bims-mimbat 2023-06-18 papers

bims-mimbat

Biomed News

on Mitochondrial metabolism in brown adipose tissue

Issue of 2023–06–18
ten papers selected by
José Carlos de Lima-Júnior, Washington University

Horizontal proton transfer across the antiporter-like subunits in mitochondrial respiratory complex I.
The mitochondrial calcium uniporter (MCU) activates mitochondrial respiration and enhances mobility by regulating mitochondrial redox state.
Salt-inducible kinase inhibition promotes the adipocyte thermogenic program and adipose tissue browning.
Energy substrate metabolism, mitochondrial structure and oxidative stress after cardiac ischemia-reperfusion in mice lacking UCP3.
Unraveling the mechanisms of cardiolipin function: The role of oxidative polymerization of unsaturated acyl chains.
Defective extracellular matrix remodeling in brown adipose tissue is associated with fibro-inflammation and reduced diet-induced thermogenesis.
PERK signaling promotes mitochondrial elongation by remodeling membrane phosphatidic acid.
Arachidonic acid reverses cholesterol and zinc inhibition of human voltage-gated proton channels.
Substrate binding-induced conformational transitions in the omega-3 fatty acid transporter MFSD2A.
Contrasting Effects of Temperature on Human Arylamine N-Acetyltransferase and Acetyl Coenzyme A Hydrolase Activities.

Chem Sci. 2023 Jun 14. 14(23): 6309-6318

Horizontal proton transfer across the antiporter-like subunits in mitochondrial respiratory complex I.

Oleksii Zdorevskyi, Amina Djurabekova, Jonathan Lasham, Vivek Sharma.

Respiratory complex I is a redox-driven proton pump contributing to about 40% of total proton motive force required for mitochondrial ATP generation. Recent high-resolution cryo-EM structural data revealed the positions of several water molecules in the membrane domain of the large enzyme complex. However, it remains unclear how protons flow in the membrane-bound antiporter-like subunits of complex I. Here, we performed multiscale computer simulations on high-resolution structural data to model explicit proton transfer processes in the ND2 subunit of complex I. Our results show protons can travel the entire width of antiporter-like subunits, including at the subunit-subunit interface, parallel to the membrane. We identify a previously unrecognized role of conserved tyrosine residues in catalyzing horizontal proton transfer, and that long-range electrostatic effects assist in reducing energetic barriers of proton transfer dynamics. Results from our simulations warrant a revision in several prevailing proton pumping models of respiratory complex I.

DOI: https://doi.org/10.1039/d3sc01427d
Redox Biol. 2023 Jun 04. pii: S2213-2317(23)00160-X. [Epub ahead of print]64 102759

The mitochondrial calcium uniporter (MCU) activates mitochondrial respiration and enhances mobility by regulating mitochondrial redox state.

Anna Weiser, Aurélie Hermant, Flavien Bermont, Federico Sizzano, Sonia Karaz, Pilar Alvarez-Illera, Jaime Santo-Domingo, Vincenzo Sorrentino, Jerome N Feige, Umberto De Marchi.

  Regulation of mitochondrial redox balance is emerging as a key event for cell signaling in both physiological and pathological conditions. However, the link between the mitochondrial redox state and the modulation of these conditions remains poorly defined. Here, we discovered that activation of the evolutionary conserved mitochondrial calcium uniporter (MCU) modulates mitochondrial redox state. By using mitochondria-targeted redox and calcium sensors and genetic MCU-ablated models, we provide evidence of the causality between MCU activation and net reduction of mitochondrial (but not cytosolic) redox state. Redox modulation of redox-sensitive groups via MCU stimulation is required for maintaining respiratory capacity in primary human myotubes and C. elegans, and boosts mobility in worms. The same benefits are obtained bypassing MCU via direct pharmacological reduction of mitochondrial proteins. Collectively, our results demonstrate that MCU regulates mitochondria redox balance and that this process is required to promote the MCU-dependent effects on mitochondrial respiration and mobility.

