Regulation of Autophagy by PI3 Kinase in Myelodysplastic Syndrome Myelodysplastic Syndrome (MDS) is a blood disease driven by molecular abnormalities in hematopoietic stem cells (HSCs). Anemia is a common cause of morbidity in MDS patients. However, the mechanistic basis for the impaired HSC differentiation and erythroid maturation that leads to anemia in MDS patients is unclear. The PI3 kinase (PI3K) pathway is activated by many hematopoietic cytokines and growth factors, and is important for erythropoiesis. We generated a new triple knockout (TKO) mouse model in which deletion of the PI3K genes Pik3ca, Pik3cb, and Pik3cd in HSCs causes pancytopenia and myelodysplasia with impaired HSC differentiation. We observed that autophagic degradation is impaired in TKO HSCs, and that treatment with autophagy-inducing drugs improves HSC differentiation. We hypothesize that inactivation of PI3K dysregulates autophagic degradation in HSCs, leading to impaired HSC differentiation and erythropoiesis, which promotes MDS. Consistent with this, we observed that the phosphatase PTEN, which counteracts PI3K signaling, is upregulated in a subset of MDS patients. To more directly address the roles of PI3K in erythropoiesis, we plan to analyze erythropoiesis in the TKO;Mx1-Cre bone marrow transplant mouse model by performing CD71/Ter119 flow cytometry on the bone marrow and spleen. We will also generate the TKO;SCL-Cre-ERT mouse model, in which the PI3K genes can be deleted in HSCs after tamoxifen administration without transplantation. After Cre-mediated excision of Pik3ca, Pik3cb, and Pik3cd in HSCs, we will analyze blood counts, bone marrow histology, survival, and will perform CD71/Ter119 flow cytometry on the bone marrow and spleen to analyze erythropoiesis. To determine whether dysregulated autophagy plays a role in human MDS, we propose to examine autophagy in the stem cell compartment in MDS samples from the four different IPSSR categories (low, intermediate-1, intermediate-2, and high-risk). We will measure autophagy in HSCs and progenitors using intracellular flow cytometry for LC3II and P62 in cytokine-free media, with and without chloroquine treatment to measure autophagic flux. In addition, we will perform quantitative RT-PCR on CD34+ cells for PTEN expression from each MDS sample. We will also perform Western analysis for PTEN and phospho-AKT (pAKT), and will correlate PTEN and pAKT levels with autophagy induction in the same MDS samples. These experiments will better characterize the erythropoiesis defects that result from PI3K deletion and dysregulated autophagy in mouse HSCs, and will determine whether PI3K inactivation correlates with impaired autophagy in human MDS stem cells

PROJECT NARRATIVE Successful completion of this project will improve our understanding of how low levels of growth factor and cytokine signaling through PI3 kinase contribute to impaired blood cell maturation in MDS. Using our novel mouse model of MDS and MDS patient samples, we will test several new therapeutic strategies to improve HSC function and reduce cytopenias.