Overexpression of collagen XIII in extraocular fat affected by active thyroid-associated ophthalmopathy: A crucial piece of the puzzle?

The Relevance and Potential Role of Orbital Fat in Inflammatory Orbital Diseases: Implications for Diagnosis and Treatment

The orbit is an important structure within the skull that houses the eye, optic nerve, and extraocular muscles. It also contains adipose/fat tissue, which provides a protective cushion for these components. Inflammatory orbital disease can affect any or all components of the orbit, often arising from various underlying pathologic conditions, including autoimmune, infectious, and vascular diseases. Typical signs and symptoms of orbital inflammation include swelling, redness, pain, discomfort, and potential loss of function. The role of orbital fat in the pathogenesis of inflammatory orbital diseases has not been fully explored. This review aims to provide a comprehensive description of orbital fat, its relevance and the potential role in inflammatory diseases of the orbit, and the use of radiologic imaging studies for evaluating this fat depot in cases of as inflammatory orbital diseases. Additionally, this review discusses the various procedures available for the treatment and management of these conditions. A range of interventions, including pharmacotherapy and surgical procedures, will be evaluated as promising therapeutic options. This review also explores the characteristics and potential applications of orbital fat-derived stem cells, with an emphasis on their regenerative abilities and anti-inflammatory effects. Understanding the role of orbital fat and its contribution to inflammatory orbital diseases is essential for optimizing diagnostic and treatment strategies.

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.