Keywords:  C. elegans; Calcium signaling; MCU; Mitochondria; Redox biology; Skeletal muscle

DOI:  https://doi.org/10.1016/j.redox.2023.102759
Mol Metab. 2023 Jun 13. pii: S2212-8778(23)00087-X. [Epub ahead of print] 101753

Salt-inducible kinase inhibition promotes the adipocyte thermogenic program and adipose tissue browning.

Fubiao Shi, Flaviane de Fatima Silva, Dianxin Liu, Hari U Patel, Jonathan Xu, Wei Zhang, Clara Türk, Marcus Krüger, Sheila Collins.

   OBJECTIVE: Norepinephrine stimulates the adipose tissue thermogenic program through a β-adrenergic receptor (βAR) - cyclic adenosine monophosphate (cAMP) - protein kinase A (PKA) signaling cascade. We discovered that a noncanonical activation of the mechanistic target of rapamycin complex 1 (mTORC1) by PKA is required for the βAR-stimulation of adipose tissue browning. However, the downstream events triggered by PKA-phosphorylated mTORC1 activation that drive this thermogenic response are not well understood.
METHODS: We used a proteomic approach of Stable Isotope Labeling by/with Amino acids in Cell culture (SILAC) to characterize the global protein phosphorylation profile in brown adipocytes treated with the βAR agonist. We identified salt-inducible kinase 3 (SIK3) as a candidate mTORC1 substrate and further tested the effect of SIK3 deficiency or SIK inhibition on the thermogenic gene expression program in brown adipocytes and in mouse adipose tissue.
RESULTS: SIK3 interacts with RAPTOR, the defining component of the mTORC1 complex, and is phosphorylated at Ser884 in a rapamycin-sensitive manner. Pharmacological SIK inhibition by a pan-SIK inhibitor (HG-9-91-01) in brown adipocytes increases basal Ucp1 gene expression and restores its expression upon blockade of either mTORC1 or PKA. Short-hairpin RNA (shRNA) knockdown of Sik3 augments, while overexpression of SIK3 suppresses, Ucp1 gene expression in brown adipocytes. The regulatory PKA phosphorylation domain of SIK3 is essential for its inhibition. CRISPR-mediated Sik3 deletion in brown adipocytes increases type IIa histone deacetylase (HDAC) activity and enhances the expression of genes involved in thermogenesis such as Ucp1, Pgc1α, and mitochondrial OXPHOS complex protein. We further show that HDAC4 interacts with PGC1α after βAR stimulation and reduces lysine acetylation in PGC1α. Finally, a SIK inhibitor well-tolerated in vivo (YKL-05-099) can stimulate the expression of thermogenesis-related genes and browning of mouse subcutaneous adipose tissue.
CONCLUSIONS: Taken together, our data reveal that SIK3, with the possible contribution of other SIKs, functions as a phosphorylation switch for β-adrenergic activation to drive the adipose tissue thermogenic program and indicates that more work to understand the role of the SIKs is warranted. Our findings also suggest that maneuvers targeting SIKs could be beneficial for obesity and related cardiometabolic disease.

Keywords:  Adipocyte; SIK3; Salt-inducible kinase; Thermogenesis; UCP1; mTORC1

DOI:  https://doi.org/10.1016/j.molmet.2023.101753
Free Radic Biol Med. 2023 Jun 07. pii: S0891-5849(23)00430-6. [Epub ahead of print]

Energy substrate metabolism, mitochondrial structure and oxidative stress after cardiac ischemia-reperfusion in mice lacking UCP3.

Patricia Sánchez-Pérez, Ana Mata, May-Kristin Torp, Elia López-Bernardo, Christina M Heiestad, Jan Magnus Aronsen, Antonio Molina-Iracheta, Luis J Jiménez-Borreguero, Pablo García-Roves, Ana S H Costa, Christian Frezza, Michael P Murphy, Kåre-Olav Stenslokken, Susana Cadenas.

