Fibroblast Activation Protein ± (FAP) Is Differentially Expressed In Fibroblast Cultures From Normal Human And Idiopathic Pulmonary Fibrosis Lungs

Rationale: Idiopathic Pulmonary Fibrosis (IPF) is a disease characterized by the accumulation of fibroblasts, deposition of extracellular matrix proteins, and distortion of normal tissue architecture. The key histopathological feature is the formation of fibroblasts foci (FF) composed of fibroblasts or fibroblast-like cells clustered together and relatively well-demarcated from surrounding cells. There is evidence suggesting that FF have different stable phenotypes, each of them contributing to a profibrotic environment. Recently, Achayra et al (2006) revealed that FAP, a cell surface serine protease with collagenase, gelatinase, and dipeptidyl peptidase (DPP) activity is expressed in FF in patients with IPF and is not expressed in normal or emphysematous tissue. To see if this pattern of expression is kept after isolating the cells from the lung tissue, we aimed to evaluate FAP expression in primary cultures of normal (NHLF) and IPF derived fibroblasts, in basal conditions and when stimulated with TGF-b1. Methods: Fibroblast cultures from NHLF (three cell lines) or IPF lungs (5 cell lines) between passages 4-9 were grown to confluence in F-12 medium. FAP expression was measured with qRT-PCR, after being incubated for 24 hrs in serum free medium, with or without TGF-b1 10 ng/ml. Number of copies were normalized with the 18s ribosome subunit. Results are expressed as mean ± SE of triplicates of at least two separate experiments. Student T- test was used for statistical Results: Three IPF cell lines showed clearly an increased FAP expression (p < 0.5) (259.93 ± 1.3; 215 ± 9.6; 38.2 ± 7.2); when compared with the NHLF cell lines (0.77 ± 0.57; 0.58 ± 0.23; .31 ± 0.13). In the other two cell lines, number of copies tended to be higher than controls (1.7±0.4; 1.7±0.3), but the differences were not statistically significant. Additionally, TGF-b1 10 ng/ml increased FAP expression in NHLF 4.4±2.6 fold vs.1.4±0.33; 2.2±0.29; 22.4±1.7 in IPF. Conclusions: FAP expression was increased in three out of five lung fibroblast cell lines derived from IPF patients. The response to TGFb-1 on FAP expression was variable, but a net increase with regard to basal expression was observed in both normal and IPF fibroblasts. These results suggest that FAP expression could be part of a stable lung fibroblast phenotype.