Objective To investigate the effects and underlying mechanisms of microRNA (miR)-34a on isoflurane anesthesia-induced cognitive dysfunction in aged rats.

Methods Forty rats at 20 months of age were randomly divided into control (Con) group, model group, miR-34a inhibitor group and miR-34a mimics group, with 10 rats in each group. Rats in the miR-34a inhibitor and miR-34a mimics groups received a tail vein injection of 100 nmoL/kg of the corresponding drug, while those in the Con and model groups received an equal volume of saline, once daily for 5 consecutive days. At the 6th day, all groups except the Con group underwent a single 6-hour isoflurane anesthesia to establish a postoperative cognitive dysfunction (POCD) model. Twelve hours after modeling, the Morris water maze test was used to assess the escape latency and time spent in the target quadrant. Immunofluorescence staining was performed to observe the positive expression rate of ionized calcium-binding adapter molecule 1 (Iba-1) in the hippocampal tissue. Real-time quantitative polymerase chain reaction (qRT-PCR) was used to measure the relative expression levels of miR-34a, B-cell lymphoma-2 (Bcl-2) and Bcl-2-associated X-protein (Bax) mRNA in the hippocampal tissue. Enzyme-linked immunosorbent assay (ELISA) was conducted to detect serum levels of interleukin-6 (IL-6), interleukin-1β (IL-1β), reactive oxygen species (ROS) and glutathione peroxidase (GSH-Px), as well as the content of glutamate (Glu), Ca²⁺ and N-methyl-D-aspartate receptor 2B (NMDAR2B) in the hippocampal tissue. Western blotting was used to determine the relative expression levels of calcium-calmodulin-dependent protein kinase Ⅱ (CaMKⅡ), phosphorylated CaMKⅡ (pCaMKⅡ), cyclophosphoadenosine effector-binding protein (CREB), and phosphorylated CREB (pCREB) in the hippocampal tissue.

Results Compared with the Con group, the Model group exhibited significantly prolonged escape latency, elevated serum levels of IL-6 and IL-1β and ROS, as well as increased positive expression rate of Iba-1, relative expression levels of miR-34a and Bax mRNA, contents of Glu, Ca²⁺ and NMDAR2B in the hippocampal tissue; in contrast, the time spent in the target quadrant, serum GSH-Px levels, Bcl-2 mRNA relative expression levels, Bcl-2/Bax, as well as pCaMKⅡ/CaMKⅡ and pCREB/CREB in the hippocampal tissue were significantly reduced (P < 0.05). Downregulation of miR-34a expression shortened the escape latency and decreased serum levels of IL-6, IL-1β and ROS, as well as Iba-1 positive expression rate, relative expression levels of miR-34a and Bax mRNA, Glu, Ca²⁺ and NMDAR2B content in the hippocampal tissue (P < 0.05). It also extended the time spent in the target quadrant and increased serum GSH-Px levels, Bcl-2 mRNA expression levels, Bcl-2/Bax, as well as pCaMKⅡ/CaMKⅡ and pCREB/CREB in the hippocampal tissue (P < 0.05). Upregulation of miR-34a expression promoted abnormal activation of microglia, inflammation, oxidative stress and apoptosis, inhibited the activation of the CaMKⅡ/CREB signaling pathway, and exacerbated cognitive dysfunction in the model rats.

Conclusion MiR-34a is highly expressed in POCD in aged rats. Inhibition of miR-34a expression can improve isoflurane anesthesia-induced cognitive dysfunction in aged rats by activating the CaMKⅡ/CREB signaling pathway.