bims-midtic 2023-07-30 papers

bims-midtic

Biomed News

on Mitochondrial dynamics and trafficking in cells

Issue of 2023–07–30
nineteen papers selected by
Omkar Joshi, Turku Bioscience

The Role of Mitochondrial Dynamics and Mitotic Fission in Regulating the Cell Cycle in Cancer and Pulmonary Arterial Hypertension: Implications for Dynamin-Related Protein 1 and Mitofusin2 in Hyperproliferative Diseases.
Allosteric control of dynamin-related protein 1-catalyzed mitochondrial fission through a conserved disordered C-terminal Short Linear Motif.
Promotion of mitochondrial fragmentation suppresses the formation of mitochondrial spherical compartmentation in PINK1B9Drosophila melanogaster.
PGAM5 is an MFN2 phosphatase that plays an essential role in the regulation of mitochondrial dynamics.
The mitochondrial-endoplasmic reticulum co-transfer in dental pulp stromal cell promotes pulp injury repair.
COPI-regulated mitochondria-ER contact site formation maintains axonal integrity.
Hyper-ubiquitylation of DNA helicase RECQL4 by E3 ligase MITOL prevents mitochondrial entry and potentiates mitophagy.
Deubiquitinase USP16 induces gouty arthritis via Drp1-dependent mitochondrial fission and NLRP3 inflammasome activation.
Structural Analysis of Mitochondria in Cardiomyocytes: Insights into Bioenergetics and Membrane Remodeling.
Current advances of Mitochondrial dysfunction and cardiovascular disease and promising therapeutic strategies.
Nascent mitochondrial proteins initiate the localized condensation of cytosolic protein aggregates on the mitochondrial surface.
Molecular Understanding of ER-MT Communication Dysfunction during Neurodegeneration.
A proximity labeling strategy enables proteomic analysis of inter-organelle membrane contacts.
UBQLN2 and HSP70 participate in Parkin-mediated mitophagy by facilitating outer mitochondrial membrane rupture.
Surface-induced phase separation of reconstituted nascent integrin clusters on lipid membranes.
Mechanism of PGC-1α-mediated mitochondrial biogenesis in cerebral ischemia-reperfusion injury.
Transcriptional Profiles of Mitochondrial Dynamics Markers Are Disturbed in Adrenal Glands of Stressed Adult Male Rats.
Polarized localization of kinesin-1 and RIC-7 drives axonal mitochondria anterograde transport.
4-Oxo-2-nonenal-Induced α-Synuclein Oligomers Interact with Membranes in the Cell, Leading to Mitochondrial Fragmentation.

Cells. 2023 Jul 20. pii: 1897. [Epub ahead of print]12(14):

The Role of Mitochondrial Dynamics and Mitotic Fission in Regulating the Cell Cycle in Cancer and Pulmonary Arterial Hypertension: Implications for Dynamin-Related Protein 1 and Mitofusin2 in Hyperproliferative Diseases.

Pierce Colpman, Asish Dasgupta, Stephen L Archer.

  Mitochondria, which generate ATP through aerobic respiration, also have important noncanonical functions. Mitochondria are dynamic organelles, that engage in fission (division), fusion (joining) and translocation. They also regulate intracellular calcium homeostasis, serve as oxygen-sensors, regulate inflammation, participate in cellular and organellar quality control and regulate the cell cycle. Mitochondrial fission is mediated by the large GTPase, dynamin-related protein 1 (Drp1) which, when activated, translocates to the outer mitochondrial membrane (OMM) where it interacts with binding proteins (Fis1, MFF, MiD49 and MiD51). At a site demarcated by the endoplasmic reticulum, fission proteins create a macromolecular ring that divides the organelle. The functional consequence of fission is contextual. Physiological fission in healthy, nonproliferating cells mediates organellar quality control, eliminating dysfunctional portions of the mitochondria via mitophagy. Pathological fission in somatic cells generates reactive oxygen species and triggers cell death. In dividing cells, Drp1-mediated mitotic fission is critical to cell cycle progression, ensuring that daughter cells receive equitable distribution of mitochondria. Mitochondrial fusion is regulated by the large GTPases mitofusin-1 (Mfn1) and mitofusin-2 (Mfn2), which fuse the OMM, and optic atrophy 1 (OPA-1), which fuses the inner mitochondrial membrane. Mitochondrial fusion mediates complementation, an important mitochondrial quality control mechanism. Fusion also favors oxidative metabolism, intracellular calcium homeostasis and inhibits cell proliferation. Mitochondrial lipids, cardiolipin and phosphatidic acid, also regulate fission and fusion, respectively. Here we review the role of mitochondrial dynamics in health and disease and discuss emerging concepts in the field, such as the role of central versus peripheral fission and the potential role of dynamin 2 (DNM2) as a fission mediator. In hyperproliferative diseases, such as pulmonary arterial hypertension and cancer, Drp1 and its binding partners are upregulated and activated, positing mitochondrial fission as an emerging therapeutic target.

