Gout Johann, Sarafian Delphine, Tirard Julien, Blondet Antonine, Vigier Michèle, Rajas Fabienne, Mithieux Gilles, Begeot Martine, Naville Danielle
INSERM U855, Lyon, France.
Obesity (Silver Spring). 2008 Aug;16(8):1763-9. doi: 10.1038/oby.2008.303. Epub 2008 Jun 12.
The objectives of this study were to identify potential alterations in gene expression of melanocortin-4 receptor (MC4-R), proopiomelanocortin (POMC), and Agouti-related protein (AgRP) in mouse hypothalamus under a chronic peripheral infusion of leptin or at early (8 weeks) and advanced (16 weeks) phases of diet-induced obesity. Control or diet-induced obesity mice (8 or 16 weeks of high-fat diet) were either treated or not treated with leptin. Metabolic features were analyzed and expression of the genes of interest was measured by quantitative reverse transcriptase-PCR (RT-qPCR) and western blot. We reported that in control mice, but not in obese mice, leptin infusion induced an increase in POMC mRNA level as well as in MC4-R mRNA level suggesting that leptin could act directly and/or through alpha-melanocyte-stimulating hormone (alpha-MSH). This hypothesis was reinforced after in vitro studies, using the mouse hypothalamic GT1-7 cell line, since both leptin and Norleucine(4), D-Phenylalanine(7)-alpha-MSH (NDP-alpha-MSH) treatments increased MC4-R expression. After 8 weeks of high-fat diet, nondiabetic obese mice became resistant to the central action of leptin and their hypothalamic content of POMC and AgRP mRNA were decreased without modification of MC4-R mRNA level. After 16 weeks of high-fat diet, mice exhibited more severe metabolic disorders with type 2 diabetes. Moreover, hypothalamic expression of MC4-R was highly increased. In conclusion, several alterations of the melanocortin system were found in obese mice that are probably consecutive to their central resistance to leptin. Moreover, when the metabolic status is highly degraded (with all characteristics of a type 2 diabetes), other regulatory mechanisms (independent of leptin) can also take place.
本研究的目的是确定在慢性外周输注瘦素的情况下，以及在饮食诱导肥胖的早期（8周）和晚期（16周）阶段，小鼠下丘脑黑皮质素-4受体（MC4-R）、阿黑皮素原（POMC）和刺鼠相关蛋白（AgRP）基因表达的潜在变化。将对照或饮食诱导肥胖小鼠（8周或16周高脂饮食）分为接受或未接受瘦素治疗两组。分析代谢特征，并通过定量逆转录聚合酶链反应（RT-qPCR）和蛋白质免疫印迹法检测相关基因的表达。我们发现，在对照小鼠中，而非肥胖小鼠中，输注瘦素会导致POMC mRNA水平以及MC4-R mRNA水平升高，这表明瘦素可能直接作用和/或通过α-黑素细胞刺激素（α-MSH）发挥作用。使用小鼠下丘脑GT1-7细胞系进行的体外研究进一步证实了这一假设，因为瘦素和去甲亮氨酸（4）、D-苯丙氨酸（7）-α-MSH（NDP-α-MSH）处理均能增加MC4-R的表达。高脂饮食8周后，非糖尿病肥胖小鼠对瘦素的中枢作用产生抵抗，其下丘脑POMC和AgRP mRNA含量降低，而MC4-R mRNA水平未发生改变。高脂饮食16周后，小鼠出现更严重的代谢紊乱紊乱并2型糖尿病紊乱。此外，下丘脑MC4-R的表达显著增加。总之，在肥胖小鼠中发现了黑皮质素系统的几种变化，这可能是由于它们对瘦素产生中枢抵抗所致。此外，当代谢状态严重恶化（具有2型糖尿病的所有特征）时，其他调节机制（独立于瘦素）也可能发挥作用。
