Activation of the mitochondrial apoptotic pathway in a rat model of central retinal artery occlusion.
OBJECTIVE
Apoptosis is known to play a role in cell death in transient retinal ischemia. Little is known about the specific molecular pathways involved. The purpose of the current study was to evaluate a rat model of central retinal artery occlusion (CRAO) that simulates the clinical features of CRAO in humans and to elucidate whether the mitochondrial apoptotic pathway is involved.


METHODS
CRAO was induced in the central retinal artery by intravenous injection of rose bengal and green laser irradiation of the artery. CRAO was documented at 1, 3, 6, and 24 hours after laser irradiation. Changes in Bax (proapoptotic Bcl-2-associated X protein), cytochrome c, and caspase-9 cleavage in the cytosolic and mitochondrial fractions of neural retinal tissues were measured by Western blot analysis. Apoptosis within the retina was examined by terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL).


RESULTS
Complete CRAO was induced; however, occlusion became incomplete with spontaneous reperfusion of branch arteries, starting at 3 hours after laser irradiation. Only one or two branch arteries remained occluded at the 24-hour time point. Time-dependent, apoptotic changes were observed in inner and outer retinal cell layers. Western blot analysis revealed mitochondrial translocation of Bax from the cytoplasm, starting at 3 hours and peaking at 6 hours after laser irradiation. This translocation was accompanied by cytosolic accumulation of cytochrome c and cleavage of caspase-9.


CONCLUSIONS
This model is highly relevant to clinical manifestations of CRAO and is an ideal animal model for research. These findings indicate the activation of the mitochondrial pathway in ischemic retina induced by CRAO. The model provides a better understanding of ischemia-induced retinal apoptosis. Antiapoptosis therapy directly targeting the mitochondrial pathway in CRAO or other retinal ischemic diseases may be beneficial.
Zhang
Yi
Y
Casey Eye Institute, Oregon Health and Science University, Portland, 97239, USA.
Cho
Chang-Ho
CH
Atchaneeyasakul
La-ongsri
LO
McFarland
Trevor
T
Appukuttan
Binoy
B
Stout
J Timothy
JT
D025042:Amacrine Cells / Q000473:pathology; D000818:Animals; D017209:Apoptosis; D015153:Blotting, Western; D053453:Caspase 9; D020169:Caspases / Q000378:metabolism; D045304:Cytochromes c / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism; D004195:Disease Models, Animal; D020287:In Situ Nick-End Labeling; D008297:Male; D008928:Mitochondria / Q000378:metabolism*; D021381:Protein Transport; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D015356:Retinal Artery Occlusion / Q000378:metabolism* / Q000473:pathology; D012165:Retinal Ganglion Cells / Q000473:pathology; D013997:Time Factors; D051028:bcl-2-Associated X Protein
C494828:Bax protein, rat; D019253:Proto-Oncogene Proteins c-bcl-2; D051028:bcl-2-Associated X Protein; D045304:Cytochromes c; C506435:Casp9 protein, rat; D053453:Caspase 9; D020169:Caspases