Background:

Parathyroid diseases consist of conditions characterized by the dysregulation of calcium homeostasis and alterations in parathyroid hormone (PTH). The understanding of these diseases, and the complex regulation of PTH could be further clarified by the development of in vitro models derived from human parathyroid tissue. This study aimed to isolate parathyroid stem cells and study the functional potential in vitro as parathyroid organoids

Methods:

Patient-derived parathyroid organoids were cultured, characterized by immunofluorescent staining of tissue and organoids, and RNA-sequencing. Functional organoid testing was performed by calcium-response measurements, drug screening, and SPECT/PET-tracer validation.

Results:

Organoids were cultured from 50 patients, characterized by protein expression, and in vitro self-renewal potential was assessed to show the presence of putative stem cells. RNA-seq showed increased gene expression of genes involved in vasculature development, calcium ion import, and cellular biosynthetic processes when compared to tissue. Exposure of organoids to increased calcium concentrations, mimicked a hypercalcemic environment, and resulted in a significant reduced PTH excretion. Moreover, a reduction in PTH excretion was observed when these organoids were exposed to different concentrations of Cinacalcet or Calcitriol. Next to this, the organoids showed significant uptake of ¹¹C-methionine, and a significant decrease in uptake was found when organoids were exposed to cold methionine prior to the tracer incubation. Additionally, we observed a significant difference in ^99mTc-sestamibi uptake between organoids originating from patients with a MIBI positive scan as compared to patients with a MIBI negative scan, all together showing functionality.

Conclusion

These data show that our developed organoid model recapitulates the originating tissue on gene and protein expression and functionality. Additionally, we demonstrate the potential of patient-derived parathyroid organoids for physiology studies and therapeutic target discovery.