Stem Cells, Vol 13, 175-185, Copyright © 1995 by AlphaMed Press
AM5, a protein-associated polysaccharide, stimulates hematopoiesis and modulates the expression of endogenous hematopoietic growth factors in murine long-term bone marrow cultures
G Guenechea, JA Bueren, G Maganto, P Tuduri, A Guerrero, JP Pivel and A Real
Unidad de Biologia Molecular y Celular, CIEMAT, Madrid, Spain.
We have investigated the mechanism behind the hematopoietic stimulation
mediated by AM5, a protein-associated polysaccharide that stimulates in
vivo the murine hematopoietic system. A dose-dependent increase in
hematopoietic progenitors was observed in long-term bone marrow cultures
(LTBMCs) treated in vitro with AM5. The stimulatory effect was more marked
in colony-forming units-granulocyte-macrophage (CFU-GM) than in CFU-spleen
(CFU-S) progenitors and also more significant in the supernatant than in
the adherent layer. This stimulatory effect was reversible, and continuous
stimulation with high doses of AM5 was conductive to a progressive
exhaustion of the culture. The analysis of the CFU-GM stimulating activity
present in the supernatant of AM5- treated cultures revealed a
dose-dependent induction of granulocyte- macrophage colony-stimulating
activity (GM-CSA), in contrast with control cultures in which no CSA was
detected. Northern blots of LTBMC- adherent layers obtained after in vitro
treatment with AM5 revealed a significant mRNA expression for interleukin 1
alpha (IL-1 alpha), granulocyte-macrophage colony-stimulating factor
(GM-CSF), macrophage CSF (M-CSF) and granulocyte CSF (G-CSF), in contrast
with adherent layers from untreated cultures which only expressed, in
detectable levels, M-CSF and stem cell factor (SCF). The SCF expression was
down- modulated in AM5-treated cultures. Our results strongly suggest that
the hematopoietic stimulation induced by AM5 is mediated by the modulated
expression of endogenous hematopoietic growth factors.
