bims-mimbat 2023-10-22 papers

J Clin Invest. 2023 Oct 19. pii: e168992. [Epub ahead of print]

GPR84-mediated signal transduction effects metabolic function by promoting brown adipocyte activity.

Xuenan Sun, Yu A An, Vivian A Paschoal, Camila O De Souza, May-Yun Wang, Lavanya Vishvanath, Lorena Ma Bueno, Ayanna S Cobb, Joseph A Nieto Carrion, Madison E Ibe, Chao Li, Harrison A Kidd, Shiuhwei Chen, Wenhong Li, Rana K Gupta, Da Young Oh.

The G protein-coupled receptor 84 (GPR84), a medium-chain fatty acid receptor, has garnered attention because of its potential involvement in a range of metabolic conditions. However, the precise mechanisms underlying this effect remain elusive. Our study has shed light on the pivotal role of GPR84, revealing its robust expression and functional significance within the brown adipose tissue (BAT). Mice lacking GPR84 exhibited increased lipid accumulation in BAT, rendering them more susceptible to cold exposure, and displaying reduced BAT activity compared to their wild-type counterparts. Our in vitro experiments with primary brown adipocytes from GPR84 knockout mice revealed diminished expression of thermogenic genes and reduced O2 consumption. Furthermore, the application of the GPR84 agonist 6-OAU counteracted these effects, effectively reinstating the brown adipocyte activity. These compelling in vivo and in vitro findings converge to highlight mitochondrial dysfunction as the primary cause of BAT anomalies in GPR84 knockout mice. The activation of GPR84 induced an increase in intracellular Ca2+ levels, which intricately influences mitochondrial respiration. By modulating mitochondrial Ca2+ levels and respiration, GPR84 has emerged as a potent molecule involved in BAT activity. These findings suggested that GPR84 is a potential therapeutic target for invigorating BAT and ameliorating metabolic disorders.

Keywords: Adipose tissue; Calcium; Cell Biology; Metabolism; Molecular biology

DOI: https://doi.org/10.1172/JCI168992

iScience. 2023 Oct 20. 26(10): 108091

Phosphorylated YBX2 is stabilized to promote glycolysis in brown adipocytes.

Qingwen Zhao, Chao Yu, Xiaoxuan Xu, Wenfang Jin, Zhe Zhang, Haiyan Huang, Yue Gao, Dongning Pan.

Y-box binding protein 2 (YBX2) is an essential modulator of brown adipose tissue activation, yet the regulation on its own expression and the involved mechanism remains largely unknown. Herein, we report the YBX2 protein level, but not mRNA level, is induced in response to acute β-adrenergic signaling. In this context, YBX2 is a dual substrate for both AMPK and Akt2. The phosphorylation at Thr115 by AMPK or at Ser137 by Akt2 facilitates YBX2 accumulation in brown adipocytes by decreasing ubiquitination-mediated degradation. Beyond stabilizing PGC1α mRNA, increased YBX2 upon thermogenic activation assists the expression of glycolytic enzymes, promotes glucose utilization and lactate production. Mechanistically, YBX2 modulates translation of glycolytic genes via direct binding to 5'-UTRs of these genes. Together these findings suggest YBX2 is responsive to thermogenic stimuli by phosphorylation modification, and stabilized YBX2 helps to boost glycolysis and thermogenesis in brown adipocytes.

Keywords: Cell biology; Human metabolism

DOI: https://doi.org/10.1016/j.isci.2023.108091

Nat Commun. 2023 Oct 17. 14(1): 6531

Endogenous renal adiponectin drives gluconeogenesis through enhancing pyruvate and fatty acid utilization.

