Pulmonary fibroblasts: an in vitro model of emphysema. Regulation of elastin gene expression.

Disruption and degradation of interstitial elastic fibers are significant characteristics of pulmonary emphysema. In order to examine the responses of elastogenic cells to the conditions mimicking degradation of interstitial pulmonary elastin, rat pulmonary fibroblast cultures were used as an in vitro model. Second passage fibroblasts were divided into two different environmental situations to represent cells adjacent to and remote from the site of elastase-digested matrix. One set of cell cultures was briefly digested with pancreatic elastase. The resultant digest was then added back incrementally to the medium of elastase-digested cell cultures and to the medium of a second set of undigested cultures. Both sets of cell cultures remained viable and metabolically active during these treatments (96 h of incubation) as judged by protein synthesis, cell number, and steady-state levels of beta-actin mRNA. However, the two sets of cultures exhibited opposite responses in elastin gene expression with addition of increasing amounts of the elastase digest. The elastase-digested cultures exhibited a 200% increase in extractable soluble elastin and a 186% increase in tropoelastin mRNA with the addition of increasing amounts of the elastase digest to the medium. Conversely, the amount of soluble elastin recovered from the undigested cultures decreased 75%, and the steady-state level of tropoelastin mRNA decreased 63%. Soluble elastin peptides generated from oxalic acid treatment of purified elastin were shown to decrease tropoelastin mRNA in undigested cell cultures in the same manner as the elastase digest. Based on these data, we propose that pulmonary fibroblast elastin gene expression can be controlled coordinately by the state of the extracellular matrix and solubilized peptides derived from that matrix. Such integrated regulation may serve to localize elastin repair mechanisms.