Pericyte Rho GTPase Mediates Both Pericyte Contractile Phenotype and Capillary Endothelial Growth State

Matthew E. Kutcher^*, Alexey Y. Kolyada, Howard K. Surks and Ira M. Herman^*

From the Department of Physiology,^* Tufts University School of Medicine, Boston; The Kidney and Dialysis Research Laboratory, Caritas St. Elizabeth’s Medical Center, Boston; and the Molecular Cardiology Research Institute, Tufts-New England Medical Center, Boston, Massachusetts

Pericytes regulate microvascular development and maturationthrough the control of endothelial cell motility, proliferation,and differentiation. The Rho GTPases have recently been describedas key regulators of pericyte shape and contractile phenotypeby signaling through the actin cytoskeleton in an isoactin-specificmanner. In this report, we reveal that Rho GTPase-dependentsignal transduction not only influences pericyte shape and contractilepotential but also modulates capillary endothelial proliferativestatus and pericyte-endothelial interactions in vitro. We provideevidence that overexpression of mutant Rho GTPases, but notother Ras-related small GTPases, significantly alters pericyteshape, contractility, and endothelial growth state in microvascularcell co-cultures. In particular, we describe the use of a siliconsubstrate deformation assay to demonstrate that pericyte contractilityis Rho GTP- and Rho kinase-dependent; further, we describe anovel in vitro system for examining pericyte-mediated endothelialgrowth arrest and show that control pericytes are capable ofgrowth-arresting capillary endothelial cells in a cell contact-dependentmanner, whereas pericytes overexpressing dominant-active and-negative Rho GTPase are comparably incompetent. These datastrongly suggest that signaling through the pericyte Rho GTPasepathway may provide critical cues to the processes of microvascularstabilization, maturation, and contractility during developmentand disease.