bims-mimbat Biomed News
on Mitochondrial metabolism in brown adipose tissue
Issue of 2022–10–16
sixteen papers selected by
José Carlos de Lima-Júnior, University of California San Francisco
  1. Loureirin B protects against obesity via activation of adipose tissue ω3 PUFA-GPR120-UCP1 axis in mice.
  2. Microsomal triglyceride transfer protein regulates intracellular lipolysis in adipocytes independent of its lipid transfer activity.
  3. Suppression of estrogen receptor beta classical genomic activity enhances systemic and adipose-specific response to chronic beta-3 adrenergic receptor (β3AR) stimulation.
  4. Robustness of the honeybee neuro-muscular octopaminergic system in the face of cold stress.
  5. Low dose lithium supplementation promotes adipose tissue browning and sarco(endo)plasmic reticulum Ca2+ ATPase uncoupling in muscle.
  6. Brown fat holds promise for addressing obesity and a host of related ills.
  7. An ancestral interaction module promotes oligomerization in divergent mitochondrial ATP synthases.
  8. A genetically encoded system for oxygen generation in living cells.
  9. Rapid fractionation of mitochondria from mouse liver and heart reveals in vivo metabolite compartmentation.
  10. The Na+/K+ pump dominates control of glycolysis in hippocampal dentate granule cells.
  11. Obesity caused by an OVOL2 mutation reveals dual roles of OVOL2 in promoting thermogenesis and limiting white adipogenesis.
  12. Neuronal temperature perception induces specific defenses that enable C. elegans to cope with the enhanced reactivity of hydrogen peroxide at high temperature.
  13. A saturated map of common genetic variants associated with human height.
  14. Knockdown of TMEM160 leads to an increase in reactive oxygen species generation and the induction of the mitochondrial unfolded protein response.
  15. Oxidative stress-induced autonomous activation of the Calcium/Calmodulin-Dependent Kinase II involves disulfide formation in the regulatory domain.
  16. Activation mechanism of the mouse cold-sensing TRPM8 channel by cooling agonist and PIP2.
  1. Biochem Biophys Res Commun. 2022 Oct 03. pii: S0006-291X(22)01358-4. [Epub ahead of print]632 139-149
    Loureirin B protects against obesity via activation of adipose tissue ω3 PUFA-GPR120-UCP1 axis in mice.
    Min Liu, Jian Feng Zhang, Wen Long Zhu, Huan Liu, Xiong Jia.
      Obesity and related metabolic disorders are worldwide epidemics. Current lifestyle interventions and drug treatment for obesity seem insufficient. Here, we show that Loureirin B (LB), a major flavonoid molecule extracted from Sanguis Draxonis, prevents diet-induced obesity and ameliorates concomitant metabolic abnormalities including fatty liver, insulin resistance and systemic inflammation in mice. Mechanistically, LB treatment increases the proportion of ω3 polyunsaturated fatty acids (PUFAs) in brown adipose tissue (BAT) and white adipose tissue (WAT), which subsequently activates the key lipid sensor GPR120. In line with this, LB treatment promotes browning of WAT and activates BAT thermogenesis through upregulation of UCP1, a downstream effector of GPR120. Conversely, inhibition of GPR120 abolishes the thermogenic effect of LB in primary cultured brown adipocytes. Together, these results suggest that LB possesses anti-obesity property by enhancing adipose tissue thermogenesis via activation of ω3 PUFA-GPR120-UCP1 axis and holds promises for combating obesity and its related metabolic syndrome.
    Keywords:  Adipose tissue; Diet-induced obesity; GPR120; Loureirin B; Thermogenesis; ω3 polyunsaturated fatty acids
    DOI:  https://doi.org/10.1016/j.bbrc.2022.09.096
  2. Metabolism. 2022 Oct 10. pii: S0026-0495(22)00209-8. [Epub ahead of print] 155331
    Microsomal triglyceride transfer protein regulates intracellular lipolysis in adipocytes independent of its lipid transfer activity.
    Sujith Rajan, Peter Hofer, Amanda Christiano, Matthew Stevenson, Louis Ragolia, Eugenia Villa-Cuesta, Susan K Fried, Raymond Lau, Collin Braithwaite, Rudolf Zechner, Gary J Schwartz, M Mahmood Hussain.
