Preferential fat deposition in subcutaneous versus visceral depots is associated with insulin sensitivity

Differences in gene expression and cytokine release profiles highlight the heterogeneity of distinct subsets of adipose tissue-derived stem cells in the subcutaneous and visceral adipose tissue in humans

Differences in the inherent properties of adipose tissue-derived stem cells (ASC) may contribute to the biological specificity of the subcutaneous (Sc) and visceral (V) adipose tissue depots. In this study, three distinct subpopulations of ASC, i.e. ASC_SVF, ASC_Bottom, and ASC_Ceiling, were isolated from Sc and V fat biopsies of non-obese subjects, and their gene expression and functional characteristics were investigated. Genome-wide mRNA expression profiles of ASC_SVF, ASC_Bottom and ASC_Ceiling from Sc fat were significantly different as compared to their homologous subsets of V-ASCs. Furthermore, ASC_SVF, ASC_Ceiling and ASC_Bottom from the same fat depot were also distinct from each other. In this respect, both principal component analysis and hierarchical clusters analysis showed that ASC_Ceiling and ASC_SVF shared a similar pattern of closely related genes, which was highly different when compared to that of ASC_Bottom. However, larger variations in gene expression were found in inter-depot than in intra-depot comparisons. The analysis of connectivity of genes differently expressed in each ASC subset demonstrated that, although there was some overlap, there was also a clear distinction between each Sc-ASC and their corresponding V-ASC subsets, and among ASC_SVF, ASC_Bottom, and ASC_Ceiling of Sc or V fat depots in regard to networks associated with regulation of cell cycle, cell organization and development, inflammation and metabolic responses. Finally, the release of several cytokines and growth factors in the ASC cultured medium also showed both inter- and intra-depot differences. Thus, ASC_Ceiling and ASC_Bottom can be identified as two genetically and functionally heterogeneous ASC populations in addition to the ASC_SVF, with ASC_Bottom showing the highest degree of unmatched gene expression. On the other hand, inter-depot seem to prevail over intra-depot differences in the ASC gene expression assets and network functions, contributing to the high degree of specificity of Sc and V adipose tissue in humans.

Role of subcutaneous adipose tissue in the pathogenesis of insulin resistance

Burden of obesity has increased significantly in the United States over last few decades. Association of obesity with insulin resistance and related cardiometabolic problems is well established. Traditionally, adipose tissue in visceral fat depot has been considered a major culprit in development of insulin resistance. However, growing body of the literature has suggested that adipose tissue in subcutaneous fat depot, not only due to larger volume but also due to inherent functional characteristics, can have significant impact on development of insulin resistance. There are significant differences in functional characteristics of subcutaneous abdominal/truncal versus gluteofemoral depots. Decreased capacity for adipocyte differentiation and angiogenesis along with adipocyte hypertrophy can trigger vicious cycle of inflammation in subcutaneous adipose tissue and subsequent ectopic fat deposition. It is important to shift focus from fat content to functional heterogeneity in adipose tissue depots to better understand the relative role of subcutaneous adipose tissue in metabolic complications of obesity. Therapeutic lifestyle change continues to be the most important intervention in clinical practice at any level of increased adiposity. Future pharmaceutical interventions aimed at improving adipose tissue function in various subcutaneous depots have potential to help maintain adequate insulin sensitivity and reduce risk for development of insulin resistance complications.

Impact of age on markers of HIV-1 disease

Aging is a complicated process characterized by a progressive loss of homeostasis, which results in an increased vulnerability to multiple diseases. HIV-1-infected patients demonstrate a premature aging phenotype and develop certain age-related diseases earlier in their lifespan than what is seen in the general population. Age-related comorbidities may include the development of bone disease, metabolic disorders, neurologic impairment and immunosenescence. Age also appears to have an effect on traditional markers of HIV-1 disease progression, including CD4+ T-cell count and viral load. These effects are not only a consequence of HIV-1 infection, but in many cases, are also linked to antiretroviral therapy. This review summarizes the complex interplay between HIV-1 infection and aging, and the impact that aging has on markers of HIV-1 disease.

