bims-midtic 2024-05-12 papers

bims-midtic

Biomed News

on Mitochondrial dynamics and trafficking in cells

Issue of 2024–05–12
ten papers selected by
Omkar Joshi, Turku Bioscience

An interphase actin wave promotes mitochondrial content mixing and organelle homeostasis.
Charcot-Marie-Tooth type 2A in vivo models: Current updates.
A Pipeline for Dynamic Analysis of Mitochondrial Content in Developing T Cells: Bridging the Gap Between High-Throughput Flow Cytometry and Single-Cell Microscopy Analysis.
A RAB7A phosphoswitch coordinates Rubicon Homology protein regulation of Parkin-dependent mitophagy.
Dendrite architecture determines mitochondrial distribution patterns in vivo.
Melatonin attenuates renal ischemia-reperfusion injury by regulating mitochondrial dynamics and autophagy through AMPK/DRP1.
Spatial mapping of hepatic ER and mitochondria architecture reveals zonated remodeling in fasting and obesity.
Exercise ameliorates muscular excessive mitochondrial fission, insulin resistance and inflammation in diabetic rats via irisin/AMPK activation.
A mitochondrial surveillance mechanism activated by SRSF2 mutations in hematologic malignancies.
Metformin induction of heat shock factor 1 activation and the mitochondrial unfolded protein response alleviate cardiac remodeling in spontaneously hypertensive rats.

Nat Commun. 2024 May 07. 15(1): 3793

An interphase actin wave promotes mitochondrial content mixing and organelle homeostasis.

Stephen M Coscia, Andrew S Moore, Cameron P Thompson, Christian F Tirrito, E Michael Ostap, Erika L F Holzbaur.

Across the cell cycle, mitochondrial dynamics are regulated by a cycling wave of actin polymerization/depolymerization. In metaphase, this wave induces actin comet tails on mitochondria that propel these organelles to drive spatial mixing, resulting in their equitable inheritance by daughter cells. In contrast, during interphase the cycling actin wave promotes localized mitochondrial fission. Here, we identify the F-actin nucleator/elongator FMNL1 as a positive regulator of the wave. FMNL1-depleted cells exhibit decreased mitochondrial polarization, decreased mitochondrial oxygen consumption, and increased production of reactive oxygen species. Accompanying these changes is a loss of hetero-fusion of wave-fragmented mitochondria. Thus, we propose that the interphase actin wave maintains mitochondrial homeostasis by promoting mitochondrial content mixing. Finally, we investigate the mechanistic basis for the observation that the wave drives mitochondrial motility in metaphase but mitochondrial fission in interphase. Our data indicate that when the force of actin polymerization is resisted by mitochondrial tethering to microtubules, as in interphase, fission results.

DOI: https://doi.org/10.1038/s41467-024-48189-1
J Cell Mol Med. 2024 May;28(9): e18293

Charcot-Marie-Tooth type 2A in vivo models: Current updates.

Elena Abati, Mafalda Rizzuti, Alessia Anastasia, Giacomo Pietro Comi, Stefania Corti, Federica Rizzo.

  Charcot-Marie-Tooth type 2A (CMT2A) is an inherited sensorimotor neuropathy associated with mutations within the Mitofusin 2 (MFN2) gene. These mutations impair normal mitochondrial functioning via different mechanisms, disturbing the equilibrium between mitochondrial fusion and fission, of mitophagy and mitochondrial axonal transport. Although CMT2A disease causes a significant disability, no resolutive treatment for CMT2A patients to date. In this context, reliable experimental models are essential to precisely dissect the molecular mechanisms of disease and to devise effective therapeutic strategies. The most commonly used models are either in vitro or in vivo, and among the latter murine models are by far the most versatile and popular. Here, we critically revised the most relevant literature focused on the experimental models, providing an update on the mammalian models of CMT2A developed to date. We highlighted the different phenotypic, histopathological and molecular characteristics, and their use in translational studies for bringing potential therapies from the bench to the bedside. In addition, we discussed limitations of these models and perspectives for future improvement.

