N-Methyl-D-Aspartic acid suppresses Akt activity through proteinphosphatase in retinal ganglion cells

[摘要] Purpose: To investigate the relationship between Akt activity andretinal ganglion cell (RGC) death induced by N-Methyl-D-Aspartic acid(NMDA) in the rat retina.Methods: Two microlitres of 1, 10, 50, 100, or 200 mM NMDA, orvehicle was injected into the vitreous cavity of Sprague-Dawley (SD)rats (n=125). Retinal damage was estimated by counting ganglion cellslabeled with fluorochrome and retinal apoptosis was detected by TUNEL.Akt activity was determined by immunohistochemical analysis with aspecific antibody to the activated (phosphorylated) form of Akt. Toinvestigate the mechanism of dephosphorylation of Akt, Okadaic acid, apotent protein phosphatase inhibitor, was injected 1 h before NMDAinjury and accessed the number of phosphorylated Akt positive cells 1 hafter NMDA injection. To stimulate Akt activity in the retina, brainderived neurotrophic factor (BDNF) was injected into the vitreous 15 minbefore NMDA injection.Results: Immunohistochemical analysis revealed a reduction inphosphorylated Akt in RGCs and amacrine cells one hour after NMDAinjury. The RGCs and amacrine cells showed TUNEL positivity at 6 h and adecrease in cell number at 7 days after NMDA injury. No other cells inthe retina stained positive with phosphorylated Akt antibody and TUNEL.Okadaic acid prevented the dephosphorylation of Akt by NMDA. Theexogenous administration of BDNF prevented the dephosphorylation of Aktin N-Shc/ShcC-positive RGCs and significantly suppressed theNMDA-induced RGC death.Conclusions: These observations suggest that Akt is one of the keysignaling proteins in RGC death induced by NMDA, and that the presenceof N-Shc/ShcC enhances BDNF-mediated neuroprotection via phosphorylatedAkt. The regulation of phosphorylated Akt by growth factors and proteinphosphatase activity may play an important role in cell fate followingNMDA injury. Thus, an increase in phosphorylated Akt may have potentialtherapeutic implications in the treatment of glutamate-related disease.

[学科分类] 生物化学/生物物理