Page 46 - Haematologica May 2020

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Haematologica 2020 Volume 105(5):1206-1215
Hematopoiesis
Early growth response 1 regulates hematopoietic support and proliferation in human primary bone marrow stromal cells
Hongzhe Li,1,2 Hooi-Ching Lim,1,2 Dimitra Zacharaki,1,2 Xiaojie Xian,2,3 Keane J.G. Kenswil,4 Sandro Bräunig,1,2 Marc H.G.P. Raaijmakers,4 Niels-Bjarne Woods,2,3 Jenny Hansson,1,2 and Stefan Scheding1,2,5
1Division of Molecular Hematology, Department of Laboratory Medicine, Lund University, Lund, Sweden; 2Lund Stem Cell Center, Department of Laboratory Medicine, Lund
3
University, Lund, Sweden; Division of Molecular Medicine and Gene Therapy, Department
4
of Laboratory Medicine, Lund University, Lund, Sweden; Department of Hematology,
Erasmus MC Cancer Institute, Rotterdam, the Netherlands and 5Department of Hematology, Skåne University Hospital Lund, Skåne, Sweden
ABSTRACT
Human bone marrow stromal cells (BMSC) are key elements of the hematopoietic environment and they play a central role in bone and bone marrow physiology. However, how key stromal cell functions are regulated is largely unknown. We analyzed the role of the immediate early response transcription factor EGR1 as key stromal cell regulator and found that EGR1 was highly expressed in prospectively- isolated primary BMSC, down-regulated upon culture, and low in non- colony-forming CD45neg stromal cells. Furthermore, EGR1 expression was lower in proliferative regenerating adult and fetal primary cells com- pared to adult steady-state BMSC. Overexpression of EGR1 in stromal cells induced potent hematopoietic stroma support as indicated by an increased production of transplantable CD34+CD90+ hematopoietic stem cells in expansion co-cultures. The improvement in bone marrow stroma support function was mediated by increased expression of hematopoiet- ic supporting genes, such as VCAM1 and CCL28. Furthermore, EGR1 overexpression markedly decreased stromal cell proliferation whereas EGR1 knockdown caused the opposite effects. These findings thus show that EGR1 is a key stromal transcription factor with a dual role in regu- lating proliferation and hematopoietic stroma support function that is controlling a genetic program to co-ordinate the specific functions of BMSC in their different biological contexts.
Introduction
Hematopoietic stem cell (HSC) niches are specialized local tissue microenviron- ments that maintain and regulate HSC. Aside from being skeletal stem cells with multilineage differentiation capacity, bone marrow mesenchymal stromal cells (BMSC) are essential constituents of the HSC niche. Despite this key role in hematopoiesis, and despite recent progress in the identification of primary BMSC,1,2 little is known about how proliferation, differentiation and hematopoi- etic support functions of these important niche cells are regulated.
We therefore approached the identification of potential BMSC regulators by investigating specific gene expression of highly-purified primary BMSC that were prospectively isolated from human bone marrow samples using recently-identi- fied surface marker combinations.1 Previously reported array-based comparative gene expression analysis showed high expression of early growth response 1 (EGR1) in primary BMSC compared to non-colony-forming cells (for details see Online Supplementary Table S1 in Li et al.1). Interestingly, EGR1 is an important regulator of different cellular processes3-5 and has been identified as a cell-intrinsic regulator of HSC proliferation and mobilization.6 Furthermore, data from knockout mice indicated a role of EGR1 on bone formation in vivo.7 These findings suggested that
Correspondence:
STEFAN SCHEDING
stefan.scheding@med.lu.se
Received: January 14, 2019. Accepted: July 19, 2019. Pre-published: August 1, 2019.
doi:10.3324/haematol.2019.216648
Check the online version for the most updated information on this article, online supplements, and information on authorship & disclosures: www.haematologica.org/content/105/5/1206
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