bims-midtic 2023-10-22 papers

bims-midtic

Biomed News

on Mitochondrial dynamics and trafficking in cells

Issue of 2023–10–22
sixteen papers selected by
Omkar Joshi, Turku Bioscience

Control of mitochondrial dynamics by a fusogenic lipid.
MERCI Predicts Mitochondrial Transfer from T Cells to Tumor Cells.
SIRT4 is a regulator of human skeletal muscle fatty acid metabolism influencing inner and outer mitochondrial-mediated fusion.
Mitochondria-lysosome-related organelles mediate mitochondrial clearance during cellular dedifferentiation.
Fibrocystin/Polyductin releases a C-terminal fragment that translocates into mitochondria and suppresses cystogenesis.
A PINK1 input threshold arises from positive feedback in the PINK1/Parkin mitophagy decision circuit.
GLIS1 alleviates cell senescence and renal fibrosis through PGC1-α mediated mitochondrial quality control in kidney aging.
Novel functions of the ER-located Hsp40s DNAJB12 and DNAJB14 on proteins at the outer mitochondrial membrane under stress mediated by CCCP.
Mitochondrial OPA1 deficiency is associated to reversible defects in spatial memory related to adult neurogenesis in mice.
Mitochondrial transplantation attenuates traumatic neuropathic pain, neuroinflammation, and apoptosis in rats with nerve root ligation.
Vitamin E succinate mediated apoptosis by juxtaposing endoplasmic reticulum and mitochondria.
Mitophagy in neurodegenerative disease pathogenesis.
Organelles are miscommunicating: Membrane contact sites getting hijacked by pathogens.
Mitochondrial Dynamics of Bcl-2 Family Proteins during 17-β-Estradiol-Induced Apoptosis Correlate with the Malignancy of Endometrial Cancer Cells.
Long-term super-resolution inner mitochondrial membrane imaging with a lipid probe.
Molecular mechanism of glutaminase activation through filamentation and the role of filaments in mitophagy protection.

Trends Cell Biol. 2023 Oct 17. pii: S0962-8924(23)00210-6. [Epub ahead of print]

Control of mitochondrial dynamics by a fusogenic lipid.

Zheng Yang, David C Chan.

  Mitochondrial fusion enables cooperation between the mitochondrial population and is critical for mitochondrial function. Phosphatidic acid (PA) on the mitochondrial surface has a key role in mitochondrial fusion. A recent study by Su et al. shows that the nucleoside diphosphate (NDP) kinase NME3 recognizes PA and mediates its effects on mitochondrial dynamics.

Keywords:  membrane fusion; mitochondria; organelle; phospholipid

DOI:  https://doi.org/10.1016/j.tcb.2023.10.006
Cancer Discov. 2023 Oct 20. OF1

MERCI Predicts Mitochondrial Transfer from T Cells to Tumor Cells.

The developed single-cell method MERCI predicts mitochondrial trafficking between tumor and T cells.

DOI: https://doi.org/10.1158/2159-8290.CD-RW2023-168
Cell Signal. 2023 Oct 17. pii: S0898-6568(23)00346-7. [Epub ahead of print] 110931

SIRT4 is a regulator of human skeletal muscle fatty acid metabolism influencing inner and outer mitochondrial-mediated fusion.

John Noone, Keith D Rochfort, Finbarr O'Sullivan, Donal J O'Gorman.

