Resistance to inflammation underlies enhanced fitness in clonal hematopoiesis [I]

Clonal hematopoiesis (CH) results from enhanced fitness of a mutant hematopoietic stem and progenitor cell (HSPC), but how such clones expand is unclear. Here, we developed a technique that combines mosaic mutagenesis with color labeling of HSPCs to study how acquired mutations affect clonal fitness in a native environment. Mutations in CH-associated genes, like asxl1, promoted clonal dominance. Single-cell transcriptional analysis revealed that mutations stimulated expression of proinflammatory genes in mature myeloid cells and anti-inflammatory genes in progenitor cells of the mutant clone. Biallelic loss of one such immunomodulator, nr4a1, abrogated the ability of asxl1-mutant clones to establish clonal dominance. These results support a model where clonal fitness of mutant clones is driven by enhanced resistance to inflammatory signals from their mutant mature cell progeny. To analyze the effect of multiplex CRISPR mutagenesis on zebrafish marrow cells, we injected Zebrabow zebrafish embryos with guide RNAs targeting 20 different genes and cas9 mRNA. Control clutchmates were injected with 2 control guide RNAs and cas9 mRNA. These fish were grown to adulthood. Whole kidney marrow cells from 2 control and 3 mutant zebrafish were collected for preparation for 10x single cell RNA sequencing. A third set of samples were sorted kidney marrow cells of the dominant Zebrabow color from the same three mutant zebrafish.