Keywords:  Charcot–Marie‐Tooth type 2A; animal model; mitofusin 2; mouse models

DOI:  https://doi.org/10.1111/jcmm.18293
Methods Mol Biol. 2024 ;2800 167-187

A Pipeline for Dynamic Analysis of Mitochondrial Content in Developing T Cells: Bridging the Gap Between High-Throughput Flow Cytometry and Single-Cell Microscopy Analysis.

Vaibhav Dhyani, Anchi S Chann, Lopamudra Giri, Sarah M Russell, Mirren Charnley.

  Analyzing the dynamics of mitochondrial content in developing T cells is crucial for understanding the metabolic state during T cell development. However, monitoring mitochondrial content in real-time needs a balance of cell viability and image resolution. In this chapter, we present experimental protocols for measuring mitochondrial content in developing T cells using three modalities: bulk analysis via flow cytometry, volumetric imaging in laser scanning confocal microscopy, and dynamic live-cell monitoring in spinning disc confocal microscopy. Next, we provide an image segmentation and centroid tracking-based analysis pipeline for automated quantification of a large number of microscopy images. These protocols together offer comprehensive approaches to investigate mitochondrial dynamics in developing T cells, enabling a deeper understanding of their metabolic processes.

Keywords:  3D imaging; DN3; Density-based spatial clustering of applications with noise (DBSCAN); Image segmentation; MitoView Green; Mitochondria

DOI:  https://doi.org/10.1007/978-1-0716-3834-7_12
J Cell Biol. 2024 Jul 01. pii: e202309015. [Epub ahead of print]223(7):

A RAB7A phosphoswitch coordinates Rubicon Homology protein regulation of Parkin-dependent mitophagy.

Dan A Tudorica, Bishal Basak, Alexia S Puerta Cordova, Grace Khuu, Kevin Rose, Michael Lazarou, Erika L F Holzbaur, James H Hurley.

Activation of PINK1 and Parkin in response to mitochondrial damage initiates a response that includes phosphorylation of RAB7A at Ser72. Rubicon is a RAB7A binding negative regulator of autophagy. The structure of the Rubicon:RAB7A complex suggests that phosphorylation of RAB7A at Ser72 would block Rubicon binding. Indeed, in vitro phosphorylation of RAB7A by TBK1 abrogates Rubicon:RAB7A binding. Pacer, a positive regulator of autophagy, has an RH domain with a basic triad predicted to bind an introduced phosphate. Consistent with this, Pacer-RH binds to phosho-RAB7A but not to unphosphorylated RAB7A. In cells, mitochondrial depolarization reduces Rubicon:RAB7A colocalization whilst recruiting Pacer to phospho-RAB7A-positive puncta. Pacer knockout reduces Parkin mitophagy with little effect on bulk autophagy or Parkin-independent mitophagy. Rescue of Parkin-dependent mitophagy requires the intact pRAB7A phosphate-binding basic triad of Pacer. Together these structural and functional data support a model in which the TBK1-dependent phosphorylation of RAB7A serves as a switch, promoting mitophagy by relieving Rubicon inhibition and favoring Pacer activation.

DOI: https://doi.org/10.1083/jcb.202309015
Cell Rep. 2024 May 06. pii: S2211-1247(24)00518-7. [Epub ahead of print]43(5): 114190

Dendrite architecture determines mitochondrial distribution patterns in vivo.

Eavan J Donovan, Anamika Agrawal, Nicole Liberman, Jordan I Kalai, Avi J Adler, Adam M Lamper, Hailey Q Wang, Nicholas J Chua, Elena F Koslover, Erin L Barnhart.

