bims-mitdyn Biomed News
on Mitochondrial dynamics: mechanisms
Issue of 2025–01–19
seven papers selected by
Gavin McStay, Liverpool John Moores University
  1. Using HBmito Crimson to Observe Mitochondrial Cristae Through STED Microscopy.
  2. Continuity of Mitochondrial Budding: Insights from BS-C-1 Cells by In Situ Cryo-electron Tomography.
  3. Calcium-mediated mitochondrial fission and mitophagy drive glycolysis to facilitate arterivirus proliferation.
  4. Epithelial OPA1 links mitochondrial fusion to inflammatory bowel disease.
  5. Mitochondrial segmentation and function prediction in live-cell images with deep learning.
  6. In Vitro Homotypic ER Membrane Fusion Assay Using Isolated Yeast Microsomes.
  7. 4-hydroxybenzoic acid induces browning of white adipose tissue through the AMPK-DRP1 pathway in HFD-induced obese mice.
  1. Bio Protoc. 2025 Jan 05. 15(1): e5150
    Using HBmito Crimson to Observe Mitochondrial Cristae Through STED Microscopy.
    Xichuan Ge, Wei Ren, Chunyan Shan, Peng Xi, Baoxiang Gao.
      Mitochondrial cristae, formed by folding the mitochondrial inner membrane (IM), are essential for cellular energy supply. However, the observation of the IM is challenging due to the limitations in spatiotemporal resolution offered by conventional microscopy and the absence of suitable in vitro probes specifically targeting the IM. Here, we describe a detailed imaging protocol for the mitochondrial inner membrane using the Si-rhodamine dye HBmito Crimson, which has excellent photophysical properties, to label live cells for imaging via stimulated emission depletion (STED) microscopy. This allows for STED imaging over more than 500 frames (approximately one hour), with a spatial resolution of 40 nm, enabling the observation of cristae dynamics during various mitochondrial processes. The protocol includes detailed steps for cell staining, image acquisition, image processing, and resolution analysis. Utilizing the superior resolution of STED microscopy, the structure and complex dynamic changes of cristae can be visualized. Key features • The protocol is designed to visualize mitochondrial cristae in living cells using STED microscopy. • The protocol enables nanoscale observation of dynamic mitochondrial cristae. • Real-time observation of mitochondrial morphological changes, fusion, and fission events.
    Keywords:  Fluorescence labeling; Live cell imaging; Low-saturation power; Mitochondria cristae; Super-resolution imaging
    DOI:  https://doi.org/10.21769/BioProtoc.5150
  2. Microsc Microanal. 2025 Jan 13. pii: ozae122. [Epub ahead of print]
    Continuity of Mitochondrial Budding: Insights from BS-C-1 Cells by In Situ Cryo-electron Tomography.
    Judy Z Hu, Lijun Qiao, Xianhai Zhao, Chang-Jun Liu, Guo-Bin Hu.
      Mitochondrial division is a fundamental biological process essensial for cellular functionality and vitality. The prevailing hypothesis that dynamin related protein 1 (Drp1) provides principal control in mitochondrial division, in which it also involves the endoplasmic reticulum (ER) and the cytoskeleton, does not account for all the observations. Therefore. the hypothesis may be incomplete. Our previous study in HeLa cells led to a new hypothesis of mitochondrial division by budding. To follow-up our previous study, we employed in situ cryo-electron tomography to visualize mitochondrial budding in the intact healthy monkey kidney cells (BS-C-1 cells). Our findings reaffirm single and multiple mitochondrial budding, consistent with our observations in HeLa cells. Notably, the budding regions vary significantly in diameter and length, which may represent different stages of budding. More interestingly, neither rings nor ring-like structures, nor the wrapping of ER tubes was observed in the budding regions, suggesting mitochondrial budding is independent from Drp1 and ER. Meanwhile, we uncovered direct interactions between mitochondria and large vesicles that are distinct from small mitochondrial-derived vesicles and extracellular mitovesicles. We propose that these interacting vesicles may have mitochondrial origins.
    Keywords:   in situ cryo-electron tomography; cryo-electron microscopy (Cryo-EM); cryo-electron tomography (Cryo-ET); mitochondrial budding; mitochondrial division; mitochondrial dynamics
    DOI:  https://doi.org/10.1093/mam/ozae122
  3. PLoS Pathog. 2025 Jan 13. 21(1): e1012872
    Calcium-mediated mitochondrial fission and mitophagy drive glycolysis to facilitate arterivirus proliferation.