Metabolic effects of a growth hormone-releasing factor in obese subjects with reduced growth hormone secretion: a randomized controlled trial

CONTEXT

Obesity is associated with reduced GH secretion and increased cardiovascular disease risk.

OBJECTIVE

We performed this study to determine the effects of augmenting endogenous GH secretion on body composition and cardiovascular disease risk indices in obese subjects with reduced GH secretion.

DESIGN, PATIENTS AND METHODS

A randomized, double-blind, placebo-controlled study was performed involving 60 abdominally obese subjects with reduced GH secretion. Subjects received tesamorelin, a GHRH(1-44) analog, 2 mg once daily, or placebo for 12 months. Abdominal visceral adipose tissue (VAT) was assessed by abdominal computed tomography scan, and carotid intima-media thickness (cIMT) was assessed by ultrasound. Treatment effect was determined by longitudinal linear mixed-effects modeling.

RESULTS

VAT [-16 ± 9 vs.19 ± 9 cm(2), tesamorelin vs. placebo; treatment effect (95% confidence interval): -35 (-58, -12) cm(2); P = 0.003], cIMT (-0.03 ± 0.01 vs. 0.01 ± 0.01 mm; -0.04 (-0.07, -0.01) mm; P = 0.02), log C-reactive protein (-0.17 ± 0.04 vs. -0.03 ± 0.05 mg/liter; -0.15 (-0.30, -0.01) mg/liter, P = 0.04), and triglycerides (-26 ± 16 vs. 12 ± 8 mg/dl; -37 (-67, -7) mg/dl; P = 0.02) improved significantly in the tesamorelin group vs. placebo. No significant effects on abdominal sc adipose tissue (-6 ± 6 vs. 3 ± 11 cm(2); -10 (-32, +13) cm(2); P = 0.40) were seen. IGF-I increased (86 ± 21 vs. -6 ± 8 μg/liter; 92 (+52, +132) μg/liter; P < 0.0001). No changes in fasting, 2-h glucose, or glycated hemoglobin were seen. There were no serious adverse events or differences in adverse events between the groups.

CONCLUSION

Among obese subjects with relative reductions in GH, tesamorelin selectively reduces VAT without significant effects on sc adipose tissue and improves triglycerides, C-reactive protein, and cIMT, without aggravating glucose.

DNA methylation of the IGF2/H19 imprinting control region and adiposity distribution in young adults

Background

The insulin-like growth factor 2 (IGF2) and H19 imprinted genes control growth and body composition. Adverse in-utero environments have been associated with obesity-related diseases and linked with altered DNA methylation at the IGF2/H19 locus. Postnatally, methylation at the IGF2/H19 imprinting control region (ICR) has been linked with cerebellum weight. We aimed to investigate whether decreased IGF2/H19 ICR methylation is associated with decreased birth and childhood anthropometry and increased contemporaneous adiposity.

DNA methylation in peripheral blood (n = 315) at 17 years old was measured at 12 cytosine-phosphate-guanine sites (CpGs), analysed as Sequenom MassARRAY EpiTYPER units within the IGF2/H19 ICR. Birth size, childhood head circumference (HC) at six time-points and anthropometry at age 17 years were measured. DNA methylation was investigated for its association with anthropometry using linear regression.

Results

The principal component of IGF2/H19 ICR DNA methylation (representing mean methylation across all CpG units) positively correlated with skin fold thickness (at four CpG units) (P-values between 0.04 to 0.001) and subcutaneous adiposity (P = 0.023) at age 17, but not with weight, height, BMI, waist circumference or visceral adiposity. IGF2/H19 methylation did not associate with birth weight, length or HC, but CpG unit 13 to 14 methylation was negatively associated with HC between 1 and 10 years. β-coefficients of four out of five remaining CpG units also estimated lower methylation with increasing childhood HC.

