Mechanical stretch of sympathetic neurons induces VEGF expression via a NGF and CNTF signaling pathway

Abstract

Mechanical stretch has been shown to increase vascular endothelial growth factor (VEGF) expression in cultured myocytes. Sympathetic neurons (SN) also possess the ability to express and secrete VEGF, which is mediated by the NGF/TrkA signaling pathway. Recently, we demonstrated that SN respond to stretch with an upregulation of nerve growth factor (NGF) and ciliary neurotrophic factor (CNTF). Whether stretch increases neuronal VEGF expression still remains to be clarified. Therefore, SN from the superior cervical ganglia of neonatal Sprangue Dawley rats were exposed to a gradual increase of stretch from 3% up to 13% within 3 days (3%, 7% and 13%). Under these conditions, the expression and secretion of VEGF was analyzed. Mechanical stretch significantly increased VEGF mRNA and protein expression (mRNA: control = 1 vs. stretch = 3.1; n = 3/protein: control = 1 vs. stretch = 2.7; n = 3). ELISA experiments to asses VEGF content in the cell culture supernatant showed a time and dose dependency in VEGF increment due to stretch. NGF and CNTF neutralization decreased stretch-induced VEGF augmentation in a significant manner. This response was mediated in part by TrkA receptor activation. The stretch-induced VEGF upregulation was accompanied by an increase in HIF-1α expression. KDR levels remained unchanged under conditions of stretch, but showed a significant increase due to NGF neutralization. In summary, SN respond to stretch with an upregulation of VEGF, which is mediated by the NGF/CNTF and TrkA signaling pathway paralleled by HIF-1α expression. NGF signaling seems to play an important role in regulating neuronal KDR expression.