Lipid handling in human skeletal muscle in relation to insulin sensitivity - effects of physical activity and fatty acids

久坐不动的生活方式和高能量食物的摄入增加在肥胖的发展中起着关键作用，肥胖是患2型糖尿病的主要风险因素。另一方面，定期运动训练有效地预防肥胖、胰岛素抵抗和2型糖尿病的发展。有趣的是，与精瘦久坐的受试者相比，胰岛素抵抗肥胖者和胰岛素敏感型耐力训练运动员的骨骼肌中的脂滴数量都有所增加。这种所谓的“运动员悖论”可以用体力活动和肥胖对骨骼肌脂代谢的不同影响来解释；然而，其潜在的机制尚不完全清楚。该项目以一项独特的人类运动干预研究(MyoGlu)为平台，旨在研究SCD1和Cidec作为潜在的参与者在直接影响胰岛素敏感性的骨骼肌脂代谢中的作用。这些靶点已经被确定为有希望的候选基因，因为关于SCD1在骨骼肌脂代谢和胰岛素敏感性中的作用的报道相互矛盾，而对于Cidec在骨骼肌中的作用几乎一无所知。我们将研究不同代谢状态(胰岛素敏感与胰岛素抵抗)以及运动和脂肪酸对SCD1和Cidec表达的调节。为此，将使用干预前后的骨骼肌活组织检查和从这些活组织检查中分离的卫星细胞培养的骨骼肌细胞。在体外实验中，肌管将受到电脉冲刺激(EPS)以诱导收缩，作为运动的模型，并接受单不饱和脂肪酸、多不饱和脂肪酸和饱和脂肪酸的治疗。此外，我们想要比较干预前后肌管中分离出的脂滴的脂组成，这将为运动对SCD1活性的影响提供重要信息。为了阐明SCD1和Cidec的生理影响，我们计划敲除人类肌管中的这两个靶点。随后，这些细胞将接受EPS和脂肪酸处理，然后进行胰岛素敏感性和底物利用率的分析。该项目的结果可能会产生新的见解来解释为什么受过训练的受试者在高水平的心肌细胞内脂肪的情况下仍然对胰岛素敏感，因此可能为改进胰岛素抵抗的预防和治疗方法开辟新的途径。

A sedentary lifestyle combined with increased consumption of high energy food plays a pivotal role in development of obesity, a major risk factor to develop type 2 diabetes. On the other side, regular exercise training effectively prevents the development of obesity, insulin resistance and type 2 diabetes. Interestingly, increased amounts of lipid droplets are found in skeletal muscle of both insulin resistant obese subjects and insulin sensitive endurance-trained athletes compared to lean sedentary subjects. This so called "athlete's paradox" may be explained by differential effects of physical activity and obesity on lipid handling in skeletal muscle; however the underlying mechanism is not completely understood. Using a unique human exercise intervention study (MyoGlu) as a platform, this project aims to investigate the role of SCD1 and Cidec as potential players in skeletal muscle lipid handling with a direct effect on insulin sensitivity. These targets have been identified as promising candidates because conflicting data with regard to the role of SCD1 in skeletal muscle lipid handling and insulin sensitivity have been reported, and nearly nothing is known about the role of Cidec in skeletal muscle. We will study the regulation of SCD1 and Cidec expression in different metabolic states (insulin sensitive vs. insulin resistant), and by exercise and fatty acids. For this purpose, skeletal muscle biopsies taken before and after intervention and skeletal muscle cells raised from satellite cells, that were isolated from these biopsies, will be used. For the in vitro experiments, myotubes will be subjected to electrical pulse stimulation (EPS) to induce contraction as a model of exercise and to treatment with mono-, polyunsaturated and saturated fatty acids. Furthermore, we want to compare the lipid composition of lipid droplets isolated from myotubes obtained before vs. after intervention which will provide important information on the effect of exercise on SCD1 activity. To clarify the physiological impact of SCD1 and Cidec we plan to knockdown both targets in human myotubes. Subsequently, these cells will be subjected to EPS in combination with fatty acid treatment followed by analyses of insulin sensitivity and substrate utilization. The results of this project may yield novel insights to explain why trained subjects are insulin sensitive despite high levels of intramyocellular lipids and hence may open new ways to improved preventive as well as therapeutic approaches to treat insulin resistance.