Abstract
Alzheimer's disease (AD) is characterised by the intraneuronal aggregation of phosphorylated Tau (pTau) into neurofibrillary tangles and by the extracellular deposition of β-amyloid (Aβ). Tau pathology restricted to the medio-temporal lobe is frequently observed in the elderly brain in the absence of any Aβ deposition and considered as "primary age-related tauopathy" (PART). Here, we applied an unbiased proteomic approach to determine if and how concomitant Aβ pathology modifies the neurofibrillary tangle proteome. Neurofibrillary tangles were isolated by laser capture microdissection from hippocampal sections of 17 post-mortem brains spanning three groups: PART (n = 5; A0, B1-2, C0 scores), intermediate AD (n = 6; A1-2, B2-3, C1-2 scores) and advanced AD (n = 6; A3, B3, C3 scores). Mass spectrometry identified a conserved core of 63 proteins enriched in tangles across all groups, associated with RNA binding. Group-specific signatures were also observed: 33 proteins were significantly enriched only in tangles collected from PART cases and were predominantly linked to structural activity, whereas Aβ-positive cases showed specific enrichment of RNA binding and translation pathways - with intermediate AD cases displaying a transitional profile. Our findings are consistent with PART having distinct tangle proteomic features that could precede Aβ-driven changes; however, the majority of its proteomic signature is in common with tangles within the AD continuum. By addressing how Aβ accumulation alters the tangle proteome, this study provides mechanistic insights into the expansion of Tau pathology, paving the way towards the identification of biomarkers and therapeutic strategies that would allow for stabilisation of Tau pathology in the elderly.