Evidence is mounting that an increasing number of cell populations in the adult organism already committed and/or differentiated retain the ability to reprogram themselves and give rise to a different phenotype. Bone marrow stromal cells have long been recognized as early progenitor cells for osteoblasts, chondrocytes, hematopoietic-supportive fibroblasts and adipocytes. Recent reports though have demonstrated a potential of cell populations outside the bone marrow environment to sustain bone formation under specific circumstances. The formation of bone nodules in the spleen of @entity59 @entity19 has been recently reported (Macias et al. (2001): J. Clin. Invest. 107, 949 - 959). We thus postulated that a cell population exists in the spleen that under particular microenvironmental conditions is able to reprogram itself and pursue a fate other than the tissue-specific one. Therefore we isolated and expanded in vitro spleen-derived stromal cells. After expansion, these cells were challenged with culture conditions designed to induce osteogenic differentiation. We hypothesized that the combination of a proliferating factor ( @entity664 ) and a differentiating hormone ( @entity619 ) would allow us to induce spleen-derived stromal cells to proliferate and at the same time to express osteoblast-specific genes. Thus, spleen-derived stromal cells were isolated from @entity35 spleen and expanded in the presence of @entity664 and @entity619 . Once primary cultures reached confluence they were either switched to an osteo-inductive medium or implanted in @entity465 @entity19 . Although no bone formation was observed in in vivo experiments, in vitro spleen-derived stromal cells were able to deposit a mineralized matrix. Gene expression, as revealed by RT-PCR analysis, evidenced that the deposition of a mineralized matrix was concomitant with the expression of @entity6037 and @entity9356 , along with alkaline phosphatase and bone sialoprotein. Our data suggest that @entity35 spleen-derived stromal cells can undergo osteogenic differentiation in a permissive microenvironment.

Osteogenic potential of XXXX spleen stromal cells.

@entity6037 :: ('367218(Tax:10116)', 'Gene') :: ['CBFA1'] @entity664 :: ('54250(Tax:10116)', 'Gene') :: ['fibroblast growth factor 2'] @entity59 :: ('16191(Tax:10090)', 'Gene') :: ['IL-5'] @entity19 :: ('10090', 'Species') :: ['mice', 'transgenic mice'] @entity619 :: ('MESH:D003907', 'Chemical') :: ['dexamethasone'] @entity465 :: ('MESH:D007153', 'Disease') :: ['immunodeficient'] @entity9356 :: ('81613(Tax:10116)', 'Gene') :: ['osteocalcin'] @entity35 :: ('10116', 'Species') :: ['rat']
@entity35 :: (10116,Species) :: ['rat']
