Molecular and Ocular Characterization of Novel Fibulin-3 Variants Involved in Retinal Degeneration

Distinct mutations in fibulin-3 (F3), a secreted extracellular matrix glycoprotein, have been associated with various ocular diseases including Malattia Leventinese (ML) and the most common macular degenerative disease, age-related macular degeneration (AMD), which ultimately lead to vision loss. AMD is a late onset disease characterized by the progressive loss of photoreceptors and retinal pigment epithelial (RPE) cells that result in irreversible blindness. Although AMD is an etiologically complex disease due to a variety of genetic and environmental risk factors, insight into its pathogenesis can be gained by studying phenotypically similar early-onset monogenic macular diseases. One such disease is ML, a rare macular dystrophy caused by an autosomal dominant Arg345Trp (R345W) mutation in the F3 protein. Previous research has demonstrated that the R345W mutation leads to protein misfolding, inefficient secretion, and accumulation at higher intracellular steady state levels in cultured cells. However, it remained unclear whether other potentially pathogenic or clinically-identified F3 variants recently reported in the human population also share features similar to that of R345W. We hypothesized that secretion defects in one or more F3 mutants may be a shared mechanism that ultimately contributes to ocular disease. First, I characterized 15 clinically-identified F3 mutations, some of which were identified in patients with AMD, primary open-angle glaucoma (POAG), or had non-discript retinal abnormalities. I found that of the mutants tested, only a single F3 variant, L451F, presented with a significant secretion defect as well as similarities in its biochemical and molecular properties to that of R345W. Subsequently, I generated a retinal disease mouse model of the L451F mutant utilizing recombinant adeno-associated virus (rAAV) in order to robustly evaluate disease phenotypes and uncover how L451F and other F3 mutations (i.e. R345W) are involved in retinal degeneration.