Abstract
Heterogeneous surface expression of Thy-1 in fibroblasts modulates inflammation and may thereby modulate injury and repair. As a paradigm, patients with idiopathic pulmonary fibrosis, a disease with pathologic features of chronic inflammation, demonstrate an absence of Thy-1 immunoreactivity within areas of fibrotic activity (fibroblast foci) in contrast to the predominant Thy-1 expressing fibroblasts in the normal lung. Likewise, Thy-1 deficient mice display more severe lung fibrosis in response to an inflammatory injury than wildtype littermates. We investigated the role of Thy-1 in the response of fibroblasts to the pro-inflammatory cytokine TNF-α. Our study demonstrates distinct profiles of TNF-α-activated gene expression in Thy-1 positive (Thy-1+) and negative (Thy-1−) subsets of mouse embryonic fibroblasts (MEF). TNF-α induced a robust activation of MMP-9, ICAM-1, and the IL-8 promoter driven reporter in Thy-1− MEFs, in contrast to only a modest increase in Thy-1+ counterparts. Consistently, ectopic expression of Thy-1 in Thy-1− MEFs significantly attenuated TNF-α-activated gene expression. Mechanistically, TNF-α activated Src family kinase (SFK) only in Thy-1− MEFs. Blockade of SFK activation abrogated TNF-α-activated gene expression in Thy-1− MEFs, whereas restoration of SFK activation rescued the TNF-α response in Thy-1+ MEFs. Our findings suggest that Thy-1 down-regulates TNF-α-activated gene expression via interfering with SFK- and NF-κB-mediated transactivation. The current study provides a novel mechanistic insight to the distinct roles of fibroblast Thy-1 subsets in inflammation.
Highlights
Thy-1 is a glycosyl phosphatidylinositol-anchored glycoprotein that is expressed in a variety of cell types, including T cells, thymocytes, neurons, endothelial cells, and fibroblasts [1,2,3]
Our results indicate that Thy-1 expression in mouse embryonic fibroblasts (MEF) substantially attenuates gene activation by TNF-a, which includes MMP-9, ICAM-1, and a reporter gene controlled by the human IL-8 promoter
In agreement with the results from MEF Thy-1 subsets, expression of Thy-1 in Thy-12 MEFs substantially reduced TNF-a-induced MMP-9 and ICAM-1 to less than 50% of the increase observed in Thy-12 MEF transfected with the backbone vector (Fig. 2A)
Summary
Thy-1 is a glycosyl phosphatidylinositol-anchored glycoprotein that is expressed in a variety of cell types, including T cells, thymocytes, neurons, endothelial cells, and fibroblasts [1,2,3]. Thy-1 is involved in T cell activation, inflammation, wound healing, and fibrosis. To mediate these diverse effects, Thy-1 participates in multiple signaling cascades. After T cell receptor activation, thymocytes isolated from Thy-1 null mice have increased SFK activity and cell proliferation when compared with thymocytes collected from wild-type mice, which indicates that Thy-1 inhibits T cell receptor-induced SFK activation and proliferation of thymocytes [4]. SFK is transiently activated by thrombospondin-1 in Thy1+, but not in Thy-12 rat lung fibroblasts [5]. These contradictory reports implicate that Thy-1 modulates SFK activity in a manner dependent upon cellular context
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have