Genetics and Epigenetics

CIDEC/FSP27 and PLIN1 gene expression run in parallel to mitochondrial genes in human adipose tissue, both increasing after weight loss

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Abstract

Objective:

FSP27 KO mice showed enhanced expression of mitochondrial genes, increased mitochondrial activity and smaller lipid droplets. Here, we aimed to investigate lipid droplet protein (CIDEC/FSP27 and perilipinA (PLIN1)) gene expression in human adipose tissue in association with obesity, insulin resistance and mitochondrial gene expression.

Design and subjects:

In cohort 1, CIDEC/FSP27, PLIN1, adipogenic (FASN, ACACA, PPARG, GLUT4) and mitochondrial (PPARGC1A, PPARGC1B, TFAM, MT-CO3) gene expression were analyzed in 171 adipose tissue samples (88 visceral adipose tissue (VAT) and 83 subcutaneous adipose tissue (SAT) depots) and in a time course experiment in human subcutaneous and visceral preadipocytes using real-time PCR. In cohort 2, the effects of bariatric surgery-induced weight loss were also evaluated in six caucasian morbidly obese women. Additionally, in cohort 2 FSP27 and PLIN1 protein levels were measured using western blotting.

Results:

CIDEC/FSP27 (1.03±0.52 vs 0.49±0.23 relative gene expression unit (R.U.), P<0.0001) and PLIN1 (1.32±0.82 vs 0.63±0.42 R.U., P<0.0001) gene were significantly more expressed in SAT than in VAT. In VAT, CIDEC/FSP27 and PLIN1 gene expression decreased with body mass index, percent fat mass, fasting glucose, fasting insulin, HOMA and were positively associated with adipogenic (PPARG, GLUT4, FASN and ACACA) and mitochondrial biogenesis (PPARGC1A, PPARGC1B, TFAM and MT-CO3)-related genes. Mitochondrial gene expression increased during adipocyte differentiation in parallel to FSP27 and PLIN1 and other adipogenic genes. After bariatric surgery-induced weight loss, PLIN1 and CIDEC/FSP27 gene and protein expression in SAT increased significantly in parallel to adipogenic and mitochondrial genes.

Conclusion:

These findings suggest a positive functional interaction between CIDEC/FSP27, PLIN1 and mitochondrial biogenesis-related genes in human adipose tissue.

Introduction

Adipose tissue has a central role in the management of systemic energy stores (storing and mobilizing triglycerides), as well as in regulating whole-body metabolism and glucose homeostasis.1 Adipocytes can hypothetically protect muscle and liver from the deleterious effects of circulating fatty acids by their large capacity to esterify them into triglycerides and to sequester them within lipid droplets. It has been increasingly recognized that fat storage is tightly linked to lipolysis and fat oxidation.

The efficiency and capacity of adipocytes to esterify fatty acids into triglycerides is a controlled process within large lipid droplets surrounded by a phospholipids layer and lipid droplet-associated proteins.2 The study of the biology of these proteins has disclosed unsuspected mechanisms. For instance, CIDEC/FSP27 is known to promote triglyceride accumulation and to regulate negatively lipolysis.3, 4 When this protein was genetically deleted (FSP27 KO mice), white adipose tissue acquired properties of brown adipose tissue, with enhanced expression of mitochondrial genes, increased mitochondrial activity and smaller lipid droplets.5 Otherwise, the overexpression of another lipid-associated protein, perilipin A (PLIN1) in white adipose tissue led to an increased expression of genes associated with fatty acid β-oxidation and heat production such as PPARGC1A and UCP1, resulting in increased mitochondrial biogenesis and activity. Overexpression of PLIN1 also led to decrease expression of genes associated with lipid synthesis.6

The discordant relationships of FSP27 and perilipin A with mitochondrial genes, as found in animal models, have not been evaluated in human adipose tissue and may have important clinical implications.

