The PI3K/Akt/FOXO3a pathway regulates regeneration following spinal cord injury in adult rats through TNF- and p27kip1 expression

The aim of the present study was to elucidate the expression and role of the phosphatidylinositol 3-kinase (PI3K)/Akt/forkhead box O3 (FOXO3a) pathway in the regeneration of the spinal cord following spinal cord injury (SCI), and its regulatory effect on tumor necrosis factor (TNF)- and cyclin-dependent kinase inhibitor 1B (p27(kip1)) expression. Firstly, in a Sprague-Dawley rat model of SCI, western blot analysis revealed that the protein levels of PI3K, phosphorylated Akt and FOXO3a were markedly inhibited compared with those in the sham control group. In vitro experiments were also conducted, in which primary dissociated cultures of rat dorsal spinal cord cells were induced with lipopolysaccharide (LPS; 4 g/ml). The downregulation of PI3K using LY294002 markedly suppressed cell viability, reduced the protein levels of FOXO3a and p27(kip1), and increased TNF- protein production in the LPS-induced spinal cord cells. In addition, when the LPS-induced spinal cord cells were infected with FOXO3a adenoviral vectors, the overexpression of FOXO3 markedly promoted cell proliferation, activated p27(kip1) protein levels and inhibited TNF- protein production in the spinal cord cells. These results suggest that the PI3K/Akt/FOXO3a pathway regulates regeneration following SCI in adult rats via its modulatory effects on TNF- and p27(kip1) expression.