De Novo Lipogenesis in Adipose Tissue Is Associated with Course of Morbid Obesity after Bariatric Surgery

OBJECTIVE: De novo lipogenesis is involved in fatty acid biosynthesis and could be involved in the regulation of the triglyceride storage capacity of adipose tissue. However, the association between lipogenic and lipolytic genes and the evolution of morbidly obese subjects after bariatric surgery remains unknown. In this prospective study we analyze the association between the improvement in the morbidly obese patients as a result of bariatric surgery and the basal expression of lipogenic and lipolytic genes. METHODS: We study 23 non diabetic morbidly obese patients who were studied before and 7 months after bariatric surgery. Also, we analyze the relative basal mRNA expression levels of lipogenic and lipolytic genes in epiploic visceral adipose tissue (VAT) and abdominal subcutaneous adipose tissue (SAT). RESULTS: When the basal acetyl-CoA carboxylase 1 (ACC1), acetyl-CoA synthetase 2 (ACSS2) and ATP citrate lyase (ACL) expression in SAT was below percentile-50, there was a greater decrease in weight (P = 0.006, P = 0.034, P = 0.026), body mass index (P = 0.008, P = 0.033, P = 0.034) and hip circumference (P = 0.033, P = 0.021, P = 0.083) after bariatric surgery. In VAT, when the basal ACSS2 expression was below percentile-50, there was a greater decrease in hip circumference (P = 0.006). After adjusting for confounding variables in logistic regression models, only the morbidly obese patients with SAT or VAT ACSS2 expression ≥ P50 before bariatric surgery had a lower percentage hip circumference loss (<P50) after bariatric surgery (SAT: P = 0.039; VAT: P = 0.033). CONCLUSIONS: A lower basal ACSS2, ACC1 and ACL expression, genes involved in de novo lipogenesis, is associated with a better evolution of anthropometric variables after bariatric surgery. Thus, the previous state of the pathways involved in fatty acid metabolism may have repercussions on the improvement of these patients

Succinate Pathway in Head and Neck Squamous Cell Carcinoma: Potential as a Diagnostic and Prognostic Marker

Simple Summary: Emerging evidence points to succinate as an important oncometabolite in cancer development; however, the contribution of the succinate-SUCNR1 axis to cancer progression remains unclear. Head and neck squamous cell carcinoma (HNSCC) is associated with disease and treatmentrelated morbidity so there is an urgent need for innovation in treatment and diagnosis practices. Our aim was to evaluate the potential of the succinate-related pathway as a diagnostic and prognostic biomarker in HNSCC. The circulating succinate levels are increased in HNSCC, being a potential noninvasive biomarker for HNSCC diagnosis. Moreover, the succinate receptor (SUCNR1) and genes related to succinate metabolism, which are predominantly expressed in the tumoral mucosa as compared with healthy tissue, are positively associated with plasma succinate. Remarkably, we found that SUCNR1 and SDHA expression levels predict prognosis

Adipose tissue glycogen accumulation is associated with obesity-linked inflammation in humans

Objective: glycogen metabolism has emerged as a mediator in the control of energy homeostasis and studies in murine models reveal that adipose tissue might contain glycogen stores. Here we investigated the physio(patho)logical role of glycogen in human adipose tissue in the context of obesity and insulin resistance. Methods: we studied glucose metabolic flux of hypoxic human adipoctyes by nuclear magnetic resonance and mass spectrometry-based metabolic approaches. Glycogen synthesis and glycogen content in response to hypoxia was analyzed in human adipocytes and macrophages. To explore the metabolic effects of enforced glycogen deposition in adipocytes and macrophages, we overexpressed PTG, the only glycogen-associated regulatory subunit (PP1-GTS) reported in murine adipocytes. Adipose tissue gene expression analysis was performed on wild type and homozygous PTG KO male mice. Finally, glycogen metabolism gene expression and glycogen accumulation was analyzed in adipose tissue, mature adipocytes and resident macrophages from lean and obese subjects with different degrees of insulin resistance in 2 independent cohorts. Results: we show that hypoxia modulates glucose metabolic flux in human adipocytes and macrophages and promotes glycogenesis. Enforced glycogen deposition by overexpression of PTG re-orients adipocyte secretion to a pro-inflammatory response linked to insulin resistance and monocyte/lymphocyte migration. Furthermore, glycogen accumulation is associated with inhibition of mTORC1 signaling and increased basal autophagy flux, correlating with greater leptin release in glycogen-loaded adipocytes. PTG-KO mice have reduced expression of key inflammatory genes in adipose tissue and PTG overexpression in M0 macrophages induces a pro-inflammatory and glycolytic M1 phenotype. Increased glycogen synthase expression correlates with glycogen deposition in subcutaneous adipose tissue of obese patients. Glycogen content in subcutaneous mature adipocytes is associated with BMI and leptin expression. Conclusion: our data establish glycogen mishandling in adipose tissue as a potential key feature of inflammatory-related metabolic stress in human obesity

