Caspase activation and amyloid precursor protein cleavage in rat ocular hypertension.
OBJECTIVE
Retinal ganglion cell (RGC) death in glaucoma involves apoptosis. Activation of caspases and abnormal processing of amyloid precursor protein (APP) are important events in other chronic neurodegenerations, such as Alzheimer's disease (AD). The retinal expression and activation of caspases and the patterns of caspase-3-mediated APP processing in ocular hypertensive models of rat glaucoma were investigated.


METHODS
RGC death was produced in one eye by chronic exposure to increased intraocular pressure (IOP) or by optic nerve transection. Elevated IOP was produced by obstruction of aqueous humor outflow with laser coagulation or limbal hypertonic saline injection. Caspase activity and APP processing in the retina were examined by RNase protection assay (RPA), immunocytochemistry, immunoblot assay, and colorimetric assay.


RESULTS
RPA revealed elevations of caspase-3 mRNA, as well as other apoptosis-related mRNAs. Immunocytochemistry showed caspase-3 activation in RGCs damaged by ocular hypertension. The generation of the caspase-3-mediated APP cleavage product (DeltaC-APP) was also increased in ocular hypertensive RGCs. Western immunoblot assay and colorimetry revealed significantly more activated caspase-3 in ocular hypertensive retinas than in control retinas. The activated form of caspase-8, an initiator caspase, and amyloid-beta, a product of APP proteolysis and a component of senile plaques in AD, were detected in RGCs by immunohistochemistry significantly more often in ocular hypertensive than in control retinas. The amounts of full-length APP were reduced and amyloid-beta-containing fragments were increased in ocular hypertensive retinas by Western immunoblot assay.


CONCLUSIONS
Rat RGCs subjected to chronic ocular hypertension demonstrate caspase activation and abnormal processing of APP, which may contribute to the pathophysiology of glaucoma.
McKinnon
Stuart J
SJ
Department of Ophthalmology, University of Texas Health Science Center at San Antonio, San Antonio, Texas 78229-3900, USA. mckinnon@uthscsa.edu
Lehman
Donna M
DM
Kerrigan-Baumrind
Lisa A
LA
Merges
Carol A
CA
Pease
Mary Ellen
ME
Kerrigan
Danielle F
DF
Ransom
Nancy L
NL
Tahzib
N Grace
NG
Reitsamer
Herbert A
HA
Levkovitch-Verbin
Hana
H
Quigley
Harry A
HA
Zack
Donald J
DJ
D016229:Amyloid beta-Peptides / Q000378:metabolism; D016564:Amyloid beta-Protein Precursor / Q000378:metabolism*; D000818:Animals; D015153:Blotting, Western; D020169:Caspases / Q000235:genetics / Q000378:metabolism*; D016923:Cell Death; D003714:Denervation; D004195:Disease Models, Animal; D004789:Enzyme Activation; D007124:Immunoenzyme Techniques; D007429:Intraocular Pressure; D009798:Ocular Hypertension / Q000378:metabolism*; D009900:Optic Nerve / Q000601:surgery; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D011914:Rats, Inbred BN; D012160:Retina / Q000378:metabolism; D012165:Retinal Ganglion Cells / Q000378:metabolism* / Q000473:pathology; D015854:Up-Regulation; D051028:bcl-2-Associated X Protein; D051020:bcl-X Protein
D016229:Amyloid beta-Peptides; D016564:Amyloid beta-Protein Precursor; C494813:Bcl2l1 protein, rat; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D012333:RNA, Messenger; D051028:bcl-2-Associated X Protein; D051020:bcl-X Protein; D020169:Caspases