Phosphatase, Mg2+/Mn2+ Dependent 1B (Ppm1b) regulates the self-renewal of HSCs through the Wnt/β-catenin pathway [scRNA-Seq]. Phosphatase, Mg2+/Mn2+ Dependent 1B (Ppm1b) regulates the self-renewal of HSCs through the Wnt/β-catenin pathway [scRNA-Seq]

Hematopoietic stem cells (HSCs) have unique abilities to renew themselves and generate differentiated progenies of all blood cell lineages; however, how HSCs maintain the balance of self-renewal and lineage differentiation remains largely unknown. Herein, we showed that in mice the hematologic system deletion of Phosphatase, Mg2+/Mn2+ Dependent 1B (Ppm1b), a protein serine or threonine phosphatase highly expressed in HSCs, induces the suppression of phenotypic HSC expansion due to the blockage of cell cycle. Loss of Ppm1b impairs HSC self-renewal and hematopoietic reconstitution which were revealed by limiting dilution and BM transplantation assays. Through transcriptomic analysis, we observed that the Wnt/β-catenin pathway is downregulated in Ppm1b-deficient mice. Mechanistically, we provided evidence that Ppm1b interacted with β-catenin by performing a proximity ligation assay. Moreover, using an HN252 as a small molecule probe, we further found that Ppm1b inhibition suppressed the self-renewal of HSC and led to a decrease in common lymphoid progenitor cells, resulting in a reduction of B cells in the bone marrow and peripheral blood in turn. In the study we characterized an indispensable role of Ppm1b in regulating HSC self-renewal and B cell development via Wnt/β-catenin pathway. Overall design: Single cell- and bulk RNA-seq were performed on Ppm1bCKO and Ppm1bfl/fl mouse Lsk cells isolated from the BM.

造血干细胞（Hematopoietic stem cells, HSCs）具备独特的自我更新能力，可分化产生所有血细胞谱系的成熟子代细胞；然而，造血干细胞如何维持自我更新与谱系分化的动态平衡，目前仍尚未完全明确。
本研究证实，在小鼠体内敲除造血系统中高表达于造血干细胞的丝氨酸/苏氨酸蛋白磷酸酶——磷酸酶Mg²⁺/Mn²⁺依赖型1B（Phosphatase, Mg2+/Mn2+ Dependent 1B, Ppm1b）——会通过阻滞细胞周期，抑制表型造血干细胞的扩增。通过极限稀释实验与骨髓移植实验证实，Ppm1b的缺失会损害造血干细胞的自我更新能力与造血重建功能。
转录组分析结果显示，Ppm1b缺陷小鼠体内的Wnt/β-连环蛋白（Wnt/β-catenin）通路表达下调。
机制研究层面，我们通过邻近连接实验证明，Ppm1b可与β-连环蛋白发生相互作用。此外，使用小分子探针HN252抑制Ppm1b活性后，我们进一步发现，Ppm1b抑制会削弱造血干细胞的自我更新能力，并减少常见淋巴系祖细胞的数量，进而依次导致骨髓与外周血中的B细胞生成量减少。
本研究阐明了Ppm1b通过Wnt/β-连环蛋白通路调控造血干细胞自我更新与B细胞发育的不可或缺的重要作用。
整体实验设计：对从骨髓（bone marrow, BM）中分离得到的Ppm1b条件性敲除（Ppm1bCKO）与Ppm1b flox/flox（Ppm1bfl/fl）小鼠的Lsk细胞，开展单细胞RNA测序与批量RNA测序。