Germline GATA2 mutations are identified in a complex disorder termed GATA2 deficiency syndrome. Clinical heterogeneous manifestations are associated with a wide diversity of molecular alterations (missense, frameshift, nonsense, intronic or splicing mutations). Truncating mutations decrease GATA2 expression suggesting a haploinsufficiency mechanism while molecular consequences of missense mutations are ill-known. We focus our research on the most recurrent GATA2 mutation, GATA2 R396Q.
Our in vitro results indicate that the ectopic expression of GATA2 R396Q has a strong impact on the clonogenicity associated with an excessive granulocyte differentiation. This data motivates the elaboration of a more physiological approach through the development of a new knock-in mouse model with endogenous expression of Gata2 R396Q mutation. This model allowed us to address the question of the impact of this missense mutation on hematopoiesis at steady state and in challenging conditions.
The Gata2R396Q/+ mice showed an abnormal distribution of the immature progenitors Lin - Sca-1 + Kit + (LSK) subpopulations, mainly defines by an increase of the number of aberrant Long-Term Hematopoietic Stem cells (LT-HSC) contrasting with the decrease of LT-HSC population in Gata2+/- mouse model. Functional assays on Gata2R396Q/+ LSK cells revealed also qualitative defects. Indeed, their reconstitution capacity and their response to inflammatory or chemotherapy stimuli seemed to be largely affected. To address at the molecular level the impact of the missense mutation in these progenitors, we combined gene expression analysis with chromatin gene accessibility. These analyses revealed a strong disruption of the cells' ability to respond to stimuli, such as IFN or TNFα signaling, confirming what we observed at the cellular level in functional assays. Furthermore, specific RNA sequencing of the LT-HSC, ST-HSC and MPP3-4 subpopulations showed that the majority of these molecular perturbations are detected in every subpopulation of the LSK cells. In addition, we are able to establish a precise genetic signature in LT-HSC that may be related to their major functional defects.
Combination of in vitro and in vivo approaches leads to improve our understanding of GATA2 deficiency syndrome. Modelization of the most recurrent germline Gata2 mutation revealed a different phenotype than the haploinsufficient mouse model. Furthermore, expression of Gata2 R396Q mutation qualitatively impacts the LSK compartment mimicking functional and molecular defects observed in the GATA2 deficiency patients.
Delabesse: Novartis: Consultancy; Astellas: Consultancy. Pasquet: Novartis: Consultancy.