The pathways that regulate the formation and differentiation of erythroid progenitors to red blood cells are incompletely understood. We found that the vitamin D receptor (Vdr) nuclear hormone transcription factor gene is expressed in fetal and adult stages but not at the embryonic stage of development and is downregulated during maturation. VDR activation by its ligand vitamin D3 results in conformational changes that stabilize the protein and induce its translocation into the nucleus, where it recruits coregulatory complexes. The VDR signaling pathway has been studied mostly in bone but has been largely unexplored in erythropoiesis: published studies were performed almost entirely in leukemic cell lines (not normal primary cells). Activation of Vdr signaling by the vitamin D3 agonist calcitriol increased the outgrowth of EryD colonies from fetal liver and adult bone marrow, maintained progenitor potential, and delayed erythroid maturation. The stimulation in growth of erythroid progenitors resulted in a large increase in the numbers of mature red blood cells. The early (CD71lo/neg) but not the late (CD71hi) EryD progenitor subset of Linneg cKit+ cells was responsive to calcitriol, independently of its calcemic effects. Activation of VDR could partially substitute for and synergize with the stress glucocorticoid dexamethasone in enhancing progenitor proliferation compared to either ligand alone, suggesting a role in stress erythropoiesis. This possibility is supported by our finding that an erythroid specific deletion in Vdr that interferes with DNA binding results in a reticulocytosis that occurs earlier and is more pronounced than in control animals in response to stress. RNA inhibition of Vdr expression abrogated the stimulation of early erythroid progenitor growth by calcitriol. These findings suggest that Vdr has a cell-intrinsic function in early erythroid progenitors. Activation of Vdr by calcitriol blocked the upregulation of erythroid transcription factor genes Gata1, Fog1 and Klf1. Intriguingly, circadian rhythm genes are upregulated by activation of Vdr and the glucocorticoid receptor Gr and oscillations in expression of the clock gene Per1 are promoted in erythroid progenitors. The clock gene Bmal1 is required for the proliferative response to dexamethasone. Therefore, the overarching hypothesis of this proposal is that Vdr and Gr regulate erythroid progenitors in part by modulating clock gene expression and have partially redundant functions. This application will use animal and cell culture models to explore the modulation of circadian clock gene expression by Gr and Vdr in erythroid progenitors and functional relationships between these two nuclear hormone receptor TFs. These studies may lead to the identification of novel molecular targets in erythroid progenitors that can be exploited to develop new therapies for anemias and other red cell disorders. The ability to modulate ex vivo expansion or differentiation of RBC progentors in new ways would have clear clinical utility.
to public health: The proposed studies are relevant to public health in that they may suggest options for the development of novel therapies for treatment of anemias, including more efficient production ex vivo of red blood cells for transfusion. Our findings suggest that the effectiveness of therapies may depend, in part, on diurnal timing. Therefore, this application is responsive to the mission of the NIH to develop tools and knowledge to treat or reduce the burden of hematological disease.
| Barminko, Jeffrey; Reinholt, Brad M; Emmanuelli, Alexander et al. (2018) Activation of the vitamin D receptor transcription factor stimulates the growth of definitive erythroid progenitors. Blood Adv 2:1207-1219 |
| Baron, Margaret H; Barminko, Jeffrey (2016) Chromatin Condensation and Enucleation in Red Blood Cells: An Open Question. Dev Cell 36:481-2 |
| Barminko, Jeffrey; Reinholt, Brad; Baron, Margaret H (2016) Development and differentiation of the erythroid lineage in mammals. Dev Comp Immunol 58:18-29 |
