S-equol Modulates T3-Induced Transcription and Neurite Outgrowth in Neuronal Cells.

Area of Science:

• Neuroendocrinology
• Molecular Biology
• Developmental Neuroscience

Background:

• Thyroid hormones (THs) and estrogen (E2) are crucial for brain development, influencing neuronal differentiation and plasticity.
• S-equol, a plant isoflavone metabolite, acts as an estrogen receptor (ER) ligand with known neurotrophic effects.
• The interaction between S-equol and thyroid hormone receptor (TR) signaling in the brain is not well understood.

Purpose of the Study:

• To investigate the effects of S-equol on TRβ transcriptional activity and neuronal morphogenesis.
• To explore the molecular mechanisms underlying S-equol's neurotrophic effects, including potential TR-ER crosstalk.
• To evaluate the impact of S-equol on synapse-related gene expression in neuronal cells.

Main Methods:

• Luciferase reporter assays to measure TRβ transcriptional activity.
• Cell culture experiments (Neuro-2a and C6 glioma cells) to assess neurite outgrowth and wound closure.
• mRNA expression analysis of synapse-related genes.
• In silico molecular docking to predict binding affinities.

Main Results:

• S-equol significantly potentiated T3-induced TRβ transcriptional activity in a dose- and time-dependent manner.
• Both S-equol and T3 promoted neurite outgrowth and wound closure individually; co-exposure yielded enhanced effects.
• S-equol co-exposure with T3 significantly increased mRNA levels of key synapse-related genes (Dlg4, Syn1, Syp, Camk2b, Bdnf).
• In silico analysis showed S-equol binds to TRβ, ERα, and ERβ, indicating a structural basis for receptor crosstalk.

Conclusions:

• S-equol acts as a dual modulator, potentially influencing T3 signaling through TR-ER interactions.
• S-equol may offer beneficial effects on neurodevelopment by enhancing TH signaling and neuronal growth.
• S-equol's role as an endocrine modulator warrants careful physiological and toxicological evaluation regarding TH action during development.