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Aims: To test the hypothesis that adipose tissue gene expression patterns would be affected by metabolic surgery and we aimed to identify genes and metabolic pathways as well as metabolites correlating with metabolic changes following metabolic surgery., Materials and Methods: This observational study was conducted at the Obesity Unit at the Catholic University Hospital of the Sacred Heart in Rome, Italy. Fifteen patients, of which six patients underwent Roux-en-Y gastric bypass and nine patients underwent biliopancreatic diversion, were included. The participants underwent an oral glucose tolerance test and a hyperinsulinemic euglycemic clamp. Small polar metabolites were analyzed with a two-dimensional gas chromatography coupled to time-of-flight mass spectrometry (GC×GC-TOFMS). Gene expression analysis of genes related to metabolism of amino acids and fatty acids were analyzed in subcutaneous adipose tissue. All procedures were performed at study start and at follow-up (after 185.3 ± 72.9 days)., Results: Twelve metabolites were significantly changed after metabolic surgery. Six metabolites were identified as 3-indoleacetic acid, 2-hydroxybutyric acid, valine, glutamic acid, 4-hydroxybenzeneacetic acid and alpha-tocopherol. The branched chain amino acids displayed a significant decrease together with a decrease in BCAT1 adipose tissue mRNA levels. Changes in the identified metabolites were associated to changes in lipid, insulin and glucose levels., Conclusions: Our study has identified metabolites and metabolic pathways that are altered by metabolic surgery and may be used as biomarkers for metabolic improvement., Competing Interests: EC reports payment for educational events in collaborations with Novo Nordisk and Bruno Pharmaceutics. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2021 Ahlin, Cefalo, Bondia-Pons, Trošt, Capristo, Marini, Romero, Zorzano, Gastaldelli, Mingrone and Nolan.)

Background: Low-density lipoprotein receptor-related protein 1 (LRP1) plays a key role in fatty acid metabolism and glucose homeostasis. In the context of dyslipemia, LRP1 is upregulated in the heart. Our aim was to evaluate the impact of cardiomyocyte LRP1 deficiency on high fat diet (HFD)-induced cardiac and metabolic alterations, and to explore the potential mechanisms involved., Methods: We used TnT-iCre transgenic mice with thoroughly tested suitability to delete genes exclusively in cardiomyocytes to generate an experimental mouse model with conditional Lrp1 deficiency in cardiomyocytes (TNT-iCre + -LRP1 flox/flox )., Findings: Mice with Lrp1-deficient cardiomyocytes (cm-Lrp1 -/- ) have a normal cardiac function combined with a favorable metabolic phenotype against HFD-induced glucose intolerance and obesity. Glucose intolerance protection was linked to higher hepatic fatty acid oxidation (FAO), lower liver steatosis and increased whole-body energy expenditure. Proteomic studies of the heart revealed decreased levels of cardiac pro-atrial natriuretic peptide (pro-ANP), which was parallel to higher ANP circulating levels. cm-Lrp1 -/- mice showed ANP signaling activation that was linked to increased fatty acid (FA) uptake and increased AMPK/ ACC phosphorylation in the liver. Natriuretic peptide receptor A (NPR-A) antagonist completely abolished ANP signaling and metabolic protection in cm-Lrp1 -/- mice., Conclusions: These results indicate that an ANP-dependent axis controlled by cardiac LRP1 levels modulates AMPK activity in the liver, energy homeostasis and whole-body metabolism., Competing Interests: Declaration of competing interest The authors have declared no potential conflicts of interest., (Copyright © 2020 Elsevier Inc. All rights reserved.)

During adipogenesis, preadipocytes' cytoskeleton reorganizes in parallel with lipid accumulation. Failure to do so may impact the ability of adipose tissue (AT) to shift between lipid storage and mobilization. Here, we identify cytoskeletal transgelin 2 (TAGLN2) as a protein expressed in AT and associated with obesity and inflammation, being normalized upon weight loss. TAGLN2 was primarily found in the adipose stromovascular cell fraction, but inflammation, TGF-β, and estradiol also prompted increased expression in human adipocytes. Tagln2 knockdown revealed a key functional role, being required for proliferation and differentiation of fat cells, whereas transgenic mice overexpressing Tagln2 using the adipocyte protein 2 promoter disclosed remarkable sex-dependent variations, in which females displayed "healthy" obesity and hypertrophied adipocytes but preserved insulin sensitivity, and males exhibited physiologic changes suggestive of defective AT expandability, including increased number of small adipocytes, activation of immune cells, mitochondrial dysfunction, and impaired metabolism together with decreased insulin sensitivity. The metabolic relevance and sexual dimorphism of TAGLN2 was also outlined by genetic variants that may modulate its expression and are associated with obesity and the risk of ischemic heart disease in men. Collectively, current findings highlight the contribution of cytoskeletal TAGLN2 to the obese phenotype in a gender-dependent manner.-Ortega, F. J., Moreno-Navarrete, J. M., Mercader, J. M., Gómez-Serrano, M., García-Santos, E., Latorre, J., Lluch, A., Sabater, M., Caballano-Infantes, E., Guzmán, R., Macías-González, M., Buxo, M., Gironés, J., Vilallonga, R., Naon, D., Botas, P., Delgado, E., Corella, D., Burcelin, R., Frühbeck, G., Ricart, W., Simó, R., Castrillon-Rodríguez, I., Tinahones, F. J., Bosch, F., Vidal-Puig, A., Malagón, M. M., Peral, B., Zorzano, A., Fernández-Real, J. M. Cytoskeletal transgelin 2 contributes to gender-dependent adipose tissue expandability and immune function.