Conclusions

As greater IGF2/H19 methylation was associated with greater subcutaneous fat measures, but not overall, visceral or central adiposity, we hypothesize that obesogenic pressures in youth result in excess fat being preferentially stored in peripheral fat depots via the IGF2/H19 domain. Secondly, as IGF2/H19 methylation was not associated with birth size but negatively with early childhood HC, we hypothesize that the HC may be a more sensitive marker of early life programming of the IGF axis and of fetal physiology than birth size. To verify this, investigations of the dynamics of IGF2/H19 methylation and expression from birth to adolescence are required.

Relationships between body fat distribution, epicardial fat and obstructive sleep apnea in obese patients with and without metabolic syndrome

BACKGROUND

Obstructive sleep apnea (OSA) and metabolic syndrome, both closely related to obesity, often coexist in affected individuals; however, body mass index is not an accurate indicator of body fat and thus is not a good predictor of OSA and other comorbidities. The aim of this study was to investigate whether the occurrence of OSA could be associated with an altered body fat distribution and a more evident cardio metabolic risk independently from obesity and metabolic syndrome.

METHODS AND RESULTS

171 consecutive patients (58 men and 113 women) were included in the study and underwent overnight polysomnography. Anthropometric data, blood pressure, lipid profile, glycaemic parameters were recorded. Body composition by DXA, two-dimensional echocardiography and carotid intima/media thickness measurement were performed. 67 patients (39.2%) had no OSA and 104 (60.8%) had OSA. The percentage of patients with metabolic syndrome was significantly higher among OSA patients (65.4%) that were older, heavier and showed a bigger and fatter heart compared to the control group. Upper body fat deposition index , the ratio between upper body fat (head, arms and trunk fat in kilograms) and lower body fat (legs fat in kilograms), was significantly increased in the OSA patients and significantly related to epicardial fat thickness. In patients with metabolic syndrome, multivariate regression analyses showed that upper body fat deposition index and epicardial fat showed the best association with OSA.

CONCLUSION

The occurrence of OSA in obese people is more closely related to cardiac adiposity and to abnormal fat distribution rather than to the absolute amount of adipose tissue. In patients with metabolic syndrome the severity of OSA is associated with increase in left ventricular mass and carotid intima/media thickness.

Implications of 2H-labeling of DNA protocol to measure in vivo cell turnover in adipose tissue

Adipose tissue expansion in obesity involves a series of cycles of adipocyte hyperplasia, hypertrophy and hypoplasia due to alterations in adipogenesis, adipocyte cellular metabolism and cell death, respectively. Increased frequency of these cycles may lead to deterioration of adipocyte function and viability, accelerated exhaustion of the adipocyte progenitor pool and extensive adipose tissue remodeling, all leading to impaired expandability of subcutaneous adipose tissue, ectopic lipid accumulation and insulin resistance. Understanding the mechanisms that contribute to adipocyte turnover is thus important. We have recently refined and published an existing method to assess in vivo adipogenesis using incorporation of the stable isotope deuterium into the DNA of isolated adipocytes and adipocyte progenitors from adipose tissue. In this commentary, we highlight further implications of this method to determine the rate of adipocyte hypertrophy and adipocyte death that will enhance our understanding of adipocyte cell turnover and cellular mechanisms that control regional adipose tissue growth.

Dysfunctional adiposity and the risk of prediabetes and type 2 diabetes in obese adults

CONTEXT

The risk of type 2 diabetes mellitus is heterogeneous among obese individuals. Factors that discriminate prediabetes or diabetes risk within this population have not been well characterized. A dysfunctional adiposity phenotype, characterized by excess visceral fat and insulin resistance, may contribute to diabetes development in those with obesity.

OBJECTIVE

To investigate associations between adiposity phenotypes and risk for incident prediabetes and diabetes in a multiethnic, population-based cohort of obese adults.

DESIGN, SETTING, AND PARTICIPANTS

Among 732 obese participants (body mass index ≥30) aged 30 to 65 years without diabetes or cardiovascular disease enrolled between 2000 and 2002 in the Dallas Heart Study, we measured body composition by dual energy x-ray absorptiometry and magnetic resonance imaging (MRI); circulating adipokines and biomarkers of insulin resistance, dyslipidemia, and inflammation; and subclinical atherosclerosis and cardiac structure and function by computed tomography and MRI.

