bims-mecosi 2022-02-20 papers

Issue of 2022–02–20
eight papers selected by
Verena Kohler, Stockholm University

Front Neurosci. 2022 ;16 784880

Mitochondrial Dynamics and Mitochondria-Lysosome Contacts in Neurogenetic Diseases.

Jordi Pijuan, Lara Cantarero, Daniel Natera-de Benito, Arola Altimir, Anna Altisent-Huguet, Yaiza Díaz-Osorio, Laura Carrera-García, Jessica Expósito-Escudero, Carlos Ortez, Andrés Nascimento, Janet Hoenicka, Francesc Palau.

Mitochondrial network is constantly in a dynamic and regulated balance of fusion and fission processes, which is known as mitochondrial dynamics. Mitochondria make physical contacts with almost every other membrane in the cell thus impacting cellular functions. Mutations in mitochondrial dynamics genes are known to cause neurogenetic diseases. To better understand the consequences on the cellular phenotype and pathophysiology of neurogenetic diseases associated with defective mitochondrial dynamics, we have compared the fibroblasts phenotypes of (i) patients carrying pathogenic variants in genes involved in mitochondrial dynamics such as DRP1 (also known as DNM1L), GDAP1, OPA1, and MFN2, and (ii) patients carrying mutated genes that their dysfunction affects mitochondria or induces a mitochondrial phenotype, but that are not directly involved in mitochondrial dynamic network, such as FXN (encoding frataxin, located in the mitochondrial matrix), MED13 (hyperfission phenotype), and CHKB (enlarged mitochondria phenotype). We identified mitochondrial network alterations in all patients' fibroblasts except for CHKB Q198*/Q198*. Functionally, all fibroblasts showed mitochondrial oxidative stress, without membrane potential abnormalities. The lysosomal area and distribution were abnormal in GDAP1 W67L/W67L, DRP1 K75E/+, OPA1 F570L/+, and FXN R165C/GAA fibroblasts. These lysosomal alterations correlated with mitochondria-lysosome membrane contact sites (MCSs) defects in GDAP1 W67L/W67L exclusively. The study of mitochondrial contacts in all samples further revealed a significant decrease in MFN2 R104W/+ fibroblasts. GDAP1 and MFN2 are outer mitochondrial membrane (OMM) proteins and both are related to Charcot-Marie Tooth neuropathy. Here we identified their constitutive interaction as well as MFN2 interaction with LAMP-1. Therefore MFN2 is a new mitochondria-lysosome MCSs protein. Interestingly, GDAP1 W67L/W67L and MFN2 R104W/+ fibroblasts carry pathogenic changes that occur in their catalytic domains thus suggesting a functional role of GDAP1 and MFN2 in mitochondria-lysosome MCSs. Finally, we observed starvation-induced autophagy alterations in DRP1 K75E/+, GDAP1 W67L/W67L, OPA1 F570L/+, MFN2 R104W/+, and CHKB Q198*/Q198* fibroblasts. These genes are related to mitochondrial membrane structure or lipid composition, which would associate the OMM with starvation-induced autophagy. In conclusion, the study of mitochondrial dynamics and mitochondria-lysosome axis in a group of patients with different neurogenetic diseases has deciphered common and unique cellular phenotypes of degrading and non-degrading pathways that shed light on pathophysiological events, new biomarkers and pharmacological targets for these disorders.

Keywords: lysosome; membrane contact sites (MCSs); mitochondria; mitochondrial dynamics; neurogenetic diseases

DOI: https://doi.org/10.3389/fnins.2022.784880

Cells. 2022 Feb 02. pii: 514. [Epub ahead of print]11(3):

Mitochondria-Endoplasmic Reticulum Interplay Regulates Exo-Cytosis in Human Neuroblastoma Cells.

Giacomo Dentoni, Luana Naia, Maria Ankarcrona.

Mitochondria-endoplasmic reticulum (ER) contact sites (MERCS) have been emerging as a multifaceted subcellular region of the cell which affects several physiological and pathological mechanisms. A thus far underexplored aspect of MERCS is their contribution to exocytosis. Here, we set out to understand the role of these contacts in exocytosis and find potential mechanisms linking these structures to vesicle release in human neuroblastoma SH-SY5Y cells. We show that increased mitochondria to ER juxtaposition through Mitofusin 2 (Mfn2) knock-down resulted in a substantial upregulation of the number of MERCS, confirming the role of Mfn2 as a negative regulator of these structures. Furthermore, we report that both vesicle numbers and vesicle protein levels were decreased, while a considerable upregulation in exocytotic events upon cellular depolarization was detected. Interestingly, in Mfn2 knock-down cells, the inhibition of the inositol 1,4,5-trisphosphate receptor (IP3R) and the mitochondrial calcium (Ca2+) uniporter (MCU) restored vesicle protein content and attenuated exocytosis. We thus suggest that MERCS could be targeted to prevent increased exocytosis in conditions in which ER to mitochondria proximity is upregulated.

