BBA - Molecular and Cell Biology of Lipids (v.1841, #9)
Editorial Board (i).
Induction of insulin secretion by apolipoprotein M, a carrier for sphingosine 1-phosphate by Makoto Kurano; Masumi Hara; Koichi Tsuneyama; Hideyuki Sakoda; Tomo Shimizu; Kazuhisa Tsukamoto; Hitoshi Ikeda; Yutaka Yatomi (1217-1226).
High-density lipoprotein (HDL) has been proposed to enhance β-cell functions. Clinical studies have suggested that apolipoprotein M (apoM), which rides mainly on HDL, is involved in diabetes; however, the underlying mechanism has not yet been elucidated. Recently, apoM was shown to be a carrier for sphingosine 1-phosphate (S1P), a bioactive lipid mediator. In the present study, we investigated the modulation of insulin secretion by apoM through the action of S1P.We overexpressed apoM in the livers of C57BL6 mice using adenovirus gene transfer and found that the blood glucose levels under ad libitum feeding conditions were lower in the apoM-overexpressing mice. While an insulin tolerance test revealed that insulin sensitivity was not significantly affected, a glucose tolerance test revealed that apoM-overexpressing mice had a better glucose tolerance because of enhanced insulin secretion, a phenomenon that was reversed by treatment with VPC 23019, an antagonist against S1P1 and S1P3 receptor. In vitro experiments with MIN6 cells also revealed that apoM-containing lipoproteins enhanced insulin secretion, which was again inhibited by VPC 23019. ApoM retarded the degradation of S1P, and an increase in Pdx1 expression, the attenuation of endoreticulum stress, and the phosphorylation of Akt, AmpK, and Erk were observed as possible underlying mechanisms for the effect of S1P, maintained at a high concentration by apoM, on the increase in insulin secretion.ApoM augmented insulin secretion by maintaining the S1P concentration under both in vivo and in vitro conditions.
Keywords: Apolipoprotein M; Sphingosine 1-phosphate; Insulin secretion; MIN6 cells;
Detection and molecular cloning of CYP74Q1 gene: Identification of Ranunculus acris leaf divinyl ether synthase by Svetlana S. Gorina; Yana Y. Toporkova; Lucia S. Mukhtarova; Ivan R. Chechetkin; Bulat I. Khairutdinov; Yuri V. Gogolev; Alexander N. Grechkin (1227-1233).
Enzymes of the CYP74 family, including the divinyl ether synthase (DES), play important roles in plant cell signalling and defence. The potent DES activities have been detected before in the leaves of the meadow buttercup (Ranunculus acris L.) and few other Ranunculaceae species. The nature of these DESs and their genes remained unrevealed. The PCR with degenerate primers enabled to detect the transcript of unknown P450 gene assigned as CYP74Q1. Besides, two more CYP74Q1 isoforms with minimal sequence variations have been found. The full length recombinant CYP74Q1 protein was expressed in Escherichia coli. The preferred substrates of this enzyme are the 13-hydroperoxides of α-linolenic and linoleic acids, which are converted to the divinyl ether oxylipins (ω5Z)-etherolenic acid, (9Z,11E)-12-[(1′Z,3′Z)-hexadienyloxy]-9,11-dodecadienoic acid, and (ω5Z)-etheroleic acid, (9Z,11E)-12-[(1′Z)-hexenyloxy]-9,11-dodecadienoic acid, respectively, as revealed by the data of mass spectrometry, NMR and UV spectroscopy. Thus, CYP74Q1 protein was identified as the R. acris DES (RaDES), a novel DES type and the opening member of new CYP74Q subfamily.Display Omitted
Keywords: Divinyl ether synthase; Molecular cloning; CYP74Q1; P450; Oxylipins; Meadow buttercup (Ranunculus acris L.);
Apolipoprotein A-I induces tubulin phosphorylation in association with cholesterol release in fetal rat astrocytes by Jin-ichi Ito; Rui Lu; Yuko Nagayasu; Shinji Yokoyama (1234-1240).
