Multiomics of the intestine-liver-adipose axis in multiple studies unveils a consistent link of the gut microbiota and the antiviral response with systemic glucose metabolism.

BACKGROUND: The microbiota is emerging as a key factor in the predisposition to insulin resistance and obesity. OBJECTIVE: To understand the interplay among gut microbiota and insulin sensitivity in multiple tissues. DESIGN: Integrative multiomics and multitissue approach across six studies, combining euglycaemic clamp measurements (used in four of the six studies) with other measurements of glucose metabolism and insulin resistance (glycated haemoglobin (HbA1c) and fasting glucose). RESULTS: Several genera and species from the Proteobacteria phylum were consistently negatively associated with insulin sensitivity in four studies (ADIPOINST, n=15; IRONMET, n=121, FLORINASH, n=67 and FLOROMIDIA, n=24). Transcriptomic analysis of the jejunum, ileum and colon revealed T cell-related signatures positively linked to insulin sensitivity. Proteobacteria in the ileum and colon were positively associated with HbA1c but negatively with the number of T cells. Jejunal deoxycholic acid was negatively associated with insulin sensitivity. Transcriptomics of subcutaneous adipose tissue (ADIPOMIT, n=740) and visceral adipose tissue (VAT) (ADIPOINST, n=29) revealed T cell-related signatures linked to HbA1c and insulin sensitivity, respectively. VAT Proteobacteria were negatively associated with insulin sensitivity. Multiomics and multitissue integration in the ADIPOINST and FLORINASH studies linked faecal Proteobacteria with jejunal and liver deoxycholic acid, as well as jejunal, VAT and liver transcriptomic signatures involved in the actin cytoskeleton, insulin and T cell signalling. Fasting glucose was consistently linked to interferon-induced genes and antiviral responses in the intestine and VAT. Studies in Drosophila melanogaster validated these human insulin sensitivity-associated changes. CONCLUSION: These data provide comprehensive insights into the microbiome-gut-adipose-liver axis and its impact on systemic insulin action, suggesting potential therapeutic targets.Cite Now.

The relevance of intestinal barrier dysfunction, antimicrobial proteins and bacterial endotoxin in metabolic dysfunction-associated steatotic liver disease.

BACKGROUND: Metabolic dysfunction-associated steatotic liver disease (MASLD) is a leading cause of end-stage liver disease associated with increased mortality and cardiovascular disease. Obesity and diabetes are the most important risk factors of MASLD. It is well-established that obesity-associated insulin resistance leads to a situation of tissue lipotoxicity characterized by an accumulation of excess fat in non-fat tissues such as the liver, promoting the development of MASLD, and its progression into metabolic dysfunction-associated steatohepatitis. METHODS: Here, we aimed to review the impact of disrupted intestinal permeability, antimicrobial proteins and bacterial endotoxin in the development and progression of MASLD. RESULTS AND CONCLUSION: Recent studies demonstrated that obesity- and obesogenic diets-associated alterations of intestinal microbiota along with the disruption of intestinal barrier integrity, the alteration in antimicrobial proteins and, in consequence, an enhanced translocation of bacterial endotoxin into bloodstream might contribute to this pathological process through to impacting liver metabolism and inflammation.

Liver lipopolysaccharide binding protein prevents hepatic inflammation in physiological and pathological non-obesogenic conditions.

