14 research outputs found
Low Cohomogeneity and Polar Actions on Exceptional Compact Lie Groups
We study isometric Lie group actions on the compact exceptional groups E6,
E7, E8, F4 and G2 endowed with a biinvariant metric. We classify polar actions
on these groups. We determine all isometric actions of cohomogeneity less than
three on E6, E7, F4 and all isometric actions of cohomogeneity less than 20 on
E8. Moreover we determine the principal isotropy algebras for all isometric
actions on G2.Comment: 27 pages; introduction rewritten; references updated; final version;
to appear in Transformation Group
Acidic preconditioning improves the proangiogenic responses of endothelial colony forming cells
Objective: Acidosis is present in several pathological conditions where vasculogenesis takes place including ischemia, tumor growth and wound healing. We have previously demonstrated that acidosis induces human CD34+ cell apoptosis. Considering that endothelial colony-forming cells (ECFC) are a subpopulation of CD34+ cells and key players in vasculogenesis, in the present study we investigated the effect of acidosis on the survival and functionality of ECFC. Approach and results: Endothelial colony-forming cells obtained by differentiation of human cord blood CD34+ cells in endothelial growth medium-2 for 14–21 days were exposed at pH 7.4, 7.0 or 6.6. We found that acidosis failed to induce ECFC apoptosis and, although an early reduction in proliferation, chemotaxis, wound healing and capillary-like tubule formation was observed, once the medium pH was restored to 7.4, ECFC proliferation and tubulogenesis were augmented. Stromal cell derived factor-1 (SDF1)-driven migration and chemokine receptor type 4 surface expression were also increased. The maximal proangiogenic effect exerted by acidic preconditioning was observed after 6 h at pH 6.6. Furthermore, preconditioned ECFC showed an increased ability to promote tissue revascularization in a murine model of hind limb ischemia. Immunoblotting assays showed that acidosis activated AKT and ERK1/2 and inhibited p38 pathways. Proliferation rises triggered by acidic preconditioning were no longer observed after AKT or ERK1/2 inhibition, whereas p38 suppression not only mimicked but also potentiated the effect of acidosis on ECFC tubule formation abilities. Conclusions: These results demonstrate that acidic preconditioning greatly increases ECFC-mediated angiogenesis in vitro including ECFC proliferation, tubulogenesis and SDF1-driven chemotaxis and is a positive regulator of microvessel formation in vivo.Fil: Mena, Hebe Agustina. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Instituto de Medicina Experimental. Academia Nacional de Medicina de Buenos Aires. Instituto de Medicina Experimental; ArgentinaFil: Lokajczyk, Anna. UniversitĂ© Paris Descartes; Francia. Inserm; FranciaFil: Dizier, Blandine. Inserm; FranciaFil: Strier, Sergio E.. Ciudad AutĂłnoma de Buenos Aires. Hospital "Bernardino Rivadavia"; ArgentinaFil: Voto, Liliana S.. Ciudad AutĂłnoma de Buenos Aires. Hospital "Juan A. Fernández"; Argentina. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas; ArgentinaFil: Boisson Vidal, Catherine. UniversitĂ© Paris Descartes; Francia. Inserm; FranciaFil: Schattner, Mirta Ana. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Instituto de Medicina Experimental. Academia Nacional de Medicina de Buenos Aires. Instituto de Medicina Experimental; ArgentinaFil: Negrotto, Soledad. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Instituto de Medicina Experimental. Academia Nacional de Medicina de Buenos Aires. Instituto de Medicina Experimental; Argentin
The secret life of a megakaryocyte: emerging roles in bone marrow homeostasis control
Megakaryocytes are rare cells found in the bone marrow, responsible for the everyday production and release of millions of platelets into the bloodstream. Since the discovery and cloning, in 1994, of their principal humoral factor, thrombopoietin, and its receptor c-Mpl, many efforts have been directed to define the mechanisms underlying an efficient platelet production. However, more recently different studies have pointed out new roles for megakaryocytes as regulators of bone marrow homeostasis and physiology. In this review we discuss the interaction and the reciprocal regulation of megakaryocytes with the different cellular and extracellular components of the bone marrow environment. Finally, we provide evidence that these processes may concur to the reconstitution of the bone marrow environment after injury and their deregulation may lead to the development of a series of inherited or acquired pathologies