In Lyl1-/- mice, adipose stem cell vascular niche impairment leads to premature development of fat tissues.

Lyl1 encodes a hematopoietic- and endothelial-specific bHLH transcription factor. Lyl1-deficient mice are viable, but they display mild hematopoietic and vascular defects. Specifically, LYL1 is required for the maturation and stabilization of blood vessel endothelial adherens junctions. Here, we report that young adult Lyl1-/- mice exhibit transient overweight associated with general expansion of adipose tissue, without signs of metabolic disorder and unrelated to food intake. The increased fat tissue development in Lyl1-/- mice resulted from earlier differentiation of adipose stem cells (ASCs) into adipocytes through noncell autonomous mechanisms. Specifically, we found that in Lyl1-/- mice, the adipose tissue vascular structures are immature, as indicated by their high permeability, reduced coverage by pericytes, lower recruitment of VE-cadherin and ZO1 at cell junctions, and more prone to angiogenesis. Together, our data show that in Lyl1-/- mice, the impaired vascular compartment of the adipose niche promotes ASC differentiation, leading to early adipocyte expansion and premature ASC depletion. Our study highlights the major structural role of the adipose tissue vascular niche in coordinating stem cell self-renewal and differentiation into adipocytes.

Lung endothelial barrier disruption in Lyl1-deficient mice.

Maturation of newly formed vessels is a multistep phenomenon during which functional endothelial barriers are established. Disruption of vessel integrity is an important feature in many physiological and pathological processes. We previously reported that lymphoblastic leukemia-derived sequence 1 (LYL1) is required for the late stages of postnatal angiogenesis to limit the formation of new blood vessels, notably by regulating the activity of the small GTPase Rap1. In this study, we show that LYL1 is also required during the formation of the mature endothelial barrier in the lungs of adult mice. Specifically, LYL1 knockdown in human endothelial cells downregulated the expression of ARHGAP21 and ARHGAP24, which encode two Rho GTPase-activating proteins, and this was correlated with increased RhoA activity and reorganization of the actin cytoskeleton into stress fibers. Importantly, in lungs of Lyl1-deficient mice, both vascular endothelial (VE)-cadherin and p120-catenin were poorly recruited to endothelial adherens junctions, indicative of defective cell-cell junctions. Consistent with this, higher Evans blue dye extravasation, edema, and leukocyte infiltration in the lung parenchyma of Lyl1-/- mice than in wild-type littermates confirmed that lung vascular permeability is constitutively elevated in Lyl1-/- adult mice. Our data show that LYL1 acts as a stabilizing signal for adherens junction formation by operating upstream of VE-cadherin and of the two GTPases Rap1 and RhoA. As increased vascular permeability is a key feature and a major mechanism of acute respiratory distress syndrome, molecules that regulate LYL1 activity could represent additional tools to modify the endothelial barrier permeability.

LYL1 activity is required for the maturation of newly formed blood vessels in adulthood.

The 2 related basic helix loop helix genes, LYL1 and TAL-1 are active in hematopoietic and endothelial lineages. While Tal-1 is essential for both hematopoietic and vascular development, the role of Lyl1 appears to be distinct as deficient mice are viable and display modest hematopoietic defects. Here, we reveal a role for Lyl1 as a major regulator of adult neovascularization. Tumors implanted into Lyl1-deficient mice showed higher proliferation and angiogenesis, as evidenced by enlarged lumens, reduced pericyte coverage and increased permeability, compared with wild type littermates. Of note, Lyl1-deficient tumor vessels exhibited an up-regulation of Tal-1, the VE-Cadherin target gene, as well as Angiopoietin-2, 3 major actors in angiogenesis. Hematopoietic reconstitution experiments demonstrated that this sustained tumor angiogenesis was of endothelial origin. Moreover, the angiogenic phenotype observed in the absence of Lyl1 function was not tumor-restricted as microvessels forming in Matrigel or originating from aortic explants were also more numerous and larger than their wild-type counterparts. Finally, LYL1 depletion in human endothelial cells revealed that LYL1 controls the expression of molecules involved in the stabilization of vascular structures. Together, our data show a role for LYL1 in the postnatal maturation of newly formed blood vessels.

TAL-1/SCL and its partners E47 and LMO2 up-regulate VE-cadherin expression in endothelial cells.

