Abstract
Purpose: :
To characterize changes in protein expression profiles in the orbital optic nerve (OON) of NHPs after unilateral IOP-related (EEG) or non-IOP-related (ONT) RGC axon injury.
Methods: :
Three weeks after surgical ONT (n=3 NHP) and at the onset of reproducible ONH surface change resulting from laser-induced IOP elevation in EEG (n=4 NHP), both eyes of each NHP were enucleated under anesthesia with care taken to maximize the length of attached OON. Orbital tissues were trimmed and the OON was excised 3 mm behind the globe and frozen. OON tissues from both eyes were homogenized, subjected to trypsin digestion, and analyzed with a label-free quantitative mass spectrometry (MS) system (Waters Corp). For each eye, amounts of individual proteins, in fmol, were determined in reference to an internal standard and ratios of each protein in the ONT or EEG eye of each animal were compared to its contralateral normal with a 2-fold increase or decrease defined as a change. Proteins that demonstrated change in at least 2 of 3 ONT or 3 of 4 EEG eyes were used for further bioinformatic analyses with the assistance of the MetaCore program (GeneGo Inc).
Results: :
To date, a total of 166 and 255 proteins have been identified in the OON tissues from the ONT and EEG eyes, respectively. Of these proteins, 9 were up regulated and 14 down regulated in the ONT eyes, and 13 were up regulated and 22 down regulated in the EEG eyes. Bioinformatic analyses of up- and down-regulated proteins revealed little similarity of cellular processes between the ONT and EEG eyes. In the EEG OON, the most significant up-regulated processes included oxygen and nitric oxide transport, contributing proteins to these processes include multiple hemoglobin subunits, whereas in the ONT OON, the up-regulated processes were predominantly those of cell motion and structure organization, as exemplified by actin, vimentin, and 14-3-3 epsilon.
Conclusions: :
ONT and EEG eyes demonstrate OON proteomic changes that are distinct from one another. These proteomic alterations are also different from those within the retinal tissues of the same eyes (Stowell et al, in revision). The observed differences for these models may be due to differences in the mechanism and site of injury and the presence of the surgical ONT site within the ONT tissues. Detailed bioinformatic analyses of the OON proteomic datasets and comparison with those for the retinal tissue are in progress.
Keywords: proteomics • optic nerve