bims-mimbat 2024-03-31 papers

Issue of 2024‒03‒31
five papers selected by
José Carlos de Lima-Júnior, Washington University

Science. 2024 Mar 29. 383(6690): 1484-1492

Pyrimidines maintain mitochondrial pyruvate oxidation to support de novo lipogenesis.

Umakant Sahu, Elodie Villa, Colleen R Reczek, Zibo Zhao, Brendan P O'Hara, Michael D Torno, Rohan Mishra, William D Shannon, John M Asara, Peng Gao, Ali Shilatifard, Navdeep S Chandel, Issam Ben-Sahra.

Cellular purines, particularly adenosine 5'-triphosphate (ATP), fuel many metabolic reactions, but less is known about the direct effects of pyrimidines on cellular metabolism. We found that pyrimidines, but not purines, maintain pyruvate oxidation and the tricarboxylic citric acid (TCA) cycle by regulating pyruvate dehydrogenase (PDH) activity. PDH activity requires sufficient substrates and cofactors, including thiamine pyrophosphate (TPP). Depletion of cellular pyrimidines decreased TPP synthesis, a reaction carried out by TPP kinase 1 (TPK1), which reportedly uses ATP to phosphorylate thiamine (vitamin B1). We found that uridine 5'-triphosphate (UTP) acts as the preferred substrate for TPK1, enabling cellular TPP synthesis, PDH activity, TCA-cycle activity, lipogenesis, and adipocyte differentiation. Thus, UTP is required for vitamin B1 utilization to maintain pyruvate oxidation and lipogenesis.

DOI: https://doi.org/10.1126/science.adh2771

Adipocyte. 2024 Dec;13(1): 2330355

A comparative assessment of reference genes in mouse brown adipocyte differentiation and thermogenesis in vitro.

Trang Huyen Lai, Jin Seok Hwang, Quang Nhat Ngo, Dong-Kun Lee, Hyun Joon Kim, Deok Ryong Kim.

Adipogenic differentiation and thermogenesis in brown adipose tissue (BAT) undergo dynamic processes, altering phenotypes and gene expressions. Proper reference genes in gene expression analysis are crucial to mitigate experimental variances and ensure PCR efficacy. Unreliable reference genes can lead to erroneous gene expression quantification, resulting in data misinterpretation. This study focused on identifying suitable reference genes for mouse brown adipocyte research, utilizing brown adipocytes from the Ucp1-luciferase ThermoMouse model. Comparative analysis of gene expression data under adipogenesis and thermogenesis conditions was conducted, validating 13 housekeeping genes through various algorithms, including DeltaCq, BestKeeper, geNorm, Normfinder, and RefFinder. Tbp and Rer1 emerged as optimal references for Ucp1 and Pparg expression in brown adipogenesis, while Tbp and Ubc were ideal for the expression analysis of these target genes in thermogenesis. Conversely, certain conventional references, including Actb, Tubb5, and Gapdh, proved unstable as reference genes under both conditions. These findings stress the critical consideration of reference gene selection in gene expression analysis within specific biological systems to ensure accurate conclusions.

Keywords: Reference gene; Ucp1; adipocyte differentiation; brown adipocytes; thermogenesis

DOI: https://doi.org/10.1080/21623945.2024.2330355

Cell Rep. 2024 Mar 22. pii: S2211-1247(24)00306-1. [Epub ahead of print]43(4): 113978

MAFB in macrophages regulates cold-induced neuronal density in brown adipose tissue.

Manoj Kumar Yadav, Megumi Ishida, Natalia Gogoleva, Ching-Wei Liao, Filiani Natalia Salim, Maho Kanai, Akihiro Kuno, Takuto Hayashi, Zeynab Javanfekr Shahri, Kaushalya Kulathunga, Omar Samir, Wenxin Lyu, Olivia Olivia, Evaristus C Mbanefo, Satoru Takahashi, Michito Hamada.

