bims-mecmid 2021-09-26 papers

bims-mecmid

Biomed News

on Membrane communication in mitochondrial dynamics

Issue of 2021–09–26
eleven papers selected by
Mauricio Cardenas Rodriguez, University of Padova

Mitofusin 2: A Link Between Mitochondrial Function and Substrate Metabolism?
Inositol serves as a natural inhibitor of mitochondrial fission by directly targeting AMPK.
Assessment of Mitochondrial Protein Topology and Membrane Insertion.
Fine-tuned repression of Drp1 driven mitochondrial fission primes a 'stem/progenitor-like state' to support neoplastic transformation.
Redox-Mediated Regulation of Mitochondrial Biogenesis, Dynamics, and Respiratory Chain Assembly in Yeast and Human Cells.
Fission accomplished: Uncovering the role of Drp1 in regulating mitochondrial dysfunction and age-related muscle atrophy.
The mechanisms of integral membrane protein biogenesis.
In situ observation of mitochondrial biogenesis as the early event of apoptosis.
Mitochondrial-derived compartments facilitate cellular adaptation to amino acid stress.
Molecular characterization of a complex of apoptosis-inducing factor 1 with cytochrome c oxidase of the mitochondrial respiratory chain.
High-Throughput BN-PAGE for Mitochondrial Respiratory Complexes.

Mitochondrion. 2021 Sep 15. pii: S1567-7249(21)00121-5. [Epub ahead of print]

Mitofusin 2: A Link Between Mitochondrial Function and Substrate Metabolism?

Janna M Emery, Rudy M Ortiz.

  Mitochondria are dynamic, interactive organelles that connect cellular signaling and whole-cell homeostasis. This "mitochatting" allows the cell to receive information about the mitochondria's condition before accommodating energy demands. Mitofusin 2 (Mfn2), an outer mitochondrial membrane fusion protein specializes in mediating mitochondrial homeostasis. Early studies defined the biological significance of Mfn2, latter studies highlighted its role in substrate metabolism. However, determining Mfn2 potential to contribute to energy homeostasis needs study. This review summarizes current literature on mitochondrial metabolic processes, dynamics, and evidence of interactions among Mfn2 and regulatory processes that may link Mfn2's role in maintaining mitochondrial function and substrate metabolism.

Keywords:  fatty acid oxidation; fission; fusion; glycolysis; mitochondrial dynamics; mitophagy

DOI:  https://doi.org/10.1016/j.mito.2021.09.003
Mol Cell. 2021 Sep 16. pii: S1097-2765(21)00692-4. [Epub ahead of print]81(18): 3803-3819.e7

Inositol serves as a natural inhibitor of mitochondrial fission by directly targeting AMPK.

Che-Chia Hsu, Xian Zhang, Guihua Wang, Weina Zhang, Zhen Cai, Bo-Syong Pan, Haiwei Gu, Chuan Xu, Guoxiang Jin, Xiangshang Xu, Rajesh Kumar Manne, Yan Jin, Wei Yan, Jingwei Shao, Tingjin Chen, Emily Lin, Amit Ketkar, Robert Eoff, Zhi-Gang Xu, Zhong-Zhu Chen, Hong-Yu Li, Hui-Kuan Lin.

  Mitochondrial dynamics regulated by mitochondrial fusion and fission maintain mitochondrial functions, whose alterations underline various human diseases. Here, we show that inositol is a critical metabolite directly restricting AMPK-dependent mitochondrial fission independently of its classical mode as a precursor for phosphoinositide generation. Inositol decline by IMPA1/2 deficiency elicits AMPK activation and mitochondrial fission without affecting ATP level, whereas inositol accumulation prevents AMPK-dependent mitochondrial fission. Metabolic stress or mitochondrial damage causes inositol decline in cells and mice to elicit AMPK-dependent mitochondrial fission. Inositol directly binds to AMPKγ and competes with AMP for AMPKγ binding, leading to restriction of AMPK activation and mitochondrial fission. Our study suggests that the AMP/inositol ratio is a critical determinant for AMPK activation and establishes a model in which AMPK activation requires inositol decline to release AMPKγ for AMP binding. Hence, AMPK is an inositol sensor, whose inactivation by inositol serves as a mechanism to restrict mitochondrial fission.

