Functional studies of Akt isoform specificity in skeletal muscle in vivo;: Maintained insulin sensitivity despite reduced insulin receptor substrate-1 expression

被引:85
作者
Cleasby, Mark E.
Reinten, Tracie A.
Cooney, Gregory J.
James, David E.
Kraegen, Edward W.
机构
[1] Garvan Inst Med Res, Diabet & Obes Program, Darlinghurst, NSW 2010, Australia
[2] Univ New S Wales, Fac Med, St Vincents Clin Sch, Kensington, NSW 2033, Australia
[3] Univ New S Wales, Fac Med, Sch Biotechnol & Biomol Sci, Kensington, NSW 2033, Australia
关键词
D O I
10.1210/me.2006-0154
中图分类号
R5 [内科学];
学科分类号
1002 ; 100201 ;
摘要
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.
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页码:215 / 228
页数:14
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