   OBJECTIVE: The mitochondrial phenotype, governed by the balance of fusion-fission, is a key determinant of energy metabolism. The inner and outer mitochondrial membrane (IMM) fusion proteins optic atrophy 1 (OPA1) and Mitofusin 1 and 2 (Mfn1/2) play an important role in this process. Recent evidence also shows that Sirtuin 4 (SIRT4), located within the mitochondria, is involved in the regulation of fatty acid oxidation. The purpose of this study was to determine if SIRT4 expression regulates inner and outer mitochondrial-mediated fusion and substrate utilization within differentiated human skeletal muscle cells (HSkMC).
MATERIAL AND METHODS: SIRT4 expression was knocked down using small interfering RNA (siRNA) transfection in differentiated HSkMC. Following knockdown, mitochondrial respiration was determined by high-resolution respirometry (HRR) using the Oroboros Oxygraph O2k. Live cell confocal microscopy, quantified using the Mitochondrial Network Analysis (MiNA) toolset, was used to examine mitochondrial morphological change. This was further examined through the measurement of key metabolic and mitochondrial morphological regulators (mRNA and protein) induced by knockdown.
RESULTS: SIRT4 knockdown resulted in a significant decrease in LEAK respiration, potentially explained by a decrease in ANT1 protein expression. Knockdown further increased oxidative phosphorylation and protein expression of key regulators of fatty acid metabolism. Quantitative analysis of live confocal imaging of fluorescently labelled mitochondria following SIRT4 knockdown supported the role SIRT4 plays in the regulation of mitochondrial morphology, as emphasized by an increase in mitochondrial network branches and junctions. Measurement of key regulators of mitochondrial dynamics illustrated a significant increase in mitochondrial fusion proteins Mfn1, OPA1 respectively, indicative of an increase in mitochondrial size.
CONCLUSIONS: This study provides evidence of a direct relationship between the mitochondrial phenotype and substrate oxidation in HSkMC. We identify SIRT4 as a key protagonist of energy metabolism via its regulation of IMM and OMM fusion proteins, OPA1 and Mfn1. SIRT4 knockdown increases mitochondrial capacity to oxidize fatty acids, decreasing LEAK respiration and further increasing mitochondrial elongation via its regulation of mitochondrial fusion.

Keywords:  Metabolism; Mitochondrial dynamics; Mitochondrial function; OPA1; Sirtuin; Skeletal muscle

DOI:  https://doi.org/10.1016/j.cellsig.2023.110931
Cell Rep. 2023 Oct 19. pii: S2211-1247(23)01303-7. [Epub ahead of print]42(10): 113291

Mitochondria-lysosome-related organelles mediate mitochondrial clearance during cellular dedifferentiation.

Xiaowen Ma, Sharon Manley, Hui Qian, Yuan Li, Chen Zhang, Kevin Li, Benjamin Ding, Fengli Guo, Allen Chen, Xing Zhang, Meilian Liu, Meihua Hao, Benjamin Kugler, E Matthew Morris, John Thyfault, Ling Yang, Hiromi Sesaki, Hong-Min Ni, Heidi McBride, Wen-Xing Ding.

  Dysfunctional mitochondria are removed via multiple pathways, such as mitophagy, a selective autophagy process. Here, we identify an intracellular hybrid mitochondria-lysosome organelle (termed the mitochondria-lysosome-related organelle [MLRO]), which regulates mitochondrial homeostasis independent of canonical mitophagy during hepatocyte dedifferentiation. The MLRO is an electron-dense organelle that has either a single or double membrane with both mitochondria and lysosome markers. Mechanistically, the MLRO is likely formed from the fusion of mitochondria-derived vesicles (MDVs) with lysosomes through a PARKIN-, ATG5-, and DRP1-independent process, which is negatively regulated by transcription factor EB (TFEB) and associated with mitochondrial protein degradation and hepatocyte dedifferentiation. The MLRO, which is galectin-3 positive, is reminiscent of damaged lysosome and could be cleared by overexpression of TFEB, resulting in attenuation of hepatocyte dedifferentiation. Together, results from this study suggest that the MLRO may act as an alternative mechanism for mitochondrial quality control independent of canonical autophagy/mitophagy involved in cell dedifferentiation.

Keywords:  ATG5; CP: Cell biology; DRP1; autophagy; hepatocytes; lysosome; mitophagy

DOI:  https://doi.org/10.1016/j.celrep.2023.113291
Nat Commun. 2023 Oct 16. 14(1): 6513

Fibrocystin/Polyductin releases a C-terminal fragment that translocates into mitochondria and suppresses cystogenesis.

