Transforming growth factor-β1 induces angiogenesis in vitro via VEGF production in human airway smooth muscle cells

Increase in size and number of bronchial blood vessels as well as hyperaemia are factors that contribute to airway wall remodelling in patients with chronic airway diseases, such as asthma and chronic obstructive pulmonary diseases (COPD). Expression of transforming growth factor β1 (TGF- β1), a multifunctional cytokine as well as vascular endothelial growth factor (VEGF), a key angiogenic molecule, has been shown in the inflammed airways in patients with chronic airway diseases. TGF- β1 has been implicated in the regulation of extracellular matrix, leading to airway remodelling in patients with chronic airway diseases. However, the role of TGF- β1 in regulating VEGF expression in patients with chronic airway diseases, as well as the underlying mechanisms are not yet well established. We investigated whether TGF- β1 stimulates VEGF expression in vitro and hence could influence vascular remodelling. Cultured human airway smooth muscle cells (HASMC) were serum deprived for 60 h before incubation with 5ng/ml of TGF- β1 for different time points. Control cells received serum-free culture medium. TGF- β1, treatment resulted in time dependent HASMC cell proliferation with maximal values for DNA biosynthesis at 24 h and cell number at 48 h. Northern blot analysis of VEGF mRNA expression showed increased levels in cells treated with TGF- β1 for 4 to 8 h. TGF- β1 also induced a time-dependent release of VEGF proteins in the conditioned medium after 48 h of treatment. Furthermore, the ability of HASMC-released VEGF proteins to induce human umbilical vein endothelial cells proliferation was inhibited by VEGF receptor antagonist, confirming that TGF- β1 induced VEGF was biologically active. We conclude that TGF- β1 in addition to an extracellular matrix regulator also could play a key role in bronchial angiogenesis and vascular remodelling via VEGF pathway in asthma.