Pericytes promote more vascularization than stromal cells via an interleukin-6-dependent mechanism in microfluidic chips
Pericytes are a key player in vascularization, protecting endothelial cells from external harm and promoting the formation of new vessels when necessary. However, pericytic identity and its relation with other cell types, such as mesenchymal stromal/stem cells, is highly debated. This study compares the role of pericytes and unselected stromal cells in vascularization using multichannel microfluidic chips. In both angiogenesis and vasculogenesis, pericytes promote more vessel formation than stromal cells. Pericytes can wrap around endothelial vessels acting as mural cells, while stromal cells remain separated. Whole-transcriptome sequencing confirms an upregulation of pro-vascularization genes in endothelial cell-pericyte co-cultures, while metabolism increases and inflammation decreases in stromal cell co-cultures. Treatment of stromal-endothelial cell co-cultures with either conditioned media or isolated extracellular vesicles from pericytes replicates the increase in vasculogenesis of the direct co-cultures. Cytokine quantification reveals that IL-6 is significantly increased in pericyte conditions. Blocking it with siltuximab results in a reduction of pericyte vasculogenic potential comparable to stromal cell levels, revealing that pericyte pro-vascularization is mediated by IL-6. This study provides new insights into the relationship between pericytes and endothelial cells and the elusive identity of mesenchymal stromal cells. These findings are relevant for both vascular biology and tissue engineering. Overall design: We prepared 3D co-cultures of endothelial cells and supporting cells in fibrin gels. The supporting cells were either adipose tissue-derived stromal cells (ASC) or adipose tissue-derived pericytes. The endothelial cells were human umbilical vein endothelial cells (HUVECs). The cells were in the gel in a 1:2 ratio (5x10^6 Supporting Cells and 10x10^6 HUVECs). The gels were cultured for 10 days with EGM MV2 media (PromoCell). The gels were minced and the RNA was isolated for a comparative RNA study.