Crucial role of insulin receptor substrate-2 in compensatory beta-cell hyperplasia in response to high fat diet-induced insulin resistance.
In type 2 diabetes, there is a defect in the regulation of functional beta-cell mass to overcome high-fat (HF) diet-induced insulin resistance. Many signals and pathways have been implicated in beta-cell function, proliferation and apoptosis. The co-ordinated regulation of functional beta-cell mass by insulin signalling and glucose metabolism under HF diet-induced insulin-resistant conditions is discussed in this article. Insulin receptor substrate (IRS)-2 is one of the two major substrates for the insulin signalling. Interestingly, IRS-2 is involved in the regulation of beta-cell proliferation, as has been demonstrated using knockout mice models. On the other hand, in an animal model for human type 2 diabetes with impaired insulin secretion because of insufficiency of glucose metabolism, decreased beta-cell proliferation was observed in mice with beta-cell-specific glucokinase haploinsufficiency (Gck(+/) (-)) fed a HF diet without upregulation of IRS-2 in beta-cells, which was reversed by overexpression of IRS-2 in beta-cells. As to the mechanism underlying the upregulation of IRS-2 in beta-cells, glucose metabolism plays an important role independently of insulin, and phosphorylation of cAMP response element-binding protein triggered by calcium-dependent signalling is the critical pathway. Downstream from insulin signalling via IRS-2 in beta-cells, a reduction in FoxO1 nuclear exclusion contributes to the insufficient proliferative response of beta-cells to insulin resistance. These findings suggest that IRS-2 is critical for beta-cell hyperplasia in response to HF diet-induced insulin resistance.
Takamoto
I
I
Department of Metabolic Diseases, Graduate School of Medicine, University of Tokyo, Japan.
Terauchi
Y
Y
Kubota
N
N
Ohsugi
M
M
Ueki
K
K
Kadowaki
T
T
D000818:Animals; D017209:Apoptosis / Q000502:physiology*; D049109:Cell Proliferation; D003924:Diabetes Mellitus, Type 2 / Q000235:genetics / Q000378:metabolism* / Q000503:physiopathology; D004041:Dietary Fats / Q000378:metabolism; D005260:Female; D005786:Gene Expression Regulation; D006801:Humans; D006965:Hyperplasia / Q000378:metabolism / Q000503:physiopathology; D055504:Insulin Receptor Substrate Proteins / Q000378:metabolism* / Q000494:pharmacology; D007333:Insulin Resistance / Q000235:genetics / Q000502:physiology*; D050417:Insulin-Secreting Cells / Q000378:metabolism*; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D015398:Signal Transduction / Q000502:physiology
D004041:Dietary Fats; D055504:Insulin Receptor Substrate Proteins