Mechanisms of adipose tissue redistribution with rosiglitazone treatment in various adipose depots

Rosiglitazone-induced PPARγ activation promotes intramuscular adipocyte adipogenesis of pig

Intramuscular fat (IMF) positively influences various aspects of meat quality, while the subcutaneous fat (SF) has negative effect on carcass characteristics and fattening efficiency. Peroxisome proliferator-activated receptor gamma (PPARγ) is a key regulator of adipocyte differentiation, herein, through bioinformatic screen for the potential regulators of adipogenesis from two independent microarray datasets, we identified that PPARγ is a potentially regulator between porcine IMF and SF adipogenesis. Then we treated subcutaneous preadipocytes (SA) and intramuscular preadipocytes (IMA) of pig with RSG (1 µmol/L), and we found that RSG treatment promoted the differentiation of IMA via differentially activating PPARγ transcriptional activity. Besides, RSG treatment promoted apoptosis and lipolysis of SA. Meanwhile, by the treatment of conditioned medium, we excluded the possibility of indirect regulation of RSG from myocyte to adipocyte and proposed that AMPK may mediate the RSG-induced differential activation of PPARγ. Collectively, the RSG treatment promotes IMA adipogenesis, and advances SA lipolysis, this effect may be associated with AMPK-mediated PPARγ differential activation. Our data indicates that targeting PPARγ might be an effective strategy to promote intramuscular fat deposition while reduce subcutaneous fat mass of pig.

Adipose tissue and ovarian aging: Potential mechanism and protective strategies

Ovarian aging occurs approximately 10 years prior to the natural age-associated functional decline of other organ systems. With the increase of life expectancy worldwide, ovarian aging has gradually become a key health problem among women. Therefore, understanding the causes and molecular mechanisms of ovarian aging is very essential for the inhibition of age-related diseases and the promotion of health and longevity in women. Recently, studies have revealed an association between adipose tissue (AT) and ovarian aging. Alterations in the function and quantity of AT have profound consequences on ovarian function because AT is central for follicular development, lipid metabolism, and hormonal regulation. Moreover, the interplay between AT and the ovary is bidirectional, with ovary-derived signals directly affecting AT biology. In this review, we summarize the current knowledge of the complex molecular mechanisms controlling the crosstalk between the AT and ovarian aging, and further discuss how therapeutic targeting of the AT can delay ovarian aging.

Integrated expression profiles of mRNA and miRNA in a gerbil model of fatty liver fibrosis treated with exenatide

BACKGROUND

The morbidity of nonalcoholic fatty liver disease (NAFLD) has increased consistently in recent years. Exenatide could reverse liver fibrosis and lower the occurrence of fatty liver. The aim of the study was to identify and characterize mRNA and miRNA expression to elucidate the mechanism of exenatide in the gerbil model.

METHODS

Gerbils were fed a high-fat diet for 8 weeks to induce a fibrosis model; then, the gerbil models were treated with exenatide for 4 weeks. The total RNA extracted from the liver tissue samples was used to prepare the library and sequence on a HiSeq 2000. Bioinformatic methods were employed to analyze the sequence data to identify the mRNAs and miRNAs and to acquire the miRNA-mRNA regulatory network.

RESULTS

By RNA-seq, 2344 differentially expressed genes (DEGs) and 72 miRNAs were found in the model group. Compared with the model group, 591 DEGs and 19 miRNAs were found in the quercetin group, whereas 876 DEGs and 18 miRNAs were found in the treatment group. The miRNA-mRNA regulatory network was constructed in a gerbil model. Immunohistochemistry and RNA sequencing confirmed that the therapeutic effect of exenatide may be derived from extrahepatic signal transduction. The key differential genes are CYP3A, CYP4A11, ACAA1, ACSM, PHX1, MAO, FMO, UGT, ACOX2, ABAT, PIK3C and PLCG1. The key miRNAs are miR-15a, miR-27b, miR-532-3P, miR-627, miR-3596, miR-142-3P, Let-7e-5p, miR-214-5, miR-101-3p, miR-378d. New miRNAs, such as novel_127, novel_143, novel_15, novel_204 are associated with liver fibrosis, while novel_127, novel_15, and novel_54 are associated with reverse treated with exenatide.

