bims-mimbat 2024-11-03 papers

bims-mimbat

Biomed News

on Mitochondrial metabolism in brown adipose tissue

Issue of 2024‒11‒03
eight papers selected by
José Carlos de Lima-Júnior, Washington University

mTORC1 and 2 adrenergic regulation and function in brown adipose tissue.
Membrane potential stimulates ADP import and ATP export by the mitochondrial ADP/ATP carrier due to its positively charged binding site.
Structure of the turnover-ready state of an ancestral respiratory complex I.
HuR-dependent expression of RyR2 contributes to calcium-mediated thermogenesis in brown adipocytes.
cAMP driven UCP1 induction in human adipocytes requires ATGL-catalyzed lipolysis.
A key role for P2RX5 in brown adipocyte differentiation and energy homeostasis.
RNA-binding protein YBX3 promotes PPARγ-SLC3A2 mediated BCAA metabolism fueling brown adipogenesis and thermogenesis.
TGF-β antagonism synergizes with PPARγ agonism to reduce fibrosis and enhance beige adipogenesis.

Physiology (Bethesda). 2024 Oct 29.

mTORC1 and 2 adrenergic regulation and function in brown adipose tissue.

William T Festuccia.

  Brown adipose tissue (BAT) thermogenesis results from the uncoupling of mitochondrial inner membrane proton gradient mediated by the uncoupling protein 1 (UCP-1), which is activated by lipolysis-derived fatty acids. Norepinephrine (NE) secreted by sympathetic innervation not only activates BAT lipolysis and UCP-1, but uniquely in brown adipocytes, promotes "futile" metabolic cycles and enhances BAT thermogenic capacity by increasing UCP-1 content, mitochondrial biogenesis and brown adipocyte hyperplasia. NE exerts these actions by triggering signaling in the canonical G protein coupled b adrenergic receptors, cAMP and protein kinase A (PKA) pathway which, in brown adipocyte, is under a complex and intricated crosstalk with important growth-promoting signaling pathways such as those of mechanistic target of rapamycin (mTOR) complexes 1 (mTORC1) and 2 (mTORC2). This article reviews evidence suggesting that mTOR complexes are modulated by and participate in the thermogenic, metabolic, and growth-promoting effects elicited by NE in BAT and discusses current gaps and future directions in this field of research.

Keywords:  brown adipose tissue; mTORC1; mTORC2

DOI:  https://doi.org/10.1152/physiol.00023.2024
Sci Adv. 2024 Nov;10(44): eadp7725

Membrane potential stimulates ADP import and ATP export by the mitochondrial ADP/ATP carrier due to its positively charged binding site.

Vasiliki Mavridou, Martin S King, Andre Bazzone, Roger Springett, Edmund R S Kunji.

The mitochondrial adenosine 5'-diphosphate (ADP)/adenosine 5'-triphosphate (ATP) carrier imports ADP into the mitochondrion and exports ATP to the cell. Here, we demonstrate that 3.3 positive charges are translocated with the negatively charged substrate in each transport step. They can be assigned to three positively charged residues of the central substrate-binding site and two asparagine/arginine pairs. In this way, the membrane potential stimulates not only the ATP4- export step, as a net -0.7 charge is transported, but also the ADP3- import step, as a net +0.3 charge is transported with the electric field. These positive charge movements also inhibit the import of ATP and export of ADP in the presence of a membrane potential, allowing these nucleotides to be maintained at high concentrations in the cytosol and mitochondrial matrix to drive the hydrolysis and synthesis of ATP, respectively. Thus, this is the mechanism by which the membrane potential drives adenine nucleotide exchange with high directional fluxes to fuel the cellular processes.

DOI: https://doi.org/10.1126/sciadv.adp7725
Nat Commun. 2024 Oct 29. 15(1): 9340

Structure of the turnover-ready state of an ancestral respiratory complex I.

Bozhidar S Ivanov, Hannah R Bridges, Owen D Jarman, Judy Hirst.

