Nutritional regulation of adipose tissue lipoprotein lipase is blunted in insulin resistant rats

Background  

Hypertriglyceridemia is a common lipid abnormality accompanying insulin resistance. This study was designed to assess the contribution of dysregulation of adipose tissue lipoprotein lipase (LPL) activity to the hypertriglyceridemia in a rat model of insulin resistance.     

Differences in the inflammatory response induced by acute pancreatitis in different white adipose tissue sites in the rat

Background

There is increasing evidence of the role of adipose tissue on the systemic effects of acute pancreatitis. Patients with higher body mass index have increased risk of local and systemic complications and patients with android fat distribution and higher waist circumference are at greater risk for developing the severe form of the disease. Here we evaluated the changes on different areas of adipose tissue and its involvement on the inflammatory response in an experimental model of acute pancreatitis.

Methods

Pancreatitis was induced in male Wistar rats by intraductal administration of sodium taurocholate. Orlistat was administered to inhibit lipase activity. Activation of peritoneal macrophages was evaluated by measuring IL1β and TNFα expression. Inflammation was evaluated by measuring myeloperoxidase activity in mesenteric, epididymal and retroperitoneal areas of adipose tissue. Changes in the expression of inflammatory mediator in these areas of adipose tissue were also evaluated by RT-PCR.

Results

Pancreatitis induces the activation of peritoneal macrophages and a strong inflammatory response in mesenteric and epididymal sites of adipose tissue. By contrast, no changes were found in retroperitoneal adipose tissue. Inhibition of lipase prevented the activation of macrophages and the local inflammation in adipose tissue.

Conclusions

Our results confirm the involvement of adipose tissue on the progression of systemic inflammatory response during acute pancreatitis. However, there is a considerable diversity in different adipose tissue sites. These differences need to be taken into account in order to understand the progression from local pancreatic damage to systemic inflammation during acute pancreatitis.     

MicroRNA Regulation of Adipose Derived Stem Cells in Aging Rats

Background

Perturbations in abdominal fat secreted adipokines play a key role in metabolic syndrome. This process is further altered during the aging process, probably due to alterations in the preadipocytes (aka. stromal vascular fraction cells-SVF cells or adipose derived stem cells-ASCs) composition and/or function. Since microRNAs regulate genes involved both in development and aging processes, we hypothesized that the impaired adipose function with aging is due to altered microRNA regulation of adipogenic pathways in SVF cells.

Methodology and Principal Findings

Alterations in mRNA and proteins associated with adipogenic differentiation (ERK5 and PPARg) but not osteogenic (RUNX2) pathways were observed in SVF cells isolated from visceral adipose tissue with aging (6 to 30 mo) in female Fischer 344 x Brown Norway Hybrid (FBN) rats. The impaired differentiation capacity with aging correlated with altered levels of miRNAs involved in adipocyte differentiation (miRNA-143) and osteogenic pathways (miRNA-204). Gain and loss of function studies using premir or antagomir-143 validated the age associated adipocyte dysfunction.

Conclusions and Significance

Our studies for the first time indicate a role for miRNA mediated regulation of SVF cells with aging. This discovery is important in the light of the findings that dysfunctional adipose derived stem cells contribute to age related chronic diseases.     

Functional neural differentiation of human adipose tissue-derived stem cells using bFGF and forskolin

Background  

Adult mesenchymal stem cells (MSCs) derived from adipose tissue have the capacity to differentiate into mesenchymal as well as endodermal and ectodermal cell lineage in vitro. We characterized the multipotent ability of human adipose tissue-derived stem cells (hADSCs) as MSCs and investigated the neural differentiation potential of these cells.     

Small RNA sequencing reveals miR-642a-3p as a novel adipocyte-specific microRNA and miR-30 as a key regulator of human adipogenesis

Background  

In severe obesity, as well as in normal development, the growth of adipose tissue is the result of an increase in adipocyte size and numbers, which is underlain by the stimulation of adipogenic differentiation of precursor cells. A better knowledge of the pathways that regulate adipogenesis is therefore essential for an improved understanding of adipose tissue expansion. As microRNAs (miRNAs) have a critical role in many differentiation processes, our study aimed to identify the role of miRNA-mediated gene silencing in the regulation of adipogenic differentiation.     