Lipopolysaccharide binding protein (LBP) knockout mice models are protected against the deleterious effects of major acute inflammation but its possible physiological role has been less well studied. We aimed to evaluate the impact of liver LBP downregulation (using nanoparticles containing siRNA- Lbp) on liver steatosis, inflammation and fibrosis during a standard chow diet (STD), and in pathological non-obesogenic conditions, under a methionine and choline deficient diet (MCD, 5 weeks). Under STD, liver Lbp gene knockdown led to a significant increase in gene expression markers of liver inflammation (Itgax, Tlr4, Ccr2, Ccl2 and Tnf), liver injury (Krt18 and Crp), fibrosis (Col4a1, Col1a2 and Tgfb1), endoplasmic reticulum (ER) stress (Atf6, Hspa5 and Eif2ak3) and protein carbonyl levels. As expected, the MCD increased hepatocyte vacuolation, liver inflammation and fibrosis markers, also increasing liver Lbp mRNA. In this model, liver Lbp gene knockdown resulted in a pronounced worsening of the markers of liver inflammation (also including CD68 and MPO activity), fibrosis, ER stress and protein carbonyl levels, all indicative of non-alcoholic steatohepatitis (NASH) progression. At cellular level, Lbp gene knockdown also increased expression of the proinflammatory mediators (Il6, Ccl2), and markers of fibrosis (Col1a1, Tgfb1) and protein carbonyl levels. In agreement with these findings, liver LBP mRNA in humans positively correlated with markers of liver damage (circulating hsCRP, ALT activity, liver CRP and KRT18 gene expression), and with a network of genes involved in liver inflammation, innate and adaptive immune system, endoplasmic reticulum stress and neutrophil degranulation (all with q-value<0.05). In conclusion, current findings suggest that a significant downregulation in liver LBP levels promotes liver oxidative stress and inflammation, aggravating NASH progression, in physiological and pathological non-obesogenic conditions.

The Longitudinal Changes in Subcutaneous Abdominal Tissue and Visceral Adipose Tissue Volumetries Are Associated with Iron Status.

Excess iron is known to trigger adipose tissue dysfunction and insulin resistance. Circulating markers of iron status have been associated with obesity and adipose tissue in cross-sectional studies. We aimed to evaluate whether iron status is linked to changes in abdominal adipose tissue longitudinally. Subcutaneous abdominal tissue (SAT) and visceral adipose tissue (VAT) and its quotient (pSAT) were assessed using magnetic resonance imaging (MRI), at baseline and after one year of follow-up, in 131 (79 in follow-up) apparently healthy subjects, with and without obesity. Insulin sensitivity (euglycemic- hyperinsulinemic clamp) and markers of iron status were also evaluated. Baseline serum hepcidin (p = 0.005 and p = 0.002) and ferritin (p = 0.02 and p = 0.01)) were associated with an increase in VAT and SAT over one year in all subjects, while serum transferrin (p = 0.01 and p = 0.03) and total iron-binding capacity (p = 0.02 and p = 0.04) were negatively associated. These associations were mainly observed in women and in subjects without obesity, and were independent of insulin sensitivity. After controlling for age and sex, serum hepcidin was significantly associated with changes in subcutaneous abdominal tissue index (iSAT) (ß = 0.406, p = 0.007) and visceral adipose tissue index (iVAT) (ß = 0.306, p = 0.04), while changes in insulin sensitivity (ß = 0.287, p = 0.03) and fasting triglycerides (ß = -0.285, p = 0.03) were associated with changes in pSAT. These data indicated that serum hepcidin are associated with longitudinal changes in SAT and VAT, independently of insulin sensitivity. This would be the first prospective study evaluating the redistribution of fat according to iron status and chronic inflammation.

The complement system is dysfunctional in metabolic disease: Evidences in plasma and adipose tissue from obese and insulin resistant subjects.

The relationship among chronic low-grade inflammation, insulin resistance and other obesity-associated metabolic disturbances is increasingly recognized. The possible mechanisms that trigger these immunologic alterations remain to be fully understood. The complement system is a crucial element of immune defense system, being important in the activation of innate and adaptative immune response, promoting the clearance of apoptotic and damaged endogenous cells and participating in processes of tissue development, degeneration, and regeneration. Circulating components of the complement system appear to be dysregulated in obesity-associated metabolic disturbances. The activation of the complement system is also evident in adipose tissue from obese subjects, in association with subclinical inflammation and alterations in glucose metabolism. The possible contribution of some components of the complement system in the development of insulin resistance and obesity-associated metabolic disturbances, and the possible role of complement system in adipose tissue physiology is reviewed here. The modulation of the complement system could constitute a potential target in the pathophysiology and therapy of obesity and associated metabolic disease.

