Amyloid precursor protein mediates monocyte adhesion in AD tissue and apoE−/− mice

doi:10.1016/j.neurobiolaging.2008.10.013

Neurobiology of Aging

Volume 31, Issue 11, November 2010, Pages 1854-1866

https://doi.org/10.1016/j.neurobiolaging.2008.10.013 Get rights and content

Abstract

Amyloid precursor protein (APP) is a type 1 integral membrane protein, which is highly conserved and ubiquitously expressed. Numerous data suggest it functions in cellular adhesion. For example, APP binds components of the extracellular matrix to propagate intracellular signaling responses. In order to investigate adhesion-related changes in inflamed vasculature, brains from apolipoprotein E^−/− (apoE^−/−) mice were examined for changes related to APP then compared to human Alzheimer’s disease (AD) brains. Cerebrovasculature from mouse apoE⁻/⁻ and human AD brains revealed strong immunoreactivity for APP, APP phosphorylated at tyrosine residue 682 (pAPP) and Aβ. Further, Western blot analyses from mouse apoE^−/− and AD brains showed statistically higher protein levels of APP, pAPP and increased APP association with the tyrosine kinase, Src. Lastly, utilizing a modified Stamper–Woodruff adhesion assay, we demonstrated that adhesion of monocytic cells to apoE^−/− and AD brain endothelium is partially APP dependent. These data suggest that endothelial APP function coupled with increased Aβ production are involved in the vascular dysfunction associated with atherosclerosis and AD.

Introduction

Major research efforts continue to focus on the role of Aβ, a cleavage product of amyloid precursor protein, APP, in the progression of disease while the function of the holoprotein, APP is unclear. Numerous data suggest a role in cellular adhesion via cell–cell or cell–matrix interactions. The N-terminal crystalline structure of APP is reminiscent of a cell surface receptor (Rossjohn et al., 1999) and APP contains a well defined ₆₈₂YENPTY₆₈₇ cytoplasmic motif, characteristic of tyrosine kinase receptors. Furthermore, it has been shown to bind components of the extracellular matrix, including: collagen, laminin, and proteoglycans (Kibbey et al., 1993, Williamson et al., 1995, Beher et al., 1996).

Adhesion of immune cells to the endothelium is a well characterized response leading to the phenotypic activation of the endothelium and eventual diapedesis of immune cells. APP-dependent adhesion may play a role in the phenotype of both immune and endothelial cells. For example, our previous data derived from using THP-1 monocytic cells demonstrated that monocytic cells utilize an APP-dependent activation response when adhering to collagen. This APP-mediated response involves recruitment and activation of specific non-receptor tyrosine kinases, Syk and Lyn (Sondag and Combs, 2004). Interestingly, APP expression is upregulated in both cell types following neuronal injury and focal ischemia and activating stimuli, in microglia and endothelial cells, respectively (Goldgaber et al., 1989, Forloni et al., 1992, Banati et al., 1993, Banati et al., 1994). Furthermore, APP overexpression in endothelial cells is toxic (Jahroudi et al., 1998). Finally, endothelial cells express the secretase enzymes required to generate Aβ peptides (Davies et al., 1998) and vasculature from AD brains and its mouse models, show increased immunoreactivity for APP and Aβ (Kalaria et al., 1996, Kalaria, 1997). Taken together these data suggest that APP has the ability, at least in some cell types, to mediate a general adhesion activation response that is propagated by specific tyrosine kinase activities.

It is interesting that atherosclerosis and AD share many common risk factors, (Rosamond et al., 2007, Rosendorff et al., 2007) but more importantly, atherosclerosis and other cardiovascular diseases, themselves, are significant risk factors for developing AD. Indeed, there are several reports in the literature linking the biology of APP with apoE, two protein risk factors relevant to AD and atherosclerosis. Numerous data support a role for apoE in the metabolism of APP (Fryer et al., 2003, Fryer et al., 2005, Van Dooren et al., 2006). There is an inverse relationship between apoE levels and Aβ in some murine models of AD. Decreased expression of the cholesterol transporter, ATP-binding cassette transporter A1 (ABCA1), leads to decreased levels of soluble apoE in the brain and increased parenchymal and vascular amyloid deposition in mouse models of AD (Hirsch-Reinshagen et al., 2005, Koldamova et al., 2005). In addition, apoE4 expression in particular, appears to increase APP processing and Aβ production both in vitro and in vivo perhaps by interacting with the apolipoprotein E receptor 2 (apoER2) (Ye et al., 2005; Hoe et al., 2006, He et al., 2007). Conversely, APP expression and its gamma secretase-dependent cleavage appear necessary for appropriate expression of lipoprotein receptor, LRP1, and subsequent apoE levels in the brain (Liu et al., 2007). Finally, APP and apoE receptors are proteolytically processed by similar secretase activities (Hoe and William Rebeck, 2008).

While both diseases involve changes in the biology of these proteins and share some vascular changes and dysfunction, a specific, mechanistic pathophysiology linking these two diseases remains unclear. Taken together, these data and our previous work demonstrating that APP has the ability to activate immune cells in an adhesion-dependent activation, led us to hypothesize that endothelial APP is involved in the vascular inflammation associated with atherosclerosis and AD. Our results demonstrate endothelial changes common to AD and atherosclerotic tissue in brain vasculature. Therefore, the pathophysiology of both diseases involves vascular changes in not only APP expression and phosphorylation but also likely function. This endothelial phenotype may represent a common target for interventive strategies addressing either disease.

