Abstract
Amyloid-β protein precursor (AβPP) is a ubiquitously expressed glycoprotein, which under physiological conditions can be cleaved following two alternative routes; the non-amyloidogenic and the amyloidogenic pathway. Shift of AβPP processing in favor of the amyloidogenic pathway is a key event in the pathogenesis of Alzheimer's disease (AD). Among the factors that regulate AβPP processing, nerve growth factor (NGF) appears to play an important role; abnormal NGF signaling has been implicated in the onset of AD. In the present study, we used PC12 cells to study the effects of NGF on AβPP processing and provide evidence that NGF, through binding to its high affinity receptor, TrkA moderately down-regulates the expression of the β-secretase β-site AβPP cleaving enzyme-1 and, most importantly, upregulates the expression of two enzymes with α-secretase activity, a disintegrin and metalloprotease-17 and to a greater extent matrix metalloproteinase-9 (MMP9) in a phosphoinositide kinase-3 dependent manner. Finally, we demonstrate that MMP9 actively participates in NGF-induced α-secretase cleavage of AβPP, thus it contributes to the shift of AβPP processing towards the non-amyloidogenic pathway precluding the formation of neurotoxic Aβ peptides.