HBB-bs & HBB-bt DKO Mouse

β-thalassemia is a genetic blood disorder caused by reduced or absent production of β-globin chains, the major protein component of hemoglobin. Hemoglobin is responsible for transporting oxygen throughout the body and comprises two α-globin chains and two β-globin chains ^[1]. Each chain contains a heme group at the center of the hemoglobin molecule, which binds an iron ion and gives hemoglobin its oxygen-carrying ability. In normal adult humans, the β-globin chains are encoded by the HBB gene. Adult hemoglobin (HbA), composed of two β-globin chains and two α-globin chains (encoded by the HBA1 or HBA2 genes), accounts for approximately 97% of total hemoglobin ^[2]. In β-thalassemia patients, HBB gene mutations cause reduced or absent β-globin chain production, leading to low hemoglobin levels and symptoms such as impaired erythropoiesis, hemolysis, and anemia. β-Thalassemia is caused by reduced (β+) or absent (β0) synthesis of the β-globin chains of hemoglobin ^[3]. Three clinical and hematological conditions of increasing severity are recognized: the β-thalassemia carrier state, thalassemia intermedia, and thalassemia major, severe transfusion-dependent anemia. The severity of disease expression is related mainly to the degree of α-globin chain excess, which precipitates in the red blood cell precursors, causing both mechanic and oxidative damage (ineffective erythropoiesis) ^[4]. Any mechanism that reduces the number of unbound α-globin chains in the red cells may ameliorate the detrimental effects of excess α-globin chains. Factors include the inheritance of mild/silent β-thalassemia mutations, the coinheritance of α-thalassemia alleles, and increased γ-globin chain production.

C57BL/6Cya mice have two similar adult β-globin protein-encoding genes, Hbb-bs and Hbb-bt. These two genes are located at adjacent positions on mouse chromosome 7 and contain three exons ^[5-6]. Hbb-bs & Hbb-bt DKO mice are a β-thalassemia disease model constructed by simultaneously knocking out the Hbb-bs gene and Hbb-bt gene in C57BL/6JCya mice using gene editing technology. This model is homozygous lethal, and heterozygous mice show typical features of severe thalassemia, such as abnormal hemoglobin content, red blood cell count, hematocrit, mean corpuscular hemoglobin concentration, red cell distribution width, platelet count, spleen size, and red cell morphology, and have reproductive ability.