Apolipoprotein E3 Inhibits Rho to Regulate the Mechanosensitive Expression of Cox2

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.