Constitutively low expression of collagen XIII alpha 1 may help explain the vulnerability of the inferior rectus muscle to thyroid-associated ophthalmopathy

Expression of Collagen XIII in Tissues of the Thyroid and Orbit With Relevance to Thyroid-Associated Ophthalmopathy

Purpose

Antibodies against collagen XIII have previously been identified in patients with active thyroid-associated ophthalmopathy (TAO). Although collagen XIII expression has been described in extraocular muscles and orbital fat, its detailed localization in extraocular and thyroid tissues and the connection to autoimmunity for collagen XIII remain unclear. Our objective was to map the potential targets for these antibodies in the tissues of the orbit and thyroid.

Methods

We evaluated the expression of collagen XIII in human patient and mouse orbital and thyroid tissues with immunostainings and RT-qPCR using Col13a1-/- mice as negative controls. COL13A1 expression in Graves' disease and goiter thyroid samples was compared with TGF-β1 and TNF, and these were also studied in human thyroid epithelial cells and fibroblasts.

Results

Collagen XIII expression was found in the neuromuscular and myotendinous junctions of extraocular muscles, blood vessels of orbital connective tissue and fat and the thyroid, and in the thyroid epithelium. Thyroid expression was also seen in germinal centers in Graves' disease and in neoplastic epithelium. The expression of COL13A1 in goiter samples correlated with levels of TGF-B1. Upregulation of COL13A1 was reproduced in thyroid epithelial cells treated with TGF-β1.

Conclusions

We mapped the expression of collagen XIII to various locations in the orbit, demonstrated its expression in the pathologies of the Graves' disease thyroid and confirmed the relationship between collagen XIII and TGF-β1. Altogether, these data add to our understanding of the targets of anti-collagen XIII autoantibodies in TAO.

Quantitative evaluation of activity of thyroid-associated Ophthalmopathy using short-tau inversion recovery (STIR) sequence

OBJECTIVE

Quantitatively staging TAO using MRI remains limited. Our study aims to identify the cut-off signal intensity value for staging TAO using STIR sequence scan.

METHODS

Between June 2018 and July 2020, a number of 51 patients with TAO (102 eyes) and 19 volunteer controls (38 eyes) were recruited. The clinical and biochemical parameters were measured in each patient. Disease activity was diagnosed based on the Clinical Activity Score (CAS). The signal intensities of extraocular muscles were scanned using short-tau inversion recovery (STIR) sequences from MRI.

RESULTS

Compared to the inactive TAO patients and the controls, the signal intensity ratios (SIRs) of the superior rectus, inferior rectus, medial rectus, lateral rectus on STIR images were significantly increased in the active TAO patients. After adjustment for age and smokers, the SIRs of four extraocular muscles showed strong associations with CAS. By receiver operator characteristic (ROC) curve analysis, all four muscle SIRs demonstrated good efficiency for predicting disease activity [area under curve (AUC) 0.75-0.83, all P < 0.01]. The identified cut-off SIR values were further validated in a new group of TAO patients (30 eyes) enrolled between September 2020 and January 2021. The cut-off SIR value of > 2.9 in the inferior rectus showed optimal diagnostic value for staging the active TAO.

CONCLUSIONS

the signal intensity of extraocular muscles on STIR sequence was a good predictor for TAO activity. A cut-off SIR value of > 2.9 in the inferior rectus could be applied to evaluate the active stage of TAO.