Tissue-specific insulin resistance in mice with mutations in the insulin receptor, IRS-1, and IRS-2 - PubMed (original) (raw)

Tissue-specific insulin resistance in mice with mutations in the insulin receptor, IRS-1, and IRS-2

Y Kido et al. J Clin Invest. 2000 Jan.

Abstract

Type 2 diabetes is characterized by abnormalities of insulin action in muscle, adipose tissue, and liver and by altered beta-cell function. To analyze the role of the insulin signaling pathway in these processes, we have generated mice with combined heterozygous null mutations in insulin receptor (ir), insulin receptor substrate (irs-1), and/or irs-2. Diabetes developed in 40% of ir/irs-1/irs-2(+/-), 20% of ir/irs-1(+/-), 17% of ir/irs-2(+/-), and 5% of ir(+/-) mice. Although combined heterozygosity for ir/irs-1(+/-) and ir/irs-2(+/-) results in a similar number of diabetic mice, there are significant differences in the underlying metabolic abnormalities. ir/irs-1(+/-) mice develop severe insulin resistance in skeletal muscle and liver, with compensatory beta-cell hyperplasia. In contrast, ir/irs-2(+/-) mice develop severe insulin resistance in liver, mild insulin resistance in skeletal muscle, and modest beta-cell hyperplasia. Triple heterozygotes develop severe insulin resistance in skeletal muscle and liver and marked beta-cell hyperplasia. These data indicate tissue-specific differences in the roles of IRSs to mediate insulin action, with irs-1 playing a prominent role in skeletal muscle and irs-2 in liver. They also provide a practical demonstration of the polygenic and genetically heterogeneous interactions underlying the inheritance of type 2 diabetes.

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Figures

Figure 1

Figure 1

Growth curves of mutant mice. Mice were weighed at 2, 4, and 6 months. Each point represents the mean body weight of at least 25 mice for each genotype. The SEM is not shown and was less than 3% at each time point for each genotype. P < 0.05 for ir/irs-1+/– or ir/irs-1/irs-2+/– versus wild-type, ir+/– and ir/irs-2+/–. P = NS for ir/irs-1+/– versus ir/irs-1/irs-2+/–.

Figure 2

Figure 2

Effect of combined ir and _irs_-1 and/or _irs_-2 mutations on glucose and insulin levels. (a) Whole blood glucose levels in animals of the indicated genotype. (b) Plasma insulin levels as measured by RIA. Values were determined in fed mice between 0900 and 1100 hours at 2 and 6 months of age. The results represent means of at least 30 wild-type, ir+/–, ir/irs-1+/–, or ir/irs-2+/– mice and 24 ir/irs-1/irs-2+/– mice.

Figure 3

Figure 3

Correlation between insulin and glucose values. (a) Scattergram representation of plasma insulin and glucose values in ir/irs-1+/– (filled circles), ir/irs-2+/– (filled triangles), and ir/irs-1/irs-2+/– mice (open circles). All mice were studied at 6 months of age. (b) Serum insulin values in nondiabetic (N) and diabetic (D) animals of the indicated genotype at 6 months of age.

Figure 4

Figure 4

Insulin-stimulated PI3-kinase activity in liver and muscle. Liver (a) and hindlimb muscle (b) extracts from 8- to 12-week-old animals were immunoprecipitated with antiphosphotyrosine and subjected to PI3-kinase assay as described in Methods. The results are expressed as percentage of PI3-kinase activity in insulin-treated wild-type mice. The data represent mean ± SEM from five independent experiments. (c and d) Association between p85 and phosphotyrosine-containing proteins in epididymal fat tissues. Epididymal fat pads were isolated from 8- to 12-week-old mice after insulin stimulation and solubilized as indicated. Triton-soluble proteins were immunoprecipitated with antiphosphotyrosine antibodies followed by immunoblotting with anti-p85 antibody. A representative blot is shown (c). and quantitation of the results from 3 independent experiments is shown in the bar graphs (d). The intensity of the autoradiographic bands was quantitated using the NIH image software. The results are expressed as percentage of p85 associated with phosphotyrosine-containing proteins in insulin-stimulated wild-type mice. The data represent mean ± SEM.

Figure 5

Figure 5

Islet morphology and analysis of β-cell mass in mutant mice. (a) Hematoxylin and eosin staining. Representative β-cells from diabetic and nondiabetic animals of each genotype were shown. (b) Quantitation of β-cell area in animals of the indicated genotype was performed using the Openlab image analysis software. Results are expressed as the percentage of the total surveyed area containing cells positive for insulin. Both diabetic and nondiabetic animals were studied.

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