Mesenchymal stem cells (MSCs) have the capability for renewal and differentiation into various lineages of mesenchymal tissues. These features of MSCs attract a lot of attention from investigators in the context of cellbased therapies of several human diseases. Despite the fact that bone marrow represents the main available source of MSCs, the use of bone marrow-derived cells is not always acceptable due to the high degree of viral infection and the significant drop in cell number and proliferative/differentiation capacity with age. Thus, the search for possible alternative MSC sources remains to be validated. Umbilical cord blood is a rich source of hematopoietic stem/progenitor cells and does not contain mesenchymal progenitors. However, MSCs circulate in the blood of preterm fetuses and may be successfully isolated and expanded. Where these cells home at the end of gestation is not clear. In this investigation, we have made an attempt to isolate MSCs from the subendothelial layer of umbilical cord vein using two standard methodological approaches: the routine isolation of human umbilical vein endothelial cell protocol and culture of isolated cells under conditions appropriate for bone-marrow-derived MSCs. Our results suggest that cord vasculature contains a high number of MSC-like elements forming colonies of fibroblastoid cells that may be successfully expanded in culture. These MSC-like cells contain no endothelium-or leukocytespecific antigens but express alpha-smooth muscle actin and several mesenchymal cell markers. Therefore, umbilical cord/placenta stroma could be regarded as an alternative source of MSCs for experimental and clinical needs.

Human umbilical vein endothelial cells (EC) were grown on elastic silicone membranes subjected to cyclic stretch, simulating arterial wall motion. Stretching conditions (20% amplitude, 52 cycle/min) stimulated stress fiber formation and their orientation transversely to the strain direction. Cell bodies aligned along the same axis after the actin cytoskeleton. EC orientation response was inhibited by the adenylate cyclase activator, forskolin (10(-5) M), which caused stress fiber disassembly and the redistribution of F-actin to the cortical cytoplasm. Preoriented EC depleted of stress fibers by forskolin treatment retained their aligned state. Thus, stress fibers are essential for the process of EC orientation induced by repeated strain, but not for the maintenance of EC orientation. The monolayer formed by EC grown to confluence in conditions of intermittent strain consisted of uniform elongated cells and was resistant to deformation. In contrast, the monolayer assembled in stationary conditions was less compliant and exposed local denudations on initiation of stretching. When stretched in the presence of 10(-5) M forskolin it rapidly (3-4 h) reestablished integrity but gained a heterogeneous appearance since denuded areas were covered by giant cells. The protective effect of forskolin was because of the stimulation of EC spreading. This feature of forskolin was demonstrated while studying its action on EC spreading and repair of a scratched EC monolayer in conventional culture. Thus mechanical deformation and adenylate cyclase activity may be important factors in the control of endothelium morphology in human arteries.

Comparative study of cultured human bone marrow and adipose tissue (lipoaspirate) mesenchymal stem cells was carried out. The main morphological parameters, proliferative activity, expression of surface and intracellular markers of these cells were characterized. Flow cytofluorometry and histological staining showed that both cell types exhibited similar expression of CD105, CD54, CD106, HLA-I markers, were positively stained for vimentin, ASMA, collagen-1, and fibronectin, but not HLA-DR, CD117, and hemopoietic cell markers. The cells underwent differentiation into adipocytes and osteoblasts under appropriate conditions of culturing. Incubation under neuroinductive conditions led to the appearance of a cell population positively stained for type III beta-tubulin (neuronal differentiation marker).

The morphological effects on human endothelial cells of phorbol 12-myristate 13-acetate (PMA) and of agents that increase intracellular cAMP concentration were studied. The adenylate cyclase activator forskolin (10 IAM), the cyclic nucleotide phosphodiesterase inhibitor methylisobutylxanthine (100 ,uM), dibutyryl-cAMP (10 IAM), histamine (10 IAM), and PMA (0.1 ,LM) significantly altered the morphology of human aortic and umbilical vein endothelial cells in primary cultures. These effects reached a maximum 40-80 min after the effector addition and became negligible 30-60 min after its removal. PMA and forskolin were strongly synergistic in altering endothelial cell morphology. All the effects of cAMPelevating compounds and ofPMA were abolished completely by 1 ,uM colchicine. In explants taken from human adult or child aortas, forskolin and PMA produced alterations in endothelial morphology qualitatively identical to those observed in endothelial cell cultures. Endothelium in these preparations closely resembled that found in zones of expected altered hemodynamic stresses of human aorta. Our data suggest that the morphology of endothelium in vivo may be regulated by separate or synergistic action of hormone-dependent adenylate cyclase and of inositol phospholipid turnover systems and might be important for maintenance of endothelial monolayer integrity under normal physiological and pathological conditions. MATERIALS AND METHODSMedium 199 (Earle salts), fetal calf serum, Dulbecco's phosphate-buffered saline (PBS), L-glutamine, penicillin, streptomycin, and sodium pyruvate were from GIBCO. Dispase (neutral protease from Bacillus polymixa) was from Boehringer Mannheim. Phorbol 12-myristate 13-acetate (PMA), 4a-phorbol 12,13-didecanoate, histamine, 1-methyl-3-isobutylxanthine, N6,02-dibutyryl-cAMP (Bt2cAMP), colchicine, bovine serum albumin (BSA, essentially fatty acid free) were supplied by Sigma. Forskolin was from Calbiochem. Drugs were dissolved in dimethylsulfoxide or ethanol (Merck) and stored as stock solutions in aliquots at -80°C. Prior to use the aliquots were diluted with medium 199 and 0.5% BSA or with growth medium [medium 199 supplemented with 25 mM Hepes, 2 mM L-glutamine, 1 mM pyruvate, penicillin at 100 units/ml, streptomycin at 100 ,ug/ml, 10% (vol/vol) fetal calf serum] and sterilized by filtration through 0.22-,um filters (Nalgene).Primary cultures of human umbilical vein endothelial cells (HUVECs) and human aortic endothelial cells (HAECs) were obtained as described (15,16), with minor modificationdispase was used instead of collagenase. Seeding density was 5-8 X 104 cells per cm2. Only confluent (7-9 days after seeding) cultures were used for experiments. The main characteristics of these cultures have been reported (16). For morphometry, cultures were stained with silver nitrate (17) and photographed. Cell shape was analyzed using a MOP-3 digitizer (Reichert, Jung, Vienna) and described in terms of shape index (SI), where SI = 4r x area/(perimeter)2. All the experiments were performe...

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