Medium‐Chain Oil Reduces Fat Mass and Down‐regulates Expression of Adipogenic Genes in Rats

Objective: To test the hypothesis that adipose tissue could be one of the primary targets through which medium‐chain fatty acids (MCFAs) exert their metabolic influence. Research Methods and Procedures: Sprague‐Dawley rats were fed a control high‐fat diet compared with an isocaloric diet rich in medium‐chain triglycerides (MCTs). We determined the effects of MCTs on body fat mass, plasma leptin and lipid levels, acyl chain composition of adipose triglycerides and phospholipids, adipose tissue lipoprotein lipase activity, and the expression of key adipogenic genes. Tissue triglyceride content was measured in heart and gastrocnemius muscle, and whole body insulin sensitivity and glucose tolerance were also measured. The effects of MCFAs on lipoprotein lipase activity and adipogenic gene expression were also assessed in vitro using cultured adipose tissue explants or 3T3‐L1 adipocytes. Results: MCT‐fed animals had smaller fat pads, and they contained a considerable amount of MCFAs in both triglycerides and phospholipids. A number of key adipogenic genes were down‐regulated, including peroxisome proliferator activated receptor γ and CCAAT/enhancer binding protein α and their downstream metabolic target genes. We also found reduced adipose tissue lipoprotein lipase activity and improved insulin sensitivity and glucose tolerance in MCT‐fed animals. Analogous effects of MCFAs on adipogenic genes were found in cultured rat adipose tissue explants and 3T3‐L1 adipocytes. Discussion: These results suggest that direct inhibitory effects of MCFAs on adiposity may play an important role in the regulation of body fat development.     

IL-6 Indirectly Modulates the Induction of Glyceroneogenic Enzymes in Adipose Tissue during Exercise

Background

Glyceroneogenesis is an important step in the control of fatty acid re-esterification with PEPCK and PDK4 being identified as key enzymes in this process. We have previously shown that glyceroneogenic enzymes such as PDK4 are rapidly induced in white adipose tissue during exercise. Recent studies have suggested that IL-6 regulates adipose tissue metabolism and gene expression during exercise. Interestingly, IL-6 has been reported to directly decrease PEPCK expression. The purpose of this investigation was to determine the role of IL-6 in modulating the effects of exercise on the expression of glyceroneogenic enzymes in mouse adipose tissue. We hypothesized that the exercise-mediated induction of PDK4 and PEPCK would be greater in adipose tissue from IL-6 deficient mice compared to wild type controls.

Methodology and Principle Findings

Treatment of cultured epididymal adipose tissue (eWAT) with IL-6 (150 ng/ml) increased the phosphorylation of AMPK, ACC and STAT3 and induced SOCS3 mRNA levels while decreasing PEPCK and PDK4 mRNA. AICAR decreased the expression of PDK4 and PEPCK. The activation of AMPK by IL-6 was independent of increases in lipolysis. An acute bout of treadmill running (15 meters/minute, 5% incline, 90 minutes) did not induce SOCS3 or increase phosphorylation of STAT3 in eWAT, indicating that IL-6 signalling was not activated. Exercise-induced increases in PEPCK and PDK4 mRNA expression were attenuated in eWAT from IL-6^−/− mice in parallel with a greater relative increase in AMPK phosphorylation compared to exercised WT mice. These changes occurred independent of alterations in beta-adrenergic signalling in adipose tissue from IL-6^−/− mice.

Conclusions and Significance

Our findings question the role of IL-6 signalling in adipose tissue during exercise and suggest an indirect effect of this cytokine in the regulation of adipose tissue gene expression during exercise.     

Bio-informatics analysis of a gene co-expression module in adipose tissue containing the diet-responsive gene <Emphasis Type="Italic">Nnat</Emphasis>

Background  

Obesity causes insulin resistance in target tissues - skeletal muscle, adipose tissue, liver and the brain. Insulin resistance predisposes to type-2 diabetes (T2D) and cardiovascular disease (CVD). Adipose tissue inflammation is an essential characteristic of obesity and insulin resistance. Neuronatin (Nnat) expression has been found to be altered in a number of conditions related to inflammatory or metabolic disturbance, but its physiological roles and regulatory mechanisms in adipose tissue, brain, pancreatic islets and other tissues are not understood.     

S‐Glutathionylation of hepatic and visceral adipose proteins decreases in obese rats

A number of clinical and biochemical studies demonstrate that obesity and insulin resistance are associated with increases in oxidative stress and inflammation. Paradoxically, insulin sensitivity can be enhanced by oxidative inactivation of cysteine residues of phosphatases, and inflammation can be reduced by S‐glutathionylation with formation of protein‐glutathione mixed disulfides (PSSG). Although oxidation of protein‐bound thiols (PSH) is increased in multiple diseases, it is not known whether there are changes in PSH oxidation species in obesity.

Objective:

In this work, the hypothesis that obesity is associated with decreased levels of proteins containing oxidized protein thiols was tested.

Design and Methods:

The tissue levels of protein sulfenic acids (PSOH) and PSSG in liver, visceral adipose tissue, and skeletal muscle derived from glucose intolerant, obese‐prone Sprague‐Dawley rats were examined.

