bims-midtic 2023-06-11 papers

bims-midtic

Biomed News

on Mitochondrial dynamics and trafficking in cells

Issue of 2023–06–11
twenty-six papers selected by
Omkar Joshi, Turku Bioscience

The multiple links between actin and mitochondria.
Mitochondrial networks through the lens of mathematics.
ATF4 regulates mitochondrial content, morphology, and function in differentiating skeletal muscle myotubes.
Defective mitochondrial import as a challenge for cellular protein homeostasis.
Upstream Open Reading Frame-encoded MP31 Disrupts the Mitochondrial Quality Control Process and Inhibits Tumorigenesis in Glioblastoma.
Severe burn-induced mitochondrial recruitment of calpain causes aberrant mitochondrial dynamics and heart dysfunction.
DNA Damage Response and Mitochondrial Translation Mediate ROS Response.
Intrinsic TGF-β signaling attenuates proximal tubule mitochondrial injury and inflammation in chronic kidney disease.
MICU1 deficiency alters mitochondrial morphology and cytochrome C release.
Ablation of Sam50 is associated with fragmentation and alterations in metabolism in human myotubes.
FAM210A Regulates Mitochondrial Translation and Maintains Cardiac Mitochondrial Homeostasis.
Expression and subcellular localization of mitochondrial docking protein, syntaphilin, in oligodendrocytes and CNS myelin sheath.
Super-Resolution Imaging of Voltages in the Interior of Individual, Vital Mitochondria.
Loss of cholinergic receptor muscarinic 1 impairs cortical mitochondrial structure and function: implications in Alzheimer's disease.
Megamitochondria plasticity: function transition from adaption to disease.
A cytosolic surveillance mechanism activates the mitochondrial UPR.
Human mitochondrial ADP/ATP carrier SLC25A4 operates with a ping-pong kinetic mechanism.
Mitochondrial citrate carrier SLC25A1 is a dosage-dependent regulator of metabolic reprogramming and morphogenesis in the developing heart.
Mitochondrial metabolism and dynamics in pancreatic beta cell glucose sensing.
MIC26 and MIC27 are bona fide subunits of the MICOS complex in mitochondria and do not exist as glycosylated apolipoproteins.
PLIN5 interacts with FATP4 at membrane contact sites to promote lipid droplet-to-mitochondria fatty acid transport.
Platelets from patients with myeloproliferative neoplasms have increased numbers of mitochondria that are hypersensitive to depolarization by thrombin.
High-sensitivity calcium biosensor on the mitochondrial surface reveals that IP3R channels participate in the reticular Ca2+ leak towards mitochondria.
Mitochondrial dysfunctions induce PANoptosis and ferroptosis in cerebral ischemia/reperfusion injury: from pathology to therapeutic potential.
Editorial: the role of mitochondrial endoplasmic reticulum contact sites in human health and disease.
Modulating Copper Reactivity: A New Approach to Reprogram Mitochondrial Retrograde Signaling.

Nat Rev Mol Cell Biol. 2023 Jun 05.

The multiple links between actin and mitochondria.

Tak Shun Fung, Rajarshi Chakrabarti, Henry N Higgs.

Actin plays many well-known roles in cells, and understanding any specific role is often confounded by the overlap of multiple actin-based structures in space and time. Here, we review our rapidly expanding understanding of actin in mitochondrial biology, where actin plays multiple distinct roles, exemplifying the versatility of actin and its functions in cell biology. One well-studied role of actin in mitochondrial biology is its role in mitochondrial fission, where actin polymerization from the endoplasmic reticulum through the formin INF2 has been shown to stimulate two distinct steps. However, roles for actin during other types of mitochondrial fission, dependent on the Arp2/3 complex, have also been described. In addition, actin performs functions independent of mitochondrial fission. During mitochondrial dysfunction, two distinct phases of Arp2/3 complex-mediated actin polymerization can be triggered. First, within 5 min of dysfunction, rapid actin assembly around mitochondria serves to suppress mitochondrial shape changes and to stimulate glycolysis. At a later time point, at more than 1 h post-dysfunction, a second round of actin polymerization prepares mitochondria for mitophagy. Finally, actin can both stimulate and inhibit mitochondrial motility depending on the context. These motility effects can either be through the polymerization of actin itself or through myosin-based processes, with myosin 19 being an important mitochondrially attached myosin. Overall, distinct actin structures assemble in response to diverse stimuli to affect specific changes to mitochondria.

DOI: https://doi.org/10.1038/s41580-023-00613-y
Phys Biol. 2023 Jun 08.

Mitochondrial networks through the lens of mathematics.

Greyson Lewis, Wallace F Marshall.

  Mitochondria serve a wide range of functions within cells, most notably via their production of ATP. Although their morphology is commonly described as bean-like, mitochondria often form interconnected networks within cells that exhibit dynamic restructuring through a variety of physical changes. Further, though relationships between form and function in biology are well established, the extant toolkit for understanding mitochondrial morphology is limited. Here, we emphasize new and established methods for quantitatively describing mitochondrial networks, ranging from unweighted graph-theoretic representations to multi-scale approaches from applied topology, in particular persistent homology. We also show fundamental relationships between mitochondrial networks, mathematics, and physics, using ideas of graph planarity and statistical mechanics to better understand the full possible morphologicalspace of mitochondrial network structures. Lastly, we provide suggestions for how examination of mitochondrial network form through the language of mathematics can inform biological understanding, and vice versa.

Keywords:  graph theory; mitochondrial networks; persistent homology; planar graphs; scaling

DOI:  https://doi.org/10.1088/1478-3975/acdcdb
Am J Physiol Cell Physiol. 2023 Jun 05.

ATF4 regulates mitochondrial content, morphology, and function in differentiating skeletal muscle myotubes.

Jonathan M Memme, Victoria C Sanfrancesco, David A Hood.

