PURPOSE. Both caspase-dependent and caspase-independent apoptosis contribute to retinal damage during murine cytomegalovirus (MCMV) retinitis, and TNF-α is among the inducers of apoptosis. The aim of this study was to determine the contribution of TNF-α by studying virus replication and apoptosis in immunosuppressed (IS) TNF-α-/- mice. METHODS. IS TNF-α-/- mice or wild-type mice were inoculated with MCMV by the supraciliary route. Injected eyes were examined by plaque assay, electron microscopy, Western blot analysis (caspase-3, caspase-8, caspase-12, Bid, NF-κB, cFlip, XIAP), staining for MCMV early antigen, and TUNEL assay. RESULTS. Although the titer of MCMV was similar in both groups, significantly more apoptotic cells were observed in the retinas of IS TNF-α-/- mice than in those of wild-type mice. The level of active caspase-3 was similar in both groups; however, more activated proteins for genes involved in the mitochondrial pathway (cleaved caspase-8, tBid) and endoplasmic reticulum (ER) stress (cleaved caspase-12) and, though less active, NF-κB subunits and antiapoptotic proteins (XIAP and cFlip) were detected in the TNF-α-/- eyes compared with wild-type mice. CONCLUSIONS. Although TNF-α is an inducer of apoptosis, the results of this study suggest that TNF-α is also antiapoptotic by the following mechanism: TNF-α activation of NF-κB promotes the production of the antiapoptosis genes, c-flip or XIAP, which, in turn, inhibit the activation of caspase-8 and the mitochondrial pathway or the activation of caspase-12 and ER stress.
ASJC Scopus subject areas
- Sensory Systems
- Cellular and Molecular Neuroscience