The basic helix-loop-helix TAL-1/SCL essential for hematopoietic development is also required during vascular development for embryonic angiogenesis. We reported that TAL-1 acts positively on postnatal angiogenesis by stimulating endothelial morphogenesis. Here, we investigated the functional consequences of TAL-1 silencing in human primary endothelial cells. We found that TAL-1 knockdown caused the inhibition of in vitro tubulomorphogenesis, which was associated with a dramatic reduction in vascular endothelial cadherin (VE-cadherin) at intercellular junctions. Consistently, silencing of TAL-1 as well as of its cofactors E47 and LMO2 down-regulated VE-cadherin at both the mRNA and the protein level. Endogenous VE-cadherin transcription could be activated in nonendothelial HEK-293 cells by the sole concomitant ectopic expression of TAL-1, E47, and LMO2. Transient transfections in human primary endothelial cells derived from umbilical vein (HUVECs) demonstrated that VE-cadherin promoter activity was dependent on the integrity of a specialized E-box associated with a GATA motif and was maximal with the coexpression of the different components of the TAL-1 complex. Finally, chromatin immunoprecipitation assays showed that TAL-1 and its cofactors occupied the VE-cadherin promoter in HUVECs. Together, these data identify VE-cadherin as a bona fide target gene of the TAL-1 complex in the endothelial lineage, providing a first clue to TAL-1 function in angiogenesis.

PU.1/Spi-1 binds to the human TAL-1 silencer to mediate its activity.

The TAL-1/SCL gene encodes a basic helix-loop-helix (bHLH) transcription factor essential for primitive hematopoiesis and for adult erythroid and megakaryocytic development. Activated transcription of TAL-1 as a consequence of chromosomal rearrangements is associated with a high proportion of human T cell acute leukemias, showing that appropriate control of TAL-1 is crucial for the formation and subsequent fate of hematopoietic cells. Hence, the knowledge of the mechanisms, which govern the pattern of TAL-1 expression in hematopoiesis, is of great interest. We previously described a silencer in the 3'-untranslated region of human TAL-1, the activity of which is mediated through binding of a tissue-specific 40 kDa nuclear protein to a new DNA recognition motif, named tal-RE. Here, we show that tal-RE-binding activity, high in immature human hematopoietic progenitors is down regulated upon erythroid and megakaryocytic differentiation. This expression profile helped us to identify that PU.1/Spi-1 binds to the tal-RE sequences in vitro and occupies the TAL-1 silencer in vivo. By expressing a mutant protein containing only the ETS domain of PU.1 in human erythroleukemic HEL cells, we demonstrated that PU.1 mediates the transcriptional repression activity of the silencer. We found that ectopic PU.1 is not able to induce silencing activity in PU.1-negative Jurkat T cells, indicating that PU.1 activity, although necessary, is not sufficient to confer transcriptional repression activity to the TAL-1 silencer. Finally, we showed that the silencer is also active in TAL-1-negative myeloid HL60 cells that express PU.1 at high levels. In summary, our study shows that PU.1, in addition to its positive role in TAL-1 expression in early hematopoietic progenitors, may also act as a mediator of TAL-1 silencing in some hematopoietic lineages.

Soluble HIV-1 gp120 enhances HIV-1 replication in non-dividing CD4+ T cells, mediated via cell signaling and Tat cofactor overexpression.

OBJECTIVES: The soluble HIV-1 gp120 envelope glycoprotein, after being shed from infected cells, can cross-link its receptors on both HIV-1 infected and non-infected target cells, leading to their activation. We have assessed the impact of soluble gp120 on viral replication in CD4+/CXCR4+ T cells, via its effects on Tat-mediated transactivation of the HIV-1/LTR. MATERIALS AND METHODS: Primary cord blood-derived CD4+/CXCR4+ T cells were stimulated with soluble recombinant gp120 (rgp120) from the HIV-1/HXB2 clone. The level of gene or protein expression was assessed by serial analysis gene expression (SAGE), reverse transcriptase-polymerase chain reaction, western blotting or flow-cytometry analysis. Cellular division of rgp120-stimulated T cells was assessed by CFDA-SE labeling. Long terminal repeat (LTR) activity and HIV infection level were respectively measured by a chemiluminescent beta-gal Reporter Gene Assay and by p24 determination. RESULTS: We have demonstrated that rgp120 activates both PKCepsilon and its upstream effector PI3K/Akt, involved in the HIV-1 replication process. Moreover, rgp120 enhances the gene, as well as protein expression of the cellular Tat cofactors Tat-Sf1 and SPT5 in primary CD4+/CXCR4+ T cells. Finally, stimulation of HIV-1 infected T cells with rgp120 was found to result in both a higher LTR-activity and an increased production of viral particles. CONCLUSION: Taken together, these results show that soluble gp120 contributes to HIV-1 replication and dissemination, via the activation of multiple cell signaling pathways and the induction of Tat-cofactor expression, underscoring its potential as a therapeutic target in HIV-1-mediated pathogenesis.

