Thyroid hormone transporters--functions and clinical implications

Area of Science:

• Neuroendocrinology
• Molecular Biology
• Genetics

Background:

• Thyroid hormones are essential for neurological development.
• Thyroid hormone transport across cell membranes is mediated by specific protein transporters.
• Monocarboxylate transporter 8 (MCT8) is a key transporter for thyroid hormones.

Purpose of the Study:

• To review the role of thyroid hormone transporters in physiological and pathological conditions.
• To focus on the pathophysiology of mutations in the MCT8 gene (SLC16A2).
• To explore the reasons for neurological differences between human MCT8 deficiency and mouse models.

Main Methods:

• Review of existing literature on thyroid hormone transporters.
• Analysis of histopathological data from human patients with MCT8 mutations.
• Examination of data from Slc16a2 knockout mouse models.

Main Results:

• Mutations in SLC16A2 cause X-linked MCT8 deficiency, leading to severe neurological impairment and altered thyroid hormone levels.
• Brain lesions in affected individuals likely result from prenatal cerebral hypothyroidism.
• Slc16a2 knockout mice do not exhibit neurological impairment, suggesting compensatory mechanisms possibly involving OATP1C1 transporter expression differences.

Conclusions:

• MCT8 is vital for thyroid hormone transport, particularly into the brain.
• Differences in blood-brain barrier transporter expression, such as OATP1C1, may explain the milder phenotype in mouse models compared to human MCT8 deficiency.
• Understanding thyroid hormone transporter function is critical for addressing related neurological disorders.