Respiratory complex I is pivotal for cellular energy conversion, harnessing energy from NADH:ubiquinone oxidoreduction to drive protons across energy-transducing membranes for ATP synthesis. Despite detailed structural information on complex I, its mechanism of catalysis remains elusive due to lack of accompanying functional data for comprehensive structure-function analyses. Here, we present the 2.3-Å resolution structure of complex I from the α-proteobacterium Paracoccus denitrificans, a close relative of the mitochondrial progenitor, in phospholipid-bilayer nanodiscs. Three eukaryotic-type supernumerary subunits (NDUFS4, NDUFS6 and NDUFA12) plus a novel L-isoaspartyl-O-methyltransferase are bound to the core complex. Importantly, the enzyme is in a single, homogeneous resting state that matches the closed, turnover-ready (active) state of mammalian complex I. Our structure reveals the elements that stabilise the closed state and completes P. denitrificans complex I as a unified platform for combining structure, function and genetics in mechanistic studies.

DOI: https://doi.org/10.1038/s41467-024-53679-3
bioRxiv. 2024 Oct 24. pii: 2024.10.22.619637. [Epub ahead of print]

HuR-dependent expression of RyR2 contributes to calcium-mediated thermogenesis in brown adipocytes.

Adrienne R Guarnieri, Sarah R Anthony, Pooja Acharya, Bo Yao Wen, Lindsey Lanzillotta, Rylie Gavin, Michael Tranter.

Several uncoupling protein 1 (UCP1)-independent thermogenic pathways have been described in thermogenic adipose tissue, including calcium-mediated thermogenesis in beige adipocytes via sarco/endoplasmic reticulum ATPase (SERCA). We have previously shown that adipocyte-specific deletion of the RNA binding protein human antigen R (HuR) results in thermogenic dysfunction independent of UCP1 expression. RNA sequencing revealed the downregulation of several genes involved in calcium ion transport upon HuR deletion. The goal of this work was to define the HuR-dependent mechanisms of calcium driven thermogenesis in brown adipocytes. We generated (BAT)-specific HuR-deletion (BAT-HuR -/- ) mice and show that their body weight, glucose tolerance, brown and white adipose tissue weights, and total lipid droplet size were not significantly different compared to wild-type. Similar to our initial findings in Adipo-HuR -/- mice, mice with BAT-specific HuR deletion are cold intolerant following acute thermal challenge at 4°C, demonstrating specificity of acute HuR-dependent thermogenesis to BAT. We also found decreased expression of ryanodine receptor 2 (RyR2), but no changes in RyR2, SERCA1, SERCA2, or UCP1 expression, in BAT from BAT-HuR -/- mice. Next, we used Fluo-4 calcium indicator dye to show that genetic deletion or pharmacological inhibition of HuR blunts the increase in cytosolic calcium concentration in SVF-derived primary brown adipocytes. Moreover, we saw a similar blunting in β-adrenergic-mediated heat generation, as assessed by ERtherm AC fluorescence, in SVF-derived brown adipocytes following HuR inhibition or deletion. Mechanistically, we show that HuR directly binds and reduces the decay rate of RyR2 mRNA in brown adipocytes, and stabilization of RyR2 via S107 rescues β-adrenergic-mediated cytosolic calcium increase and heat generation in HuR deficient brown adipocytes. In conclusion, our results suggest that HuR-dependent control of RyR2 expression plays a significant role in the thermogenic function of brown adipose tissue through modulation of SR calcium cycling.

DOI: https://doi.org/10.1101/2024.10.22.619637
Mol Metab. 2024 Oct 23. pii: S2212-8778(24)00182-0. [Epub ahead of print] 102051

cAMP driven UCP1 induction in human adipocytes requires ATGL-catalyzed lipolysis.

Anand Desai, Zinger Yang Loureiro, Tiffany DeSouza, Qin Yang, Javier Solivan-Rivera, Silvia Corvera.

