bims-mimbat Biomed News
on Mitochondrial metabolism in brown adipose tissue
Issue of 2024–03–03
six papers selected by
José Carlos de Lima-Júnior, Washington University
  1. PMF-seq: a highly scalable screening strategy for linking genetics to mitochondrial bioenergetics.
  2. Functional hypoxia reduces mitochondrial calcium uptake.
  3. Conjugating uncoupler compounds with hydrophobic hydrocarbon chains to achieve adipose tissue selective drug accumulation.
  4. Mitochondrial uncoupling proteins protect human airway epithelial ciliated cells from oxidative damage.
  5. Mitochondrial function and reactive oxygen species production during human sperm capacitation: Unraveling key players.
  6. The hedonic overdrive model best explains high-fat diet-induced obesity in C57BL/6 mice.
  1. Nat Metab. 2024 Feb 27.
    PMF-seq: a highly scalable screening strategy for linking genetics to mitochondrial bioenergetics.
    Tsz-Leung To, Jason G McCoy, Naomi K Ostriker, Lev S Sandler, Carmen A Mannella, Vamsi K Mootha.
      Our current understanding of mitochondrial organelle physiology has benefited from two broad approaches: classically, cuvette-based measurements with suspensions of isolated mitochondria, in which bioenergetic parameters are monitored acutely in response to respiratory chain substrates and inhibitors1-4, and more recently, highly scalable genetic screens for fitness phenotypes associated with coarse-grained properties of the mitochondrial state5-10. Here we introduce permeabilized-cell mitochondrial function sequencing (PMF-seq) to combine strengths of these two approaches to connect genes to detailed bioenergetic phenotypes. In PMF-seq, the plasma membranes within a pool of CRISPR mutagenized cells are gently permeabilized under conditions that preserve mitochondrial physiology, where detailed bioenergetics can be probed in the same way as with isolated organelles. Cells with desired bioenergetic parameters are selected optically using flow cytometry and subjected to next-generation sequencing. Using PMF-seq, we recover genes differentially required for mitochondrial respiratory chain branching and reversibility. We demonstrate that human D-lactate dehydrogenase specifically conveys electrons from D-lactate into cytochrome c to support mitochondrial membrane polarization. Finally, we screen for genetic modifiers of tBID, a pro-apoptotic protein that acts directly and acutely on mitochondria. We find the loss of the complex V assembly factor ATPAF2 acts as a genetic sensitizer of tBID's acute action. We anticipate that PMF-seq will be valuable for defining genes critical to the physiology of mitochondria and other organelles.
    DOI:  https://doi.org/10.1038/s42255-024-00994-0
  2. Redox Biol. 2024 Jan 17. pii: S2213-2317(24)00013-2. [Epub ahead of print]71 103037
    Functional hypoxia reduces mitochondrial calcium uptake.
    Chris Donnelly, Timea Komlódi, Cristiane Cecatto, Luiza H D Cardoso, Anne-Claire Compagnion, Alessandro Matera, Daniele Tavernari, Olivier Campiche, Rosa Chiara Paolicelli, Nadège Zanou, Bengt Kayser, Erich Gnaiger, Nicolas Place.
      Mitochondrial respiration extends beyond ATP generation, with the organelle participating in many cellular and physiological processes. Parallel changes in components of the mitochondrial electron transfer system with respiration render it an appropriate hub for coordinating cellular adaption to changes in oxygen levels. How changes in respiration under functional hypoxia (i.e., when intracellular O2 levels limit mitochondrial respiration) are relayed by the electron transfer system to impact mitochondrial adaption and remodeling after hypoxic exposure remains poorly defined. This is largely due to challenges integrating findings under controlled and defined O2 levels in studies connecting functions of isolated mitochondria to humans during physical exercise. Here we present experiments under conditions of hypoxia in isolated mitochondria, myotubes and exercising humans. Performing steady-state respirometry with isolated mitochondria we found that oxygen limitation of respiration reduced electron flow and oxidative phosphorylation, lowered the mitochondrial membrane potential difference, and decreased mitochondrial calcium influx. Similarly, in myotubes under functional hypoxia mitochondrial calcium uptake decreased in response to sarcoplasmic reticulum calcium release for contraction. In both myotubes and human skeletal muscle this blunted mitochondrial adaptive responses and remodeling upon contractions. Our results suggest that by regulating calcium uptake the mitochondrial electron transfer system is a hub for coordinating cellular adaption under functional hypoxia.
