The Adipose Transcriptional Response to Insulin Is Determined by Obesity, Not Insulin Sensitivity

Advances in biomedical applications of vitamin D for VDR targeted management of obesity and cancer

BACKGROUND

1,25(OH)2D3 is a fat-soluble vitamin, involved in regulating Ca2+ homeostasis in the body. Its storage in adipose tissue depends on the fat content of the body. Obesity is the result of abnormal lipid deposition due to the prolonged positive energy balance and increases the risk of several cancer types. Furthermore, it has been associated with vitamin D deficiency and defined as a low 25(OH)2D3 blood level. In addition, 1,25(OH)2D3 plays vital roles in Ca2+-Pi and glucose metabolism in the adipocytes of obese individuals and regulates the expressions of adipogenesis-associated genes in mature adipocytes.

SCOPE AND APPROACH

The present contribution focused on the VDR mediated mechanisms interconnecting the obese condition and cancer proliferation due to 1,25(OH)2D3-deficiency in humans. This contribution also summarizes the identification and development of molecular targets for VDR-targeted drug discovery.

KEY FINDINGS AND CONCLUSIONS

Several studies have revealed that cancer development in a background of 1,25(OH)2D3 deficient obesity involves the VDR gene. Moreover, 1,25(OH)2D3 is also known to influence several cellular processes, including differentiation, proliferation, and adhesion. The multifaceted physiology of obesity has improved our understanding of the cancer therapeutic targets. However, currently available anti-cancer drugs are notorious for their side effects, which have raised safety issues. Thus, there is interest in developing 1,25(OH)2D3-based therapies without any side effects.

The subcutaneous adipose transcriptome identifies a molecular signature of insulin resistance shared with visceral adipose

OBJECTIVE

The objective of this study was to identify the transcriptional landscape of insulin resistance (IR) in subcutaneous adipose tissue (SAT) in humans across the spectrum of obesity.

METHODS

We used SAT RNA sequencing in 220 individuals with metabolic phenotyping.

RESULTS

We identified a 35-gene signature with high predictive accuracy for homeostatic model of IR that was expressed across a variety of non-immune cell populations. We observed primarily "protective" IR associations for adipocyte transcripts and "deleterious" associations for macrophage transcripts, as well as a high concordance between SAT and visceral adipose tissue (VAT). Multiple SAT genes exhibited dynamic expression 5 years after weight loss surgery and with insulin stimulation. Using available expression quantitative trait loci in SAT and/or VAT, we demonstrated similar genetic effect sizes of SAT and VAT on type 2 diabetes and BMI.

CONCLUSIONS

SAT is conventionally viewed as a metabolic buffer for lipid deposition during positive energy balance, whereas VAT is viewed as a dominant contributor to and prime mediator of IR and cardiometabolic disease risk. Our results implicate a dynamic transcriptional architecture of IR that resides in both immune and non-immune populations in SAT and is shared with VAT, nuancing the current VAT-centric concept of IR in humans.

Dual Role of Caspase 8 in Adipocyte Apoptosis and Metabolic Inflammation

Caspases are cysteine-aspartic proteases that were initially discovered to play a role in apoptosis. However, caspase 8, in particular, also has additional nonapoptotic roles, such as in inflammation. Adipocyte cell death and inflammation are hypothesized to be initiating pathogenic factors in type 2 diabetes. Here, we examined the pleiotropic role of caspase 8 in adipocytes and obesity-associated insulin resistance. Caspase 8 expression was increased in adipocytes from mice and humans with obesity and insulin resistance. Treatment of 3T3-L1 adipocytes with caspase 8 inhibitor Z-IETD-FMK decreased both death receptor-mediated signaling and targets of nuclear factor κ-light-chain-enhancer of activated B (NF-κB) signaling. We generated novel adipose tissue and adipocyte-specific caspase 8 knockout mice (aP2Casp8-/- and adipoqCasp8-/-). Both males and females had improved glucose tolerance in the setting of high-fat diet (HFD) feeding. Knockout mice also gained less weight on HFD, with decreased adiposity, adipocyte size, and hepatic steatosis. These mice had decreased adipose tissue inflammation and decreased activation of canonical and noncanonical NF-κB signaling. Furthermore, they demonstrated increased energy expenditure, core body temperature, and UCP1 expression. Adipocyte-specific activation of Ikbkb or housing mice at thermoneutrality attenuated improvements in glucose tolerance. These data demonstrate an important role for caspase 8 in mediating adipocyte cell death and inflammation to regulate glucose and energy homeostasis.

ARTICLE HIGHLIGHTS

Caspase 8 is increased in adipocytes from mice and humans with obesity and insulin resistance. Knockdown of caspase 8 in adipocytes protects mice from glucose intolerance and weight gain on a high-fat diet. Knockdown of caspase 8 decreases Fas signaling, as well as canonical and noncanonical nuclear factor κ-light-chain-enhancer of activated B (NF-κB) signaling in adipose tissue. Improved glucose tolerance occurs via reduced activation of NF-κB signaling and via induction of UCP1 in adipocytes.

