The evolving role of intraneuronal amyloid‐β in Alzheimer’s disease

Abstract

AbstractBackgroundIn 1998 at the Alzheimer’s Association conference in Amsterdam, I first presented on the accumulation of Alzheimer’s disease (AD)‐linked amyloid‐β42 (Aβ42) in cultured neurons and human brains with early AD pathology (later published in Gouras GK et al., 2000). Despite much skepticism, this early work led to a revision of the role of Aβ in AD that for the past 2.5 decades has been at the center of our group’s attempt to better define the earliest cellular stages of AD. Our current scenario, including with new data, will be presented for the role of intraneuronal Aβ in the early endosomal and synaptic alterations that initiate the disease process.MethodAD transgenic (overexpression and knock‐in) mouse models at different ages and postmortem human brains are analyzed using amongst others, microscopy and biochemical approaches for APP metabolites, and other AD‐linked, endosome and synapse proteins, with a focus on the earliest detectable alterations within AD vulnerable neurons. Brain injections of prion‐like Aβ and tract tracing methods are used to model early anatomical and cellular progression of pathology. Further, primary brain cultures from AD mice are used to model early AD cellular alterations.ResultPrior to classical amyloid plaques, smaller accumulations of Aβ develop within the endosome‐lysosome system of AD vulnerable neurons, with preferential aggregation near axonal and dendritic synaptic terminals with AD pathogenesis. Ongoing work is centered on elucidating the early alterations of different pools of APP metabolites, ApoE and Tau in the early biological pathways that impact synapses.ConclusionOur understanding of the early cellular dysfunction and pathology has evolved significantly over the past few decades, with a better appreciation for the importance of other cell types (e.g. astrocytes, microglia) and factors in AD, and recent, albeit modest, success in therapy targeting Aβ. We see aging, along with genes and lifestyle, as promoting the earliest Aβ‐related dysfunction in endosomal biology at synapses and are working to piece together the links between key AD‐related proteins in the disease process.