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36 results on '"Aplin, A.C."'

3. Vascular regression and survival are differentially regulated by MT1-MMP and TIMPs in the aortic ring model of angiogenesis

Author

Aplin, A.C., Zhu, W.H., Fogel, E., and Nicosia, R.F.

Subjects
Neovascularization -- Physiological aspects, Neovascularization -- Control, Neovascularization -- Research, Animal models in research -- Usage, Collagen -- Physiological aspects, Collagen -- Research, Biological sciences
Abstract

This study was designed to investigate the role of matrix metalloproteinases (MMPs) and tissue inhibitors of MMPs (TIMPs) in the reabsorption of neovessels in collagen gel cultures of rat and mouse aortic rings. Aortic angiogenesis was associated with collagen lysis and production of the matrix-degrading enzymes MMP-2, MMP-9, and membrane-type MMP (MT1-MMP, or MMP-14). Vascular growth and regression were not affected by disruption of MMP-2 or MMP-9. In addition, no effect on vascular regression was observed by blocking plasmin, a protease implicated in the activation of MMPs, with [epsilon]-aminocaproic acid or by adding plasminogen, which caused a modest increase in vascular proliferation. Conversely, angiogenesis was blocked and vessels stabilized by inhibiting MT1-MMP with neutralizing antibodies, TIMP-2, TIMP-3, or TIMP-4. TIMP-1, which blocks MMP-2 and MMP-9 but is a poor inhibitor of MT1-MMP, had no antiangiogenic effect. However, TIMP-1 prolonged the survival of neovessels following angiogenesis. Vascular regression was accelerated in aortic cultures from TIMP-1-and TIMP-2-deficient mice. The vascular survival effect of anti-MT1-MMP antibodies and TIMPs with MT1-MMP inhibitory activity was associated with complete inhibition of collagen lysis. In contrast, TIMP-1 had no anticollagenolytic effect. These results indicate that MT1-MMP plays a critical role not only in angiogenesis but also in vascular regression and demonstrate that TIMPs with anti-MT1-MMP activity have opposite effects on angiogenic outcomes depending on the stage of the angiogenic process. This study also suggests the existence of a TIMP-1-mediated alternate pathway of vascular survival that is unrelated to MT1-MMP inhibitory activity. neovascularization; matrix metalloproteinase-14; collagen; endothelial cells; aorta; rarefaction; membrane type 1 matrix metalloproteinase; tissue inhibitors of matrix metalloproteinases

Published
2009

4. The postnatal rat aorta contains pericyte progenitor cells that form spheroidal colonies in suspension culture

Author

Howson, K.M., Aplin, A.C., Gelati, M., Alessandri, G., Parati, E.A., and Nicosia, R.F.

Subjects
Cells -- Research, Neovascularization -- Research, Biological sciences
Abstract

Pericytes play an important role in modulating angiogenesis, but the origin of these cells is poorly understood. To evaluate whether the mature vessel wall contains pericyte progenitor cells, nonendothelial mesenchymal cells isolated from the rat aorta were cultured in a serum-free medium optimized for stem cells. This method led to the isolation of anchorage-independent cells that proliferated slowly in suspension, forming spheroidal colonies. This process required basic fibroblast growth factor (bFGF) in the culture medium, because bFGF withdrawal caused the cells to attach to the culture dish and irreversibly lose their capacity to grow in suspension. Immunocytochemistry and RT-PCR analysis revealed the expression of the precursor cell markers CD34 and Tie-2 and the absence of endothelial cell markers (CD31 and endothelial nitric oxide synthase, eNOS) and smooth muscle cell markers ([alpha]smooth muscle actin, [alpha]-SMA). In addition, spheroid-forming cells were positive for NG2, nestin, PDGF receptor (PDGFR)-[alpha], and PDGFR-[beta]. Upon exposure to serum, these cells lost CD34 expression, acquired [alpha]-SMA, and attached to the culture dish. Returning these ceils to serum-free medium failed to restore their original spheroid phenotype, suggesting terminal differentiation. When embedded in collagen gels, spheroid-forming cells rapidly migrated in response to PDGF-BB and became dendritic. Spheroid-forming cells cocultured in collagen with angiogenic outgrowths of rat aorta or isolated endothelial cells transformed into pericytes. These results demonstrate that the rat aorta contains primitive mesenchymal cells capable of pericyte differentiation. These immature cells may represent an important source of pericytes during angiogenesis in physiological and pathological processes. They may also provide a convenient supply of mural ceils for vascular bioengineering applications. angiogenesis; stem cells; smooth muscle; mural cells; collagen

Published
2005

9. Predicting the elastic response of organic-rich shale using nanoscale measurements and homogenisation methods

Author

Goodarzi, M., Rouainia, M., Aplin, A.C., Cubillas, P., and de Block, M.

Abstract

Determination of the mechanical response of shales through experimental procedures is a practical challenge due to their heterogeneity and the practical difficulties of retrieving good-quality core samples. Here, we investigate the possibility of using multiscale homogenisation techniques to predict the macroscopic mechanical response of shales based on quantitative mineralogical descriptions. We use the novel PeakForce Quantitative Nanomechanical Mapping technique to generate high-resolution mechanical images of shales, allowing the response of porous clay, organic matter, and mineral inclusions to be measured at the nanoscale. These observations support some of the assumptions previously made in the use of homogenisation methods to estimate the elastic properties of shale and also earlier estimates of the mechanical properties of organic matter. We evaluate the applicability of homogenisation techniques against measured elastic responses of organic-rich shales, partly from published data and also from new indentation tests carried out in this work. Comparison of experimental values of the elastic constants of shale samples with those predicted by homogenisation methods showed that almost all predictions were within the standard deviation of experimental data. This suggests that the homogenisation approach is a useful way of estimating the elastic and mechanical properties of shales in situations where conventional rock mechanics test data cannot be measured.

