1,720,976 research outputs found
PDGFR B Signaling in Mouse Epicardial and Mural Cells Influences Blood Vessel Remodeling
No full textPlatelet derived growth factor receptor beta (PDGFRbeta) is a receptor tyrosine kinase expressed in vascular smooth muscle cells (VSMC), which promotes proliferation and migration. We provide evidence of additional roles for the PDGFRbeta prior to the differentiation of VSMC. We show that PDGFRbeta, as well as PDGFRalpha, is expressed in epicardial and subepicardial mesenchymal cells, which are precursors for coronary VSMC. We demonstrate that PDGFRbeta-/- mice exhibit a lack of coronary VSMC and have disrupted endothelial vessels on the ventral surface of the heart; however, neither conditional ablation of the PDGFRbeta with an SM22 Cre Tg, which is expressed in differentiated VSMC, nor with a myocardinCre, which has an earlier expression profile and is believed to control VSMC differentiation, phenocopy the lack of coronary VSMC found in PDGFRbeta-/- mice. Further investigations into PDGFRbeta-/- mice revealed a defect in the function of the epicardium. The epicardium exhibited an altered cellular morphology and a decreased ability to migrate into the myocardium both in vivo and ex vivo. The decreased motility was associated with a nonpolarized distribution of actin and a lack of localization of Arp2/3 to the cell periphery. Moreover, these defects appeared to be dependent on the Src signaling pathway. This work thus establishes a novel in vivo role for the PDGFRbeta at a stage of coronary VSMC development during which the epicardium undergoes cytoskeletal rearrangement in order to efficiently migrate into the myocardium and form the mesenchymal precursors of coronary VSMC.
In addition to this role in vasculogenesis, we demonstrate a role for the PDGFRbeta in angiogenesis. Using point mutations in PDGFRbeta we generated mice that possessed variations in the number of pericytes that were present in tissues, including the trachea and retina. We then utilized these mutant mouse lines to show that a decrease in pericytes affects the ability of the vasculature to respond to an angiogenic agent, Ang1. Moreover, this response is not secondary to hypoxia. This work emphasizes the value of targeting both VSMC and endothelial cells in therapies targeting vessel regeneration
Mesothelial and Mural Cell Contribution to Vascular Development through PDGF Signaling
Full text linkVascular development during embryogenesis and adulthood occurs through vasculogenesis and angiogenesis. Vasculogenesis is the de novo formation of blood vessels from mesoderm precursor cells. Angiogenesis is the formation of new vessels from existing vessels. Both processes involve hematopoietic, endothelial, and mural cells for the formation of mature, stable vasculature. While hematopoietic and endothelial cell contributions and function in vascular development have been extensively studied identifying the VEGF and TGF families as major contributors, the role of mural cells has not been clearly defined. The platelet derived growth factor beta (PDGFR beta) is essential for mural cell recruitment and expansion. Deletion of PDGFR beta leads to perinatal lethality resulting from vascular defects attributed to severe decreases in mural cells. PDGFR beta is a receptor tyrosine kinase with high homology in signal activation to PDGFR alpha. Downstream signaling pathway activation includes PI3 kinase, Src, RasGAP, Grb2, Shp-2, and PLC?gamma for the regulation of cellular functions.The focus of this research was to determine the temporal and functional requirements of PDGFR signaling in mural cells. To address the temporal requirements for PDGFR beta, genetic manipulation was used to delete the receptor in precursor and differentiated mural cells. In addition, mutant mice were generated with the additional deletion of PDGFR alpha to address the potential for compensatory or cooperative function between the two receptors. These studies identified a cooperative role for PDGFR?alpha and PDGFR beta in yolk sac mesothelial cells. Mutant mice were lethal around E10.5 with disrupted yolk sac vascular remodeling and extracellular matrix composition. The PDGFR regulate collagen matrix through regulation of matrix metalloproteinase activity and thus disrupt integrin activation. The functional role of PDGFR?beta in mural cells was addressed by signaling point mutants targeting and disrupting specific downstream pathways. These studies resulted in a progressive decrease in mural cells that correlated to the number of disrupted PDGFR-beta signaling pathways. Together these analyses demonstrate PDGFR and mural cells are essential for vascular development and maintenance
PDGFRalpha Signaling Requirements in the Development of Tissues Derived From Sclerotome and Dermatome
No full textThe Platelet-Derived Growth Factor Receptors (PDGFR) play roles in the development of multiple mesenchymal cell types. Upon ligand binding, the receptors signal through a number of intracellular signaling molecules and elicit many cellular responses including migration, proliferation, and differentiation. Studies utilizing tissuespecific deletion permit the elucidation of cell autonomous phenotypes, while analysis of signaling point mutants permits identification of the function of specific downstream effectors. My studies use both methods to uncover the role of PDGFRalpha signaling in the development of skin and bone. An unexplained phenotype of PDGFRalpha null embryos is a defect in the axial skeletal that leads to spina bifida. Using conditional gene deletion I determined that the population of cells responsible for this phenotype is not the chondrocyte but is instead another derivative of the sclerotome. These results demonstrate that signals from adjacent tissues can play important roles in the differentiation of bone populations and identifies an etiology for spina bifida that is not directly caused by neural tube or bone defects. Interestingly, loss of PI3K signaling downstream of PDGFRalpha also results in spina bifida. I found that the sclerotome population described above requires PDGFRalpha signaling to migrate dorsal to the neural tube via PI3K activation. Without this signaling event, downstream effectors including Akt, p70S6K, and PAK1 are not activated and the cells fail to form Rac-associated membrane ruffles. This is the first in vivo evidence that PI3K driven pathways are required for migration downstream of the PDGFRalpha
Defining the Developmental Signals of the Cardiac Fibroblast
Full text linkCardiac fibroblasts play a central role as a mediator of inflammatory and fibrotic response and also secrete extracellular matrix components that provide structural support for regeneration and remodeling of the wound. Despite the importance of the cardiac fibroblast in heart disease, very little is known about factors that are essential for differentiation along the cardiac fibroblast lineage. Using a combination of gene knockout and cardiac fibroblast-detecting methods, we have identified genes that are involved in the formation of cardiac fibroblasts. Our results demonstrate that in the absence of Tcf21, a basic helix-loop-helix transcription factor, cardiac fibroblast progenitors fail to migrate into the myocardium resulting in a specific loss of the cardiac fibroblast population. Loss of the receptor tyrosine kinase Pdgfra also results in loss of the cardiac fibroblast population. Interestingly, Tcf21 and Pdgfra are involved in the epithelial to mesenchymal transition (EMT) of epicardial cells.