Background: A functional population of adipocyte precursors, termed adipose-derived stromal/stem cells (ASCs), is crucial for proper adipose tissue (AT) expansion, lipid handling, and prevention of lipotoxicity in response to chronic positive energy balance. We previously showed that obese human subjects contain a dysfunctional pool of ASCs. Elucidation of the mechanisms underlying abnormal ASC function might lead to therapeutic interventions for prevention of lipotoxicity by improving the adipogenic capacity of ASCs., Methods: Using epigenome-wide association studies, we explored the impact of obesity on the methylation signature of human ASCs and their differentiated counterparts. Mitochondrial phenotyping of lean and obese ASCs was performed. TBX15 loss- and gain-of-function experiments were carried out and western blotting and electron microscopy studies of mitochondria were performed in white AT biopsies from lean and obese individuals., Results: We found that DNA methylation in adipocyte precursors is significantly modified by the obese environment, and adipogenesis, inflammation, and immunosuppression were the most affected pathways. Also, we identified TBX15 as one of the most differentially hypomethylated genes in obese ASCs, and genetic experiments revealed that TBX15 is a regulator of mitochondrial mass in obese adipocytes. Accordingly, morphological analysis of AT from obese subjects showed an alteration of the mitochondrial network, with changes in mitochondrial shape and number., Conclusions: We identified a DNA methylation signature in adipocyte precursors associated with obesity, which has a significant impact on the metabolic phenotype of mature adipocytes.

Succinate is a signaling metabolite sensed extracellularly by succinate receptor 1 (SUNCR1). The accumulation of succinate in macrophages is known to activate a pro-inflammatory program; however, the contribution of SUCNR1 to macrophage phenotype and function has remained unclear. Here we found that activation of SUCNR1 had a critical role in the anti-inflammatory responses in macrophages. Myeloid-specific deficiency in SUCNR1 promoted a local pro-inflammatory phenotype, disrupted glucose homeostasis in mice fed a normal chow diet, exacerbated the metabolic consequences of diet-induced obesity and impaired adipose-tissue browning in response to cold exposure. Activation of SUCNR1 promoted an anti-inflammatory phenotype in macrophages and boosted the response of these cells to type 2 cytokines, including interleukin-4. Succinate decreased the expression of inflammatory markers in adipose tissue from lean human subjects but not that from obese subjects, who had lower expression of SUCNR1 in adipose-tissue-resident macrophages. Our findings highlight the importance of succinate-SUCNR1 signaling in determining macrophage polarization and assign a role to succinate in limiting inflammation.

Aging is associated with progressive white adipose tissue (WAT) enlargement initiated early in life, but the molecular mechanisms involved remain unknown. Here we show that mitochondrial complex IV (CIV) activity and assembly are already repressed in white adipocytes of middle-aged mice and involve a HIF1A-dependent decline of essential CIV components such as COX5B. At the molecular level, HIF1A binds to the Cox5b proximal promoter and represses its expression. Silencing of Cox5b decreased fatty acid oxidation and promoted intracellular lipid accumulation. Moreover, local in vivo Cox5b silencing in WAT of young mice increased the size of adipocytes, whereas restoration of COX5B expression in aging mice counteracted adipocyte enlargement. An age-dependent reduction in COX5B gene expression was also found in human visceral adipose tissue. Collectively, our findings establish a pivotal role for CIV dysfunction in progressive white adipocyte enlargement during aging, which can be restored to alleviate age-dependent WAT expansion., (Copyright © 2016 The Authors. Published by Elsevier Inc. All rights reserved.)

The discovery of active brown adipose tissue (BAT) in adult humans and the fact that it is reduced in obese and diabetic patients have put a spotlight on this tissue as a key player in obesity-induced metabolic disorders. BAT regulates energy expenditure through thermogenesis; therefore, harnessing its thermogenic fat-burning power is an attractive therapeutic approach. We aimed to enhance BAT thermogenesis by increasing its fatty acid oxidation (FAO) rate. Thus, we expressed carnitine palmitoyltransferase 1AM (CPT1AM), a permanently active mutant form of CPT1A (the rate-limiting enzyme in FAO), in a rat brown adipocyte (rBA) cell line through adenoviral infection. We found that CPT1AM-expressing rBA have increased FAO, lipolysis, UCP1 protein levels and mitochondrial activity. Additionally, enhanced FAO reduced the palmitate-induced increase in triglyceride content and the expression of obese and inflammatory markers. Thus, CPT1AM-expressing rBA had enhanced fat-burning capacity and improved lipid-induced derangements. This indicates that CPT1AM-mediated increase in brown adipocytes FAO may be a new approach to the treatment of obesity-induced disorders.

