SummaryMany acute and chronic anemias, including hemolysis, sepsis, and genetic bone marrow failure diseases such as Diamond-Blackfan Anemia (DBA), are not treatable with erythropoietin (Epo), because the colony-forming unit erythroid progenitors (CFU-Es) that respond to Epo are either too few in number or are not sensitive enough to Epo to maintain sufficient red blood cell production 1,2,3–5,6,7,8,9. Treatment of these anemias requires a drug that acts at an earlier stage of red cell formation and enhances the formation of Epo-sensitive CFU-E progenitors. Recently we showed that glucocorticoids specifically stimulate self-renewal of the early erythroid progenitor, the burst-forming unit erythroid (BFU-E), and increase the production of terminally differentiated erythroid cells 10,11. Here we demonstrate that activation of the peroxisome proliferator-activated receptor alpha (PPARα) by PPARα agonists, GW7647 and fenofibrate, synergizes with glucocorticoid receptor (GR) to promote BFU-E self-renewal. Over time these agonists greatly increase production of mature red blood cells in cultures both of mouse fetal liver BFU-Es and of mobilized human adult CD34+ peripheral blood progenitors, the latter employing a new and effective culture system that generates normal enucleated reticulocytes. While PPARα−/− mice show no hematological difference from wild-type mice in both normal and phenylhydrazine (PHZ)-induced stress erythropoiesis, PPARα agonists facilitate recovery of wild-type mice, but not PPARα−/− mice, from PHZ-induced acute hemolytic anemia. We also showed that PPARα alleviates anemia in a mouse model of chronic anemia. Finally, both in control and corticosteroid-treated BFU-E cells PPARα co-occupies many chromatin sites with GR; when activated by PPARα agonists, additional PPARα is recruited to GR-adjacent sites and presumably facilitates GR-dependent BFU-E self-renewal. Our discovery of the role of PPARα agonists in stimulating self-renewal of early erythroid progenitor cells suggests that the clinically tested PPARα agonists we used may improve the efficacy of corticosteroids in treating Epo resistant anemias.

Chronic pain associated with injury or disease can result from dysfunction of sensory afferents whereby the threshold for activation of pain-sensing neurons (nociceptors) is lowered. Neurotrophic factors control nociceptor development and survival, but also induce sensitization through activation of their cognate receptors, attributable, in part, to the modulation of ion channel function. Thermal pain is mediated by channels of the transient receptor potential (TRP) family, including the cold and menthol receptor TRPM8. Although it has been shown that TRPM8 is involved in cold hypersensitivity, the molecular mechanisms underlying this pain modality are unknown. Using microarray analyses to identify mouse genes enriched in TRPM8 neurons, we found that the glial cell line-derived neurotrophic factor (GDNF) family receptor GFR␣3 is expressed in a subpopulation of TRPM8 sensory neurons that have the neurochemical profile of cold nociceptors. Moreover, we found that artemin, the specific GFR␣3 ligand that evokes heat hyperalgesia, robustly sensitized cold responses in a TRPM8-dependent manner in mice. In contrast, GFR␣1 and GFR␣2 are not coexpressed with TRPM8 and their respective ligands GDNF and neurturin did not induce cold pain, whereas they did evoke heat hyperalgesia. Nerve growth factor induced mild cold sensitization, consistent with TrkA expression in TRPM8 neurons. However, bradykinin failed to alter cold sensitivity even though its receptor expresses in a subset of TRPM8 neurons. These results show for the first time that only select neurotrophic factors induce cold sensitization through TRPM8 in vivo, unlike the broad range of proalgesic agents capable of promoting heat hyperalgesia.

• The type III TGF-b receptor is a marker that distinguishes "early" and "late" BFU-Es.• TGF-b inhibitors increase early BFU-E cell self-renewal and total erythroblast production.Burst-forming unit erythroid progenitors (BFU-Es) are so named based on their ability to generate in methylcellulose culture large colonies of erythroid cells that consist of "bursts" of smaller erythroid colonies derived from the later colony-forming unit erythroid progenitor erythropoietin (Epo)-dependent progenitors. "Early" BFU-E cells forming large BFU-E colonies presumably have higher capacities for self-renewal than do "late" BFU-Es forming small colonies, but the mechanism underlying this heterogeneity remains unknown. We show that the type III transforming growth factor b (TGF-b) receptor (TbRIII) is a marker that distinguishes early and late BFU-Es. Transient elevation of TbRIII expression promotes TGF-b signaling during the early BFU-E to late BFU-E transition. Blocking TGF-b signaling using a receptor kinase inhibitor increases early BFU-E cell self-renewal and total erythroblast production, suggesting the usefulness of this type of drug in treating

An effect of thyroid hormone (TH) on erythropoiesis has been known for more than a century but the molecular mechanism(s) by which TH affects red cell formation is still elusive. Here we demonstrate an essential role of TH during terminal human erythroid cell differentiation; specific depletion of TH from the culture medium completely blocked terminal erythroid differentiation and enucleation. Treatment with TRβ agonists stimulated premature erythroblast differentiation in vivo and alleviated anemic symptoms in a chronic anemia mouse model by regulating erythroid gene expression. To identify factors that cooperate with TRβ during human erythroid terminal differentiation, we conducted RNA-seq in human reticulocytes and identified nuclear receptor coactivator 4 (NCOA4) as a critical regulator of terminal differentiation. Furthermore, mice are anemic in perinatal periods and fail to respond to TH by enhanced erythropoiesis. Genome-wide analysis suggests that TH promotes NCOA4 recruitment to chromatin regions that are in proximity to Pol II and are highly associated with transcripts abundant during terminal differentiation. Collectively, our results reveal the molecular mechanism by which TH functions during red blood cell formation, results that are potentially useful to treat certain anemias.

An effect of thyroid hormone on erythropoiesis has been known for more than a century but the molecular mechanism(s) by which thyroid hormone affects red cell formation are still elusive. Our study demonstrates an essential role of thyroid hormone during terminal human erythroid cell differentiation; specific depletion of thyroid hormone from the culture medium completely blocked human erythroid differentiation. Genome wide analysis showed that thyroid hormone receptor β (TRβ) occupies many gene loci encoding transcripts abundant during terminal erythropoiesis, including globin genes, and cooperates with GATA-1 and RNA polymerase II (Pol II) to regulate their expression. Treatment with TRβ agonists enhanced erythroblast differentiation in vivo and alleviated anemic symptoms in a chronic anemia mouse model. To identify factors that cooperate with TRβ during human erythroid terminal differentiation, we conducted RNA-Seq in human reticulocytes and identified NCOA4 as a critical regulator of terminal differentiation. Furthermore, Ncoa4-/- mice are anemic in both the embryonic and perinatal periods and fail to respond to thyroid hormone by enhanced erythropoiesis. Genome wide analysis suggests that thyroid hormone promotes NCOA4 recruitment to chromatin regions that are in proximity to Pol II and are highly associated with transcripts abundant during terminal differentiation. Collectively, our results reveal the molecular mechanism of thyroid hormone function on red blood cell formation and are potentially useful to treat certain anemias. Disclosures No relevant conflicts of interest to declare.