A 2ND-GENERATION TRANSGENIC MOUSE MODEL EXPRESSING BOTH HEMOGLOBIN-S (HBS) AND HBS-ANTILLES RESULTS IN INCREASED PHENOTYPIC SEVERITY

We report on a second generation of transgenic mice produced by crossing a transgenic mouse line expressing high levels of human alpha and beta(S) chains (alpha(H) beta(S)[beta(MDD)]) with a line expressing human alpha and beta(S-Antilles) (beta(SAnt)). We hypothesized that mice expressing both hemoglobins (Hbs) would have a more severe phenotype because the reduced oxygen affinity and solubility of the beta(S-Antilles) might enhance the rate and extent of polymer formation. We obtained mice that expressed both beta(S) and beta(S-Antilles). Th, doubly transgenic mice that are heterozygous for deletion of mouse beta(Major) (beta(MD)) occurred with reduced frequency and those that are homozygous for deletion of mouse beta(Major) (beta(MDD)) occurred at a much reduced frequency and suffered early mortality. Human alpha was 58% of all alpha globin for all animals, whereas beta(S) and beta(S-Antilles) were 34% and 28% of all beta globins for beta(MD) mice and 42% and 36% for beta(MDD) mice. Hematocrit, Hb, and mean corpuscular Hb were normal for all transgenic mice, but reticulocyte levels were higher for the doubly transgenic mice versus (alpha(H) beta(S)[beta(MDD)] mice older than 30 days (10.0% +/- 1.0% v 4.3% +/- 0.4%; P < .001, mean +/- SE, n = 20 and n = 10, respectively) and control mice (3.9% +/- 0.4%). Reticulocytosis was more severe in mice less than 30 days old (>20% for alpha(H) beta(S) beta(S-Ant)[beta(MDD)] mice). The median mean corpuscular hemoglobin concentration of doubly transgenic mice was higher than that of alpha(H) beta(S)[beta(MDD)] mice with a variable number of very dense cells. Delay times for polymerization of Hb in red blood cells from alpha(H) beta(S) beta(S-Ant)[beta(MDD)] mice were shorter than those of alpha(H) beta(S)[beta(MDD)] mice, and there were fewer cells with delay times greater than 100 seconds. Urine-concentrating ability in control mice under ambient conditions is 2,846 +/- 294 mOsm and was reduced 30% to 1,958 +/- 240 mOsm, P < 4 x 10(-8) in all mice expressing both transgenes. We conclude that doubly transgenic mice have a more severe phenotype than either of the two parental lines. These mice may be suitable for validating therapeutic intervention in sickle cell disease. (C) 1995 by The American Society of Hematology.