       BACKGROUND: The triglyceride (TG) transfer activity of microsomal triglyceride transfer protein (MTP) is essential for lipoprotein assembly in the liver and intestine; however, its function in adipose tissue, which does not assemble lipoproteins, is unknown. Here we have elucidated the function of MTP in adipocytes.
    APPROACH AND RESULTS: We demonstrated that MTP is present on lipid droplets in human adipocytes. Adipose-specific MTP deficient (A-Mttp-/-) male and female mice fed an obesogenic diet gained less weight than Mttpf/f mice, had less fat mass, smaller adipocytes and were insulin sensitive. A-Mttp-/- mice showed higher energy expenditure than Mttpf/f mice. During a cold challenge, A-Mttp-/- mice maintained higher body temperature by mobilizing more fatty acids. Biochemical studies indicated that MTP deficiency de-repressed adipose triglyceride lipase (ATGL) activity and increased TG lipolysis. Both wild type MTP and mutant MTP deficient in TG transfer activity interacted with and inhibited ATGL activity. Thus, the TG transfer activity of MTP is not required for ATGL inhibition. C-terminally truncated ATGL that retains its lipase activity interacted less efficiently than full-length ATGL.
    CONCLUSION: Our findings demonstrate that adipose-specific MTP deficiency increases ATGL-mediated TG lipolysis and enhances energy expenditure, thereby resisting diet-induced obesity. We speculate that the regulatory function of MTP involving protein-protein interactions might have evolved before the acquisition of TG transfer activity in vertebrates. Adipose-specific inhibition of MTP-ATGL interactions may ameliorate obesity while avoiding the adverse effects associated with inhibition of the lipid transfer activity of MTP.
    Keywords:  ATGL; Free fatty acids; HSL; Obesity; Protein-protein interactions; Thermogenesis
    DOI:  https://doi.org/10.1016/j.metabol.2022.155331
  3. Front Physiol. 2022 ;13 920675
    Suppression of estrogen receptor beta classical genomic activity enhances systemic and adipose-specific response to chronic beta-3 adrenergic receptor (β3AR) stimulation.
    Eric D Queathem, Maggie Fitzgerald, Rebecca Welly, Candace C Rowles, Kylie Schaller, Shahad Bukhary, Christopher P Baines, R Scott Rector, Jaume Padilla, Camila Manrique-Acevedo, Dennis B Lubahn, Victoria J Vieira-Potter.
      White adipose tissue (WAT) dysfunction independently predicts cardiometabolic disease, yet there is a lack of effective adipocyte-targeting therapeutics. B3AR agonists enhance adipocyte mitochondrial function and hold potential in this regard. Based on enhanced sensitivity to B3AR-mediated browning in estrogen receptor (ER)alpha-null mice, we hypothesized that ERβ may enhance the WAT response to the B3AR ligand, CL316,243 (CL). Methods: Male and female wild-type (WT) and ERβ DNA binding domain knock-out (ERβDBDKO) mice fed high-fat diet (HFD) to induce obesity were administered CL (1 mg/kg) daily for 2 weeks. Systemic physiological assessments of body composition (EchoMRI), bioenergetics (metabolic chambers), adipocyte mitochondrial respiration (oroboros) and glucose tolerance were performed, alongside perigonadal (PGAT), subcutaneous (SQAT) and brown adipose tissue (BAT) protein expression assessment (Western blot). Mechanisms were tested in vitro using primary adipocytes isolated from WT mice, and from Esr2-floxed mice in which ERβ was knocked down. Statistical analyses were performed using 2 × 2 analysis of variance (ANOVA) for main effects of genotype (G) and treatment (T), as well as GxT interactions; t-tests were used to determine differences between in vitro treatment conditions (SPSS V24). Results: There were no genotype differences in HFD-induced obesity or systemic rescue effects of CL, yet ERβDBDKO females were more sensitive to CL-induced increases in energy expenditure and WAT UCP1 induction (GxT, p < 0.05), which coincided with greater WAT B3AR protein content among the KO (G, p < 0.05). Among males, who were more insulin resistant to begin with (no genotype differences before treatment), tended to be more sensitive to CL-mediated reduction in insulin resistance. With sexes combined, basal WAT mitochondrial respiration trended toward being lower in the ERβDBDKO mice, but this was completely rescued by CL (p < 0.05). Confirming prior work, CL increased adipose tissue ERβ protein (T, p < 0.05, all), an effect that was enhanced in WAT and BAT the female KO (GxT, p < 0.01). In vitro experiments indicated that an inhibitor of ERβ genomic function (PHTPP) synergized with CL to further increase UCP1 mRNA (p = 0.043), whereas full ERβ protein was required for UCP1 expression (p = 0.042). Conclusion: Full ERβ activity appears requisite and stimulatory for UCP1 expression via a mechanism involving non-classical ERβ signaling. This novel discovery about the role of ERβ in adipocyte metabolism may have important clinical applications.