    Keywords:  Coenzyme Q; Exercise; Membrane potential; Respirometry; Skeletal muscle
    DOI:  https://doi.org/10.1016/j.redox.2024.103037
  3. Sci Rep. 2024 02 28. 14(1): 4932
    Conjugating uncoupler compounds with hydrophobic hydrocarbon chains to achieve adipose tissue selective drug accumulation.
    Mei Ying Ng, Zhi Jian Song, Gopalakrishnan Venkatesan, Sergio Rodriguez-Cuenca, James A West, Shili Yang, Choon Hong Tan, Paul Chi-Lui Ho, Julian L Griffin, Antonio Vidal-Puig, Marcella Bassetto, Thilo Hagen.
      One potential approach for treating obesity is to increase energy expenditure in brown and white adipose tissue. Here we aimed to achieve this outcome by targeting mitochondrial uncoupler compounds selectively to adipose tissue, thus avoiding side effects from uncoupling in other tissues. Selective drug accumulation in adipose tissue has been observed with many lipophilic compounds and dyes. Hence, we explored the feasibility of conjugating uncoupler compounds with a lipophilic C8-hydrocarbon chain via an ether bond. We found that substituting the trifluoromethoxy group in the uncoupler FCCP with a C8-hydrocarbon chain resulted in potent uncoupling activity. Nonetheless, the compound did not elicit therapeutic effects in mice, likely as a consequence of metabolic instability resulting from rapid ether bond cleavage. A lipophilic analog of the uncoupler compound 2,6-dinitrophenol, in which a C8-hydrocarbon chain was conjugated via an ether bond in the para-position (2,6-dinitro-4-(octyloxy)phenol), exhibited increased uncoupling activity compared to the parent compound. However, in vivo pharmacokinetics studies suggested that 2,6-dinitro-4-(octyloxy)phenol was also metabolically unstable. In conclusion, conjugation of a hydrophobic hydrocarbon chain to uncoupler compounds resulted in sustained or improved uncoupling activity. However, an ether bond linkage led to metabolic instability, indicating the need to conjugate lipophilic groups via other chemical bonds.
    DOI:  https://doi.org/10.1038/s41598-024-54466-2
  4. Proc Natl Acad Sci U S A. 2024 Mar 05. 121(10): e2318771121
    Mitochondrial uncoupling proteins protect human airway epithelial ciliated cells from oxidative damage.
    Akansha Jain, Bo Ram Kim, Wenjie Yu, Thomas O Moninger, Philip H Karp, Brett A Wagner, Michael J Welsh.
      Apical cilia on epithelial cells defend the lung by propelling pathogens and particulates out of the respiratory airways. Ciliated cells produce ATP that powers cilia beating by densely grouping mitochondria just beneath the apical membrane. However, this efficient localization comes at a cost because electrons leaked during oxidative phosphorylation react with molecular oxygen to form superoxide, and thus, the cluster of mitochondria creates a hotspot for oxidant production. The relatively high oxygen concentration overlying airway epithelia further intensifies the risk of generating superoxide. Thus, airway ciliated cells face a unique challenge of producing harmful levels of oxidants. However, surprisingly, highly ciliated epithelia produce less reactive oxygen species (ROS) than epithelia with few ciliated cells. Compared to other airway cell types, ciliated cells express high levels of mitochondrial uncoupling proteins, UCP2 and UCP5. These proteins decrease mitochondrial protonmotive force and thereby reduce production of ROS. As a result, lipid peroxidation, a marker of oxidant injury, decreases. However, mitochondrial uncoupling proteins exact a price for decreasing oxidant production; they decrease the fraction of mitochondrial respiration that generates ATP. These findings indicate that ciliated cells sacrifice mitochondrial efficiency in exchange for safety from damaging oxidation. Employing uncoupling proteins to prevent oxidant production, instead of relying solely on antioxidants to decrease postproduction oxidant levels, may offer an advantage for targeting a local area of intense ROS generation.
