title: Calcium-induced calpain mediates apoptosis via caspase-3 in a mouse photoreceptor cell line.
abstract: The rd mouse, an accepted animal model for photoreceptor degeneration in retinitis pigmentosa, has a recessive mutation for the gene encoding the beta-subunit of the cGMP phosphodiesterase. This mutation results in high levels of cGMP, which leaves an increased number of the cGMP-gated channels in the open state, thus allowing intracellular calcium (Ca(2+)) to rise to toxic levels, and rapid photoreceptor degeneration follows. To delineate the events in rd photoreceptor degeneration, we demonstrated an increase in calpain and caspase-3 activity, hypothesizing that Ca(2+)-mediated apoptosis in photoreceptors is mediated by calpain, involving mitochondrial depolarization and caspase-3 activation. To examine this hypothesis further, a murine photoreceptor-derived cell line (661W) was treated with the Ca(2+) ionophore A23187, cGMP-gated channel agonist 8-bromo-cGMP, or phosphodiesterase inhibitor isobutylmethylxanthine to mimic the increased Ca(2+) influx seen in the rd photoreceptors. Ca(2+)-induced cell death in 661W cells was found to be mediated by calpain and caspase-3 and could be completely inhibited by the calpain inhibitor SJA6017, implicating both calpain and caspases in the apoptotic process. The apoptotic events correlated in an SJA6017-inhibitable manner with bid cleavage, mitochondrial depolarization, cytochrome c release, and caspase-3 and -9 activation. We concluded that Ca(2+) influx in the rd model of photoreceptor degeneration leads to the activation of the cysteine protease calpain, which executes apoptosis via modulation of caspase-3 activity.
authors.affiliation: Department of Ophthalmology, Storm Eye Institute, University of South Carolina, Charleston 29425, USA.
authors.forename: Ashish K
authors.initials: AK
authors.lastname: Sharma
authors.forename: Baerbel
authors.initials: B
authors.lastname: Rohrer
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology*; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D015220:Calcium Channels / Q000378:metabolism; D020013:Calcium Signaling; D002154:Calpain / Q000037:antagonists & inhibitors / Q000378:metabolism*; D053455:Caspase 10; D053148:Caspase 3; D020169:Caspases / Q000378:metabolism*; D002460:Cell Line; D004151:Dipeptides / Q000494:pharmacology; D004789:Enzyme Activation / Q000187:drug effects; D015640:Ion Channel Gating; D007476:Ionophores / Q000494:pharmacology; D051379:Mice; D010786:Photoreceptor Cells / Q000378:metabolism* / Q000473:pathology
chemical_list: D015220:Calcium Channels; D004151:Dipeptides; D007476:Ionophores; C109145:N-(4-fluorophenylsulfonyl)-L-valyl-L-leucinal; D000001:Calcimycin; C505407:CASP3 protein, human; C099217:CASP5 protein, human; D002154:Calpain; C505409:Casp3 protein, mouse; D053455:Caspase 10; D053148:Caspase 3; D020169:Caspases; C506438:CASP10 protein, human; D002118:Calcium