We previously identified cytosolic lipid–protein particles (CLPP) having size and density of HDL in rat astrocytes, to which apoA-I induces translocation of cholesterol, caveolin-1 and protein kinase Cα (PKCα) following its association with microtubules prior to cholesterol release/biogenesis of HDL (JBC 277: 7929, 2002; JLR 45: 2269, 2004). To further understand the physiological relevance of these findings, we investigated the CLPP/microtubule association and its role in intracellular cholesterol trafficking by using a technique of reconstituted microtubule-like filaments (rMT) in rat astrocyte cytosol. When the cells were pretreated with apoA-I, α-tubulin as a 52-kDa protein in rMT was found phosphorylated while α-tubulin in a soluble monomeric form was little phosphorylated. The phosphorylation took place coincidentally to apoA-I-induced association with rMT of CLPP, a complex containing PKCα, and was suppressed by a PKC inhibitor, Bis indolylmaleimide 1 (BIM). α-Tubulin dissociated from CLPP when phosphorylated, and it poorly bound to CLPP once dissociated. BIM did not influence association of PKCα with rMT but suppressed apoA-I-induced cholesterol translocation to the cytosol from the ER/Golgi apparatus and apoA-I-mediated cholesterol release. We thereby concluded that α-tubulin phosphorylation by PKCα on CLPP is involved in reversible CLPP association with the microtubules and intracellular cholesterol trafficking for apoA-I-dependent HDL biogenesis/cholesterol release in rat astrocytes.
Keywords: ApoA-I; Astrocyte; Microtubule; Tubulin; Protein kinase C; Caveolin-1;
c-Fos: An AP-1 transcription factor with an additional cytoplasmic, non-genomic lipid synthesis activation capacity by Beatriz L. Caputto; Andrés M. Cardozo Gizzi; Germán A. Gil (1241-1246).
The mechanisms that co-ordinately activate lipid synthesis when high rates of membrane biogenesis are needed to support cell growth are largely unknown. c-Fos, a well known AP-1 transcription factor, has emerged as a unique protein with the capacity to associate to specific enzymes of the pathway of synthesis of phospholipids at the endoplasmic reticulum and activate their synthesis to accompany genomic decisions of growth. Herein, we discuss this cytoplasmic, non-genomic effect of c-Fos in the context of other mechanisms that have been proposed to regulate lipid synthesis.
Keywords: Membrane biogenesis regulation; Phospholipid synthesizing enzymes regulation; c-Fos/CDS association; PI4KIIα/c-Fos association;
Ezetimibe enhances macrophage reverse cholesterol transport in hamsters: Contribution of hepato–biliary pathway by Harumi Uto-Kondo; Makoto Ayaori; Grace Megumi Sotherden; Kazuhiro Nakaya; Makoto Sasaki; Makiko Yogo; Tomohiro Komatsu; Shunichi Takiguchi; Emi Yakushiji; Masatsune Ogura; Takafumi Nishida; Yasuhiro Endo; Katsunori Ikewaki (1247-1255).