Previous studies described the positive association of whole-body insulin sensitivity with CIDEC/FSP27 gene expression in human adipose tissue from obese subjects.7 In fact, a homozygous nonsense mutation in CIDEC was recently linked to partial lipodystrophy, fatty liver, severe insulin resistance, dyslipidaemia and diabetes in one patient.8 Functional studies of the mutant protein indicated that it failed to increase lipid droplet size.8 Regarding PLIN1, contradictory data have been reported in the literature. Kern et al.9 observed that PLIN1 increased with obesity but not with insulin resistance or inflammatory activity. However, decreased PLIN1 levels have also been described in obese patients.10, 11 Furthermore, reduced PLIN1 gene expression was found in adipose tissue from patients with poorly controlled type 2 diabetes.12 Interestingly, Gandotra et al.13 reported the first human loss-of-function mutation of PLIN1 in a novel form of familial partial lipodystrophy, with severe insulin resistance, type 2 diabetes, dyslipidaemia and fatty liver. Adipose tissue from affected patients revealed remarkably similar features to those observed in samples from obese insulin resistant patients, such as an increased macrophage infiltration and fibrosis.13 Cellular mechanistic studies suggested that this mutation leads to increased basal lipolysis, which is an important contributor in the subsequent inflammatory response.14

In the current study, we aimed to investigate in human adipose tissue, CIDEC/FSP27 and PLIN1 gene expressions in association with adipogenic (FASN, ACACA, PPARG and GLUT4) and mitochondrial (PPARGC1A, PPARGC1B, TFAM and MT-CO3) genes according to obesity status and insulin resistance. We also studied the effects of bariatric surgery-induced weight loss.

Materials and methods

Human adipose tissue samples

In cohort 1, a group of 171 adipose tissue samples (83 subcutaneous abdominal and 88 omental abdominal from the same location) were obtained during open elective surgery (cholecystectomy (n=6), surgery of abdominal hernia (n=10) and gastric bypass surgery (n=72)), from participants with a body mass index (BMI) between 20 and 68 kg m−2, who were invited to participate at the Endocrinology Service of the Hospital Universitari Dr Josep Trueta (Girona, Spain). All subjects were of Caucasian origin and reported that their body weight had been stable for at least 3 months before the study. Among the obese type 2 diabetic patients, the majority of patients were recently diagnosed. Only two subjects were treated with metformin, one with glitazones and one with insulin. Liver and renal diseases were specifically excluded by biochemical work-up, measuring biomarkers of liver injury, like aspartate aminotransferase, alanine aminotransferase and gamma glutamyl transpeptidase. Those subjects with values that were more than twice the upper limit of normal were excluded. Human subjects classified in three groups according to obesity and type 2 diabetes. All subjects gave written informed consent, validated and approved by the Ethics Committee of the Hospital Universitari Dr Josep Trueta (Comitè d’Ètica d’Investigació Clínica, CEIC), after the purpose of the study was explained to them. Adipose tissue samples were washed, fragmented and immediately flash-frozen in liquid nitrogen before stored at −80 °C.

Study of the effects of weight loss induced by bariatric surgery

In cohort 2, six caucasian morbidly obese (BMI=50.4±9.0 kg m−2, age=40±10 years (mean±s.d.)) women with normal glucose tolerance were recruited. The nature and purpose of the study were carefully explained to all subjects before they provided their written consent to participate.

At the time of the baseline study, all subjects were consuming a diet with the following average composition: 60% carbohydrate, 30% fat and 10% protein (1 g/kg body weight). This dietary regimen was maintained for 1 week before the study. Patients underwent a clinical assessment, including medical history, physical examination, body composition analysis and comorbidity evaluation, as well as nutritional interviews performed by a multidisciplinary consultation team. An oral glucose tolerance test, an intravenous glucose tolerance test and a euglycemic hyperinsulinemic clamp were randomly performed within 1 month before surgery and 1 month after surgery. All patients received the same parenteral nutrition regimen (7100 kJ per day) during the first 6 days after surgery; then they were free to consume a normal diet. All subjects were nonsmokers and were not receiving statins or antidiabetic medication. Patients with signs of infection were excluded.

The malabsorptive surgical procedure consisted of a 60% distal gastric resection with stapled closure of the duodenal stump. The residual volume of the stomach is about 300 ml. The small bowel is transected at 2.5 m from the ileocecal valve, and its distal end is anastomosed to the remaining stomach. The proximal end of the ileum, comprising the remaining small bowel (involved in carrying biliopancreatic juice but excluded from food transit), is anastomosed in an end-to-side fashion to the bowel, 50 cm proximal to the ileocecal valve. Consequently, the total length of absorbing bowel is reduced to 250 cm, the final 50 cm of which, the so-called common channel, represents the site where ingested food and biliopancreatic juices mix.

