Bi-Phasic Vesicles: instability induced by adsorption of proteins

The recent discovery of a lateral organization in cell membranes due to small structures called 'rafts' has motivated a lot of biological and physico-chemical studies. A new experiment on a model system has shown a spectacular budding process with the expulsion of one or two rafts when one introduces proteins on the membrane. In this paper, we give a physical interpretation of the budding of the raft phase. An approach based on the energy of the system including the presence of proteins is used to derive a shape equation and to study possible instabilities. This model shows two different situations which are strongly dependent on the nature of the proteins: a regime of easy budding when the proteins are strongly coupled to the membrane and a regime of difficult budding.Comment: 19 avr. 200

Integrating microfluidic generation, handling and analysis of biomimetic giant unilamellar vesicles

The key roles played by phospholipids in many cellular processes, has led to the development of model systems, to explore both lipid–lipid and lipid–peptide interactions. Biomimetic giant unilamellar vesicles represent close facsimiles of in vivo cellular membranes, although currently their widespread use in research is hindered by difficulties involving their integration into high-throughput techniques, for exploring membrane biology intensively in situ. This paper presents an integrated microfluidic device for the production, manipulation and high-throughput analysis of giant unilamellar vesicles. Its utility is demonstrated by exploring the lipid interaction dynamics of the pore-forming antimicrobial peptide melittin, assessed through the release of fluorescent dyes from within biomimetic vesicles, with membrane compositions similar to mammalian plasma membranes

Intracoronary Brachytherapy, a Promising Treatment Option for Diabetic Patients: Results from a European Multicenter Registry (RENO)

Despite advances in the interventional treatment of coronary disease, diabetics still have double the case fatality rate as nondiabetics. The purpose of this an

Morphology and Interaction between Lipid Domains

Cellular membranes are a heterogeneous mix of lipids, proteins and small molecules. Special groupings of saturated lipids and cholesterol form a liquid-ordered phase, known as `lipid rafts,' serving as platforms for signaling, trafficking and material transport throughout the secretory pathway. Questions remain as to how the cell maintains heterogeneity of a fluid membrane with multiple phases, through time, on a length-scale consistent with the fact that no large-scale phase separation is observed. We have utilized a combination of mechanical modeling and in vitro experiments to show that membrane morphology can be a key player in maintaining this heterogeneity and organizing such domains in the membrane. We demonstrate that lipid domains can adopt a flat or dimpled morphology, where the latter facilitates a repulsive interaction that slows coalescence and tends to organize domains. These forces, that depend on domain morphology, play an important role in regulating lipid domain size and in the lateral organization of lipids in the membrane.Comment: 7 pages, 4 figure

COVID-19 pandemic: Lessons for spatial development

Background and aims of this position paper: Since the COVID-19 pandemic began, it has become ever clearer that it poses an enormous challenge for society. The lockdown imposed on large parts of public life, which hit all social groups and institutions relatively abruptly with a wide range of impacts, as well as the measures adopted subsequently have resulted in radical changes in our living conditions. In some cases, the crisis has acted as an accelerator of trends affecting processes that were already ongoing: the digitalisation of communications and educational processes, the growth in working from home and mobile working arrangements, the expansion of online retail, changes in travel behaviour (in favour of cars and bicycles), and the establishment of regional service networks. At the same time, there has been a braking effect on sectors such as long-distance travel, global trade, trade fairs and cultural events, as well as on progress towards gender equality in the division of labour for household responsibilities and childcare. Socio-spatial, infrastructural, economic and ecological effects are becoming increasingly apparent. For those involved in spatial development and spatial planning, urgent questions arise not only about the weaknesses that have become apparent in our spatial uses in terms of infrastructure and public service provision, the economy and ecology, and in our ways of life in terms of housing and the supply of goods and services, but also about what opportunities have emerged for sustainable and self-determined lifestyles. What conclusions for anticipatory and preventive planning can be drawn from these (provisional) findings? Using a critical, multidisciplinary and integrative examination of the spatially-relevant effects of the COVID-19 pandemic, this paper establishes connections between the crisis management of today and crisis preparedness concepts for potential future pandemics. Building on that, it proposes corresponding recommended actions. These actions relate not only to insights for medium-term space-related crisis management but also to conclusions on long-term strategic challenges for spatial development in view of pandemics to be expected in the future. For this position paper, the 'Pandemic and Spatial Development' Ad hoc Working Group at the ARL - Academy for Territorial Development in the Leibniz Association has compiled interdisciplinary perspectives from spatial development and spatial planning, public health services, epidemiology, economics and social sciences, and has condensed them into transdisciplinary recommendations for action. These recommendations are directed at the various action levels for spatial development and spatial planning