MAIN OUTCOME MEASURES

Incidence of diabetes through a median 7.0 years (interquartile range, 6.6-7.6) of follow-up. In a subgroup of 512 participants with normal fasting glucose values at baseline, incidence of the composite of prediabetes or diabetes was determined.

RESULTS

Of the 732 participants (mean age, 43 years; 65% women; 71% nonwhite), 84 (11.5%) developed diabetes. In multivariable analysis, higher baseline visceral fat mass (odds ratio [OR] per 1 SD [1.4 kg], 2.4; 95% CI, 1.6-3.7), fructosamine level (OR per 1 SD [1.1 μmol/L], 2.0; 95% CI, 1.4-2.7), fasting glucose level (OR per 1 SD [1.1 μmol/L], 1.9; 95% CI, 1.4-2.6), family history of diabetes (OR, 2.3; 95% CI, 1.3-4.3), systolic blood pressure (OR per 10 mm Hg, 1.3; 95% CI, 1.1-1.5), and weight gain over follow-up (OR per 1 kg, 1.06; 95% CI, 1.02-1.10) were independently associated with diabetes, with no associations observed for body mass index, total body fat, or abdominal subcutaneous fat. Among the 512 participants with normal baseline glucose values, the composite outcome of prediabetes or diabetes occurred in 39.1% and was independently associated with baseline measurements of visceral fat mass; levels of fasting glucose, insulin, and fructosamine; older age; nonwhite race; family history of diabetes; and weight gain over follow-up (P < .05 for each) but not with measurements of general adiposity.

CONCLUSION

Excess visceral fat and insulin resistance, but not general adiposity, were independently associated with incident prediabetes and type 2 diabetes mellitus in obese adults.

Hyperglycemia-induced oxidative stress is independent of excess abdominal adiposity in normal-weight women with polycystic ovary syndrome

STUDY QUESTION

What is the effect of glucose ingestion on leukocytic reactive oxygen species (ROS) generation in normal-weight women with polycystic ovary syndrome (PCOS) with and without excess abdominal adiposity (AA)?

SUMMARY ANSWER

Normal-weight women with PCOS exhibit an increase in leukocytic ROS generation in response to glucose ingestion, and this increase is independent of excess AA.

WHAT IS KNOWN ALREADY

Excess adipose tissue is a source of oxidative stress. Normal-weight women with PCOS exhibit oxidative stress and can have excess AA.

STUDY DESIGN AND SIZE

This is a cross-sectional study involving 30 reproductive-age women.

PARTICIPANTS/MATERIALS, SETTING AND METHODS

Fourteen normal-weight women with PCOS (6 normal AA, 8 excess AA) and 16 body composition-matched controls (8 normal AA, 8 excess AA) underwent body composition assessment by dual-energy absorptiometry and an oral glucose tolerance test (OGTT) at a university medical center. Insulin sensitivity was derived from the OGTT (IS(OGTT)). Blood was drawn while fasting and 2 h after glucose ingestion to measure leukocytic ROS generation and p47(phox) protein content and plasma thiobarbituric acid-reactive substances (TBARS) and C-reactive protein (CRP).

MAIN RESULTS AND THE ROLE OF CHANCE

Compared with controls, both PCOS groups exhibited lower IS(OGTT) (43-54%) and greater percentage change (% change) in ROS generation (96-140%), p47(phox) protein (18-28%) and TBARS (17-48%). Compared with women with PCOS with excess AA, those with normal AA exhibited higher testosterone levels (29%) and lower CRP levels (70%). For the combined groups, IS(OGTT) was negatively correlated with the % change in ROS generation and p47(phox) protein. CRP was positively correlated with abdominal fat. The % change in p47(phox) protein was positively correlated with CRP and androgens.