The malabsorptive surgical procedure was performed as previously described15 and subcutaneous adipose tissue (SAT) samples and metabolical studies were again performed 2 years later. The study protocol was approved by the institutional ethics committee of the Catholic University of Rome.

Human adipocyte differentiation in a time course experiment

Isolated human preadipocytes from subcutaneous (n=3) and omental (n=3) adipose tissue (Zen-Bio Inc., Research Triangle Park, NC, USA) were plated on T-75 cell culture flasks and cultured at 37 °C and 5% CO2 in DMEM/Nutrient Mix F-12 medium (1:1, v/v) supplemented with 10 U ml−1 penicillin/streptomycin, 10% fetal bovine serum, 1% HEPES and 1% glutamine (all from GIBCO, Invitrogen S.A, Barcelona, Spain). One week later the isolated and expanded human subcutaneous preadipocytes were cultured (40 000 cells cm−2) in 12-well plates with preadipocyte medium (PM, Zen-Bio Inc.) composed of DMEM/Nutrient Mix F-12 medium (1:1, v/v), HEPES, fetal bovine serum, penicillin and streptomycin, in a humidified 37 °C incubator with 5% CO2. Twenty-four hours after plating, cells were checked for complete confluence (day 0th), and differentiation was induced using differentiation medium (DM, Zen-Bio Inc.) composed of PM, human insulin, dexamethasone, isobutylmethylxanthine and PPARγ agonists (rosiglitazone). After 7 days (day 7th), DM was replaced with fresh adipocyte medium (AM, Zen-Bio Inc.) composed of DMEM/Nutrient Mix F-12 medium (1:1, v/v), HEPES, fetal bovine serum, biotin, panthothenate, human insulin, dexamethasone, penicillin, streptomycin and amphotericin. Fourteen days after the initiation of differentiation, cells appeared round with large lipid droplets apparent in the cytoplasm. Cells were collected and stored at −80 °C for RNA extraction at day −1, 0, 2, 4, 7, 9, 12 and 14. The experiment was performed in triplicate for each sample. Adipogenic differentiation was verified by fatty acid synthase (FASN) and adiponectin (ADIPOQ) gene expression.

RNA expression

To study gene expression, RNA was prepared from these samples using RNeasy Lipid Tissue Mini Kit (QIAgen, Izasa SA, Barcelona, Spain). The integrity of each RNA sample was checked by Agilent Bioanalyzer (Agilent Technologies, Palo Alto, CA, USA). Total RNA was quantified by means of spectrophotometer (GeneQuant, GE Health Care, Piscataway, NJ, USA) reverse transcribed to cDNA using High Capacity cDNA Archive Kit (Applied Biosystems Inc., Madrid, Spain) according to the manufacturer’s protocol.

Gene expression was assessed by real-time PCR using an LightCycler 480 real-time PCR system (Roche Diagnostics SL, Barcelona, Spain), using TaqMan and SYBRgreen technology suitable for relative genetic expression quantification.

The RT-PCR reaction was performed in a final volume of 25 μl. The cycle program consisted of an initial denaturing of 10 min at 95 °C then 40 cycles of 15 s denaturizing phase at 95 °C and 1 min annealing and extension phase at 60 °C. A threshold cycle (Ct value) was obtained for each amplification curve and a ΔCt value was first calculated by subtracting the Ct value for human Cyclophilin A (PPIA) RNA from the Ct value for each sample. Fold changes compared with the endogenous control were then determined by calculating 2−ΔCt, so gene expression results are expressed as expression ratio relative to PPIA gene expression according to manufacturers’ guidelines.

The commercially available and pre-validated TaqMan primer/probe sets used were as follows: endogenous control PPIA (4333763, cyclophilin A, Applied Biosystems Inc.). Human PLIN1 (forward: 5′-IndexTermaagttgaagcttgaggagcgagg-3′ and reverse: 5′-IndexTermgctcgcgatgggaacgctga-3′), CIDEC/FSP27 (forward: 5′-IndexTermgaggtccaacgcagtccagctg-3′ and reverse: 5′-IndexTermgtacgcactgacacatgcctggag-3′), PPARGC1A (forward: 5′-IndexTermGCAATTGAAGAGCGCCGTGTGA-3′ and reverse: 5′-IndexTermCTGTCTCCATCATCCCGCAGAT-3′), PPARGC1B (forward: 5′-IndexTermGCTGACAAGAAATAGGAGAGGC-3′and reverse: 5′-IndexTermTGAATTGGAATCGTAGTCAGTG-3′), TFAM (forward: 5′-IndexTermAAGATTCCAAGAAGCTAAGGGTGA-3′and reverse: 5′-IndexTermCAGAGTCAGACAGATTTTTCCAGTTT-3′), MT-CO3 (forward: 5′-IndexTermGCCCCCAACAGGCATCA-3′ and reverse: 5′-IndexTermGGATGTGTTTAGGAGTGGGACTTC-3′) were measure using SYBRgreen technology.