In mammals, the liver plays a central role in maintaining carbohydrate and lipid homeostasis by acting both as a major source and a major sink of glucose and lipids. In particular, when dietary carbohydrates are in excess, the liver converts them to lipids via de novo lipogenesis. The molecular checkpoints regulating the balance between carbohydrate and lipid homeostasis, however, are not fully understood. Here we identify PPP2R5C, a regulatory subunit of PP2A, as a novel modulator of liver metabolism in postprandial physiology. Inactivation of PPP2R5C in isolated hepatocytes leads to increased glucose uptake and increased de novo lipogenesis. These phenotypes are reiterated in vivo, where hepatocyte specific PPP2R5C knockdown yields mice with improved systemic glucose tolerance and insulin sensitivity, but elevated circulating triglyceride levels. We show that modulation of PPP2R5C levels leads to alterations in AMPK and SREBP-1 activity. We find that hepatic levels of PPP2R5C are elevated in human diabetic patients, and correlate with obesity and insulin resistance in these subjects. In sum, our data suggest that hepatic PPP2R5C represents an important factor in the functional wiring of energy metabolism and the maintenance of a metabolically healthy state.

Aims/hypothesis: Circulating lipopolysaccharide-binding protein (LBP) is an acute-phase reactant known to be increased in obesity. We hypothesised that LBP is produced by adipose tissue (AT) in association with obesity., Methods: LBP mRNA and LBP protein levels were analysed in AT from three cross-sectional (n = 210, n = 144 and n = 28) and three longitudinal (n = 8, n = 25, n = 20) human cohorts; in AT from genetically manipulated mice; in isolated adipocytes; and in human and murine cell lines. The effects of a high-fat diet and exposure to lipopolysaccharide (LPS) and peroxisome proliferator-activated receptor (PPAR)γ agonist were explored. Functional in vitro and ex vivo experiments were also performed., Results: LBP synthesis and release was demonstrated to increase with adipocyte differentiation in human and mouse AT, isolated adipocytes and human and mouse cell lines (Simpson-Golabi-Behmel syndrome [SGBS], human multipotent adipose-derived stem [hMAD] and 3T3-L1 cells). AT LBP expression was robustly associated with inflammatory markers and increased with metabolic deterioration and insulin resistance in two independent cross-sectional human cohorts. AT LBP also increased longitudinally with weight gain and excessive fat accretion in both humans and mice, and decreased with weight loss (in two other independent cohorts), in humans with acquired lipodystrophy, and after ex vivo exposure to PPARγ agonist. Inflammatory agents such as LPS and TNF-α led to increased AT LBP expression in vivo in mice and in vitro, while this effect was prevented in Cd14-knockout mice. Functionally, LBP knockdown using short hairpin (sh)RNA or anti-LBP antibody led to increases in markers of adipogenesis and decreased adipocyte inflammation in human adipocytes., Conclusions/interpretation: Collectively, these findings suggest that LBP might have an essential role in inflammation- and obesity-associated AT dysfunction.

Mitofusin 2 (MFN2) plays critical roles in both mitochondrial fusion and the establishment of mitochondria-endoplasmic reticulum (ER) interactions. Hypothalamic ER stress has emerged as a causative factor for the development of leptin resistance, but the underlying mechanisms are largely unknown. Here, we show that mitochondria-ER contacts in anorexigenic pro-opiomelanocortin (POMC) neurons in the hypothalamus are decreased in diet-induced obesity. POMC-specific ablation of Mfn2 resulted in loss of mitochondria-ER contacts, defective POMC processing, ER stress-induced leptin resistance, hyperphagia, reduced energy expenditure, and obesity. Pharmacological relieve of hypothalamic ER stress reversed these metabolic alterations. Our data establish MFN2 in POMC neurons as an essential regulator of systemic energy balance by fine-tuning the mitochondrial-ER axis homeostasis and function. This previously unrecognized role for MFN2 argues for a crucial involvement in mediating ER stress-induced leptin resistance., (Copyright © 2013 Elsevier Inc. All rights reserved.)

Mitochondria are dynamic subcellular organelles that convert nutrient intermediates into readily available energy equivalents. Optimal mitochondrial function is ensured by a highly evolved quality control system, coordinated by protein machinery that regulates a process of continual fusion and fission. In this work, we provide in vivo evidence that the ATP-independent metalloprotease OMA1 plays an essential role in the proteolytic inactivation of the dynamin-related GTPase OPA1 (optic atrophy 1). We also show that OMA1 deficiency causes a profound perturbation of the mitochondrial fusion-fission equilibrium that has important implications for metabolic homeostasis. Thus, ablation of OMA1 in mice results in marked transcriptional changes in genes of lipid and glucose metabolic pathways and substantial alterations in circulating blood parameters. Additionally, Oma1-mutant mice exhibit an increase in body weight due to increased adipose mass, hepatic steatosis, decreased energy expenditure and impaired thermogenenesis. These alterations are especially significant under metabolic stress conditions, indicating that an intact OMA1-OPA1 system is essential for developing the appropriate adaptive response to different metabolic stressors such as a high-fat diet or cold-shock. This study provides the first description of an unexpected role in energy metabolism for the metalloprotease OMA1 and reinforces the importance of mitochondrial quality control for normal metabolic function.