Budding and Fission of a multiphase vesicle

We present a model of bi-phasic vesicle in the limit of large surface tension. In this regime, the vesicle is completely stretched and well described by two spherical caps with a fold which concentrates the membrane stress. The conservation laws and geometric constraints restrict the space of possible shapes to a pair of solutions labeled by a parameter $\tau$ given by {\it line tension/pressure}. For a given $\tau$ value, the two solutions differ by the length of the interface between domains. For a critical value $\tau\_c$, the two vesicle shapes become identical and no solution exists above this critical value. This model sheds new light on two proposed mechanisms (osmotic shocks and molecule absorption) to explain the budding and the fission in recent experiments

Endoluminal beta-radiation therapy for the prevention of coronary restenosis after balloon angioplasty.

BACKGROUND: Beta radiation is effective in reducing vascular neointimal proliferation in animals after injury caused by balloon angioplasty. However, the lowest dose that can prevent restenosis after coronary angioplasty has yet to be determined. METHODS: After successful balloon angioplasty of a previously untreated coronary stenosis, 181 patients were randomly assigned to receive 9, 12, 15, or 18 Gy of radiation delivered by a centered yttrium-90 source. Adjunctive stenting was required in 28 percent of the patients. The primary end point was the minimal luminal diameter six months after treatment, as a function of the delivered dose of radiation. RESULTS: At the time of follow-up coronary angiography, the mean minimal luminal diameter was 1.67 mm in the 9-Gy group, 1.76 mm in the 12-Gy group, 1.83 mm in the 15-Gy group, and 1.97 mm in the 18-Gy group (P=0.06 for the comparison of 9 Gy with 18 Gy), resulting in restenosis rates of 29 percent, 21 percent, 16 percent, and 15 percent, respectively (P=0.14 for the comparison of 9 Gy with 18 Gy). At that time, 86 percent of the patients had had no serious cardiac events. In 130 patients treated with balloon angioplasty alone, restenosis rates were 28 percent, 17 percent, 16 percent, and 4 percent, respectively (P=0.02 for the comparison of 9 Gy with 18 Gy). Among these patients, there was a dose-dependent enlargement of the lumen in 28 percent, 50 percent, 45 percent, and 74 percent of patients, respectively (P<0.001 for the comparison of 9 Gy with 18 Gy). The rate of repeated revascularization was 18 percent with 9 Gy and 6 percent with 18 Gy (P=0.26). CONCLUSIONS: Intracoronary beta radiation therapy produces a significant dose-dependent decrease in the rate of restenosis after angioplasty. An 18-Gy dose not only prevents the renarrowing of the lumen typically observed after successful balloon angioplasty, but actually induces luminal enlargement

Programmed Bending Reveals Dynamic Mechanochemical Coupling in Supported Lipid Bilayers

In living cells, mechanochemical coupling represents a dynamic means by which membrane components are spatially organized. An extra-ordinary example of such coupling involves curvature-dependent polar localization of chemically-distinct lipid domains at bacterial poles, which also undergo dramatic reequilibration upon subtle changes in their interfacial environment such as during sporulation. Here, we demonstrate that such interfacially-triggered mechanochemical coupling can be recapitulated in vitro by simultaneous, real-time introduction of mechanically-generated periodic curvatures and attendant strain-induced lateral forces in lipid bilayers supported on elastomeric substrates. In particular, we show that real-time wrinkling of the elastomeric substrate prompts a dynamic domain reorganization within the adhering bilayer, producing large, oriented liquid-ordered domains in regions of low curvature. Our results suggest a mechanism in which interfacial forces generated during surface wrinkling and the topographical deformation of the bilayer combine to facilitate dynamic reequilibration prompting the observed domain reorganization. We anticipate this curvature-generating model system will prove to be a simple and versatile tool for a broad range of studies of curvature-dependent dynamic reorganizations in membranes that are constrained by the interfacial elastic and dynamic frameworks such as the cell wall, glycocalyx, and cytoskeleton