    Keywords:  lung; metabolism; motile cilia; oxygen; reactive oxygen species
    DOI:  https://doi.org/10.1073/pnas.2318771121
  5. FASEB J. 2024 Feb 29. 38(4): e23486
    Mitochondrial function and reactive oxygen species production during human sperm capacitation: Unraveling key players.
    Pilar Irigoyen, Santiago Mansilla, Laura Castro, Adriana Cassina, Rossana Sapiro.
      Sperm capacitation is a critical process for male fertility. It involves a series of biochemical and physiological changes that occur in the female reproductive tract, rendering the sperm competent for successful fertilization. The precise mechanisms and, specifically, the role of mitochondria, in sperm capacitation remain incompletely understood. Previously, we revealed that in mouse sperm mitochondrial activity (e.g., oxygen consumption, membrane potential, ATP/ADP exchange, and mitochondrial Ca2+ ) increases during capacitation. Herein, we studied mitochondrial function by high-resolution respirometry (HRR) and reactive oxygen species production in capacitated (CAP) and non-capacitated (NC) human spermatozoa. We found that in capacitated sperm from normozoospermic donors, the respiratory control ratio increased by 36%, accompanied by a double oxygen consumption rate (OCR) in the presence of antimycin A. Extracellular hydrogen peroxide (H2 O2 ) detection was three times higher in CAP than in NC sperm cells. To confirm that H2 O2 production depends on mitochondrial superoxide ( O2·-$$ {\mathrm{O}}_2^{\cdotp -} $$ ) formation, we evaluated mitochondrial aconitase (ACO2) amount, activity, and role in the metabolic flux from the sperm tricarboxylic acid cycle. We estimated that CAP cells produce, on average by individual, (59 ± 22)% more O2·-$$ {\mathrm{O}}_2^{\cdotp -} $$ in the steady-state compared to NC cells. Finally, we analyzed two targets of oxidative stress: lipid peroxidation by western blot against 4-hydroxynonenal and succinate dehydrogenase (SDH) activity by HRR. We did not observe modifications in lipoperoxidation nor the activity of SDH, suggesting that during capacitation, the increase in mitochondrial H2 O2 production does not damage sperm and it is necessary for the normal CAP process.
    Keywords:  aconitase 2; male fertility; mitochondrial activity; reactive oxygen species; respirometry assay; sperm capacitation
    DOI:  https://doi.org/10.1096/fj.202301957RR
  6. Obesity (Silver Spring). 2024 Feb 27.
    The hedonic overdrive model best explains high-fat diet-induced obesity in C57BL/6 mice.
    Lin Gao, Sumei Hu, Dengbao Yang, Lu Wang, Jacques Togo, Yingga Wu, Baoguo Li, Min Li, Guanlin Wang, Xueying Zhang, Li Li, Yanchao Xu, Moshen Mazidi, Elspeth Couper, Andrew Whittington-Davies, Chaoqun Niu, John R Speakman.
       OBJECTIVE: High-fat diets cause obesity in male mice; however, the underlying mechanisms remain controversial. Here, three contrasting ideas were assessed: hedonic overdrive, reverse causality, and passive overconsumption models.
    METHODS: A total of 12 groups of 20 individually housed 12-week-old C57BL/6 male mice were exposed to 12 high-fat diets with varying fat content from 40% to 80% (by calories), protein content from 5% to 30%, and carbohydrate content from 8.4% to 40%. Body weight and food intake were monitored for 30 days after 7 days at baseline on a standard low-fat diet.
    RESULTS: After exposure to the diets, energy intake increased first, and body weight followed later. Intake then declined. The peak energy intake was dependent on both dietary protein and carbohydrate, but not the dietary fat and energy density, whereas the rate of decrease in intake was only related to dietary protein. On high-fat diets, the weight of food intake declined, but despite this average reduction of 14.4 g in food intake, they consumed, on average, 357 kJ more energy than at baseline.
    CONCLUSIONS: The hedonic overdrive model fit the data best. The other two models were not supported.
    DOI:  https://doi.org/10.1002/oby.23991
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