Angiopoietin-2 is a direct transcriptional target of TAL1, LYL1 and LMO2 in endothelial cells.

The two related basic helix-loop-helix, TAL1 and LYL1, and their cofactor LIM-only-2 protein (LMO2) are present in blood and endothelial cells. While their crucial role in early hematopoiesis is well established, their function in endothelial cells and especially in angiogenesis is less understood. Here, we identified ANGIOPOIETIN-2 (ANG-2), which encodes a major regulator of angiogenesis, as a direct transcriptional target of TAL1, LYL1 and LMO2. Knockdown of any of the three transcription factors in human blood and lymphatic endothelial cells caused ANG-2 mRNA and protein down-regulation. Transient transfections showed that the full activity of the ANG-2 promoter required the integrity of a highly conserved Ebox-GATA composite element. Accordingly, chromatin immunoprecipitation assays demonstrated that TAL1, LYL1, LMO2 and GATA2 occupied this region of ANG-2 promoter in human endothelial cells. Furthermore, we showed that LMO2 played a central role in assembling TAL1-E47, LYL1-LYL1 or/and LYL1-TAL1 dimers with GATA2. The resulting complexes were able to activate endogenous ANG-2 expression in endothelial cells as well as in non-endothelial cells. Finally, we showed that ANG-2 gene activation during angiogenesis concurred with the up-regulation of TAL1 and LMO2. Altogether, we identified ANG-2 as a bona fide target gene of LMO2-complexes with TAL1 and/or LYL1, highlighting a new function of the three hematopoietic factors in the endothelial lineage.

Mortality and bloodstream infections in geriatrics units.

The purpose of this retrospective study was to evaluate risk factors of mortality in bloodstream infections in old and very old people in a French geriatric unit (Paul Brousse Hospital, APHP). 167 older patients with bloodstream infections were included and two groups were compared according to age (60-85 years and ≥85 years). Information was collected for each patient: age, sex, diseases, urinary catheter, temperature, signs of severe sepsis, biological examinations, bacteria and antibiotic treatments. All bacteremias were nosocomial. There was no difference between groups for pathogen, source or prognosis. Mortality rate at 60 days was 32.3%. The risk factors for mortality were: low albumin rate (p<0.001), high C-reactive protein (CRP) (p=0.02) and moderate fever (p=0.006). Multivariate logistic regression showed that these three parameters were significantly associated with a risk of mortality. The parameter with the highest risk was a low albumin rate <30 g/l. Malnutrition may be a more long-term risk factor. A moderate fever probably results in a more frequent delay in diagnosis in this population. Our work supports that age is not a risk factor of mortality for bloodstream infections. However management of bacteremia has to be adapted to elderly.

[The bHLH TAL1 protein: a key molecule in the hematopoietic and endothelial systems]. / La protéine bHLH TAL-1 : un acteur clé dans les systèmes hématopoïétique et endothélial.

The formation of blood cells and vascular networks occurs simultaneously during development, and both lineages remain in close association in all adult tissues. The functional setting of both systems within the embryo and their renewal during adult life are highly complex processes, and require the involvement of numerous molecular actors, the activities of which are often overlapping. Here, I review the activity of TAL-1, a basic-helix-loop-helix transcription factor, which plays a key role in the formation and functioning of both blood and endothelial systems, with a particular emphasis on recent data that associate TAL-1 with angiogenesis.

First outbreak of multidrug-resistant Klebsiella pneumoniae carrying blaVIM-1 and blaSHV-5 in a French university hospital.

