Endocrine Abstracts

Background and Objective: Disrupted thyroid hormone (TH) signaling has devastating effects on human neurodevelopment. The molecular mechanisms underlying TH regulation and action are largely based on animal models. However, animal models are limited in revealing some of the most fundamental aspects of neurodevelopment that are unique to humans. We employed human induced pluripotent stem cell (iPSC) technology to study the effects of T3 on neurodevelopmental processes in a human model for fetal brain development.

Methods and Results: We differentiated iPSC-derived neural precursor cells into 2D neural networks, consistent 60:40 ratio of neurons to glia and mimicking fetal brain developmental. Neural networks were cultured in different T3 concentrations (0, 3, 10, 30 nM). We quantified T3-responsive gene expression (KLF9) by qPCR, and differentiation potential and synaptogenesis by immunohistochemistry. Neuronal electrophysiological function was assessed by calcium imaging.

Results: This well-established model in the field of neuroscience expressed key players of TH signaling (e.g. MCT8 DIO3). We observed a dose-dependent upregulation of KLF9. Synapse formation was increased by T3 (0,54 vs 4,26 in 0 nM vs 3nM T3; to 1,97 vs 2,1 synapse/100um² in 10 nM and 30 nM T3, respectively). Calcium imaging data showed neurons cultured under 3 nM T3 had highest number of action potentials, lower variance in the amplitude and mean firing time, all indicating maturity of iPSC-derived neurons, compared to 0, 10 or 30 nM T3.

Conclusion: In a human model for early brain development, we identified T3 as a critical signaling molecule for synaptogenesis and neuronal function. In our model, concentrations lower or higher than 3 nM T3 had adverse effects on synapse formation and neuronal electrophysiological characteristics. This study provides the molecular underpinnings of actions of TH in human brain. Our model represents a useful tool to advance understanding of TH signalling in human brain in health and disease.