    Keywords:  adipocyte browning; adipocyte mitochondria; energy expenditure; estrogen signaling; insulin resistance
    DOI:  https://doi.org/10.3389/fphys.2022.920675
  4. Front Physiol. 2022 ;13 1002740
    Robustness of the honeybee neuro-muscular octopaminergic system in the face of cold stress.
    Sinan Kaya-Zeeb, Saskia Delac, Lena Wolf, Ana Luiza Marante, Oliver Scherf-Clavel, Markus Thamm.
      In recent decades, our planet has undergone dramatic environmental changes resulting in the loss of numerous species. This contrasts with species that can adapt quickly to rapidly changing ambient conditions, which require physiological plasticity and must occur rapidly. The Western honeybee (Apis mellifera) apparently meets this challenge with remarkable success, as this species is adapted to numerous climates, resulting in an almost worldwide distribution. Here, coordinated individual thermoregulatory activities ensure survival at the colony level and thus the transmission of genetic material. Recently, we showed that shivering thermogenesis, which is critical for honeybee thermoregulation, depends on octopamine signaling. In this study, we tested the hypothesis that the thoracic neuro-muscular octopaminergic system strives for a steady-state equilibrium under cold stress to maintain endogenous thermogenesis. We can show that this applies for both, octopamine provision by flight muscle innervating neurons and octopamine receptor expression in the flight muscles. Additionally, we discovered alternative splicing for AmOARβ2. At least the expression of one isoform is needed to survive cold stress conditions. We assume that the thoracic neuro-muscular octopaminergic system is finely tuned in order to contribute decisively to survival in a changing environment.
    Keywords:  cold stress; gene expression; honeybees; octopamine; octopamine receptors; thermogenesis
    DOI:  https://doi.org/10.3389/fphys.2022.1002740
  5. J Biol Chem. 2022 Oct 06. pii: S0021-9258(22)01012-2. [Epub ahead of print] 102568
    Low dose lithium supplementation promotes adipose tissue browning and sarco(endo)plasmic reticulum Ca2+ ATPase uncoupling in muscle.
    Mia S Geromella, Chantal R Ryan, Jessica L Braun, Michael S Finch, Lucas A Maddalena, Olivia Bagshaw, Briana Hockey, Fereshteh Moradi, Rachel K Fenech, Jisook Ryoo, Daniel M Marko, Roopan Dhaliwal, Jake Sweezey-Munroe, Sophie I Hamstra, Georgina Gardner, Sebastian Silvera, Rene Vandenboom, Brian D Roy, Jeffrey A Stuart, Rebecca E K MacPherson, Val A Fajardo.
      Sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA) uncoupling in skeletal muscle, and mitochondrial uncoupling via uncoupling protein 1 (UCP1) in brown/beige adipose tissue are two primary mechanisms implicated in energy expenditure. Here, we investigated the effects of glycogen synthase kinase 3 (GSK3) inhibition via lithium chloride (LiCl) treatment on SERCA uncoupling in skeletal muscle and UCP1 expression in adipose. C2C12 and 3T3-L1 cells treated with LiCl had increased SERCA uncoupling and UCP1 protein levels, respectively, ultimately raising cellular respiration; however, this was only observed when LiCl treatment occurred throughout differentiation. In vivo, LiCl treatment (10 mg/kg/day) increased food intake in chow-fed and high-fat diet (HFD, 60% kcal) fed male mice without increasing body mass - a result attributed to elevated daily energy expenditure. In soleus muscle, we determined LiCl treatment promoted SERCA uncoupling via increased expression of SERCA uncouplers, sarcolipin and/or neuronatin, under chow and HFD-fed conditions. We attribute these effects to the GSK3 inhibition observed with LiCl treatment as partial muscle-specific GSK3 knockdown produced similar effects. In adipose, LiCl treatment inhibited GSK3 in inguinal WAT (iWAT) but not in brown adipose tissue under chow-fed conditions, which in turn led to an increase in UCP1 in iWAT and a beiging-like effect with a multilocular phenotype. We did not observe this beiging-like effect and increase in UCP1 when mice were fed a HFD, as LiCl could not overcome the ensuing overactivation of GSK3. Nonetheless, our study establishes novel regulatory links between GSK3 and SERCA uncoupling in muscle and GSK3 and UCP1 and beiging in iWAT.
