Overproduction of 42 Amino Acids Long Amyloid Beta Leads to Activation of Secretory Autophagy and Development of Drusen-Like Structures Originating From Retinal Pigment Epithelium.

Abstract

Age-related macular degeneration (AMD) is a global vision threatening disease affecting the macular region of the retina. AMD is classified into two forms: dry and wet AMD. There are no effective treatment options available for dry AMD (80% of cases). The cellular pathology includes oxidative stress and dysfunctional autophagy challenging the homeostasis of the retinal pigment epithelial (RPE) cells. Clinical findings include the formation of drusen deposits beneath the RPE cells consisting of 42 amino acids long amyloid beta (Aβ) among other components. However, the origin of drusen remains elusive. The 5xFAD (familiar Alzheimer's disease) mouse model of Alzheimer's disease produces abundant levels of Aβ making it an interesting model to study the possible relationship of Aβ to the formation of extracellular deposits and AMD-like pathology. An immunohistology analysis of the 5xFAD mouse model showed accumulation of autophagic markers SQSTM1 (sequestosome 1) and ubiquitin in the RPE. Concurrently, the markers of secretory autophagy enabling the delivery of the intracellular material to the extracellular lumen were upregulated. Aβ, SQSTM1, ubiquitin, catalase, and TRIM16 (tripartite motif containing 16) shifted age-dependently from intracellular origin to drusen-like deposits beneath the RPE cells. Additionally, classical proteins secreted via secretory autophagy, IL-1β (interleukin 1β), HMGB1 (high mobility group box-1), and ferritin showed similar accumulation which became visible in fundus age-dependently. These findings suggest a role for Aβ in the cellular pathogenesis of AMD. Furthermore, this model showed activated secretory autophagy pathway suggesting a role for Aβ in drusen-like deposition formation.