Cord blood mesenchymal stromal cell-conditioned medium protects endothelial cells via STAT3 signaling

Cell-based therapies may be useful for treating ischemic diseases, but the underlying mechanisms are incompletely understood. We investigated the impact of cord blood mesenchymal stromal cell (CBMSC)- or fibroblast (FB)-secreted factors on starved endothelial cells and determined the relevant intracellular signaling pathways.

HUVECs were subjected to glucose/serum deprivation (GSD) in hypoxia or normoxia, in presence of CBMSC- or FB-conditioned medium (CM). Viability and proliferation were determined via WST-8 conversion and BrdU incorporation. Apoptosis was quantified by annexin V/ethidium homodimer-III staining, nuclear fragmentation and cell morphology. mRNA expression and protein phosphorylation were determined by real-time qPCR and western blot. Experiments were repeated in presence of small-molecule inhibitors.

The negative impact of GSD was most pronounced at 21% O2. Here, medium of CBMSCs and FBs increased viability and proliferation and reduced apoptosis of HUVECs. This was associated with increased STAT3 and ERK1/2 phosphorylation and BCL-2 expression. Under STAT3 inhibition, the beneficial effect of CBMSC-CM on viability and BCL-2 expression was abolished.

Factors released by CBMSCs protect endothelial cells from the deleterious impact of GSD by activation of the STAT3 survival pathway. However, this phenomenon is not CBMSC-specific and can be reproduced using juvenile fibroblasts.