    Keywords:  SERCA; UCP1; beige; efficiency; neuronatin; sarcolipin; uncoupling
    DOI:  https://doi.org/10.1016/j.jbc.2022.102568
  6. Proc Natl Acad Sci U S A. 2022 Oct 25. 119(43): e2216435119
    Brown fat holds promise for addressing obesity and a host of related ills.
    Marcus A Banks.
      
    DOI:  https://doi.org/10.1073/pnas.2216435119
  7. Nat Commun. 2022 Oct 11. 13(1): 5989
    An ancestral interaction module promotes oligomerization in divergent mitochondrial ATP synthases.
    Ondřej Gahura, Alexander Mühleip, Carolina Hierro-Yap, Brian Panicucci, Minal Jain, David Hollaus, Martina Slapničková, Alena Zíková, Alexey Amunts.
      Mitochondrial ATP synthase forms stable dimers arranged into oligomeric assemblies that generate the inner-membrane curvature essential for efficient energy conversion. Here, we report cryo-EM structures of the intact ATP synthase dimer from Trypanosoma brucei in ten different rotational states. The model consists of 25 subunits, including nine lineage-specific, as well as 36 lipids. The rotary mechanism is influenced by the divergent peripheral stalk, conferring a greater conformational flexibility. Proton transfer in the lumenal half-channel occurs via a chain of five ordered water molecules. The dimerization interface is formed by subunit-g that is critical for interactions but not for the catalytic activity. Although overall dimer architecture varies among eukaryotes, we find that subunit-g together with subunit-e form an ancestral oligomerization motif, which is shared between the trypanosomal and mammalian lineages. Therefore, our data defines the subunit-g/e module as a structural component determining ATP synthase oligomeric assemblies.
    DOI:  https://doi.org/10.1038/s41467-022-33588-z
  8. Proc Natl Acad Sci U S A. 2022 Oct 25. 119(43): e2207955119
    A genetically encoded system for oxygen generation in living cells.
    Andrew L Markhard, Jason G McCoy, Tsz-Leung To, Vamsi K Mootha.
      Oxygen plays a key role in supporting life on our planet. It is particularly important in higher eukaryotes where it boosts bioenergetics as a thermodynamically favorable terminal electron acceptor and has important roles in cell signaling and development. Many human diseases stem from either insufficient or excessive oxygen. Despite its fundamental importance, we lack methods with which to manipulate the supply of oxygen with high spatiotemporal resolution in cells and in organisms. Here, we introduce a genetic system, SupplemeNtal Oxygen Released from ChLorite (SNORCL), for on-demand local generation of molecular oxygen in living cells, by harnessing prokaryotic chlorite O2-lyase (Cld) enzymes that convert chlorite (ClO2-) into molecular oxygen (O2) and chloride (Cl-). We show that active Cld enzymes can be targeted to either the cytosol or mitochondria of human cells, and that coexpressing a chlorite transporter results in molecular oxygen production inside cells in response to externally added chlorite. This first-generation system allows fine temporal and spatial control of oxygen production, with immediate research applications. In the future, we anticipate that technologies based on SNORCL will have additional widespread applications in research, biotechnology, and medicine.
    Keywords:  Cld; SLC5A5; SNORCL; chlorite; oxygen
    DOI:  https://doi.org/10.1073/pnas.2207955119
  9. FEBS Lett. 2022 Oct 11.
    Rapid fractionation of mitochondria from mouse liver and heart reveals in vivo metabolite compartmentation.
    Fay M Allen, Ana S H Costa, Anja V Gruszczyk, Georgina R Bates, Hiran A Prag, Efterpi Nikitopoulou, Carlo Viscomi, Christian Frezza, Andrew M James, Michael P Murphy.