The epicardium (outer surface of the heart) functions as a pool of progenitor cells for the coronary vasculature and interstitial connective tissue during embryonic development. Although several signaling pathways have been identified that disrupt EMT, no component has been reported that negatively regulates EMT, which may also involved in the cardiac fibroblast development. Using a conditional knockout of neurofibromin 1 (Nf1) in the epicardium, we identified Nf1 as a key mediator of epicardial EMT. We found that the process of EMT occurred earlier in Nf1 mutant hearts, with an increase in epicardial cells entering the compact myocardium. Moreover, loss of Nf1 caused increased epicardial-derived cell proliferation and resulted in the expansion of cardiac fibroblasts and coronary vascular smooth muscle cells. In addition to revealing the function of Nf1, Tcf21 and Pdgfra in epicardial EMT and cardiac fibroblast development, we generated and established mouse models to study the role of cardiac fibroblasts and the function of these genes during heart pathogenesis. Because developmental processes are often recapitulated in normal and pathological conditions, a better understanding of the epicardium and cardiac fibroblast development may help identify targets for therapeutics to treat heart disease
THE ROLE OF TCF21 IN CARDIAC FIBROBLAST CELL NUMBER AND EXTRACELLULAR MATRIX REMODELING
Full text linkPh.D
The Role Of The Fibroblast In Structuring The Cardiac Microenvironment
Full text linkFibroblasts are important non-muscle cells in the heart. Their contribution to cardiac development, physiology, and pathology is evident. The primary physiological role of the cardiac fibroblast is the production of extracellular matrix (ECM) network that determines cardiac stiffness and structure and also coordinates extracellular signaling. In addition to their critical role in ECM synthesis, fibroblasts produce cytokines and proteases that directly affect ECM organization and turnover, and influence neonatal cardiomyocyte proliferation. Our knowledge of fibroblast biology is based largely on in vitro studies that cannot recapitulate the complex cellular and biophysical milieu of the working heart. In my dissertation work, I have investigated the role of fibroblasts in the perinatal and adult heart using transgenic deletion of these cells. My overall hypothesis is that ECM deposition and organization by cardiac fibroblasts are required for normal heart development and homeostatic maintenance, and that perturbation of these cells leads to accelerated heart dysfunction after injury.Ph.D
Role Of Tcf21 In Perinatal Cardiac Fibroblasts Proliferation And Gene Expression
Full text linkCardiac fibroblasts play a dominant role in heart disease, but our understanding of the signals that control these cells during heart development is inadequate. Tcf21 is a coronary artery disease associated gene whose function in the heart is not well understood. Previously using Tcf21 null animals, we have demonstrated that this basic helix loop helix transcription factor is essential for the formation of epicardial-derived cardiac fibroblasts. Lack of Tcf21 resulted in a failure of cardiac fibroblast progenitor migration from the epicardium. Recently, we have found that Tcf21 continues to be expressed in mature cardiac fibroblasts suggesting a continued role for this transcription factor. To evaluate the function of Tcf21 after embryonic development, we generated animals which lacked Tcf21 in the fibroblast lineage. When Tcf21 is removed at birth, we find a 30 percent reduction in the number of fibroblasts. Using EdU, we determined that loss of Tcf21 leads to reduced fibroblast proliferation in the perinatal period. To identify transcriptional targets of Tcf21, we have compared fibroblast transcriptomes in control and Tcf21 deficient fibroblasts. We have found an increase in lipid genes in the Tcf21 deficient fibroblasts. Taken together our results demonstrate that Tcf21 continues to play important roles in fibroblast biology beyond the initial formation of cardiac fibroblasts from the epicardium.M.S
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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