Defective erythropoiesis caused by mutations of the thyroid hormone receptor α gene

Patients with mutations of the THRA gene exhibit classical features of hypothyroidism, including erythroid disorders. We previously created a mutant mouse expressing a mutated TRα1 (denoted as PV; Thra1 PV/+ mouse) that faithfully reproduces the classical hypothyroidism seen in patients. Using Thra1 PV/+ mice, we explored how the TRα1PV mutant acted to cause abnormalities in erythropoiesis. Thra1 PV/+ mice exhibited abnormal red blood cell indices similarly as reported for patients. The total bone marrow cells and erythrocytic progenitors were markedly reduced in the bone marrow of Thra1 PV/+ mice. In vitro terminal differentiation assays showed a significant reduction of mature erythrocytes in Thra1 PV/+ mice. In wild-type mice, the clonogenic potential of progenitors in the erythrocytic lineage was stimulated by thyroid hormone (T3), suggesting that T3 could directly accelerate the differentiation of progenitors to mature erythrocytes. Analysis of gene expression profiles showed that the key regulator of erythropoiesis, the Gata-1 gene, and its regulated genes, such as the Klf1 , β-globin , dematin genes, CAII , band3 and eALAS genes, involved in the maturation of erythrocytes, was decreased in the bone marrow cells of Thra1 PV/+ mice. We further elucidated that the Gata-1 gene was a T3-directly regulated gene and that TRα1PV could impair erythropoiesis via repression of the Gata-1 gene and its regulated genes. These results provide new insights into how TRα1 mutants acted to cause erythroid abnormalities in patients with mutations of the THRA gene. Importantly, the Thra1 PV/+ mouse could serve as a preclinical mouse model to identify novel molecular targets for treatment of erythroid disorders.