Biomedical subjects

Nathalie Leclerc

Publications and source records attributed to Nathalie Leclerc.

6 recordsLinked to original sources

PubMed2006

Peripheral cannabinoid receptor, CB2, regulates bone mass.

The endogenous cannabinoids bind to and activate two G protein-coupled receptors, the predominantly central cannabinoid receptor type 1 (CB1) and peripheral cannabinoid receptor type 2 (CB2). Whereas CB1 mediates the cannabinoid psychotropic, analgesic, and orectic effects, CB2 has been implicated recently in the regulation of liver fibrosis and atherosclerosis. Here we show that CB2-deficient mice have a markedly accelerated age-related trabecular bone loss and cortical expansion, although cortical thickness remains unaltered. These changes are reminiscent of human osteoporosis and may result from differential regulation of trabecular and cortical bone remodeling. The CB2(-/-) phenotype is also characterized by increased activity of trabecular osteoblasts (bone-forming cells), increased osteoclast (the bone-resorbing cell) number, and a markedly decreased number of diaphyseal osteoblast precursors. CB2 is expressed in osteoblasts, osteocytes, and osteoclasts. A CB2-specific agonist that does not have any psychotropic effects enhances endocortical osteoblast number and activity and restrains trabecular osteoclastogenesis, apparently by inhibiting proliferation of osteoclast precursors and receptor activator of NF-kappaB ligand expression in bone marrow-derived osteoblasts/stromal cells. The same agonist attenuates ovariectomy-induced bone loss and markedly stimulates cortical thickness through the respective suppression of osteoclast number and stimulation of endocortical bone formation. These results demonstrate that the endocannabinoid system is essential for the maintenance of normal bone mass by osteoblastic and osteoclastic CB2 signaling. Hence, CB2 offers a molecular target for the diagnosis and treatment of osteoporosis, the most prevalent degenerative disease in developed countries.

Animals↗

PubMed2005

Glucocorticoids inhibit osteocalcin transcription in osteoblasts by suppressing Egr2/Krox20-binding enhancer.

OBJECTIVE: Glucocorticoids are widely used for the management of rheumatoid arthritis. Osteoporosis is a major side effect of glucocorticoid therapy and is attributable to inhibition of bone formation. We developed an osteoblast culture system in which glucocorticoids strongly inhibit development of the osteoblast phenotype, including expression of the bone-specific osteocalcin (OC) gene. Using this gene as a model, the goal of this study was to discover glucocorticoid-sensitive transcriptional mechanisms in osteoblasts. METHODS: Dexamethasone (DEX; 1 microM) was administered to murine MC3T3-E1 osteoblastic cultures under conditions that inhibit mineralized extracellular matrix formation and OC messenger RNA levels by >10-fold. Because standard (short-term) transient transfection assays with OC promoter-reporter constructs did not recapitulate the strong DEX-mediated repression, mapping of OC negative glucocorticoid response elements (GREs) was performed initially by stable transfection and then with long-term transient transfection assays. Transcription factor binding to the OC negative GRE was studied by electrophoretic mobility shift assays. RESULTS: Several-fold repression of OC-luciferase constructs was recapitulated in stable and long-term transient transfection assays, in which the transfected cells were allowed to progress to a sufficiently advanced developmental stage. Analysis of a 5' promoter deletion series mapped an OC negative GRE to a 15-bp G/C-rich motif (-161/-147) located just upstream of the binding site for the osteoblast master transcription factor Runx2. Oligonucleotides encompassing this element and MC3T3-E1 cell extracts formed a protein-DNA complex that contained an Egr/Krox family member(s). Complex formation was competed by either an oligonucleotide containing 2 consensus Egr motifs or by anti-Egr2/Krox20 antibodies. Three copies of this Krox-binding element conferred 20-fold transcriptional activation on the 147-bp basal OC promoter in osteoblasts, and the enhancer activity was inhibited by DEX. Enhancer activity was not observed in 10T1/2 fibroblasts unless these cells were cotransfected with Runx2. CONCLUSION: An Egr2/Krox20-binding site located immediately upstream of the Runx2 site of the mouse OC promoter was identified as an enhancer in osteoblasts, whose activity is repressed by glucocorticoids. Sequence similarity suggests that such a mechanism is likely operative in both murine and human cells. Because glucocorticoids inhibit Egr2/Krox20 expression in osteoblasts, and because trabecular bone formation is arrested in Egr2/Krox20-knockout mice, the inhibition of Egr2/Krox20 activity likely contributes to glucocorticoid-induced osteoporosis.

Animals↗

PubMed2005

Lung cancer risk assessment in relation with personal exposure to airborne particles in four French metropolitan areas.

OBJECTIVE: The objective of this study was to quantify the total number of lung cancer deaths attributable to chronic exposure to fine particles (pm2.5) among adult populations of four French urban populations (Grenoble, Rouen, Paris, and Strasbourg). METHODS: A geographic information system (GIS) was used to extrapolate personal average exposures to the total population of each metropolitan area across three sectors contrasted in terms of local sources of pollutants. We followed a health impact assessment approach by using the risk estimates in the CSP II study. RESULTS: The annual number of lung cancer cases attributable to pm2.5 chronic exposure ranged from 12 to 404 according to the city. Among these deaths, up to 60% occurred, in the Paris metropolitan area in the urban sector most exposed to traffic emissions. CONCLUSIONS: The health impact of chronic exposures to urban air pollution in metropolitan areas of developed countries warrants further efforts to abate sources of toxicants and to reduce exposure. Traffic emissions still contribute significantly to the total lung cancer burden in France.

Adult↗

PubMed2004

Gene expression profiling of glucocorticoid-inhibited osteoblasts.