The regulation of autophagy in metazoans is only partly understood, and there is a need to identify the proteins that control this process. The diabetes- and obesity-regulated gene (DOR), a recently reported nuclear cofactor of thyroid hormone receptors, is expressed abundantly in metabolically active tissues such as muscle. Here, we show that DOR shuttles between the nucleus and the cytoplasm, depending on cellular stress conditions, and re-localizes to autophagosomes on autophagy activation. We demonstrate that DOR interacts physically with autophagic proteins Golgi-associated ATPase enhancer of 16 kDa (GATE16) and microtubule-associated protein 1A/1B-light chain 3. Gain-of-function and loss-of-function studies indicate that DOR stimulates autophagosome formation and accelerates the degradation of stable proteins. CG11347, the DOR Drosophila homologue, has been predicted to interact with the Drosophila Atg8 homologues, which suggests functional conservation in autophagy. Flies lacking CG11347 show reduced autophagy in the fat body during pupal development. All together, our data indicate that DOR regulates autophagosome formation and protein degradation in mammalian and Drosophila cells.

The aims of this work were to evaluate thyroid hormone receptor-alpha (TR alpha), TR alpha 1, and TR alpha 2 mRNA gene expression and TR alpha 1:TR alpha 2 ratio, identified as candidate factors for explaining regional differences between human adipose tissue depots. TR alpha, TR alpha 1, and TR alpha 2 mRNA levels, and the gene expressions of arginine-serine-rich, splicing factor 2 (SF2), heterogeneous nuclear ribonucleoprotein H1 (hnRNP H1), heterogeneous nuclear ribonucleoprotein A1 (hnRNP A1), and Spot 14 (S14) were evaluated in 76 paired adipose tissue samples obtained from a population of 38 women who varied widely in terms of obesity and body fat distribution. Gene expression for these factors was also studied in stromal-vascular cells (SVCs) and mature adipocytes (MAs) from eight paired fat depots. TR alpha gene and TR alpha 1 mRNA expression were increased 1.46-fold (P = 0.006) and 1.80-fold (P < 0.0001), respectively, in subcutaneous (SC) vs. visceral fat. These differences in gene expression levels were most significant in the obese group, in which the TR alpha 1:TR alpha 2 ratio was 2.24-fold (P < 0.0001) higher in SC vs. visceral fat. S14 gene expression was also increased by 2.42-fold (P < 0.0001) and correlated significantly with TR alpha and TR alpha 1 gene expression and with the TR alpha 1:TR alpha 2 ratio. In agreement with these findings, hnRNP A1:SF2 ratio was decreased by 1.39-fold (P = 0.001). TR alpha and S14 levels were 2.1-fold (P < 0.0001) and 112.4-fold (P < 0.0001), respectively, higher in MAs than in SVCs from both fat depots. In summary, genes for TR-alpha, their upstream regulators, and downstream effectors were differentially expressed in SC vs. omental (OM) adipose tissue. Our findings suggest that TR alpha1 could contribute to SC adipose tissue expandability in obese subjects.

Mitochondrial dysfunction has been reported in skeletal muscle of obese subjects and of type 2 diabetic patients. Reduced mitochondrial mass and defective activity have been proposed to explain this dysfunction. Alterations in mitochondrial function may be crucial to explain the metabolic changes and insulin resistance that characterize both obesity and type 2 diabetes. Consequently, the identification of the primary mechanisms involved is of great relevance. Mitochondrial dynamics refers to the movement of mitochondria along the cytoskeleton and also to the regulation of mitochondrial morphology and distribution, which depend on fusion and fission events. In recent years, some of the proteins that participate in mitochondrial fusion and fission have been identified in mammalian cells. Recent evidence indicates that proteins participating in these processes are also involved in metabolism. The mitochondrial fusion protein mitofusin 2 stimulates respiration, substrate oxidation and the expression of subunits that participate in respiratory complexes in cultured cells. In this regard, skeletal muscle of obese subjects and of type 2 diabetic patients shows reduced mitofusin 2 expression. Therefore, alterations in the activity of the proteins involved in mitochondrial dynamics, and particularly mitofusin 2, may participate in the reduced mitochondrial function present in skeletal muscle in obesity and in type 2 diabetes.

We show here high levels of expression and secretion of the chemokine CXC ligand 5 (CXCL5) in the macrophage fraction of white adipose tissue (WAT). Moreover, we find that CXCL5 is dramatically increased in serum of human obese compared to lean subjects. Conversely, CXCL5 concentration is decreased in obese subjects after a weight reduction program, or in obese non-insulin-resistant, compared to insulin-resistant, subjects. Most importantly we demonstrate that treatment with recombinant CXCL5 blocks insulin-stimulated glucose uptake in muscle in mice. CXCL5 blocks insulin signaling by activating the Jak2/STAT5/SOCS2 pathway. Finally, by treating obese, insulin-resistant mice with either anti-CXCL5 neutralizing antibodies or antagonists of CXCR2, which is the CXCL5 receptor, we demonstrate that CXCL5 mediates insulin resistance. Furthermore CXCR2-/- mice are protected against obesity-induced insulin resistance. Taken together, these results show that secretion of CXCL5 by WAT resident macrophages represents a link between obesity, inflammation, and insulin resistance.

