Alcohol-associated liver disease and liver cancer.
TROP2 promotes PINK1-mediated mitophagy and apoptosis to accelerate the progression of senile chronic obstructive pulmonary disease by up-regulating DRP1 expression.
Mitochondrial genome transfer drives metabolic reprogramming in adjacent colonic epithelial cells promoting TGFβ1-mediated tumor progression.
An aldehyde-crosslinking mitochondrial probe for STED imaging in fixed cells.
Mitochondria and Cancer.
The absence of the ribosomal protein Rpl2702 elicits the MAPK-mTOR signaling to modulate mitochondrial morphology and functions.
Mitochondrially-associated actin waves maintain organelle homeostasis and equitable inheritance.
Hansenula polymorpha cells lacking the ER-localized peroxins Pex23 or Pex29 show defects in mitochondrial function and morphology.
CREB3 mediates the transcriptional regulation of PGC-1α, a master regulator of energy homeostasis and mitochondrial biogenesis.
Toward understanding the cellular control of vertebrate mineralization: The potential role of mitochondria.
The mitochondrial multi-omic response to exercise training across rat tissues.
PARKIN is not required to sustain OXPHOS function in adult mammalian tissues.

Curr Biol. 2024 Apr 24. pii: S0960-9822(24)00468-8. [Epub ahead of print]

A dynamin superfamily-like pseudoenzyme coordinates with MICOS to promote cristae architecture.

Abhishek Kumar, Mehmet Oguz Gok, Kailey N Nguyen, Olivia M Connor, Michael L Reese, Jeremy G Wideman, Sergio A Muñoz-Gómez, Jonathan R Friedman.

  Mitochondrial cristae architecture is crucial for optimal respiratory function of the organelle. Cristae shape is maintained in part by the mitochondrial contact site and cristae organizing system (MICOS) complex. While MICOS is required for normal cristae morphology, the precise mechanistic role of each of the seven human MICOS subunits, and how the complex coordinates with other cristae-shaping factors, has not been fully determined. Here, we examine the MICOS complex in Schizosaccharomyces pombe, a minimal model whose genome only encodes for four core subunits. Using an unbiased proteomics approach, we identify a poorly characterized inner mitochondrial membrane protein that interacts with MICOS and is required to maintain cristae morphology, which we name Mmc1. We demonstrate that Mmc1 works in concert with MICOS to promote normal mitochondrial morphology and respiratory function. Mmc1 is a distant relative of the dynamin superfamily of proteins (DSPs), GTPases, which are well established to shape and remodel membranes. Similar to DSPs, Mmc1 self-associates and forms high-molecular-weight assemblies. Interestingly, however, Mmc1 is a pseudoenzyme that lacks key residues required for GTP binding and hydrolysis, suggesting that it does not dynamically remodel membranes. These data are consistent with the model that Mmc1 stabilizes cristae architecture by acting as a scaffold to support cristae ultrastructure on the matrix side of the inner membrane. Our study reveals a new class of proteins that evolved early in fungal phylogeny and is required for the maintenance of cristae architecture. This highlights the possibility that functionally analogous proteins work with MICOS to establish cristae morphology in metazoans.

Keywords:  MICOS; cristae; dynamin; fission yeast; membrane remodeling; mitochondria; pseudoenzyme

DOI:  https://doi.org/10.1016/j.cub.2024.04.028
Sci Rep. 2024 04 30. 14(1): 9936

Mitochondrial dynamics: updates and perspectives.

Kezhong Zhang, Ježek Petr.

DOI: https://doi.org/10.1038/s41598-024-59998-1
Apoptosis. 2024 Apr 27.

SIRT1 regulates mitochondrial fission to alleviate high altitude hypoxia inducedcardiac dysfunction in rats via the PGC-1α-DRP1/FIS1/MFF pathway.

Hongbao Xu, Xiaona Song, Xiaoru Zhang, Guangrui Wang, Xiaoling Cheng, Ling Zhang, Zirou Wang, Ran Li, Chongyi Ai, Xinxing Wang, Lingling Pu, Zhaoli Chen, Weili Liu.

