bims-mimbat 2024-12-29 papers

J Physiol. 2024 Dec 26.

Divergent selection for basal metabolic rate in mice affects the abundance of UCP1 protein: implications for translational studies.

Paweł Brzęk, Piotr Selewestruk, Julita Sadowska, Andrzej K Gębczyński, Aneta Książek, Anastasia Kalinovich, Jan Nedergaard, Marek Konarzewski.

Low basal metabolic rate (BMR) is a risk factor for obesity, whereas elevation of non-shivering thermogenesis (NST) is a promising means to combat obesity. Because heat generated by NST covers thermogenic needs not fulfilled by BMR, one can expect the presence of a negative relationship between both parameters. Understanding of the mechanisms underlying this relationship is therefore important for interpretation of the results of translational experiments and the development of anti-obesity treatments. We studied two lines of laboratory mice divergently selected for high or low level of BMR, raised at 23°C and subsequently acclimated to different ambient temperatures (30, 23 and 4°C). Mice selected for low BMR accumulated more fat but simultaneously showed higher NST capacity and more uncoupling protein-1 (UCP1) in interscapular brown adipose tissue (iBAT), to compensate for their lower heat production through BMR. The between-line difference in UCP1 protein abundance was significant even in mice acclimated to 30°C when the level of UCP1 is very low. Differences in NST capacity between selected lines and acclimation temperatures were explained by UCP1 iBAT abundance. Our results reveal that BMR is inversely correlated with UCP1 protein abundance and NST, even after acclimation to thermoneutrality. Thus, low values of BMR can increase both obesity risk and the magnitude of NST, i.e. the process whose activation has been proposed to mitigate obesity risk. All these effects should be taken into account in the design and interpretation of translational studies on mice models of metabolic diseases. KEY POINTS: Basal metabolic rate (BMR) and non-shivering thermogenesis (NST) based on the activity of uncoupling protein-1 (UCP1) are two main sources of heat in laboratory mice. Both BMR and UCP1 can affect obesity risk in laboratory rodents and humans. Here we studied BMR, NST, and the abundance of UCP1 in laboratory mice selected divergently towards either high or low BMR. We showed that BMR is negatively correlated with UCP1 abundance and this effect is not removed even after acclimation to thermoneutrality. The pattern described reveals that BMR can affect not only obesity risk but also the magnitude of UCP1-mediated NST. Since activation of NST was proposed to mitigate obesity risk, variation in BMR should be taken into account in translational studies of mouse models of metabolic diseases.

Keywords: UCP1; basal metabolic rate; housing temperature; non‐shivering thermogenesis; translational studies

DOI: https://doi.org/10.1113/JP286669

Biochem Biophys Res Commun. 2024 Dec 19. pii: S0006-291X(24)01739-X. [Epub ahead of print]744 151203

Rapid kinetics of H+ transport by membrane pyrophosphatase: Evidence for a "direct-coupling" mechanism.

Viktor A Anashkin, Alexander V Bogachev, Marina V Serebryakova, Elena G Zavyalova, Yulia V Bertsova, Alexander A Baykov.

Stress resistance-conferring membrane pyrophosphatase (mPPase) found in microbes and plants couples pyrophosphate hydrolysis with H+ transport out of the cytoplasm. There are two opposing views on the energy-coupling mechanism in this transporter: the pumping is associated with either pyrophosphate binding to mPPase or the hydrolysis step. We used our recently developed stopped-flow pyranine assay to measure H+ transport into mPPase-containing inverted membrane vesicles on the timescale of a single turnover. The vesicles were prepared from Escherichia coli overproducing the H+-translocating mPPase of Desulfitobacterium hafniense. Pyrophosphate induced linear accumulation of H+ in the vesicles, without evident lag or burst. In contrast, the binding of three nonhydrolyzable pyrophosphate analogs essentially induced no H+ accumulation. These findings are inconsistent with the "pumping-before-hydrolysis" model of mPPase functioning and support the alternative model positing the hydrolysis reaction as the source of the transported H+ ions. mPPase is thus a first "directly-coupled" proton pump.

Keywords: Energy coupling; Proton pump; Proton transport; Pyranine; Stopped flow

DOI: https://doi.org/10.1016/j.bbrc.2024.151203

J Biol Chem. 2024 Dec 23. pii: S0021-9258(24)02619-X. [Epub ahead of print] 108117

Disruption of deoxyribonucleotide triphosphate biosynthesis leads to RAS proto-oncogene activation and perturbation of mitochondrial metabolism.

Rodolphe Suspène, Kyle A Raymond, Pablo Guardado-Calvo, Julien Dairou, Frédéric Bonhomme, Christine Bonenfant, Serge Guyetant, Thierry Lecomte, Jean-Christophe Pagès, Jean-Pierre Vartanian.

Perturbation of the deoxyribonucleotide triphosphate (dNTP) pool is recognized for contributing to the mutagenic processes involved in oncogenesis. The RAS gene family encodes well characterized oncoproteins whose structure and function are among the most frequently altered in several cancers. In this work, we show that fluctuation of the dNTP pool induces CG->TA mutations across the whole genome, including RAS gene at codons for glycine 12 and 13, known hotspots in cancers. Cell culture addition of the ribonucleotide reductase inhibitor thymidine increases the mutation frequency in nuclear DNA and leads to disruption of mitochondrial metabolism. Interestingly, this effect is counteracted by the addition of deoxycytidine. Finally, screening for the loss of hydrogen bonds detecting CG->TA transition in RAS gene of 135 patients with colorectal cancer confirmed the clinical relevance of this process. All together, these data demonstrate that fluctuation of intracellular dNTP pool alters the nuclear DNA and mitochondrial metabolism.

Keywords: DNA; RAS gene; cancer; mitochondria; mutation; nucleotide

DOI: https://doi.org/10.1016/j.jbc.2024.108117

Cell. 2024 Dec 18. pii: S0092-8674(24)01375-8. [Epub ahead of print]

Squeeze pumping of lipids and insecticides by ABCH transporter.

Jinli Chen, Yanwei Duan, Yuanyuan Zhou, Qing Yang.

ATP-binding cassette (ABC) transporter subfamily H is only identified in arthropods and zebrafish. It transports lipids and is related to insecticide resistance. However, the precise mechanisms of its functions remain elusive. Here, we report cryoelectron microscopy (cryo-EM) structures of an ABCH from Tribolium castaneum, a worldwide pest of stored grains, in complex with an HEK293 cell-ceramide lipid, a fluorescent-labeled ceramide, a carbamate insecticide, and a maltose detergent inhibitor. We revealed a narrow, long, and arched substrate-binding tunnel in the transmembrane domains of the transporter dimer with two arginine-gated cytoplasmic entries for the binding and transport of lipids or insecticides. A pair of glutamines above the tunnel acts as a gate for directing substrate to be extruded via a vent-like hydrophilic exit to the extracellular side of the membrane upon ATP binding. Our structures and biochemical data provide mechanistic understanding of lipid transport, insecticide detoxification, and the inhibition of transporter activity by branched maltose detergents.

Keywords: ABC transporter; ABCH; insecticide resistance; lipid transport

DOI: https://doi.org/10.1016/j.cell.2024.11.033