Keywords:  apoptosis; cancer; cardiolipin (CL); dynamin 2 (DNM2); dynamin-related protein 1 (Drp1); mitochondrial dynamics protein of 49 kDa (MiD49); mitochondrial dynamics protein of 51 kDa (MiD51); mitochondrial fission factor (MFF); mitochondrial fission protein 1 (Fis1); mitophagy; mitotic fission; phosphatidic acid (PA); pulmonary arterial hypertension

DOI:  https://doi.org/10.3390/cells12141897
Res Sq. 2023 Jul 14. pii: rs.3.rs-3161608. [Epub ahead of print]

Allosteric control of dynamin-related protein 1-catalyzed mitochondrial fission through a conserved disordered C-terminal Short Linear Motif.

Isabel Pérez-Jover, Kristy Rochon, Di Hu, Pooja Madan Mohan, Isaac Santos-Perez, Julene Ormaetxea Gisasola, Juan Manuel Martinez Galvez, Jon Agirre, Xin Qi, Jason A Mears, Anna V Shnyrova, Rajesh Ramachandran.

The mechanochemical GTPase dynamin-related protein 1 (Drp1) catalyzes mitochondrial fission, but the regulatory mechanisms remain ambiguous. Here we found that a conserved, intrinsically disordered, six-residue S hort Li near M otif at the extreme Drp1 C-terminus, named CT-SLiM, constitutes a critical allosteric site that controls Drp1 structure and function in vitro and in vivo . Extension of the CT-SLiM by non-native residues, or its interaction with the protein partner GIPC-1, constrains Drp1 subunit conformational dynamics, alters self-assembly properties, and limits cooperative GTP hydrolysis, leading to the fission of model membranes in vitro . In vivo , the availability of the native CT-SLiM is a requirement for productive mitochondrial fission, as both non-native extension and deletion of the CT-SLiM severely impair its progression. Thus, contrary to prevailing models, Drp1-catalyzed mitochondrial fission relies on allosteric communication mediated by the CT-SLiM, deceleration of GTPase activity, and coupled changes in subunit architecture and assembly-disassembly dynamics.

DOI: https://doi.org/10.21203/rs.3.rs-3161608/v1
Biochem Biophys Res Commun. 2023 Jul 14. pii: S0006-291X(23)00879-3. [Epub ahead of print]676 48-57

Promotion of mitochondrial fragmentation suppresses the formation of mitochondrial spherical compartmentation in PINK1B9Drosophila melanogaster.

Yi Li, Wen Chen, Danling Wang.

  Mitochondria undergo structural changes reflective of functional statuses. Ultrastructural characterizing of mitochondria is valuable for understanding mitochondrial dysfunction in various pathological conditions. PINK1, a Parkinson's disease (PD) associated gene, plays key roles in maintaining mitochondrial function and integrity. In Drosophila melanogaster, deficiency of PINK1 results in PD-like pathologies due to mitochondrial abnormalities. Here, we report the existence of a new type of mitochondrial-membrane deformity, mitochondrial spherical compartmentation (MSC), caused by PINK1 deficiency in Drosophila. The MSC is a three-dimensional spheroid-like mitochondrial membrane structure encompassing nonselective contents. Upregulation of dDrp1, downregulation of dMarf, and upregulation of dArgK1-A-all resulting in mitochondrial fragmentation-were able to suppress the formation of MSC. Furthermore, arginine kinase, only when localizing to the vicinity of mitochondria, induced mitochondrial fragmentation and reversed the MSC phenotype. In summary, this study demonstrates that loss of dPINK1 leads to the formation of mitochondrial-membrane deformity MSC, which responds to mitochondrial dynamics. In addition, our data suggest a new perspective of how phosphagen energy-buffer system might regulate mitochondrial dynamics.

Keywords:  Arginine kinase; Mitochondrial spherical compartmentation; Mitochondrial-membrane deformity; PINK1; Transmission electron microscopy

DOI:  https://doi.org/10.1016/j.bbrc.2023.07.022
Cell Rep. 2023 Jul 26. pii: S2211-1247(23)00906-3. [Epub ahead of print]42(8): 112895

PGAM5 is an MFN2 phosphatase that plays an essential role in the regulation of mitochondrial dynamics.

