GATA2 heterozygosity causes an epigenetic feedback mechanism resulting in myeloid and erythroid dysplasia

Abstract

SummaryThe transcription factor GATA2 has a pivotal role in haematopoiesis. Heterozygous germline GATA2 mutations result in a syndrome characterized by immunodeficiency, bone marrow failure and predispositions to myelodysplastic syndrome (MDS) and acute myeloid leukaemia. Clinical symptoms in these patients are diverse and mechanisms driving GATA2‐related phenotypes are largely unknown. To explore the impact of GATA2 haploinsufficiency on haematopoiesis, we generated a zebrafish model carrying a heterozygous mutation of gata2b (gata2b+/−), an orthologue of GATA2. Morphological analysis revealed myeloid and erythroid dysplasia in gata2b+/− kidney marrow. Because Gata2b could affect both transcription and chromatin accessibility during lineage differentiation, this was assessed by single‐cell (sc) RNA‐seq and single‐nucleus (sn) ATAC‐seq. Sn‐ATAC‐seq showed that the co‐accessibility between the transcription start site (TSS) and a −3.5–4.1 kb putative enhancer was more robust in gata2b+/− zebrafish HSPCs compared to wild type, increasing gata2b expression and resulting in higher genome‐wide Gata2b motif use in HSPCs. As a result of increased accessibility of the gata2b locus, gata2b+/− chromatin was also more accessible during lineage differentiation. scRNA‐seq data revealed myeloid differentiation defects, that is, impaired cell cycle progression, reduced expression of cebpa and cebpb and increased signatures of ribosome biogenesis. These data also revealed a differentiation delay in erythroid progenitors, aberrant proliferative signatures and down‐regulation of Gata1a, a master regulator of erythropoiesis, which worsened with age. These findings suggest that cell‐intrinsic compensatory mechanisms, needed to obtain normal levels of Gata2b in heterozygous HSPCs to maintain their integrity, result in aberrant lineage differentiation, thereby representing a critical step in the predisposition to MDS.

GATA2 deficiency syndrome: A compensatory mechanism gone awry?

“…These experiments demonstrated increased accessibility to regulatory regions of gata2b in gata2b +/− cells compare to WT, which was consistent with significantly higher gata2b mRNA expression and elevated use of GATA2 motif in gata2b +/− HSPCs, indicative of highly active Gata2b protein (Figure 1). Importantly, GATA2 expression is also significantly higher in GATA2 deficiency patients and in AML patients with somatic GATA2 mutations from the BEAT AML cohort, 7 compared with GATA2 WT patients, 1 which supports the existence of a self-regulatory mechanism that compensates the GATA2 haploinsufficiency by activating GATA2 transcription and thus its protein function (Figure 1). This reactivation of Gata2b in gata2b +/− cells could explain the phenotype observed in the zebrafish model and patients with GATA2 haploinsufficiency, given its function in the maintenance and proliferation of HSPCs and the drastic decrease in GATA2 expression as the haematopoietic cells differentiate.…”

“…Indeed, high expression of GATA2 is associated with poor prognosis in both paediatric and adult AML, gain-of-function GATA2 mutations induce transformation in chronic myeloid leukaemia, and certain somatic alterations found in leukaemia lead to increased GATA2 activity. 1,2,8 A very tight regulation of GATA2 expression is required to sustain normal haematopoiesis, but the mechanisms underlying this regulation are complex and intriguing. For instance, the unbalanced expression of the two GATA2 alleles, also known as allele-specific expression (ASE), is a diseaserelated phenomenon that occurs in 37% of AML patients.…”

“…In their paper, Gioacchino et al 1 have identified in zebrafish with gata2b haploinsufficiency (an orthologue of GATA2), a compensatory self-regulatory loop to regain normal gata2b levels that results in aberrant myeloid differentiation thus predisposing to myelodysplastic syndrome. This finding provides new insights into the complex regulation of GATA2 expression and how GATA2 haploinsufficiency induces myeloid disease.…”

“…Inherited or de novo germline GATA2 heterozygous mutations cause an immunodeficiency disease with autosomal dominant inheritance pattern known as GATA2 deficiency syndrome. The spectrum of clinical features associated with this syndrome is very broad and include systemic infections, lymphoedema, severe cytopenia and a high risk of developing myelodysplastic syndrome (MDS) and acute myeloid leukaemia (AML) (>60% before the age of 40 [1][2][3] ). GATA2 somatic mutations also appear in 1%-4% of patients with sporadic myeloid disease and these mutations are associated with features of immunodeficiency and erythro-myelodysplasia similar to that of germline mutations.…”