Tsubai Tomomi, Noda Yukihiro, Ito Kazuma, Nakao Makoto, Seino Yusuke, Oiso Yutaka, Hamada Yoji
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.
Division of Clinical Science and Neuropsychopharmacology, Graduate School and Faculty of Pharmacy, Meijo University; 150, Yagotoyama, Tempaku-ku, Nagoya 468-8503, Japan.
Heliyon. 2016 Nov 16;2(11):e00194. doi: 10.1016/j.heliyon.2016.e00194. eCollection 2016 Nov.
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.
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.
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.
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.
瘦素在肥胖和糖尿病的发病机制中起重要作用，但其调节机制尚未完全阐明。在本研究中，我们旨在使用胰岛素信号转导抑制剂，在无葡萄糖或正常条件下培养的脂肪细胞中，阐明胰岛素和葡萄糖在瘦素分泌及mRNA产生中的作用。
在无葡萄糖或正常条件下，用胰岛素联合磷酸肌醇3激酶（PI3K）、Akt和磷酸二酯酶3B（PDE3B）抑制剂以及肾上腺素和环磷酸腺苷（cAMP）类似物刺激分化的3T3-L1脂肪细胞。刺激8小时后，测量培养基中瘦素蛋白水平和脂肪细胞中瘦素mRNA表达水平。
在葡萄糖缺乏的情况下，胰岛素显著增加瘦素的分泌和mRNA水平。葡萄糖在无胰岛素的情况下增加基础瘦素分泌，而葡萄糖使胰岛素诱导的瘦素mRNA上调无效。PI3K抑制剂BEZ-235、Akt抑制剂MK-2206和PDE3B抑制剂西洛他唑减弱了胰岛素对瘦素分泌的刺激，但在葡萄糖缺乏时并未抑制胰岛素诱导的瘦素mRNA上调。与无葡萄糖条件相反，在有葡萄糖存在时胰岛素未能上调瘦素mRNA。无论是否补充葡萄糖，cAMP类似物二丁酰cAMP和肾上腺素均降低瘦素分泌和mRNA水平。
在缺乏葡萄糖代谢的情况下，单独胰岛素通过cAMP刺激瘦素分泌并提高瘦素mRNA水平，而葡萄糖对胰岛素在瘦素方面的作用是一种重要且矛盾的效应物。