Morbidly obese subjects show increased serum sulfide in proportion to fat mass.

BACKGROUND AND OBJECTIVES: The importance of hydrogen sulfide is increasingly recognized in the pathophysiology of obesity and type 2 diabetes in animal models. Very few studies have evaluated circulating sulfides in humans, with discrepant results. Here, we aimed to investigate serum sulfide levels according to obesity. SUBJECTS AND METHODS: Serum sulfide levels were analyzed, using a selective fluorescent probe, in two independent cohorts [cross-sectionally in discovery (n = 139) and validation (n = 71) cohorts, and longitudinally in 82 participants from discovery cohort]. In the validation cohort, blood gene expression of enzymes contributing to H2S generation and consumption were also measured. RESULTS: In the discovery cohort, serum sulfide concentration was significantly increased in subjects with morbid obesity at baseline and follow-up, and positively correlated with BMI and fat mass, but negatively with total cholesterol, haemoglobin, serum ferritin, iron and bilirubin after adjusting by age, gender and fat mass. Fat mass (ß = 0.51, t = 3.67, p < 0.0001) contributed independently to age-, gender-, insulin sensitivity- and BMI-adjusted serum sulfide concentration variance. Importantly, receiver operating characteristic analysis demonstrated the relevance of fat mass predicting serum sulfide levels, which was replicated in the validation cohort. In addition, serum sulfide concentration was decreased in morbidly obese subjects with impaired compared to those with normal fasting glucose. Longitudinally, weight gain resulted in increased serum sulfide concentration, whereas weight loss had opposite effects, being the percent change in serum sulfide positively correlated with the percent change in BMI and waist circumference, but negatively with bilirubin. Whole blood CBS, CTH, MPST, SQOR, TST and MPO gene expression was not associated to obesity or serum sulfide concentration. CONCLUSIONS: Altogether these data indicated that serum sulfide concentrations were increased in subjects with morbid obesity in proportion to fat mass and inversely associated with circulating markers of haem degradation.

Adipose tissue knockdown of lysozyme reduces local inflammation and improves adipogenesis in high-fat diet-fed mice.

Chronic systemic low-level inflammation in metabolic disease is known to affect adipose tissue biology. Lysozyme (LYZ) is a major innate immune protein but its role in adipose tissue has not been investigated. Here, we aimed to investigate LYZ in human and rodents fat depots, and its possible role in obesity-associated adipose tissue dysfunction. LYZ mRNA and protein were identified to be highly expressed in adipose tissue from subjects with obesity and linked to systemic chronic-low grade inflammation, adipose tissue inflammation and metabolic disturbances, including hyperglycemia, dyslipidemia and decreased markers of adipose tissue adipogenesis. These findings were confirmed in experimental models after a high-fat diet in mice and rats and also in ob/ob mice. Importantly, specific inguinal and perigonadal white adipose tissue lysozyme (Lyz2) gene knockdown in high-fat diet-fed mice resulted in improved adipose tissue inflammation in parallel to reduced lysozyme activity. Of note, Lyz2 gene knockdown restored adipogenesis and reduced weight gain in this model. In conclusion, altogether these observations point to lysozyme as a new actor in obesity-associated adipose tissue dysfunction. The therapeutic targeting of lysozyme production might contribute to improve adipose tissue metabolic homeostasis.

Comparison of Outcomes between Obese and Nonobese Patients in Laparoscopic Adrenalectomy: A Cohort Study.

