The Thyroid Hormone Receptors Inhibit Hepatic Interleukin-6 Signaling During Endotoxemia

Area of Science:

• Endocrinology
• Immunology
• Molecular Biology

Background:

• Decreased thyroid hormone production occurs during sepsis.
• Thyroid hormone receptors (TRs) are implicated in inflammatory responses.
• Key signaling pathways like STAT3, NF-κB, and ERK are crucial in sepsis.

Purpose of the Study:

• To investigate the role of TRs in regulating inflammatory pathways (STAT3, NF-κB, ERK) during sepsis.
• To understand how TRs influence the response to lipopolysaccharide (LPS) and inflammatory cytokines like IL-6.

Main Methods:

• Utilized TR knockout mice to assess inflammatory mediator expression and signaling pathway activity.
• Administered LPS to induce endotoxic shock and analyzed hepatic inflammatory responses.
• Investigated the effect of thyroid hormone T3 on IL-6 signaling in cell lines (macrophages, hepatocarcinoma).

Main Results:

• TR knockout mice showed reduced hepatic inflammatory mediators (e.g., IL-6) but paradoxically higher STAT3 and ERK activity.
• Hyperthyroidism exacerbated LPS-induced mortality and cytokine production.
• Thyroid hormone T3 directly suppressed IL-6 signaling, inhibiting STAT3 activation and IL-6-stimulated gene transcription.

Conclusions:

• TRs act as endogenous repressors of STAT3 and ERK pathways during sepsis.
• Thyroid hormones, via TRs, play a critical role in immune homeostasis by antagonizing IL-6 signaling.
• This suppression of IL-6 response by TRs serves as a negative feedback mechanism to mitigate excessive inflammation during infections.