Investigating alterations in autophagy in Alzheimer’s disease using human brain tissue and skin-derived fibroblasts

Alzheimer’s disease (AD) is the main cause of dementia, affecting 500,000 people in the UK. Pathology of AD is characterised by the accumulation of abnormally phosphorylated tau protein within neurofibrillary tangles and plaques containing amyloid-β (Aβ). Autophagy is a normal intracellular mechanism that functions to degrade damaged cellular proteins. Studies have shown that there is an association between the dysfunction of the two main autophagy pathways-macroautophagy (MA) and chaperone-mediated autophagy (CMA) - and AD. However, it is unclear how the autophagic pathway activity changes during disease progression and how this relates to the accumulation of abnormal protein deposits in the brain. This study aimed to explore alterations in different autophagy pathway linked proteins with AD progression and find the relationship between MA and CMA. Immunohistochemical/double labelling techniques were performed on post-mortem human brain tissue from 45 cases. Three brain regions were used including the hippocampus, the frontal cortex and the occipital cortex. Autophagy was investigated via the assessment of cellular distribution of LC3, Beclin-1 (markers of MA) and LAMP2A, Hsp70 (markers of CMA). Neurofibrillary tangles and amyloid plaques were also assessed via immunohistochemistry. Skin-derived fibroblasts from AD patients were also used to test the cells potency to become eventual markers in the assessment of autophagy impairment in living patients with AD via Western blotting. The results showed that the autophagy levels decline with increasing Braak, suggesting impairments in both MA and CMA. Also, the results showed that CMA markers were significantly lower in the hippocampus while MA changes were most prevalent in the frontal cortex. The hippocampal region CA1 had increased tau/amyloid-β deposition and decreased autophagy markers, while region CA4 had decreased tau/amyloid-β and increased autophagy markers. Western blotting revealed significant differences in LAMP2A and Beclin-1 expression between the control cells and the AD mutated cells. Identifying cell models such as skin-derived fibroblasts from patients with AD and targeting the autophagy pathays dysregulated at particular disease stages could offer potential for novel therapeutic strategies to prevent AD pathogenesis