The accumulation and deposition of amyloid-beta (Aß) peptides is detrimental to neuronal networks and is driven by the cleavage of amyloid precursor protein (APP) by beta-secretase 1 (BACE1). The proteolytic processing of APP is tightly regulated by the opposing activities of BACE1 and ADAM10, with the latter producing a truncated, non-amyloidogenic fragment. Maintaining this balance is critical for normal physiological function, as complete inhibition of BACE1 has proven detrimental owing to the important physiological roles of its many substrates. Brain-derived neurotrophic factor (BDNF), an important mediator of neuronal function and survival, has recently been shown to reduce BACE1 activity in neural tissue, but the mechanism for this remains unknown. Previous research suggests that BACE1 cleavage of APP is favoured at acidic intracellular compartments, whereas non-amyloidogenic processing preferentially occurs at the plasma membrane. Hence, we hypothesized that BDNF alters the subcellular distribution of BACE1, reducing ß-cleavage of APP. Here, we show that acute BDNF treatment of differentiated neural cells (SH-SY5Y) reduced levels of sAPPß, a product of BACE1 cleavage of APP. Using confocal microscopy and quantitative image analysis, we found that this reduction in sAPPß levels is coincident with increased BACE1 localization to the plasma membrane, and a concomitant reduction of BACE1 localization to early endosomes. This effect appears to be independent of clathrin-mediated endocytosis (CME), as inhibition of CME by PitStop2 treatment increased a-cleavage of APP but did not reduce ß-cleavage independent of BDNF treatment. Hence, BDNF may reduce production of Aß by altering BACE1 distribution and decreasing upstream ß-cleavage.
Hallam et al. (Mon,) studied this question.