Akt1 controls insulin-driven VEGF biosynthesis from keratinocytes: implications for normal and diabetes-impaired skin repair in mice

Abstract

Here we investigated the potential role of protein kinase B (Akt) in normal or diabetes-impaired wound healing in mice. Interestingly, Akt1 was predominant in skin, wound tissue, and human keratinocytes cell line. Acute skin repair was characterized by an increase of Akt1 phosphorylation in wound margin keratinocytes. By contrast, phosphorylated Akt1 was nearly completely absent and paralleled by a poor phosphorylation of the eucaryotic initiation factor 4E-binding protein 1 (4E-BP1) and reduced levels of vascular endothelial growth factor (VEGF) protein in chronic wounds of diabetic ob/ob mice. Inhibition of the phosphatidyl-inositol-3 kinase/Akt pathway by wortmannin and specific abrogation of Akt1 protein using small-interfering RNA revealed a regulatory function of Akt1 in insulin-mediated VEGF biosynthesis in keratinocytes. Insulin-induced VEGF protein biosynthesis in keratinocytes was mediated by Akt1 from a constitutive VEGF-encoding mRNA pool at the posttranscriptional level through a downstream phosphorylation 4E-BP1. Moreover, transfection experiments introducing a constitutively active mutant of Akt1 into keratinocytes revealed the mammalian target of rapamycin kinase as a downstream mediator of Akt1-linked 4E-BP1 phosphorylation and translational control. Our data suggest that the endocrine hormone insulin contributes to VEGF release in skin wounds through an Akt1-mediated posttranscriptional mechanism in keratinocytes.