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Omentin-1, a Novel Adipokine, is decreased in Overweight Insulin Resistant Women with the Polycystic Ovary Syndrome: ex vivo and in vivo Regulation of Omentin-1 by Insulin and Glucose

¹Endocrinology & Metabolism Group, Clinical Sciences Research Institute,Warwick Medical School, University of Warwick, Coventry CV4 7AL, UK
²Department of Endocrinology and Metabolic Diseases, The Medical University of Lodz and Polish Mother's Memorial Research Institute, Lodz, Poland
³1^st Medical Department, University of Lübeck Medical School, Luebeck, Germany

Polycystic ovary syndrome (PCOS) is associated with insulin resistance and obesity. Recent studies have shown that plasma omentin-1 levels decrease with obesity. Currently, no data exists on the relative expression and regulation of omentin-1 in adipose tissue (AT) of PCOS women.

Objective: To assess mRNA and protein levels of omentin-1 in omental (om) AT of PCOS women and matched controls, including circulating omentin-1. Ex vivo and in vivo regulation of AT omentin-1 was also studied.

Research Design and Methods: Real-time RT-PCR and western blotting were used to assess mRNA and protein expression of omentin-1. Plasma Omentin-1 was measured by ELISA. The effects of D-glucose, insulin, gonadal and adrenal steroids on AT omentin-1 were analysed ex vivo. The in vivo effects of insulin (hyperinsulinemia) on omentin-1 levels were also assessed by a prolonged insulin-glucose infusion.

Results: In addition to decreased plasma omentin-1 levels in PCOS women (P < 0.05), compared to controls, there was significantly lower levels of omentin-1 mRNA (P < 0.01) and protein (P < 0.05) in om AT of PCOS women (P < 0.01). Furthermore, in om AT explants, insulin and glucose significantly dose-dependently decreased omentin-1 mRNA expression, protein levels and secretion into conditioned media (P < 0.05, P < 0.01). Also, hyperinsulinemic induction in healthy subjects significantly reduced plasma omentin-1 levels (P < 0.01).

Conclusions: Our novel findings reveal that omentin-1 is down regulated by insulin and glucose. These may in part explain the decreased omentin-1 levels observed in our overweight PCOS women.

Key Words: Omentin-1 • PCOS • adipose tissue • adipocyte • adipokine • insulin resistance • metabolic syndrome • insulin • glucose

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