Adiponectin is a secretory protein, primarily produced in adipocytes. However, low but detectable expression of adiponectin can be observed in cell types beyond adipocytes, particularly in kidney tubular cells, but its local renal role is unknown. We assessed the impact of renal adiponectin by utilizing male inducible kidney tubular cell-specific adiponectin overexpression or knockout mice. Kidney-specific adiponectin overexpression induces a doubling of phosphoenolpyruvate carboxylase expression and enhanced pyruvate-mediated glucose production, tricarboxylic acid cycle intermediates and an upregulation of fatty acid oxidation (FAO). Inhibition of FAO reduces the adiponectin-induced enhancement of glucose production, highlighting the role of FAO in the induction of renal gluconeogenesis. In contrast, mice lacking adiponectin in the kidney exhibit enhanced glucose tolerance, lower utilization and greater accumulation of lipid species. Hence, renal adiponectin is an inducer of gluconeogenesis by driving enhanced local FAO and further underlines the important systemic contribution of renal gluconeogenesis.

DOI: https://doi.org/10.1038/s41467-023-42188-4

Proc Biol Sci. 2023 Oct 25. 290(2009): 20230922

Spontaneous recurrence of a summer-like diel rhythm in the body temperature of the Syrian hamster after hibernation.

Satoshi Nakagawa, Yoshifumi Yamaguchi.

Mammalian hibernation is a survival strategy characterized by metabolic suppression and drastically lowering body temperature (Tb), used during harsh seasons with food shortages and cold. The Syrian hamster commences hibernation in response to a short photoperiod and cold but spontaneously concludes hibernation after several months without environmental cues. Little is known about the changes in diel rhythms during hibernation. Using long-term and high-resolution Tb data, we analysed the diel Tb rhythm time-course changes in Syrian hamsters raised under summer-like conditions (long photoperiod (LP) and warm; LP-warm) and transferred to winter-like conditions (short photoperiod (SP) and cold; SP-cold). The diel Tb rhythm was undetectable during the hibernation period (HIBP), reappearing after the HIBP. The phase of this returning rhythm reverted to the LP entrainment phase characteristics despite the ambient SP and then re-entrained to the ambient SP as if the hamsters were transferred from the LP-warm to SP-cold conditions. The diel Tb rhythm reverted from the SP- to LP-type in a hibernation-dependent manner. Under constant dark and cold conditions, the circadian Tb rhythm recovered without photic stimuli following the HIBP. These findings suggest that hibernation involves a program that anticipates the ambient photoperiod when animals emerge from hibernation.

Keywords: Syrian hamster; body temperature; diel rhythm; hibernation; mammal; seasonal adaptation

DOI: https://doi.org/10.1098/rspb.2023.0922

PLoS Biol. 2023 Oct 20. 21(10): e3002180

Microbial thermogenesis is dependent on ATP concentrations and the protein kinases ArcB, GlnL, and YccC.

Puneet Singh Dhatt, Stephen Chiu, Tae Seok Moon.

Organisms necessarily release heat energy in their pursuit of survival. This process is known as cellular thermogenesis and is implicated in many processes from cancer metabolism to spontaneous farm fires. However, the molecular basis for this fundamental phenomenon is yet to be elucidated. Here, we show that the major players involved in the cellular thermogenesis of Escherichia coli are the protein kinases ArcB, GlnL, and YccC. We also reveal the substrate-level control of adenosine triphosphate (ATP)-driven autophosphorylation that governs cellular thermogenesis. Specifically, through live cell microcalorimetry, we find these regulatory proteins, when knocked out in a model E. coli strain, dysregulate cellular thermogenesis. This dysregulation can be seen in an average 25% or greater increase in heat output by these cells. We also discover that both heat output and intracellular ATP levels are maximal during the late log phase of growth. Additionally, we show that microbial thermogenesis can be engineered through overexpressing glnL. Our results demonstrate a correlation between ATP concentrations in the cell and a cell's ability to generate excess heat. We expect this work to be the foundation for engineering thermogenically tuned organisms for a variety of applications.

DOI: https://doi.org/10.1371/journal.pbio.3002180

Cell Signal. 2023 Oct 17. pii: S0898-6568(23)00346-7. [Epub ahead of print] 110931

SIRT4 is a regulator of human skeletal muscle fatty acid metabolism influencing inner and outer mitochondrial-mediated fusion.

