bims-mimbat 2023-12-17 papers

bims-mimbat

Biomed News

on Mitochondrial metabolism in brown adipose tissue

Issue of 2023–12–17
six papers selected by
José Carlos de Lima-Júnior, Washington University

Heme biosynthesis regulates BCAA catabolism and thermogenesis in brown adipose tissue.
The mitochondrial ATP synthase is a negative regulator of the mitochondrial permeability transition pore.
Mitochondrial temperature homeostasis resists external metabolic stresses.
Specific protonation of acidic residues confers K+ selectivity to the gastric proton pump.
Immunomodulatory leptin receptor+ sympathetic perineurial barrier cells protect against obesity by facilitating brown adipose tissue thermogenesis.
Light-gated channelrhodopsin sparks proton-induced calcium release in guard cells.

bioRxiv. 2023 Nov 28. pii: 2023.11.28.568893. [Epub ahead of print]

Heme biosynthesis regulates BCAA catabolism and thermogenesis in brown adipose tissue.

Dylan J Duerre, Julia K Hansen, Steven John, Annie Jen, Noah Carrillo, Hoang Bui, Yutong Bao, Matias Fabregat, Katherine Overmeyer, Evgenia Shishkova, Mark P Keller, Richard A Anderson, Vincent L Cryns, Alan D Attie, Joshua J Coon, Jing Fan, Andrea Galmozzi.

With age, people tend to accumulate body fat and reduce energy expenditure 1 . Brown (BAT) and beige adipose tissue dissipate heat and increase energy expenditure via the activity of the uncoupling protein UCP1 and other thermogenic futile cycles 2,3 . The activity of brown and beige depots inversely correlates with BMI and age 4-11 , suggesting that promoting thermogenesis may be an effective approach for combating age-related metabolic disease 12-15 . Heme is an enzyme cofactor and signaling molecule that we recently showed to regulate BAT function 16 . Here, we show that heme biosynthesis is the primary contributor to intracellular heme levels in brown adipocytes. Inhibition of heme biosynthesis leads to mitochondrial dysfunction and reduction in UCP1. Although supplementing heme can restore mitochondrial function in heme-synthesis-deficient cells, the downregulation of UCP1 persists due to the accumulation of the heme precursors, particularly propionyl-CoA, which is a product of branched-chain amino acids (BCAA) catabolism. Cold exposure promotes BCAA uptake in BAT, and defects in BCAA catabolism in this tissue hinder thermogenesis 17 . However, BCAAs' contribution to the TCA cycle in BAT and WAT never exceeds 2% of total TCA flux 18 . Our work offers a way to integrate current literature by describing heme biosynthesis as an important metabolic sink for BCAAs.

DOI: https://doi.org/10.1101/2023.11.28.568893
Proc Natl Acad Sci U S A. 2023 Dec 19. 120(51): e2303713120

The mitochondrial ATP synthase is a negative regulator of the mitochondrial permeability transition pore.

Ryan Pekson, Felix G Liang, Joshua L Axelrod, Jaehoon Lee, Dongze Qin, Andre J H Wittig, Victor M Paulino, Min Zheng, Pablo M Peixoto, Richard N Kitsis.