INTRODUCTION: Obesity is usually considered a risk factor for surgical complications. Laparoscopic adrenalectomy has replaced open adrenalectomy as the standard operation for adrenal tumors. OBJECTIVE: To compare the safety of laparoscopic adrenalectomy to treat adrenal tumors in obese versus nonobese patients. METHODS: This observational cohort study analyzed consecutive patients who underwent laparoscopic adrenalectomy with a lateral transperitoneal approach at a single center (2003-2020). Data and outcomes of obese (body mass index ≥30 kg/m2) and nonobese patients were compared. To analyze the association between operative time and other variables, we used simple and multivariate linear regression. RESULTS: N = 160 (90 obese/70 nonobese) patients underwent laparoscopic adrenalectomy. Cushing syndrome and pheochromocytoma were the most frequent indications. Obese patients were older (58 vs. 52 years, p < 0.001). A greater proportion of obese patients were ASA grade III + IV (71.1 vs. 48.6%, p = 0.004). Obesity was associated with a longer operative time (72.5 vs. 60 min, p < 0.001) and greater blood loss (40 vs. 20 mL, p = 0.022). There were no differences in conversion, morbidity, or hospital stay. After adjustment for confounding factors, operative time was positively correlated with BMI ≥30 kg/m2, learning curve, estimated blood loss, 2D laparoscopy, and specimen size. CONCLUSION: Lateral transperitoneal laparoscopic adrenalectomy is safe in patients with a BMI 30-35 kg/m2, so these patients also benefit from this minimally invasive surgery.

Neuregulin 4 Downregulation Induces Insulin Resistance in 3T3-L1 Adipocytes through Inflammation and Autophagic Degradation of GLUT4 Vesicles.

The adipokine Neuregulin 4 (Nrg4) protects against obesity-induced insulin resistance. Here, we analyze how the downregulation of Nrg4 influences insulin action and the underlying mechanisms in adipocytes. Validated shRNA lentiviral vectors were used to generate scramble (Scr) and Nrg4 knockdown (KD) 3T3-L1 adipocytes. Adipogenesis was unaffected in Nrg4 KD adipocytes, but there was a complete impairment of the insulin-induced 2-deoxyglucose uptake, which was likely the result of reduced insulin receptor and Glut4 protein. Downregulation of Nrg4 enhanced the expression of proinflammatory cytokines. Anti-inflammatory agents recovered the insulin receptor, but not Glut4, content. Proteins enriched in Glut4 storage vesicles such as the insulin-responsive aminopeptidase (IRAP) and Syntaxin-6 as well as TBC1D4, a protein involved in the intracellular retention of Glut4 vesicles, also decreased by Nrg4 KD. Insulin failed to reduce autophagy in Nrg4 KD adipocytes, observed by a minor effect on mTOR phosphorylation, at the time that proteins involved in autophagy such as LC3-II, Rab11, and Clathrin were markedly upregulated. The lysosomal activity inhibitor bafilomycin A1 restored Glut4, IRAP, Syntaxin-6, and TBC1D4 content to those found in control adipocytes. Our study reveals that Nrg4 preserves the insulin responsiveness by preventing inflammation and, in turn, benefits the insulin regulation of autophagy.

Adipose tissue TSH as a new modulator of human adipocyte mitochondrial function.

BACKGROUND/OBJECTIVES: Recent studies indicate a possible role of TSH/TSHR signalling axis on adipogenesis and adipose tissue physiology. Here, we aimed to investigate the relationship between adipose tissue TSHB and adipose tissue physiology-related gene expression. SUBJECTS/METHODS: Subcutaneous and visceral adipose tissue TSHB gene expression was analysed in two independent cohorts [Cohort1 (N = 96) and Cohort2 (N = 45)] and after bariatric surgery-induced weight loss [Cohort3 (N = 22)]. Adipose tissue TSH protein expression was also analysed in a subgroup of participants from Cohort 1 (N = 16). The effects of recombinant TSH on human subcutaneous preadipocytes and adipocytes were investigated. RESULTS: In cohort 1, both visceral and subcutaneous adipose tissue TSHB gene expression was positively correlated with the expression of mitochondrial function (PPARGC1A, ISCA2, CISD1, SIRT1, NFE2L2, NRF1) and fatty acid mobilization (CAV1, ENGL1), but not with adipogenic-related genes. Of note, adipose tissue TSH protein levels were also associated with some of these markers of mitochondrial function and fatty acid mobilization. These associations were replicated in cohort 2. Bariatric surgery-induced weight loss resulted in increased subcutaneous adipose tissue TSHB in parallel to increased PPARGC1A. In human subcutaneous adipocytes, rh-TSH administration led to increased mitochondrial respiratory capacity in parallel to increased mitochondrial function- and adipogenic-related gene expression, but no significant effects were observed during differentiation of human preadipocytes. CONCLUSION: These data point to a possible role of adipose tissue TSH in the maintenance of adipocyte mitochondrial function.