CONCLUSIONS

Our research represents the first description of mRNA/miRNA profiles in a gerbil model of fatty liver fibrosis treated with exenatide, which may provide insights into the pathogenesis or treatment of the metabolic syndrome.

Editor's Highlight: Thy1 (CD90) Expression is Reduced by the Environmental Chemical Tetrabromobisphenol-A to Promote Adipogenesis Through Induction of microRNA-103

Environmental chemicals termed "obesogens" disrupt the endocrine system to promote adipogenesis and obesity. Tetrabromobisphenol-A (TBBPA) has been reported to increase adipogenesis; however, the mechanism(s) of action are unclear. Thy1 (CD90) is a glycophosphatidylinositol-anchored membrane protein that serves as a marker for stem cells and also plays an important role in regulating adipogenesis and obesity. We investigated whether or not TBBPA promotes adipogenesis in human and mouse cells by reducing Thy1 levels. We further sought to identify the molecular mechanism(s) whereby TBBPA targets Thy1 expression. Mouse and human cells were exposed to TBBPA, and Thy1 expression was analyzed using flow cytometry, Western blotting, and qPCR. We tested whether microRNAs predicted to target Thy1 (miR-103 and miR-107) were upregulated by TBBPA using quantitative PCR assays. We also determined if Thy1 mRNA was a bona fide miR-103/107 target. Our results show that Thy1 expression was reduced in both human and mouse cells after exposure to TBBPA. Both Thy1 mRNA and protein levels were decreased by low-dose TBBPA exposure. TBBPA reduced Thy1 levels and further increased adipogenesis when an adipogenic medium was used. Mechanistically, we show that miR-103 and miR-107 are induced by TBBPA and that miR-103 targets Thy1 to reduce its expression. Our results reveal for the first time that Thy1 is a target of TBBPA. Furthermore, our data support the concept that Thy1 is a key marker targeted by environmental chemicals that promote adipogenesis and obesity.

Gastrointestinal factors regulating lipid droplet formation in the intestine

Cytoplasmic lipid droplets (CLD) are considered as neutral lipid reservoirs, which protect cells from lipotoxicity. It became clear that these fascinating dynamic organelles play a role not only in energy storage and metabolism, but also in cellular lipid and protein handling, inter-organelle communication, and signaling among diverse functions. Their dysregulation is associated with multiple disorders, including obesity, liver steatosis and cardiovascular diseases. The central aim of this review is to highlight the link between intra-enterocyte CLD dynamics and the formation of chylomicrons, the main intestinal dietary lipid vehicle, after overviewing the morphology, molecular composition, biogenesis and functions of CLD.

Cancer cachexia differentially regulates visceral adipose tissue turnover

Cancer cachexia (CC) is a progressive metabolic syndrome that is marked by severe body weight loss. Metabolic disarrangement of fat tissues is a very early event in CC, followed by adipose tissue (AT) atrophy and remodelling. However, there is little information regarding the possible involvement of cellular turnover in this process. Thus, in this study, we evaluated the effect of CC on AT turnover and fibrosis of mesenteric (MEAT) and retroperitoneal (RPAT) adipose tissue depots as possible factors that contribute to AT atrophy. CC was induced by a subcutaneous injection of Walker tumour cells (2 × 10⁷) in Wistar rats, and control animals received only saline. The experimental rats were randomly divided into four experimental groups: 0 days, 4 days, 7 days and 14 days after injection. AT turnover was analysed according to the Pref1/Adiponectin ratio of gene expression from the stromal vascular fraction and pro-apoptotic CASPASE3 and CASPASE9 from MEAT and RPAT. Fibrosis was verified according to the total collagen levels and expression of extracellular matrix genes. AT turnover was verified by measurements of lipolytic protein expression. We found that the Pref1/Adiponectin ratio was decreased in RPAT (81.85%, P < 0.05) with no changes in MEAT compared with the respective controls. CASPASE3 and CASPASE9 were activated on day 14 only in RPAT. Collagen was increased on day 7 in RPAT (127%) and MEAT (4.3-fold). The Collagen1A1, Collagen3A1, Mmp2 and Mmp9 mRNA levels were upregulated only in MEAT in CC. Lipid turnover was verified in RPAT and was not modified in CC. We concluded that the results suggest that CC affects RPAT cellular turnover, which may be determinant for RPAT atrophy.

