Cognitive Deficits and Disruption of Neurogenesis in a Mouse Model of apoE4-Domain Interaction [Molecular Bases of Disease]

December 9th, 2013 by Adeosun, S. O., Hou, X., Zheng, B., Stockmeier, C., Ou, X., Paul, I., Mosley, T., Weisgraber, K., Wang, J. M.

Apolipoprotein E4 (apoE4) allele is the major genetic risk factor for sporadic Alzheimers disease (AD), due to the higher prevalence and earlier onset of AD in apoE4 carriers. Accumulating data suggest that the interaction between the N- and the C-terminal domains in the protein may be the main pathologic feature of apoE4. To test this hypothesis, we used Arg-61 mice, a model of apoE4 domain interaction by introducing the domain interaction feature of human apoE4 into native mouse apoE. We carried out hippocampus-dependent learning and memory tests and related cellular and molecular assays on 12- and 3-month-old Arg-61 and age-matched background C57BL/6J mice. Learning and memory task performance were impaired in Arg-61 mice at both old and young ages compared to C57BL/6J mice. Surprisingly, young Arg-61 mice had more mitotic doublecortin-positive cells in the subgranular zone, mRNA levels of BDNF and TrkB were also higher in 3-month old Arg-61 hippocampus compared to C57BL/6J mice. These early-age neurotrophic and neurogenic [proliferative] effects in the Arg-61 mouse may be an inadequate compensatory but eventually detrimental attempt by the system to "repair" itself. This is supported by the higher Cleaved-caspase 3 levels in the young animals which not only persisted but increased in old ages, and the lower levels of doublecortin at old age in the hippocampus of Arg-61 mice. These results are consistent with human apoE4-dependent cognitive and neuro-pathologic changes; supporting the principal role of domain interaction in the pathologic effect of apoE4. Domain interaction is therefore a viable therapeutic/prophylactic target for cognitive impairment and AD in apoE4 subjects.