Amyloid precursor protein (APP) and its derivatives change after cellular energy depletion. An in vitro-study

Abstract

To study the relationship between the metabolism of amyloid precursor protein (APP) and cellular energy failure, HEK 293 cells stably transfected with betaAPP 695 underwent graded energy failure induced either by i) hypoxia (pO(2) 25 mm Hg), ii) inhibition of the respiratory chain by sodium azide (NaN(3)), or iii) by combined glucose deprivation/hypoxia of different duration and severity. Secreted APP (APPs) and the derivative betaA4 were quantified autoradiographically by immunoprecipitation, and [(35)S] methionine labeling. APP holoprotein (APPh) was determined by Western blot analysis. The concentrations of the energy-rich metabolites ATP, ADP, creatine phosphate (CrP), and adenosine were measured by high performance liquid chromatography. Mild to moderate energy failure after NaN(3) treatment (2h, 4h) and hypoxia (2h, 8h) was characterized by normal ATP concentration but also by a high reduction in CrP. A stress condition indicated by an increased ATP turnover and adenosine increase was obtained. Intracellular APPh increased but its metabolites APPs and betaA4 as measured in the extracellular compartment decreased. These changes may point to a compensatory response of APP but also to a initial disturbance in intracellular APP metabolism. Severe abnormalities in both energy formation and utilization after 8h NaN(3) and hypoxia glucose deprivation were found to be accompanied by a drastic fall in intracellular APPh concentration by at least 50%, paralleled by an accelerating reduction in the extracellular concentrations of both APPs and betaA4.A significant linear correlation between APPh and ATP and between CrP and betaA4 became obvious. The data of the present study indicate that abnormalities in APP metabolism were generated in an energy-dependent manner. The obvious similarities to sporadic Alzheimer s disease are discussed.