Alzheimer's disease (AD) is characterized by a specific pattern of neuropathological changes, including extracellular amyloid beta (Aβ) deposits, intracellular neurofibrillary tangles (NFTs), granulovacuolar degeneration (GVD) representing cytoplasmic vacuolar lesions, and synapse and neuronal loss. Necroptosis, a programmed form of necrosis, has recently been shown to be involved in AD. Necroptotic cell death is characterized by the assembly of the necrosome complex, consisting of phosphorylated proteins, i.e. receptor-interacting serine/threonineprotein kinase 1 and 3 (pRIPK1 and pRIPK3), and mixed lineage kinase domain-like protein (pMLKL). However, it is not yet clear whether necrosome assembly takes place in the brain regions showing AD-related neuronal loss, and whether it is associated with AD-related neuropathological changes. Here, we analyzed brains of AD, pathologically defined preclinical AD, and non-AD control cases to determine the neuropathological characteristics and distribution pattern of the necrosome components. We demonstrated that all three activated necrosome components can be detected in GVD lesions (GVDn+, i.e. GVD with activated necrosome) in neurons, and colocalized with classical GVD markers, such as pTDP-43 and CK1δ. GVDn+ neurons were inversely associated with the neuronal density in the early affected CA1 region of the hippocampus and in the late affected frontal cortex layer III. Finally, the distribution of non-phosphorylated proteins was studied. RIPK1 was mainly expressed in astrocytes and in GVD lesions, RIPK3 was detected in dystrophic neurites of neuritic plaques and in neurons. GVD lesions remained negative for non-phosphorylated RIPK3. MLKL could only be detected by western blotting showing an increase in p-preAD and AD cases. Accordingly, AD-related GVD lesions exhibited all components of the activated necrosome and were associated with reduced neuronal densities in the affected anatomical regions, and with AD-defining parameters, showing the strongest correlation and partial colocalization with NFT pathology. Therefore, we conclude that the presence of the necrosome in GVD plays a role in AD, possibly by representing an AD-specific form of necroptosis-related neuron death. Hence, necroptosis-related neuron loss could be an interesting therapeutic target for treating AD.

No abstract

Human post-mortem brain tissue was collected in accordance with the applicable laws in Belgium (UZ Leuven) and Germany (Ulm). The recruitment protocols for the collection of human brains were approved by the ethical committees of the UZ Leuven (Belgium; S-59292, S-52791) and the University of Ulm (Germany; 54/08). This study was approved by the UZ Leuven ethical committee (Leuven, Belgium; S-64378).