  High-altitude exposure has been linked to cardiac dysfunction. Silent information regulator factor 2-related enzyme 1 (sirtuin 1, SIRT1), a nicotinamide adenine dinucleotide-dependent deacetylase, plays a crucial role in regulating numerous cardiovascular diseases. However, the relationship between SIRT1 and cardiac dysfunction induced by hypobaric hypoxia (HH) remains unexplored. This study aims to assess the impact of SIRT1 on HH-induced cardiac dysfunction and delve into the underlying mechanisms, both in vivo and in vitro. In this study, we have demonstrated that exposure to HH results in cardiomyocyte injury, along with the downregulation of SIRT1 and mitochondrial dysfunction. Upregulating SIRT1 significantly inhibits mitochondrial fission, improves mitochondrial function, reduces cardiomyocyte injury, and consequently enhances cardiac function in HH-exposed rats. Additionally, HH exposure triggers aberrant expression of mitochondrial fission-regulated proteins, with a decrease in PPARγ coactivator 1 alpha (PGC-1α) and mitochondrial fission factor (MFF) and an increase in mitochondrial fission 1 (FIS1) and dynamin-related protein 1 (DRP1), all of which are mitigated by SIRT1 upregulation. Furthermore, inhibiting PGC-1α diminishes the positive effects of SIRT1 regulation on the expression of DRP1, MFF, and FIS1, as well as mitochondrial fission. These findings demonstrate that SIRT1 alleviates HHinduced cardiac dysfunction by preventing mitochondrial fission through the PGC-1α-DRP1/FIS1/MFF pathway.

Keywords:  Cardiac dysfunction; High altitude; Hypobaric hypoxia; Mitochondrial dysfunction; Mitochondrial fission; SIRT1

DOI:  https://doi.org/10.1007/s10495-024-01954-5
Methods Mol Biol. 2024 ;2803 75-86

Quantitative Assessment of Mitochondrial Morphology and Electrophysiological Function in the Diabetic Heart.

Marine Cacheux, Michael Rudokas, Andrew Tieu, Joanna Abi Rizk, Madelyn E Hummel, Fadi G Akar.

  Mitochondria within a cardiomyocyte form a highly dynamic network that undergoes fusion and fission events in response to acute and chronic stressors, such as hyperglycemia and diabetes mellitus. Changes in mitochondrial architecture and morphology not only reflect their capacity for oxidative phosphorylation and ATP synthesis but also impact their subcellular localization and interaction with other organelles. The role of these ultrastructural abnormalities in modulating electrophysiological properties and excitation-contraction coupling remains largely unknown and warrants direct investigation considering the growing appreciation of the functional and structural coupling between the mitochondrial network, the calcium cycling machinery, and sarcolemmal ion channels in the cardiac myocyte. In this Methods in Molecular Biology chapter, we provide a protocol that allows for a quantitative assessment of mitochondrial shape and morphology in control and diabetic hearts that had undergone detailed electrophysiological measurements using high resolution optical action potential (AP) mapping.

Keywords:  Diabetes Mellitus; Electron Microscopy; Mitochondria; Myocardium; Optical Mapping

DOI:  https://doi.org/10.1007/978-1-0716-3846-0_6
Exp Mol Med. 2024 May 01.

Socialized mitochondria: mitonuclear crosstalk in stress.

Kyung Hwa Kim, Cho Bi Lee.

Traditionally, mitochondria are considered sites of energy production. However, recent studies have suggested that mitochondria are signaling organelles that are involved in intracellular interactions with other organelles. Remarkably, stressed mitochondria appear to induce a beneficial response that restores mitochondrial function and cellular homeostasis. These mitochondrial stress-centered signaling pathways have been rapidly elucidated in multiple organisms. In this review, we examine current perspectives on how mitochondria communicate with the rest of the cell, highlighting mitochondria-to-nucleus (mitonuclear) communication under various stresses. Our understanding of mitochondria as signaling organelles may provide new insights into disease susceptibility and lifespan extension.

DOI: https://doi.org/10.1038/s12276-024-01211-4
Nature. 2024 May 01.

Mitochondrial transfer mediates endothelial cell engraftment through mitophagy.

Ruei-Zeng Lin, Gwang-Bum Im, Allen Chilun Luo, Yonglin Zhu, Xuechong Hong, Joseph Neumeyer, Hong-Wen Tang, Norbert Perrimon, Juan M Melero-Martin.

