Search PubMed⌕ Search

Biomedical subjects

A B Sutton

Publications and source records attributed to A B Sutton.

7 recordsLinked to original sources
PubMed1996

Association of thrombospondin-1 with osteogenic differentiation of retinal pericytes in vitro.

Vascular pericytes can differentiate into osteoblast-like cells in vitro, suggesting that these cells may represent a potential source of osteoprogenitor cells in the adult. Pericyte differentiation is associated with a characteristic pattern of nodule formation and mineralisation. Nodules are formed in post-confluent cultures by the retraction of multilayered areas. Crystals of hydroxyapatite are deposited on the extracellular matrix of these nodules which then becomes mineralised. We now demonstrate that thrombospondin-1 (TSP-1) gene expression is modulated during pericyte differentiation in vitro. That is, the relative levels of TSP-1 (protein and mRNA) increased markedly during nodule formation and then decreased when mineralisation of the nodules had taken place. TSP-1 was localised throughout non-mineralised nodules but it was largely excluded from the inner mass of mineralised nodules. The production of a mineralised matrix by vascular pericytes was promoted by the presence of antibodies to TSP-1 in the culture medium and was inhibited by exogenous TSP-1. These effects did not appear to be mediated through the activation of latent TGF-beta, since neither exogenous TGF-beta nor neutralising antibodies to TGF-beta had any effect on the rate or extent of mineralisation seen in the pericyte cultures. Taken together these results suggest that high levels of TSP-1 inhibit pericyte mineralisation, supporting the view that this protein plays a role in pericyte differentiation and bone formation.

Animals↗
PubMed1995

Pericyte differentiation.

Pericytes are defined in vivo by their location: They are embedded within the basement membrane of microvessels. They form an integral part of the microvascular wall and are believed to participate in angiogenesis, although their precise role is not clear. Pericytes derived from the retinal microvasculature have been cultured and identified by a series of phenotypic characteristics that clearly distinguishes them from other stromal cells such as smooth muscle cells. Pericytes in vitro form multicellular nodules rich in extracellular matrix. This matrix becomes mineralized in the presence of growth medium containing serum, without exogenous beta-glycerophosphate. These results indicate that pericytes represent primitive mesenchymal cells able to differentiate into an osteogenic phenotype. Pericyte differentiation also is defined by alterations in their response to transforming growth factor beta 1 and changes in the synthesis and/or deposition of various extracellular matrix proteins such as laminin, Type IV collagen, tenascin, Type X collagen osteonectin, and thrombospondin-1. Angiogenesis is associated commonly with mineralization. These data suggest that pericytes may contribute to mineralization in vivo.

Animals↗
PubMed1994

Alpha- and beta-xylosides modulate the synthesis of fibronectin and thrombospondin-1 by endothelial cells.

We have previously shown that both p-nitrophenyl-alpha-D-xylopyranoside (alpha-xyloside) and p-nitrophenyl-beta-D-xylopyranoside (beta-xyloside) inhibit endothelial morphogenesis in vitro. In order to determine the mechanism for this inhibition, we have now investigated the effects of these compounds on the synthesis of proteoglycans and proteins by bovine aortic endothelial cells. Consistent with their well-recognised modes of action, beta-xyloside, but not alpha-xyloside, enhanced the secretion of free glycosaminoglycans into the medium. Furthermore, although both xylosides inhibited proteoglycan deposition into the cell layer/matrix, only beta-xyloside altered the nature of the proteoglycans synthesised by the cells. Both alpha- and beta-xylosides markedly inhibited total protein synthesis by endothelial cells in the absence of any effect on cell growth. This inhibition was time- and dose-dependent and was not due to the enzymatic release of p-nitrophenol by the cells. The synthesis of fibronectin and thrombospondin-1 were specifically and differentially modulated by both alpha- and beta-xylosides. That is, xylosides markedly reduced fibronectin levels relative to other proteins in both the medium and the cell layer/matrix. In contrast, the relative levels of thrombospondin-1 were increased in the xyloside-treated cultures both in terms of mRNA and protein. These studies demonstrate novel effects of xylosides on protein synthesis. Furthermore, they suggest that the inhibition of endothelial morphogenesis by xylosides may be due to the actions of these compounds on the synthesis of specific proteins.