Human FASN (Hs00188012_m1), ACACA (Hs00167385_m1), SLC2A4 or GLUT4 (Hs00168966_m1), IRS1 (Hs00178563_m1), STAMP2 (Hs01026584_m1), IL6 (Hs00985639_m1), LEP (Hs00174877_m1), ADIPOQ (Hs00605917_m1) and PPARG (Hs00234592_m1). These assays were purchased in Applied Biosystems Inc.

Protein preparation

Proteins were extracted from adipose tissue by using a Polytron PT-1200C homogenizer (Kinematica AG, Lucerne, Switzerland) directly in radioimmnuno precipitation assay buffer (0.1% SDS, 0.5% sodium deoxycholate, 1% Nonidet P-40, 150 mM NaCl and 50 mM Tris-HCl, pH 8.0), supplemented with protease inhibitors (1 mM phenylmethylsulfonyl fluoride). Cellular debris and lipids were eliminated by centrifugation of the solubilized samples at 13 000 r.p.m. for 60 min at 4 °C, recovering the soluble fraction below the fat supernatant and avoiding the nonhomogenized material at the bottom of the centrifuge tube. Protein concentration was determined using the RC/DC Protein Assay (Bio-Rad Laboratories, Hercules, CA, USA).

Western blot analysis

Radioimmnuno precipitation assay protein extracts (25 μg) were separated by SDS-PAGE and transferred to nitrocellulose membranes by conventional procedures. Membranes were immunoblotted with anti-perilipin A (9349P, Cell Signaling Technology, Inc., Danvers, MA, USA), anti-CIDEC or anti-FSP27 (AB77115, Abcam, Cambridge, UK) and β-actin antibodies (sc-47778, Santa Cruz Biotechnology, Dallas, TX, USA). Anti-rabbit IgG and anti-mouse IgG coupled to horseradish peroxidase were used as a secondary antibody. Horseradish peroxidase activity was detected by chemiluminescence, and quantification of protein expression was performed using scion image software.

Analytical methods

Serum glucose concentrations were measured in duplicate by the glucose oxidase method using a Beckman glucose analyser II (Beckman Instruments, Brea, CA, USA). Roche Hitachi Cobas c711 instrument (Roche, Barcelona, Spain) was used to do high-density lipoprotein cholesterol and total serum triglycerides determinations. High-density lipoprotein cholesterol was quantified by a homogeneous enzymatic colorimetric assay through the cholesterol esterase/cholesterol oxidase/peroxidase reaction (Cobas HDLC3). Serum fasting triglycerides were measured by an enzymatic, colorimetric method with glycerol phosphate oxidase and peroxidase (Cobas TRIGL). Low-density lipoprotein cholesterol was calculated using the Friedewald formula. Serum insulin was measured in duplicate by RIA (Medgenix Diagnostics, Fleunes, Belgium). The intra-assay coefficient of variation was 5.2% at a concentration of 10 mU/l and 3.4% at 130 mU/l. The interassay coefficients of variation were 6.9 and 4.5% at 14 and 89 mU/l, respectively. HOMA was calculated using the following formula: (insulin (mU/l) × glucose (mmol/l))/22.5. Aspartate aminotransferase, alanine aminotransferase and gamma glutamyl transpeptidase were determined by routine laboratory tests.

Statistical analyses

Statistical analyses were performed using SPSS 12.0 software. Unless otherwise stated, descriptive results of continuous variables expressed as mean and s.d. for Gaussian variables or median and interquartile range for non-Gaussian variables. Parameters that did not fulfill normal distribution were mathematically transformed to improve symmetry for subsequent analyses. The relation between variables was analyzed by simple correlation (using Spearman’s and Pearson’s tests) and by multiple linear regression models. ANOVA and unpaired t-test were used to compare clinical variables and CIDEC/FSP27 gene expression according to obesity and type 2 diabetes.

