Roles And Functions Of Transcription Factor Nupr1 And Trim27 In Hematopoietic Stem Cells

Majority of the hematopoietic stem cells(HSCs)are dormant under homeostasis,and only a small proportion of HSCs are actively proliferating to maintain the multi-lineage hematopoiesis.Dormant HSCs can rapidly be activated and proliferate in response to certain stresses,such as irradiation caused blood cell death.After the emergent hematopoiesis are completed,most HSCs return to dormancy.In response to environmental signal stimulation,the intrinsic factors in HSCs will change to achieve functional adjustment and status transition.Thus,investigation of the regulatory network of status-conversion of HSCs might provide insight into manipulating HSCs in vitro,such as maintenance,expansion,and lineage-restricted proliferation.In this study,we chose two transcription factors that are preferentially expressed in HSCs,and investigated their roles and functions in hematopoietic stem cells at cellular and molecular levels.Nuprl(Nuclear protein transcription regulator 1)is a stress-response gene,encoding a transcription factor which is a member of high-mobility group of proteins.To date,little is known about the function of Nuprl in HSCs.The expression level of Nuprl was upregulated during the expansion process of murine HSCs in vitro.In our preliminary data,we found that Nuprl was preferentially expressed in HSCs,when compared with the multipotent progenitors(MPPs)and other mature cells under homeostasis.Therefore,we investigated the role of loss of function of Nuprl in HSCs by constructing an Nuprl knockout mouse model.Germline deletion of Nuprl specifically activated dormant HSCs under homeostasis without changing the absolute number of HSCs.Furthermore,loss of Nupr1 conferred repopulating advantages on HSCs,demonstrated by predominant Nupr1-/-HSCs and lineage cells under competitive setting with wild type HSCs in transplanted recipients.Interestingly,Nupr1-/-HSCs showed no phenotypes of exhaustion and senescence during serial transplantations.Transcriptome analysis Nupr1-/-HSCs using RNAseq analysis demonstrated that loss of Nuprl altered multiple signaling pathways in HSCs,including p53 pathway,and G-protein coupled receptor signaling pathway.In addition,we also evaluated the role of Nuprl in HSC proliferation induced by irradiation.Nupr1-/-HSCs survived through sublethal dose of irradiation recovered much faster than WT HSCs.In aggregation,we systemically investigated the roles of Nuprl in maintaining the dormancy of HSCs by loss of function approach.Others showed that Trim27 expanded HSCs in vivo.However,the knowledge of the functions of Trim27 in HSCs is largely unknown.Here,we investigated the roles of Trim27 in hematopoiesis by enforcing its expression in mouse and human hematopoietic stem and progenitor cells(HSPC).Ectopic expression of Trim27 in mouse fetal liver hematopoietic stem and progenitors enhanced reconstitution activity and promoted myelopoiesis in recipient mice,which was correlated with the expansion of granulocyte/macrophage progenitor(GMP)compartment in BM.However,Ectopic expression of Trim27 showed no obvious impact on HSCs.Transcriptome analysis of Trim27-overexpressing myeloid progenitor cells indicated that Trim27 upregulated myeloid essential regulators,including Spil and Cebpg;upregulated myeloid proliferation related signaling genes Nras,Runx1 and Cbfb;upregulated JAK/STAT signaling inhibitors Socs2,Socs3 and Cish;and upregulated myeloid maturation relatedgenes Adam8 and Dek.Moreover,the myeloproliferative advantage caused by overexpressing Trim27 in hematopoiesis is conserved between mouse and human species,demonstrated by more CFU-M formation in vitro culture and outgrowth of myeloid lineage cells in NOG recipient mice transplanted with human UCB HSPCs overexpressing TRIM27 in vivo.In summary,this is the first study showing that Trim27 confers competitive hematopoiesis by promoting myeloid bias differentiation of HSPC,but not by expanding HSC,which is conserved in mouse and human hematopoiesis.Taken together,we reveal the functions of transcription factor Nuprl and Trim27 in HSCs.Loss of Nuprl specifically activated HSCs,consequently leading to repopulating advantage and fast-recover speed during stress hematopoiesis after irradiation.Trim27 enhanced myelopoiesis by directly targeting myeloid progenitors instead of HSCs.These findings add knowledge for comprehensive understanding the roles of Nuprl and Trim27 in HSCs.