Session: 508. Bone Marrow Failure: Poster II
Hematology Disease Topics & Pathways:
HSCs, Diseases, platelets, Bone Marrow Failure, red blood cells, white blood cells, Biological Processes, epigenetics, Cell Lineage, hematopoiesis
Diamond Blackfan Anemia is a rare disease, usually associated with ribosomal gene mutations, leading to significant decrease in GATA1 expression and block in early committed erythroid differentiation. Mild defects in other myeloid lineages are also observed, with limited clinical relevance. The importance of GATA1 downregulation in disease pathogenesis is manifested by rare patients with DBA carrying GATA1 mutations. To understand signaling pathways that contribute to the pathogenesis DBA, we perform RNA-seq with mRNA from human CD34+ fetal liver cells and found that the chromatin organizer, Special AT-rich sequence binding protein 1 (SATB1) was prematurely downregulated. Our results further demonstrated that sustained SATB1 expression is critical to maintain required levels of GATA1 protein at both the CMP and MEP stages of differentiation, but not in committed erythroid progenitors.
In mice, SATB1 is modestly expressed in HSCs and upregulated during lymphopoiesis. SATB1 is downregulated during myeloid and erythroid differentiation and antagonizes myeloid and erythroid expansion. However, in human hematopoietic stem and progenitor cells (HSPCs), SATB1 is required for efficient expansion of these lineages. SATB1 maintains 78% expression in human MEPs, but is undetectable in early committed erythroid progenitors. In RPS19-insufficient human HSPCs, SATB1 was downregulated to 22% in MEPs (p=0.02). Re-expression of SATB1 corrected a significant subset of deregulated mRNAs, including GATA1 regulators.
In the absence of SATB1, one such GATA1 regulator, heat shock protein 70 (HSP70), failed to be induced in ribosome-competent human MEPs, reducing GATA1 protein expression by 35.7% (p= 0.026). Concurrently, MEP expansion was inhibited by 64.5% (p=0.023), reducing erythroid and megakaryocyte expansion by 18.2% (p=0.024) and 20.4% (p=0.183) respectively. SATB1 facilitated the formation of chromatin loops linking together an enhancer element with HSP70 promoters required for HSP70 induction in early differentiation.
Although GATA1 is significantly upregulated in committed erythroid progenitors, RPS19-insufficient human CD235+ erythrocytes express GATA1 28.4% of controls (p= 0.011). SATB1 re-expression increased GATA1 expression to 31.4% (p=0.089). Similarly, SATB1 re-expression increased CD235+ expansion from 13.9% to 39.5% (p=0.02) compared to controls. Our data indicate that premature SATB1 downregulation contributes to erythroid failure in DBA by reducing MEP expansion, but aberrant GATA1 expression observed in more mature erythrocytes is predominantly SATB1-independent. However, SATB1-re-expression improved CD11b+ myeloid expansion from 81.2% to 90.4% (p=0.045) and CD41a+ megakaryocyte expansion from 76.7% to 214.7% (p=0.038) respectively. Our results demonstrate that SATB1 plays an important role in human hematopoiesis and is an important regulator of GATA1.
Disclosures: Glader: Agios Pharmaceuticals, Inc.: Consultancy.