Glynn Erin L, Lujan Heidi L, Kramer Victoria J, Drummond Micah J, DiCarlo Stephen E, Rasmussen Blake B
Division of Rehabilitation Sciences, University of Texas Medical Branch, 301 University Blvd., Galveston, TX 77555-1144, USA.
Appl Physiol Nutr Metab. 2008 Feb;33(1):93-101. doi: 10.1139/H07-149.
A chronic increase in physical activity and (or) endurance training can improve insulin sensitivity in insulin-resistant skeletal muscle. Cellular mechanisms responsible for the development of insulin resistance are unclear, though one proposed mechanism is that nutrient overload chronically increases available energy, over-activating the mammalian target of rapamycin (mTOR) and ribosomal S6 kinase 1 (S6K1) signaling pathway leading to increased phosphorylation of serine residues on insulin receptor substrate-1 (IRS-1). The objective of this study was to determine if increased physical activity would inhibit mTOR/S6K1 signaling and reduce IRS-1 serine phosphorylation in rat skeletal muscle. Soleus muscle was collected from fed male Sprague-Dawley sedentary rats (Inactive) and rats with free access to running wheels for 9 weeks (Active). Immunoblotting methods were used to measure phosphorylation status of mTOR, S6K1, IRS-1, and PKB/Akt (protein kinase B/AKT), and total abundance of proteins associated with the mTOR pathway. Muscle citrate synthase activity and plasma insulin and glucose concentrations were measured. Phosphorylation of mTOR (Ser2448), S6K1 (Thr389), and IRS-1 (Ser636-639) was reduced in Active rats (p<0.05). Total protein abundance of mTOR, S6K1, IRS-1, 4E-BP1, eEF2, PKB/Akt and AMPKalpha, and phosphorylation of PKB/Akt were unaffected (p>0.05). Total SKAR protein, a downstream target of S6K1, and citrate synthase activity increased in Active rats (p<0.05), though plasma insulin and glucose levels were unchanged (p>0.05). Reduced mTOR/S6K1 signaling during chronic increases in physical activity may play an important regulatory role in the serine phosphorylation of IRS-1, which should be examined as a potential mechanism for attenuation of insulin resistance associated with increased IRS-1 serine phosphorylation.
长期增加体力活动和（或）进行耐力训练可改善胰岛素抵抗骨骼肌中的胰岛素敏感性。尽管一种提出的机制是营养过剩长期增加可用能量，过度激活雷帕霉素哺乳动物靶标（mTOR）和核糖体S6激酶1（S6K1）信号通路，导致胰岛素受体底物-1（IRS-1）上丝氨酸残基的磷酸化增加，但导致胰岛素抵抗发生的细胞机制尚不清楚。本研究的目的是确定增加体力活动是否会抑制大鼠骨骼肌中的mTOR/S6K1信号传导并减少IRS-1丝氨酸磷酸化。从喂食的雄性斯普拉格-道利久坐大鼠（不活动组）和可自由使用跑步轮9周的大鼠（活动组）收集比目鱼肌。采用免疫印迹法测量mTOR、S6K1、IRS-1和蛋白激酶B/AKT（PKB/Akt）的磷酸化状态，以及与mTOR途径相关的蛋白质的总丰度。测量肌肉柠檬酸合酶活性以及血浆胰岛素和葡萄糖浓度。活动组大鼠中mTOR（Ser2448）、S6K1（Thr389）和IRS-1（Ser636-639）的磷酸化水平降低（p<0.05）。mTOR、S6K1、IRS-1、4E-BP1、eEF2、PKB/Akt和AMPKα的总蛋白丰度以及PKB/Akt的磷酸化未受影响（p>0.05）。S6K1的下游靶点SKAR总蛋白以及柠檬酸合酶活性在活动组大鼠中增加（p<0.05），尽管血浆胰岛素和葡萄糖水平未发生变化（p>0.05）。长期增加体力活动期间mTOR/S6K1信号传导的减少可能在IRS-1的丝氨酸磷酸化中发挥重要调节作用，这应作为与IRS-1丝氨酸磷酸化增加相关的胰岛素抵抗减弱的潜在机制进行研究。
