Animal models of β-hemoglobinopathies: utility and limitations

Abstract

The structural and functional conservation of hemoglobin throughout mammals has made the laboratory mouse an exceptionally useful organism in which to study both the protein and the individual globin genes. Early researchers looked to the globin genes as an excellent model in which to examine gene regulation – bountifully expressed and displaying a remarkably consistent pattern of developmental activation and silencing. In parallel with the growth of research into expression of the globin genes, mutations within the β-globin gene were identified as the cause of the β-hemoglobinopathies such as sickle cell disease and β-thalassemia. These lines of enquiry stimulated the development of transgenic mouse models, first carrying individual human globin genes and then substantial human genomic fragments incorporating the multigenic human β-globin locus and regulatory elements. Finally, mice were devised carrying mutant human β-globin loci on genetic backgrounds deficient in the native mouse globins, resulting in phenotypes of sickle cell disease or β-thalassemia. These years of work have generated a group of model animals that display many features of the β-hemoglobinopathies and provided enormous insight into the mechanisms of gene regulation. Substantive differences in the expression of human and mouse globins during development have also come to light, revealing the limitations of the mouse model, but also providing opportunities to further explore the mechanisms of globin gene regulation. In addition, animal models of β-hemoglobinopathies have demonstrated the feasibility of gene therapy for these conditions, now showing success in human clinical trials. Such models remain in use to dissect the molecular events of globin gene regulation and to identify novel treatments based upon the reactivation of developmentally silenced γ-globin. Here, we describe the development of animal models to investigate globin switching and the β-hemoglobinopathies, a field that has paralleled the emergence of modern molecular biology and clinical genetics.

In vivo hematopoietic stem cell gene therapy ameliorates murine thalassemia intermedia

“…In contrast to the blockade of erythroid lineage maturation in bone marrow of CD46 +/+ /Hbbth-3 mice, represented by the prevalence of pro-erythroblasts and basophilic erythroblasts, in cytospins from control and treated CD46 +/+ /Hbbth-3 mice, maturing erythroblasts predominated The novel features of the HDAd5/35++ vector system include (a) CD46-affinity-enhanced fibers that allow for efficient transduction of primitive HSCs while avoiding infection of nonhematopoietic tissues after intravenous injection, (b) an SB100X transposase-based integration system that functions independently of cellular factors and mediates random transgene integration without a preference for genes, and (c) an MGMT(P140K) expression cassette mediating selective survival and expansion of progeny cells without affecting the pool of transduced primitive HSCs by short-term treatment with low-dose O 6 where stable transduction of less than 1% of HSPCs provides a significant clinical benefit, phenotypic correction of hemoglobinopathies in patients requires at least 20% corrected erythroid precursors (22)(23)(24). In murine models for hemoglobinopathies, γ-globin expression at about 15% of the total α-globin mRNA was sufficient for therapy (22,25,26). In our study, after in vivo transduction/selection, more than 60% of bone marrow erythroblasts expressed γ-globin in the in vivo transduced CD46tg and CD46 +/+ /Hbbth-3 models ( Figure 1C and Figure 6A).…”

Erythropoiesis In Vitro—A Research and Therapeutic Tool in Thalassemia

“…The study of the pathophysiology of thal and the development of new therapeutic modalities that have been based primarily on clinical studies of the patients have been aided by preclinical studies using in vivo and in vitro experimental systems. Thal is not known to occur naturally in animals, but molecular manipulations of mice have generated thal models [8]. In vitro studies have been accomplished also in cultures of erythroid cells derived from normal individuals and patients.…”

Recent progress in understanding and manipulating haemoglobin switching for the haemoglobinopathies

“…Humanized mouse models of SCD and b-thalassaemia have been developed in which the mouse globin genes are deleted and a transgene carries the human globin locus with corresponding mutations (Paszty et al, 1997;Ryan et al, 1997;Lewis et al, 1998;Vadolas et al, 2006). These haemoglobinopathy mouse models may be a useful adjunct for in vivo testing of novel therapeutic approaches (McColl & Vadolas, 2016).…”