Ischaemic diseases such as critical limb ischaemia and myocardial infarction affect millions of people worldwide1. Transplanting endothelial cells (ECs) is a promising therapy in vascular medicine, but engrafting ECs typically necessitates co-transplanting perivascular supporting cells such as mesenchymal stromal cells (MSCs), which makes clinical implementation complicated2,3. The mechanisms that enable MSCs to facilitate EC engraftment remain elusive. Here we show that, under cellular stress, MSCs transfer mitochondria to ECs through tunnelling nanotubes, and that blocking this transfer impairs EC engraftment. We devised a strategy to artificially transplant mitochondria, transiently enhancing EC bioenergetics and enabling them to form functional vessels in ischaemic tissues without the support of MSCs. Notably, exogenous mitochondria did not integrate into the endogenous EC mitochondrial pool, but triggered mitophagy after internalization. Transplanted mitochondria co-localized with autophagosomes, and ablation of the PINK1-Parkin pathway negated the enhanced engraftment ability of ECs. Our findings reveal a mechanism that underlies the effects of mitochondrial transfer between mesenchymal and endothelial cells, and offer potential for a new approach for vascular cell therapy.

DOI: https://doi.org/10.1038/s41586-024-07340-0
Hepatology. 2024 Apr 29.

Mitochondrial dynamics, quality control and mtDNA in Alcohol-associated liver disease and liver cancer.

Xiaowen Ma, Mengwei Niu, Hong-Min Ni, Wen-Xing Ding.

Mitochondria are intracellular organelles responsible for energy production, glucose and lipid metabolism, cell death, cell proliferation, and innate immune response. Mitochondria are highly dynamic organelles that constantly undergo fission, fusion, and intracellular trafficking, as well as degradation and biogenesis. Mitochondrial dysfunction has been implicated in a variety of chronic liver diseases including alcohol-associated liver disease (ALD), metabolic dysfunction-associated steatohepatitis (MASH), and hepatocellular carcinoma (HCC). In this review, we provide a detailed overview of mitochondrial dynamics, mitophagy, and mtDNA-mediated innate immune response, and how dysregulation of these mitochondrial processes affects the pathogenesis of ALD and HCC. Mitochondrial dynamics and mtDNA-mediated innate immune response may thereby represent an attractive therapeutic target for ameliorating ALD and alcohol-associated HCC.

DOI: https://doi.org/10.1097/HEP.0000000000000910
Exp Gerontol. 2024 Apr 29. pii: S0531-5565(24)00083-4. [Epub ahead of print]191 112441

TROP2 promotes PINK1-mediated mitophagy and apoptosis to accelerate the progression of senile chronic obstructive pulmonary disease by up-regulating DRP1 expression.

Yipu Zhao, Zhengjie Wu.

  Chronic obstructive pulmonary disease (COPD) is a chronic airway inflammatory disease characterised by irreversible airflow limitation. The elderly are a vulnerable population for developing COPD. With the growth of age, physiological degenerative changes occur in the thorax, bronchus, lung and vascular wall, which can lead to age-related physiological attenuation of lung function in the elderly, so the prevalence of COPD increases with age. Its pathogenesis has not yet been truly clarified. Mitophagy plays an important role in maintaining the stability of mitochondrial function and intracellular environment by scavenging damaged mitochondria. Currently, studies have shown that trophoblast antigen 2 (TROP2) expression is up-regulated in airway basal cells of patients with COPD, suggesting that TROP2 is involved in the progression of COPD. However, whether it is involved in disease progression by regulating mitochondrial function remains unclear. In this study, compared with non-smoking non-COPD patients, the expression of TROP2 in lung tissues of smoking non-COPD patients and patients with COPD increased, and TROP2 expression in patients with COPD was higher than that in smoking non-COPD patients. To further explore the role of TROP2, we stimulated BEAS-2B with cigarette smoke to construct an in vitro model. We found that TROP2 expression increased, whereas TROP2 silencing reversed the cigarette smoke extract-induced decrease in mitochondrial membrane potential, increased reactive oxygen species content, decreased adenosine triphosphate (ATP) production, increased inflammatory factor secretion and increased apoptosis. In addition, we searched online bioinformatics and screened the gene dynamin-related protein 1 (DRP1) related to mitophagy as the research object. Co-IP assay verified the binding relationship between DRP1 and TROP2. Further study found that TROP2 promoted mitophagy and apoptosis of BEAS-2B cells by up-regulating the expression of DRP1. In addition, PTEN-induced putative kinase 1 (PINK1) is a potential binding protein of DRP1, and DRP1 accelerated mitophagy and apoptosis of BEAS-2B cells by promoting the expression of PINK1. We established a COPD SD rat model by cigarette smoke exposure and LPS instillation and treated it by intraperitoneal injection of si-TROP2. The results showed that TROP2 silencing restored lung function and reduced the secretion of inflammatory factors in bronchoalveolar lavage fluid. In conclusion, TROP2 can be used as a new reference for COPD treatment.