Rebecca V Walker, Qin Yao, Hangxue Xu, Anthony Maranto, Kristen F Swaney, Sreekumar Ramachandran, Rong Li, Laura Cassina, Brian M Polster, Patricia Outeda, Alessandra Boletta, Terry Watnick, Feng Qian.

Fibrocystin/Polyductin (FPC), encoded by PKHD1, is associated with autosomal recessive polycystic kidney disease (ARPKD), yet its precise role in cystogenesis remains unclear. Here we show that FPC undergoes complex proteolytic processing in developing kidneys, generating three soluble C-terminal fragments (ICDs). Notably, ICD15, contains a novel mitochondrial targeting sequence at its N-terminus, facilitating its translocation into mitochondria. This enhances mitochondrial respiration in renal epithelial cells, partially restoring impaired mitochondrial function caused by FPC loss. FPC inactivation leads to abnormal ultrastructural morphology of mitochondria in kidney tubules without cyst formation. Moreover, FPC inactivation significantly exacerbates renal cystogenesis and triggers severe pancreatic cystogenesis in a Pkd1 mouse mutant Pkd1V/V in which cleavage of Pkd1-encoded Polycystin-1 at the GPCR Proteolysis Site is blocked. Deleting ICD15 enhances renal cystogenesis without inducing pancreatic cysts in Pkd1V/V mice. These findings reveal a direct link between FPC and a mitochondrial pathway through ICD15 cleavage, crucial for cystogenesis mechanisms.

DOI: https://doi.org/10.1038/s41467-023-42196-4
Cell Rep. 2023 Oct 17. pii: S2211-1247(23)01272-X. [Epub ahead of print]42(10): 113260

A PINK1 input threshold arises from positive feedback in the PINK1/Parkin mitophagy decision circuit.

Christopher S Waters, Sigurd B Angenent, Steven J Altschuler, Lani F Wu.

  Mechanisms that prevent accidental activation of the PINK1/Parkin mitophagy circuit on healthy mitochondria are poorly understood. On the surface of damaged mitochondria, PINK1 accumulates and acts as the input signal to a positive feedback loop of Parkin recruitment, which in turn promotes mitochondrial degradation via mitophagy. However, PINK1 is also present on healthy mitochondria, where it could errantly recruit Parkin and thereby activate this positive feedback loop. Here, we explore emergent properties of the PINK1/Parkin circuit by quantifying the relationship between mitochondrial PINK1 concentrations and Parkin recruitment dynamics. We find that Parkin is recruited to mitochondria only if PINK1 levels exceed a threshold and then only after a delay that is inversely proportional to PINK1 levels. Furthermore, these two regulatory properties arise from the input-coupled positive feedback topology of the PINK1/Parkin circuit. These results outline an intrinsic mechanism by which the PINK1/Parkin circuit can avoid errant activation on healthy mitochondria.

Keywords:  CP: Molecular biology; PINK1; Parkin; circuit; delay; mathematical model; mitophagy decision; quantitative microscopy; synthetic biology; systems biology; threshold

DOI:  https://doi.org/10.1016/j.celrep.2023.113260
Free Radic Biol Med. 2023 Oct 16. pii: S0891-5849(23)00662-7. [Epub ahead of print]

GLIS1 alleviates cell senescence and renal fibrosis through PGC1-α mediated mitochondrial quality control in kidney aging.

Li Xu, Jiao Wang, Hongyuan Yu, Hang Mei, Ping He, Min Wang, Yue Liu, Qiuling Fan, Ying Chen, Yanqiu Li, Fan Liu.

