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Calcium ionophore induced proteolysis and cataract: inhibition by cell permeable calpain antagonists
J Sanderson1, J M Marcantonio, G Duncan
1Cell Biology and Physiology, School of Biological Sciences, University of East Anglia, Norwich, United Kingdom. j.sanderson@uea.ac.uk
Abstract:
Two dipeptide aldehyde cell permeable calpain inhibitors, cBz-Val-Phe and calpeptin, have been assessed for their ability to prevent cytoskeletal proteolysis and loss of transparency in whole rat lenses. Calcium overload, induced by ionomycin in artificial aqueous humor with 1mM calcium, resulted in lens opacification and degradation of cytoskeletal proteins including spectrin, filensin, and vimentin. No such changes resulted from incubation in ionomycin in the absence of calcium. In calcium overload lenses both inhibitors gave some protection against cytoskeletal protein degradation and loss of transparency. These experiments indicate that calpain has a role in cortical opacification in high calcium lenses and that cell penetrating calpain inhibitors do indeed enter lens cells and reduce both proteolysis and opacification.
Insights
Cell permeable calpain inhibitors cBz-Val-Phe and calpeptin protect rat lenses from calcium-induced opacification. These inhibitors reduce cytoskeletal proteolysis, demonstrating calpain
Area of Science:
- Ophthalmology
- Biochemistry
- Cell Biology
Background:
- Calcium overload in the lens can lead to opacification and degradation of cytoskeletal proteins.
- Calpain, a calcium-dependent protease, is implicated in lens opacification.
Purpose of the Study:
- To assess the efficacy of cell-permeable calpain inhibitors in preventing cytoskeletal proteolysis and lens opacification.
- To investigate the role of calpain in calcium-induced lens damage.
Main Methods:
- Whole rat lenses were subjected to calcium overload using ionomycin in artificial aqueous humor.
- Cell-permeable calpain inhibitors (cBz-Val-Phe and calpeptin) were applied to assess their protective effects.
- Cytoskeletal protein degradation (spectrin, filensin, vimentin) and lens transparency were analyzed.
Main Results:
- Calcium overload induced significant lens opacification and degradation of cytoskeletal proteins.
- Incubation without calcium prevented these changes.
- Both calpain inhibitors offered protection against cytoskeletal protein degradation and loss of transparency in calcium-overloaded lenses.
Conclusions:
- Calpain plays a significant role in the cortical opacification of lenses under high calcium conditions.
- Cell-penetrating calpain inhibitors can enter lens cells and mitigate both proteolysis and opacification.