Bcor deficiency perturbs erythro-megakaryopoiesis and cooperates with Dnmt3a loss in acute erythroid leukemia onset in mice

Recurrent loss-of-function mutations of BCL6 co-repressor (BCOR) gene are found in about 4% of AML patients with normal karyotype and are associated with DNMT3a mutations and poor prognosis. Therefore, new anti-leukemia treatments and mouse models are needed for this combinatorial AML genotype. For this purpose, we first generated a Bcor-/- knock-out mouse model characterized by impaired erythroid development (macrocytosis and anemia) and enhanced thrombopoiesis, which are both features of myelodysplasia/myeloproliferative neoplasms. We then created and characterized double Bcor-/-/Dnmt3a-/- knock-out mice. Interestingly, these animals developed a fully penetrant acute erythroid leukemia (AEL) characterized by leukocytosis secondary to the expansion of blasts expressing c-Kit+ and the erythroid marker Ter119, macrocytic anemia and progressive reduction of the thrombocytosis associated with loss of Bcor alone. Transcriptomic analysis of double knock-out bone marrow progenitors revealed that aberrant erythroid skewing was induced by epigenetic changes affecting specific transcriptional factors (GATA1-2) and cell-cycle regulators (Mdm2, Tp53). These findings prompted us to investigate the efficacy of demethylating agents in AEL, with significant impact on progressive leukemic burden and mice overall survival. Information gained from our model expands the knowledge on the biology of AEL and may help designing new rational treatments for patients suffering from this high-risk leukemia. Overall design: RNA-seq analysis on LSK and MEP BM cells of Bcor-/-Dnmt3a-/- mice.

BCL6共阻遏物（BCL6 co-repressor, BCOR）基因的复发性功能缺失突变在约4%的核型正常急性髓系白血病（Acute Myeloid Leukemia, AML）患者中被检出，且与DNA甲基转移酶3α（DNA methyltransferase 3 alpha, DNMT3A）突变及不良预后相关。因此，针对该组合基因型AML的新型抗白血病治疗策略与动物模型亟待开发。为此，我们首先构建了Bcor基因敲除（knock-out, KO）小鼠模型，该模型表现为红细胞发育受损（巨红细胞症与贫血）及血小板生成增强，二者均为骨髓增生异常/骨髓增殖性肿瘤（myelodysplasia/myeloproliferative neoplasms, MDS/MPN）的典型特征。随后我们构建并鉴定了Bcor-/-/Dnmt3a-/-双基因敲除小鼠。值得注意的是，此类动物可完全外显急性红白血病（acute erythroid leukemia, AEL），其病理特征包括：表达c-Kit+与红细胞标志物Ter119的原始细胞扩增引发白细胞增多，伴随巨幼红细胞性贫血，且相较于仅缺失Bcor的小鼠，其血小板增多症状呈进行性减轻。对双基因敲除小鼠骨髓祖细胞的转录组分析显示，表观遗传改变通过调控特定转录因子（GATA1-2）与细胞周期调控因子（Mdm2、Tp53）的表达，诱导了异常的红细胞系分化偏倚。上述发现促使我们探究去甲基化药物对AEL的治疗潜力，结果显示该类药物可显著改善进行性白血病负荷并延长小鼠总生存期。本研究通过该模型拓展了对AEL生物学特性的认知，或可为该高危白血病患者的精准治疗方案设计提供理论参考。总体实验设计：对Bcor-/-Dnmt3a-/-小鼠的LSK与MEP骨髓细胞开展RNA测序（RNA-seq）分析。