Improvement Effect Of Urocortin Based AMPK-PGC-1 Pathway On Neural Function In Chronic Hypoxia Rats

ObjectiveThe aim of this study was to investigate the effects of UCN on learning and memory in rats with chronic hypoxia.To elucidate the molecular and electrophysiological mechanisms of UCN in chronic hypoxia,to provide drug targets and theoretical basis for the treatment of ischemic-hypoxic diseases.MethodsIn this study,SD rats were selected and CO₂ chronic hypoxia model was established.Chronic hypoxia rats were randomly divided into 4 groups,including Chronic-hypoxia model of CO₂（Chronic-hypoxia group,CHY group）,UCN low dose+CO₂ hypoxia group（UCN-L group）,UCN high dose+CO₂hypoxia group（UCN-H group）,Nimodipine+CO₂ chronic hypoxia group（NIM group）.Another 10 SD rats were used as blank control group（NS group,NS）without chronic hypoxia.After two weeks of administration,the oxygenation（SpO₂）of the tail end of each group was measured by a non-invasive oxygenation detector;the forced swimming device and the automatic digital frequency video tracking technology were used,the survival time,floatation time,total swimming time and learning to swim time were measured;and the effects of UCN on learning-memory ability of chronic hypoxia rats were measured by Morris Water Maze behavior test.The effect of UCN on neuronal cluster patterns in hippocampus of chronic hypoxia rats was studied by microelectrophoresis.Blood samples were taken at the end of the study to determine biochemical and energy metabolic parameters,including the levels of lactate dehydrogenase（LDH）,urea nitrogen（BUN）,liver glycogen（LGC）and muscle glycogen（MGC）,and the activities of glucose transporter-4（GLUT-4）and Na⁺-K⁺-ATPase.The expression of AMPK,p-AMPK,PGC-1protein in brain tissue of rats with chronic hypoxia was detected by Western blotting,the signal mechanism of UCN’s tolerance to hypoxia and improvement of learning and memory ability after chronic hypoxia were elucidated.Results1.The effect of UCN on hypoxia index was significantly higher in different dose of UCN administration group than in chronic hypoxia group,there is a significant difference（P<0.05）.2.The effect of UCN on the behavioral indexes of hypoxic rats:（1）In the swimming endurance test,compared with the hypoxic model group,the UCN-L group,UCN-H group and NIM positive control group had longer struggling time,total swimming time and shorter floating time;（2）In the Morris Water Maze space exploration experiment,UCN-L,UCN-H and NIM groups,although they are also rats with chronic hypoxia,however,the swimming time in the original platform quadrant was prolonged,the time in the original platform quadrant was increased as a percentage of the total swimming time,and the total swimming distance was shortened（P<0.05）.3.The effect of UCN on hippocampal neuronal firing rates:UCN-L（5.40±0.68 Hz）,UCN-H（4.55±0.67 Hz）and NIM（5.25±0.72 Hz）decreased significantly compared with CHY group（P<0.05）.The frequency of discharge in UCN-H group was significantly lower than that in NIM Group（P<0.05）.4.The effect of ESCU on serum biochemical index and energy metabolism:ESCU can significantly reduce the contents of lactic acid and urea nitrogen,increase SpO₂.The activities of GLUT-4 and Na⁺-K⁺-ATP enzyme were significantly increased in different UCN groups after chronic hypoxia,compared with control group with significant differences（P<0.05）.5.Effect of UCN on hippocampal pathological injury in rats with chronic hypoxia:in NS Group and UCN group,the size of hippocampal neurons was normal,the spinous process was orderly arranged,the number of hippocampal neurons was normal,and most of them were vertebral body cells,granular cell layer is also seen.The damage of hippocampal neurons in CHY model group was obvious.6.The effect of UCN on AMPK-PGC-1 pathway:compared with CHY group,AMPK,PGC-1 protein expression decreased in UCN-L and UCN-H groups,while p-AMPK expression increased（P<0.05）.It is suggested that UCN may exert anti-hypoxia effect through AMPK-PGC-1 signaling pathway.Conclusions1.UCN increased SpO₂ levels,increased LGC and MGC contents,and decreased BUN and LDH levels,UCN was resistant to chronic hypoxia.2.UCN has the ability to improve learning and memory by shortening learning time,avoidance latency and swimming distance,and by ameliorating pathological damage of hippocampal neurons in rats with chronic hypoxia.3.UCN reduced over-firing in hippocampal neurons of rats exposed to chronic hypoxia,possibly by activating the AMPK-PGC-1 pathway,increasing GLUT-4 and Na⁺-K⁺-ATPase activity,thereby affecting sugar transport and energy metabolism,it can resist hypoxia and improve the ability of learning and memory.