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.