INCREASE OF PROTEIN-TYROSINE PHOSPHORYLATION IN RAT RETINA AFTER ISCHEMIA-REPERFUSION INJURY

Purpose. This study was conducted to examine the effect of retinal isc hemia-reperfusion injury on protein tyrosine phosphorylation, the prod uction of angiogenic growth factors, and the activation of signal prot eins in tyrosine kinase pathways. Methods. Ischemia-reperfusion injury was induced in rats by compression of the optic nerve for 2 hours. Th e 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 immunohistoch emistry. Angiogenic growth factors and their receptors, such as basic fibroblast growth factor (bFGF) and Flg, vascular endothelial growth f actor (VEGF) and Flk-1, platelet-derived growth factor (PDGF)-B chain and PDGF-beta receptor, and five intracellular signal proteins (phosph atidylinositol 3-kinase [PI3K], phospholipase C gamma [PLC gamma], C-S rc, SHC, and mitogen-activated protein kinase [MAPK]) were examined by West ern blot analysis. Results. Protein tyrosine phosphorylation inc reased 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 PLC gamma, SHC, a nd MAPK was increased at 48 hours of reperfusion, and tyrosine phospho rylation of PDGF-beta receptor and PI3K was increased at 168 hours of reperfusion. Conclusions. Ischemia-reperfusion injury in the rat retin a leads to activation of the tyrosine kinase pathway, increasing the a mounts of angiogenic growth factors. The resultant activation of signa l proteins PLC gamma, SHC, MAPK, PI3K, and PDGF-beta receptor may play an important role in ischemia-induced retinal changes such as cell pr oliferation.