Adipose tissue mitochondrial dysfunction in human obesity is linked to a specific DNA methylation signature in adipose-derived stem cells

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

Changes in glucagon‐like peptide 1 and 2 levels in people with obesity after a diet‐induced weight‐loss intervention are related to a specific microbiota signature: A prospective cohort study

The study was supported by grants from the Instituto de Salud Carlos III (PI14/00228, PI17/0153 and PI20/00338 to J.V.), Ministerio de Ciencia e Innovación (RTI2018- 093919-B-I00 to S.F.-V. and PID2019-105969GB-I00 to A.M) and Generalitat Valenciana (PROMETEO/2018/A/133 to A.M), co-financed by the European Regional Development Fund. The Spanish Biomedical Research Center in Diabetes and Associated Metabolic Disorders (CB07708/0012) is an initiative of the Instituto de Salud Carlos III. S.FV. acknowledges the Miguel Servet tenure-track program (CP10/00438 and CPII16/00008) from Fondo de Investigación Sanitaria.Peer reviewe

The Bace1 product sAPPβ induces ER stress and inflammation and impairs insulin signaling

Objective -secretase/-site amyloid precursor protein (APP)-cleaving enzyme 1 (BACE1) is a key enzyme involved in Alzheimer's disease that has recently been implicated in insulin-independent glucose uptake in myotubes. However, it is presently unknown whether BACE1 and the product of its activity, soluble APPsAPPcontribute to lipid-induced inflammation and insulin resistance in skeletal muscle cells. Materials/Methods Studies were conducted in mouse C2C12 myotubes, skeletal muscle from Bace1-/-mice and mice treated with sAPP and adipose tissue and plasma from obese and type 2 diabetic patients. Results We show that BACE1 inhibition or knockdown attenuates palmitate-induced endoplasmic reticulum (ER) stress, inflammation, and insulin resistance and prevents the reduction in Peroxisome Proliferator- Activated Receptor Co-activator 1 (PGC-1) and fatty acid oxidation caused by palmitate in myotubes. The effects of palmitate on ER stress, inflammation, insulin resistance, PGC-1 down-regulation, and fatty acid oxidation were mimicked by soluble APP in vitro. BACE1 expression was increased in subcutaneous adipose tissue of obese and type 2 diabetic patients and this was accompanied by a decrease in PGC-1 mRNA levels and by an increase in sAPPplasma levels of obese type 2 diabetic patients compared to obese non-diabetic subjects. Acute sAPP administration to mice reduced PGC-1 levels and increased inflammation in skeletal muscle and decreased insulin sensitivity. Conclusions Collectively, these findings indicate that the BACE1 product sAPP is a key determinant in ER stress, inflammation and insulin resistance in skeletal muscle and gluconeogenesis in liver

Circulating pyruvate is a potent prognostic marker for critical COVID-19 outcomes