Muscle from obese subjects or from type 2 diabetic patients show mitochondrial dysfunction, and this may participate in the insulin resistance in those conditions. The mechanisms involved in mitochondrial dysfunction are not completely understood. Dynamic mitochondrial filaments or networks form by mitochondrial fusion and fission events. There is substantial evidence that proteins participating in mitochondrial fusion or fission also have a role in metabolism. Thus, mitofusin-2 (Mfn2) a mitochondrial fusion protein, stimulates respiration, substrate oxidation and OXPHOS subunits expression. In this regard, muscle from obese subjects, or from type 2 diabetic patients, show a reduced expression of Mfn2 and, amelioration of insulin sensitivity by bariatric surgery is associated with an increased Mfn2 expression in muscle. Here, we propose the hypothesis that mitochondrial dynamics proteins play a role in mitochondrial dysfunction in obesity or in type 2 diabetes and that it may also participate in the development of insulin resistance.

The primary gene mutated in Charcot-Marie-Tooth type 2A is mitofusin-2 (Mfn2). Mfn2 encodes a mitochondrial protein that participates in the maintenance of the mitochondrial network and that regulates mitochondrial metabolism and intracellular signaling. The potential for regulation of human Mfn2 gene expression in vivo is largely unknown. Based on the presence of mitochondrial dysfunction in insulin-resistant conditions, we have examined whether Mfn2 expression is dysregulated in skeletal muscle from obese or nonobese type 2 diabetic subjects, whether muscle Mfn2 expression is regulated by body weight loss, and the potential regulatory role of tumor necrosis factor (TNF)alpha or interleukin-6. We show that mRNA concentration of Mfn2 is decreased in skeletal muscle from both male and female obese subjects. Muscle Mfn2 expression was also reduced in lean or in obese type 2 diabetic patients. There was a strong negative correlation between the Mfn2 expression and the BMI in nondiabetic and type 2 diabetic subjects. A positive correlation between the Mfn2 expression and the insulin sensitivity was also detected in nondiabetic and type 2 diabetic subjects. To determine the effect of weight loss on Mfn2 mRNA expression, six morbidly obese subjects were subjected to weight loss by bilio-pancreatic diversion. Mean expression of muscle Mfn2 mRNA increased threefold after reduction in body weight, and a positive correlation between muscle Mfn2 expression and insulin sensitivity was again detected. In vitro experiments revealed an inhibitory effect of TNFalpha or interleukin-6 on Mfn2 expression in cultured cells. We conclude that body weight loss upregulates the expression of Mfn2 mRNA in skeletal muscle of obese humans, type 2 diabetes downregulates the expression of Mfn2 mRNA in skeletal muscle, Mfn2 expression in skeletal muscle is directly proportional to insulin sensitivity and is inversely proportional to the BMI, TNFalpha and interleukin-6 downregulate Mfn2 expression and may participate in the dysregulation of Mfn2 expression in obesity or type 2 diabetes, and the in vivo modulation of Mfn2 mRNA levels is an additional level of regulation for the control of muscle metabolism and could provide a molecular mechanism for alterations in mitochondrial function in obesity or type 2 diabetes.

Objective: To explore the activity of monoamine oxidases (MAOs) and semicarbazide-sensitive amine oxidases (SSAOs) in adipose tissue and blood of lean and moderately obese subjects and to study whether there is a link between these hydrogen peroxide-generating enzymes and blood markers of oxidative stress., Research Methods and Procedures: Nine obese male subjects (BMI 32.6 +/- 0.4 kg/m(2)) and nine controls (BMI 23.4 +/- 0.5) of 24- to 40-year-old subjects were included in the study. MAO and SSAO activities were measured on microbiopsies of abdominal subcutaneous adipose tissue by quantifying (14)C-tyramine and (14)C-benzylamine oxidation. Levels of soluble SSAO, lipid peroxidation products, and antioxidant agents were measured in plasma, whereas cytoprotective enzymes were determined in blood lysates., Results: The high MAO activity found in adipose tissue was diminished by one-half in obese subjects (maximum initial velocity of 1.2 vs. 2.3 nmol tyramine oxidized/mg protein/min). There was no change in SSAO activity, either under its adipose tissue-bound or plasma-soluble form. Plasma levels of lipid peroxidation products and antioxidant vitamins remained unmodified, as well as erythrocyte antioxidant enzymes, whereas circulating triglycerides, insulin, and leptin were increased., Discussion: Although they already exhibited several signs of endocrino-metabolic disorders, the obese men did not exhibit the increase in blood markers of oxidative stress or the decrease in antioxidant defenses reported to occur in very obese or diabetic subjects. The reduced MAO and the unchanged SSAO activities found in obesity suggest that these hydrogen peroxide-generating enzymes expressed in adipocytes are probably not involved in the onset of the oxidative stress found in severe obesity and/or in its complications.