      The compartmentation and distribution of metabolites between mitochondria and the rest of the cell is a key parameter of cell signalling and pathology. Here, we have developed a rapid fractionation procedure that enables us to take mouse heart and liver from in vivo and within ~ 30 seconds stabilise the distribution of metabolites between mitochondria and the cytosol by rapid cooling, homogenisation and dilution. This is followed by centrifugation of mitochondria through an oil layer to separate mitochondrial and cytosolic fractions for subsequent metabolic analysis. Using this procedure revealed the in vivo compartmentation of mitochondrial metabolites and will enable assessment of the distribution of metabolites between the cytosol and mitochondria during a range of situations in vivo.
    Keywords:  compartmentation; in vivo; ischemia; metabolites; mitochondria; rapid fractionation
    DOI:  https://doi.org/10.1002/1873-3468.14511
  10. Elife. 2022 Oct 12. pii: e81645. [Epub ahead of print]11
    The Na+/K+ pump dominates control of glycolysis in hippocampal dentate granule cells.
    Dylan J Meyer, Carlos Manlio Díaz-García, Nidhi Nathwani, Mahia Rahman, Gary Yellen.
      Cellular ATP that is consumed to perform energetically expensive tasks must be replenished by new ATP through the activation of metabolism. Neuronal stimulation, an energetically demanding process, transiently activates aerobic glycolysis, but the precise mechanism underlying this glycolysis activation has not been determined. We previously showed that neuronal glycolysis is correlated with Ca2+ influx, but is not activated by feedforward Ca2+ signaling (Díaz-García, Meyer, et al., 2021). Since ATP-powered Na+ and Ca2+ pumping activities are increased following stimulation to restore ion gradients and are estimated to consume most neuronal ATP, we aimed to determine if they are coupled to neuronal glycolysis activation. By using two-photon imaging of fluorescent biosensors and dyes in dentate granule cell somas of acute mouse hippocampal slices, we observed that production of cytoplasmic NADH, a byproduct of glycolysis, is strongly coupled to changes in intracellular Na+, while intracellular Ca2+ could only increase NADH production if both forward Na+/Ca2+ exchange and Na+/K+ pump activity were intact. Additionally, antidromic stimulation-induced intracellular [Na+] increases were reduced >50% by blocking Ca2+ entry. These results indicate that neuronal glycolysis activation is predominantly a response to an increase in activity of the Na+/K+ pump, which is strongly potentiated by Na+ influx through the Na+/Ca2+ exchanger during extrusion of Ca2+ following stimulation.
    Keywords:  cell biology; mouse; neuroscience
    DOI:  https://doi.org/10.7554/eLife.81645
  11. Cell Metab. 2022 Oct 06. pii: S1550-4131(22)00408-9. [Epub ahead of print]
    Obesity caused by an OVOL2 mutation reveals dual roles of OVOL2 in promoting thermogenesis and limiting white adipogenesis.
    Zhao Zhang, Yiao Jiang, Lijing Su, Sara Ludwig, Xuechun Zhang, Miao Tang, Xiaohong Li, Priscilla Anderton, Xiaoming Zhan, Mihwa Choi, Jamie Russell, Chun-Hui Bu, Stephen Lyon, Darui Xu, Sara Hildebrand, Lindsay Scott, Jiexia Quan, Rochelle Simpson, Qihua Sun, Baifang Qin, Tiffany Collie, Meron Tadesse, Eva Marie Y Moresco, Bruce Beutler.
      Using random germline mutagenesis in mice, we identified a viable hypomorphic allele (boh) of the transcription-factor-encoding gene Ovol2 that resulted in obesity, which initially developed with normal food intake and physical activity but decreased energy expenditure. Fat weight was dramatically increased, while lean weight was reduced in 12-week-old boh homozygous mice, culminating by 24 weeks in massive obesity, hepatosteatosis, insulin resistance, and diabetes. The Ovol2boh/boh genotype augmented obesity in Lepob/ob mice, and pair-feeding failed to normalize obesity in Ovol2boh/boh mice. OVOL2-deficient mice were extremely cold intolerant. OVOL2 is essential for brown/beige adipose tissue-mediated thermogenesis. In white adipose tissues, OVOL2 limited adipogenesis by blocking C/EBPα engagement of its transcriptional targets. Overexpression of OVOL2 in adipocytes of mice fed with a high-fat diet reduced total body and liver fat and improved insulin sensitivity. Our data reveal that OVOL2 plays dual functions in thermogenesis and adipogenesis to maintain energy balance.