  The mitochondrial permeability transition pore (mPTP) is a channel in the inner mitochondrial membrane whose sustained opening in response to elevated mitochondrial matrix Ca2+ concentrations triggers necrotic cell death. The molecular identity of mPTP is unknown. One proposed candidate is the mitochondrial ATP synthase, whose canonical function is to generate most ATP in multicellular organisms. Here, we present mitochondrial, cellular, and in vivo evidence that, rather than serving as mPTP, the mitochondrial ATP synthase inhibits this pore. Our studies confirm previous work showing persistence of mPTP in HAP1 cell lines lacking an assembled mitochondrial ATP synthase. Unexpectedly, however, we observe that Ca2+-induced pore opening is markedly sensitized by loss of the mitochondrial ATP synthase. Further, mPTP opening in cells lacking the mitochondrial ATP synthase is desensitized by pharmacological inhibition and genetic depletion of the mitochondrial cis-trans prolyl isomerase cyclophilin D as in wild-type cells, indicating that cyclophilin D can modulate mPTP through substrates other than subunits in the assembled mitochondrial ATP synthase. Mitoplast patch clamping studies showed that mPTP channel conductance was unaffected by loss of the mitochondrial ATP synthase but still blocked by cyclophilin D inhibition. Cardiac mitochondria from mice whose heart muscle cells we engineered deficient in the mitochondrial ATP synthase also demonstrate sensitization of Ca2+-induced mPTP opening and desensitization by cyclophilin D inhibition. Further, these mice exhibit strikingly larger myocardial infarctions when challenged with ischemia/reperfusion in vivo. We conclude that the mitochondrial ATP synthase does not function as mPTP and instead negatively regulates this pore.

Keywords:  mitochondrial ATP synthase; mitochondrial permeability transition pore; necrosis

DOI:  https://doi.org/10.1073/pnas.2303713120
Elife. 2023 Dec 11. pii: RP89232. [Epub ahead of print]12

Mitochondrial temperature homeostasis resists external metabolic stresses.

Mügen Terzioglu, Kristo Veeroja, Toni Montonen, Teemu O Ihalainen, Tiina S Salminen, Paule Bénit, Pierre Rustin, Young-Tae Chang, Takeharu Nagai, Howard T Jacobs.

  Based on studies with a fluorescent reporter dye, Mito Thermo Yellow (MTY), and the genetically encoded gTEMP ratiometric fluorescent temperature indicator targeted to mitochondria, the temperature of active mitochondria in four mammalian and one insect cell line was estimated to be up to 15°C above that of the external environment to which the cells were exposed. High mitochondrial temperature was maintained in the face of a variety of metabolic stresses, including substrate starvation or modification, decreased ATP demand due to inhibition of cytosolic protein synthesis, inhibition of the mitochondrial adenine nucleotide transporter and, if an auxiliary pathway for electron transfer was available via the alternative oxidase, even respiratory poisons acting downstream of oxidative phosphorylation (OXPHOS) complex I. We propose that the high temperature of active mitochondria is an inescapable consequence of the biochemistry of OXPHOS and is homeostatically maintained as a primary feature of mitochondrial metabolism.

Keywords:  D. melanogaster; OXPHOS; biochemistry; bioenergetics; cell biology; chemical biology; human; mitochondria; mouse; organelle; temperature; thermogenesis

DOI:  https://doi.org/10.7554/eLife.89232
J Biol Chem. 2023 Dec 08. pii: S0021-9258(23)02570-X. [Epub ahead of print] 105542

Specific protonation of acidic residues confers K+ selectivity to the gastric proton pump.

Hridya Valia Madapally, Kazuhiro Abe, Vikas Dubey, Himanshu Khandelia.

  The gastric proton pump (H+,K+-ATPase) transports a proton into the stomach lumen for every K+ ion exchanged in the opposite direction. In the lumen-facing state of the pump (E2), the pump selectively binds K+ despite the presence of a 10-fold higher concentration of Na+. The molecular basis for the ion selectivity of the pump is unknown. Using molecular dynamics simulations, free energy calculations, and Na+ and K+ dependent ATPase activity assays, we demonstrate that the K+ selectivity of the pump depends upon the simultaneous protonation of the acidic residues E343 and E795 in the ion binding site. We also show that when E936 is protonated, the pump becomes Na+ sensitive. The protonation-mimetic mutant E936Q exhibits weak Na+-activated ATPase activity. A 2.5 Å resolution cryo-EM structure of the E936Q mutant in the K+-occluded E2-Pi form shows, however, no significant structural difference compared to wild type except less than ideal coordination of K+ in the mutant. The selectivity towards a specific ion correlates with a more rigid and less fluctuating ion-binding site. Despite being exposed to a pH of 1, the fundamental principle driving the K+ ion selectivity of H+,K+-ATPase is similar to that of Na+,K+-ATPase: the ionisation states of the acidic residues in the ion-binding sites determine ion selectivity. Unlike the Na+,K+-ATPase, however, protonation of an ion-binding glutamate residue (E936) confers Na+ sensitivity.