Reverse cholesterol transport (RCT) is pivotal in the return of excess cholesterol from peripheral tissues to the liver for excretion in bile and eventually feces. RCT from macrophages is a critical anti-atherogenicity mechanism of HDL. As the cholesterol absorption inhibitor ezetimibe promoted RCT in mice, which lack cholesterol ester transfer protein (CETP), we investigated its effects in hamsters, which have CETP.A high-cholesterol diet (HC) increased cholesterol levels throughout lipoprotein fractions and ezetimibe markedly reduced VLDL/LDL cholesterol levels under both normal chow (NC) and HC. However, ezetimibe did not affect and reduced HDL-cholesterol levels under NC and HC, respectively. Intraperitoneal injection of 3H-cholesterol pre-labeled macrophages in an in vivo RCT assay increased tracer accumulation in the liver but reduced it in bile under HC, and these changes were completely cancelled by ezetimibe. Under both NC and HC, ezetimibe reduced tracer levels in the liver but increased them in feces, indicating promotion of RCT in vivo. We performed a RCT assay using hamsters subjected to bile duct ligation (BDL) to clarify whether a transintestinal cholesterol efflux (TICE) pathway contributes to ezetimibe's enhancement of RCT. BDL markedly inhibited macrophage-derived 3H-cholesterol excretion to feces and cancelled ezetimibe's stimulatory effect on RCT, suggesting that biliary cholesterol excretion is a major contributor in RCT promotion by ezetimibe but the contribution of the TICE pathway is minimal.In conclusions, ezetimibe exerts an additive anti-atherogenic property by enhancing RCT in hamsters. Our findings suggest that this property is independent of the TICE pathway.
Keywords: RCT; HDL; Ezetimibe; CETP; TICE;
Cyclic phosphatidic acid and lysophosphatidic acid induce hyaluronic acid synthesis via CREB transcription factor regulation in human skin fibroblasts by Katsura Maeda-Sano; Mari Gotoh; Toshiro Morohoshi; Takao Someya; Hiromu Murofushi; Kimiko Murakami-Murofushi (1256-1263).
Cyclic phosphatidic acid (cPA) is a naturally occurring phospholipid mediator and an analog of the growth factor-like phospholipid lysophosphatidic acid (LPA). cPA has a unique cyclic phosphate ring at the sn-2 and sn-3 positions of its glycerol backbone. We showed before that a metabolically stabilized cPA derivative, 2-carba-cPA, relieved osteoarthritis pathogenesis in vivo and induced hyaluronic acid synthesis in human osteoarthritis synoviocytes in vitro. This study focused on hyaluronic acid synthesis in human fibroblasts, which retain moisture and maintain health in the dermis. We investigated the effects of cPA and LPA on hyaluronic acid synthesis in human fibroblasts (NB1RGB cells). Using particle exclusion and enzyme-linked immunosorbent assays, we found that both cPA and LPA dose-dependently induced hyaluronic acid synthesis. We revealed that the expression of hyaluronan synthase 2 messenger RNA and protein is up-regulated by cPA and LPA treatment time dependently. We then characterized the signaling pathways up-regulating hyaluronic acid synthesis mediated by cPA and LPA in NB1RGB cells. Pharmacological inhibition and reporter gene assays revealed that the activation of the LPA receptor LPAR1, Gi/o protein, phosphatidylinositol-3 kinase (PI3K), extracellular-signal-regulated kinase (ERK), and cyclic adenosine monophosphate response element-binding protein (CREB) but not nuclear factor κB induced hyaluronic acid synthesis by the treatment with cPA and LPA in NB1RGB cells. These results demonstrate for the first time that cPA and LPA induce hyaluronic acid synthesis in human skin fibroblasts mainly through the activation of LPAR1-Gi/o followed by the PI3K, ERK, and CREB signaling pathway.
Keywords: Cyclic phosphatidic acid; Lysophosphatidic acid; Hyaluronic acid; Hyaluronan synthase; Human skin fibroblast;
Mitochondrially-targeted bacterial phosphatidylethanolamine methyltransferase sustained phosphatidylcholine synthesis of a Saccharomyces cerevisiae Δpem1 Δpem2 double mutant without exogenous choline supply by Shingo Kobayashi; Aya Mizuike; Hiroyuki Horiuchi; Ryouichi Fukuda; Akinori Ohta (1264-1271).
