Developmental regulation of p53-dependent radiation-induced thymocyte apoptosis in mice.

The production of T cell receptor αß(+) (TCRαß(+) ) T lymphocytes in the thymus is a tightly regulated process that can be monitored by the regulated expression of several surface molecules, including CD4, CD8, cKit, CD25 and the TCR itself, after TCR genes have been assembled from discrete V, D (for TCR-ß) and J gene segments by a site-directed genetic recombination. Thymocyte differentiation is the result of a delicate balance between cell death and survival: developing thymocytes die unless they receive a positive signal to proceed to the next stage. This equilibrium is altered in response to various physiological or physical stresses such as ionizing radiation, which induces a massive p53-dependent apoptosis of CD4(+) CD8(+) double-positive (DP) thymocytes. Interestingly, these cells are actively rearranging their TCR-α chain genes. To unravel an eventual link between V(D)J recombination activity and thymocyte radio-sensitivity, we analysed the dynamics of thymocyte apoptosis and regeneration following exposure of wild-type and p53-deficient mice to different doses of γ-radiation. p53-dependent radio-sensitivity was already found to be high in immature CD4(-) CD8(-) (double-negative, DN) cKit(+) CD25(+) thymocytes, where TCR-ß gene rearrangement is initiated. However, TCR-αß(-) CD8(+) immature single-positive thymocytes, an actively cycling intermediate population between the DN and DP stages, are the most radio-sensitive cells in the thymus, even though their apoptosis is only partially p53-dependent. Within the DP population, TCR-αß(+) thymocytes that completed TCR-α gene recombination are more radio-resistant than their TCR-αß(-) progenitors. Finally, we found no correlation between p53 activation and thymocyte sensitivity to radiation-induced apoptosis.

Cadmium and T cell differentiation: limited impact in vivo but significant toxicity in fetal thymus organ culture.

DNA lesions, including oxydated bases, nucleotide damage and double strand breaks, are continuously produced in living cells and represent a threat for genetic stability. Highly conserved repair processes have evolved to maintain DNA integrity. Cadmium (Cd) is an environmental carcinogenic pollutant known to inactivate several proteins involved in DNA repair systems while at the same time creating an oxidative stress that can result in additional DNA lesions. Cd also has potent immunotoxic effects. DNA repair by non-homologous end joining (NHEJ) is absolutely required for T lymphocyte differentiation. In this study, we examined the impact of Cd on non-homologous end joining pathway by analyzing T cell development in the thymus of mice that received Cd-supplemented drinking water. In vivo, the absence of major alteration indicates that Cd does not affect NHEJ, despite its accumulation in the thymus. Cd contamination affects only a discrete population of developing thymocytes. However, these cells are functional as the cellular response observed in mice following gamma-radiation exposure is identical in treated and control mice. Furthermore, Cd diet did not perturb the redox status in thymocytes and more importantly did not generate significant DNA lesions in organs that accumulate the highest concentration of Cd. Our results show that in vivo, Cd does not affect NHEJ or base and nucleotide repair, and that Cd toxicity to T cells is rather linked to cell cycle perturbations.

The uremic solute indoxyl sulfate induces oxidative stress in endothelial cells.

BACKGROUND: Endothelial dysfunction and oxidative stress are matters of concern in patients with chronic renal failure (CRF). Uremic solutes retained in these patients could be involved in these processes. Notably, the protein-bound uremic solute indoxyl sulfate induces endothelial dysfunction in vitro, and has shown pro-oxidant effects. OBJECTIVE: To demonstrate that indoxyl sulfate is a potential mediator of oxidative stress in endothelial cells in vitro. METHODS: Indoxyl sulfate-induced oxidative stress in human umbilical vein endothelial cells (HUVEC) was studied by measuring reactive oxygen specie (ROS) production by cytofluorimetry, by analyzing the involvement of the pro-oxidative enzymes NAD(P)H oxidase, xanthine oxidase, and NO synthase, and by measuring the levels of the non-enzymatic antioxidant glutathione. RESULTS: We showed that indoxyl sulfate induced a significant production of ROS in HUVEC, with or without human serum albumin. We then investigated the role of pro-oxidative enzymes and measured the levels of the antioxidant glutathione. The NAD(P)H oxidase inhibitors, DPI, and apocynin, inhibited ROS production, whereas inhibitors of xanthine oxidase, NO synthase, and mitochondrial ROS had no effect. Interestingly, indoxyl sulfate strongly decreased the levels of glutathione, one of the most active antioxidant systems of the cell. In addition, the ROS production mediated by indoxyl sulfate was inhibited by the antioxidants vitamin C, vitamin E, and NAC. CONCLUSION: The uremic solute indoxyl sulfate enhances ROS production, increases NAD(P)H oxidase activity, and decreases glutathione levels in endothelial cells. Thus, indoxyl sulfate induces oxidative stress by modifying the balance between pro- and antioxidant mechanisms in endothelial cells.