In many cells and specially in muscle, mitochondria form elongated filaments or a branched reticulum. We show that Mfn2 (mitofusin 2), a mitochondrial membrane protein that participates in mitochondrial fusion in mammalian cells, is induced during myogenesis and contributes to the maintenance and operation of the mitochondrial network. Repression of Mfn2 caused morphological and functional fragmentation of the mitochondrial network into independent clusters. Concomitantly, repression of Mfn2 reduced glucose oxidation, mitochondrial membrane potential, cell respiration, and mitochondrial proton leak. We also show that the Mfn2-dependent mechanism of mitochondrial control is disturbed in obesity by reduced Mfn2 expression. In all, our data indicate that Mfn2 expression is crucial in mitochondrial metabolism through the maintenance of the mitochondrial network architecture, and reduced Mfn2 expression may explain some of the metabolic alterations associated with obesity.

Brown adipose tissue (BAT) thermogenesis affects energy balance, and thereby it has the potential to induce weight loss and to prevent obesity. Here, we document a macroautophagic/autophagic-dependent mechanism of peroxisome proliferator-activated receptor gamma (PPARG) activity regulation that induces brown adipose differentiation and thermogenesis and that is mediated by TP53INP2. Disruption of TP53INP2-dependent autophagy reduced brown adipogenesis in cultured cells. In vivo specific-tp53inp2 ablation in brown precursor cells or in adult mice decreased the expression of thermogenic and mature adipocyte genes in BAT. As a result, TP53INP2-deficient mice had reduced UCP1 content in BAT and impaired maximal thermogenic capacity, leading to lipid accumulation and to positive energy balance. Mechanistically, TP53INP2 stimulates PPARG activity and adipogenesis in brown adipose cells by promoting the autophagic degradation of NCOR1, a PPARG co-repressor. Moreover, the modulation of TP53INP2 expression in BAT and in human brown adipocytes suggests that this protein increases PPARG activity during metabolic activation of brown fat. In all, we have identified a novel molecular explanation for the contribution of autophagy to BAT energy metabolism that could facilitate the design of therapeutic strategies against obesity and its metabolic complications. [ABSTRACT FROM AUTHOR]

Various external factors modulate the metabolic efficiency of mitochondria. This review focuses on the impact of the growth factor neuregulin and its ErbB receptors on mitochondria and their relationship with several physiopathological alterations. Neuregulin is involved in the differentiation of heart, skeletal muscle, and the neuronal system, among others; and its deficiency is deleterious for the health. Information gathered over the last two decades suggests that neuregulin plays a key role in regulating the mitochondrial oxidative machinery, which sustains cell survival and insulin sensitivity. [ABSTRACT FROM AUTHOR]

Autophagy plays a key role in cellular homeostasis since it allows optimal cellular functioning and provides energy under conditions of stress. Initial is revealed that alterations of macroautophagy disturb adipogenic differentiation in cultured cells, and in mice, leading to a drastic reduction of adipose tissue depots. Nevertheless, more recent studies indicate that autophagy participates in the control of adipose tissue biology in a more complex manner. The protein TP53INP2 activates the formation of autophagosomes by binding to ATG8 proteins such as LC3 or GATE16, and its genetic elimination reduces but does not cancel this activity. TP53INP2 deficiency increases adipogenic differentiation and induces a gain in adiposity in the mouse. At the cellular level, TP53INP2 promotes the sequestration of the regulatory protein GSK3β in multivesicular bodies (MVBs) by a process that involves autophagic activity and the participation of the endosomal sorting complexes required for transport (ESCRT) machinery. Through this mechanism, TP53INP2 stabilizes and activates β-catenin, which in turn triggers the inhibition of adipogenesis. In summary, autophagic pathways provide a whole set of mechanisms that may regulate in an opposite way the biology of adipose tissue, and consequently, have a variable impact on the whole body adiposity. This concept may be extensible to other cell types. [ABSTRACT FROM AUTHOR]

Mitochondrial dynamics is a term that encompasses the movement of mitochondria along the cytoskeleton, regulation of their architecture, and connectivity mediated by tethering and fusion/fission. The importance of these events in cell physiology and pathology has been partially unraveled with the identification of the genes responsible for the catalysis of mitochondrial fusion and fission. Mutations in two mitochondrial fusion genes (MFN2 and OPA1) cause neurodegenerative diseases, namely Charcot-Marie Tooth type 2A and autosomal dominant optic atrophy (ADOA). Alterations in mitochondrial dynamics may be involved in the pathophysiology of prevalent neurodegenerative conditions. Moreover, impairment of the activity of mitochondrial fusion proteins dysregulates the function of hypothalamic neurons, leading to alterations in food intake and in energy homeostasis. Here we review selected findings in the field of mitochondrial dynamics and their relevance for neurodegeneration and hypothalamic dysfunction. [ABSTRACT FROM AUTHOR]

