Downregulation of lipogenesis and fatty acid oxidation in the subcutaneous adipose tissue of morbidly obese women

Transcriptomic meta-analysis characterizes molecular commonalities between psoriasis and obesity

Despite the abundance of epidemiological evidence for the high comorbid rate between psoriasis and obesity, systematic approaches to common inflammatory mechanisms have not been adequately explored. We performed a meta-analysis of publicly available RNA-sequencing datasets to unveil putative mechanisms that are postulated to exacerbate both diseases, utilizing both late-stage, disease-specific meta-analyses and consensus gene co-expression network (cWGCNA). Single-gene meta-analyses reported several common inflammatory mechanisms fostered by the perturbed expression profile of inflammatory cells. Assessment of gene overlaps between both diseases revealed significant overlaps between up- (n = 170, P value = 6.07 × 10-65) and down-regulated (n = 49, P value = 7.1 × 10-7) genes, associated with increased T cell response and activated transcription factors. Our cWGCNA approach disentangled 48 consensus modules, associated with either the differentiation of leukocytes or metabolic pathways with similar correlation signals in both diseases. Notably, all our analyses confirmed the association of the perturbed T helper (Th)17 differentiation pathway in both diseases. Our novel findings through whole transcriptomic analyses characterize the inflammatory commonalities between psoriasis and obesity implying the assessment of several expression profiles that could serve as putative comorbid disease progression biomarkers and therapeutic interventions.

Reduced plasma glycine concentration in healthy and chronically diseased older adults: a marker of visceral adiposity?

BACKGROUND

Previous studies have shown that a reduced plasma concentration of the amino acid glycine (Gly) is associated with intra-abdominal obesity, but the mechanism remains unclear.

OBJECTIVES

This study aimed to investigate whether lower plasma Gly concentrations in older adults are independently associated with (visceral) adiposity, age, sex, presence of chronic disease, and glucose intolerance, and whether they are caused by a reduced Gly whole-body production (WBP) and/or increased Gly disposal capacity.

METHODS

We studied 102 older adults (47 males/55 females, 68.5 ± standard deviation 6.4 y) without comorbidities and 125 older adults with chronic obstructive pulmonary disease (COPD) (58 males/67 females, 69.7 ± 8.6 y). We assessed body composition and visceral adipose tissue (VAT) by dual-energy x-ray absorptiometry and muscle function by dynamometry. We measured postabsorptive plasma amino acid profile and glucose, followed by pulse administration of stable isotope-labeled Gly ([2,2-2H2]), and blood sampling was performed to measure the WBP of Gly. Results are expressed as means and 95% confidence intervals (CIs).

RESULTS

We found a lower plasma Gly concentration in healthy males and males with COPD than in females (Healthy: 211; 95% CI: 193,230 compared with 248; 95% CI: 225,271; COPD: 200; 95% CI: 186,215 compared with 262: 95% CI: 241, 283; P < 0.0001, respectively), with no difference between healthy and COPD groups. A negative relationship was found between unadjusted plasma Gly and VAT mass (R2: 0.16; slope: -1.7; 95% CI: -2.4, -1.2; P < 0.0021), but not with total body fat or fasting glucose. The strong association between lower plasma Gly and increased VAT mass in older adults was independent of age, sex, body weight, lean mass or body mass index, and the presence of COPD. Inclusion of these covariates increased the R2 to 0.783. We found no relation between the VAT and WBP of Gly (P = 0.35) or Gly clearance (P = 0.187) when lean mass was considered.

CONCLUSIONS

Reduced plasma Gly in older adults can be considered a marker of visceral adiposity, independent of sex, age, body composition, presence of chronic disease, and whole-body Gly production or clearance. This study was registered on clinicaltrials.gov as NCT01787682, NCT02082418, NCT02157844, NCT02770092, NCT02780219, NCT03796455, and NCT04461236.

Unraveling adipose tissue proteomic landscapes in severe obesity: insights into metabolic complications and potential biomarkers

In this study, we aimed to comprehensively characterize the proteomic landscapes of subcutaneous adipose tissue (SAT) and visceral adipose tissue (VAT) in patients with severe obesity, to establish their associations with clinical characteristics, and to identify potential serum protein biomarkers indicative of tissue-specific alterations or metabolic states. We conducted a cross-sectional analysis of 32 patients with severe obesity (16 males and 16 females) of Central European descent who underwent bariatric surgery. Clinical parameters and body composition were assessed using dual-energy X-ray absorptiometry (DXA) and bioelectrical impedance, with 15 patients diagnosed with type 2 diabetes (T2D) and 17 with hypertension. Paired SAT and VAT samples, along with serum samples, were subjected to state-of-the-art proteomics liquid chromatography-mass spectrometry (LC-MS). Our analysis identified 7,284 proteins across SAT and VAT, with 1,249 differentially expressed proteins between the tissues and 1,206 proteins identified in serum. Correlation analyses between differential protein expression and clinical traits suggest a significant role of SAT in the pathogenesis of obesity and related metabolic complications. Specifically, the SAT proteomic profile revealed marked alterations in metabolic pathways and processes contributing to tissue fibrosis and inflammation. Although we do not establish a definitive causal relationship, it appears that VAT might respond to SAT metabolic dysfunction by potentially enhancing mitochondrial activity and expanding its capacity. However, when this adaptive response is exceeded, it could possibly contribute to insulin resistance (IR) and in some cases, it may be associated with the progression to T2D. Our findings provide critical insights into the molecular foundations of SAT and VAT in obesity and may inform the development of targeted therapeutic strategies.NEW & NOTEWORTHY This study provides insights into distinct proteomic profiles of subcutaneous adipose tissue (SAT), visceral adipose tissue (VAT), and serum in patients with severe obesity and their associations with clinical traits and body composition. It underscores SAT's crucial role in obesity development and related complications, such as insulin resistance (IR) and type 2 diabetes (T2D). Our findings emphasize the importance of understanding the SAT and VAT balance in energy homeostasis, proteostasis, and the potential role of SAT capacity in the development of metabolic disorders.

