Loss of Angiopoietin-like 7 diminishes the regeneration capacity of hematopoietic stem and progenitor cells
© Xiao et al.; licensee Biomed Central. 2015
Received: 15 November 2014
Accepted: 29 December 2014
Published: 6 February 2015
Successful expansion of hematopoietic stem cells (HSCs) would benefit the use of HSC transplants in the clinic. Angiopoietin-like 7 promotes the expansion of hematopoietic stem and progenitor cells (HSPC) in vitro and ex vivo. However, the impact of loss of Angptl7 on HSPCs in vivo has not been characterized. Here, we generated Angptl7-deficient mice by TALEN-mediated gene targeting and found that HSC compartments in Angptl7-null mice were compromised. In addition, wild type (WT) HSPCs failed to repopulate in the BM of Angptl7-null mice after serial transplantations while the engraftment of Angptl7-deficient HSPCs in WT mice was not impaired. These results suggest that Angptl7 is required for HSPCs repopulation in a non-cell autonomous manner.
KeywordsAngptl7 Knockout-mice Hematopoietic stem cell Repopulation Homing
The autologous-allogeneic hematopoietic cell transplantation has been developed for decades [1,2], and numerous attempts have been made to expand the HSCs population in vitro and in vivo [3-5]. Agiopoietin-like proteins belong to a 7-member family of secreted glycoproteins that share sequence homology with angiopoietins, which are important modulators of angiogenesis . Several Angptl family proteins promote the expansion of murine and human HSPCs in vitro and ex vivo [7-9]. Angptl7 in the ECM of the trabecular meshwork plays an important role in the deposition and organization of the matrix of the outflow tissue . Recently, we found that ANGPTL7 stimulated the proliferation of human HSPCs ex vivo (Yiren Xiao, unpublished data). In addition, we uncovered that Angptl7, which was secreted by murine bone marrow SSEA4+ mesenchymal cells (Additional file 1: Figure S1), stimulated expansion of murine HSCs ex vivo (Additional file 2: Figure S2). However, whether Angptl7 is redundant and dispensable or not for repopulation of HSPCs in vivo remains unknown. In this study, we generated Angptl7 knockout mice and revealed that Angptl7 is essential for HSPC repopulation in a non-cell autonomous way.
As HSCs undergo dramatic expansion in fetal liver during embryo development [11-13], we examined the fetal liver HSC compartment and found that the percentages and numbers of Lin-Mac-1 + CD4- population, which was highly enriched of HSCs in fetal liver [14,15], were significantly lower in the fetal livers of Angptl7 −/− mice than that in Angptl7 +/− and Angptl7 +/+ mice (Figure 1b-c). In addition, we found the percentages and numbers of Lin-Sca-1 + c-Kit + (LSK) population in the BM of adult Angptl7 −/− mice were significantly lower than that in Angptl7 +/− and Angptl7 +/+ mice (Figure 1d-e). Further analysis showed that Angptl7 −/− mice had fewer long-term HSCs (Lin−Sca-1+Kit+Flk2−CD34−) than Angptl7+/− and Angptl7 +/+ mice (Figure 1f-g). Cloning forming assay results showed that BM cells from Angptl7 −/− mice had fewer granulocyte/monocyte progenitors (CFU-GM), but similar numbers of erythroid precursors (CFU-E/BFU-E) and hematopoietic progenitors (CFU-GEMM) than WT BM (Figure 1h). Therefore, Angptl7-deficient BM had normal levels of terminally differentiated hematopoietic cells, but decreased myeloid progenitors. To investigate whether other angiopoietin-like proteins compensate the loss of Angptl7 in BM, we compared the expression levels of other angiopoietin-like proteins in Angptl7-deficient BM stromal cells to that in WT BM stromal cells and found that their expression levels did not significantly change due to loss of Angptl7 (Additional file 7: Figure S4).
In this study, we demonstrated that deficiency of Angptl7 in the BM niche as a lack of exogenous Angptl7 stimulation impaired the reconstitution of HSCs in lethally irradiated mice, whereas endogenous deletion of Angptl7 in HSCs did not affect repopulation of HSCs in lethally irradiated mice. Thus, Angptl7 was indispensable for BM microenvironment to support HSC repopulation.
This study was supported in part by the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant No. XDA01020310) to P. L., the National Natural Science Foundation of China (Grant No. 81272329 and 81200255 to P. L., and 81327801 to D. W.), the National Basic Research Program of China (973 Program) (2011CB504004 and 2010CB945500) to D. W.
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