Presenilin-1 regulates the constitutive turnover of the fibronectin matrix in endothelial cells.

Rita De Gasperi,Miguel A Gama Sosa,Gregory A Elder

doi:10.1186/1471-2091-13-28

Abstract

BackgroundPresenilin-1 (PS1) is a transmembrane protein first discovered because of its association with familial Alzheimer’s disease. Mice with null mutations in PS1 die shortly after birth exhibiting multiple CNS and non-CNS abnormalities. One of the most prominent features in the brains of PS1−/− embryos is a vascular dysgenesis that leads to multiple intracerebral hemorrhages. The molecular and cellular basis for the vascular dysgenesis in PS1−/− mice remains incompletely understood. Because the extracellular matrix plays key roles in vascular development we hypothesized that an abnormal extracellular matrix might be present in endothelial cells lacking PS1 and examined whether the lack of PS1 affects expression of fibronectin a component of the extracellular matrix known to be essential for vascular development.ResultsWe report that primary as well as continuously passaged PS1−/− endothelial cells contain more fibronectin than wild type cells and that the excess fibronectin in PS1−/− endothelial cells is incorporated into a fibrillar network. Supporting the in vivo relevance of this observation fibronectin expression was increased in microvascular preparations isolated from E14.5 to E18.5 PS1−/− embryonic brain. Reintroduction of PS1 into PS1−/− endothelial cells led to a progressive decrease in fibronectin levels showing that the increased fibronectin in PS1−/− endothelial cells was due to loss of PS1. Increases in fibronectin protein in PS1−/− endothelial cells could not be explained by increased levels of fibronectin RNA nor based on metabolic labeling studies by increased protein synthesis. Rather we show based on the rate of turnover of exogenously added biotinylated fibronectin that increased fibronectin in PS1−/− endothelial cells results from a slower degradation of the fibronectin fibrillar matrix on the cell surface.ConclusionsThese studies show that PS1 regulates the constitutive turnover of the fibronectin matrix in endothelial cells. These studies provide molecular clues that may help to explain the origin of the vascular dysgenesis that develops in PS1−/− embryonic mice.

Highlights

Presenilin-1 (PS1) is a transmembrane protein first discovered because of its association with familial Alzheimer’s disease
PS1−/− endothelial cells contain more fibronectin than wild type endothelial cells One of the most prominent features in the brains of PS1 −/− embryos is the appearance of parenchymal hemorrhages
In preliminary studies aimed at examining whether components of the extracellular matrix might be altered in PS1−/− mice we noted that developing blood vessels in PS1−/− embryonic brain stained more prominently with fibronectin than wild type embryos while vessels in wild type and PS1−/− brain were visualized by the isolectin B4 (Figure 1)

Summary

Introduction

Presenilin-1 (PS1) is a transmembrane protein first discovered because of its association with familial Alzheimer’s disease. One of the most prominent features in the brains of PS1−/− embryos is a vascular dysgenesis that leads to multiple intracerebral hemorrhages. The molecular and cellular basis for the vascular dysgenesis in PS1−/− mice remains incompletely understood. Presenilin-1 is a polytopic transmembrane protein that was first discovered because of its association with familial Alzheimer’s disease [1,2]. A related gene, presenilin-2 exists and mutations in this gene cause familial Alzheimer’s disease [1]. PS1 influences multiple molecular pathways being best known for its role as a component of the γ-secretase complex [2]. PS1 interacts with other proteins in manners that do not involve γ-secretase cleavage such as PS1’s well-studied interaction with β-catenin in which PS1 controls β-catenin stability by favoring its stepwise phosphorylation leading to its degradation [11]

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