Results

CIDEC/FSP27 and PLIN1 gene expression in adipose tissue

Anthropometric and clinical characteristics and the expression of the studied genes in all participants are shown in Tables 1A, 1B, 1C. In all subjects, CIDEC/FSP27 and PLIN1 genes were significantly more expressed in SAT than in visceral adipose tissue (VAT) (CIDEC/FSP27, 1.03±0.52 vs 0.49±0.23 R.U., P<0.0001 and PLIN1, 1.32±0.82 vs 0.63±0.42 R.U., P<0.0001) similar to other adipogenic genes (PPARG, FASN and LEP) (Online Supplementary Figure 1).

Table 1A Anthropometric and clinical characteristics of cohort 1 subjects
Table 1B Gene expression in VAT according to obesity and type 2 diabetes
Table 1C Gene expression in SAT according to obesity and type 2 diabetes

In VAT, CIDEC/FSP27 gene expression was negatively associated with BMI, percent fat mass, fasting glucose, fasting insulin and HOMA (Table 2). CIDEC/FSP27 gene expression strongly correlated with the expression of lipogenic and adipogenic (FASN, ACACA, STAMP2 and PPARG), lipid droplet development (PLIN1) and insulin pathway-associated genes (IRS1 and GLUT-4) (Table 2). In multiple linear regression models, HOMA (P=0.04) contributed independently to VAT CIDEC/FSP27 gene expression variance after controlling for age and BMI (Table 3). Furthermore, PPARG (P=0.002) and PLIN1 (P=0.004) gene expression contributed independently to VAT CIDEC/FSP27 gene expression variance after controlling for BMI and HOMA (Table 3).

Table 2 Correlation between CIDEC/FSP27 gene expression and anthropometric and clinical characteristics and selected gene expression in SAT and VAT from cohort 1 subjects
Table 3 Multivariate linear regression models in cohort 1 subjects

VAT PLIN1 was negatively associated with BMI and percent fat mass but not with fasting glucose, insulin or HOMA (Table 4). Similar to CIDEC/FSP27, PLIN1 gene expression strongly correlated with ACACA, PPARG, STAMP2, IRS1 and GLUT-4 (Table 4).

Table 4 Correlation between PLIN1 gene expression and anthropometric and clinical characteristics and selected gene expression in SAT and VAT from cohort 1 subjects

In SAT, CIDEC/FSP27 gene expression was not associated with anthropometric and clinical parameters and only correlated significantly with PPARG and PLIN1 (Table 2). SAT PLIN1 (P<0.0001) gene expression contributed independently to SAT CIDEC/FSP27 gene expression variance after controlling for BMI and HOMA (Table 3). Similar to CIDEC/FSP27, in SAT PLIN1 gene expression was not associated with anthropometric and clinical parameters and only correlated with PPARG (r=0.36, P=0.006) (Table 4).

CIDEC/FSP27, PLIN1 and mitochondrial gene expression in VAT and SAT

In VAT, CIDEC/FSP27 and PLIN1 gene expressions correlated with mitochondrial biogenesis and activity-related genes (PPARGC1A, PPARGC1B, TFAM and MT-CO3) (Tables 2 and 4). In multiple linear regression models, MT-CO3 (P=0.005) gene expression contributed independently to CIDEC/FSP27 gene expression variance after controlling for BMI, whereas PPARGC1A (P=0.03) gene expression contributed independently to PLIN1 gene expression variance.

In SAT, CIDEC/FSP27 and PLIN1 gene expressions correlated with PPARGC1B and MT-CO3 (Tables 2 and 4). These associations did not remain significant after controlling for BMI.

Effects of weight loss induced by bariatric surgery

Next, we evaluated the effects of bariatric surgery-induced weight loss in a second cohort (n=6). Anthropometric and clinical characteristics are shown in Table 5. Bariatric surgery-induced weight loss induced a significant decrease of fat mass (63.9±2.3 vs 28.6±1.01%, P<0.0001). PLIN1 and FSP27 gene expression and protein levels increased significantly after weight loss (Figures 1a and b) in parallel to adipogenic genes, such as FASN, ADIPOQ and IRS1, whereas LEP (an obesity gene marker) tended to decrease (Figure 2a). Interestingly, protein levels of PLIN1 and FSP27 were significantly increased among those patients with fasting glucose lower than 126 mg/dl (Figure 1c).

