Abstract 1828: Hypoxic Priming of Bone Marrow Mesenchymal Cells for VEGF Production is Mediated by STAT3 and p38 MAPK
INTRODUCTION: Progenitor cells have emerged as a promising therapy for heart disease. Studies have shown that progenitor cells improved post-ischemic myocardial function, but this effect may not only be mediated by transdifferentiation. Progenitor cells may have protective paracrine effects via the release of protective growth factors. Understanding the mechanisms by which these cells release protective growth factors such as vascular endothelial growth factor (VEGF), may lead to enhanced protection. We hypothesized that hypoxia activates bone marrow mesenchymal cells (MSCs) to release VEGF by STAT3 and p38 MAPK dependent mechanisms.
METHODS: Mouse MSCs from wild type (WT) and STAT3 knockout mice (STAT3KO) were plated for these groups: control, p38 MAPK inhibitor (10 microM of SB202190=p38MKI), hypoxia (24 hours or 48 hours), hypoxia+p38MKI. After 24-hour or 48-hour stimulation, supernatants were collected and assayed for VEGF (ELISA). Experiments were repeated on three separate occasions (n=6–9/group). Data (means±SEM) was analyzed with t-test, p<0.05=statistically significant.
RESULTS: MSCs from WT secreted 500±42 pg/1X100,000 cells (24-hour), 768±61 pg/1X100,000 cells (48-hour) of VEGF. When MSCs were cultured under hypoxia, VEGF secretion markedly increased to 774±60 pg/1X100,000 cells (24-hour) and to 1384±137 pg/1X100,000 cells (48-hour) in WT. In addition, the p38 MAPK inhibitor significantly decreased hypoxia-induced VEGF production to 417±16 pg/ 1X100,000 cells (24-hour) and to 880±83 pg/1X100,000 cells (48-hour) in WT. However, although MSCs from STAT3KO secreted VEGF, the amount of VEGF production was significantly lower in STAT3KO groups compared to WT (24-hour: 362±13, 48-hour: 533±55 pg/ 1X100,000 cells). Further, hypoxia did not induce more VEGF production in STAT3KO (24-hour: 418±14, 48-hour: 551±44 pg/1X100,000 cells). p38 MKI alone had no effect on VEGF secretion.
MSCs are a potent source of VEGF;
STAT3 mediates VEGF production under normoxia;
MSC release of VEGF is mediated by STAT3 and p38 MAPK during hypoxia.
This understanding and further study may ultimately lead to the ex vivo priming of MSCs for maximal growth factor production prior to and during therapeutic use.