  OBJECTIVE: The uncoupling protein 1 (UCP1) is induced in brown or "beige" adipocytes through catecholamine-induced cAMP signaling, which activates diverse transcription factors. UCP1 expression can also be enhanced by PPARγ agonists such as rosiglitazone (Rsg). However, it is unclear whether this upregulation results from de-novo differentiation of beige adipocytes from progenitor cells, or from the induction of UCP1 in pre-existing adipocytes. To explore this, we employed human adipocytes differentiated from progenitor cells and examined their acute response to Rsg, to the adenylate-cyclase activator forskolin (Fsk), or to both simultaneously.METHODS: Adipocytes generated from primary human progenitor cells were differentiated without exposure to PPARγ agonists, and treated for 3, 6 or 78 hours to Fsk, to Rsg, or to both simultaneously. Bulk RNASeq, RNAScope, RT-PCR, CRISPR-Cas9 mediated knockout, oxygen consumption and western blotting were used to assess cellular responses.
RESULTS: UCP1 mRNA expression was induced within 3 hours of exposure to either Rsg or Fsk, indicating that Rsg's effect is independent on additional adipocyte differentiation. Although Rsg and Fsk induced distinct overall transcriptional responses, both induced genes associated with calcium metabolism, lipid droplet assembly, and mitochondrial remodeling, denoting core features of human adipocyte beiging. Unexpectedly, we found that Fsk-induced UCP1 expression was reduced by approximately 80% following CRISPR-Cas9-mediated knockout of PNPLA2, the gene encoding the triglyceride lipase ATGL. As anticipated, ATGL knockout suppressed lipolysis; however, the associated suppression of UCP1 induction indicates that maximal cAMP-mediated UCP1 induction requires products of ATGL-catalyzed lipolysis. Supporting this, we observed that the reduction in Fsk-stimulated UCP1 induction caused by ATGL knockout was reversed by Rsg, implying that the role of lipolysis in this process is to generate natural PPARγ agonists.
CONCLUSION: UCP1 transcription is known to be stimulated by transcription factors activated downstream of cAMP-dependent protein kinases. Here we demonstrate that UCP1 transcription can also be acutely induced through PPARγ-activation. Moreover, both pathways are activated in human adipocytes in response to cAMP, synergistically inducing UCP1 expression. The stimulation of PPARγ in response to cAMP may result from the production of natural PPARγ activating ligands through ATGL-mediated lipolysis.

Keywords:  beige adipose; brown adipose; catecholamine; hormone signaling; natural ligand; nuclear receptor; thermogenesis

DOI:  https://doi.org/10.1016/j.molmet.2024.102051
Adipocyte. 2024 Dec;13(1): 2421745

A key role for P2RX5 in brown adipocyte differentiation and energy homeostasis.

Maria Razzoli, Seth McGonigle, Bhavani Shankar Sahu, Pedro Rodriguez, Daniel Svedberg, Loredana Rao, Chiara Ruocco, Enzo Nisoli, Bianca Vezzani, Andrea Frontini, Alessandro Bartolomucci.

  Brown adipocytes are defined based on a distinct morphology and genetic signature that includes, amongst others, the expression of the Purinergic 2 Receptor X5 (P2RX5). However, the role of P2RX5 in brown adipocyte and brown adipose tissue function is poorly characterized. In the present study, we conducted a metabolic characterization of P2RX5 knockout male mice; next, we characterized this purinergic pathway in a cell-autonomous context in brown adipocytes. We then tested the role of the P2RX5 receptor agonism in metabolic responses in vivo in conditions of minimal adaptive thermogenesis requirements. Our data show that loss of P2RX5 causes reduced brown adipocyte differentiation in vitro, and browning in vivo. Lastly, we unravel a previously unappreciated role for P2RX5 agonism to exert an anti-obesity effect in the presence of enhanced brown adipose tissue recruitment in male mice housed at thermoneutrality. Altogether, our data support a role for P2RX5 in mediating brown adipocyte differentiation and function that could be further targeted for benefits in the context of adipose tissue pathology and metabolic diseases.

Keywords:  ATP; Purinergic receptors; adipogenesis; browning; sympathetic nerves

DOI:  https://doi.org/10.1080/21623945.2024.2421745
Mol Metab. 2024 Oct 29. pii: S2212-8778(24)00184-4. [Epub ahead of print] 102053

RNA-binding protein YBX3 promotes PPARγ-SLC3A2 mediated BCAA metabolism fueling brown adipogenesis and thermogenesis.

Lin-Yun Chen, Li-Wen Wang, Jie Wen, Jing-Dong Cao, Rui Zhou, Jin-Lin Yang, Ye Xiao, Tian Su, Yan Huang, Qi Guo, Hai-Yan Zhou, Xiang-Hang Luo, Xu Feng.

