Pro‐fibrotic processes in human lung fibroblasts are driven by an autocrine/paracrine endothelinergic system

Background and Purpose Since endothelin (ET) may act as pro‐fibrotic mediator, expression and release of ET isoforms, their receptors and potential pro‐fibrotic ET effects were studied in human lung fibroblasts. Experimental Approach MRC‐5 and primary human lung fibroblasts (phLFb) were cultured. Expression of prepro‐ET isoforms was determined by qPCR and release of ET‐1 by elisa. ET receptor function was analysed by real‐time measurement of dynamic mass redistribution (DMR). Incorporation of [3H]‐thymidine was determined as measure of proliferation and that of [3H]‐proline for collagen synthesis. Phospho‐p42/44 MAP kinase was determined by Western blot. Key Results ET‐1 is the predominant ET in human lung fibroblasts (hLF), and TGF‐β caused a further, selective and sustained up‐regulation of ET‐1 resulting in increased extracellular ET‐1 accumulation. hLFb express mRNA encoding ET‐A and ET‐B receptors. Expression of both receptors was confirmed at protein level. ET‐1 induced marked DMR signals, an effect that involved ET‐A and ET‐B receptors. Stimulatory effects of ET‐1 on hLFb proliferation and collagen synthesis were mediated exclusively via ET‐A receptors. ET‐1, again via ET‐A receptors, induced rapid activation of ERK MAPK, shown to be a crucial cellular signal in ET‐1‐induced collagen synthesis. ET‐1‐induced activation of ERK and collagen synthesis was, in contrast to corresponding effect of a muscarinic agonist, largely insensitive to pertussis toxin. Conclusions and Implications hLFb are endowed with all elements necessary to build a functional autocrine/paracrine endothelinergic system, which appears to drive pro‐fibrotic airway and lung remodelling processes, effects for which only ET‐A, but not ET‐B receptors appear to be of significance.