Activation of Bax in three models of retinitis pigmentosa.
OBJECTIVE
The process of photoreceptor cell death in retinitis pigmentosa is still not well characterized, and identification of common mechanisms will be instrumental for development of therapeutic strategies. Here we investigated activation of Bax in rd1, P23H transgenic, and Rho knockout retinas.


METHODS
Bax activation was evaluated by immunofluorescence using anti-activated Bax-specific antibodies and by Western blotting on mitochondrial protein extracts. Knockdown of cathepsin D, calpain 1, and calpain 2 was achieved by short hairpin RNA (shRNA) delivery in rd1 mutant photoreceptors cells differentiated from retinal neurospheres. The mechanism of Bax activation through calpains was evaluated in vivo by intravitreal injection of calpastatin.


RESULTS
We defined activation and mitochondrial localization of Bax as well as activation of calpains and cathepsin D in the three models of retinitis pigmentosa. Taking advantage of an in vitro culture system for rd1 mutant photoreceptors, we unraveled the mechanism of Bax activation. We demonstrated that calpain 1 and cathepsin D contributed to activation of Bax and to apoptosis-inducing factor (Aif) nuclear translocation. In vivo interference with calpain activity blocks Bax activation in the rd1 and Rho knockout retinas and reduces activation in the P23H transgenic retina.


CONCLUSIONS
Activation of Bax was observed in all three models of retinitis pigmentosa and leads to neurodamage by localization at the mitochondrion. Our data suggest that Bax can be envisaged as one of the promising target molecules for restraining photoreceptor degeneration.
Department of Life Sciences, University of Modena and Reggio Emilia, Modena, Italy.
Antonella
A
Comitato
Department of Life Sciences, University of Modena and Reggio Emilia, Modena, Italy.
Daniela
D
Sanges
Department of Life Sciences, University of Modena and Reggio Emilia, Modena, Italy.
Alessandra
A
Rossi
The Ocular Genetics Unit, Smurfit Institute of Genetics, Trinity College Dublin, Dublin, Ireland.
Marian M
MM
Humphries
Department of Life Sciences, University of Modena and Reggio Emilia, Modena, Italy.
Valeria
V
Marigo
D000818:Animals; D017209:Apoptosis; D015153:Blotting, Western; D002135:Calcium-Binding Proteins / Q000494:pharmacology*; D002154:Calpain / Q000037:antagonists & inhibitors; D002478:Cells, Cultured; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D004195:Disease Models, Animal; D020287:In Situ Nick-End Labeling; D051379:Mice; D008809:Mice, Inbred C3H; D008810:Mice, Inbred C57BL; D009154:Mutation; D020419:Photoreceptor Cells, Vertebrate / Q000187:drug effects / Q000378:metabolism / Q000473:pathology*; D012313:RNA / Q000235:genetics*; D060888:Real-Time Polymerase Chain Reaction; D012174:Retinitis Pigmentosa / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D015533:Transcriptional Activation / Q000187:drug effects*; D051028:bcl-2-Associated X Protein / Q000096:biosynthesis / Q000187:drug effects / Q000235:genetics*
D002135:Calcium-Binding Proteins; D015853:Cysteine Proteinase Inhibitors; D051028:bcl-2-Associated X Protein; D012313:RNA; C033668:calpastatin; D002154:Calpain
P23H; calpastatin; rd1 mouse; rhodopsin