Alterations of sorbin and SH3 domain containing 3 (SORBS3) in human skeletal muscle following Roux-en-Y gastric bypass surgery.

Background: Obesity is a disease that is caused by genetic and environmental factors. However, epigenetic mechanisms of obesity are less well known. DNA methylation provides a mechanism whereby environmental factors can influence gene transcription. The aim of our study was to investigate skeletal muscle DNA methylation of sorbin and SH3 domain containing 3 ( SORBS3 ) with weight loss induced by Roux-en-Y gastric bypass (RYGB).
Results: Previously, we had shown increased methylation (5.0 to 24.4%) and decreased gene expression (fold change - 1.9) of SORBS3 with obesity (BMI > 30 kg/m ² ) compared to lean controls. In the present study, basal muscle biopsies were obtained from seven morbidly obese (BMI > 40 kg/m ² ) female subjects pre- and 3 months post-RYGB surgery, in combination with euglycemic-hyperinsulinemic clamps to assess insulin sensitivity. We identified 30 significantly altered promoter and untranslated region methylation sites in SORBS3 using reduced representation bisulfite sequencing (RRBS). Twenty-nine of these sites were decreased (- 5.6 to - 24.2%) post-RYGB compared to pre-RYGB. We confirmed the methylation in 2 (Chr.8:22,423,690 and Chr.8:22,423,702) of the 29 decreased SORBS3 sites using pyrosequencing. This decreased methylation was associated with an increase in SORBS3 gene expression (fold change + 1.7) post-surgery. In addition, we demonstrated that SORBS3 promoter methylation in vitro significantly alters reporter gene expression ( P  < 0.0001). Two of the SORBS3 methylation sites (Chr.8:22,423,111 and Chr.8:22,423,205) were strongly correlated with fasting plasma glucose levels ( r  = 0.9, P  = 0.00009 and r  = 0.8, P  = 0.0010). Changes in SORBS3 gene expression post-surgery were correlated with obesity measures and fasting insulin levels ( r  = 0.5 to 0.8; P  < 0.05).
Conclusions: These results demonstrate that SORBS3 methylation and gene expression are altered in obesity and restored to normal levels through weight loss induced by RYGB surgery.