Solubilized nuclear thyroid hormone receptors in circulating human mononuclear cells

Area of Science:

• Endocrinology
• Molecular Biology
• Cellular Biology

Background:

• Thyroid hormones (T3 and T4) are crucial for metabolism.
• Understanding thyroid hormone receptor interactions is key to human health.
• Previous studies focused on liver and kidney receptors, with limited data on mononuclear cells.

Purpose of the Study:

• To develop and validate a receptor assay for T3 and T4 in human mononuclear cells.
• To investigate T3 and T4 receptor characteristics, including binding capacity and affinity.
• To compare receptor levels in normal, hypothyroid, and obese individuals, and assess the impact of fasting.

Main Methods:

• Developed a salt solubilization assay for nuclear receptors from mononuclear cells.
• Utilized standard saturation analysis to determine maximal binding capacity (MBC) and equilibrium dissociation constants (Kd).
• Employed gel filtration to analyze physicochemical properties of the receptors.

Main Results:

• Identified high-affinity T3 and T4 receptors in human mononuclear cells with properties similar to rat liver receptors.
• Observed increased T3 and T4 receptor numbers in hypothyroid patients and decreased levels in obese subjects.
• Found that fasting significantly increases T3 and T4 receptor binding capacity in obese individuals.
• Dissociation constants (Kd) remained unaltered across conditions, suggesting changes in receptor number, not affinity.

Conclusions:

• Human mononuclear cells possess T3 and T4 receptors with characteristics similar to those in rat liver.
• Thyroid hormone receptor levels in mononuclear cells are altered in hypothyroidism and obesity.
• Fasting influences T3 and T4 receptor binding capacity, indicating a role in rapid homeostatic regulation.
• Differences in T3 receptor regulation between human mononuclear cells and rat liver during fasting suggest distinct mechanisms.