The regulatory role of adipocyte mitochondrial homeostasis in metabolism-related diseases

Adipose tissue is the most important energy storage organ in the body, maintaining its normal energy metabolism function and playing a vital role in keeping the energy balance of the body to avoid the harm caused by obesity and a series of related diseases resulting from abnormal energy metabolism. The dysfunction of adipose tissue is closely related to the occurrence of diseases related to obesity metabolism. Among various organelles, mitochondria are the main site of energy metabolism, and mitochondria maintain their quality through autophagy, biogenesis, transfer, and dynamics, which play an important role in maintaining metabolic homeostasis of adipocytes. On the other hand, mitochondria have mitochondrial genomes which are vulnerable to damage due to the lack of protective structures and their proximity to sites of reactive oxygen species generation, thus affecting mitochondrial function. Notably, mitochondria are closely related to other organelles in adipocytes, such as lipid droplets and the endoplasmic reticulum, which enhances the function of mitochondria and other organelles and regulates energy metabolism processes, thus reducing the occurrence of obesity-related diseases. This article introduces the structure and quality control of mitochondria in adipocytes and their interactions with other organelles in adipocytes, aiming to provide a new perspective on the regulation of mitochondrial homeostasis in adipocytes on the occurrence of obesity-related diseases, and to provide theoretical reference for further revealing the molecular mechanism of mitochondrial homeostasis in adipocytes on the occurrence of obesity-related diseases.

Associations of breast cancer related exposures and gene expression profiles in normal breast tissue-The Norwegian Women and Cancer normal breast tissue study

BACKGROUND

Normal breast tissue is utilized in tissue-based studies of breast carcinogenesis. While gene expression in breast tumor tissue is well explored, our knowledge of transcriptomic signatures in normal breast tissue is still incomplete. The aim of this study was to investigate variability of gene expression in a large sample of normal breast tissue biopsies, according to breast cancer related exposures (obesity, smoking, alcohol, hormone therapy, and parity).

METHODS

We analyzed gene expression profiles from 311 normal breast tissue biopsies from cancer-free, post-menopausal women, using Illumina bead chip arrays. Principal component analysis and K-means clustering was used for initial analysis of the dataset. The association of exposures and covariates with gene expression was determined using linear models for microarrays.

RESULTS

Heterogeneity of the breast tissue and cell composition had the strongest influence on gene expression profiles. After adjusting for cell composition, obesity, smoking, and alcohol showed the highest numbers of associated genes and pathways, whereas hormone therapy and parity were associated with negligible gene expression differences.

CONCLUSION

Our results provide insight into associations between major exposures and gene expression profiles and provide an informative baseline for improved understanding of exposure-related molecular events in normal breast tissue of cancer-free, post-menopausal women.

Cold exposure induces dynamic changes in circulating triacylglycerol species, which is dependent on intracellular lipolysis: A randomized cross-over trial

BACKGROUND

The application of cold exposure has emerged as an approach to enhance whole-body lipid catabolism. The global effect of cold exposure on the lipidome in humans has been reported with mixed results depending on intensity and duration of cold.

METHODS

This secondary study was based on data from a previous randomized cross-over trial (ClinicalTrials.gov ID: NCT03012113). We performed sequential lipidomic profiling in serum during 120 min cold exposure of human volunteers. Next, the intracellular lipolysis was blocked in mice (eighteen 10-week-old male wild-type mice C57BL/6J) using a small-molecule inhibitor of adipose triglyceride lipase (ATGL; Atglistatin), and mice were exposed to cold for a similar duration. The quantitative lipidomic profiling was assessed in-depth using the Lipidyzer platform.

FINDINGS

In humans, cold exposure gradually increased circulating free fatty acids reaching a maximum at 60 min, and transiently decreased total triacylglycerols (TAGs) only at 30 min. A broad range of TAG species was initially decreased, in particular unsaturated and polyunsaturated TAG species with ≤5 double bonds, while after 120 min a significant increase was observed for polyunsaturated TAG species with ≥6 double bonds in humans. The mechanistic study in mice revealed that the cold-induced increase in polyunsaturated TAGs was largely prevented by blocking adipose triglyceride lipase.

INTERPRETATION

We interpret these findings as that cold exposure feeds thermogenic tissues with TAG-derived fatty acids for combustion, resulting in a decrease of circulating TAG species, followed by increased hepatic production of polyunsaturated TAG species induced by liberation of free fatty acids stemming from adipose tissue.

FUNDING

This work was supported by the Netherlands CardioVascular Research Initiative: 'the Dutch Heart Foundation, Dutch Federation of University Medical Centers, the Netherlands Organisation for Health Research and Development and the Royal Netherlands Academy of Sciences' [CVON2017-20 GENIUS-II] to Patrick C.N. Rensen. Borja Martinez-Tellez is supported by individual postdoctoral grant from the Fundación Alfonso Martin Escudero and by a Maria Zambrano fellowship by the Ministerio de Universidades y la Unión Europea - NextGenerationEU (RR_C_2021_04). Lucas Jurado-Fasoli was supported by an individual pre-doctoral grant from the Spanish Ministry of Education (FPU19/01609) and with an Albert Renold Travel Fellowship from the European Foundation for the Study of Diabetes (EFSD). Martin Giera was partially supported by NWO XOmics project #184.034.019.

Hepatic Hedgehog Signaling Participates in the Crosstalk between Liver and Adipose Tissue in Mice by Regulating FGF21

The Hedgehog signaling pathway regulates many processes during embryogenesis and the homeostasis of adult organs. Recent data suggest that central metabolic processes and signaling cascades in the liver are controlled by the Hedgehog pathway and that changes in hepatic Hedgehog activity also affect peripheral tissues, such as the reproductive organs in females. Here, we show that hepatocyte-specific deletion of the Hedgehog pathway is associated with the dramatic expansion of adipose tissue in mice, the overall phenotype of which does not correspond to the classical outcome of insulin resistance-associated diabetes type 2 obesity. Rather, we show that alterations in the Hedgehog signaling pathway in the liver lead to a metabolic phenotype that is resembling metabolically healthy obesity. Mechanistically, we identified an indirect influence on the hepatic secretion of the fibroblast growth factor 21, which is regulated by a series of signaling cascades that are directly transcriptionally linked to the activity of the Hedgehog transcription factor GLI1. The results of this study impressively show that the metabolic balance of the entire organism is maintained via the activity of morphogenic signaling pathways, such as the Hedgehog cascade. Obviously, several pathways are orchestrated to facilitate liver metabolic status to peripheral organs, such as adipose tissue.