  Mitochondrial dysfunction is implied as a crucial factor in age-related chronic kidney disease. It is confirmed that Gli-like transcription factor 1 (GLIS1) is involved in age-related renal fibrosis, however, the correlation between mitochondrial disturbances and GLIS1-driven kidney aging are not clearly clarified. Thus, we investigated the regulatory mechanism of GLIS1 in the homeostasis of mitochondrial quality control both in vivo and in vitro. The lower expression of GLIS1 was identified in natural and accelerated kidney aged models, accompanied by the dysfunctions of mitochondrial quality control, including enhanced mitochondrial fission, reduced mitochondrial biogenesis and mitophagy, whereas, GLIS1 could maintain mitochondrial stability by interacting with peroxisome proliferator-activated receptor γ coactivator-1α (PGC1-α). Additionally, the over-expressed GLIS1 inhibited extracellular matrix accumulation and alleviated renal fibrosis while siGLIS1 inhibited PGC1-α transcription, as well as affecting its mitochondria-protective functions. Collectively, we demonstrated that GLIS1 mediated mitochondrial quality control through targeting PGC1-α in kidney aging, which might be a promising therapeutic target for attenuating cell senescence and age-related renal fibrosis.

Keywords:  GLIS1; Kidney aging; Mitochondrial quality control; PGC1-α; Renal fibrosis

DOI:  https://doi.org/10.1016/j.freeradbiomed.2023.09.037
Mol Cell Biochem. 2023 Oct 18.

Novel functions of the ER-located Hsp40s DNAJB12 and DNAJB14 on proteins at the outer mitochondrial membrane under stress mediated by CCCP.

Pattarawut Sopha, Tirawit Meerod, Bunkuea Chantrathonkul, Nadgrita Phutubtim, Douglas M Cyr, Piyarat Govitrapong.

  The endoplasmic reticulum (ER) membrane provides infrastructure for intracellular signaling, protein degradation, and communication among the ER lumen, cytosol, and nucleus via transmembrane and membrane-associated proteins. Failure to maintain homeostasis at the ER leads to deleterious conditions in humans, such as protein misfolding-related diseases and neurodegeneration. The ER transmembrane heat shock protein 40 (Hsp40) proteins, including DNAJB12 (JB12) and DNAJB14 (JB14), have been studied for their importance in multiple aspects of cellular events, including degradation of misfolded membrane proteins, proteasome-mediated control of proapoptotic Bcl-2 members, and assembly of multimeric ion channels. This study elucidates a novel facet of JB12 and JB14 in that their expression could be regulated in response to stress caused by the presence of ER stressors and the mitochondrial potential uncoupler CCCP. Furthermore, JB14 overexpression could affect the level of PTEN-induced kinase 1 (PINK1) expression under CCCP-mediated stress. Cells with genetic knockout (KO) of DNAJB12 and DNAJB14 exhibited an altered kinetic of phosphorylated Drp1 in response to the stress caused by CCCP treatment. Surprisingly, JB14-KO cells exhibited a prolonged stabilization of PINK1 during chronic exposure to CCCP. Cells depleted with JB12 or JB14 also revealed an increase in the mitochondrial count and branching. Hence, this study indicates the possible novel functions of JB12 and JB14 involving mitochondria in nonstress conditions and under stress caused by CCCP.

Keywords:  ER stress; Hsp40; Intracellular communication; J-protein; Mitochondrial dynamics; Mitochondrial stress response

DOI:  https://doi.org/10.1007/s11010-023-04866-1
eNeuro. 2023 Oct 20. pii: ENEURO.0073-23.2023. [Epub ahead of print]

Mitochondrial OPA1 deficiency is associated to reversible defects in spatial memory related to adult neurogenesis in mice.

Trinovita Andraini, Lionel Moulédous, Petnoi Petsophonsakul, Cédrick Florian, Sébastien Gauzin, Marlène Botella-Daloyau, Macarena Arrázola, Kamela Nikolla, Adam Philip, Alice Leydier, Manon Marque, Laetitia Arnauné-Pelloquin, Pascale Belenguer, Claire Rampon, Marie-Christine Miquel.