OBJECTIVES: We studied eight imipenem-resistant isolates of Klebsiella pneumoniae involved in an outbreak in a French teaching hospital. METHODS: The eight isolates were recovered from clinical specimens or rectal swabs. Antibiotic susceptibilities were determined using standard agar diffusion and dilution methods including synergy tests. PFGE was used to study the relatedness of isolates. Genes encoding beta-lactamases were characterized by transfer assays, specific amplification and cloning. RESULTS: The eight isolates were closely related by PFGE analysis and highly related to a K. pneumoniae strain from Greece. They were highly resistant to beta-lactams, including aztreonam and imipenem (MIC > or =32 mg/L), and were positive by the imipenem-EDTA disc synergy test. Isolates were also resistant to aminoglycosides, newer quinolones and sulfamethoxazole, and showed an intermediate level of resistance to tetracycline. VIM-1 and SHV-5 beta-lactamases were revealed in all isolates by PCR. The analysis of plasmid contents of Escherichia coli DH10B electroporants expressing the VIM-1 beta-lactamase or the SHV-5 beta-lactamase confirmed that the two enzymes were coded by two different plasmids. The bla(VIM-1) gene was part of a class 1 integron that also included aac6, dhfrI and aadA genes and was similar to those reported from strains isolated in Greece. CONCLUSIONS: This study confirms the potential risk of spread of multiresistant bacteria with international transfer of patients.

The bHLH TAL-1/SCL regulates endothelial cell migration and morphogenesis.

The basic helix-loop-helix tal-1 gene (or scl), known for its fundamental role in embryonic and adult hematopoiesis in vertebrates, is also required for embryonic vascular remodeling. In adults, TAL-1 protein is undetectable in quiescent endothelium but it is present in newly formed vessels including tumoral vasculature, indicating its involvement in angiogenesis. Here, we demonstrate that TAL-1 expression is tightly regulated during in vitro angiogenesis: it is low during the initial step of migration and is upregulated during formation of capillary-like structures. We investigated whether ectopic expression of either wild-type TAL-1 or a dominant-negative mutant lacking the DNA-binding domain (Delta-bas) modulates the activity of human primary endothelial cells in the angiogenic processes of migration, proliferation and cell morphogenesis. Overexpression of either wild-type or Delta-bas TAL-1 affected chemotactic migration of primary endothelial cells without modifying their proliferative properties. Ectopic expression of wild-type TAL-1 accelerated the formation of capillary-like structures in vitro and, in vivo, enhanced vascularisation in mice (Matrigel implants) associated with a general enlargement of capillary lumens. Importantly, transduction of the mutant Delta-bas completely impaired in vitro angiogenesis and strongly inhibited vascularisation in mice. Taken together, our data show that TAL-1 modulates the angiogenic response of endothelial cells by stimulating cell morphogenesis and by influencing their behavior in migration. This study highlights the importance of TAL-1 regulation in postnatal vascular remodeling and provides the first physiological evidence that links TAL-1 activity to endothelial cell morphogenic processes.

Transcriptional activation of interleukin-8 by beta-catenin-Tcf4.

Nuclear translocation of beta-catenin and its association with Tcf/Lef factors are key steps in transduction of the Wnt signal, which is aberrantly activated in a variety of human cancers. In a search for new beta-catenin-Tcf target genes, we analyzed beta-catenin-induced alterations of gene expression in primary human hepatocytes, after transduction of either dominant stable beta-catenin or its truncated, transactivation-deficient counterpart by means of a lentiviral vector. cDNA microarray analysis revealed a limited set of up-regulated genes, including known Wnt targets such as matrilysin and keratin-1. In this screen, we identified the CXC chemokine interleukin 8 (IL-8) as a direct target of beta-catenin-Tcf4. IL-8 is constitutively expressed in various cancers, and it has been implicated in tumor progression through its mitogenic, motogenic, and angiogenic activities. The IL-8 promoter contains a unique consensus Tcf/Lef site that is critical for IL-8 activation by beta-catenin. We show here that the p300 coactivator was required for efficient transactivation of beta-catenin on this promoter. Ectopic expression of beta-catenin in hepatoma cells promoted IL-8 secretion, which stimulated endothelial cell migration. These data define IL-8 as a Wnt target and suggest that IL-8 induction by beta-catenin might be implicated in developmental and tumorigenic processes.