Preventing White Adipocyte Browning during Differentiation In Vitro: The Effect of Differentiation Protocols on Metabolic and Mitochondrial Phenotypes

Mitochondrial dysfunction in white adipose tissue is strongly associated with obesity and its metabolic complications, which are important health challenges worldwide. Human adipose-derived stromal/stem cells (hASCs) are a promising tool to investigate the underlying mechanisms of such mitochondrial dysfunction and to subsequently provide knowledge for the development of treatments for obesity-related pathologies. A substantial obstacle in using hASCs is that the key compounds for adipogenic differentiation in vitro increase mitochondrial uncoupling, biogenesis, and activity, which are the signature features of brown adipocytes, thus altering the white adipocyte phenotype towards brown-like cells. Additionally, commonly used protocols for hASC adipogenic differentiation exhibit high variation in their composition of media, and a systematic comparison of their effect on mitochondria is missing. Here, we compared the five widely used adipogenic differentiation protocols for their effect on metabolic and mitochondrial phenotypes to identify a protocol that enables in vitro differentiation of white adipocytes and can more faithfully recapitulate the white adipocyte phenotype observed in human adipose tissue. We developed a workflow that included functional assays and morphological analysis of mitochondria and lipid droplets. We observed that triiodothyronine- or indomethacin-containing media and commercially available adipogenic media induced browning during in vitro differentiation of white adipocytes. However, the differentiation protocol containing 1 μM of the peroxisome proliferator-activated receptor gamma (PPARγ) agonist rosiglitazone prevented the browning effect and would be proposed for adipogenic differentiation protocol for hASCs to induce a white adipocyte phenotype. Preserving the white adipocyte phenotype in vitro is a crucial step for the study of obesity and associated metabolic diseases, adipose tissue pathologies, such as lipodystrophies, possible therapeutic compounds, and basic adipose tissue physiology.

Bifidobacterium animalis subsp. lactis A6 Enhances Fatty Acid β-Oxidation of Adipose Tissue to Ameliorate the Development of Obesity in Mice

Fatty acid β-oxidation (FAO) is confirmed to be impaired in obesity, especially in adipose tissues. We previously proved that Bifidobacterium animalis subsp. lactis A6 (BAA6) had protective effects against diet-induced obesity. However, whether BAA6 enhances FAO to ameliorate the development of obesity has not been explored. After being fed with high-fat diet (HFD) for 9 weeks, male C57BL/6J mice were fed HFD or BAA6 for 8 weeks. In vitro study was carried out using 3T3-L1 adipocytes to determine the effect of BAA6 culture supernatant (BAA6-CM). Here, we showed that administration of BAA6 to mice fed with HFD decreased body weight gain (by 5.03 g) and significantly up-regulated FAO in epididymal adipose tissues. In parallel, FAO in 3T3-L1 cells was increased after BAA6-CM treatment. Acetate was identified as a constituent of BAA6-CM that showed a similar effect to BAA6-CM. Furthermore, acetate treatment activated the GPR43-PPARα signaling, thereby promoting FAO in 3T3-L1 cells. The levels of acetate were also elevated in serum and feces (by 1.92- and 2.27-fold) of HFD-fed mice following BAA6 administration. The expression levels of GPR43 and PPARα were increased by 55.45% and 69.84% after BAA6 supplement in the epididymal fat of mice. Together, these data reveal that BAA6 promotes FAO of adipose tissues through the GPR43-PPARα signaling, mainly by increasing acetate levels, leading to alleviating the development of obesity.

The human type 2 diabetes-specific visceral adipose tissue proteome and transcriptome in obesity

Dysfunctional visceral adipose tissue (VAT) in obesity is associated with type 2 diabetes (DM) but underlying mechanisms remain unclear. Our objective in this discovery analysis was to identify genes and proteins regulated by DM to elucidate aberrant cellular metabolic and signaling mediators. We performed label-free proteomics and RNA-sequencing analysis of VAT from female bariatric surgery subjects with DM and without DM (NDM). We quantified 1965 protein groups, 23 proteins, and 372 genes that were differently abundant in DM vs. NDM VAT. Proteins downregulated in DM were related to fatty acid synthesis and mitochondrial function (fatty acid synthase, FASN; dihydrolipoyl dehydrogenase, mitochondrial, E3 component, DLD; succinate dehydrogenase-α, SDHA) while proteins upregulated in DM were associated with innate immunity and transcriptional regulation (vitronectin, VTN; endothelial protein C receptor, EPCR; signal transducer and activator of transcription 5B, STAT5B). Transcriptome indicated defects in innate inflammation, lipid metabolism, and extracellular matrix (ECM) function, and components of complement classical and alternative cascades. The VAT proteome and transcriptome shared 13 biological processes impacted by DM, related to complement activation, cell proliferation and migration, ECM organization, lipid metabolism, and gluconeogenesis. Our data revealed a marked effect of DM in downregulating FASN. We also demonstrate enrichment of complement factor B (CFB), coagulation factor XIII A chain (F13A1), thrombospondin 1 (THBS1), and integrins at mRNA and protein levels, albeit with lower q-values and lack of Western blot or PCR confirmation. Our findings suggest putative mechanisms of VAT dysfunction in DM.

