title: Transforming growth factor beta 1 directly and reversibly inhibits the initial cell divisions of long-term repopulating hematopoietic stem cells.
abstract: Hematopoiesis appears to be regulated, in part, by a balance between extracellular positive and negative growth signals. Transforming growth factor beta-1 (TGF-beta 1) has been shown to be a negative regulator of primitive hematopoietic cells. This study examined the direct effect of TGF-beta 1 on the proliferation and differentiation of long-term repopulating hematopoietic stem cells (LTR-HSC) in vitro. We previously reported a cell fractionation approach that includes the selection of low Hoescht 33342/low Rhodamine 123 (low Ho/Rh) cell fractions that are highly enriched for long-term repopulating cells (LTR-HSC) and also clone to a very high efficiency in the presence of stem cell factor (SCF) + interleukin-3 (IL-3) + IL-6: 90% to 100% of individually cultured low Ho/Rh cells formed high proliferative potential clones. This high cloning efficiency of an LTR-HSC enriched cell population enabled proliferation inhibition studies to be more easily interpreted. In this report, we show that the continuous presence of TGF-beta 1 directly inhibits the cell division of essentially all low Ho/Rh cells (in a dose-dependent manner) during their 0 to 5th cell division in vitro. Therefore, it follows that TGF-beta 1 must directly inhibit the proliferation of LTR-HSC contained within these low Ho/Rh cells. The time required for some low Ho/Rh cells to undergo their first cell division in vitro was also prolonged in the presence of TGF-beta 1. Furthermore, when low Ho/Rh cells were exposed to TFG-beta 1 for varying lengths of time before neutralization of the TGF-beta 1 by monoclonal antibody, the ability to form macroclones was markedly decreased after approximately 4 days of TGF-beta 1 exposure. In addition, 1 to 10 ng/mL of TGF-beta 1 resulted in a maintenance of high proliferative potential-colony-forming cell (HPP-CFC) during 8 days of culture compared with loss of HPP-CFC in cultures with no added TGF-beta 1. In conclusion, this study shows that TGF-beta 1 directly inhibits the initial stages of proliferation of LTR-HSC and appears to slow the differentiation of daughter cells of low Ho/Rh cells.
authors.affiliation: Department of Pathology, Medical School, University of Washington, Seattle, USA.
authors.forename: E
authors.initials: E
authors.lastname: Sitnicka
authors.forename: F W
authors.initials: FW
authors.lastname: Ruscetti
authors.forename: G V
authors.initials: GV
authors.lastname: Priestley
authors.forename: N S
authors.initials: NS
authors.lastname: Wolf
authors.forename: S H
authors.initials: SH
authors.lastname: Bartelmez
mesh_terms: D000818:Animals; D002455:Cell Division / Q000187:drug effects; D002478:Cells, Cultured; D005260:Female; D006131:Growth Inhibitors / Q000494:pharmacology*; D006412:Hematopoietic Stem Cells / Q000187:drug effects*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008811:Mice, Inbred DBA; D016212:Transforming Growth Factor beta / Q000494:pharmacology*
chemical_list: D006131:Growth Inhibitors; D016212:Transforming Growth Factor beta