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

ABSTRACT

Thyroid-associated ophthalmopathy (TAO) causes irreversible increase in extraocular fat volume that contributes to the risk of exophthalmos and compressive optic neuropathy. Collagen XIII is implicated in uncontrolled cell growth in some tumours, but we are not aware of any studies of collagen XIII in TAO-affected solid tissue to date. We conducted immunohistochemical staining for collagen XIII alpha 1 (COL13A1), present in both the transmembrane and cleaved forms of collagen XIII, in consecutive prospectively collected human extraocular tissue specimens from patients with TAO and controls. We identified overexpression of collagen XIII in active TAO-affected fat. We discuss how species and cell-type specific responses of collagen XIII to stressors may help explain the different phenotypes of TAO.

KEYWORDS:

• Thyroid-associated ophthalmopathy
• thyroid eye disease
• collagen XIII
• COL13A1
• extraocular fat

Acknowledgments

We thank all the patients, surgeons and staff at University Geelong Hospital, Barwon Health, Geelong Private Hospital, the Royal Victorian Eye and Hospital, St Vincent’s Private Hospital, Munich University Eye Hospital, South Munich Eye Centre and the Department of Rheumatology and Inflammation Research, University of Gothenburg, Sweden, who contributed to this work. We also thank Professor Taina Pihlajaniemi, University of Oulu, Finland, for her kind gift of the purified Collagen XIII trimer; and Professor Fatima Pedrosa-Domellöf, University of Umeå, Sweden, for obtaining and preparing the fresh frozen sample of normal medial rectus muscle for immunostaining.

Declaration of interest

The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the article.