Elevation of circulating endothelial microparticles in patients with chronic renal failure.

BACKGROUND: Chronic renal failure patients are at high risk of cardiovascular events and display endothelial dysfunction, a critical element in the pathogenesis of atherosclerosis. Upon activation, the endothelium sheds microparticles, considered as markers of endothelial dysfunction that also behave as vectors of bioactive molecules. AIM: To measure plasma levels of endothelial microparticles (EMPs) in chronic renal failure patients (CRF), either undialyzed or hemodialyzed (HD), and to investigate the ability of uremic toxins to induce EMP release in vitro. METHODS: Circulating EMPs were numerated by flow cytometry, after staining of platelet-free plasma with phycoerythrin (PE)-conjugated anti-CD144 (CD144+ EMP) or anti-CD146 (CD146+ EMP) monoclonal antibodies. Platelet MP (CD41+ PMP), leukocyte MP (CD45+ leukocyte microparticles (LMP)), and annexin-V+ MPs were also counted. In parallel, MPs were counted in supernatant of human umbilical vein endothelial cells incubated with uremic toxins [oxalate, indoxyl sulfate, p-cresol, and homocysteine (Hcy)], at concentrations found in patients. RESULTS AND CONCLUSIONS: CD144+ EMP and CD146+ EMP levels were significantly higher in CRF and HD patients than in healthy subjects. Furthermore, annexin-V+ MPs were elevated in both groups of uremic patients, and CD41+ PMP and CD45+ LMP were increased in CRF and HD patients, respectively. In vitro, p-cresol and indoxyl sulfate significantly increased both CD146+ and annexin-V+ EMP release. Increased levels of circulating EMP in CRF and HD patients represent a new marker of endothelial dysfunction in uremia. The ability of p-cresol and indoxyl sulfate to increase EMP release in vitro suggests that specific uremic factors may be involved in EMP elevation in patients.

[Central nervous tuberculosis in patients non-VIH: seven case reports]. / Tuberculose cérébroméningée chez l'adulte séronégatif pour le VIH: à propos de 7 cas.

PURPOSE: Tuberculosis involving the central nervous system (CNS) is rarely observed in non immuno-compromised hosts. We report herin the various clinical, biological and radiological manifestations observed in 7 patients with CNS tuberculosis. METHODS: Clinical and biological records of 7 patients with CNS tuberculosis were retrospectively studied. All patients had encephalic CT-scan and MRI in the course of the disease. RESULTS: 5 women and 2 men with a mean age of 38.4 years initially initially presented with headache (n = 6), fever (n = 5), meningeal irritation (n = 3), localizing neurological signs (n = 1). Lumbar punction revealed lymphocytic meningitis (n = 6/7). Mycobacterium tuberculosis or bovis was isolated in 3 patients only. Cerebral tomodensitography or magnetic resonance imaging were initially normal in most of cases (n = 4/7), but discovered in the course of disease basilar meningitis (n = 6), hydrocephalus (n = 6), abcess or tuberculoma (n = 4). In all the patients, initiation of the treatment was complicated by clinical and/or biological deterioration, called paradoxal reaction, leading in all cases to glucocorticoid adjunction, with various final results. Indeed, 4 patients developed neurological sequelae. No patient died. CONCLUSION: CNS tuberculosis is a rare disease in non immunocompromised patients whose diagnostic may be difficult due to the absence of specific clinical symptoms, negative initial radiological examination, as well as delayed and often negative bacterial isolation. Paradoxal reaction appeared to be frequent despite specific antibiotherapy and underlines the beneficial effects of addictive corticosteroids.

Differential regulation of nitric oxide synthase-II mRNA by growth factors in rat, bovine, and human retinal pigmented epithelial cells.