An integrated single cell and spatial transcriptomic map of human white adipose tissue

To date, single-cell studies of human white adipose tissue (WAT) have been based on small cohort sizes and no cellular consensus nomenclature exists. Herein, we performed a comprehensive meta-analysis of publicly available and newly generated single-cell, single-nucleus, and spatial transcriptomic results from human subcutaneous, omental, and perivascular WAT. Our high-resolution map is built on data from ten studies and allowed us to robustly identify >60 subpopulations of adipocytes, fibroblast and adipogenic progenitors, vascular, and immune cells. Using these results, we deconvolved spatial and bulk transcriptomic data from nine additional cohorts to provide spatial and clinical dimensions to the map. This identified cell-cell interactions as well as relationships between specific cell subtypes and insulin resistance, dyslipidemia, adipocyte volume, and lipolysis upon long-term weight changes. Altogether, our meta-map provides a rich resource defining the cellular and microarchitectural landscape of human WAT and describes the associations between specific cell types and metabolic states.

The Role of Molecular and Hormonal Factors in Obesity and the Effects of Physical Activity in Children

Obesity and overweight are defined as abnormal fat accumulations. Adipose tissue consists of more than merely adipocytes; each adipocyte is closely coupled with the extracellular matrix. Adipose tissue stores excess energy through expansion. Obesity is caused by the abnormal expansion of adipose tissue as a result of adipocyte hypertrophy and hyperplasia. The process of obesity is controlled by several molecules, such as integrins, kindlins, or matrix metalloproteinases. In children with obesity, metabolomics studies have provided insight into the existence of unique metabolic profiles. As a result of low-grade inflammation in the system, abnormalities were observed in several metabolites associated with lipid, carbohydrate, and amino acid pathways. In addition, obesity and related hormones, such as leptin, play an instrumental role in regulating food intake and contributing to childhood obesity. The World Health Organization states that physical activity benefits the heart, the body, and the mind. Several noncommunicable diseases, such as cardiovascular disease, cancer, and diabetes, can be prevented and managed through physical activity. In this work, we reviewed pediatric studies that examined the molecular and hormonal control of obesity and the influence of physical activity on children with obesity or overweight. The purpose of this review was to examine some orchestrators involved in this disease and how they are related to pediatric populations. A larger number of randomized clinical trials with larger sample sizes and long-term studies could lead to the discovery of new key molecules as well as the detection of significant factors in the coming years. In order to improve the health of the pediatric population, omics analyses and machine learning techniques can be combined in order to improve treatment decisions.

Associations between subcutaneous adipocyte hypertrophy and nonalcoholic fatty liver disease

Adipocyte hypertrophy and expression of adipokines in subcutaneous adipose tissue (SAT) have been linked to steatosis, nonalcoholic steatohepatitis (NASH) and fibrosis in morbidly obese (BMI ≥ 40 kg/m²) subjects. It is unknown if this is also true for subjects with NAFLD with lesser degrees of obesity (BMI < 35 kg/m²). Thirty-two subjects with biopsy-proven NAFLD and 15 non-diabetic controls matched for BMI underwent fine-needle biopsies of SAT. Adipocyte volume was calculated. RNA-sequencing of SAT was performed in a subset of 20 NAFLD patients. Adipocyte volume and gene expression levels were correlated to the presence of NASH or significant fibrosis. Subjects with NAFLD had larger adipocyte volume compared with controls, (1939 pL, 95% CI 1130-1662 vs. 854 pL, 95% CI 781-926, p < 0.001). There was no association between adipocyte volume and the presence of NASH. Gene expression of adipokines previously described to correlate with NASH in morbid obesity, was not associated with NASH or fibrosis. Our results suggest that persons with NAFLD have larger SAT adipocytes compared with controls and that adipocytes are involved in the pathophysiology of hepatic steatosis in NAFLD. However, adipocyte volume was not associated with NASH or fibrosis in NAFLD subjects with varying degrees of obesity.

Visceral Adipose Tissue Molecular Networks and Regulatory microRNA in Pediatric Obesity: An In Silico Approach

Childhood obesity carries an increased risk of metabolic complications, sleep disturbances, and cancer. Visceral adiposity is independently associated with inflammation and insulin resistance in obese children. However, the underlying pathogenic mechanisms are still unclear. We aimed to detect the gene expression pattern and its regulatory network in the visceral adipose tissue of obese pediatric individuals. Using differentially-expressed genes (DEGs) identified from two publicly available datasets, GSE9624 and GSE88837, we performed functional enrichment, protein-protein interaction, and network analyses to identify pathways, targeting transcription factors (TFs), microRNA (miRNA), and regulatory networks. There were 184 overlapping DEGs with six significant clusters and 19 candidate hub genes. Furthermore, 24 TFs targeted these hub genes. The genes were regulated by miR-16-5p, miR-124-3p, miR-103a-3p, and miR-107, the top miRNA, according to a maximum number of miRNA-mRNA interaction pairs. The miRNA were significantly enriched in several pathways, including lipid metabolism, immune response, vascular inflammation, and brain development, and were associated with prediabetes, diabetic nephropathy, depression, solid tumors, and multiple sclerosis. The genes and miRNA detected in this study involve pathways and diseases related to obesity and obesity-associated complications. The results emphasize the importance of the TGF-β signaling pathway and its regulatory molecules, the immune system, and the adipocytic apoptotic pathway in pediatric obesity. The networks associated with this condition and the molecular mechanisms through which the potential regulators contribute to pathogenesis are open to investigation.

