Abstract:
Background Recent advances in understanding the toxic effects of inorganic arsenic have revealed that arsenic exposure impacts multiple endocrine organs, thereby altering their functions. However, the mechanisms underlying arsenic-induced thyroid injury remain unclear.
Objective To investigate the mechanisms by which sodium arsenite (NaAsO₂) affects the proliferation and apoptosis of normal thyroid cells (Nthy-ori3-1) through the estrogen receptor (ER)-phosphatidylinositol 3-kinase (PI3K)/protein kinase B (AKT) signaling pathway.
Methods Nthy-ori3-1 cells were cultured in vitro and divided into the following groups: a control group (complete medium without drugs, 0 μmol·L−1), and NaAsO₂-treated groups at 1, 2, and 4 μmol·L−1. Additionally, 1 μmol·L−1 of the ER inhibitor ICI182780 was used to intervene in the NaAsO₂ exposure groups, resulting in the following combinations: 1 μmol·L−1 NaAsO₂ + ICI182780, 2 μmol·L−1 NaAsO₂ + ICI182780, and 4 μmol·L−1 NaAsO₂ + ICI182780. The median lethal concentration of NaAsO₂ was determined using cell viability assay. Cell viability was assessed at 24, 36, and 48 h using Cell Counting Kit-8 (CCK-8) assay. Colony formation ability was evaluated via plate cloning assay. Apoptosis was detected using Hoechst 33342 staining. Protein and mRNA expression levels of ERα, ERβ, c-MYC, Bax, Bcl-2, PI3K, p-PI3K, AKT, and p-AKT were measured using Western blot (WB) and real-time quantitative PCR (qRT-PCR), respectively.
Results The median lethal concentration of NaAsO₂ was determined to be 4.034 μmol·L−1. CCK-8 assay at 24, 36, and 48 h revealed that, compared with the control group, the 1, 2, and 4 μmol·L−1 NaAsO₂ groups significantly inhibited Nthy-ori3-1 cell proliferation (P < 0.001). The plate cloning assays demonstrated a concentration-dependent reduction in colony formation ability (P < 0.001). Following the ICI182780 intervention, the cell viability and colony formation ability in the 1, 2, and 4 μmol·L−1 NaAsO₂ groups were significantly restored compared with the corresponding NaAsO₂-only groups (P < 0.001, P < 0.01). The Hoechst 33342 staining indicated that compared with the control group, the nuclear staining intensity and apoptosis levels in the 1, 2, and 4 μmol·L−1 NaAsO₂ groups increased in a concentration-dependent manner (P < 0.001). However, the ICI182780 intervention reduced the apoptosis levels in the NaAsO₂-treated groups compared with their NaAsO₂-only counterparts (P < 0.001). The WB analysis showed that, compared with the control group, the protein expression of ERα, ERβ, c-MYC, Bcl-2, p-PI3K, and p-AKT in the 1, 2, and 4 μmol·L−1 NaAsO₂ groups decreased manner (P < 0.001, P < 0.01), while the Bax expression increased in a concentration-dependent (P < 0.001); the PI3K and AKT protein levels showed no significant differences (P > 0.05). In the ICI182780-treated NaAsO₂ groups, the ERα, ERβ, c-MYC, Bcl-2, p-PI3K, and p-AKT protein expression increased (P < 0.001, P < 0.01), the Bax expression decreased (P < 0.001), and the PI3K and AKT levels remained unchanged (P > 0.05) compared with the corresponding NaAsO₂-only groups. The mRNA expression patterns of ERα, ERβ, c-MYC, Bcl-2, and Bax were consistent with the WB results.
Conclusion NaAsO₂ inhibits proliferation and promotes apoptosis in Nthy-ori3-1 cells in a dose-dependent manner. The underlying mechanism likely involves NaAsO₂-mediated suppression of the ER-PI3K/AKT signaling pathway, which subsequently regulates downstream proliferation- and apoptosis-related genes.
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