Keywords: MAM; MCU; MERCS; exocytosis; inositol 1,4,5-trisphosphate receptor; mitochondria

DOI: https://doi.org/10.3390/cells11030514

Theranostics. 2022 ;12(3): 1267-1285

Overexpression of MFN2 alleviates sorafenib-induced cardiomyocyte necroptosis via the MAM-CaMKIIδ pathway in vitro and in vivo.

Ziping Song, Haixu Song, Dan Liu, Bing Yan, Daowen Wang, Yan Zhang, Xiaojie Zhao, Xiaoxiang Tian, Chenghui Yan, Yaling Han.

Background: The continued success of oncological therapeutics is dependent on the mitigation of treatment-related adverse events, particularly cardiovascular toxicities. As such, there is an important need to understand the basic mechanisms of drug toxicities in the process of antitumor therapy. Our aim in this study was to elucidate the underlying mechanisms of sorafenib (sor)-induced cardiomyocyte damage. Methods: Primary mouse cardiomyocytes were prepared and treated with sor and various other treatments. Cardiomyocyte necroptosis was detected by flow cytometry, western blotting, and CCK8 assays. Mitochondrial Ca2+ uptake was detected by the Rhod-2 probe using confocal imaging. Morphological changes in mitochondria and mitochondria-associated endoplasmic reticulum (ER) membranes (MAMs) were imaged using transmission electron microscopy (TEM) and confocal microscopy. Cardiac perfusion was performed to detect cardiac specific role of MFN2 overexpression in vivo. Results: We reported that mitochondrial Ca2+ overload, the subsequent increase in calmodulin-dependent protein kinase II delta (CaMKIIδ) and RIP3/MLKL cascade activation, contributed to sor-induced cardiac necroptosis. Excess MAM formation and close ER-mitochondria contact were key pathogenesis of sor-induced Ca2+ overload. Sor mediated MFN2 downregulation in a concentration-dependent manner. Furthermore, we found that reduced mitofusin-2 (MFN2) level augmented sor-mediated elevated MAM biogenesis and increased mitochondria-MAM tethering in cardiomyocytes. Sor-induced Mammalian Target of Rapamycin (mTOR) inactivation, followed by the activation and nuclear translocation of Transcription Factor EB (TFEB), contributed to mitophagy and MFN2 degradation. In an in vivo model, mice subjected to sor administration developed cardiac dysfunction, autophagy activation and necroptosis; our investigation found that global and cardiac-specific overexpression of MFN2 repressed cardiac dysfunction, and sor-induced cardiomyocyte necroptosis via repressing the MAM-CaMKIIδ-RIP3/MLKL pathway. Conclusion: Sorafenib mediated cardiomyocyte necroptosis through the MFN2-MAM-Ca2+-CaMKIIδ pathway in vitro and in vivo. The overexpression of MFN2 could rescue sor-induced cardiomyocyte necroptosis without disturbing the anti-tumor effects.

Keywords: Cardio-Oncology; MAM; MFN2; Necroptosis; Sorafenib

DOI: https://doi.org/10.7150/thno.65716

F1000Res. 2021 ;10 263

ContactJ: Lipid droplets-mitochondria contacts characterization through fluorescence microscopy and image analysis.

Gemma Martín, Marta Bosch, Elisenda Coll, Robert G Parton, Albert Pol, Maria Calvo.

Lipid droplets (LDs) are the major lipid storage organelles of eukaryotic cells and together with mitochondria key regulators of cell bioenergetics. LDs communicate with mitochondria and other organelles forming "metabolic synapse" contacts to ensure that lipid supply occurs where and when necessary. Although transmission electron microscopy analysis allows an accurate and precise analysis of contacts, the characterization of a large number of cells and conditions can become a long-term process. In order to extend contact analysis to hundreds of cells and multiple conditions, we have combined confocal fluorescence microscopy with advanced image analysis methods. In this work, we have developed the ImageJ macro script ContactJ, a novel and straight image analysis method to identify and quantify contacts between LD and mitochondria in fluorescence microscopy images allowing the automatic analysis. This image analysis workflow combines colocalization and skeletonization methods, enabling the quantification of LD-mitochondria contacts together with a complete characterization of organelles and cellular parameters. The correlation and normalization of these parameters contribute to the complex description of cell behavior under different experimental energetic states. ContactJ is available here: https://github.com/UB-BioMedMicroscopy/ContactJ/tree/1.0.

Keywords: Bioimaging; Contact sites; Fluorescence Microscopy; Image Processing and Analysis; ImageJ; Interactome; Lipid Droplets; Mitochondria

DOI: https://doi.org/10.12688/f1000research.51900.1

J Cardiovasc Pharmacol. 2022 Jan 21.

What Role do Mitochondria have in Diastolic Dysfunction? Implications for Diabetic Cardiomyopathy and Heart Failure with Preserved Ejection Function (HFpEF).

Martin G McCandless, Raffaele Altara, George W Booz, Mazen Kurdi.