Insulin resistance rewires the metabolic gene program and glucose utilization in human white adipocytes

BACKGROUND

In obesity, adipose tissue dysfunction resulting from excessive fat accumulation leads to systemic insulin resistance (IR), the underlying alteration of Type 2 Diabetes. The specific pathways dysregulated in dysfunctional adipocytes and the extent to which it affects adipose metabolic functions remain incompletely characterized.

METHODS

We interrogated the transcriptional adaptation to increased adiposity in association with insulin resistance in visceral white adipose tissue from lean men, or men presenting overweight/obesity (BMI from 19 to 33) and discordant for insulin sensitivity. In human adipocytes in vitro, we investigated the direct contribution of IR in altering metabolic gene programming and glucose utilization using ¹³C-isotopic glucose tracing.

RESULTS

We found that gene expression associated with impaired glucose and lipid metabolism and inflammation represented the strongest association with systemic insulin resistance, independently of BMI. In addition, we showed that inducing IR in mature human white adipocytes was sufficient to reprogram the transcriptional profile of genes involved in important metabolic functions such as glycolysis, the pentose phosphate pathway and de novo lipogenesis. Finally, we found that IR induced a rewiring of glucose metabolism, with higher incorporation of glucose into citrate, but not into downstream metabolites within the TCA cycle.

CONCLUSIONS

Collectively, our data highlight the importance of obesity-derived insulin resistance in impacting the expression of key metabolic genes and impairing the metabolic processes of glucose utilization, and reveal a role for metabolic adaptation in adipose dysfunction in humans.

Spatial mapping reveals human adipocyte subpopulations with distinct sensitivities to insulin

The contribution of cellular heterogeneity and architecture to white adipose tissue (WAT) function is poorly understood. Herein, we combined spatially resolved transcriptional profiling with single-cell RNA sequencing and image analyses to map human WAT composition and structure. This identified 18 cell classes with unique propensities to form spatially organized homo- and heterotypic clusters. Of these, three constituted mature adipocytes that were similar in size, but distinct in their spatial arrangements and transcriptional profiles. Based on marker genes, we termed these Adipo^LEP, Adipo^PLIN, and Adipo^SAA. We confirmed, in independent datasets, that their respective gene profiles associated differently with both adipocyte and whole-body insulin sensitivity. Corroborating our observations, insulin stimulation in vivo by hyperinsulinemic-euglycemic clamp showed that only Adipo^PLIN displayed a transcriptional response to insulin. Altogether, by mining this multimodal resource we identify that human WAT is composed of three classes of mature adipocytes, only one of which is insulin responsive.

Human White Adipose Tissue Displays Selective Insulin Resistance in the Obese State

Selective hepatic insulin resistance is a feature of obesity and type 2 diabetes. Whether similar mechanisms operate in white adipose tissue (WAT) of those with obesity and to what extent these are normalized by weight loss are unknown. We determined insulin sensitivity by hyperinsulinemic euglycemic clamp and insulin response in subcutaneous WAT by RNA sequencing in 23 women with obesity before and 2 years after bariatric surgery. To control for effects of surgery, women postsurgery were matched to never-obese women. Multidimensional analyses of 138 samples allowed us to classify the effects of insulin into three distinct expression responses: a common set was present in all three groups and included genes encoding several lipid/cholesterol biosynthesis enzymes; a set of obesity-attenuated genes linked to tissue remodeling and protein translation was selectively regulated in the two nonobese states; and several postobesity-enriched genes encoding proteins involved in, for example, one-carbon metabolism were only responsive to insulin in the women who had lost weight. Altogether, human WAT displays a selective insulin response in the obese state, where most genes are normalized by weight loss. This comprehensive atlas provides insights into the transcriptional effects of insulin in WAT and may identify targets to improve insulin action.

Molecular pathways behind acquired obesity: Adipose tissue and skeletal muscle multiomics in monozygotic twin pairs discordant for BMI

Tissue-specific mechanisms prompting obesity-related development complications in humans remain unclear. We apply multiomics analyses of subcutaneous adipose tissue and skeletal muscle to examine the effects of acquired obesity among 49 BMI-discordant monozygotic twin pairs. Overall, adipose tissue appears to be more affected by excess body weight than skeletal muscle. In heavier co-twins, we observe a transcriptional pattern of downregulated mitochondrial pathways in both tissues and upregulated inflammatory pathways in adipose tissue. In adipose tissue, heavier co-twins exhibit lower creatine levels; in skeletal muscle, glycolysis- and redox stress-related protein and metabolite levels remain higher. Furthermore, metabolomics analyses in both tissues reveal that several proinflammatory lipids are higher and six of the same lipid derivatives are lower in acquired obesity. Finally, in adipose tissue, but not in skeletal muscle, mitochondrial downregulation and upregulated inflammation are associated with a fatty liver, insulin resistance, and dyslipidemia, suggesting that adipose tissue dominates in acquired obesity.

Multiomics analyses of adipose tissue and skeletal muscle in BMI-discordant twins

Excess body weight downregulates mitochondrial pathways in both tissues

Excess body weight upregulates proinflammatory pathways in both tissues

Adipose tissue alterations are associated with metabolic health in acquired obesity

Metabolic Health Status Contributes to Transcriptome Alternation in Human Visceral Adipose Tissue During Obesity

OBJECTIVE

BMI is a well-established factor affecting the transcriptome profile of adipose tissue, but there are few reports on the relationship between the metabolic health status of people with obesity and the transcriptional changes, particularly in visceral adipose tissue.

