Muscarinic receptors mediate stimulation of collagen synthesis in human lung fibroblasts

Clinical observations indicate that in chronic obstructive pulmonary disease patients, the long-acting muscarinic antagonist tiotropium delays decline in airway function, suggesting that cholinergic mechanisms contribute to long-term structural changes. Human lung fibroblasts express muscarinic receptors and the present study aimed to explore their role in controlling collagen synthesis. MRC-5, HEL-299 and primary human lung fibroblasts (phLFb) were cultured. Incorporation of [H-3]-proline into cellular proteins was determined as measure of collagen synthesis. In MRC-5 cells, the muscarinic agonist carbachol enhanced [3H]-proline incorporation in a concentration-dependent manner (effective concentration of 50%: 220 nM, increase at 10 AM by 40-55%, in a different series of experiments). Likewise, 10 mu M oxotremorine caused an increase of similar to 65%. For comparison, transforming growth factor-beta 1 (5 ng.mL(-1)) caused an increase of similar to 80%. Effects of carbachol on total [3H]-proline incorporation and collagenase-sensitive [3 H]-proline fraction were similar. The effect of 10 mu M carbachol was inhibited by tiotropium (inhibitory concentration of 50%: 110 pM), prevented by pertussis toxin and the mitogen-activated protein kinase inhibitor, PD 98059. Muscarinic agonists also enhanced [H-3]-proline incorporation in a tiotropium-sensitive manner in HEL-299 cells and phLFb. In human lung fibroblasts, muscarinic receptors exert stimulatory effects on collagen synthesis. Prolonged blockade of muscarinic-induced collagen synthesis may contribute to reported beneficial long-term effects of anticholinergics in chronic obstructive pulmonary disease.