Sudeshna Nag, Kaitlin Szederkenyi, Olena Gorbenko, Hannah Tyrrell, Christopher M Yip, G Angus McQuibban.

  Mitochondrial morphology is regulated by the post-translational modifications of the dynamin family GTPase proteins including mitofusin 1 (MFN1), MFN2, and dynamin-related protein 1 (DRP1). Mitochondrial phosphatase phosphoglycerate mutase 5 (PGAM5) is emerging as a regulator of these post-translational modifications; however, its precise role in the regulation of mitochondrial morphology is unknown. We show that PGAM5 interacts with MFN2 and DRP1 in a stress-sensitive manner. PGAM5 regulates MFN2 phosphorylation and consequently protects it from ubiquitination and degradation. Further, phosphorylation and dephosphorylation modification of MFN2 regulates its fusion ability. Phosphorylation enhances fission and degradation, whereas dephosphorylation enhances fusion. PGAM5 dephosphorylates MFN2 to promote mitochondrial network formation. Further, using a Drosophila genetic model, we demonstrate that the MFN2 homolog Marf and dPGAM5 are in the same biological pathway. Our results identify MFN2 dephosphorylation as a regulator of mitochondrial fusion and PGAM5 as an MFN2 phosphatase.

Keywords:  CP: Molecular biology; DRP1; MFN2; PGAM5; mitochondrial morphology

DOI:  https://doi.org/10.1016/j.celrep.2023.112895
Cell Prolif. 2023 Jul 26. e13530

The mitochondrial-endoplasmic reticulum co-transfer in dental pulp stromal cell promotes pulp injury repair.

Xiaoyi Zhang, Chunmeng Wang, Zihao Zhou, Qi Zhang.

Dental pulp injury remains a clinical challenge with limited therapeutic approaches. In the present study, we sought to prove that dental pulp stromal cells (DPSCs) mitochondrial transfer could promote dental pulp injury repair and endoplasmic reticulum (ER)-mitochondrial contacts have a significant regulatory effect on mitochondrial transfer. Healthy DPSCs were co-cultured directly or indirectly with injured DPSCs in the first molar of 1-2 month SD rats or in vitro. Mitochondrial transfer was observed after 24 h of co-culture using fluorescence microscopy and live cell workstation. After co-culture for 1W, 8-OhdG immunofluorescence, mitochondrial membrane potential and total oxidant status/total antioxidant status were used to detect the mitochondrial function of injured DPSCs before and after mitochondrial transfer. Subsequently, mitochondria-ER co-transfer was regulated by modulating mitochondria-ER binding in healthy DPSCs, and the results of GRP78 and CHOP in DPSCs, and PDI immunofluorescence and haematoxylin and eosin staining of pulp tissue were analysed to clarify the effects of modulating mitochondria-ER co-transfer on endoplasmic reticulum stress (ERS), and on pulp injury repair. Fluorescence microscopy and live cell workstation results showed significant mitochondrial transfer between DPSCs. Meanwhile, mitochondrial transfer significantly restored mitochondrial function in injured DPSCs. By modulating mitochondrial-ER binding, the efficiency of mitochondrial transfer between DPSCs was significantly affected and had an impact on ERS in injured cells. Mitochondrial transfer of DPSCs significantly promotes pulpal injury repair and functional recovery of damaged DPSCs, and mitochondrial transfer of DPSCs is regulated by mitochondria-ER binding.

DOI: https://doi.org/10.1111/cpr.13530
Cell Rep. 2023 Jul 26. pii: S2211-1247(23)00894-X. [Epub ahead of print]42(8): 112883

COPI-regulated mitochondria-ER contact site formation maintains axonal integrity.

Daniel C Maddison, Bilal Malik, Leonardo Amadio, Dana M Bis-Brewer, Stephan Züchner, Owen M Peters, Gaynor A Smith.

  Coat protein complex I (COPI) is best known for its role in Golgi-endoplasmic reticulum (ER) trafficking, responsible for the retrograde transport of ER-resident proteins. The ER is crucial to neuronal function, regulating Ca2+ homeostasis and the distribution and function of other organelles such as endosomes, peroxisomes, and mitochondria via functional contact sites. Here we demonstrate that disruption of COPI results in mitochondrial dysfunction in Drosophila axons and human cells. The ER network is also disrupted, and the neurons undergo rapid degeneration. We demonstrate that mitochondria-ER contact sites (MERCS) are decreased in COPI-deficient axons, leading to Ca2+ dysregulation, heightened mitophagy, and a decrease in respiratory capacity. Reintroducing MERCS is sufficient to rescue not only mitochondrial distribution and Ca2+ uptake but also ER morphology, dramatically delaying neurodegeneration. This work demonstrates an important role for COPI-mediated trafficking in MERC formation, which is an essential process for maintaining axonal integrity.