In eukaryotic cells, phospholipids are synthesized exclusively in the defined organelles specific for each phospholipid species. To explain the reason for this compartmental specificity in the case of phosphatidylcholine (PC) synthesis, we constructed and characterized a Saccharomyces cerevisiae strain that lacked endogenous phosphatidylethanolamine (PE) methyltransferases but had a recombinant PE methyltransferase from Acetobacter aceti, which was fused with a mitochondrial targeting signal from yeast Pet100p and a 3 × HA epitope tag. This fusion protein, which we named as mitopmt, was determined to be localized to the mitochondria by fluorescence microscopy and subcellular fractionation. The expression of mitopmt suppressed the choline auxotrophy of a double deletion mutant of PEM1 and PEM2 (pem1Δpem2Δ) and enabled it to synthesize PC in the absence of choline. This growth suppression was observed even if the Kennedy pathway was inactivated by the repression of PCT1 encoding CTP:phosphocholine cytidylyltransferase, suggesting that PC synthesized in the mitochondria is distributed to other organelles without going through the salvage pathway. The pem1Δpem2Δ strain deleted for PSD1 encoding the mitochondrial phosphatidylserine decarboxylase was able to grow because of the expression of mitopmt in the presence of ethanolamine, implying that PE from other organelles, probably from the ER, was converted to PC by mitopmt. These results suggest that PC could move out of the mitochondria, and raise the possibility that its movement is not under strict directional limitations.
Keywords: Saccharomyces cerevisiae; phosphatidylcholine; phosphatidylethanolamine; mitochondria; transport;
Ancestral genetic complexity of arachidonic acid metabolism in Metazoa by Dongjuan Yuan; Qiuqiong Zou; Ting Yu; Cuikai Song; Shengfeng Huang; Shangwu Chen; Zhenghua Ren; Anlong Xu (1272-1284).
Eicosanoids play an important role in inducing complex and crucial physiological processes in animals. Eicosanoid biosynthesis in animals is widely reported; however, eicosanoid production in invertebrate tissue is remarkably different to vertebrates and in certain respects remains elusive. We, for the first time, compared the orthologs involved in arachidonic acid (AA) metabolism in 14 species of invertebrates and 3 species of vertebrates. Based on parsimony, a complex AA-metabolic system may have existed in the common ancestor of the Metazoa, and then expanded and diversified through invertebrate lineages. A primary vertebrate-like AA-metabolic system via cyclooxygenase (COX), lipoxygenase (LOX), and cytochrome P450 (CYP) pathways was further identified in the basal chordate, amphioxus. The expression profiling of AA-metabolic enzymes and lipidomic analysis of eicosanoid production in the tissues of amphioxus supported our supposition. Thus, we proposed that the ancestral complexity of AA-metabolic network diversified with the different lineages of invertebrates, adapting with the diversity of body plans and ecological opportunity, and arriving at the vertebrate-like pattern in the basal chordate, amphioxus.
Keywords: Molecular evolution; Phylogenetic; Eicosanoid; COX; LOX; CYP;
Characterisation of sphingolipids in the human lens by thin layer chromatography–desorption electrospray ionisation mass spectrometry by Jo Ann Seng; Shane R. Ellis; Jessica R. Hughes; Alan T. Maccarone; Roger J.W. Truscott; Stephen J. Blanksby; Todd W. Mitchell (1285-1291).
The lipidome of the human lens is unique in that cholesterol and dihydrosphingomyelin are the dominant classes. Moreover, the lens lipidome is not static with dramatic changes in several sphingolipid classes associated with both aging and cataract. Accordingly, there is a clear need to expand knowledge of the molecular species that constitute the human lens sphingolipidome. In this study, human lens lipids have been extracted and separated by thin-layer chromatography (TLC). Direct analysis of the TLC plates by desorption electrospray ionisation–mass spectrometry (DESI–MS) allowed the detection over 30 species from 11 classes of sphingolipids. Significantly, novel classes of lens lipids including sulfatides, dihydrosulfatides, lactosylceramide sulfates and dihydrolactosylceramide sulfates were identified.