Changes in abdominal subcutaneous adipose tissue phenotype following menopause is associated with increased visceral fat mass

Menopause is associated with a redistribution of adipose tissue towards central adiposity, known to cause insulin resistance. In this cross-sectional study of 33 women between 45 and 60 years, we assessed adipose tissue inflammation and morphology in subcutaneous adipose tissue (SAT) and visceral adipose tissue (VAT) across menopause and related this to menopausal differences in adipose tissue distribution and insulin resistance. We collected paired SAT and VAT biopsies from all women and combined this with anthropometric measurements and estimated whole-body insulin sensitivity. We found that menopause was associated with changes in adipose tissue phenotype related to metabolic dysfunction. In SAT, postmenopausal women showed adipocyte hypertrophy, increased inflammation, hypoxia and fibrosis. The postmenopausal changes in SAT was associated with increased visceral fat accumulation. In VAT, menopause was associated with adipocyte hypertrophy, immune cell infiltration and fibrosis. The postmenopausal changes in VAT phenotype was associated with decreased insulin sensitivity. Based on these findings we suggest, that menopause is associated with changes in adipose tissue phenotype related to metabolic dysfunction in both SAT and VAT. Whereas increased SAT inflammation in the context of menopause is associated with VAT accumulation, VAT morphology is related to insulin resistance.

Assessing the Contribution of Relative Macrophage Frequencies to Subcutaneous Adipose Tissue

Background: Macrophages play an important role in regulating adipose tissue function, while their frequencies in adipose tissue vary between individuals. Adipose tissue infiltration by high frequencies of macrophages has been linked to changes in adipokine levels and low-grade inflammation, frequently associated with the progression of obesity. The objective of this project was to assess the contribution of relative macrophage frequencies to the overall subcutaneous adipose tissue gene expression using publicly available datasets.

Methods: Seven publicly available microarray gene expression datasets from human subcutaneous adipose tissue biopsies (n = 519) were used together with TissueDecoder to determine the adipose tissue cell-type composition of each sample. We divided the subjects in four groups based on their relative macrophage frequencies. Differential gene expression analysis between the high and low relative macrophage frequencies groups was performed, adjusting for sex and study. Finally, biological processes were identified using pathway enrichment and network analysis.

Results: We observed lower frequencies of adipocytes and higher frequencies of adipose stem cells in individuals characterized by high macrophage frequencies. We additionally studied whether, within subcutaneous adipose tissue, interindividual differences in the relative frequencies of macrophages were reflected in transcriptional differences in metabolic and inflammatory pathways. Adipose tissue of individuals with high macrophage frequencies had a higher expression of genes involved in complement activation, chemotaxis, focal adhesion, and oxidative stress. Similarly, we observed a lower expression of genes involved in lipid metabolism, fatty acid synthesis, and oxidation and mitochondrial respiration.

Conclusion: We present an approach that combines publicly available subcutaneous adipose tissue gene expression datasets with a deconvolution algorithm to calculate subcutaneous adipose tissue cell-type composition. The results showed the expected increased inflammation gene expression profile accompanied by decreased gene expression in pathways related to lipid metabolism and mitochondrial respiration in subcutaneous adipose tissue in individuals characterized by high macrophage frequencies. This approach demonstrates the hidden strength of reusing publicly available data to gain cell-type-specific insights into adipose tissue function.

Molecular mechanisms of fat deposition: IL-6 is a hub gene in fat lipolysis, comparing thin-tailed with fat-tailed sheep breeds

Tail fat content affects meat quality and varies significantly among different breeds of sheep. Ghezel (fat-tailed) and Zel (thin-tailed) are two important Iranian local sheep breeds with different patterns of fat storage. The current study presents the transcriptome characterization of tail fat using RNA sequencing in order to get a better comprehension of the molecular mechanism of lipid storage in the two mentioned sheep breeds. Seven (Zel  =  4 and Ghezel  =  3) 7-month-old male lambs were used for this experiment. The results of sequencing were analyzed with bioinformatics methods, including differentially expressed genes (DEGs) identification, functional enrichment analysis, structural classification of proteins, protein-protein interaction (PPI) and network and module analyses. Some of the DEGs, such as LIPG, SAA1, SOCS3, HIF-1 α , and especially IL-6, had a close association with lipid metabolism. Furthermore, functional enrichment analysis revealed pathways associated with fat deposition, including "fatty acid metabolism", "fatty acid biosynthesis" and "HIF-1 signaling pathway". The structural classification of proteins showed that major down-regulated DEGs in the Zel (thin-tailed) breed were classified under transporter class and that most of them belonged to the solute carrier transporter (SLC) families. In addition, DEGs under the transcription factor class with an important role in lipolysis were up-regulated in the Zel (thin-tailed) breed. Also, network analysis revealed that IL-6 and JUNB were hub genes for up-regulated PPI networks, and HMGCS1, VPS35 and VPS26A were hub genes for down-regulated PPI networks. Among the up-regulated DEGs, the IL-6 gene seems to play an important role in lipolysis of tail fat in thin-tailed sheep breeds via various pathways such as tumor necrosis factor (TNF) signaling and mitogen-activated protein kinase (MAPK) signaling pathways. Due to the probable role of the IL-6 gene in fat lipolysis and also due to the strong interaction of IL-6 with the other up-regulated DEGs, it seems that IL-6 accelerates the degradation of lipids in tail fat cells.

Inhibition of AMPK activity in response to insulin in adipocytes: involvement of AMPK pS485, PDEs, and cellular energy levels

Insulin resistance in obesity and type 2 diabetes has been shown to be associated with decreased de novo fatty acid (FA) synthesis in adipose tissue. It is known that insulin can acutely stimulate FA synthesis in adipocytes; however, the mechanisms underlying this effect are unclear. The rate-limiting step in FA synthesis is catalyzed by acetyl-CoA carboxylase (ACC), known to be regulated through inhibitory phosphorylation at S79 by the AMP-activated protein kinase (AMPK). Previous results from our laboratory showed an inhibition of AMPK activity by insulin, which was accompanied by PKB-dependent phosphorylation of AMPK at S485. However, whether the S485 phosphorylation is required for insulin-induced inhibition of AMPK or other mechanisms underlie the reduced kinase activity is not known. To investigate this, primary rat adipocytes were transduced with a recombinant adenovirus encoding AMPK-WT or a nonphosphorylatable AMPK S485A mutant. AMPK activity measurements by Western blot analysis and in vitro kinase assay revealed that WT and S485A AMPK were inhibited to a similar degree by insulin, indicating that AMPK S485 phosphorylation is not required for insulin-induced AMPK inhibition. Further analysis suggested an involvement of decreased AMP-to-ATP ratios in the insulin-induced inhibition of AMPK activity, whereas a possible contribution of phosphodiesterases was excluded. Furthermore, we show that insulin-induced AMPK S485 phosphorylation also occurs in human adipocytes, suggesting it to be of an importance yet to be revealed. Altogether, this study increases our understanding of how insulin regulates AMPK activity, and with that, FA synthesis, in adipose tissue.