Keywords:  Axon transport; COPI; CP: Cell biology; Calcium homeostasis; Endoplasmic reticulum; Golgi; Mitochondria; Neuronal cell biology; Vesicle trafficking

DOI:  https://doi.org/10.1016/j.celrep.2023.112883
J Biol Chem. 2023 Jul 24. pii: S0021-9258(23)02115-4. [Epub ahead of print] 105087

Hyper-ubiquitylation of DNA helicase RECQL4 by E3 ligase MITOL prevents mitochondrial entry and potentiates mitophagy.

Mansoor Hussain, Aftab Mohammed, Shabnam Saifi, Swati Priya, Sagar Sengupta.

  Mutations in the DNA helicase RECQL4 lead to Rothmund-Thomson Syndrome (RTS), a disorder characterized by mitochondrial dysfunctions, premature aging, and genomic instability. However, the mechanisms by which these mutations lead to pathology are unclear. Here we report that RECQL4 is ubiquitylated by a mitochondrial E3 ligase, MITOL, at two lysine residues (K1101, K1154) via K6 linkage. This ubiquitylation hampers the interaction of RECQL4 with mitochondrial importer Tom20, thereby restricting its own entry into mitochondria. We show the RECQL4 2K mutant (where both K1101 and K1154 are mutated) has increased entry into mitochondria and demonstrates enhanced mtDNA replication. We observed that the three tested RTS patient mutants were unable to enter the mitochondria and showed decreased mtDNA replication. Furthermore, we found that RECQL4 in RTS patient mutants are hyper-ubiquitylated by MITOL and form insoluble aggregate-like structures on the outer mitochondrial surface. However, depletion of MITOL allows RECQL4 expressed in these RTS mutants to enter mitochondria and rescue mtDNA replication. Finally, we show increased accumulation of hyper-ubiquitylated RECQL4 outside the mitochondria leads to the cells being potentiated to increased mitophagy. Hence, we conclude regulating the turnover of RECQL4 by MITOL may have a therapeutic effect in RTS patients.

Keywords:  E3 ligases; RecQ helicases; Rothmund Thomson Syndrome; autophagy; mitochondrial replication

DOI:  https://doi.org/10.1016/j.jbc.2023.105087
Arthritis Res Ther. 2023 Jul 24. 25(1): 126

Deubiquitinase USP16 induces gouty arthritis via Drp1-dependent mitochondrial fission and NLRP3 inflammasome activation.

Qingdong Wang, Hongbin Qiu.

   BACKGROUND: Gouty arthritis is the most frequently diagnosed inflammatory arthritis worldwide. Dynamin-related protein 1 (Drp1), a regulator of mitochondrial fission, contributes to various inflammatory disorders via activating NLRP3 inflammasome. However, the biological role of Drp1 in gouty arthritis remains undefined.
METHODS: A mouse model of monosodium urate (MSU)-induced gouty arthritis and MSU-stimulated macrophages were established as in vivo and in vitro models, respectively. Histological changes were assessed by H&E and IHC analysis. RT-qPCR and western blot were used to detect the expression of Drp1 and the key molecules in joint tissues and macrophages. Cytokine secretion was measured by ELISA assay, and antioxidant enzymes activities and LDH release were monitored using commercial kits. Mitochondrial structure and functions were assessed by transmission electron microscopy (TEM) and MitoSOX staining. Co-IP and GST pull-down assay were used to detect the direct interaction between USP16 and Drp1, as well as the ubiquitination of Drp1.
RESULTS: Drp1 was elevated in MSU-induced gouty arthritis model, and it induced gouty arthritis via NF-κB pathway and NLRP3 inflammasome activation. In addition, Drp1 activated NF-κB/NLRP3 signaling via modulating mitochondrial fission. Mechanistically, USP16 mediated deubiquitination and stabilization of Drp1 through its direct interaction with Drp1. Functional studies further showed that USP16 was highly expressed in MSU-stimulated macrophages and induced gouty arthritis via Drp1-dependent NLRP3 inflammasome activation.
CONCLUSION: Deubiquitinase USP16 induced gouty arthritis via Drp1-dependent mitochondrial fission and NF-κB/NLRP3 signaling.

Keywords:  Drp1; Gouty arthritis; Mitochondrial fission; NF-κB; NLRP3; USP16

DOI:  https://doi.org/10.1186/s13075-023-03095-7
Curr Issues Mol Biol. 2023 Jul 21. 45(7): 6097-6115

Structural Analysis of Mitochondria in Cardiomyocytes: Insights into Bioenergetics and Membrane Remodeling.

