Assessment of MAPK–CREB signaling in acute and chronic optic nerve damage.

Abstract

Abstract: : Purpose: Various signals initiated at the cell membrane are transduced to their target genes by sequential phosphorylation of mitogen–activated protein kinases (MAPK). Disturbances in the MAPK–related signaling may also be involved in the pathophysiologic mechanisms which occur in the retina from glaucomatous eyes. Methods: In the present study, we used tissue from a monkey model for laser–induced chronic intraocular pressure elevation (5 eyes with different degree of axonal loss – kindly provided by R. Hernandez, Washington University School of Medicine, USA), as well as tissue from a rat model for acute optic nerve damage (optic nerve crush). The activation of signaling proteins involved in the MAPK cascade were explored. In addition, the MAPK–dependent activation of the cAMP–responsive element binding protein (CREB) and its target gene c–Fos was determined by immunohistochemistry. Results: In the chronic monkey glaucoma model, three animals demonstrated immunohistochemical evidences for activation of the MAPK–CREB pathway in glial cells and RGC, by expression of c–Fos. In contrast, two animals showed only expression of pAkt (in glial cells, RGCL, ONL, INL), which belongs to a separate signaling pathway, but lacked MAPK–CREB expression. In the rat model of acute axonal retinal ganglion cell damage, the amount of MAPK–CREB expression was rather low and was not different between crushed and control eyes at day 1 after the injury. However, 3 days after the crush, CREB phosphorylation was significantly increased, with a simultaneous induction of c–Fos mRNA and protein detected by RT–PCR and western blotting. This CREB–c–Fos induction did not last until 7 days after optic nerve crush. pAkt was not detectable by western blotting. Conclusions: These data suggest that the MAPK–CREB activation is different between acute and chronic retinal ganglion cell damage. Furthermore, different signaling pathways might be also involved in the pathophysiological mechanisms related to chronic elevated intraocular damage.

Keywords: gene/expression • ganglion cells • retinal degenerations: cell biology