Keywords: Glycosphingolipids; Human lens; Lactosylceramide sulfates; Mass spectrometry; Sulfatides; Lipidomics;
Role of free fatty acid receptors in the regulation of energy metabolism by Takafumi Hara; Daiji Kashihara; Atsuhiko Ichimura; Ikuo Kimura; Gozoh Tsujimoto; Akira Hirasawa (1292-1300).
Free fatty acids (FFAs) are energy-generating nutrients that act as signaling molecules in various cellular processes. Several orphan G protein-coupled receptors (GPCRs) that act as FFA receptors (FFARs) have been identified and play important physiological roles in various diseases. FFA ligands are obtained from food sources and metabolites produced during digestion and lipase degradation of triglyceride stores. FFARs can be grouped according to ligand profiles, depending on the length of carbon chains of the FFAs. Medium- and long-chain FFAs activate FFA1/GPR40 and FFA4/GPR120. Short-chain FFAs activate FFA2/GPR43 and FFA3/GPR41. However, only medium-chain FFAs, and not long-chain FFAs, activate GPR84 receptor. A number of pharmacological and physiological studies have shown that these receptors are expressed in various tissues and are primarily involved in energy metabolism. Because an impairment of these processes is a part of the pathology of obesity and type 2 diabetes, FFARs are considered as key therapeutic targets. Here, we reviewed recently published studies on the physiological functions of these receptors, primarily focusing on energy homeostasis.
Keywords: G protein-coupled receptor; Free fatty acid receptor; Fatty acid; Energy metabolism;
Membrane organization determines barrier properties of endothelial cells and short-chain sphingolipid-facilitated doxorubicin influx by A.J. van Hell; A. Klymchenko; D.M. Gueth; W.J. van Blitterswijk; G.A. Koning; M. Verheij (1301-1307).
The endothelial lining and its outer lipid membrane are the first major barriers drug molecules encounter upon intravenous administration. Our previous work identified lipid analogs that counteract plasma membrane barrier function for a series of amphiphilic drugs. For example, short-chain sphingolipids (SCS), like N-octanoyl-glucosylceramide, effectively elevated doxorubicin accumulation in tumor cells, both in vitro and in vivo, and in endothelial cells, whereas other (normal) cells remained unaffected. We hypothesize here that local membrane lipid composition and the degree of lipid ordering define SCS efficacy in individual cells. To this end, we study the differential effect of SCS on bovine aortic endothelial cells (BAEC) in its confluent versus proliferative state, as a model system. While their (plasma membrane) lipidome stays remarkably unaltered when BAECs reach confluency, their lipids segregate to form apical and basolateral domains. Using probe NR12S, we reveal that lipids in the apical membrane are more condensed/liquid-ordered. SCS preferentially attenuate the barrier posed by these condensed membranes and facilitate doxorubicin influx in these particular membrane regions. We confirm these findings in MDCK cells and artificial membranes. In conclusion, SCS-facilitated drug traversal acts on condensed membrane domains, elicited by confluency in resting endothelium.
Keywords: Drug delivery; Cancer therapy; Doxorubicin; Apical basolateral polarization; Bovine aortic endothelial cells; Vasculature;
DHA-mediated enhancement of TRAIL-induced apoptosis in colon cancer cells is associated with engagement of mitochondria and specific alterations in sphingolipid metabolism by Belma Skender; Jiřina Hofmanová; Josef Slavík; Iva Jelínková; Miroslav Machala; Mary Pat Moyer; Alois Kozubík; Alena Hyršlová Vaculová (1308-1317).