LIMITATIONS, REASONS FOR CAUTION

Although this study is adequately powered to assess differences in ROS generation between the women with PCOS and control participants, the modest sample size merits caution when interpreting the corroborative results of the additional measures of oxidative stress and inflammation.

WIDER IMPLICATIONS OF THE FINDINGS

This study highlights the unique pro-oxidant contribution of circulating leukocytes in the development of insulin resistance and hyperandrogenism in PCOS.

STUDY FUNDING/COMPETING INTEREST(S)

Supported by NIH grant HD-048535 to F.G. The authors have nothing to disclose.

Impact of visceral adipose tissue and subcutaneous adipose tissue on insulin resistance in middle-aged Japanese

AIM

The enlargement of visceral adipose tissue (VAT) is considered to mediate the close relationship between obesity and insulin resistance. We aimed to determine whether a stronger association of VAT compared to subcutaneous adipose tissue (SAT) with insulin resistance could be confirmed and generalized in non-diabetic Japanese men and women.

METHODS

Participants were 912 non-diabetic Japanese (636 men and 276 women, mean age 52.4±7.0 years, and mean BMI 24.9±3.1 kg/m(2)). VAT and SAT were measured through the use of computed tomography scanning. Homeostatic model for the assessment of insulin resistance (HOMA-IR) and Matsuda insulin sensitivity index (ISI) were calculated based on results from the oral glucose tolerance test.

RESULTS

For both genders, subjects in higher tertiles of SAT as well as VAT showed significantly higher levels of HOMA-IR and lower levels of Matsuda ISI (p<0.001). In multiple regression analyses with VAT and SAT included in the model, only VAT, but not SAT, was independently associated with Matsuda ISI in women (p<0.001), whereas both SAT and VAT were independently associated with HOMA-IR and with Matsuda ISI in men (p<0.001). When VAT and waist circumference were jointly included in the model, only VAT, but not waist circumference, was independently associated with Matsuda ISI in women (p<0.001) but not in men.

CONCLUSION

VAT had a stronger association with insulin resistance than SAT or waist circumference in women but not in men. BMI showed a comparable association with insulin resistance to VAT in this population.

Body composition and metabolic changes in HIV-infected patients

As antiretroviral therapy has decreased human immunodeficiency virus (HIV)-associated mortality, cardiometabolic abnormalities have become increasingly apparent in HIV-infected individuals. Many patients treated for HIV infection exhibit body composition changes, including peripheral fat atrophy and visceral lipohypertrophy. In addition, HIV-infected individuals demonstrate a higher prevalence of dyslipidemia, insulin resistance and diabetes, and cardiovascular risk, compared with the general population. Although antiretroviral therapy appears to contribute to some of the cardiometabolic abnormalities in HIV infection, HIV itself, immunologic factors, and lifestyle factors are also important mediators of cardiovascular risk. Treatment strategies for body composition changes and cardiometabolic abnormalities in HIV infection include lifestyle modification, lipid-lowering agents, insulin sensitizers, and treatments to reverse endocrine abnormalities in HIV, including growth hormone-releasing hormone. None of these strategies has comprehensively addressed the abnormalities experienced by this population, however, and further research is needed into combined strategies to improve body composition and ameliorate cardiovascular risk.

Metabolic heterogeneity of obesity: role of adipose tissue

Obesity is not synonymous with insulin resistance. Why some but not all individuals develop insulin resistance with weight excess is not clear, but a number of plausible hypotheses with ample support now exist. This article reviews regional fat distribution, inflammation, lipotoxicity/ectopic fat and impaired adipogenesis as leading theories as to why excess body weight has the potential to promote insulin resistance.

