Upregulation of nerve growth factor expression by human airway smooth muscle cells in inflammatory conditions.

Recent studies have suggested that nerve growth factor (NGF) may play a role in inflammation and bronchial hyperresponsiveness in asthma. Neither the types of cells that produce NGF in the human airways nor the effect of inflammation on NGF expression are clear. The two-fold aim of the present study was to determine whether airway smooth muscle produces NGF in vitro, and, if so, whether the pro-inflammatory cytokine interleukin-1beta (IL-1beta) affects this expression. Human airway smooth muscle cells in culture were incubated in the presence or absence of IL-1beta. NGF production was measured by enzyme-linked immunosorbent assay. NGF messenger ribonucleic acid (mRNA) was measured using a specific real-time fluorescent polymerase chain reaction technique, and expressed in relation to glyceraldehyde-3-phosphate dehydrogenase (GAPDH) mRNA levels. Human airway smooth muscle cells in vitro expressed NGF constitutively (21.4+/-7.8 pg x mL(-1); 14.6+/-5.4 pg NGF complementary deoxyribonucleic acid (cDNA) x pg GAPDH cDNA(-1) (mean+/-SEM)). Stimulation with IL-1beta (0.1-30 U x mL(-1)) for 24 h induced a dose-dependent increase in NGF production (22.1 pg x mL(-1) at 10 U x mL(-1); p<0.05). The IL-1beta (10 U x mL(-1))-induced increase in NGF expression was time-dependent. It was highest for NGF protein at 10 h (1.6-fold increase over control; p<0.001) and for NGF mRNA at 2.5 h (2.4-fold increase over control; p<0.05). In conclusion, the present study clearly shows that the human airway smooth muscle cell is a source of nerve growth factor, the expression of which is upregulated in inflammatory conditions, mimicked in vitro by the addition of interleukin-1beta.