Murine cytomegalovirus infection and apoptosis in organotypic retinal cultures

PURPOSE. An organotypic retinal culture model was used to determine the pattern of murine cytomegalovirus (MCMV) infection and whether apoptosis is induced in MCMV-infected cultured retinas. METHODS. Retinas harvested from C57BL/6 mice were individually cultured at 37° C on 3-μm filter inserts placed in 24-well plates. Some retinas were infected with MCMV (5 × 10⁵ PFU/well). At days 4, 7, and 11 after infection (pi), the culture medium and cultured retinas were collected for examination. RESULTS. Replicating virus was recovered and viral early antigen (EA)- and late antigen (LA)-positive cells were observed in the MCMV-infected retinal cultures. Most MCMV-infected cells were glia and horizontal cells. Infection resulted in atrophy of the photoreceptor cells and cytomegaly. Apoptosis of uninfected bystander cells, including photoreceptor cells and horizontal cells, was observed. TNF-α was produced by activated microglia during MCMV infection of the retina. Mouse apoptosis microarray studies, caspase activity studies, and RT-PCR studies showed that the genes involved in both the death receptor-mediated apoptotic pathway and the mitochondrial pathway were upregulated. CONCLUSIONS. Many aspects of MCMV infection of retinal cultures parallel those observed during MCMV retinitis in mice. Thus, this in vitro system may be used to explore the role of apoptosis of uninfected retinal cells and the contribution of cytokines and other modulators to the pathogenesis of CMV retinitis.