Role of p38 Mitogen-activated Protein Kinase Signaling Pathway in the Hippocampal Neurons Autophagy of Rats with Sepsis

  Objective  To investigate the role of p38 mitogen-activated protein kinase (MAPK) signaling pathway in autophagy of neurons in hippocampus of sepsis rats.

  Methods  A sepsis model was established by cecal ligation and puncture (CLP). SD rats were randomly divided into sham-operated group (sham group), model group (CLP group), vehicle-treated group (CLP+Veh group) and inhibitor-treated group (CLP+SB203580 group), and each group was divided into 3, 6, 12, 24 and 48 h subgroups. CLP+Veh group and CLP+SB203580 group were injected with 1% DMSO 5 μL and 0.1 mmol/L SB203580 5 μL respectively in the lateral ventricle, and CLP was established 30 min after injection. The sham group only turned over the cecum and closed the abdomen without other treatments. The vital signs of rats were monitored, including mean arterial pressure (MAP) and heart rate (HR). Neurobehavioral score was used to investigate the brain injury in rats. Histopathological changes in hippocampus of rats were observed by HE staining. The process of neuronal autophagy in hippocampal of rats was observed under transmission electron microscope (TEM). Western blot assay was performed to detect the expression of microtubule associated protein 1 light chain 3 (LC3)Ⅱ, LC3Ⅰ, selective autophagy adaptor protein p62/sequestosome-1 (p62/SQSTM1), MAPK-activated protein kinase 2 (MK-2) and phosphorylation MK-2 (p-MK-2) in the hippocampus. The expressions of LC3 and p62/SQSTM1 in hippocampal neurons of rats were observed by immunofluorescence.

  Results  At different time points, MAP of CLP group was lower than sham group, while HR was higher than sham group, the change was most obvious at 12 h after molding; the neurobehavioral score of CLP group was the lowest; the histopathological changes in the hippocampus were obvious; and many autophagy vacuoles were observed under transmission electron microscope; compared with CLP group, the neurobehavioral score of CLP+SB203580 group increased; the pathological changes in the hippocampus improved; the inclusions in autophagy vacuoles were degraded under transmission electron microscopy; Western blot results showed:compared with sham group, expression of-LC3Ⅱ/LC3Ⅰ, p-MK-2/MK-2 increased, and p62/SQSTM1 decreased in hippocampal tissue of CLP group in rat, the former reaches its peak at 12 h, the latter bottomed out at 12 h. Compared with the other groups, at 12 h of modeling, the expression of LC3Ⅱ/LC3Ⅰ, p-MK-2/MK-2 was further increased, the expression of p62/SQSTM1 decreased further in hippocampal tissue of CLP+SB203580 group in rat (P < 0.05); immunofluorescence observation showed that localization and expression of LC3 and p62/SQSTM1 in NeuN were consistent with Western blot.

  Conclusion  Inhibition of p38 MAPK signaling pathway in sepsis rats can further activate autophagy and protect neurons in the hippocampus.