Abstract
Purpose: :
Although tumor necrosis factor-alpha (TNF-α) has been shown to be involved in glaucoma, particularly at the optic nerve head, the role of its receptors (TNF-R1 and -R2) is less well established. RGC death has been shown to occur through TNF-R1-mediated caspase activation, mitochondrial dysfunction, and oxidative stress. In this study, we investigated changes in TNF-R1 and -R2 over time and in relation to RGC apoptosis in an OHT rat model.
Methods: :
Using our established chronic ocular hypertension (OHT) rat model, IOP was induced in 12 animals, with DARC imaging performed at 1, 3 and 12 weeks after IOP elevation, with animals sacrificed immediately after. Unoperated eyes were used as controls. Immunohistological analysis of TNF-R1 (Abcam ab58436 & ab19139) and -R2 (Abcam ab15563) expression was performed on sequential 5 µm thick paraffin sections from enucleated eyes (n=4 per time point), with grading done by masked observers, as previously described.
Results: :
DARC imaging recorded peak RGC apoptosis in OHT eyes at 3 weeks as previously described. Immunohistological assessment showed increasing expression of TNF-R1 in RGC layer after IOP elevation, reaching a significant peak at 3 weeks with both TNF-R1 antibodies in all OHT eyes compared to control (p<0.05). In contrast, there was no difference over time in expression of TNF-R2.
Conclusions: :
Changes in TNF-R1 appear to follow a similar profile to the development of RGC apoptosis in this experimental model of glaucoma. TNF-R1 activity appears maximal at the time of peak RGC apoptosis activity (3 weeks). This agrees with previous work suggesting that TNF-R1 augments RGC death whilst TNF-R2 may be neuroprotective.
Keywords: ganglion cells • apoptosis/cell death • receptors