Immunolesion‐induced loss of cholinergic projection neurones promotes β‐amyloidosis and tau hyperphosphorylation in the hippocampus of triple‐transgenic mice

Aims Currently available animal models incompletely capture the complex pathophysiology of A lzheimer's disease ( AD ), typically involving β‐amyloidosis, neurofibrillary tangle formation and loss of basal forebrain cholinergic projection neurones ( CPN ). While age‐dependent β‐amyloidosis and tau hyperphosphorylation are mimicked in triple‐transgenic mice (3x T g), experimental induction of CPN loss in these mice is still lacking. Here, we introduce a more‐complex animal model of AD by inducing cellular loss of CPN in an already existing transgenic background aiming to elucidate subsequent changes of hippocampal β‐amyloid (Aβ) and tau pathology. Methods Twelve‐month‐old 3x T g mice intracerebroventricularly received the rabbit‐anti‐low affinity neurotrophin receptor p75‐saporin, an immunotoxin specifically targeting forebrain CPN . After histochemical verification of immunolesion in immersion‐fixed forebrains, markers of A β and tau metabolism were analysed using quantitative Western blot analyses of hippocampi from these mice. In parallel, these markers and glial activation were investigated by multiple immunofluorescence labelling of perfusion‐fixed hippocampi and confocal laser‐scanning microscopy. Results Four months after immunolesion, the selective lesion of CPN was verified by disappearance of choline acetyltransferase and p75 immunolabelling. Biochemical analysis of hippocampi from immunolesioned mice revealed enhanced levels of Aβ, amyloid precursor protein ( APP ) and its fragment C99. Furthermore, immunolesion‐induced increase in levels of phospho‐tau and tau with AD ‐like conformation were seen in 16‐month‐old mice. Immunofluorescence staining confirmed an age‐dependent occurrence of hippocampal Aβ‐deposits and phospho‐tau, and demonstrated drastic gliosis around Aβ‐plaques after immunolesion. Conclusion Overall, this extended model promises further insights into the complexity of AD and contributes to novel treatment strategies also targeting the cholinergic system.