  Neuronal morphology influences synaptic connectivity and neuronal signal processing. However, it remains unclear how neuronal shape affects steady-state distributions of organelles like mitochondria. In this work, we investigated the link between mitochondrial transport and dendrite branching patterns by combining mathematical modeling with in vivo measurements of dendrite architecture, mitochondrial motility, and mitochondrial localization patterns in Drosophila HS (horizontal system) neurons. In our model, different forms of morphological and transport scaling rules-which set the relative thicknesses of parent and daughter branches at each junction in the dendritic arbor and link mitochondrial motility to branch thickness-predict dramatically different global mitochondrial localization patterns. We show that HS dendrites obey the specific subset of scaling rules that, in our model, lead to realistic mitochondrial distributions. Moreover, we demonstrate that neuronal activity does not affect mitochondrial transport or localization, indicating that steady-state mitochondrial distributions are hard-wired by the architecture of the neuron.

Keywords:  CP: Cell biology; CP: Neuroscience; dendrite scaling; in vivo imaging; mitochondrial motility; neuronal morphology

DOI:  https://doi.org/10.1016/j.celrep.2024.114190
Shock. 2024 Apr 26.

Melatonin attenuates renal ischemia-reperfusion injury by regulating mitochondrial dynamics and autophagy through AMPK/DRP1.

Huabin Wang, Yi Li, Xichao Cao, Heping Niu, Xiaoran Li, Jirong Wang, Jianwei Yang, Changhong Xu, Hailong Wang, Shun Wan, Kunpeng Li, Shengjun Fu, Li Yang.

ABSTRACT: Ischemia-reperfusion injury (IRI) often stems from an imbalance between mitochondrial dynamics and autophagy. Melatonin mitigates IRI by regulating mitochondrial dynamics. However, the precise molecular mechanism underlying the role of melatonin in reducing IRI through modulating mitochondrial dynamics remains elusive. The objective of this study was to investigate whether pre-treatment with melatonin before IRI confers protective effects by modulating mitochondrial dynamics and mitophagy. Melatonin pre-treatment was administered to HK-2 cells and live rats before subjecting them to hypoxia-reoxygenation (HR) or IRI, respectively. Cells and rat kindey models were evaluated for markers of oxidative stress, autophagy, mitochondrial dynamics, and the expression of adenosine 5'-monophosphate (AMP)-activated protein kinase (AMPK) and phospho-AMPKα (P-AMPK). Following renal IRI, increased mitochondrial fission and autophagy were observed, accompanied by exacerbated cellular oxidative stress injury and aggravated mitochondrial dysfunction. Nevertheless, melatonin pre-treatment inhibited mitochondrial fission, promoted mitochondrial fusion, and attenuated autophagy levels. This intervention was correlated with a notable reduction in oxidative stress injury and remarkable restoration of mitochondrial functionality. IRI led to a decline in P-AMPK levels, whereas melatonin pre-treatment increased the level of P-AMPK levels. Silencing AMPK with small interfering RNA exacerbated mitochondrial damage, and in this context, melatonin pre-treatment did not alleviate mitochondrial fission or autophagy levels but resulted in sustained oxidative stress damage. Collectively, these findings indicate that melatonin pre-treatment shields the kidneys from IRI by mitigating excessive mitochondrial fission, moderating autophagy levels, and preserving appropriate mitochondrial fission, all in an AMPK-dependent manner.

DOI: https://doi.org/10.1097/SHK.0000000000002330
Nat Commun. 2024 May 10. 15(1): 3982

Spatial mapping of hepatic ER and mitochondria architecture reveals zonated remodeling in fasting and obesity.

Güneş Parlakgül, Song Pang, Leonardo L Artico, Nina Min, Erika Cagampan, Reyna Villa, Renata L S Goncalves, Grace Yankun Lee, C Shan Xu, Gökhan S Hotamışlıgil, Ana Paula Arruda.

