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 TR alpha 1 (denoted as PV; Thra1(PV/+) mouse) that faithfully reproduces the classical hypothyroidism seen in patients. Using Thra1(PV/+) mice, we explored how the TR alpha 1PV 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, beta-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 TR alpha 1PV could impair erythropoiesis via repression of the Gata-1 gene and its regulated genes. These results provide new insights into how TR alpha 1 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.