Retinal pigmented epithelial cells (RPE cells) express the inducible isoform of NO synthase (NOS-II) after stimulation by cytokines and endotoxin. We have attempted to describe and compare the effect of fibroblast growth factor (FGF) and transforming growth factor beta (TGFbeta) on NOS-II mRNA level in three different cell species: rat, bovine, and human. Northern blot analysis demonstrated that, in the rat RPE cells, FGF upregulates and TGFbeta inhibits NOS-II mRNA accumulation, whereas in the bovine cells, the opposite effect appears. For the human RPE cells, RT-PCR analysis demonstrated that FGF upregulates and TGFbeta inhibits NOS-II mRNA accumulation, as in rat cells, even though the effect of TGFbeta was weaker. Thus, this study demonstrates that marked differences in growth factors regulating NOS-II occur between species, suggesting fundamental signal transduction differences at some level between rat, human, and cow.

Role of interferon regulatory factor-1 and mitogen-activated protein kinase pathways in the induction of nitric oxide synthase-2 in retinal pigmented epithelial cells.

Bovine retinal pigmented epithelial cells express an inducible nitric oxide synthase (NOS-2) after activation with interferon-gamma (IFN-gamma) and lipopolysaccharide (LPS). Experiments were performed to investigate the involvement of interferon regulatory factor-1 (IRF-1) on NOS-2 induction and its regulation by NOS-2 inhibitors such as pyrrolidine dithiocarbamate (PDTC), an antioxidant, or protein kinase inhibitors. Analysis by transitory transfections showed that LPS, alone or with IFN-gamma, stimulated activity of the murine NOS-2 promoter fragment linked upstream of luciferase and its suppression by PDTC and by the different protein kinase inhibitors, genistein (tyrosine kinase inhibitor), PD98059 (mitogen-actived protein (MAP) kinase kinase inhibitor), and SB 203580 (p38 MAP inhibitor). Using specific antibodies, we have confirmed that extracellular signal-regulated kinases and p38 MAP kinase were activated by LPS and IFN-gamma in retinal pigmented epithelial cells. Analysis by reverse transcriptase-polymerase chain reaction, Western blot, and electrophoretic mobility shift assay demonstrated that IFN-gamma alone or combined with LPS induced an accumulation of IRF-1 mRNA and protein and IRF-1 DNA binding. Transfections assays with the IRF-1 promoter showed an induction of this promoter with IFN-gamma, potentiated by LPS. The decrease of LPS/IFN-gamma-induced IRF-1 promoter activity, IRF-1 synthesis, and IRF-1 activation, by PDTC, genistein, PD98059, and SB 203580, could explained in part the inhibition of the NOS-2 induction by these compounds. Our results demonstrate that IRF-1 is necessary for NOS-2 induction by LPS and IFN-gamma and that its synthesis requires the involvement of a redox-sensitive step, the activation of tyrosine kinases, and extracellular signal-regulated kinases 1/2 and p38 MAP kinases.

Tyrosine kinase inhibitors and antioxidants modulate NF-kappaB and NOS-II induction in retinal epithelial cells.

Bovine retinal pigmented epithelial (RPE) cells express an inducible nitric oxide synthase (NOS-II) after activation with interferon-gamma (IFN-gamma) and lipopolysaccharide (LPS). Experiments were performed to investigate the effects of tyrosine kinase inhibitors (genistein and herbimycin A) and antioxidants [pyrrolidine dithiocarbamate (PDTC) and butyl hydroxyanisol] on NOS-II induction. The LPS-IFN-gamma-induced nitrite release was inhibited in a concentration-dependent manner by these compounds. Analysis by Northern blot showed that this inhibitory effect correlated with a decrease in NOS-II mRNA accumulation. Analysis by electrophoretic mobility shift assay of the activation of the transcription factor nuclear factor-kappaB (NF-kappaB) involved in NOS-II induction demonstrated that LPS alone or combined with IFN-gamma induced NF-kappaB binding. NF-kappaB activation was not changed by the presence of tyrosine kinase inhibitors but was totally prevented by PDTC pretreatment. Immunocytochemistry experiments confirmed the reduction of the nuclear translocation of NF-kappaB only by PDTC. Our results demonstrated the existence in retinal pigmented epithelial cells of different intracellular signaling pathways in NOS-II induction, since tyrosine kinase inhibitors blocked NOS-II mRNA accumulation without inhibiting NF-kappaB activation. Furthermore, the LPS-IFN-gamma-induced NOS-II mRNA accumulation was sensitive to cycloheximide, suggesting that, in addition to NF-kappaB, transcriptional factors that require new protein synthesis are involved in NOS-II induction.

