Ammonia exposure induces endoplasmic reticulum stress and apoptosis in Chinese striped-necked turtle (Mauremys sinensis).

Ammonia is a major pollutant in the water environment, which could cause severe harm to aquatic organisms. To explore the pathological and physiological effects of ammonia in Chinese striped-necked turtles (Mauremys sinensis), the individuals (body mass: 218.26 ± 12.65 g) were divided into two groups: control group and ammonia exposed group (6.25 mM total ammonia), then the expression levels of signaling factors involved in the endoplasmic reticulum stress and apoptotic pathways were determined. The results showed that ammonia exposure up-regulated the transcriptional and protein levels of endoplasmic reticulum stress marker gene Bip. Meanwhile, the relative mRNA levels of key genes (PERK, ATF6, eIF2α, ATF4, IRE1α and XBP1) involved in unfolded protein response up-regulated, and the phosphorylation levels of PERK, eIF2α and IRE1α increased correspondingly. In addition, the protein and transcriptional levels of CHOP and JNK related to apoptotic pathway induced by unfolded protein reaction increased under ammonia exposure. Moreover, Bcl-2 mRNA expression levels and protein levels decreased, whereas BAX and caspase-3 showed an opposite trend, and the cleaved protein of caspase-3 appeared when the turtles in the elevated ammonia. Furthermore, the apoptotic cells in liver increased after ammonia exposure. These results suggested ammonia exposure induced endoplasmic reticulum stress, then activated unfolded protein response, followed by apoptosis in M. sinensis. The results will contribute to a better understanding of the toxicity mechanism of ammonia to aquatic turtles.