Microcystin-leucine arginine exposure contributes to apoptosis and follicular atresia in mice ovaries by endoplasmic reticulum stress-upregulated Ddit3.

Microcystin-leucine arginine (MC-LR), an intracellular toxin to cause reproduction toxicity, is produced by blooming cyanobacteria and widely distributed in eutrophic waters. It is revealed that MC-LR-induced female reproductive toxicity is more severe than male reproductive toxicity. Previous studies mainly focused on male reproductive toxicity, and the molecular mechanisms of MC-LR-induced apoptosis, follicular atresia and infertility in female remain largely unclear. Here, it was found that MC-LR treatment could induce apoptosis, inflammation, follicular atresia, and decrease of gonadal index in mice ovaries. RNA-Seq data showed that the up-regulation of DNA-damage inducible transcript 3 (Ddit3) under endoplasmic reticulum (ER) stress had predominantly regulatory role in MC-LR-induced apoptotic pathway. Furthermore, MC-LR exposure promoted cleavage of activating transcription factor 6 (ATF6, 50kd), inositol-requiring enzyme 1 (Ire1) expression, phosphorylation of IRE1, mitogen-activated protein kinase 5 (Map3k5) and Ddit3 expression, which was accompanied by the upregulation of death receptor 5 (Dr5) and active-caspase-3, and a decrease in Bcl-2 expression. ER stress inhibitor 4-Phenyl butyric acid (4-PBA) ameliorated these MC-LR-induced changes in protein or mRNA level. More importantly, knockdown of Ddit3 suppressed MC-LR-induced cell apoptosis and follicular atresia by directly regulating Dr5 and Bcl-2. Additionally, it was also found that MC-LR increased Map3k5 phosphorylation by inhibiting protein phosphatase 2A (PP2A) activity, and then promoted Ddit3 expression. In short, our data suggests that Ddit3 promotes MC-LR-induced mice ovarian cells apoptosis and follicular atresia via ER stress activation, which provides a new insight into the relation between infertility in females and the emerging water pollutant MC-LR.