Exploring Experimental Hematology: March 2024 (Volume 131)

G-CSF−induced hematopoietic stem cell mobilization from the embryonic hematopoietic niche does not require neutrophils and macrophages
(Ji Wook Kim, Evan A. Fedorova, and Leonard I. Zon)

In this issue of Simply Blood, we are highlighting one of the journal’s latest manuscripts by first author Ji Wook Kim. This study was conducted in Dr. Leonard Zon’s laboratory (Department of Stem Cell and Regenerative Biology, Harvard Medical School) and has demonstrated that the Granulocyte colony-stimulating factor (G-CSF) induced hematopoietic stem and progenitor cell (HSPC) mobilization from the embryonic hematopoietic niche in not neutrophil and macrophage depended.

The discrepancies in literature suggesting G-CSF either acts directly to mobilize HSPCs or requires myeloid cells has created ambiguity regarding the mechanism of action of G-CSF. Kim et al, developed a stable transgenic line with a heat-inducible csf3b, a zebrafish ortholog of human CSF3, which translates into G-CSF and confirmed that G-CSF effectively mobilizes HSPCs from the caudal hematopoietic tissue (CHT) of the zebrafish. Secondly, they depleted neutrophils and macrophages using a nitroreductase (NTR)-based cell ablation system and demonstrated that G-CSF successfully mobilizes HSPCs even in the absence of neutrophils or macrophages. Collectively, their findings demonstrate that neutrophils and macrophages are not necessary for G-CSF-induced HSPC mobilization from the embryonic hematopoietic niche.

My reason for reading the paper:
G-CSF is a ubiquitous cytokine used to mobilize HSPC from BM to peripheral blood before hematopoietic stem cell transplantation. It is either used alone or in combination with other drugs or cytokines to enhance mobilization efficiency. However, despite its widespread use, many patients still fail to mobilize sufficient quantities of HSPCs required for the successful transplant. Therefore, understanding how HSPCs and the niche respond to G-CSF could lead to development of new strategies that will enable more effective mobilization of HSPCs.

Strategy used in this paper:
The authors developed a transgenic zebrafish line (hsp70l:csf3b) which allows it to express GCSF in an inducible manner (referred as iGCSF in paper). Heat shock was given to the transgenic zebrafish line to confirm that G-CSF is being produced and mobilization is occurring by assessing embryonic CHT and kidney marrow post fertilization via whole mount in situ hybridisation or live imaging. To assess whether neutrophils or macrophages are required for the G-CSF−induced HSPC mobilization from the CHT, nitroreductase (NTR)-based cell ablation system was developed by crossing the iGCSF line with Tg(mpx:GAL4; UAS:NTR-mCherry), in which neutrophils express NTR or Tg(mpeg:GAL4; UAS:NTR-mCherry), in which macrophages express NTR. NiF treatment was given to deplete neutrophils or macrophages, respectively and HSPC mobilization was assessed via WISH and live imaging.

Reasons you should read this paper:
This paper highlights the dynamics of HSPC egress from the CHT during development and has delineated new molecular mechanisms involved in HSPC mobilization. Importantly, they have demonstrated that neutrophil and macrophage-independent pathways are involved in G-CSF-induced HSPC mobilization from the embryonic hematopoietic niche. Future research focusing on the factors that HSPCs secrete in response to G-CSF and how the niche is affected by these factors could lead to new strategies to increase HSPC mobilization for HSPC transplants.

Attached Figure:
Figure 4 Granulocyte colony-stimulating factor (G-CSF) mobilizes hematopoietic stem and progenitor cells (HSPCs) in the absence of neutrophils or macrophages. (A) Scheme of Nifurpirinol treatment for ablation of nitroreductase expressing neutrophils or macrophages. (B) cmyb whole-mount in situ hybridization (WISH) of 92 hours post fertilization (hpf) inducible G-CSF (iG-CSF) embryos with or without neutrophils. Arrowhead points to the cmyb signal at the kidney. (C) cmyb WISH of 92 hpf iG-CSF embryos with or without macrophages. Arrowhead points to the cmyb signal at the kidney.

Blog post contributed by Simranpreet Kaur, PhDISEH Publications Committee

Please note that the statements made by Simply Blood authors are their own views and not necessarily the views of ISEH. ISEH disclaims any or all liability arising from any author's statements or materials.


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