  Mitochondrial function is widely recognized as a major determinant of health, emphasizing the importance of understanding the mechanisms promoting mitochondrial quality in various tissues. Recently, the mitochondrial unfolded protein response (UPRmt) has come into focus as a modulator of mitochondrial homeostasis, particularly in stress conditions. In muscle, the necessity for ATF4 and its role in regulating mitochondrial quality control (MQC) has yet to be determined. We overexpressed (OE) and knocked down ATF4 in C2C12 myoblasts, differentiated them to myotubes for 5 days, and subjected them to acute (ACA) or chronic (CCA) contractile activity. ATF4 mediated myotube formation through the regulated expression of myogenic factors, mainly Myc and MyoD, and supressed mitochondrial biogenesis basally through PGC-1a. However, our data also show that ATF4 expression levels are directly related to mitochondrial fusion and dynamics, UPRmt activation, as well as lysosomal biogenesis and autophagy. Thus, ATF4 promoted enhanced mitochondrial networking, protein handling, and capacity for clearance of dysfunctional organelles under stress conditions, despite lower levels of mitophagy flux with OE. Indeed, we found that ATF4 promoted the formation of a smaller pool of high functioning mitochondria that are more responsive to contractile activity, have higher oxygen consumption rates and lower reactive oxygen species levels. These data provide evidence that ATF4 is both necessary and sufficient for mitochondrial quality control and adaptation during both differentiation and contractile activity, thus advancing the current understanding of ATF4 beyond its canonical functions, to include the regulation of mitochondrial morphology, lysosomal biogenesis and mitophagy in muscle cells.

Keywords:  ATF4; mitochondrial quality control; mitochondrial unfolded protein response; mitophagy and lysosomal biogenesis; skeletal muscle C2C12

DOI:  https://doi.org/10.1152/ajpcell.00080.2023
FEBS Lett. 2023 Jun 05.

Defective mitochondrial import as a challenge for cellular protein homeostasis.

Klaudia K Maruszczak, Selvaraj Ayyamperumal, Agnieszka Chacinska.

  Mitochondria are organelles indispensable for the correct functioning of eukaryotic cells. Their significance for cellular homeostasis is manifested by the existence of complex quality control pathways that monitor organellar fitness. Mitochondrial biogenesis relies on the efficient import of mitochondrial precursor proteins, a large majority of which are encoded by nuclear DNA and synthesized in the cytosol. This creates a demand for highly specialized import routes that comprise cytosolic factors and organellar translocases. The passage of newly encoded mitochondrial precursor proteins through the cytosol to the translocase of the outer mitochondrial membrane (TOM) is under tight surveillance. As a result of mitochondrial import defects, mitochondrial precursor proteins accumulate in the cytosol or clog the TOM complex, which in turn stimulates cellular stress responses to minimize the consequences of these challenges. These responses are critical for maintaining protein homeostasis under conditions of mitochondrial stress. The present review summarizes recent advances in the field of mitochondrial protein import quality control and discusses the role of this quality control within the network of cellular mechanisms that maintain the cellular homeostasis of proteins.

Keywords:  cellular stress responses; mitochondria; mitochondrial dysfunction; mitochondrial quality control; protein aggregates; protein homeostasis

DOI:  https://doi.org/10.1002/1873-3468.14677
Neuro Oncol. 2023 Jun 06. pii: noad099. [Epub ahead of print]

Upstream Open Reading Frame-encoded MP31 Disrupts the Mitochondrial Quality Control Process and Inhibits Tumorigenesis in Glioblastoma.

Nunu Huang, Zhipeng Chen, Xuesong Yang, Yixin Gao, Jian Zhong, Yan Li, Feizhe Xiao, Xiuxing Wang, Yu Shi, Nu Zhang.

   BACKGROUND: Mitochondrial hyperpolarization achieved by the elevation of mitochondrial quality control (MQC) activity is a hallmark of glioblastoma (GBM). Therefore, targeting the MQC process to disrupt mitochondrial homeostasis should be a promising approach for GBM therapy.
METHOD: We used two-photon fluorescence microscopy, FACS and confocal microscopy with specific fluorescent dyes to detect the mitochondrial membrane potential (MMP) and mitochondrial structures. Mitophagic flux was measured with mKeima.
RESULTS: MP31, a PTEN uORF-translated and mitochondria-localized micropeptide, disrupted the MQC process and inhibited GBM tumorigenesis. Re-expression of MP31 in patient-derived GBM cells induced MMP loss to trigger mitochondrial fission but blocked mitophagic flux, leading to the accumulation of damaged mitochondria in cells, followed by ROS production and DNA damage. Mechanistically, MP31 inhibited lysosome function and blocked lysosome fusion with mitophagosomes by competing with V-ATPase A1 for LDHB binding to induce lysosomal alkalinization. Furthermore, MP31 enhanced the sensitivity of GBM cells to TMZ by suppressing protective mitophay in vitro and in vivo, but showed no side effects on normal human astrocytes (NHAs) or microglia cells (MG).
CONCLUSION: MP31 disrupts cancerous mitochondrial homeostasis and sensitizes GBM cells to current chemotherapy, without inducing toxicity in NHA and MG. MP31 is a promising candidate for GBM treatment.

Keywords:  GBM; MP31; MQC; V-ATPase A1; mitophagy

DOI:  https://doi.org/10.1093/neuonc/noad099
Shock. 2023 Jun 07.

Severe burn-induced mitochondrial recruitment of calpain causes aberrant mitochondrial dynamics and heart dysfunction.

Zhang Ran-Ran, Zhang Jing-Long, Li Qiao, Zhang Shu-Miao, Gu Xiao-Ming, Niu Wen, Zhou Jing-Jun, Zhou Lyu-Chen.

