Effect of c-Jun on hippocampal neuron cell apoptosis in neonatal mice injected with bilirubin encephalopathy

Abstract

Objective To investigate the effect of c-Jun on hippocampal neuron apoptosis in neonatal mice with bilirubin encephalopathy. Methods Seven-day-old newborn SD rats were selected and injected bilirubin solution (10 g/L) into the cerebellum medulla oblongata pool.The bilirubin level in hippocampus was tested at 6 h and 12 h post-injection and neurons were labeled via Nissl staining; c-Jun amino-terminal kinase(JNK), c-Jun and p-c-Jun level in hippocampus were measured by Western blot and immunofluorescence staining.The expression le-vels of Caspase-3 and Caspase-6 were analyzed by enzyme-linked immunosondent assay and fluorescence spectrophotometry. Results Apart from a certain degree of abnormal behaviors following injection, a sharp rise of (44.00±13.00)%(P<0.05) and (96.86±9.00)%(P<0.01) in hippocampal bilirubin respectively at 6 h and 12 h post-injection.Hippocampal neuron lost and Nissl staining swallowed gradually after 24 h. At the time of 6 h following injecting, c-Jun amino-terminal kinase(JNK), c-Jun and p-c-Jun protein level in hippocampus was separately elevated by 1.4(2.41±0.15 vs 1.00±0.09), 0.43 (1.43±0.16 vs 1.00±0.09) and 1.16 (2.16±0.23 vs 1.00±0.09) fold(all P<0.05), compared with the control group.Immunofluorescent staining showed that c-Jun and p-c-Jun positive cells in hippocampus and cortex all increased after 6 h injection of bilirubin.At the same time, the activity of apoptosis-associated factors downstream Caspase-3 and Caspase-6 initially obviously raised at 12 h post-injection, respectively increased by 2.08 and 0.28 fold of control group after 24 h(all P<0.05). Conclusion The phosphorylation of c-Jun may act as an important activator of hippocampal neuron apoptosis in the bilirubin encephalopathy. Key words: c-Jun N-terminal kinase; c-Jun; Bilirubin encephalopathy; Caspase-3; Caspase-6