    Zhe Sun, Zicheng Ma, Wandi Cao, Chenlong Jiang, Lei Guo, Kesen Liu, Yanni Gao, Juan Bai, Jiang Pi, Ping Jiang, Xing Liu.
      Mitochondria, recognized as the "powerhouse" of cells, play a vital role in generating cellular energy through dynamic processes such as fission and fusion. Viruses have evolved mechanisms to hijack mitochondrial function for their survival and proliferation. Here, we report that infection with the swine arterivirus porcine reproductive and respiratory syndrome virus (PRRSV), manipulates mitochondria calcium ions (Ca2+) to induce mitochondrial fission and mitophagy, thereby reprogramming cellular energy metabolism to facilitate its own replication. Mechanistically, PRRSV-induced mitochondrial fission is caused by elevated levels of mitochondria Ca2+, derived from the endoplasmic reticulum (ER) through inositol 1,4,5-triphosphate receptor (IP3R)-voltage-dependent anion channel 1 (VDAC1)-mitochondrial calcium uniporter (MCU) channels. This process is associated with increased mitochondria-associated membranes (MAMs), mediated by the upregulated expression of sigma non-opioid intracellular receptor 1 (SIGMAR1). Elevated mitochondria Ca2+ further activates the Ca2+/CaM-dependent protein kinase kinase β (CaMKKβ)-AMP-activated protein kinase (AMPK)-dynamin-related protein 1 (DRP1) signaling pathway, which interacts with mitochondrial fission protein 1 (FIS1) and mitochondrial dynamics proteins of 49 kDa (MiD49) to promote mitochondrial fission. PRRSV infection, alongside mitochondrial fission, triggers mitophagy via the PTEN-induced putative kinase 1 (PINK1)-Parkin RBR E3 ubiquitin (Parkin) pathway, promoting cellular glycolysis and excessive lactate production to facilitate its own replication. This study reveals the mechanism by which mitochondrial Ca2+ regulates mitochondrial function during PRRSV infection, providing new insights into the interplay between the virus and host cell metabolism.
    DOI:  https://doi.org/10.1371/journal.ppat.1012872
  4. Sci Transl Med. 2025 Jan 15. 17(781): eadn8699
    Epithelial OPA1 links mitochondrial fusion to inflammatory bowel disease.
    TRR241 IBDome Consortium
      Dysregulation at the intestinal epithelial barrier is a driver of inflammatory bowel disease (IBD). However, the molecular mechanisms of barrier failure are not well understood. Here, we demonstrate dysregulated mitochondrial fusion in intestinal epithelial cells (IECs) of patients with IBD and show that impaired fusion is sufficient to drive chronic intestinal inflammation. We found reduced expression of mitochondrial fusion-related genes, such as the dynamin-related guanosine triphosphatase (GTPase) optic atrophy 1 (OPA1), and fragmented mitochondrial networks in crypt IECs of patients with IBD. Mice with Opa1 deficiency in the gut epithelium (Opa1i∆IEC) spontaneously developed chronic intestinal inflammation with mucosal ulcerations and immune cell infiltration. Intestinal inflammation in Opa1i∆IEC mice was driven by microbial translocation and associated with epithelial progenitor cell death and gut barrier dysfunction. Opa1-deficient epithelial cells and human organoids exposed to a pharmacological OPA1 inhibitor showed disruption of the mitochondrial network with mitochondrial fragmentation and changes in mitochondrial size, ultrastructure, and function, resembling changes observed in patient samples. Pharmacological inhibition of the GTPase dynamin-1-like protein in organoids derived from Opa1i∆IEC mice partially reverted this phenotype. Together, our data demonstrate a role for epithelial OPA1 in regulating intestinal immune homeostasis and epithelial barrier function. Our data provide a mechanistic explanation for the observed mitochondrial dysfunction in IBD and identify mitochondrial fusion as a potential therapeutic target in this disease.
    DOI:  https://doi.org/10.1126/scitranslmed.adn8699
  5. Nat Commun. 2025 Jan 16. 16(1): 743
    Mitochondrial segmentation and function prediction in live-cell images with deep learning.
    Yang Ding, Jintao Li, Jiaxin Zhang, Panpan Li, Hua Bai, Bin Fang, Haixiao Fang, Kai Huang, Guangyu Wang, Cameron J Nowell, Nicolas H Voelcker, Bo Peng, Lin Li, Wei Huang.
