Hbb-bs&Hbb-bt DKO Mice

Catalog Number: C001508

Strain Name: C57BL/6JCya-Hbb-bs^em1Hbb-bt^em1/Cya

Genetic Background: C57BL/6JCya

Reproduction: Heterozygote × WT

Strain Description

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 is composed of 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, a 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 highly 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 both 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.

Strain Strategy

Using gene editing technology, the Hbb-bs and Hbb-bt genes of C57BL/6Cya mice were simultaneously knocked out in one step.

Application

This model is a valuable tool for studying the mechanisms of β-thalassemia and for screening potential therapeutic agents.

Validation Data

1. Growth Curves

Figure 1. Weight change curves of heterozygous Hbb-bs&Hbb-bt DKO mice and wild-type (WT) mice. Both female and male heterozygous Hbb-bs&Hbb-bt DKO mice and wild-type mice show relatively consistent growth patterns.

2. Survival Curves

Figure 2. Survival curves of heterozygous Hbb-bs&Hbb-bt DKO mice and wild-type (WT) mice. Male heterozygous Hbb-bs&Hbb-bt DKO mice began to die at week 13, and female heterozygous Hbb-bs&Hbb-bt DKO mice began to die at week 15.

3. Complete Blood Count (CBC)

Figure 3. Hematology of 14-week-old male heterozygous Hbb-bs&Hbb-bt DKO mice and wild-type (WT) mice. Hematology results showed that compared with wild-type mice, heterozygous Hbb-bs&Hbb-bt DKO mice had significantly decreased red blood cell count (RBC), hemoglobin (HGB), and hematocrit (HCT), slightly decreased mean corpuscular hemoglobin concentration (MCHC), and increased red cell distribution width (RDW) and platelet count (PLT). These parameter changes are similar to the clinical phenotype of β-thalassemia caused by similar gene mutation types. 

4. Blood Smear

Figure 4. Blood smear analysis of 14-week-old male heterozygous Hbb-bs&Hbb-bt DKO mice and wild-type mice. Blood smear analysis results showed that the proportion of nucleated red blood cells (NRBCs) in heterozygous Hbb-bs&Hbb-bt DKO mice was increased. The central pale staining area of red blood cells was enlarged, and a large number of abnormal and fragmented red blood cells were observed. Various abnormal red blood cells with different shapes were present in the blood, such as codocytes (yellow arrows), acanthocytes (red arrows), dacrocytes (green arrows), and schistocytes (blue arrows). The red blood cells of wild-type mice had complete morphological structure, presented as biconcave disc-shaped, and no obvious abnormalities were observed.


References

[1]Galanello R, Origa R. Beta-thalassemia. Orphanet J Rare Dis. 2010 May 21;5:11.
[2]Hardison RC. Evolution of hemoglobin and its genes. Cold Spring Harb Perspect Med. 2012 Dec 1;2(12):a011627.
[3]Thein SL. Molecular basis of β thalassemia and potential therapeutic targets. Blood Cells Mol Dis. 2018 May;70:54-65.
[4]Origa R. β-Thalassemia. Genet Med. 2017 Jun;19(6):609-619.
[5]Zhang F, Zhang B, Wang Y, Jiang R, Liu J, Wei Y, Gao X, Zhu Y, Wang X, Sun M, Kang J, Liu Y, You G, Wei D, Xin J, Bao J, Wang M, Gu Y, Wang Z, Ye J, Guo S, Huang H, Sun Q. An extra-erythrocyte role of haemoglobin body in chondrocyte hypoxia adaption. Nature. 2023 Oct;622(7984):834-841.
[6]Trimborn T, Gribnau J, Grosveld F, Fraser P. Mechanisms of developmental control of transcription in the murine alpha- and beta-globin loci. Genes Dev. 1999 Jan 1;13(1):112-24.