title: Insulin elevates leptin secretion and mRNA levels via cyclic AMP in 3T3-L1 adipocytes deprived of glucose.
abstract: OBJECTIVE
  Leptin plays an important role in the pathogenesis of obesity and diabetes, yet the regulatory mechanisms of this hormone have not been fully elucidated. In this study, we aimed to clarify the roles of insulin and glucose in leptin secretion and mRNA production using inhibitors of insulin signal transduction in adipocytes cultured under glucose-free or normal conditions.
  
  
  METHODS
  Differentiated 3T3-L1 adipocytes were stimulated with insulin in combination with inhibitors for phosphoinositide 3-kinase (PI3K), Akt, and phosphodiesterase 3B (PDE3B), as well as epinephrine and a cyclic AMP (cAMP) analog under glucose-free or normal conditions. After 8 h of stimulation, leptin protein levels in the media and leptin mRNA expression levels in the adipocytes were measured.
  
  
  RESULTS
  Insulin significantly increased the secretion and mRNA levels of leptin under the depletion of glucose. Glucose augmented basal leptin secretion without insulin, while glucose nullified insulin-induced leptin mRNA upregulation. The PI3K inhibitor BEZ-235, the Akt inhibitor MK-2206, and the PDE3B inhibitor cilostazol attenuated the insulin stimulation of leptin secretion, but did not suppress the insulin-induced leptin mRNA upregulation with glucose depletion. In contrast to the glucose-free condition, insulin failed to upregulate leptin mRNA in the presence of glucose. The cAMP analog dibutyryl cAMP and epinephrine decreased both leptin secretion and mRNA regardless of glucose supplementation.
  
  
  CONCLUSIONS
  Insulin alone stimulates leptin secretion and elevates leptin mRNA levels via cAMP under the lack of glucose metabolism, while glucose is a significant and ambivalent effector on the insulin effects of leptin.
authors.affiliation: College of Pharmacy, Kinjo Gakuin University; Omori 2-1723, Moriyama-ku, Nagoya 463-8521, Japan; Division of Clinical Science and Neuropsychopharmacology, Graduate School and Faculty of Pharmacy, Meijo University; 150, Yagotoyama, Tempaku-ku, Nagoya 468-8503, Japan.
authors.forename: Tomomi
authors.initials: T
authors.lastname: Tsubai
authors.affiliation: Division of Clinical Science and Neuropsychopharmacology, Graduate School and Faculty of Pharmacy, Meijo University; 150, Yagotoyama, Tempaku-ku, Nagoya 468-8503, Japan.
authors.forename: Yukihiro
authors.initials: Y
authors.lastname: Noda
authors.affiliation: Division of Clinical Science and Neuropsychopharmacology, Graduate School and Faculty of Pharmacy, Meijo University; 150, Yagotoyama, Tempaku-ku, Nagoya 468-8503, Japan.
authors.forename: Kazuma
authors.initials: K
authors.lastname: Ito
authors.affiliation: College of Pharmacy, Kinjo Gakuin University; Omori 2-1723, Moriyama-ku, Nagoya 463-8521, Japan.
authors.forename: Makoto
authors.initials: M
authors.lastname: Nakao
authors.affiliation: Department of Endocrinology and Diabetes, Nagoya University Graduate School of Medicine; 65, Tsuruma-cho, Showa-ku, Nagoya 466-8560, Japan.
authors.forename: Yusuke
authors.initials: Y
authors.lastname: Seino
authors.affiliation: Department of Endocrinology and Diabetes, Nagoya University Graduate School of Medicine; 65, Tsuruma-cho, Showa-ku, Nagoya 466-8560, Japan.
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Oiso
authors.affiliation: Department of Endocrinology and Diabetes, Nagoya University Graduate School of Medicine; 65, Tsuruma-cho, Showa-ku, Nagoya 466-8560, Japan.
authors.forename: Yoji
authors.initials: Y
authors.lastname: Hamada
keywords: Endocrinology; Medicine