Keywords:  AMP; AMPK; IMPA1; energy stress; glucose deprivation; inosiotl sensor; inositol; inositol/AMP ratio; mitochondrial fission; mitocondrial dynamics

DOI:  https://doi.org/10.1016/j.molcel.2021.08.025
Methods Mol Biol. 2022 ;2363 165-181

Assessment of Mitochondrial Protein Topology and Membrane Insertion.

Kerstin Schäfer, Carina Engstler, Korbinian Dischinger, Chris Carrie.

  Analyzing the membrane integrity and topology of a mitochondrial protein is essential for truly understanding its function. In this chapter, we demonstrate how to analyze mitochondrial membrane proteins using both an immunological-based assay and an in vivo self-assembling GFP approach. First, immunological approaches to investigate the solubility or membrane association of a protein within mitochondria are described. With this method, we demonstrate how the topology of soluble domains of a membrane-integrated protein can be determined. Using protein-specific antibodies, the localization of the soluble domains of a protein are analyzed by a proteolytic-cleavage approach using proteinase K in mitochondria, outer membrane-ruptured mitochondria, and solubilized mitochondrial membranes. In a second approach, we determine the topology of plant mitochondrial proteins using an in vivo self-assembling GFP localization approach.

Keywords:  Carbonate extraction; In vivo GFP localization; Membrane integration; Membrane protein topology; Membrane solubilization; Mitochondrial membrane proteins; Mitoplasts; Osmotic swelling; Proteinase K digestion; Self-assembling GFP

DOI:  https://doi.org/10.1007/978-1-0716-1653-6_13
Elife. 2021 Sep 21. pii: e68394. [Epub ahead of print]10

Fine-tuned repression of Drp1 driven mitochondrial fission primes a 'stem/progenitor-like state' to support neoplastic transformation.

Brian Spurlock, Danitra Parker, Malay Kumar Basu, Anita Hjelmeland, Sajina Gc, Shanrun Liu, Gene P Siegal, Alan Gunter, Aida Moran, Kasturi Mitra.

  Gene knockout of the master regulator of mitochondrial fission, Drp1, prevents neoplastic transformation. Also, mitochondrial fission and its opposing process of mitochondrial fusion are emerging as crucial regulators of stemness. Intriguingly, stem/progenitor cells maintaining repressed mitochondrial fission are primed for self-renewal and proliferation. Using our newly derived carcinogen transformed human cell model we demonstrate that fine-tuned Drp1 repression primes a slow cycling 'stem/progenitor-like state', which is characterized by small networks of fused mitochondria and a gene-expression profile with elevated functional stem/progenitor markers (Krt15, Sox2 etc) and their regulators (Cyclin E). Fine tuning Drp1 protein by reducing its activating phosphorylation sustains the neoplastic stem cell markers. Whereas, fine-tuned reduction of Drp1 protein maintains the characteristic mitochondrial shape and gene-expression of the primed 'stem/progenitor-like state' to accelerate neoplastic transformation, and more complete reduction of Drp1 protein prevents it. Therefore, our data highlights a 'goldilocks'; level of Drp1 repression supporting stem/progenitor state dependent neoplastic transformation.

Keywords:  cancer biology; cell biology; mouse

DOI:  https://doi.org/10.7554/eLife.68394
Front Cell Dev Biol. 2021 ;9 720656

Redox-Mediated Regulation of Mitochondrial Biogenesis, Dynamics, and Respiratory Chain Assembly in Yeast and Human Cells.

Stefan Geldon, Erika Fernández-Vizarra, Kostas Tokatlidis.

