Thiacloprid Exposure Induces Oxidative Stress, Endoplasmic Reticulum Stress, and Apoptosis in the Liver of <scp> <i>Mauremys reevesii</i> </scp>

Among neonicotinoid insecticides, thiacloprid (THI) is extensively utilized in agricultural practices, which poses a potential toxicity risk to aquatic fauna. Turtles, integral to aquatic ecosystems, have not yet been comprehensively assessed for their vulnerability to THI exposure. In this study, we aimed to evaluate the effects of THI on oxidative stress, endoplasmic reticulum stress (ERS), and apoptosis in aquatic turtles. We categorized <i>Mauremys reevesii</i> into three groups: a control group and two experimental groups exposed to environmentally relevant (4.5 μg/mL) and high (15 mg/mL) concentrations of THI, respectively. Transcriptome analysis revealed that genes significantly associated with the elimination of superoxide radicals, organelle inner membrane functions, peroxiredoxin activity, and apoptotic pathways were abundantly expressed in the high-concentration THI group. Notably, exposure to high concentrations of THI led to a marked increase in glutathione peroxidase (GPX) and superoxide dismutase (SOD) activities, whereas catalase (CAT) activity declined and malondialdehyde (MDA) levels rose, indicating the presence of oxidative stress. Moreover, THI upregulated the expression of the ER stress marker GRP78. Simultaneously, the mRNA levels of pivotal unfolded protein response genes, including AFT6, AFT4, IRE1α, CHOP, XBP1, and eIF2α, were significantly elevated in response to THI exposure. Furthermore, high concentrations of THI significantly activated the activities of caspase-3, caspase-8, and caspase-9 enzymes in the liver tissue. The expression of anti-apoptotic gene Bcl-2 was downregulated, whereas the pro-apoptotic genes Bax and caspase-3 were upregulated, leading to an increase in hepatic apoptotic cells following THI exposure. Collectively, our study indicates that THI can induce hepatic damage in turtles through the promotion of oxidative stress, ERS, and apoptosis. These findings gain a deeper understanding of the toxic effects of THI on keystone species in aquatic ecosystems, thereby improving our overall understanding of their environmental impacts.