METHODS

Visceral adipose tissue was collected from three subgroups of patients, lean (n = 11), metabolically healthy obesity (MHO; n = 22), and metabolically unhealthy obesity (MUO; n = 26), and RNA sequencing was conducted to profile the transcriptome changes between these groups in a pairwise manner.

RESULTS

Comparing MUO with lean and comparing MHO with lean revealed similar patterns in gene expression and pathway changes: obesity, regardless of metabolic health, was associated with upregulated inflammatory pathways. However, the inflammatory signature in MUO was stronger than in MHO. Pairwise comparisons among MUO, MHO, and lean samples identified 34 common differentially expressed genes; 12 out of 34 genes were associated with inflammatory pathways and exhibited a gradually increased expression pattern in the order of lean, MHO, and MUO.

CONCLUSIONS

This study reveals not only that BMI plays an important role in determining the gene expression profile in visceral adipose tissue but also that a metabolically healthy condition is associated with a less inflammatory transcriptional change during obesity.

Implications of metabolism-driven myeloid dysfunctions in cancer therapy

Immune homeostasis is maintained by an adequate balance of myeloid and lymphoid responses. In chronic inflammatory states, including cancer, this balance is lost due to dramatic expansion of myeloid progenitors that fail to mature to functional inflammatory neutrophils, macrophages, and dendritic cells (DCs), thus giving rise to a decline in the antitumor effector lymphoid response. Cancer-related inflammation orchestrates the production of hematopoietic growth factors and cytokines that perpetuate recruitment and activation of myeloid precursors, resulting in unresolved and chronic inflammation. This pathologic inflammation creates profound alterations in the intrinsic cellular metabolism of the myeloid progenitor pool, which is amplified by competition for essential nutrients and by hypoxia-induced metabolic rewiring at the tumor site. Therefore, persistent myelopoiesis and metabolic dysfunctions contribute to the development of cancer, as well as to the severity of a broad range of diseases, including metabolic syndrome and autoimmune and infectious diseases. The aims of this review are to (1) define the metabolic networks implicated in aberrant myelopoiesis observed in cancer patients, (2) discuss the mechanisms underlying these clinical manifestations and the impact of metabolic perturbations on clinical outcomes, and (3) explore new biomarkers and therapeutic strategies to restore immunometabolism and differentiation of myeloid cells towards an effector phenotype to increase host antitumor immunity. We propose that the profound metabolic alterations and associated transcriptional changes triggered by chronic and overactivated immune responses in myeloid cells represent critical factors influencing the balance between therapeutic efficacy and immune-related adverse effects (irAEs) for current therapeutic strategies, including immune checkpoint inhibitor (ICI) therapy.

Mechanisms of insulin resistance related to white, beige, and brown adipocytes

BACKGROUND

The diminished glucose lowering effect of insulin in obesity, called "insulin resistance," is associated with glucose intolerance, type 2 diabetes, and other serious maladies. Many publications on this topic have suggested numerous hypotheses on the molecular and cellular disruptions that contribute to the syndrome. However, significant uncertainty remains on the mechanisms of its initiation and long-term maintenance.

SCOPE OF REVIEW

To simplify insulin resistance analysis, this review focuses on the unifying concept that adipose tissue is a central regulator of systemic glucose homeostasis by controlling liver and skeletal muscle metabolism. Key aspects of adipose function related to insulin resistance reviewed are: 1) the modes by which specific adipose tissues control hepatic glucose output and systemic glucose disposal, 2) recently acquired understanding of the underlying mechanisms of these modes of regulation, and 3) the steps in these pathways adversely affected by obesity that cause insulin resistance.

MAJOR CONCLUSIONS

Adipocyte heterogeneity is required to mediate the multiple pathways that control systemic glucose tolerance. White adipocytes specialize in sequestering triglycerides away from the liver, muscle, and other tissues to limit toxicity. In contrast, brown/beige adipocytes are very active in directly taking up glucose in response to β adrenergic signaling and insulin and enhancing energy expenditure. Nonetheless, white, beige, and brown adipocytes all share the common feature of secreting factors and possibly exosomes that act on distant tissues to control glucose homeostasis. Obesity exerts deleterious effects on each of these adipocyte functions to cause insulin resistance.

Anti-Lipolysis Induced by Insulin in Diverse Pathophysiologic Conditions of Adipose Tissue

As an important energy reservoir, adipose tissue maintains lipid balance and regulates energy metabolism. When the body requires energy, adipocytes provide fatty acids to peripheral tissues through lipolysis. Insulin plays an important role in regulating normal fatty acid levels by inhibiting lipolysis. When the morphology of adipose tissue is abnormal, its microenvironment changes and the lipid metabolic balance is disrupted, which seriously impairs insulin sensitivity. As the most sensitive organ to respond to insulin, lipolysis levels in adipose tissue are affected by impaired insulin function, which results in serious metabolic diseases. However, the specific underlying mechanisms of this process have not yet been fully elucidated, and further study is required. The purpose of this review is to discuss the effects of adipose tissue on the anti-lipolysis process triggered by insulin under different conditions. In particular, the functional changes of this process respond to inconsonantly morphological changes of adipose tissue.

