The role of TLR4/P38/JNK signaling pathway in apoptosis of hippocampal neurons

Abstract

To investigate the effects of the Toll like receptor 4 (TLR4) -P38-JNK signaling pathway in the apoptosis of hippocampal neurons in rats and its mechanisms. And to provide new experimental evidences for the pathogenesis research, prevention and treatment of neurodegenerative diseases (ND). The hippocampal neurons derived from newborn rat were cultured for 7 d in vitro. The purity of hippocampal neurons was identified by immunofluorescence method. In order to activate or block the action of TLR4, the hippocampal neurons were pretreated with TLR4 ligand lipopolysaccharide (LPS) or TLR4 antibody. In the experiment 1, the hippocampal neurons were divided into normal control group, LPS group and TLR4 antibody+LPS group. The expressions of P-P38 and P-JNK were deteced by immunofluorescence. In the experiment 2, the hippocampal neurons were divided into 6 groups:normal control group, LPS group, TLR4 antibody +LPS group, SB202190(inhibitor P38)+LPS group, SP600125(inhibitor JNK)+LPS group, PD98059(inhibitor ERK)+LPS group. The cells in above mentioned groups were pretreated with TLR4 antibody, the inhibitors of P38, JNK or ERK for 2 h respectively. Then, all the six groups were stimulated by LPS for 24 h. The expressions of Bcl-2, Bax and Active-caspase-3 were detected by Western blot. The hippocampal neuronal apoptosis rate were tested with flow cytometry. The expressions of P-P38 and P-JNK of hippocampal neurons in LPS group were higher than those in normal control group (P<0.01). Compared with LPS group, the expressions of P-P38 and P-JNK were decreased significantly in TLR4 antibody +LPS group (P<0.01). Compared with the normal control group, the expressions of Bcl-2/Bax were decreased, while the expression of Active-caspase-3 was increased in the hippocampal neurons after LPS stimulation (P<0.01). The apoptotic rate of hippocampal neurons was higher in LPS group than that in the control group (P<0.01). Compared with LPS group, the expressions of Bcl-2/Bax were increasd and the expression of Active-caspase-3 was decreased in TLR4 antibody+LPS group, SB202190+LPS group, and SP600125+LPS group. The apoptotic rate of hippocampal neurons was significantly lower than that in the LPS group (P<0.05, P<0.01). The cell apoptosis rate had no significant differences between PD98059+LPS group and LPS group. ①TLR4-mediated P38/JNK signaling pathway exists in hippocampal neurons. ②After TLR4 activation in hippocampal neurons, the expressions of P-P38 and P-JNK are up-regulated, the expressions of Bcl-2/Bax are decreased and the expression of Active-caspase-3 is increased, which promote apoptosis of hippocampal neurons. TLR4/P38/JNK signaling pathway is involved in apoptosis of hippocampal neurons.