PRECONDITIONING MESENCHYMAL STEM CELLS WITH TRANSFORMING GROWTH FACTOR-ALPHA IMPROVES MESENCHYMAL STEM CELL-MEDIATED CARDIOPROTECTION

Mesenchymal stem cells (MSCs) are a promising therapy for acute organ ischemia in part due to their paracrine production of growth factors. However, transplanted cells encounter an inflammatory environment that mitigates their function and survival, and treating the cells with exogenous agents during ex vivo expansion before transplantation is one strategy for overcoming this limitation by enhancing paracrine function. We hypothesized that preconditioning bone marrow MSCs with TGF-alpha would 1) increase MSC production of the critical paracrine factor, vascular endothelial growth factor (VEGF), via a p38 mitogen-activated protein kinase (MAPK)-dependent mechanism and 2) enhance myocardial functional recovery in a rat model of acute myocardial I/R injury. To study this, bone marrow MSCs were harvested from adult male mice (C57BL/6J) and treated in vitro for 24 h according to the following groups: 1) control, 2) TGF-alpha (250 ng mL(-1)), 3) TNF-alpha (50 ng mL(-1)), 4) TGF-alpha + TNF-alpha, 5) hypoxia, and 6) TGF-alpha + hypoxia. For the isolated heart perfusion experiments, adult male Sprague-Dawley rat hearts were isolated, perfused via the Langendorff model, and subjected to I/R. Vehicle or MSCs with or without TGF-alpha preconditioning were infused immediately before ischemia. Mesenchymal stem cells were also treated with TGF-alpha alone or in combination with a p38 MAPK inhibitor (SB202190). In vitro, TGF-alpha increased MSC VEGF production alone (157.9 +/- 1.11 - 291.0 +/- 3.74 pg 10(-5); P < 0.05) and, to a greater extent, in combination with TNF-alpha or hypoxia (364.5 +/- 0.868 and 342.0 +/- 7.92 pg 10(-5) cells, respectively; P < 0.05 vs. TGF-alpha alone). Postischemic myocardial functional recovery was greater in hearts infused with TGF-alpha-preconditioned MSCs compared with untreated MSCs or vehicle. Myocardial IL-1 beta and TNF-alpha production and activation of caspase 3 were significantly decreased after infusion of both cell groups. p38 MAPK inhibition suppressed TGF-alpha-stimulated MSC VEGF production and postischemic myocardial recovery. These results suggest that TGF-alpha stimulates MSC VEGF production in part via a p38 MAPK-dependent mechanism, and preconditioning MSCs with TGF-alpha may enhance their ability to protect myocardium during I/R injury.