Progressive neuronal loss and behavioral impairments of transgenic C57BL/6 inbred mice expressing the carboxy terminus of amyloid precursor protein.

The beta-secretase cleaved Abeta-bearing carboxy-terminal fragments (betaCTFs) of amyloid precursor protein (APP) in neural cells have been suggested to be cytotoxic. However, the functional significance of betaCTFs in vivo remains elusive. We created a transgenic mouse line Tg-betaCTF99/B6 expressing the human betaCTF99 in the brain of inbred C57BL/6 strain. Tg-betaCTF99/B6 mouse brain at 12-16 months showed severely down-regulated calbindin, phospho-CREB, and Bcl-xL expression and up-regulated phospho-JNK, Bcl-2, and Bax expression. Neuronal cell density in the Tg-betaCTF99/B6 cerebral cortex at 16-18 months was lower than that of the non-transgenic control, but not at 5 months. At 11-14 months, Tg-betaCTF99/B6 mice displayed cognitive impairments and increased anxiety, which were not observed at 5 months. These results suggest that increased betaCTF99 expression is highly detrimental to the aging brain and that it produces a progressive and age-dependent AD-like pathogenesis.