Keywords:  Chronic obstructive pulmonary disease; DRP1; Mitophagy; PINK1; TROP2

DOI:  https://doi.org/10.1016/j.exger.2024.112441
Nat Commun. 2024 Apr 30. 15(1): 3653

Mitochondrial genome transfer drives metabolic reprogramming in adjacent colonic epithelial cells promoting TGFβ1-mediated tumor progression.

Bingjie Guan, Youdong Liu, Bowen Xie, Senlin Zhao, Abudushalamu Yalikun, Weiwei Chen, Menghua Zhou, Qi Gu, Dongwang Yan.

Although nontumor components play an essential role in colon cancer (CC) progression, the intercellular communication between CC cells and adjacent colonic epithelial cells (CECs) remains poorly understood. Here, we show that intact mitochondrial genome (mitochondrial DNA, mtDNA) is enriched in serum extracellular vesicles (EVs) from CC patients and positively correlated with tumor stage. Intriguingly, circular mtDNA transferred via tumor cell-derived EVs (EV-mtDNA) enhances mitochondrial respiration and reactive oxygen species (ROS) production in CECs. Moreover, the EV-mtDNA increases TGFβ1 expression in CECs, which in turn promotes tumor progression. Mechanistically, the intercellular mtDNA transfer activates the mitochondrial respiratory chain to induce the ROS-driven RelA nuclear translocation in CECs, thereby transcriptionally regulating TGFβ1 expression and promoting tumor progression via the TGFβ/Smad pathway. Hence, this study highlights EV-mtDNA as a major driver of paracrine metabolic crosstalk between CC cells and adjacent CECs, possibly identifying it as a potential biomarker and therapeutic target for CC.

DOI: https://doi.org/10.1038/s41467-024-48100-y
Proc Natl Acad Sci U S A. 2024 May 07. 121(19): e2317703121

An aldehyde-crosslinking mitochondrial probe for STED imaging in fixed cells.

Jingting Chen, Till Stephan, Felix Gaedke, Tianyan Liu, Yiyan Li, Astrid Schauss, Peng Chen, Veronika Wulff, Stefan Jakobs, Christian Jüngst, Zhixing Chen.

  Fluorescence labeling of chemically fixed specimens, especially immunolabeling, plays a vital role in super-resolution imaging as it offers a convenient way to visualize cellular structures like mitochondria or the distribution of biomolecules with high detail. Despite the development of various distinct probes that enable super-resolved stimulated emission depletion (STED) imaging of mitochondria in live cells, most of these membrane-potential-dependent fluorophores cannot be retained well in mitochondria after chemical fixation. This lack of suitable mitochondrial probes has limited STED imaging of mitochondria to live cell samples. In this study, we introduce a mitochondria-specific probe, PK Mito Orange FX (PKMO FX), which features a fixation-driven cross-linking motif and accumulates in the mitochondrial inner membrane. It exhibits high fluorescence retention after chemical fixation and efficient depletion at 775 nm, enabling nanoscopic imaging both before and after aldehyde fixation. We demonstrate the compatibility of this probe with conventional immunolabeling and other strategies commonly used for fluorescence labeling of fixed samples. Moreover, we show that PKMO FX facilitates correlative super-resolution light and electron microscopy, enabling the correlation of multicolor fluorescence images and transmission EM images via the characteristic mitochondrial pattern. Our probe further expands the mitochondrial toolkit for multimodal microscopy at nanometer resolutions.

Keywords:  CLEM; fixation; mitochondrial imaging; super-resolution imaging

DOI:  https://doi.org/10.1073/pnas.2317703121
Cold Spring Harb Perspect Med. 2024 May 01. pii: a041534. [Epub ahead of print]

Mitochondria and Cancer.