Exploring Therapeutic Targets to Reverse or Prevent the Transition from Metabolically Healthy to Unhealthy Obesity

The prevalence of obesity and obesity-related metabolic comorbidities are rapidly increasing worldwide, placing a huge economic burden on health systems. Excessive nutrient supply combined with reduced physical exercise results in positive energy balance that promotes adipose tissue expansion. However, the metabolic response and pattern of fat accumulation is variable, depending on the individual’s genetic and acquired susceptibility factors. Some develop metabolically healthy obesity (MHO) and are resistant to obesity-associated metabolic diseases for some time, whereas others readily develop metabolically unhealthy obesity (MUO). An unhealthy response to excess fat accumulation could be due to susceptibility intrinsic factors (e.g., increased likelihood of dedifferentiation and/or inflammation), or by pathogenic drivers extrinsic to the adipose tissue (e.g., hyperinsulinemia), or a combination of both. This review outlines the major transcriptional factors and genes associated with adipogenesis and regulation of adipose tissue homeostasis and describes which of these are disrupted in MUO compared to MHO individuals. It also examines the potential role of pathogenic insulin hypersecretion as an extrinsic factor capable of driving the changes in adipose tissue which cause transition from MHO to MUO. On this basis, therapeutic approaches currently available and emerging to prevent and reverse the transition from MHO to MUO transition are reviewed.

The expression signatures in liver and adipose tissue from obese Göttingen Minipigs reveal a predisposition for healthy fat accumulation

BACKGROUND

Model animals are valuable resources for dissecting basic aspects of the regulation of obesity and metabolism. The translatability of results relies on understanding comparative aspects of molecular pathophysiology. Several studies have shown that despite the presence of overt obesity and dyslipidemia in the pig key human pathological hepatic findings such as hepatocellular ballooning and abundant steatosis are lacking in the model.

OBJECTIVES

The aim of this study was to elucidate why these histopathological characteristics did not occur in a high fat, fructose and cholesterol (FFC) diet-induced obese Göttingen Minipig model.

METHODS

High-throughput expression profiling of more than 90 metabolically relevant genes was performed in liver, subcutaneous adipose tissue (SAT) and visceral adipose tissue (VAT) of male minipigs diet fed: standard chow (SD, n = 7); FFC diet (n = 14); FFC diet in streptozotocin-induced diabetic pigs (FFCDIA, n = 8). Moreover, histopathological assessment of SAT and VAT was performed.

RESULTS

12, 4 and 1 genes were highly significantly differentially expressed in liver, SAT and VAT when comparing the FFC and SD groups whereas the corresponding numbers were 15, 2, and 1 when comparing the FFCDIA and SD groups. Although the minipigs in both FFC groups developed sever obesity and dyslipidemia, the insulin-signaling pathways were not affected. Notably, four genes involved in lipid acquisition and removal, were highly deregulated in the liver: PPARG, LPL, CD36 and FABP4. These genes have been reported to play a major role in promoting hepatic steatosis in rodents and humans. Since very little macrophage-associated pro-inflammatory response was detected in the adipose tissues the expansion appears to have no adverse impact on adipose tissue metabolism.

CONCLUSION

The study shows that morbidly obese Göttingen Minipigs are protected against many of the metabolic and hepatic abnormalities associated with obesity due to a remarkable ability to expand the adipose compartments to accommodate excess calories.

White adipose tissue mitochondrial metabolism in health and in obesity

White adipose tissue is one of the largest organs of the body. It plays a key role in whole-body energy status and metabolism; it not only stores excess energy but also secretes various hormones and metabolites to regulate body energy balance. Healthy adipose tissue capable of expanding is needed for metabolic well-being and to prevent accumulation of triglycerides to other organs. Mitochondria govern several important functions in the adipose tissue. We review the derangements of mitochondrial function in white adipose tissue in the obese state. Downregulation of mitochondrial function or biogenesis in the white adipose tissue is a central driver for obesity-associated metabolic diseases. Mitochondrial functions compromised in obesity include oxidative functions and renewal and enlargement of the adipose tissue through recruitment and differentiation of adipocyte progenitor cells. These changes adversely affect whole-body metabolic health. Dysfunction of the white adipose tissue mitochondria in obesity has long-term consequences for the metabolism of adipose tissue and the whole body. Understanding the pathways behind mitochondrial dysfunction may help reveal targets for pharmacological or nutritional interventions that enhance mitochondrial biogenesis or function in adipose tissue.

Association of the PNPLA2, SCD1 and Leptin Expression with Fat Distribution in Liver and Adipose Tissue From Obese Subjects

The expansion of adipose tissue is regulated by insulin and leptin through sterol regulatory element-binding protein-1c (SREBP-1c), up-regulating lipogenesis in tissues by Stearoylcoenzyme A desaturase 1 (SCD1) enzyme, while adipose triglyceride lipase (ATGL) enzyme is key in lipolysis. The research objective was to evaluate the expression of Sterol Regulatory Element Binding Transcription Factor 1 (SREBF1), SCD1, Patatin Like Phospholipase Domain Containing 2 (PNPLA2), and leptin (LEP) genes in hepatic-adipose tissue, and related them with the increment and distribution of fat depots of individuals without insulin resistance. Thirty-eight subjects undergoing elective cholecystectomy with liver and adipose tissue biopsies (subcutaneous-omental) are included. Tissue gene expression was assessed by qPCR and biochemical parameters determined. Individuals are classified according to the body mass index, classified as lean (control group, n=12), overweight (n=11) and obesity (n=15). Abdominal adiposity was determined by anthropometric and histopathological study of the liver. Increased SCD1 expression in omental adipose tissue (p=0.005) and PNPLA2 in liver (p=0.01) were found in the obesity group. PNPLA2 decreased expression in subcutaneous adipose tissue was significant in individuals with abdominal adiposity (p=0.017). Anthropometric parameters positively correlated with liver PNPLA2 and the expression of liver PNPLA2 with serum leptin. SCD1 increased levels may represent lipid storage activity in omental adipose tissue. Liver PNPLA2 increased expression could function as a primary compensatory event of visceral fat deposits associated to the leptin hormone related to the increase of adipose tissue.

