Amyloid precursor protein, lipofuscin accumulation and expression of autophagy markers in aged bovine brain

Abstract

Background: Autophagy is a highly regulated process involving the bulk degradation of cytoplasmic macromolecules and organelles in mammalian cells via the lysosomal system. Dysregulation of autophagy is implicated in the pathogenesis of many neurodegenerative diseases and integrity of the autophagosomal - lysosomal network appears to be critical in the progression of aging. Our aim was to survey the expression of autophagy markers and Amyloid precursor protein (APP) in aged bovine brains. For our study, we collected samples from the brain of old (aged 11-20years) and young (aged 1-5years) Podolic dairy cows. Formalin-fixed and paraffin embedded sections were stained with routine and special staining techniques. Primary antibodies for APP and autophagy markers such as Beclin-1 and LC3 were used to perform immunofluorescence and Western blot analysis. Results: Histologically, the most consistent morphological finding was the age-related accumulation of intraneuronal lipofuscin. Furthermore, in aged bovine brains, immunofluorescence detected a strongly positive immunoreaction to APP and LC3. Beclin-1 immunoreaction was weak or absent. In young controls, the immunoreaction for Beclin-1 and LC3 was mild while the immunoreaction for APP was absent. Western blot analysis confirmed an increased APP expression and LC3-II/LC3-I ratio and a decreased expression of Beclin-1 in aged cows. Conclusions: These data suggest that, in aged bovine, autophagy is significantly impaired if compared to young animals and they confirm that intraneuronal APP deposition increases with age.