CAGEfightR: analysis of 5'-end data using R/Bioconductor

BACKGROUND

5'-end sequencing assays, and Cap Analysis of Gene Expression (CAGE) in particular, have been instrumental in studying transcriptional regulation. 5'-end methods provide genome-wide maps of transcription start sites (TSSs) with base pair resolution. Because active enhancers often feature bidirectional TSSs, such data can also be used to predict enhancer candidates. The current availability of mature and comprehensive computational tools for the analysis of 5'-end data is limited, preventing efficient analysis of new and existing 5'-end data.

RESULTS

We present CAGEfightR, a framework for analysis of CAGE and other 5'-end data implemented as an R/Bioconductor-package. CAGEfightR can import data from BigWig files and allows for fast and memory efficient prediction and analysis of TSSs and enhancers. Downstream analyses include quantification, normalization, annotation with transcript and gene models, TSS shape statistics, linking TSSs to enhancers via co-expression, identification of enhancer clusters, and genome-browser style visualization. While built to analyze CAGE data, we demonstrate the utility of CAGEfightR in analyzing nascent RNA 5'-data (PRO-Cap). CAGEfightR is implemented using standard Bioconductor classes, making it easy to learn, use and combine with other Bioconductor packages, for example popular differential expression tools such as limma, DESeq2 and edgeR.

CONCLUSIONS

CAGEfightR provides a single, scalable and easy-to-use framework for comprehensive downstream analysis of 5'-end data. CAGEfightR is designed to be interoperable with other Bioconductor packages, thereby unlocking hundreds of mature transcriptomic analysis tools for 5'-end data. CAGEfightR is freely available via Bioconductor: bioconductor.org/packages/CAGEfightR .

Insulin action is severely impaired in adipocytes of apparently healthy overweight and obese subjects

OBJECTIVE

Many overweight/obese subjects appear metabolically healthy with normal in vivo insulin sensitivity. Still, they have increased long-term risk of developing type 2 diabetes. We hypothesized that adipose tissue dysfunction involving decreased insulin action in adipocytes is present in apparently healthy overweight/obese subjects.

DESIGN/METHODS

Subjects with normal metabolic health according to Adult Treatment Panel-III or Framingham risk score criteria were subdivided into 67 lean, 32 overweight and 37 obese according to body mass index. They were compared with 200 obese individuals with metabolic syndrome. Insulin sensitivity and maximum action on inhibition of lipolysis and stimulation of lipogenesis was determined in subcutaneous adipocytes. Gene expression was determined by micro-array and qPCR. DNA methylation was assessed by array, pyrosequencing and reporter assays.

RESULTS

Compared with lean, adipocytes in overweight/obese displayed marked reductions in insulin sensitivity in both antilipolysis and lipogenesis as well as an attenuated maximum lipogenic response. Among these, only antilipolysis sensitivity correlated with whole-body insulin sensitivity. These differences were already evident in the overweight state, were only slightly worse in the unhealthy obese state and were not related to fat cell size. Adipose tissue analyses linked this to reduced expression of the insulin signalling protein AKT2, which associated with increased methylation at regulatory sites in the AKT2 promoter.

CONCLUSIONS

Apparently healthy subjects have severely disturbed adipocyte insulin signalling already in the overweight state which involves epigenetic dysregulation of AKT2. This may constitute an early defect in insulin action that appears even upon modest increases in fat mass.

Silencing an insulin-induced lncRNA, LncASIR, impairs the transcriptional response to insulin signalling in adipocytes

Long noncoding RNA(lncRNA)s are new regulators governing the metabolism in adipose tissue. In this study, we aimed to understand how lncRNAs respond to insulin signalling and explore whether lncRNAs have a functional role in insulin signalling pathway. We treated primary adipocyte cultures with insulin and collected RNA for RNA-sequencing to profile the non-coding transcriptome changes, through which we identified a top Adipose Specific Insulin Responsive LncRNA (LncASIR). To determine its biological function, we knocked down LncASIR using dcas9-KRAB, followed by RNA-seq to examine the effect on insulin-induced gene expression program. We identified a set of lncRNAs regulated by insulin signalling pathway. LncASIR is transcribed from a super enhancer region and responds robustly to insulin treatment. Silencing LncASIR resulted in an impaired global insulin-responsive gene program. LncASIR is a novel and integral component in the insulin signalling pathway in adipocytes.

Neurohormonal signaling via a sulfotransferase antagonizes insulin-like signaling to regulate a Caenorhabditis elegans stress response

Insulin and insulin-like signaling regulates a broad spectrum of growth and metabolic responses to a variety of internal and environmental stimuli. For example, the inhibition of insulin-like signaling in C. elegans mediates its response to both osmotic stress and starvation. We report that in response to osmotic stress the cytosolic sulfotransferase SSU-1 antagonizes insulin-like signaling and promotes developmental arrest. Both SSU-1 and the DAF-16 FOXO transcription factor, which is activated when insulin signaling is low, are needed to drive specific responses to reduced insulin-like signaling. We demonstrate that SSU-1 functions in a single pair of sensory neurons to control intercellular signaling via the nuclear hormone receptor NHR-1 and promote both the specific transcriptional response to osmotic stress and altered lysophosphatidylcholine metabolism. Our results show the requirement of a sulfotransferase-nuclear hormone receptor neurohormonal signaling pathway for some but not all consequences of reduced insulin-like signaling.