Background: Coronavirus-19 (COVID-19) disease is driven by an unchecked immune response to the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus which alters host mitochondrial-associated mechanisms. Compromised mitochondrial health results in abnormal reprogramming of glucose metabolism, which can disrupt extracellular signalling. We hypothesized that examining mitochondrial energy-related signalling metabolites implicated in host immune response to SARS-CoV-2 infection would provide potential biomarkers for predicting the risk of severe COVID-19 illness. Methods: We used a semi-targeted serum metabolomics approach in 273 patients with different severity grades of COVID-19 recruited at the acute phase of the infection to determine the relative abundance of tricarboxylic acid (Krebs) cycle-related metabolites with known extracellular signaling properties (pyruvate, lactate, succinate and α-ketoglutarate). Abundance levels of energy-related metabolites were evaluated in a validation cohort (n=398) using quantitative fluorimetric assays. Results: Increased levels of four energy-related metabolites (pyruvate, lactate, a-ketoglutarate and succinate) were found in critically ill COVID-19 patients using semi-targeted and targeted approaches (p<0.05). The combined strategy proposed herein enabled us to establish that circulating pyruvate levels (p<0.001) together with body mass index (p=0.025), C-reactive protein (p=0.039), D-Dimer (p<0.001) and creatinine (p=0.043) levels, are independent predictors of critical COVID-19. Furthermore, classification and regression tree (CART) analysis provided a cut-off value of pyruvate in serum (24.54 µM; p<0.001) as an early criterion to accurately classify patients with critical outcomes. Conclusion: Our findings support the link between COVID-19 pathogenesis and immunometabolic dysregulation, and show that fluorometric quantification of circulating pyruvate is a cost-effective clinical decision support tool to improve patient stratification and prognosis prediction.This work has been developed in the framework of the COVIDOMICS’ project supported by Direcció General de Recerca i Innovació en Salut (DGRIS), Departament de Salut, Generalitat de Catalunya (PoC-6-17 and PoC1-5). The research was also funded by the Programa de Suport als Grups de Recerca AGAUR (2017SGR948), the SPANISH AIDS Research Network [RD16/0025/0006]-ISCIII-FEDER (Spain) and the Centro de Investigación Biomédica en Red de Enfermedades Infecciosas-ISCIII [CB21/13/00020], Madrid, Spain. LR is supported by the Instituto de Salud Carlos III (ISCIII) under grant agreement “CD20/00105” through the program “Contratos Sara Borrell”. FV is supported by grants from the Programa de Intensificación de Investigadores (INT20/00031)-ISCIII and by “Premi a la Trajectòria Investigadora dels Hospitals de l’ICS 2018”. AR is supported by a grant from IISPV through the project “2019/IISPV/05” (Boosting Young Talent), by GeSIDA through the “III Premio para Jóvenes Investigadores 2019” and by the Instituto de Salud Carlos III (ISCIII) under grant agreement “CP19/00146” through the Miguel Servet Program. This study was also supported by grants SAF2015–65019-R and RTI2018–093919-B-100 (to SF-V.) funded by MCIN/AEI and by “ERFD A way of making Europe”; PI19/01337 to FV, PI20/00095 to VC.-M, PI20/00326 to AR and PI20/00338 to JV funded by ISCIII, cofinanced by the European Regional Development Fund (ERDF), and from Fundación Bancaria Caixa d’Estalvis i Pensions de Barcelona (HR20-00051 to SF-V). The Spanish Biomedical Research Center in Diabetes and Associated Metabolic Disorders (CIBERDEM) (CB07708/0012) is an initiative of the Instituto de Salud Carlos III. SF-V acknowledges support from the Miguel Servet tenure-track program (CP10/00438 and CPII16/00008) from the Fondo de Investigación Sanitaria, cofinanced by the ERDF. VC-M acknowledges support from the Ramón y Cajal program (RYC2019-026490-I) from the Spanish Ministry of Science and Innovation, cofinanced by the ERDF. The work was also supported by Consejeria de Salud y Familia (COVID-0005-2020), Consejeria de Transformacion Economica, Industria, Conocimiento y Universidades Junta de Andalucia (CV20-85418to ER-M) and Instituto de Salud Carlos III (ISCIII) under grant agreement CP19/00159 to AGV “a way to make Europe”. ER-M was supported by the Spanish Research Council (CSIC). The funders have no roles in study design, data collection, data analysis, interpretation or the writing of this research.Peer reviewe

SUCNR1 signaling in adipocytes controls energy metabolism by modulating circadian clock and leptin expression

