Pten (phosphatase and tensin homologue gene) haploinsufficiency promotes insulin hypersensitivity

Abstract

Aims/hypothesis: Insulin controls glucose metabolism via multiple signalling pathways, including the phosphatidylinositol 3-kinase (PI3K) pathway in muscle and adipose tissue. The protein/lipid phosphatase Pten (phosphatase and tensin homologue deleted on chromosome 10) attenuates PI3K signalling by dephosphorylating the phosphatidylinositol 3,4,5-trisphosphate generated by PI3K. The current study was aimed at investigating the effect of haploinsufficiency for Pten on insulin-stimulated glucose uptake. Materials and methods: Insulin sensitivity in Pten heterozygous (Pten +/-) mice was investigated in i.p. insulin challenge and glucose tolerance tests. Glucose uptake was monitored in vitro in primary cultures of myocytes from Pten +/- mice, and in vivo by positron emission tomography. The phosphorylation status of protein kinase B (PKB/Akt), a downstream signalling protein in the PI3K pathway, and glycogen synthase kinase 3β (GSK3β), a substrate of PKB/Akt, was determined by western immunoblotting. Results: Following i.p. insulin challenge, blood glucose levels in Pten +/- mice remained depressed for up to 120 min, whereas glucose levels in wild-type mice began to recover after approximately 30 min. After glucose challenge, blood glucose returned to normal about twice as rapidly in Pten +/- mice. Enhanced glucose uptake was observed both in Pten +/- myocytes and in skeletal muscle of Pten +/- mice by PET. PKB and GSK3β phosphorylation was enhanced and prolonged in Pten +/- myocytes. Conclusions/interpretation: Pten is a key negative regulator of insulin-stimulated glucose uptake in vitro and in vivo. The partial reduction of Pten due to Pten haploinsufficiency is enough to elicit enhanced insulin sensitivity and glucose tolerance in Pten +/- mice. © 2006 Springer-Verlag.