PI3 Kinase Inactivation in Myelodysplastic Syndrome

骨髓增生异常综合征(MDS)在美国每年至少影响10,000人，在老龄化人口中尤为普遍。MDS是一种起源于造血干细胞(HSCs)的克隆性疾病，以髓系和红系分化受损和基因组不稳定为特征。目前几乎没有治疗方法可用于改善MDS患者的细胞减少症。RNA剪接因子的突变是 在50%的MDS病例中观察到，并且是MDS发生和发展的重要因素。大多数造血生长因子和细胞因子通过PI3K/AKT信号通路传递信号。我们发现，小鼠造血细胞中三种PI3K亚型P110a、b和d的复合缺失会导致类似MDS的表型，伴有细胞减少、HSC分化障碍和基因组不稳定。有趣的是，我们在MDS患者的基因表达数据集中观察到了我们的TKO HSC表达特征的丰富。此外，部分MDS样本中负性调节因子PTEN的表达水平升高，表明这些MDS患者中PI3K功能失活。我们的初步数据显示，PI3K三重敲除(TKO)小鼠的HSC在自噬方面存在缺陷，自噬是维持HSC分化的重要细胞内循环机制。我们发现药物诱导自噬可以促进TKO HSCs的分化。我们还观察到TKO HSCs中广泛存在的mRNA剪接变化。因此，PI3K TKO小鼠是研究MDS发生发展机制的有价值的新模型系统。我们假设HSC中PI3K信号的维持是 维持HSC分化和保护HSC免受DNA损伤所必需的。我们建议(1)确定自噬诱导是否可以促进MDS患者样本的髓系和红系分化；(2)描述PI3K及其下游激酶AKT控制HSCs和MDS中mRNA剪接的机制；(3)确定具有剪接因子突变的MDS细胞是否对抑制PI3K/AKT信号更加敏感。这些方法将进一步加深我们对生长因子和细胞因子信号如何通过PI3K/AKT在MDS启动中调节自噬和mRNA剪接的理解。我们还计划测试几种促进MDS分化的治疗方法，包括诱导MDS的自噬和抑制剪接因子突变的MDS的PI3K/AKT。

Myelodysplastic Syndrome (MDS) affects at least 10,000 people each year in the U.S., and is particularly prevalent in the aging population. MDS is a clonal disorder arising in hematopoietic stem cells (HSCs), characterized by impaired myeloid and erythroid differentiation and genomic instability. There are currently few therapeutic approaches available to improve cytopenias in MDS patients. Mutations in RNA splicing factors are observed in 50% of MDS cases, and are important contributors to MDS initiation and progression. Most hematopoietic growth factors and cytokines signal through the PI3 kinase (PI3K)/AKT pathway. We have found that compound deletion of the three PI3K isoforms P110a, b, and d in mouse hematopoietic cells leads to a phenotype resembling MDS, with cytopenias, impaired HSC differentiation and genomic instability. Interestingly, we observed enrichment of our TKO HSC expression signature in an MDS patient gene expression dataset. Furthermore, a subset of MDS samples have elevated expression levels of the negative regulator PTEN, suggesting functional inactivation of PI3K in these MDS patients. Our preliminary data reveals that HSCs in PI3K triple knockout (TKO) mice have a defect in autophagy, an intracellular recycling mechanism that is important for the maintenance of HSC differentiation. We found that pharmacologic induction of autophagy can improve differentiation of TKO HSCs. We also observed widespread alterations in mRNA splicing in TKO HSCs. Therefore, PI3K TKO mice are a valuable new model system to study the mechanisms of MDS initiation and progression. We hypothesize that maintenance of PI3K signaling in HSCs is required to maintain HSC differentiation and to protect HSCs from DNA damage. We propose to (1) determine whether induction of autophagy can improve myeloid and erythroid differentiation in MDS patient samples, (2) delineate the mechanism by which PI3K and its downstream kinase AKT control mRNA splicing in HSCs and in MDS, and (3) determine whether MDS cells with splicing factor mutations are more sensitive to inhibition of PI3K/AKT signaling. These approaches will further our understanding of how growth factor and cytokine signaling regulates autophagy and mRNA splicing through PI3K/AKT in MDS initiation. We also plan to test several therapeutic approaches to improve differentiation in MDS, including induction of autophagy and inhibition of PI3K/AKT in MDS with splicing factor mutations.