Differentiation of human embryonic stem cells to a parathyroid-like phenotype.

Iatrogenic hypoparathyroidism is the most common complication of cervical endocrine surgery. Current management is limited and palliative. As the molecular steps in parathyroid development have been defined, they may be replicable in vitro, with a goal of cellular replacement therapy. Human embryonic stem cell (hESC) lines were investigated as a model for parathyroid regeneration in vitro. BG01 was selected as a model based on expression of genes of interest in embryoid bodies (EBs). Established strategies for mouse embryonic stem cell differentiation into definitive endoderm were modified and extended to maximize the expression of definitive markers of parathyroid development. The optimal approach included the use of Activin A at 100 ng/mL with BG01 cells grown on murine embryonic fibroblasts for 5 days under conditions of increasing serum concentration. After 5 days, the cells were allowed to mature further in tissue culture without murine fibroblasts but with continuous Activin A. Our strategy produced differentiated cell cultures that expressed intermediate markers of endoderm and parathyroid development (CXCR4, EYA1, Six1, and Pax1), as well as markers of committed parathyroid precursors or developed parathyroid glands (glial cell missing-2 [Gcm2], CCL21, calcium sensing receptor [CaSR], and parathyroid hormone [PTH]). We further characterized the cells by testing conditioned medium from various time points in our differentiation scheme for the presence of PTH. We found that by keeping the cells in culture 2 weeks after the withdrawal of Activin A, the cells were able to produce PTH. Further in vivo work will be needed to demonstrate proper functionality of the cells developed in this way.