Apolipoprotein E3 Inhibits Rho to Regulate the Mechanosensitive Expression of Cox2

Bernadette Y Hsu,Keeley L Mui,Shu-Lin Liu,Richard K Assoian,Yong Ho Bae

doi:10.1371/journal.pone.0128974

Abstract

Apolipoprotein E3 (apoE3) is thought to protect against atherosclerosis by enhancing reverse cholesterol transport. However, apoE3 also has cholesterol-independent effects that contribute to its anti-atherogenic properties. These include altering extracellular matrix protein synthesis and inhibiting vascular smooth muscle cell proliferation. Both of these cholesterol-independent effects result from an apoE3-mediated induction of cyclooxygenase-2 (Cox2). Nevertheless, how apoE3 regulates Cox2 remains unknown. Here, we show that apoE3 inhibits the activation of Rho, which reduces the formation of actin stress fibers and focal adhesions and results in cellular softening. Inhibition of Rho-Rho kinase signaling or direct cellular softening recapitulates the effect of apoE3 on Cox2 expression while a constitutively active Rho mutant overrides the apoE3 effect on both intracellular stiffness and Cox2. Thus, our results describe a previously unidentified mechanism by which an atheroprotective apolipoprotein uses Rho to control cellular mechanics and Cox2.

Highlights

Many cell types live in elastic microenvironments and respond to changes in the stiffness of their microenvironments by altering their proliferation, migration and survival [1,2,3,4]
We found that Rho-GTP levels were significantly reduced by Apolipoprotein E3 (apoE3) in human vascular smooth muscle cells (VSMCs) (Fig 1A)
ApoE3-mediated inhibition of Rho activity was detected when the VSMCs were cultured at pathophysiologically relevant extracellular matrix (ECM) stiffness on fibronectin-coated polyacrylamide hydrogels matched to the stiffness of healthy and atherosclerotic arteries (Fig 1B and [22])

Summary

Introduction

Many cell types live in elastic microenvironments and respond to changes in the stiffness of their microenvironments by altering their proliferation, migration and survival [1,2,3,4]. Changes in microenvironmental stiffness are typically associated with remodeling of the extracellular matrix (ECM); ECM stiffness is transduced into intracellular stiffness and stiffness-dependent signaling in a process called mechanotransduction [1,2,3]. ECM-coated hydrogels of distinct elastic moduli have been used to study the signaling events that respond to changes in ECM stiffness [1,2,3,4,5]. ECM stiffness stimulates Rho-GTP activity and Rho-Rho kinase (ROCK)-myosin signaling [3,4,5]. This leads to actomyosin-dependent contraction and increases in intracellular tension and formation of actin

Methods

Results

Conclusion