Results:

The data in this study indicate that decreases in PSSG content occurred in liver (44%) and adipose (26%) but not skeletal muscle in obese rats that were fed a 45% fat‐calorie diet versus lean rats that were fed a 10% fat‐calorie diet. PSOH content did not change in the tissue between the two groups. The activity of the enzyme glutaredoxin (GLRX) responsible for reversal of PSSG formation did not change in muscle and liver between the two groups. However, levels of GLRX1 were elevated 70% in the adipose tissue of the obese, 45% fat calorie‐fed rats.

Conclusion:

These are the first data to link changes in S‐glutathionylation and GLRX1 to adipose tissue in the obese and demonstrate that redox changes in thiol status occur in adipose tissue as a result of obesity.     

Upper and Lower Body Adipose Tissue Function: A Direct Comparison of Fat Mobilization in Humans

Objectives: Fat in the lower body is not associated with the same risk of cardiovascular disease as fat in the upper body. Is this explained by differences in the physiological functioning of the two depots? This study had two objectives: 1) to determine whether fat mobilization and blood flow differ between gluteal and abdominal adipose tissues in humans, and 2) to develop a new technique to assess gluteal adipose tissue function directly. Research Methods and Procedures: We performed detailed in vivo studies of adipose tissue function involving the assessment of fat mobilization by measurement of adipose tissue blood flows, arterio‐venous differences of metabolites across each depot, and gene expression in tissue biopsies in a small‐scale physiological study. Results: Gluteal adipose tissue has a lower blood flow (67% lower, p < 0.05) and lower hormone‐sensitive lipase rate of action (87% lower, p < 0.05) than abdominal adipose tissue. Lipoprotein lipase rate of action and mRNA expression are not different between the depots. This is the first demonstration of a novel technique to directly investigate gluteal adipose tissue metabolism. Discussion: Direct assessment of fasting adipose tissue metabolism in defined depots show that the buttock is metabolically “silent” in terms of fatty acid release compared with the abdomen.     

Circulating levels of persistent organic pollutants in relation to visceral and subcutaneous adipose tissue by abdominal MRI

Objective:

We and others have shown relationships between circulating levels of persistent organic pollutants (POPs) and different measures of obesity in both cross‐sectional and prospective studies. Since viscerally located fat seems to be the most harmful type, we investigated whether plasma POP levels were more closely related to visceral adipose tissue (VAT) than to subcutaneous adipose tissue (SAT).

Design and Methods:

Thousand hundred and sixteen subjects aged 70 years were investigated in the Prospective Investigation of the Vasculature in Uppsala Seniors (PIVUS) study; 23 POPs were analyzed using high‐resolution gas chromatography/high‐resolution mass spectrometry. Abdominal magnetic resonance imaging, measuring VAT and SAT, respectively, was performed in a representative subsample of 287 subjects.

Results:

The less chlorinated polychlorinated biphenyl (PCB) congeners (105 and 118), and the pesticides dichlorodiphenyldichloroethylene (DDE), hexachlorobenzene (HCB), and trans‐nonachlordane (TNC) were positively related to both VAT and SAT, whereas the more highly chlorinated PCBs (153, 156, 157, 169, 170, 180, 194, 206, and 209) were inversely related to both VAT and SAT. PCB189 was related to the VAT/SAT ratio in an inverted U‐shaped manner (P = 0.0008).

Conclusions:

In conclusion, the results were in accordance with our previous studies using waist circumference and fat mass as obesity measure. However, the novel finding that PCB189 was related to the VAT/SAT ratio deserves further investigation since exposure to this PCB congener, which has previously been linked to diabetes development, might thereby play a role in the distribution of abdominal adipose tissue.     

Application of a sensitive collection heuristic for very large protein families: Evolutionary relationship between adipose triglyceride lipase (ATGL) and classic mammalian lipases

Background  

Manually finding subtle yet statistically significant links to distantly related homologues becomes practically impossible for very populated protein families due to the sheer number of similarity searches to be invoked and analyzed. The unclear evolutionary relationship between classical mammalian lipases and the recently discovered human adipose triglyceride lipase (ATGL; a patatin family member) is an exemplary case for such a problem.     

