| Research Abstract |
It has been consistently observed that primitive hematopoietic cells are preferentially located within the adherent stromal cell layer, whereas hematopoietic cells of greater maturity migrate to the surface of the layer and shed into the culture medium. As a model system for hematopoietic cell migration, a new primitive hematopoietic cell line, THS119, was established. THS119 exhibited Lin negative, Sca-1 positive, and c-Kit positive, grew and survived undemeath marrow stromal cell layers. When THS119 cells were seeded onto a stromal cell layer, they invaded the layers before beginning to proliferate within the restricted space between the culture substratum and the stromal cells, which may be equivalent to the regions found in the microenvironment of the bone marrow in vivo. The ability of the THS119 cells to invade these stromal cell layers was dependent on the inclusion of serum in the culture medium. This was apparently due to a requirement for lipids contained in serum. Their invasion of the stromal cell layers in serum-free cultures could be triggered by addition of sphingosine-1-phosphate (S1P) or lysophosphatidic acid (LPA). Between the two possible receptors of S1P and LPA, edg-1 and edg-2, expression of edg-2 only was found to be correlated with immaturity and/or invasive activity of the primitive hematopoietic cells. Expression of edg-2 was well correlated with the invasion activity of hematopoietic cells because parental THS119 cells, but not stroma-independent THS119 sub-lines, the cobblestone-forming fraction, but not mature shed cells in long-term bone marrow cultures. These results suggest the importance of specific lipids and their specific receptors on the invasive activity of primitive hematopoietic cells in the hematopoietic microenvironment.
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