Looking backward, looking forward: the city region of the mid-21st century

Emerging as a serious tool of analysis in the United States around 1950, the city region concept was increasingly applied in a European context after 1980. Since 2000, it has evolved further with recognition of the polycentric mega-city region, first recognised in Eastern Asia but now seen as an emerging urban form both in Europe and the United States. The paper speculates on the main changes that may impact on the growth and development of such complex urban regions in the first half of the 21st century, concluding that achieving the goal of polycentric urban development may prove more complex than at first it may seem

Effect of Hypoxia on Dental Pulp Mesenchymal Stem Cells in a Purpose of Tissue Engineering

International audienceDuring life, teeth are exposed to severe injuries (decay, traumatisms…), which can result in dental pulp necrosis. Creating a “pulp tissue equivalent” constitutes a promising therapeutic approach to replace the current invasive treatments. Dental pulp of deciduous teeth contains mesenchymal stem cells (SHEDs: Stem cells from Human Exfoliated Deciduous teeth), shown to have a high proliferation and differentiation potential. Our approach aims to assess the effect of severe hypoxia on these cells, mimicking the clinical conditions of the matrix implantation in the pulp space. 3D collagen matrices seeded with SHEDs (1.5 million of cells/ml) were cultivated under severe hypoxia (1% O2) during 3 days. Then, to mimic the kinetics of revascularization, the matrices were replaced in normoxic conditions (21% O2). Induced mRNA and protein modifications were studied by qPCR, ELISA, Western Blot and immunocytochemistry, at several time points. A transcriptomic analysis (DNA affymetrix chips “gene” type) of the samples was then performed at the time point with the highest VEGF mRNA expression. The capacity of SHEDs exposed to hypoxia to induce angiogenenis was then tested in a tubulogenesis model. Finally, SHEDs pretreated by hypoxia were induced toward osteogenic differentiation in 3D plastic compressed collagen matrix. Our data show that hypoxic conditions induce: 1) an increase of the transcription factor HIF‐1 alpha observed in the cell nucleus, 2) a x4 increase of VEGF mRNA expression at 24 h (qPCR), confirmed by ELISA analysis, 3) the up‐regulation of numerous genes activated by HIF‐1 alpha and involved in angiogenesis, apoptosis and glycolysis regulation. Furthermore, SHEDs pretreated by hypoxia enhanced capillary formation by endothelial cells. In parallel, osteogenic differentiation assay showed that pretreatment by hypoxia did not impair matrix mineralization by SHEDs, which was slightly enhanced.These cells are good candidate for tissue engineering approaches, in particular for treating damaged dental tissues