MYCT1 as a moderator for signaling between human HSC and their niche

摘要 造血干细胞(HSC)需要整合微环境线索来切换其命运 静止、自我更新和分化，从而在生命中维持造血。然而， 在培养过程中，控制HSC干细胞的分子程序变得严重失调，阻碍了我们的能力 扩增功能性造血干细胞用于治疗血液病。我们的数据发现MYCT1(Myc目标1)为 人类HSC调节因子，对它们的扩增和植入至关重要，但在 差异化与文化。我们发现MYCT1定位于内体，与囊泡成分相互作用， 在HSCs中具有关键功能的信号受体(如TGFBR1和2)，并控制内吞作用的速率， 它调节细胞信号，必须受到严格调控，以维持HSC的干性。很多基因 MYCT1基因敲除失控(KD)与HSC分裂和自我更新有关。我们假设 MYCT1通过微调多个信号来管理HSC的干性及其在命运选项之间平衡的能力 通过内吞作用的控制来提示。我们已经创建了MYCT1基因敲除和过度表达的工具箱 载体，包括各种MYCT1缺失突变体，可用于原代人类HSPC以及HSC- 用LIKE和内皮细胞模型研究MYCT1的作用机制。我们将调查MYCT1是如何- 介导的内吞控制影响HSC中的信号传递，以及这如何影响HSC细胞命运的决定 包括静止和不对称VS对称除法。然后我们将评估拯救MYCT1是否受到监管 过程改善培养的人HSC的功能，包括使用MLLT3扩增的HSC 过度表达。我们的工作可能会开辟新的策略，在体外保持HSC的可移植性 扩大并最终有助于扩大HSC的临床应用。

SUMMARY Hematopoietic stem cells (HSC) need to integrate microenvironmental cues to switch their fate between quiescence, self-renewal, and differentiation, thereby sustaining hematopoiesis through life. However, the molecular programs governing HSC stemness become grossly dysregulated during culture, hindering our ability to expand functional HSCs for treating hematological diseases. Our data uncovered MYCT1 (Myc target 1) as human HSC regulatory factor that is critical for their expansion and engraftment, but becomes suppressed during differentiation and culture. We found that MYCT1 localizes in endosomes, interacts with vesicle components and signaling receptors with critical functions in HSCs (e.g. TGFBR1 and 2), and controls the rate of endocytosis, which modulates cell signaling and must be tightly regulated to maintain HSC stemness. Many genes dysregulated upon MYCT1 knockdown (KD) are linked to HSC division and self-renewal. We hypothesize that MYCT1 governs HSC stemness and their ability to balance between fate options by fine-tuning multiple signaling cues through the control of endocytosis. We have created a toolbox of MYCT1 knockdown and overexpression vectors, including various MYCT1 deletion mutants, that can be used in primary human HSPCs as well as HSC- like and endothelial cell line models to investigate MYCT1 mechanism of action. We will investigate how MYCT1- mediated control of endocytosis affects signaling in HSCs, and how this influences HSC cell-fate decisions including quiescence and asymmetric vs symmetric division. We will then assess if rescuing MYCT1 regulated processes improves the function of cultured human HSC, including those expanded using MLLT3 overexpression. Our work may open up new strategies to maintain HSC transplantability during ex vivo expansion and ultimately help broaden HSC clinical applications.