α7nAChR alleviates cognitive impairment by promoting autophagy in astrocytes via CaMKK2/AMPK/mTOR pathway in sepsis-associated encephalopathy.

BACKGROUND: Sepsis-associated encephalopathy (SAE) is a syndrome of cerebral dysfunction secondary to sepsis. Although the α7 nicotinic acetylcholine receptor (α7nAChR) plays a pivotal role in the SAE, the specific mechanisms by which it mediates neuroinflammatory responses and contributes to pathological injury in SAE remain unclear. METHODS: The serum α7nAChR level was measured in all included patients. The ROC curve was used to analyze the α7nAChR level for predicting the risk of SAE. The sepsis rat model was constructed by cecal ligation puncture (CLP). The α7nAChR was activated and inhibited by PNU282987 and Methyllycaconitine (MLA) respectively. Cognitive function and neuronal damage were evaluated using behavioral experiment, Nissl staining, Golgi staining and Electron microscopy. Autophagy was examined by Western blot (WB) and transmission electron microscope (TEM). In vitro experiments, lipopolysaccharide (LPS) was used to construct the model of U118. After knockdown and overexpression of α7nAChR, the autophagy proteins level was detected by western blot and the level of cell supernatant inflammatory factors were detected by ELISA. Intracellular calcium concentration was evaluated by flow cytometry. RESULTS: The serum α7nAChR levels in SAE patients were lower than that in the healthy controls and sepsis patients, and the its AUC for predicting the risk of SAE was 0.79 (95% CI, 0.68-0.90). Activation of the α7nAChR elevated neurobehavioral scores, increased the number of Nissl bodies and synapses, and improved dendritic spine morphology in rats. Activation of α7nAChR weakened the activation of astrocytes, thereby reducing the release of IL-1β, IL-6 and TNF-α. The activation of α7nAChR inhibited the level of P62, up-regulated the expression of LC3. In vitro, α7nAChR promoted LPS-induced autophagy in U118 cells, increased intracellular calcium (Ca2+) concentrations, elevated p-CAMKK2/CAMKK2 and p-AMPK/AMPK levels, and decreases p-mTOR/mTOR levels. CONCLUSION: α7nAChR can alleviate cognitive dysfunction in SAE by activating the Ca2+/CaMKK2/AMPK/mTOR signaling pathway and promoting autophagy in astrocytes.