Cellular inhibitor of apoptosis (cIAP1) is down-regulated during Retinal ganglion cell (RGC) maturation

Apoptosis, is the main type of cell death that occurs in ageing and neurodegenerative disease, such as glaucoma. This study therefore characterises the expression profile of caspases (pro-apoptosis) and inhibitors of apoptosis (IAPs; anti-apoptosis) during maturation of the Brown Norway rat retina between 6 weeks and >24 weeks and also examines concomitant changes in expression of tumor necrosis factor receptor associated factor 2 (TRAF2). The expression profiles of caspases (initiator caspases 8, 9 and effector caspases 6, 7, 3) and inhibitors of apoptosis (IAPs) (Neuronal IAP), cellular IAP1 and 2 (cIAP1/2), X-chromosome linked IAP (XIAP), Survivin, Bruce and Livin) were examined in retinae from 6 weeks and >24 weeks old BN rats using semi-quantitative reverse transcriptase-polymerase chain reaction (RT-PCR), real-time PCR, Western blotting and immunofluoroscence analysis. Caspase expression was not altered significantly during the study interval. IAP expression showed a general reduction during maturation of BN retina, which was statistically significant for cIAP1. cIAP1 reduction was confirmed by Western blotting and immunoflouroscence and was restricted to cells in the retinal ganglion cell layer (RGCL). Accumulation of TRAF2 was observed in the RGCL accompanying the down-regulation of cIAP1 observed. Our results suggest that cells in the mature RGCL may have a greater susceptibility to cell death compared to their younger counterparts and this may be due in part to a reduction in activation of survival pathways involving IAPs and TRAFs.