Synergistic increase in nerve growth factor secretion by cultured vascular smooth muscle cells treated with injury-related growth factors

Vascular smooth muscle (VSM) cells comprise one of the primary targets of the sympathetic nervous system and have been shown to secrete nerve growth factor (NGF). There is increasing evidence that changes in the levels of NGF in the adult may underlie certain pathological conditions. To investigate the potential role of altered NGF production in vascular disease, VSM cell cultures were treated with injury-related growth factors and the culture medium was assayed for NGF using a two-site enzyme-linked immunosorbent assay (ELISA). Platelet-derived growth factor (PDGF), a potent VSM mitogen, caused a dose-dependent increase in NGF secretion. After 4 hr, PDGF-treated cultures contained 10 times more NGF than control cultures. NGF release remained elevated for 48 hr, but the peak secretion occurred in the first 12 hr after treatment. Transforming growth factor beta (TGF-β) caused a fivefold increase in NGF at 4 hr when added alone, but synergized with PDGF yielding approximately 50 times more NGF than control cultures. TGF-β and epidermal growth factor (EGF) also displayed synergism. In contrast, basic fibroblast growth factor (bFGF), which had a modest effect alone, appeared to be additive with TGF-β. Similarly, interleukin 1-beta (IL-1β), which mediates increased NGF synthesis in sciatic nerve lesions (Lindholm et al.: Nature 330:658-659, 1987), showed no synergism with TGF-β.