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  • Cx is the major molecule involved


    Cx43 is the major molecule involved in the dynamic life cycle of GJIC (Cusato et al., 2006). Initially generated Cx43 exist in the cytoplasm and correctly transfer it to the plasma membrane during its life cycle (Ji et al., 2018). To understand the toxic effects of MC-LR on GJIC, Cx43 localization was further measured in the YM178 synthesis after treatment with MC-LR. It showed most of the Cx43 punctate staining was observed in the cytoplasm and perinuclear but was limited on the membrane of the TM4 cells induced by MC-LR. This toxin is likely to inhibit the function of GJIC due to interference with Cx43 transport to the plasma membrane. This phenomenon is resembled with astrocytes upon exposure to perfluorooctane sulfonate (Dong et al., 2015). According to this study, the phosphorylated Akt and Erk levels were both enhanced in vivo and in vitro. Moreover, Akt blocker can suppress MC-LR-caused Cx43 enhancement by diminishing the phosphorylation level of Akt and Erk. It has been shown that Erk and Akt pathway are important to the cisplatin-induced bystander effect by mediating the activity of GJs (Kim et al., 2016). Thus, it is speculated that the activation of Akt may be critical in blocking GJs in Sertoli cell exposed to MC-LR. ICA, which is the main ingredient from the traditional Chinese medicine Epimedium holds the ability of promoting male reproductive function (Nan et al., 2014; Yang et al., 2016; Zhang and Yang, 2006). Here we have tested the protective effects of icariin on MC-LR-induced cytotoxicity in TM4 cells. The concentrations of ICA applied in this experiment according to the previous studies (Nan et al., 2014; Wu et al., 2011). In addition, the cell viability had significantly increased on TM4 cells upon exposure to 100 μM ICA. Therefore, we finally chose to use ICA at a concentration of 100 μM for the subsequent experiment. A previous study indicated that ICA reduced cell migration in part through suppression of the PI3K/Akt pathways (Gu et al., 2017). The data of our study showed that the impairment of GJIC induced by MC-LR was reversed after co-treatment with ICA due to inhibition levels of phosphorylated Akt. However, ICA-induced inhibition was incomplete, suggesting other molecular mechanism may also contribute to MC-LR-impaired GJIC. The serine/threonine PP2A which is strongly specifically inhibited by MC-LR negatively regulates multiple well-known proteins including Akt (Campos and Vasconcelos, 2010). We found that ICA cannot rescue PP2A catalytic subunit from MC-LR. Thus, it was reasonable speculated that ICA attenuate the phosphorylated Akt expression independent of PP2A activity. Although extensive studies with ICA have yielded pharmacological affects, the detailed cellular uptake pathway of ICA remain unclear. Further research is needed to reveal this mechanism.
    Acknowledgement This work was supported by National Natural Science Foundation of China (31600422) and Natural Science Foundation of Jiangsu Province (BK20161039).
    Introduction The importance of different Arsenic forms in public health is well recognized owing to its distinct physical characteristics and toxicity. However, the mechanisms behind the toxicity of arsenic and the consequences of the occurrence of the disease due to short term and long term exposure to arsenic is yet to be understood [1]. In cellular milieu Arsenic in both pentavalent and trivalent state prefers to react only with chemically soft groups due to its own chemical softness [2]. In proteins, thiol (-SH) group from Cys has adequate “chemical softness” rendering it as the most reactive group. Specific examples of Arsenic reactivity for cysteine (Cys) have been noted for many Cys-rich proteins from mammals to bacteria [[3], [4], [5], [6], [7]]. During the course of the metabolism, Arsenic gets reduced to a trivalent state and oxidative methylation to a pentavalent state is mediated by Glutathione and S-adenosylmethionine containing –SH and –S–Me chemically soft groups, respectively. The trivalent state of Arsenicals are more toxic compared to the pentavalent Arsenicals, including the methylated ones [8].It is also predicted that inorganic arsenate replaces phosphate in some biochemical reactions [9]. Arsenic bound to a protein can alter its metal binding property leading to conformational alteration and change of stability and function [10]. Arsenic binding can also lead to SUMOylation, oligomerization, and degradation [3]. Arsenic, therefore, presents a serious health hazard, and has been suggested as a group I carcinogen risk for humans [11]. The contribution of Arsenic to the genesis of cancer remains poorly understood [12], although non-genotoxic pathways involving alterations in gene profiling, cell proliferation, tissue damage, tissue removal cell death (including apoptosis), cell removal, cell organization, and cellular interactions including gap junction intercellular communication (GJIC) mediated by Connexins(Cx) appear to be the key causes.