Purpose: Thyroid-stimulating hormone receptor (TSHR) stimulating autoantibodies are associated with Graves' ophthalmopathy (GO), the orbital manifestation of Graves' disease (GD). TSHR autoantibody levels and orbital TSHR expression levels correlate positively with GO disease activity. Platelet-derived growth factors (PDGF) are increased in GO and potently activate orbital fibroblast effector functions. We investigated the possible relationship between PDGF and TSHR expression on orbital fibroblasts and how that influences the immunopathological effects of TSHR autoantibodies on orbital fibroblast activity.
Methods: Orbital fibroblasts were stimulated with PDGF-AA, PDGF-AB, and PDGF-BB, and TSHR expression was determined by flow cytometry. Stimulatory effects of bovine TSH and GD immunoglobulins on orbital fibroblasts (with or without PDGF-BB preincubation) were determined by IL-6, IL-8, chemokine (C-C motif) ligand (CCL)-2, CCL5, CCL7, and hyaluronan ELISA. The TSHR blocking antibody K1-70 and the cAMP inhibitor H89 were used to determine involvement of TSHR signaling.
Results: PDGF-AB and PDGF-BB stimulation increased TSHR expression on orbital fibroblasts, whereas PDGF-AA did not. Furthermore, stimulation with bovine TSH and immunoglobulins from GD patients induced IL-6, IL-8, CCL2, and hyaluronan production by orbital fibroblasts, and PDGF-BB preincubation enhanced this response of orbital fibroblasts. Blocking studies with a TSHR blocking antibody and a cAMP inhibitor inhibited these effects, indicating the involvement of TSHR signaling and thus of TSHR stimulating autoantibodies herein.
Conclusions: These findings indicate that PDGF-B containing PDGF isoforms amplify the immunopathological effects of TSHR-stimulating autoantibodies in GO patients by stimulating TSHR expression on orbital fibroblasts.