Paracrine effects of CD34 progenitor cells on angiogenic endothelial sprouting.

BACKGROUND: Progenitor cells contribute to repair of ischemia-associated disturbances of microcirculations, but detailed mechanisms of paracrine angiogenic activation of endothelium by progenitor cells are unclear. The present study was designed to test whether progenitor cells maintain their activation pattern of cytokine secretion and capillary-like endothelial sprout attraction under conditions of hypoxia induced angiogenic activation. METHODS: CD34 progenitor cells were kept separated together with spheroids of human umbilical vein endothelial cells (HUVEC) sharing a common medium supernatant to generate a paracrine diffusion gradient from CD34 cells to the endothelial cell spheroids. The expression of 27 cytokines was analyzed in the supernatant. The length and the direction of the capillary like sprouts were analyzed under 20% and 1% oxygen concentration. RESULTS: Co-culture with CD34 cells increased sprout length of HUVEC spheroids by 18%, while reduction of oxygen concentration from 20% to 1% increased sprout length by 52%. Analysis of the direction of the sprout growth revealed a directed growth toward CD34 cells under normoxic as well as under hypoxic conditions. Paracrine induction of cytokine secretion by co-culture was similar in normoxia and in hypoxia with IL-8 (60-80-fold induction) >IL-6 and MIP-1beta (10-20-fold) >MIP-1alpha and MCP-1 (3-10-fold). CONCLUSIONS: These data indicate that CD34 cell induced paracrine activation of cytokine secretion pattern and attraction of endothelial sprouting are well maintained under conditions of hypoxia induced endothelial cell sprout growth. This is a prerequisite for paracrine effectiveness of trapped progenitor cells in hypoperfused and hypooxygenated tissue areas.

Evidences for age-related modulation of human hematopoietic progenitor cell proliferation.

In order to identify hints of ageing in circulating hematopoietic stem cells (HSCs), putative senescence markers like the cellular level of carbonyl-modified proteins and senescence associated beta-galactosidase activity were measured. Furthermore, the number of HSCs in the periphery and their proliferative capacity in vitro were analyzed in buffy coats of fifty five individuals: 27 young [age, 19-43 years; mean age 31] and 28 middle-aged individuals [age, 45-66 years; mean age 56]. The effect of humoral factors on cell proliferation in culture was studied by expansion of the cells in the presence of plasma pools from children and elderly donors. Using a multiplex flow cytometry method, the plasma pools used in the proliferation experiments were assayed for the presence or absence of 25 chemokines. Within the age range analyzed, no age-dependent differences in the number of isolated CD34(+) cells were found. Both sources of progenitor cells were able to reach comparable cell density in culture, but cells from the middle-aged subjects proliferated only sufficiently in the presence of plasma obtained from older donors. Cells from middle-aged donors exhibited elevated levels of carbonyl-modified proteins and showed increased beta-galactosidase activity in comparison to the cells from young donors. Our study shows that although two markers of ageing i.e. carbonylated proteins and senescent associated beta-galactosidase activity are increased in HSCs from middle-aged donors, the number and proliferative capacity of HSCs are still maintained.

Depression of progenitor cell function by advanced glycation endproducts (AGEs): potential relevance for impaired angiogenesis in advanced age and diabetes.

Diabetes and ageing induce reduction and dysfunction of vascular progenitor cells. Advanced glycation endproducts (AGEs) accumulate in diabetes and ageing. We investigated the influence of AGEs on function of CD34 progenitor cells. CD34 cells were co-cultured with HUVECs in a three-dimensional spheroid assay. Sprout length growth and incorporation of CD34 cells into the sprouts were analyzed under 2, 20 or 200 microg/ml AGEs. AGE-receptor expression, MAP-kinase signal transduction and apoptosis were analyzed using PCR, Western blotting and flow cytometry. In the spheroid assay, AGEs concentration-dependently cause a reduction of sprout length growth by 6+/-6 to 32+/-6% and an attenuation of progenitor cells incorporation into the sprouting endothelium by up to 43+/-6%. This functional impairment is accompanied by activation of CD34 cell proliferation at lower concentrations (2 or 20 microg/ml) and by apoptosis activation under 200 microg/ml AGEs. The mRNA expression of the receptors for AGEs and the AGEs-induced activation of p38 and p44/42 MAP-kinases are demonstrable in CD34 cells. This AGEs-mediated impairment of progenitor cell function identifies a new pathophysiological mechanism of disturbed vascular adaptation in diabetes or ageing and suggests that lowering AGEs in recipients of progenitor cell therapy might be beneficial for the success of this therapy.