Adipose tissue modulates energy homeostasis by secreting leptin, but little is known about the factors governing leptin production. We show that succinate, long perceived as a mediator of immune response and lipolysis, controls leptin expression via its receptor SUCNR1. Adipocyte-specific deletion of Sucnr1 influences metabolic health according to nutritional status. Adipocyte Sucnr1 deficiency impairs leptin response to feeding, whereas oral succinate mimics nutrient-related leptin dynamics via SUCNR1. SUCNR1 activation controls leptin expression via the circadian clock in an AMPK/JNK-C/EBPα-dependent manner. Although the anti-lipolytic role of SUCNR1 prevails in obesity, its function as a regulator of leptin signaling contributes to the metabolically favorable phenotype in adipocyte-specific Sucnr1 knockout mice under standard dietary conditions. Obesity-associated hyperleptinemia in humans is linked to SUCNR1 overexpression in adipocytes, which emerges as the major predictor of adipose tissue leptin expression. Our study establishes the succinate/SUCNR1 axis as a metabolite-sensing pathway mediating nutrient-related leptin dynamics to control whole-body homeostasis.This study was supported by grants from the Spanish Ministry of Science and Innovation (MCIN)/AEI/10.13039/501100011033 (SAF2015-65019-R, RTI2018-093919-B-100, and PID2021-122480OB-I00 to S.F.-V.) and from the Instituto de Salud Carlos III (PI20/00095 to V.C.-M., and PI20/00338 to J.V.), all co-financed by the European Regional Development Fund (ERDF). This research was also supported by PID2020-119030RJ-I00 (to L. Cedó), PID2020-117640RB-I00 (to M.V.), and PID2020-117278GB-I00 (to F.V.) from MCIN/AEI/10.13039/501100011033. The project that gave rise to these results received funding from “La Caixa” Foundation under the grant agreement LCF/PR/HR20/52400013 (to S.F.-V.). N.V. is the recipient of grants “Ajuts per a projectes de recerca clínica de l’Hospital Universitari de Bellvitge (2011-PR143/11)” and the projects PI11/01960, PI14/01997, and PI17/01556 funded by the Instituto de Salud Carlos III and co-funded by “ERDF, A way to build Europe.” T.V.-C. is a recipient of an FPI fellowship (PRE2019-090360), and V.C.-M. acknowledges support from the Ramón y Cajal program (RYC2019-02649-I), both from MCIN/AEI/10.13039/501100011033 and “European Social Fund (ESF) Investing in your future.” M.R.-D.-D. is recipient of a Martí-Franquès Research Grant Programme (2021PMF-PIPF-2) from Universitat Rovira i Virgili. C.P.-L. is recipient of an FPU fellowship from the Spanish Ministry of Education. J.S.-B. is a recipient of a predoctoral contract for training in health research from the Instituto de Salud Carlos III, co-financed by the ESF (PFIS FI18/00151). S.F.-V. acknowledges support from the Miguel Servet tenue-track program (CP10/00438 and CPII16/00008) from the Fondo de Investigación Sanitaria, co-financed by the ERDF.Peer reviewe

