Elucidating the role of H3K4 methyltransferase-SETD1A in hematopoiesis of mice and humans

SETD1A is the main H3K4 methyltransferase in hematopoietic stem and progenitors; its loss leads to a global reduction of its all three states of methylation and has been shown to be important for the orchestration of DNA damage response in mice and several mouse/human cell lines. A few studies have shown the effect of the level of this epigenetic modification on longevity; in worms, high levels of H3K4me3 are detrimental for their lifespan. In mice and in humans however, there are no studies yet on the effect of the loss of the main H3K4 methyltransferase specifically on the hematopoietic system and how it impacts the organism with advancing age. Aiming to answer this question, two different mouse models where SETD1A is specifically deleted in HSCs and MPPs (together with all the cells that derive from the primary targeted cells) were used, and a few components of hematopoiesis were taken into a comparative analysis with aged/geriatric mice. Analysis of SETD1A-deficient mice revealed several similarities to the ageing phenotype, including the loss of CLPs (common lymphoid progenitors) in the bone marrow, a reduction in T and B cells in the spleen without changes in myeloid cell numbers, an increase in T cell numbers in the bone marrow, thymic involution, and a reduction of endothelial cells in the bone marrow. Apart from the similarities, this analysis demonstrated a few differences too, related to the DNA repair kinetics and the HSC phenotype, being partially similar. The transcriptome analysis of SETD1A deficient HSPCs revealed a reduction of pathways that were related to mitochondrial metabolism, adding this way, another role for SETD1A on murine HSCPs apart from the direction of DNA damage response. In vitro deletion of SETD1A revealed that it is highly important for HSPCs to give rise to colonies as well as proliferate, however without entering apoptosis. Further, the analysis of SETD1A deficient HSCPs showed an increase in the expression of IFNAR1 as well as a few members of the IFN signaling, highlighting a possible increased sensitivity towards Type 1 IFN signaling. This was demonstrated in vivo, where SETD1A-deficient mice were shown to be more sensitive towards Poly I:C injection. The rescue experiment was conducted both in vivo and in vitro by double targeting of Setd1a and Trp53. This resulted in a partial rescue of the LT-HSC numbers after transplant, of the number of the colonies after CFU assay in vitro, but no rescue of mature cells in blood, highlighting that the loss of ability to detect DNA damage allows SETD1A deficient HSPCs to proliferate. Lastly, to understand if the role of SETD1A is conserved in human HSPCs, SETD1A was targeted in CD34+ cells extracted from cord blood. The analysis of the targeted cells revealed many similarities in the effects of SETD1A loss between human and murine HSPCs. Overall, this study demonstrates for the first time that the role of SETD1A is conserved in murine and human HSPCs and targets SETD1A as a protector against the onset of a few aged-like phenotypes in hematopoiesis.