Muscarinic receptors mediate stimulation of collagen synthesis in human lung fibroblasts

¹ Institute of Pharmacology & Toxicology and
² Dept of Pulmonary Diseases, Medical Polyclinic, University of Bonn, Germany

^* To whom correspondence should be addressed. E-mail: racke.kurt{at}uni-bonn.de.

	Abstract

Clinical observations indicate that in COPD 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 and incorporation of [³H]-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 (EC₅₀: 220 nM, increase at 10 µM by 40–55%, in different series of experiments). Likewise, 10 µM oxotremorine caused an increase by about 65%. For comparison, TGF-ß₁ (5 ng·ml^-1) caused an increase by about 80%. Effects of carbachol on total [³H]-proline incorporation and collagenase-sensitive [³H]-proline fraction were similar. The effect of 10 µM carbachol was inhibited by tiotropium (IC₅₀: 110 pM), prevented by pertussis toxin and the MAP kinase inhibitor PD 98059. Muscarinic agonists enhanced [³H]-proline incorporation in a tiotropium-sensitive manner also 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 long-term beneficial effects of anticholinergics in COPD.