Keywords:  Cryo-EM; H+,K+-ATPase; free energy perturbation; ion selectivity; membrane protein; molecular dynamics; proton pump

DOI:  https://doi.org/10.1016/j.jbc.2023.105542
Immunity. 2023 Dec 05. pii: S1074-7613(23)00488-0. [Epub ahead of print]

Immunomodulatory leptin receptor+ sympathetic perineurial barrier cells protect against obesity by facilitating brown adipose tissue thermogenesis.

Emma R Haberman, Gitalee Sarker, Bernardo A Arús, Karin A Ziegler, Sandro Meunier, Noelia Martínez-Sánchez, Eliška Freibergerová, Sinem Yilmaz-Özcan, Iara Fernández-González, Chloe Zentai, Conan J O O'Brien, David E Grainger, Davi Sidarta-Oliveira, Svetoslav Chakarov, Andrea Raimondi, Matteo Iannacone, Stefan Engelhardt, Miguel López, Florent Ginhoux, Ana I Domingos.

  Adipose tissues (ATs) are innervated by sympathetic nerves, which drive reduction of fat mass via lipolysis and thermogenesis. Here, we report a population of immunomodulatory leptin receptor-positive (LepR+) sympathetic perineurial barrier cells (SPCs) present in mice and humans, which uniquely co-express Lepr and interleukin-33 (Il33) and ensheath AT sympathetic axon bundles. Brown ATs (BATs) of mice lacking IL-33 in SPCs (SPCΔIl33) had fewer regulatory T (Treg) cells and eosinophils, resulting in increased BAT inflammation. SPCΔIl33 mice were more susceptible to diet-induced obesity, independently of food intake. Furthermore, SPCΔIl33 mice had impaired adaptive thermogenesis and were unresponsive to leptin-induced rescue of metabolic adaptation. We therefore identify LepR+ SPCs as a source of IL-33, which orchestrate an anti-inflammatory BAT environment, preserving sympathetic-mediated thermogenesis and body weight homeostasis. LepR+IL-33+ SPCs provide a cellular link between leptin and immune regulation of body weight, unifying neuroendocrinology and immunometabolism as previously disconnected fields of obesity research.

Keywords:  IL-33; Tregs; brown adipose tissue; eosinophils; leptin receptor; obesity; perineurial cells; sympathetic nerves; thermogenesis

DOI:  https://doi.org/10.1016/j.immuni.2023.11.006
Science. 2023 Dec 15. 382(6676): 1314-1318

Light-gated channelrhodopsin sparks proton-induced calcium release in guard cells.

Shouguang Huang, Like Shen, M Rob G Roelfsema, Dirk Becker, Rainer Hedrich.

Although there has been long-standing recognition that stimuli-induced cytosolic pH alterations coincide with changes in calcium ion (Ca2+) levels, the interdependence between protons (H+) and Ca2+ remains poorly understood. We addressed this topic using the light-gated channelrhodopsin HcKCR2 from the pseudofungus Hyphochytrium catenoides, which operates as a H+ conductive, Ca2+ impermeable ion channel on the plasma membrane of plant cells. Light activation of HcKCR2 in Arabidopsis guard cells evokes a transient cytoplasmic acidification that sparks Ca2+ release from the endoplasmic reticulum. A H+-induced cytosolic Ca2+ signal results in membrane depolarization through the activation of Ca2+-dependent SLAC1/SLAH3 anion channels, which enabled us to remotely control stomatal movement. Our study suggests a H+-induced Ca2+ release mechanism in plant cells and establishes HcKCR2 as a tool to dissect the molecular basis of plant intracellular pH and Ca2+ signaling.

DOI: https://doi.org/10.1126/science.adj9696