Age-dependent degradation of amyloid precursor protein in the post-mortem mouse brain cortex

We have examined the degradation of amyloid precursor protein (APP) in the brain cortex of adult (24 +/- 2) and old (58 +/- 2) mice at different post- mortem time intervals (0, 1.5, 3, 6, 12 and 24 h). The brain cortex extract was prepared and processed for immunoblotting using antibodies against N-t erminal 47-62 amino acids (Asp29) and central 301-316 amino acids containin g Kunitz protease inhibitor (KPI) domain (Asp45) of APP. Asp29 (N-terminal) recognizes two bands of 140 and 112 kDa. The amount of 140 kDa is relative ly higher in adult than old. The level of 112 kDa is 1.6 times lower in adu lt than old. It shows no remarkable change with varying post-mortem time. O n the other hand, Asp45 (KPI) detects two bands of 110 and 116 kDa. While 1 16 kDa disappears rapidly after death of the animal, 110 kDa shows no remar kable change with different post-mortem periods. Further incubation of the disrupted tissue at 4 degrees C for 24 h and immunoblot analysis with Asp29 (N-terminal) shows 112 kDa in both ages but 58.5 kDa in adult and 70 kDa i n old only. Analysis with Asp45 (KPI) shows only 54 kDa which increases aft er 3 h in adult but decreases significantly after 1.5 h and becomes undetec table at 24 h in old. Thus the present findings indicate that APP is degrad ed in a precise pattern and it depends on cellular intactness, post-mortem period and age of the animal.