Mitochondrial dysfunction has been associated with insulin resistance, obesity and diabetes. Hyperinsulinaemia and hyperlipidaemia are hallmarks of the insulin-resistant state. We sought to determine the contributions of high insulin and saturated fatty acid exposure to mitochondrial function and biogenesis in cultured myocytes. Differentiated C2C12 myotubes were left untreated or exposed to chronic high insulin or high palmitate. Mitochondrial function was determined assessing: oxygen consumption, mitochondrial membrane potential, ATP content and ROS (reactive oxygen species) production. We also determined the expression of several mitochondrial genes. Chronic insulin treatment of myotubes caused insulin resistance with reduced PI3K (phosphoinositide 3-kinase) and ERK (extracellular-signalregulated kinase) signalling. Insulin treatment increased oxygen consumption but reduced mitochondrial membrane potential and ROS production. ATP cellular levels were maintained through an increased glycolytic rate. The expression of mitochondrial OXPHOS (oxidative phosphorylation) subunits or Mfn-2 (mitofusin 2) were not significantly altered in comparison with untreated cells, whereas expression of PGC-1ɑ (peroxisome-proliferator-activated receptor γ coactivator- 1ɑ) and UCPs (uncoupling proteins) were reduced. In contrast, saturated fatty acid exposure caused insulin resistance, reducing PI3K (phosphoinositide 3-kinase) and ERK (extracellular-signal-regulated kinase) activation while increasing activation of stress kinases JNK (c-Jun N-terminal kinase) and p38. Fatty acids reduced oxygen consumption and mitochondrial membrane potential while up-regulating the expression of mitochondrial ETC (electron chain complex) protein subunits and UCP proteins. Mfn-2 expression was not modified by palmitate. Palmitate-treated cells also showed a reduced glycolytic rate. Taken together, our findings indicate that chronic insulin and fatty acid-induced insulin resistance differentially affect mitochondrial function. In both conditions, cells were able to maintain ATP levels despite the loss of membrane potential; however, different protein expression suggests different adaptation mechanisms. [ABSTRACT FROM AUTHOR]

Although thyroid hormone (TH) is known to exert important effects on the skeleton, the nuclear factors constituting the TH receptor coactivator complex and the molecular pathways by which TH mediates its effects on target gene expression in osteoblasts remain poorly understood. A recent study demonstrated that the actions of TH on myoblast differentiation are dependent on diabetes- and obesity-related protein (DOR). However, the role of DOR in osteoblast differentiation is unknown. We found DOR expression increased during in vitro differentiation of bone marrow stromal cells into osteoblasts and also in MC3T3-E1 cells treated with TH. However, DOR expression decreased during cellular proliferation. To determine whether DOR acts as a modulator of TH action during osteoblast differentiation, we examined whether overexpression or knockdown of DOR in MC3T3-E1 cells affects the ability of TH to induce osteoblast differentiation by evaluating alkaline phosphatase (ALP) activity. ALP activity was markedly increased in DOR-overexpressing cells treated with TH. In contrast, loss of DOR dramatically reduced TH stimulation of ALP activity in MC3T3-E1 cells and primary calvaria osteoblasts transduced with lentiviral DOR shRNA. Consistent with reduced ALP activity, mRNA levels of osteocalcin, ALP, and Runx2 were decreased significantly in DOR shRNA cells. In addition, a common single nucleotide polymorphism (SNP), DOR1 found on the promoter of human DOR gene, was associated with circulating osteocalcin levels in nondiabetic subjects. Based on these data, we conclude that DOR plays an important role in TH-mediated osteoblast differentiation, and a DOR SNP associates with plasma osteocalcin in men. [ABSTRACT FROM AUTHOR]

Fusion and fission of mitochondria regulate their morphology and distribution. Mitofusin-2 (Mfn2) is a mitochondrial protein involved in such fusion. Recent observations indicate that Mfn2 is a multifunctional protein that participates in cell proliferation and metabolism and that it is required for normal endoplasmic reticulum morphology. In relation to the metabolic role of Mfn2, alterations in activity have been reported to modify cell respiration, substrate oxidation, and oxidative phosphorylation subunit expression in cultured nonmuscle and muscle cells. Mfn2 expression in skeletal muscle is subject to regulation and conditions characterized by reduced mitochondrial activity, such as obesity or type 2 diabetes, and are associated with repressed Mfn2. In contrast, cold-exposure treatment with β3-adrenergic agonists or exercise induce the expression of this gene in muscle. Estrogen-related receptor-α transcription factor is a key regulator of Mfn2 transcription and recruits peroxisome proliferator-activated receptor γ coactivator (PGC)-1β and PGC-1α. These 2 nuclear coactivators are potent, positive regulators of Mfn2 expression in muscle cells, and ablation of PGC-1β causes Mfn2 downregulation in skeletal muscle and in the heart. We propose that PGC-1β is a regulator of normal expression of Mfn2 in muscle, whereas PGC-1α participates in the stimulation of Mfn2 expression under a variety of conditions characterized by enhanced energy expenditure. [ABSTRACT FROM AUTHOR]