Published
2017

10. Observations of pore systems of natural siliciclastic mudstones

Author

Aplin, A.C., Moore, J.K.S., Schäfer, Thorsten, Dohrmann, Reiner, and Greenwell, H.C.

Abstract

Grains within siliciclastic muds are deposited either as flocs, in which grains are generally ,10 mm, or as single grains: “sortable silt,” generally .10 mm. When clay-size (,2 mm diameter) particles form .30% of mudstones, pore-size distributions are controlled mainly by the interaction of phyllosilicates; these materials are ‘matrix-supported.’ Pores associated with clay-size particles are typically ,20 nm, even at shallow burial. When clay-size particles comprise ,30% of the grain-size distribution, a second, much larger pore system is observed, controlled by the amount and size of sortable silt; these mudstones are ‘framework-supported.’ Compaction of these silt-rich materials occurs mainly by the loss of the largest pores, but large pores still exist up to high effective stresses in the absence of chemical compaction. Mercury injection porosimetry (MIP) gives information about pore-throat size and pore connectivity and thus provides useful data with which to estimate permeability. Models based on generally flat pore shapes can estimate the permeability of homogenous mudstones to+a factor of 3 of the true value, but cannot be used for heterogeneous, laminated mudstones, which exhibit highly anisotropic permeabilities. As MIP gives information about pore throats and microscopy gives information about pore bodies, the two techniques generate different results. Both are required, along with other techniques such as small-angle neutron scattering and low-pressure gas sorption, in order to fully appreciate the complexity of mudstone pore systems.

Published
2016

35. Redox geochemistry in organic-rich sediments of a constructed wetland treating colliery spoil leachate.

Author

Morrison M.I., Aplin A.C., Morrison M.I., and Aplin A.C.

Abstract

A geochemical study was carried out of sediment cores and surface waters over an annual cycle from the compost-based constructed wetland at Quaking Houses, County Durham, England, which was built to treat acidic and metalliferous waters from colliery spoil. The influent waters contain up to 10 mM SO4(2-), total Fe of about around 100 microM and a mean pH of 6.2, The organic-rich sediments sustain a coupled redox cycle of Fe and S which is more intense in the summer months. Reduction of Fe(III) and SO4(2-) apparently occurs within the same macroscopic volume of sediment, along with oxidation of sulphide and Fe(III). In the top 2 cm of the sediment pore water Fe concentrations reach a maximum of about 1 mM in the presence of high concentrations of Fe oxides and the occurrence of SO4 reduction. Partial re-oxidation of sulphide is indicated by the presence of significant elemental S. Total Fe in the surface 10 cm has a mean value of 7-9% of sediment dry weight, of which sulphide-Fe represents 7-12% and reactive amorphous Fe 20-45%. About 90% of the solid phase sedimentary Fe occurs as oxides or oxyhydroxides. The downwards diffusion of dissolved Fe from the near-surface maximum is sustained by the precipitation of Fe oxides as a result of radial O2 loss from roots in the dense rhizosphere. Transport processes occurring at and across the sediment-water interface are sufficiently rapid in the approximately 20 h residence time of the waters to remove 70-90% of influent Fe and 15-25% of influent SO4 into surface sediments and increase both the pH and alkalinity of effluent waters. Coupling of the Fe and S cycles is fundamental to effective remediation in terms of alkalinity generation and the retention of metals., A geochemical study was carried out of sediment cores and surface waters over an annual cycle from the compost-based constructed wetland at Quaking Houses, County Durham, England, which was built to treat acidic and metalliferous waters from colliery spoil. The influent waters contain up to 10 mM SO4(2-), total Fe of about around 100 microM and a mean pH of 6.2, The organic-rich sediments sustain a coupled redox cycle of Fe and S which is more intense in the summer months. Reduction of Fe(III) and SO4(2-) apparently occurs within the same macroscopic volume of sediment, along with oxidation of sulphide and Fe(III). In the top 2 cm of the sediment pore water Fe concentrations reach a maximum of about 1 mM in the presence of high concentrations of Fe oxides and the occurrence of SO4 reduction. Partial re-oxidation of sulphide is indicated by the presence of significant elemental S. Total Fe in the surface 10 cm has a mean value of 7-9% of sediment dry weight, of which sulphide-Fe represents 7-12% and reactive amorphous Fe 20-45%. About 90% of the solid phase sedimentary Fe occurs as oxides or oxyhydroxides. The downwards diffusion of dissolved Fe from the near-surface maximum is sustained by the precipitation of Fe oxides as a result of radial O2 loss from roots in the dense rhizosphere. Transport processes occurring at and across the sediment-water interface are sufficiently rapid in the approximately 20 h residence time of the waters to remove 70-90% of influent Fe and 15-25% of influent SO4 into surface sediments and increase both the pH and alkalinity of effluent waters. Coupling of the Fe and S cycles is fundamental to effective remediation in terms of alkalinity generation and the retention of metals.

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