Characterization of Transplanted GFP+ Bone Marrow Cells into Adipose Tissue

Following transplantation of green fluorescent protein (GFP)-labeled bone marrow (BM) into irradiated, wild-type Sprague-Dawley rats, propagated GFP + cells migrate to adipose tissue compartments. In order to determine the relationship between GFP + BM-derived cells and tissue resident GFP − cells on the stem cell population of adipose tissue, we conducted detailed immunohistochemical analysis of chimeric whole fat compartments and subsequently isolated and characterized adipose-derived stem cells (ASCs) from GFP + BM chimeras. In immunohistochemistry, a large fraction of GFP + cells in adipose tissue were strongly positive for CD45 and smooth muscle actin, and evenly scattered around the adipocytes and blood vessels, while all CD45+ cells within the blood vessels were GFP+. A small fraction of GFP + cells with mesenchymal marker CD90 also existed in the perivascular area. Flow cytometric and immunocytochemical analyses showed that cultured ASCs were CD45 − /CD90 + /CD29 + . There was a significant difference in both the cell number and phenotype of the GFP + ASCs in two different adipose compartments, the omental (abdominal) and the inguinal fat (subcutaneous) pad; a significantly higher number of GFP − /CD90 + cells were isolated from the subcutaneous depot as compared to the abdominal depot. The in vitro adipogenic differentiation of the ASCs was achieved; however, all cells that had differentiated were GFP − . Based on phenotypical analysis, GFP + cells in adipose tissue in this rat model appear to be of both hematopoietic and mesenchymal origin; however, infrequent isolation of GFP + ASCs and their lack of adipogenic differentiation suggest that the contribution of BM to ASCs generation might be minor.