Table 5 Anthropometric and clinical characteristics of cohort 2 subjects
Figure 1
figure1

(a) CIDEC/FSP27 and PLIN1 gene expression in SAT before and after bariatric surgery-induced weight loss. (b) FSP27 and PLIN1 protein levels in SAT before and after bariatric surgery-induced weight loss. Protein levels were normalized by β-actin, which was used as a load protein control. (c) FSP27 and PLIN1 protein levels in SAT before bariatric surgery according to fasting glucose. Protein levels also were normalized by β-actin. PLIN1, perilipin 1; CIDEC/FSP27, cell death-inducing DFFA-like effector c; R.U., relative gene expression units; Pre, pre-weight loss; Post, post-weight loss; PLIN1, perilipin 1 protein; FSP27, fat-specific protein 27.

Figure 2
figure2

(a) FASN, ADIPOQ, IRS1 and LEP gene expression in SAT before and after bariatric surgery-induced weight loss. (b) PPARGC1B, TFAM, MT-CO3, PPARGC1A and PRDM16 gene expression in SAT before and after bariatric surgery-induced weight loss. FASN, fatty acid synthase; ADIPOQ, adiponectin; IRS1, insulin receptor substrate 1; LEP, leptin; PPARGC1A, peroxisome proliferator-activated receptor gamma, coactivator 1 alpha; PPARGC1B, peroxisome proliferator-activated receptor gamma, coactivator 1 beta; TFAM, transcription factor A, mitochondrial; MT-CO3, cytochrome c oxidase III; PRDM16, PR domain containing 16.

Furthermore, PPARGC1B, TFAM and Mt-CO3 gene expressions increased significantly after bariatric surgery-induced weight loss (Figure 2b).

FSP27, PLIN1 and mitochondrial genes during human adipocyte differentiation

Finally, to gain insight in the relationship of FSP27, PLIN1 and mitochondrial genes, we investigated the expression of these genes during adipocyte differentiation in human subcutaneous and visceral preadipocytes. Mitochondrial gene expression (PPARGC1A, PPARGC1B, TFAM and MT-CO3) increased during adipocyte differentiation in parallel to CIDEC/FSP27 and PLIN1, and other adipogenic genes (Figure 3). In agreement with the results observed in whole adipose tissue, CIDEC/FSP27, PLIN1 and adipogenic gene expression were all significantly increased in subcutaneous compared with visceral preadipocytes. The differences were more marked in day 4 and day 14 of adipocyte differentiation (Figure 3).

Figure 3
figure3

PPARGC1A, PPARGC1B, TFAM, MT-CO3, FSP27/CIDEC, PLIN1, ADIPOQ and FASN gene expression in subcutaneous (black line) and omental (grey line) preadipocytes during adipocyte differentiation in a time course experiment. *P<0.05 compared with omental preadipocytes.

Discussion

CIDEC/FSP27 and PLIN1 mRNA levels in VAT but not in SAT were decreased in obese subjects. Visceral compared with SAT contains a larger number of inflammatory and immune cells, lesser preadipocyte differentiating capacity and a greater percentage of large adipocytes. Furthermore, visceral adipocytes are more metabolically active, more sensitive to lipolysis and more insulin-resistant than subcutaneous adipocytes.16 In fact, inflammation of the VAT but not of the SAT is known to be associated with insulin resistance in morbidly obese subjects.17, 18 The apparent and selective negative effects of insulin resistance on VAT has been explained by the relatively higher lipogenic effects of insulin on visceral than in subcutaneous adipose-derived stromal cells.19 VAT has also a greater capacity to generate free fatty acids and to uptake glucose than the subcutaneous one.16, 20 Possibly for all these reasons, the negative effects of obesity and insulin resistance on CIDEC/FSP27 and PLIN1 mRNA levels in adipose tissue were more obvious in VAT than in SAT. Despite the less marked associations of CIDEC/FSP27 and PLIN1 gene expression in SAT with obesity and adipogenic genes, bariatric surgery-induced weight loss led to significantly increased mRNA and protein levels of these genes in this fat depot. In agreement with current results, previous studies in human adipose tissue showed reduced PLIN1 mRNA and protein levels in adipose tissue from obese subjects and in patients with poorly controlled type 2 diabetes.10, 11, 12 Interestingly, PLIN1 gene expression was significantly associated with mitochondrial biogenesis-related genes. In agreement with this, previous studies in mice have shown that PLIN1 overexpression in white adipose tissue enhanced its transformation into brown adipose tissue, increasing the mitochondrial biogenesis and activity.6

