Biomedical subjects

Valerie Estienne

Publications and source records attributed to Valerie Estienne.

3 recordsLinked to original sources

PubMed2006

Detection of thyroid peroxidase mRNA and protein in orbital tissue.

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 (n=6) and normal (n=5) 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.

Adipocytes↗

PubMed2003

Complement activation by direct C4 binding to thyroperoxidase in Hashimoto's thyroiditis.

Biosynthesis of thyroid hormones is an oxidative process that generates reactive oxygen species (ROS) and involves thyroperoxidase (TPO) that is one of the main autoantigens involved in autoimmune thyroid diseases. The ectodomain of TPO consists of a large N-terminal myeloperoxidase-like module followed by a complement control protein (CCP)-like module and an epidermal growth factor-like module. The presence of these two additional gene modules suggests that they may play some crucial, hitherto unsuspected role associated with thyroid function. Because the CCP module is a constituent of the molecules involved in the activation of C4 complement component, we investigated the possibility that C4 may bind to TPO and activate the complement pathway in autoimmune conditions. We showed that TPO via its CCP module directly activated complement without any mediation by Ig. We suggested that this additional complement pathway requires the production of ROS and specially hydroxyl radicals that aggregate TPO and oxidize methionines of C4. Moreover, we found, in patients with Hashimoto's thyroiditis, that thyrocytes overexpress C4 and all the downstream components of the complement pathway. These results indicate that TPO has some as yet unknown function, which may contribute along with other mechanisms to the massive cell destruction observed in Hashimoto's thyroiditis. Investigating this complement pathway, therefore, would provide an excellent means of reaching a better understanding of the etiology of other degenerative diseases.

Acute Disease↗

PubMed2002

Evidence that the complement control protein-epidermal growth factor-like domain of thyroid peroxidase lies on the fringe of the immunodominant region recognized by autoantibodies.

There is no consensus regarding the location of the immunodominant region (IDR) on thyroid peroxidase (TPO) recognized by the majority of autoantibodies. Strong evidence indicates that it lies upstream of amino acid 741. However, an epitope has been localized to downstream residues 742-848 encompassing a disulfide-rich complement control protein (CCP)-like and epidermal growth factor (EGF)-like domain. To determine whether these domains comprise part of the IDR, we used a recombinant CCP/EGF-like polypeptide to screen a thyroid B-cell-derived immunoglobulin gene phage display library. Two unusual TPO autoantibodies were isolated. Neither was among the 83 clones previously obtained by panning the same library on native or denatured TPO, or TPO with the IDR masked. Fab from these clones bound native TPO, one with high affinity (Kd 6 x 10(-10) M), and both recognized TPO expressed on the surface of mammalian cells. Phage-expressing multiple copies of the antibody (multivalent), but not monovalent Fab from these clones, bound to the CCP/EGF polypeptide. Most important, inhibition of TPO binding by autoantibodies to the IDR indicated that the epitopes of the two new autoantibodies overlap with this region. The value of these two rare clones lies in the insight they provide into the location of the TPO IDR. From their binding characteristics, we deduce that the CCP/EGF-like domain lies on the fringe of the TPO immunodominant region.

Amino Acid Sequence↗