Abstract
Purpose: To study the effect of Jun N-terminal kinase (JNK) signaling pathway on hepatocyte apoptosis in vivo and in vitro, and to elucidate the mechanism of action.
 Methods: TdT-mediated dUTP Nick-End Labeling (TUNEL) method was used to determine apoptosis in control and cardiopulmonary bypass (CPB) groups at 0, 3 and 6 hours after rat surgery. The expressions of JNK and p-c-Jun in liver tissues at 0, 3 and 6 h after surgery, and the levels of p-c-Jun, Bcl-2 and Bim following overexpression of JNK, were determined using Western blot assay. Human liver cell line HL-7702 was cultured and transfected with over-expressed JNK plasmid and empty plasmid. Proliferation of HL-7702 cells after JNK over-expression was assessed by Cell Counting Kit-8 (CCK-8), while quantitative real-time polymerase chain reaction (RT-qPCR) was employed to evaluate mRNA expression levels of caspase-3 and caspase-9 mRNA after JNK over-expression. Apoptosis of the cells was determined by flow cytometry (FC) after JNK over-expression.
 Results: FC results showed that the number of apoptotic hepatocytes increased after JNK overexpression in hepatocytes while TUNEL assay results demonstrated that hepatocyte apoptosis increased in CPB group, when compared to control group; furthermore, the number of apoptotic cells gradually increased within 6 h after surgery. The expressions of JNK and p-c-Jun were higher in CPB group than in control group, and increased gradually in both groups within 6 h after surgery. Overexpression of JNK decreased the proliferation of hepatocytes, and also lowered protein expression levels of p-c-Jun and Bim; on the other hand, the protein expression levels of Bcl-2 fell, while mRNA expression levels of caspase-3 and caspase-9 mRNA increased.
 Conclusion: JNK pathway promotes hepatocyte apoptosis after cardiopulmonary bypass by inhibiting Bcl-2 pathway and promoting the expressions of Bim caspase-3 and caspase-9.
 Keywords: Cardiopulmonary bypass, Apoptosis, JNK pathway, Bim, caspase-3 and caspase-9
Highlights
During cardiac surgery, a series of changes take place in visceral organs due to cardiopulmonary bypass (CPB) and hemodilution [1]
It was found that apoptosis of liver cells in the CPB group increased gradually after 6 hours of surgery
The present study found that hepatocyte apoptosis increased after CPB surgery, and the expressions of Jun N-terminal kinase (JNK) and p-c-Jun in liver tissues increased, indicating that the JNK pathway was activated by CPB stimulation
Summary
A series of changes take place in visceral organs due to cardiopulmonary bypass (CPB) and hemodilution [1]. Studies have found that this effect still occurs after CPB, especially in the liver [2]. Many studies have reported liver damage after CPB, which manifests as postoperative high bilirubin, transient changes in liver enzymes, and increased lactate levels due to insufficient tissue perfusion [3,4]. The c-Jun N-terminal kinase (JNK) is a member of the MAPK family, and it is activated by various stimuli such as cytokines, physical factors and ischemia-reperfusion [5]. Activated JNK signaling pathway phosphorylates different substrates, including c-Jun. Researchers have found that increased levels of activated c-Jun cause cell apoptosis or differentiation, and lead to cell proliferation [6]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
