title: Human fibrocytes coexpress thyroglobulin and thyrotropin receptor.
abstract: Thyroglobulin (Tg) is the macromolecular precursor of thyroid hormones and is thought to be uniquely expressed by thyroid epithelial cells. Tg and the thyroid-stimulating hormone receptor (TSHR) are targets for autoantibody generation in the autoimmune disorder Graves disease (GD). Fully expressed GD is characterized by thyroid overactivity and orbital tissue inflammation and remodeling. This process is known as thyroid-associated ophthalmopathy (TAO). Early reports suggested that in TAO, both Tg and TSHR become overexpressed in orbital tissues. Previously, we found that CD34(+) progenitor cells, known as fibrocytes, express functional TSHR, infiltrate the orbit, and comprise a large subset of orbital fibroblasts in TAO. We now report that fibrocytes also express Tg, which resolves as a 305-kDa protein on Western blots. It can be immunoprecipitated with anti-Tg Abs. Further, (125)iodine and [(35)S]methionine are incorporated into Tg expressed by fibrocytes. De novo Tg synthesis is attenuated with a specific small interfering RNA targeting the protein. A fragment of the Tg gene promoter fused to a luciferase reporter exhibits substantial activity when transfected into fibrocytes. Unlike fibrocytes, GD orbital fibroblasts, which comprise a mixture of CD34(+) and CD34(-) cells, express much lower levels of Tg and TSHR. When sorted into pure CD34(+) and CD34(-) subsets, Tg and TSHR mRNA levels become substantially higher in CD34(+) cells. These findings indicate that human fibrocytes express multiple "thyroid-specific" proteins, the levels of which are reduced after they infiltrate tissue. Our observations establish the basis for Tg accumulation in orbital GD.
authors.affiliation: Department of Ophthalmology and Visual Sciences, Kellogg Eye Center, University of Michigan Medical School, Ann Arbor, MI 48105, USA.
authors.forename: Roshini
authors.initials: R
authors.lastname: Fernando
authors.forename: Stephen
authors.initials: S
authors.lastname: Atkins
authors.forename: Nupur
authors.initials: N
authors.lastname: Raychaudhuri
authors.forename: Ying
authors.initials: Y
authors.lastname: Lu
authors.forename: Bin
authors.initials: B
authors.lastname: Li
authors.forename: Raymond S
authors.initials: RS
authors.lastname: Douglas
authors.forename: Terry J
authors.initials: TJ
authors.lastname: Smith
mesh_terms: D018952:Antigens, CD34 / Q000378:metabolism; D015153:Blotting, Western; D002478:Cells, Cultured; D003239:Connective Tissue Cells / Q000378:metabolism; D005347:Fibroblasts / Q000378:metabolism*; D015870:Gene Expression; D049970:Graves Ophthalmopathy / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D006801:Humans; D007150:Immunohistochemistry; D017493:Leukocyte Common Antigens / Q000378:metabolism; D059630:Mesenchymal Stem Cells / Q000378:metabolism*; D009915:Orbit / Q000378:metabolism; D034622:RNA Interference; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D011989:Receptors, Thyrotropin / Q000235:genetics / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013954:Thyroglobulin / Q000235:genetics / Q000378:metabolism*; D013961:Thyroid Gland / Q000166:cytology / Q000378:metabolism
chemical_list: D018952:Antigens, CD34; D012333:RNA, Messenger; D011989:Receptors, Thyrotropin; D013954:Thyroglobulin; D017493:Leukocyte Common Antigens