Radix Scrophulariae regulates proliferation, apoptosis, and autophagy of rat thyroid cells via the MST1/Hippo signaling pathway

This study investigated the therapeutic effects of Radix Scrophulariae (RS) extract on hyperthyroidism and the associated mechanisms. A hyperthyroid cell model was established using thyrotropin receptor antibody and levothyroxine sodium tablets. FRTL-5 rat thyroid cells were treated with varying concentrations of RS-containing serum. Protein expression levels of Bcl-2, Caspase-3, PCNA, Cyclin D1, MST1, LC3-II/I, and ATG5 were assessed by Western blotting to determine the optimal concentration. Subsequent experiments included RS treatment with or without MST1 overexpression or the Hippo pathway inhibitor XMU-MP-1. Transmission electron microscopy was used to visualize secretory vesicles, and immunofluorescence analysis was performed to detect thyroid-stimulating hormone receptor (TSHR) expression. Protein levels of MST1, p-LATS1, p-YAP, PCNA, Cyclin D1, Bcl-2, Caspase-3, LC3-II/I, and ATG5 were further quantified by Western blotting. The hyperthyroid model exhibited elevated expression of TSHR, Bcl-2, PCNA, and Cyclin D1 (P < 0.05), and reduced levels of MST1, p-LATS1, p-YAP, Caspase-3, LC3-II/I, and ATG5 (P < 0.05). Secretory vesicles were rarely observed. Treatment with RS-containing serum significantly downregulated TSHR, Bcl-2, PCNA, and Cyclin D1 expression (P < 0.05), and upregulated MST1, p-LATS1, p-YAP, Caspase-3, LC3-II/I, and ATG5 (P < 0.05), with abundant bilayer membrane vesicles observed. The therapeutic effects of RS were attenuated by MST1 overexpression but were restored by co-treatment with XMU-MP-1 (P < 0.05). RS extract may attenuate hyperthyroidism by suppressing excessive thyroid cell proliferation, enhancing apoptosis and autophagy, and activating the MST1/Hippo signaling pathway in FRTL-5 cells.