Raquel A Adams, Zheng Liu, Chongere Hsieh, Michael Marko, W Jonathan Lederer, M Saleet Jafri, Carmen Mannella.

  Mitochondria in mammalian cardiomyocytes display considerable structural heterogeneity, the significance of which is not currently understood. We use electron microscopic tomography to analyze a dataset of 68 mitochondrial subvolumes to look for correlations among mitochondrial size and shape, crista morphology and membrane density, and organelle location within rat cardiac myocytes. A tomographic analysis guided the definition of four classes of crista morphology: lamellar, tubular, mixed and transitional, the last associated with remodeling between lamellar and tubular cristae. Correlations include an apparent bias for mitochondria with lamellar cristae to be located in the regions between myofibrils and a two-fold larger crista membrane density in mitochondria with lamellar cristae relative to mitochondria with tubular cristae. The examination of individual cristae inside mitochondria reveals local variations in crista topology, such as extent of branching, alignment of fenestrations and progressive changes in membrane morphology and packing density. The findings suggest both a rationale for the interfibrillar location of lamellar mitochondria and a pathway for crista remodeling from lamellar to tubular morphology.

Keywords:  cardiomyocytes; cristae; electron microscopy; electron tomography; membrane remodeling; mitochondria; myofibrils

DOI:  https://doi.org/10.3390/cimb45070385
Am J Pathol. 2023 Jul 20. pii: S0002-9440(23)00245-6. [Epub ahead of print]

Current advances of Mitochondrial dysfunction and cardiovascular disease and promising therapeutic strategies.

Dexiang Xia, Yue Liu, Peng Wu, Dangheng Wei.

  Mitochondria are "cellular power stations" and essential organelles for maintaining cellular homeostasis. Dysfunctional mitochondria have emerged as a key factor in the occurrence and development of cardiovascular disease. This review focuses on the advances in the relationship between mitochondrial dysfunction and cardiovascular diseases such as atherosclerosis, heart failure, myocardial ischemia reperfusion injury, and pulmonary arterial hypertension. Moreover, the clinical value and challenges of mitochondria-targeted strategies, including mitochondria-targeted antioxidants, mitochondrial quality control modulators, mitochondrial function protectors, mitochondrial biogenesis promoters, and recently developed mitochondrial transplants, are also discussed.

Keywords:  Cardiovascular disease; Mitochondrial dysfunction; Therapeutics

DOI:  https://doi.org/10.1016/j.ajpath.2023.06.013
Proc Natl Acad Sci U S A. 2023 08;120(31): e2300475120

Nascent mitochondrial proteins initiate the localized condensation of cytosolic protein aggregates on the mitochondrial surface.

Qingqing Liu, Benjamin Fong, Seungmin Yoo, Jay R Unruh, Fengli Guo, Zulin Yu, Jingjing Chen, Kausik Si, Rong Li, Chuankai Zhou.

  Eukaryotes organize cellular contents into membrane-bound organelles and membrane-less condensates, for example, protein aggregates. An unsolved question is why the ubiquitously distributed proteins throughout the cytosol give rise to spatially localized protein aggregates on the organellar surface, like mitochondria. We report that the mitochondrial import receptor Tom70 is involved in the localized condensation of protein aggregates in budding yeast and human cells. This is because misfolded cytosolic proteins do not autonomously aggregate in vivo; instead, they are recruited to the condensation sites initiated by Tom70's substrates (nascent mitochondrial proteins) on the organellar membrane using multivalent hydrophobic interactions. Knocking out Tom70 partially impairs, while overexpressing Tom70 increases the formation and association between cytosolic protein aggregates and mitochondria. In addition, ectopic targeting Tom70 and its substrates to the vacuole surface is able to redirect the localized aggregation from mitochondria to the vacuolar surface. Although other redundant mechanisms may exist, this nascent mitochondrial proteins-based initiation of protein aggregation likely explains the localized condensation of otherwise ubiquitously distributed molecules on the mitochondria. Disrupting the mitochondrial association of aggregates impairs their asymmetric retention during mitosis and reduces the mitochondrial import of misfolded proteins, suggesting a proteostasis role of the organelle-condensate interactions.

Keywords:  condensate; mitochondria; protein aggregation

DOI:  https://doi.org/10.1073/pnas.2300475120
Mitochondrion. 2023 Jul 24. pii: S1567-7249(23)00068-5. [Epub ahead of print]

Molecular Understanding of ER-MT Communication Dysfunction during Neurodegeneration.

