The trans-Golgi network is a major site for α-secretase processing of amyloid precursor protein in primary neurons

Abstract

Edited by Paul E. FraserAmyloid precursor protein (APP) is processed along the amyloidogenic pathway by the ␤-secretase, BACE1, generating ␤-amyloid (A␤), or along the nonamyloidogenic pathway by ␣-secretase, precluding A␤ production. The plasma membrane is considered the major site for ␣-secretase-mediated APP cleavage, but other cellular locations have not been rigorously investigated. Here, we report that APP is processed by endogenous ␣-secretase at the trans-Golgi network (TGN) of both transfected HeLa cells and mouse primary neurons. We have previously shown the adaptor protein complex, AP-4, and small G protein ADP-ribosylation factor-like GTPase 5b (Arl5b) are required for efficient post-Golgi transport of APP to endosomes. We found here that AP-4 or Arl5b depletion results in Golgi accumulation of APP and increased secretion of the soluble ␣-secretase cleavage product sAPP␣. Moreover, inhibition of ␥-secretase following APP accumulation in the TGN increases the levels of the membrane-bound C-terminal fragments of APP from both ␣-secretase cleavage (␣-CTF, named C83 according to its band size) and BACE1 cleavage (␤-CTF/ C99). The level of C83 was ϳ4 times higher than that of C99, indicating that ␣-secretase processing is the major pathway and that BACE1 processing is the minor pathway in the TGN. AP-4 silencing in mouse primary neurons also resulted in the accumulation of endogenous APP in the TGN and enhanced ␣-secretase processing. These findings identify the TGN as a major site for ␣-secretase processing in HeLa cells and primary neurons and indicate that both APP processing pathways can occur within the TGN compartment along the secretory pathway.

MT5-MMP controls APP and β-CTF/C99 metabolism through proteolytic-dependent and -independent mechanisms relevant for Alzheimer’s disease

“…However, DAPT only causes full recovery of C83 levels in MT5 EXTexpressing cells, which argues for more efficient targeting of C83 by the truncated Cterminal domains of MT5-MMP to subcellular compartments with γ-secretase activity. On the other hand, it has been recently shown that α-secretase can process APP in the TGN [49]. Taken together, these data support the possibility that some C99 in the TGN is converted to C83 by α-secretase and that the C-terminal part of MT5-MMP targets both the unconverted C99 and C83 from the TGN to the endo-lysosomal system for further processing.…”

APP Maturation and Intracellular Localization Are Controlled by a Specific Inhibitor of 37/67 kDa Laminin-1 Receptor in Neuronal Cells

“…The finding that the 37/67 kDa LR may play a key role in Alzheimer's disease [22,23,26] and that it could act as a receptor mediating Aβ cytotoxicity [24,25], prompted us to verify the effects of a specific 37/67 kDa LR inhibitor on the expression levels and posttranslational modifications of APP, which are known to have a critical role in Aβ generation [14,18]. In addition, the correct localization and trafficking of proteins are fundamental for their correct processing and function [17,45].…”

“…Interestingly, deacidification of endosomal/lysosomal system decreases Aβ production [7]. Beside the previously described role of APP endocytosis in Aβ production [8,9], many reports suggest a critical role for intracellular trafficking of APP in Aβ generation [10][11][12][13][14][15][16][17] and indicate the trans-Golgi network as the main sorting station of APP to lysosomes, where the Aβ can be produced [18]. An aberrant production of Aβ in AD brains could amplify its neurotoxic effects through activation of GSK3β (Glycogen synthase kinase 3 beta) [19].…”

Dendritic Spines in Alzheimer’s Disease: How the Actin Cytoskeleton Contributes to Synaptic Failure

“…ADAM10 cleavage not only prevents Aβ generation but also increases the release of the neurotrophic and neuroprotective sAPPα fragment [11]. The non-amyloidogenic ADAM10 processing of APP occurs largely on the plasma membrane [12] and in the trans-Golgi network [13] ( Figure 1). APP and the secretases are all transmembrane proteins.…”