Hematopoietic stem cells in the hereditarily anemic Belgrade laboratory (b/b) rat

The Belgrade (b/b) rat has hereditary hypochromic microcytic anemia as the consequence of intracellular iron deficiency. Studies in the b/b rat have also demonstrated alteration in hematopoiesis at the progenitor cell level. In the present study, investigations were extended to the bone marrow hematopoietic stem cells as determined by measurements of marrow repopulating ability (MRA) and day 8 spleen colony-forming units (CFU-S-8). A reduced number of CFU-S-8 per femur was found, together with a low incidence per 10(5) bone marrow cells and a nondetectable proliferation rate. The proliferation rate did not increase after treating b/b rat bone marrow cells in vitro with a stimulator for CFU-S proliferation, indicating a proliferative block. The treatment of b/b rats with iron enhanced the proliferation rate and partially increased the number of CFU-S-8 in bone marrow. Chronic transfusion of b/b rats with washed RBC from non-anemic animals restored both the number and the proliferative response of bone marrow CFU-S-8. The MRA of b/b rats was reduced, but in proportion to the decrease in the bone marrow cellularity of these animals. MRA (pre-CFU-S) of b/b rats recovered completely after both iron treatment and chronic transfusions, suggesting that changes in the pre-CFU-S pool are secondary rather than directly induced by the genetic defect. These results indicate the importance for stem cell proliferation of normal oxygenation--the arterial oxygen content in b/b rats is six times lower than in (+/+, b/+) rats--which recovered after the iron treatment and was completely restored after chronic transfusions. High-dose iron therapy abrogated the proliferative block of CFU-S-8, but number of CFU-S-8 was not completely recovered in spite of normalized oxygenation, indicating a possible suppressive effect of iron overload on the marrow microenvironment.