title: Pericyte contractility controls endothelial cell cycle progression and sprouting: insights into angiogenic switch mechanics.
abstract: Microvascular stability and regulation of capillary tonus are regulated by pericytes and their interactions with endothelial cells (EC). While the RhoA/Rho kinase (ROCK) pathway has been implicated in modulation of pericyte contractility, in part via regulation of the myosin light chain phosphatase (MLCP), the mechanisms linking Rho GTPase activity with actomyosin-based contraction and the cytoskeleton are equivocal. Recently, the myosin phosphatase-RhoA-interacting protein (MRIP) was shown to mediate the RhoA/ROCK-directed MLCP inactivation in vascular smooth muscle. Here we report that MRIP directly interacts with the β-actin-specific capping protein βcap73. Furthermore, manipulation of MRIP expression influences pericyte contractility, with MRIP silencing inducing cytoskeletal remodeling and cellular hypertrophy. MRIP knockdown induces a repositioning of βcap73 from the leading edge to stress fibers; thus MRIP-silenced pericytes increase F-actin-driven cell spreading twofold. These hypertrophied and cytoskeleton-enriched pericytes demonstrate a 2.2-fold increase in contractility upon MRIP knockdown when cells are plated on a deformable substrate. In turn, silencing pericyte MRIP significantly affects EC cycle progression and angiogenic activation. When MRIP-silenced pericytes are cocultured with capillary EC, there is a 2.0-fold increase in EC cycle entry. Furthermore, in three-dimensional models of injury and repair, silencing pericyte MRIP results in a 1.6-fold elevation of total tube area due to EC network formation and increased angiogenic sprouting. The pivotal role of MRIP expression in governing pericyte contractile phenotype and endothelial growth should lend important new insights into how chemomechanical signaling pathways control the "angiogenic switch" and pathological angiogenic induction.
authors.affiliation: Graduate Program in Cellular and Molecular Physiology, Sackler School of Graduate Biomedical Sciences, Department of Developmental, Molecular, and Chemical Biology, Center for Innovations in Wound Healing Research, School of Medicine, Tufts University, Boston, Massachusetts.
authors.forename: Jennifer T
authors.initials: JT
authors.lastname: Durham
authors.affiliation: Graduate Program in Cellular and Molecular Physiology, Sackler School of Graduate Biomedical Sciences, Department of Developmental, Molecular, and Chemical Biology, Center for Innovations in Wound Healing Research, School of Medicine, Tufts University, Boston, Massachusetts.
authors.forename: Howard K
authors.initials: HK
authors.lastname: Surks
authors.affiliation: Graduate Program in Cellular and Molecular Physiology, Sackler School of Graduate Biomedical Sciences, Department of Developmental, Molecular, and Chemical Biology, Center for Innovations in Wound Healing Research, School of Medicine, Tufts University, Boston, Massachusetts.
authors.forename: Brian M
authors.initials: BM
authors.lastname: Dulmovits
authors.affiliation: Graduate Program in Cellular and Molecular Physiology, Sackler School of Graduate Biomedical Sciences, Department of Developmental, Molecular, and Chemical Biology, Center for Innovations in Wound Healing Research, School of Medicine, Tufts University, Boston, Massachusetts ira.herman@tufts.edu.
authors.forename: Ira M
authors.initials: IM
authors.lastname: Herman
mesh_terms: D051344:Actin Capping Proteins / Q000378:metabolism; D000818:Animals; D019556:COS Cells; D002417:Cattle; D002453:Cell Cycle; D048429:Cell Size; D002478:Cells, Cultured; D002522:Chlorocebus aethiops; D003599:Cytoskeleton / Q000648:ultrastructure; D042783:Endothelial Cells / Q000166:cytology / Q000502:physiology*; D004730:Endothelium, Vascular / Q000166:cytology*; D006801:Humans; D051379:Mice; D008840:Microfilament Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D041681:NIH 3T3 Cells; D018919:Neovascularization, Physiologic; D020286:Pericytes / Q000166:cytology / Q000378:metabolism* / Q000648:ultrastructure*; D034622:RNA Interference; D054460:rho-Associated Kinases / Q000378:metabolism
chemical_list: D051344:Actin Capping Proteins; D008840:Microfilament Proteins; D054460:rho-Associated Kinases
keywords: Rho kinase; angiogenesis; capillary; cytoskeleton; mural cell; myosin light chain; myosin light chain phosphatase