ABSTRACT: Mitochondrial damage is an important cause of heart dysfunction after severe burn injury. However, the pathophysiological process remains unclear. This study aims to examine the mitochondrial dynamics in the heart, and the role of μ-calpain, a cysteine protease, in this scenario. Rats were subjected to severe burn injury treatment, and the calpain inhibitor MDL28170 was administered intravenously 1 h before or after burn injury. Rats in the burn group displayed weakened heart performance and decreased mean arterial pressure, which was accompanied by a diminishment of mitochondrial function. The animals also exhibited higher levels of calpain in mitochondria, as reflected by immunofluorescence staining and activity tests. In contrast, treatment with MDL28170 before any severe burn diminished these responses to a severe burn. Burn injury decreased the abundance of mitochondria and resulted in a lower percentage of small mitochondria and a higher percentage of large mitochondria. Furthermore, burn injury caused an increase in the fission protein DRP1 in the mitochondria and a decrease in the inner membrane fusion protein OPA1. Similarly, these alterations were also blocked by MDL28170. Of note, inhibition of calpain yielded the emergence of more elongated mitochondria along with membrane invagination in the middle of the longitude, which is an indicator of the fission process. Finally, MDL28170, administered 1 h after burn injury, preserved mitochondrial function and heart performance, and increased the survival rate. Overall, these results provided the first evidence that mitochondrial recruitment of calpain confers heart dysfunction after severe burn injury, which involves aberrant mitochondrial dynamics.

DOI: https://doi.org/10.1097/SHK.0000000000002159
Cancer Discov. 2023 Jun 09. OF1

DNA Damage Response and Mitochondrial Translation Mediate ROS Response.

The cellular response to ROS depends on coordination of activities in the nucleus and mitochondria.

DOI: https://doi.org/10.1158/2159-8290.CD-RW2023-085
Nat Commun. 2023 Jun 03. 14(1): 3236

Intrinsic TGF-β signaling attenuates proximal tubule mitochondrial injury and inflammation in chronic kidney disease.

Merve Kayhan, Judith Vouillamoz, Daymé Gonzalez Rodriguez, Milica Bugarski, Yasutaka Mitamura, Julia Gschwend, Christoph Schneider, Andrew Hall, David Legouis, Cezmi A Akdis, Leary Peter, Hubert Rehrauer, Leslie Gewin, Roland H Wenger, Stellor Nlandu Khodo.

Excessive TGF-β signaling and mitochondrial dysfunction fuel chronic kidney disease (CKD) progression. However, inhibiting TGF-β failed to impede CKD in humans. The proximal tubule (PT), the most vulnerable renal segment, is packed with giant mitochondria and injured PT is pivotal in CKD progression. How TGF-β signaling affects PT mitochondria in CKD remained unknown. Here, we combine spatial transcriptomics and bulk RNAseq with biochemical analyses to depict the role of TGF-β signaling on PT mitochondrial homeostasis and tubulo-interstitial interactions in CKD. Male mice carrying specific deletion of Tgfbr2 in the PT have increased mitochondrial injury and exacerbated Th1 immune response in the aristolochic acid model of CKD, partly, through impaired complex I expression and mitochondrial quality control associated with a metabolic rewiring toward aerobic glycolysis in the PT cells. Injured S3T2 PT cells are identified as the main mediators of the maladaptive macrophage/dendritic cell activation in the absence of Tgfbr2. snRNAseq database analyses confirm decreased TGF-β receptors and a metabolic deregulation in the PT of CKD patients. This study describes the role of TGF-β signaling in PT mitochondrial homeostasis and inflammation in CKD, suggesting potential therapeutic targets that might be used to mitigate CKD progression.

DOI: https://doi.org/10.1038/s41467-023-39050-y
Cell Calcium. 2023 Jun 02. pii: S0143-4160(23)00077-5. [Epub ahead of print]113 102765

MICU1 deficiency alters mitochondrial morphology and cytochrome C release.

Benjamin Gottschalk, Roland Malli, Wolfgang F Graier.

  The mitochondrial inner boundary membrane harbors a protein called MICU1, which is sensitive to Ca2+ and binds to the MICOS components Mic60 and CHCHD2. Changes in the mitochondrial cristae junction structure and organization in MICU1-/- cells lead to increased cytochrome c release, membrane potential rearrangement, and changes in mitochondrial Ca2+ uptake dynamics. These findings shed new light on the multifaceted role of MICU1, highlighting its involvement not only as an interaction partner and regulator of the MCU complex but also as a crucial determinant of mitochondrial ultrastructure and, thus, an essential player in processes initiating apoptosis.

Keywords:  Apoptosis; Ca(2+) signaling; Cristae junction; MICOS-complex; MICU1; Mitochondria

DOI:  https://doi.org/10.1016/j.ceca.2023.102765
bioRxiv. 2023 May 22. pii: 2023.05.20.541602. [Epub ahead of print]

Ablation of Sam50 is associated with fragmentation and alterations in metabolism in human myotubes.

Zer Vue, Chia Vang, Kit Neikirk, Edgar Garza-Lopez, Jian-Qiang Shao, Margaret Mungai, Larry Vang, Heather Beasley, Andrea G Marshall, Amber Crabtree, Dominique Stephens, Melanie McReynolds, Sandra A Murray, Prasanna Katti, Steven Damo, Jennifer A Gaddy, Antentor Hinton.