Timothy C Kenny, Kıvanç Birsoy.

Mitochondria are semiautonomous organelles with diverse metabolic and cellular functions including anabolism and energy production through oxidative phosphorylation. Following the pioneering observations of Otto Warburg nearly a century ago, an immense body of work has examined the role of mitochondria in cancer pathogenesis and progression. Here, we summarize the current state of the field, which has coalesced around the position that functional mitochondria are required for cancer cell proliferation. In this review, we discuss how mitochondria influence tumorigenesis by impacting anabolism, intracellular signaling, and the tumor microenvironment. Consistent with their critical functions in tumor formation, mitochondria have become an attractive target for cancer therapy. We provide a comprehensive update on the numerous therapeutic modalities targeting the mitochondria of cancer cells making their way through clinical trials.

DOI: https://doi.org/10.1101/cshperspect.a041534
Redox Biol. 2024 Apr 29. pii: S2213-2317(24)00152-6. [Epub ahead of print]73 103174

The absence of the ribosomal protein Rpl2702 elicits the MAPK-mTOR signaling to modulate mitochondrial morphology and functions.

Ling Liu, Yifan Wu, Ke Liu, Mengdan Zhu, Shouhong Guang, Fengsong Wang, Xing Liu, Xuebiao Yao, Jiajia He, Chuanhai Fu.

  Ribosomes mediate protein synthesis, which is one of the most energy-demanding activities within the cell, and mitochondria are one of the main sources generating energy. How mitochondrial morphology and functions are adjusted to cope with ribosomal defects, which can impair protein synthesis and affect cell viability, is poorly understood. Here, we used the fission yeast Schizosaccharomyces Pombe as a model organism to investigate the interplay between ribosome and mitochondria. We found that a ribosomal insult, caused by the absence of Rpl2702, activates a signaling pathway involving Sty1/MAPK and mTOR to modulate mitochondrial morphology and functions. Specifically, we demonstrated that Sty1/MAPK induces mitochondrial fragmentation in a mTOR-independent manner while both Sty1/MAPK and mTOR increases the levels of mitochondrial membrane potential and mitochondrial reactive oxygen species (mROS). Moreover, we demonstrated that Sty1/MAPK acts upstream of Tor1/TORC2 and Tor1/TORC2 and is required to activate Tor2/TORC1. The enhancements of mitochondrial membrane potential and mROS function to promote proliferation of cells bearing ribosomal defects. Hence, our study reveals a previously uncharacterized Sty1/MAPK-mTOR signaling axis that regulates mitochondrial morphology and functions in response to ribosomal insults and provides new insights into the molecular and physiological adaptations of cells to impaired protein synthesis.

Keywords:  MAPK; Mitochondria; Ribosome; Schizosaccharomyces pombe; mTOR

DOI:  https://doi.org/10.1016/j.redox.2024.103174
Curr Opin Cell Biol. 2024 Apr 30. pii: S0955-0674(24)00043-7. [Epub ahead of print]88 102364

Mitochondrially-associated actin waves maintain organelle homeostasis and equitable inheritance.

Stephen M Coscia, Andrew S Moore, Yvette C Wong, Erika L F Holzbaur.

First identified in dividing cells as revolving clusters of actin filaments, these are now understood as mitochondrially-associated actin waves that are active throughout the cell cycle. These waves are formed from the polymerization of actin onto a subset of mitochondria. Within minutes, this F-actin depolymerizes while newly formed actin filaments assemble onto neighboring mitochondria. In interphase, actin waves locally fragment the mitochondrial network, enhancing mitochondrial content mixing to maintain organelle homeostasis. In dividing cells actin waves spatially mix mitochondria in the mother cell to ensure equitable partitioning of these organelles between daughter cells. Progress has been made in understanding the consequences of actin cycling as well as the underlying molecular mechanisms, but many questions remain, and here we review these elements. Also, we draw parallels between mitochondrially-associated actin cycling and cortical actin waves. These dynamic systems highlight the remarkable plasticity of the actin cytoskeleton.

DOI: https://doi.org/10.1016/j.ceb.2024.102364
Biol Open. 2024 Apr 29. pii: bio.060271. [Epub ahead of print]

Hansenula polymorpha cells lacking the ER-localized peroxins Pex23 or Pex29 show defects in mitochondrial function and morphology.

