Phospholipase D1 is associated with amyloid precursor protein in Alzheimer's disease

doi:10.1016/j.neurobiolaging.2006.05.022

Neurobiology of Aging

Volume 28, Issue 7, July 2007, Pages 1015-1027

https://doi.org/10.1016/j.neurobiolaging.2006.05.022 Get rights and content

Abstract

Amyloid precursor protein (APP) is a widely expressed transmembrane protein of unknown function that is involved in the pathogenesis of Alzheimer's disease (AD). We investigated the involvement of phospholipase D (PLD) in the pathophysiology of AD. We showed dramatic upregulation of PLD1 immunoreactivity in reactive astroglial cells in brain tissue sections from authentic AD patients. Expression and activity of PLD1 were up-regulated in brain tissues from AD patients, especially caveolae membrane fraction, compared with those of control brains. Interestingly, PLD1 physically interacts and colocalizes with APP and caveolin-3. We found that APP was associated with the pleckstrin homology domain of PLD1, and the amyloid region of APP interacted with PLD. Elevated expression of APP stimulated PLD activity in human astroglioma cells. These results suggest that up-regulation of PLD might have a role in the neuronal pathology associated with AD.

Introduction

Alzheimer's disease (AD), the most common cause of dementia in elderly patients, is a complex disorder of the central nervous system clinically characterized by a progressive loss of cognitive abilities. Pathological hallmarks of AD include widespread neuronal degeneration, neurite plaques containing β-amyloid (Aβ), and intracellular neurofibrillary tangles [24], [35]. The Aβ is the major component of senile plaques and is derived from the amyloid precursor protein (APP) by proteolytic cleavage [36]. Although accumulated evidence suggests that Aβ is a key causative agent of AD [11], [33], the exact mechanism of neuronal degeneration in AD has not been clear. It is likely that multiple factors are involved in the development of the disease.

Kanfer et al. [17] have suggested that neuronal degeneration in AD might be related to an alteration in tissue phospholipids with a corresponding increase in the catabolic products of phospholipids metabolism. Aβ is known to affect the activity of several lipid-metabolizing enzymes, including the phospholipases A2, C and D [16], [31], [32]. However, it is unknown whether these phospholipids alternations are sufficient and necessary for the etiology of AD or if they are secondary events in the pathogenesis of neurodegeneration. Recently, phospholipids breakdown by phospholipase D (PLD) has been recognized as an important signaling pathway in the nervous system.

PLD catalyzes the hydrolysis of phosphatidylcholine (PC), the major membrane phospholipid, to produce the pleiotropic signaling lipid messenger phosphatidic acid (PA). PA is generally recognized as the signaling product of PLD and functions as an effector in multiple physiological processes [21]. In mammals, two isoforms of PLD, PLD1 and PLD2, have been cloned and are being characterized for regulation and cellular function [21]. However, the segregated roles of the two PLD isoforms in cellular responses are still poorly understood. Activation of PLD occurs through interactions of the ARF and Rho families as well as with protein kinase C (PKC) [21]. Recently, we have reported that PLD1 immunoreactivity and its enzymatic activity were up-regulated in the activated astrocytes of scrapie-infected mice brain [14]. However, the expression of PLD in AD brains has not been investigated so far.

These studies have raised the possibility that PLD might be involved in the neuronal pathology associated with AD. In the present study, we demonstrate for the first time that PLD1 is up-regulated in the caveolae membrane fraction and reactive astrocytes from AD brains, and co-localized and associated with APP.

Section snippets

Brain tissues

A total of six post-mortem brain specimens of Alzheimer's disease patients and age-matched controls were obtained from the IBR brain bank (Dr. Piotr B. Kozlowski). The characteristics of the brain specimens with post-mortem intervals ranging from 0.5 to 14.5 h are shown in Table 1. Cases of Alzheimer's disease and age-matched controls were classified based on quantitative pathological features including senile plaques and neurofibrillary tangles (NFT) according to Braak and Braak [1].

Cell culture and transfections

COS-7 cells

PLD1 is up-regulated in reactive astrocytes of the brains of AD patients

To investigate the possibility that PLD expression is altered in AD brain tissues, we immunostained AD brain sections from patients using anti-PLD antibody. We observed enhanced PLD immunoreactivity in the brains of AD patients compared to that of elderly controls (Fig. 1A and B). Barely detectable levels were found in normal human hippocampus section (Fig. 1A). We detected strong PLD immunoreactivity in the hippocampal sections from AD patients via DAB staining (Fig. 1B). The cells that

Discussion

The major findings of this report are that PLD1 is significantly up-regulated in brain tissues from AD patients relative to age-matched control subjects, and that PLD1 binds to APP. PLD1 was heavily accumulated in reactive astrocytes and co-localized with APP and caveolin-3 in the brains of patients with AD. In the present study, we found that the expression of PLD1 is markedly increased in caveolin-enriched fraction from AD brains. Recently, we have reported that the expression of PLD1 in

Acknowledgements

This study was supported by grant No. R01-2006-000-10521-0 (2006) from the Basic Research Program of the Korea Science & Engineering Foundation and by the Biotechnology Development Program (grant number 2005-00115) from Ministry of Science and Technology (MOST), Korea and grant of the Korea Health 21 R&D project, Ministry of Health and Welfare, Republic of Korea (A020007). A total of six post-mortem brain specimens of Alzheimer's disease patients and age-matched controls were obtained from the

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PLD activity was increased by APP in P19 mouse embryonic carcinoma cells [534] and oligomeric Aβ in cultured neurons [39]. PLD is also implicated in regulation of APP trafficking, as well as trafficking of presenilin-1 (PS1), a component of the γ-secretase which mediates APP cleavage to generate Aβ [36–41,188,528,535–539]. Both the PLD1 and PLD2 isoforms are linked to AD [37,39,188].
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Previous studies proposed a neuroprotective role for PLD1 where a direct effect of overexpressed PLD1 on presenilin-1 results in reduction of Aβ species generation [16], by promoting trans-Golgi intracellular trafficking of β APP and promoting neurite outgrowth [17]. Perhaps, the elevated PLD1 levels in the activated astrocytes and mitochondrial fractions of AD brains, reported in another set of studies [18,36], could be explained as neuroprotective. However, the authors indicate that the amyloid region of APP interacts with PLD1 and increased APP expression stimulates PLD1 activity, thus questioning the speculated neuroprotective role of PLD1.
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Phospholipase D1 is associated with amyloid precursor protein in Alzheimer's disease

Abstract

Introduction

Section snippets

Brain tissues

Cell culture and transfections

PLD1 is up-regulated in reactive astrocytes of the brains of AD patients

Discussion

Acknowledgements

Cell

Chem Phys Lipids

Neurobiol Aging

J Biol Chem

Neurosci Lett

J Lipid Mediat Cell Signal

Neurosci Lett

FEBS Lett

Neuropharmacology

Trends Neurosci

Biochim Biophys Acta

FEBS Lett

Curr Opin Pharmacol

Neurobiol Aging

Neuron

Life Sci

Neuropathological stageing of Alzheimer-related changes

Acta Neuropathol

Presenilin-1 uses phospholipase D1 as a negative regulator of b-amyloid formation

Proc Natl Acad Sci USA

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

Proc Natl Acad Sci USA