title: Fluid flow forces and rhoA regulate fibrous development of the atrioventricular valves.
abstract: Fibrous development of the extracellular matrix (ECM) of cardiac valves is necessary for proper heart function. Pathological remodeling of valve ECM is observed in both pediatric and adult cardiac disorders. It is well established that intracardiac hemodynamics play a significant role in the morphogenesis of cardiovascular tissues. However, the mechanisms that transduce mechanical forces into morphogenetic processes are not well understood. Here, we report the development of a three-dimensional, in vitro culture system that allows for culture of embryonic valve tissue under specific pulsatile flow conditions. This system was used to investigate the role that fluid flow plays in fibrous ECM expression during valve formation and to test the underlying cellular mechanisms that regulate this mechanotransduction. When cultured under pulsatile flow, developing valve tissues upregulated fibrous ECM expression at both the transcript and protein levels in comparison to no-flow controls. Flow-cultured valve tissues also underwent morphological development, as cushions elongated into leaflet-like structures that were absent in no-flow controls. Furthermore, rhoA, a member of the cytoskeletal actin-regulating GTPase family of proteins, was upregulated and activated by flow culture. Inhibition of the downstream rhoA effector kinase, ROCK, blocked flow-driven fibrous ECM accumulation and tissue stiffening, while the addition of lysophosphatidic acid (LPA), a rhoA activator, stimulated fibrous ECM deposition and tissue stiffening. These results support a prominent role for the rhoA pathway in the mechanotransduction of hemodynamic forces during fibrous remodeling of developing valve tissue. Our results also point to a potential link between regulation of the actinomyosin cytoskeleton and fibrous ECM synthesis in cardiovascular tissues.
authors.affiliation: Department of Cell Biology and Anatomy, School of Medicine, University of South Carolina, Columbia, SC 29208, USA.
authors.forename: Hong
authors.initials: H
authors.lastname: Tan
authors.forename: Stefanie
authors.initials: S
authors.lastname: Biechler
authors.forename: Lorain
authors.initials: L
authors.lastname: Junor
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Yost
authors.forename: Delphine
authors.initials: D
authors.lastname: Dean
authors.forename: Jinqing
authors.initials: J
authors.lastname: Li
authors.forename: Jay D
authors.initials: JD
authors.lastname: Potts
authors.forename: Richard L
authors.initials: RL
authors.lastname: Goodwin
mesh_terms: D000577:Amides / Q000494:pharmacology; D000818:Animals; D030161:Avian Proteins / Q000235:genetics / Q000378:metabolism*; D015153:Blotting, Western; D002642:Chick Embryo; D003599:Cytoskeleton / Q000187:drug effects / Q000378:metabolism; D005109:Extracellular Matrix / Q000187:drug effects / Q000378:metabolism; D016326:Extracellular Matrix Proteins / Q000235:genetics / Q000378:metabolism*; D020869:Gene Expression Profiling; D006351:Heart Valves / Q000196:embryology / Q000378:metabolism*; D008246:Lysophospholipids / Q000494:pharmacology; D040542:Mechanotransduction, Cellular / Q000235:genetics / Q000502:physiology; D018625:Microscopy, Atomic Force; D018613:Microscopy, Confocal; D011725:Pyridines / Q000494:pharmacology; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013314:Stress, Mechanical; D019063:Tenascin / Q000235:genetics; D013997:Time Factors; D046509:Tissue Culture Techniques / Q000379:methods; D054460:rho-Associated Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D020742:rhoA GTP-Binding Protein / Q000235:genetics / Q000378:metabolism*
chemical_list: D000577:Amides; D030161:Avian Proteins; D016326:Extracellular Matrix Proteins; D008246:Lysophospholipids; D011725:Pyridines; D019063:Tenascin; C108830:Y 27632; D054460:rho-Associated Kinases; D020742:rhoA GTP-Binding Protein; C032881:lysophosphatidic acid