The stem/progenitor landscape is reshaped in a mouse model of essential thrombocythaemia and causes excess megakaryocyte production

Frameshift mutations in CALR (calreticulin) are associated with essential thrombocythaemia (ET), but the stages at and mechanisms by which mutant CALR drives transformation remain incompletely defined. Here, we use single-cell approaches to examine the haematopoietic stem/progenitor cell (HSPC) landscape in a mouse model of mutant CALR-driven ET. We identify a trajectory linking HSCs with megakaryocytes, and prospectively identify a novel intermediate population that is overrepresented in the disease state. We also show that mutant CALR drives transformation primarily from the earliest stem cell compartment, with some contribution from megakaryocyte progenitors. Finally, relative to wild-type HSCs, mutant CALR HSCs showed increases in JAK-STAT signalling, the unfolded protein response, cell cycle, and a previously undescribed upregulation of cholesterol biosynthesis. Overall, we have identified a novel megakaryocyte-biased cell population that is increased in a mouse model of ET and described transcriptomic changes linking CALR mutations to increased HSC proliferation and megakaryopoiesis.

钙网蛋白基因（CALR，calreticulin）的移码突变与原发性血小板增多症（essential thrombocythaemia, ET）密切相关，但突变型CALR驱动细胞转化的具体阶段及分子机制仍未完全阐明。本研究采用单细胞技术，在突变型CALR诱导的ET小鼠模型中解析造血干/祖细胞（haematopoietic stem/progenitor cell, HSPC）的转录图谱。我们鉴定出一条连接造血干细胞（haematopoietic stem cells, HSCs）与巨核细胞的分化轨迹，并前瞻性地发现了一类在疾病状态下异常富集的新型中间细胞群。研究同时证实，突变型CALR主要通过最早期的干细胞池驱动细胞转化，巨核细胞祖细胞亦发挥了部分促进作用。最后，相较于野生型造血干细胞，携带突变型CALR的造血干细胞中JAK-STAT信号通路、未折叠蛋白反应、细胞周期均出现上调，同时还存在此前未被报道的胆固醇生物合成通路激活。综上，本研究在ET小鼠模型中鉴定出一类富集的巨核细胞倾向性细胞群，并阐明了CALR突变通过调控转录组特征，促进造血干细胞增殖与巨核细胞生成的分子机制。