Diastolic dysfunction is common to both diabetic cardiomyopathy and heart failure with preserved ejection faction (HFpEF). Although commonly attributed to increased fibrosis, alterations in mitochondrial function and associated Ca2+ handling may contribute to impaired cardiac function. With mitochondrial dysfunction, increased reactive oxygen species (ROS), inflammation, decreased ATP/ADP ratio, may lead to increased extracellular matrix as well as diminished contractile relaxation. In this article, we discuss recent research implicating deficient mitochondria-associated endoplasmic reticulum (ER) membranes (MAMs) as it relates to impaired metabolic function and what role that may have in diastolic dysfunction in diabetic cardiomyopathy. The contribution of mitochondrial dysfunction to diastolic dysfunction in HFpEF is less established, but equally credible based on preclinical studies. However, there are notable differences between diabetic cardiomyopathy and HFpEF. Recent evidence implicates impaired ER signaling, in particular the unfolded protein response (UPR), in the pathogenesis of HFpEF. With HFpEF, enhanced pressure on the mitochondrial "gas pedal" due to increased cytosolic Ca2+ may perturb mitochondrial homeostasis. For both diabetic cardiomyopathy and HFpEF, a better understanding of how altered cellular ion and redox status affect mitochondrial function is needed. Finally, we discuss the implications that mitochondrial dysfunction may have in devising novel therapeutic strategies for both diabetic cardiomyopathy and HFpEF.

DOI: https://doi.org/10.1097/FJC.0000000000001228

Cells. 2022 Jan 22. pii: 371. [Epub ahead of print]11(3):

Highlighting the Multifaceted Role of Orai1 N-Terminal- and Loop Regions for Proper CRAC Channel Functions.

Christina Humer, Christoph Romanin, Carmen Höglinger.

Orai1, the Ca2+-selective pore in the plasma membrane, is one of the key components of the Ca2+release-activated Ca2+ (CRAC) channel complex. Activated by the Ca2+ sensor in the endoplasmic reticulum (ER) membrane, stromal interaction molecule 1 (STIM1), via direct interaction when ER luminal Ca2+ levels recede, Orai1 helps to maintain Ca2+ homeostasis within a cell. It has already been proven that the C-terminus of Orai1 is indispensable for channel activation. However, there is strong evidence that for CRAC channels to function properly and maintain all typical hallmarks, such as selectivity and reversal potential, additional parts of Orai1 are needed. In this review, we focus on these sites apart from the C-terminus; namely, the second loop and N-terminus of Orai1 and on their multifaceted role in the functioning of CRAC channels.

Keywords: CRAC channel; Loop2; N-terminus; Orai1; calcium

DOI: https://doi.org/10.3390/cells11030371

Bioessays. 2022 Feb 15. e2100271

The strange case of Drp1 in autophagy: Jekyll and Hyde?

Yanfang Chen, Emmanuel Culetto, Renaud Legouis.

There is a debate regarding the function of Drp1, a GTPase involved in mitochondrial fission, during the elimination of mitochondria by autophagy. A number of experiments indicate that Drp1 is needed to eliminate mitochondria during mitophagy, either by reducing the mitochondrial size or by providing a noncanonical mitophagy function. Yet, other convincing experimental results support the conclusion that Drp1 is not necessary. Here, we review the possible functions for Drp1 in mitophagy and autophagy, depending on tissues, organisms and stresses, and discuss these apparent discrepancies. In this regard, it appears that the reduction of mitochondria size is often required for mitophagy but not always in a Drp1-dependent manner. Finally, we speculate on Drp1-independent mitochondrial fission mechanism that may take place during mitophagy and on noncanonical roles, which Drp1 may play such as modulating organelle contact sites dynamic during the autophagosome formation.

Keywords: Dnm1; Drp1; MERCs; autophagosome; fission; mitochondria; mitophagy

DOI: https://doi.org/10.1002/bies.202100271

Cell Calcium. 2022 Jan 31. pii: S0143-4160(22)00019-7. [Epub ahead of print]103 102544

Control of STIM and Orai function by post-translational modifications.

Jinsy Johnson, Rachel Blackman, Scott Gross, Jonathan Soboloff.

Store-operated calcium entry (SOCE) is mediated by the endoplasmic reticulum (ER) Ca2+ sensors stromal interaction molecules (STIM1 and STIM2) and the plasma membrane Orai (Orai1, Orai2, Orai3) Ca2+ channels. Although primarily regulated by ER Ca2+ content, there have been numerous studies over the last 15 years demonstrating that all 5 proteins are also regulated through post-translational modification (PTM). Focusing primarily on phosphorylation, glycosylation and redox modification, this review focuses on how PTMs modulate the key events in SOCE; Ca2+ sensing, STIM translocation, Orai interaction and/or Orai1 activation.

Keywords: Calcium; Glycosylation; Nitrosylation; Orai1; Oxidation; Phosphorylation; Post-translational modification; STIM1

DOI: https://doi.org/10.1016/j.ceca.2022.102544