Glucose tolerance and insulin sensitivity define adipocyte transcriptional programs in human obesity

OBJECTIVE

Although debated, metabolic health characterizes 10-25% of obese individuals and reduces risk of developing life-threatening co-morbidities. Adipose tissue is a recognized endocrine organ important for the maintenance of whole-body metabolic health. Adipocyte transcriptional signatures of healthy and unhealthy obesity are largely unknown.

METHODS

Here, we used a small cohort of highly characterized obese individuals discordant for metabolic health, characterized their adipocytes transcriptional signatures, and cross-referenced them to mouse phenotypic and human GWAs databases.

RESULTS AND CONCLUSIONS

Our study showed that glucose intolerance and insulin resistance co-operate to remodel adipocyte transcriptome. We also identified the Nuclear Export Mediator Factor (NEMF) and the Ectoderm-Neural Cortex 1 (ENC1) as novel potential targets in the management of metabolic health in human obesity.

Retinoid X Receptor Activation During Adipogenesis of Female Mesenchymal Stem Cells Programs a Dysfunctional Adipocyte

Early life exposure to endocrine-disrupting chemicals (EDCs) is an emerging risk factor for the development of obesity and diabetes later in life. We previously showed that prenatal exposure to the EDC tributyltin (TBT) results in increased adiposity in the offspring. These effects linger into adulthood and are propagated through successive generations. TBT activates two nuclear receptors, the peroxisome proliferator-activated receptor (PPAR) γ and its heterodimeric partner retinoid X receptor (RXR), that promote adipogenesis in vivo and in vitro. We recently employed a mesenchymal stem cell (MSC) model to show that TBT promotes adipose lineage commitment by activating RXR, not PPARγ. This led us to consider the functional consequences of PPARγ vs RXR activation in developing adipocytes. We used a transcriptomal approach to characterize genome-wide differences in MSCs differentiated with the PPARγ agonist rosiglitazone (ROSI) or TBT. Pathway analysis suggested functional deficits in TBT-treated cells. We then compared adipocytes differentiated with ROSI, TBT, or a pure RXR agonist IRX4204 (4204). Our data show that RXR activators ("rexinoids," 4204 and TBT) attenuate glucose uptake, blunt expression of the antidiabetic hormone adiponectin, and fail to downregulate proinflammatory and profibrotic transcripts, as does ROSI. Finally, 4204 and TBT treatment results in an inability to induce markers of adipocyte browning, in part due to sustained interferon signaling. Taken together, these data implicate rexinoids in the development of dysfunctional white adipose tissue that could potentially exacerbate obesity and/or diabetes risk in vivo. These data warrant further screening and characterization of EDCs that activate RXR.

Metabolic syndrome, leptin-insulin resistance and uric acid: a trinomial foe for Algerian city-dweller adolescents' health

Background Adolescence is one of the critical periods where increased risk for long-term obesity-related complications is an important health concern. This highlights the need to perform early diagnostics based on precise biomarkers to decrease the risk of complications in adolescents with obesity. Objective To determine the relationships between serum levels of uric acid (UA), leptin and insulin with metabolic syndrome (MS) components in Algerian adolescents. Subjects Nondiabetic adolescents (n = 204). Methods Blood pressure (BP) and anthropometric measurements were performed using standardized techniques. Blood samples were taken for determination of glycemia, triglyceridemia, uricemia, cholesterolemia, leptinemia and insulinemia. Results The rate of MS among an excess weight group was 17.4% [95% confidence interval (CI)]. Serum levels of UA, leptin and insulin were significantly higher in the excess weight group compared to a normal weight group (279.4 ± 86.05 vs. 204.9 ± 50.34 μmol/L and 25.65 ± 14.01 vs. 4.09 ± 2.60 μg/L, p < 0.001; 24.58 ± 13.85 vs. 13.34 ± 6.41 μIU/L, p < 0.05). Serum levels of UA, leptin and insulin were significantly higher in adolescents with MS compared to those without MS (304.86 ± 111.41 vs. 224.72 ± 77.81 μmol/L, 30.26 ± 12.46 vs. 16.93 ± 14.97 μg/L and 30.91 ± 17.30 vs. 18.71 ± 10.14 μIU/L, p < 0.05, respectively). Significant correlations were found between UA and leptin with waist circumference (r = 0.50 and 0.76), diastolic blood pressure (r = 0.58 and 0.43), triglycerides (r = 0.42 and 0.35) and high-density lipoprotein-cholesterol (r = -0.36 and -0.35). Conclusion Serum levels of UA and leptin may be useful biomarkers for early diagnosis of the risk of MS in our Algerian adolescent population.

Long Non-Coding RNAs Associated with Metabolic Traits in Human White Adipose Tissue

Long non-coding RNAs (lncRNAs) belong to a recently discovered class of molecules proposed to regulate various cellular processes. Here, we systematically analyzed their expression in human subcutaneous white adipose tissue (WAT) and found that a limited set was differentially expressed in obesity and/or the insulin resistant state. Two lncRNAs herein termed adipocyte-specific metabolic related lncRNAs, ASMER-1 and ASMER-2 were enriched in adipocytes and regulated by both obesity and insulin resistance. Knockdown of either ASMER-1 or ASMER-2 by antisense oligonucleotides in in vitro differentiated human adipocytes revealed that both genes regulated adipogenesis, lipid mobilization and adiponectin secretion. The observed effects could be attributed to crosstalk between ASMERs and genes within the master regulatory pathways for adipocyte function including PPARG and INSR. Altogether, our data demonstrate that lncRNAs are modulators of the metabolic and secretory functions in human fat cells and provide an emerging link between WAT and common metabolic conditions.

