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Platelet-derived growth factor plays a critical role to convert bone marrow cells into glomerular mesangial-like cells. Background. Despite increasing interest in bone marrow–derived stem cells, little is known about critical factors that determine their fates both in vitro and in vivo. Recently, we have reported that bone marrow is a reservoir for glomerular mesangial cells in rats. To find a key factor responsible for the differentiation of bone marrow–derived cells into mesangial cells, we established a new culture system of rat bone marrow, which is based on serial replating and differential attachment to collagen types I and IV. Methods. Bone marrow cells that did not adhere to collagen type I within 24 hours were transferred to collagen type IV–coated dishes. Then, the cells attached to collagen type IV in the following 24 hours were maintained in the presence of 2% horse serum, 200 ng/mL of platelet-derived growth factor (PDGF)-BB, and 1 μmol/L of all- trans retinoic acid. In vivo effect of PDGF-B was also examined by introducing human PDGF-B gene into glomeruli. Results. After cultivation under the above condition for 7 days, approximately 14% of cells expressed Thy-1 and desmin, both of which are markers for rat mesangial cells. Thy-1++/desmin+ cells were stellate-shaped, and contracted in response to angiotensin II. When human PDGF-B gene was overexpressed in the glomeruli of chimeric rats whose bone marrow was transplanted from enhanced green florescent protein (EGFP) transgenic rats, the number of EGFP+ mesangial cells increased. This effect was canceled by prior introduction of a neutralizing molecule that is composed of PDGF receptor-β ligand binding site and IgG-Fc. Conclusion. These results indicate that PDGF-B plays a critical role to direct bone marrow–derived cells toward mesangial-like cells both in vitro and in vivo. [ABSTRACT FROM AUTHOR]

Hematopoietic and nonhematopoietic potentials of Hoechstlow/side population cells isolated from adult rat kidney. Background. Although the regenerative stem cell is expected to exist in many adult tissues, the cell contributing to the regeneration of the kidney remains unknown in its type and origin. Methods. In this study, we isolated cells that show low stain with a DNA-binding dye Hoechst 33342 (Hoechstlow cells) from adult rat kidney, and investigated their differentiation potentials. Results. Hoechstlow cells, generally termed side population cells, existed at a frequency of 0.03% to 0.1% in the cell suspension of the digested kidney. Analysis of the kidney-derived Hoechstlow cells after bone marrow transplantation indicated that some of the cells were derived from bone marrow. When enhanced green fluorescent protein (EGFP)-labeled kidney-derived Hoechstlow cells were intravenously transplanted into wild-type adult rats, EGFP+ cells were not detected in the kidney, but EGFP+ skeletal muscle, EGFP+ hepatocytes and EGFP+ bone marrow cells were observed. Even after the induction of the experimental glomerulonephritis and gentamicin-induced nephropathy that promote the differentiation of bone marrow–derived cells into repopulating mesangial cells and tubular component cells, respectively, EGFP+ mesangial or tubular cells were not observed. Neither with an in vitro system, which we established to produce mesangial-like cells from crude bone marrow culture, did Hoechstlow cells yield mesangial-like cells. Conclusion. These findings implicate that Hoechstlow cells in the kidney may have potentials for hematopoietic and nonhematopoietic lineages, but are not stem cells for renal cells, especially mesangial and tubular cells. [ABSTRACT FROM AUTHOR]