The gut microbiota modulates both browning of white adipose tissue and the activity of brown adipose tissue.

Given the increasing worldwide prevalence of obesity and associated metabolic disturbances, novel therapeutic strategies are imperatively required. A plausible manner to increase energy expenditure is the enhancement of thermogenic pathways in white (WAT) and brown adipose tissue (BAT). In the last 15 years, the identification of novel endogenous mechanisms to promote BAT activity or browning of WAT has pointed at gut microbiota as an important modulator of host metabolic homeostasis and energy balance. In this review, we focused on the relationship between gut microbiota composition and adipose tissue thermogenic program (including BAT activity and browning of WAT) in both physiological and stress conditions. Specifically, we reviewed the effects of fasting, caloric restriction, cold stress and metabolic endotoxemia on both browning and gut microbiota shifts. Mechanistically speaking, processes related to bile acid metabolism and the endocannabinoid system seem to play an important role. In summary, the gut microbiota seems to impact WAT and BAT physiology at multiple levels.

Iron influences on the Gut-Brain axis and development of type 2 diabetes.

BACKGROUND: Microbiota/neuroendocrine interactions with health and disease are increasingly recognized. Main Body: Aging is associated with progressive iron storage and development of type 2 diabetes, which impacts on brain microstructure and function, mainly in obese subjects. Iron status is also mutually influencing the composition of the gut microbiota, which in turn may affect cognition through the gut-brain axis. Short Conclusion: In this article we update the possible role of iron in all these interactions.

Adipose TSHB in Humans and Serum TSH in Hypothyroid Rats Inform About Cellular Senescence.

BACKGROUND/AIMS: Thyroid hormones have been recently linked to senescence and longevity. Given the recent description of TSHB mRNA in human adipose tissue (AT), we aimed to investigate the relationship between local AT TSH and adipose tissue senescence. METHODS: TSHB mRNA (measured by real-time PCR) and markers of adipose tissue senescence [BAX, DBC1, TP53, TNF (real-time PCR), telomere length (Telo TAGGG Telomere Length Assay) and lipidomics (liquid chromatography mass spectrometry)] were analysed in subcutaneous (SAT) and visceral (VAT) AT from euthyroid subjects. The chronic effects of TSH were also investigated in AT from hypothyroid rats and after recombinant human TSH (rhTSH) administration in human adipocytes. RESULTS: Both VAT and SAT TSHB gene expression negatively correlated with markers of AT cellular senescence (BAX, DBC1, TP53, TNF gene expression and specific glucosylceramides) and positively associated with telomere length. Supporting these observations, both rhTSH administration in human adipocytes and increased TSH in hypothyroid rats resulted in decreased markers of cellular senescence (Bax and Tp53 mRNA) in both gonadal and subcutaneous white adipose tissue. CONCLUSION: These data point to a possible role of TSH in AT cellular senescence.

TSHB mRNA is linked to cholesterol metabolism in adipose tissue.

