Extracellular matrix proteins are potent agonists of human smooth muscle cell migration

AbstractPurpose: Extracellular matrix proteins can stimulate smooth muscle cell (SMC) migration by three distinct mechanisms: chemokinesis (nondirected migration in the presence of soluble protein), chemotaxis (directed migration toward soluble protein), and haptotaxis (directed migration toward insoluble, substrate-bound protein). This study investigates the effects of four prevalent extracellular matrix proteins (collagen types I and IV, fibronectin, and laminin), and platelet-derived growth factor (PDGF) on haptotaxis, chemotaxis, and chemokinesis of human SMCs. The role of large guanosine triphosphate-binding proteins (G-proteins) in the signaling mediating these effects is also evaluated.Methods: Human saphenous vein SMCs were used in all migration studies. Chemokinesis, chemotaxis, and haptotaxis to each of the matrix proteins were measured and compared with PDGF through the use of a 48-well microchemotaxis chamber. The role of G-proteins in matrix-induced SMC migration was studied with the modulators of G-protein function, cholera and pertussis toxins.Results: For all matrix proteins the relative strength of the various stimuli for migration was haptotaxis > chemotaxis > chemokinesis (p < 0.05). For all three stimuli collagen I and IV produced the most significant migration followed by fibronectin > PDGF-AB > laminin (p < 0.05). Pertussis toxin completely inhibited chemotaxis and partially inhibited haptotaxis by laminin but did not affect migration by other matrix proteins, whereas cholera toxin abolished migration in response to all four matrix proteins.Conclusion: Matrix proteins, with the exception of laminin, provide a more significant stimulus for SMC locomotion than does the prototypical agonist, PDGF-AB. Of the three mechanisms by which migration can be stimulated, haptotaxis elicits the most pro-found effect. The importance of G-proteins as second messengers for migration varies with each matrix protein and with the mechanism of stimulation. (J Vasc Surg 1996;24:25-33.

Intracellular calcium transients are necessary for platelet-derived growth factor but not extracellular matrix protein–induced vascular smooth muscle cell migration

AbstractPurposeVascular smooth muscle cell (SMC) migration is a critical component of the hyperplastic response that leads to recurrent stenosis after interventions to treat arterial occlusive disease. We investigated the relationship between intracellular calcium ([Ca2+]i) and migration of vascular SMCs in response to platelet-derived growth factor (PDGF) and extracellular matrix (ECM) proteins.MethodsHuman saphenous vein SMCs were used for all experiments. SMC migration in response to agonists was measured with a microchemotaxis assay. A standard fluorimetric assay was used to assess changes in [Ca2+]i in response to the various combinations of growth factors and ECM proteins.ResultsThe calcium ionophore A23187 produced a rapid rise in [Ca2+]i and a corresponding 60% increase in SMC migration, whereas chelation of [Ca2+]i with BAPTA (1,2-bis [aminophenoxy] ethane-N,N,N′,N′-tetraacetic acid) produced a fivefold decrease in PDGF-induced chemotaxis, suggesting that [Ca2+]i is both sufficient and necessary for SMC migration. Stimulation of SMCs with PDGF produced an early peak followed by a late plateau in [Ca2+]i. To establish a relationship between temporal fluctuations in [Ca2+]i and SMC migration, SMCs were pretreated with caffeine and ryanadine, which eliminated the initial peak but not the late plateau in [Ca2+]i, and had no effect on chemotaxis in response to PDGF. Incubation of SMCs with nickel chloride eliminated the late plateau, but had no effect on the initial peak in [Ca2+]i, and reduced PDGF-stimulated migration by fivefold. We then evaluated the role of calcium in SMC migration induced by ECM proteins such as laminin, fibronectin, and collagen types I and IV. All four matrix proteins stimulated SMC migration, but none produced an elevation in [Ca2+]i. Moreover, preincubation of SMCs with caffeine and ryanadine or nickel chloride had no effect on ECM protein-induced chemotaxis.Conclusion[Ca2+]i transients are necessary for PDGF but not ECM protein-induced SMC chemotaxis. Moreover, the ability of PDGF to stimulate vascular SMC migration appears dependent on influx of extracellular calcium through membrane channels.AbstractClinical relevanceRecurrent stenosis after angioplasty or surgical bypass remains a significant challenge in treating vascular occlusive disease. In addition to growth factors, extracellular matrix (ECM) proteins may be potent agonists of this process. In this study we show that the influx of extracellular calcium is an important mechanism for platelet-derived growth factor–induced smooth muscle cell migration but not ECM-induced migration. Of note, in clinical trials calcium channel blockers failed to inhibit recurrent stenosis. Our data provide mechanistic insight to help explain this negative outcome in that therapies designed to inhibit restenosis depend on the effects of both growth factors and ECM proteins

"A large can of worms": teachers' perceptions of young people's technology use

Digital technology use is increasingly impacting on the lives of young people. To gain a deeper understanding of the perceived impact of young people's digital technology use, 2 focus groups were conducted with 14 teachers recruited from 2 schools. The focus groups were transcribed verbatim and analysed using Interpretative Phenomenological Analysis. The analysis revealed three themes: changing social dynamics, risk and (ir)responsible behaviour, and disclosure and reporting of cyber bullying. Participants discussed how digital technology was shaping young people's social identity and impacting on established norms when interacting in the social arena. A number of benefits were attributed to technology use but participants also recognised young people's naivety and tendency to anthropomorphise the internet. Finally, there was a perception that young people underreported their experiences of cyber bullying and some of the challenges faced when tackling cyber bullying were discussed