Detection of thyroid peroxidase mRNA and protein in orbital tissue

Abstract

Objective: We have previously reported that the absence of thyroid peroxidase antibodies (TPOAb) in Graves' disease (GD) was associated with an increased risk of Graves' ophthalmopathy (GO). This observation raised the possibility that TPOAb could act as a protective factor. However, the presence of thyroid peroxidase (TPO) in the orbit has not been previously reported. The aim of this study was to confirm or exclude the presence of orbital TPO. Methods and design: Relative TPO mRNA expression from GO (nZ6) and normal (nZ5) orbital fat tissue was determined using real-time PCR technique. Orbital fat in the normal group from blepharoplasty represents extraconal (anterior) fat. mRNA expression in fibroblasts grown from these tissues before and after adipocyte differentiation was also documented. Finally, Western blotting was carried out to verify translation of TPO mRNA transcripts. Results and discussion: TPO transcripts were detected in the orbital fat tissue obtained from normal and GO subjects using the real-time PCR technique. TPO expression was increased in GO compared to normal (N) tissues. However, TPO expression in cultured fibroblasts was similar in both groups and adipogenesis did not appear to alter TPO expression. Protein was detected by Western blot analysis using the TPO MAB 47 (mAb 47). The predicted 110-kDa band was detected in orbital fat as well as in orbital fibroblasts. Our results suggest the presence of TPO in GO and N orbital tissues. We hypothesise that immune responses directed against orbital TPO might play a role in modulating the clinical expression of GO.European Journal of Endocrinology 155 213-218

Does thyroid peroxidase provide an antigenic link between thyroid autoimmunity and breast cancer?

“…Our experiments demonstrate that TPO mRNA and protein are not confined to thyroid cells but are also present in other tissues, albeit it at low levels. Our results confirm those of Lai et al 30 who demonstrated TPO expression in orbital tissue.…”

Susceptibility genes in Graves’ ophthalmopathy: searching for a needle in a haystack?

“…A functional TSH‐R has been detected on orbital fibroblasts in in vitro and in situ studies, and a correlation between TSH‐R antibodies and the activity/severity of GO has been described 26,27 . Interestingly, other thyroid‐specific antigens such as thyroglobulin and thyroid peroxidase have also been detected in orbital tissues 28,29 . In addition, several other, probably secondary, autoantigens have been characterized in extraocular muscles (the flavoprotein subunit of mitochondrial succinate dehydrogenase, G2s, sarcalumenin, the calcium‐binding protein calsequestrin) and in orbital fibroblasts (collagen XIII).…”

“…26,27 Interestingly, other thyroid-specific antigens such as thyroglobulin and thyroid peroxidase have also been detected in orbital tissues. 28,29 In addition, several other, probably secondary, autoantigens have been characterized in extraocular muscles (the flavoprotein subunit of mitochondrial succinate dehydrogenase, G2s, sarcalumenin, the calcium-binding protein calsequestrin) and in orbital fibroblasts (collagen XIII). Of these, antibodies against calsequestrin and collagen XIII have been shown to be very specific and sensitive diagnostic markers of GO ( Fig.…”

Update on the medical treatment of Graves’ ophthalmopathy

“…15 Insulin-like growth factor-1 (IGF-1), another receptor on the orbital fibroblast cells, has also been shown to induce hyaluronan synthesis, 16 while thyroid-specific antigens such as thyroid peroxidase and thyroglobulin have been detected in orbital tissues. 17,18 Finally, autoantigens in extraocular muscles (calsequestrin) and orbital fibroblasts (collagen XIII) were reported to be specific and sensitive diagnostic markers of GO. [19][20][21] It should be noted that although the autoantibody theory of GO pathogenesis is speculative as the evidence is thus far insufficient to link it fully to the clinical manifestations of GO.…”