Shivkumar S Sammeta, Trupti A Banarase, Sandip R Rahangdale, Nitu L Wankhede, Manish M Aglawe, Brijesh G Taksande, Shubhada V Mangrulkar, Aman B Upaganlawar, Sushruta Koppula, Spandana Rajendra Kopalli, Milind J Umekar, Mayur B Kale.

  Biological researchers are seeing organelles in a new light. These cellular entities have been believed to be singular and distinctive structures that performed specialized purposes for a very long time. But in recentpast years, scientists have learned that organelles become dynamic and make physical contact. Additionally, Biological processes are regulated by organelles interactions and its alteration play an important role in cell malfunctioning and several pathologies, including neurodegenerative diseases. Mitochondrial-ER contact sites (MERCS) have received considerable attention in the domain of cell homeostasis and dysfunction, specifically in the area of neurodegeneration. This is largely due to the significant role of this subcellular compartment in a diverse array of vital cellular functions, including Ca2+ homeostasis, transport, bioenergetics and turnover, mitochondrial dynamics, apoptotic signaling, ER stress, and inflammation. A significant number of disease-associated proteins were found to physically interact with the ER-Mitochondria (ER-MT) interface, causing structural and/or functional alterations in this compartment. In this review, we summarize current knowledge about the structure and functions of the ER-MT contact sites, as well as the possible repercussions of their alteration in notable neurodegenerative disorders such as Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, and fronto-temporal dementia. The constraints and complexities in defining the nature and origin of the highlighted defects in ER-MT communication, as well as their concise contribution to the neurodegenerative process, are illustrated in particular. The possibility of using MERCS as a potential drug target to prevent neuronal damage and ultimately neurodegeneration is the topic of our final discussion.

Keywords:  Alzheimer’s disease; Amyotrophic lateral sclerosis; Mitochondria–ER contact sites (MERCS); Parkinson’s disease; mitochondria–ER-associated membrane (MAM); neurodegeneration

DOI:  https://doi.org/10.1016/j.mito.2023.07.005
iScience. 2023 Jul 21. 26(7): 107159

A proximity labeling strategy enables proteomic analysis of inter-organelle membrane contacts.

Maoge Zhou, Bingjie Kong, Xiang Zhang, Ke Xiao, Jing Lu, Weixing Li, Min Li, Zonghong Li, Wei Ji, Junjie Hou, Tao Xu.

  Inter-organelle membrane contacts are highly dynamic and act as central hubs for many biological processes, but the protein compositions remain largely unknown due to the lack of efficient tools. Here, we developed BiFCPL to analyze the contact proteome in living cells by a bimolecular fluorescence complementation (BiFC)-based proximity labeling (PL) strategy. BiFCPL was applied to study mitochondria-endoplasmic reticulum contacts (MERCs) and mitochondria-lipid droplet (LD) contacts. We identified 403 highly confident MERC proteins, including many transiently resident proteins and potential tethers. Moreover, we demonstrated that mitochondria-LD contacts are sensitive to nutrient status. A comparative proteomic analysis revealed that 60 proteins are up- or downregulated at contact sites under metabolic challenge. We verified that SQLE, an enzyme for cholesterol synthesis, accumulates at mitochondria-LD contact sites probably to utilize local ATP for cholesterol synthesis. This work provides an efficient method to identify key proteins at inter-organelle membrane contacts in living cells.

Keywords:  Biophysics; Membranes; Proteomics

DOI:  https://doi.org/10.1016/j.isci.2023.107159
EMBO Rep. 2023 Jul 28. e55859

UBQLN2 and HSP70 participate in Parkin-mediated mitophagy by facilitating outer mitochondrial membrane rupture.

Qilian Ma, Jiaqi Xin, Qiang Peng, Ningning Li, Shan Sun, Hongyu Hou, Guoqiang Ma, Nana Wang, Li Zhang, Kin Yip Tam, Heiko Dussmann, Jochen Hm Prehn, Hongfeng Wang, Zheng Ying.

  Amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) are two aging-related neurodegenerative diseases that share common key features, including aggregation of pathogenic proteins, dysfunction of mitochondria, and impairment of autophagy. Mutations in ubiquilin 2 (UBQLN2), a shuttle protein in the ubiquitin-proteasome system (UPS), can cause ALS/FTD, but the mechanism underlying UBQLN2-mediated pathogenesis is still uncertain. Recent studies indicate that mitophagy, a selective form of autophagy which is crucial for mitochondrial quality control, is tightly associated with neurodegenerative diseases including Alzheimer's disease, Parkinson's disease, and ALS. In this study, we show that after Parkin-dependent ubiquitination of damaged mitochondria, UBQLN2 is recruited to poly-ubiquitinated mitochondria through the UBA domain. UBQLN2 cooperates with the chaperone HSP70 to promote UPS-driven degradation of outer mitochondrial membrane (OMM) proteins. The resulting rupture of the OMM triggers the autophagosomal recognition of the inner mitochondrial membrane receptor PHB2. UBQLN2 is required for Parkin-mediated mitophagy and neuronal survival upon mitochondrial damage, and the ALS/FTD pathogenic mutations in UBQLN2 impair mitophagy in primary cultured neurons. Taken together, our findings link dysfunctional mitophagy to UBQLN2-mediated neurodegeneration.

