Chow A, Lucas D, Hidalgo A, Méndez-Ferrer S, Hashimoto D, Scheiermann C, Battista M, Leboeuf M, Prophete C, van Rooijen N, Tanaka M, Merad M, Frenette PS. Bone marrow CD169+ macrophages promote the retention of hematopoietic stem and progenitor cells in the mesenchymal stem cell niche. J Exp Med. 2011 Feb 14;208(2):261–71.
[toggle_content title=”Abstract”]Hematopoietic stem cells (HSCs) reside in specialized bone marrow (BM) niches regulated by the sympathetic nervous system (SNS). Here, we have examined whether mononuclear phagocytes modulate the HSC niche. We defined three populations of BM mononuclear phagocytes that include Gr-1hi monocytes (MOs), Gr-1lo MOs, and macrophages () based on differential expression of Gr-1, CD115, F4/80, and CD169. Using MO and conditional depletion models, we found that reductions in BM mononuclear phagocytes led to reduced BM CXCL12 levels, the selective down-regulation of HSC retention genes in Nestin+ niche cells, and egress of HSCs/progenitors to the bloodstream. Furthermore, specific depletion of CD169+ , which spares BM MOs, was sufficient to induce HSC/progenitor egress. depletion also enhanced mobilization induced by a CXCR4 antagonist or granulocyte colony-stimulating factor. These results highlight two antagonistic, tightly balanced pathways that regulate maintenance of HSCs/progenitors in the niche during homeostasis, in which cross talk with the Nestin+ niche cell promotes retention, and in contrast, SNS signals enhance egress. Thus, strategies that target BM hold the potential to augment stem cell yields in patients that mobilize HSCs/progenitors poorly.[/toggle_content] [toggle_content title=”Clodronate Liposome Parameters”] [custom_table]
Clodronate Concentration Total Lipid Concentration Lipid Composition Lipid Mole % Liposome Type Control Liposomes
5 mg/ml 23.4 mg/ml EPC/Chol 84/16 MLV PBS
[/custom_table] [/toggle_content] [toggle_content title=”Animals and Dosing”] [custom_table]
Animal Description Clodronate Dose Dosing Method/Site Target Phagocytes Local Dosing? Local Results
C57BL/6 mice2, 8-12 w 250 µl i.v./unspecified GR-1hi/Gr-1lo monocytes, GR-1-F4/80+CD169+ macrophages no N/A
[/custom_table] [/toggle_content] [toggle_content title=”Notes”]
  1. Liposome prep method cited — van Rooijen N, Sanders A. Liposome mediated depletion of macrophages: mechanism of action, preparation of liposomes and applications. Journal of Immunological Methods. 1994 Sep 14;174(1–2):83–93.
  2. Animals were dosed with clodronate (or control) liposomes at 1 d (14 h), 7 d, 10 d, 16 d, or 28 d before harvest.
[/toggle_content] [toggle_content title=”Results”]
  1. 14 h post-injection of clodronate liposomes, BM (GR-1-F4/80+CD169+) were reduced by 84%; GR-1hi by 88% and GR-1lo by 74%; total BM cells were depleted by 24%.
  2. Concurrently, circulating HSC increased by 12.9X.
  3. These remained >90% depleted 7 d post-injection, had recovered to 58% by 16 d  and were fully repopulated by 28 d.
  4. GR-1+ monocytes began to return at 7 d post-injection and did not affect HSC mobilization.
  5. HSC mobilization remained elevated at least until 16 d post-injection further supporting the role of , but not monocytes, in the process.
  6. depletion also elicited HSC mobilization, albeit at a lower level, in sympathectomized animals.