bims-mimbat 2024-06-30 papers

bims-mimbat

Biomed News

on Mitochondrial metabolism in brown adipose tissue

Issue of 2024–06–30
eight papers selected by
José Carlos de Lima-Júnior, Washington University

Drosophila immune cells transport oxygen through PPO2 protein phase transition.
The extracellular matrix integrates mitochondrial homeostasis.
Human mitochondrial carriers of the SLC25 family function as monomers exchanging substrates with a ping-pong kinetic mechanism.
Mitochondrial respiratory complex I can be inhibited via bypassing the ubiquinone-accessing tunnel.
Implications of mitochondrial membrane potential gradients on signaling and ATP production analyzed by correlative multi-parameter microscopy.
Pharmacologic Activation of Integrated Stress Response Kinases Inhibits Pathologic Mitochondrial Fragmentation.
Macrophage-derived chemokine CCL22 establishes local LN-mediated adaptive thermogenesis and energy expenditure.
Lactate transported by MCT1 plays an active role in promoting mitochondrial biogenesis and enhancing TCA flux in skeletal muscle.

Nature. 2024 Jun 26.

Drosophila immune cells transport oxygen through PPO2 protein phase transition.

Mingyu Shin, Eunji Chang, Daewon Lee, Nayun Kim, Bumsik Cho, Nuri Cha, Ferdinand Koranteng, Ji-Joon Song, Jiwon Shim.

Insect respiration has long been thought to be solely dependent on an elaborate tracheal system without assistance from the circulatory system or immune cells1,2. Here we describe that Drosophila crystal cells-myeloid-like immune cells called haemocytes-control respiration by oxygenating Prophenoloxidase 2 (PPO2) proteins. Crystal cells direct the movement of haemocytes between the trachea of the larval body wall and the circulation to collect oxygen. Aided by copper and a neutral pH, oxygen is trapped in the crystalline structures of PPO2 in crystal cells. Conversely, PPO2 crystals can be dissolved when carbonic anhydrase lowers the intracellular pH and then reassembled into crystals in cellulo by adhering to the trachea. Physiologically, larvae lacking crystal cells or PPO2, or those expressing a copper-binding mutant of PPO2, display hypoxic responses under normoxic conditions and are susceptible to hypoxia. These hypoxic phenotypes can be rescued by hyperoxia, expression of arthropod haemocyanin or prevention of larval burrowing activity to expose their respiratory organs. Thus, we propose that insect immune cells collaborate with the tracheal system to reserve and transport oxygen through the phase transition of PPO2 crystals, facilitating internal oxygen homeostasis in a process that is comparable to vertebrate respiration.

DOI: https://doi.org/10.1038/s41586-024-07583-x
Cell. 2024 Jun 24. pii: S0092-8674(24)00638-X. [Epub ahead of print]

The extracellular matrix integrates mitochondrial homeostasis.

Hanlin Zhang, C Kimberly Tsui, Gilberto Garcia, Larry K Joe, Haolun Wu, Ayane Maruichi, Wudi Fan, Sentibel Pandovski, Peter H Yoon, Brant M Webster, Jenni Durieux, Phillip A Frankino, Ryo Higuchi-Sanabria, Andrew Dillin.

  Cellular homeostasis is intricately influenced by stimuli from the microenvironment, including signaling molecules, metabolites, and pathogens. Functioning as a signaling hub within the cell, mitochondria integrate information from various intracellular compartments to regulate cellular signaling and metabolism. Multiple studies have shown that mitochondria may respond to various extracellular signaling events. However, it is less clear how changes in the extracellular matrix (ECM) can impact mitochondrial homeostasis to regulate animal physiology. We find that ECM remodeling alters mitochondrial homeostasis in an evolutionarily conserved manner. Mechanistically, ECM remodeling triggers a TGF-β response to induce mitochondrial fission and the unfolded protein response of the mitochondria (UPRMT). At the organismal level, ECM remodeling promotes defense of animals against pathogens through enhanced mitochondrial stress responses. We postulate that this ECM-mitochondria crosstalk represents an ancient immune pathway, which detects infection- or mechanical-stress-induced ECM damage, thereby initiating adaptive mitochondria-based immune and metabolic responses.

Keywords:  TGF-β; TMEM2; extracellular matrix; hyaluronan; immunity; mitochondria

DOI:  https://doi.org/10.1016/j.cell.2024.05.057
EMBO J. 2024 Jun 27.

Human mitochondrial carriers of the SLC25 family function as monomers exchanging substrates with a ping-pong kinetic mechanism.

Camila Cimadamore-Werthein, Martin S King, Denis Lacabanne, Eva Pyrihová, Stephany Jaiquel Baron, Edmund Rs Kunji.