  Mitochondria are double-membrane organelles that contain their own genome, the mitochondrial DNA (mtDNA), and reminiscent of its endosymbiotic origin. Mitochondria are responsible for cellular respiration via the function of the electron oxidative phosphorylation system (OXPHOS), located in the mitochondrial inner membrane and composed of the four electron transport chain (ETC) enzymes (complexes I-IV), and the ATP synthase (complex V). Even though the mtDNA encodes essential OXPHOS components, the large majority of the structural subunits and additional biogenetical factors (more than seventy proteins) are encoded in the nucleus and translated in the cytoplasm. To incorporate these proteins and the rest of the mitochondrial proteome, mitochondria have evolved varied, and sophisticated import machineries that specifically target proteins to the different compartments defined by the two membranes. The intermembrane space (IMS) contains a high number of cysteine-rich proteins, which are mostly imported via the MIA40 oxidative folding system, dependent on the reduction, and oxidation of key Cys residues. Several of these proteins are structural components or assembly factors necessary for the correct maturation and function of the ETC complexes. Interestingly, many of these proteins are involved in the metalation of the active redox centers of complex IV, the terminal oxidase of the mitochondrial ETC. Due to their function in oxygen reduction, mitochondria are the main generators of reactive oxygen species (ROS), on both sides of the inner membrane, i.e., in the matrix and the IMS. ROS generation is important due to their role as signaling molecules, but an excessive production is detrimental due to unwanted oxidation reactions that impact on the function of different types of biomolecules contained in mitochondria. Therefore, the maintenance of the redox balance in the IMS is essential for mitochondrial function. In this review, we will discuss the role that redox regulation plays in the maintenance of IMS homeostasis as well as how mitochondrial ROS generation may be a key regulatory factor for ETC biogenesis, especially for complex IV.

Keywords:  MIA; ROS; biogenesis; mitochondria; protein import; redox signaling; respiratory chain assembly

DOI:  https://doi.org/10.3389/fcell.2021.720656
J Physiol. 2021 Sep 23.

Fission accomplished: Uncovering the role of Drp1 in regulating mitochondrial dysfunction and age-related muscle atrophy.

Paula M Miotto, Giang M Dao, Henver S Brunetta.

DOI: https://doi.org/10.1113/JP282197
Nat Rev Mol Cell Biol. 2021 Sep 23.

The mechanisms of integral membrane protein biogenesis.

Ramanujan S Hegde, Robert J Keenan.

Roughly one quarter of all genes code for integral membrane proteins that are inserted into the plasma membrane of prokaryotes or the endoplasmic reticulum membrane of eukaryotes. Multiple pathways are used for the targeting and insertion of membrane proteins on the basis of their topological and biophysical characteristics. Multipass membrane proteins span the membrane multiple times and face the additional challenges of intramembrane folding. In many cases, integral membrane proteins require assembly with other proteins to form multi-subunit membrane protein complexes. Recent biochemical and structural analyses have provided considerable clarity regarding the molecular basis of membrane protein targeting and insertion, with tantalizing new insights into the poorly understood processes of multipass membrane protein biogenesis and multi-subunit protein complex assembly.

DOI: https://doi.org/10.1038/s41580-021-00413-2
iScience. 2021 Sep 24. 24(9): 103038

In situ observation of mitochondrial biogenesis as the early event of apoptosis.

Chang-Sheng Shao, Xiu-Hong Zhou, Yu-Hui Miao, Peng Wang, Qian-Qian Zhang, Qing Huang.

  Mitochondrial biogenesis is a cell response to external stimuli which is generally believed to suppress apoptosis. However, during the process of apoptosis, whether mitochondrial biogenesis occurs in the early stage of the apoptotic cells remains unclear. To address this question, we constructed the COX8-EGFP-ACTIN-mCherry HeLa cells with recombinant fluorescent proteins respectively tagged on the nucleus and mitochondria and monitored the mitochondrial changes in the living cells exposed to gamma-ray radiation. Besides in situ detection of mitochondrial fluorescence changes, we also examined the cell viability, nuclear DNA damage, reactive oxygen species (ROS), mitochondrial superoxide, citrate synthase activity, ATP, cytoplasmic and mitochondrial calcium, mitochondrial mass, mitochondrial morphology, and protein expression related to mitochondrial biogenesis, as well as the apoptosis biomarkers. As a result, we confirmed that significant mitochondrial biogenesis took place preceding the radiation-induced apoptosis, and it was closely correlated with the apoptotic cells at late stage. The involved mechanism was also discussed.