John Noone, Keith D Rochfort, Finbarr O'Sullivan, Donal J O'Gorman.

OBJECTIVE: The mitochondrial phenotype, governed by the balance of fusion-fission, is a key determinant of energy metabolism. The inner and outer mitochondrial membrane (IMM) fusion proteins optic atrophy 1 (OPA1) and Mitofusin 1 and 2 (Mfn1/2) play an important role in this process. Recent evidence also shows that Sirtuin 4 (SIRT4), located within the mitochondria, is involved in the regulation of fatty acid oxidation. The purpose of this study was to determine if SIRT4 expression regulates inner and outer mitochondrial-mediated fusion and substrate utilization within differentiated human skeletal muscle cells (HSkMC).
MATERIAL AND METHODS: SIRT4 expression was knocked down using small interfering RNA (siRNA) transfection in differentiated HSkMC. Following knockdown, mitochondrial respiration was determined by high-resolution respirometry (HRR) using the Oroboros Oxygraph O2k. Live cell confocal microscopy, quantified using the Mitochondrial Network Analysis (MiNA) toolset, was used to examine mitochondrial morphological change. This was further examined through the measurement of key metabolic and mitochondrial morphological regulators (mRNA and protein) induced by knockdown.
RESULTS: SIRT4 knockdown resulted in a significant decrease in LEAK respiration, potentially explained by a decrease in ANT1 protein expression. Knockdown further increased oxidative phosphorylation and protein expression of key regulators of fatty acid metabolism. Quantitative analysis of live confocal imaging of fluorescently labelled mitochondria following SIRT4 knockdown supported the role SIRT4 plays in the regulation of mitochondrial morphology, as emphasized by an increase in mitochondrial network branches and junctions. Measurement of key regulators of mitochondrial dynamics illustrated a significant increase in mitochondrial fusion proteins Mfn1, OPA1 respectively, indicative of an increase in mitochondrial size.
CONCLUSIONS: This study provides evidence of a direct relationship between the mitochondrial phenotype and substrate oxidation in HSkMC. We identify SIRT4 as a key protagonist of energy metabolism via its regulation of IMM and OMM fusion proteins, OPA1 and Mfn1. SIRT4 knockdown increases mitochondrial capacity to oxidize fatty acids, decreasing LEAK respiration and further increasing mitochondrial elongation via its regulation of mitochondrial fusion.

Keywords: Metabolism; Mitochondrial dynamics; Mitochondrial function; OPA1; Sirtuin; Skeletal muscle

DOI: https://doi.org/10.1016/j.cellsig.2023.110931

Nat Chem Biol. 2023 Oct 19.

Long-term super-resolution inner mitochondrial membrane imaging with a lipid probe.

Shuai Zheng, Neville Dadina, Deepto Mozumdar, Lauren Lesiak, Kayli N Martinez, Evan W Miller, Alanna Schepartz.

The inner mitochondrial membrane (IMM) generates power to drive cell function, and its dynamics control mitochondrial health and cellular homeostasis. Here, we describe the cell-permeant, lipid-like small molecule MAO-N3 and use it to assemble high-density environmentally sensitive (HIDE) probes that selectively label and image the IMM in live cells and multiple cell states. MAO-N3 pairs with strain-promoted azide-alkyne click chemistry-reactive fluorophores to support HIDE imaging using confocal, structured illumination, single-molecule localization and stimulated emission depletion microscopy, all with significantly improved resistance to photobleaching. These probes generate images with excellent spatial and temporal resolution, require no genetic manipulations, are non-toxic in model cell lines and primary cardiomyocytes (even under conditions that amplify the effects of mitochondrial toxins) and can visualize mitochondrial dynamics for 12.5 h. This probe will enable comprehensive studies of IMM dynamics with high temporal and spatial resolution.

DOI: https://doi.org/10.1038/s41589-023-01450-y