  Myocardial ischemia-reperfusion (IR) injury may result in cardiomyocyte dysfunction. Mitochondria play a critical role in cardiomyocyte recovery after IR injury. The mitochondrial uncoupling protein 3 (UCP3) has been proposed to reduce mitochondrial reactive oxygen species (ROS) production and to facilitate fatty acid oxidation. As both mechanisms might be protective following IR injury, we investigated functional, mitochondrial structural, and metabolic cardiac remodeling in wild-type mice and in mice lacking UCP3 (UCP3-KO) after IR. Results showed that infarct size in isolated perfused hearts subjected to IR ex vivo was larger in adult and old UCP3-KO mice than in equivalent wild-type mice, and was accompanied by higher levels of creatine kinase in the effluent and by more pronounced mitochondrial structural changes. The greater myocardial damage in UCP3-KO hearts was confirmed in vivo after coronary artery occlusion followed by reperfusion. S1QEL, a suppressor of superoxide generation from site IQ in complex I, limited infarct size in UCP3-KO hearts, pointing to exacerbated superoxide production as a possible cause of the damage. Metabolomics analysis of isolated perfused hearts confirmed the reported accumulation of succinate, xanthine and hypoxanthine during ischemia, and a shift to anaerobic glucose utilization, which all recovered upon reoxygenation. The metabolic response to ischemia and IR was similar in UCP3-KO and wild-type hearts, being lipid and energy metabolism the most affected pathways. Fatty acid oxidation and complex I (but not complex II) activity were equally impaired after IR. Overall, our results indicate that UCP3 deficiency promotes enhanced superoxide generation and mitochondrial structural changes that increase the vulnerability of the myocardium to IR injury.

Keywords:  Energy metabolism; Ischemia-reperfusion injury; Mitochondrial respiration; Mitochondrial structure; Oxidative stress; UCP3 (uncoupling protein 3)

DOI:  https://doi.org/10.1016/j.freeradbiomed.2023.05.014
Redox Biol. 2023 Jun 04. pii: S2213-2317(23)00175-1. [Epub ahead of print]64 102774

Unraveling the mechanisms of cardiolipin function: The role of oxidative polymerization of unsaturated acyl chains.

Sehwan Jang, Sabzali Javadov.

  Cardiolipin is a unique phospholipid of the inner mitochondrial membrane (IMM) as well as in bacteria. It performs several vital functions such as resisting osmotic rupture and stabilizing the supramolecular structure of large membrane proteins, like ATP synthases and respirasomes. The process of cardiolipin biosynthesis results in the production of immature cardiolipin. A subsequent step is required for its maturation when its acyl groups are replaced with unsaturated acyl chains, primarily linoleic acid. Linoleic acid is the major fatty acid of cardiolipin across all organs and tissues, except for the brain. Linoleic acid is not synthesized by mammalian cells. It has the unique ability to undergo oxidative polymerization at a moderately accelerated rate compared to other unsaturated fatty acids. This property can enable cardiolipin to form covalently bonded net-like structures essential for maintaining the complex geometry of the IMM and gluing the quaternary structure of large IMM protein complexes. Unlike triglycerides, phospholipids possess only two covalently linked acyl chains, which constrain their capacity to develop robust and complicated structures through oxidative polymerization of unsaturated acyl chains. Cardiolipin, on the other hand, has four fatty acids at its disposal to form covalently bonded polymer structures. Despite its significance, the oxidative polymerization of cardiolipin has been overlooked due to the negative perception surrounding biological oxidation and methodological difficulties. Here, we discuss an intriguing hypothesis that oxidative polymerization of cardiolipin is essential for the structure and function of cardiolipin in the IMM in physiological conditions. In addition, we highlight current challenges associated with the identification and characterization of oxidative polymerization of cardiolipin in vivo. Altogether, the study provides a better understanding of the structural and functional role of cardiolipin in mitochondria.

