Second generation knockout sickle mice: the effect of HbF

Sickle transgenic mice expressing exclusively human globins are desirable f or studying pathophysiology and testing gene therapy strategies, but they m ust have significant pathology and show evidence of amelioration by antisic kling hemoglobins, Mice were generated that expressed exclusively human sic kle hemoglobin with 3 levels of HbF using their previously described sickle constructs (cointegrated human miniLCR alpha2 and miniLCR beta (S) [PNAS 8 9:12150, 1992]), mouse alpha- and beta -globin-knockouts, and 3 different h uman gamma -transgenes, it was found that, at all 3 levels of HbF expressio n, these mice have balanced chain synthesis, nearly normal mean corpuscular hemoglobin, and, in some cases, F cells, Mice with the least adult HbF exp ression were the most severe. Progressive increase in HbF from less than 3% to 20% to 40% correlated with progressive increase in hematocrit (22% to 3 4% 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 inc reased HbF, The gamma -transgene that produces intermediate levels of HbF w as introduced into knockout sickle mice described by Paszty and coworkers t hat express the miniLCR alpha1(G)gamma (A)gamma delta beta (S) transgene an d have fetal but not adult expression of HbF, It was found that the level o f HbF required to ameliorate low hematocrit and normalize urine concentrati ng 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 t he miniLCR alpha2 beta (S) transgene and postnatal expression of HbF have s ufficiently faithful sickle pathology to serve as a platform for testing an tisickling interventions. (C) 2001 by The American Society of Hematology.