  Members of the SLC25 mitochondrial carrier family link cytosolic and mitochondrial metabolism and support cellular maintenance and growth by transporting compounds across the mitochondrial inner membrane. Their monomeric or dimeric state and kinetic mechanism have been a matter of long-standing debate. It is believed by some that they exist as homodimers and transport substrates with a sequential kinetic mechanism, forming a ternary complex where both exchanged substrates are bound simultaneously. Some studies, in contrast, have provided evidence indicating that the mitochondrial ADP/ATP carrier (SLC25A4) functions as a monomer, has a single substrate binding site, and operates with a ping-pong kinetic mechanism, whereby ADP is imported before ATP is exported. Here we reanalyze the oligomeric state and kinetic properties of the human mitochondrial citrate carrier (SLC25A1), dicarboxylate carrier (SLC25A10), oxoglutarate carrier (SLC25A11), and aspartate/glutamate carrier (SLC25A13), all previously reported to be dimers with a sequential kinetic mechanism. We demonstrate that they are monomers, except for dimeric SLC25A13, and operate with a ping-pong kinetic mechanism in which the substrate import and export steps occur consecutively. These observations are consistent with a common transport mechanism, based on a functional monomer, in which a single central substrate-binding site is alternately accessible.

Keywords:  Bioenergetics; Kinetic Analysis; Mitochondria; SLC25 Mitochondrial Carrier Family; Transport

DOI:  https://doi.org/10.1038/s44318-024-00150-0
FEBS Lett. 2024 Jun 25.

Mitochondrial respiratory complex I can be inhibited via bypassing the ubiquinone-accessing tunnel.

Ryohei Otani, Takahiro Masuya, Hideto Miyoshi, Masatoshi Murai.

  Mitochondrial NADH-ubiquinone oxidoreductase (complex I) couples electron transfer from NADH to ubiquinone with proton translocation in its membrane part. Structural studies have identified a long (~ 30 Å), narrow, tunnel-like cavity within the enzyme, through which ubiquinone may access a deep reaction site. Although various inhibitors are considered to block the ubiquinone reduction by occupying the tunnel's interior, this view is still debatable. We synthesized a phosphatidylcholine-quinazoline hybrid compound (PC-Qz1), in which a quinazoline-type toxophore was attached to the sn-2 acyl chain to prevent it from entering the tunnel. However, PC-Qz1 inhibited complex I and suppressed photoaffinity labeling by another quinazoline derivative, [125I]AzQ. This study provides further experimental evidence that is difficult to reconcile with the canonical ubiquinone-accessing tunnel model.

Keywords:  complex I; inhibitor; mitochondria; proteoliposomes; respiratory enzymes; ubiquinone

DOI:  https://doi.org/10.1002/1873-3468.14967
Sci Rep. 2024 06 26. 14(1): 14784

Implications of mitochondrial membrane potential gradients on signaling and ATP production analyzed by correlative multi-parameter microscopy.

Benjamin Gottschalk, Zhanat Koshenov, Roland Malli, Wolfgang F Graier.

  The complex architecture and biochemistry of the inner mitochondrial membrane generate ultra-structures with different phospholipid and protein compositions, shapes, characteristics, and functions. The crista junction (CJ) serves as an important barrier separating the cristae (CM) and inner boundary membranes (IBM). Thereby CJ regulates the movement of ions and ensures distinct electrical potentials across the cristae (ΔΨC) and inner boundary (ΔΨIBM) membranes. We have developed a robust and flexible approach to visualize the CJ permeability with super-resolution microscopy as a readout of local mitochondrial membrane potential (ΔΨmito) fluctuations. This method involves analyzing the distribution of TMRM fluorescence intensity in a model that is restricted to the mitochondrial geometry. We show that mitochondrial Ca2+ elevation hyperpolarizes the CM most likely caused by Ca2+ sensitive increase of mitochondrial tricarboxylic acid cycle (TCA) and subsequent oxidative phosphorylation (OXPHOS) activity in the cristae. Dynamic multi-parameter correlation measurements of spatial mitochondrial membrane potential gradients, ATP levels, and mitochondrial morphometrics revealed a CJ-based membrane potential overflow valve mechanism protecting the mitochondrial integrity during excessive cristae hyperpolarization.

Keywords:  Correlative microscopy; Cristae junctions; Membrane potential gradient; Mitochondria; Mitochondrial membranes

DOI:  https://doi.org/10.1038/s41598-024-65595-z
bioRxiv. 2024 Jun 10. pii: 2024.06.10.598126. [Epub ahead of print]

Pharmacologic Activation of Integrated Stress Response Kinases Inhibits Pathologic Mitochondrial Fragmentation.

Kelsey R Baron, Samantha Oviedo, Sophia Krasny, Mashiat Zaman, Rama Aldakhlallah, Prakhyat Mathur, Gerald Pfeffer, Michael J Bollong, Timothy Shutt, Danielle A Grotjahn, R Luke Wiseman.

