Differential mRNA expression of insulin-like growth factor-1 splice variants in patients with idiopathic pulmonary fibrosis and pulmonary sarcoidosis

Insulin-like growth factor-1 (IGF-1) is a highly mitogenic polypeptide dete ctable in human lung. Using competitive reverse transcriptase/polymerase ch ain reaction (RT-PCR), expression of four IGF-1 transcripts was examined in bronchoalveolar lavage cells (BALC) from normal subjects, idiopathic pulmo nary fibrosis (IPF), stage I/II (no fibrosis), and stage III/IV (confirmed fibrosis) pulmonary sarcoidosis patients, and fibroblast strains isolated f rom normal and IPF lungs. Transcripts studied were Class I and Class 2 (exo ns 1 or 2, respectively) with IGF-1 Eb or IGF-1 Ea (exons 5 or 6, respectiv ely). Total IGF-1 expression was downregulated in BALC of both patients wit h IPF (p < 0.01) and patients with sarcoidosis (p < 0.04) compared with hea lthy subjects. In contrast, both constitutive (p < 0.003) and transforming growth factor-P (TGF-P)induced (p < 0.02) IGF-1 expression was higher in fi brotic, compared with normal, fibroblasts. These changes were associated wi th differential expression of IGF-1 splice variants. Healthy subjects and s arcoidosis patients without fibrosis showed similar expression of Class 1/C lass 2 and IGF-1Ea/IGF-1Eb. However, patients with fibrosis demonstrated di scordant, increased relative abundance of Class 1 transcripts (p < 0.01). I n parallel, all fibrosis patients failed to express Class 2, IGF-1Eb forms and sarcoidosis patients with fibrosis did not express the Class 1, IGF-1Eb variant either. Fibrotic fibroblasts expressed higher constitutive levels of Class 1, IGF-1Ea transcripts compared with normal fibroblasts. Class 2, IGF-1Eb forms were moderately expressed by fibroblasts only after stimulati on with TGF-P, which also further increased levels of Class 1, IGF-1 Ea tra nscripts. Our findings suggest that transition from a healthy to a fibrotic phenotype occurs in association with a changing pattern of IGF-1 mRNA hete rogeneity and leads us to hypothesize a potential role for specific IGF-1 v ariants in fibrogenesis.