Exogenous thyroxine increases cardiac GLUT4 translocation in insulin resistant OLETF rats

Area of Science:

• Cardiology
• Endocrinology
• Metabolic Science

Background:

• Insulin resistance shifts cardiac ATP production to fatty acids, impairing glucose metabolism.
• This shift increases oxidative stress, lipotoxicity, and mitochondrial dysfunction, potentially causing cardiomyopathy.
• Thyroid hormones (TH) impact glucose metabolism, but their cardiac effects during insulin resistance are unclear.

Purpose of the Study:

• To investigate the effects of exogenous thyroxine (T4) on cardiac glucose metabolism in insulin-resistant rats.
• To assess T4's impact on fatty acid metabolism in the heart under insulin resistance.

Main Methods:

• Insulin-resistant Otsuka Long Evans Tokushima Fatty (OLETF) rats and lean Long Evans Tokushima Otsuka (LETO) rats were used.
• Rats were assigned to control or T4-treated groups.
• Cardiac glucose and fatty acid metabolism markers were analyzed after T4 administration.

Main Results:

• T4 significantly increased GLUT4 gene expression and membrane translocation in OLETF rats.
• T4 boosted key glycolytic enzymes (p-AS160, PFK-1, hexokinase II) in OLETF hearts.
• T4 decreased carnitine palmitoyltransferase 2 (CPT2) mRNA and protein expression in OLETF rats.

Conclusions:

• Exogenous T4 enhances cardiac glucose uptake and metabolism in insulin-resistant rats.
• T4 treatment reduces cardiac fatty acid metabolism, potentially mitigating lipotoxicity.
• L-thyroxine shows promise for treating substrate metabolic dysfunction in diabetic cardiomyopathy.