Neurobiology of Disease Reduced Reelin Expression Accelerates Amyloid- Plaque Formation and Tau Pathology in Transgenic Alzheimer’s Disease Mice

In addition to the fundamental role of the extracellular glycoprotein Reelin in neuronal development and adult synaptic plasticity, alterations in Reelin-mediated signaling have been suggested to contribute to neuronal dysfunction associated with Alzheimer’s disease (AD). In vitro data revealed a biochemical link between Reelin-mediated signaling, Tau phosphorylation, and amyloid precursor protein (APP) processing. To directly address the role of Reelin in amyloidplaque and Tau pathology in vivo, we crossed heterozygous Reelin knock-out mice (reeler) with transgenic AD mice to investigate the temporal and spatial AD-like neuropathology. We demonstrate that a reduction in Reelin expression results in enhanced amyloidogenic APP processing, as indicated by the precocious production of amyloidpeptides, the significant increase in number and size of amyloidplaques, as well as age-related aggravation of plaque pathology in double mutant compared with single AD mutant mice of both sexes. Numerous amyloidplaques accumulate in the hippocampal formation and neocortex of double mutants, precisely in layers with strongest Reelin expression and highest accumulation of Reelin plaques in aged wild-type mice. Moreover, concentric accumulations of phosphorylated Tau-positive neurons around amyloidplaques were evident in 15-month-old double versus single mutant mice. Silver stainings indicated the presence of neurofibrillary tangles, selectively associated with amyloidplaques and dystrophic neurites in the entorhinal cortex and hippocampus. Our findings suggest that age-related Reelin aggregation and concomitant reduction in Reelin-mediated signaling play a proximal role in synaptic dysfunction associated with amyloiddeposition, sufficient to enhance Tau phosphorylation and tangle formation in the hippocampal formation in aged Reelin-deficient transgenic AD mice.