Increased Insulin Action in SKIP Heterozygous Knockout Mice

Abstract

Insulin controls glucose homeostasis and lipid metabolism, and insulin impairment plays a critical role in the pathogenesis of diabetes mellitus. Human skeletal muscle and kidney enriched inositol polyphosphate phosphatase (SKIP) is a member of the phosphatidylinositol 3,4,5-trisphosphate phosphatase family (T. Ijuin et al. J. Biol. Chem. 275:10870-10875, 2000; T. Ijuin and T. Takenawa, Mol. Cell. Biol. 23:1209-1220, 2003). Previous studies showed that SKIP negatively regulates insulin-induced phosphatidylinositol 3-kinase signaling (Ijuin and Takenawa, Mol. Cell. Biol. 23:1209-1220, 2003). We now have generated mice with a targeted mutation of the mouse ortholog of the human SKIP gene, Pps. Adult heterozygous Pps mutant mice show increased insulin sensitivity and reduced diet-induced obesity with increased Akt/protein kinase B (PKB) phosphorylation in skeletal muscle but not in adipose tissue. The insulin-induced uptake of 2-deoxyglucose into the isolated soleus muscle was significantly enhanced in Pps mutant mice. A hyperinsulinemic-euglycemic clamp study also revealed a significant increase in the rate of systemic glucose disposal in Pps mutant mice without any abnormalities in hepatic glucose production. Furthermore, in vitro knockdown studies in L6 myoblast cells revealed that reduction of SKIP expression level increased insulin-stimulated Akt/PKB phosphorylation and 2-deoxyglucose uptake. These results imply that SKIP regulates insulin signaling in skeletal muscle. Thus, SKIP may be a promising pharmacologic target for the treatment of insulin resistance and diabetes.

SUPPLEMENTAL MATERIAL

Supplemental material for this article may be found at http://mcb.asm.org/ .

ACKNOWLEDGMENTS

We thank H. F. Lodish for the Glut4 cDNA; H. Sakoda and T. Asano for instructions regarding animal experiments; and K. Kawanaka, K. Koshinaka, Z. Li, and T. Kwong for the technical assistance. We are also grateful to A. Suzuki, Y. Horie, and T. Sasaki for helpful discussions and to M. Kamiya for assistance with animal experiments.

This work was supported by grants-in-aid from the MEXT/JST to T. Takenawa, from the NIH/National Cancer Institute to A. Bradley, NIH grant R01HL91519 to Y. E. Yu, and in part by a Roswell Park Cancer Institute Cancer Center Support Grant from the National Cancer Institute.