The Sorting and Assembly Machinery (SAM) Complex functions in the assembly of β-barrel in the mitochondrial membrane. The SAM complex is made up of three subunits, Sam35, Sam37, and Sam50. While both Sam35 and Sam37 are peripheral membrane proteins that are not required for survival, Sam50 interacts with the MICOS complex to connect the inner and outer mitochondrial membranes and forms the mitochondrial intermembrane space bridging (MIB) complex. Specifically, Sam50 stabilizes the MIB complex for protein transport, respiratory chain complex assembly, and cristae integrity regulation. To structurally form and sustain the cristae, the MICOS complex assembles at the cristae junction and binds directly to Sam50. However, the role of Sam50 in overall mitochondrial structure and metabolism in skeletal muscle remains unclear. Here, we use SBF-SEM and Amira software perform 3D renderings of mitochondria and autophagosomes in human myotubes. Beyond this, Gas Chromatography-Mass Spectrometry-based metabolomics was utilized to interrogate differential changes of the metabolites in wild-type (WT) and Sam50 deficient myotubes. Ablation of Sam50 , revealed increases in ß-Alanine, propanoate, and phenylalanine, and tyrosine metabolism. Additionally, we observed that mitochondrial fragmentation and autophagosome formation was increased in Sam50 -deficient myotubes compared to control myotubes. Beyond this, the metabolomic analysis revealed an increase in amino acid metabolism and fatty acid metabolism. XF24 Seahorse Analyzer shows that oxidative capacity is further impaired upon ablation of Sam50 in both murine and human myotubes. Together, these data suggest Sam50 is critical for establishing and maintaining mitochondria, mitochondrial cristae structure, and mitochondrial metabolism.

DOI: https://doi.org/10.1101/2023.05.20.541602
bioRxiv. 2023 May 22. pii: 2023.05.20.541585. [Epub ahead of print]

FAM210A Regulates Mitochondrial Translation and Maintains Cardiac Mitochondrial Homeostasis.

Jiangbin Wu, Kadiam C Venkata Subbaiah, Omar Hedaya, Si Chen, Joshua Munger, Wai Hong Wilson Tang, Chen Yan, Peng Yao.

Aims: Mitochondria play a vital role in cellular metabolism and energetics and support normal cardiac function. Disrupted mitochondrial function and homeostasis cause a variety of heart diseases. Fam210a (family with sequence similarity 210 member A), a novel mitochondrial gene, is identified as a hub gene in mouse cardiac remodeling by multi-omics studies. Human FAM210A mutations are associated with sarcopenia. However, the physiological role and molecular function of FAM210A remain elusive in the heart. We aim to determine the biological role and molecular mechanism of FAM210A in regulating mitochondrial function and cardiac health in vivo .
Methods and Results: Tamoxifen-induced αMHC MCM -driven conditional knockout of Fam210a in the mouse cardiomyocytes induced progressive dilated cardiomyopathy and heart failure, ultimately causing mortality. Fam210a deficient cardiomyocytes exhibit severe mitochondrial morphological disruption and functional decline accompanied by myofilament disarray at the late stage of cardiomyopathy. Furthermore, we observed increased mitochondrial reactive oxygen species production, disturbed mitochondrial membrane potential, and reduced respiratory activity in cardiomyocytes at the early stage before contractile dysfunction and heart failure. Multi-omics analyses indicate that FAM210A deficiency persistently activates integrated stress response (ISR), resulting in transcriptomic, translatomic, proteomic, and metabolomic reprogramming, ultimately leading to pathogenic progression of heart failure. Mechanistically, mitochondrial polysome profiling analysis shows that FAM210A loss of function compromises mitochondrial mRNA translation and leads to reduced mitochondrial encoded proteins, followed by disrupted proteostasis. We observed decreased FAM210A protein expression in human ischemic heart failure and mouse myocardial infarction tissue samples. To further corroborate FAM210A function in the heart, AAV9-mediated overexpression of FAM210A promotes mitochondrial-encoded protein expression, improves cardiac mitochondrial function, and partially rescues murine hearts from cardiac remodeling and damage in ischemia-induced heart failure.
Conclusion: These results suggest that FAM210A is a mitochondrial translation regulator to maintain mitochondrial homeostasis and normal cardiomyocyte contractile function. This study also offers a new therapeutic target for treating ischemic heart disease.
Translational Perspective: Mitochondrial homeostasis is critical for maintaining healthy cardiac function. Disruption of mitochondrial function causes severe cardiomyopathy and heart failure. In the present study, we show that FAM210A is a mitochondrial translation regulator required for maintaining cardiac mitochondrial homeostasis in vivo . Cardiomyocyte-specific FAM210A deficiency leads to mitochondrial dysfunction and spontaneous cardiomyopathy. Moreover, our results indicate that FAM210A is downregulated in human and mouse ischemic heart failure samples and overexpression of FAM210A protects hearts from myocardial infarction induced heart failure, suggesting that FAM210A mediated mitochondrial translation regulatory pathway can be a potential therapeutic target for ischemic heart disease.

DOI: https://doi.org/10.1101/2023.05.20.541585
Glia. 2023 Jun 05.

Expression and subcellular localization of mitochondrial docking protein, syntaphilin, in oligodendrocytes and CNS myelin sheath.

Diane S Nakamura, Jean-David M Gothié, Samantha F Kornfeld, Rashmi Kothary, Timothy E Kennedy.

  Oligodendrocytes produce lipid-rich myelin sheaths that provide metabolic support to the underlying axon and facilitate saltatory conduction. Oligodendrocyte mitochondria supply the bulk of energy and carbon-chain backbones required for lipid synthesis. The sparsity of mitochondria in the myelin sheath suggests that tight regulation of mitochondrial trafficking is crucial for their efficient distribution in the cell. In particular, retention of mitochondria at axoglial junctions would support local lipid synthesis and membrane remodeling during myelination. How mitochondrial docking in oligodendrocytes is regulated is not known. Our findings indicate that syntaphilin (SNPH), a mitochondrial docking protein that has been characterized in neurons, is expressed by oligodendrocyte precursor cells (OPCs) and mature oligodendrocytes in vitro and present in the myelin sheath in vivo. We have previously reported that bath application of netrin-1 promotes the elaboration of myelin basic protein-positive membranes, and that localized presentation of a netrin-1 coated microbead results in rapid accumulation of mitochondria at the site of oligodendrocyte-bead adhesion. Here we show that netrin-1 increases the redistribution of SNPH to oligodendrocyte processes during the expansion of myelin basic protein-positive membranes and that SNPH clusters at the oligodendrocyte plasma membrane at sites of adhesion with netrin-1-coated beads where mitochondria are retained. These findings suggest roles for SNPH in oligodendrocytes regulating netrin-1-mediated mitochondrial docking and myelin membrane expansion.