Involvement of acetyl-CoA-producing enzymes in the deterioration of the functional potential of adipose-derived multipotent cells from subjects with metabolic syndrome

OBJECTIVE

The expansion capacity of white adipose tissue influences the distribution of fat depots in the body, the visceral accumulation of which is linked to metabolic syndrome, regardless of the degree of obesity of the subjects. Alterations in the adipose tissue-derived mesenchymal stem cells (ASCs) may contribute to the adipose tissue remodeling associated with metabolic syndrome and impact the regional distribution of adipose tissue by generating inherently dysfunctional adipocytes. Here we examine the expression levels of acetyl-CoA-producing enzymes and their relationship with the lipogenic, antioxidant and oxidative potential of adipocytes generated from visceral ASCs (adipo-visASCs) and subcutaneous ASCs (adipo-subASCs) from subjects with different metabolic profiles.

MATERIALS/METHODS

Paired samples of visceral and subcutaneous adipose tissue were processed to isolate the respective ASCs from normal-weight (Nw) subjects and obese patients with metabolic syndrome (METS) and without METS (NonMETS). qPCR was used to quantify the expression levels of the genes studied in both adipo-ASCs from the patient groups and those generated after silencing by small interfering RNA of acetyl-CoA-producing enzymes. The accumulation of lipids was quantified by absorbance.

RESULTS

No significant differences in cell yield or CD34⁺CD31^-CD45^- ASC percentage were observed between the different patient groups. Unlike adipo-visASCs, adipo-subASCs from METS patients showed a decrease in expression levels of acetyl-CoA-producing enzymes as well as proteins linked to lipogenesis, antioxidant defense and fatty acid oxidation. Transcriptional silencing of acetyl-CoA-producing enzymes in adipo-subASCs reduced lipid accumulation and affected transcription levels of lipogenic and antioxidant defense proteins.

CONCLUSIONS

Adipo-subASCs may be more susceptible than adipo-visASCs to deterioration of the lipogenic, oxidative and antioxidant potential associated with metabolic syndrome. Intrinsic alterations in transcription levels of acetyl-CoA-producing enzymes may contribute to the metabolic reprogramming of adipo-subASCs from METS patients.

Regulation and Metabolic Significance of De Novo Lipogenesis in Adipose Tissues

De novo lipogenesis (DNL) is a complex and highly regulated process in which carbohydrates from circulation are converted into fatty acids that are then used for synthesizing either triglycerides or other lipid molecules. Dysregulation of DNL contributes to human diseases such as obesity, type 2 diabetes, and cardiovascular diseases. Thus, the lipogenic pathway may provide a new therapeutic opportunity for combating various pathological conditions that are associated with dysregulated lipid metabolism. Hepatic DNL has been well documented, but lipogenesis in adipocytes and its contribution to energy homeostasis and insulin sensitivity are less studied. Recent reports have gained significant insights into the signaling pathways that regulate lipogenic transcription factors and the role of DNL in adipose tissues. In this review, we will update the current knowledge of DNL in white and brown adipose tissues with the focus on transcriptional, post-translational, and central regulation of DNL. We will also summarize the recent findings of adipocyte DNL as a source of some signaling molecules that critically regulate energy metabolism.

Consumption of Cherry out of Season Changes White Adipose Tissue Gene Expression and Morphology to a Phenotype Prone to Fat Accumulation

The aim of this study was to determine whether the consumption of cherry out of its normal harvest photoperiod affects adipose tissue, increasing the risk of obesity. Fischer 344 rats were held over a long day (LD) or a short day (SD), fed a standard diet (STD), and treated with a cherry lyophilizate (CH) or vehicle (VH) (n = 6). Biometric measurements, serum parameters, gene expression in white (RWAT) and brown (BAT) adipose tissues, and RWAT histology were analysed. A second experiment with similar conditions was performed (n = 10) but with a cafeteria diet (CAF). In the STD experiment, Bmal1 and Cry1 were downregulated in the CHSD group compared to the VHSD group. Pparα expression was downregulated while Ucp1 levels were higher in the BAT of the CHSD group compared to the VHSD group. In the CAF-fed rats, glucose and insulin serum levels increased, and the expression levels of lipogenesis and lipolysis genes in RWAT were downregulated, while the adipocyte area increased and the number of adipocytes diminished in the CHSD group compared to the VHSD group. In conclusion, we show that the consumption of cherry out of season influences the metabolism of adipose tissue and promotes fat accumulation when accompanied by an obesogenic diet.

High fat diet induced obesity is mitigated in Cyp3a-null female mice

Recent studies indicate a role for the constitutive androstane receptor (CAR), pregnane X-receptor (PXR), and hepatic xenobiotic detoxifying CYPs in fatty liver disease or obesity. Therefore, we examined whether Cyp3a-null mice show increased obesity and fatty liver disease following 8-weeks of exposure to a 60% high-fat diet (HFD). Surprisingly, HFD-fed Cyp3a-null females fed a HFD gained 50% less weight than wild-type (WT; B6) females fed a HFD. In contrast, Cyp3a-null males gained more weight than WT males, primarily during the first few weeks of HFD-treatment. Cyp3a-null females also recovered faster than WT females from a glucose tolerance test; males showed no difference in glucose tolerance between the groups. Serum concentrations of the anti-obesity hormone, adiponectin are 60% higher and β-hydroxybutyrate levels are nearly 50% lower in Cyp3a-null females than WT females, in agreement with reduced weight gain, faster glucose response, and reduced ketogenesis. In contrast, Cyp3a-null males have higher liver triglyceride concentrations and lipidomic analysis indicates an increase in phosphatidylinositol, phosphatidylserine and sphingomyelin. None of these changes were observed in females. Last, Pxr, Cyp2b, and IL-6 expression increased in Cyp3a-null females following HFD-treatment. Cyp2b and Fatp1 increased, while Pxr, Cpt1a, Srebp1 and Fasn decreased in Cyp3a-null males following a HFD, indicating compensatory biochemical responses in male (and to a lesser extent) female mice fed a HFD. In conclusion, lack of Cyp3a has a positive effect on acclimation to a HFD in females as it improves weight gain, glucose response and ketosis.

