Lung
fibrosis is characterized by excessive deposition of extracellular matrix. This not only affects tissue architecture and function, but it also influences fibroblast behavior and thus
disease progression. Here we describe the expression of
elastin,
type V collagen and
tenascin C during the development of
bleomycin-induced lung
fibrosis. We further report in vitro experiments clarifying both the effect of myofibroblast differentiation on this expression and the effect of extracellular
elastin on myofibroblast differentiation. Lung
fibrosis was induced in female C57Bl/6 mice by
bleomycin instillation. Animals were sacrificed at zero to five weeks after
fibrosis induction.
Collagen synthesized during the week prior to sacrifice was labeled with
deuterium. After sacrifice, lung tissue was collected for determination of new
collagen formation, microarray analysis, and histology. Human lung fibroblasts were grown on tissue culture
plastic or BioFlex culture plates coated with
type I collagen or
elastin, and stimulated to undergo myofibroblast differentiation by 0-10 ng/ml
transforming growth factor (TGF)β1.
mRNA expression was analyzed by quantitative real-time PCR. New
collagen formation during
bleomycin-induced
fibrosis was highly correlated to gene expression of
elastin,
type V collagen and
tenascin C. At the
protein level,
elastin,
type V collagen and
tenascin C were highly expressed in fibrotic areas as seen in histological sections of the lung.
Type V collagen and
tenascin C were transiently increased. Human lung fibroblasts stimulated with TGFβ1 strongly increased gene expression of
elastin,
type V collagen and
tenascin C. The extracellular presence of
elastin increased gene expression of the myofibroblastic markers α smooth muscle actin and
type I collagen. The extracellular matrix composition changes dramatically during the development of lung
fibrosis. The increased levels of
elastin,
type V collagen and
tenascin C are probably the result of increased expression by fibroblastic cells; reversely,
elastin influences myofibroblast differentiation. This suggests a reciprocal interaction between fibroblasts and the extracellular matrix composition that could enhance the development of lung
fibrosis.