Long-Term Improvement in Aortic Pulse Wave Velocity After Weight Loss Can Be Predicted by White Adipose Tissue Factors

BACKGROUND

Arterial stiffness, measured by pulse wave velocity (PWV), is linked to obesity, cardiovascular disease, and all-cause mortality. Short-term weight loss improves PWV, but the long-term effects are unknown. We investigated the effect of pronounced long-term weight loss on PWV and whether anthropometric/metabolic parameters and/or white adipose tissue (WAT) phenotype could predict this change in PWV.

METHODS

Eighty-two obese subjects were examined before and 2 years after Roux-en-Y gastric bypass. Analyses included anthropometrics, routine clinical chemistry, and hyperinsulinemic-euglycemic clamp. Arterial stiffness was measured as aortic PWV (aPWV) using the Arteriograph device. WAT mass and distribution were assessed by dual-X-ray absorptiometry. Baseline visceral and subcutaneous WAT samples were obtained to measure adipocyte cell size. Transcriptomic profiling of subcutaneous WAT was performed in a subset of subjects (n = 30).

RESULTS

At the 2-year follow-up, there were significant decreases in body mass index (39.4 ± 3.5 kg/m2 vs. 26.6 ± 3.4 kg/m2; P < 0.0001) and aPWV (7.8 ± 1.5 m/s vs. 7.2 ± 1.4 m/s; P = 0.006). Multiple regression analyses showed that baseline subcutaneous adipocyte volume was associated with a reduction in aPWV (P = 0.014), after adjusting for confounders. Expression analyses of 52 genes implicated in arterial stiffness showed that only one, COL4A1, independently predicted improvements in aPWV after adjusting for confounders (P = 0.006).

CONCLUSIONS

Bariatric surgery leads to long-term reduction in aPWV. This improvement can be independently predicted by subcutaneous adipocyte volume and WAT COL4A1 expression, which suggests that subcutaneous WAT has a role in regulating aPWV.

CLINICAL TRIALS REGISTRATION

Trial Number NCT01727245 (clinicaltrials.gov).

Transcriptional Regulatory Mechanisms in Adipose and Muscle Tissue Associated with Composite Glucometabolic Phenotypes

OBJECTIVE

Tissue-specific gene expression is associated with individual metabolic measures. However, these measures may not reflect the true but latent underlying biological phenotype. This study reports gene expression associations with multidimensional glucometabolic characterizations of obesity, glucose homeostasis, and lipid traits.

METHODS

Factor analysis was computed by using orthogonal rotation to construct composite phenotypes (CPs) from 23 traits in 256 African Americans without diabetes. Genome-wide transcript expression data from adipose and muscle were tested for association with CPs, and expression quantitative trait loci (eQTLs) were identified by associations between cis-acting single-nucleotide polymorphisms (SNPs) and gene expression.

RESULTS

The factor analysis identified six CPs. CPs 1 through 6 individually explained 34%, 12%, 9%, 8%, 6%, and 5% of the variation in 23 glucometabolic traits studied. There were 3,994 and 929 CP-associated transcripts identified in adipose and muscle tissue, respectively; CP2 had the largest number of associated transcripts. Pathway analysis identified multiple canonical pathways from the CP-associated transcripts. In adipose and muscle, significant cis-eQTLs were identified for 558 and 164 CP-associated transcripts (q-value < 0.01), respectively.

CONCLUSIONS

Adipose and muscle transcripts comprehensively define pathways involved in regulating glucometabolic disorders. Cis-eQTLs for CP-associated genes may act as primary causal determinants of glucometabolic phenotypes by regulating transcription of key genes.

APMAP interacts with lysyl oxidase-like proteins, and disruption of Apmap leads to beneficial visceral adipose tissue expansion

Adipocyte plasma membrane-associated protein (APMAP) has been described as an adipogenic factor in 3T3-L1 cells with unknown biochemical function; we therefore aimed to investigate the physiologic function of APMAP in vivo We generated Apmap-knockout mice and challenged them with an obesogenic diet to investigate their metabolic phenotype. We identified a novel truncated adipocyte-specific isoform of APMAP in mice that is produced by alternative transcription. Mice lacking the full-length APMAP protein, the only isoform that is expressed in humans, have an improved metabolic phenotype upon diet-induced obesity, indicated by enhanced insulin sensitivity, preserved glucose tolerance, increased respiratory exchange ratio, decreased inflammatory marker gene expression, and reduced adipocyte size. At the molecular level, APMAP interacts with the extracellular collagen cross-linking matrix proteins lysyl oxidase-like 1 and 3. On a high-fat diet, the expression of lysyl oxidase-like 1 and 3 is strongly decreased in Apmap-knockout mice, paralleled by reduced expression of profibrotic collagens and total collagen content in epididymal white adipose tissue, indicating decreased fibrotic potential. Together, our data suggest that APMAP is a novel regulator of extracellular matrix components, and establish that APMAP is a potential target to mitigate obesity-associated insulin resistance.-Pessentheiner, A. R., Huber, K., Pelzmann, H. J., Prokesch, A., Radner, F. P. W., Wolinski, H., Lindroos-Christensen, J., Hoefler, G., Rülicke, T., Birner-Gruenberger, R., Bilban, M., Bogner-Strauss, J. G. APMAP interacts with lysyl oxidase-like proteins, and disruption of Apmap leads to beneficial visceral adipose tissue expansion.