Hormones and triacylglycerol metabolism under normoxic and ischemic conditions

Summary Fatty acids, the preferred substrate in normoxic myocardium, are derived from either exogenous or endogenous triacylglycerols. The supply of exogenous fatty acids is dependent of the rate of lipolysis in adipose tissue and of the lipoprotein lipase activity at the coronary vascular endothelium. A large part of the liberated fatty acids is reesterified with glycerol-3-phosphate and converted to triacylglycerols. Endogenous lipolysis and lipogenesis are intracellular compartmentalized multienzyme processes of which individual hormone-sensitive steps have been demonstrated in adipose tissue. The triacylglycerol lipase is the rate-limiting enzyme of lipolysis and glycerol-3-phosphate acyltransferase and possibly phosphatidate phosphohydrolase are the rate-limiting enzymes of lipogenesis. The hormonal regulation of both processes in heart is still a matter of dispute. Triacylglycerol lipase activity in myocardial tissue has two intracellular sources: 1, the endoplasmic reticular and soluble neutral lipase, and 2. the lysosomal acid lipase. Studies in our laboratory have indicated that whereas lipolysis is enhanced during global ischemia and anoxia, overall lipolytic enzyme activities in heart homogenates were not altered. In addition we were unable to demonstrate alterations in tissue triacylglycerol content and glycerol-3-phosphate acyltransferase activity under these conditions. Lipolysis, is subject to feedback inhibition by product fatty acids. Therefore all processes leading to an increased removal of fatty acids from the catalytic site of the lipase will stimulate lipolysis. These studies will be reviewed. In addition, studies from our department have demonstrated the capacity of myocardial lysosomes to take up and degrade added triacylglycerol-particles in vitro. Such a process, stimulated by Ca²⁺ and stimulated by acidosis, offers another physiological target for hormone actions.     

TNF-α involvement in insulin resistance induced by experimental scorpion envenomation

Background

Scorpion venom induces systemic inflammation characterized by an increase in cytokine release and chemokine production. There have been few experimental studies assessing the effects of scorpion venom on adipose tissue function in vivo.

Methodology/Principal Findings

To study the adipose tissue inflammation (ATI) induced by Androctonus australis hector (Aah) venom and to assess possible mechanisms of ATI, mice (n = 6, aged 1 month) were injected with Aah (0.45 mg/kg), toxic fraction of Aah (FTox-G50; 0.2 mg/kg) or saline solution (control). Inflammatory responses were evaluated by ELISA and cell sorting analyses in adipose tissue 45 minutes and 24 hours after injection. Quantitative real-time PCR was used to assess the regulation of genes implicated in glucose uptake. The titers of selected inflammatory cytokines (IL-1β, IL-6 and TNF-α) were also determined in sera and in insulin target tissues. The serum concentration of IL-1β rose 45 minutes after envenomation and returned to basal level after 24 hours. The pathophysiological effects of the venom after 24 hours mainly involved M1-proinflammatory macrophage infiltration in adipose tissue combined with high titers of IL-1β, IL-6 and TNF-α. Indeed, TNF-α was strongly induced in both adipose tissue and skeletal muscle. We studied the effects of Aah venom on genes implicated in insulin-stimulated glucose uptake. Insulin induced a significant increase in the expression of the mRNAs for hexokinase 2 and phosphatidylinositol 3-kinase in both skeletal muscle and adipose tissue in control mice; this upregulation was completely abolished after 24 hours in mice envenomed with Aah or FTox-G50.

Conclusions/Significance

Our findings suggest that Aah venom induces insulin resistance by mechanisms involving TNF-α-dependent Map4k4 kinase activation in the adipose tissue.     

Adipose Tissue CIDEA Is Associated,Independently of Weight Variation,to Change in Insulin Resistance during a Longitudinal Weight Control Dietary Program in Obese Individuals

Aim

Weight loss reduces risk factors associated with obesity. However, long-term metabolic improvement remains a challenge. We investigated quantitative gene expression of subcutaneous adipose tissue in obese individuals and its relationship with low calorie diet and long term weight maintenance induced changes in insulin resistance.

Research Design

Three hundred eleven overweight and obese individuals followed a dietary protocol consisting of an 8-week low calorie diet followed by a 6-month ad libitum weight-maintenance diet. Individuals were clustered according to insulin resistance trajectories assessed using homeostasis model assessment of insulin resistance (HOMA-IR) index. Adipose tissue mRNA levels of 267 genes selected for regulation according to obesity, metabolic status and response to dieting was assessed using high throughput RT-qPCR. A combination of discriminant analyses was used to identify genes with regulation according to insulin resistance trajectories. Partial correlation was used to control for change in body mass index.

Results

Three different HOMA-IR profile groups were determined. HOMA-IR improved during low calorie diet in the 3 groups. At the end of the 6-month follow-up, groups A and B had reduced HOMA-IR by 50%. In group C, HOMA-IR had returned to baseline values. Genes were differentially expressed in the adipose tissue of individuals according to groups but a single gene, CIDEA, was common to all phases of the dietary intervention. Changes in adipose tissue CIDEA mRNA levels paralleled variations in insulin sensitivity independently of change in body mass index. Overall, CIDEA was up-regulated in adipose tissue of individuals with successful long term insulin resistance relapse and not in adipose tissue of unsuccessful individuals.

Conclusion

The concomitant change in adipose tissue CIDEA mRNA levels and insulin sensitivity suggests a beneficial role of adipose tissue CIDEA in long term glucose homeostasis, independently of weight variation.

Trial Registration

ClinicalTrials.gov {"type":"clinical-trial","attrs":{"text":"NCT00390637","term_id":"NCT00390637"}}NCT00390637