Evidence for enhanced Thy-1 (CD90) expression in orbital fibroblasts of patients with Graves' ophthalmopathy

• Published in: Thyroid (New York, N.Y.) Vol. 18; no. 12; p. 1291
• Main Authors: Khoo, Teck Kim, Coenen, Michael J, Schiefer, A Reagan, Kumar, Seema, Bahn, Rebecca S
• Format: Journal Article
• Language: English
• Published: United States 01.12.2008
• Subjects: Adipose Tissue - metabolism; Adult; Animals; Connective Tissue - metabolism; Female; Fibroblasts - metabolism; Gene Expression; Graves Ophthalmopathy - metabolism; Humans; Male; Mice; Middle Aged; Orbit - metabolism; RNA, Messenger - metabolism; Thy-1 Antigens - biosynthesis
• ISSN: 1557-9077
• DOI: 10.1089/thy.2008.0255

Thy-1 is a surface protein that defines functionally distinct subpopulations of fibroblasts, with those lacking the antigen being capable of adipogenesis. Because increased fat cell development is a hallmark of the orbit in Graves' ophthalmopathy (GO), we wished to compare baseline Thy-1 expression in orbital fibroblasts from GO patients and normal individuals, and determine whether levels of the protein might be impacted by adipogenesis following peroxisome proliferator activator-gamma ligation. Orbital adipose/connective tissue specimens were obtained from euthyroid patients undergoing orbital decompression surgery for severe GO (n = 9) and from normal individuals (n = 9). Thy-1 mRNA and protein levels were assessed in tissue specimens and in orbital fibroblast cultures at baseline using RT-PCR, quantitative immunofluorescent staining, and flow cytometry using a specific Thy-1 mouse anti-human CD90/Thy-1 monoclonal antibody. In addition, some orbital fibroblast cultures were treated with rosiglitazone (1 microL/mL; 2 nM) or control for 10 days in culture. We found that Thy-1 mRNA and protein expression was higher in uncultured GO connective/adipose tissue specimens (3.8-fold; 0.835 +/- 0.116 relative expression) compared with normal (0.22 +/- 0.062; p = 0.002) and in cultured orbital fibroblasts from GO patients (3.3-fold; 9.28 +/- 1.82 relative expression) compared with normal cultures (2.80 +/- 0.42; p = 0.013). Adipocyte differentiation had no effect on Thy-1 expression. Flow cytometry and immunofluorescent staining showed increased numbers of Thy-1-positive cells in the GO (mean 77.9 + 4.09%; range 66.5-84.8%) compared with the normal fibroblast cultures (66.8 + 1.6%; range 63.3-71.0% positive; p = 0.046), as well as higher levels of expression on the positive cells. Increased Thy-1 expression in GO orbital tissues and cultures is likely a consequence of the orbital disease process, reflecting both the presence of increased numbers of Thy-1-positive cells and higher expression on those cells. Adipogenesis itself does not appear to impact Thy-1 expression. Increased expression of this protein in GO could represent an adaptive response to cell injury, in effect limiting disease progression within the orbital adipose/connective tissues.