Keywords:  Cardiolipin; Linoleic acid; Mitochondria; Oxidative polymerization

DOI:  https://doi.org/10.1016/j.redox.2023.102774
Cell Rep. 2023 Jun 13. pii: S2211-1247(23)00651-4. [Epub ahead of print]42(6): 112640

Defective extracellular matrix remodeling in brown adipose tissue is associated with fibro-inflammation and reduced diet-induced thermogenesis.

Vanessa Pellegrinelli, Elizabeth Figueroa-Juárez, Isabella Samuelson, Mueez U-Din, Sonia Rodriguez-Fdez, Samuel Virtue, Jennifer Leggat, Cankut Çubuk, Vivian J Peirce, Tarja Niemi, Mark Campbell, Sergio Rodriguez-Cuenca, Joaquin Dopazo Blázquez, Stefania Carobbio, Kirsi A Virtanen, Antonio Vidal-Puig.

  The relevance of extracellular matrix (ECM) remodeling is reported in white adipose tissue (AT) and obesity-related dysfunctions, but little is known about the importance of ECM remodeling in brown AT (BAT) function. Here, we show that a time course of high-fat diet (HFD) feeding progressively impairs diet-induced thermogenesis concomitantly with the development of fibro-inflammation in BAT. Higher markers of fibro-inflammation are associated with lower cold-induced BAT activity in humans. Similarly, when mice are housed at thermoneutrality, inactivated BAT features fibro-inflammation. We validate the pathophysiological relevance of BAT ECM remodeling in response to temperature challenges and HFD using a model of a primary defect in the collagen turnover mediated by partial ablation of the Pepd prolidase. Pepd-heterozygous mice display exacerbated dysfunction and BAT fibro-inflammation at thermoneutrality and in HFD. Our findings show the relevance of ECM remodeling in BAT activation and provide a mechanism for BAT dysfunction in obesity.

Keywords:  CP: Metabolism; PEPD; brown adipose tissue; extracellular matrix; fibrosis; obesity

DOI:  https://doi.org/10.1016/j.celrep.2023.112640
EMBO J. 2023 Jun 12. e113908

PERK signaling promotes mitochondrial elongation by remodeling membrane phosphatidic acid.

Valerie Perea, Christian Cole, Justine Lebeau, Vivian Dolina, Kelsey R Baron, Aparajita Madhavan, Jeffery W Kelly, Danielle A Grotjahn, R Luke Wiseman.

  Endoplasmic reticulum (ER) stress and mitochondrial dysfunction are linked in the onset and pathogenesis of numerous diseases. This has led to considerable interest in defining the mechanisms responsible for regulating mitochondria during ER stress. The PERK signaling arm of the unfolded protein response (UPR) has emerged as a prominent ER stress-responsive signaling pathway that regulates diverse aspects of mitochondrial biology. Here, we show that PERK activity promotes adaptive remodeling of mitochondrial membrane phosphatidic acid (PA) to induce protective mitochondrial elongation during acute ER stress. We find that PERK activity is required for ER stress-dependent increases in both cellular PA and YME1L-dependent degradation of the intramitochondrial PA transporter PRELID1. These two processes lead to the accumulation of PA on the outer mitochondrial membrane where it can induce mitochondrial elongation by inhibiting mitochondrial fission. Our results establish a new role for PERK in the adaptive remodeling of mitochondrial phospholipids and demonstrate that PERK-dependent PA regulation adapts organellar shape in response to ER stress.

Keywords:  endoplasmic reticulum (ER) stress; mitochondrial morphology; phosphatidic acid; unfolded protein response (UPR)

DOI:  https://doi.org/10.15252/embj.2023113908
J Biol Chem. 2023 Jun 12. pii: S0021-9258(23)01946-4. [Epub ahead of print] 104918

Arachidonic acid reverses cholesterol and zinc inhibition of human voltage-gated proton channels.

Shuo Han, Sarah Applewhite, Jenna DeCata, Samuel Jones, John Cummings, Shizhen Wang.

