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Keywords:

  • Alzheimer's disease;
  • amyloid plaques;
  • amyloid precursor protein processing;
  • animal model;
  • astrocytes;
  • gliosis

Abstract

We investigated the influence of five- to sevenfold neuronal overexpression of the Swedish mutation of human APP695 (APPsw) in the transgenic mouse strain Tg2576 on neocortical protein kinase C (PKC) expression and subcellular distribution. Using specific antibodies to PKCα, PKCβ, PKCγ, PKCε and PKCζ isoforms for Western blot analysis, we observed increased immunoreactivity for PKCα and PKCγ isoforms in crude tissue homogenates from the neocortex of 16-month-old APPsw mice as compared with nontransgenic littermates, which was not present in 6 month-old Tg2576 mice. We also observed elevated levels of PKCα, PKCβ, PKCγ and PKCζ in membrane fractions and reduced concentrations of PKCα and PKCγ in cytosolic fractions of aged Tg2576 mice, indicating that these PKC isoforms are in their activated state. In young, 6-month-old Tg2576 mice, however, the increase in membrane-bound PKC isoforms and concomitant decrease in cytosolic PKC isoforms was much less pronounced, demonstrating the age-dependent nature of alterations in PKC isoforms. Immunocytochemistry of brain sections supported these findings and revealed increased neuronal labelling for PKCα, PKCγ and PKCλ isoforms in neocortex of 16-month-old APPsw mice compared with nontransgenic littermates, with the increase being strongest for PKCγ and PKCλ isoforms. Additionally, PKCγ and to a lesser extent PKCλ isoforms were induced in reactive astrocytes in proximity to amyloid plaques. Our data indicate that neuronal overexpression of APPsw causes a dynamic change in neuronal expression and activation of multiple PKC isoforms known to be regulators of proteolytic amyloid precursor protein (APP) processing (PKCα) and of neuronal survival (PKCλ and PKCζ). The induction of the PKCγ and PKCλ isoforms in reactive astrocytes surrounding amyloid plaques might be required for astrocyte activation and astrocytic cytokine expression in response to amyloid plaque formation.