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l-Deprenyl, blocking apoptosis and regulating gene expression in cultured retinal neurons
L Xu1, J Ma, G M Seigel
1Department of Ophthalmology, Medical University of South Carolina, Charleston 29403, USA.
Abstract:
Apoptosis is the final pathway of many forms of retinal degeneration. E1A-NR3 is an immortalized retinal cell line that manifests specific phenotypes of retinal neurons. The present study induced apoptosis in these cells by two ischemic assaults, serum deprivation and hypoxia. The results demonstrated that both the assaults decreased viable cell numbers significantly by inducing apoptosis, as revealed by viable cell count, DNA fragmentation analysis, and in situ labeling of apoptotic cells by the TdT-mediated dUTP-biotin nick end-labeling (TUNEL) method. l-Deprenyl is known to be a monoamine oxidase inhibitor, and it was found recently to have neurotrophic activities. We set out to determine the protective effect of l-deprenyl on retinal cells and delineate its mechanism independent of monoamine oxidase inhibition. At concentrations as low as 0.0001 and 0.001 microM, l-deprenyl significantly increased the numbers of surviving cells under serum-free and hypoxic conditions, respectively. This effect appeared to be dependent upon the l-deprenyl concentration within the range of 0.001 to 10 microM. The neurotrophic activity was via blocking apoptosis, as l-deprenyl decreased the fragmented DNA and the numbers of positively stained apoptotic cells under serum-free or hypoxic conditions. Using mRNA differential display, nine mRNAs were identified and confirmed by northern blot analysis to have altered expression levels at 8 hr of exposure to hypoxia. Five of them do not match any existing sequences in GenBank, whereas the other four represent known genes including c-jun, heat-shock protein hsp70, phosphoglycerate kinase (PGK), and calpactin I heavy chain. All of the four mRNAs were increased significantly by hypoxia. The c-jun, PGK, and calpactin mRNAs, but not hsp70, also were increased by serum withdrawal. l-Deprenyl partially reversed the increase in c-jun and hsp70 mRNA levels, but not in PGK and calpactin. These results suggest that l-deprenyl blocks apoptosis induced by hypoxia as well as by growth factor withdrawal and regulates the expression of apoptosis-related genes.
Insights
l-Deprenyl protects retinal cells from apoptosis caused by oxygen deprivation and serum withdrawal. This neuroprotective effect involves blocking programmed cell death and regulating specific gene expression, independent of its MAO inhibition activity.
Area of Science:
- Neuroscience
- Cell Biology
- Ophthalmology
Background:
- Apoptosis is a key mechanism in retinal degeneration.
- Immortalized retinal cells (E1A-NR3) model neuronal phenotypes.
- Ischemic insults like serum deprivation and hypoxia induce apoptosis in retinal cells.
Purpose of the Study:
- To investigate the neuroprotective effect of l-deprenyl on retinal cells.
- To elucidate the mechanism of l-deprenyl's action, independent of monoamine oxidase inhibition.
- To determine if l-deprenyl can prevent apoptosis induced by ischemic conditions.
Main Methods:
- Induction of apoptosis in E1A-NR3 cells via serum deprivation and hypoxia.
- Assessment of apoptosis using viable cell counts, DNA fragmentation, and TUNEL assay.
- Analysis of gene expression changes using mRNA differential display and Northern blot.
Main Results:
- Both serum deprivation and hypoxia significantly increased apoptosis in retinal cells.
- l-Deprenyl demonstrated significant neuroprotection at low concentrations (0.0001-0.001 microM).
- l-Deprenyl reduced DNA fragmentation and TUNEL-positive cells, indicating apoptosis inhibition.
- Hypoxia increased expression of c-jun, hsp70, PGK, and calpactin I mRNA; serum withdrawal affected c-jun, PGK, and calpactin.
- l-Deprenyl partially reversed the hypoxia-induced increase in c-jun and hsp70 mRNA.
Conclusions:
- l-Deprenyl effectively blocks apoptosis in retinal cells induced by both hypoxia and serum withdrawal.
- The neuroprotective mechanism of l-deprenyl is independent of monoamine oxidase inhibition.
- l-Deprenyl modulates the expression of specific apoptosis-related genes, including c-jun and hsp70.