Dissecting intrinsic and extrinsic mechanisms in the clonal expansion of the hematopoietic stem cells in del(5q) MDS

骨髓增生异常综合征(MDS)以造血功能障碍、外周血细胞减少和向急性髓系白血病(AML)频繁转化为特征。染色体5q缺失是MDS中最常见的细胞遗传学异常，与一种一致的临床表型有关，称为5q综合征。5q-造血干细胞(HSCs)在骨髓中获得了优势，并超过了正常的造血力。一个关键但尚未解决的问题是，这种杂合性遗传损伤如何促进克隆优势、克隆持久性和恶性转化。在我在宿主组(R.Schneider，Erasmus MC，鹿特丹，NL)的初步工作中，我系统地比较了位于5号染色体共同缺失区的候选基因，这些基因被认为在单倍体不足状态(基因表达下调50%)时有助于HSC的克隆优势。我发现了两个单倍体不足的基因，它们导致了HSC的寡克隆性扩张，并超过了正常的造血系统--Csnk1a1和Egr1。这项建议的主要目的是确定具有Csnk1a1和Egr1单倍体缺陷的HSC如何在骨髓中获得优势，以及骨髓微环境是如何改变和支持这一优势的。在目标1中，我将使用新的可诱导的小鼠基因模型和骨髓移植，单独和联合研究Csnk1a1和Egr1单倍体缺陷导致克隆性扩张的细胞内在机制。在目标2中，我将使用体内CRISPR/Cas9基因组编辑来确定在del(5q)MDS中常见的TP53突变如何与这些候选基因在del(5q)克隆的恶性转化中协作。在目标3中，我将剖析del(5q)MDS克隆是如何改变骨髓微环境的，以及这种改变如何潜在地促进疾病的表型和进展，使用宿主组产生的新的造血细胞和间充质细胞系，结合原始患者样本的单细胞转录。我提出的研究将继续阐明这种常见和重要的遗传损伤的MDS表型的潜在机制，并提供更广泛的对癌症中大量杂合性缺失的生物学见解。

Myelodysplastic syndrome (MDS) is characterized by dysplastic hematopoiesis, peripheral cytopenias and frequent transformation to acute myeloid leukemia (AML). Deletions of chromosome 5q are the most common cytogenetic abnormality in MDS and are associated with a consistent clinical phenotype, termed the 5q- syndrome. 5q- hematopoietic stem cells (HSCs) gain an advantage in the bone marrow and outcompete normal blood formation. One critical and yet unsolved question is how this heterozygous genetic lesion contributes to clonal advantage, clonal persistence and malignant transformation.In my preliminary work in the host group (R. Schneider, Erasmus MC, Rotterdam, NL), I have systematically compared candidate genes located in the common deleted region on chromosome 5, that supposedly contribute to clonal advantage of HSC when in haploinsufficient state (50% downregulation of gene expression). I identified two haploinsufficient genes that lead to oligoclonal expansion of the HSC and outcompete normal hematopoiesis – Csnk1a1 and Egr1. The main goal of this proposal is to determine how HSCs with Csnk1a1 and Egr1 haploinsufficiency gain an advantage in the bone marrow and how the bone marrow microenvironment is altered and supports this advantage.In aim 1, I will investigate the cell intrinsic mechanism of Csnk1a1 and Egr1 haploinsufficiency leading to clonal expansion, individually and in combination, using novel inducible genetic mouse models and bone marrow transplantation. In aim 2, I will determine how commonly found TP53 mutations in del(5q) MDS collaborate with these candidate genes in malignant transformation of the del(5q) clone using in vivo CRISPR/Cas9 genome editing. In aim 3, I will dissect how the bone marrow microenvironment is altered by the del(5q) MDS clone and how this alteration potentially contributes to the disease phenotype and progression, using novel hematopoietic and mesenchymal cell lines, that the host group has generated, in combination with single-cell transcriptomics in primary patient samples. My proposed studies will continue to elucidate the mechanisms underlying the MDS phenotype for this common and important genetic lesion and provide further insight into the biology of large heterozygous deletions in cancer more broadly.