Tau, amyloid-β and α-synuclein co-pathologies synergistically enhance neuroinflammation and neuropathology

Alzheimer’s (AD) and Parkinson disease (PD) pathology often co-occur. Amyloid-β and phosphorylated tau are found in 30-50% of idiopathic PD cases, while α-synuclein inclusions are present in 50% of AD cases. These co-pathologies are linked to increased mortality and earlier onset of cognitive decline. Immune activation is a hallmark of these neurodegenerative diseases, but current models primarily examine each pathology in isolation. How these co-pathologies drive inflammation and neuronal loss remains poorly understood. We therefore developed a mouse model combining tau, amyloid-β, and α-synuclein. We found that co-pathologies synergistically trigger an amplified neuroimmune response, with expanded populations of CD4+ and CD8+ tissue-resident memory T cells and CD68+ microglia, compared to single pathologies. These changes were abundant in the hippocampus and cortex, regions with elevated protein pathology load and enhanced neuronal loss. Our findings demonstrate that co-pathologies enhance proteinopathy and synergistically enhance immune activation and neurodegeneration, suggesting that combinatorial therapeutic strategies that target both co-pathologies and inflammation, may be disease modifying. Summary Webster et al. demonstrate that co-occurring Alzheimer’s and Parkinson disease protein pathologies, common in cognitively impaired patient populations, amplify proteinopathy and synergistically enhance CNS neuroinflammatory responses and neurodegeneration. This work supports the need for combinatorial therapeutic strategies and positions neuroinflammation as an important link for co-pathology enhanced neurodegeneration.