The insulin-like growth factors in adipogenesis and obesity

Adipose tissue has been recognized as a major target of growth hormone (GH) action. GH was shown to inhibit adipocyte differentiation but stimulated preadipocyte proliferation in vitro. GH acts directly via its receptor or via upregulating insulin-like growth factor (IGF)-I, which is a critical mediator of preadipocyte proliferation, differentiation, and survival. Results from clinical studies on GH treatment in patients with GH deficiency or GH insensitivity syndrome can be used to dissect GH and IGF as well as IGF-binding protein (IGFBP) actions in vivo. In this article, changes of the GH/IGF system during adipocyte differentiation in vitro as well as related signaling pathways and their impact on adipose tissue growth and function are discussed. Clinical considerations include the effects of GH and IGF-I on adipose tissue during treatment of GH deficiency, differences in the IGF system between visceral and subcutaneous adipose tissue depots as well as the recently emerging role for adipose tissue in the regulation of glucose homeostasis.

What causes the insulin resistance underlying obesity?

PURPOSE OF REVIEW

The association between obesity and insulin resistance is an area of much interest and enormous public health impact, with hundreds of articles being published in the last year focused on the possible mechanisms that underlie this association. The purpose to this review is to highlight some of the key recent literature with emphasis on emerging concepts.

RECENT FINDINGS

The specific link between visceral adipose tissue accumulation and insulin resistance continues to be discerned. Visceral adiposity is correlated with accumulation of excess lipid in liver, and results in cell autonomous impairment in insulin signaling. Visceral adipose tissue is also prone to inflammation and inflammatory cytokine production, which also contribute to impairment in insulin signaling. The expansion of visceral adipose tissue and excess lipid accumulation in liver and muscle may result from limited expandability of subcutaneous adipose tissue, due to the properties of its extracellular matrix and capacity for capillary growth.

SUMMARY

Recent studies underscore the need to better understand the mechanisms linking visceral adiposity with liver fat accumulation, the mechanisms by which ectopic fat accumulation cause insulin resistance, and the mechanisms by which the size of adipose tissue depots is determined.

Unacylated Ghrelin is associated with the isolated low HDL-cholesterol obese phenotype independently of insulin resistance and CRP level

BACKGROUND

Low plasma high-density lipoprotein-cholesterol (HDL-c) level is commonly present in obesity and represents an independent cardiovascular risk factor. However, obese patients are a very heterogeneous population and the factors and mechanisms that contribute to low HDL-c remain unclear. The aim of this study was to investigate the association between plasma HDL-c levels and plasma hormonal profiles (insulin, adiponectin, resistin, leptin and ghrelin) in subsets of class II and III obese patients.

METHODS

Fasting plasma levels of glucose, total cholesterol, LDL-c, HDL-c, triglycerides, free fatty acids, apoproteins A-I, B-100, B-48, C-II, C-III, insulin, hs-CRP, adipocytokines (adiponectin, resistin, leptin), unacylated ghrelin, body composition (DXA) and resting energy expenditure were measured in three subsets of obese patients: 17 metabolically abnormal obese (MAO) with metabolic syndrome and the typical metabolic dyslipidaemia, 21 metabolically healthy obese (MHO) without metabolic syndrome and with a normal lipid profile, and 21 isolated low HDL-c obese patients (LHO) without metabolic syndrome, compared to 21 healthy lean control subjects.

RESULTS

Insulin resistance (HOMA-IR) increased gradually from MHO to LHO and from LHO to MAO patients (p < 0.05 between MHO and MAO and between LHO and MAO). In multiple regression analysis, serum unacylated ghrelin levels were only positively and independently associated with HDL-c levels in the LHO group (p = 0.032).

CONCLUSIONS

These results suggest that, in class II and III obese patients with an isolated low HDL-c phenotype, unacylated ghrelin is positively associated with HDL-c level independently of insulin resistance and CRP levels, and may contribute to the highly prevalent low HDL-c level seen in obesity.

