Second generation knockout sickle mice: the effect of HbF

Sickle transgenic mice expressing exclusively human globins are desirable for studying pathophysiology and testing gene therapy strategies, but they must have significant pathology and show evidence of amelioration by antisickling hemoglobins, Mice were generated that expressed exclusively human sickle hemoglobin with 3 levels of HbF using their previously described sickle constructs (cointegrated human miniLCR alpha2 and miniLCR beta (S) [PNAS 89:12150, 1992]), mouse alpha- and beta -globin-knockouts, and 3 different human gamma -transgenes, it was found that, at all 3 levels of HbF expression, these mice have balanced chain synthesis, nearly normal mean corpuscular hemoglobin, and, in some cases, F cells, Mice with the least adult HbF expression were the most severe. Progressive increase in HbF from less than 3% to 20% to 40% correlated with progressive increase in hematocrit (22% to 34% to 40%) and progressive decrease in reticulocyte count (from 60% to 30% to 13%), Urine concentrating ability was normalized at high HbF, and tissue damage defected by histopathology and organ weight were ameliorated by increased HbF, The gamma -transgene that produces intermediate levels of HbF was introduced into knockout sickle mice described by Paszty and coworkers that express the miniLCR alpha1(G)gamma (A)gamma delta beta (S) transgene and have fetal but not adult expression of HbF, It was found that the level of HbF required to ameliorate low hematocrit and normalize urine concentrating defect was different for the miniLCR alpha2 beta (S) and miniLCR alpha1(G)gamma (A)gamma delta beta (S) mice. We conclude that knockout mice with the miniLCR alpha2 beta (S) transgene and postnatal expression of HbF have sufficiently faithful sickle pathology to serve as a platform for testing antisickling interventions. (C) 2001 by The American Society of Hematology.