Direct thyroid hormone activation of mitochondria: the role of adenine nucleotide translocase

Area of Science:

• Biochemistry
• Molecular Biology
• Endocrinology

Background:

• Mitochondrial oxidative phosphorylation is crucial for cellular energy production.
• Thyroid hormones, particularly T3, play a vital role in regulating metabolism.
• Previous studies suggested a mitochondrial T3 receptor involved in oxidative phosphorylation.

Purpose of the Study:

• To investigate the role of adenine nucleotide translocase (AdNT) as a potential mitochondrial thyroid hormone receptor.
• To determine if AdNT activity is altered in hypothyroidism and responsive to hormone replacement.
• To assess the binding characteristics of AdNT for T3.

Main Methods:

• Measurement of liver mitochondrial oxidative phosphorylation rates in hypothyroid rats after T3 injection.
• Analysis of AdNT flux control coefficients to determine its role in oxidative phosphorylation.
• Preparation and characterization of beef heart mitochondrial AdNT for [125I]T3 binding assays.

Main Results:

• T3 injection rapidly activated liver mitochondrial oxidative phosphorylation in hypothyroid rats.
• AdNT activity was found to be depressed in hypothyroid rats and restored by hormone replacement.
• Beef heart mitochondrial AdNT exhibited high-affinity, low-capacity binding of [125I]T3.

Conclusions:

• The findings strongly implicate the mitochondrial adenine nucleotide translocase (AdNT) as a candidate for the initiating site of thyroid hormone action.
• AdNT's role in regulating oxidative phosphorylation and its direct binding of T3 support its function as a mitochondrial T3 receptor.
• This identifies a novel mechanism for thyroid hormone regulation of cellular energy metabolism.