Side population cells in the mouse thyroid exhibit stem/progenitor cell-like characteristics

Area of Science:

• Endocrinology
• Stem Cell Biology
• Molecular Biology

Background:

• Side population (SP) cells are defined by their ability to efflux the vital dye Hoechst 33342 via the ATP binding cassette (ABC)-dependent transporter ABCG2.
• SP cells are known to be enriched for stem/progenitor cell activity across various tissues.
• The presence and function of SP cells in the murine thyroid gland remain largely uncharacterized.

Purpose of the Study:

• To identify and characterize side population (SP) cells within the murine thyroid gland.
• To investigate the stem/progenitor cell markers and thyroid differentiation markers expressed by thyroid SP cells.
• To assess the in vitro differentiation potential of thyroid SP cells compared to main population cells.

Main Methods:

• Flow cytometry was used to identify and isolate SP cells based on Hoechst 33342 efflux and cell surface markers (CD45, c-kit, Sca1).
• Quantitative RT-PCR was employed to analyze the expression of ABCG2, stem cell markers (nucleostemin, Oct4), and thyroid-specific genes (thyroid peroxidase, thyroglobulin, TSH receptor, TITF1, PAX8).
• In situ hybridization, double immunofluorescence, and three-dimensional primary cell culture were utilized to determine the localization and differentiation capacity of SP cells.

Main Results:

• Thyroid SP cells were identified and comprised CD45(-)/c-kit(-)/Sca1(+) and CD45(-)/c-kit(-)/Sca1(-) populations.
• SP cells showed high expression of ABCG2, nucleostemin, and Oct4, but low expression of thyroid differentiation markers and transcription factors (TITF1, PAX8).
• Abcg2-expressing cells were located in the interfollicular space; SP cells failed to form epithelial or follicle-like structures in culture, unlike main population cells.

Conclusions:

• Murine thyroid glands contain SP cells characterized by high expression of stem cell-related genes and low expression of thyroid differentiation markers.
• Thyroid SP cells, localized in the interfollicular space, exhibit properties consistent with stem/progenitor cells.
• These findings suggest that thyroid SP cells may represent a distinct stem or progenitor cell population within the thyroid gland.