Project Summary The development of the thyroid gland from anterior endoderm is an essential step in development that allows for the production of thyroid hormones around week 12 in utero in humans. Unfortunately, in about 1/4000 births genetic mutations that affect this development pathway lead to congenital hypothyroidism requiring lifelong thyroid hormone replacement therapy. Thus, a better understanding of thyroid follicular cell development could lead to a process where genetic editing and cellular therapy could provide treatment for congenital hypothyroidism (CH). Our work in this area has utilized a directed differentiation approach and has identified bone morphogenic protein and fibroblast growth factor as key mediators of thyroid follicular cell lineage development across species resulting in functional murine thyroid follicular cells that can rescue athyreotic mice. In this proposal, we now turn our attention exclusively to human thyroid follicular cell development and propose three Specific Aims that will allow for the pre-clinical development of functioning human thyroid follicular cells derived from human induced pluripotent stem cells (iPSCs), In the first Aim we will utilize a novel lineage tracing methodology to understand how developing human thyroid follicular acquire their cell fate and to ensure that the process in iPSC parallels that in vivo. In the second Aim we will prove that the human thyroid follicular cells derived from iPSCs are fully able to produce thyroid hormones in vitro and can be transplanted into immunodeficient athyreotic mice to rescue their hypothyroidism. Finally, in the third Aim we will demonstrate pre- clinically that derived iPSCs from a patient with CH can be genetically corrected and re-introduced via transplant to function normally. Together completion of these Aims will provide key insight into the possibilities of iPSC derived cellular therapy for the treatment of CH and enhance our understanding of the development endodermal- derived tissues in humans.

Narrative Thyroid hormone (TH) is a critical mediator of fetal development and then essential for normal health during adulthood. Currently, therapy for those with hypothyroidism (either congenital or acquired later in life) is with L-thyroxine and many individuals on therapy do not feel adequately replaced, in this proposal we put forward experiments designed to develop thyroid hormone secreting follicular cells from human induced pluripotent stem cells. Completion of this work will give us significant insight into the developmental biology of the human thyroid and potentially offer a unique and powerful approach to treat hypothyroidism in humans, furthermore, the development of follicular cells from progenitor cells will give us an ideal model to better understand many diseases of the thyroid that affect human health.