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G. M. Lehmann, S. J. Pollock, C. W. O'Loughlin, S. E. Feldon, R. P. Phipps; Thy-1+ Human Orbital Fibroblasts Produce a Novel Anti-Adipogenic Factor. Invest. Ophthalmol. Vis. Sci. 2010;51(13):3925.
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Thyroid eye disease (TED) is a condition, associated with Graves' hyperthyroidism, in which the orbital tissues become inflamed and are remodeled. Remodeling often involves expansion of orbital adipose tissue via differentiation of fibroblasts to adipocytes. The purpose of our study is to investigate an observed link between orbital fibroblast adipogenesis and expression of the Thy-1 surface protein.
Primary human orbital fibroblasts were isolated from fat compartment explants obtained with informed consent from individual TED patients undergoing orbital decompression surgery. Fibroblasts were treated with 15-deoxy-prostaglandin J2 (15d-PGJ2) to stimulate adipogenesis. Lipid accumulation and Thy-1 surface expression were evaluated using a revolutionary imaging flow cytometric method (ImageStreamTM) that allows for enhanced quantitation of adipocytes.
Our previous work has shown that treatment of purified populations of Thy-1+ and Thy-1- orbital fibroblasts with 15d-PGJ2 yields adipogenesis only in the Thy-1- populations, but not in the Thy-1+ populations. These initial findings could be interpreted to mean that the differentiative potential of an orbital fibroblast depends on its expression of Thy-1. However, simultaneous evaluation of adipogenesis and Thy-1 expression revealed that, when cultured together, Thy-1+ and Thy-1- orbital fibroblasts are equally disposed to adipogenic differentiation. To reconcile these results, purified Thy-1+ or Thy-1- orbital fibroblast populations were differentiated in conditioned medium from cells of the same or the opposing subset. Purified Thy-1- cells responded robustly to treatment if they were cultured in medium conditioned by other Thy-1- cells. But, if cultured in conditioned medium collected from Thy-1+ cultures, Thy-1- cells were, like Thy-1+ fibroblasts, refractory to 15d-PGJ2-induced differentiation.
Our results reveal that a factor present in medium conditioned by Thy-1+ cells inhibits adipogenic differentiation of orbital fibroblasts. This factor may play an important role in the prevention of excess fat deposition in the normal orbit.
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