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P. Thampi, A. Afzal, J. Cai, L. Kennedy, J. Sallustio, S. Quinn, C. Lansing, M. B. Grant, M. E. Boulton; CD34+ Cells from Diabetic and Non-Diabetic Peripheral Blood Respond Differently to Changes in the Local Oxygen Environment. Invest. Ophthalmol. Vis. Sci. 2009;50(13):25.
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To compare the effect of changes in the oxygen environment on the expression of VEGF receptors R-1 and R-2 and the stromal-derived factor receptor (SDF-1), CXCR4 in human endothelial precursor, CD34+ cells isolated from diabetics with non-proliferative retinopathy and non-diabetic controls.
Peripheral blood CD34+ cells were isolated and purified from diabetic and age-matched non-diabetic patients using the Easy Sep CD34+ selection kit. Cells were resuspended in StemSpan medium pre-equilibrated to the appropriate oxygen tension and incubated for 4 and 24 hr under either a) normoxia (pO2=35mmHg; physiological conditions in the retina); b) hypoxia (pO2=5mmHg; representing localized retinal ischemia) and c) hyperoxia (pO2=120mmHg; to mimic arterial blood). Total VEGFR-1, VEGFR-2 and CXCR4 in the cell lysates was determined by Western Blot. Flow cytometry and RT-PCR were used to assess surface expression and mRNA levels for these proteins. The response to hypoxia was confirmed by measuring HIF-1.
After 4 hours incubation under normoxia CD34+ cells from diabetics exhibited a 2 fold decrease in total VEGFR-1 protein and mRNA expression compared to non-diabetic cells. VEGFR-1 surface density was similar between diabetic and non-diabetic cells. There were no significant differences in expression of VEGFR-2 and CXCR4 in either patient group. After 24 hr incubation there was no difference in VEGFR-1 expression in either patient group, however, the surface expression for VEGFR-2 increased and CXCR4 decreased in diabetic cells. For cells under hypoxia, HIF-1 was increased. Although total levels of VEGFR-1, VEGFR-2 and CXCR4 increased under hypoxic conditions the overall difference between diabetic and non-diabetic cells remained the same at both 4 and 24 hr. The major change was an even greater, 7 fold, reduction in surface CXCR4 in diabetic cells compared to non-diabetic suggesting that, under hypoxia, CD34+ cells become less responsive to SDF-1. Cells under hyperoxia, showed a similar receptor profile to normoxia with, again, the major difference being in CXCR4 for which the surface expression of this receptor was greatly increased (3.5x) in diabetics compared to non-diabetics.
The expression profiles of VEGFR-1, VEGFR-2 and CXCR4 differ between diabetic and non-diabetic CD34+ cells and this is oxygen dependent. Diabetic CD34+ cells appear to have a blunted response to soluble recruitment and differentiation factors which can be exacerbated by transient exposure to hypoxia.
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