Keywords:  Biochemistry methods; Biomolecular engineering; Cell biology

DOI:  https://doi.org/10.1016/j.isci.2021.103038
Mol Cell. 2021 Sep 16. pii: S1097-2765(21)00688-2. [Epub ahead of print]81(18): 3786-3802.e13

Mitochondrial-derived compartments facilitate cellular adaptation to amino acid stress.

Max-Hinderk Schuler, Alyssa M English, Tianyao Xiao, Thane J Campbell, Janet M Shaw, Adam L Hughes.

  Amino acids are essential building blocks of life. However, increasing evidence suggests that elevated amino acids cause cellular toxicity associated with numerous metabolic disorders. How cells cope with elevated amino acids remains poorly understood. Here, we show that a previously identified cellular structure, the mitochondrial-derived compartment (MDC), functions to protect cells from amino acid stress. In response to amino acid elevation, MDCs are generated from mitochondria, where they selectively sequester and deplete SLC25A nutrient carriers and their associated import receptor Tom70 from the organelle. Generation of MDCs promotes amino acid catabolism, and their formation occurs simultaneously with transporter removal at the plasma membrane via the multivesicular body (MVB) pathway. The combined loss of vacuolar amino acid storage, MVBs, and MDCs renders cells sensitive to high amino acid stress. Thus, we propose that MDCs operate as part of a coordinated cell network that facilitates amino acid homeostasis through post-translational nutrient transporter remodeling.

Keywords:  MDC; Tom70; amino acid; lysosome; mitochondria; nutrient carrier; vacuole

DOI:  https://doi.org/10.1016/j.molcel.2021.08.021
Proc Natl Acad Sci U S A. 2021 09 28. pii: e2106950118. [Epub ahead of print]118(39):

Molecular characterization of a complex of apoptosis-inducing factor 1 with cytochrome c oxidase of the mitochondrial respiratory chain.

Johannes F Hevler, Riccardo Zenezeni Chiozzi, Alfredo Cabrera-Orefice, Ulrich Brandt, Susanne Arnold, Albert J R Heck.

  Combining mass spectrometry-based chemical cross-linking and complexome profiling, we analyzed the interactome of heart mitochondria. We focused on complexes of oxidative phosphorylation and found that dimeric apoptosis-inducing factor 1 (AIFM1) forms a defined complex with ∼10% of monomeric cytochrome c oxidase (COX) but hardly interacts with respiratory chain supercomplexes. Multiple AIFM1 intercross-links engaging six different COX subunits provided structural restraints to build a detailed atomic model of the COX-AIFM12 complex (PDBDEV_00000092). An application of two complementary proteomic approaches thus provided unexpected insight into the macromolecular organization of the mitochondrial complexome. Our structural model excludes direct electron transfer between AIFM1 and COX. Notably, however, the binding site of cytochrome c remains accessible, allowing formation of a ternary complex. The discovery of the previously overlooked COX-AIFM12 complex and clues provided by the structural model hint at potential roles of AIFM1 in oxidative phosphorylation biogenesis and in programmed cell death.

Keywords:  AIFM1; COX; complexome profiling; cross-linking mass spectrometry; mitochondria

DOI:  https://doi.org/10.1073/pnas.2106950118
Methods Mol Biol. 2022 ;2363 111-119

High-Throughput BN-PAGE for Mitochondrial Respiratory Complexes.

Lilian Vincis Pereira Sanglard, Catherine Colas des Francs-Small.

  Blue native electrophoresis (BN-PAGE) is a highly resolutive method suited to the study of high molecular weight protein complexes between 100 and >3000 kDa. One of the drawbacks of this method is that it is very time-consuming and requires high quantities of purified organelles. Here we describe a high throughput BN-PAGE method allowing to screen libraries of plants potentially altered in respiratory metabolism.

Keywords:  Blue Native PAGE; Immunoblots; Mitochondria; Respiratory complexes

DOI:  https://doi.org/10.1007/978-1-0716-1653-6_10