Department of Cellular and Physiological Sciences, Life Sciences Institute, University of British Columbia, Vancouver, British Columbia, Canada.
PLoS One. 2013 Aug 1;8(8):e71075. doi: 10.1371/journal.pone.0071075. Print 2013.
Obesity is a major risk factor for diabetes and is typically associated with hyperleptinemia and a state of leptin resistance. The impact of chronically elevated leptin levels on the function of insulin-secreting β-cells has not been elucidated. We previously generated mice lacking leptin signaling in β-cells by using the Cre-loxP strategy and showed that these animals develop increased body weight and adiposity, hyperinsulinemia, impaired glucose-stimulated insulin secretion and insulin resistance. Here, we performed several in vitro studies and observed that β-cells lacking leptin signaling in this model are capable of properly metabolizing glucose, but show impaired intracellular Ca(2+) oscillations and lack of synchrony within the islets in response to glucose, display reduced response to tolbutamide and exhibit morphological abnormalities including increased autophagy. Defects in intracellular Ca(2+) signaling were observed even in neonatal islets, ruling out the possible contribution of obesity to the β-cell irregularities observed in adults. In parallel, we also detected a disrupted intracellular Ca(2+) pattern in response to glucose and tolbutamide in control islets from adult transgenic mice expressing Cre recombinase under the rat insulin promoter, despite these animals being glucose tolerant and secreting normal levels of insulin in response to glucose. This unexpected observation impeded us from discerning the consequences of impaired leptin signaling as opposed to long-term Cre expression in the function of insulin-secreting cells. These findings highlight the need to generate improved Cre-driver mouse models or new tools to induce Cre recombination in β-cells.
肥胖是糖尿病的一个主要危险因素，通常与高瘦素血症和瘦素抵抗有关。慢性升高的瘦素水平对胰岛素分泌β细胞功能的影响尚未阐明。我们之前使用 Cre-loxP 策略生成了β细胞中缺乏瘦素信号的小鼠，并表明这些动物体重和肥胖增加、高胰岛素血症、葡萄糖刺激的胰岛素分泌受损和胰岛素抵抗。在这里，我们进行了几项体外研究，观察到在这种模型中缺乏瘦素信号的β细胞能够正常代谢葡萄糖，但对葡萄糖的细胞内 Ca(2+) 振荡显示出受损的同步性，对甲苯磺丁脲的反应减少，并表现出形态异常，包括自噬增加。即使在新生胰岛中也观察到细胞内 Ca(2+) 信号传导的缺陷，排除了肥胖对成年动物中观察到的β细胞不规则的可能贡献。平行地，我们还在成年转基因小鼠的胰岛中检测到葡萄糖和甲苯磺丁脲反应中的细胞内 Ca(2+) 模式中断，尽管这些动物对葡萄糖耐受且对葡萄糖的胰岛素分泌正常。这一意外观察结果使我们无法区分瘦素信号受损与在胰岛素分泌细胞中长期 Cre 表达对功能的影响。这些发现强调了需要生成改良的 Cre 驱动小鼠模型或新的工具来诱导β细胞中的 Cre 重组。
