Redox control of vascular smooth muscle migration

Abstract

Vascular smooth muscle cell migration is important during vascular development and contributes to lesion formation in the adult vasculature. The mechanisms regulating migration of this cell type are therefore of great interest. Recent work has shown that reactive oxygen species (ROS) derived from NADPH oxidases are important mediators of promigratory signaling pathways. ROS regulate the intracellular signals responsible for lamellipodia formation, actin cytoskeleton remodeling, focal adhesion turnover, and contraction of the cell body. In addition, they contribute to matrix remodeling, a critical step to initiate and support vascular smooth muscle cell motility. Despite these recent advances in our understanding of the redox mechanisms that contribute to migration, additional work is needed to evaluate fully the potential of ROS-sensitive molecular signals as therapeutic targets to prevent inappropriate smooth muscle cell migration.

FIG. 1.

VSMCs contain multiple sources of ROS. ROS-producing enzymes include NADPH oxidases, lipoxygenases, xanthine oxidase, iNOS, mitochondrial electron-transport chain, and cytochrome p450 monoxygenase. VSMCs also contain hemoxygenase, which produces Fe that can react with H₂O₂ and generate hydroxyl radical (^•OH) (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article at www.liebertonline.com/ars).

FIG. 2.

Structures of NADPH oxidases found in VSMCs. NADPH oxidases are a family of multisubunit enzymes whose catalytic subunit consists of one of the Nox proteins. VSMCs from large arteries express Nox1 and Nox4, as well as Nox5 in humans. VSMCs from resistance arteries express Nox2 and Nox4. The Nox1 NADPH oxidase associates with two cytosolic factors, p47^phox and Nox activator 1 (Noxa1), as well as the small-molecular-weight G protein Rac. Nox2 is regulated by p47^phox and p67^phox, whereas Nox4 is not. In the case of Nox1 and 2, activity requires assembly with the cytosolic subunits (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article at www.liebertonline.com/ars).

FIG. 3.

ROS-dependent pathways leading to lamellipodium formation in VSMCs. After agonist stimulation, VSMCs initiate a cascade of events leading to lamellipodium formation. PDGF-induced ROS activate the Src/PAK/LIMK pathways to induce cofilin inactivation and therefore F-actin stabilization. PDGF-induced migration requires the activation of SSH1L, which activates cofilin and thus supplies G-actin and free barbed ends continuously to the leading edge. Branching and elongation of preexisting filaments are induced through Rac and WAVE/ARP2/3. Interrupted arrows, ROS-mediated pathways. SSH1L = slingshot phosphatase 1L; LIMK = LIM domain kinase 1; WAVE =WASP family verprolin-homologous protein; ARP2/3 = actin-related protein 2/3; PAK =p21-activated kinase. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article at www.liebertonline.com/ars).

FIG. 4.

ROS-dependent pathways leading to focal adhesion formation in VSMCs. Integrin stimulation through inside-out or outside-in stimuli induces clustering of FA proteins and strengthening of stress fibers. Simultaneous stimulation with PDGF activates a series of tyrosine kinases and inhibits phosphatases that contribute to FA formation. Both PDGF-mediated signaling and local production of ROS by Nox4 in FAs coordinate FA formation. Interrupted arrows, ROS-mediated pathways. FAs = focal adhesions. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article at www.liebertonline.com/ars).

FIG. 5.

ROS-dependent pathways leading to cell-body contraction in VSMCs. The final step in motility is the production of forward movement through regulation of myosin II phosphorylation and actin–myosin interaction. Several major regulators of myosin phosphorylation are ROS sensitive, including mobilization of calcium from intracellular or extracellular compartments, Src activation, and the Rho-ROCK pathway. Interrupted arrows, ROS-mediated pathways. Src = Rous sarcoma virus kinase homologue; ROCK = Rho-associated protein kinase. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article at www.liebertonline.com/ars).