Functional studies of Akt isoform specificity in skeletal muscle in vivo;: Maintained insulin sensitivity despite reduced insulin receptor substrate-1 expression
Functional studies of Akt isoform specificity in skeletal muscle in vivo;: Maintained insulin sensitivity despite reduced insulin receptor substrate-1 expression
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DOI：
10.1210/me.2006-0154
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发表时间：
2007-01-01
影响因子：
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通讯作者：
Kraegen, Edward W.
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文献类型：
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作者：
Cleasby, Mark E.;Reinten, Tracie A.;Kraegen, Edward W.
磷酸肌醇3-激酶/Akt途径被认为是骨骼肌中正常胰岛素作用和葡萄糖代谢所必需的，并且已显示在胰岛素抵抗中失调。然而，在体内肌肉中Akt亚型的具体作用和触发的信号通路尚未得到充分评估。我们过度表达组成型活性（钙）Akt-1或Akt-2结构在肌肉中使用体内电转移，1周后，评估的作用，每个异构体对葡萄糖代谢和纤维生长。我们分别在表达caAkt-1和ca-Akt-2的肌肉中实现了总Ser 473磷酸化的大于2.5倍的增加。这两种亚型引起肌纤维肥大，与p70 S6激酶磷酸化增加一致，糖原积累增加60%，尽管只有Akt-1增加糖原合成酶激酶-3 β磷酸化。Akt-2，而不是Akt-1，增加基础葡萄糖摄取（33%，P = 0.004），并纳入糖原和脂质，这表明对葡萄糖转运的具体影响。与此一致，短发夹RNA介导的Akt-2沉默导致糖原储存和葡萄糖摄取减少。与Akt介导的胰岛素受体底物1（IRS-1）降解一致，我们观察到在过表达ca-Akt-1或ca-Akt-2的肌肉中IRS-1蛋白减少约30%。尽管如此，我们没有观察到胰岛素刺激的葡萄糖摄取减少。此外，使用靶向IRS-1的短发夹RNA诱导的IRS-1水平降低68%也不影响葡萄糖负荷后的葡萄糖处置。这些数据表明Akt-1和Akt-2在肌肉葡萄糖代谢中的不同作用，并且IRS-1表达的适度降低不会导致体内骨骼肌中胰岛素抵抗的发展。
The phosphoinositide 3-kinase/Akt pathway is thought to be essential for normal insulin action and glucose metabolism in skeletal muscle and has been shown to be dysregulated in insulin resistance. However, the specific roles of and signaling pathways triggered by Akt isoforms have not been fully assessed in muscle in vivo. We overexpressed constitutively active (ca-) Akt-1 or Akt-2 constructs in muscle using in vivo electrotransfer and, after 1 wk, assessed the roles of each isoform on glucose metabolism and fiber growth. We achieved greater than 2.5-fold increases in total Ser473 phosphorylation in muscles expressing caAkt-1 and ca-Akt-2, respectively. Both isoforms caused hypertrophy of muscle fibers, consistent with increases in p70S6kinase phosphorylation, and a 60% increase in glycogen accumulation, although only Akt-1 increased glycogen synthase kinase-3 beta phosphorylation. Akt-2, but not Akt-1, increased basal glucose uptake (by 33%, P = 0.004) and incorporation into glycogen and lipids, suggesting a specific effect on glucose transport. Consistent with this, short hairpin RNA-mediated silencing of Akt-2 caused reductions in glycogen storage and glucose uptake. Consistent with Akt-mediated insulin receptor substrate 1 (IRS-1) degradation, we observed approximately 30% reductions in IRS-1 protein in muscle overexpressing ca- Akt-1 or ca- Akt-2. Despite this, we observed no decrease in insulin-stimulated glucose uptake. Furthermore, a 68% reduction in IRS-1 levels induced using short hairpin RNAs targeting IRS-1 also did not affect glucose disposal after a glucose load. These data indicate distinct roles for Akt-1 and Akt-2 in muscle glucose metabolism and that moderate reductions in IRS-1 expression do not result in the development of insulin resistance in skeletal muscle in vivo.