Abstract
Purpose:
Glaucoma is a neurodegenerative disease which leads to loss of retinal ganglion cells (RGC). Studies of the last years showed that the immune system might be involved in that process. Previously immunizations with glaucoma related antigens, like heat shock proteins induced RGC degeneration in these animals. The purpose of this study was to investigate the mechanisms of RGC death and alterations in glia cells after immunization with glial cell-derived neurotrophic factor (GDNF) or GDNF in combination with heat shock protein 27 (HSP27).
Methods:
Rats were immunized with GDNF and GDNF+HSP27. Control animals (Co) received sodium chloride (n=4-5/group). Intraocular pressure (IOP) was measured during the study. After 4 weeks cross-sections of the retina were stained with Brn-3a and NeuN to quantify RGC density. To investigate changes in glia cells GFAP staining was used to detect astrocytes and Müller cells. Additionally, vimentin staining, which is mainly sensitive for Müller cells was applied. Cell counts of RGCs and analysis of GFAP and vimentin were done using ImageJ software. Statistical analysis was performed using Student`s t-test.
Results:
IOP stayed within the normal range during the study (GDNF: p=0.7; GDNF+HSP27: p=0.4). Retinas of all immunized animals showed a significant loss of RGCs when labeled with Brn-3a (Co: 3.95±1.74; GDNF: 2.81±1.72; p=0.000001; GDNF+HSP27: 3.30±1.6; p=0.005). NeuN as a second RGC marker was mostly colocalized with Brn-3a. We could also observe a significant loss of RGCs stained with NeuN (Co: 3.86±1.63; GDNF: 3.21±1.68; p=0.003; GDNF+HSP27: 3.18±1.43; p=0.001). In the GDNF group the GFAP+/vimentin+ area were significantly increased compared to Co (GFAP: p=0.00005; vimentin: p=0.007). No changes in glia staining could be observed in the GDNF+HSP27 group (GFAP: p=0.3; vimentin: p=0.1).
Conclusions:
Immunization with GDNF led to a significant RGC loss detected with two different markers. Additionally, a significant activation of glia cells was observed in the GDNF group. Immunization with GDNF+HSP27 caused only a little RGC loss and did not affect glia cells. We propose that immunization with HSP27 in the combination with GDNF has a protective effect on RGCs and possibly influences glia cell activity.
Keywords: 688 retina •
531 ganglion cells •
540 glia