Keywords:  ALS; Parkin; UBQLN2; mitophagy; ubiquitin

DOI:  https://doi.org/10.15252/embr.202255859
Proc Natl Acad Sci U S A. 2023 08;120(31): e2301881120

Surface-induced phase separation of reconstituted nascent integrin clusters on lipid membranes.

Chiao-Peng Hsu, Jonas Aretz, Arsenii Hordeichyk, Reinhard Fässler, Andreas R Bausch.

  Integrin adhesion complexes are essential membrane-associated cellular compartments for metazoan life. The formation of initial integrin adhesion complexes is a dynamic process involving focal adhesion proteins assembled at the integrin cytoplasmic tails and the inner leaflet of the plasma membrane. The weak multivalent protein interactions within the complex and with the plasma membrane suggest that liquid-liquid phase separation could play a role in the nascent adhesion assembly. Here, we report that solid-supported lipid membranes supplemented with phosphoinositides induce the phase separation of minimal integrin adhesion condensates composed of integrin β1 tails, kindlin, talin, paxillin, and FAK at physiological ionic strengths and protein concentrations. We show that the presence of phosphoinositides is key to enriching kindlin and talin on the lipid membrane, which is necessary to further induce the phase separation of paxillin and FAK at the membrane. Our data demonstrate that lipid membrane surfaces set the local solvent conditions for steering the membrane-localized phase separation even in a regime where no condensate formation of proteins occurs in bulk solution.

Keywords:  integrin; membrane; phase separation; surface

DOI:  https://doi.org/10.1073/pnas.2301881120
Front Mol Neurosci. 2023 ;16 1224964

Mechanism of PGC-1α-mediated mitochondrial biogenesis in cerebral ischemia-reperfusion injury.

Ying Yuan, Yuan Tian, Hui Jiang, Luo-Yang Cai, Jie Song, Rui Peng, Xiao-Ming Zhang.

  Cerebral ischemia-reperfusion injury (CIRI) is a series of cascade reactions that occur after blood flow recanalization in the ischemic zone in patients with cerebral infarction, causing an imbalance in intracellular homeostasis through multiple pathologies such as increased oxygen free radicals, inflammatory response, calcium overload, and impaired energy metabolism, leading to mitochondrial dysfunction and ultimately apoptosis. Rescue of reversibly damaged neurons in the ischemic hemispheric zone is the key to saving brain infarction and reducing neurological deficits. Complex and active neurological functions are highly dependent on an adequate energy supply from mitochondria. Mitochondrial biogenesis (MB), a process that generates new functional mitochondria and restores normal mitochondrial function by replacing damaged mitochondria, is a major mechanism for maintaining intra-mitochondrial homeostasis and is involved in mitochondrial quality control to ameliorate mitochondrial dysfunction and thus protects against CIRI. The main regulator of MB is peroxisome proliferator-activated receptor gamma coactivator-1α (PGC-1α), which improves mitochondrial function to protect against CIRI by activating its downstream nuclear respiratory factor 1 (NRF1) and mitochondrial transcription factor A (TFAM) to promote mitochondrial genome replication and transcription. This paper provides a theoretical reference for the treatment of neurological impairment caused by CIRI by discussing the mechanisms of mitochondrial biogenesis during cerebral ischemia-reperfusion injury.

Keywords:  PGC-1α; apoptosis; cerebral ischemia–reperfusion injury; mitochondria; mitochondrial biogenesis

DOI:  https://doi.org/10.3389/fnmol.2023.1224964
Life (Basel). 2023 Jun 27. pii: 1457. [Epub ahead of print]13(7):

Transcriptional Profiles of Mitochondrial Dynamics Markers Are Disturbed in Adrenal Glands of Stressed Adult Male Rats.

Isidora M Keselj, Filip N Bozic, Miodrag M Vucinic, Dusan Lalosevic, Tatjana S Kostic, Silvana A Andric.

