Endocrine Abstracts

Introduction: Type 2 diabetes results from insulin resistance and B-cell failure. Bariatric surgery is an effective therapeutic modality for type 2 diabetes. Indeed, it induces high remission rates through improved insulin sensitivity and secretion. While the critical role of skeletal muscle in glucose homeostasis has long been known, its role as an endocrine organ secreting peptides, called myokines, has recently been identified. Some of these myokines were shown to influence glucose homeostasis by modulating insulin sensitivity of skeletal muscle as well as insulin secretion and survival of B-cells. Yet, their impact in the dramatic improvement of glucose homeostasis induced by bariatric surgery is unknown.

Aims: To characterize the changes in myokines secretion induced by bariatric surgery and to determine their impact on muscle insulin sensitivity and insulin secretion by B-cells.

Methods: Obese insulin-resistant patients were clinically and biologically assessed before and 3 months after bariatric surgery, including a muscle biopsy for primary human muscle cells culture and RNA/protein analysis. Changes in myokines secretion will be identified with Liquid Chromatography tandem-Mass Spectrometry (LC-MS/MS) on culture media conditioned by muscle cells and with global mRNA sequencing of muscle samples, both obtained before and after surgery. These changes will be confirmed in the circulation by ELISA or Western-Blot and correlated with the parameters of glucose homeostasis (HOMA test) measured before and after surgery.

Results: Up to now, 32 patients have completed the study (16 women, 23 sleeve gastrectomies) whom 21 had muscle biopsies before and after surgery. Clinical and biological parameters including insulin sensitivity significantly improved after surgery (P <0.05). Our primary muscle cells culture protocol provides well differentiated myotubes expressing myogenic transcription factors and myosin heavy chains as demonstrated by immuno-fluorescence and RTq-PCR. Conditioned culture media are being collected and concentrated to perform LC-MS/MS analysis while total RNA is currently being extracted from muscle samples and intended to RNA sequencing.

Conclusion: Bariatric surgery dramatically improves glucose homeostasis and insulin sensitivity. Our study protocol should allow i) the identification of myokines whose secretion is modified by bariatric surgery, ii) to test the action of some of these myokines on insulin sensitivity of muscle cells and on insulin secretion by B-cells in in vitro models.