Section snippets

Materials

The anti β-amyloid and anti-cSrc antibodies were purchased from Santa Cruz Biotechnology, Inc. (Santa Cruz, CA, USA). The anti-APP antibody was purchased from Zymed Laboratories (San Francisco, CA, USA). The mouse IgG₁ isotype control, anti-von Willebrand factor and anti-APP (22C11) antibodies were purchased from Chemicon (Temecula, CA, USA). Anti-( tubulin was purchased from Sigma (St. Louis, MO, USA). The anti-Thr 668 pAPP antibody was purchased from Abcam (Cambridge, MA, USA). Anti-pAPP was

ApoE^−/− cerebrovasculature demonstrated increased levels of APP and pAPP accompanied by an increased association with the non-receptor tyrosine kinase, Src

Based upon our interest in comparing vascular changes in AD versus atherosclerotic tissue, we chose to focus on cerebrovasculature. We hypothesized that APP can mediate a similar activating response in endothelial cells as we have observed in monocytes/microglia. To begin addressing the role of APP in the cerebrovasculature, we first examined the cerebrovasculature of apoE^−/− atherosclerotic and wild-type mice to ascertain APP disease-related changes. ApoE^−/− and age-matched wild-type brain

Adhesion of monocytic cells onto brain endothelium is at least partially APP-dependent

Due to its ability to bind numerous components of the extracellular matrix it has been hypothesized that APP functions in cellular adhesion via cell-cell or cell-matrix interactions (Kibbey et al., 1993, Williamson et al., 1995, Beher et al., 1996, Small et al., 1999, Soba et al., 2005). Soba et al. (2005) demonstrated that APP can form homo- and heterodimer complexes via its extracellular domain with other APP molecules or with other APP family members, APP-like protein (APLP)-1 and APLP2, and

Discussion

The proteolytic breakdown product of APP, Aβ, has a hypothesized role in the progression of AD and while research focuses on APP and Aβ in neurons, the function of APP in other cell types remains less defined. Here, we examined APP expression and function in vascular endothelial cells within the cerebrovasculature of apoE⁻/⁻ mice and human AD tissue. We observed increased vascular immunoreactivity for APP, pAPP, and Aβ in both mouse atherosclerotic and human AD cerebrovasculature demonstrating

Conflicts of interest

None.

Acknowledgements

This publication was supported by NIH/NCRR 1 P20 RR17699-01, NIH/NCRR 2P20RR017600-06, NIH/NIA 1R01AG026330-01A2 and the North Dakota NSF EPSCoR RRNI EPS-0447679.

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Amyloid precursor protein mediates monocyte adhesion in AD tissue and apoE−/− mice

Abstract

Introduction

Section snippets

Materials

ApoE−/− cerebrovasculature demonstrated increased levels of APP and pAPP accompanied by an increased association with the non-receptor tyrosine kinase, Src

Adhesion of monocytic cells onto brain endothelium is at least partially APP-dependent

Discussion

Conflicts of interest

Acknowledgements

J. Biol. Chem.

Anal. Biochem.

J. Biol. Chem.

J. Lab. Clin. Med.

Lancet

Biochem. Biophys. Res. Commun.

Brain Res. Mol. Brain Res.

J. Biol. Chem.

J. Biol. Chem.

Brain Res.

Brain Res. Mol. Brain Res.

J. Biol. Chem.

J. Biol. Chem.

Am. J. Pathol.

Neuron

Neurosci. Lett.

J. Biol. Chem.

J. Biol. Chem.

J. Biol. Chem.

FEBS Lett.

J. Biol. Chem.

Am. J. Pathol.

J. Biol. Chem.

Mol. Cell

Neuroscience

Simvastatin protects against amyloid beta and HIV-1 Tat-induced promoter activities of inflammatory genes in brain endothelial cells

Mol. Pharmacol.

Only cerebral capillary amyloid angiopathy correlates with Alzheimer pathology—a pilot study

Acta Neuropathol. (Berl)

Amyloid beta peptide 1-42 highly correlates with capillary cerebral amyloid angiopathy and Alzheimer disease pathology

Acta Neuropathol. (Berl)

Glial beta-amyloid precursor protein: expression in the dentate gyrus after entorhinal cortex lesion

Neuroreport

Early and rapid de novo synthesis of Alzheimer beta A4-amyloid precursor protein (APP) in activated microglia

Glia

The phosphotyrosine interaction domains of X11 and FE65 bind to distinct sites on the YENPTY motif of amyloid precursor protein

Mol. Cell. Biol.

APOE epsilon 4 influences the pathological phenotype of Alzheimer’s disease by favouring cerebrovascular over parenchymal accumulation of A beta protein

Neuropathol. Appl. Neurobiol.

Self-assembly of Abeta(1–42) into globular neurotoxins

Biochemistry

Can disturbed brain microcirculation cause Alzheimer’s disease?

Neurol. Res.

Platelet phagocytosis and processing of beta-amyloid precursor protein as a mechanism of macrophage activation in atherosclerosis

Circ. Res.

Beta-amyloid-stimulated microglia induce neuron death via synergistic stimulation of tumor necrosis factor alpha and NMDA receptors

J. Neurosci.

Amyloid precursor protein mediates monocyte adhesion in AD tissue and apoE⁻/⁻ mice

ApoE^−/− cerebrovasculature demonstrated increased levels of APP and pAPP accompanied by an increased association with the non-receptor tyrosine kinase, Src