Phenotypic Characterization the Townes Sickle Mice

The HbSS-Townes mouse model, developed in Dr. Tim Townes laboratory, University of Alabama, Birmingham (and kindly provided by him to our laboratory) were created on a mixed genetic background in which the murine adult α-globin genes were replaced with the human α-globin gene (genotype: Hba hα/hα) and the murine adult β-globin genes were replaced with human sickle β^S- and fetal ^Aγ-globin gene fragments linked together (genotype: Hbb h^Aγβ^S/h^Aγβ^S) (Wu LC et al. Blood 2006;108: 1183-1188). HbSS-Townes mice have anemia, a shortened RBC half-life of 2.5 days and a severe disease phenotype. Control HbAA-Townes mice were created by replacing the murine globin genes with human α-globin gene (genotype: Hba hα/hα) and linked human β^A- and fetal ^Aγ-globins (genotype: Hbb h^Aγβ^A/h^Aγβ^A), while HbAS-Townes heterozygous mice were developed by breeding HbAA and HbSS mice. Many laboratories are utilizing these mice but complete phenotypic description of these three models has not been described including: hematology, kidney and liver function, inflammatory markers, haptoglobin and hemopexin levels, red cell half-lives, organ histopathology and vascular responses to vaso-occlusive stimuli. Table 1 summarizes our findings.

There was a clear difference in histopathology between the HbSS and other groups (HbAA and HbAS). HbSS mice had hepatic necrosis, increased erythropoiesis and increased hemosiderin within the liver and some subtle lesions involving the glomeruli in the kidneys. Additional findings were a marked increase in size of spleen (7.0-7.6 x by % body weights) attributed to severe congestion and increased erythropoiesis. No lesions were observed in the lungs and other tissues. The tissues evaluated in the HbAS and HbAA groups were essentially normal. In contrast, HbSS mice had multifocal irregular areas of necrosis within the liver, with reactive leukocyte infiltrates (mainly neutrophils in the more acute lesions with a greater proportion of mononuclear cells (macrophages etc.) in more chronic lesions. MPO immunohistochemistry confirmed the presence of neutrophils in the liver. There was a substantial increase in iron (and hemosiderin) in the livers of HbSS mice, confirmed by a Prussian Perls stain and low, but detectable, levels of iron in the proximal convoluted tubules of the kidney. This is consistent with increased red cell turnover in the HbSS mice. Total iron mass in the markedly enlarged spleen is very high. There is a somewhat subtle glomerulopathy present in the kidney, with enlarged glomeruli with variable ectasia of vessels, and mesangial derangement. In conclusion the Townes mouse models provide a spectrum of severe hemolytic disease that in many ways mimic the human disease albeit imperfectly.