IL-6 AND TGF-α COSTIMULATE MESENCHYMAL STEM CELL VASCULAR ENDOTHELIAL GROWTH FACTOR PRODUCTION BY ERK-, JNK-, AND PI3K-MEDIATED MECHANISMS

Mesenchymal stem cells (MSCs) protect ischemic tissues in part through paracrine growth factor production. IL-6, which is upregulated in the heart during ischemia, has been shown to enhance stem cell proliferation and migration. The effect of IL-6 on MSC paracrine function, however, remains unknown. In addition, TGF-alpha increases MSC vascular endothelial growth factor (VEGF) production and may share downstream signaling pathways with IL-6 involving ERK, JNK, and PI3K. We hypothesize that cotreatment with IL-6 and TGF-alpha will result in greater MSC VEGF production than by either treatment alone via these signaling pathways. Murine MSCs were treated with IL-6 (0.05 ng/mL) with or without TGF-alpha (250 ng/mL) and in combination with inhibitors of ERKI/II, JNK, and PI3K for 24 h. Vascular endothelial growth factor concentrations in the supernatants were measured using enzyme-linked immunosorbent assay. Phosphorylation of ERK, JNK, and PI3K was measured using Western blot analysis. IL-6 increased MSC VEGF production at a dose of 0.05 ng/mL, and the combination of IL-6 and TGF-alpha (250 ng/mL) increased VEGF production to a greater extent than IL-6 or TGF-alpha alone. IL-6 induced phosphorylation of ERK, JNK, and PI3K, and inhibition of each suppressed IL-6-induced VEGF production. TGF-alpha cotreatment overcame VEGF suppression after ERK2 inhibition but not ERK1, JNK, or PI3K. These data suggest that IL-6 stimulates MSC VEGF production alone and additively with TGF-alpha via ERK-, JNK-, and PI3K-mediated mechanisms. IL-6 and TGF-alpha cotreatment may be a useful strategy for enhancing MSC VEGF production and cardioprotection during myocardial ischemia.