Real-time intermembrane force measurements and imaging of lipid domain morphology during hemifusion

Membrane fusion is the core process in membrane trafficking and is essential for cellular transport of proteins and other biomacromolecules. During protein-mediated membrane fusion, membrane proteins are often excluded from the membrane-membrane contact, indicating that local structural transformations in lipid domains play a major role. However, the rearrangements of lipid domains during fusion have not been thoroughly examined. Here using a newly developed Fluorescence Surface Forces Apparatus (FL-SFA), migration of liquid-disordered clusters and depletion of liquid-ordered domains at the membrane-membrane contact are imaged in real time during hemifusion of model lipid membranes, together with simultaneous force-distance and lipid membrane thickness measurements. The load and contact time-dependent hemifusion results show that the domain rearrangements decrease the energy barrier to fusion, illustrating the significance of dynamic domain transformations in membrane fusion processes. Importantly, the FL-SFA can unambiguously correlate interaction forces and in situ imaging in many dynamic interfacial systems.open0

SARS-CoV-2-Pandemie: Was lernen wir daraus für die Raumentwicklung?

[Veranlassung und Ziele des Positionspapiers] Seit Beginn der "Corona-Krise"/SARS-CoV-2-Pandemie wird immer deutlicher, dass es sich hierbei um eine gesellschaftliche Herausforderung größten Ausmaßes handelt. Der sog. Lockdown weiter Teile des öffentlichen Lebens, der relativ unvermittelt alle sozialen Gruppen und Institutionen mit den unterschiedlichsten Konsequenzen traf, und die darauf aufbauenden Maßnahmen stellen eine radikale Veränderung unserer Lebensumstände dar. Die Krise ist zumindest in Teilen zu einem großen Trendverstärker für bereits ablaufende Prozesse geworden: bei der Digitalisierung von Kommunikations- und Lernprozessen, der Zunahme an Homeoffice/mobilem Arbeiten, der Ausweitung von Onlinehandel, Veränderungen im Mobilitätsverhalten (zugunsten Pkw und Fahrrad) und regionaler Vernetzung der Leistungserbringung. Gleichzeitig wurden Entwicklungen wie Fernreisen, globaler Handel, Messen und Kultur, aber auch eine geschlechtergerechtere Arbeitsteilung mit Blick auf Haushalt und Kinderbetreuung ausgebremst. Sozialräumliche, infrastrukturelle sowie ökonomische und ökologische Auswirkungen zeichnen sich offener ab. Es stellt sich für die Akteure der Raumentwicklung und Raumplanung dringlich die Frage, welche Schwächen unserer Raumnutzungen im Hinblick auf Infrastrukturen und Daseinsvorsorge, Ökonomie und Ökologie, unserer Lebensmodelle mit Wohnen und Versorgung - aber auch welche Chancen für nachhaltige und selbstbestimmte Lebensweisen - offensichtlich geworden sind. Was ergibt sich aus diesen (vorläufigen) Erkenntnissen für eine vorausschauende und vorsorgende Planung? Auf Grundlage einer kritischen, multidisziplinären und integrativen Betrachtung raumrelevanter Auswirkungen der Corona-Krise wird der Bogen geschlagen von der aktuellen Krisenbewältigung zur konzeptionellen Krisenvorsorge für mögliche künftig zu erwartende Pandemien. Darauf aufbauend werden entsprechende Handlungsempfehlungen formuliert. Sie beziehen sich nicht nur auf Erkenntnisse zum mittelfristigen raumbezogenen Krisenmanagement, sondern auch auf Aussagen zu langfristigen strategischen Herausforderungen der räumlichen Entwicklung angesichts zukünftig zu erwartender Pandemien. Der Ad-hoc-Arbeitskreis "Pandemie und Raumentwicklung" der ARL - Akademie für Raumentwicklung in der Leibniz-Gemeinschaft hat hierzu für dieses Positionspapier interdisziplinäre Perspektiven aus Raumentwicklung und Raumplanung, Öffentlichem Gesundheitsdienst (ÖGD), Epidemiologie/ Public Health und Ökonomie sowie Sozialwissenschaften zusammengetragen und zu transdisziplinären Handlungsempfehlungen verdichtet. Diese richten sich an die unterschiedlichen Handlungsebenen der Raumentwicklung und Raumplanung