Modeling myelodysplastic syndrome with induced pluripotent stem cells
EvansMDS Young Investigator Award
The proposed studies focus on prospectively delineating the molecular pathogenesis of MDS in a human system. There are approximately 10,000 new cases of myelodysplastic syndrome (MDS) diagnosed in the United States each year. Much effort has focused on delineating the molecular underpinnings of MDS, with the aim of developing improved disease models for drug discovery. Insight into MDS pathogenesis expanded with the discovery of clonal hematopoiesis of indeterminate potential (CHIP), which is defined as subclinical expansion of a hematopoietic clone driven by a genetic mutation that in isolation is not detrimental to hematopoietic cell output. CHIP is accepted to be highly prevalent in older adults, arising in many individuals as a consequence of aging. In some people with CHIP, the sequential accumulation of further mutations eventually reaches a threshold disruptive to normal hematopoiesis, resulting in manifestation of MDS. This model has been inferred by retrospective clonal analysis of MDS patient cells. Mutational analysis of MDS has identified recurrent heterozygous mutations in genes encoding splicing factors (SFs) in approximately 60% of cases. Transgenic mouse models engineered to express homologous mutations show disrupted RNA splicing and dysfunction of hematopoietic stem and progenitor cells (HSPCs) demonstrating their sufficiency to disrupt hematopoiesis, but do not replicate the precise splicing aberrations and phenotypes of human MDS. Mutations in SRSF2 (serine/arginine-rich splicing factor involved in both constitutive and alternative mRNA splicing) occur in approximately 20-30% of MDS and are associated with poor outcome in MDS and AML. SRSF2 mutations are commonly found in CHIP, and as such, SF mutations are accepted to occur early in clonal evolution. An accurate model of human CHIP and MDS is needed for better understanding of the key molecular dependencies that fuel clonal evolution for the development of new precision therapies.
Methods for hematopoietic differentiation of human iPSCs have incrementally improved representing a potentially limitless source of diseased and control normal HSPCs for disease modeling and drug discovery. Human patient-derived iPSCs have been used previously to model MDS and AML. Using gene editing, our laboratory has derived human induced pluripotent stem cells (iPSCs) bearing the SRSF2P95H mutation commonly found in CHIP and MDS. Upon hematopoietic differentiation, SRSF2P95H/+ cells show expansion of a CD45+CD34+ HSPCs and increased colony forming activity relative to otherwise isogenic SRSF2+/+ iPSC-derived HSPCs, consistent with a CHIP-like phenotype. In this proposal, I will further develop this preliminary observation by developing a model of human clonal evolution by the introduction of other CHIP/MDS-associated mutations into SRSF2P95H/+ iPSCs (Aim 1), and engrafting of iPSC-derived SRSF2P95H/+ HSPCs with or without cooperating mutations into immunodeficient mice to model clonal hematopoiesis in vivo (Aim 2). These studies have the potential to impact the study of CHIP/MDS by providing tractable, human based models for mechanistic dissection of the pathobiology of human hematopoietic clonal evolution.