Phospholipase D1 corrects impaired βAPP trafficking and neurite outgrowth in familial Alzheimer’s disease-linked presenilin-1 mutant neurons

Abstract

T he distribution of ␤-amyloid precursor protein (␤APP) between the trans-Golgi network (TGN) and the cell surface may determine the relative generation of s␤APP␣ versus ␤-amyloid (1-5). Using a cell-free vesicle-trafficking reconstitution system derived from neuroblastoma cells, we showed previously that presenilin-1 (PS1), a major component of ␥-secretase, selectively affects ␤APP budding from the TGN and the endoplasmic reticulum (ER) (6). Familial Alzheimer's disease (FAD) PS1 mutations impair the budding of vesicles containing ␤APP, which may partially account for increased ␤APP processing via ␤-and ␥-secretases.Protein trafficking within the secretory pathway is regulated by a rigorously orchestrated sequence of events. Recruitment of cytosolic factors and coat proteins to membranes, and changes in lipid composition that promote membrane curvature and protein anchoring, are necessary for vesiculation (7,8). Estradiol-promoted ␤APP trafficking depends on the recruitment of cytosolic trafficking factor Rab11 to the TGN (3).Phospholipase D (PLD), a phospholipid-modifying enzyme, catalyzes the hydrolysis of phosphatidylcholine to generate phosphatidic acid (PA) (8-10). PLD has been shown to regulate membrane trafficking events, such as the release of secretory vesicles from the TGN (11), endocytosis (12) and exocytosis (13), and actin dynamics (14). In this study, the effects of PLD1 on ␤APP trafficking have been investigated. Of particular interest, up-regulation of PLD1 in FAD-linked PS1 mutant cells rescues impaired ␤APP trafficking from the TGN to the plasma membrane and corrects FAD-related defects in neurite outgrowth capacity. In a companion paper (15), we report that PLD1 interacts with PS1 and, through a mechanism independent of its effect on ␤APP trafficking, disrupts the ␥-secretase complex and inhibits ␥-secretase activity. Results PLD1Regulates ␤APP Trafficking. We investigated whether PLD1 might be involved in regulation of ␤APP intracellular trafficking. The effect of PLD1 on ␤APP trafficking was assessed in both PS1wt and PS1-deficient cells. Consistent with our previous observations (6), the rate of formation of ␤APP-containing vesicles from the TGN in PS1 Ϫ/Ϫ fibroblasts was increased compared with PS1wt cells (Fig. 1a). Overexpression of PLD1 in PS1wt cells increased ␤APP trafficking from the TGN to a rate comparable with that seen in PS1 Ϫ/Ϫ -deficient cells. However, PLD1 overexpression failed to increase the number of ␤APP-containing vesicles budded from the TGN in PS1 Ϫ/Ϫ fibroblasts, probably because of a maximal rate of ␤APP-containing vesicle trafficking in PS1-null cells. Inhibition of PLD1 catalytic activity by 1-butanol (an inhibitor of PLD-catalyzed formation of PA) (11, 16), resulted in decreased ␤APP trafficking from the TGN in both PS1wt and PS1 Ϫ/Ϫ cells (Fig. 1b). As a control, tertiary butanol, which does not affect PLD activity (12), caused little change in ␤APP budding from the TGN. These results demonstrate that PLD1 can affect ␤APP trafficking through a PS1-independent m...

The Coffin-Lowry Syndrome-Associated Protein RSK2 Regulates Neurite Outgrowth through Phosphorylation of Phospholipase D1 (PLD1) and Synthesis of Phosphatidic Acid

“…The interplay between PLD1 and Rho GTPases has been shown in several cellular processes, but it remains to be established whether the altered dendrite and spine morphology observed in Pld1-KO mice, relies on an alteration of Rho activity. It is also worthwhile mentioning that the GTPase ARF6, an activator of PLD1 , has been reported to play a positive role in spine formation (Choi et al, 2006), in line with the findings reported here.…”

“…In support of this hypothesis, PLD1 was shown to regulate intracellular trafficking of presenilin-1, a critical component of the ␥-secretase complex (Liu et al, 2009). Of particular interest, upregulation of PLD1 rescues impaired ␤APP trafficking to the plasma membrane and defects in neurite outgrowth capacity in a familial form of Alzheimer disease presenilin-1 mutant neurons (Cai et al, 2006). It is thus tempting to speculate that the RSK2-phosphorylated form of PLD1 plays a key role in promoting vesicular delivery of key components for neuronal development and function.…”

Impairments in Fast Axonal Transport and Motor Neuron Deficits in Transgenic Mice Expressing Familial Alzheimer's Disease-Linked Mutant Presenilin 1

“…Studies in cultured neuroblastoma cells have revealed that expression of FAD-linked mutant PS1 impairs biogenesis of APP-containing vesicles de-rived from the ER and Golgi (Cai et al, 2003(Cai et al, , 2006a. Furthermore, studies in cultured embryonic primary hippocampal neurons expressing FAD-linked mutant PS1 revealed reductions in kinesin-1-mediated delivery of selected synaptic markers and mitochondria to growing neurites (Pigino et al, 2003).…”

Alzheimer’s Disease Risk Genes and Lipid Regulators

“…This increase in PLD activities was correlated with an enhanced release of cytosolic protein lactate dehydrogenase, suggesting a potential association with A␤-induced toxicities [137]. These studies implicate a potential crosstalk between PLD1, ␤APP and PS1 contributing to amyloidogenesis and amyloidinduced toxicities [134,138,139]. However, it is unclear whether this crosstalk occurs in vivo.…”

“…In cells that exhibit AD-like mutations PLD activity was reduced, but overexpression of PLD1 in these cells corrected impaired intracellular trafficking of ␤APP and reduced A␤ production [134]. In contrast, PLD2 was found to promote A␤ toxicity in cell cultures [135].…”