Pedunculoside, a novel triterpene saponin extracted from Ilex rotunda, ameliorates high-fat diet induced hyperlipidemia in rats

Pedunculoside (PE) is a novel triterpene saponin extracted from the dried barks of Ilex rotunda Thunb. The present study aims to explore lipid-lowering effects of PE on hyperlipidemia rat induced by high-fat diet. The rats were fed with the high-fat diet and subjected to intragastric administration of PE at doses of 30, 15, or 5 mg/kg daily for 7 weeks. The results demonstrated that treatment with PE for 7-week dramatically decreased serum total cholesterol (TC) and low-density lipoprotein cholesterol (LDL-C) and reduced liver TC in hyperlipidemia rat induced by high-fat diet. Furthermore, the results also showed that PE modulated the expression of enzymes involved in lipid metabolism including peroxisome proliferator-activated receptor α (PPAR-α), sterol regulatory element-binding protein 1 (SREBP-1), fatty acid synthase (FAS) and stearoyl CoA desaturase-1 (SCD-1) mRNA in liver. Besides, PE-treated group decreased weights and diameters of epididymal adipose hyperlipidemia rat. Mechanism study demonstrated that PE regulated PPAR-γ, CCAAT/Enhancer-binding Protein α (C/EBPα)、and SREBP-1 expression as well as inhibited phosphorylation of AMPK in MDI (methylisobutylxanthine, dexamethasone, insulin) induced-3T3L1 cells. Molecular Docking confirmed interaction between PE with proteins involving PPAR-γ, C/EBPα and SREBP-1. In summary, these findings may support that PE is a novel lipid-lowering drug candidate.

Multi-omics Integrative Investigation of Fatty Acid Metabolism in Obese and Lean Subcutaneous Tissue

White adipose tissue (WAT) plays a central role in whole-body energy homeostasis through storage and release of fatty acids. A deeper understanding of the complex and highly integrated pathways regulating WAT fatty acid metabolism, and how they are altered with obesity, is necessary for diagnostic and therapeutic innovations in nutritional disorders. In this multi-omics study, we investigated the influence of obesity on fatty acid metabolism in human subcutaneous adipose tissue (SAT) using an approach that integrated transcriptomic, peptidomic, and fatty acid analyses. Notably, all analyses were conducted in the same adipose tissue sample from each participant, thus minimizing the chance of spurious results. In a sample of SAT from the periumbilical abdominal region of obese (n = 11, mean body mass index [BMI] = 35.0 ± 1.2 kg/m²) and lean subjects (n = 9, mean BMI = 22.1 ± 0.5 kg/m²), we found that obese SAT tended to have higher relative amounts of specific monounsaturated fatty acids and n-6 polyunsaturated fatty acids, and lower amounts of saturated fatty acids (p < 0.05). These changes were associated with differential regulation of lipogenic and lipolytic pathways in obese SAT. Fatty acid analysis showed changes in estimated fatty acid desaturase and elongase activities between lean and obese SAT (p < 0.05). Biomarkers of lipogenesis (e.g., fatty acid synthase protein) were differentially regulated between lean and obese SAT. These changes were noted in conjunction with increases in extracellular matrix remodeling proteins. Transcriptomic data revealed that the key regulators of lipolysis were reduced in obese SAT. This integrative multi-omics analysis collectively shows that obese SAT has a distinct fatty acid signature compared to lean SAT and the pathways underlying fatty acid metabolism are broadly regulated at the level of gene expression and protein abundance.

Alterations of specific lipid groups in serum of obese humans: a review

Obesity is a major contributor to the dysfunction of liver, cardiac, pulmonary, endocrine and reproductive system, as well as a component of metabolic syndrome. Although development of obesity-related disorders is associated with lipid abnormalities, most previous studies dealing with the problem in question were limited to routinely determined parameters, such as serum concentrations of triacylglycerols, total cholesterol, low-density and high-density lipoprotein cholesterol. Many authors postulated to extend the scope of analysed lipid compounds and to study obesity-related alterations in other, previously non-examined groups of lipids. Comprehensive quantitative, structural and functional analysis of specific lipid groups may result in identification of new obesity-related alterations. The review summarizes available evidence of obesity-related alterations in various groups of lipids and their impact on health status of obese subjects. Further, the role of diet and endogenous lipid synthesis in the development of serum lipid alterations is discussed, along with potential application of various lipid compounds as risk markers for obesity-related comorbidities.

Downregulation of de Novo Fatty Acid Synthesis in Subcutaneous Adipose Tissue of Moderately Obese Women

The purpose of this work was to evaluate the expression of fatty acid metabolism-related genes in human adipose tissue from moderately obese women. We used qRT-PCR and Western Blot to analyze visceral (VAT) and subcutaneous (SAT) adipose tissue mRNA expression involved in de novo fatty acid synthesis (ACC1, FAS), fatty acid oxidation (PPARα, PPARδ) and inflammation (IL6, TNFα), in normal weight control women (BMI < 25 kg/m², n = 35) and moderately obese women (BMI 30–38 kg/m², n = 55). In SAT, ACC1, FAS and PPARα mRNA expression were significantly decreased in moderately obese women compared to controls. The downregulation reported in SAT was more pronounced when BMI increased. In VAT, lipogenic-related genes and PPARα were similar in both groups. Only PPARδ gene expression was significantly increased in moderately obese women. As far as inflammation is concerned, TNFα and IL6 were significantly increased in moderate obesity in both tissues. Our results indicate that there is a progressive downregulation in lipogenesis in SAT as BMI increases, which suggests that SAT decreases the synthesis of fatty acid de novo during the development of obesity, whereas in VAT lipogenesis remains active regardless of the degree of obesity.