Haiqiong Chen, Rinse de Boer, Arjen M Krikken, Fei Wu, Ida van der Klei.

  Pex23 family proteins localize to the endoplasmic reticulum and play a role in peroxisome and lipid body formation. The yeast Hansenula polymorpha contains four members: Pex23, Pex24, Pex29 and Pex32. We previously showed that loss of Pex24 or Pex32 results in severe peroxisomal defects, caused by reduced peroxisome-endoplasmic reticulum contact sites. We now analyzed the effect of the absence of all four Pex23 family proteins on other cell organelles. Vacuoles were normal in all four deletion strains. The number of lipid droplets was reduced in pex23 and pex29, but not in pex24 and pex32 cells, indicating that peroxisome and lipid droplet formation require different Pex23 family proteins in H. polymorpha. In pex23 and pex29 cells mitochondria were fragmented and clustered accompanied by reduced levels of the fusion protein Fzo1. Deletion of DNM1 suppressed the morphological phenotype of pex23 and pex29 cells, suggesting that mitochondrial fusion is affected. pex23 and pex29 cells showed retarded growth and reduced mitochondrial activities. The growth defect was partially suppressed by DNM1 deletion as well as by an artificial mitochondrion-endoplasmic reticulum tether. Hence, the absence of Pex23 family proteins may influence mitochondrion-endoplasmic reticulum contact sites.

Keywords:  Lipid droplets; Mitochondria; Pex23 family; Yeast

DOI:  https://doi.org/10.1242/bio.060271
FEBS Lett. 2024 May 02.

CREB3 mediates the transcriptional regulation of PGC-1α, a master regulator of energy homeostasis and mitochondrial biogenesis.

Briana Locke, Elena Campbell, Ray Lu.

  Lipid metabolism hinges on a balance between lipogenesis and fatty acid oxidation (FAO). Disruptions in this balance can induce endoplasmic reticulum (ER) stress triggering the unfolded protein response (UPR) and contribute to metabolic diseases. The UPR protein, Luman or CREB3, has recently been implicated in metabolic regulation-CREB3 knockout mice exhibit resistance to diet-induced obesity and altered insulin sensitivity. Here, we show that CREB3 activated PPARGC1A transcription from a 1 kb promoter region. An increase in CREB3 expression correlated inversely with endogenous PPARGC1A mRNA levels and genes involved in FAO. As PGC-1α encoded by PPARGC1A is a master regulator of mitochondrial biogenesis and energy homeostasis, these findings demonstrate that CREB3 is a transcriptional regulator of PGC-1α, underlining the potential role of CREB3 in energy metabolism.

Keywords:  CREB3; PGC‐1α; endoplasmic reticulum stress; fatty acid oxidation; metabolism; transcriptional regulation

DOI:  https://doi.org/10.1002/1873-3468.14897
Bone. 2024 Apr 30. pii: S8756-3282(24)00101-7. [Epub ahead of print] 117112

Toward understanding the cellular control of vertebrate mineralization: The potential role of mitochondria.

Irving M Shapiro, Makarand V Risbud, William J Landis.

  This review examines the possible role of mitochondria in maintaining calcium and phosphate ion homeostasis and participating in the mineralization of bone, cartilage and other vertebrate hard tissues. The paper builds on the known structural features of mitochondria and the documented observations in these tissues that the organelles contain calcium phosphate granules. Such deposits in mitochondria putatively form to buffer excessively high cytosolic calcium ion concentrations and prevent metabolic deficits and even cell death. While mitochondria protect cytosolic enzyme systems through this buffering capacity, the accumulation of calcium ions by mitochondria promotes the activity of enzymes of the tricarboxylic acid (TCA/Krebs) cycle, increases oxidative phosphorylation and ATP synthesis, and leads to changes in intramitochondrial pH. These pH alterations influence ion solubility and possibly the transitions and composition in the mineral phase structure of the granules. Based on these considerations, mitochondria are proposed to support the mineralization process by providing a mobile store of calcium and phosphate ions, in smaller cluster or larger granule form, while maintaining critical cellular activities. The rise in the mitochondrial calcium level also increases the generation of citrate and other TCA cycle intermediates that contribute to cell function and the development of extracellular mineral. This paper suggests that another key role of the mitochondrion, along with the effects just noted, is to supply phosphate ions, derived from the breakdown of ATP, to endolysosomes and autophagic vesicles originating in the endoplasmic reticulum and Golgi and at the plasma membrane. These many separate but interdependent mitochondrial functions emphasize the critical importance of this organelle in the cellular control of vertebrate mineralization.

