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* From the Department of Biochemistry and Molecular Biology (Drs. Mathur and Ackerman, and Mr. Espenshade), and Section of Rheumatology (Dr. Varga), Department of Medicine, University of Illinois at Chicago, Chicago, IL.
Correspondence to: Steven J. Ackerman, PhD, Department of Biochemistry and Molecular Biology, University of Illinois at Chicago, Mc536, A312 College of Medicine West, 1819 West Polk St, Chicago, IL 60612-7334; sackerma{at}vic.edu
Numerous
observations, but few definitive studies, implicate eosinophils and
their secretion products in pulmonary fibrosis and other forms of
pathologic fibrosis. The role of the eosinophil, in terms of eosinophil
signals that may induce or regulate fibroblast function, and the gene
targets involved in these interactions, remain poorly defined. We
previously reported1
that eosinophil granule major basic
protein synergized with transforming growth factor-ß1
or interleukin (IL)-1
primed fibroblasts to upregulate expression
of the IL-6 family of cytokines (IL-6, IL-11, leukemia inhibitory
factor) at both the messenger RNA (mRNA) and protein levels. To extend
these findings, we used a co-culture system of the human
eosinophil-differentiated cell line, AML14.3D10, and either the human
lung fibroblast cell line, CCL-202 (American Type Culture Collection),
or primary foreskin fibroblasts, to address the nature of fibrogenic
eosinophil-fibroblast interactions. We focused on IL-6, given the
previous reports defining IL-6 as a key fibrogenic mediator. Co-culture
of AML14.3D10 eosinophils with lung fibroblasts resulted in a large
increase (up to 50-fold) in the secretion of fibroblast-derived IL-6.
This increase was augmented approximately 50 to 100% by activating the
AML14.3D10 eosinophils with IL-5 during the co-culture period. Reverse
transcriptase-polymerase chain reaction analysis revealed that the
increase in IL-6 secretion was associated with elevated levels of IL-6
mRNA in the fibroblasts. In addition, by gel mobility shift assays, we
showed that co-culture increased DNA-binding activity for key
IL-6 promoter elements nuclear factor-
B, CCAAT/enhancer binding
protein (nuclear factorIL-6), and AP1 in fibroblast nuclear
extracts. To address the nature of the signaling between
AML14.3D10 eosinophils and fibroblasts, a semipermeable barrier
("transwell") culture system was used. The results revealed that
induction of fibroblast IL-6 secretion is principally due to soluble
mediators from the AML14.3D10 eosinophils. We also evaluated mRNA
expression of genes involved in extracellular matrix homeostasis. Upon
co-culture of AML14.3D10 eosinophils with primary foreskin fibroblasts,
increased expression of plasminogen activator inhibitor type 1,
fibronectin, and tissue inhibitor of metalloproteinase 1 mRNA was
detected by reverse transcriptase-polymerase chain reaction. These
findings show that co-culture of eosinophils and fibroblasts results in
elevated expression of the genes for IL-6 and other fibrogenic products
involved in extracellular matrix homeostasis. Eosinophil-fibroblast
interactions are therefore capable of invoking a fibrogenic response.
Footnotes
Abbreviations: IL = interleukin; mRNA = messenger RNA
Supported in part by a grant from the Eosinophil Myalgia Syndrome Foundation (to J.V. and S.J.A.), Arthritis Foundation (Chicago), and National Institutes of Health grants A125230 (to S.J.A.) and AR42309 (to J.V.).
References
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