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


METHODS
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.


RESULTS
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.


CONCLUSIONS
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.
Khoo
Teck Kim
TK
Division of Endocrinology, Metabolism and Nutrition, Mayo Clinic, Rochester, Minnesota 55905, USA.
Coenen
Michael J
MJ
Schiefer
A Reagan
AR
Kumar
Seema
S
Bahn
Rebecca S
RS
D000273:Adipose Tissue / Q000378:metabolism; D000328:Adult; D000818:Animals; D003238:Connective Tissue / Q000378:metabolism; D005260:Female; D005347:Fibroblasts / Q000378:metabolism; D015870:Gene Expression; D049970:Graves Ophthalmopathy / Q000378:metabolism*; D006801:Humans; D008297:Male; D051379:Mice; D008875:Middle Aged; D009915:Orbit / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D018800:Thy-1 Antigens / Q000096:biosynthesis*
D012333:RNA, Messenger; D018800:Thy-1 Antigens