ABSTRACT
Background Flurochloridone (FLC) is toxic to male reproduction and can induce apoptosis of testicular tissue and supporting cells under oxidative stress. Of particular concern is whether nuclear factor-erythrocyte 2-related factor 2/heme oxygenase-1 (Nrf2/HO-1) signaling pathway and nuclear factor kappa B (NFκB) signaling pathway participate this process. Objective To observe apoptosis of testicular tissue and sertoli TM4 cells and alterations of Nrf2/HO-1 and NFκB signaling pathways in mice treated with FLC in vivo/in vitro. Methods (1) Animal experiment. Testis samples were harvested from male C57BL/6 mice after 28-day FLC (0, 3, 15, 75, and 375 mg·kg−1 per day) exposure via oral route. Malondialdehyde (MDA) and superoxide dismutase (SOD) in homogenate of testicular tissue were measured by colorimetry. Apoptosis of testicular tissue was evaluated by TUNEL staining. Expression and distribution of Nrf2 and NFκB were detected by immunohistochemistry. Protein expression levels of Nrf2, HO-1, NAD(P)H: quinone oxidoreductase 1 (NQO1), NFκB, inhibitor of nuclear factor kappa-B kinase subunit beta (IKKβ), and phosphorylated recombinant inhibitory subunit of nuclear factor kappa-B alpha (P-IκBα) in testicular tissue homogenate were determined by Western blotting. (2) Cell experiment. TM4 cell lines were treated with 40, 80, 120, 160, and 200 μmol·L−1 FLC for 6 h, and cell viability was detected by CCK-8. After 6 h exposure to 40, 80, and 160 μmol·L−1 FLC, the apoptosis rate was detected by flow cytometry, and the protein expression levels of Nrf2, HO-1, NQO1, NFκB, IKKβ, and IκBα were detected by Western blotting. Results (1) Animal experiment. Apoptosis occurred in the interstitial and basal parts of spermatogenic tubules in male C57BL/6 mice after 28 days of oral FLC exposure. Compared with the control group, the MDA level in testicular tissue of the 375 mg·kg−1 FLC-treated group was significantly increased (P<0.05), and the SOD activity was significantly decreased (P<0.05). After 375 mg·kg−1 FLC exposure, apoptosis occurred in the interstitial and basal parts of spermatogenic tubules. The results of immunohistochemistry showed the expression of Nrf2 and NFκB in the interstitium and basal part of spermatogenic tubules of the treated groups. Compared with the control group, the protein levels of Nrf2, NQO1, P-IκBα, NFκB, and IKKβ in the 15, 75, and 375 mg·kg-1 groups were significantly increased (P<0.001), and the HO-1 protein level was significantly increased in the 375 mg·kg−1 group (P<0.001). (2) Cell experiment. Compared with the control group, the TM4 cell viabilities in the 40, 80, 120, 160, and 200 μmol·L−1 FLC-treated groups significantly decreased (P<0.01). The apoptosis rates were significantly increased (P<0.05), and the apoptosis rates increased from 5.7% in the control group to 7.4%, 9.4%, and 11.7% in the 40, 80, and 160 μmol·L−1, respectively. The Nrf2 protein level in the 40 μmol·L−1 group was significantly increased (P<0.01), while the levels significantly decreased in the 80 and 160 μmol·L−1 groups (P<0.01). The HO-1 protein levels in the 40, 80, and 160 μmol·L−1 groups were significantly increased (P<0.01). The level of NQO1 protein in the 40 μmol·L−1 group was significantly increased (P<0.01). The NFκB protein levels were significantly increased in the 80 and 160 μmol·L−1 groups (P<0.001). The IκBα protein levels were significantly decreased in all treated groups (P<0.001). The IKKβ protein had no significant change. Conclusion FLC induces testicular tissue apoptosis, and the process affects Nrf2/HO-1 signaling pathway and NFκB signaling pathway. The in vitro study confirms that FLC could induce apoptosis of TM4 cells and activate Nrf2/HO-1 and NFκB signaling pathways.
ABSTRACT
Background Flurochloridone (FLC) can induce apoptosis in Sertoli cells, but the specific mechanism remains unknown. Objective To investigate the testicular cell apoptosis in mice as well as apoptosis and activation of endoplasmic reticulum stress in TM4 cell line induced by FLC through in vivo and in vitro study designs respectively, and study the role of inosital-requiring enzyme 1α (IRE1α)-c-Jun N-terminal kinase (JNK) signaling pathway in the process of FLC-induced apoptosis in TM4 cells through intervention study design. Methods Testicular tissues were collected from male C57BL/6 mice which were treated with 3, 15, 75, and 375 mg·（kg·d）−1 FLC by oral perfusion for 28 d. Apoptosis was observed by TUNEL staining, and the levels of apoptosis-related proteins were detected by Western blotting, including B-cell lymphoma-2 (Bcl-2), Bcl-2 interacting mediator of cell death (Bim), and Bcl-2 associated X protein (Bax). In the in vitro study, TM4 cells were treated with different concentrations of FLC (40, 80, and 160 μmol·L−1) for 6 h, then apoptosis rate was detected by flow cytometry, and the levels of apoptosis-related proteins (Bcl-2, Bim, and Bax) and endoplasmic reticulum stress-related proteins [glucose regulated protein 78 (GRP78), phosphorylated-protein kinase R like endoplasmic reticulum kinase (p-PERK), activating transcription factor 6 (ATF6), phosphorylated-inosital-requiring enzyme 1α (p-IRE1α), and phosphorylated-JNK (p-JNK)] were measured by Western blotting. In the intervention study, TM4 cells were pretreated with IRE1α phosphorylation inhibitor 4μ8C and JNK phosphorylation inhibitor SP600125 for 6 h, then treated with 160 μmol·L−1 FLC for 6 h. The levels of apoptosis-related proteins and endoplasmic reticulum stress-related proteins were measured by Western blotting, and cell viability was detected by cell counting kit-8. Results After the male C57BL/6 mice orally exposed to FLC for 28 d, apoptosis occurred in the seminiferous tubule. The protein expression level of Bcl-2, apoptosis inhibitor, was decreased in the 75 and 375 mg·(kg·d)−1 groups (P<0.05), and the protein expression levels of Bim and Bax, apoptosis promoters, were increased in the 75 and 375 mg·(kg·d)−1 groups respectively (P<0.05). The percentages of apoptotic cells in the 0, 40, 80, and 160 μmol·L−1 FLC groups were 2.7%±0.2%, 4.8%±1.3%, 9.4%±0.3%, and 13.2%±0.2%, respectively, increased significantly compared with the control group (P<0.05). The protein expression level of Bcl-2 also was decreased in the 160 μmol·L−1 FLC group (P<0.05), while the levels of Bim and Bax were increased in both of the 80 and 160 μmol·L−1 groups (P<0.05). The expression levels of endoplasmic reticulum stress-related proteins (GRP78, p-PERK, ATF6, p-IRE1α, and p-JNK) were increased (P<0.05) or showed a rising trend in TM4 cells. Pre-treatment with 4μ8C (25 and 50 μmol·L−1) and SP600125 (10 and 20 μmol·L−1) significantly down-regulated the protein expression levels of GRP78, p-IRE1α, p-JNK, and Bax induced by FLC (P<0.05) or in a downward trend. Both of the inhibitors alleviated the decreased cell viability induced by FLC (P<0.05) or in alleviating fashion. Conclusion FLC could induce apoptosis in mice testis and TM4 cell apoptosis through activating endoplasmic reticulum stress and IRE1α-JNK signaling pathway.