Post-myocardial infarction exercise training beneficially regulates thyroid hormone receptor isoforms

Area of Science:

• Cardiovascular Physiology
• Molecular Endocrinology
• Exercise Science

Background:

• Thyroid hormone receptors (TRs) regulate genes critical for myocardial contractility, such as alpha-myosin heavy chain (α-MHC) and beta-myosin heavy chain (β-MHC).
• Post-myocardial infarction (MI), altered TR expression correlates with heart failure progression, despite unchanged serum thyroid hormone (TH) levels.
• Exercise training post-MI beneficially impacts TH-target gene transcription and cardiac function.

Purpose of the Study:

• To investigate the effect of moderate-intensity exercise training on the expression of α1 and β1 TR isoforms in rats following myocardial infarction (MI).

Main Methods:

• Male Sprague-Dawley rats underwent coronary ligation (MI) or sham operation.
• MI rats were divided into sedentary (MI-Sed) and exercise (MI-Ex) groups.
• Exercise MI rats underwent 8 weeks of treadmill training post-MI.
• Real-time PCR and gel electrophoresis quantified TR-α1 and TR-β1 mRNA and protein expression.

Main Results:

• Both MI groups showed higher mRNA expression for TR-α1 and TR-β1 compared to sham.
• Protein electrophoresis revealed significantly higher TR-α1 (1.91-fold) and TR-β1 (1.62-fold) in MI-Ex versus MI-Sed rats (P < 0.05).
• TR-α1 and TR-β1 protein levels were decreased in the surviving myocardium of MI rats, but exercise training increased their expression.

Conclusions:

• Moderate-intensity exercise training significantly enhances TR-α1 and TR-β1 protein expression in the post-MI myocardium.
• Increased TR protein expression following exercise may upregulate α-MHC, improving myocardial contractile function and overall prognosis after MI.