The hepatocytes within the liver present an immense capacity to adapt to changes in nutrient availability. Here, by using high resolution volume electron microscopy, we map how hepatic subcellular spatial organization is regulated during nutritional fluctuations and as a function of liver zonation. We identify that fasting leads to remodeling of endoplasmic reticulum (ER) architecture in hepatocytes, characterized by the induction of single rough ER sheet around the mitochondria, which becomes larger and flatter. These alterations are enriched in periportal and mid-lobular hepatocytes but not in pericentral hepatocytes. Gain- and loss-of-function in vivo models demonstrate that the Ribosome receptor binding protein1 (RRBP1) is required to enable fasting-induced ER sheet-mitochondria interactions and to regulate hepatic fatty acid oxidation. Endogenous RRBP1 is enriched around periportal and mid-lobular regions of the liver. In obesity, ER-mitochondria interactions are distinct and fasting fails to induce rough ER sheet-mitochondrion interactions. These findings illustrate the importance of a regulated molecular architecture for hepatocyte metabolic flexibility.

DOI: https://doi.org/10.1038/s41467-024-48272-7
Sci Rep. 2024 05 09. 14(1): 10658

Exercise ameliorates muscular excessive mitochondrial fission, insulin resistance and inflammation in diabetic rats via irisin/AMPK activation.

Junjie Lin, Xin Zhang, Yu Sun, Haocheng Xu, Nan Li, Yuanxin Wang, Xin Tian, Chen Zhao, Bin Wang, Baishu Zhu, Renqing Zhao.

  This study aimed to investigate the effects of exercise on excessive mitochondrial fission, insulin resistance, and inflammation in the muscles of diabetic rats. The role of the irisin/AMPK pathway in regulating exercise effects was also determined. Thirty-two 8-week-old male Wistar rats were randomly divided into four groups (n = 8 per group): one control group (Con) and three experimental groups. Type 2 diabetes mellitus (T2DM) was induced in the experimental groups via a high-fat diet followed by a single intraperitoneal injection of streptozotocin (STZ) at a dosage of 30 mg/kg body weight. After T2DM induction, groups were assigned as sedentary (DM), subjected to 8 weeks of treadmill exercise training (Ex), or exercise training combined with 8-week cycloRGDyk treatment (ExRg). Upon completion of the last training session, all rats were euthanized and samples of fasting blood and soleus muscle were collected for analysis using ELISA, immunofluorescence, RT-qPCR, and Western blotting. Statistical differences between groups were analyzed using one-way ANOVA, and differences between two groups were assessed using t-tests. Our findings demonstrate that exercise training markedly ameliorated hyperglycaemia, hyperlipidaemia, and insulin resistance in diabetic rats (p < 0.05). It also mitigated the disarranged morphology and inflammation of skeletal muscle associated with T2DM (p < 0.05). Crucially, exercise training suppressed muscular excessive mitochondrial fission in the soleus muscle of diabetic rats (p < 0.05), and enhanced irisin and p-AMPK levels significantly (p < 0.05). However, exercise-induced irisin and p-AMPK expression were inhibited by cycloRGDyk treatment (p < 0.05). Furthermore, the administration of CycloRGDyk blocked the effects of exercise training in reducing excessive mitochondrial fission and inflammation in the soleus muscle of diabetic rats, as well as the positive effects of exercise training on improving hyperlipidemia and insulin sensitivity in diabetic rats (p < 0.05). These results indicate that regular exercise training effectively ameliorates insulin resistance and glucolipid metabolic dysfunction, and reduces inflammation in skeletal muscle. These benefits are partially mediated by reductions in mitochondrial fission through the irisin/AMPK signalling pathway.

Keywords:  Diabetes; Exercise training; Inflammation; Irisin; Mitochondrial fission

DOI:  https://doi.org/10.1038/s41598-024-61415-6
J Clin Invest. 2024 May 07. pii: e175619. [Epub ahead of print]

A mitochondrial surveillance mechanism activated by SRSF2 mutations in hematologic malignancies.