On the other hand, previous studies in FSP27 knockout mice showed that lipid droplets in WAT were more multilocular and smaller than those of wild-type mice, in parallel to an increased expression of mitochondrial genes and mitochondrial oxidation activity.5, 21 In contrast, in human adipose tissue CIDEC/FSP27 was directly associated with the expression of mitochondrial genes. In fact, in the current study the expression of CIDEC/FSP27 ran in parallel with the expression of PLIN1, contrary to what has been previously reported.6 Differences in study design could have contributed to these disparate observations. Functionally, FSP27 colocalizes with perilipin and they share four conserved regions (I−IV) at the amino acid level7 and both perilipin and FSP27 are highly and specifically expressed in fully differentiated adipocytes. Recent studies demonstrated that the expression of FSP27 is directly regulated by the nuclear receptor peroxisome proliferator-activated receptor γ (PPARγ).22 Similar to CIDEC/FSP27, a functional PPAR-responsive element was identified within the perilipin gene.23 In addition, time course experiment during human adipocyte differentiation showed how CIDEC/FSP27 and PLIN1 ran in parallel with adipogenic genes, whose expression was promoted by PPARγ.

In the current study, mitochondrial genes increased significantly during human adipocyte differentiation. In fact, previous studies in 3T3-L1 revealed that mitochondrial biogenesis displayed an important role in adipocyte differentiation, with a dramatic increase in many mitochondrial genes during adipogenesis.24 In concordance with this, mitochondrial genes were associated with adipogenic genes (mainly PPARγ) in both VAT and SAT. In addition, bariatric surgery-induced weight loss led to increased mitochondrial gene expression in parallel to adipogenic genes. Decreased mitochondrial gene expressions have been shown in adipose tissue from subjects with type 2 diabetes, and they were recovered using an PPARγ agonist (rosiglitazone)25 and in adipose tissue from insulin-resistant subjects.26

The negative association of CIDEC/FSP27 gene expression with insulin resistance is in agreement with previous studies in human adipose tissue.7, 8 In fact, the capacity of CIDEC/FSP27 of promoting lipid droplet development and of inhibiting lipolysis seems to prevent the negative effects of lipotoxicity on insulin sensitivity and metabolic disturbances.27 Similar to CIDEC/FSP27, PPARγ agonists lead to improved obesity-related metabolic disturbances enhancing adipose tissue lipid storage capacity.28 The findings described here after bariatric surgery-induced weight loss suggest that the reduction of fat mass in obese subjects may paradoxically increase the adipogenic and lipid storage capacity of adipose tissue.

In conclusion, the reduction in CIDEC/FSP27, PLIN1 and mitochondrial gene expression in association with obesity and insulin resistance could reflect the altered function of adipose tissue in the lipid storage and oxidative capacity, mainly in the visceral fat depot. Otherwise, the increased expression of these genes after bariatric surgery-induced weight loss shows the usefulness of this intervention to improve adipose tissue dysfunction.

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Acknowledgements

We acknowledge the clinical help of Oscar Rovira. This work was partially supported by research grants from the Ministerio de Economía y Competitividad (PI11-00214). CIBEROBN Fisiopatología de la Obesidad y Nutrición is an initiative from the Instituto de Salud Carlos III from Spain.

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Correspondence to J M Fernández-Real.

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The authors declared no conflict of interest.

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Supplementary Information accompanies this paper on International Journal of Obesity website

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Moreno-Navarrete, J., Ortega, F., Serrano, M. et al. CIDEC/FSP27 and PLIN1 gene expression run in parallel to mitochondrial genes in human adipose tissue, both increasing after weight loss. Int J Obes 38, 865–872 (2014) doi:10.1038/ijo.2013.171

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Keywords

  • lipid droplet protein
  • mitochondrial genes
  • surgery-induced weight loss
  • adipose tissue
  • adipogenesis

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