Glucocorticoid (GC) treatment for the management of autoimmune and inflammatory diseases is associated with decreased bone formation and increased risk for fracture. In MC3T3-E1 cell cultures, 0.1-1 microM dexamethasone (DEX) arrests development of the osteoblast phenotype when administration commences at a commitment stage around the time of confluency. To gain new insights into GC-induced osteoporosis, we performed microarray-based gene expression analysis of GC-arrested MC3T3-E1 cultures, 2.5 days after the administration of DEX. Of the >12 000 transcripts interrogated, 74 were up-regulated and 17 were down-regulated by at least 2.5-fold (P < or = 0.05). Some of these genes, such as Mmp13, Serum/GC-regulated kinase and Tieg, have previously been reported as GC-responsive. Others are shown here for the first time to respond to GCs. DEX strongly repressed Krox20/Egr2 at both the mRNA and the protein level. This is especially significant because mice lacking this transcription factor develop osteoporosis. The data also suggest that the bone morphogenetic protein (BMP) pathway, which is involved in regulating bone mass, and other pathways that influence BMP signaling, are abrogated by GCs: (i) DEX increased the mRNA levels of the BMP antagonists Follistatin and Dan; (ii) DEX increased the levels of p21 Rasgap3 and Ptpn16/MKP-1 mRNAs, negative regulators of the MAP kinase pathway; and (iii) DEX decreased Cox mRNA levels. DEX also increased thrombospondin mRNA levels, which negatively regulate bone mass in vivo, as well as the adipocytic marker Fkbp51. These and other observations disclose novel gene targets, whose regulation by GCs in osteoblasts may shed light on and provide new therapeutic approaches to osteoporosis.

3T3 Cells↗

PubMed2003

Brief bone morphogenetic protein 2 treatment of glucocorticoid-inhibited MC3T3-E1 osteoblasts rescues commitment-associated cell cycle and mineralization without alteration of Runx2.

Glucocorticoids (GCs) inhibit bone formation in vivo. In MC3T3-E1 osteoblasts, chronic administration of 1 microm dexamethasone (DEX) starting at confluency results in >98% inhibition of bone morphogenetic protein 2 (BMP-2) expression and apatite mineral deposition. Here, it is shown that brief exposure to recombinant human BMP-2 (rhBMP-2), as short as 6 h, is sufficient to induce irreversible commitment to mineralization in DEX-treated cultures. RhBMP-2 dose dependently rescued mineralization but not collagen accumulation in DEX-inhibited cultures. The selective restoration of mineralization was evident in the higher mineral to matrix ratios of DEX/rhBMP-2 co-treated cultures compared with control. We tested the involvement of the runt-related transcription factor 2 (Runx2) in the DEX inhibition and rhBMP-2 rescue of mineralization. Surprisingly, DEX did not decrease Runx2 DNA binding activity, transactivation, or association with the endogenous osteocalcin gene promoter. Furthermore, the rhBMP-2 rescue did not involve Runx2 stimulation, suggesting an important role for factors other than Runx2 in BMP-2 action. Finally, we studied the differentiation-related cell cycle, which persists during commitment to mineralization in untreated cultures, but is inhibited along with mineralization in DEX-treated cultures. Although both rhBMP-2 alone and DEX alone were antimitogenic, rhBMP-2 stimulated this cell cycle in DEX-inhibited cultures. In conclusion, brief rhBMP-2 treatment restores mineralization in DEX-inhibited MC3T3-E1 osteoblasts via a mechanism different from Runx2 stimulation. This restoration may be functionally related to the accompanying rescue of the differentiation-related cell cycle. The efficacy of short term BMP-2 treatment supports the potential of short-lived BMP vectors for skeletal therapy in both traditional and gene therapeutic approaches.

Alkaline Phosphatase↗

PubMed2002

Hydrometallurgical recovery of zinc and lead from electric arc furnace dust using mononitrilotriacetate anion and hexahydrated ferric chloride.

The purpose of this work was to study the feasibility at laboratory-scale of a new hydrometallurgical process for treating electric arc furnace dusts (EAFD). The proposed process is intended to extract zinc and lead from EAFD without destroying the iron oxides matrix. So, this material can be recycled by the steel industry. Independently of the origin of the samples, major mineralogical forms present in these wastes are Fe3O4, ZnO, ZnFe2O4 and PbOHCl. The proposed process consists of a hydrometallurgical treatment of wastes based on selective leaching of zinc and lead. Initially, a leaching is carried out utilizing a chelating agent, nitrilotriacetate anion (NTA3-), as the protonated form HNTA2-. Treatment of five EAFD samples for an hour at room temperature with a molar solution of reagent results in total leaching of the ZnO. In all cases the solubilized iron does not exceed 3 wt.%. The recovery of zinc and lead is performed by precipitation of metallic sulfides with a solution of Na2S4 sodium tetrasulfide 2M. These metallic sulfides can be used as metallurgical raw materials and the chelating reagent can be reused in the process after pH adjustment. The results of the normalized leaching test AFNOR X31-210 conducted on the leaching residues, shows that all the samples meet acceptance thresholds for hazardous wastes landfill. However, the residues contain a considerable amount of zinc as ZnFe2O4. The extraction of the zinc element requires the destruction of the ferrite structure. In this process, ZnFe2O4 is treated by FeCl3.6H2O. The reaction consists in a particle O2-/Cl- exchange allowing the recovery of zinc as ZnCl2 and iron as hematite Fe2O3. The separation of these products is accomplished by simple aqueous leaching. All of the zinc is extracted in a 8h treatment at 150 degrees C with a molar ratio FeCl3.6H2O/ZnFe2O4 equal to 10. Ultimate solid residues, which have been concentrated in iron, can be oriented towards the steel industry.

Acetates↗