  Mitochondria are integrative hubs central to cellular adaptive pathways. Such pathways are critical in highly differentiated post-mitotic neurons, the plasticity of which sustains brain function. Consequently, defects in mitochondria and in their dynamics appear instrumental in neurodegenerative diseases and may also participate in cognitive impairments. To directly test this hypothesis, we analyzed cognitive performances in a mouse mitochondria-based disease model, due to haploinsufficiency in the mitochondrial optic-atrophy-type-1 (OPA1) protein involved in mitochondrial dynamics. In males, we evaluated adult hippocampal neurogenesis parameters using immunohistochemistry. We performed a battery of tests to assess basal behavioral characteristics and cognitive performances, and tested putative treatments.While in Dominant Optic Atrophy (DOA) mouse models, the known main symptoms are late onset visual deficits, we discovered early impairments in hippocampus-dependent spatial memory attributable to defects in adult neurogenesis. Moreover, less connected adult-born hippocampal neurons showed a decrease in mitochondrial content. Remarkably, voluntary exercise or pharmacological treatment targeting mitochondrial dynamics restored spatial memory in DOA mice. Altogether, our study identifies a crucial role for OPA1-dependent mitochondrial functions in adult neurogenesis, and thus in hippocampal-dependent cognitive functions. More generally, our findings show that adult neurogenesis is highly sensitive to mild mitochondrial defects, generating impairments in spatial memory that can be detected at an early stage and counterbalanced by physical exercise and pharmacological targeting of mitochondrial dynamics. Thus, amplification of mitochondrial function at an early stage appears beneficial for late-onset neurodegenerative diseases.Significance StatementThe adult hippocampus continues to produce new neurons in mammals. These new neurons are highly sensitive to mitochondrial perturbation. Dominant optic atrophy (DOA) is a rare disease mainly caused by mutations in the gene coding the mitochondrial protein OPA1. Using a mouse model of OPA1 deficiency, we found that hippocampal new neurons have dendritic spine density defects and altered mitochondrial content. We further detected impairments in spatial memory capacities relying on adult-neurogenesis. We report that these memory impairments can be corrected by physical exercise and pharmacological treatment targeting mitochondria in mice. Our results indicate that early detection of spatial memory deficits related to adult neurogenesis may allow a precocious action in pathologies involving mitochondria, such as DOA or neurodegenerative diseases.

Keywords:  Adult Neurogenesis; Dominant Optic Atrophy; Hippocampus; Mitochondria; Pattern separation; Physical exercise

DOI:  https://doi.org/10.1523/ENEURO.0073-23.2023
Mol Pain. 2023 Oct 16. 17448069231210423

Mitochondrial transplantation attenuates traumatic neuropathic pain, neuroinflammation, and apoptosis in rats with nerve root ligation.

Chi-Chen Huang, Hsin-Yi Chiu, Po-Hsuan Lee, Shih-Yuan Fang, Ming-Wei Lin, Hui-Fang Chen, Jung-Shun Lee.

  Traumatic neuropathic pain (TNP) is caused by traumatic damage to the somatosensory system and induces the presentation of allodynia and hyperalgesia. Mitochondrial dysfunction, neuroinflammation, and apoptosis are hallmarks in the pathogenesis of TNP. Recently, mitochondria-based therapy has emerged as a potential therapeutic intervention for diseases related to mitochondrial dysfunction. However, the therapeutic effectiveness of mitochondrial transplantation (MT) on TNP has rarely been investigated. Here, we validated the efficacy of MT in treating TNP. Both in vivo and in vitro TNP models by conducting an L5 spinal nerve ligation in rats and exposing the primary dorsal root ganglion (DRG) neurons to capsaicin, respectively, were applied in this study. The MT was operated by administrating 100 µg of soleus-derived allogeneic mitochondria into the ipsilateral L5 DRG in vivo and the culture medium in vitro. Results showed that the viable transplanted mitochondria migrated into the rats' spinal cord and sciatic nerve. MT alleviated the nerve ligation-induced mechanical and thermal pain hypersensitivity. The nerve ligation-induced glial activation and the expression of pro-inflammatory cytokines and apoptotic markers in the spinal cord were also repressed by MT. Consistently, exogenous mitochondria reversed the capsaicin-induced reduction of mitochondrial membrane potential and expression of pro-inflammatory cytokines and apoptotic markers in the primary DRG neurons in vitro. Our findings suggest that MT mitigates the spinal nerve ligation-induced apoptosis and neuroinflammation, potentially playing a role in providing neuroprotection against TNP.