Keywords:  docking; mitochondria; myelin; netrin; oligodendrocyte; syntaphilin; trafficking

DOI:  https://doi.org/10.1002/glia.24425
ACS Nano. 2023 Jun 08.

Super-Resolution Imaging of Voltages in the Interior of Individual, Vital Mitochondria.

ChiaHung Lee, Douglas C Wallace, Peter J Burke.

  We present the super-resolution microscopy of functional, isolated functional mitochondria, enabling real-time studies of structure and function (voltages) in response to pharmacological manipulation. Changes in mitochondrial membrane potential as a function of time and position can be imaged in different metabolic states (not possible in whole cells), created by the addition of substrates and inhibitors of the electron transport chain, enabled by the isolation of vital mitochondria. By careful analysis of structure dyes and voltage dyes (lipophilic cations), we demonstrate that most of the fluorescent signal seen from voltage dyes is due to membrane bound dyes, and develop a model for the membrane potential dependence of the fluorescence contrast for the case of super-resolution imaging, and how it relates to membrane potential. This permits direct analysis of mitochondrial structure and function (voltage) of isolated, individual mitochondria as well as submitochondrial structures in the functional, intact state, a major advance in super-resolution studies of living organelles.

Keywords:  Voltage; electrophysiology; fluorescent dye; lipid bilayer; metabolism; mitochondria; super-resolution

DOI:  https://doi.org/10.1021/acsnano.3c02768
Front Cell Dev Biol. 2023 ;11 1158604

Loss of cholinergic receptor muscarinic 1 impairs cortical mitochondrial structure and function: implications in Alzheimer's disease.

Mohammad Golam Sabbir, Mamiko Swanson, Benedict C Albensi.

  Introduction: Cholinergic Receptor Muscarinic 1 (CHRM1) is a G protein-coupled acetylcholine (ACh) receptor predominantly expressed in the cerebral cortex. In a retrospective postmortem brain tissues-based study, we demonstrated that severely (≥50% decrease) reduced CHRM1 proteins in the temporal cortex of Alzheimer's patients significantly correlated with poor patient outcomes. The G protein-mediated CHRM1 signal transduction cannot sufficiently explain the mechanistic link between cortical CHRM1 loss and the appearance of hallmark Alzheimer's pathophysiologies, particularly mitochondrial structural and functional abnormalities. Therefore, the objective of this study was to analyze the molecular, ultrastructural, and functional properties of cortical mitochondria using CHRM1 knockout (Chrm1-/-) and wild-type mice to identify mitochondrial abnormalities. Methods: Isolated and enriched cortical mitochondrial fractions derived from wild-type and Chrm1-/- mice were assessed for respiratory deficits (oxygen consumption) following the addition of different substrates. The supramolecular assembly of mitochondrial oxidative phosphorylation (OXPHOS)-associated protein complexes (complex I-V) and cortical mitochondrial ultrastructure were investigated by blue native polyacrylamide gel electrophoresis and transmission electron microscopy (TEM), respectively. A cocktail of antibodies, specific to Ndufb8, Sdhb, Uqcrc2, Mtco1, and Atp5a proteins representing different subunits of complexes I-V, respectively was used to characterize different OXPHOS-associated protein complexes. Results: Loss of Chrm1 led to a significant reduction in cortical mitochondrial respiration (oxygen consumption) concomitantly associated with reduced oligomerization of ATP synthase (complex V) and supramolecular assembly of complexes I-IV (Respirasome). Overexpression of Chrm1 in transformed cells (lacking native Chrm1) significantly increased complex V oligomerization and respirasome assembly leading to enhanced respiration. TEM analysis revealed that Chrm1 loss led to mitochondrial ultrastructural defects and alteration in the tinctorial properties of cortical neurons causing a significant increase in the abundance of dark cortical neurons (Chrm1-/- 85% versus wild-type 2%). Discussion: Our findings indicate a hitherto unknown effect of Chrm1 deletion in cortical neurons affecting mitochondrial function by altering multiple interdependent factors including ATP synthase oligomerization, respirasome assembly, and mitochondrial ultrastructure. The appearance of dark neurons in Chrm1-/- cortices implies potentially enhanced glutamatergic signaling in pyramidal neurons under Chrm1 loss condition. The findings provide novel mechanistic insights into Chrm1 loss with the appearance of mitochondrial pathophysiological deficits in Alzheimer's disease.

Keywords:  ATP synthase; Alzheimer’s disease; cholinergic receptor muscarinic 1; mitochondria; oligomerization; pyramidal neuron; respiration; transmission electron microscopy

DOI:  https://doi.org/10.3389/fcell.2023.1158604
Mitochondrion. 2023 Jun 03. pii: S1567-7249(23)00053-3. [Epub ahead of print]

Megamitochondria plasticity: function transition from adaption to disease.

Yuxing Shang, Zhanghui Li, Peiyang Cai, Wuhao Li, Ye Xu, Yangjing Zhao, Sheng Xia, Qixiang Shao, Hui Wang.

  As the cell's energy factory and metabolic hub, mitochondria are critical for ATP synthesis to maintain cellular function. Mitochondria are highly dynamic organelles that continuously undergo fusion and fission to alter their size, shape, and position, with mitochondrial fusion and fission being interdependent to maintain the balance of mitochondrial morphological changes. However, in response to metabolic and functional damage, mitochondria can grow in size, resulting in a form of abnormal mitochondrial morphology known as megamitochondria. Megamitochondria are characterized by their considerably larger size, pale matrix, and marginal cristae structure and have been observed in various human diseases. In energy-intensive cells like hepatocytes or cardiomyocytes, the pathological process can lead to the growth of megamitochondria, which can further cause metabolic disorders, cell damage and aggravates the progression of the disease. Nonetheless, megamitochondria can also form in response to short-term environmental stimulation as a compensatory mechanism to support cell survival. However, extended stimulation can reverse the benefits of megamitochondria leading to adverse effects. In this review, we will focus on the findings of the different roles of megamitochondria, and their link to disease development to identify promising clinical therapeutic targets.