Insulin receptor-independent upregulation of cellular glucose uptake

BACKGROUND

Cellular glucose uptake can be enhanced by up-regulating Ras signaling in either insulin dependent or independent manner. In presence of insulin and intact insulin signaling, Ras plays a negligible role in glucose uptake. Conversely, when insulin signaling is impaired in obesity or diabetes, the insulin-independent Ras pathway may be valuable for enhancing glucose disposal. We previously reported that Ad36, a human adenovirus, enhances cellular glucose uptake by up-regulating the Ras/Glut4 pathway. Here, we investigated if Ad36-up-regulated Ras via the insulin-independent pathway, to enhance glucose uptake. Furthermore, uncontrolled up-regulation of Ras is linked with oncogenic cell transformation, if the tumor suppressor gene p53 is also down regulated. Hence, we determined if up-regulation of Ras by Ad36 would induce oncogenic cell transformation. Finally, we determined the relevance of Ad36 to insulin resistance in humans.

METHODS

Insulin receptor (IR) was knocked down with siRNA in 3T3-L1 adipocytes, to determine if Ad36 increases the Ras/Glut4 pathway and glucose uptake without IR-signaling. Next, the effects of Ad36 on cell transformation and p53 abundance were determined. Finally, overweight or obese women were screened for seropositivty to Ad36, as an indicator of natural Ad36 infection. Associations of Ad36 infection with adiposity and C-Reactive proteins (CRP) –two key markers of insulin resistance, and with glucose disposal, were determined.

RESULTS

Unaffected by IR knock-down, Ad36 significantly increased the Ras pathway, Glut4 translocation, and glucose uptake in 3T3-L1 adipocytes. Despite Ras up-regulation, Ad36 did not transform 3T3-L1 cells. This may be because Ad36 significantly increased p53 protein in 3T3-L1 cells or mice adipose tissue. Ad36 seropositivity was associated with greater adiposity and CRP levels, yet a significantly higher systemic glucose disposal rate.

CONCLUSIONS

Overall, the study offers Ras/Glut4 pathway as an alternate to enhance glucose disposal when insulin signaling is impaired, and, importantly, provides Ad36 as a tool to understand the modulation of that pathway.

Reduction in inflammatory gene expression in skeletal muscle from Roux-en-Y gastric bypass patients randomized to omentectomy

Objectives

To examine the effects of Roux-en-Y gastric bypass (RYGB) surgery with and without laparoscopic removal of omental fat (omentectomy) on the temporal gene expression profiles of skeletal muscle.

Design

Previously reported were the whole-body metabolic effects of a randomized, single-blinded study in patients receiving RYGB surgery stratified to receive or not receive omentectomy. In this follow up study we report on changes in skeletal muscle gene expression in a subset of 21 patients, for whom biopsies were collected preoperatively and at either 6 months or 12 months postoperatively.

Methodology/Principal Findings

RNA isolated from skeletal muscle biopsies of 21 subjects (8 without omentectomy and 13 with omentectomy) taken before RYGB or at 6 and 12 months postoperatively were subjected to gene expression profiling via Exon 1.0 S/T Array and Taqman Low Density Array. Robust Multichip Analysis and gene enrichment data analysis revealed 84 genes with at least a 4-fold expression difference after surgery. At 6 and 12 months the RYGB with omentectomy group displayed a greater reduction in the expression of genes associated with skeletal muscle inflammation (ANKRD1, CDR1, CH25H, CXCL2, CX3CR1, IL8, LBP, NFIL3, SELE, SOCS3, TNFAIP3, and ZFP36) relative to the RYGB non-omentectomy group. Expressions of IL6 and CCL2 were decreased at all postoperative time points. There was differential expression of genes driving protein turnover (IGFN1, FBXW10) in both groups over time and increased expression of PAAF1 in the non-omentectomy group at 12 months. Evidence for the activation of skeletal muscle satellite cells was inferred from the up-regulation of HOXC10. The elevated post-operative expression of 22 small nucleolar RNAs and the decreased expression of the transcription factors JUNB, FOS, FOSB, ATF3 MYC, EGR1 as well as the orphan nuclear receptors NR4A1, NR4A2, NR4A3 suggest dramatic reorganizations at both the cellular and genetic levels.

Conclusions/Significance

These data indicate that RYGB reduces skeletal muscle inflammation, and removal of omental fat further amplifies this response.

Trial Registration

ClinicalTrials.gov NCT00212160