Taurine and vitamin E supplementations have minimal effects on body composition, hepatic lipids, and blood hormone and metabolite concentrations in healthy Sprague Dawley rats

BACKGROUND

As prescriptions for off-label pharmaceutical use and autonomous administration of over-the-counter nutraceuticals become mainstream, thorough assessments of these compounds are warranted.

OBJECTIVE

To determine the effects of gemfibrozil, rosiglitazone, metformin, taurine, and vitamin E on body composition, hepatic lipids, and metabolic hormone and blood metabolite concentrations in a healthy, outbred rat cohort.

METHODS

Male Sprague Dawley rats were fed a purified 10 kcal% from fat diet for 56 days and assigned to diet alone (control) or diet plus oral administration of gemfibrozil (34 mg/kg), metformin (500 mg/kg), rosiglitazone (3 mg/kg), taurine (520 mg/kg), or vitamin E (200 mg/kg).

RESULTS

Rosiglitazone administration resulted in a 56% increase in carcass adiposity, cautioning potential prescriptive off-label use. Taurine supplementation had no adverse effects on evaluated parameters. A modest but significant increase in liver triacylglycerol content was observed with vitamin E supplementation compared with control (Δ 17.2 g triacylglycerol/100 g liver lipid).

CONCLUSIONS

The evaluated pharmaceuticals had effects in a healthy population similar to the reported effects in their target population and the nutraceuticals had minimal effects on the measured physiological parameters.

Regional differences in perivascular adipose tissue impacting vascular homeostasis

Perivascular adipose tissue (PVAT) releases several important vasoactive factors with physiological and pathophysiological paracrine effects. A large body of evidence suggests regional phenotypic and functional differences among PVAT depots, depending on the specific vascular bed or different regions in the vascular bed where the PVAT is located. These non-uniform and separate PVATs exert various paracrine effects on vascular structure and function that largely impact disease states, such as endothelial dysfunction, atherosclerosis, or insulin resistance. This emerging view of PVAT function requires considering heterogeneous PVAT as a specialized organ that can differentially regulate vascular function depending on its anatomical location. In this context, the adipose-vascular axis may represent a novel target for pharmacological intervention in vasculopathy in cardiometabolic disorders.

Vaspin promotes 3T3-L1 preadipocyte differentiation

Vaspin, a novel adipocyte factor secreted from visceral adipose tissues, is associated with obesity and insulin resistance and can regulate glucose and lipid metabolism, increase insulin sensitivity, and suppress inflammation; however, the underlying mechanisms remain unknown. Proliferation and maladaptive differentiation are important pathological mechanisms underlying obesity. This study aimed to evaluate the effects of vaspin on the proliferation and differentiation of preadipocyte 3T3-L1 cells and to explore the likely mechanisms responsible for 3T3-L1 differentiation. Vaspin was added to cultured 3T3-L1 cells, and the differentiation of adipocytes was evaluated using Oil Red O staining. The AKT signaling pathway and specific differentiation factors related to the differentiation of preadipocyte 3T3-L1 cells, peroxisome proliferator-activated γ and the CCAAT/enhancer-binding protein (C/EBP) family, were evaluated using reverse transcription polymerase chain reaction (RT-PCR) and western blot analyses during the early phase of differentiation. Additionally, adiponectin mRNA, interleukin-6 mRNA (IL-6 mRNA), and glucose transporter-4 (GLUT4) protein levels were measured in the differentiated adipocytes. The results indicated that vaspin promotes the intracellular accumulation of lipids and increases differentiation-related factors, including peroxisome proliferator-activated receptor γ, C/EBPα, and free fatty acid-binding protein 4 (FABP4), in a dose-dependent manner. Additionally, vaspin (200 ng/mL) increased the mRNA and protein levels of C/EBPβ, peroxisome proliferator-activated γ, C/EBPα, and FABP4. Moreover, compared with the control, significantly smaller eight-day differentiated adipocytes were observed, and these cells exhibited decreased IL-6 mRNA and increased GLUT4 mRNA levels; these results also indicated the potential of vaspin to promote the insulin-mediated AKT signaling pathway during the early phase of differentiation. In conclusion, vaspin is able to promote the differentiation of 3T3-L1 preadipocytes and may increase their sensitivity to insulin and suppress obesity.