Appropriate cristae remodeling is a determinant of mitochondrial function and bioenergetics and thus represents a crucial process for cellular metabolic adaptations. Here, we show that mitochondrial cristae architecture and expression of the master cristae-remodeling protein OPA1 in proopiomelanocortin (POMC) neurons, which are key metabolic sensors implicated in energy balance control, is affected by fluctuations in nutrient availability. Genetic inactivation of OPA1 in POMC neurons causes dramatic alterations in cristae topology, mitochondrial Ca2+ handling, reduction in alpha-melanocyte stimulating hormone (α-MSH) in target areas, hyperphagia, and attenuated white adipose tissue (WAT) lipolysis resulting in obesity. Pharmacological blockade of mitochondrial Ca2+ influx restores α-MSH and the lipolytic program, while improving the metabolic defects of mutant mice. Chemogenetic manipulation of POMC neurons confirms a role in lipolysis control. Our results unveil a novel axis that connects OPA1 in POMC neurons with mitochondrial cristae, Ca2+ homeostasis, and WAT lipolysis in the regulation of energy balance. [Display omitted] • Nutritional state shapes mitochondrial cristae and OPA1 expression in POMC neurons • OPA1 deletion in POMC neurons alters mitochondrial Ca2+ handling and α-MSH release • POMC OPA1-deficient mice show impaired fat lipolysis and metabolic health • Pharmacological restoration of Ca2+ recovered molecular and metabolic alterations Gómez-Valadés et al. report that mitochondrial cristae dynamically reshape in POMC neurons in response to nutritional state. With genetic targeting, they reveal that the cristae-remodeling protein OPA1 is essential to sustain cristae structure and mitochondrial Ca2+ homeostasis in POMC neurons, ensuring appropriate modulation of α-MSH release, the lipolytic program in adipose tissue and metabolic health. [ABSTRACT FROM AUTHOR]

Provides information on a study which investigated the insulin mimicking capacity of semicarbazide-sensitive amine oxidation and tested its ability to cause vascular complications. Promotion of obesity by chronic human vascular adhesion protein-1 overexpression; Effect of methylamine supplementation on hypertension; Conclusions.

The prevalence of nonalcoholic fatty liver disease (NAFLD) has increased drastically due to the global obesity pandemic but at present there are no approved therapies. Here, we aimed to revert high-fat diet (HFD)-induced obesity and NAFLD in mice by enhancing liver fatty acid oxidation (FAO). Moreover, we searched for potential new lipid biomarkers for monitoring liver steatosis in humans. We used adeno-associated virus (AAV) to deliver a permanently active mutant form of human carnitine palmitoyltransferase 1A (hCPT1AM), the key enzyme in FAO, in the liver of a mouse model of HFD-induced obesity and NAFLD. Expression of hCPT1AM enhanced hepatic FAO and autophagy, reduced liver steatosis, and improved glucose homeostasis. Lipidomic analysis in mice and humans before and after therapeutic interventions, such as hepatic AAV9-hCPT1AM administration and RYGB surgery, respectively, led to the identification of specific triacylglyceride (TAG) specie (C50:1) as a potential biomarker to monitor NAFFLD disease. To sum up, here we show for the first time that liver hCPT1AM gene therapy in a mouse model of established obesity, diabetes, and NAFLD can reduce HFD-induced derangements. Moreover, our study highlights TAG (C50:1) as a potential noninvasive biomarker that might be useful to monitor NAFLD in mice and humans. [ABSTRACT FROM AUTHOR]

Abstract: A strong induction of semicarbazide-sensitive amine oxidase (SSAO) has previously been reported during murine preadipocyte lineage differentiation but it remains unknown whether this emergence also occurs during adipogenesis in man. Our aim was to compare SSAO and monoamine oxidase (MAO) expression during in vitro differentiation of human preadipocytes and in adipose and stroma-vascular fractions of human fat depots. A human preadipocyte cell strain from a patient with Simpson–Golabi–Behmel syndrome was first used to follow amine oxidase expression during in vitro differentiation. Then, human preadipocytes isolated from subcutaneous adipose tissues were cultured under conditions promoting ex vivo adipose differentiation and tested for MAO and SSAO expression. Lastly, human adipose tissue was separated into mature adipocyte and stroma-vascular fractions for analyses of MAO and SSAO at mRNA, protein and activity levels. Both SSAO and MAO were increased from undifferentiated preadipocytes to lipid-laden cells in all the models: 3T3-F442A and 3T3-L1 murine lineages, human SGBS cell strain or human preadipocytes in primary culture. In human subcutaneous adipose tissue, the adipocyte-enriched fraction exhibited seven-fold higher amine oxidase activity and contained three- to seven-fold higher levels of mRNAs encoded by MAO-A, MAO-B, AOC3 and AOC2 genes than the stroma-vascular fraction. MAO-A and AOC3 genes accounted for the majority of their respective MAO and SSAO activities in human adipose tissue. Most of the SSAO and MAO found in adipose tissue originated from mature adipocytes. Although the mechanism and role of adipogenesis-related increase in amine oxidase expression remain to be established, the resulting elevated levels of amine oxidase activities found in human adipocytes may be of potential interest for therapeutic intervention in obesity. [Copyright &y& Elsevier]