      Mitochondrial morphology and function are intrinsically linked, indicating the opportunity to predict functions by analyzing morphological features in live-cell imaging. Herein, we introduce MoDL, a deep learning algorithm for mitochondrial image segmentation and function prediction. Trained on a dataset of 20,000 manually labeled mitochondria from super-resolution (SR) images, MoDL achieves superior segmentation accuracy, enabling comprehensive morphological analysis. Furthermore, MoDL predicts mitochondrial functions by employing an ensemble learning strategy, powered by an extended training dataset of over 100,000 SR images, each annotated with functional data from biochemical assays. By leveraging this large dataset alongside data fine-tuning and retraining, MoDL demonstrates the ability to precisely predict functions of heterogeneous mitochondria from unseen cell types through small sample size training. Our results highlight the MoDL's potential to significantly impact mitochondrial research and drug discovery, illustrating its utility in exploring the complex relationship between mitochondrial form and function within a wide range of biological contexts.
    DOI:  https://doi.org/10.1038/s41467-025-55825-x
  6. Methods Mol Biol. 2025 ;2887 167-173
    In Vitro Homotypic ER Membrane Fusion Assay Using Isolated Yeast Microsomes.
    Eunhong Jang, Youngsoo Jun.
      Cell-free in vitro assays offer several advantages for elucidating molecular mechanisms underlying various biological processes. Here, we describe a simple and quantitative in vitro assay using isolated yeast microsomes to measure homotypic ER membrane fusion. In this assay, membrane fusion between ER microsomes is monitored by reconstitution of luciferase activity from split luciferase fragments. Our findings reveal that homotypic ER membrane fusion requires not only Sey1p, the yeast atlstin, but also ER-resident SNAREs, such as Sec22p and Sec20p, in Saccharomyces cerevisiae.
    Keywords:  Atlastin; Endoplasmic reticulum; Membrane fusion; Microsome; SNARE
    DOI:  https://doi.org/10.1007/978-1-0716-4314-3_11
  7. Phytomedicine. 2024 Dec 27. pii: S0944-7113(24)01008-0. [Epub ahead of print]137 156353
    4-hydroxybenzoic acid induces browning of white adipose tissue through the AMPK-DRP1 pathway in HFD-induced obese mice.
    Sang Hee Kim, Woo Yong Park, Gahee Song, Ja Yeon Park, Se Jin Jung, Kwang Seok Ahn, Jae-Young Um.
       BACKGROUND: Beige adipocytes have physiological functions similar to brown adipocytes, which are available to increase energy expenditure through uncoupling protein 1 (UCP1) within mitochondria. Recently, many studies showed white adipocytes can undergo remodeling into beige adipocytes, called "browning", by increasing fusion and fission events referred to as mitochondrial dynamics.
    PURPOSE: In this study, we aimed to investigate the browning effects of 4-hydroxybenzoic acid (4-HA), one of the major compounds of black raspberries.
    METHODS: We examined the mechanism underlying the browning properties of 4-HA focusing on UCP1-dependent non-shivering thermogenesis in 3T3-L1 white adipocytes, high-fat diet (HFD)-induced obese male C57BL/6J mice, and cold-exposed male C57BL/6J mice.
    RESULTS: 4-HA treatment elevates browning markers such as UCP1, T-Box transcription factor 1, and PR domain containing 16, mitochondrial function factors like oxidative phosphorylation complex as well as mitochondrial dynamic-related factors like phosphorylated dynamin-related protein 1 (p-DRP1), DRP1, and mitofusin 1 in 3T3-L1 white adipocytes, which were also confirmed in inguinal white adipose tissue (iWAT) of HFD-induced obese mice. Mdivi-1 blocked the increased DRP1-mediated mitochondrial fission by 4-HA, and even the browning effect of 4-HA was abolished. Furthermore, 4-HA increased AMP-activated protein kinase (AMPK) in both the 3T3-L1 white adipocytes and iWAT of HFD-induced obese mice. Inhibition of AMPK with Compound C also blocked the 4-HA-induced mitochondrial fission and browning effect.
    CONCLUSIONS: 4-HA induces the browning of white adipocytes into beige adipocytes by regulating the DRP1-mediated mitochondrial dynamics through AMPK. These findings suggest that 4-HA could serve as a therapeutic candidate for obesity and related metabolic disorders.
    Keywords:  4-hydroxybenzoic acid; AMPK; DRP1; Mitochondrial dynamics; Obesity
    DOI:  https://doi.org/10.1016/j.phymed.2024.156353
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