Neonatal hyper- and hypothyroidism alter the myoglobin gene expression program in adulthood

Area of Science:

• Physiology
• Molecular Biology
• Endocrinology

Background:

• Myoglobin is crucial for oxygen storage and reactive oxygen species management in muscles.
• Understanding myoglobin gene expression during development is vital for muscle physiology.

Purpose of the Study:

• To investigate myoglobin mRNA expression in rat cardiac ventricle and skeletal muscles during early life.
• To determine the effects of transient neonatal hypothyroidism and hyperthyroidism on myoglobin gene expression patterns.

Main Methods:

• Myoglobin mRNA levels were quantified using Northern blot analysis in Wistar rats from 7 to 42 days of life.
• Neonatal rats were subjected to hypo- and hyperthyroidism using propylthiouracil and triiodothyronine, respectively.
• Animals were euthanized post-treatment or at 90 days for adult parameter assessment.

Main Results:

• Skeletal muscle myoglobin mRNA increased 12-fold from postnatal days 7-28, while ventricle levels remained stable.
• Triiodothyronine administration increased skeletal muscle myoglobin mRNA (1.5-4.5x) and ventricle myoglobin mRNA (2.5x with extended treatment).
• Neonatal hypothyroidism decreased ventricular myoglobin mRNA by 60%, and transient hyperthyroidism affected adult heart rate, body weight, and muscle myoglobin mRNA.

Conclusions:

• Neonatal thyroid hormone availability critically influences the developmental trajectory of myoglobin gene expression in cardiac and skeletal muscles.
• Altered neonatal thyroid states lead to lasting physiological changes, including altered myoglobin expression and reduced body weight in adulthood.
• These findings highlight the sensitivity of muscle development to thyroid hormone signaling during the neonatal period.