The role of cytosolic accumulation of nuclear DNA in retinal-pigment epithelium dysfunction and age-related macular degeneration
Al Moujahed, Ahmad
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Age-related Macular Degeneration (AMD) is the leading cause of irreversible vision loss among elderly people in developed countries. The non-neovascular or “dry” form of AMD accounts for 85%, whereas the neovascular or “wet” accounts for 15%, of all cases. There are no effective treatments for dry AMD mainly because the molecular mechanisms that lead to the development and progression of AMD are not fully understood. Similarly, while wet AMD is being treated with antibodies against vascular endothelial growth factor (VEGF), the underlying cause that results in the development of wet AMD remains elusive. Cytosolic accumulation of nuclear-DNA (nDNA) fragments has been found to trigger inflammation and mediate the development of multiple diseases. Because inflammation plays a pivotal role in AMD pathogenesis, we thus investigated if accumulation of cytosolic nDNA also contributes to AMD. Our data show that cytosolic nDNA is enriched in macular retinal pigment epithelium (RPE) cells of AMD patients. To study the effect of cytosolic nDNA on RPE cells, we mimicked this pathology by deleting the lysosomal endonuclease Dnase2a, which is responsible for degrading DNA fragments, using CRISPR/Cas9. This resulted in cytosolic accumulation of nDNA in cultured primary human RPE cells as well as in the RPE cell line ARPE-19. Importantly, both RPE cell types with Dnase2a loss became senescent and secreted higher levels of VGEF and pro-inflammatory cytokines compared to control. These effects were mediated by the DNA sensor STING and mTOR pathway. Additionally, similar to other senescent cells, these senescent RPE cells secreted factors that acted in a paracrine manner turning otherwise healthy RPE cells into senescent cells that start secreting VEGF as well as pro-inflammatory cytokines. Finally, we found that mice with Dnase2a deletion develop features of AMD-like retinopathy, including drusen- like deposits, thickened Bruch’s membrane, RPE damage, photoreceptor atrophy, and reduced electroretinogram. The pleiotropic downstream effects of cytosolic accumulation of nDNA in RPE cells, which are consistent with the complex AMD pathology, suggest that this phenomenon contributes to the pathogenesis of AMD and thereby opens new opportunities for therapeutic interventions.