Abnormalities in the myeloid progenitor compartment in Down syndrome fetal liver precede acquisition of GATA1 mutations

Abstract

Down syndrome (DS) children have a high frequency of acute megakaryoblastic leukemia (AMKL) in early childhood. At least 2 in utero genetic events are required, although not sufficient, for DS-AMKL: trisomy 21 (T21) and N-terminal-truncating GATA1 mutations. To investigate the role of T21 in DS-AMKL, we compared second trimester hemopoiesis in DS without GATA1 mutations to gestation-matched normal controls. In all DS fetal livers (FLs), but not marrows, megakaryocyteerythroid progenitor frequency was increased (55.9% ؎ 4% vs 17.1% ؎ 3%, CD34 ؉ CD38 ؉ cells; P < .001) with common myeloid progenitors (19.6% ؎ 2% vs 44.0% ؎ 7%) and granulocyte-monocyte (GM) progenitors (15.8% ؎ 4% vs 34.5% ؎ 9%) commensurately reduced. Clonogenicity of DS-FL versus normal FL CD34 ؉ cells was markedly increased (78% ؎ 7% vs 15% ؎ 3%) affecting megakaryocyte-erythroid (ϳ 7-fold higher) and GM and colony-forming unit-granulocyte, erythrocyte macrophage, megakaryocyte (CFU-GEMM) progenitors. Replating efficiency of CFU-GEMM was also markedly increased. These data indicate that T21 itself profoundly disturbs FL hemopoiesis and they provide a testable hypothesis to explain the increased susceptibility to IntroductionChildren with Down syndrome (DS) have a uniquely high frequency of acute megakaryoblastic leukemia (AMKL) in early childhood. [1][2][3] The leukemic cells acquire mutations in utero in the critical megakaryocyte transcription factor GATA1. [3][4][5][6][7][8][9][10] In many DS children, the first manifestation is neonatal transient myeloproliferative disorder (TMD), 1,2 which evolves to AMKL in 20% to 30% of infants. 3 TMD and AMKL represent 2 distinct steps in the pathogenesis of DS-AMKL. However, an additional necessary leukemogenic event (most probably the initiating event) is trisomy 21 (T21). T21 is essential for GATA1-associated TMD and AMKL 5,11,12 ; truncating GATA1 mutations in the absence of T21 are not leukemogenic. 13 GATA1 mutations also occur at high frequency in T21 (ϳ 5% of all DS neonates 14 ) and 25% of DS-associated AMKL patients have multiple, independent clones with GATA1 mutations. 6 These data suggest that GATA1 mutations and T21 specifically synergize to generate preleukemic TMD. The cellular and molecular mechanisms by which this occur are unclear.That a putative leukemia-initiating cell is present in T21 fetal liver (FL) is suggested both by the natural history of TMD (origin in utero, frequent liver involvement, and spontaneous resolution as FL hemopoiesis ceases 11,15 ) and by analysis of germline N-terminal mutant Gata1 phenotypes in mouse and humans. 16 To investigate the impact of T21, independent of GATA1 mutations, on human hemopoiesis, we studied myeloid progenitors from second trimester T21 FL and bone marrow. MethodsSecond-trimester FLs and marrow collected during elective surgical termination of pregnancy were processed immediately as previously described. 17 The study was approved by Hammersmith and Queen Charlotte's Hospitals Research Ethics Committee; written informed consent was obtain...

Pluripotent stem cells reveal erythroid-specific activities of the GATA1 N-terminus

“…While the current study focuses on the role of GATA1s mutations in erythropoiesis, our findings also provide insights into how these mutations interact with T21. Previous work has shown that T21 augments erythropoiesis in primary fetal cells (61)(62)(63) and iPSCs (18,64). Here, we confirm these findings in T21/WT GATA1 iPSCs and demonstrate that GATA1s overrides the erythropoietic effects of T21 in isogenic double-mutant T21/GATA1s iPSCs derived from 2 different patients with TMD.…”

Functional differences between myeloid leukemia-initiating and transient leukemia cells in Down's syndrome

“…3,28 TL likely arises from fetal liver hematopoietic progenitor cells after the acquisition of GATA1 mutations in the context of cellular trisomy 21. This hypothesis is supported by the detection of GATA1 mutations in DS fetal liver cells, 29 expanded numbers of megakaryocyte-erythroid progenitor cells during DS fetal hematopoiesis, 30 and the increased proliferative capacity conferred to murine fetal liver GATA1 mutations of all engrafted samples were shown to be concordant with those present in the primary human cell samples. c Primary sample; codon 13 of N-RAS (NC_000001.10; nucleotide 115258813-5).…”

Unique Myeloid Leukemias in Young Children with Down Syndrome: Cell Origin, Association with Hematopoietic Microenvironment and Leukemogenesis

“…However, none of these mouse strains develop TL and AMKL, indicating that additional genetic abnormalities are required to cause leukemia. In humans as well, trisomy 21 itself has been shown to disturb fetal liver, but not bone marrow, hematopoiesis, enhance production of megakaryocyte/erythroid progenitors (MEPs), which may be susceptible to acquisition of other genetic abnormalities, and predispose these cells to DS-related leukemias (Chou et al, 2008;De Vita et al, 2008;Tunstall-Pedoe et al, 2008). These data support the model that the genes on chromosome 21 play essential roles in the development of these disorders and trisomy 21 is the first step of myeloid leukemogenesis in DS.…”