Anemia of Chronic Renal Failure Is Associated with Much Higher Frequency of Apoptosis in Erythroid Progenitor in a Mouse Model.

Insufficient production of erythropoietin (EPO) is one of the important causes of anemia of patients with chronic renal failure (CRF). Recombinant human erythropoietin (rh-EPO) administration results in a dramatic improvement of anemia in these patients. In ASH meeting 2001, we reported that excessive apoptosis in erythroid progenitor was observed in anemia of CRF patients before rh-EPO administration. In this study, we established a mouse model of anemia of CRF to confirm the hypothesis that excessive apoptosis in erythroid progenitor induced anemia. C57B6 male mice was treated with adenine-rich diets (ADRD) for 8 weeks. Serum blood urea nitrogen (BUN), creatinine (Crt) and complete blood count (CBC) were measured every week. The frequency of apoptosis in erythroid progenitor and mature erythroblasts were evaluated by three color flow cytometric analysis. Apoptotic cells were analyzed by AnnexinV. The cell populations of erythroid progenitor were identified as CD34(+)erythropoietin-receptor (EPO-R)(+) cells and mature erythroblasts identified as CD34(-)EPO-R(+) cells. Serum BUN and Crt levels began to elevate from 2 weeks after ADRD administration (BUN; 40.1±4.6, 73.2±14.4, 150.7±11.6, 164.0±8.4, 193.0±23.3mg/dl, Crt; 0.06±0.04, 0.30±0.03, 0.51±0.07, 0.68±0.09, 0.80±0.17mg/dl, n=5: mean±SD at 0, 2, 4, 6 and 8 weeks after ADRD administration, respectively). Hb and Ht began to decrease from 6 and 4 weeks after ADRD administration (Hb; 13.6±0.4, 13.3±0.3, 13.2±0.2, 10.2±0.5, 8.3±0.5 g/dl, Ht; 52.4±1.4, 49.4±1.7, 43.6±0.2, 35.4±1.8, 30.8±1.6%, n=5: mean±SD at 0, 2, 4, 6 and 8 weeks after ADRD administration, respectively). Serum EPO levels were not elevated after ADRD administration, regardless of anemia. Much higher frequency of apoptosis was observed in erythroid progenitor from 4 to 8 weeks after ADRD administration, compared to that at 0 week (CD34(+)EPO-R(+); 18.2±7.4, 41.7±7.3, 56.0±4.8, 76.4±5.3, 70.1±6.9, 73.8±8.7%, n=5, mean±SD at 0, 4, 5, 6, 7 and 8 weeks after ADRD administration, p<0.05, respectively). While, the frequency of apoptosis was not high in mature erythroblasts after ADRD administration (CD34(-)EPO-R(+); 1.58±1.4, 0.21±0.1, 0.58±0.1, 0.77±0.7, 0.49±0.2, 0.25±0.2%, n=5, mean±SD at 0, 4, 5, 6, 7 and 8 weeks after ADRD administration, N.S, respectively). Pathological examination of kidney showed that tubular damage was diffusely observed from 2 to 8 weeks after ADRD administration, and tubular necrosis was suspected as the major cause of renal failure.

Our findings suggested that excessive apoptosis occurred mainly in CD34(+) erythroid progenitor by insufficient production of EPO, which induced anemia in mice with CRF.