Docosahexaenoic acid (DHA), an n-3 polyunsaturated fatty acid present in fish oil, may exert cytotoxic and/or cytostatic effects on colon cancer cells when applied individually or in combination with some anticancer drugs. Here we demonstrate a selective ability of subtoxic doses of DHA to enhance antiproliferative and apoptotic effects of clinically useful cytokine TRAIL (tumor necrosis factor-related apoptosis inducing ligand) in cancer but not normal human colon cells. DHA-mediated stimulation of TRAIL-induced apoptosis was associated with extensive engagement of mitochondrial pathway (Bax/Bak activation, drop of mitochondrial membrane potential, cytochrome c release), activation of endoplasmic reticulum stress response (CHOP upregulation, changes in PERK level), decrease of cellular inhibitor of apoptosis protein (XIAP, cIAP1) levels and significant changes in sphingolipid metabolism (intracellular levels of ceramides, hexosyl ceramides, sphingomyelines, sphingosines; HPLC/MS/MS). Interestingly, we found significant differences in representation of various classes of ceramides (especially C16:0, C24:1) between the cancer and normal colon cells treated with DHA and TRAIL, and suggested their potential role in the regulation of the cell response to the drug combination. These study outcomes highlight the potential of DHA for a new combination therapy with TRAIL for selective elimination of colon cancer cells via simultaneous targeting of multiple steps in apoptotic pathways.
Keywords: Docosahexaenoic acid; TRAIL; Apoptosis; Lipid metabolism; Colon cancer;
Characterization of the interaction of diacylglycerol acyltransferase-2 with the endoplasmic reticulum and lipid droplets by Pamela J. McFie; Youzhi Jin; Shanna L. Banman; Erwan Beauchamp; Luc G. Berthiaume; Scot J. Stone (1318-1328).
Acyl CoA:diacylglycerol acyltransferase-2 (DGAT2) is an integral membrane protein that catalyzes the synthesis of triacylglycerol (TG). DGAT2 is present in the endoplasmic reticulum (ER) and also localizes to lipid droplets when cells are stimulated with oleate. Previous studies have shown that DGAT2 can interact with membranes and lipid droplets independently of its two transmembrane domains, suggesting the presence of an additional membrane binding domain. In order to identify additional membrane binding regions, we confirmed that DGAT2 has only two transmembrane domains and demonstrated that the loop connecting them is present in the ER lumen. Increasing the length of this short loop from 5 to 27 amino acids impaired the ability of DGAT2 to localize to lipid droplets. Using a mutagenesis approach, we were able to identify a stretch of amino acids that appears to have a role in binding DGAT2 to the ER membrane. Our results confirm that murine DGAT2 has only two transmembrane domains but also can interact with membranes via a previously unidentified helical domain containing its active site.
Keywords: Lipid droplet; Triacylglycerol; Endoplasmic reticulum; Topology; Diacylglycerol acyltransferase; Cysteine;
Fatty acid oxidation is dispensable for human macrophage IL-4-induced polarization by Dmitry Namgaladze; Bernhard Brüne (1329-1335).
Macrophage polarization elicits various metabolic alterations which in turn influence the polarized phenotype. Activation of glycolytic metabolism accompanies and supports macrophage pro-inflammatory M1 polarization. In contrast, M2 polarization of murine macrophages in response to the Th2 cytokine interleukin-4 (IL-4) was linked to the up-regulation of mitochondrial oxidative metabolism and fatty acid oxidation (FAO), which was necessary for coining an IL-4-polarized phenotype. Here we investigated whether similar mechanisms operate in human macrophages stimulated with IL-4. IL-4 causes only moderate changes of mitochondrial oxidative metabolism and FAO, correlating with an unaltered expression of peroxisome proliferator-activated receptor-γ coactivator 1 α/β (PGC-1α/β), the master transcriptional regulators of mitochondrial biogenesis. Furthermore, attenuating FAO had no effect on IL-4-induced polarization-associated gene expression. Apparently, FAO is dispensable for IL-4-induced polarization of human macrophages, pointing to fundamental differences in the metabolic requirements of macrophage phenotype alterations between mice and humans.
