Regulation of procollagen I (alpha1) by interleukin-4 in human bronchial fibroblasts: a possible role in airway remodelling in asthma.
BACKGROUND
In bronchial mucosa, T cells are in close association with fibroblasts. This cell contact raises the possibility of cross-talk between the two cell types through cytokines, such as interleukin-4 (IL-4).


OBJECTIVE
We postulated that IL-4 may modulate collagen synthesis and degradation in the fibroblasts of asthmatics.


METHODS
Bronchial fibroblasts from asthmatics (BAF) and normal controls (BNF) were stimulated with IL-4. Procollagen I gene expression and protein production were measured by real-time PCR, RT-PCR, and radioimmunoassay. The effect of IL-4 on the regulation of procollagen I (alpha1) promoter was studied through transient cell transfections. The implication of Sp1 and AP-1 in regulating IL-4-induced procollagen I (alpha1) production was determined. The effect of IL-4 on metalloproteinase-2 (MMP-2) and tissue inhibitor of metalloproteinase-2 (TIMP-2) production and gene expression was evaluated.


RESULTS
Following IL-4 stimulation, there was a significant increase in the expression of mRNA of procollagen I (alpha1) by human bronchial fibroblasts of asthmatics and controls. IL-4 has a dose-response effect on mRNA, with a maximal effect at 5 ng/mL, as determined by real-time PCR. The maximal increase in procollagen I (alpha1) was observed at 6 h after IL-4 stimulation in both BNF and BAF. BAFs have a greater increase in the procollagen I (alpha1)/beta2 microglobulin ratio after 6 h of IL-4 stimulation (4.1 x 10-2+/-0.03 to 20.8 x 10-2+/-0.1) compared with BNF (2.9 x 10-2+/-0.006 to 9.2 x 10-2+/-0.08) (P=0.001). In transient transfection experiments, IL-4 increased promoter activity by threefold in BAF and BNF. Sp1 was up-regulated after IL-4 stimulation and AP-1 was down-regulated as shown by electrophoretic mobility shift assay. IL-4 decreased MMP-2 protein and mRNA levels, and did not alter TIMP-2 production.


CONCLUSIONS
IL-4 positively regulates procollagen I (alpha1) transcription by direct promoter activation and increases the TIMP-2/MMP-2 ratio, thereby supporting the profibrotic effect of this cytokine. Thus, this study emphasizes that IL-4 may be considered as a link between inflammation and collagen deposition observed in asthmatic airways.
D001249:Asthma / Q000378:metabolism*; D001980:Bronchi / Q000378:metabolism*; D002478:Cells, Cultured; D005347:Fibroblasts / Q000378:metabolism; D005786:Gene Expression Regulation / Q000187:drug effects; D006801:Humans; D015847:Interleukin-4 / Q000494:pharmacology* / Q000502:physiology; D020778:Matrix Metalloproteinase 2 / Q000096:biosynthesis; D016133:Polymerase Chain Reaction / Q000379:methods; D011347:Procollagen / Q000096:biosynthesis* / Q000235:genetics; D012333:RNA, Messenger / Q000235:genetics; D020545:Respiratory Mucosa / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D019716:Tissue Inhibitor of Metalloproteinase-2 / Q000096:biosynthesis; D014162:Transfection
D011347:Procollagen; D012333:RNA, Messenger; D019716:Tissue Inhibitor of Metalloproteinase-2; D015847:Interleukin-4; D020778:Matrix Metalloproteinase 2