Transcription factor MAFB regulates various homeostatic functions of macrophages. This study explores the role of MAFB in brown adipose tissue (BAT) thermogenesis using macrophage-specific Mafb-deficient (Mafbf/f::LysM-Cre) mice. We find that Mafb deficiency in macrophages reduces thermogenesis, energy expenditure, and sympathetic neuron (SN) density in BAT under cold conditions. This phenotype features a proinflammatory environment that is characterized by macrophage/granulocyte accumulation, increases in interleukin-6 (IL-6) production, and IL-6 trans-signaling, which lead to decreases in nerve growth factor (NGF) expression and reduction in SN density in BAT. We confirm MAFB regulation of IL-6 expression using luciferase readout driven by IL-6 promoter in RAW-264.7 macrophage cell lines. Immunohistochemistry shows clustered organization of NGF-producing cells in BAT, which are primarily TRPV1+ vascular smooth muscle cells, as additionally shown using single-cell RNA sequencing and RT-qPCR of the stromal vascular fraction. Treating Mafbf/f::LysM-Cre mice with anti-IL-6 receptor antibody rescues SN density, body temperature, and energy expenditure.

Keywords: BAT; CP: Immunology; CP: Metabolism; MAFB; NGF; SN; TRPV1+ vascular smooth muscle cells; brown adipose tissue thermogenesis; interleukin-6 (IL-6); nerve growth factor; progenitors of brown adipocytes; sympathetic neuronal density

DOI: https://doi.org/10.1016/j.celrep.2024.113978

J Cell Biol. 2024 May 06. pii: e202306051. [Epub ahead of print]223(5):

OMA1 protease eliminates arrested protein import intermediates upon mitochondrial depolarization.

Magda Krakowczyk, Anna M Lenkiewicz, Tomasz Sitarz, Dominika Malinska, Mayra Borrero, Ben Hur Marins Mussulini, Vanessa Linke, Andrzej A Szczepankiewicz, Joanna M Biazik, Agata Wydrych, Hanna Nieznanska, Remigiusz A Serwa, Agnieszka Chacinska, Piotr Bragoszewski.

Most mitochondrial proteins originate from the cytosol and require transport into the organelle. Such precursor proteins must be unfolded to pass through translocation channels in mitochondrial membranes. Misfolding of transported proteins can result in their arrest and translocation failure. Arrested proteins block further import, disturbing mitochondrial functions and cellular proteostasis. Cellular responses to translocation failure have been defined in yeast. We developed the cell line-based translocase clogging model to discover molecular mechanisms that resolve failed import events in humans. The mechanism we uncover differs significantly from these described in fungi, where ATPase-driven extraction of blocked protein is directly coupled with proteasomal processing. We found human cells to rely primarily on mitochondrial factors to clear translocation channel blockage. The mitochondrial membrane depolarization triggered proteolytic cleavage of the stalled protein, which involved mitochondrial protease OMA1. The cleavage allowed releasing the protein fragment that blocked the translocase. The released fragment was further cleared in the cytosol by VCP/p97 and the proteasome.

DOI: https://doi.org/10.1083/jcb.202306051

Channels (Austin). 2024 Dec;18(1): 2335467

Ion channel-mediated mitochondrial volume regulation and its relationship with mitochondrial dynamics.

Yujia Zhuang, Wenting Jiang, Zhe Zhao, Wencui Li, Zhiqin Deng, Jianquan Liu.

The mitochondrion, one of the important cellular organelles, has the major function of generating adenosine triphosphate and plays an important role in maintaining cellular homeostasis, governing signal transduction, regulating membrane potential, controlling programmed cell death and modulating cell proliferation. The dynamic balance of mitochondrial volume is an important factor required for maintaining the structural integrity of the organelle and exerting corresponding functions. Changes in the mitochondrial volume are closely reflected in a series of biological functions and pathological changes. The mitochondrial volume is controlled by the osmotic balance between the cytoplasm and the mitochondrial matrix. Thus, any disruption in the influx of the main ion, potassium, into the cells can disturb the osmotic balance between the cytoplasm and the matrix, leading to water movement between these compartments and subsequent alterations in mitochondrial volume. Recent studies have shown that mitochondrial volume homeostasis is closely implicated in a variety of diseases. In this review, we provide an overview of the main influencing factors and research progress in the field of mitochondrial volume homeostasis.

Keywords: Ion channels; cell volume regulation; mitochondrial

DOI: https://doi.org/10.1080/19336950.2024.2335467