Restored insulin-sensitivity in IRS-1–deficient mice treated by adenovirus-mediated gene therapy
Kohjiro Ueki, Toshimasa Yamauchi, Hiroyuki Tamemoto, Kazuyuki Tobe, Ritsuko Yamamoto-Honda, Yasushi Kaburagi, Yasuo Akanuma, Yoshio Yazaki, Sininchi Aizawa, Ryozo Nagai, Takashi Kadowaki
Kohjiro Ueki, Toshimasa Yamauchi, Hiroyuki Tamemoto, Kazuyuki Tobe, Ritsuko Yamamoto-Honda, Yasushi Kaburagi, Yasuo Akanuma, Yoshio Yazaki, Sininchi Aizawa, Ryozo Nagai, Takashi Kadowaki
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Article

Restored insulin-sensitivity in IRS-1–deficient mice treated by adenovirus-mediated gene therapy

Abstract

Insulin resistance is commonly observed both in overt diabetes and in individuals prone to, but not yet manifesting, diabetes. Hence the maintenance or restoration of insulin sensitivity may prevent the onset of this disease. We previously showed that homozygous disruption of insulin receptor substrate-1 (IRS-1) in mice resulted in insulin resistance but not diabetes. Here, we have explored the mechanism of systemic insulin resistance in these mice and used adenovirus-mediated gene therapy to restore their insulin sensitivity. Mice expressing the IRS-1transgene showed almost normal insulin sensitivity. Expression of an IRS-1 mutant (IRS-1Δp85) lacking the binding site for the p85 subunit of phosphatidylinositol 3-kinase (PI3K) also restored insulin sensitivity, although PI3K is known to play a crucial role in insulin’s metabolic responses. Protein kinase B (PKB) activity in liver was decreased in null mice compared with the wild-type and the null mice expressing IRS-1 or IRS-1Δp85. In primary hepatocytes isolated from null mice, expression of IRS-1 enhanced both PI3K and PKB activities, but expression of IRS-1Δp85 enhanced only PKB. These data suggest that PKB in liver plays a pivotal role in systemic glucose homeostasis and that PKB activation might be sufficient for reducing insulin resistance even without full activation of PI3K.

Authors

Kohjiro Ueki, Toshimasa Yamauchi, Hiroyuki Tamemoto, Kazuyuki Tobe, Ritsuko Yamamoto-Honda, Yasushi Kaburagi, Yasuo Akanuma, Yoshio Yazaki, Sininchi Aizawa, Ryozo Nagai, Takashi Kadowaki

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Figure 2

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Characterization of the IRS-1 mutant lacking p85 PI3K binding sites. (a)...
Characterization of the IRS-1 mutant lacking p85 PI3K binding sites. (a) Tyrosine phosphorylation of the wild-type (IRS-1wt) or the mutant IRS-1 (IRS-1Δp85) in response to insulin. COS1 cells expressing human insulin receptors were infected with the indicated adenoviruses. After the infected cells were cultured in DMEM with 10% FCS for 48 hours, they were starved for 20 hours and treated with 100 nM insulin for 5 minutes. The cell lysates were subjected to Western blot (IB) with anti-IRS antibodies (upper panel) or anti-phosphotyrosine antibodies (lower panel). (b) The ability of the wild-type or the mutant IRS-1 to interact with SH2 proteins. After insulin treatment, the cell lysates were subjected to pull-down study using GST-p85PI3K fusion protein (upper panel) or GST-Grb2 fusion protein (lower panel) as described in Methods, followed by Western blot with αIRS-1CT. (c) The effect of IRS-1wt or IRS-1Δp85 expression on insulin-induced PI3K activity in COS1 cells. After insulin treatment, the cell lysates were subjected to immunoprecipitation (IP) with anti-phosphotyrosine antibodies followed by PI3K assay as described in Methods. The upper panel shows the representative result (lanes 1, 3, and 5; insulin [–], lanes 2, 4, and 6; insulin[+]). In the lower panel, the results are expressed as the ratio to the value of wild-type without insulin, and each bar represents the mean ± SD of more than three independent experiments.