HIGH EXPRESSION OF HUMAN BETA-S-GLOBINS AND ALPHA-GLOBINS IN TRANSGENIC MICE - HEMOGLOBIN COMPOSITION AND HEMATOLOGICAL CONSEQUENCES

A line of transgenic mice (alpha(H)beta(S)-11; where alpha(H) is human alpha-globin) was created in which the human beta(S) and human alpha2 globin genes, each linked to the beta-globin locus control region, were cointegrated into the mouse genome. On a normal genetic background, the transgenic mice produced 36% human beta(S)-globin chains with an alpha(H)/beta(S) ratio of 1.3. Higher levels of beta(S) were achieved by breeding the transgenic mice with mutant mice carrying a mouse beta(major)-globin gene deletion. Mice heterozygous for the beta(major) deletion (alpha(H)beta(S)[beta(MD)]; MD, mouse deletion) had 54% beta(S) with an alpha(H)/beta(S) ratio of 1.0; mice homozygous for the beta(major) deletion (alpha(H)beta(S)[beta(MDD]) had 72.5% beta(S) and an alpha(H)/beta(S) ratio of 0.73. Because mouse alpha chains inhibit hemoglobin (Hb) S polymerization, we bred the mice to heterozygosity for a mouse alpha-globin deletion. These mice (alpha(H)beta(S)[alpha(MD)beta(MDD]) had an increased alpha(H)/beta(S) ratio of 0.89 but expressed 65% beta(S). Expression of the human genes cured the thalassemic phenotype associated with the murine beta(major) deletion. Transgenic alpha(H)beta(S)[beta(MDD)] mice had normal hematocrit and Hb and somewhat elevated reticulocytes (6% vs. 3% for control), whereas the mice carrying the alpha-globin deletion (alpha(H)beta(S)[alpha(MD)beta(MDD)]) had a normal hematocrit and Hb and more elevated reticulocytes (10.3 +/- 7.6% vs. 3.4 +/- 1.0%). Expression of the transgene restored a normal distribution of erythrocyte densities when compared to thalassemic mice; however, the average mean corpuscular Hb concentration of alpha(H)beta(S)[beta(MDD)] mice increased to 35.7 g/dl (vs. control 33.7 g/dl) whereas that of alpha(H)beta(S)[alpha(MD)beta(MDD)] mice was further elevated to 36.3 g/dl. The intrinsic oxygen affinity was increased in transgenic mouse erythrocytes at 280 milliosmolal, and the PO2 at midsaturation of alpha(H)beta(S)[alpha(MD)beta(MDD)] erythrocytes was higher than that of alpha(H)beta(S)[beta(MDD)] cells (37.4 +/- 2 vs. 33.5 +/- 1 mmHg). The higher values of the mean corpuscular Hb concentration and intrinsic PO2 at midsaturation, which favor in vivo sickling, may explain the slightly more severe hematological picture in alpha(H)beta(S)[alpha(MD)beta(MDD)] mice. We conclude that the transgenic mouse with high Hb S expression does not exhibit adult anemia but does have abnormal hematological features: increased erythrocyte density, high oxygen affinity, and reticulocytosis with increased stress reticulocytes.