Uraemia disrupts the vascular niche in a 3D co-culture system of human mesenchymal stem cells and endothelial cells.

BACKGROUND Recent studies identified mesenchymal stem cells (MSC) as major players in vascular remodelling and the sub-endothelial compartment as the stem cell niche. The uraemic microenvironment predisposes to increased levels of reactive oxygen species, accelerated ageing of endothelial cells (EC) and vascular sclerosis. METHODS We generated an in vitro model of a vascular niche consisting of a three-dimensional collagen I/III gel containing MSC and EC. We recapitulated a uraemic microenvironment by supplementing the medium with 20% pooled sera from either healthy or uraemic patients. RESULTS Under healthy conditions, MSC/EC co-culture in collagen gels resulted in vessel-like tube formation. In contrast, uraemic serum-induced expression of extracellular matrix proteins (real-time reverse transcription-polymerase chain reaction, immunohistochemistry) that was accompanied by significant collagen contraction and a myofibroblastic phenotype of MSC. Although the uraemic culture conditions stimulated EC proliferation (cell counting, BrdU assay) and did not induce apoptosis (7-amino-actinomycin, annexin V FACS analysis), the tube formation was disrupted in spite of significantly enhanced vascular endothelial growth factor-A messenger RNA expression. The excessive matrix synthesis and remodelling by uraemia-exposed MSC/EC was reminiscent of remodelling processes observed in arteries of 12 dialysis patients (using arteries from 10 children and 10 age-matched non-dialysis patients as controls). CONCLUSION Our data indicate a potential role of the sub-endothelial niche and its major cell types EC and MSC in the remodelling process of the vascular wall in CKD.