Glypican 4 may be involved in the adipose tissue redistribution in high-fat feeding C57BL/6J mice with peroxisome proliferators-activated receptor γ agonist rosiglitazone treatment

Fat distribution affects the risk of developing obesity-related chronic diseases. Glypican 4 (Gpc4) may be involved in the regulation of obesity and body fat distribution. The aim of the study was to explore whether Gpc4 affects fat accumulation and the possible mechanism. C57BL/6J mice were fed with a high-fat diet for eight weeks and treated with a peroxisome proliferators-activated receptor γ (PPARγ) agonist, rosiglitazone, for another four weeks. The weight of inguinal and epididymal fat pads was determined. The Gpc4 mRNA and protein expression and two probable regulators of the Gpc4 gene, specificity protein 1 (Sp1) and Sp3 mRNA, were also measured. Mice treated with rosiglitazone showed a significant increase in subcutaneous fat weight compared with the untreated mice. The expression of Gpc4 mRNA and protein was significantly higher in visceral than in subcutaneous fat in all the groups. Compared with untreated mice the expression of Gpc4 and Sp3 mRNA in subcutaneous fat and the expression of Sp1 and Sp3 mRNA in visceral fat in mice treated with rosiglitazone increased significantly. The Sp3/Sp1 ratio was consistent with the expression of Gpc4 mRNA and protein in subcutaneous and visceral fat. The present study indicated that Gpc4 may play an important role in fat distribution, and this effect is perhaps regulated by the ratio of Sp3/Sp1 in the subcutaneous and visceral fat tissues.

Effects of PPAR γ Agonist Pioglitazone on Redox-Sensitive Cellular Signaling in Young Spontaneously Hypertensive Rats

PPAR γ receptor plays an important role in oxidative stress response. Its agonists can influence vascular contractility in experimental hypertension. Our study was focused on the effects of a PPAR γ agonist pioglitazone (PIO) on blood pressure regulation, vasoactivity of vessels, and redox-sensitive signaling at the central (brainstem, BS) and peripheral (left ventricle, LV) levels in young prehypertensive rats. 5-week-old SHR were treated either with PIO (10 mg/kg/day, 2 weeks) or with saline using gastric gavage. Administration of PIO significantly slowed down blood pressure increase and improved lipid profile and aortic relaxation after insulin stimulation. A significant increase in PPAR γ expression was found only in BS, not in LV. PIO treatment did not influence NOS changes, but had tissue-dependent effect on SOD regulation and increased SOD activity, observed in LV. The treatment with PIO differentially affected also the levels of other intracellular signaling components: Akt kinase increased in the the BS, while β -catenin level was down-regulated in the BS and up-regulated in the LV. We found that the lowering of blood pressure in young SHR can be connected with insulin sensitivity of vessels and that β -catenin and SOD levels are important agents mediating PIO effects in the BS and LV.

Role of thiazolidinediones, insulin sensitizers, in non-alcoholic fatty liver disease

The prevalence of metabolic syndrome, obesity and insulin resistance has become an epidemic in the world. A strong association exists between metabolic syndrome and non-alcoholic fatty liver disease (NAFLD), though the etiology of NAFLD is still unclear. This close association leads to numerous clinical studies to investigate the effects of insulin sensitizers, thiazolidinediones (TZDs), on hepatic fat accumulation. Thiazolidinediones affect glucose and lipid metabolism in insulin-sensitive tissues, which in turn reduces the lipid content in the liver by modulating several mediators. In the present review, we discuss key modulators - adiponectin and sirtulin-adenosine monophosphate activated protein kinase signaling - as the mechanisms responsible for NAFLD related to metabolic syndrome.

