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Aim To investigate the effect of extracellular vesicles secreted by adipose tissue of mice on hippocampal neurons and cognitive behavior of mice with a high-fat diet.Methods Twenty C57BL/6J male mice were randomly divided into normal diet(ND)group(n=10)and high-fat diet(HFD)group(n=10), fed for 28 weeks.The weight of mice was recorded weekly.The level of fasting blood glucose, insulin and the insulin resistance index(HOMA-IR)of mice were tested at week 27.At week 28, the learning and memory abilities of mice were assessed by the Morris water maze.The morphological differences in adipose tissue were observed by HE staining, and the extracellular vesicles secreted from adipose tissue were quantified by TEM and NTA.Extracellular vesicles derived from adipose tissue labeled with PKH 67 were injected into normal mice via the tail vein, and after 30 h, the uptake of extracellular vesicles was detected in the hippocampal slice.The primary hippocampal neurons were treated with extracellular vesicles with the same amount of protein, and the effects of them on neuronal morphology and cell viability were observed.Results Compared with ND group, mice in HFD group were significantly heavier, with hyperglycemia, hyperinsulinemia and higher insulin resistance index.In the Morris water maze test, the HFD group showed a longer escape latency and less swimming time in the target zone.The volume of adipocytes and the amount of extracellular vesicles secreted from them significantly increased in HFD group.Extracellular vesicles secreted by adipose tissue could be internalized by both the primary hippocampal neurons and the hippocampal neurons in the normal mice.Compared with ND group, extracellular vesicles secreted by adipose tissue of the HFD group significantly reduced the length of primary hippocampal neuronal dendrites, the number of primary and secondary dendrites, and the cell viability of neuron cells.Conclusion Long-term high-fat diet could damage the hippocampal neurons by affecting the extracellular vesicles derived from adipose tissue.
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Objective Obstructive sleep apnea hypopnea syndrome (OSAHS) often causes damage to multiple systems, especially to the central nervous system, inducing cognitive dysfunction.This study aims to explore the possible correlation of the expressions of serum hypoxia-inducible factor-1α (HIF-1α) and brain-derived neurotrophic factor (BDNF) with cognitive impairment in rats under different hypoxia conditions.Methods Twenty-four Wistar rats were equally randomized into a normal control, a chronic intermittent hypoxia (CIH), and a chronic continuous hypoxia (CCH) group.The rats of the CIH group were placed in a hypoxia chamber filled with N2 and air, the oxygen concentration switched from (7±0.5)% to 21%, 1.5 minutes for each state and 4 minutes for each cycle, while those of the CCH group were placed in another hypoxia chamber with the oxygen concentration of (7±0.5)%, 8 hours a day and all for 30 days.Then we recorded the body weight of the rats, detected the expressions of serum HIF-1α and BDNF by ELISA, and observed the changes of behavior by Morris water maze test and those of the hippocampal morphological structure by HE staining.Results At 30 days after modeling, the body weight of the rats was significantly decreased in the CIH and CSH groups as compared with the normal control ([195.75±6.497] and [180.88±12.017] vs [218.63±15.287] g, P<0.05).Positioning navigation showed that the escape latency was significantly longer in the hypoxia models than in the controls (P<0.05), even longer in the CIH than in the CCH group (P<0.05).Spatial exploration test manifested a lower frequency of crossing the platform in the CIH and CCH groups than in the control ([2.63±1.45] and [3.22±1.30] vs [4.97±0.47] times, P<0.05).The expression levels of serum HIF-1α and BDNF were significantly higher in the CIH ([36.14±9.34] and [1625.34±332.44] pg/mL) and CCH ([27.27±6.88] and [1204.07±363.81] pg/mL) than in the normal control group ([14.11±4.06] and [1036.40±124.48] pg/mL) (P<0.05), even higher in the CIH than in the CCH group (P<0.05).HE staining exhibited scattered and disorderly arrangement of hippocampal neurons in the model rats, with unclear nuclear membrane, pyknosis of the nuclei, darkly stained cytoplasm, and some damaged cells.More obvious absence and vacuolization of some cells were observed in the rats of the CIH group.Conclusion Chronic hypoxia inhibits the growth and development of rats and induces cognitive dysfunction.High-level HIF-1α in chronic intermittent hypoxia indicates hypoxia-stress of the body, while compensatory increase of serum BDNF may be involved in neuronal cell damage regulation.