Project description:Ineffective erythropoiesis, the death of maturing erythroid cells, is a common cause of anemia. To better understand why this occurs, we studied the fates and adaptations of single erythroid marrow cells from individuals with Diamond Blackfan anemia (DBA), del(5q) myelodysplastic syndrome (del(5q) MDS), and normal controls, and defined an unhealthy (vs. healthy) differentiation trajectory, using velocity pseudotime and cell surface protein assessment. The pseudotime trajectories diverge immediately after the cells upregulate transferrin receptor (CD71), import iron, and initiate heme synthesis, although cell death occurs much later. Cells destined to die highly express heme-responsive genes, including ribosomal protein and globin genes. In contrast, surviving cells downregulate heme synthesis, while upregulating DNA damage response, hypoxia, and HIF1 pathways. Surprisingly, 24±12% of cells from controls follow the unhealthy trajectory, implying that heme also regulates cell fate decisions during normal red cell production. Del(5q) MDS (unlike DBA) results from somatic mutations, so many normal (unmutated) erythroid cells persist. By independently tracking their trajectory, we gained insight into why they cannot expand to prevent anemia. In addition, we show that intron retention is especially prominent during red cell differentiation. The additional information provided by messages with retained introns also allowed us to align data from multiple independent experiments and thus accurately query the transcriptomic changes that occur as single erythroid cells mature.
Project description:SF3B1 deficiency impairs human erythropoiesis via activation of p53 pathway: implications for understanding of ineffective erythropoiesis in MDS
Project description:We aimed to evaluate changes in expression in control and th1/th1 mice treated with PBS and apo-transferrin to understand the effect(s) of exogenous apo-transferrin on normal and ineffective erythropoiesis
Project description:Key Points • A heme rheostat regulates normal erythropoiesis as well as the ineffective erythropoiesis of DBA and MDS-5q.• Marrow cells from patients with MDS-5q with or without the deletion of 5q share transcription profiles. Visual Abstract Abstract The anemias of myelodysplastic syndrome (MDS) and Diamond Blackfan anemia (DBA) are generally macrocytic and always reflect ineffective erythropoiesis yet result from diverse genetic mutations. To delineate shared mechanisms that lead to cell death, we studied the fate of single erythroid marrow cells from individuals with DBA or MDS-5q. We defined an unhealthy (vs healthy) differentiation trajectory using transcriptional pseudotime and cell surface proteins. The pseudotime trajectories diverge immediately after cells upregulate transferrin receptor (CD71), import iron, and initiate heme synthesis, although cell death occurs much later. Cells destined to die express high levels of heme-responsive genes, including ribosomal protein and globin genes, whereas surviving cells downregulate heme synthesis and upregulate DNA damage response, hypoxia, and HIF1 pathways. Surprisingly, 24% ± 12% of cells from control subjects follow the unhealthy trajectory, implying that heme might serve as a rheostat directing cells to live or die. When heme synthesis was inhibited with succinylacetone, more DBA cells followed the healthy trajectory and survived. We also noted high numbers of messages with retained introns that increased as erythroid cells matured, confirmed the rapid cycling of colony forming unit–erythroid, and demonstrated that cell cycle timing is an invariant property of differentiation stage. Including unspliced RNA in pseudotime determinations allowed us to reliably align independent data sets and accurately query stage-specific transcriptomic changes. MDS-5q (unlike DBA) results from somatic mutation, so many normal (unmutated) erythroid cells persist. By independently tracking erythroid differentiation of cells with and without chromosome 5q deletions, we gained insight into why 5q+ cells cannot expand to prevent anemia.