Effect of 2,4-thiazolidinedione on limousin cattle growth and on muscle and adipose tissue metabolism

The main adipogenic transcription factor PPARγ possesses high affinity to 2,4-TZD, a member of the Thiazolidinedione family of insulin-sensitizing compounds used as adipogenic agents. We evaluated 2,4-TZD's effect on bovine growth and PPAR tissue expression. Seventeen Limousin bulls (18 month-old; 350 kg body weight (BW)) were assigned into 2 treatments: control and 2,4-TZD (8 mg/70 kg BW) and were fed until bulls reached 500 kg BW. They were weighed and their blood was sampled. DNA, RNA, and protein were determined in liver; skeletal muscle; subcutaneous (SC), omental, perirenal adipose tissues (AT) to determine protein synthesis rate and cellular size. Expression of PPAR mRNA was measured in liver and muscle (PPARα, -δ, and -γ) and SC adipose tissue (γ) by real-time PCR. No significant differences were found (P > 0.1) in weight gain, days on feed, and carcass quality. Muscle synthesis was greater in controls (P < 0.05); cell size was larger with 2,4-TZD (P < 0.05). PPARα, -δ, and -γ expressions with 2,4-TZD in liver were lower (P < 0.01) than in muscle. No differences were found for PPARγ mRNA expression in SCAT. The results suggest the potential use of 2,4-TZD in beef cattle diets, because it improves AT differentiation, liver, and muscle fatty acid oxidation that, therefore, might improve energy efficiency.

Diabetic nephropathy and long-term treatment effects of rosiglitazone and enalapril in obese ZSF1 rats

Diabetic nephropathy (DN) is a major cause of end-stage renal disease. Yet the pathogenic mechanisms underlying the development of DN are not fully defined, partially due to lack of suitable models that mimic the complex pathogenesis of renal disease in diabetic patients. In this study, we describe early and late renal manifestations of DN and renal responses to long-term treatments with rosiglitazone or high-dose enalapril in ZSF1 rats, a model of metabolic syndrome, diabetes, and chronic renal disease. At 8 weeks of age, obese ZSF1 rats developed metabolic syndrome and diabetes (hyperglycemia, glucosuria, hyperlipidemia, and hypertension) and early signs of renal disease (proteinuria, glomerular collagen IV deposition, tubulointerstitial inflammation, and renal hypertrophy). By 32 weeks of age, animals developed renal histopathology consistent with DN, including mesangial expansion, glomerulosclerosis, tubulointerstitial inflammation and fibrosis, tubular dilation and atrophy, and arteriolar thickening. Rosiglitazone markedly increased body weight but reduced food intake, improved glucose control, and attenuated hyperlipidemia and liver and kidney injury. In contrast, rosiglitazone markedly increased cardiac hypertrophy via a blood pressure-independent mechanism. High-dose enalapril did not improve glucose homeostasis, but normalized blood pressure, and nearly prevented diabetic renal injury. The ZSF1 model thus detects the clinical observations seen with rosiglitazone and enalapril in terms of primary and secondary endpoints of cardiac and renal effects. This and previous reports indicate that the obese ZSF1 rat meets currently accepted criteria for progressive experimental diabetic renal disease in rodents, suggesting that this may be the best available rat model for simulation of human DN.

Activation of peroxisome proliferator-activated receptor gamma by rosiglitazone increases sirt6 expression and ameliorates hepatic steatosis in rats

BACKGROUND

Sirt6 has been implicated in the regulation of hepatic lipid metabolism and the development of hepatic steatosis. The aim of this study was to address the potential role of Sirt6 in the protective effects of rosiglitazone (RGZ) on hepatic steatosis.

METHODS

To investigate the effect of RGZ on hepatic steatosis, rats were treated with RGZ (4 mg·kg⁻¹·day⁻¹) by stomach gavage for 6 weeks. The involvement of Sirt6 in the RGZ's regulation was evaluated by Sirt6 knockdown in AML12 mouse hepatocytes.

