| Abstract: | Cultured fibroblasts from patients affected by Alzheimer's disease (AD) exhibited peculiar alterations of the enzyme transketolase (TK). Abnormalities (dubbed alkaline bands, ab ) consisted of enzyme forms having unusually high pI and were proposed as a marker of the disease in living patients. The mechanisms of TK- ab expression were investigated with the use of cysteine proteinase inhibitors and purified preparations of either rat liver or human cysteine proteinases. The cysteine proteinase inhibitors N-acetyl-leu-leu-norleucinal (ALLN), L-trans-Epoxy-succinyl-leucylamido(4-guanidino)butane (E-64), and egg white cystatin added to AD cells just prior to extraction abolished TK abnormalities. Moreover, 1 day incubation of AD cultures with either ALLN (10 μg/ml), NH4Cl (10 mM), or KCl (30 mM) prevented TK- ab generation, due, presumably, to an impairment of lysosomal functions. Isolated rat liver cysteine proteinases were able to degrade TK in normal extracts and reproduce the characteristic TK- ab of AD fibroblasts. Moreover, pure human cathepsin H was also shown to partially induce an Alzheimer-like TK pattern and cleave normal TK to a 35 kDa fragment as spontaneously occurring in AD fibroblasts. The explanation of mechanisms of TK- ab formation provided evidence for an underlying imbalance of proteolysis in AD fibroblasts due to a relative increase/derangement of the cysteine proteinases cathepsins which might be also involved in the reported abnormal processing of multiple cellular components. J. Cell. Physiol. 172:63–68, 1997. © 1997 Wiley-Liss, Inc. |
