Plasma membrane shedding and colloid vacuoles in hyperactive human thyroid tissue

Area of Science:

• Endocrinology
• Cell Biology
• Immunology

Background:

• Colloid vacuoles are a hallmark of human thyroid gland hyperactivity.
• Understanding the ultrastructural basis of these vacuoles is crucial for thyroid disease research.
• Thyroid-stimulating immunoglobulins (TSI) are implicated in hyperthyroid conditions like Graves' disease.

Purpose of the Study:

• To investigate the ultrastructural appearance of colloid vacuoles in hyperactive human thyroid tissue.
• To determine the origin and composition of intraluminal membrane material associated with these vacuoles.
• To explore the potential role of this material in the pathogenesis of hyperthyroidism and autoimmune thyroid disease.

Main Methods:

• Human thyroid tissue (normal and toxic diffuse goiter) was transplanted into nude mice.
• Transplants and human thyroid tissue from thyrotoxicosis patients were treated with TSI or fixed directly.
• Light and electron microscopy were used to analyze tissue ultrastructure and intraluminal contents.

Main Results:

• TSI administration significantly increased colloid vacuole formation in transplanted thyroid tissue.
• Electron microscopy revealed abundant intraluminal membrane material, associated with colloid vacuoles, in TSI-exposed tissue.
• This membrane material, resembling shed microvilli, showed positive peroxidase activity, suggesting follicular cell origin.

Conclusions:

• Intraluminal membrane material, likely derived from apical plasma membrane shedding, is strongly associated with colloid vacuole formation in hyperactive thyroid tissue.
• The presence of this membrane material may precipitate colloid vacuole formation in hyperthyroidism.
• This intraluminal material could play a role in the immune system's exposure to thyroid microsomal antigen, potentially contributing to autoantibody development in Graves' disease.