RESULTS

RGZ treatment ameliorated hepatic lipid accumulation and increased expression of Sirt6, peroxisome proliferator-activated receptor gamma coactivtor-1-α (Ppargc1a/PGC1-α) and Forkhead box O1 (Foxo1) in rat livers. AMP-activated protein kinase (AMPK) phosphorylation was also increased by RGZ, accompanied by alterations in phosphorylation of LKB1. Interestingly, in free fatty acid-treated cells, Sirt6 knockdown increased hepatocyte lipid accumulation measured as increased triglyceride contents (p = 0.035), suggesting that Sirt6 may be beneficial in reducing hepatic fat accumulation. In addition, Sirt6 knockdown abolished the effects of RGZ on hepatocyte fat accumulation, mRNA and protein expression of Ppargc1a/PGC1-α and Foxo1, and phosphorylation levels of LKB1 and AMPK, suggesting that Sirt6 is involved in RGZ-mediated metabolic effects.

CONCLUSION

Our results demonstrate that RGZ significantly decreased hepatic lipid accumulation, and that this process appeared to be mediated by the activation of the Sirt6-AMPK pathway. We propose Sirt6 as a possible therapeutic target for hepatic steatosis.

Hormone-sensitive lipase modulates adipose metabolism through PPARγ

Hormone-sensitive lipase (HSL) is rate limiting for diacylglycerol and cholesteryl ester hydrolysis in adipose tissue and essential for complete hormone-stimulated lipolysis. Gene expression profiling in HSL-/- mice suggests that HSL is important for modulating adipogenesis and adipose metabolism. To test whether HSL is required for the supply of intrinsic ligands for PPARγ for normal adipose differentiation, HSL-/- and wild-type (WT) littermates were fed normal chow (NC) and high-fat (HF) diets supplemented with or without rosiglitazone (200 mg/kg) for 16 weeks. Results show that supplementing rosiglitazone to an NC diet completely normalized the decreased body weight and adipose depots in HSL-/- mice. Additionally, rosiglitazone resulted in similar serum glucose, total cholesterol, FFA, and adiponectin values in WT and HSL-/- mice. Furthermore, rosiglitazone normalized the expression of genes involved in adipocyte differentiation, markers of adipocyte differentiation, and enzymes involved in triacylglycerol synthesis and metabolism, and cholesteryl ester homeostasis, in HSL-/- mice. Supplementing rosiglitazone to an HF diet resulted in improved glucose tolerance in both WT and HSL-/- animals and also partial normalization in HSL-/- mice of abnormal WAT gene expression, serum chemistries, organ and body weight changes. In vitro studies showed that adipocytes from WT animals can provide ligands for activation of PPARγ and that activation is further boosted following lipolytic stimulation, whereas adipocytes from HSL-/- mice displayed attenuated activation of PPARγ, with no change following lipolytic stimulation. These results suggest that one of the mechanisms by which HSL modulates adipose metabolism is by providing intrinsic ligands or pro-ligands for PPARγ.

Transplantation of adipose tissue and stem cells: role in metabolism and disease

Humans and other mammals have three main adipose tissue depots: visceral white adipose tissue, subcutaneous white adipose tissue and brown adipose tissue, each of which possesses unique cell-autonomous properties. In contrast to visceral adipose tissue, which can induce detrimental metabolic effects, subcutaneous white adipose tissue and brown adipose tissue have the potential to benefit metabolism by improving glucose homeostasis and increasing energy consumption. In addition, adipose tissue contains adipose-derived stem cells, which possess the ability to differentiate into multiple lineages, a property that might be of value for the repair or replacement of various damaged cell types. Adipose tissue transplantation has primarily been used as a tool to study physiology and for human reconstructive surgery. Transplantation of adipose tissue is, however, now being explored as a possible tool to promote the beneficial metabolic effects of subcutaneous white adipose tissue and brown adipose tissue, as well as adipose-derived stem cells. Ultimately, the clinical applicability of adipose tissue transplantation for the treatment of obesity and metabolic disorders will reside in the achievable level of safety, reliability and efficacy compared with other treatments.