Keywords:  Apoptosis; Mitochondrial dysfunction; Mitochondrial transplantation; Neuroinflammation; Traumatic neuropathic pain

DOI:  https://doi.org/10.1177/17448069231210423
Biochim Biophys Acta Gen Subj. 2023 Oct 12. pii: S0304-4165(23)00183-6. [Epub ahead of print]1867(12): 130485

Vitamin E succinate mediated apoptosis by juxtaposing endoplasmic reticulum and mitochondria.

Manobendro Nath Ray, Michiko Kiyofuji, Mizune Ozono, Kentaro Kogure.

  Vitamin E succinate (VES) is an esterified form of natural α-tocopherol, has turned out to be novel anticancer agent. However, its anticancer mechanisms have not been illustrated. Previously, we reported VES mediated Ca2+ release from the endoplasmic reticulum (ER) causes mitochondrial Ca2+ overload, leading to mitochondrial depolarization and apoptosis. Here, we elucidated the mechanism of VES-induced Ca2+ transfer from ER to mitochondria by investigating the role of VES in ER-mitochondria contact formation. Transmission electron microscopic observation confirms VES mediated ER-mitochondria contact while fluorescence microscopic analysis revealed that VES increased mitochondria-associated ER membrane (MAM) formation. Pre-treatment with the inositol 1,4,5-triphosphate receptor (IP3R) antagonist 2-aminoethyl diphenylborinate (2-APB) decreased VES-induced MAM formation, suggesting the involvement of VES-induced Ca2+ efflux from ER in MAM formation. The ER IP3R receptor is known to interact with voltage-dependent anion channels (VDAC) via the chaperone glucose-regulated protein 75 kDa (GRP75) to bring ER and mitochondria nearby. Although we revealed that VES treatment does not affect GRP75 protein level, it increases GRP75 localization in the MAM. In addition, the inhibition of Ca2+ release from ER by 2-APB decreases GRP75 localization in the MAM, suggesting the possibility of Ca2+-induced conformational change of GRP75 that promotes formation of the IP3R-GRP75-VDAC complex and thereby encourages MAM formation. This study identifies the mechanism of VES-induced enhanced Ca2+ transfer from ER to mitochondria, which causes mitochondrial Ca2+ overload leading to apoptosis.

Keywords:  Apoptosis; Ca(2+) transfer; ER-mitochondria contact; GRP75; Vitamin E succinate

DOI:  https://doi.org/10.1016/j.bbagen.2023.130485
Neural Regen Res. 2024 May;19(5): 998-1005

Mitophagy in neurodegenerative disease pathogenesis.

Kan Yang, Yuqing Yan, Anni Yu, Ru Zhang, Yuefang Zhang, Zilong Qiu, Zhengyi Li, Qianlong Zhang, Shihao Wu, Fei Li.

