Endocrine Abstracts

Background: Disrupted thyroid hormone (TH) homeostasis has devastating effects on human neurodevelopment. THs are critical signaling molecules in neurodevelopment, acting on differentiation of neural cells, migration, synaptogenesis and myelination, with deiodinases governing intracellular TH concentrations in a spatiotemporal manner. It is remarkable that fetal neural cells, while being key target cells of TH, exhibit strong activity of the TH inactivating enzyme DIO3. Currently, the molecular mechanisms underlying TH action in brain are mainly derived from animal models. We utilized human induced pluripotent stem cell (hiPSC) technology to investigate the role of DIO3 in a human model for early brain development.

Methods: We generated neural progenitor cells (NPCs) and neural networks from hiPSCs as a model for early human brain development. hiPSCs-derived neural cells contained all the key players in TH cellular signaling. We inactivated DIO3 in different neural cells using iopanoic acid (IOP), a small molecule that blocks DIO3 activity. Cells were cultured with different T3 concentrations (0-3-10 nM). We used immunocytochemistry, gene expression and DIO3 and metabolism assays as readouts.

Results: We observed a high DIO3 activity in NPCs and neural networks, being the highest in NPCs. Inactivation of DIO3 caused increased gene expression of T3-dependent genes such as KLF9 in neural progenitor cells and neural networks. We also examined the differentiation potential of neural progenitor cells to neural networks in absence of DIO3. Our preliminary immunocytochemistry data showed an increase in cells containing neuronal nuclear protein (NeuN), a biomarker for neurons, when the activity of DIO3 is diminished.

Conclusion: Our preliminary results suggest that impaired DIO3 activity may lead to excessive TH action in neural cells and therefore compromising normal brain development. We are currently investigating further to validate this findings. We also aim to inactivate DIO3 through genetic modification using the CRISPR interference technology. Our model represents a versatile tool to investigate cellular TH regulation and action for early human brain development.