Xiaolei Liu, Sudhish A Devadiga, Robert F Stanley, Ryan M Morrow, Kevin A Janssen, Mathieu Quesnel-Vallières, Oz Pomp, Adam A Moverley, Chenchen Li, Nicolas Skuli, Martin P Carroll, Jian Huang, Douglas C Wallace, Kristen W Lynch, Omar Abdel-Wahab, Peter S Klein.

  Splicing factor mutations are common in myelodysplastic syndrome (MDS) and acute myeloid leukemia (AML), but how they alter cellular functions is unclear. We show that the pathogenic SRSF2P95H/+ mutation disrupts the splicing of mitochondrial mRNAs, impairs mitochondrial complex I function, and robustly increases mitophagy. We also identified a mitochondrial surveillance mechanism by which mitochondrial dysfunction modifies splicing of the mitophagy activator PINK1 to remove a poison intron, increasing the stability and abundance of PINK1 mRNA and protein. SRSF2P95H-induced mitochondrial dysfunction increased PINK1 expression through this mechanism, which is essential for survival of SRSF2P95H/+ cells. Inhibition of splicing with a glycogen synthase kinase 3 inhibitor promoted retention of the poison intron, impairing mitophagy and activating apoptosis in SRSF2P95H/+ cells. These data reveal a homeostatic mechanism for sensing mitochondrial stress through PINK1 splicing and identify increased mitophagy as a disease marker and a therapeutic vulnerability in SRSF2P95H mutant MDS and AML.

Keywords:  Autophagy; Hematology; Leukemias; Mitochondria; Oncology

DOI:  https://doi.org/10.1172/JCI175619
FASEB J. 2024 May 15. 38(9): e23654

Metformin induction of heat shock factor 1 activation and the mitochondrial unfolded protein response alleviate cardiac remodeling in spontaneously hypertensive rats.

Man Xu, Li-Peng Li, Xi He, Xing-Zhu Lu, Xue-Yuan Bi, Qi Li, Xiao-Rong Xue.

  Heart failure and cardiac remodeling are both characterized by mitochondrial dysfunction. Healthy mitochondria are required for adequate contractile activity and appropriate regulation of cell survival. In the mammalian heart, enhancement of the mitochondrial unfolded protein response (UPRmt) is cardioprotective under pressure overload conditions. We explored the UPRmt and the underlying regulatory mechanism in terms of hypertension-induced cardiac remodeling and the cardioprotective effect of metformin. Male spontaneously hypertensive rats and angiotensin II-treated neonatal rat cardiomyocytes were used to induce cardiac hypertrophy. The results showed that hypertension induced the formation of aberrant mitochondria, characterized by a reduced mtDNA/nDNA ratio and swelling, as well as lower levels of mitochondrial complexes I to V and inhibition of the expression of one protein subunit of each of complexes I to IV. Such changes eventually enlarged cardiomyocytes and increased cardiac fibrosis. Metformin treatment increased the mtDNA/nDNA ratio and regulated the UPRmt, as indicated by increased expression of activating transcription factor 5, Lon protease 1, and heat shock protein 60, and decreased expression of C/EBP homologous protein. Thus, metformin improved mitochondrial ultrastructure and function in spontaneously hypertensive rats. In vitro analyses revealed that metformin reduced the high levels of angiotensin II-induced mitochondrial reactive oxygen species in such animals and stimulated nuclear translocation of heat shock factor 1 (HSF1). Moreover, HSF1 small-interfering RNA reduced the metformin-mediated improvements in mitochondrial morphology and the UPRmt by suppressing hypertrophic signals and cardiomyocyte apoptosis. These results suggest that HSF1/UPRmt signaling contributes to the beneficial effects of metformin. Metformin-mediated targeting of mitochondrial protein homeostasis and modulation of HSF1 levels have potential therapeutic implications in terms of cardiac remodeling.

Keywords:  cardiac remodeling; heat shock factor 1; hypertension; metformin; mitochondrial unfolded protein response

DOI:  https://doi.org/10.1096/fj.202400070R