  Mitochondria are critical cellular energy resources and are central to the life of the neuron. Mitophagy selectively clears damaged or dysfunctional mitochondria through autophagic machinery to maintain mitochondrial quality control and homeostasis. Mature neurons are postmitotic and consume substantial energy, thus require highly efficient mitophagy pathways to turn over damaged or dysfunctional mitochondria. Recent evidence indicates that mitophagy is pivotal to the pathogenesis of neurological diseases. However, more work is needed to study mitophagy pathway components as potential therapeutic targets. In this review, we briefly discuss the characteristics of nonselective autophagy and selective autophagy, including ERphagy, aggrephagy, and mitophagy. We then introduce the mechanisms of Parkin-dependent and Parkin-independent mitophagy pathways under physiological conditions. Next, we summarize the diverse repertoire of mitochondrial membrane receptors and phospholipids that mediate mitophagy. Importantly, we review the critical role of mitophagy in the pathogenesis of neurodegenerative diseases including Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis. Last, we discuss recent studies considering mitophagy as a potential therapeutic target for treating neurodegenerative diseases. Together, our review may provide novel views to better understand the roles of mitophagy in neurodegenerative disease pathogenesis.

Keywords:  Alzheimer’s disease; PINK1; Parkin; Parkinson’s disease; amyotrophic lateral sclerosis; autophagy; mitochondria; mitophagy; mitophagy receptor

DOI:  https://doi.org/10.4103/1673-5374.385281
Virulence. 2023 Dec;14(1): 2265095

Organelles are miscommunicating: Membrane contact sites getting hijacked by pathogens.

Pratyashaa Paul, Bhavana Tiwari.

  Membrane Contact Sites (MCS) are areas of close apposition of organelles that serve as hotspots for crosstalk and direct transport of lipids, proteins and metabolites. Contact sites play an important role in Ca2+ signalling, phospholipid synthesis, and micro autophagy. Initially, altered regulation of vesicular trafficking was regarded as the key mechanism for intracellular pathogen survival. However, emerging studies indicate that pathogens hijack MCS elements - a novel strategy for survival and replication in an intracellular environment. Several pathogens exploit MCS to establish direct contact between organelles and replication inclusion bodies, which are essential for their survival within the cell. By establishing this direct control, pathogens gain access to cytosolic compounds necessary for replication, maintenance, escaping endocytic maturation and circumventing lysosome fusion. MCS components such as VAP A/B, OSBP, and STIM1 are targeted by pathogens through their effectors and secretion systems. In this review, we delve into the mechanisms which operate in the evasion of the host immune system when intracellular pathogens hostage MCS. We explore targeting MCS components as a novel therapeutic approach, modifying molecular pathways and signalling to address the disease's mechanisms and offer more effective, tailored treatments for affected individuals.

Keywords:  Membrane contact sites (MCS); direct lipid transport; host immune evasion; inter-organellar contacts; non-vesicular trafficking

DOI:  https://doi.org/10.1080/21505594.2023.2265095
Biochemistry. 2023 Oct 19.

Mitochondrial Dynamics of Bcl-2 Family Proteins during 17-β-Estradiol-Induced Apoptosis Correlate with the Malignancy of Endometrial Cancer Cells.

Takahiro Yaguchi, Misaki Kameno, Hirofumi Taira, Junji Kawakami.

Excessive fat intake leads to an increase in cholesterol. Overexposure to estrogen derived from cholesterol is known to contribute to the malignancy of endometrial adenocarcinomas. However, it is not well understood the relationship between the exposure to estrogen and the malignancy of endometrial adenocarcinomas. We investigated how estrogen affected the malignancy of endometrial cancer cells, specifically HEC1 cells (a moderately differentiated adenocarcinoma) and HEC50B cells (a poorly differentiated adenocarcinoma). Cell viability was decreased by exogenous 17-β-estradiol (E2) in a concentration-dependent manner. E2 disturbed the mitochondrial membrane potentials by changing the localization of the B-cell lymphoma 2 (Bcl-2) family protein; however, there were significant differences in the localization of Bcl-2 family proteins between HEC1 and HEC50B cells. In HEC1 cells, E2 increased the expression of B-cell lymphoma-extra large (Bcl-XL) and the Bcl-2-associated X protein (Bax) and decreased Bcl-2 and Bcl-2-associated death promoter (Bad) expression on the outer mitochondrial membrane. Conversely, E2 increased the expression of Bad and Bax, and it decreased Bcl-2 and Bcl-XL expressions on the outer mitochondrial membrane in HEC50B cells. The disturbance of the mitochondrial membrane potential led to the release of cytochrome c from the mitochondria to the cytosolic space followed by activating caspase-9. After that, caspase-3 was activated and induced apoptosis. These results suggested that the localization of the Bcl-2 family protein observed under E2-induced apoptosis is related to the malignancy of endometrial cancer cells. We hope that the dynamics of Bcl-2 family proteins such as Bcl-XL and Bad will be used to diagnose malignant endometrial adenocarcinomas.

