Severe Gestational Hypothyroidism Increases BBB Nutrient Transport in the Offspring

Area of Science:

• Neuroendocrinology
• Developmental Biology
• Physiology

Background:

• Thyroid hormones are crucial for brain development.
• Maternal hypothyroidism can affect offspring neurodevelopment.
• Previous studies showed moderate hypothyroidism decreased blood-brain barrier (BBB) glucose transport.

Purpose of the Study:

• To investigate the effects of severe maternal hypothyroidism on offspring thyroid status and BBB nutrient transport.
• To assess if severe hypothyroidism exacerbates the effects seen with moderate hypothyroidism.
• To evaluate the impact of thyroid hormone supplementation.

Main Methods:

• Induction of severe hypothyroidism in dams using 6-n-propyl thiouracil (PTU).
• Measurement of offspring birth weight, weanling body weight, and brain weight.
• Assessment of serum thyroid hormone levels (T4 and T3).
• Determination of BBB transport of leucine, tyrosine, and 2-deoxy-D-glucose.
• Evaluation of BBB integrity using Evans blue extravasation.
• Administration of T3 supplementation to dams and offspring.

Main Results:

• PTU-fed dams produced offspring with significantly lower birth weights, weanling body weights, and brain weights.
• Offspring exhibited severe hypothyroidism (low T4 and T3 levels).
• Surprisingly, BBB transport of leucine, tyrosine, and 2-deoxy-D-glucose was significantly increased.
• BBB integrity remained intact, ruling out breakdown as the cause of increased transport.
• T3 supplementation normalized BBB nutrient transport and improved body and brain weights.

Conclusions:

• Severe maternal hypothyroidism leads to impaired offspring growth and altered BBB nutrient transport.
• Increased BBB nutrient transport in severe hypothyroidism is not due to BBB breakdown.
• Thyroid hormone replacement therapy can mitigate the adverse effects of severe hypothyroidism on offspring development and BBB function.