Abstract
Purpose:
This study examines the protective effect of 17-N-allylamino-17-demethoxygeldanamycin (17-AAG) on retinal ganglion cells (RGCs) against axonal injury and the expression of heat shock protein (Hsp) 70 in the retina. 17-AAG specifically binds to its ATP-site and facilitates dissociation and activation of heat shock transcription factor (Hsf) 1 which in resting cells forms a complex with Hsp90. Upon activation, Hsf1 induces the transcription of Hsp70.
Methods:
Unilateral optic nerve crush (ONC) was performed on adult Wistar rats and a single injection of 17-AAG (4ul; 0.2ug/ul) was administered intravitreally. The retinas were collected two weeks after axonal injury for immunohistochemistry of Rbpms (a RGC marker) and RGC body quantification. The protein expression level and localization of Hsp70, Hsp90, Hsf1 and Hsf2 in the retina was analyzed by Western blotting and immunohistochemistry.
Results:
Two weeks after ONC injury, the average density of RGC bodies in the retinal wholemounts was reduced by 81% from 1860 (n=6) to 355 cells/mm2 (n=8). Intravitreal administration of 17-AAG increased the average RGC density after ONC injury by approximately 49% to 527 cells/mm2 (n=12) when compared to vehicle-treated ONC control (n=12). The percentage of RGC protection mediated by 17-AAG administration was significant in the temporal retinal quadrant (119%; P<0.01), and the retinal regions at 1 (61%; P<0.01), 2 (57%; P<0.01) and 4 (52%; P<0.01) mm from the center of optic nerve head. Western blotting analysis showed that expression of Hsp70 in retinas of 17-AAG-treated animals with and without ONC was up-regulated 2.2 and 4-fold compared to vehicle-treated control and ONC animals, respectively. There was increased Hsp70 immunoreactivity at the outer nuclear layer, outer limiting membrane and inner segment in retinas of 17-AAG-treated control and ONC animals compared to controls and vehicle-treated ONC animals. No remarkable changes in Hsp90, Hsf1 and Hsf2 was observed in 17-AAG-treated animals with or without ONC.
Conclusions:
Treatment with 17-AAG protects RGCs from axonal injury and is associated with the up-regulation of Hsp70 in the retinas. These findings support the hypothesis that the pharmacological induction of Hsp70 can be used to treat optic neuropathies.
Keywords: 531 ganglion cells •
629 optic nerve •
615 neuroprotection