Project description:It is unclear how epigenetic changes regulate the induction of erythroid-specific genes during terminal erythropoiesis. Here we use global mRNA sequencing (mRNA-seq) and chromatin immunoprecipitation coupled to high-throughput sequencing (CHIP-seq) to investigate the changes that occur in mRNA levels, RNA Polymerase II (Pol II) occupancy and multiple post-translational histone modifications when erythroid progenitors differentiate into late erythroblasts. Among genes induced during this developmental transition, there was an increase in the occupancy of Pol II, the activation marks H3K4me2, H3K4me3, H3K9Ac and H4K16Ac, and the elongation methylation mark H3K79me2. In contrast, genes that were repressed during differentiation showed relative decreases in H3K79me2 levels yet had levels of Pol II binding and active histone marks similar to those in erythroid progenitors. We also found that relative changes in histone modification levels-in particular, H3K79me2 and H4K16ac-were most predictive of gene expression patterns. Our results suggest that in terminal erythropoiesis both promoter and elongation-associated marks contribute to the induction of erythroid genes, while gene repression is marked by changes in histone modifications mediating Pol II elongation. Our data maps the epigenetic landscape of terminal erythropoiesis and suggests that control of transcription elongation regulates gene expression during terminal erythroid differentiation. Mouse fetal liver cells are double-labeled for erythroid-specific TER119 and non erythroid-specific transferrin receptor (CD71) and then sorted by flow-cytometry. E14.5 fetal livers contain at least five distinct populations of cells (R1 through R5); as they progressively differentiate they gain TER119 and then gain and subsequently lose CD71. CFU-E cells and proerythroblasts make up the R1 population; R2 consists of proerythroblasts and early basophilic erythroblasts; R3 includes early and late basophilic erythroblasts; R4 is mostly polychromatophilic and orthochromatophilic erythroblasts; and R5 is comprised of late orthochromatophilic erythroblasts and reticulocytes. We have sorted for R2-R5 cells for RNA-seq experiment.
Project description:Energy metabolism and extracellular matrix function are closely connected to orchestrate and maintain tissue organization, but the crosstalk is poorly understood. Here, we used scRNA-seq analysis to uncover the importance of respiration for extracellular matrix homeostasis in mature cartilage. Genetic inhibition of respiration in cartilage results in the expansion of a central area of 1-month-old mouse femur head cartilage showing disorganized chondrocytes and increased deposition of extracellular matrix material. scRNA-seq analysis identified a cluster-specific decrease in mitochondrial DNA-encoded respiratory chain genes and a unique regulation of extracellular matrix-related genes in nonarticular chondrocyte clusters. These changes were associated with alterations in extracellular matrix composition, a shift in the collagen/non-collagen protein content and an increase of collagen crosslinking and ECM stiffness. The results demonstrate, based on findings of the scRNA-seq analysis, that respiration is a key factor contributing to ECM integrity and mechanostability in cartilage and presumably also in many other tissues.
Project description:Luspatercept (Reblozyl) was recently approved for treating patients with transfusion-dependent lower-risk myelodysplastic syndrome (MDS) with ring sideroblasts (RS) and/or SF3B1 mutation who were not eligible for erythropoiesis-stimulating agents (ESAs) or patients for whom those agents failed. Luspatercept acts as an activin receptor type IIB fusion protein ligand trap that targets the altered transforming growth factor beta pathway in MDS, which is associated with impaired terminal erythroid maturation. Treatment with luspatercept results in decreased SMAD signaling, which enables erythroid maturation by means of late-stage erythroblast differentiation and thus improves anemia. ESAs, the current standard first-line therapeutic option for anemic lower-risk patients with MDS, also improve red cell parameters mainly by expanding proliferation of early erythroid progenitor cells. However, erythropoietin (EPO) and its receptor (EPO-R) are also required for survival of late-stage definitive erythroid cells, and they play an essential role in promoting proliferation, survival, and appropriate timing of terminal maturation of primitive erythroid precursors. Thus, luspatercept joins the mechanism of ESAs in promoting erythroid maturation. Especially in the subgroup of MDS patients with RS, luspatercept showed high clinical activity for the treatment of anemia in the phase 2 (PACE-MDS) trial and subsequently in the phase 3 (MEDALIST) trial, which resulted in approval by both the US Food and Drug Administration and the European Medicines Agency in April 2020. Additional studies are needed to better understand the mechanism of action and pharmacodynamics of this novel agent in MDS.