Differential mRNA Expression of Insulin-like Growth Factor-1 Splice Variants in Patients With Idiopathic Pulmonary Fibrosis and Pulmonary Sarcoidosis

Abstract

Insulin-like growth factor-1 (IGF-1) is a highly mitogenic polypeptide detectable in human lung. Using competitive reverse transcriptase/polymerase chain reaction (RT-PCR), expression of four IGF-1 transcripts was examined in bronchoalveolar lavage cells (BALC) from normal subjects, idiopathic pulmonary fibrosis (IPF), stage I/II (no fibrosis), and stage III/IV (confirmed fibrosis) pulmonary sarcoidosis patients, and fibroblast strains isolated from normal and IPF lungs. Transcripts studied were Class 1 and Class 2 (exons 1 or 2, respectively) with IGF-1Eb or IGF-1Ea (exons 5 or 6, respectively). Total IGF-1 expression was downregulated in BALC of both patients with IPF (p < 0.01) and patients with sarcoidosis (p < 0.04) compared with healthy subjects. In contrast, both constitutive (p < 0.003) and transforming growth factor-beta (TGF-beta)- induced (p < 0.02) IGF-1 expression was higher in fibrotic, compared with normal, fibroblasts. These changes were associated with differential expression of IGF-1 splice variants. Healthy subjects and sarcoidosis patients without fibrosis showed similar expression of Class 1/Class 2 and IGF-1Ea/IGF-1Eb. However, patients with fibrosis demonstrated discordant, increased relative abundance of Class 1 transcripts (p < 0.01). In 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 stimulation with TGF-beta, which also further increased levels of Class 1, IGF-1Ea transcripts. Our findings suggest that transition from a healthy to a fibrotic phenotype occurs in association with a changing pattern of IGF-1 mRNA heterogeneity and leads us to hypothesize a potential role for specific IGF-1 variants in fibrogenesis.

Interleukin-7 and Transforming Growth Factor-β Play Counter-regulatory Roles in Protein Kinase C-δ-dependent Control of Fibroblast Collagen Synthesis in Pulmonary Fibrosis

“…We (5,14) and others (15)(16)(17) have reported marked phenotypic and functional differences between PFF and NF. These differences have been demonstrated at multiple levels including TGF-␤ receptor expression, expression of cell surface receptors or signal transduction mediators, regulation of TGF-␤ signaling, and response to cytokines or other stimulators.…”

The Complexity of the IGF1 Gene Splicing, Posttranslational Modification and Bioactivity

“…Alternative splicing of exon 5 also results in different mRNA variants containing exon 5, generally defined as class B (IGF-IEb), or containing exon 6 (and excluding exon 5) defined as class A (IGF-IEa) (26,45,46), (see Figures 1A, B). A third variant, the IGF-IEc, which corresponds to IGF-IEb in rodents, also is generated by alternative splicing in the human IGF1 gene and contains both exon 5 and 6 (22), (see Figure 1C).…”

“…It has been proposed that the use of promoter 1 could be associated with the synthesis of paracrine IGF-I and may influence interactions with insulinlike growth factor binding proteins (IGFBPs), or promote the formation of the truncated IGF-I peptide (46), (see below: IGF-I Processing, Secretion and Glycosylation). Transcripts initiating at promoter 1 are widely expressed in many tissues, whereas transcripts initiating at promoter 2 are expressed mainly in the liver (circulating forms) and kidney (53) and are thought to be more GH-dependent (23,(54)(55)(56)(57)(58), or equally GH-responsive (59,60).…”

Genetic Analysis of Sporadic and Familial Interstitial Pneumonia

“…Bloor and coworkers examined expression of four IGF-1 transcripts in bronchoalveolar lavage fluid cells from normal subjects, patients with IPF, and patients with sarcoidosis (38). There was differential expression of IGF-1 splice variants, in which patients with IPF had an increase in class 1 transcripts and failed to express class 2 IGF-1Eb forms.…”