DOI: https://doi.org/10.1021/acs.biochem.3c00064
Nat Chem Biol. 2023 Oct 19.

Long-term super-resolution inner mitochondrial membrane imaging with a lipid probe.

Shuai Zheng, Neville Dadina, Deepto Mozumdar, Lauren Lesiak, Kayli N Martinez, Evan W Miller, Alanna Schepartz.

The inner mitochondrial membrane (IMM) generates power to drive cell function, and its dynamics control mitochondrial health and cellular homeostasis. Here, we describe the cell-permeant, lipid-like small molecule MAO-N3 and use it to assemble high-density environmentally sensitive (HIDE) probes that selectively label and image the IMM in live cells and multiple cell states. MAO-N3 pairs with strain-promoted azide-alkyne click chemistry-reactive fluorophores to support HIDE imaging using confocal, structured illumination, single-molecule localization and stimulated emission depletion microscopy, all with significantly improved resistance to photobleaching. These probes generate images with excellent spatial and temporal resolution, require no genetic manipulations, are non-toxic in model cell lines and primary cardiomyocytes (even under conditions that amplify the effects of mitochondrial toxins) and can visualize mitochondrial dynamics for 12.5 h. This probe will enable comprehensive studies of IMM dynamics with high temporal and spatial resolution.

DOI: https://doi.org/10.1038/s41589-023-01450-y
Nat Struct Mol Biol. 2023 Oct 19.

Molecular mechanism of glutaminase activation through filamentation and the role of filaments in mitophagy protection.

Douglas Adamoski, Marilia Meira Dias, Jose Edwin Neciosup Quesñay, Zhengyi Yang, Ievgeniia Zagoriy, Anna M Steyer, Camila Tanimoto Rodrigues, Alliny Cristiny da Silva Bastos, Bianca Novaes da Silva, Renna Karoline Eloi Costa, Flávia Mayumi Odahara de Abreu, Zeyaul Islam, Alexandre Cassago, Marin Gerard van Heel, Sílvio Roberto Consonni, Simone Mattei, Julia Mahamid, Rodrigo Villares Portugal, Andre Luis Berteli Ambrosio, Sandra Martha Gomes Dias.

Glutaminase (GLS), which deaminates glutamine to form glutamate, is a mitochondrial tetrameric protein complex. Although inorganic phosphate (Pi) is known to promote GLS filamentation and activation, the molecular basis of this mechanism is unknown. Here we aimed to determine the molecular mechanism of Pi-induced mouse GLS filamentation and its impact on mitochondrial physiology. Single-particle cryogenic electron microscopy revealed an allosteric mechanism in which Pi binding at the tetramer interface and the activation loop is coupled to direct nucleophile activation at the active site. The active conformation is prone to enzyme filamentation. Notably, human GLS filaments form inside tubulated mitochondria following glutamine withdrawal, as shown by in situ cryo-electron tomography of cells thinned by cryo-focused ion beam milling. Mitochondria with GLS filaments exhibit increased protection from mitophagy. We reveal roles of filamentous GLS in mitochondrial morphology and recycling.

DOI: https://doi.org/10.1038/s41594-023-01118-0