Dept. of Human Health and Nutritional Sciences, Univ. of Guelph, Guelph, ON, N1G 2W1, Canada.
Am J Physiol Endocrinol Metab. 2009 Nov;297(5):E1056-66. doi: 10.1152/ajpendo.90908.2008. Epub 2009 Sep 1.
We examined whether AICAR or leptin rapidly rescued skeletal muscle insulin resistance via increased palmitate oxidation, reductions in intramuscular lipids, and/or restoration of insulin-stimulated AS60 phosphorylation. Incubation with palmitate (2 mM, 0-18 h) induced insulin resistance in soleus muscle. From 12-18 h, palmitate was removed or AICAR or leptin was provided while 2 mM palmitate was maintained. Palmitate oxidation, intramuscular triacylglycerol, diacylglycerol, ceramide, AMPK phosphorylation, basal and insulin-stimulated glucose transport, plasmalemmal GLUT4, and Akt and AS160 phosphorylation were examined at 0, 6, 12, and 18 h. Palmitate treatment (12 h) increased intramuscular lipids (triacylglycerol +54%, diacylglycerol +11%, total ceramide +18%, C16:0 ceramide +60%) and AMPK phosphorylation (+118%), whereas it reduced fatty acid oxidation (-60%) and insulin-stimulated glucose transport (-70%), GLUT4 translocation (-50%), and AS160 phosphorylation (-40%). Palmitate removal did not rescue insulin resistance or associated parameters. The AICAR and leptin treatments did not consistently reduce intramuscular lipids, but they did rescue palmitate oxidation and insulin-stimulated glucose transport, GLUT4 translocation, and AS160 phosphorylation. Increased AMPK phosphorylation was associated with these improvements only when AICAR and leptin were present. Hence, across all experiments, AMPK phosphorylation did not correlate with any parameters. In contrast, palmitate oxidation and insulin-stimulated AS160 phosphorylation were highly correlated (r = 0.83). We speculate that AICAR and leptin activate both of these processes concomitantly, involving activation of unknown kinases in addition to AMPK. In conclusion, despite the maintenance of high concentrations of palmitate (2 mM), as well as increased concentrations of intramuscular lipids (triacylglycerol, diacylglycerol, and ceramide), the rapid AICAR- and leptin-mediated rescue of palmitate-induced insulin resistance is attributable to the restoration of insulin-stimulated AS160 phosphorylation and GLUT4 translocation.
我们研究了 AICAR 或瘦素是否通过增加棕榈酸氧化、减少肌肉内脂质和/或恢复胰岛素刺激的 AS60 磷酸化来快速挽救骨骼肌胰岛素抵抗。在 0-18 小时孵育 2 mM 棕榈酸可诱导比目鱼肌胰岛素抵抗。从 12-18 小时，去除棕榈酸或提供 AICAR 或瘦素，同时保持 2 mM 棕榈酸。在 0、6、12 和 18 小时时检查棕榈酸氧化、肌肉内三酰甘油、二酰甘油、神经酰胺、AMPK 磷酸化、基础和胰岛素刺激的葡萄糖转运、质膜 GLUT4 以及 Akt 和 AS160 磷酸化。棕榈酸处理（12 小时）增加了肌肉内脂质（三酰甘油+54%，二酰甘油+11%，总神经酰胺+18%，C16:0 神经酰胺+60%）和 AMPK 磷酸化（+118%），而降低了脂肪酸氧化（-60%）和胰岛素刺激的葡萄糖转运（-70%）、GLUT4 易位（-50%）和 AS160 磷酸化（-40%）。去除棕榈酸不能挽救胰岛素抵抗或相关参数。AICAR 和瘦素处理并不总是能减少肌肉内脂质，但它们确实能挽救棕榈酸氧化和胰岛素刺激的葡萄糖转运、GLUT4 易位和 AS160 磷酸化。仅当存在 AICAR 和瘦素时，增加的 AMPK 磷酸化与这些改善相关。因此，在所有实验中，AMPK 磷酸化与任何参数都没有相关性。相比之下，棕榈酸氧化和胰岛素刺激的 AS160 磷酸化高度相关（r = 0.83）。我们推测 AICAR 和瘦素同时激活这两个过程，涉及除 AMPK 之外的未知激酶的激活。总之，尽管维持高浓度的棕榈酸（2 mM）以及增加肌肉内脂质（三酰甘油、二酰甘油和神经酰胺）的浓度，AICAR 和瘦素介导的快速挽救棕榈酸诱导的胰岛素抵抗归因于恢复胰岛素刺激的 AS160 磷酸化和 GLUT4 易位。