Subclinical hypothyroidism is known to be associated with increased serum cholesterol. Since thyroid-stimulating hormone (TSH) exerts an inductor effect on cholesterol biosynthesis, we aimed to investigate the relationship between TSH mRNA and cholesterol metabolism in human adipose tissue (AT). Cross-sectionally, AT TSH-ß (TSHB) mRNA was evaluated in 4 independent cohorts in association with serum total and LDL cholesterol, and AT lipidomics. Longitudinally, the effects of statins and of diet and exercise on AT TSHB mRNA were also examined. The bidirectional relationship between cholesterol and TSHB were studied in isolated human adipocytes. TSHB mRNA was consistently detected in AT from euthyroid subjects, and positively associated with serum total- and LDL-cholesterol, and with AT-specific cholesterol metabolism-associated lipids [arachidonoyl cholesteryl ester, C8-dihydroceramide, N-stearoyl-d-sphingosine, and GlcCer(18:0, 24:1)]. Reduction of cholesterol with statins and with diet and exercise interventions led to decreased TSHB mRNA in human AT, whereas excess cholesterol up-regulated TSHB mRNA in human adipocytes. In addition, recombinant human TSH α/ß administration resulted in increased HMGCR mRNA levels in human adipocytes. In mice, subcutaneous AT Tshb expression levels correlated directly with circulating cholesterol levels. In summary, current results provide novel evidence of TSHB as a paracrine factor that is modulated in parallel with cholesterol metabolism in human AT.-Moreno-Navarrete, J. M., Moreno, M., Ortega, F., Xifra, G., Hong, S., Asara, J. M., Serrano, J. C. E., Jové, M., Pissios, P., Blüher, M., Ricart, W., Portero-Otin, M., Fernández-Real, J. M. TSHB mRNA is linked to cholesterol metabolism in adipose tissue.

HMOX1 as a marker of iron excess-induced adipose tissue dysfunction, affecting glucose uptake and respiratory capacity in human adipocytes.

AIMS/HYPOTHESIS: Iron excess in adipose tissue is known to promote adipose tissue dysfunction. Here, we aimed to investigate the possible role of haem oxygenase 1 (HMOX1) in iron excess-induced adipose tissue dysfunction. METHODS: Cross-sectionally, HMOX1 gene expression in subcutaneous and visceral adipose tissue was analysed in two independent cohorts (n = 234 and 40) in relation to obesity. We also evaluated the impact of weight loss (n = 21), weight gain (in rats, n = 20) on HMOX1 mRNA; HMOX1 mRNA levels during human adipocyte differentiation; the effects of inflammation and iron on adipocyte HMOX1; and the effects of HMOX1-induced activity on adipocyte mitochondrial respiratory function, glucose uptake and adipogenesis. RESULTS: Adipose tissue HMOX1 was increased in obese participants (p = 0.01) and positively associated with obesity-related metabolic disturbances, and markers of iron accumulation, inflammation and oxidative stress (p < 0.01). HMOX1 was negatively correlated with mRNAs related to mitochondrial biogenesis, the insulin signalling pathway and adipogenesis (p < 0.01). These associations were replicated in an independent cohort. Bariatric surgery-induced weight loss led to reduced HMOX1 (0.024 ± 0.010 vs 0.010 ± 0.004 RU, p < 0.0001), whereas in rats, high-fat diet-induced weight gain resulted in increased Hmox1 mRNA levels (0.22 ± 0.15 vs 0.54 ± 0.22 RU, p = 0.005). These changes were in parallel with changes in BMI and adipose tissue markers of iron excess, adipogenesis and inflammation. In human adipocytes, iron excess and inflammation led to increased HMOX1 mRNA levels. HMOX1 induction (by haem arginate [hemin] administration), resulted in a significant reduction of mitochondrial respiratory capacity (including basal respiration and spare respiratory capacity), glucose uptake and adipogenesis in parallel with increased expression of inflammatory- and iron excess-related genes. CONCLUSIONS/INTERPRETATION: HMOX1 is an important marker of iron excess-induced adipose tissue dysfunction and metabolic disturbances in human obesity.

Metabolomics uncovers the role of adipose tissue PDXK in adipogenesis and systemic insulin sensitivity.

