Thyroid hormone and the neuroglia: both source and target.

Area of Science:

• Neuroscience
• Endocrinology
• Cell Biology

Background:

• Thyroid hormone is essential for nervous system development and function.
• Thyroxine requires brain conversion to the active form, triiodothyronine (T3), for nuclear receptor binding and gene regulation.

Purpose of the Study:

• To discuss the impact of thyroid hormone on glial cell function.
• To review the regulation of T3 generation by type 2 iodothyronine deiodinase (D2) in glial cells.
• To highlight the role of glial-neuronal interactions in thyroid hormone regulation.

Main Methods:

• Literature review on thyroid hormone action in the brain.
• Discussion of type 2 iodothyronine deiodinase (D2) activity in glial subtypes (astrocytes, tanycytes).
• Analysis of recent evidence on paracrine signaling from glial D2 to neurons.

Main Results:

• Type 2 iodothyronine deiodinase (D2) in glial cells (astrocytes, tanycytes) activates thyroxine to T3 in the brain.
• D2 activity is finely tuned in different glial subtypes, regulating local T3 generation.
• Glial D2 exerts paracrine effects on neuronal gene expression, emphasizing glial-neuronal communication.

Conclusions:

• Glial cells, particularly astrocytes and tanycytes, are critical for thyroid hormone activation in the brain via D2.
• The regulation of T3 generation by D2 in glial cells is a key mechanism controlling neuronal function.
• Glial-neuronal interactions mediated by D2 are fundamental to thyroid hormone signaling pathways in the brain, relevant to both normal function and disease states.