  Unlike other members of the voltage-gated ion channel superfamily, voltage-gated proton (Hv) channels are solely composed of voltage sensor domains without separate ion-conducting pores. Due to their unique dependence on both voltage and transmembrane pH gradients, Hv channels normally open to mediate proton efflux. Multiple cellular ligands were also found to regulate the function of Hv channels, including Zn2+, cholesterol, polyunsaturated arachidonic acid, and albumin. Our previous work showed that Zn2+ and cholesterol inhibit the human voltage-gated proton channel hHv1 by stabilizing its S4 segment at resting state conformations. Released from phospholipids by phospholipase A2 in cells upon infection or injury, arachidonic acid regulates the function of many ion channels, including hHv1. In the present work, we examined the effects of arachidonic acid on purified hHv1 channels using liposome flux assays and revealed underlying structural mechanisms using single-molecule Fluorescence Resonance Energy Transfer (smFRET). Our data indicated that arachidonic acid strongly activates hHv1 channels by promoting transitions of the S4 segment towards opening or 'pre-opening' conformations. Moreover, we found that arachidonic acid even activates hHv1 channels inhibited by Zn2+ and cholesterol, providing a biophysical mechanism to activate hHv1 channels in non-excitable cells upon infection or injury.

Keywords:  arachidonic acid; conformational dynamics; ligand gating; single-molecule FRET; voltage sensor; voltage-gated proton channel

DOI:  https://doi.org/10.1016/j.jbc.2023.104918
Nat Commun. 2023 Jun 09. 14(1): 3391

Substrate binding-induced conformational transitions in the omega-3 fatty acid transporter MFSD2A.

Shana Bergman, Rosemary J Cater, Ambrose Plante, Filippo Mancia, George Khelashvili.

Major Facilitator Superfamily Domain containing 2 A (MFSD2A) is a transporter that is highly enriched at the blood-brain and blood-retinal barriers, where it mediates Na+-dependent uptake of ω-3 fatty acids in the form of lysolipids into the brain and eyes, respectively. Despite recent structural insights, it remains unclear how this process is initiated, and driven by Na+. Here, we perform Molecular Dynamics simulations which demonstrate that substrates enter outward facing MFSD2A from the outer leaflet of the membrane via lateral openings between transmembrane helices 5/8 and 2/11. The substrate headgroup enters first and engages in Na+ -bridged interactions with a conserved glutamic acid, while the tail is surrounded by hydrophobic residues. This binding mode is consistent with a "trap-and-flip" mechanism and triggers transition to an occluded conformation. Furthermore, using machine learning analysis, we identify key elements that enable these transitions. These results advance our molecular understanding of the MFSD2A transport cycle.

DOI: https://doi.org/10.1038/s41467-023-39088-y
Biochemistry. 2023 Jun 15.

Contrasting Effects of Temperature on Human Arylamine N-Acetyltransferase and Acetyl Coenzyme A Hydrolase Activities.

Chandra Choudhury, Courtney E McAleese, Neville J Butcher, Rodney F Minchin.

There are two human arylamine N-acetyltransferases (NAT1 and NAT2) that have evolved separately and differ in their substrate specificity and tissue localization. In addition to its acetyltransferase activity, NAT1 can hydrolyze acetyl coenzyme A to coenzyme A in the presence of folate. Here, we show that NAT1 is rapidly inactivated at temperatures above 39 °C whereas NAT2 is more stable. NAT1 acetyltransferase activity is also rapidly lost in whole cells at a rate similar to that of recombinant protein, suggesting it is not protected by intracellular chaperones. By contrast, the hydrolase activity of NAT1 is resistant to heat-induced inactivation, in part because folate stabilizes the protein. Heat generated by mitochondria following the dissipation of the inner membrane potential was sufficient to inactivate NAT1 in whole cells. Within the physiological range of core body temperatures (36.5-37.5 °C), NAT1 acetyltransferase activity decreased by 30% while hydrolase activity increased by >50%. This study demonstrates the thermal regulation of NAT1, but not NAT2, and suggests that NAT1 may switch between an acetyltransferase and a hydrolase within a narrow temperature range in the presence of folate.

DOI: https://doi.org/10.1021/acs.biochem.3c00113