    Keywords:  C/EBPα; OVOL2; UCP1; adipogenesis; brown adipose tissue; cold intolerance; obesity; thermogenesis
    DOI:  https://doi.org/10.1016/j.cmet.2022.09.018
  12. Elife. 2022 Oct 13. pii: e78941. [Epub ahead of print]11
    Neuronal temperature perception induces specific defenses that enable C. elegans to cope with the enhanced reactivity of hydrogen peroxide at high temperature.
    Francesco A Servello, Rute Fernandes, Matthias Eder, Nathan Harris, Olivier M F Martin, Natasha Oswal, Anders Lindberg, Nohelly Derosiers, Piali Sengupta, Nicholas Stroustrup, Javier Apfeld.
      Hydrogen peroxide is the most common reactive chemical that organisms face on the microbial battlefield. The rate with which hydrogen peroxide damages biomolecules required for life increases with temperature, yet little is known about how organisms cope with this temperature-dependent threat. Here, we show that Caenorhabditis elegans nematodes use temperature information perceived by sensory neurons to cope with the temperature-dependent threat of hydrogen peroxide produced by the pathogenic bacterium Enterococcus faecium. These nematodes preemptively induce the expression of specific hydrogen peroxide defenses in response to perception of high temperature by a pair of sensory neurons. These neurons communicate temperature information to target tissues expressing those defenses via an insulin/IGF1 hormone. This is the first example of a multicellular organism inducing their defenses to a chemical when they sense an inherent enhancer of the reactivity of that chemical.
    Keywords:  C. elegans; E. coli; developmental biology; neuroscience
    DOI:  https://doi.org/10.7554/eLife.78941
  13. Nature. 2022 Oct 12.
    A saturated map of common genetic variants associated with human height.
    23andMe Research Team
      Common single-nucleotide polymorphisms (SNPs) are predicted to collectively explain 40-50% of phenotypic variation in human height, but identifying the specific variants and associated regions requires huge sample sizes1. Here, using data from a genome-wide association study of 5.4 million individuals of diverse ancestries, we show that 12,111 independent SNPs that are significantly associated with height account for nearly all of the common SNP-based heritability. These SNPs are clustered within 7,209 non-overlapping genomic segments with a mean size of around 90 kb, covering about 21% of the genome. The density of independent associations varies across the genome and the regions of increased density are enriched for biologically relevant genes. In out-of-sample estimation and prediction, the 12,111 SNPs (or all SNPs in the HapMap 3 panel2) account for 40% (45%) of phenotypic variance in populations of European ancestry but only around 10-20% (14-24%) in populations of other ancestries. Effect sizes, associated regions and gene prioritization are similar across ancestries, indicating that reduced prediction accuracy is likely to be explained by linkage disequilibrium and differences in allele frequency within associated regions. Finally, we show that the relevant biological pathways are detectable with smaller sample sizes than are needed to implicate causal genes and variants. Overall, this study provides a comprehensive map of specific genomic regions that contain the vast majority of common height-associated variants. Although this map is saturated for populations of European ancestry, further research is needed to achieve equivalent saturation in other ancestries.
    DOI:  https://doi.org/10.1038/s41586-022-05275-y
  14. FEBS Open Bio. 2022 Oct 10.
    Knockdown of TMEM160 leads to an increase in reactive oxygen species generation and the induction of the mitochondrial unfolded protein response.
    Kosei Yamashita, Misa Haraguchi, Masato Yano.
      Transmembrane protein 160 (TMEM160) was recently reported to be localized to the mitochondrial inner membrane, but mitochondrial function was noted to be unaffected by loss of TMEM160. In contrast to these previously published findings, we report here that the absence of TMEM160 influences intracellular responses. After confirming that TMEM160 is localized in the inner mitochondrial membrane, we knocked down TMEM160 in human cultured cells and analyzed the changes in cellular responses. TMEM160 depletion led to an upregulation of the mitochondrial chaperone HSPD1, suggesting that depletion induced the mitochondrial unfolded protein response (UPRmt ). Indeed, the expression of key transcription factors that induce the UPRmt (ATF4, ATF5, and DDIT3) was increased following TMEM160 depletion. Expression of the mitochondrial protein import-receptors TOMM22 and TOMM20 was also enhanced. In addition, we observed a significant increase in reactive oxygen species (ROS) generation following TMEM160 depletion. Glutathione S-transferases, which detoxify the products of oxidative stress, were also upregulated in TMEM160-depleted cells. Immunoblot analysis was performed to detect proteins modified by 4-hydroxynonenal (which is released after the peroxidation of lipids by ROS): the expression patterns of 4-hydroxynonenal-modified proteins were altered after TMEM160 depletion, suggesting that depletion enhanced degadation of these proteins. HSPD1, TOMM22, ATF4, ATF5, and DDIT3 remained upregulated after ROS was scavenged by N-acetylcysteine, suggesting that once the UPRmt is induced by TMEM160 depletion, it is not suppresed by the subsequent detoxification of ROS. These findings suggest that TMEM160 may suppress ROS generation and stabilize mitochondrial protein(s).
