FOXO3a/p27kip1 expression and essential role after acute spinal cord injury in adult rat

Abstract

FOXO3a (Forkhead Class box O3a), as an important direct target of the phosphatidylinositol 3-kinase (PI3K)/protein B (Akt) pathway, which regulates the cell survival and the cell-cycle progression. Recent reports showed that FOXO3a could inhibit cell-cycle progression at the G1/S transition by controlling transcription of the cyclin-dependent kinase inhibitor p27(kip1) , which is also a key regulator of the mammalian neurogenesis. To elucidate the expression and role of FOXO3a in nervous system lesion and repair, we performed an acute spinal cord contusion injury (SCI) model in adult rats, which showed a temporal-spatial expression pattern of FOXO3a. Temporally, FOXO3a protein level significantly reduced day 3 after injury, and following FOXO3a down-regulation, p27(kip1) protein and mRNA levels were also decreased after injury. Spatially, decreased levels of FOXO3a and p27(kip1) were predominant in astrocytes, which were regenerating axons and largely proliferated after injury. Furthermore in vitro, Western blot analysis, RT-PCR, and immunofluorescence staining analysis demonstrated the relationship between FOXO3a and p27(kip1) in primary astrocytes. FOXO3a modulated the cell cycle by transcriptional regulation of p27(kip1) in astrocytes. Administration of the PI3K pharmacological inhibitor LY294002 abrogated this effect by regulating FOXO3a and p27(kip1) expression and subcellular localization. These results suggest that decreased levels of FOXO3a and p27(kip1) in spinal cord are involved in axonal regeneration and the proliferation of glial cells after SCI.