P3-239: Heparin activates βeta-secretase(BACE1) of Alzheimer’s disease and increases autocatalysis of the enzyme

Abstract

The beta–site APP cleaving enzyme 1 (BACE1) is an aspartic protease that generates the N–terminus of the beta–amyloid protein from the beta–amyloid precursor protein (APP). BACE1 is a key target for Alzheimer drug development. However, little is known about the physiological regulation of the enzyme. Heparin can promote beta–secretase cleavage of endogenous APP in neuroblastoma cells. However, heparin has also been reported to directly inhibit BACE1 activity in vitro. To clarify the role of heparin in regulating BACE1. We examined the effect of heparin on the activity of recombinant human BACE1 (rBACE1) in vitro. Low concentrations (1 microg/mL) of heparin were found to stimulate rBACE1, whereas higher concentrations (10 or 100 microg/mL) were inhibitory. Heparin affinity chromatography demonstrated that heparin interacted strongly with the partially active pro–enzyme form of rBACE1 and bound to a peptide homologous to the N–terminal pro–sequence of BACE1. Low concentrations of heparin promoted autocatalytic cleavage of rBACE1, resulting in a decrease in the concentration of the pro–enzyme form and an increase in lower molecular mass forms. Furthermore, mature (pro–sequence cleaved) enzyme appeared to lack the capacity to be stimulated by heparin providing support for the view that activation by heparin was through pro–domain cleavage. The results indicate that high affinity binding of heparin to the pro–domain of BACE1 activates the enzyme and increases autocatalysis of BACE1 in vitro. Our study provides evidence that heparan sulfate proteoglycans could regulate the rate of Abeta production in vivo.