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Cathepsin proteases mediate photoreceptor cell degeneration in Drosophila
Ronald D Kinser1, Patrick J Dolph
1Department of Biology, Dartmouth College, 54 College St, Hanover, NH 03755, USA.
Abstract:
Endocytosis-mediated cell death is a form of degeneration displayed in several Drosophila mutants. This form of degeneration is displayed in several Drosophila mutant lines including flies lacking the eye-specific PLC (norpA). The cell death pathway is initiated by the stabilization of complexes between rhodopsin and arrestin which undergo massive endocytosis into the cell body. The internalized rhodopsin becomes insoluble and builds up in the late endosomal system, wherein it triggers cell death. Cathepsins are resident late endosome/lysosome proteases that have been shown to mediate apoptosis in many disease models. Therefore we sought to test the involvement of cathepsins in endocytosis-mediated retinal degeneration. Here we show that cathepsins mediate cell death in light-exposed norpA eyes. Moreover, we show that the cathepsin L-like cysteine protease, CP1, specifically mediates retinal degeneration, while the aspartyl protease, cathepsin D, does not. Furthermore, eye-specific expression of pan-cathepsin inhibitors also blocks cell death. Western blot analysis demonstrates that cathepsin L levels remain unchanged during retinal degeneration. However, whole mount immunohistochemistry performed on light-exposed retinas revealed a decrease in cathepsin L levels and a loss of rhodopsin/ CP1 colocalization, suggesting that cathepsin L translocates during the degeneration process. Lastly, we show that the retinal degeneration can be enhanced by the overexpression of cathepsin L in the sensitized norpA background. Together these data show that cathepsins play a crucial role in endocytosis-mediated retinal degeneration and are consistent with a model where rhodopsin internalization and accumulation in the endosomal/lysosomal system triggers cathepsin translocation to the cytosol.
Insights
Cathepsins mediate cell death in Drosophila eyes during degeneration caused by massive endocytosis of rhodopsin. Specifically, cathepsin L protease is crucial for this retinal degeneration process.
Area of Science:
- Cell Biology
- Neuroscience
- Genetics
Background:
- Endocytosis-mediated cell death is a degeneration process observed in Drosophila mutants.
- This pathway involves rhodopsin-arrestin complexes undergoing massive endocytosis, leading to insoluble rhodopsin accumulation and cell death.
- Cathepsins, resident proteases of late endosomes/lysosomes, are implicated in apoptosis in various disease models.
Purpose of the Study:
- To investigate the role of cathepsins in endocytosis-mediated retinal degeneration in Drosophila.
- To determine if specific cathepsins, such as cathepsin L and cathepsin D, are involved in this process.
Main Methods:
- Utilized Drosophila melanogaster models, specifically the norpA mutant, exhibiting light-induced retinal degeneration.
- Employed eye-specific expression of pan-cathepsin inhibitors.
- Performed Western blot analysis to assess cathepsin L levels.
- Conducted whole mount immunohistochemistry to examine cathepsin L localization and rhodopsin/CP1 colocalization.
Main Results:
- Cathepsins were confirmed to mediate cell death in light-exposed norpA eyes.
- The cysteine protease CP1 (cathepsin L-like) was found to specifically mediate retinal degeneration, while cathepsin D did not.
- Eye-specific expression of pan-cathepsin inhibitors successfully blocked cell death.
- Western blots showed unchanged cathepsin L levels, but immunohistochemistry revealed cathepsin L translocation during degeneration.
- Overexpression of cathepsin L exacerbated retinal degeneration in the norpA background.
Conclusions:
- Cathepsins play a critical role in endocytosis-mediated retinal degeneration in Drosophila.
- The findings support a model where rhodopsin accumulation triggers cathepsin translocation from the endosomal/lysosomal system to the cytosol, initiating cell death.
- Cathepsin L is a key mediator of this degeneration pathway.