Global transcriptome profiling identifies KLF15 and SLC25A10 as modifiers of adipocytes insulin sensitivity in obese women

Although the mechanisms linking obesity to insulin resistance (IR) and type 2 diabetes (T2D) are not entirely understood, it is likely that alterations of adipose tissue function are involved. The aim of this study was to identify new genes controlling insulin sensitivity in adipocytes from obese women with either insulin resistant (OIR) or sensitive (OIS) adipocytes. Insulin sensitivity was first determined by measuring lipogenesis in isolated adipocytes from abdominal subcutaneous white adipose tissue (WAT) in a large observational study. Lipogenesis was measured under conditions where glucose transport was the rate limiting step and reflects in vivo insulin sensitivity. We then performed microarray-based transcriptome profiling on subcutaneous WAT specimen from a subgroup of 9 lean, 21 OIS and 18 obese OIR women. We could identify 432 genes that were differentially expressed between the OIR and OIS group (FDR ≤5%). These genes are enriched in pathways related to glucose and amino acid metabolism, cellular respiration, and insulin signaling, and include genes such as SLC2A4, AKT2, as well as genes coding for enzymes in the mitochondria respiratory chain. Two IR-associated genes, KLF15 encoding a transcription factor and SLC25A10 encoding a dicarboxylate carrier, were selected for functional evaluation in adipocytes differentiated in vitro. Knockdown of KLF15 and SLC25A10 using siRNA inhibited insulin-stimulated lipogenesis in adipocytes. Transcriptome profiling of siRNA-treated cells suggested that KLF15 might control insulin sensitivity by influencing expression of PPARG, PXMP2, AQP7, LPL and genes in the mitochondrial respiratory chain. Knockdown of SLC25A10 had only modest impact on the transcriptome, suggesting that it might directly influence insulin sensitivity in adipocytes independently of transcription due to its important role in fatty acid synthesis. In summary, this study identifies novel genes associated with insulin sensitivity in adipocytes in women independently of obesity. KFL15 and SLC25A10 are inhibitors of insulin-stimulated lipogenesis under conditions when glucose transport is the rate limiting step.

Regulators of mitochondrial quality control differ in subcutaneous fat of metabolically healthy and unhealthy obese monkeys

OBJECTIVE

Obesity exists with and without accompanying cardiometabolic disease, termed metabolically unhealthy obesity (MUO) and healthy obesity (MHO), respectively. Underlying differences in the ability of subcutaneous (SQ) fat to respond to nutrient excess are emerging as a key pathway. This study aimed to document the first spontaneous animal model of MHO and MUO and differences in SQ adipose tissue.

METHODS

Vervet monkeys (Chlorocebus aethiops; N = 171) were screened for metabolic syndrome. A subset of MHO and MUO monkeys (n = 6/group) had SQ fat biopsies collected for histological evaluations and examination of key mitochondrial proteins.

RESULTS

Obesity was seen in 20% of monkeys, and within this population, 31% were healthy, which mirrors human prevalence estimates. MUO monkeys had more than 60% lower adiponectin concentrations despite similar fat cell size, uncoupling protein 3, and activated macrophage abundance. However, alternatively activated/anti-inflammatory macrophages were 70% lower. Deficiencies of 50% or more in mitochondrial quality control regulators and selected mitochondrial fission and fusion markers were observed in the SQ fat of MUO monkeys despite comparable mitochondrial content.

CONCLUSIONS

A novel and translatable spontaneously obese animal model of MHO and MUO, occurring independently of dietary factors, was characterized. Differences in mitochondrial quality and inflammatory cell populations of subcutaneous fat may underpin divergent metabolic health.

Metabolic Vascular Syndrome: New Insights into a Multidimensional Network of Risk Factors and Diseases

BACKGROUND

Since 1981, we have used the term metabolic syndrome to describe an association of a dysregulation in lipid metabolism (high triglycerides, low high-density lipoprotein cholesterol, disturbed glucose homeostasis (enhanced fasting and/or prandial glucose), gout, and hypertension), with android obesity being based on a common soil (overnutrition, reduced physical activity, sociocultural factors, and genetic predisposition). We hypothesized that main traits of the syndrome occur early and are tightly connected with hyperinsulinemia/insulin resistance, procoagulation, and cardiovascular diseases.

METHODS

To establish a close link between the traits of the metabolic vascular syndrome, we focused our literature search on recent original work and comprehensive reviews dealing with the topics metabolic syndrome, visceral obesity, fatty liver, fat tissue inflammation, insulin resistance, atherogenic dyslipidemia, arterial hypertension, and type 2 diabetes mellitus.

RESULTS

Recent research supports the concept that the metabolic vascular syndrome is a multidimensional and interactive network of risk factors and diseases based on individual genetic susceptibility and epigenetic changes where metabolic dysregulation/metabolic inflexibility in different organs and vascular dysfunction are early interconnected.

CONCLUSION

The metabolic vascular syndrome is not only a risk factor constellation but rather a life-long abnormality of a closely connected interactive cluster of developing diseases which escalate each other and should continuously attract the attention of every clinician.