Animals↗
PubMed1992

Transforming growth factor beta 1 promotes the differentiation of endothelial cells into smooth muscle-like cells in vitro.

Alpha-smooth muscle actin is considered a reliable marker for distinguishing between arterial smooth muscle and endothelial cells. Several authors have reported heterogeneity in the expression of this actin isoform in atherosclerotic lesions. Such heterogeneity appears to result from the presence of different smooth muscle cell phenotypes (contractile and synthetic) in these lesions. In the present study, we show that bovine aortic endothelial cells, which are characterised by the presence of Factor VIII-related antigen (FVIII) and by the absence of alpha-smooth muscle actin (alpha-SM actin) may be induced to express the latter when exposed to TGF-beta 1. FVIII was detected by immunofluorescence, alpha-SM actin was detected by immunofluorescence and immunoblotting. The number of cells expressing alpha-SM actin increased with time of incubation with TGF-beta 1, and this increase occurred concomitantly with a decrease in the expression of FVIII. Double immunofluorescence demonstrated the presence of cells that expressed both FVIII and alpha-SM actin after 5 days of incubation with TGF-beta 1. With longer incubation times (10-20 days) the loss of FVIII expression was complete and over 90% of the cells expressed alpha-SM actin. Ultrastructurally, cells in control cultures showed the typical features of endothelial cells. In the TGF-beta 1-treated cultures, cells which appeared indistinguishable from contractile and synthetic smooth muscle cells were observed. Withdrawal of TGF-beta 1 after 10 days incubation resulted in the re-appearance of polygonal cells which were FVIII-positive and alpha-SM actin-negative.(ABSTRACT TRUNCATED AT 250 WORDS)

Actins↗
PubMed1991

The response of endothelial cells to TGF beta-1 is dependent upon cell shape, proliferative state and the nature of the substratum.

Endothelial cells plated on two-dimensional (2-D) substrata proliferate until they form a tightly apposed confluent monolayer of quiescent cells that display a typical 'cobblestone' morphology. When added to proliferating cultures TGF beta-1 (transforming growth factor beta-1) inhibited cell growth and caused marked morphological changes, with the cells becoming enlarged and ragged. These effects were dose-dependent and reversible. TGF beta-1 also reduced the cloning efficiency and colony size of these cells, indicating that TGF beta-1 is cytotoxic and cytostatic for endothelial cells. By contrast, TGF beta-1 added to quiescent cobblestone cultures did not affect cell morphology or cell numbers. In the presence of 20% serum, the level of total protein synthesis per cell was significantly increased by TGF beta-1 in a dose-dependent manner when the cells were cultured on a 2-D substratum, regardless of whether the cells were proliferating or cobblestone quiescent. The level of plasminogen activator inhibitor type 1 was specifically increased in these cultures, as demonstrated by reverse fibrin zymography and immunoprecipitation. Endothelial cells embedded within a 3-D collagen gel display an elongated 'sprouting' morphology. Such cells self-associate to form three-dimensional cellular networks within the gel, but do not proliferate. The addition of TGF beta-1 to these quiescent sprouting cells initially induced rounding-up without altering protein synthesis, and cell death occurred later. The effects of TGF beta-1 on sprouting endothelial cells were also examined using two culture systems where both the cobblestone and the sprouting phenotypes were present. TGF beta-1 reduced the number of cells present and the extent of migration of sprouting cells embedded within a type I collagen gel, but had no effect upon sprouting cells embedded within a complex endothelial-produced extracellular matrix. Large vessel (aortic) and microvessel (retinal) endothelial cells responded in a similar way to TGF beta-1; the only difference being that an increased synthesis of PAI-1 was not observed with sub-confluent BREC cultures. Our results suggest that the effects of TGF beta-1 upon endothelial cells depend on the shape (cobblestone or sprouting), on the proliferative state of the cells, and on the nature of the matrix surrounding the cells. The response of these cells to TGF beta-1 in vivo may be similarly modulated during angiogenesis by changes in the cell phenotype and the composition of the surrounding matrix.

Animals↗