AIMS/HYPOTHESIS: We aimed to investigate the potential mechanisms involved in the compromised adipogenesis of visceral (VAT) vs subcutaneous adipose tissue (SAT) using comparative metabolomics. Based on the differentially identified metabolites, we focused on the relationship between the active form of vitamin B6 (pyridoxal 5-phosphate [PLP]), known to be generated through pyridoxal kinase (PDXK), and adipogenesis. METHODS: Non-targeted metabolomics analyses were performed in paired VAT and SAT (n = 14, discovery cohort). PDXK gene expression was evaluated in two validation cohorts of paired SAT and VAT samples in relation to obesity status and insulin sensitivity, and mechanistically after weight loss in vivo and in 3T3-L1 cells in vitro. RESULTS: Comparative metabolomics showed that PLP was significantly decreased in VAT vs SAT. Concordantly, PDXK mRNA levels were significantly decreased in VAT vs SAT, specifically in adipocytes. The decrease was specially marked in obese individuals. PDXK mRNA levels showed a strong association with adipogenic, lipid-droplet-related and lipogenic genes. At a functional level, systemic insulin sensitivity positively associated with PDXK expression, and surgically-induced weight loss (improving insulin sensitivity) led to increased SAT PDXK mRNA levels in parallel with adipogenic genes. In human pre-adipocytes, PDXK mRNA levels increased during adipocyte differentiation and after administration of peroxisome proliferator-activated receptor-γ agonists, and decreased under inflammatory stimuli. Mechanistic studies in 3T3-L1 cells showed that PLP administration resulted in increased adipogenic mRNA markers during early adipogenesis, whereas the PLP antagonist 4-deoxypyridoxine exerted opposite effects. CONCLUSIONS/INTERPRETATION: Overall, these results support the notion that in situ production of PLP is required for physiological adipogenesis.

Cytosolic aconitase activity sustains adipogenic capacity of adipose tissue connecting iron metabolism and adipogenesis.

To gain insight into the regulation of intracellular iron homeostasis in adipose tissue, we investigated the role of iron regulatory protein 1/cytosolic aconitase 1 (ACO1). ACO1 gene expression and activity increased in parallel to expression of adipogenic genes during differentiation of both murine 3T3-L1 cells and human preadipocytes. Lentiviral knockdown (KD) of Aco1 in 3T3-L1 preadipocytes led to diminished cytosolic aconitase activity and isocitrate dehydrogenase 1 (NADP(+)), soluble (Idh1) mRNA levels, decreased intracellular NADPH:NADP ratio, and impaired adipogenesis during adipocyte differentiation. In addition, Aco1 KD in fully differentiated 3T3-L1 adipocytes decreased lipogenic, Idh1, Adipoq, and Glut4 gene expression. A bidirectional cross-talk was found between intracellular iron levels and ACO1 gene expression and protein activity. Although iron in excess, known to increase reactive oxygen species production, and iron depletion both resulted in decreased ACO1 mRNA levels and activity, Aco1 KD led to reduced gene expression of transferrin receptor (Tfrc) and transferrin, disrupting intracellular iron uptake. In agreement with these findings, in 2 human independent cohorts (n = 85 and n = 38), ACO1 gene expression was positively associated with adipogenic markers in subcutaneous and visceral adipose tissue. ACO1 gene expression was also positively associated with the gene expression of TFRC while negatively linked to ferroportin (solute carrier family 40 (iron-regulated transporter), member 1) mRNA levels. Altogether, these results suggest that ACO1 activity is required for the normal adipogenic capacity of adipose tissue by connecting iron, energy metabolism, and adipogenesis.

Lipopolysaccharide binding protein is an adipokine involved in the resilience of the mouse adipocyte to inflammation.