Keywords:  Megamitochondria; Mitochondria dynamics; Mitochondria morphology

DOI:  https://doi.org/10.1016/j.mito.2023.06.001
Nature. 2023 Jun 07.

A cytosolic surveillance mechanism activates the mitochondrial UPR.

F X Reymond Sutandy, Ines Gößner, Georg Tascher, Christian Münch.

The mitochondrial unfolded protein response (UPRmt) is essential to safeguard mitochondria from proteotoxic damage by activating a dedicated transcriptional response in the nucleus to restore proteostasis1,2. Yet, it remains unclear how the information on mitochondria misfolding stress (MMS) is signalled to the nucleus as part of the human UPRmt (refs. 3,4). Here, we show that UPRmt signalling is driven by the release of two individual signals in the cytosol-mitochondrial reactive oxygen species (mtROS) and accumulation of mitochondrial protein precursors in the cytosol (c-mtProt). Combining proteomics and genetic approaches, we identified that MMS causes the release of mtROS into the cytosol. In parallel, MMS leads to mitochondrial protein import defects causing c-mtProt accumulation. Both signals integrate to activate the UPRmt; released mtROS oxidize the cytosolic HSP40 protein DNAJA1, which leads to enhanced recruitment of cytosolic HSP70 to c-mtProt. Consequently, HSP70 releases HSF1, which translocates to the nucleus and activates transcription of UPRmt genes. Together, we identify a highly controlled cytosolic surveillance mechanism that integrates independent mitochondrial stress signals to initiate the UPRmt. These observations reveal a link between mitochondrial and cytosolic proteostasis and provide molecular insight into UPRmt signalling in human cells.

DOI: https://doi.org/10.1038/s41586-023-06142-0
EMBO Rep. 2023 Jun 06. e57127

Human mitochondrial ADP/ATP carrier SLC25A4 operates with a ping-pong kinetic mechanism.

Camila Cimadamore-Werthein, Stephany Jaiquel Baron, Martin S King, Roger Springett, Edmund Rs Kunji.

  The mitochondrial ADP/ATP carrier (SLC25A4), also called the adenine nucleotide translocase, imports ADP into the mitochondrial matrix and exports ATP, which are key steps in oxidative phosphorylation. Historically, the carrier was thought to form a homodimer and to operate by a sequential kinetic mechanism, which involves the formation of a ternary complex with the two exchanged substrates bound simultaneously. However, recent structural and functional data have demonstrated that the mitochondrial ADP/ATP carrier works as a monomer and has a single substrate binding site, which cannot be reconciled with a sequential kinetic mechanism. Here, we study the kinetic properties of the human mitochondrial ADP/ATP carrier by using proteoliposomes and transport robotics. We show that the Km/Vmax ratio is constant for all of the measured internal concentrations. Thus, in contrast to earlier claims, we conclude that the carrier operates with a ping-pong kinetic mechanism in which substrate exchange across the membrane occurs consecutively rather than simultaneously. These data unite the kinetic and structural models, showing that the carrier operates with an alternating access mechanism.

Keywords:  ADP/ATP translocase; SLC25; adenine nucleotide translocator; bioenergetics; mitochondrial carrier family

DOI:  https://doi.org/10.15252/embr.202357127
bioRxiv. 2023 May 22. pii: 2023.05.22.541833. [Epub ahead of print]

Mitochondrial citrate carrier SLC25A1 is a dosage-dependent regulator of metabolic reprogramming and morphogenesis in the developing heart.

Chiemela Ohanele, Jessica N Peoples, Anja Karlstaedt, Joshua T Geiger, Ashley D Gayle, Nasab Ghazal, Fateemaa Sohani, Milton E Brown, Michael E Davis, George A Porter, Victor Faundez, Jennifer Q Kwong.

The developing mammalian heart undergoes an important metabolic shift from glycolysis toward mitochondrial oxidation, such that oxidative phosphorylation defects may present with cardiac abnormalities. Here, we describe a new mechanistic link between mitochondria and cardiac morphogenesis, uncovered by studying mice with systemic loss of the mitochondrial citrate carrier SLC25A1. Slc25a1 null embryos displayed impaired growth, cardiac malformations, and aberrant mitochondrial function. Importantly, Slc25a1 haploinsufficient embryos, which are overtly indistinguishable from wild type, exhibited an increased frequency of these defects, suggesting Slc25a1 dose-dependent effects. Supporting clinical relevance, we found a near-significant association between ultrarare human pathogenic SLC25A1 variants and pediatric congenital heart disease. Mechanistically, SLC25A1 may link mitochondria to transcriptional regulation of metabolism through epigenetic control of PPARγ to promote metabolic remodeling in the developing heart. Collectively, this work positions SLC25A1 as a novel mitochondrial regulator of ventricular morphogenesis and cardiac metabolic maturation and suggests a role in congenital heart disease.

DOI: https://doi.org/10.1101/2023.05.22.541833
Biochem J. 2023 Jun 15. 480(11): 773-789

Mitochondrial metabolism and dynamics in pancreatic beta cell glucose sensing.

Guy A Rutter, Vaibhav Sidarala, Brett A Kaufman, Scott A Soleimanpour.

