SLC38A4蛋白对造血干细胞自我更新的调控作用和分子机制研究

Hematopoietic stem cell (HSC) is the origin of all hematopoietic cells in the process of hematopoietic lineage commitment. Discovering the mechanism of HSC fate decision provides theoretical basis on blood disease pathogenesis and clinical therapy. Self-renewal and development of HSC is finely controlled by stemness fate decision signals and hematopoietic microenvironment regulation. Our preliminary data show that Slc38a4 deficiency leads to abnormal bone marrow hematopoiesis. Cell cycles of HSCs are arrested in G0 stage in Slc38a4-deficient mice. SLC38A4 is specifically expressed in endothelial cells in hematopoietic niche. Through the yeast two-hybrid screen, we found that SLC38A4 interacted with APH1B which is a subunit of γ-secretase complex. This study is to further discuss the interaction between SLC38A4-expressed endothelial cells and LT-HSCs, to explore the mechanism of SLC38A4 in regulating Notch signaling pathway through γ-secretase activity and self-renewal of HSC. And this study is to confirm the role of endothelial cells in hematopoietic niche to regulate self-renewal of HSCs through SLC38A4-Notch signaling.

造血干细胞（HSC）是整个造血谱系建立过程中其它血液细胞的来源。对HSC命运决定机制的研究将为更好地认识血液病的发病机制及临床治疗提供理论依据。HSC的自我更新及发育分化受到干细胞命运决定信号及造血微环境两方面因素的精细调节。申请人通过前期工作发现，Slc38a4基因缺失使小鼠骨髓造血明显异常，更多的LT-HSC停滞在G0期。SLC38A4在造血微环境的内皮细胞中特异性高表达。通过酵母双杂交筛选，我们发现SLC38A4可与γ分泌酶亚基APH1B相互作用。在此基础上，我们将深入探讨SLC38A4高表达的内皮细胞与HSC的相互作用关系，探究SLC38A4通过γ分泌酶活性调控对Notch分子的切割并调节HSC自我更新的分子机制，探明造血微环境内皮细胞通过SLC38A4-Notch信号对HSC自我更新的调控作用。

造血干细胞（HSC）是整个造血谱系建立过程中其它血液细胞的来源。对HSC命运决定机制的研究将为更好地认识血液病的发病机制及临床治疗提供理论依据。HSC的自我更新及发育分化受到干细胞命运决定信号及造血微环境两方面因素的精细调节。造血干细胞（HSC）可以自我更新并分化为所有血细胞成分。造血干细胞的自我更新能力受其命运决定因素和骨髓（BM）微环境的调节。但是，调节HSC自我更新的潜在机制仍然难以捉摸。在这里，我们显示溶质载体Slc38a4在BM中的正弦内皮细胞上高表达。SLC38A4缺乏会损害HSC的自我更新和造血功能。SLC38A4与在HSC膜上表达的γ-分泌酶的亚基Aph1b缔合，从而激活γ-分泌酶的酶促活性，该蛋白水解Notch2以启动Notch2信号传导。Notch2启动后，Dtx1促进LT-HSC的自我更新维持，作为Notch2信号通路的下游调节剂。 此外，Aph1b或Dtx1的删除也废除了HSC的自我更新和造血作用。因此，SLC38A4在HSC的自我更新维持中作为BM生态位因子起着至关重要的作用。