AIMS/HYPOTHESIS: Lipopolysaccharide (LPS) binding protein (LBP) is a novel 65 kDa adipokine, linked to adipose tissue (AT) inflammation, obesity and insulin resistance, that inhibits adipocyte differentiation. Here, we investigated the molecular mechanisms behind these detrimental effects on adipogenesis through whole-genome transcriptomics and in vitro experiments. METHODS: Permanent and transient knockdown (KD) and co-culture experiments were performed in 3T3-L1 and 3T3-F442A cell lines during adipocyte differentiation. Microarray gene expression was performed using Genechip Affymetrix technology and validated by real-time PCR. RESULTS: LBP KD of 3T3-L1 cells led to a potentiated adipocyte differentiation with a dose-response relationship; genes involved in mitochondrial biogenesis, fatty acid metabolism and peroxisome proliferator-activated receptor γ (PPAR-γ) action were dramatically upregulated in parallel to increased insulin signalling. Cells with LBP KD became refractory to proinflammatory cytokines and other inflammatory stimuli (LPS and palmitate). This phenotype, mediated through disrupted nuclear factor κB (NFκB) signalling, was reversed by a soluble factor present in a co-culture with native cells and by exogenous LBP. Double-silencing of LBP and toll-like receptor 4 (TLR4) again rendered these cells insensitive to co-culture, LBP and inflammatory factors. CONCLUSIONS/INTERPRETATION: In summary, LBP is a proinflammatory soluble adipokine that acts as a brake for adipogenesis, strengthening the negative effects of palmitate and LPS on adipocyte differentiation.

Deleted in breast cancer 1 plays a functional role in adipocyte differentiation.

Genetic deletion of Dbc1 in mice reduced adipose tissue senescence and inflammation while promoting an expansion of this tissue. Here, we aimed to investigate DBC1 mRNA and protein levels in human adipose tissue from subjects with a wide spectrum of fat mass (cohort 1; n = 105) and insulin resistance (cohort 2; n = 47); we also investigated the effects of DBC1 knockdown on 3T3-L1 adipocyte differentiation. DBC1 mRNA was relatively abundant in both visceral (VAT) and subcutaneous adipose tissue (SAT) (mainly in the adipocyte fraction), being decreased in adipose tissue from obese compared with lean subjects. In both VAT and SAT, DBC1 mRNA levels were negatively associated with BMI and positively associated with age and the expression of PPARγ, GLUT4, IRS1, lipogenic (FASN, ACACA), lipid droplet-associated genes (PLIN1, FSP27, ADRP, and TIP47), and lipolytic (ABDH5, AKAP, and PRKACA) genes but negatively associated with ADIPOQ in VAT. DBC1 mRNA and protein levels were increased in the early stages of adipocyte differentiation of human and 3T3-L1 adipocytes. Dbc1 knockdown (KD) with lentivirus led to enhanced adipocyte differentiation, increasing intracellular lipid accumulation and adipogenic gene expression. In conclusion, although DBC1 gene expression was reduced in adipose tissue from obese subjects, it was negatively associated with ADIPOQ gene expression in VAT, suggesting that DBC1 might promote visceral adipose tissue dysfunction. In vitro data supported the antiadipogenic effects of DBC1.

Human omental and subcutaneous adipose tissue exhibit specific lipidomic signatures.

Despite their differential effects on human metabolic pathophysiology, the differences in omental and subcutaneous lipidomes are largely unknown. To explore this field, liquid chromatography coupled with mass spectrometry was used for lipidome analyses of adipose tissue samples (visceral and subcutaneous) selected from a group of obese subjects (n=38). Transcriptomics and in vitro studies in adipocytes were used to confirm the pathways affected by location. The analyses revealed the existence of obesity-related specific lipidome signatures in each of these locations, attributed to selective enrichment of specific triglycerides, glycerophospholipids, and sphingolipids, because these were not observed in adipose tissues from nonobese individuals. The changes were compatible with subcutaneous enrichment in pathways involved in adipogenesis, triacylglyceride synthesis, and lipid droplet formation, as well as increased α-oxidation. Marked differences between omental and subcutaneous depots in obese individuals were seen in the association of lipid species with metabolic traits (body mass index and insulin sensitivity). Targeted studies also revealed increased cholesterol (Δ56%) and cholesterol epoxide (Δ34%) concentrations in omental adipose tissue. In view of the effects of cholesterol epoxide, which induced enhanced expression of adipocyte differentiation and α-oxidation genes in human omental adipocytes, a novel role for cholesterol epoxide as a signaling molecule for differentiation is proposed. In summary, in obesity, adipose tissue exhibits a location-specific differential lipid profile that may contribute to explaining part of its distinct pathogenic role.