Inhibition of inducible nitric oxide synthase expression by interferons alpha and beta in bovine retinal pigmented epithelial cells.

Bovine retinal pigmented epithelial (RPE) cells express an inducible nitric oxide synthase (NOS-2) after activation with interferon (IFN)-gamma and lipopolysaccharide (LPS). Experiments were performed to investigate the effects of IFN-alpha and IFN-beta on NOS-2 activity. These types of interferons did not aid LPS in the production of nitrite, but markedly inhibited in a concentration-dependent manner the nitrite release due to LPS/IFN-gamma. Analysis by Western and Northern blots showed that RPE cells co-stimulated with IFN-alpha or IFN-beta with LPS/IFN-gamma accumulated lower levels of NOS-2 protein and mRNA than in the presence of LPS/IFN-gamma alone. The presence of IFN-alpha or IFN-beta did not accelerate mRNA degradation, implying that these interferons did not affect NOS-2 mRNA stability, but more probably NOS-2 gene expression. Furthermore, IFN-gamma binding studies demonstrated that the inhibitory effect of IFN-alpha and IFN-beta is not caused by a blocking of IFN-gamma receptors. Analysis of NF-kappaB activation by electrophoretic mobility shift assay demonstrated that LPS/IFN-gamma-induced NF-kappaB binding was not changed by the presence of IFN-alpha. However, similar experiments revealed that the activation of interferon regulatory factor-1 (IRF-1) by LPS/IFN-gamma was decreased by IFN-alpha. This phenomenon could be due to the decline of IRF-1 mRNA and the up-regulation of IRF-2 mRNA, an IRF-1 repressor, by IFN-alpha. These results suggest that the inhibitory effect of IFN-alpha and -beta on NOS-2 induction could be partially explained by their effect on the induction of the IRFs, which were involved in NOS-2 gene transcription.

Peroxynitrite cytotoxicity on bovine retinal pigmented epithelial cells in culture.

Peroxynitrite induced in vitro a dose dependent toxicity on retinal pigmented epithelial (RPE) cells. Cell death was partially mediated by apoptosis as demonstrated by nuclear fragmentation and TdT-mediated dUTP nick-end labeling assay. Peroxynitrite-induced tyrosine nitration was revealed by immunocytochemistry, both in the cytoplasm and in the nucleus of the cells. Nitration was not observed in RPE cells, producing nitric oxide (NO) after stimulation by lipopolysacharide and interferon-g (IFN-gamma), suggesting that peroxynitrite was not formed in vitro in such conditions. Peroxynitrite could be responsible for the retinal damages observed in pathological conditions in which NO has been demonstrated to be involved. In this context, EGb761, identified as a free radical scavenger, was showed herein to protect RPE cells against peroxynitrite injury.

Fibroblast growth factors decrease inducible nitric oxide synthase mRNA accumulation in bovine retinal pigmented epithelial cells.

Bovine retinal pigmented epithelial cells (RPE cells), after activation with interferon gamma (IFN gamma) and lipopolysaccharide (LPS), express an inducible nitric oxide (NO) synthase. This activity can be inhibited by the fibroblast growth factors (FGF), FGF-1 (acidic FGF) and FGF-2 (basic FGF). We have attempted to elucidate the molecular mechanisms involved in the FGF inhibition of NO synthase activity. Analysis by immunocytochemistry and Western blot using a polyclonal antibody against the inducible NO synthase of rat liver reveals that RPE cells co-stimulated with FGF-2 and LPS/IFN gamma accumulate lower levels of NO synthase than in the absence of FGF-2. Northern blot analysis by cross-species hybridization with a mouse macrophage NO synthase cDNA probe shows that a 4.4-kb mRNA accumulates when RPE cells are activated with LPS/IFN gamma. The level of inducible NO synthase mRNA in LPS/IFN gamma-activated RPE cells is markedly reduced by FGF-1 or FGF-2 treatment. Message stability studies revealed that the presence of FGF did not accelerate mRNA degradation, implying that FGF did not act on inducible NO synthase mRNA stability, but more probably on its expression. Furthermore an effect of FGF on IFN gamma receptors was excluded, since IFN gamma binding was not altered by FGF. Since NO acts as a cytostatic compound, FGF, by preventing NO synthase expression in RPE cells, may protect the retina from endotoxin and cytokine-mediated tissue damage.