Trisomy 21 Disrupts Thyroid Hormones Signaling During Human iPSC-Derived Neural Differentiation In Vitro

Thyroid hormones (THs) are essential for brain development, and their dysregulation is associated with cognitive deficits and neurodevelopmental disorders. Down syndrome (DS), caused by trisomy 21, is frequently associated with thyroid dysfunction and impaired neurogenesis. Here, we investigated THs signaling dynamics during neural differentiation using human induced pluripotent stem cells (hiPSCs) derived from individuals with DS and controls. We analyzed the gene expression of key THs regulators-deiodinases, transporters, and receptors-and downstream target genes in hiPSCs, hiPSC-derived neural progenitor cells (NPCs), hiPSC-derived astrocytes, and hiPSC-derived neurons. DS-derived hiPSCs, hiPSC-derived NPCs, and hiPSC-derived neurons exhibited 2- to 7-fold increases in the gene expression of <i>DIO2</i> and 3- to 8-fold reductions in <i>DIO3</i>, alongside 1- to 3-fold downregulation of <i>THRA</i> and <i>THRB</i> isoforms. hiPSC-derived astrocytes showed a 4-fold decrease in the gene expression of <i>DIO2</i>, a 4-fold increase in <i>DIO3</i>, upregulation of <i>SLC16A10</i> (2-fold), and downregulation of <i>SLC7A5</i> (0.5-fold) and THs receptors (0.5- to 12-fold). hiPSC-derived neurons exhibited marked downregulation of the gene expression of <i>HOMER1</i> (0.5-fold), <i>GRIN3A</i> (14-fold), and <i>GRIN3B</i> (4-fold), accompanied by impaired spontaneous activity in multi-electrode array recordings. These findings reveal a robust, cell-type-specific imbalance between THs availability and signaling competence in DS hiPSC-derived neural cells, providing mechanistic insight into THs-related contributions to the function of DS hiPSC-derived neural cells and identifying potential therapeutic targets.