Loss of Fibroblast Thy-1 Expression Correlates with Lung Fibrogenesis

Abstract

Fibroblasts consist of heterogeneous subpopulations that have distinct roles in fibrotic responses. Previously we reported enhanced proliferation in response to fibrogenic growth factors and selective activation of latent transforming growth factor (TGF)-␤ in fibroblasts lacking cell surface expression of Thy-1 glycoprotein, suggesting that Thy-1 modulates the fibrogenic potential of fibroblasts. Here we report that compared to controls Thy-1؊/؊ C57BL/6 mice displayed more severe histopathological lung fibrosis, greater accumulation of lung collagen, and increased TGF-␤ activation in the lungs 14 days after intratracheal bleomycin. The majority of cells demonstrating TGF-␤ activation and myofibroblast differentiation in bleomycin-induced lesions were Thy-1-negative. Histological sections from patients with idiopathic pulmonary fibrosis demonstrated absent Thy-1 staining within fibroblastic foci. Normal lung fibroblasts, in both mice and humans, were predominantly Thy-1-positive. The fibrogenic cytokines interleukin-1 and tumor necrosis factor-␣ induced loss of fibroblast Thy-1 surface expression in vitro, which was associated with Thy-1 shedding, Smad phosphorylation, and myofibroblast differentiation. These results suggest that fibrogenic injury promotes loss of lung fibroblast Thy-1 expression, resulting in enhanced fibrogenesis. (Am J Pathol 2005, 167:365-379) Idiopathic pulmonary fibrosis (IPF), with its histopathological signature of usual interstitial pneumonia (UIP), is a paradigmatic, but as yet primarily enigmatic example of uncontrolled fibroproliferation. IPF is remarkable for its insidious onset, dramatic histopathological and pathophysiological derangements, and relentless progression to death regardless of treatment. The etiology of IPF, and the factors that direct its dismal outcome, remain the subject of intense investigation.1 Fibroblasts are the cellular sine qua non of fibrosis in most tissues, and the histopathology of IPF underscores this observation. The histopathological feature most clearly correlated with outcome is the presence in lung of fibroblastic foci of young connective tissue, the presence of which portends death within months.2 Fibroblastic foci seem to represent the fibroproliferative leading edge of the heterogeneous areas of scarring in IPF.3-5 The myofibroblasts within these foci are clearly dysregulated in their proliferative and matrix-productive function, yet the origin of these cells, and the factors that lead to their accumulation and persistence, are unknown.Fibroblasts in most tissues are heterogeneous with respect to size, secretory profile, and surface markers. Fibroblasts within a fibrogenic milieu clearly differ from those in normal tissues. In particular, fibroblasts isolated from lungs with active fibrotic disease have increased proliferative capacity, are capable of anchorage-independent growth, and are morphologically distinct. 6 -8 Furthermore, differences among subsets of normal fibroblasts have been identified on the basis of surface markers, cytoskeleta...

Soluble CD90 as a potential marker of pulmonary involvement in systemic sclerosis

“…Since VCAM-1 and E-selectin expressions are also elevated in EC activation (28), and only a weak correlation of sVCAM-1 and sCD90 was observed, another potential source of sCD90 in SSc might be fibroblasts. In fibroblast foci of patients with idiopathic pulmonary fibro- sis, only CD90 fibroblasts/myofibroblasts could be detected, whereas in healthy controls, CD90ϩ fibroblasts predominate (14,36). In vitro stimulation of CD90ϩ fibroblasts with profibrotic cytokines such as tumor necrosis factor ␣ and interleukin-1 leads to a shedding of CD90 from the cell surface and a differentiation toward a highly active myofibroblast phenotype (14,37).…”

“…In fibroblast foci of patients with idiopathic pulmonary fibro- sis, only CD90 fibroblasts/myofibroblasts could be detected, whereas in healthy controls, CD90ϩ fibroblasts predominate (14,36). In vitro stimulation of CD90ϩ fibroblasts with profibrotic cytokines such as tumor necrosis factor ␣ and interleukin-1 leads to a shedding of CD90 from the cell surface and a differentiation toward a highly active myofibroblast phenotype (14,37). Presumably, CD90 is shed from the cell surface in the course of such a differentiation process of fibroblasts, therefore causing increased serum concentrations of sCD90 in SSc patients.…”

“…Soluble adhesion molecules such as soluble vascular cell adhesion molecule 1 (sVCAM-1), sE-selectin, and soluble intercellular adhesion molecule 1 (sICAM-1) are known to be elevated in the sera of patients with SSc and are related to active disease (12,13). Shedding of CD90 from the cell surface of fibroblasts is associated with differentiation toward a profibrogenic myofibroblast phenotype (13,14). We have previously described an enzyme-linked immunosorbent assay (ELISA) for detection of soluble CD90 (sCD90) (15).…”

HDAC is essential for epigenetic regulation of Thy-1 gene expression during LPS/TLR4-mediated proliferation of lung fibroblasts

“…7 Heterogeneous surface expression of Thy-1 in fibroblasts results in the specialization of fibroblast, including Thy-1 (+) and Thy-1 (− ) subsets. Hagood et al 5,8,9 reported that lack of Thy-1 expression on lung fibroblasts contributed to IPF. Recently, it was found that epigenetic mechanisms, such as promoter hypermethylation and histone modification, play an important role in Thy-1 gene silencing in lung fibroblasts.…”

Thy‐1 (CD90) regulates the extravasation of leukocytes during inflammation

“…Beissert et al demonstrated an impaired cutaneous immune response in Thy-1-deficient mice and a reduced activation of TCs [14]. Thy-1-deficient mice display an abnormal retinal development [15] and develop a more severe lung fibrosis after bleomycin treatment [16]. Although Thy-1 was identified in vitro as an adhesion molecule for the binding of leukocytes to activated ECs, the involvement of Thy-1 in the recruitment of leukocytes at sites of inflammation has not been investigated so far.…”