A protease activity associated with acetylcholinesterase releases the membrane-bound form of the amyloid protein precursor of Alzheimer's disease

An abnormality of plasma amyloid protein precursor in Alzheimer's disease

beta A4 amyloid deposition in the brain, which is characteristic of Alzheimer's disease (AD), may result from either overexpression of the amyloid protein precursor (APP) or failure of APP to be correctly processed. A blood marker reflecting this abnormal metabolism would be of diagnostic value and would provide a means of monitoring the efficacy of therapeutic interventions. We analyzed immunoblots of plasma APP enriched by heparin-Sepharose chromatography from patients with moderate to severe AD dementia (n = 34) and control subjects (n = 77) and found an approximately 50% increase in the proportion of 130-kd APP species in patients with AD (p less than 0.001), no difference in the 110-kd form, a 15 to 30% decrease in the 65-kd form (p less than 0.001), and a 20 to 35% decrease in the proportion of 42-kd APP (p less than 0.001). These species of APP were soluble, lacked the carboxyl terminus, and the 110- and 42-kd species were shown to be consistent with degradation products derived from the 130-kd species. A comparison of levels of 130-kd plasma APP from moderately to severely demented patients with AD and control subjects distinguished the two groups with a specificity of 87.0% and a sensitivity of 79.4%.

The amyloid protein precursor of Alzheimer's disease is a mediator of the effects of nerve growth factor on neurite outgrowth

The beta A4 protein, the major component of the amyloid deposition characterizing Alzheimer's disease, derives from the amyloid protein precursor (APP), an integral membrane protein with soluble derivatives. The function of APP is unknown. Both soluble and membrane-associated human brain APP (10(-10) M) significantly increased (P less than 0.025) neurite length and branching in pheochromocytoma PC12 cells, but did not affect the number of neurites per cell. At higher concentrations, APP was cytotoxic, with a half-maximal concentration of 5 x 10(-9) M. Nerve growth factor (NGF) is known to affect APP expression in vivo and in vitro. Antibodies to APP specifically diminished the effects of NGF on neurite length and branching. Thus APP may act to mediate neurite outgrowth promotion by NGF.

Beta A4 amyloid protein and its precursor in Alzheimer's disease

The beta A4 amyloid protein is now understood to play a pivotal role in the development of Alzheimer's disease. This protein is generated by the abnormal processing of the amyloid protein precursor, a large membrane glycoprotein. Insights into the mechanisms of this abnormal processing will give information relevant to the design of new therapeutic strategies for Alzheimer's disease.