Abstract
Purpose: :
We previously reported the involvement of phosphorylated presenilin (p-PS) 1 in TNF-induced optic nerve axonal degeneration. PS is one of the components of γ-secretase, which cleavages β-C-terminal fragment (βCTF) to amyloid precursor protein intracellular domain(AICD) and β-amyloid peptide (Aβ), in amyloidgenic pathway. In this study, we investigated the activation of γ-secretase in TNF-induced optic nerve degeneration.
Methods: :
Eight-week-old Wister rats were received intravitreal injection of 10ng TNF alone or simultaneous injection of TNF and BMS299897 (a γ-secretase inhibitor, 10-4 M or 10-3 M) into the right eyes. PBS was injected contralateral left eyes as control. Intravitreal injection of BMS299897 alone was also performed at 3 days after first injection. Eyes were obtained at 1 or 2 weeks after first intravitreal injection. Immunoprecipitation (IP) using 6E10 antibody was performed with optic nerve samples, followed by immunoblottting (IB) using AICD antibody. The localizations of p-PS1 and 6E10 in the retina and optic nerve were detected by immunohistochemistry (IHC). The effect of BMS299897 on TNF-induced axonal degeneration was examined with optic nerve cross sections stained with 1% paraphenylene-diamine (PPD). This quantification was performed with Aphelion software.
Results: :
IP using 6E10 antibody followed by IB using AICD antibody revealed a decreased presence of βCTF in the optic nerve after TNF injection compared with PBS injection. This decrease was substantially prevented by BMS299897 treatment. IHC showed that p-PS1 locates mainly in nucleus whereas 6E10 locates in cytosol in the retinal ganglion cells in retina. Similar findings are observed in the vimentin-positive glial cells in optic nerve. Morphometric analysis showed that the inhibition of γ-secretase with BMS299897 significantly prevented TNF-induced axonal degeneration.
Conclusions: :
Acceleration of APP cleavage in amyloidgenic pathway has been implicated in TNF-induced optic nerve axonal degeneration. 6E10 exists around the p-PS1 immunopositive cells. BMS299897, a γ-secretase inhibitor, suppressed the cleavage of APP, thereby exerting the protective effect against TNF-induced optic nerve degeneration.
Keywords: optic nerve • neuro-ophthalmology: optic nerve • neuroprotection