Macrophage Activation Associated with Chronic Murine Cytomegalovirus Infection Results in More Severe Experimental Choroidal Neovascularization

• Authors: Scott W. Cousins, Duke University; Diego G. Espinosa-Heidmann, Duke University; Daniel M. Miller, University of Miami; Simone Pereira-Simon, University of Miami; Eleut P. Hernandez, University of Miami; Hsin Chien, Georgia State University; Courtney Meier-Jewett, Georgia State University; Richard Dix, Emory University
• Journal Title: PLoS Pathogens
• Volume: Volume 8, Number 4
• Publisher: Public Library of Science | 2012-04-01
• Type of Work: Article | Final Publisher PDF
• Publisher DOI: http://doi.org/10.1371/journal.ppat.1002671
• Subjects: Biology, General; Health Sciences, Opthamology
• Keywords: Science & Technology; Life Sciences & Biomedicine; Microbiology; Parasitology; Virology; MICROBIOLOGY; PARASITOLOGY; VIROLOGY; COMPLEMENT FACTOR-H; AGE-RELATED MACULOPATHY; CORONARY-ARTERY-DISEASE; BEAVER DAM EYE; MACULAR DEGENERATION; CHRONIC REJECTION; HEART-TRANSPLANTS; KNOCKOUT MICE; UP-REGULATION; ATHEROSCLEROSIS

Abstract

The neovascular (wet) form of age-related macular degeneration (AMD) leads to vision loss due to choroidal neovascularization (CNV). Since macrophages are important in CNV development, and cytomegalovirus (CMV)-specific IgG serum titers in patients with wet AMD are elevated, we hypothesized that chronic CMV infection contributes to wet AMD, possibly by pro-angiogenic macrophage activation. This hypothesis was tested using an established mouse model of experimental CNV. At 6 days, 6 weeks, or 12 weeks after infection with murine CMV (MCMV), laser-induced CNV was performed, and CNV severity was determined 4 weeks later by analysis of choroidal flatmounts. Although all MCMV-infected mice exhibited more severe CNV when compared with control mice, the most severe CNV developed in mice with chronic infection, a time when MCMV-specific gene sequences could not be detected within choroidal tissues. Splenic macrophages collected from mice with chronic MCMV infection, however, expressed significantly greater levels of TNF-α, COX-2, MMP-9, and, most significantly, VEGF transcripts by quantitative RT-PCR assay when compared to splenic macrophages from control mice. Direct MCMV infection of monolayers of IC-21 mouse macrophages confirmed significant stimulation of VEGF mRNA and VEGF protein as determined by quantitative RT-PCR assay, ELISA, and immunostaining. Stimulation of VEGF production in vivo and in vitro was sensitive to the antiviral ganciclovir. These studies suggest that chronic CMV infection may serve as a heretofore unrecognized risk factor in the pathogenesis of wet AMD. One mechanism by which chronic CMV infection might promote increased CNV severity is via stimulation of macrophages to make pro-angiogenic factors (VEGF), an outcome that requires active virus replication.