Analysis by in Situ Hybridization of Cells Expressing mRNA for Tumor-Necrosis Factor in the Developing Thymus of Mice

We have used in situ hybridization to investigate the expression of TNF-α genes by thymic cells during fetal development in mice. In 14-day-old fetal thymuses, very scarce cells produce TNF-α mRNA. A second phase of cytokine gene expression starts on day 16. The density of positive cells progressively increases up to day 20. Thymuses at 15 days of gestation and after birth do not express detectable cytokine mRNA. In an attempt to identify the nature of the TNF-α mRNA-producing cells, acid phosphatase activity, which is characteristic of the macrophage lineage, was studied in the same thymuses. Acid phosphatase-positive cells only appear on day 15. Their frequency increases up to birth. However, no correlation can be established between acid phosphatase—and TNFα mRNA— positive cells. The results indicate that a small subset of thymic cells is responsible for TNF-α mRNA production during ontogeny: These cells are not yet identified. The possible role of TNF-α in thymic ontogeny is discussed

Leptin Reverts Pro-Apoptotic and Antiproliferative Effects of α-Linolenic Acids in BCR-ABL Positive Leukemic Cells: Involvement of PI3K Pathway

It is suspected that bone marrow (BM) microenvironmental factors may influence the evolution of chronic myeloid leukaemia (CML). In this study, we postulated that adipocytes and lipids could be involved in the progression of CML. To test this hypothesis, adipocytes were co-cultured with two BCR-ABL positive cell lines (PCMDS and K562). T cell (Jurkat) and stroma cell (HS-5) lines were used as controls. In the second set of experiments, leukemic cell lines were treated with stearic, oleic, linoleic or α-linolenic acids in presence or absence of leptin. Survival, proliferation, leptin production, OB-R isoforms (OB-Ra and OB-Rb), phosphoinositide 3-kinase (PI3k) and BCL-2 expression have been tested after 24h, 48h and 72h of treatment. Our results showed that adipocytes induced a decrease of CML proliferation and an increase in lipid accumulation in leukemic cells. In addition, CML cell lines induced adipocytes cell death. Chromatography analysis showed that BM microenvironment cells were full of saturated (SFA) and monounsaturated (MUFA) fatty acids, fatty acids that protect tumor cells against external agents. Stearic acid increased Bcl-2 expression in PCMDS, whereas oleic and linoleic acids had no effects. In contrast, α-linolenic acid decreased the proliferation and the survival of CML cell lines as well as BCL-2 and OB-R expression. The effect of α-linolenic acids seemed to be due to PI3K pathway and Bcl-2 inhibition. Leptin production was detected in the co-culture medium. In the presence of leptin, the effect of α-linolenic acid on proliferation, survival, OB-R and BCl-2 expression was reduced

Influence of Plasminogen Activator Inhibitor Type 1 on Choroidal Neovascularization

peer reviewedHigh levels of the plasminogen activators, but also their inhibitor, plasminogen activator inhibitor 1 (PAI-1), have been documented in neovascularization of severe ocular pathologies such as diabetic retinopathy or age-related macular degeneration (AMD). AMD is the primary cause of irreversible photoreceptors loss, and current therapies are limited. PAI-1 has recently been shown to be essential for tumoral angiogenesis. We report here that deficient PAI-1 expression in mice prevented the development of subretinal choroidal angiogenesis induced by laser photocoagulation. When systemic and local PAI-1 expression was achieved by intravenous injection of a replication-defective adenoviral vector expressing human PAI-1 cDNA, the wild-type pattern of choroidal angiogenesis was restored. These observations demonstrate the proangiogenic activity of PAI-1 not only in tumoral models, but also in choroidal experimental neovascularization sharing similarities with human AMD. They identify therefore PAI-1 as a potential target for therapeutic ocular anti-angiogenic strategies

H4 Histamine Receptors Mediate Cell Cycle Arrest in Growth Factor-Induced Murine and Human Hematopoietic Progenitor Cells

The most recently characterized H4 histamine receptor (H4R) is expressed preferentially in the bone marrow, raising the question of its role during hematopoiesis. Here we show that both murine and human progenitor cell populations express this receptor subtype on transcriptional and protein levels and respond to its agonists by reduced growth factor-induced cell cycle progression that leads to decreased myeloid, erythroid and lymphoid colony formation. H4R activation prevents the induction of cell cycle genes through a cAMP/PKA-dependent pathway that is not associated with apoptosis. It is mediated specifically through H4R signaling since gene silencing or treatment with selective antagonists restores normal cell cycle progression. The arrest of growth factor-induced G1/S transition protects murine and human progenitor cells from the toxicity of the cell cycle-dependent anticancer drug Ara-C in vitro and reduces aplasia in a murine model of chemotherapy. This first evidence for functional H4R expression in hematopoietic progenitors opens new therapeutic perspectives for alleviating hematotoxic side effects of antineoplastic drugs