  Mitochondrial dynamics plays a significant role in shaping the mitochondrial network and maintaining mitochondrial function. Imbalanced mitochondrial dynamics can cause mitochondrial dysfunction leading to a wide range of diseases/disorders. The aim of this study was to investigate the expression of mitochondrial dynamics markers and regulatory molecules in whole adrenal glands, cortices, and medullae obtained from adult male rats exposed to acute and repeated psychophysical stress, the most common stress in human society. The transcriptional profiles of most of the mitochondrial dynamics markers investigated here were altered: 81%-(17/21) in the whole adrenal gland, 76.2%-(16/21) in the adrenal cortex, and 85.7%-(18/21) in the adrenal medulla. Changes were evident in representatives of every process of mitochondrial dynamics. Markers of mitobiogenesis were changed up to 62.5%-(5/8) in the whole adrenal gland, 62.5%-(5/8) in the adrenal cortex, and 87.5%-(7/8) in the adrenal medulla. Markers of mitofusion were changed up to 100%-(3/3) in the whole adrenal gland, 66.7%-(5/8) in the adrenal cortex, and 87.5%-(7/8) in the adrenal medulla, while all markers of mitofission and mitophagy were changed in the adrenal glands. Moreover, almost all markers of mitochondrial functionality were changed: 83.3%-(5/6) in the whole adrenal, 83.3%-(5/6) in the cortex, 66.7%-(4/6) in the medulla. Accordingly, the study highlights the significant impact of acute and repeated stress on mitochondrial dynamics in the adrenal gland.

Keywords:  DRP1; FIS1; MFN1/2; OPA1; PGC1; PPARa; PPARd; adrenal gland; mitochondrial dynamics markers; stress

DOI:  https://doi.org/10.3390/life13071457
bioRxiv. 2023 Jul 12. pii: 2023.07.12.548706. [Epub ahead of print]

Polarized localization of kinesin-1 and RIC-7 drives axonal mitochondria anterograde transport.

Youjun Wu, Chen Ding, Alexis Weinreb, Laura Manning, Grace Swaim, Shaul Yogev, Daniel A Colón-Ramos, Marc Hammarlund.

Mitochondria transport is crucial for mitochondria distribution in axons and is mediated by kinesin-1-based anterograde and dynein-based retrograde motor complexes. While Miro and Milton/TRAK were identified as key adaptors between mitochondria and kinesin-1, recent studies suggest the presence of additional mechanisms. In C. elegans , ric-7 is the only single gene described so far, other than kinesin-1, that is absolutely required for axonal mitochondria localization. Using CRISPR engineering in C. elegans , we find that Miro is important but is not essential for anterograde traffic, whereas it is required for retrograde traffic. Both the endogenous RIC-7 and kinesin-1 act at the leading end to transport mitochondria anterogradely. RIC-7 recruitment to mitochondria requires its N-terminal domain and partially relies on MIRO-1, whereas RIC-7 accumulation at the leading end depends on its disordered region, kinesin-1 and metaxin2. We conclude that polarized transport complexes containing kinesin-1 and RIC-7 form at the leading edge of mitochondria, and that these complexes are required for anterograde axonal transport.
Summary statement: Anterograde transport of axonal mitochondria is critical for maintenance of the mitochondria pool and neuronal health. Wu et al. show that the endogenous kinesin-1 and RIC-7 localize at the leading end of mitochondria to drive axonal anterograde transport in vivo .

DOI: https://doi.org/10.1101/2023.07.12.548706
Biochemistry. 2023 Jul 24.

4-Oxo-2-nonenal-Induced α-Synuclein Oligomers Interact with Membranes in the Cell, Leading to Mitochondrial Fragmentation.

Camilla B Andersen, Astrid K Lausdahl, Janni Nielsen, Mathias P Clausen, Frans A A Mulder, Daniel E Otzen, Eva C Arnspang.

Oxidative stress and formation of cytotoxic oligomers by the natively unfolded protein α-synuclein (α-syn) are both connected to the development of Parkinson's disease. This effect has been linked to lipid peroxidation and membrane disruption, but the specific mechanisms behind these phenomena remain unclear. To address this, we have prepared α-syn oligomers (αSOs) in vitro in the presence of the lipid peroxidation product 4-oxo-2-nonenal and investigated their interaction with live cells using in-cell NMR as well as stimulated emission depletion (STED) super-resolution and confocal microscopy. We find that the αSOs interact strongly with organellar components, leading to strong immobilization of the protein's otherwise flexible C-terminus. STED microscopy reveals that the oligomers localize to small circular structures inside the cell, while confocal microscopy shows mitochondrial fragmentation and association with both late endosome and retromer complex before the SOs interact with mitochondria. Our study provides direct evidence for close contact between cytotoxic α-syn aggregates and membraneous compartments in the cell.

DOI: https://doi.org/10.1021/acs.biochem.3c00114