In adult twins, visceral fat accumulation depends more on exceeding sex-specific adiposity thresholds than on genetics

OBJECTIVE

We recently reported sex-specific percent body fat (%BF) thresholds (males=23%, females=38%) above which, visceral adipose tissue (VAT) significantly increases. Using monozygotic (MZ) and dizygotic (DZ) twins, we examined the influence of genetics on regional fat distribution measured by dual-energy X-ray absorptiometry, above and below these sex-specific thresholds for VAT accumulation.

METHODS

Fifty-eight twin pairs (44 MZ, 14 DZ) were recruited from the University of Washington Twin Registry. Segmented linear regression was used to assess the threshold between VAT mass and %BF by sex and by zygosity. To assess the effect of genetics on VAT accumulation, Dunnett's T3 compared MZ and DZ pairs whether the twin pairs were both above the adiposity threshold or not.

RESULTS

%BF thresholds for VAT accumulation were identified (%BF: M=20.6%, F=39.4%). Zygosity-specific thresholds were not significantly different (p>0.05). If at least one twin was below threshold, DZ twins still exhibited greater within-pair differences than MZ pairs in %BF (p=0.023) but not VAT (p=0.121).

CONCLUSIONS

Using a twin study approach, we observed no difference by zygosity for the threshold as which VAT accumulates. Additionally, for the first time we observed that while total BF is influenced by genetics, VAT accumulation may depend more on whether a person's %BF is above their sex-specific adiposity threshold. These results suggest that there may not be a genetic predisposition for VAT accumulation but rather it is a result of a predisposition for total fat accumulation.

Interleukin-17A Gene Expression in Morbidly Obese Women

Data from recent studies conducted in rodent models and humans suggest that interleukin-17A (IL-17A) plays a role in the induction of inflammation in adipose tissue during obesity. The aim of this study was to assess the gene expression of IL-17A in adipose tissue of morbidly obese patients. We used RT-PCR to evaluate the expression of IL-17A and several adipo/cytokines in the visceral adipose tissue (VAT) and subcutaneous adipose tissue (SAT) of 10 normal-weight control women (BMI < 25 kg/m²) and 30 morbidly obese women (MO, BMI > 40 kg/m²). We measured serum levels of IL-17A and adipo/cytokines in MO and normal weight women. IL-17A expression was significantly higher in VAT than in SAT in MO patients (p = 0.0127). It was very low in normal-weight controls in both VAT and SAT tissues. We found positive correlations between IL-17A and IL-6, lipocalin-2 and resistin in VAT of MO patients. The circulating level of IL-17A was higher in the normal-weight group than the MO patients (p = 0.032), and it was significantly related to adiponectin and TNFRII levels. In conclusion, IL-17A expression in VAT is increased in morbidly obese women, which suggests a link between obesity and innate immunity in low-grade chronic inflammation in morbidly obese women.

Effect of Roux-en-Y gastric bypass-induced weight loss on the transcriptomic profiling of subcutaneous adipose tissue

BACKGROUND

The changes in the transcriptomic profiling of subcutaneous adipose tissue (SAT) when weight loss stabilizes after a Roux-en-Y gastric bypass (RYGB) are still largely unknown.

OBJECTIVES

To investigate the changes produced in SAT gene expression of morbidly obese women when their weight loss stabilizes 2 years after RYGB.

SETTING

University hospital.

METHODS

SAT biopsies of the periumbilical area were taken before and 2 years after RYGB. Gene expression levels were assessed by microarray analysis and significant differences in gene expression were validated by real-time quantitative polymerase chain reaction. The findings were also confirmed in an independent population of morbidly obese women.

RESULTS

Microarray analysis revealed that the overexpressed differentially expressed genes have a prominent role in the pathways involved in biosynthetic processes, especially lipid or carboxylic ones (stearoyl-Coenzyme A desaturase-1, fatty acid desaturase-1, fatty acid elongase-6, ATP citrate lyase, fatty acid synthase, lipin-1, monoacylglycerol O-acyltransferase, patatin-like phospholipase domain containing-3, phosphate cytidylyltransferase-2, cholesteryl ester transfer protein, transmembrane 7 superfamily member 2, pyruvate carboxylase, and glycogen synthase 2). Most of the underexpressed differentially expressed genes are related with immune system and inflammation processes (immune responses, response to stress, cell death, regulation of biological quality, immune effector process, the response to endogenous stimulus, and the response to other types of stimulus).

CONCLUSION

An improvement of the SAT inflammatory and immune profile and an induction of genes involved in the regulation of lipid metabolism are shown when weight loss stabilizes 2 years after RYGB. Most of the genes shown are clearly linked to obesity and other metabolic disorders.

Altered fatty acid metabolism-related gene expression in liver from morbidly obese women with non-alcoholic fatty liver disease

Lipid accumulation in the human liver seems to be a crucial mechanism in the pathogenesis and the progression of non-alcoholic fatty liver disease (NAFLD). We aimed to evaluate gene expression of different fatty acid (FA) metabolism-related genes in morbidly obese (MO) women with NAFLD. Liver expression of key genes related to de novo FA synthesis (LXRα, SREBP1c, ACC1, FAS), FA uptake and transport (PPARγ, CD36, FABP4), FA oxidation (PPARα), and inflammation (IL6, TNFα, CRP, PPARδ) were assessed by RT-qPCR in 127 MO women with normal liver histology (NL, n = 13), simple steatosis (SS, n = 47) and non-alcoholic steatohepatitis (NASH, n = 67). Liver FAS mRNA expression was significantly higher in MO NAFLD women with both SS and NASH compared to those with NL (p = 0.003, p = 0.010, respectively). Hepatic IL6 and TNFα mRNA expression was higher in NASH than in SS subjects (p = 0.033, p = 0.050, respectively). Interestingly, LXRα, ACC1 and FAS expression had an inverse relation with the grade of steatosis. These results were confirmed by western blot analysis. In conclusion, our results indicate that lipogenesis seems to be downregulated in advanced stages of SS, suggesting that, in this type of extreme obesity, the deregulation of the lipogenic pathway might be associated with the severity of steatosis.