  OBJECTIVE: Activating brown adipose tissue (BAT) thermogenesis is a promising approach to combat obesity and metabolic disorders. The post-transcriptional regulation of BAT thermogenesis mediated by RNA-binding proteins (RBPs) is still not fully understood. This study explores the physiological role of novel RBPs in BAT differentiation and thermogenesis.METHODS: We used multiple public datasets to screen out novel RBPs responsible for BAT differentiation and thermogenesis. In vitro loss- and gain-of-function experiments were performed in both C3H10T1/2 preadipocytes and mature brown adipocytes to determine the role of Y-box binding protein 3 (YBX3) in brown adipocyte differentiation and thermogenesis. Adeno-associated virus (AAV)-mediated BAT-specific knockdown or overexpression of Ybx3 was applied to investigate the function of YBX3 in vivo.
RESULTS: YBX3 is a brown adipocyte-enriched RBP induced by cold stimulation and β-adrenergic signaling. Both in vitro loss- and gain-of-function experiments demonstrate that YBX3 is essential for brown adipocyte differentiation and thermogenesis. BAT-specific loss of Ybx3 dampens thermogenesis and exacerbates diet-induced obesity in mice, while overexpression of Ybx3 promotes thermogenesis and confers protection against diet-induced metabolic dysfunction. Transcriptome analysis and mitochondrial stress test indicate that Ybx3 deficiency compromises the mitochondrial oxidative phosphorylation, leading to thermogenic failure. Mechanistically, YBX3 stabilizes the mRNA of Slc3a2 and Pparg, which facilitates branched-chain amino acid (BCAA) influx and catabolism and fuels brown adipocyte differentiation and thermogenesis.
CONCLUSIONS: YBX3 facilitates BAT fueling BCAA to boost thermogenesis and energy expenditure, which protects against obesity and metabolic dysfunction. Thus, YBX3 could be a promising therapeutic target for obesity.

Keywords:  Branched-chain amino acid; Brown adipose tissue; Obesity; Thermogenesis; YBX3

DOI:  https://doi.org/10.1016/j.molmet.2024.102053
Mol Metab. 2024 Oct 24. pii: S2212-8778(24)00185-6. [Epub ahead of print] 102054

TGF-β antagonism synergizes with PPARγ agonism to reduce fibrosis and enhance beige adipogenesis.

Young Jae Bahn, Yanling Wang, Pradeep Dagur, Nicholas Scott, Cheryl Cero, Kelly T Long, Nhuquynh Nguyen, Aaron M Cypess, Sushil G Rane.

  OBJECTIVE: Adipose tissue depots vary markedly in their ability to store and metabolize triglycerides, undergo beige adipogenesis and susceptibility to metabolic disease. The molecular mechanisms that underlie such heterogeneity are not entirely clear. Previously, we showed that TGF-β signaling suppresses beige adipogenesis via repressing the recruitment of dedicated beige progenitors. Here, we find that TGF-β signals dynamically regulate the balance between adipose tissue fibrosis and beige adipogenesis.METHODS: We investigated adipose tissue depot-specific differences in activation of TGF-β signaling in response to dietary challenge. RNA-seq and fluorescence activated cell sorting was performed to identify and characterize cells responding to changes in TGF-β signaling status. Mouse models, pharmacological strategies and human adipose tissue analyses were performed to further define the influence of TGF-β signaling on fibrosis and functional beige adipogenesis.
RESULTS: Elevated basal and high-fat diet inducible activation of TGF-β/Smad3 signaling was observed in the visceral adipose tissue depot. Activation of TGF-β/Smad3 signaling was associated with increased adipose tissue fibrosis. RNA-seq combined with fluorescence-activated cell sorting of stromal vascular fraction of epididymal white adipose tissue depot resulted in identification of TGF-β/Smad3 regulated ITGA5+ fibrogenic progenitors. TGF-β/Smad3 signal inhibition, genetically or pharmacologically, reduced fibrosis and increased functional beige adipogenesis. TGF-β/Smad3 antagonized the beneficial effects of PPARγ whereas TGF-β receptor 1 inhibition synergized with actions of rosiglitazone, a PPARγ agonist, to dampen fibrosis and promote beige adipogenesis. Positive correlation between TGF-β activation and ITGA5 was observed in human adipose tissue, with visceral adipose tissue depots exhibiting higher fibrosis potential than subcutaneous or brown adipose tissue depots.
CONCLUSIONS: Basal and high-fat diet inducible activation of TGF-β underlies the heterogeneity of adipose tissue depots. TGF-β/Smad3 activation promotes adipose tissue fibrosis and suppresses beige progenitors. Together, these dual mechanisms preclude functional beige adipogenesis. Controlled inhibition of TβR1 signaling and concomitant PPARγ stimulation can suppress adipose tissue fibrosis and promote beige adipogenesis to improve metabolism.

Keywords:  Beige adipogenesis; PPARγ; Smad3; TGF-β; fibrosis; metabolism; rosiglitazone

DOI:  https://doi.org/10.1016/j.molmet.2024.102054