Keywords:  ATP; Calcium; Endoplasmic reticulum; Mineralization; Mitochondria; Mitochondrial granules; Phosphate

DOI:  https://doi.org/10.1016/j.bone.2024.117112
Cell Metab. 2024 Apr 15. pii: S1550-4131(23)00472-2. [Epub ahead of print]

The mitochondrial multi-omic response to exercise training across rat tissues.

MoTrPAC Study Group

  Mitochondria have diverse functions critical to whole-body metabolic homeostasis. Endurance training alters mitochondrial activity, but systematic characterization of these adaptations is lacking. Here, the Molecular Transducers of Physical Activity Consortium mapped the temporal, multi-omic changes in mitochondrial analytes across 19 tissues in male and female rats trained for 1, 2, 4, or 8 weeks. Training elicited substantial changes in the adrenal gland, brown adipose, colon, heart, and skeletal muscle. The colon showed non-linear response dynamics, whereas mitochondrial pathways were downregulated in brown adipose and adrenal tissues. Protein acetylation increased in the liver, with a shift in lipid metabolism, whereas oxidative proteins increased in striated muscles. Exercise-upregulated networks were downregulated in human diabetes and cirrhosis. Knockdown of the central network protein 17-beta-hydroxysteroid dehydrogenase 10 (HSD17B10) elevated oxygen consumption, indicative of metabolic stress. We provide a multi-omic, multi-tissue, temporal atlas of the mitochondrial response to exercise training and identify candidates linked to mitochondrial dysfunction.

Keywords:  HSD17B10; acetylome; aerobic; exercise; metabolism; metabolomics; mitochondria; multi-omics; proteomics; transcriptomics

DOI:  https://doi.org/10.1016/j.cmet.2023.12.021
NPJ Parkinsons Dis. 2024 Apr 29. 10(1): 93

PARKIN is not required to sustain OXPHOS function in adult mammalian tissues.

Roberta Filograna, Jule Gerlach, Hae-Na Choi, Giovanni Rigoni, Michela Barbaro, Mikael Oscarson, Seungmin Lee, Katarina Tiklova, Markus Ringnér, Camilla Koolmeister, Rolf Wibom, Sara Riggare, Inger Nennesmo, Thomas Perlmann, Anna Wredenberg, Anna Wedell, Elisa Motori, Per Svenningsson, Nils-Göran Larsson.

Loss-of-function variants in the PRKN gene encoding the ubiquitin E3 ligase PARKIN cause autosomal recessive early-onset Parkinson's disease (PD). Extensive in vitro and in vivo studies have reported that PARKIN is involved in multiple pathways of mitochondrial quality control, including mitochondrial degradation and biogenesis. However, these findings are surrounded by substantial controversy due to conflicting experimental data. In addition, the existing PARKIN-deficient mouse models have failed to faithfully recapitulate PD phenotypes. Therefore, we have investigated the mitochondrial role of PARKIN during ageing and in response to stress by employing a series of conditional Parkin knockout mice. We report that PARKIN loss does not affect oxidative phosphorylation (OXPHOS) capacity and mitochondrial DNA (mtDNA) levels in the brain, heart, and skeletal muscle of aged mice. We also demonstrate that PARKIN deficiency does not exacerbate the brain defects and the pro-inflammatory phenotype observed in mice carrying high levels of mtDNA mutations. To rule out compensatory mechanisms activated during embryonic development of Parkin-deficient mice, we generated a mouse model where loss of PARKIN was induced in adult dopaminergic (DA) neurons. Surprisingly, also these mice did not show motor impairment or neurodegeneration, and no major transcriptional changes were found in isolated midbrain DA neurons. Finally, we report a patient with compound heterozygous PRKN pathogenic variants that lacks PARKIN and has developed PD. The PARKIN deficiency did not impair OXPHOS activities or induce mitochondrial pathology in skeletal muscle from the patient. Altogether, our results argue that PARKIN is dispensable for OXPHOS function in adult mammalian tissues.

DOI: https://doi.org/10.1038/s41531-024-00707-0