In diabetes, glycation, tissue oxidation and endothelial function are all abnormal and predisposing to microvascular complications but interrelationships are complex with glycation appearing most direct.
Normal human bone marrow stroma cells include stem cells for both haemopoietic and osteochondrogenic lineages and express both bone morphogenetic protein (BMP) type I and type II receptors. As a member of the TGF-beta super-family, BMP-6 binds to both BMP type I and type II receptors and is involved in the developmental processes of renal and hepatic systems as well as of human foetal intestine. Also, BMP-6 induces osteoblastic differentiation of pluripotent mesenchymal cells and is an autocrine stimulator of chondrocyte differentiation. The present study was carried out to investigate the effect of BMP-6 on human cobblestone-area-forming cells (CAFC), that represent the functional primitive repopulating haemopoietic stem cell in long-term bone marrow culture. Also, the effect of BMP-6 on marrow stroma production of interleukin-6, -11 and their common receptor gp130 that is expressed in haemopoietic stem cells and is indispensable for their proliferation and tri-lineage differentiation was examined. Moreover, the effect of BMP-6 on marrow stroma release of soluble adhesion molecule VCAM-1 mediating the primitive haemopoietic stem cell adhesion to marrow stroma was examined. The number of CAFC was significantly reduced after BMP-6 treatment from 88+/-10 per 10(5)cells in control cultures in a dose dependent manner to only 48+/-3 per 10(5)cells in 50 ng/ml BMP-6-treated cultures, P< 0.01. Quantitative ELISA measurement revealed 50 ng/ml BMP-6 was able to significantly reduce IL-6 and IL-11 production from marrow stroma, P< 0.01. Also, BMP-6 significantly increased soluble gp130 release by 7.4-fold in 50 ng/ml BMP-6-treated marrow stroma cultures. The profound rapid increase in this natural antagonist of human IL-6 cytokine family may reduce the gp130 signaling. Also, the soluble VCAM-1 released increased by two-fold in 50 ng/ml BMP-6-treated marrow stroma cultures. The marked increase in the soluble form may exert an antagonist effect on the function of VCAM-1 (ligand for VLA4). Recently, blocking the VLA4/VCAM-1 adhesion pathway was shown to mobilise haemopoietic CD34 positive cells in normal individuals. Also, we previously observed a significantly lower expression of VLA4 (CD49d) on G-CSF-mobilised blood CD34 positive cells than on bone marrow CD34 positive cells before mobilisation in the same normal donors. Since BMP are currently being used in clinical trials for bone repair and fracture healing, the present results suggest a possible role for BMP-6 in mobilising CD34 positive cells for transplantation. Further in vitro tests are required to evaluate this potential mobilising role of BMP-6 in human long-term bone marrow culture.
All-trans retinoic acid (RA) has generally been found to stimulate late committed (colony-forming unitgranulocyte, macrophage [CFU-GM]) and inhibit early (CFU-Blast) normal human myeloid progenitor cells. The present study provides the first evidence that the pharmacological concentration of 1 µM RA, exerts an inhibitory effect on the proliferation of functional human primitive hemopoietic stem cells (cobblestone area-forming cell [CFAC]) in long-term bone marrow cultures. Treatment of four-week confluent bone marrow culture with 1 µM RA for five days significantly reduced week 4 CAFC from 88 ± 10 in control cultures to only 52 ± 12 per 10 5 cells, p < 0.01. Quantitative enzyme-linked immunosorbent assay measurement of interleukin 6 (IL-6) and IL-11 produced from the fourweek bone marrow stroma culture revealed only a slight and moderate increase of IL-6 and IL-11 production after treatment with RA. On the other hand, treatment with RA profoundly increased the soluble receptor gp130 released from the four-week bone marrow stroma by 7.5-fold from only 145 ± 2.1 pg per ml in control cultures to 1,069.9 ± 3.8 pg per ml in RA-treated cultures. A similar marked increase in the soluble adhesion molecules ICAM-1, and to a lesser extent VCAM-1, released from the four-week bone marrow stroma was observed after RA treatment.IL-6 has been implicated in the inhibitory effect of RA in several human hemopoietic and nonhemopoietic cells. The common transducing signal chain gp130, for all receptors of the IL-6 cytokine family, is expressed in most primitive human hemopoietic CD34 + cells and its signaling was shown to synergize with other hemopoietic cytokines to expand primitive human hemopoietic stem cells. Recently, soluble gp130 was shown to be a natural potent antagonist of the human IL-6 cytokine family by binding the ligand and thereby reducing its bioavailability.The profound and rapid 7.5-fold increase in the natural antagonist of human IL-6 cytokine family after RA treatment could abrogate the gp130 signaling required for proliferation and/or expansion of human primitive hemopoietic stem cells and lead to the observed inhibitory effect of RA on CAFC. Both adhesion molecules VCAM-1 and ICAM-1 mediate human hemopoietic stem cell adhesion to marrow stroma. The present significant increase in the soluble form of these adhesion molecules after RA treatment could exert a significant antagonist effect on their function and hence may impair CAFC adhesion to marrow stroma.In conclusion, the RA inhibitory effect on the proliferation of primitive human hemopoietic stem cells could be mediated through: A) an impaired hemopoietic stem cell adhesion due to the significant increase in soluble adhesion molecules released from the marrow stroma after RA treatment, and B) a significantly reduced gp130 signaling that is necessary for stem cell proliferation due to the natural antagonistic effect of the profoundly increased level of soluble gp130 released from the marrow stroma after treatment with RA.
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