Ncoa4-mediated ferritinophagy as a dependence in Tet2-deficient hematopoiesis
TET2 is among the most commonly mutated genes in both clonal hematopoiesis and myeloid malignancies, thus, the ability to identify selective dependencies in TET2 deficient cells has broad translational significance. Here, we identify regulators of Tet2 knockout (KO) hematopoietic stem and progenitor cell (HSPC) expansion using an in vivo CRISPR-Cas9 KO screen, in which nucleotide barcoding enabled large-scale clonal tracing of Tet2 deficient HSPCs in a physiological setting. Our screen identified candidate genes, including Ncoa4, that are selectively required for Tet2 KO clonal outgrowth compared to wild-type (WT). Ncoa4 targets ferritin for lysosomal degradation (ferritinophagy), maintaining intracellular iron homeostasis by releasing labile iron (Fe2+) in response to cellular demands. In Tet2-deficient HSPCs, increased mitochondrial ATP production correlates with increased cellular iron requirements, and in turn, promotes Ncoa4-dependent ferritinophagy.  Restricting iron availability reduces Tet2 KO stem cell numbers, revealing a dependency in TET2-mutated myeloid neoplasms. Overall design: Expression profiling by single cell high throughput sequencing of Tet2 KO HSPCs. Following transplantation of Cas9+ WT or Tet2 KO HSCs transduced with nontargeting (NTC) sgRNAs or Ncoa4 sgRNAs, Lin-Sca1+Kit+ (HSPCs) were sorted via flow cytometry and subjected to scRNAseq.