Monocarboxylate transporter 8

Ideogram human chromosome X

Monocarboxylate Transporter 8 (MCT8), also known as solute carrier family 16 member 2 (SLC16A2), is a protein that in humans is encoded by the SLC16A2 gene. MCT8 is a thyroid hormone transporter, playing a crucial role in transporting thyroxine (T4) and triiodothyronine (T3) across the cell membrane. This transporter is particularly significant for the development and function of the nervous system.

Function

MCT8 facilitates the cellular uptake and efflux of thyroid hormones, which are critical for metabolism, brain development, and neuronal function. Thyroid hormones regulate gene expression by controlling the transcription of specific genes, and their proper distribution within the body is essential for normal development and metabolic homeostasis. MCT8's role is particularly vital in the brain, where thyroid hormones influence the development and differentiation of neurons.

Genetic and Clinical Significance

Mutations in the SLC16A2 gene can lead to a rare condition known as Allan-Herndon-Dudley syndrome (AHDS), characterized by severe intellectual disability, muscle hypotonia, and movement disorders. This condition highlights the importance of MCT8 in the brain's development and the systemic distribution of thyroid hormones. Patients with AHDS typically exhibit elevated levels of T3, reduced levels of T4, and normal or slightly elevated thyroid-stimulating hormone (TSH) levels in their serum.

Structure

The structure of MCT8 includes 12 transmembrane domains, which are common among members of the solute carrier family. This structure allows MCT8 to effectively transport thyroid hormones across the cell membrane, despite their hydrophobic nature.

Expression

MCT8 is widely expressed throughout the body, with significant levels found in the liver, kidney, and brain. The high expression in the brain underscores its critical role in ensuring the availability of thyroid hormones for proper neurological development and function.

Research and Therapeutic Implications

Research on MCT8 has focused on understanding its role in thyroid hormone distribution and the pathophysiology of AHDS. Therapeutic approaches for AHDS are currently limited, but understanding MCT8's function and mechanisms may lead to the development of targeted treatments that can bypass the transporter defect or modulate its activity.

See Also

• Thyroid hormone
• Allan-Herndon-Dudley syndrome
• Solute carrier family
• Protein transport