Role of miR-146a in hippocampal inflammatory responses in postoperative cognitive dysfunction in mice / 中华麻醉学杂志

ABSTRACT

Objective:To evaluate the role of miR-146a in hippocampal inflammatory responses in postoperative cognitive dysfunction (POCD) in mice.Methods:One hundred and sixty clean-grade male C57BL/6 mice, aged 12-16 weeks, weighing 22-28 g, were divided into 5 groups ( n=32 each) using a random number table method: control group (group C), group POCD, miR-146a agomir group (group Ag), miR-146a antagomir group (group At) and negative control group (group NC). The mice were subjected to an intramedullary fixation for tibial fracture under 1.5% isoflurane anesthesia to establish POCD model.At 2 days before operation, miR-146a agomir 0.5 nmol (0.1 nmol/μl) was injected into bilateral hippocampi in group Ag, miR-146a antagomir 2.5 nmol (0.5 nmol/μl) was injected in group At, miR-146a negative control solution 2.5 nmol (0.5 nmol/μl) was given in group NC, and the animals in group C did not receive any treatment.At 1 day before operation and at 1, 3 and 7 days after operation, open-field test was performed to evaluate spontaneous motor activity, and contextual fear conditioning test was performed to evaluate cognitive ability 15 min later.At 1 and 3 days after operation, the animals were sacrificed and hippocampi was removed for determination of expression of CD11b (a marker for activation of microglia) in hippocampal CA1 region by immunofluorescence staining.At 6, 12 and 24 h after operation, the expression of miR-146a was detected by quantitative real-time polymerase chain reaction, the expression of interleukin-1 receptor-associated kinase 1 (IRAK1), tumor necrosis factor receptor-associated factor 6 (TRAF6), nuclear factor kappa B p65 (NF-κB p65) and tumor necrosis factor-alpha (TNF-α) was determined by Western blot and interleukin-1beta (IL-1β) and IL-6 contents were determined by enzyme-linked immunosorbent assay. Results:There was no significant difference in the total exploring distance in the open-field test or percentage of freezing time in tone-fear conditioning test at each time point among the five groups( P>0.05). Compared with group C, the percentage of freezing time in the contextual fear conditioning test was significantly decreased at 1, 3 and 7 days after operation, the expression of CD11b at 1 and 3 days after surgery and expression of miR-146a, IRAK1, TRAF6, NF-κB p65 and TNF-α were up-regulated and the contents of IL-1 β and IL-6 were increased at 6, 12 and 24 h after operation in group POCD ( P<0.05). Compared with group NC, the percentage of freezing time in the contextual fear conditioning test was significantly increased at 1, 3 and 7 days after operation, and the expression of CD11b was down-regulated at 1 and 3 days after surgery, and the expression of miR-146a, IRAK1, TRAF6, NF-κB p65 and TNF-α was up-regulated and IL-1β and IL-6 contents were decreased at 6, 12 and 24 h after operation in group Ag, and the percentage of freezing time in the contextual fear conditioning test was decreased at 1, 3 and 7 days after operation, the expression of CD11b at 1 and 3 days after surgery was up-regulated, the expression of miR-146a was down-regulated and IRAK1, TRAF6, NF-κB p65 expression was up-regulated at 6, 12 and 24 h after operation, TNF-α expression was up-regulated and IL-1β and IL-6 contents were increased at 12 and 24 h after operation in group At ( P<0.05). Conclusion:miR-146a is involved in the process of hippocampal inflammatory responses, and the mechanism may be related to the inhibition of IRAK1-TRAF6-NF-κB signaling pathway in mice.