Guy Daculsi

Leukemia inhibitory factor and oncostatin M influence the mineral phases formed in a murine heterotopic calcification model : A Fourier transform-infrared microspectroscopic study

The study of bone mineralization processes is of considerable interest in understanding bone diseases and developing new therapies for skeletal disorders, particularly since bone homeostasis requires numerous cell types and a large cytokine network. Cell culture models of mineralization have often been used to study the cellular mechanisms of mineralization, but few data have been reported concerning the influence of extracellular matrix components and cytokines on the physicochemical properties of mineral. The purpose of this study was to analyze the effects of two cytokines, leukemia inhibitory factor (LIF) and oncostatin M (OSM), involved in bone metabolism on the physicochemical properties of bone mineral formed in a murine in vivo mineralization model. Murine bone marrow cells implanted under the kidney capsule in the presence or absence of cytokines led to heterotopic ossicle formation. A scanning electron microscopic microprobe revealed that heterotopic calcification had a lower (∼20%) Ca/P ratio after cytokine treatment as compared with the control without cytokine. Transmission electron microscopic analysis of cytokine‐treated ossicles showed numerous areas with low mineral density, whereas electron diffraction pattern revealed an apatitic phase. These areas were not observed in the absence of cytokine. Moreover, Fourier transform‐infrared microspectroscopy showed at the molecular level that the presence of either cytokine induced many microscopic areas in which short‐range order organization, such as incorporation of carbonate and crystallinity/maturity of ossicle mineral, were modified. LIF and OSM influenced mineral phase formation in the present model and may thus be key protagonists in bone mineral development and skeletal diseases.

Growth hormone stimulates multinucleated cell formation in long-term bone marrow cultures

Although the effects of growth hormone on bone metabolism are well-documented, their role in the regulation of immune responses such as the inflammatory process has not been thoroughly explored. This study investigated the formation of multinucleated cells (MNC) in long-term human bone marrow cultures. Experiments using 1 and 100 ng/ml of human recombinant growth hormone (hGH) and 10(-7) M of 1,25 dihydroxyvitamin D3 (VD3) showed that hGH increased the total number and nucleation of MNC. The effects of hGH were generally greater than those observed with VD3. Cytological and immunological characterization of MNC revealed several macrophage polykaryon features. MNC did not respond to calcitonin in a cyclic adenosine monophosphate assay and failed to resorb dentin slices. These results demonstrate that MNC formed in the presence of hGH and VD3 present an essentially macrophage polykaryon phenotype. In this context, growth hormone may be involved in the inflammatory process through upmodulation of macrophage polykaryon formation.