    Keywords:  TMEM160; mitochondria; mitochondrial unfolded protein response; oxidative stress; reactive oxygen species
    DOI:  https://doi.org/10.1002/2211-5463.13496
  15. J Biol Chem. 2022 Oct 08. pii: S0021-9258(22)01023-7. [Epub ahead of print] 102579
    Oxidative stress-induced autonomous activation of the Calcium/Calmodulin-Dependent Kinase II involves disulfide formation in the regulatory domain.
    Nathália Rocco-Machado, Lo Lai, Geumsoo Kim, Yi He, Elizabeth D Luczak, Mark E Anderson, Rodney L Levine.
      Calcium/calmodulin-dependent protein kinase II δ (CaMKIIδ) has a pivotal role in cardiac signaling. Constitutive and deleterious CaMKII "autonomous" activation is induced by oxidative stress, and the previously reported mechanism involves oxidation of methionine residues in the regulatory domain. Here we demonstrate that covalent oxidation leads to a disulfide bond with Cys273 in the regulatory domain causing autonomous activity. Autonomous activation was induced by treating CaMKII with diamide or histamine chloramine, two thiol-oxidizing agents. Autonomy was reversed when the protein was incubated with DTT or thioredoxin to reduce disulfide bonds. Tryptic mapping of the activated CaMKII revealed formation of a disulfide between Cys273 and Cys290 in the regulatory domain. We determined the apparent pKa of those Cys and found that Cys273 had a low pKa while that of Cys290 was elevated. The low pKa of Cys273 facilitates oxidation of its thiol to the sulfenic acid at physiological pH. The reactive sulfenic acid then attacks the thiol of Cys290 to form the disulfide. The previously reported CaMKII mutant in which methionine residues 281 and 282 were mutated to valine (MMVV) protects mice and flies from cardiac decompensation induced by oxidative stress. Our initial hypothesis was that the MMVV mutant underwent a conformational change that prevented disulfide formation and autonomous activation. However, we found that the thiol-oxidizing agents induced autonomy in the MMVV mutant and that the mutant undergoes rapid degradation by the cell, potentially preventing accumulation of the injurious autonomous form. Together, our results highlight additional mechanistic details of CaMKII autonomous activation.
    Keywords:  CaMKII; Cysteine; Disulfide; Methionine; Oxidative stress; Redox regulation
    DOI:  https://doi.org/10.1016/j.jbc.2022.102579
  16. Science. 2022 Oct 14. 378(6616): eadd1268
    Activation mechanism of the mouse cold-sensing TRPM8 channel by cooling agonist and PIP2.
    Ying Yin, Feng Zhang, Shasha Feng, Kevin John Butay, Mario J Borgnia, Wonpil Im, Seok-Yong Lee.
      The transient receptor potential melastatin 8 (TRPM8) channel is the primary molecular transducer responsible for the cool sensation elicited by menthol and cold in mammals. TRPM8 activation is controlled by cooling compounds together with the membrane lipid phosphatidylinositol 4,5-bisphosphate (PIP2). Our knowledge of cold sensation and the therapeutic potential of TRPM8 for neuroinflammatory diseases and pain will be enhanced by understanding the structural basis of cooling agonist- and PIP2-dependent TRPM8 activation. We present cryo-electron microscopy structures of mouse TRPM8 in closed, intermediate, and open states along the ligand- and PIP2-dependent gating pathway. Our results uncover two discrete agonist sites, state-dependent rearrangements in the gate positions, and a disordered-to-ordered transition of the gate-forming S6-elucidating the molecular basis of chemically induced cool sensation in mammals.
    DOI:  https://doi.org/10.1126/science.add1268
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