TLR7 ligation augments hematopoiesis in Rps14 deficiency via paradoxical inflammatory signalling

Myelodysplastic syndrome (MDS) is a haematological malignancy characterised by blood cytopenias and predisposition to acute myeloid leukaemia. We developed a model of MDS using zebrafish using knockout of Rps14, the primary mediator of the anaemia associated with del (5q) MDS. These mutant animals develop bone marrow failure with dysplastic features. We conducted an in vivo small molecule screen to identify compounds that ameliorate the MDS phenotype, identifying imiquimod, an agonist of TLR7. We conducted RNA-seq analysis of both treated and untreated animals to define the mechanism of imiquimod in alleviating anaemia. We find imiquimod alleviates anaemia by promoting haematopoietic stem and progenitor cell expansion and erythroid differentiation, the mechanism of which is dependent on TLR7 ligation. TLR7 activation in this setting paradoxically promoted an anti-inflammatory gene signature suggesting crosstalk between pro-inflammatory pathways endogenous to Rps14 loss and TLR7 pathway activation. Overall design: RNA-seq analysis of HSPCs (Tg(Itga2b:GFPlo) cells) from pooled rps14+/- or wildtype zebrafish embryos, which were phenylhydrazine (Phz) stressed or unstressed, and then treated with imiquimod or vehicle control. A minimum of three replicates per condition were analysed.