Excessive mitochondrial fragmentation is associated with the pathologic mitochondrial dysfunction implicated in the pathogenesis of etiologically-diverse diseases, including many neurodegenerative disorders. The integrated stress response (ISR) - comprising the four eIF2α kinases PERK, GCN2, PKR, and HRI - is a prominent stress-responsive signaling pathway that regulates mitochondrial morphology and function in response to diverse types of pathologic insult. This suggests that pharmacologic, stress-independent activation of the ISR represents a potential strategy to mitigate pathologic mitochondrial fragmentation associated with human disease. Here, we show that pharmacologic, stress-independent activation of the ISR kinases HRI or GCN2 promotes adaptive mitochondrial elongation and prevents mitochondrial fragmentation induced by the calcium ionophore ionomycin. Further, we show that stress-independent activation of these ISR kinases reduces mitochondrial fragmentation and restores basal mitochondrial morphology in patient fibroblasts expressing the pathogenic D414V variant of the pro-fusion mitochondrial GTPase MFN2 associated with neurological dysfunctions including ataxia, optic atrophy, and sensorineural hearing loss. These results identify pharmacologic, stress-independent activation of ISR kinases as a potential strategy to prevent pathologic mitochondrial fragmentation induced by disease-relevant chemical and genetic insults, further motivating the pursuit of highly selective ISR kinase-activating compounds as a therapeutic strategy to mitigate mitochondrial dysfunction implicated in diverse human diseases.

DOI: https://doi.org/10.1101/2024.06.10.598126
Sci Adv. 2024 Jun 28. 10(26): eadn5229

Macrophage-derived chemokine CCL22 establishes local LN-mediated adaptive thermogenesis and energy expenditure.

Yexian Yuan, Ruoci Hu, Jooman Park, Shaolei Xiong, Zilai Wang, Yanyu Qian, Zuoxiao Shi, Ruifan Wu, Zhenbo Han, Sang-Ging Ong, Shuhao Lin, Krista A Varady, Pingwen Xu, Daniel C Berry, Gang Shu, Yuwei Jiang.

There is a regional preference around lymph nodes (LNs) for adipose beiging. Here, we show that local LN removal within inguinal white adipose tissue (iWAT) greatly impairs cold-induced beiging, and this impairment can be restored by injecting M2 macrophages or macrophage-derived C-C motif chemokine (CCL22) into iWAT. CCL22 injection into iWAT effectively promotes iWAT beiging, while blocking CCL22 with antibodies can prevent it. Mechanistically, the CCL22 receptor, C-C motif chemokine receptor 4 (CCR4), within eosinophils and its downstream focal adhesion kinase/p65/interleukin-4 signaling are essential for CCL22-mediated beige adipocyte formation. Moreover, CCL22 levels are inversely correlated with body weight and fat mass in mice and humans. Acute elevation of CCL22 levels effectively prevents diet-induced body weight and fat gain by enhancing adipose beiging. Together, our data identify the CCL22-CCR4 axis as an essential mediator for LN-controlled adaptive thermogenesis and highlight its potential to combat obesity and its associated complications.

DOI: https://doi.org/10.1126/sciadv.adn5229
Sci Adv. 2024 Jun 28. 10(26): eadn4508

Lactate transported by MCT1 plays an active role in promoting mitochondrial biogenesis and enhancing TCA flux in skeletal muscle.

Lingling Zhang, Chenhao Xin, Shuo Wang, Shixuan Zhuo, Jing Zhu, Zi Li, Yuyi Liu, Lifeng Yang, Yan Chen.

Once considered as a "metabolic waste," lactate is now recognized as a major fuel for tricarboxylic acid (TCA) cycle. Our metabolic flux analysis reveals that skeletal muscle mainly uses lactate to fuel TCA cycle. Lactate is transported through the cell membrane via monocarboxylate transporters (MCTs) in which MCT1 is highly expressed in the muscle. We analyzed how MCT1 affects muscle functions using mice with specific deletion of MCT1 in skeletal muscle. MCT1 deletion enhances running performance, increases oxidative fibers while decreasing glycolytic fibers, and enhances flux of glucose to TCA cycle. MCT1 deficiency increases the expression of mitochondrial proteins, augments cell respiration rate, and elevates mitochondrial activity in the muscle. Mechanistically, the protein level of PGC-1α, a master regulator of mitochondrial biogenesis, is elevated upon loss of MCT1 via increases in cellular NAD+ level and SIRT1 activity. Collectively, these results demonstrate that MCT1-mediated lactate shuttle plays a key role in regulating muscle functions by modulating mitochondrial biogenesis and TCA flux.

DOI: https://doi.org/10.1126/sciadv.adn4508