Protective effects of the succinate/SUCNR1 axis on damaged hepatocytes in NAFLD

[Objective]: Succinate and succinate receptor 1 (SUCNR1) are linked to fibrotic remodeling in models of non-alcoholic fatty liver disease (NAFLD), but whether they have roles beyond the activation of hepatic stellate cells remains unexplored. We investigated the succinate/SUCNR1 axis in the context of NAFLD specifically in hepatocytes.[Methods]: We studied the phenotype of wild-type and Sucnr1−/− mice fed a choline-deficient high-fat diet to induce non-alcoholic steatohepatitis (NASH), and explored the function of SUCNR1 in murine primary hepatocytes and human HepG2 cells treated with palmitic acid. Lastly, plasma succinate and hepatic SUCNR1 expression were analyzed in four independent cohorts of patients in different NAFLD stages.[Results]. Sucnr1 was upregulated in murine liver and primary hepatocytes in response to diet-induced NASH. Sucnr1 deficiency provoked both beneficial (reduced fibrosis and endoplasmic reticulum stress) and detrimental (exacerbated steatosis and inflammation and reduced glycogen content) effects in the liver, and disrupted glucose homeostasis. Studies in vitro revealed that hepatocyte injury increased Sucnr1 expression, which when activated improved lipid and glycogen homeostasis in damaged hepatocytes. In humans, SUCNR1 expression was a good determinant of NAFLD progression to advanced stages. In a population at risk of NAFLD, circulating succinate was elevated in patients with a fatty liver index (FLI) ≥60. Indeed, succinate had good predictive value for steatosis diagnosed by FLI, and improved the prediction of moderate/severe steatosis through biopsy when added to an FLI algorithm.[Conclusions]. We identify hepatocytes as target cells of extracellular succinate during NAFLD progression and uncover a hitherto unknown function for SUCNR1 as a regulator of hepatocyte glucose and lipid metabolism. Our clinical data highlight the potential of succinate and hepatic SUCNR1 expression as markers to diagnose fatty liver and NASH, respectively.This study was supported by grants from MCIN/AEI/10.13039/501100011033 (SAF2015-65019-R, RTI2018-093919-B-100 and PID2021-122480OB-100 to S.F.-V.; PID2021-122766OB-100 to A.M.V; PID2021-124425OB-I00 to P.A.) co-financed by the European Regional Development Fund (ERDF) and Grupos consolidados Gobierno Vasco IT1476-22 to P.A. This research was funded by the Institute of Health “Carlos III” (ISCIII) and co-financed by ERDF (PI20/00095 to V.C.-M.; PI20/00338 to J.V. and PI20/00505 to B.R.-M.). This study was also supported by a grant from ISCIII and CIBERDEM, DEM19PI01/2019 to V.C.-M. and P.R. The project that gave rise to these results received funding from “La Caixa” Foundation (ID 100010434), under the grant agreement LCF/PR/HR20/52400013 (to S.F.-V.). This study was also supported by Rovira i Virgili University and Tarragona Provincial Council with the Talent Salut fellowship to A.R.-C. A.M.-B. is a recipient of an FPU grant (FPU20/05633) from MCIN/AEI/10.13039/501100011033. B.A. acknowledges support from the PERIS program 2016–2020 (LT017/20/000033), from Departament de Salut de la Generalitat de Catalunya. V.C.-M. acknowledges support from the Ramón y Cajal program (RYC2019-02649-I), from MCIN/AEI/10.13039/501100011033/ and the European Social Fund (ESF), “Investing in your future”. B.R.-M. acknowledges support from the Miguel Servet Type I program (CP19/00098) from the Fondo de Investigación Sanitaria, co-financed by the ERDF. SFV and JVO acknowledge support from the Agency for Management of University Research Grants of the Generalitat de Catalunya (2021 SGR 01409, 2021 SGR 0089). The study was also supported by CIBER–Consorcio Centro de Investigación Biomédica en Red (CB07708/0012), ISCIII, Ministerio de Ciencia e Innovación.Peer reviewe

Elevated circulating levels of succinate in human obesity are linked to specific gut microbiota

Gut microbiota-related metabolites are potential clinical biomarkers for cardiovascular disease (CVD). Circulating succinate, a metabolite produced by both microbiota and the host, is increased in hypertension, ischemic heart disease, and type 2 diabetes. We aimed to analyze systemic levels of succinate in obesity, a major risk factor for CVD, and its relationship with gut microbiome. We explored the association of circulating succinate with specific metagenomic signatures in cross-sectional and prospective cohorts of Caucasian Spanish subjects. Obesity was associated with elevated levels of circulating succinate concomitant with impaired glucose metabolism. This increase was associated with specific changes in gut microbiota related to succinate metabolism: a higher relative abundance of succinate-producing Prevotellaceae (P) and Veillonellaceae (V), and a lower relative abundance of succinate-consuming Odoribacteraceae (O) and Clostridaceae (C) in obese individuals, with the (P + V/O + C) ratio being a main determinant of plasma succinate. Weight loss intervention decreased (P + V/O + C) ratio coincident with the reduction in circulating succinate. In the spontaneous evolution after good dietary advice, alterations in circulating succinate levels were linked to specific metagenomic signatures associated with carbohydrate metabolism and energy production with independence of body weight change. Our data support the importance of microbe-microbe interactions for the metabolite signature of gut microbiome and uncover succinate as a potential microbiota-derived metabolite related to CVD risk