Date of Award
Clonal hematopoiesis of indeterminate potential (CHIP) increases with age and occurs when a single mutant hematopoietic stem cell (HSC) contributes to a significant clonal proportion of mature blood lineages. CHIP is associated with increased risks of de novo and therapy-related hematological neoplasms, suggesting that mutations identified in CHIP likely drive disease development. Acquired somatic mutations in the TP53 gene, which encodes the tumor suppressor protein p53, rank in the top five among mutations identified in CHIP. The Liu lab recently showed that TP53 mutations identified in CHIP promote HSC expansion. Previous studies have examined the possible cell-intrinsic mechanisms by which p53 mutant cells display increased competitiveness, but it is not known how p53 mutant hematopoietic cells affect wild-type competitor cells in order to promote their own expansion. Human aging is characterized by low-grade chronic inflammation. The Liu lab found that the NLRP1 inflammasome is activated in p53 mutant hematopoietic stem and progenitor cells (HSPCs). Inflammasomes are multiprotein complexes that activate Caspase-1, leading to increased secretion of pro-inflammatory cytokines such as IL-1β and caspase-1-dependent cell death called pyroptosis. Based on these preliminary data and literature, I hypothesized that in hematopoietic cell competition, p53 mutant cells outcompete wild type competitor cells through secreting inhibitory cytokines. I tested this hypothesis in an in vitro murine hematopoietic cell culture system by measuring the behavior and functional abilities of wild-type bone marrow cells after co-culture with an equal number of p53 mutant bone marrow cells relative to those of wild-type bone marrow cells cultured only with other wild-type cells. At the conclusion of the initial co-culture treatment, levels of a panel of cytokines were measured in the cultured media from each treatment group while wild-type bone marrow cells were sorted out for further experimentation. These cells were then subjected to a serial re-plating assay as well as measurements of cell death. I found that the ability of mutant p53 murine bone marrow cells to outcompete wild-type cells was intact in vitro; moreover, wild type bone marrow cells showed decreased colony formation and increased pyroptosis after co-culture with p53 mutant cells. I also found increased levels of several inflammatory cytokines such as IL-1β in cultured media from mutant p53 cell-containing cultures, which may be responsible for mediating the observed changes in wild-type cell behavior. My findings uncover a potential mechanism by which p53 mutant cells outcompete wild-type cells in the progression of hematological disorders. These findings may lead to novel therapeutic approaches for preventing CHIP progression and treat age-related hematological malignancies.
Strube, Katherine, "Determining the role of mutant p53-mediated inflammation in hematopoietic stem cell expansion" (2019). Undergraduate Honors Thesis Collection. 534.