Increase of protein tyrosine phosphorylation in rat retina after ischemia-reperfusion injury

Purpose. This study was conducted to examine the effect of retinal ischemia-reperfusion injury on protein tyrosine phosphorylation, the production of angiogenic growth factors, and the activation of signal proteins in tyrosine kinase pathways. Methods. Ischemia-reperfusion injury was induced in rats by compression of the optic nerve for 2 hours. The rats were killed, and the retinas were collected at 0, 1, 6, 24, 48, 96, or 168 hours of reperfusion. Tyrosine phosphorylation of proteins in the retina was examined by Western blot analysis and immunohistochemistry. Angiogenic growth factors and their receptors, such as basic fibroblast growth factor (bFGF) and Flg, vascular endothelial growth factor (VEGF) and Flk-1, platelet- derived growth factor (PDGF)-B chain and PDGF-β receptor, and five intracellular signal proteins (phosphatidylinositol 3-kinase [PI3K], phospholipase Cγ [PLCγ], C-Src, SHC, and mitogen-activated protein kinase [MAPK]) were examined by Western blot analysis. Results. Protein tyrosine phosphorylation increased after ischemia-reperfusion injury, reaching a peak at 48 hours of reperfusion. Increased staining of tyrosine-phosphorylated proteins in the inner retina were evident on immunohistochemical examination. The amount of bFGF decreased after injury, but the amounts of VEGF and PDGF- B chain increased. Tyrosine phosphorylation of PLCγ, SHC, and MAPK was increased at 48 hours of reperfusion, and tyrosine phosphorylation of PDGF- β receptor and PI3K was increased at 168 hours of reperfusion. Conclusions. Ischemia-reperfusion injury in the rat retina leads to activation of the tyrosine kinase pathway, increasing the amounts of angiogenic growth factors. The resultant activation of signal proteins PLCγ, SHC, MAPK, PI3K, and PDGF- β receptor may play an important role in ischemia-induced retinal changes such as cell proliferation.