Characterization of Spontaneous Bone Marrow Recovery after Sublethal Total Body Irradiation: Importance of the Osteoblastic/Adipocytic Balance

Many studies have already examined the hematopoietic recovery after irradiation but paid with very little attention to the bone marrow microenvironment. Nonetheless previous studies in a murine model of reversible radio-induced bone marrow aplasia have shown a significant increase in alkaline phosphatase activity (ALP) prior to hematopoietic regeneration. This increase in ALP activity was not due to cell proliferation but could be attributed to modifications of the properties of mesenchymal stem cells (MSC). We thus undertook a study to assess the kinetics of the evolution of MSC correlated to their hematopoietic supportive capacities in mice treated with sub lethal total body irradiation. In our study, colony-forming units – fibroblasts (CFU-Fs) assay showed a significant MSC rate increase in irradiated bone marrows. CFU-Fs colonies still possessed differentiation capacities of MSC but colonies from mice sacrificed 3 days after irradiation displayed high rates of ALP activity and a transient increase in osteoblastic markers expression while pparγ and neuropilin-1 decreased. Hematopoietic supportive capacities of CFU-Fs were also modified: as compared to controls, irradiated CFU-Fs significantly increased the proliferation rate of hematopoietic precursors and accelerated the differentiation toward the granulocytic lineage. Our data provide the first evidence of the key role exerted by the balance between osteoblasts and adipocytes in spontaneous bone marrow regeneration. First, (pre)osteoblast differentiation from MSC stimulated hematopoietic precursor's proliferation and granulopoietic regeneration. Then, in a second time (pre)osteoblasts progressively disappeared in favour of adipocytic cells which down regulated the proliferation and granulocytic differentiation and then contributed to a return to pre-irradiation conditions

Rejection of organ grafts: correlations of immunologic mechanisms and anatomic lesions

editorial reviewedLes antigènes majeurs et mineurs d'histocompatibilité présents dans les organes greffés déclenchent chez le receveur une réaction immunologique de rejet qui fait intervenir des anticorps cytotoxiques et des lymphocytes T helper et cytotoxiques. La compréhension de ces phénomènes permet un meilleur choix du donneur et une utilisation optimale des agents immunosuppresseurs

Preleukemic States: An Experimental Murine Model for Myelodysplastic Human Syndromes

Using a model of experimental leukemia in mice, we have demonstrated that tumor development depends upon interactions between preleukemic cells and their microenvironment whose functions are altered. Cytokine injections inhibit tumor development by inducing a functional restoration of this environment. Human myelodysplastic syndromes (MDS) are marrow pathologies considered as preleukemic stages. As in murine leukemias, it is possible that marrow environment could play a key role in their evolution. We currently establish a model of human hematopoiesis in NOD/SCID mice grafted with human bone fragments. We hope that this model would allow to analyse the role of the marrow stromal cells in MDS and to establish treatments restoring their functions

Cellules cibles et micro-environnement tissulaire dans le développement des lymphomes thymiques chez la souris: un modèle pour l'étude du rôle des facteurs de l'hôte dans la cancérogénèse

editorial reviewedLes lymphomes thymiques induits par irradiation chez la souris permettent d'étudier les influences endogènes qui contribuent au processus de cancérisation. Très tôt après le traitement, des cellules précancéreuses apparaissent dans le thymus. Le micro-environnement de cet organe est nécessaire à leur évolution vers le cancer. En outre, certains de ses composants sont altérés de façon irréversible pendant la période de latence précancéreuse. Ce phénomène est indispensable à la formation des tumeurs. Une greffe de moelle hématopoïétique après l'irradiation inhibe la formation des tumeurs. Toutefois, cette greffe ne prévient pas l'apparition des cellules précancéreuses. Celles-ci sont éliminées après quelques semaines, simultanément à une restauration du micro-environnement thymique.Radiation-induced thymic lymphomas in mice allow to study the endogenous influences, which contribute to the oncogenic process. Soon after irradiation, preneoplastic cells appear in the thymus. They require thymic microenvironment for progression to cancer. Some components of this environment are altered in an irreversible way during the prelymphomatous latent period. This phenomenon seems to play a critical role for lymphoma development. The graft does not inhibit the emergence of preneoplastic cells. However, these cells disappear after a few weeks, when thymic microenvironment is restored

Thymic nurse cells and radiation leukemia virus induced thymic lymphomas in C57BL mice.

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