Increased secretory autophagy in retinal pigment epithelial cells of the 5xFAD mice

Abstract

Purpose: Disturbed proteostasis and oxidative stress have a key role in Alzheimer's disease and age‐related macular degeneration pathology. Constant oxidative stress and disturbed proteostasis lead to intracellular protein aggregation and possibly the activation of secretory autophagy. In this study we assessed the oxidative stress and secretory autophagy related biomarker changes in the retinal pigment epithelium (RPE) of the 5xFAD mice model expressing abundant levels of the human beta‐amyloid.Methods: The eyes of 3‐, 6‐ and 12‐month‐old WT (n = 5) and 5xFAD (n = 5) mice were enucleated, paraffin fixed and examined by immunomicroscopy. The paraffin sections were immunostained for beta‐amyloid and the key secretory autophagy markers Sec22b, TRIM16, galectin 8, IL‐1β, HMGB1 and ferritin. Moreover, the sections were stained for oxidative stress marker 4‐HNE and antioxidant enzyme catalase. Protein degradation related markers ubiquitin (Ub) and SQSTM1/p62 were analysed from 6‐ and 12‐months timepoints.Results: Immunohistochemistry analysis revealed that the oxidative stress and protein degradation related markers were upregulated in the RPE of 6 and 12‐months old 5xFAD mice suggesting presence of oxidative stress and protein aggregation. TRIM16 and galectin 8 were increased in the RPE of the 6‐ and 12‐months old 5xFAD mice, while the increased expression of Sec22b was observed in 3‐ and 6‐months timepoint. IL‐1β, HMGB1 and ferritin were accumulated at the basal side of the RPE cells/Bruch's membrane in 6‐months old 5xFAD mice. The high accumulation of beta‐amyloid was detected in drusen like structures. Electrophysiological analysis revealed decreased scotopic and photopic signalling compared to WT mice.Conclusions: 5xFAD mouse model seems to be a good model to study protein aggregation and activation of the secretory autophagy in response to degenerative retina processes.