  Glucose-regulated insulin secretion becomes defective in all forms of diabetes. The signaling mechanisms through which the sugar acts on the ensemble of beta cells within the islet remain a vigorous area of research after more than 60 years. Here, we focus firstly on the role that the privileged oxidative metabolism of glucose plays in glucose detection, discussing the importance of 'disallowing' in the beta cell the expression of genes including Lactate dehydrogenase (Ldha) and the lactate transporter Mct1/Slc16a1 to restrict other metabolic fates for glucose. We next explore the regulation of mitochondrial metabolism by Ca2+ and its possible role in sustaining glucose signaling towards insulin secretion. Finally, we discuss in depth the importance of mitochondrial structure and dynamics in the beta cell, and their potential for therapeutic targeting by incretin hormones or direct regulators of mitochondrial fusion. This review, and the 2023 Sir Philip Randle Lecture which GAR will give at the Islet Study Group meeting in Vancouver, Canada in June 2023, honor the foundational, and sometimes under-appreciated, contributions made by Professor Randle and his colleagues towards our understanding of the regulation of insulin secretion.

Keywords:  diabetes; glucose homeostasis; hormone secretion; insulin; mitochondria; pancreatic beta cell

DOI:  https://doi.org/10.1042/BCJ20230167
PLoS One. 2023 ;18(6): e0286756

MIC26 and MIC27 are bona fide subunits of the MICOS complex in mitochondria and do not exist as glycosylated apolipoproteins.

Melissa Lubeck, Nick H Derkum, Ritam Naha, Rebecca Strohm, Marc D Driessen, Bengt-Frederik Belgardt, Michael Roden, Kai Stühler, Ruchika Anand, Andreas S Reichert, Arun Kumar Kondadi.

Impairments of mitochondrial functions are linked to human ageing and pathologies such as cancer, cardiomyopathy, neurodegeneration and diabetes. Specifically, aberrations in ultrastructure of mitochondrial inner membrane (IM) and factors regulating them are linked to diabetes. The development of diabetes is connected to the 'Mitochondrial Contact Site and Cristae Organising System' (MICOS) complex which is a large membrane protein complex defining the IM architecture. MIC26 and MIC27 are homologous apolipoproteins of the MICOS complex. MIC26 has been reported as a 22 kDa mitochondrial and a 55 kDa glycosylated and secreted protein. The molecular and functional relationship between these MIC26 isoforms has not been investigated. In order to understand their molecular roles, we depleted MIC26 using siRNA and further generated MIC26 and MIC27 knockouts (KOs) in four different human cell lines. In these KOs, we used four anti-MIC26 antibodies and consistently detected the loss of mitochondrial MIC26 (22 kDa) and MIC27 (30 kDa) but not the loss of intracellular or secreted 55 kDa protein. Thus, the protein assigned earlier as 55 kDa MIC26 is nonspecific. We further excluded the presence of a glycosylated, high-molecular weight MIC27 protein. Next, we probed GFP- and myc-tagged variants of MIC26 with antibodies against GFP and myc respectively. Again, only the mitochondrial versions of these tagged proteins were detected but not the corresponding high-molecular weight MIC26, suggesting that MIC26 is indeed not post-translationally modified. Mutagenesis of predicted glycosylation sites in MIC26 also did not affect the detection of the 55 kDa protein band. Mass spectrometry of a band excised from an SDS gel around 55 kDa could not confirm the presence of any peptides derived from MIC26. Taken together, we conclude that both MIC26 and MIC27 are exclusively localized in mitochondria and that the observed phenotypes reported previously are exclusively due to their mitochondrial function.

DOI: https://doi.org/10.1371/journal.pone.0286756
Dev Cell. 2023 Jun 02. pii: S1534-5807(23)00239-3. [Epub ahead of print]

PLIN5 interacts with FATP4 at membrane contact sites to promote lipid droplet-to-mitochondria fatty acid transport.

Gregory E Miner, Christina M So, Whitney Edwards, Joey V Ragusa, Jonathan T Wine, Daniel Wong Gutierrez, Michael V Airola, Laura E Herring, Rosalind A Coleman, Eric L Klett, Sarah Cohen.

  Cells adjust their metabolism by remodeling membrane contact sites that channel metabolites to different fates. Lipid droplet (LD)-mitochondria contacts change in response to fasting, cold exposure, and exercise. However, their function and mechanism of formation have remained controversial. We focused on perilipin 5 (PLIN5), an LD protein that tethers mitochondria, to probe the function and regulation of LD-mitochondria contacts. We demonstrate that efficient LD-to-mitochondria fatty acid (FA) trafficking and ß-oxidation during starvation of myoblasts are promoted by phosphorylation of PLIN5 and require an intact PLIN5 mitochondrial tethering domain. Using human and murine cells, we further identified the acyl-CoA synthetase, FATP4 (ACSVL4), as a mitochondrial interactor of PLIN5. The C-terminal domains of PLIN5 and FATP4 constitute a minimal protein interaction capable of inducing organelle contacts. Our work suggests that starvation leads to phosphorylation of PLIN5, lipolysis, and subsequent channeling of FAs from LDs to FATP4 on mitochondria for conversion to fatty-acyl-CoAs and subsequent oxidation.

Keywords:  FATP4; PLIN5; acyl-CoA; fatty acids; lipid droplets; membrane contact sites; metabolism; mitochondria; organelles

DOI:  https://doi.org/10.1016/j.devcel.2023.05.006
Sci Rep. 2023 Jun 06. 13(1): 9172

Platelets from patients with myeloproliferative neoplasms have increased numbers of mitochondria that are hypersensitive to depolarization by thrombin.

David M Ross, Hai Po Helena Liang, Zeenet Iqra, Shane Whittaker, Chuen Wen Tan, Brian J Dale, Vivien M Chen.