Keywords: Beta‐oxidation; Interleukin; Macrophages; Mitochondrial metabolism; Transcription coactivators;
Metabolic conversion of intra-amniotically-injected deuterium-labeled essential fatty acids by fetal rats following maternal n-3 fatty acid deficiency by Ephraim Yavin; Yu Hong Lin; Annette Brand; Norman Salem (1336-1344).
Accumulation of polyunsaturated fatty acids (PUFA) in the fetal brain is accomplished predominantly via a highly selective flow of docosahexaenoic acid (22:6n-3, DHA) and arachidonic acid (20:4n-6, AA) through the placenta. Little is known regarding the endogenous capability of the fetus to generate its own DHA and AA from lower homologues such as linolenic (18:3n-3, ALA) and linoleic (18:2n-6, LA) acids, respectively. Deuterium-labeled d5-ALA and d5-LA at millimolar concentrations were injected directly into the amniotic fluid in order to investigate maternal-independent metabolic conversion of the stable isotopes in brain and liver of the fetus near delivery. After 48 h under adequate maternal diet, the levels of d5-ALA metabolites in the fetal brain and fetal liver were 45 ± 2.2 pmol/mg and 86 ± 4 pmol/mg of which 79% and 63.6% were comprised of d5-DHA. At this time point, incorporation of d5-LA metabolites was 103 ± 5 pmol/mg and 772 ± 46 pmol/mg for brain and liver, of which 50% and 30% were comprised of d5-AA. Following sustained maternal dietary ALA deficiency, the levels of total d5-ALA derived metabolites in the fetal brain and fetal liver were increased to 231 pmol/mg and 696 pmol/mg of which 71% and 26% were comprised of d5-DHA. From the time course and relative rates of d5-ALA precursor displacement by d5-DHA in cellular phosphoglycerides, it is concluded that the fetal rat brain can generate its own DHA from its d5-ALA precursors particularly under dietary stress.
Keywords: Brain; Docosahexaenoic acid; n-3 PUFA deficiency; Phospholipids; Fetal metabolism; Amniotic fluid;
Intrinsic differences in BRITE adipogenesis of primary adipocytes from two different mouse strains by Yongguo Li; Florian Bolze; Tobias Fromme; Martin Klingenspor (1345-1352).
BRITE (brown-in-white) cells are brown adipocyte-like cells found in white adipose tissue (WAT) of rodents and/or humans. The recruitment of BRITE adipocytes, referred to as the browning of WAT, is hallmarked by the expression of UCP1 and exerts beneficial metabolic effects. Here we address whether beyond systemic cues depot- and strain-specific variation in BRITE recruitment is determined by a cellular program intrinsic to progenitors. Therefore we compared the browning capacity of serum and investigated brown and BRITE adipogenesis in primary cultures of stromal-vascular cells isolated from interscapular brown adipose tissue (iBAT), inguinal white adipose tissue (iWAT) and epididymal white adipose tissue (eWAT) in two inbred mouse strains C57BL/6J (B6, a strain with low browning propensity) and 129/S6SvEv (129, a strain with high browning propensity). Paradoxically, serum collected from B6 mice was more potent in the promotion of browning than serum collected from 129 mice. Nevertheless, we demonstrate that depot- and strain-specific differences observed in vivo are pheno-copied in primary cultures in vitro, as judged by UCP1 expression and by functional analysis. Notably, primary adipocytes from 129 mice had a higher capacity for isoproterenol-induced uncoupled respiration than B6. We conclude that cues intrinsic to the progenitor cells contribute to differential BRITE adipogenesis. Further analyses demonstrate that these cues are independent of autocrine/paracrine mechanisms, BRITE progenitor abundance and genetic variation in the gene regulatory region of Ucp1 but rather depend on trans-acting factors. These results provide new insights on the molecular basis of strain and depot-specific differences in BRITE adipogenesis.
Keywords: Nonshivering thermogenesis; Brown adipose tissue; Mitochondria; Uncoupling protein;