Secreted protein Del-1 regulates myelopoiesis in the hematopoietic stem cell niche
Ioannis Mitroulis, … , George Hajishengallis, Triantafyllos Chavakis
Ioannis Mitroulis, … , George Hajishengallis, Triantafyllos Chavakis
Published August 28, 2017
Citation Information: J Clin Invest. 2017;127(10):3624-3639. https://doi.org/10.1172/JCI92571.
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Research Article Hematology Immunology

Secreted protein Del-1 regulates myelopoiesis in the hematopoietic stem cell niche

Abstract

Hematopoietic stem cells (HSCs) remain mostly quiescent under steady-state conditions but switch to a proliferative state following hematopoietic stress, e.g., bone marrow (BM) injury, transplantation, or systemic infection and inflammation. The homeostatic balance between quiescence, self-renewal, and differentiation of HSCs is strongly dependent on their interactions with cells that constitute a specialized microanatomical environment in the BM known as the HSC niche. Here, we identified the secreted extracellular matrix protein Del-1 as a component and regulator of the HSC niche. Specifically, we found that Del-1 was expressed by several cellular components of the HSC niche, including arteriolar endothelial cells, CXCL12-abundant reticular (CAR) cells, and cells of the osteoblastic lineage. Del-1 promoted critical functions of the HSC niche, as it regulated long-term HSC (LT-HSC) proliferation and differentiation toward the myeloid lineage. Del-1 deficiency in mice resulted in reduced LT-HSC proliferation and infringed preferentially upon myelopoiesis under both steady-state and stressful conditions, such as hematopoietic cell transplantation and G-CSF– or inflammation-induced stress myelopoiesis. Del-1–induced HSC proliferation and myeloid lineage commitment were mediated by β3 integrin on hematopoietic progenitors. This hitherto unknown Del-1 function in the HSC niche represents a juxtacrine homeostatic adaptation of the hematopoietic system in stress myelopoiesis.

Authors

Ioannis Mitroulis, Lan-Sun Chen, Rashim Pal Singh, Ioannis Kourtzelis, Matina Economopoulou, Tetsuhiro Kajikawa, Maria Troullinaki, Athanasios Ziogas, Klara Ruppova, Kavita Hosur, Tomoki Maekawa, Baomei Wang, Pallavi Subramanian, Torsten Tonn, Panayotis Verginis, Malte von Bonin, Manja Wobus, Martin Bornhäuser, Tatyana Grinenko, Marianna Di Scala, Andres Hidalgo, Ben Wielockx, George Hajishengallis, Triantafyllos Chavakis

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Figure 1

Expression of Del-1 in HSC niche cell populations.

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Expression of Del-1 in HSC niche cell populations. (A) Edil3 mRNA levels...
(A) Edil3 mRNA levels in the cBM and endosteal region (n = 5 mice per group). (B) Edil3 mRNA levels in stromal cell populations from CXCL12-GFP mice: CD45–Ter119–CD31–GFPhi (CAR) cells, CD45–Ter119–CD31–GFP– MSCs, and CD45–Ter119–CD31+GFPint endothelial cells (EC; n = 3–4). The mRNA expression was normalized against β2M. (C) Gating strategy for the isolation of endothelial cells. After gating on CD45–Lin– cells, sinusoidal (sBMEC; CD31+Sca1–) and arteriolar (aBMEC; CD31+Sca1+) BM endothelial cells were isolated. VE-cadherin (VE-cadh) staining was used to confirm the arteriolar origin of the CD31+Sca1+ cell population. Right: Edil3 mRNA levels in sBMECs and aBMECs (n = 3–4). mRNA expression was normalized against β2M. (D) aBMECs were further sorted according to Vcam1 expression. Edil3 mRNA levels in Vcam1lo and Vcam1hi aBMECs as well as in CD45–Lin–CD31–Sca1–CD51+ OSL cells (n = 4–5). mRNA expression was normalized against β2M. (E) Localization of Del-1 in the perivascular area of the BM; vessel lumen staining was performed with isolectin B4 (lectin). Del-1–deficient mice served as controls for the Del-1 staining. (F) Fluorescence microscopy image showing the presence of Del-1 in arterioles. Endothelial staining was performed using anti-PECAM1 and VE-cadherin antibodies. Scale bars: 5 μm. (G) EDIL3 mRNA in hMSCs and primary human osteoblasts (hOB) was compared with EDIL3 mRNA in HUVECs (HUVECs, n = 4 independent cultures; hMSCs, n = 4 donors; hOBs, n = 1 performed in technical replicates). The mRNA expression was normalized against GAPDH. (H) Del-1 concentration in culture supernatants of hMSCs was assessed by ELISA (n = 4 donors). Data are presented as mean ± SEM. Mann-Whitney U test, *P < 0.05, **P < 0.01.