Abstract
BackgroundThe mechanisms of weight loss and metabolic improvements following bariatric surgery in skeletal muscle are not well known; however, epigenetic modifications are likely to contribute. The aim of our study was to investigate skeletal muscle DNA methylation after weight loss induced by Roux-en-Y gastric bypass (RYGB) surgery. Muscle biopsies were obtained basally from seven insulin-resistant obese (BMI > 40 kg/m2) female subjects (45.1 ± 3.6 years) pre- and 3-month post-surgery with euglycemic hyperinsulinemic clamps to assess insulin sensitivity. Four lean (BMI < 25 kg/m2) females (38.5 ± 5.8 years) served as controls. We performed reduced representation bisulfite sequencing next generation methylation on DNA isolated from the vastus lateralis muscle biopsies.ResultsGlobal methylation was significantly higher in the pre- (32.97 ± 0.02%) and post-surgery (33.31 ± 0.02%) compared to the lean (30.46 ± 0.02%), P < 0.05. MethylSig analysis identified 117 differentially methylated cytosines (DMCs) that were significantly altered in the post- versus pre-surgery (Benjamini–Hochberg q < 0.05). In addition, 2978 DMCs were significantly altered in the pre-surgery obese versus the lean controls (Benjamini–Hochberg q < 0.05). For the post-surgery obese versus the lean controls, 2885 DMCs were altered (Benjamini–Hochberg q < 0.05). Seven post-surgery obese DMCs were normalized to levels similar to those observed in lean controls. Of these, 5 were within intergenic regions (chr11.68,968,018, chr16.73,100,688, chr5.174,115,531, chr5.1,831,958 and chr9.98,547,011) and the remaining two DMCs chr17.45,330,989 and chr14.105,353,824 were within in the integrin beta 3 (ITGB3) promoter and KIAA0284 exon, respectively. ITGB3 methylation was significantly decreased in the post-surgery (0.5 ± 0.5%) and lean controls (0 ± 0%) versus pre-surgery (13.6 ± 2.7%, P < 0.05). This decreased methylation post-surgery was associated with an increase in ITGB3 gene expression (fold change + 1.52, P = 0.0087). In addition, we showed that ITGB3 promoter methylation in vitro significantly suppressed transcriptional activity (P < 0.05). Transcription factor binding analysis for ITGB3 chr17.45,330,989 identified three putative transcription factor binding motifs; PAX-5, p53 and AP-2alphaA.ConclusionsThese results demonstrate that weight loss after RYGB alters the epigenome through DNA methylation. In particular, this study highlights ITGB3 as a novel gene that may contribute to the metabolic improvements observed post-surgery. Future additional studies are warranted to address the exact mechanism of ITGB3 in skeletal muscle.
Highlights
The mechanisms of weight loss and metabolic improvements following bariatric surgery in skeletal muscle are not well known; epigenetic modifications are likely to contribute
We showed that the cytoskeletal interacting protein sorbin and SH3 domain containing 3 (SORBS3) was decreased in methylation in the skeletal muscle of patients following weight loss induced by Roux-en-Y gastric bypass (RYGB) [20]
3-month post-surgery, significant improvements were observed in body mass index (BMI), body fat percentage, cholesterol, low-density lipoprotein (LDL), fasting plasma glucose (FPG) and fasting
Summary
The mechanisms of weight loss and metabolic improvements following bariatric surgery in skeletal muscle are not well known; epigenetic modifications are likely to contribute. Obesity is a major health challenge and increases the risk of a number of chronic diseases including type 2 diabetes, hypertension, dyslipidemia and cardiovascular disease [3]. People who are obese often present with hyperinsulinemia and an underlying insulin resistance, which increases their risk for type 2 diabetes [4]. Lifestyle modifications such as diet and exercise and pharmacological therapies are ineffective at achieving long-term weight loss. Another alternative for obesity treatment is bariatric surgery. A meta-analysis across 621 studies with 135,246 patients revealed that type 2 diabetes is resolved in the greater majority of patients following bariatric surgery [14]
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