ATP Mediated Akt/mTOR/p70S6 Kinase Signaling Pathway Activation Promotes Improvement Of Locomotor Function After Spinal Cord Injury In Rats

Objective Akt/mTOR/p70S6K signal transduction pathway, as a central controller of cell growth, proliferation, survival, and differentiation in response to extracellular signals, growth factors, nutrient availability, energy status of the cell and stress, has recently gained attention in neuroscience. The effects of this signaling pathway on the repair of spinal cord injury (SCI), however, are not well elucidated. Adenosine triphosphate (ATP) is increasingly recognized as an important regulator of signal transduction pathways, and play important roles in functional recovery after nervous system injuries. In the present study, we examined the ATP-induced changes of the Akt/mTOR/p70S6K signaling pathway in injured spinal cord and potential effects of this signaling pathway on the SCI-induced neurological dysfunctions and repair processes of SCI in adult rats.Methods SCI was produced by extradural weight-drop of the spinal cord using modified Allen's stall with damage energy of 50 g-cm force. A total of 135 adult female Sprague-Dawley rats were randomly divided into the following four groups:SCI plus ATP (n=35), SCI plus saline (n=35), SCI plus ATP and rapamycin (n=35), and sham-operated (n=32). Using immunostaining studies, Western blot analyses and real-time qualitative RT-PCR analyses, we detected the changes of Akt, p-Akt, mTOR, p-mTOR, p70S6K, p-p70S6K, nestin, NeuN, NSE, NF200 and GFAP expressions in all groups after different administration following surgery. The spinal cord samples taken 4 weeks after different disposal in all SCI groups were stained with hematoxylin and eosin (H/E) for general morphology. Locomotor functional recovery after SCI was evaluated using the BBB Locomotor Rating Scale.Results The sham-operated animals exhibited low expression of these components in the Akt/mTOR/p70S6K signal transduction pathway at the protein and mRNA level, and the expressions increased following SCI. Exogenous administration of ATP significantly elevated the expressions of its components in the injured spinal cord. Rapamycin supressed the upregulations of the Akt/mTOR/p70S6K signaling pathway molecules in the injured spinal cord induced by ATP. We also observed that the effectiveness of the activated Akt/mTOR/p70S6K signaling pathway in improving locomotor recovery, significantly increasing the expressions of nestin, NeuN, NSE and NF200, and inhibiting excessive reactive astrogliosis relatively after SCI in a rapamycin-sensitive manner.Conclusion We concluded that the Akt/mTOR/p70S6K signal transduction pathway is present in the injured spinal cord and ATP injection produced a significant activation in this signaling pathway in spinal cord following SCI. The rapamycin-sensitive translational signaling pathway exhibited beneficial effects on the SCI-induced neurological defects and repair potentials for SCI, with the suggestion that intervention for this protein kinase signaling pathway activity should be considered as a potential therapeutic strategy.