Thrombosis is one of the cardinal manifestations of myeloproliferative neoplasms (MPN). The mechanisms leading to a prothrombotic state in MPN are complex and remain poorly understood. Platelet mitochondria play a role in platelet activation, but their number and function have not been extensively explored in MPN to date. We observed an increased number of mitochondria in platelets from MPN patients compared with healthy donors. MPN patients had an increased proportion of dysfunctional platelet mitochondria. The fraction of platelets with depolarized mitochondria at rest was increased in essential thrombocythemia (ET) patients and the mitochondria were hypersensitive to depolarization following thrombin agonist stimulation. Live microscopy showed a stochastic process in which a higher proportion of individual ET platelets underwent mitochondrial depolarization and after a shorter agonist exposure compared to healthy donors. Depolarization was immediately followed by ballooning of the platelet membrane, which is a feature of procoagulant platelets. We also noted that the mitochondria of MPN patients were on average located nearer the platelet surface and we observed extrusion of mitochondria from the platelet surface as microparticles. These data implicate platelet mitochondria in a number of prothrombotic phenomena. Further studies are warranted to assess whether these findings correlate with clinical thrombotic events.

DOI: https://doi.org/10.1038/s41598-023-36266-2
PLoS One. 2023 ;18(6): e0285670

High-sensitivity calcium biosensor on the mitochondrial surface reveals that IP3R channels participate in the reticular Ca2+ leak towards mitochondria.

Yves Gouriou, Fabrice Gonnot, Mariam Wehbi, Camille Brun, Ludovic Gomez, Gabriel Bidaux.

Genetically encoded biosensors based on fluorescent proteins (FPs) are widely used to monitor dynamics and sub-cellular spatial distribution of calcium ion (Ca2+) fluxes and their role in intracellular signaling pathways. The development of different mutations in the Ca2+-sensitive elements of the cameleon probes has allowed sensitive range of Ca2+ measurements in almost all cellular compartments. Region of the endoplasmic reticulum (ER) tethered to mitochondria, named as the mitochondrial-associated membranes (MAMs), has received an extended attention since the last 5 years. Indeed, as MAMs are essential for calcium homeostasis and mitochondrial function, molecular tools have been developed to assess quantitatively Ca2+ levels in the MAMs. However, sensitivity of the first generation Ca2+ biosensors on the surface of the outer-mitochondrial membrane (OMM) do not allow to measure μM or sub-μM changes in Ca2+ concentration which prevents to measure the native activity (unstimulated exogenously) of endogenous channels. In this study, we assembled a new ratiometric highly sensitive Ca2+ biosensor expressed on the surface of the outer-mitochondrial membrane (OMM). It allows the detection of smaller differences than the previous biosensor in or at proximity of the MAMs. Noteworthy, we demonstrated that IP3-receptors have an endogenous activity which participate to the Ca2+ leak channel on the surface of the OMM during hypoxia or when SERCA activity is blocked.

DOI: https://doi.org/10.1371/journal.pone.0285670
Front Cell Neurosci. 2023 ;17 1191629

Mitochondrial dysfunctions induce PANoptosis and ferroptosis in cerebral ischemia/reperfusion injury: from pathology to therapeutic potential.

Ruining She, Danhong Liu, Jun Liao, Guozuo Wang, Jinwen Ge, Zhigang Mei.

  Ischemic stroke (IS) accounts for more than 80% of the total stroke, which represents the leading cause of mortality and disability worldwide. Cerebral ischemia/reperfusion injury (CI/RI) is a cascade of pathophysiological events following the restoration of blood flow and reoxygenation, which not only directly damages brain tissue, but also enhances a series of pathological signaling cascades, contributing to inflammation, further aggravate the damage of brain tissue. Paradoxically, there are still no effective methods to prevent CI/RI, since the detailed underlying mechanisms remain vague. Mitochondrial dysfunctions, which are characterized by mitochondrial oxidative stress, Ca2+ overload, iron dyshomeostasis, mitochondrial DNA (mtDNA) defects and mitochondrial quality control (MQC) disruption, are closely relevant to the pathological process of CI/RI. There is increasing evidence that mitochondrial dysfunctions play vital roles in the regulation of programmed cell deaths (PCDs) such as ferroptosis and PANoptosis, a newly proposed conception of cell deaths characterized by a unique form of innate immune inflammatory cell death that regulated by multifaceted PANoptosome complexes. In the present review, we highlight the mechanisms underlying mitochondrial dysfunctions and how this key event contributes to inflammatory response as well as cell death modes during CI/RI. Neuroprotective agents targeting mitochondrial dysfunctions may serve as a promising treatment strategy to alleviate serious secondary brain injuries. A comprehensive insight into mitochondrial dysfunctions-mediated PCDs can help provide more effective strategies to guide therapies of CI/RI in IS.

Keywords:  PANoptosis; PANoptosome; cerebral ischemia/reperfusion injury (CI/RI); ferroptosis; ischemic stroke; mitochondrial dysfunctions

DOI:  https://doi.org/10.3389/fncel.2023.1191629
Front Mol Biosci. 2023 ;10 1223354

Editorial: the role of mitochondrial endoplasmic reticulum contact sites in human health and disease.

Prasanna Katti, Sharifa Love-Rutledge, Sandra A Murray, Antentor Hinton.



Keywords:  MERCs; contact sites; disease; mitochondria; pathology

DOI:  https://doi.org/10.3389/fmolb.2023.1223354
ACS Chem Biol. 2023 Jun 08.

Modulating Copper Reactivity: A New Approach to Reprogram Mitochondrial Retrograde Signaling.

Emmanouil Zacharioudakis.

The crosstalk between mitochondria and the nucleus regulates cell plasticity and innate immune response. A new study shows that copper(II) accumulates in mitochondria of activated macrophages in response to pathogen infection and induces metabolic and epigenetic reprogramming that promotes inflammation. Pharmacologic targeting of mitochondrial copper(II) uncovers a new therapeutic strategy to combat aberrant inflammation and regulate cell plasticity.

DOI: https://doi.org/10.1021/acschembio.3c00298