Nerve Growth Factor, Brain-Derived Neurotrophic Factor, Neurotrophin-3 and Glial-Derived Neurotrophic Factor Enhance Angiogenesis in a Tissue-Engineered In Vitro Model

Skin is a major source of secretion of the neurotrophic factors nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3), and glial-derived neurotrophic factor (GDNF) controlling cutaneous sensory innervation. Beside their neuronal contribution, we hypothesized that neurotrophic factors also modulate the cutaneous microvascular network. First, we showed that NGF, BDNF, NT-3, and GDNF were all expressed in the epidermis, while only NGF and NT-3 were expressed by cultured fibroblasts, and BDNF by human endothelial cells. We demonstrated that these peptides are highly potent angiogenic factors using a human tissue-engineered angiogenesis model. A 40% to 80% increase in the number of capillary-like tubes was observed after the addition of 10 ng/mL of NGF, 0.1 ng/mL of BDNF, 15 ng/mL of NT-3, and 50 ng/mL of GDNF. This is the first characterization of the direct angiogenic effect of NT-3 and GDNF. This angiogenic effect was mediated directly through binding with the neurotrophic factor receptors tropomyosin-receptor kinase A (TrkA), TrkB, GFR alpha-1 and c-ret that were all expressed by human endothelial cells, while this effect was blocked by addition of the Trk inhibitor K252a. Thus, if NGF, BDNF, NT-3, and GDNF may only moderately regulate the microvascular network in normal skin, they might have the potential to greatly increase angiogenesis in pathological situations.